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UHP-metamorphic rocks from Dora Maira/Western Alps and Kokchetav/Kazakhstan: New insights using cathodoluminescence petrography
Abstract
Thin sections of ultrahigh pressure (UHP) metamorphic rocks from the Dora Maira Massif (Italy) and the Kokchetav Massif (Kazakhstan) were investigated using the hot cathode cathodoluminescence (CL) technique. Coloured images of important, but otherwise invisible growth features could be easily identified with this tool within seconds. These features are in excellent correlation with chemical variations of minerals revealed by electron microprobe (EMP). Generally, CL is induced by activator-elements (e.g. Mn and REE) and lattice defects whereas so-called quencher-elements like Fe may reduce or even extinct luminescence. Since X-ray-intensity mapping images (MAPS) of minerals can take up to 50 hours, the CL-method represents an ideal and rapid approach prior to chemical characterization. In addition to typical carbonates such as calcite, Mg-bearing calcite and dolomite, a number of rock forming and accessory minerals including Mg- and Mg-Ca-gamets, diopsidic and jadeitic pyroxenes, kyanite, K-feldspar, quartz, coesite, diamond, zircon, apatite, and bearthite were examined. Features observed in garnets include small-scale oscillatory zoning patterns, changes in morphology during growth as well as different crack generations which were partly annealed. SiO2 phases (coesite, quartz, chalcedony) as well as exsolution textures of dolomite and Mg-bearing calcite are easy to distinguish due to their different CL-colours. Pyroxene displays complex zonation patterns and -to some extent- exsolution-textures of K-feldspar. Kyanite reveals distinct growth zones; in combination with mineral inclusion studies it is possible to discriminate between different kyanite-forming reactions. The different crystallographical orientation of twinned kyanite crystals leads to various luminescence colours, thus, the suture of the twin plane is well defined. Prior to SHRIMP analyses, knowledge of the internal structures of zircon is indispensable. Even very tiny coesite crystals are easy to distinguish from quartz or chalcedony by their disparate luminescence colours. Accessory luminescent minerals like diamond, apatite, bearthite are easy to identify in thin section even if they occur in very small abundance within the matrix or as inclusions. The CL method presented here for UHP-metamorphic rocks is recommended as a pathfinder for the discovery of internal structures of minerals prior to their chemical characterization using EMP.
... Corfu et al., 2003;Hanchar & Miller, 1993;Rubatto, 2017;Taylor et al., 2016) and quartz (Götze et al., 2001, and references therein;Rusk et al., 2008;Wark & Watson, 2006), multiple generations of mineral growth, chemical reactions, and deformation may be identified using CL images (e.g. Boggs & Krinsley, 2006;Götze & Kempe, 2008;Götze et al., 2013;Schertl et al., 2004;Sullivan & Peterman, 2017;Wiebe et al., 2007). Similarly, kyanite preserves distinct internal textures evident in CL (Figure 1), including sector zoning, oscillatory zoning, and patchy domains. ...
... Similarly, kyanite preserves distinct internal textures evident in CL (Figure 1), including sector zoning, oscillatory zoning, and patchy domains. Most kyanite grains preserve evidence of cross-cutting relationships among different textural domains (Götze et al., 2013;Horkley et al., 2013;Kendrick & Indares, 2018;Müller et al., 2016;Schertl et al., 2004). Trace element variation explains much of the observed variation in CL intensity and colour: Cr 3+ enrichment drives much of the red luminescence (centred at 734 nm; Müller et al., 2016) and Ti 4+ concentrations correlate with blue luminescence at 485 nm (Gaft & Panczer, 2013;Götze et al., 2013;Habermann, 2002;Horkley et al., 2013;Müller et al., 2012;Schertl et al., 2004;Wojtowicz, 1991;Wojtowicz et al., 1991). ...
... Most kyanite grains preserve evidence of cross-cutting relationships among different textural domains (Götze et al., 2013;Horkley et al., 2013;Kendrick & Indares, 2018;Müller et al., 2016;Schertl et al., 2004). Trace element variation explains much of the observed variation in CL intensity and colour: Cr 3+ enrichment drives much of the red luminescence (centred at 734 nm; Müller et al., 2016) and Ti 4+ concentrations correlate with blue luminescence at 485 nm (Gaft & Panczer, 2013;Götze et al., 2013;Habermann, 2002;Horkley et al., 2013;Müller et al., 2012;Schertl et al., 2004;Wojtowicz, 1991;Wojtowicz et al., 1991). Although variations in the concentrations of Cr and Ti correlate well with observed colour and intensity shifts (Müller et al., 2016), there are several examples where these trace elements do not fully explain the CL emission. ...
Cathodoluminescence (CL) images of kyanite reveal several internal textures, including sector zoning, oscillatory zoning, and cross‐cutting relationships among different domains. Many textures observed in kyanite correspond to discrete events, thereby connecting kyanite textures to the pressure‐temperature (P‐T) history of the rock. To evaluate the record of metamorphism preserved by kyanite, metapelites were selected from three different orogens that reflect P‐T conditions ranging from amphibolite to ultrahigh‐pressure (UHP) facies. Cross‐correlation of variations in CL intensity, chemistry, and crystal orientation within kyanite indicate the following findings. First, the preservation of original growth zones in kyanite from poly‐metamorphic rocks demonstrates that growth zoning in kyanite persists through metamorphic events and is not erased by diffusion or complete recrystallization. In some samples, kyanite retains evidence of its reaction history during growth. Second, measured changes in absolute crystallographic orientation do not correspond with changes in CL intensity in any of the measured samples, including kyanite twins. Third, both kink banding and undulatory extinction are present across all samples, consistent with rotation about <010> in the (100)[001] slip system. Kyanite from (U)HP samples exhibits higher amplitude undulations than kyanite from lower grade lithologies, suggesting that crystallographic orientation data may provide complementary insight about deformation along the P‐T path. Fourth, specific CL and trace element signatures in kyanite can be correlated with discrete metamorphic histories; yet CL intensity and color are affected by multiple elements, not a single controlling element. In sum, multiple generations of kyanite can be identified by careful cross‐correlation of CL and geochemical data, and when combined with crystal orientation data, kyanite provides a robust record of a rock’s P‐T evolution.
... Colored cathodoluminescence (CL) images were obtained using a 'hot cathode' scanning-electron microscope of the type HCL-LM at RUB; operating conditions were 14 keV beam energy and ca. 9 μA mm -2 current beam density (for further details see Schertl et al., 2005Schertl et al., , 2004. ...
... One key method to study and display internal structures and growth zones of jadeite crystals is cathodoluminescence (CL) microscopy (Sorensen et al., 2006;Harlow and Sorensen, 2005;Schertl et al., 2004). Vein precipitation or "P-type" jadeite crystals from the RSJC are typically characterized by oscillatory growth zones clearly seen in CL images (Figs. ...
... Fine-grained pyrope is characterized by bluish-reddish CL colors. In general, pyrope shows an increase of brightness from core to rim and an oscillatory zoning pattern (Schertl et al., 2018(Schertl et al., , 2004. Since the amount of iron in the outermost domains of pyrope is higher than in the core and mantle regions, and iron serves as a quencher element, luminescence of this outermost domain is subdued ( Fig. 4a; see also Schertl et al., 2004). ...
This paper shows how a faulty approach to the study of mineral inclusions in zircon can lead to misleading interpretations of the geological context. We present and discuss two well-documented examples. Zircon grains separated from HP metamorphic jadeitite of the Rio San Juan Complex, Dominican Republic, and from UHP pyrope quartzite of the Dora Maira Massif, northern Italy, were studied using cathodoluminescence (CL) techniques, in combination with mineral inclusion and age data. In general, zircon from both localities shows inherited magmatic core domains with oscillatory zoning and metamorphic rims. The magmatic cores of zircon from the jadeitite yield ages of 115–117 Ma and host jadeite and omphacite which are of metamorphic origin and formed at about 78 Ma. Zircon from lawsonite blueschist, representing the country rock of the jadeitite, contains domains with oscillatory zoning that are nearly identical in age to the zircon cores from the adjacent jadeitite, and also contains younger metamorphic minerals such as lawsonite, albite, phengite (Si3.68), chlorite, and omphacite. Similar observations were made on the magmatic cores of zircon from the pyrope quartzite. These are about 275 Ma in age and host pyrope, phengite (Si3.55), talc, and kyanite, all of which formed during UHP metamorphism at about 35 Ma. Zircon from the biotite-phengite-gneiss country rock (metagranite) shows oscillatory zoning and yields ages that are identical to those of the magmatic cores of zircon from pyrope quartzite, which thus reflect granitic intrusion ages. The country-rock zircon also encloses metamorphic minerals with ages of about 35 Ma. Such minerals are, for example, garnet and phengite, as well as a polymineralic assemblage of clinopyroxene+garnet+phengite+quartz, that point to formation at UHP metamorphic conditions around 40 kbar/750 °C. Based on these examples we suggest an effective approach centered on key evidence from CL studies to show that magmatic domains of zircon may actually contain pseudo-inclusions which were not entrapped during an early stage of formation, but were instead introduced during later metamorphic or metasomatic events along microcracks representing pathways for fluid influx. Cathodoluminescence microscopy is thus an excellent tool for avoiding such pitfalls by allowing distinction between true inclusions and pseudo-inclusions in zircon.
... Corfu et al., 2003;Hanchar & Miller, 1993;Rubatto, 2017;Taylor et al., 2016) and quartz (Götze et al., 2001, and references therein;Rusk et al., 2008;Wark & Watson, 2006), multiple generations of mineral growth, chemical reactions, and deformation may be identified using CL images (e.g. Boggs & Krinsley, 2006;Götze & Kempe, 2008;Götze et al., 2013;Schertl et al., 2004;Sullivan & Peterman, 2017;Wiebe et al., 2007). Similarly, kyanite preserves distinct internal textures evident in CL (Figure 1), including sector zoning, oscillatory zoning, and patchy domains. ...
... Similarly, kyanite preserves distinct internal textures evident in CL (Figure 1), including sector zoning, oscillatory zoning, and patchy domains. Most kyanite grains preserve evidence of cross-cutting relationships among different textural domains (Götze et al., 2013;Horkley et al., 2013;Kendrick & Indares, 2018;Müller et al., 2016;Schertl et al., 2004). Trace element variation explains much of the observed variation in CL intensity and colour: Cr 3+ enrichment drives much of the red luminescence (centred at 734 nm; Müller et al., 2016) and Ti 4+ concentrations correlate with blue luminescence at 485 nm (Gaft & Panczer, 2013;Götze et al., 2013;Habermann, 2002;Horkley et al., 2013;Müller et al., 2012;Schertl et al., 2004;Wojtowicz, 1991;Wojtowicz et al., 1991). ...
... Most kyanite grains preserve evidence of cross-cutting relationships among different textural domains (Götze et al., 2013;Horkley et al., 2013;Kendrick & Indares, 2018;Müller et al., 2016;Schertl et al., 2004). Trace element variation explains much of the observed variation in CL intensity and colour: Cr 3+ enrichment drives much of the red luminescence (centred at 734 nm; Müller et al., 2016) and Ti 4+ concentrations correlate with blue luminescence at 485 nm (Gaft & Panczer, 2013;Götze et al., 2013;Habermann, 2002;Horkley et al., 2013;Müller et al., 2012;Schertl et al., 2004;Wojtowicz, 1991;Wojtowicz et al., 1991). Although variations in the concentrations of Cr and Ti correlate well with observed colour and intensity shifts (Müller et al., 2016), there are several examples where these trace elements do not fully explain the CL emission. ...
Interpreting metamorphic histories in kyanite by interpreting growth features and patterns that are elucidated through cathodoluminescence (CL) imaging.
... The CL-examinations (see Figs. 1, 2) were performed using a HC1-LM hot cathode microscope at Ruhr-University Bochum; the beam energy was 14 keV and the beam current density ~9 μA/mm 2 on the sample surface. The device used allowed simul- taneous investigation of polished thin sections under linear po- larized light (LPL), crossed polars (XPL) and the electron beam (for details see Götze et al., 2013;Schertl et al., 2004). Photos were taken by a highly sensitive digital microscope camera (DP73, Olympus). ...
... Pyrope typically is characterized by non-to low-luminescent core regions; the mantle region shows intense to less intense bluish-white to brownish-violet luminescent, oscillatory growth zones and the rim zones are lacking luminescence (Figs. 2d-2f; see also Schertl et al., 2004). In general, the intense luminescent oscillatory mantle zone yields a concentrical zoning. ...
... Occasionally, however, this mantle zone is not present throughout the whole grain and the non-luminescent rim does not always envelope the entire garnet grain. Schertl et al. (2004; Fig. 1a therein) described a change of crystal morphology during growth, observed in the core of pyrope. Numbers 1-3 in Figs. ...
Garnet is one of the most significant minerals in metamorphic rocks, that provides key information on prograde, peak-metamorphic and retrograde parts of the pressure-temperature (PT) path. Such results require a detailed knowledge of its different growth domains. For iron-poor compositions, the cathodoluminescence (CL) microscopy is an important and often overlooked method and allows to identify the internal structures of all garnet grains in one thin section within only a few seconds. The advantage of the CL-microscope is to deliver low magnification images in true color, not only of garnet but also, for instance, of other rock forming silicates, carbonates, sulfates, etc., of metamorphic, but also of sedimentary and magmatic origin, using polished thin sections. Internal structures of grossular from Mexico and pyrope from the Italian Alps were characterized and visualized by CL-microscopy. The different growth domains were additionally studied using CL-spectra and electron microprobe (EMP) analysis. Grossular shows a patchy zonation in its core while in mantle and rim zones oscillatory zoning is observed. It contains zones of anomalous birefringence, zones of orange and bluish luminescence and zones lacking luminescence. Different but low amounts of the activator elements Mn²⁺ and Eu²⁺ are responsible for the orange and bluish luminescent domains. Pyrope is also characterized by oscillatory growth zones, shows a dull luminescent core with a change of crystal morphology during growth, and displays an increase of brightness from core towards rim—the outermost rim, however, is lacking luminescence. The different luminescent zones are characterized by different amounts of Dy³⁺, Tb³⁺, Sm³⁺ and Sm²⁺ as activator elements. Because of slow diffusion rates of activators such as the REEs Sm, Dy and Tb, it can be still possible to visualize possible prograde and/or peak pressure stage growth domains of garnet, even if later high temperature events may have homogenized the major element profiles. Such domains may help to identify respective assemblages of mineral inclusions, and hence these results can represent an integral part of a detailed PT path. Thus the CL-information can be used as an important pathfinder prior to supplementary investigations, as for instance EMP, ion probe, mineral or fluid inclusion studies.
... Sobolev et al. (2009) described relics of dolomite that were surrounded by calcite (and closely associated with phlogopite) as inclusions within diamonds from the Sputnik-pipe kimberlite. The calcite may represent the low-pressure breakdown phase of a former aragonite inclusion or a replacement product of dolomite http://dx.doi.org/10.1016/j.jseaes.2017.06.009 (Schertl et al., 2004), similar to UHP carbonate-rich metamorphic rocks from the Kokchetav Massif. Melting experiments (e.g., Palyanov et al., 2015) also present significant data for the possible involvement of mantle carbonate fluids, with regards to kimberlitic diamond formation. ...
... Traditional CL microscopy has focused on carbonates, feldspars, and quartz of sedimentary rocks (e.g., Richter et al., 2003 and references therein). However, more recent studies have demonstrated that this method is also of significance for rock-forming minerals of metamorphic (Neuser, 1995;Houzar and Leichmann, 2003;Schertl et al., 2004Schertl et al., , 2005Satish-Kumar et al., 2006;Sobolev et al., 2007;Müller et al., 2016) and magmatic rocks (Słaby and Götze, 2004;Wiebe et al., 2007;Catlos et al., 2010). In addition, Cl microscopy is useful for minerals of hydrothermal and metasomatic formations (Harlow and Sorensen, 2005 well as for meteorites (Jones and Carey, 2006). ...
... Textbooks emphasizing the significance of CL, for instance, are those of Marfunin (1979), Marshall (1988) and Pagel et al. (2000). Detailed investigations applied to carbonates in sedimentary rocks were introduced by Richter et al. (2003); CL-studies of carbonates of UHP-metamorphic origin were presented by Schertl et al. (2004Schertl et al. ( , 2015. Götze et al. (2012) published a review paper which focused on the general application of the use of CL in the geosciences. ...
Cathodoluminescence (CL) microscopy studies were performed to unravel internal structures and zonations of carbonates from 6 unaltered hypabyssal kimberlites from several Mesozoic - Paleozoic kimberlite pipes of the Siberian craton. Different generations of prograde and retrograde carbonate grains/domains were identified. Most investigated kimberlite samples are unusually fresh and contain abundant unaltered olivine. Only minor amounts of carbonates of a primary magmatic origin were found; most carbonates are of secondary origin formed during late metasomatic or hydrothermal events. A rare carbonatite xenolith discovered in the Malokuonapskaya kimberlite contains abundant apatite and monazite; an apatite inclusion was detected in one zircon grain. Some apatites contain oriented lamellae of monazite. Early studies of the carbonate minerals in this xenolith demonstrated a trace amount of Sr; all these characteristics are typical of carbonatite.
... During the last 50 years cathodoluminescence (CL) microscopy has become a standard tool in geoscience. While early studies mainly focused on sedimentary rocks, within the last 2 decades this technique has also been applied to various metamorphic and magmatic rocks (Götze et al., 2013;Schertl et al., 2004). In addition, CL is indispensable as a scientific tool for the identification of different zircon domains, which need to be characterized prior to ion probe dating (SHRIMP; e.g., Gebauer et al., 1997). ...
... Cathodoluminescence (CL)-examinations were performed using a HC6-LM hot cathode microscope (beam energy 14 keV; beam current density ~9 μA/mm 2 on the sample surface) developed at Ruhr-University Bochum. The device used here allows simultaneous investigation of polished thin sections under linear polarized light, crossed polars and an electron beam (for detailed information see Götze et al., 2013;Schertl et al., 2004). ...
... Thus, even in hand specimen size, samples were found with alternating discrete Mg-calcite-dominated, garnet plus clinopyroxene-dominated and dolomitedominated layers. Figure 1 shows such a compositional layering (see Schertl et al., 2004) indicating its primary mineral assemblages as well as specific features. In general, the matrix of some of the layers are dolomite hosted whereas others mainly consist of Mg-dolomite. ...
A comprehensive study of a key calc-silicate rock of complex composition, an ultrahigh-pressure metamorphic rock of the Kokchetav massif, has been performed. New thin sections were examined by cathodoluminescence microscopy, electron probe microanalysis, and transmission/analytical electron microscopy. The obtained results confirmed the presence of microdiamonds and indicative signs of ultrahigh pressures (K in clinopyroxene) for seven of the eight previously recognized layers of the sample. Only one layer (3) containing paragenesis forsterite + Ti-clinohumite + dolomite + luminescent garnet (Mg# = 86–95) + clinopyroxene free of potassium and perovskite lacks diamonds. Symplectitic rims replacing garnet in this layer are formed by spinel growing into augite clinopyroxene with a scarce impurity of sapphirine and corundum and lack hydrous minerals. Garnets (Mg# = 81–83) of the diamond-containing layers (1 and 2a) and (4–8), having Mg# = 38–53, do not exhibit luminescence. They are present, together with K-clinopyroxenes, in the Mg-calcite matrix. A distinctive feature of the symplectitic rims is abundant segregations of corundum, often needle-like, and sapphirine in the augite clinopyroxene matrix with a minor spinel impurity. The symplectitic rims contain high-Mg phlogopite and K-amphibole; the latter was found in the metamorphic rocks for the first time. The different roles of hydrous minerals at the early stages of retrograde metamorphism for different layers reflect different fluid mobilities even within a sample.
... Results on the studies of layered calcsilicate rocks, combining features of both dolomite-and dolomitic marbles (Ogasawara, 2005) and Grt-Cpx rocks, were presented by Schertl et al. (2004), Shatsky et al. (2006a), Sobolev et al. (2006Sobolev et al. ( , 2007, and Korsakov et al. (2011b). Schertl et al. (2004) focussed on cathodoluminescence (CL) studies using a hot cathode scanning electron microscope (Neuser, 1995). ...
... Results on the studies of layered calcsilicate rocks, combining features of both dolomite-and dolomitic marbles (Ogasawara, 2005) and Grt-Cpx rocks, were presented by Schertl et al. (2004), Shatsky et al. (2006a), Sobolev et al. (2006Sobolev et al. ( , 2007, and Korsakov et al. (2011b). Schertl et al. (2004) focussed on cathodoluminescence (CL) studies using a hot cathode scanning electron microscope (Neuser, 1995). Promising candidates for such CLstudies are iron-poor garnets and pyroxenes, kyanite, carbonates, apatite, diamonds and silica-modifications . ...
... and secondary (sec.) Cpx, CL; (f) zoned primary diopsidic Cpx in Mg-dolomite matrix, CL; (g) calcite (yellow) + serpentine (non-luminescent)-bearing pseudomorph after forsterite rimmed by secondary Cpx (bluish-green) in Dol matrix (red), CL; (h) Cpx (non-luminescent) with Kfs (blue) exsolutions; CL (f and g, see also Schertl et al., 2004). and chlorite. ...
... Cathodoluminescence (CL) has developed to a standard technique for mineralogical and petrological investigations in geosciences. A number of publications have shown that CL is an excellent tool to provide information of internal textures of minerals and thus for the reconstruction of geological processes (e.g., Marshall 1988; Barker and Kopp 1991;Hanchar and Miller 1993;Hanchar and Rudnick 1995;Götze 2000a;Pagel et al. 2000;Gorobets and Rogozine 2002;Corfu et al. 2003;Nasdala et al. 2004;Schertl et al. 2004Schertl et al. , 2005Gaft et al. 2005;Boggs and Krinsley 2006;Gucsik 2009;Nasdala et al. 2012). ...
... Exsolution features are common in magmatic K-feldspar crystals (perthite, antiperthite) and are clearly detectable using CL (Fig. 1c/d). (Schertl et al. 2004) showing exsolved blue K-feldspar lamellae from potassium bearing diopside. ...
... Interestingly, for some species the twin plane between two different twin crystals is easy to detect due to their different CL-intensity (e.g. kyanite, Schertl et al. 2004). However, although visible under crossed polars, other minerals do not show twinning under CL (e.g. ...
Optical microscope-cathodoluminescence (OM-CL) microscopy is a modern luminescence technique with widespread applications in geosciences. Many rock-forming and accessory minerals show specific CL properties that can be successfully used in geoscience and materials science research. One of the most spectacular applications is the visualization of growth textures, alteration, and other internal textures in minerals that are not discernible with other analytical techniques. These results provide information about the real structure of minerals and materials and can be used for the reconstruction of geological processes of mineral formation and subsequent alteration. The information obtained from CL imaging in combination with spectral measurements of the CL emission allows for a more thorough understanding of structural states of solids and/or trace-element incorporation. Additional information can be obtained when luminescence studies are combined with other analytical techniques with high sensitivity and high spatial resolution.
... Diamondiferous metamorphic rocks from the Kokchetav Massif (Kazaksthan) are mostly represented by biotite gneisses (85 vol.%) with subordinate dolomite marbles (calcsilicate) and garnet-pyroxene rocks with (or without) carbonates (15 vol.%). The latter rocks have attracted much attention because of their unusual high diamond grade (up to 3,000 carats per metric ton) and variations in garnet and clinopyroxene compositions, even within a single hand specimen (Shatsky et al. 2006a, b;Sobolev et al. 2001Sobolev et al. , 2007Schertl et al. 2004). Some rare calcsilicate rock samples are layered and include different lithologies. ...
... The highest Mg#s (up to 94) of garnets are detected in very rare Mg-Ca garnet relics within dolomite-rich layers. Those garnets generally were found to contain bright-luminescent randomly distributed irregular spots of 50-500 lm in size as well as vein-like structures lacking luminescence (Schertl et al. 2004). The proportions of luminescent areas vary between about 5 and 70% of a grain's cross-section. ...
... Such garnets are not stable at pressures below 32 kbar (Boyd 1970), which is also confirmed by diamond presence in xenoliths containing MgCa-garnet from kimberlites (Ponomarenko et al. 1976) as well as by the presence of diamond in the sample of this study. Coesite (Katayama et al. 2002) and magnesite inclusions are found in zircons from calcsilicates of the Kokchetav Massif, and forsteritic olivine and Ti-clinohumite are found in dolomitic matrix (Schertl et al. 2004;Sobolev et al. 2007). ...
Calcsilicates (dolomite marbles) and garnet-pyroxene rocks with Mg-calcite matrix represent the most unusual rock types within dominant UHPM diamondiferous biotite gneisses and schists of the Kokchetav Massif. They are characterized by extremely high diamond grade (up to 3,000 carats per metric ton) and an unusual assemblage of very high Mg-garnet (Mg# up to 93.7) with varied Ca-numbers (42.5 - 66.5) and K-bearing diopside. A calcsilicate sample with alternating layers showing different lithologies with considerable amounts of garnet and clinopyroxene in dolomite or Mg-calcite matrix was selected for careful oxygen isotope and EPMA study of garnets and pyroxenes. A grain of fresh garnet with a luminescent core indicating very low iron contents (Mg# 92.6 - 93.7) and a non-luminescent part (Mg# 87.1 - 88.2) was selected for the study of delta18O with a CAMECA IMS-1280 ion probe (10 micron spot). No cracks were found within the selected layered sample, which is a ``micro-outcrop'' of several rock types at cm-scale. In parts, a symplectite composed of pyroxene and spinel is developed around studied garnet. A significant difference in delta18O between 12.9 - 13.50/00 VSMOW for high Mg luminescent core and 11.9 - 12.6 for non-luminescent overgrowth was found. Additional separates of hand-picked garnet and clinopyroxene grains from different parts of the same 0.1 kg-size sample fragment (selected by color differences) were analyzed for delta18O by laser fluorination at mm-scale. Values of delta18O measured in this work vary between 6.25 and 10.63, demonstrating delta18O-gradients of over 70/00 in garnets over distances of less than 2 cm. Thus oxygen isotopic ratios of garnets and clinopyroxenes of one hand specimen are heterogeneous and even can vary within single crystals. The delta18O values for the garnets analyzed here belong to the highest observed for UHP-origin (both for metamorphic rocks and for kimberlites). The unusual zonation in delta18O within mineral grains of the same species in different lithologies may reflect initial heterogeneities of the sedimentary precursors. On the other hand, the delta18O zonation within a single garnet grain of the same lithology requires a certain permeability of the rock in order to promote fluid flow and oxygen isotope exchange during growth.
... Cathodoluminescence studies were carried out with a hot-cathode microscope to follow the technique developed at Ruhr University Bochum, Germany [14,15]. We studied the carbon-coated polished thin sections usually used for analyzing minerals with an electron microscope. ...
... We studied the carbon-coated polished thin sections usually used for analyzing minerals with an electron microscope. The operating conditions are as follows: energy 14 keV and density of beam current, about 9 µA/mm 2 [15,16]. The color of luminescence is affected not only by various impurities, structural defects or different crystallographic orientations but also by the sample temperature. ...
... Of special interest are samples of calc-silicate rocks with banded structure caused by interlayering of zones enriched in carbonates and silicates, respectively. These samples demonstrate the complexity and inhomogeneity of the compositions of these rocks and can be considered as specific microexposures especially recording the relationships of some parageneses both with and without diamond [12,15]. ...
Study of a series of samples of homogeneous and inhomogeneous ( banded) calc-silicate rocks with contrasting diamond contents from the Kumdy-Kol' deposit of metamorphic diamonds ( northern Kazakhstan) has shown an extremely wide diversity of compositions of pyrope-grossular garnets in association with dolomite, Mg-calcite, magnesite, diopside with up to 1.5 wt.% K2O, forsterite, Ti-clinohumite, and phlogopite. Perovskite as an inclusion in forsterite has been discovered in these rocks for the first time. In some samples of complex composition interbeds with and without diamond alternate. Garnet forms a series of compositions with wide variations of Mg# [100 . Mg/(Mg + Fe)] from 70 to 95 and Ca# [100 . Ca/(Ca + Mg + Fe + Mn)] from 42 to 85, which has first been found for these rocks. Wide variations in garnet zoning have been revealed, with a decrease in Ca# towards the rims. Relict Mg-rich garnets which were firstly recognized under natural conditions persistently occur as light irregular spots, with uniquely low amounts of FeO, within 1 - 2 wt.% ( Mg# is 92 - 95 and Ca# is 60 - 66). These relics make up 5 to 70 vol.% of the respective grain surfaces in thin section and are revealed only by cathodoluminescence ( CL) approximately in only 10 - 20% of garnet grains for each sample. Thus, these unusual relics are typical of the diverse samples under study, and their composition is relatively homogeneous. The outer zones of most of these garnets completely correspond to typical well-studied compositions with Mg# of 70 - 80 and Ca# of 40 - 55. Supposedly, these relics are the earliest garnets formed under the conditions corresponding to the maximum of ultrahigh-pressure metamorphism. These garnets are often surrounded by reactionary rims irregularly developed around the grains made up of clinopyroxene and spinel symplectite. Occasionally, sapphirine and corundum are found in these rims. The symplectite paragenesis was formed as a result of retrograde metamorphism, in the early stages of exhumation, and is direct evidence of the granulite facies conditions, probably, at 1.8 GPa and about 900 degrees C.
... The beam energy was 14 keV and the beam current density~9 μA/mm 2 on the sample surface. Photos were taken by a digital microscope camera (Olympus DP73); the device allows simultaneous investigation of polished thin sections under linear polarized light, crossed polarizers and the electron beam (for details see Schertl et al., 2004). ...
... Schertl et al. (2012;their Fig. 5d) demonstrated that in the case of the jadeite-rich rocks of the Dominican Republic, jadeite domains with diverse luminescence colors (bluish-red to yellowishgreen) may correlate with quite pure end-member compositions (Jd 99 and Jd 98 , respectively). The only general conclusion that can be drawn is with respect to iron, which acts as a quencher element (e.g., Götze et al., 2013;Schertl et al., 2004;Takahashi et al., 2017). These diverse CL-colors in jadeite may be a result of low amounts of REE as activators. ...
Freezing-point depression was measured in aqueous fluid inclusions to determine salinities in six samples of jadeitite and jadeite-rich rock from the Jagua Clara serpentinite mélange of the Rio San Juan Complex, Dominican Republic. The mélange represents a fossil subduction-zone channel from a cold, mature subduction zone with a geothermal gradient of ~6 °C/km. One hundred and twenty-five determinations of salinity in primary inclusions hosted in jadeite, quartz, apatite and lawsonite range between extremes of 1.2 and 8.7, but yield a well-defined mean of 4.5 ± 1.1 wt% (±1 s.d.) NaCl equiv, slightly higher than mean seawater (3.5 wt%). In one sample, eight additional fluid inclusions in quartz aligned along grain boundaries yield slightly lower values of 2.7 ± 1.3 wt% NaCl equiv. Homogenization temperatures were also measured for 47 fluid inclusions in two samples, but primary entrapment densities are not preserved. It is significant that the suite includes two types of samples: those precipitated directly from an aqueous fluid as well as examples of metasomatic replacement of a pre-existing magmatic rock. Nevertheless, the results indicate identical salinity for both types and suggest a much stronger genetic link between the two types of jadeitite and jadeite-rich rock than has previously been assumed. Based on the results of conductivity measurements in modern subduction zones, we envision a pervasive fluid in the subduction channel that evolved from salinity levels lower than those in sea-water up to the measured values due to on-going but largely completed serpentinization in the subduction channel. The present data represent a reference marker for the subduction channel of the Rio San Juan intra-oceanic subduction zone at 30–50 km depth and after 50–60 Myr of operation.
... Over the past few years, CL color imagery has been explored for its applications in metamorphic geology. It has been demonstrated that this imagery is a powerful tool to reveal internal textures of specific minerals (e.g., Schertl et al., 2004Schertl et al., , 2015Sobolev et al., 2007Sobolev et al., , 2011Götze et al., 2013). Compared with X-ray mapping, CL color imagery can give instant qualitative information on the distribution of trace elements and microstructural defects in corresponding minerals. ...
... However, a major disadvantage of this method is that it is not applicable to minerals rich in the so-called quencher elements like Fe. In this light, marble and calc-silicate rock are two ideal rock types, which can be successfully studied using CL color imagery because minerals in these rocks usually contain low amount of Fe (e.g., Schertl et al., 2004Schertl et al., , 2015Sobolev et al., 2007Sobolev et al., , 2011. ...
Petrography and mineral chemistry of an ultrahigh pressure (UHP) impure marble from the Dabie Shan, eastern China, was studied using cathodoluminescence color imagery, X-ray mapping, electron microprobe analytics, laser ablation inductively coupled plasma mass spectrometry and phase equilibrium calculations. Diopside in the marble shows two generations of fluid-altered zones, which contain more Na, Al, Fe, Ti, Sr, Y, REE, and transition metal elements (TMEs: Sc, V, Co, Ni, Zn) and less Mg, Ca, and K compared to the original diopside. Apatite contains oriented monazite inclusions and high Cl contents (1.2–2.5 wt%) with negative Eu anomalies (EuN/EuN⁎ = 2EuN / (SmN + GdN) = 0.61–0.68). Rutile in the matrix displays fluid-mediated microstructures and becomes depleted in Zr and Fe compared to rutile inclusions in dolomite and diopside. All these microstructural and geochemical features are demonstrated to be caused by eclogite-facies metasomatism during exhumation of the marble. Two Na-Al-Fe-rich aqueous fluids have been involved in the metasomatism in tandem, as indicated by the two fluid-altered diopside zones and their major element compositional differences compared to the original diopside. Based on available partition coefficients of trace elements between clinopyroxene and aqueous fluid, both metasomatic fluids were calculated to display enrichments in LILE (Cs, Rb, B, Pb, Sr, Li) and LREE and depletions in HFSE (Th, U, Nb, Ta, Zr, Hf), HREE, and TME (V, Cr, Ni). A recently-determined Cl-OH exchange coefficient for apatite-aqueous fluid was applied to the high-Cl apatite and indicates a high chlorinity (≥ 30 wt%) for one (or both) of the metasomatic fluids. Either the decompression breakdown of peak hydrous minerals (such as lawsonite) in coexisting eclogite and/or paragneiss or the dehydration of the subducted oceanic crust before the collision between the Yangtze and North China blocks may have given rise to such metasomatic fluids. This study implies that pervasive external fluid-rock interaction during exhumation, before the amphibolite-facies overprint, is much more common than previously thought in the Dabie-Sulu UHP rocks. Moreover, important constraints are provided on the fluid nature and behavior in subduction zones.
... Jadeite displays very intense luminescence colours, so that cathodoluminescence (CL) microscopy is an excellent tool for revealing crystal growth features (e.g., Ponalho, 1999;Schertl et al., 2004;Harlow & Sorensen, 2005;Sorensen et al., 2006). The colour may vary from yellowish-green to blue and red (Schertl et al., 2004;Harlow & Sorensen, 2005), depending mainly on small variations in the New jadeitite and jadeite-rich rocks: the Dominican Republic 203 eschweizerbart_xxx concentration of minor and/or trace activator and quencher elements. ...
... Jadeite displays very intense luminescence colours, so that cathodoluminescence (CL) microscopy is an excellent tool for revealing crystal growth features (e.g., Ponalho, 1999;Schertl et al., 2004;Harlow & Sorensen, 2005;Sorensen et al., 2006). The colour may vary from yellowish-green to blue and red (Schertl et al., 2004;Harlow & Sorensen, 2005), depending mainly on small variations in the New jadeitite and jadeite-rich rocks: the Dominican Republic 203 eschweizerbart_xxx concentration of minor and/or trace activator and quencher elements. Using such CL characterization, internal structures of luminescent minerals can be made visible within seconds, and thus, for instance, different generations of jadeite growth can be distinguished very easily. ...
... These reactionary structures occur both in the matrix and in the inclusions in clinopyroxene and garnet. Similar zoning was earlier established by Schertl et al. (2004). ...
... Hermann et al. (2006a) assumed the presence of sulfide melts in carbonate-silicate rocks, based on findings of sulfide melts in garnets, which they interpreted as decrepitated sulfide melt inclusions. Schertl et al. (2004) noted that sulfide-rich rocks usually lack diamonds, which suggests the influence of sulfides on diamond crystallization. Findings of sulfides with clinopyroxene-spinel symplectite rim in dolomite-containing zone III of the sample G0 evidence that they existed under granulite facies conditions at <1.8 GPa and ~900 ºC (Sobolev Fig. 12. SEM image of secondary polyphase inclusions in clinopyroxene. ...
We present data on carbonatite, silicate, and sulfide melts and their immiscibility at different stages of ultrahigh-pressure metamorphism of rocks of the Kokchetav Massif (northern Kazakhstan). The identified silicate, silicate–carbonate, and sulfide inclusions are regarded as crystallization products of high-pressure melts. The detected reactionary garnet–K-feldspar–allanite–calcite symplectite structures as inclusions in garnet and as identical structures around it evidence that they resulted from carbonatite melt crystallization. Carbonate melting was probably triggered by the presence of a free fluid phase (mostly H 2 O) and/or a high content of alkalies in the system. The coexistence of carbonate and silicate inclusions testifies to the immiscibility of carbonatite and silicate melts. The presence of K-cymrite in the polyphase inclusions indicates that the minimum pressure of silicate melt intake is ~4.5 GPa. The maximum pressure of this intake is 6–7 GPa at 1000–1100 ºC and corresponds to the peak of metamorphism of the Kokchetav Massif rocks. Most likely, the field of immiscibility of carbonatite and silicate melts lies within 4.5–7 GPa and 950–1100 ºC. The carbonatite melt can dissolve up to 18 wt.% SiO 2 , and the silicate melt, up to 4.5 vol.% CaCO 3 .
... Jadeite displays very intense luminescence colours, so that cathodoluminescence (CL) microscopy is an excellent tool for revealing crystal growth features (e.g., Ponalho, 1999;Schertl et al., 2004;Harlow & Sorensen, 2005;Sorensen et al., 2006). The colour may vary from yellowish-green to blue and red (Schertl et al., 2004;Harlow & Sorensen, 2005), depending mainly on small variations in the New jadeitite and jadeite-rich rocks: the Dominican Republic 203 eschweizerbart_xxx concentration of minor and/or trace activator and quencher elements. ...
... Jadeite displays very intense luminescence colours, so that cathodoluminescence (CL) microscopy is an excellent tool for revealing crystal growth features (e.g., Ponalho, 1999;Schertl et al., 2004;Harlow & Sorensen, 2005;Sorensen et al., 2006). The colour may vary from yellowish-green to blue and red (Schertl et al., 2004;Harlow & Sorensen, 2005), depending mainly on small variations in the New jadeitite and jadeite-rich rocks: the Dominican Republic 203 eschweizerbart_xxx concentration of minor and/or trace activator and quencher elements. Using such CL characterization, internal structures of luminescent minerals can be made visible within seconds, and thus, for instance, different generations of jadeite growth can be distinguished very easily. ...
New occurrences of jadeitite and jadeite-rich rocks have been discovered in the Rio San Juan Complex (RSJC) of the northern Dominican Republic in serpentinite melanges associated with a former intra-oceanic subduction zone. Allochthonous blocks in lag deposits developed on the melange outcrops or boulders in river beds are common. A very unusual feature for the RSJC is the occurrence of concordant layers and discordant veins of cm to dm thickness in blocks of jadeite +/- lawsonite- or omphacite-garnet-bearing blueschist of the melange. Two suites of jadeite-rich rocks can be recognized. The first is represented by quartz-free jadeitite s.str. (> 90 vol% jadeite) found so far only as blocks and boulders. The second suite comprises quartz-bearing jadeitite s.str. grading into jadeitite quartzite (JQ), jadeite-lawsonite quartzite (JLQ) and jadeite-free lawsonite quartzite (LQ). The second suite is found both as blocks and boulders as well as layers and veins in blueschist blocks. One single occurrence of a cross-cutting omphacitite vein in blueschist has also been observed. Additional important phases so far found in both suites are omphacite, phengite, glaucophane, epidote, albite, calcite, titanite and zircon. Apatite and pumpellyite have only been identified in quartz-free jadeitite s.str.; almandine-rich garnet has so far been observed only in JLQ. The two suites of jadeite-bearing rocks occur in various shades of green, are fine-to coarse-grained, and usually equigranular. Mineral distribution is commonly homogeneous, but may be patchy in JLQ, giving this rock type a distinctly mottled appearance. Cathodoluminescence (CL) images show oscillatory zoning patterns in jadeite, zircon, apatite and calcite; this is evidence for crystallization from an aqueous fluid under open-system conditions. Zircons separated from a sample of quartz-free jadeitite s.str. contain primary inclusions of high-pressure matrix minerals such as jadeite and omphacite, indicating coeval zircon growth. The cores of the zircons yield ages of 114.9 +/- 2.9 Ma, thus defining a crystallization age close to the initiation of subduction in the Rio San Juan Complex, when "warm'' geotherms of approximate to 15 degrees/km prevailed. These ages are in contrast with the crystallization ages of the blueschists hosting the second, quartz-bearing suite of jadeite-rich rocks. These range from 80 to 62 Ma, towards the end of subduction-zone activity at approximate to 55 Ma and "cool'' geotherms of 8-9 degrees C/km. For the younger quartz-bearing suite, the combination of phengite compositions with the available P-T-t paths of the host blueschists suggests crystallization temperatures of approximate to 350 to approximate to 500 degrees C at minimum pressures of 15-16 kbar. The P-T conditions for the older quartz-free suite are more difficult to constrain, but the combination of phengite compositions with the prevailing geotherms in the young and warm subduction zone suggest minimum conditions of at least 500 degrees C and 11 kbar. However, temperatures and pressures as high as 600 degrees C and 15 kbar, as documented for jadeitites of similar age in the same subduction zone exposed in neighbouring eastern Cuba, are possible. Jadeitites and jadeite-rich rocks of the RSJC are thus interpreted to have crystallized over a time-span of >= 60 Myr at initial temperatures of at least 500 degrees C, later evolving down to 350 degrees C in a single, thermally self-organizing, cooling subduction zone. The P-T conditions suggested for the younger quartz-bearing suite correlate well with those of jadeitite formation in Guatemala south of the Motagua Fault Zone, the only other occurrence world-wide where jadeitite with both lawsonite and quartz appears to be common. Further evidence is needed to corroborate that the older quartz-free suite represents another example of rare high-temperature jadeitite as documented in Cuba.
... Studies of sub-solidus rocks have suggested that kyanite preserves growth zoning through (poly-)metamorphic cycles (Peterman et al. 2021). CL imagery of kyanite has been shown to reveal subtle textural details that have been linked to trace element variations (Horkley et al. 2013;Kendrick and Indares 2017;Müller et al. 2016;Peterman et al. 2021;Schertl et al. 2004;Tarantola et al. 2019). Different elements may act as CL quenchers or activators: Cr and Ti, for example, are known to be CL activators, whereas Fe is a known CL quencher (Gaft et al. 2015;Habermann 2002;Pagel et al. 2000;Wojtowicz 1991). ...
Aluminosilicates (kyanite, sillimanite and andalusite) are useful pressure-temperature (P-T) indicators that can form in a range of rock types through different mineral reactions, including those that involve partial melting. However, the presence of xenocrystic or inherited grains may lead to spurious P-T interpretations. The morphologies, microtextural positions, cathodoluminescence responses and trace element compositions of migmatite-hosted kyanite from Eastern Bhutan were investigated to determine whether sub-solidus kyanite could be distinguished from kyanite that crystallised directly from partial melt, or from kyanite that grew peritectically during muscovite dehydration reactions. Morphology and cathodoluminescence response were found to be the most reliable petrogenetic indicators. Trace element abundances generally support petrographic evidence, but protolith bulk composition exerts a strong control over element abundance in kyanite. Sample-normalised concentrations show distinctive differences between petrogenetic types, especially for Mg, Ti, V, Cr, Mn, Fe and Ge. LA-ICP-MS maps, especially of Cr/V, provide additional information about changing geochemical environments during kyanite growth. Most kyanite in the studied migmatitic leucosomes is of sub-solidus origin, with less widespread evidence for peritectic crystallisation. Where present, grain rims commonly crystallised directly from the melt; however, entire grains crystallised exclusively from melt are rare. The presence of kyanite in leucosomes does not therefore necessarily constrain the P-T conditions of melting, and the mechanism of growth should be determined before using kyanite as a P-T indicator. This finding has significant implications for the interpretation of kyanite-bearing migmatites as representing early stages of melting during Himalayan evolution.
... The CL-examinations (see Figs. 4 and 5) were performed using a HC1-LM hot cathode microscope at Ruhr-University Bochum; the beam energy was 14 keV and the beam current density ~9 μA/mm2 on the sample surface. Besides CL studies, the device used allows simultaneous investigation of polished thin sections under linear polarized light (LPL), crossed polars (XPL); the same thin sections can then be used for EPMA studies (for details see Schertl et al., 2004). Photos were taken by a highly sensitive digital microscope camera (DP73, Olympus). ...
Garnet-bearing mafic and felsic granulites associated with magnetite deposits that have undergone high-pressure (HP) and ultrahigh-temperature (UHT) metamorphism occur in the Yangjiazhai area of the Jiaobei terrane within the Jiao-Liao-Ji Belt, North China Craton. In mafic granulite, the early prograde assemblage (M1) is preserved as inclusions in the core of garnet. Matrix minerals and the garnet mantle define the peak metamorphic assemblage (M2). Near-isothermal decompression (M3) is recorded by the garnet rim and symplectitic minerals. The final cooling process is defined by the late growth of amphibole (M4). Abundant magnetite occurring in some mafic granulite samples may be inherited from the protolith. The felsic granulite records the peak metamorphic stage (M2) defined by the matrix minerals and the garnet mantle, and the retrograde stage defined by the symplectite and the garnet rim (M3). P-T estimations using pseudosection techniques and two-feldspar thermometry yield ∼8-9.8 kbar/710-828°C for the prograde stage M1, ∼14.5-15 kbar / 1040-1073°C for the peak P-T stage M2, 9.1-10 kbar / 965-1015°C for the post-peak stage M3 and 6.6-9.4 kbar / 820-853°C for the cooling stage M4 as recorded by the mafic granulite. P-T conditions of ∼14-16.5 kbar/985-1077°C for the peak P-T stage M2 and ∼7.8-9 kbar/889-902°C for the post-peak stage M3 were derived from the felsic granulite. Thus a clockwise trajectory can be defined by constraining peak-metamorphic high-pressure/ultrahigh-temperature (HP-UHT) conditions. Zircon U-Pb dating and REE characteristics show a contrasting information. Oscillatory zoned zircon domains yield an age of ∼2150 Ma with a steep HREE characteristic, which is interpreted to indicate a magmatic origin of the mafic granulite. The peak HP-UHT stage obtained from metamorphic zircon domains in felsic and mafic granulites is constrained by an age of ∼1950-1900 Ma, which possibly corresponds to a collisional event shortly after subduction. The decompression occurred at ∼1880 Ma following the subsequent cooling at ∼1820 Ma indicating a rapid exhumation of the HP-UHT granulite followed by slow cooling.
... CL, which is light or electromagnetic radiation produced by an electron beam, is an important technique that can be used for mineralogical studies in geosciences. Thus, the CL method is used to obtain information of internal textures of minerals and for the reconstruction of geological processes (e.g., Hanchar and Miller, 1993;Hanchar and Rudnick, 1995;Götze, 2000;Gorobets and Rogojine, 2002;Nasdala et al., 2004;Schertl et al., 2004;Nasdala et al., 2012). Optical cathodoluminescence microscopy (OCLM) study was carried out on uncovered polished thin sections using a CITL MK5 CL instrument mounted on a Nikon eclipse LV100 scope and integrated with an optical spectral analysis (OSA) unit and energy dispersive analysis (EDX) detector. ...
Şenkaya chrysoprase is a gemstone and can be found near the Turnalı village located in the west-northwest of Şenkaya (Erzurum) county in the uplifted Kırdağ of Northeast Anatolia of Turkey. Chrysoprase only found in Şenkaya County and known with the same name commercially in Turkey is a light-dark green and cryptocrystalline structure gemstone encountered in the Örükyayla Mélange. Samples were collected from the field for defining mineralogical-petrographical, XRD, XRF, ICP-MS, optical cathodoluminescence microscopy (OCLM), FTIR-Raman and stable isotopic properties of Şenkaya chrysoprase. According to mineralogical and petrographic examination, Şenkaya chrysoprase has generally heterogeneous color distribution in macroscale and has 5 Mohs mineral hardness. Microquartz filling (10%-15%) was seen in the microexamination with serpentine as main component with partly massive opal type silica. The XRF analyses indicate that many samples had high SiO2 values (91.45-94.38 wt%). As a result of trace elements, rare earth elements, Au-Pt group analyses using ICP-MS, Ni (167-387 ppm) and Co (12.57-74.78 ppm) values are quite remarkable. In the OCLM studies, few metallic minerals which could produce CL and could spread CL in different colors due to some trace activator elements were observed. Oxygen isotopic (δ18OV-SMOW) values obtained from three chrysoprase samples are 24.8‰, 27.7‰ and 30.63‰, respectively and mean formation temperature is 96-99 oC.
... Kyanite can incorporate 100's-1000's ppm of Fe, V, Cr and Ti as well as lower concentrations of other trace elements (Pearson and Shaw 1960;Herz and Dutra 1964;Chinner et al. 1969; Albee and Chodos 1969;Neiva 1984;Yang and Rivers 2001;Deer et al. 2013). Recent studies have shown that kyanite zoning revealed by cathodoluminescence (CL) imaging can be linked to trace element concentrations, which in turn can help to constrain rock reaction histories (Schertl et al. 2004;Horkley et al. 2013;Müller et al. 2016;Kendrick and Indares 2017;Tarantola et al. 2019;Peterman et al. 2021). Cr and Ti are known to be CL activators while Fe is a known CL quencher (Wojtowicz 1991;Pagel et al. 2000;Habermann 2002;Gaft et al. 2005), and variations in these elements have been shown to correlate well with changes in CL intensity (Müller et al. 2003). ...
Aluminosilicates (kyanite, sillimanite and andalusite) are useful pressure-temperature (P-T)indicators that can form in a range of rock types through different mineral reactions, including thosethat involve partial melting. Their involvement in melting reactions means that the presence ofaluminosilicates in migmatite mineral assemblages can help to (broadly) constrain the P-T conditionsof melt formation, which then has implications for evaluating models of orogenic tectonics.Xenocrystic grains could lead to spurious tectonic interpretations, so being able to distinguishbetween different petrogenetic sources is important. Petrological and geochemical investigation ofmigmatite-hosted kyanite from Eastern Bhutan shows that kyanite petrogenesis may be constrainedby combining information from morphology, cathodoluminescence response, microtextural positionand geochemical zoning patterns. Mg, Ti, Ca, Fe, Cr and Ge concentrations provide diagnostic cluesthat distinguish sub-solidus kyanite from kyanite that crystallised directly from melt, or grewperitectically during muscovite dehydration reactions. The abundance of these elements in kyanite isalso strongly controlled by protolith composition, with considerable inter-sample variation observedin this sample set. LA-ICP-MS maps, especially of Cr/V, provide additional information aboutchanging geochemical environments during kyanite growth. These data and observations show thatmost kyanite is of xenocrystic origin in the analysed samples, and therefore that its presence does notnecessarily constrain the P-T conditions of the melt reaction(s). This finding has significantimplications for the interpretation of kyanite-bearing migmatites as representing early stages ofmelting during Himalayan evolution.
... The Fe/Mn ratio is more important than their absolute 42 concentration (e.g., Jarc and Zupancic, 2009). Crystallographic structure, reticular defects, and crystallographic orientation of minerals also influence their luminescence (e.g., Schertl et al., 2004). ...
The balance between the carbon input in subduction zone, mainly by carbonate mineral-bearing rock subduction, and the output of CO2 to the atmosphere by volcanic and metamorphic degassing is critical to the carbon cycle. At fore arc-subarc conditions (75-100 km), carbon is thought to be released from the subducting rocks by devolatilization reactions and by fluid-induced dissolution of carbonate minerals. All together, devolatilization, dissolution, coupled with other processes like decarbonation melting and diapirism, are thought to be responsible for the complete transfer of the subducted carbon into the crust and lithospheric mantle during subduction metamorphism. Carbon-bearing fluids will form after devolatilization and dissolution reactions. The percolation of these fluids through the slab- and mantle-forming rocks is not only critical to carbon cycling, but also for non-volatile element mass transfer, slab and mantle RedOx conditions, as well as slab- and mantle-rock rheology. The evolution of such fluids through interactions with rocks at high-pressure conditions is, however, poorly constrained. This study focuses on the petrological, geochemical and isotopic characteristic of carbonated-metasomatic rocks from the lawsonite-eclogite unit in Alpine Corsica (France). The study rocks are found along major, inherited lithospheric lithological boundaries of the subducted oceanic-to-transitional plate and can inform on the evolution of carbon-bearing high-pressure fluids during subduction. In this work, it will be demonstrated that the interaction of carbon-bearing fluids with slab lithologies can lead to high-pressure carbonation (modeled conditions: 2 to 2.3 GPa and 490-530°C), characterized by silicate dissolution and Ca-carbonate mineral precipitation. A detailed petrological and geochemical characterization of selected samples, coupled with oxygen, carbon and strontium, neodymium isotopic systematic will be used to infer composition and multi-source origin of the fluids involved. Geochemical fluid-rock interactions will be quantified by mass balance and time-integrated fluid fluxes estimations. This study highlights the importance of carbonate-bearing fluids decompressing along down-T paths, such as along slab-parallel lithological boundaries, for the sequestration of carbon in subduction zones. Moreover, rock-carbonation by fluid-rock interactions may have an important impact on the residence time of carbon and oxygen in subduction zones and lithospheric mantle reservoirs as well as carbonate isotopic signatures in subduction zones. Lastly, carbonation may modulate the emission of CO2 at volcanic arcs over geological time scales.
... Note that diamond has been identified as inclusions in pyrrhotite from the Kumdy-Kol deposit for the first time ( Figure 2a). Previously, Schertl et al. [85] and Mikhno and Korsakov [86] claimed that samples enriched in sulphides are diamond-free. Zone III is enriched in graphite cuboids, with some of these cuboids containing a diamond core. ...
Graphite cuboids are abundant in ultrahigh-pressure metamorphic rocks and are generally interpreted as products of partial or complete graphitization of pre-existing diamonds. The understanding of the graphite cuboid structure and its formation mechanisms is still very limited compared to nanotubes, cones, and other carbon morphologies. This paper is devoted to the natural occurrences of graphite cuboids in several metamorphic and magmatic rocks, including diamondiferous metamorphic assemblages. The studied cuboids are polycrystalline aggregates composed either of numerous smaller graphite cuboids with smooth surfaces or graphite flakes radiating from a common center. Silicates, oxides, and sulphides are abundant in all the samples studied, testifying that the presence of oxygen, sulfur, or sulphides in natural systems does not prevent the spherulitic growth of graphite. The surface topography and internal morphology of graphite cuboids combined with petrological data suggest that graphite cuboids originated from a magmatic or metamorphic fluid/melt and do not represent products of diamond-graphite transformation processes, even in diamond-bearing rocks.
... white paper 2 Cathodoluminescence (CL) is used in a wide range of geological applications, including sedimentary petrology, igneous petrology, metamorphic petrology, crystal growth, and gemstone identification [e.g., [1][2][3][4][5][6][7][8][9][10][11]. The focus of this study is on the application of CL to minerals, specifically, colour-zoned sapphires. ...
One of the main purposes of cathodoluminescence (CL) imaging and spectroscopy of geological materials is to study zonation and crystallisation histories in minerals such as zircon. Despite common co-occurrence of zircons and sapphires in alluvial gemfields, there have been limited studies using CL to study chemical zonation of natural sapphire crystals. This study utilises CL to assess crystallisation histories of sapphire and underlying causes for luminescence. Alluvial sapphires from eastern Australia were analysed by CL and correlated with complementary laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) measurements, to determine trace element compositions. Results illustrate a strong correlation between colour, trace element concentrations, and spectral CL measurements of sapphires. CL spectra can potentially indicate relative oxidised or reduced conditions during sapphire crystallisation.
... The Fe/Mn ratio, in particular, is more important than their absolute concentrations (e.g., Jarc and Zupancic 2009). Crystallographic structure, reticular defects, and crystallographic orientation of minerals also influence their luminescence (e.g., Schertl et al. 2004). ...
In deep and cold subduction such as that experienced by the UHP Units of the Western Alps, carbon dissolution is a relevant mechanism for carbon transfer from the slab into the mantle. The UHP impure Cal-Dol-marbles from the Dora-Maira Massif are studied to investigate the poorly known evolution of dolomite during deep subduction. Dolomite shows four stages of growth, from pre-Alpine to early-retrograde Alpine, coupled with chemical variations and distinct included mineral assemblages. To explain the evidence for growth and partial reabsorption of dolomite through HP prograde, UHP peak, and UHP early-retrograde Alpine metamorphism, a chemically simple marble (Cal, Dol, Di, Fo, and retrograde Atg, Tr, Mg-Chl) has been studied in detail. Microstructural relationships, coupled with mineral chemistry, indicate the growth of the assemblage dolomite+diopside+forsterite±aragonite during HP prograde, UHP peak, and UHP early-retrograde evolution.
Mixed-volatile P-T projection modeled in the simple CaO-(FeO)-MgO-SiO2-H2O-CO2 system and T-P-XCO2 petrogenetic grids and pseudosections predict the prograde (1.7 GPa, 560 °C) growth of dolomite in equilibrium with diopside and forsterite through the breakdown of antigorite+aragonite. In a H2O-CO2-saturated system, the subsequent HP-UHP evolution is predicted in the Di+Fo+Dol+Arg stability field in equilibrium with a dominantly aqueous COH fluid [0.0003 < XCO2 < 0.0008], whose composition is internally buffered by the equilibrium assemblage. Thermodynamic modeling indicates that neither the consumption nor the growth of new dolomite generations at UHP conditions can have been induced by metamorphic reactions. The abundant primary H2O+Cal+Dol+Cl-rich Tr+Cl-rich Tlc±chloride fluid inclusions present in UHP Cpx indicate that a dominantly aqueous, saline (salinity >26.3 wt% of NaCleq) COH fluid, containing Ca, Mg, and Si as dissolved cations was present during the growth of the UHP assemblage Dol+Cpx+Ol+Arg.
The complex zoning of dolomite is therefore interpreted as due to protracted episodes of dissolution and precipitation in saline aqueous fluids at HP/UHP conditions. Kinetics of dolomite dissolution in aqueous fluids is poorly known, and experimental and thermodynamic data under HP conditions are still lacking. Data on calcite indicate that dissolution at HP is enhanced by a prograde increase in both P and T, by high salinity in aqueous fluids, and/or low-pH conditions. In the studied marble, the P-T path and the occurrence of free high-saline fluids represent favorable conditions: (1) for the inferred dissolution-precipitation processes of the stable dolomite in a closed system, and (2) for possible migration of the dissolved carbonate, if the system would have been open during subduction.
... Nitrogen isotope data and negative δ 13 C values of Kokchetav diamonds indicate a metasedimentary origin (e.g., De Corte et al., 2000;Cartigny, 2005). Schertl et al. (2004Schertl et al. ( , 2015 focused on cathodoluminescense (CL) microscopy of Kokchetav UHP minerals and were able to uncover important internal structures as, for instance, irregular net-like zoning of garnet, exsolution lamellae in carbonate and clinopyroxene, growth zoning of diamond, carbonates and potassium-bearing clinopyroxene. Many of such structures could easily have become overlooked without applying CL microscopy but provide important genetic information in deriving geological and tectonic interpretations. ...
... Nitrogen isotope data and negative δ 13 C values of Kokchetav diamonds indicate a metasedimentary origin (e.g., De Corte et al., 2000;Cartigny, 2005). Schertl et al. (2004Schertl et al. ( , 2015 focused on cathodoluminescense (CL) microscopy of Kokchetav UHP minerals and were able to uncover important internal structures as, for instance, irregular net-like zoning of garnet, exsolution lamellae in carbonate and clinopyroxene, growth zoning of diamond, carbonates and potassium-bearing clinopyroxene. Many of such structures could easily have become overlooked without applying CL microscopy but provide important genetic information in deriving geological and tectonic interpretations. ...
No abstract is available for this article.
... However, all these arguments may not conclusively indicate direct precipitation of crystals from fluid. For example, both oscillatory zoning and fluid inclusions were observed in minerals of metamorphic origin (e.g., Philippot et al., 1995;Schumacher et al., 1999;Schertl et al., 2004). The vein-like occurrence could also be interpreted as being inherited from the protolith -igneous dike in ultramafic rock/serpentinite. ...
The jadeite–quartz rock (or jadeitite) from the Yorii area, the Kanto Mountains, central Japan occurs in greenstone mélange subjected to metamorphism related to the Sanbagawa event. This rock was previously suggested to have formed through “vein precipitation” process contemporaneous with the Jurassic accretionary event. Mineral inclusions in zircons from this jadeite–quartz rock were re-examined in this study. The results clearly showed that these zircons contain mineral inclusions of both primary (igneous) and secondary (metasomatic) origin. The former are not present in matrix of the jadeite–quartz rock and the latter are pseudo-inclusions. These zircons are thus inherited or incompletely recrystallized ones. The geochemical characteristics of these zircons, including Th/U ratio and Ce anomaly, are also in accord with this conclusion. The jadeite–quartz rock should therefore have formed through “wholesale metasomatic replacement” process at an age younger than 141 Ma from a protolith of probable igneous origin aged at 162.2 ± 0.6 Ma.
Based on the available data, a few criteria, including texture, mineral inclusion, Th/U ratio and Ce anomaly of zircon, were proposed to categorize zircons in jadeitite into inherited, incompletely recrystallized and metasomatic ones. The results may be used to infer the formation mechanism of the hosting jadeitite. Some possible ambiguities in applying the proposed criteria were discussed. Following the proposition, it was shown that previous genetic conclusions for some jadeitites from various occurrences around the world would be subjected to question and should be re-examined by careful investigation of mineral inclusions in zircons, similar to this study, in the future.
... These rocks contain information on the peak P-T histories of metamorphism and the earliest exhumation stages (Sobolev et al., 2011). A study of symplectitic rims around garnet confirmed an important role of secondary clinopyroxene, spinel, as well as corundum and sapphirine, which represent an early, high-T retrograde stage of metamorphism related to subduction (Schertl et al., 2004;Sobolev et al., 2001Sobolev et al., , 2006Sobolev et al., , 2011 (Fig. 1). A strong predominance of acicular corundum grains has been revealed in the matrix of secondary clinopyroxene in assemblage with phlogopite and high-K (up to 4.5 wt.% ...
We present a systematic review of the key results and research trends in the Deep Carbon Cycle program. The first section addresses the issues related to subduction zones with emphasis on geological and geophysical data on Kamchatka and Kokchetav paleosubduction zone. Experimental studies over a wide pressure range are discussed in the section “Crystallogenesis and experimental mineralogy”. The papers addressing the diamond issues on the example of the Yakutian diamondiferous province are grouped in the sections “Diamond crystallogenesis” and “Diamond and kimberlite magmatism”.
... Particularly interesting is oscillatory zoning in the rims of some of the studied olivine phenocrysts. The number of such zones with regular faces, which are typical of olivine, reaches at least ten in the regenerated rims of the grains, and this zoning is similar to that in pyrope from Dora Maira quartzites (Schertl et al., 2004) as well as pyrochlore-group minerals (Sharygin et al., 2009) and skarn garnets (Zhai et al., 2014). ...
Unaltered Mg-olivine (Fo = 85–94) is a predominant mineral of the kimberlite block (serpentine-free) of the Udachnaya-East pipe, and it prevails in peridotite xenoliths and as inclusions in diamonds. The kimberlite of this pipe, like a series of hypabyssal kimberlites in other regions, contains two main types of olivine macrocrysts according to their size and morphology: those rounded or irregularly shaped (olivine I) and euhedral phenocrysts (olivine II), which are usually no larger than 0.5 mm and very seldom reach 1 mm in size. This study was focused on several thousand olivine samples assigned both to olivines I and to olivines II, with a gradual transition between them. Particular attention was paid to the search for mineral inclusions in olivine and for phenocrysts with a clear zoning. In the phenocryst cores of homogeneous composition, we have revealed orthopyroxene inclusions as well as clinopyroxene (chrome-diopside and chrome-omphacite) inclusions with wide variations in the Na 2 O and Cr 2 O 3 contents, significantly higher than the previously established ones: up to 6.00 wt.% Na 2 O and 4.23 wt.% Cr 2 O 3 . Convincing evidence for the high-pressure origin of the olivine macrocryst cores is the presence of pyrope inclusions with 1.41–9.14 wt.% Cr 2 O 3 , 4.64–6.61 wt.% CaO, and Mg# = 75.6–83.7 in six samples, which testifies to the high-pressure lherzolite paragenesis of the phenocrysts cores. The cores of the studied olivine phenocrysts are identical in the contents of Ni, Co, Ca, Cr, and Mn to olivines from diamonds and peridotite xenoliths. However, they differ significantly in the steady elevated Ti content, equal to 100–300 ppm for the majority of the phenocrysts, including those containing pyroxene and pyrope inclusions.
... K-feldspar (+phengite) exsolutions in clinopyroxene (e.g., Katayama et al., 2002;Sakamaki and Ogasawara, 2013) demonstrate that potassium can be incorporated in the Cpx structure at upper mantle pressures. Other significant observations are (1) coesite exsolution and hydroxyls in titanite Sakamaki and Ogasawara, 2013), (2) quartz rods and phengite exsolution in Cpx (e.g., Katayama and Maruyama, 2009), (3) corundum, sapphirine and spinel in garnet rims and perovskite inclusions in forsterite from a layered calcsilicate rock (Schertl et al., 2004), (4) the occurrence of akdalaite (5Al 2 O 3 ÁH 2 O) from a Kulet whiteschist (Hwang et al., 2006), (5) longsdaleite, the 2H hexagonal polytype of carbon, from a Grt-Bt gneiss (Dubinchuk et al., 2010), (6) hogbomite associated with spinel in diamond-free dolomite marble (Schertl and Sobolev, 2013), and (7) a host of high-Mg-bearing phases. Several new minerals including kokchetavite (Hwang et al., 2004(Hwang et al., , 2013, a hexagonal polymorph of K-feldspar, and kumdykolite (Hwang et al., 2009), an orthorhombic polymorph of albite, have been reported. ...
... Imamura et al. (2013) showed carbon isotope heterogeneity of the microdiamonds in dolomite marble and validity of the two-stage growth theory. Furthermore, many other studies have demonstrated that the Kokchetav UHP diamonds are zoned in CL (Bruce et al., 2011;De Corte et al., 2002;Iancu et al., 2008;Korsakov et al., 2005;Schertl et al., 2004). Bruce et al. (2011) also conducted a photoluminescence (PL) study of various metamorphic diamonds, however, their Kokchetav UHP microdiamonds were too small for their PL measurements. ...
We conducted detailed in-situ Raman, photoluminescence (PL) and cathodoluminescence (CL) studies on microdiamonds in a tourmaline-rich quartzofeldspathic rock from the Kokchetav Massif, Kazakhstan. The microdiamonds occur as inclusions in the cores of K-tourmaline and in zoned zircons with varying U contents. The results of 2D Raman mapping of zircon showed that the U-rich parts were more metamictized than the U-poor parts. All the diamonds showed a strong Raman band at approximately 1332 cm− 1, however, the features of the Raman bands were distinctly different depending on the host minerals. At the one hand, diamonds in tourmaline had a sharp Raman band that is similar to that of kimberlite diamonds [full width at half maximum (FWHM): 2–3 cm− 1]. On the other hand, diamonds in zircon had a broad and downshifted band compared to those in tourmaline. In particular, diamonds in U-rich cores of zircons (up to 0.15 wt% UO2) showed broader and more downshifted Raman bands (FWHMs and peak positions varied up to 9.3 cm− 1 and 1328 cm− 1, respectively), with additional small bands at approximately 1490 cm− 1 and 1630 cm− 1. A negative correlation was observed between the peak position and the FWHM of the principal Raman band of microdiamonds. Furthermore, the PL and CL spectra showed systematic variations. Diamonds in zircons with low to moderate U-concentrations had very strong PL and CL compared to diamonds in U-rich zircons and in tourmalines. Several characteristic peaks appeared in the PL and CL spectra, indicating the presence of irradiation and/or nitrogen-related point defects in the diamonds. PL and CL of microdiamonds in high-U zircon were weak, but still showed irradiation-related peaks. The relationship between the occurrence of microdiamonds (i.e., corresponding to the estimated total α-dose since crystallization) and the Raman, PL, and CL spectral characteristics of microdiamonds strongly suggests that radiation damage predominantly caused by α-particle emission from radioactive decay of actinides (mainly U) in zircon is a principal factor for the spectral variations. Radiation damage (metamictization) is probably a common phenomenon among microdiamonds in zircons in various diamond-bearing rocks from the Kokchetav Massif. To discuss the genesis of diamonds based on their Raman, PL, or CL spectra, it is highly recommended that microdiamonds included in actinide-bearing minerals (e.g., zircon) should be treated with the most careful attention, because post-crystallization radiation damage significantly influences the spectra.
... Garnet-pyroxene and pyroxene-carbonate rocks of the Kumdy-Kol' deposit intrigue petrologists very much [1][2][3][4][5][6][7][8][9]. The reason is that these rocks drastically differ in diamond potential and the suite of their minerals is quite remarkable. ...
Banded samples of calc-silicate rocks with contrasting diamond potential from the Kumdy-Kol' metamorphic diamond deposit, northern Kazakhstan, were examined. The sample Kar-4 is enriched in diamonds. At the same time, the sample Kar-98-6 contains few diamond crystals, and the sample Kar-200 lacks diamonds. The data obtained show that the composition of minerals and zoning character may considerably vary even within one sample. In particular, in the sample Kar-200 the content of grossular component in garnets varies from 81 to 57%. Pyroxenes from different layers are distinguished in content of potassium impurity. For example, the pyroxene from layer A contains up to 0.6% K2O and phengite lamelles, whereas the pyroxenes from other layers contain as little as 0.2% potassium, if any. Study of calc-silicate rocks under a scanning electron microscope has shown that dolomite is replaced by an aggregate of tremolite, talc, and calcite. Garnets from the sample Kar-4 contain rounded inclusions of dolomite, with globules of intricate composition in their core, which are composed of magnesite, amorphous hydrous silica, dolomite, and calcite. These globules are interpreted as a carbonatite melt. As a result of our studies, the following stages were distinguished in the metamorphic evolution of calc-silicate rocks. The protoliths of calc-silicate rocks are clayey calcareous dolomites. At the progressive stage of metamorphism, these rocks underwent partial melting initiated by a water fluid that appeared on zoisite decomposition. At higher pressures and temperatures, the decomposition of phengite led to the formation of a high-K fluid. Diamonds are crystallized just at this stage. At the regressive stage, in the stability field of zoisite, garnet was replaced by pyroxene-zoisite-calcite symplectite. At the final stage of exhumation, the carbonate rocks interacted with a Si-enriched aqueous fluid.
... In contrast to the extensive petrological and geochronological work on the various ultrahigh-pressure (UHP) metamorphic rocks of the coesite-bearing unit (or ''Brossasco-Isasca Unit''; Compagnoni et al., 1994) of the Dora-Maira Massif (e.g. Chopin, 1984;Paquette et al., 1989;Tilton et al., 1989Tilton et al., , 1991Chopin et al., 1991;Monié & Chopin, 1991;Schertl et al., 1991;Hirajima & Compagnoni, 1993;Philippot, 1993;Compagnoni et al., 1995;Schertl & Schreyer, 1996;Gebauer et al., 1997;Simon et al., 1997;Tilton et al., 1997;Paquette et al., 1999;Ferraris et al., 2000;Nowlan et al., 2000;Rubatto & Hermann, 2001;Simon & Chopin, 2001;Hermann, 2003;Mosenfelder et al., 2004;Schertl et al., 2004;Ferraris et al., 2005;Castelli et al., 2007;Groppo et al., 2007), there is still a deficiency of basic geochemical data. The present publication fills this gap by reporting on the bulk chemical compositions as well as on trace-element patterns of some important rock types for this unit. ...
In contrast to the extensive petrological and geochronological work on the various ultrahigh-pressure (UHP) metamorphic rocks of the coesite-bearing unit of the Dora Maira Massif, there is still a deficiency of basic geochemical data. A complete suite of geochemical data for pyrope quartzites, various intercalations of phengite-schists and jadeite-bearing rocks, as well as country rock gneisses from different localities within the southern Dora Maira Massiv is now available, which was studied in detail in order to establish the nature of the different protoliths and their primary relationships (Schertl and Schreyer, 2008; see also Chopin, 1984 and Compagnoni and Hirajima, 2001). Typically, the pyrope quartzites are high in Mg and strongly depleted in Na, Ca, Fe, Cu, P, Rb, Ba, Sr against their country rock gneisses which essentially exhibit a granitic bulk composition. The country rocks have a peraluminous chemistry; they generally are corundum normative and best attributed to S-type granites. Trace element contents of phengite-schist inclusions in pyrope quartzite confirm their close relationship to the granitic country rocks. Internal variations of Na, Ca versus K, Mg are matched by Rb, Ba and Sr, which is in line with some phengite-schists to contain higher amounts of phengite or higher amounts of jadeite-pseudomorphs, respectively. The origin of the jadeite-rich rocks is still a matter of debate. Jadeite-bearing layers and jadeite quartzite forming conformable bands and boudins within pyrope quartzite differ generally by their lower contents in K, Mg, Rb and higher contents in Na, Fe, Ca, Mn, P and Zn. Earlier suggestions that these layers represent former melts seem unlikely in the view of their almost constant mass behaviour for SiO2 and Al2O3 relative to the surrounding pyrope quartzites. The present study indicates that the pyrope quartzites were formed metasomatically whereas an evaporitic nature of the protolith can be ruled out. Discrimination plots demonstrate that the whiteschist-type pyrope quartzites can be clearly distinguished chemically from metasedimentary whiteschists of former evaporite environments. Field relations of trails of pyrope quartzites, now forming lensoid inclusions within a former granite intrusion, would also make a metasedimentary origin rather unlikely. On the other hand, consistent genetical relationships between pyrope quartzites and their adjacent granitic country rocks were obtained, which virtually match those of Mg-metasomatic leucophyllites from the Eastern Alps occurring along shear zones within granitic gneisses. Similar Mg-rich rocks to be found within the Tauern Window and the Monte Rosa and Gran Paradiso Massivs of the Western Alps indicate that throughout the entire range of the Alps local processes of Mg-metasomatism occurred. References Chopin, C. (1984): Coesite and pure pyrope in high-grade blueschists of the Western Alps: a first record and some consequences. Contrib. Mineral. Petrol., 86, 107-118. Compagnoni, R. and Hirajima, T. (2001): Superzoned garnets in the coesite-bearing Brossasco-Isasca Unit, Dora-Maira massif, Western Alps, and the origin of the whiteschists. Lithos, 57, 219- 236. Schertl, H.-P. and Schreyer, W. (2008): Geochemistry of coesite-bearing "pyrope quartzites" and related rocks from the Dora-Maira Massif, Western Alps. Eur. J. Mineral., in press.
... Anorthite was reported as stably coexisting with Cal + Dol + Fo + Sp + Cpx + Amp (pargasite) in granulite-facies marbles from southern India by Janardhan et al. (2001). The only garnet-spinel assemblage we are aware of is a retrograde spinel-diopside symplectite developed occasionally around garnet from Kokchetav calcsilicate assemblages (mainly Cal + Dol + Grt + Di + Phl) described by Schertl et al. (2004) and Sobolev et al. (2006). This texture is an expression of the strongly curved reaction (3) that limits the maximum stability of spinel to higher pressures also for the Rhodope marbles. ...
Four different types of parageneses of the minerals calcite, dolomite, diopside, forsterite, spinel, amphibole (pargasite), (Ti–)clinohumite and phlogopite were observed in calcite–dolomite marbles collected in the Kimi-Complex of the Rhodope Metamorphic Province (RMP). The presence of former aragonite can be inferred from carbonate inclusions, which, in combination with an analysis of phase relations in the simplified system CaO–MgO–Al2O3–SiO2–CO2 (CMAS–CO2) show that the mineral assemblages preserved in these marbles most likely equilibrated at the aragonite–calcite transition, slightly below the coesite stability field, at ca. 720 °C, 25 kbar and aCO2~0.01. The thermodynamic model predicts that no matter what activity of CO2, garnet has to be present in aluminous calcite–dolomite-marble at UHP conditions.
... Measuring conditions were: acceleration voltage 15 kV, beam current 15 nA, measuring time 20 s. In addition to using EMP, X-ray intensity mapping (MAPS) was performed where four elements were analyzed semiquantitatively at the same time during one cycle in order to measure chemical zonation (measuring time 1 s; for more information, see Schumacher et al., 1999;Schertl et al., 2004). Finally, the electron backscatter diffraction (EBSD) technique was used to obtain structural information on zoisite and on garnet but also on their potential structural relationship. ...
Intergrowth textures of garnet and zoisite have been discovered in the coesite-bearing unit of the Dora Maira Massif near Bastoneri, Valle Gilba. Garnet is rich in grossular- and almandine-component and forms lath-shaped lamellae that are oriented parallel to (100) of zoisite. Electron backscatter diffraction (EBSD) studies show that zoisite/garnet symplectites typically form clusters where the crystallographical c-axes of each zoisite are characterized by a planar orientation. No epitaxial relationship between the structures of zoisite and garnet was recognized. Three different but typical examples of garnet lamellae can be distinguished where (1) one single garnet lamella has one distinct crystallographical orientation, (2) one single garnet lamella exhibits different domains of random orientations, and (3) different parts of a single garnet lamella show in general the same crystallographical orientation but contain microdomains of different orientations that were repeated by 30° along a great circle.In all probability these garnet lamellae are exsolved from an earlier-generation epidote-group mineral. A potential mechanism of formation is the break down of the former clinozoisite/epidote precursor during metamorphism due to a reduction of trivalent iron to form grossular/almandine lamellae in zoisite. High amounts of divalent cations in the precursor may play a significant role in that their incorporation is favored by pressure. Pressure release during exhumation of the rocks could then lead to the "exsolution" of garnet from precursor clinozoisite/epidote.
Cadmium tungstate, CdWO4, is widely used as a material for scintillating detectors in medicine, prevailingly, in computer tomography, as well as in high energy physics. Many studies consider luminescent properties of these crystals. However, there are few publications concerning structural defects, which can influence practically important properties of cadmium tungstate. In this work strain induced twinning and dislocation slip of CdWO4 single crystals are investigated.
A series of precise nondestructive analytical methods (Raman spectroscopy, cathodoluminescence, and EBSD-electron backscatter diffraction) has been employed to investigate the internal textures of kyanite porphyroblasts from diamondiferous and diamond-free ultrahigh-pressure metamorphic rocks (Kokchetav massif, Northern Kazakhstan). Such internal kyanite characteristics as twinning, radial fibrous pattern, and spotty zoning were identified by means of Raman and cathodoluminescence imaging, whereas an intergrowth of two kyanite crystals was distinguished only by Raman imaging. The EBSD analysis recorded an ~10-25° changing of orientations along the elongation in the investigated kyanite porphyroblasts. The absence of a radial fibrous pattern and a spotty zoning on the EBSD maps indicates that these textures are not related to variations in crystallographic orientation. The absence of clear zoning patterns (cores, mantles, and rims) on the Raman, cathodoluminescence, or EBSD maps of the kyanite porphyroblasts indicates the rapid single-stage formation of these porphyroblasts near the peak metamorphic conditions and the lack of recrystallization processes. The obtained results provide important implications for deciphering of mineral internal textures, showing that the data obtained by cathodoluminescence mapping can be clearly reproduced by Raman imaging, with the latter method occasionally being even more informative. This observation is of significant importance for the study of minerals that are unexposed on a thin section surface or Fe- and Ni-rich minerals that do not show luminescence emission. The combination of the Raman spectroscopic, cathodoluminescence, and EBSD techniques may provide better spatial resolution for distinguishing different domains and textural peculiarities of mineral than the selective application of individual approaches.
Cathodoluminescence (CL) mapping of kyanite in high-P, aluminous granulites from the central Grenville Province reveals internal structures that are linked to their metamorphic reaction history. In two samples, individual kyanite crystals are shown to be composite porphyroblasts comprising three distinct generations, defined by their CL intensity and Cr (± V, Ti, Fe and Ga) content, and each separated by resorbed interfaces. In contrast, a sub-aluminous sample contains two types of kyanite, one as resorbed inclusions in garnet and another in the groundmass or replacing garnet. These textural variants of kyanite are interpreted within the framework of phase equilibria modelling. In P–T pseudosections, a first generation of kyanite, which is only present in the most aluminous samples, is potentially linked to staurolite breakdown, and its resorption is consistent with a subsequent increase in pressure. This kyanite represents the earliest remnant of prograde metamorphism identifiable in these rocks. The second generation, present in the porphyroblasts in the same samples and as inclusions in garnet in the sub-aluminous sample, is interpreted to be the peritectic product of muscovite dehydration melting. Resorption of this kyanite is consistent with subsequent continuous dehydration melting of biotite, which is also inferred based on microstructural considerations. The final generation of kyanite, present as rims on the prograde kyanite porphyroblasts in aluminous samples and as part of the groundmass or replacing garnet in the sub-aluminous rock, is interpreted to have grown during melt crystallization upon retrogression. The presence of retrograde kyanite implies that the melt crystallized over a wide range of temperatures, and provides an important constraint on the P–T conditions of the metamorphic peak and on the retrograde P–T paths. Cathodoluminescence mapping is crucial for identifying retrograde kyanite in aluminous samples, as it preferentially overgrows existing kyanite rather than replacing other prograde phases. The scarcity of kyanite in sub-aluminous rocks allows retrograde kyanite to grow as discrete crystals that can be identified by optical microscopy. This work attests to the potential of unconventional tools such as CL imaging for deciphering the metamorphic history of rocks.
Many archeological sites with jadeitite artefacts are known in the Caribbean region, but defining the source of the raw material is a major problem, because of great mineralogical heterogeneity both in potential sources and in artefacts. The archaeological settlement site of Playa Grande on the northern coast of the Dominican Republic is particularly significant, because it yielded evidence of on-site axe manufacture, and lies only 20-30 km NE of a recently discovered potential source area of serpentinite mélanges in the near-by Río San Juan Complex (RSJC). A suite of nine artefacts was chosen from a collection of over 100 excavated woodworking tools rich in jadeite, as well as two blueschist artefacts. Permission to perform destructive analysis allowed data on petrography, mineral chemistry and bulk-rock chemistry to be obtained. Seven of the nine artefacts are jadeitite s.str. (> 90 vol.% jadeite), which are identical to material known from the RSJC. Two artefacts are jadeite-lawsonite rocks. These and the two blueschists show only minor differences from corresponding rocks of the RSJC source. With this direct linking of source and site material it is now possible to better define source discriminators for the Caribbean and to assess sampling bias.
In recent years diamonds and other unusual minerals (carbides, nitrides, metal alloys and native elements) have been recovered from mantle peridotites and chromitites (both high–Cr chromitites and high–Al chromitites) from a number of ophiolites of different ages and tectonic settings. Here we report a similar assemblage of minerals from the Skenderbeu massif of the Mirdita zone ophiolite, west Albania. So far, more than 20 grains of microdiamonds and 30 grains of moissanites (SiC) have been separated from the podiform chromitite. The diamonds are mostly light yellow, transparent, euhedral crystals, 200–300 μm across, with a range of morphologies; some are octahedral and cuboctahedron and others are elongate and irregular. Secondary electron images show that some grains have well–developed striations. All the diamond grains have been analyzed and yielded typical Raman spectra with a shift at ~1325 cm–1. The moissanite grains recovered from the Skenderbeu chromitites are mainly light blue to dark blue, but some are yellow to light yellow. All the analyzed grains have typical Raman spectra with shifts at 766 cm–1, 787 cm–1, and 967 cm–1. The energy spectrums of the moissanites confirm that the grains are composed entirely of silicon and carbon. This investigation expands the occurrence of diamonds and moissanites to Mesozoic ophiolites in the Neo–Tethys. Our new findings suggest that diamonds and moissanites are present, and probably ubiquitous in the oceanic mantle and can provide new perspectives and avenues for research on the origin of ophiolites and podiform chromitites.
With the use of optical microscope-based cathodoluminescence (OM-CL), many kinds of growth textures of minerals can be observed, which are either indiscernable or to be omitted easily with other routine analytical methods. OM-CL is an effective pre-research technique prior to other follow-up component analysis, which can provide important information for reconstructing formation and evolution processes of minerals. This technique has wide-spread applications in international petromineralogy, oil and gas reservoir and mineral deposits, but is relatively weak in metamorphic rocks. The applications of OM-CL in the UHP (ultra high power) metamorphic rocks are reviewed in this paper, as well as preliminary studies by OM-CL on ultrahigh-pressure eclogites, micaschist and marble at classical areas in the Dabie-Sulu UHP metamorphic belt. And its application and prospect in the fast identification of multi-phase tiny mineral facies and internal structural characterization, including growth zoning, distribution of trace elements, twinning and exsolution texture are discussed. A new perspective for our research on ultrahigh-pressure metamorphic rocks can be developed when combining OM-CL with mineral chemistry analysis techniques such as Roman spectrum, scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA).
Data on compositions and parageneses of coexisting garnets and pyroxenes trapped by diamonds containing coesite from different deposits of the world and from xenoliths of coesite eclogites have been generalized. Remarkably, the diamonds of coesite inclusions (over 250 specimens) have been established in all deposits in operation. Diamonds with coesite as well as xenoliths of coesite eclogites contain all the parageneses represented in cclogite (E-type) diamonds in kimberlites and mantle-derived eclogites. These parageneses include a wide continuous series of compositions from websterites (pyroxenites) to kyanite eclogites, grospydites, and calc-silicate compositions. Data on exclusively wide variations of composition of mantle-derived coesite-bearing rocks and the available data on oxygen isotopy of coesite as well as carbon and nitrogen isotopes of diamonds with coesite inclusions suggest the formation of coesite-bearing eclogite parageneses of kimberlites and lamproites as a result of the subduction of ancient oceanic crust. Similar features of diamonds have been recorded in coesite as well as in diamondiferous UHP metamorphic rocks.
The occurrence of graphite-coated microdiamonds is a characteristic feature of ultrahigh-pressure metamorphic rocks. Nonetheless, their tiny dimension was an insurmountable obstacle for the study of these aggregates for a long time. Our observations show that graphite-coated diamonds were formed before their capture by the host mineral (garnet, clinopyroxene, zircon, and others). This fact is very important for the development of a genetic model. If we assume that crystallization of graphite is related to pressure decrease (i.e., graphite growth in the thermodynamic stability field), then the minerals with the graphite-coated diamond should be formed at the retrograde stage and they cannot characterize PT conditions corresponding to the peak of metamorphism.
Confocal 2-D and 3-D Raman imaging of the Kokchetav metamorphic diamonds from different rock types reveals that these diamonds have a rather complex internal morphology. The diamond shows a strong change in the position of the diamond Raman line as well as the width of this line, which could be found both in the XY and in the YZ scan. These features indicate variations in the crystalline quality of the diamond. The broadest lines are located in the center of the octahedral diamond inclusion whereas the material close to the diamond–garnet interface shows smaller line widths. These features were also found for thermochemically extracted diamond crystals, which are not armored by host mineral, and in situ for inter- and intragranular diamond. Furthermore, host–garnet display no evidence for broadening or up-shift of main Raman bands, indicating very low (below detection limit) residual strain. Thus the broadening and upshift of main diamond band do not relate to residual strain in inclusion–host systems. A comparison of Raman imaging results with cathodoluminescence images reveals that the distribution of defects, which cause the cathodoluminescence of diamond crystals, can be traced by Raman imaging. The 2-D and 3-D Raman imaging is a very powerful tool for study of internal morphology and growth pattern of metamorphic diamond, even it is a small crystal less than 10 µm in size. The growth pattern for octahedral diamond crystals from garnet–clinozoisite gneisses were obtained for the first time by Raman imaging. Copyright © 2015 John Wiley & Sons, Ltd.
The oxygen isotope compositions of calcite, diopside, dolomite, forsterite, garnet, K-feldspar, kyanite, plagioclase, quartz, and wollastonite were analyzed in suites of contact and regional metamorphic rocks using an ion microprobe. Spatial resolution was ∼10 μm. Precision, measured as the standard deviation of working standards averaged over the entire project, was 0.13–0.18‰ for three carbonate standards and 0.11–0.12‰ for two silicate standards. A total of 1176 analyses (excluding standards) were made of 73 minerals in 23 samples. Both intercrystalline and intracrystalline variability in δ18O is greater in contact than in regional metamorphic rocks. Of 27 minerals analyzed in contact metamorphosed rocks, 70% exhibit statistically significant grain-to-grain variability in δ18O over areas ⩽1.41 cm2 with the largest range in silicates and carbonates in a single sample of 7.4‰ (forsterite) and 10.6‰ (dolomite). Of 88 grains analyzed in two or more places in contact metamorphosed rocks, 32% exhibit statistically significant intracrystalline variability in δ18O with the largest range in a single silicate and carbonate grain of 3.1‰ (forsterite) and 10.1‰ (dolomite). In contrast, 44% of 45 minerals in regional metamorphic rocks exhibit significant grain-to-grain variability in δ18O over areas ⩽1.17 cm2 with the largest range in silicates and carbonates in a single sample of only 1.1‰ (plagioclase) and 0.9‰ (calcite). Only 6% of 144 grains analyzed in two or more places in regional metamorphic rocks exhibit significant intracrystalline variability in δ18O with the largest range in a single silicate and carbonate grain of only 1.5‰ (diopside) and 0.7‰ (calcite). The difference in intercrystalline and intracrystalline variability in δ18O between contact and region metamorphic rocks is explained by the longer duration and slower reaction rates of regional metamorphism rather than to differences in temperature. There is no significant difference in intercrystalline and intracrystalline variability in δ18O in regional metamorphic rocks among samples from the biotite, garnet, and kyanite zones. Calcite inclusions in forsterite, and calcite and quartz inclusions in garnet either have δ18O that is statistically indistinguishable from δ18O of the same mineral occurring as nearby matrix grains or have statistically significant lower δ18O. No reversed isotope fractionations were measured between coexisting mineral pairs. Minerals in individual samples, however, exhibit a wide range in the degree to which they attained and preserve oxygen isotope fractionations consistent with metamorphic temperatures recorded by mineral equilibria. Processes that account for grain-scale departures from isotope exchange equilibrium include: (a) overstepping of prograde mineral reactions, (b) growth zoning in low-diffusivity minerals, (c) interaction of rocks with fluids at the peak of metamorphism and/or during cooling, (d) retrograde mineral reactions, and (e) closed-system isotope exchange between coexisting minerals during cooling. This study provides new information about (1) the degree to which a variety of textural changes experienced by rocks during metamorphism are associated with changes in δ18O, (2) oxygen isotope homogenization at the outcrop scale among contrasting lithologies, (3) changes in δ18O with increasing grade of regional metamorphism, and (4) time scales of metamorphic process.
The accumulation of structural damage that is created in minerals upon corpuscular irradiation, has two apparently contrarious effects on their luminescence behaviour. First, irradiation may cause the generation of luminescent defect centres, which typically results in broad-band emissions. Such defect emissions are characteristic of low levels of radiation damage. Second, radiation damage depletes in general the luminescence of minerals, which is associated with broadenings and intensity losses of individual emission lines. Minerals that have suffered elevated levels of irradiation hence tend to be virtually non-luminescent. This review paper aims at giving an overview of the possible correlations of radiation damage and emission characteristics of minerals. After a brief, introductory summary of the damage-accumulation process and its causal corpuscular radiation, an array of examples is presented for how internal and/or external irradiation may change appreciably the emission of rock-forming and accessory minerals. As a detailed example for the complexity of changes of emissions upon damage accumulation, preliminary results of a case study of the photoluminescence (PL) of synthetic CePO4 irradiated with 8.8 MeV He ions are presented. Irradiation-induced spectral changes include (i) the initial creation, and subsequent depletion, of a broad-band, defect-related PL emission of orange colour, and (ii) gradual broadenings and intensity losses of PL lines related to electronic transitions of rare-earth elements, eventually leading to gradual loss of their splitting into multiple Stark levels (shown for the 4F3/2 → 4I9/2 transition of Nd3+).
Homogeneity of a peridotitic garnet inclusion in diamond demonstrating excess in Si concentration (i.e. presence of majorite component) was investigated by TEM using FIB prepared foils. The host diamond is a low-nitrogen brown stone, which can be related to type IIa with features of strong plastic deformation. The studied sample is represented by Ca-poor Cr-pyrope of harzburgitic (H) paragenesis from Snap Lake dyke, Canada The garnet had been previously reported to contain Si = = 3.16 apfu. The revised examination of the sample, resulted in detection of extremely fine-grained symplectite consisting of low Ca-orthopyroxene, clinopyroxene, Cr-spinel and coesite completely located and isolated in the inner part of the garnet crystal, which forms a sharp interface with the surrounding homogeneous garnet. XRD study confirmed the presence of the minerals constituting the symplectite. EPMA showed an identical bulk chemistry of the nanometer-sized symplectite and garnet. Further polishing of the garnet inclusion on the same surface with diamond removed the symplectite, which possibly was present as a thin lens within garnet. The remaining garnet is completely homogeneous as checked by two profiles, and contains unusually high Ni (118.2 ppm) and depleted REE patterns. Estimated PT formation conditions of this garnet are 10.8 GPa and 1450 °C within asthenosphere. Symplectite testifies partial retrograde isochemical phase transformation of the examined garnet which is suggested to be caused by decompression along with plastic deformation of diamond within the coesite stability field at T > 1000 °C and depth no less than 100 km. Because previously published studies of rare majoritic garnets composition were performed by EPMA only, it is possible that the traces of partial phase transformation (symplectite formation) could have been overlooked without additional XRD and/or TEM/AEM studies.
The microfabrics of quartz formed from coesite during exhumation of ultrahigh pressure (UHP) metamorphic rocks of the Dora Maira Massif (western Alps) are investigated using polarizing microscopy with universal (U)-stage, electron back-scattered diffraction (EBSD), and cathodoluminescence (CL) microscopy. Three types of microstructures are distinguished: aggregates of small elongate quartz grains with radial orientation (palisades) replacing coesite single crystals included in other minerals (type I); platy quartz single crystals showing tapered margins and midribs observed by CL-microscopy occurring associated with type I microstructures in the same inclusions (type II); radial aggregates of large elongate quartz grains in the rock matrix, where coesite is not preserved (type III). The radial shape preferred orientation (SPO) in the type I and III palisade structures is not combined with a crystallographic preferred orientation (CPO). There is no systematic orientation relation between quartz grains in type I aggregates and relict coesite or the host mineral of the inclusion. This indicates that the coesite-quartz transformation started with a distinct random nucleation stage along the original interphase boundary between coesite and the host mineral. The elongate grain shape reflects the progress of the reaction front, which is not influenced by crystallographic orientation. The concentric discontinuities in grain shape frequently observed in type I quartz palisades are attributed to distinct events during transformation, presumably brittle failure of the host mineral. By analogy, coarse-grained quartz palisades (type III) in the rock matrix originated by random nucleation of quartz along the high angle grain boundaries of coesite. Each aggregate of radially oriented elongate grains (type I and III) impinging at a centerline represents the size and shape of a single original coesite grain, with a grain size of up to several millimeters in the matrix of pyrope quartzites (type III), and significantly smaller in metagranites. Type II platy quartz crystals with tapered margins are interpreted to have grown along cracks in coesite, which formed in several generations with distinct orientation during progressive transformation, indicating a very low nucleation probability of quartz for that stage.
A complete set of geochemical data for "pyrope quartzite", various phengite-schist and jadeite-bearing rock intercalations, as well as for enclosing orthogneiss from different localities within the southern Dora-Maira Massif is presented, in order to establish the nature of the different protoliths and their primary relationships. For comparison, Mg-rich rocks from the Eastern Alps occurring along shear zones within granitic gneiss, as well as metaevaporitic rocks from Sar e Sang, Afghanistan, were also studied. Typically, the "pyrope quartzite" and its retrograde derivative are enriched in Mg and strongly depleted in Na, Ca, Fe, Cu, P, Rb, Ba, and Sr with respect to the enclosing orthogneiss of granitic bulk composition. This orthogneiss is usually peraluminous, has normative corundum, and may be best related to S-type granite protoliths. Trace-element contents of the different phengite schists included in the "pyrope quartzite" confirm their close overall kinship to the enclosing orthogneiss. Jadeite-bearing rocks, which occur as conformable layers and boudins within "pyrope quartzite", in general differ by having lower contents in K, Mg, Rb, and higher contents in Na, Fe, Ca, Mn, P, and Zn. The present study indicates that the "pyrope quartzite" has a metasomatic origin, whereas an evaporitic nature of the protolith can be ruled out. Discrimination plots demonstrate that the "pyrope quartzite" can clearly be distinguished chemically from metasedimentary whiteschist derived from former evaporite environments. The field relations of trails of "pyrope quartzite", now forming lensoid inclusions within an orthogneiss (former granite), would also make a metasedimentary origin rather unlikely. On the other hand, consistent genetic relationships between "pyrope quartzite" and its enclosing orthogneiss were obtained that virtually match those of Mg-metasomatic leucophyllites from the Eastern Alps Occurring along shear zones within granitic gneisses. Similar Mg-rich rocks within the Tauern Window Such as within the Monte Rosa and Gran Paradiso Massifs of the Western Alps indicate that local processes of Mg metasomatism occurred throughout the entire range of the Alps.
Hot cathode cathodoluminescence (CL) microscopy is used as a powerful tool to distinguish between different silica phases and between different generations of the same breakdown product of coesite. The rock type investigated is a fine-grained pyrope-quartzite from Parigi, Dora Maira Massif, Italy. While coesite inclusions within pyrope display bright bluish-green luminescence colors, their palisade-like breakdown products of quartz are characterized by heterogeneously brownish-violet colors. Cracks within coesite are filled with quartz, which shows brown luminescence colors indicating a different generation. Quartz of the matrix exhibits a homogeneously dark-blue luminescence. Fine-grained, partly also fibrous chalcedony, which is difficult to distinguish from quartz breakdown products of coesite under the polarizing microscope, shows bright brownish-yellow luminescence colors. Consequently, even tiny crystals of coesite can easily be separated from different quartz generations or chalcedony due to their characteristic CL emission. Thus, CL-microscopy is an elegant and inexpensive method to discover chronological breakdown sequences of silica and to develop specific features and informations of minerals which may have become otherwise overlooked. Twinning of metamorphic coesite resembles of polysynthetic plagioclase exhibiting albite- and periclinelaw individuals. Two respective types of lamellae were identified, which intersect each other at an angle of ca. 90°; they are twinned after (021) and (-101).
Cathodoluminescence (CL) imaging and spectroscopy, as well as backscattered electron imaging, were used to assign the occurrence of several mineral phases and rock structures in altered nordmarkites and calcite-bearing granites from the Nb-Zr- REE deposits from Khaldzan Buregte and Tsakhir (Mongolian Altai) to three events: (1) intrusion of barren nordmarkites; (2) intrusion of small bodies of calcite-bearing granites with metasomatic alteration of the wall-rocks; and (3) alteration by F-rich fluids.
Unusual red and yellow CL caused by Fe ³⁺ and Mn ²⁺ emission centres were detected in microcline and albite. Fe ³⁺ centres were also established (along with others) in quartz, zircon, and possibly in fluorite.
Magmatic and metasomatic rock structures and internal structures of the minerals coexist in the samples. The primary magmatic features were in part preserved during alteration. In contrast, the internal and the centre structures may be changed during alteration even in non-replaced mineral phases. Euhedral minerals may be formed by secondary processes as shown for lath-shaped albite. The occurrence of pseudomorphs, the inheritance of elements during replacement, and the mechanical effects of secondary minerals on earlier mineral phases during metasomatic growth are proposed as criteria for the reconstruction of the mineral succession in altered rocks. Snowball structures may be formed as a result of metasomatic alteration rather than as a magmatic intergrowth.
The first report on cathodoluminescence (CL) of zircon goes back to the second half of the nineteenth century (Crookes 1879), however, only in the last 40 years has this phenomenon been addressed more frequently. The main CL emission bands have been related to different trace elements such as Mn and V (Leverenz 1968), Hf and Y (Ono 1976), Dy (e.g. Mariano 1978), Gd and Tb (e.g. Ohnenstetter et al. 1991). These elements would act as “activators” and enhance the “intrinsic” luminescence of pure zircon by non-stoichiometry, lattice damage or by structural defects (Marshall 1988). It has also been pointed out that elements such as Y can have a “quenching” effect on CL of zircon (Ohnenstetter et al. 1991) as they reduce the CL emission. A second approach to CL relates to the studies of CL zoning patterns to assist in the interpretation of U-Pb dating. This tool has proved to be indispensable when combined with U-Pb zircon dating by ion microprobe (e.g. SHRIMP). CL allows the identification of different types of zircon domains that then may be dated in situ by SHRIMP, with spatial resolutions between ca. 30 µm (e.g. Gebauer et al. 1988) and 15–20 µm (e.g. Gebauer 1996; Vavra et al. 1996).
Both the coarse- and fine-grained varieties of the partly coesite-bearing pyrope-quartzites, their interlayered jadeite-kyanite
rocks, and the biotite-phengite gneiss country rock common to all of them were subjected to detailed petrographic and textural
studies in order to determine the sequence of crystallisation of their mineral constituents, which were also studied analytically
by microprobe. Prior to pyrope and coesite growth, the Mg-rich metapelites were talc-kyanite-chlorite-rutile-ellenbergerite
schists which — upon continued prograde metamorphism — developed first pyrope megacrysts in silica-deficient local environments
at the expense of chlorite + talc + kyanite, and subsequently the smaller pyrope crystals with coesite inclusions from reacting
talc + kyanite. Based on geobarometrically useful mineral inclusions as well as on experimentally determined phase relations,
a prograde PT-path — simplified for water activity = 1 — is constructed which passes through the approximate PT-conditions
16 kbar and 560° C, 29 kbar and 720° C, and finally up to 37 kbar at about 800° C, where the Mg-rich metapelite was a pyrope-coesite
rock with phengite, kyanite, and talc still present. During the retrograde path, pyrope was altered metasomatically either
into phlogopite + kyanite + quartz or, at a later stage, to chlorite + muscovite + quartz. Both assemblages yield PT-constraints,
the latter about 7–9 kbar, 500–600° C. The country rock gneisses have also endured high-pressures of at least 15 kbar, but
they provide mostly constraints on the lowest portion of the uplift conditions within the greenschist facies (about 5 kbar,
450° C). Microprobe data are presented for the following minerals: pyrope, ellenbergerite, dumortierite (unusually MgTi-rich),
jadeite, vermiculite (formed after Na-phlogopite?), paragonite, and for several generations of phengite, chlorite, talc, phlogopite,
dravite, and glaucophane in the high-pressure rocks, as well as for biotite, chlorite, phengites, epidote, garnet, albite,
and K-feldspar in the country rock gneisses. An outstanding open problem identified in this study is the preservation of minerals
as inclusions within kyanite and pyrope beyond their PT-stability limits.
Growth zoning patterns of garnet grains in phyllite and mica schist from the Garnet-Phyllite Unit and the Mica-Schist/Eclogite Unit of the Western Erzgebirge, in Saxony, Germany, have been studied in detail by electron microprobe and are characterized with X-ray-intensity mapping images (MAPS) and quantitative chemical analyses. Zoned grains of garnet in the phyllite show a continuous decrease in spessartine component from core (28 mole %) to rim (19 mole %), and, over about 100 μm at the rim, a discontinuous, oscillatory increase, decrease and further increase to 30 mole %. These changes are correlated with an antithetic, oscillatory zoning of comparable amplitude in the almandine component (47% in the core, 56% toward the rim, 49% at the extreme rim). Available data for diffusion rates in garnet suggest that no significant modification of growth zoning attributable to later intracrystalline diffusion has occurred. In two samples of mica schist, oscillatory zoning with respect to the grossular component is correlated with an antithetic pattern of the almandine component (e.g., sample E 514: 17.0 mole % grossular component in the core, decreasing to 4.7 mole %, then increasing to 6.8 mole % and decreasing again to 4.3 mole % at the extreme rim). Although the patterns of zoning in themselves do not yield any evidence of modification after growth, available data on diffusion do not entirely rule out this possibility. In agreement with the observed textural relationships, we attribute the oscillatory changes in garnet composition to specific continuous reactions during regional metamorphism, indicating a complex growth-and-resorption history of the garnet resulting from small-scale variations in the rate of decompression of the rocks. No evidence in support of an open-system behavior of the fluid phase, such as highly variable and irregular patterns of oscillatory zoning, could be found. Where oscillatory zoning occurs, the number of oscillations and their relative changes in composition are the same throughout that sample, and may even be correlated between samples collected many kilometers apart.
Coesite (the dense, high-pressure polymorph of quartz) occurs as inclusions in mechanically strong minerals in deeply subducted, metamorphosed crustal rocks in a number of Eurasian collisional orogens. It is the primary indicator mineral of ultrahigh-pressure (P) metamorphism. Whereas some coesite inclusions are untransformed, most exhibit partial transformation to palisade quartz and a concomitant increase in volume (resulting in rupture and radial fracturing of the host grain). Coesite can be identified by its diagnostic Raman spectrum; the strongest band (at atmospheric pressure, room temperature) is at 521 cm-1. Laser Raman microspectroscopic analyses of coesite inclusions within garnet and zircon in ultrahigh-P metamorphic rocks from Kazakhstan, Indonesia, and China reveal consistent differences in the Raman spectra of (1) partially transformed coesite + quartz (main Raman band at 521 cm-1) and (2) untransformed monomineralic coesite grains (main band at 525 526 cm-1). Applying the room-temperature calibration of pressure dependence of the coesite Raman spectrum, we conclude that the latter coesite inclusions are subject to a remarkable pressure differential of 19 23 kbar with the host grains, and are still undergoing pressure-temperature conditions on or close to the quartz-coesite equilibrium boundary.
586. The present paper is a continuation of the Bakerian Lecture “On the Illumination of Lines of Molecular Pressure and the Trajectory of Molecules read before the Royal Society, December 5, 1878. Phenomena there briefly referred to have since been more fully examined; new facts have been observed, and their theoretical bearings discussed; and numerous experiments suggested by Professor Stokes and others have been tried, with the result of acquiring much information which cannot fail to be of value in assisting to evolve a theory capable of embracing all the phenomena under discussion. 587. In par. 514 I described a piece of apparatus by means of which the molecular rays electrically projected from the negative pole at a high exhaustion were converged to a focus, the pole itself being hemi-cylindrical in shape. On referring to the coloured drawing illustrating the experiments it will be observed that the green phosphorescence of the glass (by means of which the presence of the molecular rays is manifested) does not take place close to the negative pole.
Eclogitic (E-type) and related parageneses of natural diamonds are represented by suites of diamond inclusions and xenoliths of diamondiferous eclogites. Major-element data are presented for 32 coexisting minerals forming 19 bimineralic and trimineralic inclusions from diamonds, including omphacite-orthopyroxene (1 sample), garnet-omphacite (5 samples), garnet-coesite (5 samples), omphacite-coesite (2 samples), garnet-picroilmenite (2 samples), garnet-kyanite (1 sample), omphacite-phlogopite (2 samples), and garnel-omphacite-phlogopite (1 sample). Major-element variations of coexisting minerals are typical of corresponding eclogites. Omphacite with 5.02 wt% Na2O, inter-grown with orthopyroxene with Mg# 83.7, represents the first example of a diamondiferous websterite paragenesis including Na-clinopyroxene. This indicates a broader range in mineral compositions of E-type-related websteritepyroxenite-associated diamonds than known previously. This unique websterite-pyroxenitic mineral assemblage represents a transitional paragenesis between peridotitic or ultramafic (U-type) and E-type parageneses.Bimineralic eclogites, ilmenite eclogites, coesite + corundum + kyanite eclogites, and grospydites occur not only as sets of inclusions in diamonds but, with a few exceptions (ilmenite and coesite eclogites), also as diamondiferous eclogite xenoliths. The coesite eclogite paragenesis is a significant inclusion suite in diamonds, and was detected in about 15 diamond occurrences worldwide. It represents from 15% to 22% of all E-type diamonds in several occurrences, and thus should not be considered as rare.
The use of cathodoluminescence (CL) and/or back-scattered electron (BSE) imaging techniques with in situ ion probe analyses of zircons can help unravel complex crustal histories of metamorphic rocks that otherwise might remain elusive. Using these techniques we have imaged zircons from three lower crustal xenolith suites that have previously been dated by SHRIMP (sensitive high-resolution ion microprobe). In all three cases, the zircons are featureless in transmitted light but CL and BSE reveal internal structures that correlate with distinct growth events. Generally, CL and BSE images reveal similar structures, with CL showing finer detail. Neither imaging technique is capable of delineating all growth features in every sample and the best results are obtained using a combination of the two techniques. Igneous cores in zircons commonly emit a different color CL emission. In many cases zoning in the cores is truncated, indicating that the zircons either spent time in the supracrustal environment after their initial crystallization and prior to the granulite facies event (s) or that part of the core zircon was resorbed during the subsequent metamorphic event. Metamorphic rims, when present, are commonly 10 to 30 μm thick, and are nearly always unzoned and featureless.Igneous cores and metamorphic overgrowths commonly have distinctive CL emission spectra and trace element concentrations. However, the CL spectra can only be used to qualify chemical differences, as a linear relationship has not been shown to exist between CL intensity and trace element concentration in natural zircons. In many cases the Hf, Y, P, U and the heavy rare-earth elements (HREEs) concentrations can be correlated to igneous and metamorphic growth using a combination of CL and BSE imaging techniques and in situ trace element analyses with either the electron microprobe or PIXE (particle induced X-ray emission).
The purpose of this study was to characterize cathodoluminescence and X-ray induced luminescence in the visible range of the spectrum for Mn2+ activated carbonate minerals.The cathodoluminescence emission varied from approximately 590 mμ for calcite to approximately 677 mμ for magnesite, illustrating the effect of decreasing bond distance between the alkaline earth cations and the ligands and the resulting increased crystal field splitting parameter, Dq. Although the direction of the wavelength shift was in keeping with crystal field theory, the magnitude of the shift was not. Distortions in the structure as a result of the discrepancy in ionic size between Mg2+ and Ca2+ and the increasing degree of covalency of the metal-oxygen bond, as the Mg2+ concentration was increased, were thought to be the major causes of the deviation from theoretical predictions.Manganese in the aragonite-strontianite series was found to emit from approximately 540 mμ (aragonite) to approximately 590 mμ (strontianite). The direction of wavelength shift was to higher wavelength with apparently longer bond length, in opposition to crystal field theoretical considerations.The similar emission spectra of vaterite and calcite indicated the effective coordination of Ca2+ (Mn2+) in vaterite was six rather than eight. Vaterite emits at approximately 595 mμ. Otavite, CdCO3, on excitation of incorporated Mn2+ ions, showed an emission band centered at about 594 mμ. Because CdCO3 and CaCO3 are almost identical in all structural parameters, the slight difference in emission is attributed to the greater degree of covalency of the CdO bond in otavite. Dolomite showed the emission behavior of calcite and magnesite with Mn2+ populating both the Ca2+ and the Mg2+ sites. Dolomite emitted at about 597 mμ and 675 mμ.No evidence was found to substantiate the belief that the increased polarizability of the ions as one progresses from Ca to Sr to Ba reduces bond length to the extent of creating a shift to higher wavelength with decreasing bond length. This study does not support the hypothesis of transitions from a split T1g level or from the T1g and T2g levels accounting for the emission characteristics of aragonite, strontianite and witherite. Rather, transitions from an unsplit T1g level to the ground state (6S) are believed to be responsible for the 540 mμ emission of aragonite. The theoretical Dq value calculated for an eight-coordinated site in CaCO3 for a cubic crystal field is very close to the Dq found for aragonite where the coordination number is nine. Similarly, the 590 mμ emission of strontianite and the 677 mμ emission of witherite were attributed to transitions from the T1g level to ground state. Local distortions arising from the discrepancy in size between the activator ion (Mn2+) and the host cation in aragonite, strontianite and witherite were thought to be a major consideration accounting for the shift of emission wavelength towards higher wavelength with increasing bond length.In general, intensity of cathodoluminescence decreases with increasing emission wavelength for the aragonite-strontianite-witherite series and for the calcite-magnesite series. Otavite, vaterite and calcite have comparable intensities for similar emission wavelengths.
Abstract Dolomite marble from the Kumdy–Kol area of the Kokchetav Massif contains abundant microdiamond, mainly in garnet and a few in diopside. The mineral assemblage at peak metamorphic condition consists of dolomite + diopside + garnet (+ aragonite) ± diamond. Inclusions of very low MgCO3 calcite and almost pure calcite occur in diopside and are interpreted as aragonite and/or aragonite + dolomite. Single-phase Mg–calcite in diopside with a very high MgCO3 component (up to 21.7 mol%) was also found in diamond-free dolomitic marble, and is interpreted as a retrograde product from aragonite + dolomite to Mg–calcite. The dolomite stability constrains the maximum pressure (P) at < 7 GPa using previous experimental data, whereas the occurrence of diamond yields the minimum peak pressure–temperature (P–T) condition at 4.2 GPa and 980 °C at X co2 = 0.1. The highest MgCO3 in Mg–calcite constrains the minimum P–T condition higher than 2.5 GPa and 800 °C for the exhumation stage. As these marbles were subjected to nearly identical P–T metamorphic conditions, the appearance of diamond in some carbonate rocks was explained by high X co2. A low X co2 condition refers to high oxidized conditions and diamond (and/or graphite) becomes unstable. Difference in X co2 for marble from the same area suggests local heterogeneity of fluid compositions during ultrahigh-pressure metamorphism.
Representative diamond-bearing gneisses and dolomitic marble, eclogite and Ti-clinohumite-bearing garnet peridotite from Unit I at Kumdy Kol and whiteschist from Unit II at Kulet, eastern Kokchetav Massif, northern Kazakhstan, were studied. Diamond-bearing gneisses contain variable assemblages, including Grt+Bt+Qtz±Pl±Kfs±Zo±Chl±Tur±Cal and minor Ap, Rt and Zrn; abundant inclusions of diamond, graphite+chlorite (or calcite), phengite, clinopyroxene, K-feldspar, biotite, rutile, titanite, calcite and zircon occur in garnet. Diamond-bearing dolomitic marbles consist of Dol+Di±Grt+Phl; inclusions of diamond, dolomite±graphite, biotite, and clinopyroxene were identified in garnet. Whiteschists carry the assemblage Ky+Tlc+Grt+Rt; garnet shows compositional zoning, and contains abundant inclusions of talc, kyanite and rutile with minor phlogopite, chlorite, margarite and zoisite. Inclusions and zoning patterns of garnet delineate the prograde P–T path. Inclusions of quartz pseudomorphs after coesite were identified in garnet from both eclogite and gneiss. Other ultrahigh-pressure (UHP) indicators include Na-bearing garnet (up to 0.14 wt% Na2O) with omphacitic Cpx in eclogite, occurrence of high-K diopside (up to 1.56 wt% K2O) and phlogopite in diamond-bearing dolomitic marble, and Cr-bearing kyanite in whiteschist. These UHP rocks exhibit at least three stages of metamorphic recrystallization. The Fe-Mg partitioning between clinopyroxene and garnet yields a peak temperature of 800–1000 °C at P >40 kbar for diamond-bearing rocks, and about 740–780 °C at >28–35 kbar for eclogite, whiteschist and Ti-bearing garnet peridotite. The formation of symplectitic plagioclase+amphibole after clinopyroxene, and replacement of garnet by biotite, amphibole, or plagioclase mark retrograde amphibolite facies recrystallization at 650–680 °C and pressure less than about 10 kbar. The exsolution of calcite from dolomite, and development of matrix chlorite and actinolite imply an even lower grade greenschist facies overprint at c. 420 °C and 2–3 kbar. A clockwise P–T path suggests that supracrustal sediments together with basaltic and ultramafic lenses apparently were subjected to UHP subduction-zone metamorphism within the diamond stability field. Tectonic mixing may have occurred prior to UHP metamorphism at mantle depths. During subsequent exhumation and juxtaposition of many other tectonic units, intense deformation chaotically mixed and mylonitized these lithotectonic assemblages.
A pyrope-quartzite originally described by Vialon (1966) from the Dora Maira massif was resampled and reinvestigated. Garnet (up to 25 cm in size), phengite, kyanite, talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz. The garnet is a pyrope-almandine solid solution with 90 to 98 mol % Mg end-member. It contains inclusions of coesite which has partially inverted to quartz, resulting in a typical radial cracking of the host garnet around the inclusions. Several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite.
The formidable pressures of formation implied (≧28 kbar) are independently indicated by i) the coexistence of nearly pure pyrope with free silica and talc, ii) the coexistence of jadeite with kyanite, iii) the high Si content of phengite. Water activity must have been low. The stability of talc-phengite and the presence of rare glaucophane inclusions in pyrope point to low formation temperatures (about 700 °C) and to a probable Alpine age for the assemblage.
This is evidence that low temperature gradients, how essentially transient they are, may nevertheless persist to considerable depths. Moreover, the upper crustal (evaporite-related?) origin of the quartzite and its interbedding within a continental unit implies that continental crust may also be subducted to depths of 90 km or more. The return back to the surface is problematic; the retrograde assemblages observed show that it must be tectonic. If the rocks remain at depth, new perspectives open for the genesis of intermediate to acidic magmas. Eventually, the role of continental crust in geodynamics may have to be reconsidered.
Several types of growth morphologies and alteration mechanisms of zircon crystals in the high-grade metamorphic Ivrea Zone
(IZ) are distinguished and attributed to magmatic, metamorphic and fluid-related events. Anatexis of pelitic metasediments
in the IZ produced prograde zircon overgrowths on detrital cores in the restites and new crystallization of magmatic zircons
in the associated leucosomes. The primary morphology and Th-U chemistry of the zircon overgrowth in the restites show a systematic
variation apparently corresponding to the metamorphic grade: prismatic (prism-blocked) low-Th/U types in the upper amphibolite
facies, stubby (fir-tree zoned) medium-Th/U types in the transitional facies and isometric (roundly zoned) high-Th/U types
in the granulite facies. The primary crystallization ages of prograde zircons in the restites and magmatic zircons in the
leucosomes cannot be resolved from each other, indicating that anatexis in large parts of the IZ was a single and short lived
event at 299 ± 5 Ma (95% c. l.). Identical U/Pb ages of magmatic zircons from a metagabbro (293 ± 6 Ma) and a metaperidotite
(300 ± 6 Ma) from the Mafic Formation confirm the genetic context of magmatic underplating and granulite facies anatexis in
the IZ. The U-Pb age of 299 ± 5 Ma from prograde zircon overgrowths in the metasediments also shows that high-grade metamorphic
(anatectic) conditions in the IZ did not start earlier than 20 Ma after the Variscan amphibolite facies metamorphism in the
adjacent Strona–Ceneri Zone (SCZ). This makes it clear that the SCZ cannot represent the middle to upper crustal continuation
of the IZ. Most parts of zircon crystals that have grown during the granulite facies metamorphism became affected by alteration
and Pb-loss. Two types of alteration and Pb-loss mechanisms can be distinguished by cathodoluminescence imaging: zoning-controlled
alteration (ZCA) and surface-controlled alteration (SCA). The ZCA is attributed to thermal and/or decompression pulses during
extensional unroofing in the Permian, at or earlier than 249 ± 7 Ma. The SCA is attributed to the ingression of fluids at
210 ± 12 Ma, related to hydrothermal activity during the breakup of the Pangaea supercontinent in the Upper Triassic/Lower
Jurassic.
Thus far, all reported work on luminescence petrography has been accomplished by use of the microprobe, a very expensive instrument beyond the grasp of most petrographers. A simple device is described here which attaches to an ordinary petrographic microscope and permits luminescent observations as well as ordinary white or polarized light observations. The instrument has the advantages of short pump down time (two min), large area of illumination by the electron beam (1×3 cm), and a minimum of charging and sparking problems. In addition, ordinary uncoated rock or mineral thin sections may be used. The instrument has proven to be superior to the microprobe for luminescent observations of geological specimens. Other (nongeological) applications in fields such as ceramics and solid state physics are also likely.
Zircon exhibits an extraordinary memory. Its stability, durability, low solubility and low elemental diffusivities combine to preserve in it a record of most of the important events that have affected it, its host rocks, and the crust of which it is a part. Zonation in zircon grains delineates the boundaries of discrete geochemical packages formed at different times, each effectively a closed system. The elemental and isotopic compositions of these packages reflect the timing and conditions of growth events, and the morphology of the zonation indicates qualitatively the nature of both growth and intervening degradation events.Cathodoluminescence (CL) and backscattered electron (BSE) imaging reveals detailed zonation patterns that are commonly invisible or barely visible with conventional transmitted and reflected light microscopy. Characteristic patterns are visible in almost all zircons that serve to distinguish igneous from metamorphic growth, to distinguish truncation surfaces of different types (e.g., sedimentary fracturing vs. resorption), and possibly to identify ancient metamictization. Zircons from many rocks record multistage histories that reflect two or more events; those from rocks such as peraluminous granites and high-grade paragneisses are especially likely to reveal long and complex histories.Studies of zonation patterns in zircons provide a clear, though qualitative, history of a rock and its heritage. Furthermore, they provide the basis for a quantification of that history. Elemental and isotopic compositions can reveal the environment in which a zone grew. U-Pb analysis of a zone provides an age for its growth. shrimp analyses that are not guided by detailed knowledge of zonation can straddle two (or more) zones and a discordant U-Pb result from such an analysis may falsely suggest Pb loss, and important growth zones may be missed entirely. Thus, the combined use of CL, BSE, electron microprobe and ion probe methods can elucidate complex crustal histories.
Ion microprobe (SHRIMP) data on zircons from various rock types of an ultrahigh-pressure (UHP) metamorphic whiteschist-type pyrope quartzite lens of the Dora Maira Massif (DMM) consistently show domains giving a Late Eocene age of 35.4 ± 1.0 Ma which is taken as the age of UHP metamorphism. These domains partially replace the older oscillatory zoning pattern of the zircons formed during primary magmatic crystallization at about 275 Ma. Zircons of a metagranitic country rock next to the UHP metamorphic lens have these primary features best preserved. All zircons measured also yield intermediate ‘ages’ between 275 and 35 Ma with a statistical concentration between 260 and 210 Ma. Thus the uniformity of the initial zircon population both in the lens and the country rock evidences a common protolith, that is a granite intruded during the Late Herynian. While the intermediate ages are at least partly due to incomplete resetting of the zircons during UHP metamorphism, those in the 260–210 Ma range may be related to rifting episodes in the Permotriassic. The Mg-rich chemistry of the whiteschist lenses is due to local metasomatic alterations of the granite, perhaps by fluids derived from evaporitic sediments dating as early as the Permotriassic as well. The more pervasive resetting of zircon ages during UHP metamorphism in the pyrope quartzite lenses is explained by the ubiquity of fluids and/or melts produced during subduction by a series of dehydration reactions that occurred only in the more hydrous Mg-rich protoliths and not in their drier granitic neighborhood. Fission track ages determined partly on the same zircon samples yielding 29.9 ± 1.4 Ma mark the time when the UHPM unit had reached about 290°C at a shallow location within the crust. Thus exhumation over a vertical distance of about 120 km must have occurred within about 5–6 Ma indicating an average uplift rate of about 20–24 km/Ma and an average cooling rate of about 85–100°C/Ma. The radiometric data obtained do not lend any support to an Eo-Alpine Cretaceous subduction event so that deep subduction and immediately following exhumation all took place during Early to Mid Tertiary time. This scenario seems to apply to large portions of the Western and Central Alps as well calling for drastic geodynamic reinterpretations of these parts of the Alps.
A standardized, internationally applicable set of symbols for rock-forming mineral phases and mineral components is presented.-J.A.Z.
DIAMONDS commonly occur in kimberlites, lamproites and alluvial sediments derived from these rocks. More recently, diamonds (or their graphite pseudomorphs) have been discovered in ultramafic massifs1 and picrites2. Here we report the occurrence of diamonds in situ in crustal rocks: highly retrograded high-pressure metamorphic garnet-pyroxene and pyroxene-carbonate-garnet rocks, biotite gneisses and schists from the Kokchetav massif, northern Kazakhstan, USSR. The diamonds are cubo-octahedral, averaging 12 mum in size, and occur in zircons, and with euhedral graphite as inclusions in unzoned garnets. We believe that the zircon and garnet matrices protected these diamonds from retrogressive transformation to graphite. Mica, rutile, titanite, clinopyroxene, kyanite and zircon also occur as inclusions in garnet, often intergrown with the diamonds. Equilibration relations of inclusions and host garnets indicate that both diamonds and graphite crystallized from a fluid phase under static conditions at pressures of >=40 kbar and temperatures >900-1,000 °C.