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Petrogenesis and metallogenesis of the Kawuliuke Fe-P-Ti oxide-rich intrusive complex in the Kuluketage Block, northeastern Tarim Craton
Abstract
The Kawuliuke Fe-P-Ti oxide-rich intrusive complex is one of the largest layered mafic–ultramafic complexes associated with Fe-P-(Ti) oxide deposits in the Kuluketage Block, northeastern Tarim Craton, NW China. Here, based on new field observations, whole-rock trace element, radiometric dating analyses as well as Sr-Nd-Hf isotopes we propose a non-cogenetic origin of the parental magmas of the mafic–ultramafic rocks and syenite in the Kawuliuke intrusive complex (KIC), both of which formed synchronously at circa 808 Ma.
Geochemical characteristics and Sr-Nd-Hf-S isotopes ((⁸⁷Sr/⁸⁶Sr)i = 0.70437–0.70560; εNd(t) = -2.60 to −7.15; εHf(t) = -1.3 to −10.0; δ³⁴S = -2.98 ‰ to + 2.36 ‰), in combination with minerals composition and previous research, strongly indicate that the mafic–ultramafic rocks of the KIC formed via extensive crystal fractionation/cumulation of a tholeiitic magma, possibly derived from partial melting of an enriched subcontinental lithospheric mantle previously modified by slab-released fluids in a continental rift setting. The Kawuliuke syenite, meanwhile, is interpreted as generated by the emplacement of syenitic melts from the differentiation of newly coeval underplating basaltic magmas at depth based on lines of evidence from petrography, geochemical signatures and Sr-Nd-Hf isotopes. Our newly presented enriched Sr-Nd-Hf isotopic signatures, together with previous research, suggest that the enriched subcontinental lithospheric mantle could be metasomatized by asthenosphere mantle melts in different degrees. We further show the Kawuliuke clinopyroxenite-related apatite-rich oxide ores were the products of normal fractional crystallization/cumulation of H2O-Fe-P-Ti enriched residual magma in high oxygen fugacity condition, which experienced high differentiation. The tempo-spatial relationships of the KIC and other regional coeval mafic rocks jointly suggest that the KIC was most likely formed in response to the proposed mid-Neoproterozoic mantle plume in Tarim Craton, which likely induced partial malting of, and likely mixed with, the metasomatized subcontinental lithospheric mantle, to form the KIC with clinopyroxenite-related Fe-P-Ti oxide mineralization.
... Magmatic-related deposits are not only a significant source of P but also a potential source of rare earth elements (REE) (Frietsch, 1978;Jonsson et al., 2013;Taylor et al., 2019). This deposit type is typically found in association with alkali-calcic intermediate to felsic rocks and rare mafic-ultramafic intrusions in spatial and temporal terms (Chen et al., 2022;He et al., 2018;Jonsson et al., 2013;Tornos et al., 2016). The genesis of REE-rich apatite deposits is still being hotly debated. ...
... REE-bearing P deposits associated with mafic-ultramafic systems are less common than those associated with felsic systems. Only a few P-Fe deposits have been reported in ultramafic intrusions (Fanshan, Jiang et al., 2004;Sri Lanka, He et al., 2018), Kuluketage Block (Chen et al., 2022) and ophiolite mélanges (Orthys Complex, Greece, Mitsis & Economou-Eliopoulos, 2001; Lizard Complex, U.K., Hopkinson & Roberts, 1995). Despite their petrologic and economic importance, the origin of REE-rich P deposits associated with ultramafic magmatism remains unclear and controversial (He et al., 2018;Jiang et al., 2004). ...
... Iizuka & Hirata, 2005), and a beam diameter of 44 μm was utilized for all samples. The instrumental conditions, data acquisition and calculated parameters for Hf isotopes are described in Chen et al.(Chen et al., 2019;Chen et al., 2022). CHUR values of 176 Lu/ 177 Hf = 0.0336, 176 Hf/ 177 Hf = 0.282785(Bouvier et al., 2008) ...
The origin of giant rare earth element (REE)-rich phosphorus deposits related to ultramafic rocks is unclear. To characterize the genetic linkage between ultramafic rocks and P–REE mineralization, we investigated the whole-rock geochemistry, geochronology and Hf isotopic compositions, along with previously published data of barren and ore-bearing clinopyroxenites from the giant Shangzhuang REE-rich apatite deposit (containing about 51.1 million tonnes of P2O5 and 157,400 tonnes of REEs) in the Lajishan suture, Western China. The P–REE ores and barren biotite clinopyroxenites are composed predominantly of clinopyroxene and biotite, with high levels of apatite, amphibole, allanite, sulfide and oxide minerals in the ore-bearing samples. Zircon and allanite U–Pb ages for the barren and ore-bearing clinopyroxenites indicate they were formed between 467 and 465 Ma. The barren and ore-bearing samples are characterized by high CaO and low SiO2 contents, as well as similar Hf isotope ratios (εHf[t]: +3.4 to +7.7), indicating that they represent an ultramafic magma system and have been derived from a similar source. They are enriched in light REEs and depleted in Nb–Ta–Zr–Hf–Ti, similar to arc-related lavas found worldwide. The weakly evolved barren samples have high Ba/La, Rb/Y and Dy/Yb values, and their ages are coeval with calc-alkaline granitic plutons in the belt, which postdate the formation of the Lajishan ophiolite by ~30 myr. This suggests that the primary magma originated from garnet peridotite mantle modified by subducted Proto-Tethys oceanic crust-derived fluids in an arc setting. The presence of apatite intergrowth with cumulus clinopyroxene without alteration features indicates that the deposit has a magmatic origin. The ore-bearing clinopyroxenite contains higher contents of P, REEs, and high-field-strength elements than the barren clinopyroxenite, which could be attributed to the in situ accumulation of apatite and allanite in the residual magma. Thus, the formation of the P-dominated orebodies results from phosphate saturation due to the extensive fractionation crystallization of clinopyroxene and biotite during magmatic evolution. REEs were primarily enriched in the late-stage melt, which was compatible with apatite and allanite. We propose that the formation of the Shangzhuang REE-rich apatite deposit can be attributed to a simple differentiation of ultramafic melts in an evolved magmatic system.
... Dapingliang), a porphyry Cu-Au deposit (Qiongtage) and magmatic Fe-P-(Ti) oxide deposits (e.g. Kawuliuke, Daxigou) (Chen, 1989;Feng et al. 1995;Li et al. 1998;Yuan et al. 2002;Sun & Huang, 2007;Xia et al. 2009Xia et al. , 2011Xia et al. , 2012Cao et al. 2011Cao et al. , 2015Ye et al. 2013;Yuan et al. 2013Yuan et al. , 2014Yuan et al. , 2022Han et al. 2016;Chen et al. 2019bChen et al. , 2022. Among those deposits, the Fe-P-(Ti) oxide deposits (Kawuliuke, Qieganbulake, Aoertang, Daxigou and Duosike) were discovered in the southern Kuluketage block along the Xingdi fault (Fig. 1b), hosted in layered mafic-ultramafic-carbonatite complexes (Xia et al. 2008(Xia et al. , 2011Yuan et al. 2013Yuan et al. , 2022Cao et al. 2015;Han et al. 2016;Chen et al. 2019bChen et al. , 2022W. ...
... Kawuliuke, Daxigou) (Chen, 1989;Feng et al. 1995;Li et al. 1998;Yuan et al. 2002;Sun & Huang, 2007;Xia et al. 2009Xia et al. , 2011Xia et al. , 2012Cao et al. 2011Cao et al. , 2015Ye et al. 2013;Yuan et al. 2013Yuan et al. , 2014Yuan et al. , 2022Han et al. 2016;Chen et al. 2019bChen et al. , 2022. Among those deposits, the Fe-P-(Ti) oxide deposits (Kawuliuke, Qieganbulake, Aoertang, Daxigou and Duosike) were discovered in the southern Kuluketage block along the Xingdi fault (Fig. 1b), hosted in layered mafic-ultramafic-carbonatite complexes (Xia et al. 2008(Xia et al. , 2011Yuan et al. 2013Yuan et al. , 2022Cao et al. 2015;Han et al. 2016;Chen et al. 2019bChen et al. , 2022W. Chen, unpub. ...
... 840-810 Ma) in the northern rock belt of the Xingdi fault were the products of the differentiation of mantle-derived alkaline olivine basaltic magma and carbonatitic magma related to mantle plume activities, with the metallogenic specificity of Fe-P-(Ti) oxide deposits (e.g. Kawuliuke, Qieganbulake) (Fig. 1b;Cao et al. 2012Cao et al. , 2015Xia et al. 2012;Yuan et al. 2013;Han et al. 2016;Chen et al. 2019bChen et al. , 2022. Among those discovered Fe-P-(Ti) oxide deposits, only the Qieganbulake deposit contains carbonatites (Ye et al. 2013;Q. ...
The Qieganbulake deposit associated with a mafic–ultramafic–carbonatite complex in the Kuluketage block is not only the world’s second-largest vermiculite deposit, but also a medium-size carbonatite-related phosphate deposit. Field observations, radiometric dating results and Sr–Nd–Hf isotopes reveal that the parental magmas of the carbonatite and mafic–ultramafic rocks are cogenetic and formed synchronously at c . 810 Ma. Geochemical characteristics and Sr–Nd–Hf–S isotopes (( ⁸⁷ Sr/ ⁸⁶ Sr) i = 0.70581–0.70710; ϵ Nd (t) = −0.20 to −11.80; ϵ Hf (t) = −7.5 to −10.3; δ ³⁴ S = +0.7 ‰ to +3.0 ‰ (some sulfides with high δ ³⁴ S values (+3.2 to +6.6) were formed by late hydrothermal sulfur)), in combination with mineral compositions and previous research, strongly indicate that the Qieganbulake mafic–ultramafic–carbonatite complex formed via extensive crystal fractionation/cumulation and liquid immiscibility of a carbonated tholeiitic magma, possibly derived from partial melting of an enriched subcontinental lithospheric mantle previously modified by slab-released fluids and sediment input in a continental rift setting. The coupled enriched Sr–Nd isotopic signatures, in combination with previous research, suggest that the enriched subcontinental lithospheric mantle could have been metasomatized by asthenospheric mantle melts to different degrees. The Qieganbulake carbonatite-related phosphate ores were the products of normal fractional crystallization/cumulation of P–Fe ³⁺ complex enriched carbonatite magma in high oxygen fugacity conditions, which was generated by liquid immiscibility of CO 2 –Fe–Ti–P-rich residual magma undergoing high differentiation.
The nature of Precambrian metamorphic basement rocks and overall tectonic evolution of the Qaidam block in northern Tibet remains debated despite being important to understanding the assembly of Asia. Paleogeographic reconstructions of Precambrian supercontinents rarely consider Phanerozoic tectonic modification of its constituent Precambrian blocks. This issue is particularly relevant for the Qaidam block and its neighboring crustal fragments, which experienced significant Phanerozoic overprinting from multiple tectonic episodes. To address this problem, we systematically reviewed key geological observations and regional datasets related to Proterozoic magmatism, metamorphism, and sedimentation of major Precambrian blocks in China. This synthesis provided new constraints on the Proterozoic tectonic evolution of the Qaidam block, including paleogeographic supercontinent configurations and nature of multiple continental-drift-collision events. New results of field mapping, geochronological, and geochemical analyses allow us to divide the Precambrian rocks of the Qaidam block into four divisions: (1) Paleoproterozoic gneiss and schist; (2) Meso- and (3) Neoproterozoic metasedimentary rocks; and (4) Proterozoic intrusions. We propose that the Qaidam block was part of a “Greater North China” block, which experienced early Paleoproterozoic post-collisional extension and continental collision along the Paleoproterozoic Northern Margin orogen to form the Columbia-Nuna supercontinent. The Greater North China block subsequently experienced Mesoproterozoic extension related to supercontinent breakup. In addition, we propose that the Greater North China block was affixed to the western margin of Laurentia and Siberia as part of Rodinia in the Neoproterozoic, rifted in the late Neoproterozoic, and drifted in the early Paleozoic as a series of microcontinents.
An emerging consensus suggests that large igneous provinces (LIPs) are a significant driver
of dramatic global environmental and biological changes, including several Phanerozoic
mass extinctions, leading to plausible links with geological time scale (GTS) boundaries. LIP-
induced environmental changes are now being identified in the Precambrian record,
suggesting potential for the use of LIPs to define natural pre-Phanerozoic GTS boundaries.
There is now opportunity for more systematic integration of the sedimentary and LIP records …
In the past ten years, a great deal of geological study has been reported on the magmatic rocks exposed in the central and western region of the Kuluketage Block, while similar research in the eastern region has rarely been reported. In this paper, we report zircon U–Pb geochronological, zircon Lu–Hf isotopic, whole-rock elemental and Sr–Nd–Pb isotopic data for the Dapingliang intermediate-acid intrusive rocks in the eastern Kuluketage Block, in order to evaluate its petrogenesis and tectonic significance. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating provided a weighted mean ²⁰⁶ Pb/ ²³⁸ U age of 735 ± 3 Ma for the albitophyre (D1), 717 ± 2 Ma for the granite porphyry (D2) and 721 ± 1 Ma for the diorite porphyrite (D3). Geochemical analyses reveal that D1 and D2 belong to Na-rich alkaline A-type granites, and D3 shows the features of high-K calc-alkaline I-type granite. D1 and D2 are characterized by light rare earth element (LREE) enrichment and relative depletion of high field strength element (HFSE), with relatively flat heavy rare earth element (HREE) patterns and obviously negative Eu anomalies. D3 is characterized by the enrichment of LREE and depletion of HFSE, with negative slope HREE patterns and slightly negative Eu anomalies. In tectonic discrimination diagrams, D1 and D2 fall in the within-plate granite (WPG) field, indicating a rift setting. Although D3 falls within the volcanic arc granite (VAG) field, it most likely formed in a rift setting, as inferred from its petrology, Sr–Nd–Hf isotopes and regional tectonic evolution. Based on pronounced εNd ( t ), εHf ( t ), Pb isotopic data, TDM2 and high ( ⁸⁷ Sr/ ⁸⁶ Sr) i and elemental compositions, D1 was derived from the partial melting of basement amphibolites of the old lower crust. D2 originated from a mixture of the old lower crust and depleted mantle-derived magmas and was dominated by partial melting of the basement amphibolites of the lower crust. D3 could have been formed by partial melting of K-rich hornblende in the lower crust. Combining previous studies, we think that the c . 745–710 Ma magmatic rocks were formed in a continental rift setting. A partial melting scheme, triggered by underplating of mantle plume-derived magmas, is proposed to interpret the formation of c . 745–710 Ma A-type and I-type granitoids, mantle-derived mafic dykes, bimodal intrusive rocks, adakitic granites and volcanic rocks. These magmatic activities were probably a reflection of the break-up of the Rodinia supercontinent.
Highlights
(1) Circa 720 Ma magmatism in the eastern Kuluketage Block.
(2) Na-rich granite was derived from partial melting of basement amphibolites.
(3) The c . 745–710 Ma magmatic rocks were formed in a continental rift setting.
(4) The underplating of mantle plume-derived magmas is proposed.
During the past 50 years, many geological and ore-deposit investigations have led to the discovery of the Fe–P–(Ti)-oxide deposits associated with mafic–ultramafic–carbonatite complexes in the Kuluketage block, northeastern Tarim Craton. In this paper, we discuss the genetic and ore-forming ages, tectonic setting, and the genesis of these deposits (Kawuliuke, Qieganbulake and Duosike). LA-ICP-MS zircon U–Pb dating yielded a weighted mean ²⁰⁶Pb/²³⁸U ages of 811 ± 5 Ma, 811 ± 4 Ma, and 840 ± 5 Ma for Kawuliuke ore-bearing pyroxenite, Qieganbulake gabbro and Duosike ore-bearing pyroxenite, respectively. The CL images of the Kawuliuke apatite grains show core–rim structure, suggesting multi-phase crystallisation, whereas the apatite grains from Qieganbulake and Dusike deposits do not show any core–rim texture, suggesting a single-stage crystallisation. LA-ICP-MS apatite ²⁰⁷Pb-corrected U–Pb dating provided weighted mean ²⁰⁶Pb/²³⁸U ages of 814 ± 21 Ma and 771 ± 8 Ma for the Kawuliuke ores, and 810 ± 7 Ma and 841 ± 7 Ma for Qieganbulake and Duosike ores, respectively. The core–rim texture in apatite by CL imaging as well as two different ore-forming ages in the core and rim of the apatite indicate two metallogenic events for the Kawuliuke deposit. The first metallogenic period was magmatic in origin, and the second period was hydrothermal in origin. The initial ore-forming age of the Kawuliuke Fe–P–Ti mineralisation was ca 814 Ma and the second one was ca 771 Ma. On the other hand, the ore-forming ages of the Qieganbulake and Duosike deposits were ca 810 Ma and ca 841 Ma, respectively. Qieganbulake and Duosike deposits were of magmatic origin. Combined with previous geochronological data and the research on the tectonic background, we infer that the Kawuliuke, Qieganbulake and Duosike Fe–P–(Ti)-oxide deposits were formed in a subduction-related tectonic setting and were the product of subduction-related magmatism.
The origin of iron oxide-apatite deposits is controversial. Silicate liquid immiscibility and separation of an iron-rich melt has been invoked, but Fe-Ca-P-rich and Si-poor melts similar in composition to the ore have never been observed in natural or synthetic magmatic systems. Here we report experiments on intermediate magmas that develop liquid immiscibility at 100 MPa, 1000-1040 °C, and oxygen fugacity conditions (fO2) of ∆FMQ = 0.5-3.3 (FMQ = fayalite-magnetite-quartz equilibrium). Some of the immiscible melts are highly enriched in iron and phosphorous ± calcium, and strongly depleted in silicon (<5 wt.% SiO2). These Si-poor melts are in equilibrium with a rhyolitic conjugate and are produced under oxidized conditions (~FMQ + 3.3), high water activity (aH2O ≥ 0.7), and in fluorine-bearing systems (1 wt.%). Our results show that increasing aH2O and fO2 enlarges the two-liquid field thus allowing the Fe-Ca-P melt to separate easily from host silicic magma and produce iron oxide-apatite ores.
Phosphorus contents in cumulus rocks occurring close to the level of apatite appearance in the basic rocks of the Bushveld Complex, South Africa, provide a method of calculating the proportion of intercumulus component in these rocks. Previous experimental studies have accurately constrained the phosphorus content of magmas when apatite becomes stable. The ratio of the phosphorus content in the cumulates immediately below the appearance of apatite to this liquid composition defines the proportion of trapped liquid.
Application of this method to rocks from the uppermost mafic rocks of the Bushveld Complex leads to the conclusion that there is from 1 to 6 per cent intercumulus component. Many of these rocks are multiphase cumulates and in such rocks estimation of intercumulus component from textural criteria is difficult.
If crystals grow In situ on the floor of the magma chamber such small proportions of interstitial component can be produced without appealing to excessive diffusion and circulation of magma through an unconsolidated crystal pile. The geometry of the intrusion as well as its size might have a major influence on the proportion of the liquid ultimately solidifying within a cumulus rock.
Cumulate rocks of the Upper Main Zone and Upper Zone (UUMZ) of the Bushveld Complex South Africa, contain the world’s major resources of Fe-Ti-V±P, hosted in Ti-magnetite and apatite, and are commonly considered as having crystallized from the last major injection of magma into the magma chamber. In this study, we present the petrography, modal proportions, whole-rock major element chemistry (260 samples), electron microprobe data (∼ca.10,000 individual analyses for plagioclase, olivine, and pyroxene), and compiled analyses of Cr in magnetite (239 samples) for the UUMZ sampled over 2.1 km of the Bierkraal drill cores in the western limb of the Complex. The UUMZ section exhibits a broad normal fractionation trend upwards, but a series of reversals to more primitive anorthite contents in plagioclase, Mg# in pyroxenes and olivine, Cr in whole-rocks and Cr in magnetite separates are observed, accompanied by the appearance or disappearance of various minerals. Anorthosite or leucogabbro layers are closely linked to these reversals; the reversals in An % of plagioclase are used as boundaries to divide the UUMZ into 18 cycles. These cycles are interpreted as indications of magma chamber replenishment by plagioclase-laden magmas (up to 20 vol % plagioclase) and are also marked by spikes in Cr content. In addition, abundant Fe-Ti oxide-bearing plagioclase-rich rocks are identified in the lower half of the UUMZ. These have crystallized from a hybrid melt produced by the mixing of a new plagioclase-bearing magma batch and the resident magma. Further crystallization of this hybrid liquid may lead to the formation of magnetite layers in the lower part of the UUMZ. The Bushveld UUMZ therefore grew by multiple emplacements of crystal-laden magmas coming from deep-seated chambers. Slow cooling in a shallow chamber explains the systematic bottom-up compositional evolution in the cumulate pile within individual cycles. The residual melt reached silicate liquid immiscibility soon after the saturation of apatite. Thereafter, segregation of conjugate Fe-rich and Si-rich melts and crystallization of the paired melts produces cumulates with a smooth upward decrease in Fe-Ti oxides, while plagioclase mode increases in each apatite-bearing cycle. A comparison of systematic geochemical analyses and a detailed lithological stratigraphy between the different Bushveld limbs demonstrates the possible connectivity between the western and eastern Upper Zone but indicates notable differences with the Bellevue section of the northern limb.
Models for the nelsonite formation are currently highly contentious, with liquid immiscibility and fractional crystallization as frequently proposed formation mechanisms. The nelsonites in the Damiao massif anorthosite complex in the North China Craton are revisited here together with experimental evidence for the existence of silica-free CaO-FeO-Fe2O3-TiO2-P2O5 immiscible nelsonitic liquids. Our results of differential scanning calorimetry (DSC) and internally heated pressure vessel (IHPV) demonstrate that nelsonite with the composition of one-third apatite and two-thirds Fe-Ti oxides by weight 1) completely melts well above 1450 °C at dry condition, which is in good agreement with numerous experimental studies of the CaO-P2O5-FexO system for metallurgical purposes; 2) does not melt at the temperature up to 1200 °C with presence of considerable amount of volatiles, e.g., fluorine and water. Therefore, the composition of the nelsonite cannot be molten at temperatures relevant for crystallization of the Damiao magma. A review of experimental studies of liquid immiscibility and analyses of natural immiscible glasses show that all the liquids on the Fe- and P-rich side of the miscibility gap have at least 20 wt.% of aluminosilicate components.
Massif-type anorthosites, mainly Proterozoic in age, have long been recognized as a signature rock type of crust-mantle interactions in the Proterozoic Eon. The Daxigou Anorthosite Complex (DAC) is one such massif situated in the Kuluketage block, a tectonically important domain between the Tarim Craton and the Central Asian Orogenic Belt. In this contribution, a combination of geochronological and geochemical analyses of fine-grained DAC diabase are used to constrain the characteristics of the parental magma and the initiation time of DAC magmatism. We then pinpoint the DAC’s closure time by in-situ petrographic thin section U–Pb dating of zircon coronas around Fe-Ti oxides identified in a gabbroic anorthosite. Within data uncertainty, we find that the closing age of 1813 ± 9 Ma, is indistinguishable from the 1804 ± 7 Ma crystallization age of its last episode of parental magma. MELTS simulations of the parental diabase magma suggest a pressure of 8 kbar at a fayalite-magnetite-quartz oxygen fugacity leads to broadly observed mineral compositions and mineral phases. The bulk rock major and trace elements, integrated with the Sr–Nd and Hf isotopes in zircon, indicate that the DAC was formed by partially melting of a metasomatized sub-continental lithospheric mantle, which was likely induced by a post-collisional slab break-off with minor crustal assimilation. Finally, we propose that DAC magmatism can be ascribed to a series of Paleoproterozoic tectono-thermal events along the northern and southern margins of the Tarim Craton, which could have provided important implications for the Tarim Craton and the North China Craton associated with the assembly of Columbia supercontinent.
The Archean Mayurbhanj mafic complex in the Singhbhum Craton (eastern India) contains a magmatic Fe-Ti-(V) oxide ore deposit within a gabbro-norite-anorthosite suite of rocks. Immediate country rocks belong to the early Archean Gorumahisani greenstone belt and 3.1 Ga granitic complex. The gabbro-noritic rocks of the Mayurbhanj complex consist of plagioclase (An26-69), clinopyroxene (En42-54Fs4-36Wo22-42), and orthopyroxene (En67-81Fs15-28Wo4-5) as cumulus phases with Fe-Ti-oxides (magnetite and ilmenite) and sulfides (pyrite, pyrrhotite, chalcopyrite) as disseminated phases. Two-pyroxene thermometry yields temperatures of 1199°C - 956°C which are close to the primary liquidus temperature of pyroxene from a fractionated basaltic magma. The co-existing magnetite and ilmenite pairs in gabbro and magnetitite yield equilibrium temperatures of 498 - 797°C and oxygen fugacities of 11.38 - 27.1 (log fO2) reflecting various stages of cooling and subsolidus re-equilibration of the mineral phases. Disseminated sulfides are mainly present along the grain boundaries of accessory Fe-Ti oxide grains, within interstitial spaces of silicate minerals, as inclusions within the silicate minerals and along altered fracture zones of the silicate host whereas the magnetitite bodies are devoid of such sulfide mineralization. In-situ trace element analysis of oxide and sulfide minerals from the gabbro-noritic rocks and magnetitite ores reveals a higher concentration of Cr (22301 - 67433 ppm) and Ni (896 - 3880 ppm) in the magnetite of gabbro than in the magnetitite bodies. This is due to early fractionation of the accessory magnetite in the gabbro from a Fe-rich basaltic magma. The lower concentration of V (30211 - 34608 ppm) in the accessory magnetite of the gabbro-noritic rocks than in the magnetitite (48534 - 64855 ppm) suggests partitioning of vanadium into clinopyroxene within the gabbroic rocks. Higher chalcophile element (Pb ≈ 2 - 11 ppm, Zn ≈ 6773 - 8139 ppm, Mo ≈ 25 - 68 ppm) concentrations in magnetite of the gabbro-noritic rocks indicate equilibration with co-magmatic sulfide mineral assemblages. The partitioning behavior of HFSE (Zr, Hf, Ta, Nb) in the magnetite and ilmenite is mainly dependent on the Ti⁴⁺ content of the minerals. The rim of iron-oxide minerals around sulfide grains and negative Ni anomaly in the trace element pattern of pyrite suggest that these pyrite grains have formed after pyrrhotite which is magmatic in origin. Enrichment of Pb (≈ 27 - 3120 ppm), Ag (≈ 8 - 15 ppm), Bi (≈ 0.2 - 9 ppm), As (≈ 48 - 6561 ppm), and Sb (≈ 0.4 - 18 ppm) in a few pyrites suggests hydrothermal alteration of primary magmatic pyrite grains.
This chapter reviews the present-day composition of the continental crust, the methods employed to derive these estimates, and the implications of the continental crust composition for the formation of the continents, Earth differentiation, and its geochemical inventories. We review the composition of the upper, middle, and lower continental crust. We then examine the bulk crust composition and the implications of this composition for crust generation and modification processes. Finally, we compare the Earth's crust with those of the other terrestrial planets in our solar system and speculate about what unique processes on Earth have given rise to this unusual crustal distribution.
Presently, laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) is the main micro-analysis technique for isotopic ratios. It provides high precision and spatially resolved isotopic information in solid samples for earth science research. Data reduction of LA-MC-ICP-MS is inherently challenging owing to the severe mass spectral interferences and complex mass bias behaviors that occur during the analytical process. In this study, we present a new freeware software, Iso-Compass, for isotope data reduction of LA-MC-ICP-MS. This software provides highly practical functions, including simple data input, arbitrary selection of laser and background signals, background correction, internal or external mass bias correction, interference correction, visual data presentation, and formatted data output. These functions can achieve easier and more efficient data reduction of LA-MC-ICP-MS. The flexible formula editing mode enables Iso-Compass to be used in different isotope systems, thereby offering the potential to become a universal isotope data reduction platform in the geochemical community. Moreover, we present two application examples (radiogenic Sr isotope analysis and stable Zr isotope analysis) to demonstrate the effectiveness of Iso-Compass.
Many Fe-Ti oxide bodies associated with anorthosite suites and with some tholeiitic plutonic bodies have cross-cutting relationships with their host rocks suggesting that they may have been emplaced as oxide melts. Pure Fe-Ti oxides melt at temperatures much higher than is considered to be geologically realistic, so various fluxes (mainly apatite, fluorine, or carbon) have been called upon to stabilize the melts down to plausible temperatures. This review traces our experimental attempts to test the effectiveness of proposed fluxes and therefore to demonstrate the existence of such melts at geologically realistic temperatures. Neither F-apatite nor carbon act to stabilize Ti-rich Fe-Ti oxide melts at 1300 °C and below, and we conclude that-unless some totally unforeseen material does serve as a flux-Fe-Ti oxide magmas almost certainly do not exist. Although our data are not conclusive, it appears that increasing contents of FeO (and possibly TiO2) and P2O5 mutually enhance their solubilities in silicate melts, allowing extensive buildup of those components in melts residual to anorthosite. We interpret that oxide orebodies form by gravitational accumulation of crystalline oxides from such liquids. Once those melts become saturated with either Fe-Ti oxides or apatite, both phases will tend to co-precipitate, thus explaining the common occurrence of apatite with oxide orebodies ("nelsonites"). Cross-cutting oxide bodies were probably emplaced as crystalline oxides, possibly lubricated by small amounts of residual silicate liquid. Oxidation of the Fe2TiO4 component in initially ulvospinel-rich spinel and concomitant formation of ilmenite grains by granule-oxy-"exsolution" may have weakened the crystalline oxide and facilitated its flow during emplacement. It seems clear, though, that the presence of carbon does stabilize Ti-poor iron oxide melts to very low temperatures (at and even below 1000 °C), consistent with the (disputed!) magmatic origin of the magnetite lavas at El Laco, Chile.
The geometry and spatial distribution of mafic dyke swarms provide information about geodynamics. However, mapping large-scale dyke swarms manually is a time-consuming and expensive process. Here we present an efficient method to map dyke swarms semi-automatically by using multi-resolution remote sensing images. This method is applied in the Kuluketage region in the northeastern Tarim Block, northwest China where mafic dykes of multiple trends are widely exposed and with the dominant NW trend being of probable Neoproterozoic age. The tracing of dykes, including their orientation, length, thickness, density, and distribution is done by integrating 30-m multispectral Landsat 8 and 2-m panchromatic CORONA KH-4B imagery. The Gramm-Schmidt Spectral Sharpening approach is used to generate color composite and fusion images with 2-m resolution. The Canny edge detector and Hough transform are used to detect dyke edges. Combining the detection of dyke edges with ArcGIS™, the dyke orientation, length, density, thickness, and exposed area are measured. The accuracy of the semi-automatic method exceeds 75% in comparison with manual mapping of the dykes in the Kuluketage region.
The Wajilitag and Puchang intrusive complexes of the Tarim large igneous province (TLIP) are associated with significant resources of Fe–Ti oxide ores. These two mafic–ultramafic intrusions show differences in lithology and mineral chemistry. Clinopyroxenite and melagabbro are the dominant rock types in the Wajilitag complex, whereas the Puchang complex is generally gabbroic and anorthositic in composition with minor plagioclase–bearing clinopyroxenites in the marginal zone. Disseminated Fe–Ti oxide ores are found in the Wajilitag complex and closely associated with clinopyroxenites, whereas the Puchang complex hosts massive to disseminated Fe–Ti oxide ores mainly within its gabbroic rocks. The Wajilitag intrusive rocks are characterized by a restricted range of initial ⁸⁷Sr/⁸⁶Sr ratios (0.7038–0.7048) and positive εNd(t) (+0.04–+3.01), indicating insignificant involvement of continental crustal contamination. The slightly higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.7039–0.7059) and lower εNd(t) values (–1.05–+2.35) of the Puchang intrusive rocks also suggest that the isotopic characteristics was controlled primarily by their mantle source, rather than by crustal contamination. Both complexes have Sr–Nd isotopic compositions close the neighboring kimberlitic rocks and their hosted mantle xenoliths in the TLIP. This indicates that the ferrobasaltic parental magmas were most probably originated from partial melting of a metasomatized subcontinental lithospheric mantle, modified recently with subduction–related materials by the impingement of the ascending mantle plume. The recycled subduction–related materials preserved in the lithospheric mantle could play a key role in the formation of the parental Fe–rich magmas in the context of an overall LIP system. The distinct variations in mineral assemblage for each complex and modeled results indicated that the Wajilitag and Puchang complexes experienced different crystallization path. Fe–Ti oxides in Wajilitag joined the liquidus earlier in the crystallization sequence, especially relative to the crystallization of plagioclase. This is attributed to the relatively high TFeO, TiO2 and initial H2O contents of the parental magma. In combination with definitive field and petrological evidence, the enrichment of highly incompatible elements (e.g., Zr, Hf, Nb and Ta) and the depletion of rare earth elements in the Fe–Ti oxide ores is consistent with the plausible interpretation that the ores could be formed by fractional crystallization and crystal accumulation of the Fe–Ti oxide crystals from the ferrobasaltic parental magmas. A considerable amount of the Fe–Ti oxides in the Puchang has transported and sunk from higher up in the chamber to the underlying unconsolidated silicate crystal pile. The highly dense Fe–Ti oxide crystal slurries further tended to effective accumulate Fe–Ti oxides to form high–grade Fe–Ti oxide ore bodies, and subsequent rapid collapse and intrusive into lower lithologies within the complex under a H2O–rich environment during the late–stage of magmatic differentiation. The development of massive Fe–Ti oxide ores in the case of the Puchang, could plausibly result from a combination of the protracted differentiation history of a Fe highly enriched parental magma and the later addition of external H2O from the country rocks (e.g., carbonates) to the slowly cooling magma chamber.
In situ Sr isotope analysis of geological materials by laser ablation multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) is a powerful tracer technique for tracking magmatic source components and geological processes. However, the accuracy and precision of the ⁸⁷Sr/⁸⁶Sr ratio are limited in the analysis of natural minerals because of the low-Sr concentration, the isobaric interference or small grains with complex textural contexts, especially for transparent minerals such as feldspars. In this study, analytical results demonstrated that ablation rates in fs laser ablation were consistent for various samples (0.08-0.11μm per pulse), but those in ns laser ablation were obviously material properties-dependent, such as the rates of 0.026μm per pulse and 0.144μm per pulse for feldspar and pyrite, respectively. In addition, at similar energy fluences, the sensitivities of Sr in feldspars analyzed by the fs laser were 3.4 times higher than those analyzed by the ns laser due to the higher ablation efficiency of the fs pulse. These advantages of the fs laser not only offer the benefit of eliminating or weakening the matrix effect during the laser ablation processes but also help to improve the analytical precision for transparent minerals. We also demonstrated that the isobaric interferences of calcium dimers and argides (CaAr⁺+CaCa⁺) and Kr⁺ were dramatically reduced by factors of 6.5-11.7 and 5-12.5 in the presence of 6-12mlmin⁻¹ N2, respectively. Furthermore, with the addition of N2 (12mlmin⁻¹), the sensitivity of Rb was inhibited, resulting in a decrease of 1.47 times in Rb/Sr signal ratios. Due to the effect of suppressing interferences by adding N2, both the stability and accuracy of the ⁸⁷Sr/⁸⁶Sr and ⁸⁴Sr/⁸⁶Sr ratios show improvement, especially for the Rb-rich feldspars.Combining the advantages of the fs laser system with the addition of nitrogen, an improved in situ Sr isotope analytical method is then developed. The satisfactory accuracy and precision of the ⁸⁷Sr/⁸⁶Sr ratio from natural plagioclases, a K-feldspar with high Rb/Sr ratios (0.46) and a low-Sr clinopyroxene were obtained, demonstrating the reliability of the proposed method. Four feldspars, which have different contents of the major elements, Sr and Rb, showed homogeneous Sr isotope compositions and were recommended as potential suitable reference materials for in situ Sr isotope analysis. As an application, two plagioclases in mafic microgranular enclaves (MMEs) with small grain sizes (200-300μm) and wide ranges of Rb/Sr ratios were analyzed and showed obvious variations of the ⁸⁷Sr/⁸⁶Sr ratios from core to rim, which indicated that the proposed method in this study can provide high spatial resolution geochemical information for a single mineral.
The origin of magmatic episodes between final assembly and initial breakup of Rodinia is crucial for deciphering geodynamic transition and continental crust growth processes. However, few igneous rocks were identified during the quiescent time from 900 Ma to 830 Ma in the Tarim Craton. Along its northwestern margin, our field investigations identified abundant granitic debris in the Cryogenian Qiaoenbrak Group. Zircon U-Pb age determination revealed crystallization age at ca. 850 Ma. Detrital zircon crystals within Cryogenian to Ediacaran clastic rocks and schists of the basement Aksu Group also contain a major population having crystallized at ca. 860-840 Ma. Thus, we suggest that a hitherto unknown major magmatic event occurred ca. 850 Ma ago in northern Tarim. Granite gravels exhibit typical fractionated granite features, with high values of SiO2 (73.1-75.7 wt%), alkali oxides (Na2O + K2O = 7.8-8.7 wt%) and Na2O/K2O (avg. 1.3 wt%), and low values of P2O5 (≤ 0.04 wt%) and A/CNK (0.87-1.01), together with Rb, Th, U and K enrichment, and depletion in Nb, Ta, Sr, P, Ti and Eu, negative Eu anomalies (δEu = 0.21–0.74) and fairly low Ga/Al ratios. Including detrital crystals, ca. 850 Ma zircon crystals display a large range of εHf(t) values from -17.0 up to +11.6. Elemental and zircon Hf isotopes suggest that granites were derived from melting of juvenile lower crust, with addition of reworked upper crust and mantle-derived melts. We propose (1) before ca. 850 Ma, arc-continental collision setting related to southward accretionary assembly along Tarim margin, (2) progressive assembly of Tarim Craton, and (3) position of Tarim Craton within Rodinia supercontinent probably closer to North India Block than to Australia at ca. 850 Ma.
The Tarim Craton is an important tectonic unit and a suitable target to investigate and understand the Proterozoic tectonic framework of the Central Asian orogenic belt and supercontinent Rodinia. Mafic-ultramafic-carbonatite rocks are widely distributed in the Quruqtagh domain of NE-tarim. In Quruqtagh, Cu-Ni, Fe-P and apatite-vermiculite deposits hosted in the mafic-ultramafic-carbonatite rocks occur in the Xingdi, Qieganbulake, Daxigou and Kawuliuke. These deposits related to the mafic-ultramafic-carbonatite rocks in Quruqtagh formed in the period between Paleoproterozoic and Neoproterozoic. The Paleoproterozoic Fe-P deposit is represented by the Daxigou deposit that yielded a SIMS U-Pb zircon age of 2 452± 10 Ma. The other Cu-Ni, Fe-P and apatite-vermiculite deposits hosted in the mafic-ultramafic rocks formed in the Neoproterozoic, represented by the Xingdi, Kawuliuke and Qieganbulake deposits that formed between 812 Ma and 707 Ma. The Paleoproterozoic mineralization event was coincident with the global collisional events that led to the assembly of the Paleo-Mesoproterozoic Columbia (Nuna) supercontinent. And the emplacement of these Neoproterozoic mafic-ultramafic-carbonatite rocks was related to a mantle plume event that led to the breakup of the Tarim Craton from the Rodinia supercontinent.
The Xingdi II mafic–ultramafic complex is located in the northern rim of the Tarim Craton, Northern Xinjiang, NW China. This complex is mainly composed of gabbro, gabbronorite, websterite and lherzolite, plus minor granodiorites and granites. The geodynamic setting of this complex and other Neoproterozoic mafic–ultramafic complexes in the region is debated, with opinions varying from mantle plume to a continental arc. A new zircon U–Pb age from this study reveals > 7-myr difference for two gabbroic intrusive phases in the Xingdi II mafic–ultramafic complex and up to a 21-myr difference between this complex and the nearby mafic–ultramafic complexes that occur < 12 km from this complex. The age changes for the Neoproterozoic (730–820 Ma) mafic–ultramafic complexes in the area occur in different directions and hence a mantle plume origin for the complexes is unlikely. The Xingdi II mafic–ultramafic intrusive rocks are characterized by moderate light-REE enrichments and pronounced negative Nb anomaly, which are common for mafic–ultramafic rocks in convergent tectonic settings, and negative εNd(t) values (− 9.2 to − 5.1) and elevated initial ⁸⁷Sr/⁸⁶Sr ratios (0.7061 to 0.7086), which indicate enriched source mantle plus crustal contamination. The εHf(t) values of zircon crystals from the Xingdi II mafic–ultramafic complex are between − 2.8 and − 7.0. The trace element and isotope data together indicate that this complex formed from multiple pulses of contaminated subduction-related basaltic magma that were emplaced separately with a time gap of at least 7 myr. The results from this study support the viewpoint that in the Neoproterozoic the northern rim of the Tarim Craton was an active continental margin that belongs to the Circum-Rodinia Subduction System.
A single mantle plume model for the Neoproterozoic mafic-ultramafic intrusive rocks (760–820 Ma) in the northern rim of the Tarim Craton (Kuluketage, Xinjiang, China) is not supported by the protracted nature of magma emplacement that does not show a hot spot track, and whole-rock trace element compositions that clearly show arc signatures. New and previous zircon U-Pb age data reveal an age difference of up to 11 myr for a single mafic-ultramafic intrusive complex and an age difference of up to 32 myr for two mafic-ultramafic intrusive complexes separated by only ∼10 km. Such age differences are more than 2–5 times the analytical uncertainties. No major faults are present between the two intrusive complexes with different ages so their original distance is still well preserved. In addition, the age change of the mafic-ultramafic intrusive rocks in the region occurs in different directions. The temporal-spatial distribution of these rocks can be well explained by subduction-related magmatism that can last for a very long period of time at the same location. The protracted Neoproterozoic mafic-ultramafic intrusive rocks in the Kuluketage district are all characterized by moderate light rare earth element enrichments, pronounced negative Nb-Ta anomalies and low εNd(t) values (1 to -11) coupled with elevated initial ⁸⁷Sr/⁸⁶Sr ratios (0.706 to 0.71), which are consistent with the products of arc basalts contaminated with crustal materials. The results from this study support the notion that the northern margin of the Tarim Craton was part of the Neoproterozoic Circum-Rodinia Subduction System.
In many large, layered, mafic-ultramafic intrusions worldwide cumulus apatite commonly occurs in the highly fractionated Fe-Ti oxide-rich lithological units at the top of the intrusions and the associated plagioclase and olivine, if present, have An content <50 mol% and Fo content <40 mol%. These are not true for several Fe-Ti oxide ore-bearing mafic-mafic intrusions in the Emeishan large igneous province, SW China. A good example is the Taihe intrusion, which is described in this paper. In this intrusion the associated olivine and plagioclase are significantly more primitive, containing 69 mol% Fo and 59 mol% An, respectively. MELTS simulation reveals that such unusual association is the result of previous cotectic crystallization of Fe-Ti oxides with silicate minerals during magma evolution under oxidizing condition close to that of nickel–nickel oxide buffer. Supports for this new model include the observed upward decrease in plagioclase An contents coupled by lack of significant change in original olivine Fo contents in the Fe-Ti oxide ore-bearing sequence below the apatite-rich horizon, which is in turn supported by the facts that Fe-Ti oxide crystallization has a counter effect on MgO/FeO, but no effect on CaO/Na2O in the residual magma and that the addition of Fe-Ti oxides in the cumulus assemblage expedites the arrival of apatite on the liquidus. Our new findings support the interpretation that the oxide ores in the Taihe intrusion formed by gravitational accumulation of Fe-Ti oxides crystallizing from a basaltic magma, not a Fe-Ti-P-rich immiscible liquid segregated from such magma.
The Bushveld Complex in South Africa is the largest layered intrusion on Earth. Its upper part is known for huge resources of iron, titanium, vanadium and phosphorus. Associated with the layered character of the rocks, these resources are enriched at certain levels of the intrusion, which makes it important to understand the formation processes of those layers. In this paper we give an introduction and overview of recent debates and challenges.
The Tarim Craton is an important tectonic unit and a suitable target to investigate and understand the Proterozoic tectonic framework of the Central Asian Orogenic Belt and supercontinent Rodinia. Precambrian ultramafic–mafic-carbonatite rocks are widely distributed in the Quruqtagh domain of NE-Tarim. In the Quruqtagh, Cu-Ni, Fe-P and apatite-vermiculite deposits hosted in the ultramafic-mafic-carbonatite rocks occur in the Xingdi, Qieganbulake, Daxigou, and Kawuliuke. These deposits associated with the ultramafic-mafic-carbonatite rocks in Quruqtagh formed in a period between the Paleoproterozoic and Neoproterozoic. The Paleoproterozoic Fe-P deposit is represented by the Daxigou deposit that yielded a SIMS U-Pb zircon age of 2452 ± 10 Ma. The other Cu-Ni, Fe-P and apatite-vermiculite deposits, hosted in the ultramafic–mafic rocks, formed in the Neoproterozoic, represented by the Xingdi, Kawuliuke, and Qieganbulake deposits that formed between 812 Ma and 707 Ma. The Paleoproterozoic mineralization event was coincident with the global collisional events that led to the assembly of the Paleo-Mesoproterozoic Columbia (Nuna) supercontinent. And the emplacement of these Neoproterozoic ultramafic-mafic-carbonatite rocks was related to a mantle plume event that led to the breakup of the Tarim Craton from the Rodinia supercontinent.
The Taihe intrusion is one of the layered intrusions situated in the central zone of the Emeishan Large Igneous Province (ELIP), SW China. The cyclic units in the Middle Zone of the intrusion are composed of apatite-magnetite clinopyroxenite at the base and gabbro at the top. The apatite-rich oxide ores contain 6-12 modal% apatite and 20-50 modal% Fe-Ti oxides evidently distinguished from the coeval intrusions in which apatite-rich rocks are poor in Fe-Ti oxides. Most of apatites of the Taihe Middle and Upper Zones are fluorapatite, although four samples show slightly high Cl content in apatite suggesting that they crystallize from a hydrous parental magma. Compared to the apatite from the gabbro of the Panzhihua intrusion, situated 100 km to the south of the Taihe intrusion, the apatite of the Taihe rocks is richer in Sr and depleted in HREE relative to LREE. The calculated magma in equilibrium with apatite of the Taihe Middle and Upper Zones also shows weakly negative Sr anomalies in primitive mantle normalized trace element diagrams. These features indicate that the apatite of the Taihe Middle and Upper Zones crystallizes after clinopyroxene and before plagioclase. The apatite of the Taihe Middle and Upper Zones shows weakly negative Eu anomalies suggesting a high oxygen fugacity condition. The high iron and titanium contents in the oxidizing magma result in crystallization of Fe-Ti oxides. Crystallization of abundant Fe-Ti oxides and clinopyroxenes lowers the solubility of phosphorus and elevates SiO2 concentration in the magma triggering the saturation of apatite. The positive correlations of Sr, V, total REE contents and Ce/Yb ratio in apatite with cumulus clinopyroxene demonstrate approximately compositional equilibrium between these phases suggesting they crystallized from the same ferrobasaltic magma. Early crystallization and accumulation of Fe-Ti oxide together with apatite produced the apatite-rich oxide ores at the base of the cyclic units of the Taihe Middle Zone.
The Bushveld Complex (South Africa) is the largest layered intrusion on Earth and plays a considerable role in our understanding of magmatic differentiation and ore-forming processes. In this study, we present new geochemical data for apatite-hosted multiphase inclusions in gabbroic cumulates from the Bushveld Upper Zone. Inclusions re-homogenized at high-temperature (1060-1100 °C) display a range of compositions in each rock sample, from iron-rich (35 wt.% FeOtot; 28 wt.% SiO2) to silica-rich (5 wt.% FeOtot; 65 wt.% SiO2). This trend is best explained by an immiscible process and trapping of contrasted melts in apatite crystals during progressive cooling along the binodal of a two-liquid field. The coexistence of both Si-rich and Fe-rich immiscible melts in single apatite grains is used to discuss the ability of immiscible melts to segregate from each other, and the implications for mineral and bulk cumulate compositions. We argue that complete separation of immiscible liquids did not occur, resulting in crystallization of similar phases from both melts but in different proportions. However, partial segregation in a crystal mush and the production of contrasting phase proportions from the Fe-rich melt and the Si-rich melt can be responsible for the cyclic evolution from melanocratic (Fe-Ti-P-rich) to leucocratic (plagioclase-rich) gabbros which is commonly observed in the Upper Zone of the Bushveld Complex where it occurs at a vertical scale of 50 to 200 m.
A super-large vermiculite-apatite deposit originated from the Qieganbulak ultrabasic complex and is located in Southern Kuluketage fault block, northeastern margin of Tarim. A study of the Sm-Nd isotope composition of Qieganbulak ultrabasic complex make known isochron age 802 ± 52Ma, εNd (t) = 0.471, and its model age (tTMNd ) in the range of 1206 - 1635Ma, in dicates that the complex was formed in the late stage of the Upper Proterozoic Subera. In combination with its facies association, petrochemistry, REE Patterns, trace elements, C, 0, Sr isotopic compositions and associated vermiculite-apatite orebodies, it is believed that the Qieganbulak complex magma derived from the enrich-mantle Source formed by mantle metasomatism and formed in continental rift.
This paper analyzed the polyphase tectono - magmatism features, the LA - ICP - MS zircon U - Pb ages on the Precambrian igneous rocks and cinematic sense of ductile shear for the Xingdi fault zone. Results suggest that four - phase tectonic evolution took placed in the Xingdi fault zone including two phases of Precambrian tectonism. The first event took place in pre - Nanhua Period that is characterized by strong folding, ductile shearing and magmatism. The second event occurred in the Nanhua - Sinian Period when bimodal magmatism, composite magmatic flow and basic dyke swarm were widely developed, followed by a large - scale glacier and depressions, which is corresponded with the Rodinia supercontinental breakup. The LA - ICP - MS zircon U - Pb dating data reveal that a Meso - Neoarchean and Paleoproterozoic basement is likely buried under the deep part of studied area, dating at 3114 ± 20Ma, 2509 ± 42Ma and 1916 ± 36Ma on the captured zircons from gabbro. The dating results on the bimodal igneous rocks show that a peak bimodal magmatism took place during the 820 - 800Ma (798 ± 7Ma for granitic dyke and 816 ± 15Ma for diabase dyke). Cinematic analysis suggests that two phases of pre - Nanhua ductile deformation occurred in the Xingdi fault zone whereas the deformed age is not clear. The first belongs to a top - to - the north thrusting and the second - phase is a dextral strike - slip deformation along a sub - E - W direction. Since Nanhua Period, regional metamorphism and ductile shearing were very weak, only ductile - brittle deformation was widely developed.
Kuluketage block is one of the best areas for Precambrian geology studies in Xinjiang, however, the regional metallogeny of the research area is still too poon. In this paper, all the published literatures are summarized. Then, the geology of main ore deposits and the classified metallogenic series in this block are systematically described. The following seven tectonothermal periods are distinguished: Archean crust nucleus growing stage (3.3-3.0 Ga), Neoarchean-Paleoproterozoic crust growth and transformation stage (2.6-2.3 Ga), middle-late Paleoproterozoic crust transformation stage (2.1-1.8 Ga), Late Mesoproterozoic to Early Neoproterozoic orogeny stage (1.1-0.86 Ga), Middle Neoproterozoic orogenic extensional stage (830-800 Ma), middle-late Neoproterozoic intracontinental breakup stage (770-630 Ma) and Early Paleozoic land building stage. Mineralization mainly occurred at Paleoproterozoic, Neoproterozoic and Early Paleozoic. According to the ore-forming tectonic settings, ore-bearing rock formations and ore deposit genesis, six typical metallogenic series are identified in our study, including Fe-P-Cu-Au metallogenic series formed at Paleoproterozoic crust growth and transformation stage, Cu-Au metallogenic series formed at Early Neoproterozoic orogeny stage, Cu-Mo-Au-Fe-P-REE metallogenic series formed at Neoproterozoic post-collision stage, Cu-Ni metallogenic series formed at Neoproterozic rifting stage, Ag-V-Mo-Au-U-P metallogenic series formed at Early Paleozoic sedimentary basin and Cu-Au metallogenic series formed at Early Paleozoic arc subduction stage.
Qieganbulake complex located in the southwest margin of the Kuluketage massif, as a block mass, was tectonically migrated into continental crust from the top of upper mantle. The complex had undergone complicated metasomatism during 862 ± 12Ma. First, serpentinites were replaced by diopsides; then, diopsidites and serpentinites were replaced by phlolopites, which formed the largest scale of roseite deposit in China throuth epigene; finally, phlolopitic carbonatite veins injected and metasomated various rocks formed previously. The studies have proved that metasomating solution may be carbonatic alkali-silicate melt mass or fluid, which was differentiated into two conjugate parters: carbonatic magma and alkali-silicate melt mass or fluid. Nd, Sr, Ph, O, C and H isotopic compositions of metasomating solution, with universally low Ta, Nb, Ti, Zr and Hf, showing characteristics of EM I, EM II mantle end-member and crust material. All facts indicate that metasomating solution came mainly from deep-sea sediments of the subducting plate and terrigeuous turbidites urapped in the sea-floor trench.
A group of Permain vein rocks, which intrude into the stratum of Sliurian system, Devonian system, Carboniferous system and lower Permain series, occur in Mazhartag region, located in the west margin of the Tarimu plate, eastern Bachu county. Their main rock types have diabases, diabase-prophyrites, chromocratic olivine gabbros and lamprophyres. The chromocratic olivine gabbros, with Fe2O3+FeO=14.40%-16.88%, MgO=17.21%-18.59%, Mg#=67-68, FeOt/MgO<1 and Ni=469×10-6-635×10-6, belong to the Fe-riched-type high-Mg magma and are more or less representative of the primary magma, while Mg#, FeOt/MgO and Ni abundance of the diabases and diabase-prophyrites show these rocks belong to the moderately evolved magma. It is proved by the petrography and petrochemistry that the fractional crystallization of the olivines and clinopyzoxenes is the main mechanism of the magmatic evolution. All varial vein rocks have the characteristics of the rare earth element and trace element geochemical characteristics of basalts formed under the extension settings of the intra-plate. All rocks, with 143Nd/144Nd = 0.512508-0.512786, 87Sr/86Sr = 0.704246-0.706444, 206Pb/204Pb = 18.17-19.24, 207Pb/204Pb = 15.47-15.71 and 208Pb/204Pb = 38.63-39.32, have the identical Nd, Sr and Pb isotopic compositions. Therefor, it can be proved that these vein rocks have Nd, Sr and Pb isotopic compositions of the primitive mantle and their magmatic source maybe lay in the lower mantle.
The metaluminous Watergums granite, from a bimodal association of A-type granite/rhyolite with basalt in SE Australia, has been experimentally studied so that constraints can be placed on its origin. Petrological, geochemical and experimental data support an origin by direct, high-T partial melting of a melt-depleted I-type source rock in the lower crust.-J.A.Z.
The SHRIMP analyses of zircons from the volcanic rocks at the top of the Beiyisi Formation, in Quruqtagh area, Xinjiang, yield a weighted mean 206Pb/238 U age of 732 ± 7Ma, which gives the upper limit for the Beiyixi glaciation. Considering a previous age from volcanic rocks below the Beiyisi diamictites, the Beiyisi glaciation has been constrained between 740Ma and 732Ma. Combining with previous SHRIMP data from other three volcanic rock levels of the Neoproterozoic in study area, four tillite-contained formations of the Neoproterozoic can be divided into three durations from 740 to 732Ma of the Beiyixi Formation, from 732 to 615Ma of the Altungal and Tereeken formations and from 615 to 542Ma of the Hangelchaok Formation, respectively, which suggests that isolated glaciations occur during the Neoproterozoic in Quruqtagh. Data analyses related with glaciation indicate that the Beiyixi, Altungol and Tereekan and Hangelchaok glaciations could be correlated with the Kaigas, Sturtian and Elatina, and Gaskiers glaciations, respectively.
Precise age determination of the Qingir gray gneisses from the northern margin of the Tarim Basin is important for our understanding of crustal evolution of the Tarim Craton. The present SIMS zircon U-Pb dating yielded an age of 2565 ± 18(2σ) Ma for the Qingir gray gneiss, which is the dominant constituent of the Tuokelakebulake complex in this region. The new result is comparable with zircon U-Pb age of blue-quartz-bearing granite from the central section of region of Kuluketage. It indicates that they are all Neo-Archean magmatites with TTG component. Together with the literature data, including a Sm-Nd isochron age of 3263 ± 126 Ma (2σ), with ε Nd(t) = + 3.2 ± 0.7, for amphibolite enclaves in the gray gneisses from the Qingir (Hu and Rogers, 1992), and several Nd model ages (TDM) of 3200 to 2600 Ma for gneisses, granites, and schists from the area (Hu et al., 2000;Dong et al., 1999; Feng et al., 1998), it strongly suggests that the basement rocks in the northern margin of the Tarim Basin were formed in the Meso- to Neo-Archean times. However, all these Archean rocks have undergone post-Archean tectonic activities and metamorphism, which are witnesses by zircon U-Pb ages of ∼2300 Ma and ∼2000 Ma for the Qingir gray gneiss, ∼2000 Ma for granitic gneiss intruded into the Qingir gray gneisses (Gao et al., 1993; Guo et al., 2003), and ∼1800 Ma for an amphibolite from Tiemenguan (Guo et al., 2003). K-Ar age study also reveals Neo-Proterozoic thermal events in the northern margin of the Tarim Basin. 40Ar/39Ar plateau ages and laser 40Ar/39Ar isochron ages for hornblendes, biotites and muscovites from various metamorphic rocks in different parts of the northern Tarim range from 850 Ma to 500 Ma. These ages indicate that the northern Tarim probably underwent diachronous uplift in different regions during the late Neoproterozoic to early Paleozoic (Hu et al., in press).
The partitioning of the trace elements Rb, Cs, Zr, Nb, Hf, Th, U, La, Ce, Nd, Sm, Eu, Dy, Er, Yb, Mn, Co, Mo, Ni, Cu, Zn, Cr, Cr, V, Ti and Ag between immiscible silicate melts in the systems Fe2SiO4-Fe3O4-KAlSi2O6-SiO2, Fe3O4-KAlSi2O6-SiO2, Fe3O4-Fe2O3-KAlSi2O6-SiO2, and Fe3O4-Fe2O3-KAlSi2O6-SiO2-Ca0.5Na.5Al1.5Si2.5O8 (An(50)) with or without H2O, P, S, F and Cl at 1200 degrees C, P = 200 MPa has been determined at fO(2) = QFM, NNO and MH oxygen buffers. H2O is shown to increase the partitioning of HFSE, REE and transition elements into the Fe-rich melt. H2O alone or with 6.67 x 10(-4) mol/g of P or S produces nearly similar partitioning trends for HFSE and REE, at experimental fO(2) = QFM, NNO and MH. H2O + F causes Rb and Cs to partition into the Fe-rich melt and significantly increases U partitioning into the Fe-rich melt. Absolute partitioning values of Mn, Co, Mo, Ni, Cu, Zn, Cr, Cr, V, Ti and Ag are strongly dependent on the H2O, P, S, F, and Cl compositions of the melt.
We report the petrology, whole-rock geochemistry, zircon LA-ICP-MS U-Pb chronology and zircon Hf isotopic data of Daxigou granitoids (western part of the Kuluketage Block, NW China) to evaluate their likely petrogenesis and tectonic setting. Zircons from syenogranite can be divided into two groups: 1) those that display oscillatory zoning and high Th/U ratios (average = 1.38), implying their magmatic origin and 2) those that exhibit weak zoning and extremely high U and Pb contents but low Th/U ratios (average = 0.35), resembling zircons that experienced hydrothermal alteration. The zircon LA-ICP-MS U-Pb dating of the two groups of zircons yielded weighted mean ages of 1830 ± 12 Ma (MSWD = 0.78) and 1798 ± 21 Ma (MSWD = 1.6) respectively. The Daxigou granitoids belong mostly to normal-K and sodium-rich metaluminous calc-alkaline type, systematically enriched in LREE and large ion lithophile elements (LILE, e.g., K, Ba and Rb), but significantly depleted in high field strength elements (HFSE, e.g., Ti, P, Nb, Ta and U). Their εHf(t) values and two-stage Hf model ages range from -7.16 to -5.03 and 2.69 to 2.76 Ga, respectively. Taken together, it is suggested that Daxigou granitoids are of I-type affinity and that they were derived by partial melting of a Neoarchaean TTG (e.g., Tuoge Complex) rocks in a continental-arc environment. These new data, combined with previous regional geological studies, demonstrate that a series of Palaeoproterozoic (c. 2.0-1.8 Ga) tectono-magmatic events occurred in Kuluketage Block during the assembly of Columbia.
The low Sr content (generally < 100 μg g−1) in clinopyroxene from peridotite makes accurate Sr isotopic determination by LA-MC-ICP-MS a challenge. The effects of adding N2 to the sample gas and using a Guard Electrode (GE) on instrumental sensitivity for Sr isotopic determination by LA-MC-ICP-MS were investigated. Results revealed no significant sensitivity enhancement of Sr by adding N2 to the ICP. Although using a GE led to a 2-fold sensitivity enhancement, it significantly increased the yield of polyatomic ion interferences of Ca-related ions and TiAr+ on Sr isotopes. Applying the method established in this work, 87Sr/86Sr ratios (Rb/Sr < 0.14) of natural clinopyroxene from mantle and silicate glasses were accurately measured with similar measurement repeatability (0.0009–0.00006, 2SE) to previous studies but using a smaller spot size of 120 μm and low to moderate Sr content (30–518 μg g−1). The measurement reproducibility was 0.0004 (2s, n = 33) for a sample with 100 μg g−1 Sr. Destruction of the crystal structure by sample fusion showed no effect on Sr isotopic determination. Synthesised glasses with major element compositions similar to natural clinopyroxene have the potential to be adopted as reference materials for Sr isotopic determination by LA-MC-ICP-MS.This article is protected by copyright. All rights reserved.
The Hongge giant Fe-Ti-V oxide ore deposit is hosted by a layered intrusion located in the central part of the Emeishan large igneous province, SW China. The intrusion is relatively small in comparison with other typical oxide-bearing intrusions worldwide; it consists of a lower olivine clinopyroxenite zone, a middle clinopyroxenite zone, and an upper gabbro zone (herein referred to as the lower, middle, and upper zones). Most of the economic Fe-Ti-V oxide ore layers occur within the middle zone. The Hongge oxide ores are depleted in REE and enriched in Zr, Hf, Nb, and Ta as compared to the associated clinopyroxenites. This enrichment of elements that are compatible in titanomagnetite is consistent with the interpretation that the ores formed by accumulation of magnetite and ilmenite. As in the nearby coeval Panzhihua Fe-Ti-V oxide deposit described previously by others, mafic silicates in the Hongge deposit have much higher MgO contents than those in other oxide deposits associated with large layered intrusions in the world. This highlights the importance of relatively primitive parental magma becoming saturated in titanomagnetite at an early stage in the genesis of the giant Fe-Ti-V oxide deposits in the Emeishan large igneous province. Phase equilibrium constraints suggest that the parental magma of the Hongge deposit is similar to that of some of the most primitive high Ti basalts in the Emeishan large igneous province. The ferrobasaltic parental magma and the ferropicritic primary magma of the Hongge intrusion are similar in major and trace element composition to the ferropicritic-ferrobasaltic magma in the Pechenga belt, Kola peninsula, Russia. Depletion of incompatible trace elements in the oxide ores and associated rocks in the Hongge intrusion as compared to the coeval high-Ti basalts suggest that not all the magma involved in the development of the Hongge intrusion has been retained in the intrusion. The occurrence of multiple Fe-Ti oxide layers alternating with Fe-Ti oxide-bearing silicate layers within a single zone and the repetitive appearance of sulfides, olivine, and Cr-rich layers suggest that multiple pulses of magma were involved in the formation of the Hongge intrusion and related Fe-Ti-V oxide deposit. We propose that the middle zone of the Hongge intrusion was a magma stepwise flow-through system and that some of the liquid was lost to the peripheral lavas to form the basalt.