Petrogenesis of the Late Jurassic peraluminous biotite granites and muscovite-bearing granites in SE China: geochronological,elemental and Sr–Nd–O–Hf isotopic constraints

Biotite granites and muscovite-bearing granites are dominant rock types of the widespread granites in SE China. However, their petrogenesis has been enigmatic. A combined study of zircon U–Pb dating and Lu–Hf isotopes, whole-rock element geochemistry and Sr–Nd–O isotopes was performed for three late Mesozoic granitic plutons (Xinfengjie, Jiangbei and Dabu) in central Jiangxi province, SE China. All the plutons are composed of biotite granites and muscovite-bearing granites that have been poorly investigated previously. The new data not only allow us to assess their sources and magma evolution processes, but also helps us to better understand the genetic link to the large-scale polymetallic mineralization in SE China. LA-ICP-MS zircon U–Pb dating shows that three plutons were emplaced in the Late Jurassic (159–148 Ma) and that the muscovite-bearing granites are almost contemporaneous with the biotite granites. The biotite granites have SiO₂ contents of 70.3–74.4 wt% and are weakly to strongly peraluminous with ASI from 1.00 to 1.26, and show a general decrease in ASI with increasing SiO₂. They have relatively high zircon saturation temperatures (T _Zr = 707–817 °C, most > 745 °C) and show a general decrease in T _Zr with increasing SiO₂. They have high initial ⁸⁷Sr/⁸⁶Sr ratios (0.7136 to 0.7166) and high δ¹⁸O values (9.1–12.8‰, most > 9.5‰) and clearly negative ε _Nd (T) (? 9.5 to ? 11.8) and ε _Hf (T) (in situ zircon) (? 13.1 to ? 13.5). The muscovite-bearing granites have high SiO₂ contents (74.7–78.2 wt%). They are also weakly to strongly peraluminous with ASI of 1.04–1.18 but show a general increase in ASI with increasing SiO₂. They have relatively low T _Zr (671–764 °C, most < 745 °C) and also show a general decrease in T _Zr with increasing SiO₂. The muscovite-bearing granites have high Rb (up to 810 ppm) and high (K₂O + Na₂O)/CaO (up to 270), Rb/Sr (up to 42) and Rb/Ba (up to 30) as well as low K/Rb (< 150, down to 50), Zr/Hf (< 24, down to 11) and Nb/Ta (< 6, down to 2). They show similar Nd–O–Hf isotopic compositions to the biotite granites with ε _Nd (T) of ? 8.7 to ? 12.0, δ¹⁸O of 8.7–13.0‰ (most > 9.5‰) and ε _Hf (T) (in situ zircon) of ? 11.3 to ? 13.1. Geochemical data suggest the origin of the biotite granites and muscovite-bearing granites as follows: Partial melting of Precambrian metasedimentary rocks (mainly two-mica schist) in the lower crust at temperatures of ca. 820 °C generated the melts of the less felsic biotite granites. Such primary crustal melts underwent biotite-dominant fractionation crystallization, forming the felsic biotite granites. Progressive plagioclase-dominant fractionation crystallization from the evolved biotite granites produced the more felsic muscovite-bearing granites. Thus, the biotite granites belong to the S-type whereas the muscovite-bearing granites are highly fractionated S-type granites. We further suggest that during the formation of the muscovite-bearing granites the fractional crystallization was accompanied by fluid fractionation and most likely the addition of internally derived mineralizing fluids. That is why the large-scale polymetallic mineralization is closely related to the muscovite-bearing granites rather than biotite granites in SE China. This is important to further understand the source and origin of biotite granites and muscovite-bearing granites in SE China even worldwide.     

Jurassic–Cretaceous tectonic evolution of Southeast China: geochronological and geochemical constraints of Yanshanian granitoids

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.     

Carboniferous magmatism and mineralization in the area of the Fuxing Cu deposit,Eastern Tianshan,China: Evidence from zircon U–Pb ages,petrogeochemistry, and Sr–Nd–Hf–O isotopic compositions

The newly discovered Fuxing porphyry Cu deposit is located in the Dananhu–Tousuquan arc, adjacent to the Tuwu–Yandong Cu deposits of Eastern Tianshan, in the southern Central Asian Orogenic Belt. The Fuxing deposit is hosted by volcanic rocks (basalt and dacite) in the Early Carboniferous Qi'eshan Group and Carboniferous felsic intrusions (plagiogranite porphyry, monzogranite, and quartz diorite). New SIMS zircon U–Pb dating indicates that the plagiogranite porphyry and monzogranite emplaced at 332.1 ± 2.2 Ma and 328.4 ± 3.4 Ma, respectively. The basalts are characterized by low SiO₂ contents (47.47–54.90 wt.%), a lack of Eu anomalies, strong depletion of Na, Ta, and Ti elements but positive Sr, U, and Pb anomalies, high Y (20.8–28.2 ppm) and HREE concentrations (Yb = 2.23–3.06 ppm), and relatively low (La/Yb)_N (2.20–3.92) values; the dacite samples have high SiO₂ contents (66.13–76.93 wt.%), clearly negative Eu anomalies, high Mg^# values (36–51), and high Y (41.8–54.9 ppm) and Yb (5.76–8.98 ppm) concentrations. The basalts and dacites exhibit similar signatures as normal arc rocks, and were considered to be derived from partial melting of mantle-wedge peridotite that was previously metasomatized by slab melts. In contrast, the plagiogranite porphyry, monzogranite, and quartz diorite show the same geochemical affinity with modern adakites, which are characterized by high SiO₂ contents (67.55–79.00 wt.%), minor negative to positive Eu anomalies, strong depletion of heavy rare earth elements (Yb = 0.17–1.19 ppm) and Y (1.86–10.1 ppm), positive K, Rb, Sr, and Ba but negative Nb, Ta, Th, and Ti anomalies, and high (La/Yb)_N ratios and Mg^# values. Moreover, these adakitic felsic intrusions display relatively high positive zircon ε_Hf(t) values (+ 11.4 to + 18.3), low ⁸⁷Sr/⁸⁶Sr (0.706080–0.711239), high ¹⁴³Nd/¹⁴⁴Nd (0.512692–0.512922) ratios, and consistent zircon δ¹⁸O values (4.41‰–5.48‰), suggesting that their parental magma were most likely derived from partial melting of the subducted oceanic crust followed by mantle peridotite interaction. Based on the whole-rock geochemical and Sr–Nd–Hf–O isotopic data, as well as detailed petrographic analyses, we further suggest that the Fuxing igneous rocks and associated porphyry Cu mineralization were generated by the northward subduction of the paleo-Tianshan oceanic plate beneath the Dananhu–Tousuquan island arc during the Early Carboniferous.     

Petrogenesis and geodynamic setting of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli–Erguna area of Inner Mongolia,China: Geochronological,geochemical and Hf isotopic evidence

U–Pb dating and Hf isotopic analyses of zircons from various granitoids, combined with major and trace element analyses, were undertaken to determine the petrogenesis and geodynamic setting of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli–Erguna area of Inner Mongolia, China. The Neoproterozoic granitoids are mainly biotite monzogranites with zircon U–Pb ages of 894 ± 13 Ma and 880 ± 10 Ma, and they are characterised by enrichment in large ion lithophile elements (LILEs; e.g., Rb, Ba, K) and light rare earth elements (LREEs), depletion in high field strength elements (HFSEs; e.g., Nb, Ta, Ti) and heavy rare earth elements (HREEs). The Late Devonian granitoids are dominantly syenogranites and mylonitised syenogranites with zircon U–Pb ages of 360 ± 4 Ma, and they form a bimodal magmatic association with subordinate gabbroic rocks of the same age. The Late Devonian syenogranites have A-type characteristics including high total alkalis, Zr, Nb, Ce and Y contents, and high FeOt/MgO, Ga/Al and Rb/Sr ratios. The Carboniferous granitoids are mainly tonalites, granodiorites and monzogranites with U–Pb ages varying from 319 to 306 Ma, and they show very strong adakitic characteristics such as high La/Yb and Sr/Y ratios but low Y and Yb contents. The Late Permian granitoids are dominated by monzogranites and syenogranites with zircon U–Pb ages ranging between 257 and 251 Ma. Isotopically, the ε_Hf(t) values of the Neoproterozoic granitoids range from +4.3 to +8.3, and the two-stage model ages (T_DM2) from 1.2 to 1.5 Ga. The Late Devonian granitoids are less radiogenic [ε_Hf(t) from +12.0 to +12.8 and T_DM2 from 545 to 598 Ma] than the Carboniferous [ε_Hf(t) from +6.8 to +9.5 and T_DM2 from 722 to 894 Ma] and Late Permian granitoids [ε_Hf(t) from +6.1 to +9.4 and T_DM2 in the range of 680–895 Ma]. These data indicate (1) the Neoproterozoic granitoids may have been generated by melting of a juvenile crust extracted from the mantle during the Mesoproterozoic, probably during or following the final stages of assembly of Rodinia as a result of the collision and amalgamation of Australia and the Tarim Craton; (2) the Late Devonian granitoids may have formed by partial melting of a new mantle-derived juvenile crust in a post-orogenic extensional setting; (3) the Carboniferous granitoids appear to have been produced by melting of garnet-bearing amphibolites within a thickened continental crust during and following the collision of the Songnen and Erguna–Xing’an terranes; and (4) the Late Permian granitoids may have been generated by melting of garnet-free amphibolites within the Neoproterozoic juvenile continental crust, probably in the post-collisional tectonic setting that followed the collision of the North China and Siberian cratons.     

Zircon U–Pb geochronology and Hf isotopic constraints on the petrogenesis of the Late Silurian Shidonggou granite from the Wulonggou area in the Eastern Kunlun Orogen,Northwest China

ABSTRACT

The Wulonggou area in the Eastern Kunlun Orogen (EKO) in Northwest China is characterized by extensive granitic magmatism, ductile faulting, and orogenic gold mineralizations. The Shidonggou granite is located in the central part of the Wulonggou area. This study investigated the major as well as trace-element compositions, zircon U–Pb dates, and zircon Hf isotopic compositions of the Shidonggou granite. Three Shidonggou granite samples yielded an average U–Pb zircon age of 416 Ma (Late Silurian). The Late Silurian Shidonggou granite is peraluminous, with high alkali contents, high Ga/Al ratios, high (K₂O + Na₂O)/CaO ratios, and high Fe₂O₃^T/MgO ratios, suggesting an A-type granite. The Shidonggou granite samples have zircon ε_Hf(t) values ranging from ?7.1 to +4.4. The Hf isotopic data suggest that the Late Silurian granite was derived from the partial melting of Palaeo- to Mesoproterozoic juvenile mantle-derived mafic lower crust. Detailed geochronological and geochemical data suggest that the Late Silurian granite was emplaced in a post-collisional environment following the closure of the Proto-Tethys Ocean. Combining data of other A-type granitic rocks with ages of Late Early Silurian to Middle Devonian, such post-collisional setting related to the Proto-Tethys Ocean commenced at least as early as ~430 Ma (Late Early Silurian), and sustained up to ~389 Ma (Middle Devonian) in the EKO.     

Petrogenesis and tectonic implications of Triassic A-type granites in southeastern China: insights from zircon U–Pb–Hf isotopic and whole-rock geochemical compositions of the Luoguyan and Guiyantou granites in northwestern Fujian Province

Triassic A-type granites in eastern South China Block (SCB) are abundant in the Wuyi–Yunkai tectonic domain and provide an important opportunity to explore the early Mesozoic evolution of continental crust of the SE part of the SCB. We carried out U–Pb zircon dating, Lu–Hf isotope analyses of zircon, and whole-rock geochemical analyses for two granitic plutons, the Guiyantou (GYT) and Luoguyan (LGY) granites, from northwestern Fujian Province. LA–ICP–MS U–Pb zircon analyses yielded ages of 232 ± 4 to 231 ± 7 Ma and 221 ± 5 Ma (Middle-Late Triassic) for the GYT and LGY granites. These two granites belong to metaluminous to weakly peraluminous high K calc-alkaline A-type granite that are enriched in K, Al, light rare earth element and Rb, Th, U, and Pb, and depleted in Nb, Ta, P, and Ti. Their rare earth element patterns are highly fractionated with (La/Yb)_N ratios of 2–21 and strong negative Eu anomalies (Eu/Eu* = 0.02–0.31). In situ Hf isotopic analysis of zircon from the GYT and LGY granites yielded ε_Hf(t) values ranging from –11.5 to –1.1, with corresponding two-stage Hf model ages from 1.98 to 1.33 Ga, from which it is inferred that the GYT and LGY magmas formed by partial melting of Proterozoic metasedimentary rock in the Cathaysia block. The two granites were emplaced at 232 and 221 Ma and together with Triassic A-type granites in coastal region of the SCB, which is in agreement with an extensional tectonic setting in the Middle-Late Triassic. We suggest that the Middle-Late Triassic A-type granites in eastern SCB were probably formed in an intracontinental, post-orogenic extensional regime that collision was between the SCB and an ‘unknown block’ or the eastern extension of Indochina block.     

Origin of the Tongshankou porphyry–skarn Cu–Mo deposit,eastern Yangtze craton,Eastern China: geochronological,geochemical, and Sr–Nd–Hf isotopic constraints

The Tongshankou Cu–Mo deposit, located in the westernmost Daye district of the Late Mesozoic Metallogenic Belt along the Middle-Lower reaches of the Yangtze River, eastern China, consists mainly of porphyry and skarn ores hosted in the Tongshankou granodiorite and along the contact with the Lower Triassic marine carbonates, respectively. Sensitive high-resolution ion microprobe zircon U–Pb dating constrains the crystallization of the granodiorite at 140.6 ± 2.4 Ma (1σ). Six molybdenite samples from the porphyry ores yield Re–Os isochron age of 143.8 ± 2.6 Ma (2σ), while a phlogopite sample from the skarn ores yields an ⁴⁰Ar/³⁹Ar plateau age of 143.0 ± 0.3 Ma and an isochron age of 143.8 ± 0.8 Ma (2σ), indicating an earliest Cretaceous mineralization event. The Tongshankou granodiorite has geochemical features resembling slab-derived adakites, such as high Sr (740–1,300 ppm) and enrichment in light rare earth elements (REE), low Sc (<10 ppm), Y (<13.3 ppm), and depletion in heavy REE (<1.2 ppm Yb), and resultant high Sr/Y (60–92) and La/Yb (26–75) ratios. However, they differ from typical subduction-related adakites by high K, low MgO and Mg#, and radiogenic Sr–Nd–Hf isotopic compositions, with (⁸⁷Sr/⁸⁶Sr) _t  = 0.7062–0.7067, ɛ _Nd(t) = −4.37 to −4.63, (¹⁷⁶Hf/¹⁷⁷Hf) _t  = 0.282469–0.282590, and ɛ _Hf(t) = −3.3 to −7.6. The geochemical and isotopic data, coupled with geological analysis, indicate that the Tongshankou granodiorite was most likely generated by partial melting of enriched lithospheric mantle that was previously metasomitized by slab melts related to an ancient subduction system. Magmas derived from such a source could have acquired a high oxidation state, as indicated by the assemblage of quartz–magnetite–titanite–amphibole–Mg-rich biotite in the Tongshankou granodiorite and the compositions of magmatic biotite that fall in the field between the NiNiO and magnetite–hematite buffers in the Fe³⁺–Fe²⁺–Mg diagram. Sulfur would have been present as sulfates in such highly oxidized magmas, so that chalcophile elements Cu and Mo were retained as incompatible elements in the melt, contributing to subsequent mineralization. A compilation of existing data reveals that porphyry and porphyry-related Cu–Fe–Au–Mo mineralization from Daye and other districts of the Metallogenic Belt along the Middle-Lower reaches of the Yangtze River took place coevally in the Early Cretaceous and was related to an intracontinental extensional environment, distinctly different from the arc-compressive setting of the Cenozoic age that has been responsible for the emplacement of most porphyry Cu deposits of the Pacific Rim.     

Zircon U–Pb geochronology and Hf isotopic constraints on the petrogenesis of Early Triassic granites in the Wulonggou area of the Eastern Kunlun Orogen,Northwest China

Widespread granitic intrusions in the northeast part of the Wulonggou area were previously thought to be emplaced into the Palaeoproterozoic Jinshuikou Group during the Neoproterozoic. This contribution presents detailed LA-ICP-MS zircon U–Pb geochronology, major and trace element geochemistry, and zircon Hf isotope systematic on the Wulonggou Granodiorite and Xiaoyakou Granite from the Wulonggou area. Three granodiorite samples yielded U–Pb zircon ages of 247 ± 2, 248 ± 1, and 249 ± 1 Ma, and one granite sample yielded U–Pb zircon age of 246 ± 3 Ma. The granodiorite samples are metaluminous with an alumina saturation index of 0.90–0.96, as well as intermediate- to high-alkali contents of 5.49–6.14 wt.%, and low Zr+Nb+Ce+Y contents, and low Fe₂O_3T/MgO ratios, which suggest an I-type classical island arc magmatic source. The granite samples are peraluminous with an alumina saturation index of 1.02–1.03, Sr content of 305.00–374.00 ppm, Sr/Y ratios of between 17.68 and 28.77, (La/Yb)_N values of 16.98–25.07, low HREEs (Yb = 1.10–2.00 ppm), and low Y (13.00–21.10 ppm), which suggest adakite-like rocks. All granodiorite samples have zircons ε_Hf(t) values ranging from ?2.9 to +3.9, and granite samples have zircon ε_Hf(t) values ranging from ?7.8 to +3.2. These Hf isotopic data suggest that the Early Triassic granites were derived from the partial melting of a mafic Mesoproterozoic lower crust, although the degree of ancient crustal assimilation may be higher for the Xiaoyakou Granite. It is suggested here that the ca. 246–248 Ma magma was generated during the northward subduction of the Palaeo-Tethys oceanic plate.     

Age and geochemistry of the Neoproterozoic granitoids in the the Songnen–Zhangguangcai Range Massif, NE China: Petrogenesis and tectonic implications

<正>1 Introduction The Songnen–Zhangguangcai Range Massif(SZRM)crops out over an extensive part of NE China and was thought to contain Precambrian crystalline basement material,as evidenced by the presence of what appears to bePaleoproterozoicbasementmaterialwithin exploration drillholes(Pei et al.,2007).An alternative view is that the basement within the SZRM is     

Geochemistry,geochronology and Sr–Nd–Pb–Hf isotopic compositions of Middle to Late Jurassic syenite–granodiorites–dacite in South China: Petrogenesis and tectonic implications

In situ zircon U–Pb ages and Hf isotope data, major and trace elements and Sr–Nd–Pb isotopic compositions are reported for coeval syenite–granodiorites–dacite association in South China. The shoshonitic syenites are characterized by high K₂O contents (5.9–6.1 wt.%) and K₂O/Na₂O ratios (1.1–1.2), negative Eu anomalies (Eu/Eu* = 0.65 to 0.77), enrichments of Rb, K, Nb, Ta, Zr and Hf, but depletion of Sr, P and Ti. The adakitic granodiorite and granodiorite porphyry intrusions are characterized by high Al₂O₃ contents (15.0–16.8 wt.%), enrichment in light rare earth elements (LREEs), strongly fractionated LREEs (light rare earth elements) to HREEs (heavy rare earth elements), high Sr (438–629 ppm), Sr/Y (29.2–53.6), and low Y (11.7–16.8 ppm) and HREE contents (e.g., Yb = 1.29–1.64 ppm). The calc-alkaline dacites are characterized by LREE enrichment, absence of negative Eu anomalies, and enrichment of LILEs such as Rb, Ba, Th, U and Pb, and depletion of HFSEs such as Nb, Ta, P and Ti.Geochemical and Sr–Nd–Hf isotopic compositions of the syenites suggest that the shoshonitic magmas were differentiated from parental shoshonitic melts by fractional crystallization of olivine, clinopyroxene and feldspar. The parent magmas may have originated from partial melting of the lithospheric mantle with small amount contribution from crustal materials. The adakitic granodiorite and granodiorite porphyry have Sr–Nd–Pb isotopic compositions that are comparable to that of the mafic lower crust. They have low Mg# and MgO, Ni and Cr contents, abundant inherited zircons, low ε_Nd(t) and ε_Hf(t) values as well as old whole-rock Nd and zircon Hf model ages. These granodiorites were likely generated by partial melting of Triassic underplated mafic lower crust. The Hf isotopic compositions of the dacites are relatively more depleted than the Cathaysia enriched mantle, suggesting those magmas were derived from the partial melting of subduction-modified mantle sources. The coeval shoshonitic, high-K calc-alkaline and calc-alkaline rocks in Middle to Late Jurassic appear to be associated with an Andean-type subduction. This subduction could have resulted in the upwelling of the asthenosphere beneath the Cathaysia Block, which induced partial melting of the mantle as well as the mafic lower crust, and formed an arc regime in the coastal South China during Middle to Late Jurassic.     

U–Pb zircon dating, geochemical and Sr–Nd–Hf isotopic compositions of Early Indosinian intrusive rocks in West Qinling, central China: petrogenesis and tectonic implications

The Qinling–Dabie–Sulu orogenic belt is the junction between the North and South China blocks, which resulted from the final amalgamation of China continents during the Indosinian. Indosinian granitoids are widespread in the Qinling orogen, and their geneses can thus constrain the evolution of China continent. We carried out a combined U–Pb zircon dating and geochemical study for the Shuangpengxi granodiorite pluton and the Xiekeng diorite–granodiorite pluton in the middle part of the West Qinling orogen. U–Pb zircon dating shows that the magma crystallization ages of 242 ± 3 Ma for the Shuangpengxi pluton and ~244–242 Ma for the Xiekeng pluton. Geochemical and Sr–Nd–Hf isotopic compositions reveal that the magma of the Shuangpengxi granodiorite was derived from partial melting of crustal materials. The Xiekeng diorites can be divided into high-Al diorite and high-Mg diorite. Both of them resulted from partial melting of enriched lithospheric mantle, but their mantle source had been modified by previous slab-derived melt. The high-Al diorite was formed by fractional crystallization of olivine, pyroxene and/or preferential accumulation of plagioclase, and the high-Mg diorite was formed by fractional crystallization of olivine and/or preferential accumulation of pyroxene. The Xiekeng granodioritic porphyry was formed by mixing of crust-derived and mantle-derived melts. We propose that the Early Indosinian magmatism resulted from break-off of subducted oceanic slab after collision. The slab break-off model can well explain the linear distribution of the Early Indosinian plutons and rapid crustal uplift during the Middle Triassic in the West Qinling.     

Petrogenesis of Early Cretaceous volcanic rocks of the Manketouebo Formation in the Wuchagou region,central Great Xing’an Range,NE China,and tectonic implications: geochronological,geochemical, and Hf isotopic evidence

ABSTRACT

This study presents new whole-rock major and trace element geochemistry, zircon U–Pb ages, and Hf-isotope compositions for volcanic rocks from the Manketouebo Formation of the central Great Xing’an Range, NE China. These data provide precise ages and information on the petrogenesis and source of the magmas that formed this formation, furthering our understanding of the geodynamic setting of the large-scale late Mesozoic magmatism in the Great Xing’an Range and other areas in NE China. The Manketouebo Formation in the study area is dominated by rhyolites and rhyolitic tuffs with minor trachydacites. The LA-ICP-MS zircon U–Pb dating indicates that these volcanic rocks formed between 143 and 139 Ma. The volcanic rocks contain high silica (66.70–79.91 wt.%) and total alkali (5.93–9.72 wt.%) concentrations, and low concentrations of MgO (0.08–1.15 wt.%), total FeO (0.68–4.50 wt.%), and CaO (0.10–2.56 wt.%). They are enriched in large-ion lithophile elements (LILEs; e.g. Rb, Th, and U) and light rare earth elements (LREEs), and depleted in high field strength elements (HFSEs; e.g. Nb, Ta, Ti, and P) and heavy rare earth elements (HREEs), indicating that they are similar to highly fractionated I-type igneous rocks. All of the magmatic zircons from the analysed samples have high initial ¹⁷⁶Hf/¹⁷⁷Hf ratios (0.282900–0.283093), positive ε_Hf(t) values (7.48–14.19), and young Hf two-stage model ages (954–344 Ma) that suggest the primary magma that formed the volcanic rocks of the Manketouebo Formation was derived from the partial melting of Neoproterozoic to Phanerozoic juvenile crustal material, indicating in turn that significant crustal growth occurred at this time within the Xing’an Terrane. These data, combined with previous research into the spatial–temporal distribution of Mesozoic volcanic rocks in NE China, suggest that the Early Cretaceous magmatism in the Great Xing’an Range was influenced by both the subduction of the Palaeo-Pacific Plate and the closure of the Mongol–Okhotsk Ocean. This was a crucial period in the transformation from the Mongol–Okhotsk Ocean to the Palaeo-Pacific tectonic regimes. In summary, the early stages of Early Cretaceous magmatism in this area were related to the closure of the Mongol–Okhotsk Ocean, whereas the later stages of magmatism in this area and elsewhere in NE China were related to the subduction of the Palaeo-Pacific Plate.     

Geochemical and Hf isotopic compositions of Late Triassic–Early Jurassic intrusions of the Erguna Block,Northeast China: petrogenesis and tectonic implications

Late Triassic–Early Jurassic intrusions of the Erguna Block, Northeast China, are located along the southern margin of the Mongol–Okhotsk orogenic belt. They comprise granodiorite, monzogranite, syenogranite, and lesser gabbro–diorite, of adakitic and calc­alkaline affinity. The adakite-like and calc­alkaline granites share similar light rare earth elements (LREE) characteristics; however, their heavy rare earth elements (HREE) trends differ from one another. The relative abundances of HREE in the calc­alkaline granites are relatively consistent and are similar to those of intrusive rocks formed from dehydration melting of garnet-free amphibolitic source rocks at relatively low pressures. In contrast, the adakite-like granites show more prominent HREE fractionation trends, indicating that they crystallized at higher pressures, where garnet in the source rocks was stable. At least two isotopically distinct sources were involved in the petrogenesis of the granites, but the extent to which they contributed varies between plutons. Most intrusions have incorporated an isotopically primitive component, possibly juvenile mafic crust. The other sources include a small proportion of old continental crustal material and isotopically evolved wall rocks. The gabbro–diorites have high MgO contents (>7 wt.%), a high Mg^# (>0.6), and show moderate LREE and HREE fractionation, indicating they formed from the melting of subducted metasomatized lithospheric mantle. All of the intrusions in the study area are characterized by a relative enrichment in large ion lithophile elements (LILE) and depletion in high field strength elements (HFSE), indicating they were emplaced in an Andean-type active continental margin setting related to southward subduction of the Mongol–Okhotsk oceanic plate.     

Ordovician volcano–sedimentary iron deposits of the Eastern Tianshan area,Northwest China: the Tianhu example

ABSTRACT

The stratabound Tianhu iron deposit, with a reserve of 104 Mt at 42% Fe, is located in the eastern part of the Central Tianshan zone in the southern part of the Central Asian Orogenic Belt. The deposit hosts schist, quartzite, marble, amphibolite, and granitic gneiss belonging to the Tianhu Group. Laser ablation inductively coupled plasma mass spectrometry was used to perform zircon U–Pb geochronology, bulk-rock geochemistry, and in situ zircon Hf isotope analyses of the metavolcanic host rocks for constraining the timing and genesis of the Tianhu iron deposit. According to the newly determined age constraints of 452 ± 3 and 477 ± 4 Ma, the iron deposit was concluded to be Ordovician in age. Geochemistry and zircon Lu–Hf isotope analyses suggested that the host rocks of the deposit represent metamorphosed arc-type volcanic rocks generated by the partial melting of a lower crustal source. Combined with geological and ore petrographic characteristics, the Tianhu iron deposit is interpreted to be of volcano–sedimentary origin with enrichment during subsequent metamorphism. The early Palaeozoic marks a critical iron mineralization epoch in the Eastern Tianshan area. The results also support the model of the Central Tianshan area as a volcanic-arc during the early Palaeozoic, associated with the subduction of the Northern Tianshan Ocean.     

Geochemistry and Sr–Nd isotope composition of Carboniferous volcanic rocks of the Jueluotage Orogenic Belt: implications for the tectonic evolution of Eastern Tianshan,China

The major and trace element, and Sr–Nd isotopic compositions of the Carboniferous Qi’eshan, Wutongwozi, and Yamansu volcanic rocks from the northern and southern parts of the Jueluotage Orogenic Belt in East Tianshan, China, were analysed to understand their genesis and geodynamic implications. The early Carboniferous Qi’eshan basalts are characterized by high Al₂O₃, with La/Sm (1.38–1.79) and Ba/La (27.06–58.76) values higher than those of typical normal mid-ocean ridge basalt. They are relatively enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), and depleted in high field strength elements. Overall, their initial Nd–Sr isotopic compositions are ε_Nd(t) = (5.6–7.0) and Isr = 0.70397–0.70429, implying the magma originated from a mantle wedge source that was metasomatized by subduction-related fluids. In contrast, the late Carboniferous Wutongwozi basalts have lower Ba/La (4.86–12.82), La/Nb (0.87–2.45), and LILE concentrations. They have the isotopic characteristics of depleted asthenosphere, relatively high and heterogeneous ε_Nd(t) (9.3–9.4), and high Isr (0.70471–0.70533). Thus, the late Carboniferous Wutongwozi basalts may have been derived from the partial melting of mantle sources during asthenospheric upwelling. The early Carboniferous Yamansu acid volcanic rocks are characterized by high Mg# (46–48) and Lu/Y (~0.15), and low K₂O/Na₂O (0.01–0.20), similar to M-type granites. However, their ε_Nd(t) (5.0–5.5) and Isr (0.70642–0.70768) values are lower than those of depleted mantle, indicating they were contaminated by lower crustal material. The magma source originated from a mantle-derived magma that was contaminated by middle Tianshan massif in a continental margin arc setting. Based on the results and previous field-based studies, we conclude that the Carboniferous volcanics in the Jueluotage Orogenic Belt formed in a complex trench–arc–basin setting in the Kuguertage–Aqikuduke Suture Zone.     

Late Jurassic–Early Cretaceous tectonic evolution of the Great Xing’an Range: geochronological and geochemical evidence from granitoids and volcanic rocks in the Erguna Block,NE China

ABSTRACT

The late Mesozoic magmatic record within the Erguna Block is critical to evaluate the tectonic history and geodynamic evolution of the Great Xing’an Range, NE China. Here, we provide geochronological and geochemical data on Late Jurassic–Early Cretaceous plutonic-volcanic rocks in the northern Erguna Block and discuss their origin within a regional tectonic framework. Late Mesozoic magmatism in the Erguna Block can be divided into two major periods: Late Jurassic (162–150 Ma) and Early Cretaceous (140–125 Ma). Late Jurassic quartz monzonite and dacite show adakite characteristics such as high Al₂O₃, high Sr, and steeply fractionated REE patterns. Contemporary granitoids and rhyolites are also characterized by strong enrichment of light rare earth elements (LREE) and significant depletion in heavy rare earth elements (HREE), but with more pronounced negative Eu anomalies. Early Cretaceous trachytes and monzoporphyries exhibit moderate LREE enrichment and relatively flat HREE distributions. Coeval granites and rhyolites have transitional signatures between A-type and fractionated I-type felsic rocks. Both Late Jurassic and Early Cretaceous rocks have distinctive negative Nb, Ta, and Ti anomalies, and positive zircon ε_Hf(t) values, suggesting that these magmas were derived from partial melting of Meso-Neoproterozoic accreted lower crust, although melting occurred at a variety of crustal levels. The transition from adakite to non-adakite magmatism reflects continued crustal thinning from Late Jurassic to Early Cretaceous. Our data, together with recently reported isotopic data for plutonic and volcanic rocks, as well as geochemical data, in NE China, suggest that Late Jurassic–Early Cretaceous magmatism in the Erguna Block was possibly induced by post-collisional extension after closure of the Mongol-Okhotsk Ocean.     

Petrological,geochemical, isotopic,and geochronological constraints for the Late Devonian–Early Carboniferous magmatism in SW Gondwana (27–32°LS): an example of geodynamic switching

International Journal of Earth Sciences - We report a study integrating 13 new U–Pb LA-MC-ICP-MS zircon ages and Hf-isotope data from dated magmatic zircons together with complete...     

Zircon U–Pb geochronological,trace element,and Hf isotopic constraints on the genesis of the Fe and Cu skarn deposits in the Qiman Tagh area,Qinghai Province,Eastern Kunlun Orogen,China

Fe and Cu skarn deposits are very important skarn types worldwide, but it is currently unclear whether the nature of intrusions related to Fe and Cu skarn deposits exerts a key influence on variations in metal associations between Fe and Cu skarn deposits. The Qiman Tagh area of Qinghai Province (QTQP), located in the Eastern Kunlun Orogen (EKO), provides a good opportunity to address this issue. Here, integrating new zircon U–Pb ages, trace elements and Hf isotopes from this study with published data, we constrain the sources of magma associated with Fe and Cu skarn deposits within the QTQP and discuss their role in controlling differences between Fe and Cu skarn deposits.Combined with published data, two discrete suites of the intrusions associated Fe and Cu skarn deposits have been recognized in the QTQP: (1) 245.1 ± 1.5 Ma granodiorite (related to a 245.5 ± 1.6 Ma Cu skarn deposit) has zircon εHf(t) values of −11.9 to −2.1; (2) 235–224 Ma monzonites, quartz monzonites, granodiorite porphyries, monzogranites, and granites associated with 234–225 Ma Fe skarn deposits are characterized by relatively high zircon εHf(t) values (−5.1 to +5.9). The Sr–Nd–Hf isotopic data suggest that the intrusions of Suite 1 and 2 were dominantly derived by partial melting of a Mesoproterozoic juvenile mafic lower crust. Suite 2 intrusions associated with Fe skarn deposits have more mantle components in their magma sources than rocks of Suite 1 that are related to a Cu skarn deposit. Furthermore, zircon εHf(t) values of intrusions associated with Fe and Cu skarn deposits in the QTQP show a negative correlation between mantle components in the magma sources and the contents of Cu and Zn in these deposits. Zircon trace elements indicate that the intrusions associated with Fe skarn deposits are relatively less oxidized than the rock associated with Cu skarn deposit in the QTQP, reflecting a positive correlation between crustal components in the magma sources and oxygen fugacity of the magmas. This indicates that different proportions of mantle and crustal materials in the magma sources may affect oxygen fugacity and Fe contents of the magmas, which possibly leads to the variations in metal associations between Fe and Cu skarn deposits in the QTQP. Zircon U–Pb ages, trace elements and Hf isotopic compositions, combined with geological, geochronological, and geochemical evidence, indicates that having different proportions of mantle components in the magma sources of intrusions associated with Fe and Cu skarn deposits is one of the most critical factors controlling differences in metal association between Fe and Cu skarn deposits.