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Towards a comprehensive classification of igneous rocks and magmas
Abstract
The IUGS Subcommission on the Systematics of Igneous Rocks has recently published an excellent book on the classification of these rocks. This event has shifted the vexed question of classification towards the top of the agenda in igneous petrology. Over the years the Subcommission has used many different criteria to establish the positions of the boundaries between the various common igneous rocks. It now has to adopt a holistic approach and develop a comprehensive, coherent classification that is purged of all the minor anomalies that arise between the various classifications that it has approved. It is appreciated that the Subcommission's classification was never intended to have any genetic implications; however, it is suggested that an ideal classification should he presented in such a way that it is able to group rocks into an order that directs attention to petrogenetic relationships between individual rocks and larger groups of rocks. Unfortunately, many of the Subcommission's definitions are Earth chauvinistic; for example, igneous rocks are defined as being those rocks that solidified from a molten state either within or on the surface of the Earth. Nowhere in the book is it acknowledged that during the past 20 years, while the Subcommission has been framing its many recommendations, a whole new science of planetary petrology has subsumed classical petrology. In any new edition of the book, the Subcommission should acknowledge that rocks are essentially the solid materials of which planets, natural satellites and other broadly similar cosmic bodies are made.
... Most Bushveld Complex rock types are adequately catered for in a logical and systematic way, and there is no need to revert to poor rock naming practices. There is also a considerable amount of literature available on the subject, eg Jahns (1955), Streckeisen (1976), Le Maitre (1976), Irvine (1982), Lee (1987), Morimoto (1988), Le Maitre (Ed) (1989), Le Bas & Streckeisen (1991), Middlemost (1991Middlemost ( , 1994, Wilson (1992), Scoon & Mitchell (1994), Gillespie & Styles (1999). ...
... Good accounts of the history and evolution of the systematics of igneous rock classification are given by Irvine (1982), Le Bas & Streckeisen (1991), Middlemost (1991Middlemost ( , 1994, and more recently, by Gillespie & Styles (1999). Much of the original work is attributed to Streckeisen (1976). ...
... wt %). According to the K 2 O þ Na 2 O versus SiO 2 diagram of Middlemost (1991), the analysed samples are classified as diorite (Ghahan) and granodiorite (Sarbadan) (Fig. 6a). The data define a calc-alkaline trend on the AFM diagram (Fig. 6b). ...
... The Tafresh granitoids have arc-like, calc-alkaline signatures with similar REE patterns (especially in the HREEs), with Nb, Ta, Ti and Ba depletion, and with LREE and LILE enrichment (Fig. 9). Although negative anomalies in high field strength elements (HFSEs) might be linked to crustal contamination, we favour an interpretation that these anomalies typify subduction-related (Middlemost, 1991); composition of studied samples ranges from diorite (Ghahan stock) to granodiorite (Sarbadan stock). (b) AFM (A = Na 2 O þ K 2 O; F = FeO t ; M = MgO) diagram with differentiation lines of Irvine & Barager (1971), showing a calc-alkaline affinity for the granitoids (Irvine & Baragar, 1971). ...
Granitoid stocks crop out in the Ghahan and Sarbadan areas near Tafresh city, which is situated in the central part of the Urumieh–Dokhtar Magmatic Arc, Iran. The stocks, consisting of porphyritic and sub-granular diorite and granular granodiorite, intruded into Eocene volcano-sedimentary units. Normalized multi-element diagrams indicate that the analysed rocks are enriched in large-ion lithophile elements and depleted in high field strength elements. These geochemical features are typical of subduction-related calc-alkaline arc magmas. The stocks belong to the ferromagnetic and I-type granitoid series. Anisotropy of magnetic susceptibility provides information about the internal fabric of the granitoids. Susceptibility values range from 5.6 × 10 ⁻³ to more than 71.6 × 10 ⁻³ , averaging 27.9 × 10 ⁻³ SI. Relatively low anisotropy values (P%) rarely exceed 10 %. Shape parameters (T) vary between −0.48 and +0.74, averaging + 0.2. Each stock is interpreted to contain a distinct feeder zone in which magnetic lineation plunges steeply (> 60°), suggesting that the magma ascended mainly in a NW–SE conduit and, to a lesser extent, in an E–W direction. Integration of magnetic fabric data, field observations and tectonic setting indicates that the shear zone that was developed between the Indes and Talkhab faults had created an opening into which the Ghahan and Sarbadan stocks were emplaced by way of creating a suitable tensional space for the ascent of magma.
... -123 -Diagramas TAS (álcalis versus sílica) para a classificação de rochas plutônicas, segundo Middlemost (1994), aplicados às rochas das Intrusões Múltiplas do BMSGU. A curva tracejada divide as séries alcalinas, acima, das subalcalinas, abaixo, (Irvine & Baragar, 1971). ...
... Diagramas TAS (álcalis versus sílica) para a classificação de rochas plutônicas, segundo Middlemost (1994), aplicados às rochas das Intrusões Tardias do BMSGU. A curva tracejada divide as séries alcalinas, acima, das subalcalinas, abaixo, (Irvine & Baragar, 1971 (Fig. 7.1). ...
The Guanambi-Urandi Monzo-Syenitic Batholith (BMSGU) is located in south-western Bahia, Brazil, where it forms part of the Urandi-Paratinga mobile belt. The batholith extends over an area of almost 6000 km2 and is mainly composed of syenites and monzonites, with subordinate granites and mafic syenites. Two main lithologies can be recognized: the multiple intrusions, accounting for 90% of the outcrops in the BMSGU and being divided into the four regions Paratinga, Laguna, Igaporã and Guanambi, and the so-called late-intrusions forming the Cara Suja, Ceraíma and Estreito massifs. Flow structures commonly observed in these rocks indicate that the batholith was probably emplaced into a pull-apart system. U-Pb isotopic data demonstrate that the emplacement occurred at 2.05 Ga.
The textures of the two lithological groups are similar and suggest the following magmatic crystallisation sequence: (zircon, apatite) ⇨ opaque minerals-1 ⇨ diopside ⇨ plagioclase ⇨ alkali feldspar ⇨ (amphibole, mica, perthitic feldspar) ⇨ quartz ⇨ opaque minerals-2 ⇨ titanite. Muscovite, epidote and chlorite crystallisation characterises late recrystallisation. Magmatic crystallisation has occurred in two stages: a first stage at low fO2, high PH2O, and transolvus conditions, accompanied by apatite, ilmenite and clinopyroxene crystallization, was followed by a second stage at hypersolvus conditions, characterized by amphibole and feldspar crystallization. The titanite + magnetite + quartz association present at the second stage indicates high fO2 between the NiNiO and HM buffers. Geobarometers and geothermometers based on amphibole and plagioclase composition indicate a pressure range of 2.2-4.4 kbar and a temperature of about 850 °C.
Geochemical data show that the BMSGU consists of saturated to over-saturated alkaline, potassic to ultrapotassic rocks with a metaluminous character, which become peraluminous in some evolved lithologies. The BMSGU is also characterised by enrichment in incompatible elements (e.g. LILE such as Ba, Sr and Rb), and by low contents in HFSE (Nb, Th and Pb). Isotopic results show that the BMSGU has (i) highly negative εNd(T) (-7.42 up to -10.61), pointing to an enriched source, and (ii) Sr initial ratios between 0.704 and 0.707. These signatures are identical to those of other post-collisional shoshonitic and ultrapotassic suites commonly interpreted to be generated by melting of a metasomatically enriched mantle.
... -123 -Diagramas TAS (álcalis versus sílica) para a classificação de rochas plutônicas, segundo Middlemost (1994), aplicados às rochas das Intrusões Múltiplas do BMSGU. A curva tracejada divide as séries alcalinas, acima, das subalcalinas, abaixo, (Irvine & Baragar, 1971). ...
... Diagramas TAS (álcalis versus sílica) para a classificação de rochas plutônicas, segundo Middlemost (1994), aplicados às rochas das Intrusões Tardias do BMSGU. A curva tracejada divide as séries alcalinas, acima, das subalcalinas, abaixo, (Irvine & Baragar, 1971 (Fig. 7.1). ...
... As amostras iniciadas com a letra M são máficas, as com F correspondem às félsicas, EGN corresponde ao enclave de sienogranito da Supersuíte G5. Bas et al. (1986), adaptado por Middlemost (1991). A fim de compreender as possíveis reações químicas associadas à assimilação dos xenocristais de K-feldspato, foram realizadas análises em microssonda nas amostras de gabro tardio e de quartzo monzonito por meio de perfis traçados da borda para o centro do grão (Tab. ...
... As anomalias negativas em P, Eu, Sr e Ti mais acentuadas em rochas leucocráticas e intermediárias, além de reforçarem essa ideia, confirmam a interpretação realizada nos diagramas de Harker.CISA: Maciço Santa Angélica. Figura 17. Diagrama de TAS: (A) segundoHall (1987), com a evolução das séries basálticas toleítica, alcalina transicional e alcalina sódica; (B) segundo LeBas et al. (1986), adaptado porMiddlemost (1991), com a possível evolução magmática das rochas da Supersuíte G5 do Maciço Santa Angélica a partir da cristalização fracionada de um magma de composição gabroica alcalina transicional. ...
O Maciço Santa Angélica (CISA) está localizado na região sul do Espírito Santo e corresponde a um dos corpos intrusivos mais importantes da Supersuíte G5 associada ao estágio pós-colisional do Orógeno Araçuaí. Ele é constituído por dois núcleos gabroicos e bordas félsicas, estas separadas por uma extensa zona de mistura de magmas. Suas rochas encaixantes fazem parte da Supersuíte G1 (fase pré-colisional) e do Grupo Bom Jesus do Itabapuana (antigo Complexo Paraíba do Sul). A fim de compreender os possíveis processos de dinâmica físico-química entre o magmatismo máfico e félsico desse maciço, bem como suas possíveis relações com sua borda ortoderivada (G1), foram realizados estudos de campo, petrográfico, litogeoquímico e em microssonda eletrônica. A análise dos dados confirmou o modelo tectono-magmático proposto pela literatura e indicou novas informações: as zonas de cisalhamento dextrais regionais favoreceram a entrada desse corpo intrusivo, dando a ele uma forma alongada e sigmoidal e causando a deformação dos gnaisses do G1. Sua formação foi acompanhada de processos de diferenciação magmática (cristalização fracionada) e da geração de uma extensa zona de mistura mecânica de magmas (mingling).
... Major and trace element compositions are presented in Table 1. Rocks have been classified according to the total alkali-silica diagram of Middlemost (1994). Analyses have been performed on representatives of the main rock types, preferentially selecting relatively undeformed and unaltered examples. ...
... U and Th contents can be rather high (U up to 37 ppm). Depletion in Pb results in U/Pb and Th/Pb ratios Fig. 3. A) Total alkali-silica (TAS) diagram adapted to plutonic rocks (after Middlemost, 1994); black circles and dark gray triangles: this work; light gray circles and light gray triangles: data from Lobo-Guerrero Sanz (2005); the dashed line separating alkaline series (triangles) from subalkaline series (circles) is after Irvine and Baragar (1971). B) AFM diagram for the subalkaline rocks, after Irvine and Baragar (1971). ...
The Pan-African Hook Batholith formed during the assembly of the Gondwana supercontinent as a result of syn-collisional stage interaction between the Congo and Kalahari Cratons. The bimodal magmatism (mafic to predominantly felsic) is characterized by both an alkali-calcic and an alkalic suite, with typical A-type, metaluminous, high Fe/Mg and K/Na geochemical signature. Occasionally, sodic granitoids have been documented. Compositions were driven to more differentiated products by fractional crystallization, while Sr–Nd isotopes exclude crustal assimilation during crystallization. Recent new U–Pb age data constrain most of the felsic magmatism between 550 and 540 Ma. Scattered outcrops of gabbroic rocks, both tholeiitic and alkaline, testify to periodic input of mantle material, and, in some cases, to interaction with metasomatizing fluids. Crystallization ages on mafic rocks span from 570 to 520 Ma, thus indicating that they were contemporaneous with the major granitic intrusion, which was the result of a number of successive felsic batches, eventually forming a coalescing batholith. Highly radiogenic Pb isotopic values attest to the radiogenic character of the rocks. Such an anomalous signature was acquired during, or soon after, magma emplacement, perhaps as result of metasomatizing fluids. Enrichment in Th–U of large portions of the crust along this part of the margin of the Congo Craton is suggested. Geochemical and isotopic evidence support the interaction between mantle components and portions of the deep crust at pressure of < 10 kbar, while decompression melting of rising asthenospheric mantle ponding at the base of the crust heated, and ultimately melted, crustal material. An additional and crucial contribution to the crustal melting was likely provided by internal radiogenic heat production of the thickened crust, and is in agreement with the high radioactivity of the pluton. A tectono-thermal model, implying crustal accretion accompanied by slab retreat and lithospheric mantle thinning, is proposed to reconcile coeval orogenic contraction in the crust and A-type magmatism. Low-pressure mineral phases in metasedimentary wall rocks along the eastern margin of the pluton indicate that the magma was emplaced at shallow crustal depths. This study further supports the idea that A-type granites, commonly considered to be restricted to anorogenic or extension-related environments, can also occur in compressional regimes.
... In the total alkali versus silica diagram (TAS, Figure 12 [37]), amphibolite protolith is an alkali-diorite and albitite protolith is an alkaline rock ranging from syenodiorite to syenite. Furthermore, in S1, S2, S3, and T fields from Figure 12, rocks belonging to transalkali suite of [39] must be classified as "sodic" if Na 2 O -2.0 >K 2 O or "potassic" if Na 2 O -2.0 <K 2 O after [40]. Three of five alkali-diorite samples are sodic as well as all of the nine syenodiorite (albitite protolith) samples. ...
... In other words, reasonable trends suggest differentiation of an alkali-dioritic basic magma by fractional crystallization to an intermediate syenitic magma either before or during metamorphism along shear zones. Both alkalidiorite and syenite belong to the same transalkaline series (also named transalkali suite - Figure 12; [39]), which is silica-saturated and characterized by absence of modal nepheline and presence of normative nepheline (see CIPW norm, samples amp# and some alb# - Table 6). Quartz-syenites (non-uraniferous quartz-albitite protolith) are lithostructurally related to uraniferous albitites (see cross-section of the Figure 1) and certainly represent the last magmatic evolutionary step of syenites in the transalkaline series. ...
New evidence supported by petrography (including mineral chemistry), lithogeochemistry, U-Pb geochronology by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), and physicochemical study of fluid and melt inclusions by LA-ICP-MS and microthermometry, point to an orogenic setting of Lagoa Real (Bahia-Brazil) involving uraniferous mineralization. Unlike the previous models in which uraniferous albitites represent Na-metasomatised 1.75 Ga anorogenic granitic rocks, it is understood here that they correspond to metamorphosed sodium-rich and quartz-free 1.9 Ga late-orogenic syenitic rocks (Na-metasyenites). These syenitic rocks are rich not only in albite, but also in U-rich titanite (source of uranium). The interpretation of geochemical data points to a petrogenetic connection between alkali-diorite (local amphibolite protolith) and sodic syenite by fractional crystallization through a transalkaline series. This magmatic differentiation occurred either before or during shear processes, which in turn led to albitite and amphibolite formation. The metamorphic reactions, which include intense recrystallization of magmatic minerals, led uraninite to precipitate at 1.87 Ga under Oxidation/Reduction control. A second population of uraninites was also generated by the reactivation of shear zones during the 0.6 Ga Brasiliano Orogeny. The geotectonic implications include the importance of the Orosirian event in the Paramirim Block during paleoproterozoic Săo Francisco Craton edification and the influence of the Brasiliano event in the Paramirim Block during the West-Gondwana assembly processes. The regional microcline-gneiss, whose protolith is a 2.0 Ga syn-collisional potassic granite, represents the albitite host rock. The microcilne-gneiss has no petrogenetic association to the syenite (albitite protolith) in magmatic evolutionary terms.
... Figure 9f presents the multi-element patterns of Crspinel-bearing lherzolites (NC3, VD49C), clinopyroxenite (JZ25A), and eclogite SFVZ1C. The latter has lower element concentrations and a minor negative Sr anomaly, contrasting with the positive Sr anomalies in NC3 and SFVZ1C Bas et al. 1986) showing the primal, subalkaline, transalkaline, alkaline and foidite fields from Middlemost (1991). The boundary between subalkaline and alkaline fields follows Irvine and Baragar (1971). ...
Upper Cretaceous to Miocene continental volcanism in NE Brazil spans 350 km in a N–S direction and 60 km in width, forming the Macau-Queimadas alignment (MQA). This study combines fieldwork, petrography, geochemistry, and Sr–Nd–Pb isotopes to explore its origin and evolution. The MQA consists of volcanic and hypabyssal mafic rocks intruding Cretaceous and Precambrian basement rocks, divided into two groups: (i) alkaline (foidite to trachy-basalt); and (ii) subalkaline (basalt and basaltic andesite). Both are sodic and LREE-enriched, with distinct La/Yb ratios. The alkaline group reflects an asthenospheric source (Nd model age of 1.1–0.4 Ga), while the subalkaline group incorporates an older lithospheric component (Nd model age of 2.1–1.2 Ga). These magmas originated from picritic parental melts, with < 15% melting for the alkaline group and ~ 25–30% melting for the subalkaline group, derived from spinel- to garnet-bearing peridotite. Differentiated series formed by successive small melt volumes, with some samples undergoing crustal fractional crystallization of clinopyroxene + olivine + plagioclase (alkaline group), and clinopyroxene + orthopyroxene + Ca-plagioclase (subalkaline group). The persistence of basaltic magmatism over ~ 90 Myr indicates sustained upper mantle melting. The alignment of volcanics, its association with a positive geoid anomaly, and its parallelism with the Mid-Atlantic Ridge suggest the MQA may represent an aborted ridge that never progressed to an oceanic stage.
... It is worth mentioning that the examined volume in one standard-size thin section (46 × 27 × 0.03 mm) is insignificant compared to the relatively large rock volume used in the whole-rock geochemical analysis. In fact, some researchers have raised serious issues related to the modal classification of phaneritic rocks as proposed by the IUGS (e.g., Glazner et al. 2019;Middlemost 1991). In addition, determining the correct compositional variation of mineral groups such as feldspars, olivine, and pyroxene (Barron 1980;Frost et al. 2019;Paktunc 1998) is another difficulty in petrographic analyses. ...
In this paper, a novelty-free software to assess an efficient CIPW Norm (± 0.006 wt.% in differences between input and output data) is presented. The package is available in the official repository for user-contributed R packages (CRAN: Comprehensive R Archive Network). The software is able to handle big data sets and considers minor and trace element compositions. The algorithm can calculate odd minerals in igneous rocks, such as cancrinite and calcite, adjust the Fe+3/Fe+2 ratio in different standard approaches, and recalculate the compositions of the rocks in an anhydrous basis (100 ± 0.003 wt.% volatile-free adjusted). Furthermore, the package calculates several petrological parameters, and the graphical outputs are displayed following IUGS scheme standards. The prime aspect of shinyNORRRM is the symbiosis of native R functions with the R package’s shiny (Web Application Framework for R) to run the
norm in a user-friendly interface. shinyNORRRM can be executed in any operating system and requires no previous programming knowledge, thus promising to be the universal computational program in this matter. The output data are printed in the
standard comma-separated values (*.csv) format, which is highly compatible with general spreadsheet editors. In this work, the algorithm of our program is validated using already compiled whole-rock geochemical databases.
... %) and three samples have normative forstrite (Table 1). We used the total alkali vs. SiO 2 diagram of Middlemost (1991) for MBG nomenclature (Fig. 2a). MBG samples plot in the monzodiorite-gabbro-tonalite field. ...
Some small gabbro patches emplaced along the thrust fault with WE trend in the vicinity of Maien Bolagh village at the HT/MP metapelites, a part of the Central Iran zone (near to Sanandaj-Sirjan zone). The coarse-grained dark gabbro samples consist of amphibole, clinopyroxene, plagioclase, minor quartz, titanite, and biotite. Gabbros have high potassic calc-alkaline to shoshonitic affinity. The highly incompatible elements concentrations (e.g. Nb and La) and Zr/Y and Zr/Nb ratios are similar to those within plate gabbros. At the assorted discrimination diagrams the gabbros exhibit mostly non-orogenic resemblance. The geochemical characteristics show that the gabbros can be interpreted as melts formed from an enriched mantle in a passive rift position, during an extensional or transtensional tectonics.
... They generally show an A-type character (after Loiselle and Wones, 1979), with the exception of samples KAC43-45, KAC208-205 and KAC221-219. Such an affinity is emphasized by the discrimination diagrams of Whalen et al. (1987) in Fig. 9a, b, and is also supported by other features that are distinctive of A-type granites, such as the alkalicalcic to alkali character (Frost et al., 2001), relatively high Ti/Mg, K 2 O/ Na 2 O and Ga/Al, enrichment in LILE and HFSE, as well as negative Sr, P, Ti and Eu anomalies (e.g., Dall'Agnol et al., 1999, and references Middlemost, 1994); symbols and colors as in the legend. Symbols with an orange border refer to granites showing a tetrad effect in REE (see text); the dashed line separating alkaline from subalkaline series is after Irvine and Baragar (1971). ...
Anorthosite-mangerite-charnockite-granite (AMCG) suites form large batholiths emplaced during the Proterozoic Eon. Magma source(s), emplacement mechanisms, and the tectonic setting of AMCG suites remain poorly understood.
We present new major and trace element geochemistry combined with U-Pb zircon geochronology and Lu-Hf isotopes for the Red Granite Suite, part of the Mesoproterozoic Kunene AMCG Complex (Angola and Namibia), and its Paleoproterozoic host rocks, to elucidate the petrogenesis and tectonic setting of the Kunene Complex granitoids. The studied samples are mostly granite with minor syenite and quartz monzonite. LA-MCICPMS U-Pb zircon dates indicate that felsic magmatism was active for at least 90 Myr (1450–1360 Ma) and shows spatial and temporal similarities with emplacement of the main anorthositic body. The geochemistry of the granitoids did not change substantially over time, with predominant alkali-calcic, A-type granites. The εHf(t)
of zircon grains in the Red Granite Suite ranges between - 11.3 and + 1.6. These results, when considered together with Hf isotopic compositions of zircon from the Paleoproterozoic host rocks (εHf(t) = -11.3 to + 0.4) and xenocrysts in the Red Granite, suggest the suite is derived from the mixing of a Paleoproterozoic crustal
component with juvenile mantle-derived material. Syn-magmatic east–west shortening has been documented in both the anorthosites and Red Granites at the southwestern margin of the Kunene Complex in the period 1400–1380 Ma. The results from the Hf isotopes on zircon, combined with the long-lived nature of magmatism, the syn-contractional magmatism, at least locally, and the requirement for extensive crustal melting, suggest that the Red Granite Suite was formed in a convergent margin setting. This challenges the traditional view that A-type granitoids are restricted to anorogenic, extensional settings, and is in agreement with recent views on the petrogenesis of massif-type anorthosites and their associated MCG magmatism.
... All analyses were recalculated to 100% on a volatile-free basis. The boundary lines for sodic, transitional and potassic fields are based on Le Bas et al. (1986), Middlemost (1991) and Comin-Chiaramonti et al. (1997); ultrapotassic boundary line according to Foley et al. (1987); 'picritic field' after Le Maitre et al. (2002). All samples were reclassified according to our scheme; for those with available mode (Supplementary Table A1), we used the dominant light-coloured phase; for those without a mineral mode, we followed the original petrographic descriptions as far as possible. ...
The current International Union of Geological Sciences (IUGS) recommendations for nomenclature of kalsilite-bearing volcanic rocks do not consider the possible coexistence of kalsilite (KAlSiO4) and nepheline (KNa3Al4Si4O16), nor do they address volcanic rocks containing kalsilite, other than the archetypal kamafugites. This review highlights the most important shortcomings in the existing IUGS nomenclature against the classical literature and the most recent reports on kalsilite-bearing volcanic rocks. In addition, a new modal classification system, more logical and complete, is proposed. This scheme follows the IUGS principles as far as possible and denotes an updated version of the most applied historical terminology. Based on the presence of the main light-coloured constituents of kalsilite-bearing volcanic rocks, only four rock names are required for petrographic classification: katungite (melilite dominant), ugandite (leucite dominant), mafurite (kalsilite dominant), and kalsilite nephelinite (nepheline dominant). Such terminology should only be applied for volcanic rocks that definitely contain kalsilite. This requires the use of advanced analytical methods (e.g. electron microprobe analysis coupled with back-scattered electron imaging), besides conventional transmitted-light microscopy, as kalsilite and nepheline are optically indistinguishable. The coexistence of these two minerals in K-rich volcanic rocks is much more common than previously recognised. Volcanic rocks with kalsilite can be separated into potassic and ultrapotassic groups. This highlights a major problem concerning the indiscriminate use of the term kamafugite and the existing confusion between the modal and chemical classifications of kalsilite-bearing volcanic rocks. Our recommendations are purely based on descriptive attributes.
... They generally show an A-type character (after Loiselle and Wones, 1979), with the exception of samples KAC43-45, KAC208-205 and KAC221-219. Such an affinity is emphasized by the discrimination diagrams of Whalen et al. (1987) in Fig. 9a, b, and is also supported by other features that are distinctive of A-type granites, such as the alkalicalcic to alkali character (Frost et al., 2001), relatively high Ti/Mg, K 2 O/ Na 2 O and Ga/Al, enrichment in LILE and HFSE, as well as negative Sr, P, Ti and Eu anomalies (e.g., Dall'Agnol et al., 1999, and references Middlemost, 1994); symbols and colors as in the legend. Symbols with an orange border refer to granites showing a tetrad effect in REE (see text); the dashed line separating alkaline from subalkaline series is after Irvine and Baragar (1971). ...
Anorthosite-mangerite-charnockite-granite (AMCG) suites form large batholiths emplaced during the Proterozoic Eon. Magma source(s), emplacement mechanisms, and the tectonic setting of AMCG suites remain poorly understood. We present new major and trace element geochemistry combined with U-Pb zircon geochronology and Lu-Hf isotopes for the Red Granite Suite, part of the Mesoproterozoic Kunene AMCG Complex (Angola and Namibia), and its Paleoproterozoic host rocks, to elucidate the petrogenesis and tectonic setting of the Kunene Complex granitoids. The studied samples are mostly granite with minor syenite and quartz monzonite. LA-MC-ICPMS U-Pb zircon dates indicate that felsic magmatism was active for at least 90 Myr (1450–1360 Ma) and shows spatial and temporal similarities with emplacement of the main anorthositic body. The geochemistry of the granitoids did not change substantially over time, with predominant alkali-calcic, A-type granites. The εHf(t) of zircon grains in the Red Granite Suite ranges between −11.3 and + 1.6. These results, when considered together with Hf isotopic compositions of zircon from the Paleoproterozoic host rocks (εHf(t) = -11.3 to + 0.4) and xenocrysts in the Red Granite, suggest the suite is derived from the mixing of a Paleoproterozoic crustal component with juvenile mantle-derived material. Syn-magmatic east–west shortening has been documented in both the anorthosites and Red Granites at the southwestern margin of the Kunene Complex in the period 1400–1380 Ma. The results from the Hf isotopes on zircon, combined with the long-lived nature of magmatism, the syn-contractional magmatism, at least locally, and the requirement for extensive crustal melting, suggest that the Red Granite Suite was formed in a convergent margin setting. This challenges the traditional view that A-type granitoids are restricted to anorogenic, extensional settings, and is in agreement with recent views on the petrogenesis of massif-type anorthosites and their associated MCG magmatism.
... Breiter et al. Maniar and Piccoli, 1989), (c) SiO 2 vs. Na 2 O + K 2 O diagram of Middlemost (1991), and (d) discrimination diagram of Sylvester (1989) for rocks with >68 wt% SiO 2 . ...
The Nuweibi intrusion was emplaced during the final tectono-magmatic stage of Arabian-Nubian Shield development (ANS). Two cogenetic phases of intrusion can be recognized in the field: the early phase is represented by porphyritic albite granite and the final phase by non-porphyritic albite granite. Mineralogically, both phases are essentially composed of albite, quartz, and K-feldspars with subordinate muscovite. Accessory minerals include fluorite, zircon, Nb-Ta oxides, cassiterite, beryl, topaz, and garnet. Geochemically, the Nuweibi intrusion consists of extensively fractionated rare-metal granite with low contents of TiO 2 , FeO t , CaO, MgO, P 2 O 5 , Sr, and Ba in contrast to elevated concentrations of alkalis, Rb, Nb, Ta, and Hf. Their peraluminous (molar Al 2 O 3 /[CaO + Na 2 O + K 2 O] = 1.06-1.15) and low-P (P 2 O 5 < 0.008 wt%) character identify them as highly fractionated I-type granites. The primary magma of the Nuweibi intrusion was most likely generated by partial melting of the juvenile crust of the ANS. We document numerous lines of evidence that the Nuweibi albite granite was formed by extensive fractional crystallization followed by interaction with magmatically-derived, F-rich hydrothermal solutions. The REE patterns of the Nuweibi albite granite show marked negative Eu anomalies (Eu/Eu* = 0.01-0.15) as well as prominent M-type tetrad effects (TE 1,3 = 1.332-3.536), typically seen in highly differentiated granites and attributed to exchange with hydrothermal fluid. Anomalous ratios of isovalent "twin" elements such as Nb/Ta, Zr/Hf, and Y/Ho likewise indicate exchange with hydrothermal fluid. The primary rare-metal accessory minerals are restricted to the Mn-rich part of the columbite-tantalite series; this manganoan trend is characteristic of highly fractionated granites. Likewise, the presence of wodginite, a Sn-bearing mineral, is a unique fingerprint of highly evolved rare-metal granites. Late-stage hydrothermal overprint of the primary rare-metal mineralization is preserved by rims of fluorcalciomicrolite partly replacing columbite-(Mn) and tantalite-(Mn). Accumulation of residual volatile-rich melt and exsolved fluids in the upper part of the magma chamber produced stockscheider pegmatite, greisen, and quartz veins that cut the peripheries of the Nuweibi intrusion and the surrounding country rocks.
... Breiter et al. Maniar and Piccoli, 1989), (c) SiO 2 vs. Na 2 O + K 2 O diagram of Middlemost (1991), and (d) discrimination diagram of Sylvester (1989) for rocks with >68 wt% SiO 2 . ...
The Nuweibi intrusion was emplaced during the final tectono-magmatic stage of Arabian-Nubian Shield development (ANS). Two cogenetic phases of intrusion can be recognized in the field: the early phase is represented by porphyritic albite granite and the final phase by non-porphyritic albite granite. Mineralogically, both phases are essentially composed of albite, quartz, and K-feldspars with subordinate muscovite. Accessory minerals include fluorite, zircon, Nb-Ta oxides, cassiterite, beryl, topaz, and garnet. Geochemically, the Nuweibi intrusion consists of extensively fractionated rare-metal granite with low contents of TiO 2 , FeO t , CaO, MgO, P 2 O 5 , Sr, and Ba in contrast to elevated concentrations of alkalis, Rb, Nb, Ta, and Hf. Their peraluminous (molar Al 2 O 3 /[CaO + Na 2 O + K 2 O] = 1.06-1.15) and low-P (P 2 O 5 < 0.008 wt%) character identify them as highly fractionated I-type granites. The primary magma of the Nuweibi intrusion was most likely generated by partial melting of the juvenile crust of the ANS. We document numerous lines of evidence that the Nuweibi albite granite was formed by extensive fractional crystallization followed by interaction with magmatically-derived, F-rich hydrothermal solutions. The REE patterns of the Nuweibi albite granite show marked negative Eu anomalies (Eu/Eu* = 0.01-0.15) as well as prominent M-type tetrad effects (TE 1,3 = 1.332-3.536), typically seen in highly differentiated granites and attributed to exchange with hydrothermal fluid. Anomalous ratios of isovalent "twin" elements such as Nb/Ta, Zr/Hf, and Y/Ho likewise indicate exchange with hydrothermal fluid. The primary rare-metal accessory minerals are restricted to the Mn-rich part of the columbite-tantalite series; this manganoan trend is characteristic of highly fractionated granites. Likewise, the presence of wodginite, a Sn-bearing mineral, is a unique fingerprint of highly evolved rare-metal granites. Late-stage hydrothermal overprint of the primary rare-metal mineralization is preserved by rims of fluorcalciomicrolite partly replacing columbite-(Mn) and tantalite-(Mn). Accumulation of residual volatile-rich melt and exsolved fluids in the upper part of the magma chamber produced stockscheider pegmatite, greisen, and quartz veins that cut the peripheries of the Nuweibi intrusion and the surrounding country rocks.
... Though popular, the Irvine & Baragar (1971) dividing line is irrelevant, as it separates silica-undersaturated and silica-saturated rocks within the alkaline field. To cope with the incorrect use of "subalkaline", Lameyre et al. (1982) suggested the term "transalkaline", while Middlemost (1991) defined "transalkali" suites, as these rocks plot along the alkaline-subalkaline boundary in the TAS diagram. ...
... To cope with the incorrect use of 'subalkaline', Lameyre et al. (1982) suggested the term 'transalkaline', while Middlemost (1991) defined 'transalkali' suites, i.e. suites of rocks plotting along the alkalinesubalkaline boundary in the TAS diagram. ...
Granites (s.l.) come in many types and flavours, defining distinct magmatic series/suites/types. A good classification not only gives generally accepted and understandable names to similar rocks, but also links the bulk chemical composition to the stoichiometry of the constituent minerals and, potentially, also to the likely source, magmatic evolution and tectonic setting.
The ‘ideal’ granitoid classification should be based on chemical criteria amenable to an objective treatment. Statistical analysis helps to identify the most discriminant variables. The key properties are (i) acidity/maficity, (ii) alkalinity (balance of Na + K v. Ca), (iii) aluminosity (balance of Al v. Ca, Na and K), (iv) Fe/Mg balance and (v) Na/K balance and K contents at the given SiO2 level. These are used by successful classifications; e.g., the I/S dichotomy is based mainly on aluminosity, and the Frost et al. (2001) classification includes all but Na/K. While it is commonplace to use weight percentages of oxides, we suggest that a better strategy is to employ simple atomic parameters (e.g., millications-based) that can be directly linked to modal proportions and compositions/crystal structure of individual rock-forming minerals. This facilitates a petrological interpretation, which in turn can be related to petrogenesis and, ultimately, to likely tectonic setting(s).
... All the REE patterns of the NAG are subparallel, with enrichment of heavy REEs (HREEs) relative to light REEs (LREEs), reflected in (La/Lu) n values from 0.21 Figure 6. a, SiO 2 -versus-Na 2 O 1 K 2 O diagram of Middlemost (1991). b, Ga/Al-versus-FeO (t) /MgO diagram of Whalen et al. (1987). ...
We present new data and interpretationsfor the Nuweibi albite granite(NAG)intrusionin thecentral Eastern Desert of Egypt.The NAG isa post-collisional intrusionemplacedasa high-levelmagmatic cupolainto metamorphic and syn-tectonic calc-alkaline country rocks. It consists oftwo cogenetic intrusive bodies:the western,non-porphyritic,albite granitewasemplaceddeeperthanthe eastern,fine-grained porphyritic albite granite.In places the non-porphyritic phasecrosscuts the earlierporphyriticphase, but the occurrence of gradational contacts betweenthephasesimpliesa near-coincidence in time, with the non-porphyritic phase emplacedbeforecrystallization of the porphyriticphase was complete.The steeply-dippingslope of the westerncontact of the Nuweibi plutonagainstcountry rocks, in contrast togently-dipping contacts abovetheeastern and northeastern parts,indicatestheprobable location ofthecupola apex intheeastern part of the pluton.The NAGintrusionishighly evolvedmeta-to peraluminousleucocratic rare-metal albite granitewith the common geochemical characteristics of post-collisional A-type magmas.Itspronounced negative Eu anomalies (Eu/Eu* = 0.04-0.09)reflectextreme magmatic fractionationand perhaps the effects of latefluid-rock interaction.TheNAGintrusionis chemicallyzoned,withupwardincreasesofAl2O3, Na2O, Sr, GaandTaconcentrations,alongsideupward decreases inSiO2, K2O, Rb, Nb, Zn, Zr, Th, Sn andrare earthelement (REE)concentrations.These trends are interrupted by acompositional gapwithdiscontinuities inevolutionary trends ofbothcompatible and incompatible elements, suggestingmultiplepulses ofintrusion.The REE patterns of NAG show tetrad effect which is typical featureof highly differentiated granite evolved in transitional magmatic–hydrothermal system.The NAGwas generated via partial melting of a juvenile crustal crust that undergone extensive fractionalcrystallization combined with late magmatic fluid overprint.Accumulation of residual volatile-richmelt and exsolved fluidsin the apical part of themagmatic cupolaproduced stockscheiderpegmatite, greisen andquartz veins that cut the peripheries of theNAG plutonand thesurrounding country rocks.Metasomaticactivity by late-to post-magmatic fluids drovechangesinthebulk compositionof the cupola,removing K and drivingthe alkali feldspars towardspurealbite.
... The petrogenetic relation by magmatic differentiation between alkali-gabbro and syenite can be better understood from alkali-silica diagram (Cox et al., 1978), where albitite (circle) protolith range from syenite to syenodiorite, microcline-gneiss (triangle) protolith is an alkali-granite, and amphibolite (cross) protolith would be understood as an alkali-gabbro. (Saggerson & Williams, 1964), where both rocks belong to the same transitional alkaline series (figure 8a), also named transalkaline series by Middlemost (1991). ...
After Chaves et al. (2007), the crystallization and coeval deformation of the Lagoa Real uraniferous sodic syenite (uraniferous albitite protolith) took place along paleoproterozoic shear zones developed under regional late-orogenic tectonic conditions. The interpretation of new major elements, Zr and Th lithogeochemical data points to a petrogenetic connection between alkali-gabbro (local amphibolite protolith) and sodic syenite by fractional crystallization through transitional alkaline series. This magmatic differentiation occurred either before or during shear process, which in turn led to albitite and amphibolite formation. The regional microcline-gneiss, whose protolith is a syn-collisional potassic granite, represents the albitite host rock, and, apparently, it has no petrogenetic association to syenite (albitite protolith) in magmatic evolutive terms.
... Em termos conceituais, segundo Middlemost (1991), rochas de uma série alcalina saturada em sílica, por ele denominada série transalcalina, distribuem-se no diagrama TAS (Le Bas et al., 1986) de classificação de rochas vulcânicas, em sequência ao longo dos campos S1 (traqui-basálticas), S2 (andesíticas traquibasálticas), S3 (traqui-andesíticas) e T (traquíticas), sendo caracterizadas pela ausência de nefelina modal e pela presença de nefelina normativa. Utilizando o diagrama TAS em adaptação para as rochas plutônicas da suíte Lagoa Real sódica e da suíte Gouveana potássica, nota-se pela Figura 6 que ambas pertencem de fato à referida série alcalina saturada em sílica. ...
A começar pela idade, há inúmeras semelhanças entre as suítes magmáticas alcalinas Lagoa Real sódica (1,90 Ga, Bahia) e Gouveana potássica (1,95 Ga, Minas Gerais). Ambas apresentam desde lamprófiros e monzonitos até sienitos e quartzo-sienitos metaluminosos, pertencentes à série magmática alcalina saturada em sílica. Sugere-se que a fusão parcial do manto litosférico, que havia sido metassomatizado por fluidos derivados de uma placa subductada antes da colisão, teria inicialmente gerado um magma lamprofírico. A cristalização fracionada deste magma teria levado ao surgimento de magmas monzoníticos que, por sua vez, evoluíram para os sieníticos e quartzo-sieníticos. Ambas suítes alcalinas fazem parte de um domínio estrutural alinhado na direção N-S, com mais de 1.000 km de comprimento, dentro do qual ocorrem outras associações alcalinas, como a sienítica de 2,0 Ga na borda sul do Cráton São Francisco (Minas Gerais), o batólito Guanambi (2,05 Ga, Bahia) e seus termos lamprofíricos, monzoníticos e sieníticos, de gênese associada à dos lamprófiros e sienitos da Suíte Paciência (norte de Minas Gerais) e, ainda, o complexo sienítico-lamprofírico-carbonatítico Angico dos Dias de 2,0 Ga (norte da Bahia). Aparentemente, todas estas associações representam os fragmentos de uma província alcalina orosiriana pós-colisional Minas-Bahia, de idade entre 1,90 e 2,05 Ga.
... O caráter alcalino sódico é bem marcado no MSSA e se expressa por razões Na 2 O/K 2 O entre 1,6 e 0,7, sendo decrescentes com o aumento de SiO 2 (Fig. 4B) Maître et al. (1989) com a nomenclatura plutônica de acordo com Middlemost (1994) de: Souto (1972), Fujimori (1978), Lima et al. (1981), Arcanjo (1993), Martins & Santos (1993), Marques et al. (2001), Oliveira (2003), Cunha (2003). Complexo Alcalino Floresta Azul (CAFA). ...
2 ) is a Brasiliano aged intrusion (single zircon Pb-Pb age of 739 ± 2 Ma), located in the South area of an alignment of alkaline rocks that constitute the Alkaline Province of South Bahia. These rocks are predominantly hypersolvus syenites with biotite, hornblende an d occasionally quartz, which gradually evolve into blue quartz-alkaline granites in the core. The massif has been passively empla ced at a Mesoproterozoic geosuture, which was re-activated during the Neoproterozoic. Geochemical data suggest that the syenitic and granitic rocks are cogenetic. The chemical evolution of Araras rocks allows explaining the generation of alkaline granites by f ractional crystallization of syenitic magma, with a mafic syenitic cumulates similar to those observed in this massif. The negative epsil on Nd values, associated with the low HREE contents, indicate an enriched mantelic source at the garnet stability zone. The patterns observed to the syenitic rocks, in the multielement diagram normalized by the primitive mantle, and the absence of Nb negative anomalies, indicate an OIB signature and do not suggest any important process of crustal assimilation. 2 ) é uma intrusão brasiliana (idade Pb-Pb em monozircão 739 ± 2 Ma) que se localiza na porção sul do alinhamento de rochas alcalinas que constituem a Província Alcalina do Sul do Estado da Bahia. Est e corpo é formado por sienitos hipersolvus com biotita, hornblenda e ocasionalmente quartzo, que evoluem gradualmente para granitos alcalinos com quartzo de cor azul na sua porção central. Sua colocação processou-se de forma passiva e condicionada por geossut ura Mesoproterozóica reativada durante o Neoproterozóico. Os dados químicos obtidos para as rochas deste maciço apontam para a cogeneticidade entre as rochas sieníticas e graníticas. A evolução química exibida por estas rochas permite explicar a geração dos granitos alcalinos a partir da cristalização fracionada de magma sienítico, gerando cumulato com composição sienítica, próxima à dos sienitos máficos presentes no maciço. Os valores negativos de εNdT associados aos baixos valores dos ETR Pesados, indicam fonte mantélica enriquecida e sugerem que o magma sienítico foi gerado na zona de estabilidade da granada. Em diagrama multielementar , normalizado pelo manto primitivo, as curvas obtidas para as rochas sieníticas, sem anomalias negativas em Nb, não evidenciam importante processo de assimilação crustal e apontam para fonte com assinatura astenosférica (OIB). Palavras-chave: Geologia, petrografia, idade Pb-Pb, geoquímica, Maciço Sienítico Serra das Araras
... On the total alkalis-silica (TAS) diagram of Middlemost (1991) (Fig. 4a), the graphic granite, biotite granite and alkali feldspar granites fall in the granite field, whereas the biotite granodiorite and porphyritic granodiorite plotted on the quartz monzonite field. The gabbro, pyroxene diorite and quartz diorite plotted in the gabbro, diorites and granodiorite fields, respectively. ...
The igneous rocks of the Wadi Hamad area are exposed in the northernmost segment of the Arabian-Nubian Shield (ANS). These rocks represent part of crustal section of Neoproterozoic continental island arc which is intruded by late to post-collisional alkali feldspar granites. The subduction-related intrusives comprise earlier gabbro-diorites and later granodiorites-granites. Subduction setting of these intrusives is indicated by medium- to high-K calc-alkaline affinity, Ta-Nb troughs on the spider diagrams and pyroxene and biotite compositions similar to those crystallized from arc magmas. The collisional alkali feldspar granites have high-K highly fractionated calc-alkaline nature and their spider diagrams almost devoid of Ta-Nb troughs. The earlier subduction gabbro-diorites have lower alkalis, LREE, Nb, Zr and Hf values compared with the later subduction granodiorites-granites, which display more LILE-enriched spider diagrams with shallower Ta-Nb troughs, reflecting variation of magma composition with arc evolution. The later subduction granitoids were generated by lower degree of partial melting of mantle wedge and contain higher arc crustal component compared with the earlier subduction gabbro-diorites. The highly silicic alkali feldspar granites represent extensively evolved melts derived from partial melting of intermediate arc crustal sources during the collisional stage. Re-melting of arc crustal sources during the collisional stage results in geochemical differentiation of the continental arc crust and the silicic collisional plutonism drives the composition of its upper part towards that of mature continental crust.
... Ma (U/Pb zircon and 40 Ar/ 39 Ar in Hornblende, respectively) (Miller et al. 1994). Middlemost (1991), the shading marks the mildly alkaline (transalkali) field. Alkaline and subalkaline divide of Miyashiro (1978) b The same diagram with trends of Lameyre (1987) and Lameyre and Bonin (1991): 1 calc-alkaline tonalitictrondhjemitic, 2 tholeiitic, 3 calc-alkaline granodioritic, 4 monzonitic, 5 alkaline. ...
The magmatic arc in the southernmost Andes is represented by the Fuegian Batholith and satellite plutons, plus minor volcanic and volcaniclastic sequences. Magmatism was active from the Late Jurassic to the Miocene in response to subduction of the Pacific plates beneath South America. The batholith was constructed episodically and includes a calc-alkaline trench-side arc and shoshonitic rear-arc suites. The oldest components are minor S-like granitoids; recent volcanism is very scarce. The volcanic front shifted, and the composition of magmas changed several times due to a variable subduction configuration. Major tectonic events included the opening and closure of the Rocas Verdes marginal basin in the Jurassic–Cretaceous and oroclinal bending during the latest Cretaceous–Paleogene. A well-established slab shallowing event initiated in the mid-Cretaceous, causing a cratonward migration of the volcanic front, the widening of the arc, and inception of potassic magmatism in the rear-arc. This event was associated with marginal basin inversion, regional peak metamorphism, and orogenic deformation. Different timing and position of rear-arc suites with respect to the volcanic front in the Fuegian and Southern Patagonian Andes may have been influenced by differential development of the marginal basin, which was wider to the south. The vanishing of magmatism in the Miocene may have responded to highly oblique convergence plus buoyant subduction.
... Los valores de CaO y MgO son bajos, otra característica común en las rocas pertenecientes a este complejo. El quimismo del complejo volcánico en Arroyo Verde es transicional entre las rocas alcalinas y subalcalinas, característica ya mencionada por Rapela y Pankhurst (1993) quienes las incluyen en un campo de rocas transalcalinas en el sentido de Middlemost (1991). La divisoria entre las alcalinas y transalcalinas está dada por la presencia de Q o Ne en la norma. ...
Marifil Complex volcanic facies that crop out in the locality of Arroyo Verde, SE slope of Macizo de Somún Cura, are described here. Rhyolitic ignimbrite facies, pyroclastic breccias, traquitic domes and vitreous domes, and rhyolitic dikes are distinguished. Field relationships point out the ignimbrites as the first effusive event. Some sporadically block and ash flows are intercalated within the ignimbrites. These deposits were intruded by domes; the latest event is represented by the intrusion of the rhyolitic dykes. Chemical composition of these rocks varies between high K rhyolites and traquites, which correspond to typical characteristics of the Marifil Complex rocks. The observations allow proposing a fissural mechanism of eruption for these facies in this locality.
... Em termos conceituais, segundo Middlemost (1991), rochas de uma série alcalina saturada em sílica, por ele denominada série transalcalina, distribuem-se no diagrama TAS (Figura 3) (Le Bas et al. 1986) em sequência ao longo dos campos S1 (traqui-basálticas), S2 (andesíticas traqui-basálticas), S3 (traqui-andesíticas), T (traquíticas) e são caracterizadas pela ausência de nefelina modal e pela presença de nefelina normativa. De acordo com os parâmetros de Shand (1943), são geralmente metaluminosas. ...
Close to Gouveia town (MG) and located inside granitoids and gneiss of the Gouveia Complex, porphyritic latites (or trachy-andesites) slightly metamorphosed are identified, with plagioclase and sanidine phenocrysts and matrix also feldspar-rich containing biotite, magmatic epidote and quartz. Occurring adjacent to the porphyrites, metamorphosed phanerites also appear, with terms ranging from ultramelanocratic lamprophyres (rich in amphibole and phlogopite with interstitial microcline), melanocratic monzonites (or syeno-diorite with hornblende, biotite, microcline and plagioclase), mesocratic syenites up to leucocratic quartz-syenites (with microcline, biotite and quartz). Lithochemistly, porphyrites and phanerites are metaluminous rocks, however the porphyrites are subalkaline, high-K tholeiitic and tardi-orogenic, while phanerites comprise a silica-saturated alkaline shoshonitic magmatic suite, called Gouveana Suite, whose lithotypes are genetically interrelated by magmatic fractionation processes occurred during an episode of post-collisional uplift. Apparently derived from distinct mantle sources, porphyrites and phanerites should be tectonically associated to regional transcurrent faults at the end of either Transamazonic or Brasiliano Events.
... El contenido total de álcali ha sido comúnmente utilizado como un índice para determinar el carácter subalcalino o alcalino de las series magmáticas (Irvine y Baragar, 1971;Middlemost, 1991). La correlación del contenido total de álcali con Si0 2 mues- tra que la mayoría de las rocas (alteradas y no alteradas) son compatibles con las series subalcalinas (Fig. 6). ...
RESUMEN Las menas de hierro de los distritos ferríferos Cerro Negro Norte y Cerro Imán, pertenecientes a la Franja Ferrffera Cretácica de la Cordillera de la Costa de Chile, se encuentran fuertemente enriquecidas en Au con respecto a las rocas volcánicas andesrticas que constituyen sus rocas de caja. El emplazamiento de la mena ferrífera, cuya formación se interpreta a partir de un magma de mena, ocurrió en un ambiente de arco magmático de afinidad calco-alcalina. Este proceso fue acompañado por una intensa actividad hidrotermal, responsable de la generación de mineralización ferrffera tipo 'stockwork' y diseminada en la proximidad de los cuerpos macizos de magnetita, de brechas hidrotermales y de la alteración de la roca de caja. Las rocas alteradas presentan una zonación mineralógica y geoquímica entorno a los cuerpos de mena, con rocas fuertemente actinolitizadas en la parte interna próxima a la mena y albitizadas en el lado opuesto. Un halo extemo silicificado y turmalinizado se sobreimpone a las rocas actinolitizadas y albitizadas. De acuerdo con las relaciones de contacto entre las distintas unidades de rocas alteradas y su composición mineralógica, se infieren, a lo menos, dos eventos principales de alteración hidroterrnal: el primero, caracterizado por soluciones de alta temperatura, pH neutro a ligeramente alcalino y rico en Mg, Fe, Ca, CO 2 , F, P Y CI, produce la actinolitización y, en parte, albitización de las rocas volcánicas. Un segundo evento, con soluciones de menor temperatura, pH neutro a ligeramente ácido, rico en sílice, By F, se sobreimpone al anterior. la distribución del oro en los minerales de la mena (magnetita y pirita) Y roca de caja (alterada y no alterada) sugiere que la generación de un magma de mena (magnetita-apatita) favoreció la concentración primaria del oro en la magnetita, dando lugar a una importante fuente primaria de este elemento en un nivel superficial de la corteza. Las características de las soluciones hidrotermales que acompañan el emplazamiento de las menas de hierro son las aprop.iadas para removilizar, y posteriormente, redepositar el oro inicialmente contenido en los cuerpos macizos de magnetita-apatita, pudiendo dar origen a concentraciones de potencial interés económico. Palabras claves: Oro. HIerro. Geoqulm/ca. Franja Ferrlfera, Cordillera de la Costa. Cerro Negro Norte, Cerro Imlln. Chile.
... Analytical results are listed in Table 2. The younger Jurassic-Early Cretaceous magmatic rocks at Chizhou are plotted as diorite, monzonite, quartz monzonite, granodiorite, syenite, and granite on the SiO 2 versus K 2 O + Na 2 O classification diagram of Middlemost (1991) (Fig. 3a). The diorite-monzonites span a range of 57.1-57.3 ...
... Los valores de CaO y MgO son bajos, otra característica común en las rocas pertenecientes a este complejo. El quimismo del complejo volcánico en Arroyo Verde es transicional entre las rocas alcalinas y subalcalinas, característica ya mencionada por Rapela y Pankhurst (1993) quienes las incluyen en un campo de rocas transalcalinas en el sentido de Middlemost (1991). La divisoria entre las alcalinas y transalcalinas está dada por la presencia de Q o Ne en la norma. ...
Se describen en este trabajo las facies volcánicas pertenecientes al Complejo Marifil que afloran en la localidad de Arroyo Verde, vertiente suroriental del macizo de Somún Cura, provincia del Chubut. Se discriminan facies de ignimbritas riolíticas, brechas piroclásticas, domos y domos vítreos traquíticos y diques riolíticos. Las relaciones de campo indican que las ignimbritas fueron el primer evento eruptivo que se alternaron con esporádicas coladas de bloques y cenizas. Luego se produjo la intrusión de las facies dómicas y por último la de los diques riolíticos. Las facies descriptas tienen composiciones que varían entre riolitas y traquitas con altos contenidos de K, característicos de las rocas pertenecientes a este complejo. Teniendo en cuenta las características observadas se propone un mecanismo fisural de erupción en esta localidad.
The Southern Pamir region, a critical part of the Alpine-Himalayan orogenic belt, exhibits a complex tectonomagmatic history that offers insights into the geodynamic evolution of the Pamir Plateau. This study presents comprehensive data on the Cretaceous granitoids from the Kyzylrabat area, including whole-rock geochemistry, zircon U-Pb geochronology and Sr-Nd-Hf isotopic analyses. The analysed granitoids are high-K calc-alkaline to shoshonitic, exhibiting A-type geochemical signatures.
Zircon U-Pb ages range from 98.5 to 111.7 Ma, correlating well with contemporaneous volcanic activities. Isotopic data indicate a mixed magmatic origin involving a mantle-derived high-K magma and a crustal-derived felsic component. Petrogenetic analyses reveal co-magmatic trends and magma mixing processes, with geochemical evidence suggesting a mantle source metasomatized by subduction-related fluids. Geodynamic interpretations propose that the granitoids formed in an
extensional back-arc setting during the northward subduction of the Shyok branch of the Neotethys Ocean. These findings provide critical constraints on the mid-Cretaceous tectonic and magmatic processes in the Southern Pamir, contributing to a deeper understanding of the orogenic plateau formation and evolution.
Feldspars are essential components in the ceramic industry, and the increasing demand for high-grade fluxes has recently elevated their status as critical raw materials for the European Union. This survey aims to evaluate, for the first time, Italy’s mining potential for the production of ceramic fluxes through a methodological approach that considers lithology, technological value, degree of alteration and potential for mining exploitation. The most promising resources are identified in the Alps, the Apennines, Sardinia and the Calabro–Peloritan Arc, based on the chemical composition of rocks without any beneficiation. Key parameters include the equivalent feldspar content and the sum of Fe2O3 + TiO2. Factors that may influence the feasibility of exploitation are critically discussed for granitoids and syenites, acidic volcanics, aplites and pegmatites, albitites, felsic metamorphics, silica-saturated and silica-undersaturated volcanics, arkosic sandstones and rocks that have undergone epithermal alteration. All resources are compared with deposits currently under extraction and assessed against benchmarks or well-recognized raw materials used as market proxies. This review lays the groundwork for operational mining exploration by clearly defining Italy’s potential for feldspathic fluxes. The exploratory assessment approach to feldspathic resources can also be applied in other countries.
High-pressure-low-temperature (HP-LT) rocks such as eclogites and blueschists preserve valuable information about the history and geodynamics of subduction zones. HP-LT rocks exposed in Iran formed during subduction of Paleo-Tethys and Neo-Tethys oceanic lithosphere beneath the Iran microplate and were subsequently exhumed from the Permian to the Early Eocene. The Shanderman and Anarak complexes are associated with Paleo-Tethys, and the Shahrekord, Hajiabad-Esfandaghe, Sistan, Makran, and Sabzevar complexes are related to Neo-Tethys. The assemblage garnet + omphacite + amphibole (Na-, Na-Ca) + white mica + albite ± zoisite formed at the peak metamorphism stage of the eclogites, and amphibole (Na-, Na-Ca) + albite ± white mica ± zoisite ± epidote ± lawsonite formed in blueschists. Retrograde metamorphism replaced peak assemblages with epidote-amphibolite and greenschist facies mineral assemblage (Ca-amphibole + Na-Ca plagioclase + epidote + chlorite). For the various complexes, geothermobarometry calculations and phase diagram modeling show peak P-T conditions of 23 kbar - 600 °C (Shanderman), 14 kbar - 560 °C (Anarak), 25 kbar - 670 °C (Shahrekord), 17 kbar - 530 °C (Hajiabad-Esfandaghe), 24 kbar - 650 °C (Sistan), 15 kbar - 560 °C (Makran), and 17 kbar - 570 °C (Sabzevar). Their retrograde P-T conditions are ~6 kbar - 470 °C, 7 kbar - 500 °C, 6 kbar - 530 °C, 10 kbar - 450 °C, 8 kbar - 500 °C, 7 kbar -500 °C and 6 kbar - 490 °C, respectively. The obtained P-T conditions represent a geothermal gradient of 12-16 °C/km for the Paleo-Tethys HP-LT complexes and 7-11 °C/km for the Neo-Tethys. Field and petrographic studies reveal that subduction metamorphism occurred mostly along clockwise P-T paths, except for the Hajiabad-Esfandaghe, Makarn and a subunit of the Anarak complexes that endured counter-clockwise paths. The differences may show a greater subduction angle of Neo-Tethys oceanic lithosphere than Paleo-Tethys, resulting in a cold geothermal gradient and development of continental back-arc basins during the Mesozoic.
Rasht Abad Cu±Au deposit is a part of the Tarom-Hashtjin metallogenic belt in the western Alborz-Azerbaijan zone. The exposed units in the area include volcanic, sub-volcanic calc-alkaline to shoshonitic rocks with Upper Eocene age and belongs to magmatic arcs setting. The most important alterations related to mineralization include low temperature silicification and sericitic alterations. Mineralization with quartz-sulfide veins in the area consist of a series of oxide (hematite), sulfide (chalcopyrite, galena, bornite, covelite), sulfate (barite) and carbonate (malachite, azurite). Fluid inclusions measurements on primary two-phase L+V inclusions determined homogenization temperatures between 138 to 320°C (229°C) and salinity between 2.49 to 9.41wt% (9.41) NaCl eq, evidence of isothermal mixing and dilution. The δ13C (-9.21to -6.81‰) and δ18O (-14 to -15‰) also show the influence of meteoric waters in late carbonate veins. The results of this study show that the high similarity between Rasht Abad and intermediate sulfidation epithermal deposits
Tarazoj-Soushab tectonic window is located between Tarazoj and Soushab villages in the end of the northeast of 1:100,000 Hashjin sheet. This area is part of the West Alborz Tertiary magmatic belt. Mafic igneous rocks include basaltic pillow lava and gabbro bodies and felsic igneous rocks include granite and trachytic flows. The main minerals of the gabbroic and basaltic rocks are plagioclase, olivine and clinopyroxene and the main minerals of the granitic rocks include plagioclase, orthoclase and quartz, and the trachyte consists mainly of potassium feldspar. Gabbroic and basaltic rocks show calc-alkaline nature and granitic and trachytic rocks have shoshonitic nature. Examination of chondrite and primitive-mantle normalized spider diagrams in basalts and gabbros indicates enrichment of LREEs relative to HREEs. The LILE and LREE enrichment and HREE depletion in the pattern may indicate low melting rate, high fugacity of CO2/H2O in the magma formation environment or high depth of generation of basaltic and gabbroic magma. Examination of chondrite and ORG-normalized spider diagrams in granites and trachytes indicates enrichment of light rare earth elements (LREE) and incompatible elements relative to heavy rare earth elements (HREE). These patterns show a marked depletion of Eu (especially in granites). Gabbroic and basaltic rocks are located in an oceanic environment with E-MORB basalts tendency and the granites and trachites associated with this assemblage belong to anorogenic granitoids (A-type) and subgroup A1. These features indicate that the studied outcrops in the Tarazoj-Soushab tectonic window belong to the rift-related magmatism and opening of the Paleo-Tethys ocean (Paleo-Tethys II) in the northwest of Iran.
Petrographical and geochemical study, consistent with observed field relations show that the Boula Ibi syn- and post-kinematic granitoids in north Cameroon, occurred in banded gneisses. These syn- and post-kinematic granitoids consist of deformed monzonites typified by its granoblastic texture, diorites, syenites, granites and basic xenoliths of dioritic and monzonitic composition. They are calc-alkaline, hyperpotassic, metaluminous to slightly peraluminous and I-Type granitoids. They display high content in Fe2O3 + MgO + CaO (2.16 – 23.24 %) that reveals their intermediate affinity, magnesian and metaluminous character whilst the low A/CNK (< 1.1) content indicates their mantle origin. Harker diagrams and La/Sm vs La define the fractional crystallization and partial melting as the two main processes that led the geodynamic evolution of the Boula Ibi syn- and post-kinematic granitoids. These are consistent with low-content of Cs, Ta, Nb, Tb and Hf, supporting high melting rates ranging between 20 and 40% as well as molar Al2O3/(MgO + FeOt) vs CaO/(MgO + FeOt) plot showing magmatic evolutions from metabasaltic and metagreywackes sources.
پیامبر خدا (صلیالله علیه و آله و سلّم) فرمودند:
هر گاه مؤمن یک برگه که روى آن علمى نوشته شده باشد از خود برجاى گذارد، روز قیامت آن برگه پرده میان او و آتش می شود و خداوند تبارکوتعالی به ازاى هر حرفى که روى آن نوشته شده، شهرى هفت برابر پهناورتر از دنیا به او میدهد.
سلام علیکم؛
ایزد دانا را سپاس میگویم که بنده را یاری بخشید تا بتوانم در زمینه تحقق اهداف خویش، گام بردارم. برای پاسداشت و ترویج علم مقدس زمینشناسی، پایان نامه کارشناسی ارشد خود در دانشگاه تهران را به همه فرهیختگان جامعه علمی زمینشناسی ایران تقدیم مینمایم. شایسته است انشالله همه بزرگواران امانت داری کامل علمی را رعایت بفرمایند. پیروزی و موفقیت شما را در تمامی امور زندگی آرزومندم.
دکتر رامین صمدی
The Study area is Located at SE of Bostan-Ābad, in NW of Iran. Based on structural
zoning of Iran, the above mentioned district is a part of Western Alborz- Azer
baijan structural zone and consists of Eocene volcanics,Oligomiocene plntons and
finally, the Sahand volcanism Pyroclastic unites. Based on microscopic assessment,
the studied rocks are consist mainly from Diorites, Granites and Monzonites.Their
main paragenesis are consist from K-Feldspars, Plagioclases and Quartz. Petrologic
investing ations showed Calk- Alkaline- Shoshonitic series and probabely High
potassic they formed in to volcanic arcs regime.
The study area is located in 7km of north of Takhte Soleiman and from structure point
comforted in Central Iran. According to petrography study, main composition of this
intrusive are porphiric granite, quartze monzodiorit ,quartze diorite and aplite dikes.The
mineralogy composition of porphiric granite include Alkalifeldespar (Ortoz), Plagioclase
(Albit-Oligoclase), quartze, Biotit, Amphibole, Zircon, Apatit and Sphen. Quartze
monzodiorit include Plagioclase, Quartze, low percent Alkalifeldespar, Biotit. Quartze
diorite also include Plagioclase, quartze, high percent Amphibole, low percent
Alkalifeldespar. Negetive anomaly of Eu shows plagioclase fractionation and depleting in
Ta, Nb, Ti. This intrusive is I- type Granitoids and situated in active continental margin
arcs.
Minor rhyolite intrusives spatially associated with granophyric granites occur along the eastern and southwestern friage of the Archaean Singhbhum Gramite batholith in the eastern Indian Craton. Some minor trachyte dykes occur within the batholith and both are of post-Archaean age. On the basis of major and trace element studies it has been inferred that a process more complex than simple fractional crystallisation has controlled the observed chemical variation in both the rocks. However, the two are genetically uarelated and have been generated from different sources. All the rhyolites, which are scattered as small bodies over an extensive area, are produced from similar source compositions. The chemical variation among the rhyolites is the result of a difference in degree of melting and the samples eariched in LREE and other incompatible elements represent a lower degree of partial melt. Composition of the rhyolites suggests that neither muscovite nor aluminosilicates were present in the source. The likly source is therefore the trondhjemites and mafic-ultramafie rocks constituting the Archaean crust of the region. Similar source for rhyolites distributed over a large area indicates a homogeneous composition for the Archaean crust.
Tongcun deposit in Kaihua, Zhejiang Province is a newly discovered medium-sized porphyry-Mo(Cu) deposit. The lithology, petrochemistry, and Sr, Nd isotopes of the intrusion from Tongcun deposit are studied in this paper and the following conclusions can be drawn: (1)the ore-bearing porphyry belongs to the calc-alkali rock with high SiO2, K2O and low Na2O concentrations. It is rich in Rb, Th, K, U, La, Ce, and Pb, and poor in Ti, P, Nb, Ta, Zr, and Hf. The enrichment of LREE and HREE fractionation are obvious with weak negative Eu anomalies; (2)concordia age of Tongcun porphyry is 162±3 Ma, MSWD=2.7, with a mean age of 162.1±3.4 Ma and MSWD=2.7, indicative of a Middle-late Jurassic magma intrusion; (3)the ore-bearing porphyry has relative high ISr(0.71221) and low εNd(t)(-6.7 - 2.0) value, and the modal age is 1628 - 2029 Ma, which suggests that the source rock of porphyry possibly originated from the Early Proterozoic bed rock. The source region seems to be of crust-mantle mixed type. The granite porphyry and granitoid porphyry are the outcome of different evolutionary stages of magmas from the same source region. High oxidation state, strong evolution and more crust-contamination may be one of the important causes of a limited scale in Tongcun deposit.
The studied area is located in the SE of Mianeh and north of Zanjan, and it is a part of Western Alborz- Azarbaijan structural zone. This area consists of volcanic rocks including rhyolite, rhyodacite, dacite and pumiceous tuff with Oligocene age and andesitic lithic tuff with Eocene age. Acidic volcanic rocks crop out in the form of domes, lava flows and tuffs. Perlites crop out in lower part of the rhyolitic- rhyodacitic domes. All acidic rocks have shoshonitic nature and classified as peraluminous rocks. These rocks are characterized by LREE- rich patterns with high LREE/HREE ratio and distinctive negative Eu anomaly. There are distinctive positive anomalies of Rb, Th and Pb on the spider diagrams which is related to continental crust role in genesis and evolution of the parent magma. On the tectonic setting discrimination diagrams, these rocks are plotted within the Post-COLG setting. The overal petrographic, petrologic and geochemical evidences demonstrate that during the final stages of the continental collision, the thickened sub- continental lithosphere in the Alborz was delaminated and replaced by hot asthenosphere mantle. Rapid upwelling of hot asthenosphere gave rise to the partial melting of asthenosphere which is produced the Oligocene basaltic rocks near the studied area. Emplacement of basaltic magma in the upper part of the continental crust led to the partial melting of the crust and generation of the parent magma of the acidic rocks. Acidic lavas cooled rapidly and formed the glassy rocks such as obsidian which changed to perlite in contact with meteoric and warm waters.
We report results of laser ablation inductively coupled plasma-mass spectrometry-based dating, as well as the analysis of bulk-rock major and trace elements, and Sr–Nd isotopes to address the genesis and tectonic settings of the Yanshanian granitoids in neighbouring sections of Zhejiang, Jiangxi, and Anhui provinces (the WZG region) within the Yangtze block. Geochronological results indicate that intense magmatic activity took place during Jurassic to Cretaceous time in the WZG region. Three episodes can be clearly distinguished by their bulk-rock geochemistry. (1) Early–Middle Jurassic granitoids (180–170 Ma) have high Sr and low Yb content, high Nd(t) and low initial 87Sr/86Sr ratios, and weakly negative Eu anomalies. These granitoids are strongly enriched with LREE, Rb, K, and Th but are depleted of HREE, Nb, and Ta. (2) Late Jurassic to Early Cretaceous granitoids (165–140 Ma) have relatively low Sr and low Yb contents, as well as low Nd(t) and high initial 87Sr/86Sr ratios, with characteristics similar to those of the Early–Middle Jurassic granitoids in terms of the rare earth element and trace element patterns. (3) Early Cretaceous granitoids (140–120 Ma) have extremely low Sr and high Yb concentrations, as well as high SiO2 but low MgO, CaO, and Al2O3 content, with strong negative anomalies in Eu, Ba, Sr, P, and Ti. These characteristics indicate that the WZG Jurassic granitoids were related to northwestward subduction of the Izanagi plate, whereas the Early Cretaceous granitoids formed in a within-plate extensional setting. The time of transition between the two tectonic environments can be constrained to ∼140 Ma. This tectonic transition may be attributed to progressive slab roll-back of the Izanagi plate. The presence of two A-type granite belts in the WZG region probably reflects lithospheric thinning. The NE trend of the A-type granite belts indicates that this extension in Southeast China was controlled by underflow of the Izanagi plate.
Drilling at Soultz-sous-Forêts, France, conducted as part of the
European 'Hot Dry Rock' Project, penetrated the Rhine Graben basement
down to 5 090 m and revealed a porphyritic monzogranite. Chemical
composition and REE patterns of three samples at 5 km depth indicate
homogeneous composition with a slight vertical differentiation,
suggesting stable P- T conditions after the magma emplacement. U/Pb
ion-probe zircon dating provides an emplacement age at 331±9 Ma.
This age is in agreement with those of the other intrusive granitoids in
this part of the Variscan segment, indicating a period of intensive
magmatic activity around 330 Ma.
The study area is located about 20 km to the east of the Heris town in northwest Iran, and lies in the Alborz-Azarbaijan geological zone. The occurrence of lava domes associated with thick lava flows, volcanic breccias, and ignimbrite layers indicate an important eruptive center in the study area. The investigated volcanic rocks are of lower-middle Eocene time and associated with upper Eocene I-type granitoid intrusions. Hydrothermal fluids derived from the granitoid rocks, considered to be cogenetic with the volcanic rocks, led to local alteration and mineralization in the volcanic rocks. According to chemical classification, the volcanic rocks are andesite, andesitic-basalt and trachy-andesite. The textures vary from porphyry to microlitic porphyry and hyalomicrolitic and the phenocrysts are mostly plagioclase, alkali-feldspar, augite, hornblende and biotite. Sieve texture and selective alteration in some plagioclases, occurrence of biotite and hornblende with opacitic rims, associated with other disequilibrium textures are characteristic features of the rocks. Plots of the samples on the SiO2 vs. Na2O+K2O, AFM, and SiO2 vs. K2O diagrams show that, similar to the associated granitoids, the volcanic rocks are high- to medium- potassium calc-alkaline in nature. Chemical characteristics of the rocks suggest enrichments in a subduction zone or crustal contamination, rather than a within-plate enrichment trend. Plots of Rb/Ba vs. Ti/Y, and Nb/Zr vs. Nb show that the chemical composition of these rocks were controlled typically by fractional crystallization and the role of magma mixing was not significant in the evolution of the rocks. Plots of the samples on tectonic setting discrimination diagrams of basalts and andesites, based on Th, Ti, Zr, Nb, and Sr contents, indicate that the studied rocks belong to calc-alkaline volcanic arcs. Compared to andesitic rocks from typical tectonic environments, the compatible and incompatible elements patterns for the andesitic rocks from the study area are more consistent with a post-collision volcanic arc setting.
پیامبر خدا (صلیالله علیه و آله و سلّم) فرمودند:
هر گاه مؤمن یک برگه که روى آن علمى نوشته شده باشد از خود برجاى گذارد، روز قیامت آن برگه پرده میان او و آتش می شود و خداوند تبارکوتعالی به ازاى هر حرفى که روى آن نوشته شده، شهرى هفت برابر پهناورتر از دنیا به او میدهد.
سلام علیکم؛
ایزد دانا را سپاس میگویم که بنده را یاری بخشید تا بتوانم در زمینه تحقق اهداف خویش، گام بردارم. برای پاسداشت و ترویج علم مقدس زمینشناسی، پایان نامه کارشناسی ارشد خود در دانشگاه تهران را به همه فرهیختگان جامعه علمی زمینشناسی ایران تقدیم مینمایم. شایسته است انشالله همه بزرگواران امانت داری کامل علمی را رعایت بفرمایند. پیروزی و موفقیت شما را در تمامی امور زندگی آرزومندم.
دکتر رامین صمدی
In this paper the geological occurrence, geochemistry and mineralogy of ultrapotassic (K 2 O/Na 2 O > 3 (molar ratio)) and perpotassic (K 2 O/Al 2 O 3 > 1 (molar ratio)) igneous rocks, especially lamproites, are reviewed and discussed in the context of compositionally-similar mantle-derived melts.
Lamproites are K- and Mg-rich igneous rocks (typically K 2 O > 5 wt.%, MgO > 5 wt.%) which possess an exotic and diagnostic mineralogy and geochemistry. Known lamproites occur in 21 major suites or localities in continental regions with a variety of geological and tectonic environments; they range in age from the early Proterozoic dykes at Holsteinsborg, W Greenland, and Chelima, India, and Precambrian pipe at Argyle, W Australia, to the Middle Pleistocene flows and the Recent volcanics of the Leucite Hills, Wyoming, and Gaussberg, Antarctica, respectively. Intrusive and extrusive forms of lamproites include flows, a variety of pyroclastics (welded tuffs, piperno, air-fall tuffs, volcanic breccias etc.), cinder cones, dykes, sills and diatremes. Whereas kimberlite diatremes tend to be carrot shaped, the shape of olivine lamproite diatremes approximates a sherbet-glass. The recent discovery of diamondiferous lamproties of large volumetric proportion in the E and W Kimberleys, NW Australia, and the reclassification of the diamondiferous micaceous peridotite at Prairie Creek, Arkansas, as a lamproite substantiate their economic importance. The 21 lamproite suites considered here tend to be localized marginal to continental craton cores in areas that overlie fossil Benioff zones, in contrast with the general occurrence of kimberlites more interior to continental cratons.
The petrographic diversity of lamproites has historically hindered the development of a concise and universal classification and nomenclature. Lamproites are distinguished from kimberlites and alkali basalts (and lamprophyres) in terms of mineralogy, mineral chemistry, geochemistry and volcanic extrusive character. Relative to kimberlites, lamproites are enriched in K, Si, Ti, Al, Rb, Sr, Zr and Ba and depleted in CO 2 , Ca, Mg, Fe, Ni, Co and Cr. Lamproites are characterized by the general presence of phlogopite, diopside, leucite and K-richterite, occasional glass, olivine, sanidine, priderite, perovskite, wadeite, apatite and chrome spinel, and very rare ilmenite. Lamproite amphiboles, diopsides and phlogopites are distinctly depleted in Al 2 O 3 relative to those of nearly all other igneous rocks. Lamproite magmas are produced by the partial melting of old refractory mantle peridotite (approaching a dunite or harzburgite in mineralogy) that was enriched in K-bearing and other incompatible-element-enriched phases, such as phlogopite and apatite, most probably as a result of some metasomatic event which occurred prior to melting. In contrast with alkali basalt and kimberlite melts which are apparently produced from the partial melting of a CO 2 -enriched mantle periodtite (i.e. a source with a relatively high CO 2 /H 2 O ratio), water is the key volatile species involved with lamproite petrogenesis (source with a low CO 2 /H 2 O ratio).
New high precision ⁴⁰Ar/³⁹Ar ages are presented which more tightly constrain the eruption ages of the West Kimberley lamproites of northwestern Western Australia. The data show a southward progression in ages of the lamproites over a distance of ∼135 km, from ∼22.5 Ma in the northernmost lamproites of the Ellendale Field to ∼19 Ma in the Noonkanbah Field in the south, excluding the Walgidee Hill lamproite. The large (∼490 ha) zoned Walgidee Hills lamproite at the northern edge of the Noonkanbah Field is the youngest of the West Kimberley lamproites and represents a later pulse of lamproite magmatism at 17.4 Ma, >1 Ma after the main lamproite magmatism.
The southward progression of lamproite ages extends across a wide swath from the Proterozoic King Leopold Orogen at the southern margin of the Kimberley Craton to the Phanerozoic Fitzroy Trough in the Canning Basin. The magmatism does not appear to be the result of the migration of a mantle plume, but more likely reflects small degrees of partial melting of old, thick, metasomatised lithosphere extending from the craton margin beneath the basin, with melting triggered by regional uplift and/or small-scale mantle convection at the craton margin. Emplacement of the lamproites likely exploited ancient trans-lithospheric structures associated with the Proterozoic orogen at the craton margin and structures associated with the formation of the Canning Basin in the Phanerozoic.
The author offers an overview of the complex phenomenon of andesite genesis to help clarify the long-standing problem and to identify profitable areas for future research. It is considered that conventional explanations better account for more of the data than do the more elegantly simple theories produced by plate tectonic theory. -R.A.H.
The lamprophyres contain olivine and Ti-phlogopite phenocrysts in a groundmass of Ti-phlogopite, spinel, apatite, perovskite and carbonate.-K.A.R.
The IUGS Commisssion on Systematics in Petrology coordinates international efforts in the field of petrological nomenclature. To reconcile contrasting intepretations of what individual names mean in different languages in different countries is necessarily a complex and slow process. Nevertheless, one of the finest achievements of IUGS in setting international standards has been the now widely accepted modal classification of plutonic and volcanic rocks developed by the Commission. -Author
IGCP Project 163, which ended in 1985, designed and began the construction of a retrospective world data base for petrology that contains readily sortable and retrievable petrographic, mineralogical, chemical and geological data concerning igneous rocks of all types and ages. The present article describes the data base, IGBADAT, now being expanded and disseminated by the IUGS Subcommission on Data Bases for Petrology (a part of its Commission for Systematics in Petrology) and IGCP Project 239, each of which has a mandate considerably broader than that of Project 163. An account of how these new organizations plan to maintain, expand, and manage the data base is also given. (Author's abstract)-P.Br.
Kimberlitic, melilititic, trachytic, and carbonatite eruptives occur in association at Saltpetre Kop, Sutherland, South Africa. This magmatic assemblage is believed to have originated as a result of crystal fractionation, liquid immiscibility and crystal-liquid reaction phenomena operative in an ascending kimberlitic magma generated by limited mantle melting in the depth range 100–200 km. The kimberlitic rocks at Saltpetre Kop are considered to represent part of the original magma which erupted from a relatively low pressure regime (20–25 kb). Slow uprise of the remainder was accompanied by olivine fractionation, separation of an immiscible carbonatite phase and the onset of an olivine-liquid reaction resulting in the formation of olivine melilitite; continued fractionation of the magma to beyond the limit of melilite stability gave rise to the feldspathic assemblages of the trachytic eruptives.
The preceding chapters covering simple experimental systems give an indication of the ways in which natural magmas might be expected to evolve by processes involving liquid—solid fractionation during melting and crystallisation. This knowledge is part of the essential background to hypothesis formation. It enables us to make sensible initial guesses as to possible ways in which particular magmatic series may have formed. We also require a method of examining the compositional data of natural rocks which will enable the formulation of precise hypotheses and thus refine and test the initial ideas. However, this is only part of the problem and we shall see in later chapters how a consideration of the petrography of rocks and of melting experiments carried out on natural samples both contribute further to the refinement of hypotheses.
Volcanic activity takes many forms, ranging from quiet lava emissions to extremely violent and explosive bursts, many of which can be related to magma composition as discussed in Chapter 3. The kinds of eruptions can be correlated to volcano shapes and sizes, and in this chapter we explore the connection between pyroclastic systems, eruptive mechanisms and their influences upon juvenile particles.
Several previous chapters have been concerned with the way in which major element compositional data can be put to work in the formulation and testing of petrogenetic hypotheses. Trace elements have not so far been considered in detail because the way in which they are best handled is often substantially different from the treatment for major elements.
This book is about the petrology of kimberlites (and not about upper mantle xenoliths, diamonds, etc.). It aims to provide a comprehensive survey and critique of the advanaces made in kimberlite studies over the last 25 years. After chapters on kimberlite magmatism and the textural genetic classification of kimberlites, diatremes, and kimberlite provinces and their tectonic setting, there are important descriptions of the mineralogy and the geochemistry of kimberlites, followed by a discussion of relevant experimental studies, before a concluding statement on the petrogenesis and evolution of kimberlite magma.-R.A.H.
Basanites (which mineralogically should be characterized by an abundance of plagioclase and only a little feldspathoid) and
nephelinitic rocks (which normally lack modal plagioclase but should contain nepheline) are not easily distinguished in the
field, and both are commonly confused with basalts. Since the mineralogical distinction sometimes cannot be applied, as in
the case when no modal felsic minerals are apparent in the groundmass, a chemical distinction between nephelinitic and basanitic
rocks becomes desirable. The best solution is provided by the use of the CIPW norm with basanites recognized as having > 5%
normative ab and < 20% normative ne, melanephelinites as having < 5% normative ab and < 20% normative ne, and nephelinites
as having > 20% normative ne. It is proposed that melanephelinites defined in this manner can be further divided and that
rocks formerly termed olivine nephelinite should now be called olivine melanephelinite, and that the pyroxene-phyric, olivine-poor
melanephelinites should now be termed pyroxene melanephelinite.
The Tertiary flood-basalt sequence of eastern Iceland is intermittently disturbed by central volcanic activity with the voluminous eruption of acid magma. Associated with one of these central volcanoes, described in this paper, is an intense swarm of acid and basic dykes, a set of acid cone-sheets, and extensive superimposed hydrothermal alteration. The lavas and intrusions which make up the volcano grade in composition from olivine-tholeiites, through olivine-free tholeiites, basaltic-andesites, and andesites (icelandites), to rhyolites. This series is unusually rich in iron, titanium, and manganese, and poor in magnesium; alumina and total alkalis also tend to be low in the basic members. Magnetite (sensu lato) plays a varied role in the order of crystallization, and it is only in the intermediate stages of this fractionated series that magnetite is available for crystal fractionation. The otherwise progressive enrichment of iron relative to magnesium throughout the successive liquids of the series is halted during an intermediate stage, as magnetite becomes an early-crystallizing phase.
The chemical variability of 39 groups of igneous rocks has been investigated using a data base of 26,373 published analyses.
Each group was extracted from the data base using the name given in the reference from which the analysis was collected. The
numerical data for each group includes wt. per cent and molecular per cent means, standard deviations, C.I.P.W. norms, Niggli
values, the first three eigenvalues and eigenvectors together with a breakdown of the geographical distribution of the analyses
used. Nine variation diagrams are also given for each group.
Zusammenfassung Die IUGS hat eine Subcommission on the Systematics of Igneous Rocks gebildet mit dem Auftrag, Klassifikation und Nomenklatur der Eruptivgesteine zu überprüfen und ihr entsprechende Vorschläge vorzulegen. Die Subcommission hat sich zunächst mit Tiefengesteinen befaßt. Sie unterbreitet hier eine kurze Zusammenfassung der Empfehlungen für Plutonite, denen sie bei ihrer Sitzung in Montreal (August 1972) zugestimmt hat. Eine ausführlichere Darstellung ist in Vorbereitung.
Average chemical compositions are given for the common plutonic rock types and their volcanic equivalents. An attempt has been made also to give the general average chemical compositions of silicic, intermediate, subsilicic and ultramafic igneous rocks
In northeast India, Early Cretaceous lamprophyres intrude both the Gondwana (Permian-Lower Cretaceous) sedimentary sequence and older cratonic blocks. Spessartite is the typical lamprophyre of the Proterozoic Meghalaya craton; whereas a minette-lamproite suite intrudes the Gondwana coal-bearing sequence. Cores from exploration boreholes, and rocks from deep coal mines, have provided excellent fresh samples. The petrography, mineral chemistry, geochemistry and isotope geochemistry of such samples have been examined. Essential characteristics of the minette-lamproite suite are: (a) depletion in Ca, Al and Na; (b) enrichment in K, Ti and other incompatible elements; and (c) presence of phlogopite megacrysts of possible mantle origin.Preliminary Sr, Pb and Nd isotopic data demonstrate significant differences between the minette-lamproite suite and the spessartites.It is concluded that the minette-lamproite suite evolved from a primary magma generated by the partial melting of a carbonate-bearing harzburgite that had been extensively metasomatised.
Rocks consisting essentially of iron-titanium oxides and apatite occur as small intrusive-like bodies associated with anorthosites and some alkaline igneous complexes. They have a consistent composition of two-thirds by volume oxides and one-third apatite, and invariably have dikes rich in ferromagnesian minerals and apatite associated with them. Reconnaissance experiments in the system magnetite-fluorapatite indicate a eutectic at a composition of approximately two-thirds by volume of magnetite and one-third apatite, which provides an explanation for the common occurrence of rocks with this composition. Experiments indicate that eutectic mixtures of magnetite and apatite form immiscible liquids with silicate melts having the composition of the dioritic dike rocks commonly associated with oxide-apatite deposits. Mixtures of magnetite, diorite and apatite, containing apatite in excess of thirty percent form three immiscible liquids on melting: an apatite-rich one, a magnetite-apatite melt and a silicate melt. Analysis of coexisting magnetites and ilmenites from naturally occurring oxide-apatite rocks indicate temperatures of formation in the range of 850 to 1,000° C. Oxide-apatite rocks are concluded to have formed as immiscible liquids, which separated from magmas that underwent strong differentiation. It is postulated that high sodium contents in the silicate magmas play an important role in forming these immiscible liquids.
This contribution summarizes and brings up to date the recommendations made by the IUGS Subcommission on the Systematics of
Igneous Rocks for the classification of volcanic rocks when modal analyses are lacking. The classification is on a non-genetic
basis using the total alkali-silica (TAS) diagram, and is as nearly consistent as possible with the QAPF modal classification.
The diagram is divided into 15 fields, two of which contain two root names which are separated according to other chemical
criteria, giving the following 17 root names: basalt, basaltic andesite, andesite, dacite, rhyolite, trachybasalt, basaltic
trachyandesite, trachyandesite, trachyte, trachydacite, picrobasalt, basanite, tephrite, phonotephrite, tephriphonolite, phonolite
and foidite. Using Na-K criteria, trachybasalt may be further divided into the sub-root names hawaiite and potassic trachybasalt,
basaltic trachyandesite into the sub-root names mugearite and shoshonite, and trachyandesite into the sub-root names benmoreite
and latite.
Kimberlites are rare ultrabasic potassic low-volume melts that originate in the diamond stability field of the upper mantle. They are petrographically complex, and wide mineralogical and chemical variations suggest that they should be regarded as a group or clan rather than a single narrowly-defined rock type. In S African kimberlites there is a major division between highly-micaceous (Group II) kimberlites that are mineralogically, chemically and isotopically distinct from poorly-micaceous (Group I) kimberlites.
Nd and Sr isotope studies of diamondiferous olivine and leucite lamproites from NW Australia indicate that they are isotopically similar to Group II kimberlites but are distinct from Group I. New bulk rock analyses of Group II kimberlites indicate closer chemical similarities with olivine lamproites than previously supposed.
In this volume, an international team of scientists provides an up-to-date overview of the nature, origin, and evolution of alkaline magmas. Particular attention is paid to carbonatites, lamprophyres, and lamproites which are rock suites of current interest not recently reviewed elsewhere. Recent work on the classical alkaline provinces of East Africa, South Greenland, and the Kola Peninsula is included together with reviews of other areas of alkaline magmatism in North and South America, East Greenland, Europe, West Africa, and the ocean basins. Other papers discuss the impact of experimental isotopic and geochemical studies of the petrogenesis of alkaline rocks. This book will be of interest to petrologists and geochemists studying alkaline igneous rocks, and to other earth scientists as a reference on the rapidly expanding field of igneous petrology.
The IUGS Subcommission on the Systematics of Igneous Rocks recommends that volcanic rocks should be classified on a non‐genetic basis using the total alkali silica (TAS) diagram. This is divided into 14 fields, three of which contain two root names which are separated according to other chemical criteria, giving the following 17 root names: basalt, basaltic andesite, andesite, dacite, rhyolite, alkali rhyolite, trachybasalt, trachyandesite, trachyte, alkali trachyte, picrobasalt, basanite, tephrite, phonotephrite, tephriphonolite, phonolite and foidite. Using other simple parameters, trachybasalt may be further divided into the sub‐root names of hawaiite and potassic trachybasalt, and trachyandesite may be further divided into the sub‐root names of mugearite, shoshonite, benmoreite and latite.
At present one is not able to devise a single, standard classification of igneous rocks that is acceptable to all petrologists. This is mainly because igneous petrology consists of an uneasy union between the descriptive science of petrography and the explanatory science of petrogenesis, and at present the latter discipline is unable to provide a coherent model, or series of models, that can account for the origin and evolution ofall igneous rocks. Some of the more significant concepts used in the classification of volcanic rocks are examined, and three separate, yet complementary, classifications are presented.
The IUGS Subcommission on the Systematics of Igneous Rocks presents recommendation for the classification and nomenclature of volcanic rocks, lamprophyres, carbonatites and melilitic rocks. It is recommended to classify volcanic rocks according to mineral contents and by using the QAPF double triangle, provided that the modal mineral composition can be determined or estimated with sufficient approximation. Further recommendations refer to pheno-types, glass-bearing and glassy rocks, paleo-volcanic rocks and the definitions of several rock terms.Die IUGS Subcommission on the Systematics of Igneous Rocks legt Empfehlungen vor fr Klassifikation und Nomenklatur der Vulkanite, Lamprophyre, Karbonatite und Melilith-Gesteine. Vulkanite sollen — unter Verwendung des QAPF Doppeldreiecks — nach dem modalen Mineralbestand klassifiziert werden, sofern sich dieser genau genug bestimmen oder abschtzen lt; andernfalls mu die chemische Zusammensetzung herangezogen werden. Weitere Empfehlungen beziehen sich auf Phno-Typen, glasfhrende und glasige Gesteine, die sog. palo-vulkanischen Gesteine sowie auf Definitionen einiger Gesteinsnamen.La IUGS Subcommission on the Systematics of Igneous Rocks prsente des recommandations pour la classification et nomenclature des roches volcaniques, lamprophyres, carbonatites et roches mlilitiques. Il est recommand de classifier les roches volcaniques selon leur composition minralogique et en utilisant le double triangle QAPF, pourvu que la composition modale puisse tre dtermine avec une approximation suffisante; sinon, la composition chimique doit tre prise en considration. Des recommandations supplmentaires concernent les phno-types , les roches vitreuses, les roches dites palo-volcaniques et la dfinition de certains termes.
Normative minerals are an integral part of most chemical classifications of volcanic rocks; however, when calculating the norms of these rocks the ratio has a powerful influence on the abundance and nature of these minerals. This arises because when the norms of the common, non-peralkaline rocks are computed at low ratios (< 1.1), every molecular unit of Fe2O3 uses a molecular unit of FeO to form magnetite, thus releasing a molecular unit of SiO2. At higher ratios rocks eventually contain an excess of Fe2O3 relative to FeO, and normative haematite forms. One of the basalts examined in the present study is nepheline and olivine normative when its ratio is 0.2, olivine and hypersthene normative when the ratio is 0.5, and hypersthene and quartz normative when the ratio is 1.2. The precise nature of such changes in both normal and peralkaline rocks is examined; and the concept of a set of standard ratios is evaluated.The following standard ratios are recommended: foidite 0.15–0.40, picrobasalt 0.15, basanite/tephrite 0.20–0.30, basalt 0.20, trachybasalt 0.30, basaltic andesite 0.30, phonotephrite 0.35, basaltic trachyandesite 0.35, andesite 0.35, tephriphonolite 0.40, trachyandesite 0.40, dacite 0.40, phonolite 0.50, trachyte/trachydacite 0.50 and rhyolite 0.50.After examining many erroneous, and a few bizzare, norms that have been published in recent times, it is recommended that a standard igneous norm (SIN) should be developed and used. This programme should use a set of standardized iron oxidation ratios, and also be able to correct the anomalies inherent in the original CIPW system of calculation.
The major element compositions of the various rocks that belong to the basalt clan are examined, and the basalt clan is defined as consisting of those volcanic rocks that contain between 44.0% and 53.5% silica. After examining both the diverse tectonic environments in which the basaltic rocks are found, and also the various petrographic suites to which they belong, or appear to belong, new chemical criteria were devised to divide them into the following groups: (1) low-potash basalt, (2) high-alumina basalt, (3) continental-flood basalt, (4) komatiitic basalt, (5) sodic basalt, (6) hawaiite, (7) phonolitic basalt, (8) potassic basalt, (9) trachybasalt, (10) leucitite, (11) sodic transitional basalt, and (12) potassic transitional basalt. The lunar mare-basalts are regarded as being transitional in their chemical character between the low-potash, ocean-floor basalts and the komatiitic basalts. While it was relatively easy to discover petrogenetic models that were able to account for the origin and evolution of the common sub-alkalic basalts, and even the sodic basalts, a variety of possible petrogenetic models had to be explored in order to account for the origin and evolution of the different basaltic rocks of the potash- and high-potash series.
Previously reported initial 87Sr/86Sr and
143Nd/144Nd ratios of non-micaceous southern
African Cretaceous kimberlites indicate that their mantle source rocks
are undifferentiated to slightly depleted relative to the bulk
Earth1-6. Anomalously radiogenic Pb isotopic ratios of these
kimberlites, on the other hand, are smilar to those of oceanic island
basalts and indicate that the source regions have had high U/Pb
ratios7. Some micaceous kimberlites have a different Sr and
Pb isotopic character, reflecting different source regions characterized
by higher Rb/Sr, but lower U/Pb ratios1,2,7. Nd isotopic
analyses have not been reported for the micaceous kimberlites. I present
here new whole-rock Pb, Sr and Nd isotopic analyses of examples of both
types of kimberlite which, in conjunction with previously published
data, confirm the existence of both depleted and enriched upper mantle
sources for southern African Cretaceous kimberlites.
Ultramafic lamprophyres (UML) are rare but widespread, hypabyssal rocks, rich in K, Mg, Cr, Ni, Sr, Ba, REE, and volatiles, containing less Si and more Ca than other silicate igneous rocks, and grading into carbonatites. They carry phenocryst combinations of olivine (Fo 92–72 ), phlogopite (rich in Ti, Fe3+ , Ba or F), Al-Ti-(Fe3+ and richteritic to eckermannitic amphiboles. Groundmasses include Ca-Fe-Mg-carbonates (?partly primary), feldspathoids, Ca-Fe-Ti-Zr-garnets, soda-melilite, monti cellite, Mg-Mn-ilmenite, perovskite, serpentine, Fe- Mg-Ti-Mn-Cr-Al-spinels � glass. Megacrysts include (?cognate) salitic pyroxenes, phiogopites or Ti-hastingsites, and more rarely, xenocrystic Cr-Ti-pyrope, orthopyroxenes and diopsides. Xenoliths include spinel and/or garnet-lherzolites, dunites, and phlogopite�amphibole-bearing pendotites. UML are readily distinguished from kimberlites by petrological association (e.g. with ijolites), geochemistry (e.g. lower Mg, higher Ca, P), texture (e.g. lack of two olivine generations) and mineralogy (e.g. presence of groundmass feldspathoids � melilite). UML are distinguished also from melilitites by lower Si, Al, Na, higher Ca, K, P; more abundant primary carbonate, phiogopite and amphibole; and by lack of groundmass olivine and phenocryst melilite. Closer extrusive equivalents of UML may however occur among ankaratrites. The most common UML types are aln�ite (melilite-rich) and aillikite (melilite-free, carbonate-rich). Aillikites are compositionally closer to carbonatites than alnOites. Rarer types include poizenite (melilite + feldspathoids), ouachitite (feldspathoids + carbonates) and damkjernite (feldspathoids + carbonates+ < 10 per cent alkali feldspars). UML form localized dyke-swarms or diatreme-clusters, mainly related to continental rifting, and may represent parent magmas for coeval carbonatite complexes. Their additional occurrence in an oceanic setting, their mantle xenolith content, and their high mg , Cr and Ni, together suggest that many of them are primary, mantle-derived magmas, generated at depths between those of melilitites and kimberlites ( c . 100–150 km), but at higher CO 2 pressures than melilitites. Other UML, however, have been extensively modified from primary compositions by fractionation, accumulation, or interaction with alkali+volatile-rich fluids.
Kimberlites and their Xenoliths
- Dawson
Dawson, J.B., 1980. Kimberlites and their Xenoliths. Springer, Berlin, 252 pp.