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Mesozoic igneous rocks are widely distributed in the South China Sea (SCS) and its adjacent areas and are exposed in the SCS, South China, Hainan, Indochina, Taiwan, the Philippines, and Borneo; these rocks are mostly dominated by granitoids. This paper presents a complete map of the Mesozoic igneous rocks of the SCS and its adjacent areas. This paper also presents an analysis of geological survey and published data in terms of seismic profiles, ages, geochemistry and isotopic systematics of the Mesozoic igneous complexes of the SCS and its adjacent areas. Three periods of igneous activity can be distinguished: (1) Permian – Triassic that spans from 250–201 Ma; (2) Jurassic (201–145 Ma); and (3) Latest Jurassic/Cretaceous to Maastrichtian (145–66 Ma), of which the Cretaceous is the best preserved and could possibly be the most widespread. Triassic igneous rocks are distributed in the northwestern and southern SCS (Qiongdongnan Basin, Yinggehai-Song Hong Basin, Beibu Gulf Basin, the Dangerous Grounds, and the Reed Bank); Jurassic igneous rocks are distributed in the northern and southern SCS (Pearl River Mouth Basin, Qiongdongnan Basin, Yinggehai-Song Hong Basin, Beibu Gulf Basin, and the Reed Bank); and Cretaceous igneous rocks are distributed in the northern, western and southern SCS. The igneous activity of the SCS is mostly distributed in the continent slope. Mesozoic igneous rocks of the SCS include at least 350 rock masses: the smallest being 0.182 km2, the largest being 5,5,502 km2, and the total area covering 688,539 km2. Mesozoic magmatism in the SCS and its adjacent areas migrated oceanward (southeastward). Our new seismic profiles and the wells from the literature highlight that Jurassic granites occur not only inland of South China but also in coastal South China and the northern and southern SCS. The YING6 well in the northern SCS encountered andesite with an age of 68.24 Ma, which is the youngest age found for the SCS Mesozoic volcanic rocks. The XY1 well in the western SCS encountered granite with an age of 68.9 Ma, which is the youngest age found for the SCS Mesozoic intrusive rocks. The WZ12-3-1 well in the northern SCS encountered granite with an age of 243.3 Ma, which is the oldest age found for the SCS Mesozoic intrusive rocks. The encountered dacite ages (219.1 ± 1.4 Ma) of the NK-1 well in the southern SCS were the oldest ages found for the SCS Mesozoic volcanic rocks. The thickest Mesozoic igneous rocks (>1022.5 m) were encountered in the NK-1 well. Igneous rocks in the SCS and its adjacent areas are closely related to tectonic movements such as faults, plate movement, and mantle-derived igneous fluid ascent. They are controlled by the subduction of the Tethys lithospheric and Paleo-Pacific domains. [ABSTRACT FROM AUTHOR]

In this paper, we present an integrated study of petrology, zircon U–Pb geochronology, whole-rock geochemistry, and zircon Lu–Hf isotopes for the basic–intermediate dykes in the western Gonghe basin, northeastern Qinghai–Tibetan Plateau. LA–MC–ICP–MS zircon U–Pb dating indicates that these dykes were emplaced in the Middle Triassic (240 ± 1.6 Ma). Geochemically, these basic–intermediate dykes are characterized by enrichments in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs; e.g. K, Rb, and Pb), coupled with depletions in high-field-strength elements (HFSEs; e.g. Nb, Ta, and Ti). These geochemical features, along with the relatively low zircon εHf values (−7.2 to 1.6), suggest that these mafic dykes were originated from enriched mantle metasomatized by subduction-related fluids in a back-arc extensional environment. Literature investigations indicate that Middle Triassic mafic dykes are widespread in central China and are geochemically of arc affinities. Therefore, a regional back-arc extensional event occurred in central China during Middle Triassic time, which was likely caused by rollback of the subducting Kunlun–Animaqin Paleo-Tethyan slab. [ABSTRACT FROM AUTHOR]

The Naxiguole Banded Iron Formation (BIF), located in the Eastern Kunlun Orogenic Belt, Northwest China, is hosted by the Jinshuikou Group and has a Fe of 75 Mt at a grade of 15–28.83 wt.% Fe. In this paper, we use integrated petrological, geochemical, and geochronological data to limit the age and origin of the Naxiguole BIF. Country rocks mainly comprise marble, felsic paragneiss, plagioclase amphibolite schist, and biotite plagioclase gneiss. The features of sedimentary structure (blastopsammitic texture and blastobedding structure) and trace elements (e.g. La, Ni, Zr) from the country rock indicate that their protoliths are sedimentary rock. The 141 detrital zircons from the Jinshuikou Group yield a minimum age of 908 Ma, which can be considered the upper limit for the Naxiguole BIF. According to the age (602 Ma) of the mafic rocks intruding into the Jinshuikou Group, it is reasonable to assume that the formation age of BIF can be limited at 908–602 Ma (i.e. Neoproterozoic). The high contents of Al2O3 + TiO2 (3–6 wt.%), ΣREE (36–135 ppm) for BIF samples suggest that terrestrial clastic material contributed to BIF formation. The BIF samples show seawater-like features, such as depletion in LREEs, positive Y anomaly and high Y/Ho ratios (30.7–57.5, average = 42.5), implying that the Naxiguole BIF precipitated from seawater. The positive Eu/Eu*PAAS anomalies (average 1.52) suggest the influence of high-T hydrothermal fluids. Based on positive Eu anomalies and high terrestrial clastic components and no obvious Ce anomalies, the Naxiguole BIF was formed in an anoxic or suboxic sedimentary basin within active continental island arc, and is similar to Superior-type BIFs worldwide. [ABSTRACT FROM AUTHOR]

Li–Be mineralization in the northeastern Pamir is the most westerly portion of the newly defined Western Kunlun–Songpan–Ganze rare metal belt in China. This paper discusses the geochemistry and isotopic U–Pb–Sr–Nd–Hf systems of two Triassic granites and Li–Be pegmatites, trying to identify their genetic relationship. Our study shows that although the biotite monzogranites, the muscovite granites, and the Li–Be pegmatites have similar zircon and coltan U–Pb ages of 210 Ma, continuous crystallization could not completely account for their compositional and Sr–Nd–Hf isotopic diversity. In comparison with the biotite monzogranites, the muscovite granites exhibit strongly fractionated characteristics, with higher levels of SiO2, K2O, P2O5, Li, Be, Cs, Rb, and Ta, and are sourced from a partial melt of meta-pelite rocks, showing a genetical relationship with the Li–Be pegmatites. A model of volatile accumulation is an attempt to interpret some characteristics of the strongly fractionated muscovite granites and Li-Be pegmatites, which show dramatically elevated contents of P2O5 of 0.20–0.23% to Li–Be pegmatites of 0.4–2.64%, respectively. P2O5 might be an agency of the accumulation of fluxing compositions also including B, F, and H2O. Succeeding pegmatite-forming fluid exsolution and selective removal of Ca–Na–K to precipitate feldspar minerals far away from the parent granites should be accountable for some strongly fractionated characteristics in the residual melt, e.g. the enrichment of Rb, loss of Sr and Ba, and elevated negative Eu anomaly. Furthermore, this selective extractant of alkalis metal triggered by the accumulation of flux notably enhanced the contents of Li and Be in the remaining melts by three times, which might be also an important mechanism for the rare metal concentration in the Li–Be pegmatites by thousands of times. [ABSTRACT FROM AUTHOR]

When the Neo-Tethys subduction initiated has been a subject of debate, perhaps due to the lack of reliable evidence. This paper reports geochronological, geochemical, and Hf isotopic data for recently identified gabbro as well as diorite exposed in the Chanv area of the Gangdese in the southernmost margin of the western Lhasa block, western China. Zircon U–Pb dating indicates the Chanv magmatic rocks formed in two stages: latest Permian (gabbro, 254.8 ± 1.5 Ma) and Late Triassic (gabbro, 214.2 ± 2.0 Ma; diorite, 202.8 ± 1.1 Ma). Geochemical and Hf isotopic analyses reveal that the Chanv magmatic rocks of both stages have contrasting characters. The latest Permian gabbro has apparently higher TiO2 concentrations (> 3 wt.%) than the Late Triassic gabbro (0.86–1.24 wt.%). Although they all are enriched in light rare-earth elements (LREEs), the latest Permian gabbro displays no depletions in Nb and Ta, while the Late Triassic gabbro and diorite are apparently depleted in these two elements. In addition, the zircons from the latest Permian gabbro are all characterized by positive εHf(t) values whereas those from the Late Triassic gabbro dominantly by negative εHf(t) values. Conventional plots using multi-elements or elemental ratios all indicate the latest Permian gabbro has inherent resemblance to intraplate oceanic-island basalt (OIB) whereas the Late Triassic gabbro and diorite are of distinct arc affinity. Therefore, The Chanv latest Permian–Late Triassic magmatic rocks testify a switch of the tectonic environment in the southernmost Eurasian margin from latest Permian post-break-up to Late Triassic arc-related setting and thus constrain the initiation of the Neo-Tethys subduction between 255 Ma and 214 Ma. [ABSTRACT FROM AUTHOR]

Late Mesozoic volcanic rocks are widespread in the Great Xing'an Range (GXR), Northeast (NE) China. However, details of the tectono-magmatic evolution during the Late Mesozoic are poorly understood. In this paper, new zircon U–Pb, Lu–Hf, and whole-rock geochemical data from Late Mesozoic volcanics in the southern GXR, are used to further constrain the tectono-magmatic evolution of the region. Late Mesozoic magmatism in the GXR, eastern Mongolia and southern Transbaikalia occurred during the Early Cretaceous (120–140 Ma) and Late Jurassic (150–163 Ma) periods. Late Jurassic trachyandesites-trachytes show a low rare earth element and moderate light rare earth element (LREE) enrichment with no Eu anomalies. Early Cretaceous trachytes are characterized by an LREE enrichment and negative Eu anomalies. Contemporaneous rhyolites exhibit a significant LREE enrichment, A–type granitoid affinity, and pronounced negative Eu anomalies. Different negative Nb, Ta, and Ti anomalies, and positive zircon εHf(t) values, indicate that the ~160 Ma trachyandesites-trachytes are derived from partial melting of the lithospheric mantle that was metasomatized by subduction-related fluids. The ~125 Ma trachytes and rhyolites were possibly generated by partial melting of the accreted Meso-Neoproterozoic lower crust. New and previously published geochemical, isotopic and geochronological data from the southern GXR, eastern Mongolia and East-Transbaikalia, suggest that Late Jurassic–Early Cretaceous volcanism in the southern GXR occurred during the post-collisional extension after the closure of the Mongol–Okhotsk Ocean. [ABSTRACT FROM AUTHOR]

Large volumes of Early Cretaceous adakitic rocks crop out in northeast China. In this paper, we summarize their spatial-temporal distribution and geochemical characteristics. These adakitic rocks exhibit variable MgO, Cr and Ni contents, as well as potassium enrichments, in contrasting with those of the slab melting derived adakites. Positive εNd(t) and εHf(t) values and low 87Sr/86Sr(i) indicate significant Phanerozoic crust growth in NE China. Based on their geochemistry, these adakitic rocks are mainly derived from partial melting of juvenile lower crust. We interpret the melting to have resulted from extension and associated delamination. The ages of adakitic rocks are 141–120 Ma in the Xing'an region, 129–113 Ma in the Songliao basin, and 113–90 Ma in the Jiamusi region. Based on the lower-crustal-melting geochemical characteristics and spatial distribution of ages, we propose a new two-stage convergent bidirectional subduction model: Mongol-Okhotsk oceanic plate subduction and associated slab rollback in the west from 141–114 Ma and the Paleo-Pacific oceanic plate subduction and associated slab rollback in the east from 113–90 Ma. [ABSTRACT FROM AUTHOR]

This paper presents geochronological, geochemical, and zircon Hf–O isotope data for late Mesozoic intrusive rocks from the northeastern North China Craton (NCC), with the aim of constraining the late Mesozoic tectonic nature of the NE Asian continental margin. U–Pb zircon data indicate that the Late Mesozoic magmatism in the northeastern NCC can be subdivided into two stages: Late Jurassic (161 − 156 Ma) and Early Cretaceous (125 − 120 Ma). Late Jurassic magmatism consists mainly of monzogranites. These monzogranites display high Sr/Y ratios and the tetrad effect in their REE, respectively, and have negative εHf(t) values (−22.6 to −15.8). The former indicates that the primary magma was generated by partial melting of thickened NCC lower crust, the latter suggests that the monzogranites were crystallized from highly fractionated magma, with the primary magma derived from partial melting of lower continental crust. Combined with the spatial distribution and rock associations of the Late Jurassic granitoids, we conclude that the Late Jurassic magmatism in the eastern NCC formed in a compressional environment related to oblique subduction of the Paleo-Pacific Plate beneath the Eurasia. The Early Cretaceous magmatism consists mainly of granitoids and quartz diorites. The quartz diorites formed by mixing of melts derived from the mantle and lower crust. The coeval granitoids are classified as high-K calc-alkaline and metaluminous to weakly peraluminous series. Some of the granitoids are similar to A-type granites. The granitoid εHf(t) values and TDM2 range from −14.3 to −1.4 and 2089 to 1274 Ma, respectively. These values indicate that their primary magma was derived from partial melting of lower crustal material of the NCC, but with a contribution of mantle-derived material. We therefore conclude that Early Cretaceous magmatism in the northeastern NCC occurred in an extensional environment related to westward subduction of the Paleo-Pacific Plate beneath Eurasia. [ABSTRACT FROM AUTHOR]

The mechanism that triggered large-scale Late Mesozoic magmatism in the northeastern Great Xing'an Range (NE GXAR) is strongly controversial. In this paper, we present whole rock geochemistry and zircon trace element, U-Pb and Hf isotopic data on the volcanic rocks in the Longjiang and Guanghua formations in the northeastern Xing'an Block. Zircons with ages of 120–119 Ma indicate that these volcanic rocks were formed in the Early Cretaceous. Combined with previous data, it is clear that volcanic rocks in the NE GXAR erupted between 128 and 108 Ma. The andesite samples of the Longjiang Formation show high contents of Al2O3, CaO, and MgO, significant negative Nb, Ta, and Ti anomalies; εHf (t) values of zircons from the andesite sample vary from +4.13 to +7.67, indicating an enriched mantle source. The rhyolites of the Guanghua Formation show high SiO2 and K2O concentrations, low P2O5, MgO, Cr, and Ni contents and Mg# values. The positive εHf (t) values (+5.72 to +10.58) with two-stage Hf model ages ranging from 939 to 701 Ma indicate that the rhyolites are derived from the partial melting of basaltic lower crust. Combined with the regional geological evolution, we conclude that the generation of the Early Cretaceous volcanic rocks in the NE GXAR might be triggered by the dehydration, disintegration, and foundering of the Mongol-Okhotsk Oceanic flat-slab and the subsequent upwelling of the asthenosphere. [ABSTRACT FROM AUTHOR]

Northeast (NE) China is characterized by large areas of Mesozoic and Paleozoic granitoids, whereas Cenozoic granitoids are scarce. This paper reports LA-ICP-MS zircon U-Pb ages and whole-rock geochemical data for late Paleocene-early Eocene granitoids from the Jiamusi Massif, NE China, in order to determine their petrogenesis and tectonic implications. Geochronological data indicate that the granodiorite and dioritic porphyry from the Wudingshan pluton formed at 51.5 ± 0.3 Ma and 56.3 ± 0.8 Ma, respectively. The biotite-quartz diorite, biotite granodiorite, and dioritic porphyry have high SiO2 (68.38-70.06 wt.%), Al2O3 (15.34-15.79 wt.%), and Na2O (3.96-4.49 wt.%) contents, low MgO contents (1.10-1.26 wt.%), A/CNK ratios of 0.99-1.11, and are classified as medium- to high-K calc-alkaline and weakly peraluminous I-type granitoids. They are enriched in LREEs and LILEs, and depleted in HFSEs, with Nb/Ta ratios of 10.4-15.0. Moreover, they have negative Nb-Ta-Ti anomalies, indicating that they were derived from continental crust. Combining with the previously published isotopic data and regional geological results, we suggest that the late Paleocene-early Eocene granitoids (56-52 Ma) were probably derived from partial melting of juvenile lower crust, and formed in an active continental margin setting, possibly related to subduction slab rollback of the Paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

The northwest Zhejiang Province is a key domain for providing deep insight into the crust–mantle interaction and tectonic evolution of the South China block. In this paper, we collect geochemical, geochronological, and isotopic data of the Jurassic porphyries in this region, and investigated the Huangbaikeng ore-bearing porphyry in the Tongcun Mo–Cu deposit, using it as an example to uncover the porphyry petrogenesis and evaluate their metallogenic potential. Two varieties of the Huangbaikeng porphyry were distinguished: the medium- to coarse-grained type and medium- to fine-grained type. Zircon Sensitive High-Resolution Ion Microprobe U–Pb dating indicates that they were emplaced at 161.8 ± 2.8 and 162.7 ± 3.5 Ma, respectively, which are consistent with the molybdenite Re–Os ages of 163.9–161.8 Ma. The inherited zircons age spectrum significantly recorded a series of geological events, for example, assembly and breakup of the Columbia and Rodinia supercontinent, and the Triassic collision of Yangtze and North China blocks. Whole rock Sr–Nd and Jurassic zircon Hf isotopic data yield mostly negativeεHf(t) values (0.5 to −8.4) andεNd(t) values (−0.79 to −4.82). Besides the Huangbaikeng porphyry, all the Jurassic porphyries in the northwest Zhejiang Province have a wide range of SiO2contents (76.78–60.91 wt.%). They do not contain typical aluminous minerals (e.g. cordierite and garnet), and are mainly metaluminous to weakly peraluminous with high Na2O, low FeOT/MgO, and Zr + Nb + Ce + Y concentrations in composition. They thus fit the I-type granite definition. Some major and trace elements show strong correlations with SiO2, possibly indicating extensive fractional crystallization during their magma evolution. Tectonic discriminations imply that these plutons were likely formed in a volcanic arc regime possibly related to subduction of the Palaeo-Pacific plate. Sr–Nd–Hf isotopic data suggest a mixed source of the Mesoproterozoic crust and 30–50% mantle components. Compared with the adjacent Dexing Cu-bearing porphyies, which have more positiveεHf(t) andεNd(t) values with more significant mantle components (55–70%), the Jurassic porphyries in the northwest Zhejiang Province probably lack metallogenic potential to form a giant porphyry copper deposit as Dexing. [ABSTRACT FROM PUBLISHER]

Southern Hunan Province, located in the Cathaysia Block where the Shi–Hang zone and Nanling belt meet, is characterized by extensive Mesozoic magmatism and coeval polymetallic mineralization. The Huangshaping W–Mo–Pb–Zn–(Cu) deposit is representative in this area. However, the petrogenesis of the granitoids associated with the Huangshaping deposit, and their relationships with mineralization, remain undetermined. In this paper we focus on zircon U–Pb dating, whole-rock geochemistry, and Sr–Nd–Pb–Hf isotopic compositions in order to further our understanding of these issues, as well as their regional implications. The Huangshaping granitoids are characterized by two pulses of intrusive activity: a first-stage quartz porphyry and a second-stage felsite and granite porphyry, our new data show that the quartz porphyry and felsite formed at 160.5 ± 1.3 and 156.6 ± 1.4 Ma, respectively, representing a period of Late Jurassic magmatism. Granitic enclaves within the quartz porphyry crystallized at 160.2 ± 1.6 Ma, and zircons and apatites from the enclaves exhibit Hf isotopic and geochemical compositions that suggest a Palaeoproterozoic lower crustal melt as one end-member of the magma that formed the quartz porphyry, whereas another likely end-member was coeval mantle-derived magma, as indicated by the geochemistry and Sr–Nd–Pb–Hf isotopes. However, both the felsite and granite porphyry were probably derived from the melting of metamorphic basement rocks in the upper crust. The felsite clearly formed as a result of the rapid ascent and cooling of magma, whereas the granite porphyry underwent fractional crystallization. The magma sources and evolution of the granitoids, as well as their association with the Huangshaping mineralization, suggest that melting of upper crustal components controlled the W–Mo and Pb–Zn mineralization, whereas dehydration of a subducted slab provided the Cu mineralization in southern Hunan Province. [ABSTRACT FROM PUBLISHER]

The paper presents new U–Pb zircon ages and geochemical data from early Carboniferous volcanic rocks of the Wuerkashier Mountains in the northern West Junggar region, NW China, and of the Char suture–shear zone in East Kazakhstan. The study included analysis of geological setting, major and trace elements, and rock petrogenesis. Both localities host early Carboniferous volcanic units dominated by plagioclase-porphyry andesites and dacites. A West Junggar dacite yielded a206Pb/238U age of 331 ± 3 Ma. The Junggar volcanic rocks are tholeiitic, and the Char samples are intermediate between tholeiitic and calc-alkaline. Both the Junggar and Char volcanic units are characterized by LREE enriched rare-earth spectra (La/Smn = 1.1–2.4) with Eu negative anomalies (Eu/Eu* = 0.12–1.0) and Nb-Ta minimums (Nb/Thpm = 0.15–0.35; Nb/Lapm = 0.3–0.7) on multi-element spectra. The Junggar andesites and dacites have higher REE and HFSE (Ti, Nb, Zr, Y, and Th) compared with the Char rocks, suggesting their derivation from a different mantle source. The melting modelling in the Nb-Yb system showed that the Junggar volcanic rocks formed by low- to medium- (2–5%) degree melting of depleted mantle harzburgite and spinel lherzolite. The Char volcanic rocks formed by high-degree melting (15–20%) of spinel lherzolite and garnet-bearing peridotite. The regional geology of West Junggar and East Kazakhstan and the geochemical features of the rocks under study (i.e. depletion in Nb, Ta, and Ti and enrichment in Th, and combination of LREE enrichment and HFSE depletion) all suggest a subduction-related origin of both Junggar and Char volcanic rocks. The early Carboniferous volcanic rocks of West Junggar possibly formed by subduction of the Junggar-Balkhash ocean beneath an active margin of the Kazakhstan continent, whereas those of East Kazakhstan formed by subduction of the Irtysh-Zaisan Ocean beneath an intra-oceanic arc at the active margin of the Siberian continent. [ABSTRACT FROM AUTHOR]

The evolution history of the Hegenshan Ocean is an important part of studying the evolution of the Xingmeng orogenic belt, but it is still controversial. Here we present an integrated study of petrology, zircon U–Pb geochronology, whole-rock geochemistry, and Sr–Nd isotopes on a series of intrusive rocks from the Baiyinguole area, Xiwuqi, central Inner Mongolia, NE China. Chronological data indicate that the intrusive rocks can be divided into three stages: 326–317, 297–295, and 259–254 Ma. The 326–317-Ma gabbros and diorites belong to the calc-alkaline series, and are characterized by positive whole-rock εNd(t) values (+1.1–+6.7), relatively low La/Ba ratios (0.04–0.10), and high La/Nb ratios (1.82–3.18), indicating that the magma source is from a subduction-modified lithospheric mantle. These samples have arc features owing to the southward subduction of the Hegenshan oceanic crust. The 297–295-Ma granodiorites and monzogranites show positive εNd(t) values (+1.9–+2.4), low 87Sr/86Sri ratios (0.704185–0.705234), and young Nd two-stage model ages (TDM2), which is consistent with typical I-type granites. On various tectonic setting discrimination diagrams, the granodiorites and monzogranites are plotted in the syn-collisional field. The 259–254-Ma syenogranites have low abundances of mafic minerals, low contents of Zr/Hf (18.31–31.35) and Nb/Ta (6.80–11.80) values, high SiO2 (76.36–78.54 wt.%) content, A/CNK (1.08–1.76), and D.I. of 96.8–97.4 (average 97.1), and notable negative Eu anomalies (δEu* = 0.07–0.17) and weakly tetrad-effects in REE pattern, which is affinity to the characteristics of highly differentiated granites. Moreover, they have positive εNd(t) values (+2.0–+2.1) with scattered TDM2 of 730–1217 Ma and low Nb/U ratios. This study suggests that the syenogranites are formed in a post-collisional tectonic setting, which is related to the closure of the Hegenshan Ocean. In addition, based on a review of the pre-existing literature data, a model of southward ridge subduction is proposed to explain the tectonic evolution of the Hegenshan Ocean. [ABSTRACT FROM AUTHOR]

New whole-rock major and trace element, Sr-Nd isotopic, Zircon U-Pb, and Hf isotopic data for the Late Triassic intermediate-felsic intrusive rocks in the Liaodong Peninsula in the northeastern part of the North China Craton (NCC) were obtained in order to investigate their petrogenesis and provide insights into the Late Triassic tectonic evolution of the eastern segment of the NCC. The laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb ages indicate that they were emplaced at 230–219 Ma. Based on the petrology, petrography, and geochemistry, we divided these intrusions into dioritic rocks and granitic rocks. The dioritic rocks are mainly high-K calk-alkaline to shoshonitic biotite diorite and biotite amphibolite diorite. They are metaluminous, have high MgO contents at low to intermediate silica contents, are depleted in heavy rare earth elements (HREEs) and high field-strength elements (HFSEs), are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), and have εNd(t) values of −16.99 to −9.78 and εHf(t) values of −15.2 to −6.9, indicating that they were mainly derived from the lithospheric mantle, possibly with a small contribution from ancient continental crust. The granitic rocks mainly include biotite monzogranite and monzogranite. They have low MgO, Yb, and Y concentrations and high Sr/Y, La/Yb, and silica contents. They are high-K calk-alkaline to shoshonitic and metaluminous to weakly peraluminous adakitic I-type granites. They are enriched in LREEs and LILEs, are depleted in HREEs and HFSEs, and have εNd(t) values of −16.95 to −14.21 and εHf(t) values of −18.4 to −10.8, indicating that they were mainly derived from partial melting of a thickened ancient lower continental crust. Combined with the spatial and temporal distributions of the Late Triassic rocks, we conclude that these Late Triassic rocks were formed in an extensional environment resulting from slab break-off of the subducted Yangtze Craton beneath the North China Craton, which also resulted in lithospheric thinning of the North China Craton. [ABSTRACT FROM AUTHOR]

The West Bogda Mountains separate the two largest petroliferous sedimentary basins in Northwest (NW) China and may record the evolution history of the Central Asian Orogenic Belt (CAOB). The timing of the initial uplift of the West Bogda Mountains is debated, which may provide the robust constraint on the CAOB evolution. Here we present an integrated study of sedimentology, geochemistry, and detrital zircon geochronology to constrain the timing of the initial uplift of the West Bogda Mountains. The late Lower Permian Lucaogou Formation in the West Bogda Mountains is dominated by organic-rich laminated shale, gravity flow deposits and dolomite without shallow-water sedimentary structures, suggesting a deep-water lacustrine depositional environment. The Middle Permian Quanzijie Formation is mainly composed of poorly sorted and sub-rounded conglomerate, which indicates that the depositional environment changed to an alluvial fan. The depositional environment changed to a meandering river system in the early Upper Permian Wutonggou Formation, with evidence from the widely developed cross-bedding in its sandstone and the typical 'dual structure'. The compositions of immobile elements and detrital zircon U-Pb geochronology reveal changes in sediment sources from the early to late Permian. The sediments of the late Lower Permian Lucaogou Formation were mainly sourced from the North Tianshan, while the sediments in the Middle Permian were mostly locally derived. Combining these evidences, we infer that the initial uplift of the West Bogda Mountains likely occurred in the period from the late Lower to Middle Permian (~289.8 Ma to ~265.7 Ma), and was probably caused by the intracontinental collision between Junggar Block in the north and the Tarim Block in the south. [ABSTRACT FROM AUTHOR]

Early Paleozoic subduction beneath peri-Gondwana microcontinents formed a major Proto-Tethys magmatic arc system. Appinite suite rocks constitute important components within that magmatic arc. Herein, we report hornblende 40Ar/39Ar and zircon U–Pb geochronology data, zircon Hf isotope, mineral chemistry, whole-rock geochemistry, and Sr–Nd–Pb isotope data for the rocks of hornblende gabbro-diorite-quartz diorite-quartz monzodiorite from the Renda appinite suite and adjacent granite porphyry in the southeastern Qilian Orogen. Hornblende 40Ar/39Ar and zircon U–Pb isotopic data constrain ages of the intrusions of the Renda appinite suite to 439–435 Ma. Rocks in this suite represent the calc-alkalic to alkali-calcic series, and they are enriched in large-ion lithophile elements and depleted in high-field-strength elements. The hornblende gabbros exhibit moderate initial 87Sr/86Sr ratios (0.7046–0.7055) and higher whole-rock εNd(t) (–1.3 to +1.7) and zircon εHf(t) (+7.2 to +11.2) values relative to the other rocks of the suite (0.7047–0.7064, – 7.7 to – 1.1, and – 6.6 to +6.8, respectively) as well as Pb isotopic features similar to EM2 lithospheric mantle. These geochemical characteristics suggest that the Renda appinite suite originates from partial melting of an enriched lithospheric mantle, with subsequent fractional crystallization and hybridization with crustal components. The granite porphyry formed by partial melting of the crust coeval with the emplacement of juvenile magma. This study suggests emplacement occurred during a short-lived collision with slab failure (breakoff) after latest stage (cessation) of Proto-Tethys oceanic subduction along the northern side of the southeastern Qilian Orogen. The heat supplied by the asthenospheric upwelling through a gap in the subducted slab induced melting in lithospheric mantle and deep crust producing Renda appinite suite rocks and granite porphyry. [ABSTRACT FROM AUTHOR]

The Wanbaogou granitic plutons are exposed along with coeval volcanic rocks, and provide an opportunity to investigate Silurian tectonism in the South Kunlun belt, northwest China. This study presents new whole-rock geochemical, and zircon U–Pb geochronological and Lu–Hf isotope data for Silurian intrusive rocks of the Wanbaogou area. We analysed four samples: a porphyritic monzogranite and dioritic dike from the Wanbaogou pluton and a granodiorite and monzogranite from the Wudaogou pluton. Zircon U–Pb dating yielded similar ages of 423.8 ± 1.9, 422.9 ± 1.9, 424.9 ± 2.0, and 425.3 ± 2.6 Ma, respectively. indicating that the intrusions were coeval. The granitic samples are mostly transitional between the high-K and shoshonite series. The Wanbaogou monzogranite is metaluminous and has features typical of A-type granites in terms of trace element geochemistry, whereas the Wudaogou granitoids are metaluminous to weakly peraluminous I-type granites. The Wanbaogou dikes are intermediate to mafic in composition and belong to the low- to medium-K series. The four intrusive samples have εHf(t) values of −10.62 to +0.99 (average = −2.52), similar to the εHf(t) values of intraplate volcanic rocks (−6.35 to +2.89; average = −1.82) and, combined with the geochemical data, indicate the 430–420 Ma magmatism could have been generated by crustal melting with input from mantle-derived materials, followed by crustal contamination. Data for the Wanbaogou and Wudaogou plutons, dikes, and volcanic rocks from the same area suggest rapid orogenic uplift at 430–420 Ma. Our data and the results of previous research on the Kunlun high- to ultra-high-pressure metamorphic belt and coeval volcanic and intrusive rocks elsewhere in the region suggest that collisional tectonism ceased abruptly at 430–420 Ma. Slab break-off may be responsible for this termination of tectonism and rapid uplift. [ABSTRACT FROM AUTHOR]

The modification of the Archaean lithospheric mantle root beneath the eastern North China Craton (NCC) has been noticed. However, the degree of modification and the characteristics of metasomatic agents for the NCC lithospheric mantle are still unclear. Here, we compile the geochemistry and 87Sr/86Sr and 143Nd/144Nd isotope ratios of Cretaceous primitive basalts (Yixian, Sihetun, Fangcheng and Feixian) from the eastern NCC and estimate the inputs of subduction-related elements into the Archaean lithospheric mantle beneath the NCC. These basalts show primitive (high MgO, Cr and Ni contents) and arc-like geochemical features (enrichments in LILEs and depletions in HFSEs) that indicate that the mantle sources were modified by fluids related to subducted crustal materials. Substantial proportions of subduction-mobile elements (e.g. ~95% Ba and ~90% Th) transferred to the basalt sources via hydrous melts. Thus, a large volume of fluids transferred into the lithospheric mantle. The data support the model that the NCC Archaean lithospheric mantle was weakened by hydrous melts, which resulted in a fusible weakened lithospheric mantle. Preliminary lithospheric thinning was induced by the extension of the NCC resulting from trench retreat of the Paleo-Pacific plate at ~140-120 Ma. Then, decompression melting of the lithospheric mantle caused pervasive melts in the weakened lithospheric mantle, resulting in the lithospheric mantle having a low viscosity comparable to the asthenospheric mantle, which principally reduced the lithospheric mantle. [ABSTRACT FROM AUTHOR]

There is a broad consensus that subduction of the Paleo-Pacific oceanic plate has caused extensive magmatism, lithospheric deformation, and metal mineralization in the eastern margin of the Eurasian continent during the Late Mesozoic. However, the onset and extent of subduction of the Paleo-Pacific Ocean, especially the timing of the transition in tectonic regime from the Paleo-Asian Ocean to Paleo-Pacific, and extent of the subduction of the Paleo-Pacific Ocean remain poorly constrained. To address these key issues, we present regional geological observations, zircon U–Pb dating, whole-rock geochemistry, and Hf isotopic compositions of the Jurassic intrusions at the northern margin of the North China Craton, with the aim of constraining their petrogenesis and the tectono-magmatic events related to subduction of the Paleo-Pacific Ocean. The geochronological and geochemical results indicate that these intrusions were emplaced between 177 and 155 Ma, with distinct geochemical features. The Huajianggou pluton (HJG), Tongjiatun pluton (TJT), and Haoguantun pluton (HGT) are characterized by high Al2O3 and Sr contents, and low MgO, TFe2O3, Y, Yb, and heavy rare earth elements (HREEs) contents, coupled with high Sr/Y values (34.10–94.36), showing adakitic affinities. Based on these geochemical characteristics, we suggest that these adakitic magmas (i.e. the HJG, TJT, and HGT plutons) were produced by partial melting of thickened lower crust in response to earlier subduction of the Paleo-Pacific oceanic plate beneath the northern margin of the North China Craton. In contrast, the Baijiagou pluton (BJG) and Sheshangou pluton (SSG) are high-K calc-alkaline rocks with low Sr/Y ratios (0.80–17.77), and they exhibit petrological and geochemical characteristics of I-type granites, indicating an origin from the lower crust, with variable degrees of fractional crystallization. In addition, the Bakeshu pluton (BKS) is mainly comprised of diorite that displays high SiO2, low MgO, Cr, and Ni contents, with Mg# of 39.8–42.9, indicating a lower crustal origin. Despite the range in ages of these intrusions, all the Jurassic calc-alkaline intrusions show typical geochemical characteristics of active continental margins, such as enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depletion in high field strength elements (HFSEs). Combined with spatial-temporal variations of coeval magmatic rocks along the northern margin of the North China Craton, we suggest that the transition in tectonic regime from the Paleo-Asian Ocean to Paleo-Pacific Ocean was initiated in the Early Jurassic. These Jurassic intrusions formed in an active continental margin setting, related to westward subduction of the Paleo-Pacific oceanic plate. Importantly, the Early Jurassic subduction-related calc-alkaline magmatic rocks in northeast (NE) China constitute a NE-trending magmatic arc belt, which is best explained as continental magmatism triggered by the westward subduction of the Paleo-Pacific oceanic plate. [ABSTRACT FROM AUTHOR]

Late Mesozoic lithospheric extension in NE China resulted in the development of a large extensional province and widespread formation of volcanic-sedimentary basins. The Songliao Basin is the largest one and contains voluminous volcanic rocks composing the majority of the basin fill. This study focuses on two adjacent eruption cycles, the Huoshiling Formation (K1h) and the first member of the Yingcheng Formation (K1yc1), in the Changling fault depression of the Songliao basin, constrains their time ranges and compares the origins of volcanic rocks. Zircon populations from K1h yield U-Pb ages of 124–118 Ma; those from K1yc1 yield younger ones (115–106 Ma). Different volcanic rocks are identified in K1h (alkaline basic rocks, calc-alkaline intermediate-acid rocks) and K1yc1 (alkaline basic rocks, A-type rhyolites), and their geochemistry and isotope characteristics confirm their different origins. The alkaline basic rocks from K1h have the similar magma source as those from K1yc1; both formed under within-plate conditions from an ocean island basalt (OIB)-type mantle source, assumed to be the heterogeneous shallow asthenosphere. The calc-alkaline intermediate-acid volcanic rocks from K1h formed by fractional crystallization of magma, related to the enriched lithospheric mantle, whereas the A-type rhyolites from K1yc1 directly originated from the partial melting of crust newly formed from the depleted mantle. The development of alkaline basic rocks and A-type acid rocks, a typical bimodal volcanic assemblage in K1yc1, requires a relatively thin lithosphere and thus implies that lithospheric thinning reached its maximum during this time (115–106 Ma). However, the rare expression of alkaline basic rocks and the formation of acid rocks mainly by fractional crystallization in K1h indicate that the lithosphere was relatively thick; during this time (124–118 Ma), the lithosphere below the Songliao Basin had just begun thinning. These different stages of lithospheric extension may be due to the intermittent rollback of the Palaeo-Pacific Plate. [ABSTRACT FROM AUTHOR]

Early Carboniferous magmatism of the southern West Junggar (SWJ) region is essential for understanding the accretionary processes and crustal growth in the southwestern segment of the Central Asian Orogenic Belt. A comprehensive study of geochronological, geochemical, and Sr-Nd-Pb-Hf isotopic compositions was carried out in this study for basalts from the Baogutu Formation in Sulushuoke region, aiming to provide constraints on the Early Carboniferous tectonic evolution of the SWJ, NW China. LA-ICP-MS zircon U-Pb dating of four basalt samples yielded crystallization ages ranging from 339 Ma to 347 Ma, indicating the presence of early Carboniferous volcanic rocks in West Junggar. The studied tholeiitic basalts are geochemically characterized by nearly flat REE patterns, enriched large iron lithosphere elements (e.g. K) and depleted high field strength elements (e.g. Nb, Ta, Zr, Hf) relative to those in N-MORB, resembling those of modern Mariana Trough back-arc basin basalts. In addition, they have high positive εNd(t) values (+5.86 to +6.59) with initial 87Sr/86Sr ratios in the range of 0.704783–0.705315 and variable εHf(t) values (+3.99 to +15.6). The rocks cover restricted ranges in initial Pb isotope ratios with (206Pb/204Pb)i from 17.529 to 18.289, (207Pb/204Pb)i from 15.509 to 15.627, and (208Pb/204Pb)i from 37.628 to 38.397. These signatures indicate that the tholeiitic basalts were derived from 10% to 20% partial melting of a spinel-lherzolitic N-MORB-like depleted mantle source modified by fluids released from the subducted lithosphere in a back-arc extensional setting. From our new data presented in this study and in conjunction with those from previous works, we, therefore, suggest that a back-arc basin related to the northwestward subduction of the Junggar oceanic crust was developed in the Hatu-Baogutu region during the early Carboniferous time. [ABSTRACT FROM AUTHOR]

The palaeoproterozoic tectonic/geodynamic evolution of the Jiao-Liao-Ji Belt (JLJB), one of the three representative palaeoproterozoic tectonic units in the North China Craton (NCC), remains controversial. The palaeoproterozoic mafic dikes sampled in the Jiaobei terrane, situated in the southern segment of the JLJB, could provide significant evidence for the JLJB's evolution. Their LA-ICP-MS zircon U-Pb dating data show that these dikes were emplaced at the period of ~2175 Ma. They have relatively low SiO2 contents and relatively high contents of Al2O3, MgO, Cr, and Ni. Further, they exhibit high field strength elements (HFSE) (e.g. Nb and Ta) depletion and weak Eu anomalies. Also, they show limited initial 87Sr/86Sr ratios (0.700478–0.705069) and low ɛNd(t) values (−2.07 to −0.09) with model ages (TDM1) of 2722–2967 Ma. The magmatic crystal zircons yielded low ɛHf(t) values of −9.22 ~ −3.82 relative to the corresponding Hf model ages of 2627–2870 Ma. These geochemical characteristics of the dikes indicate that they originated via 5–10% partial melting of the North China Craton's enriched lithospheric mantle within the spinel stability field. In combination with contemporaneous A-type granites, mafic rocks, and other meta-volcanic associations, palaeoproterozoic Jiaobei mafic dikes formed in a back-arc extensional tectonic setting. This further indicates that the JLJB experienced back-arc extending triggered by slab rollback of subducted oceanic plate at ~2175 Ma ago. This study reports new evidence regarding the evolution of Precambrian tectonics of the North China Craton. [ABSTRACT FROM AUTHOR]

Formation of a large igneous province, an explosive magmatic event in earth, is intimately related to geodynamic processes. The Tarim large igneous province, a famous representative in China, contains A-type granites. However, the petrogenesis of the A-type granites is debated. Some researchers think that the A-type granites are developed through extensive fractionation of magma derived from partial melting of newly underplated or gabbroic rocks. Others insist that the A-type granites are developed through intensive fractional crystallization of plume-derived mafic magma. Here, we present zircon U–Pb ages and whole-rock geochemical and Sr–Nd isotopic data for the Kezilekezitage, Keziertuo, Tamu, and Halajun II intrusions in northwest Tarim to elucidate their petrogenesis and geodynamic implications. Zircon U–Pb dating yielded crystallization ages of the Kezilekezitage, Keziertuo, and Halajun II intrusions of 275.1 ± 3.1 Ma (MSWD = 1.14), 274.8 ± 1.8 (MSWD = 0.46) and 275.6 ± 0.7 (MSWD = 1.04), respectively. The whole-rock geochemistry of the four intrusions is characterized by REE and HFSE enrichment, Ba, Sr, P, Ti, and Eu depletion, εNd (t) values of – 1.2 to +0.3, two-stage Nd model ages (T2DM) of 1.14–1.02 Ga, and an A1-type granite affinity. Whole-rock zircon geothermometry indicates a high formation temperature of 721–924°C. It is concluded that these A-type granites were generated by partial melting of Neoproterozoic OIB-like rocks, coupled with extensive fractional crystallization and minor crustal contamination. The production of the A-type granites at ca. 275 Ma represented the termination and greatest degree of lithospheric thinning during large igneous province formation. [ABSTRACT FROM AUTHOR]

NE Asia has experienced Significant extensional events in the Early Cretaceous, including related volcanic rocks, extensional basins, metamorphic core complexes (MCCs), and low-angle detachment faults. Previous studies primarily focused on the eastern North China Craton (NCC); however, the extensional manifestations in the western NCC are poorly studied and the mechanism is still controversial. This study reports Wuliji volcanic clusters in northern Alxa Block, westmost NCC. Geologic mapping shows that the volcanic cluster is mainly composed of dark grey basalts with interlayered pyroclastic rocks showing columnar joints. The youngest LA-ICP-MS zircon U-Pb age is 103 Ma, consistent with the age constrained by fossils in the interlayered sandstones. Though the Wuliji basalts have amounts of captured zircons, the high MgO, TFe2O3 and low SiO2, along with Nb/U, Nb/Ta, Zr/Hf ratios and positive Nb, Ta anomalies, indicating no contamination of continental crustal materials. These alkaline basalts are characterized by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), slightly positive Eu anomalies and no Nb and Ta depletions similar to other volcanic rocks in Alxa Block, implying an affinity with ocean island basalts (OIB). These volcanic rocks could have been derived from the partial melting of spinel lherzolite in an intracontinental rift setting. The basalts in the Alxa Block are slightly younger than basalts in the eastern NCC in the Early Cretaceous. The occurrence of Early Cretaceous basalts and coeval rift basins with various extensional faults in the westmost NCC may have resulted from the eastward movement of mantle materials due to the rollback of the Paleo-Pacific Plate to the east. [ABSTRACT FROM AUTHOR]

Neoproterozoic rocks in the Phan Si Pan Zone, NW Vietnam are considered to be the remnant of the ancient continental crust. They recorded the evolution of the Gondwana supercontinent. A combined study of U-Pb geochronology and Sr-Nd-Hf isotopic geochemistry has been carried out for the Neoproterozoic granites in the Phan Si Pan Zone. Zircon LA-ICP-MS data yield crystallization ages ranging from 758.0 ± 5.0 to 762.0 ± 8.1 Ma. The Neoproterozoic granites have variable (87Sr/86Sr)i ratios of 0.7029 to 0.708 and a wide range of εNd(t) values (−2.02 to 0.04) and of zircon εHf(t) values (−5.1 to 0.0). All these characteristics suggest an origin through partial melting of ancient crustal source rocks with small amount input from the mantle material. Whole-rock Nd and zircon Hf isotopic model ages mostly vary from 1.67 Ga to 1.99 Ga, indicating the existence of the Paleoproterozoic source material in the study area. Neoproterozoic granites in the Phan Si Pan Zone, NW Vietnam have a similar tectonic evolution to those in SW Yangtze, South China. [ABSTRACT FROM AUTHOR]

Mesozoic magmatic rocks are widely distributed in and around the Tan-Lu fault zone (TLF) and show great significance related to the destruction processes of the lithosphere and the evolution of magma sources. This study aims to decipher the petrogenesis of the Early Cretaceous magmatism along the TLF, in order to address the tectonic mechanism for the North China Craton (NCC) lithospheric destruction. This contribution combines investigations of geochemistry, SHRIMP zircon U-Pb ages and O-Hf isotopes of the intermediate to felsic rocks from middle-southern TLF with previous geochronological and geochemical characteristics of other rocks from the study area. Four different rocks are identified: high Mg# adakitic rocks (HMA), low Mg# adakitic rocks (LMA), normal intermediate-felsic rocks (NIF) and A-type granitoids. The emplacement time of the LMA rocks in the Dabie area (143 Ma) were earlier than in the Sulu area (130 Ma). The HMA rocks were formed at the same time (~135 Ma) in the above two areas but the magmatism lasted longer in Jiaodong area, which was near the subduction zone of the Paleo-pacific plate. The HMA rocks are concluded to be derived from the melting of a delaminated thickened lower crust and including reaction with overlying mantle. After 135 Ma, the magmatism in this area exhibited an eastward-younging trend, consistent with plate retreat in the Early Cretaceous. Plutons that were emplaced during 135–125 Ma have higher Ba/Th, Ba/La and Ce/Pb, suggesting magma source for these rocks was metasomatized by hydrous fluids from the subducted plate. At ~125 Ma, A-type granitoids began to be formed. The TLF acted as a favourable channel for transporting mantle material and fluids which made the lithosphere in this area more likely to be destroyed and thinned. [ABSTRACT FROM AUTHOR]

The tectonic evolution of the Hegenshan Ocean is an important but poorly understood issue in the geology of the southeastern Central Asian Orogenic Belt (CAOB). Here we present an integrated study of petrology, geochronology, geochemistry, and Sr–Nd–Hf isotopes on a volcanic suite from the Baoligaomiao Formation near Dongwuqi, central Inner Mongolia, NE China. LA-ICP-MS zircon U–Pb dating indicates that the volcanic rocks formed at the Carboniferous–Permian boundary (ca. 301–297 Ma). Geochemistry data reveal that the rocks belong to alkaline to sub-alkaline series, and are characterized by enrichments in light rare earth elements (LaN/YbN = 13.01–39.30) and large ion lithophile elements and depletions in heavy rare earth elements and high field strength elements (e.g., Nb, Ta, and Ti). They have relatively low initial 87Sr/86Sr ratios (0.702570–0.708084) and highly positive whole-rock ԐNd(t) (2.27–2.72) and zircon ԐHf(t) values (0.66–11.92). These geochemical characteristics and Sr–Nd–Hf isotopic compositions reveal that the rocks originated from partial melts of a juvenile, arc-type middle-lower crust, with fractional crystallization as a dominant factor controlling the magma differentiation. The rocks were generated in a post-collisional regime, and occurred as a magmatic response to the final closure of the Hegenshan Ocean at the Late Carboniferous (ca. 305 Ma). In addition, based on a review of the pre-existing literature data, a model of continental arc–back-arc basin system at the southern margin of South Mongolian microcontinent is proposed to explain the tectonic evolution of the Hegenshan Ocean. [ABSTRACT FROM AUTHOR]

Mesozoic granitoid rocks in the eastern Qinling terrane along the southern margin of the North China Craton are significant for understanding geodynamics processes related to lithospheric delamination in the Late Mesozoic. In addition, these rocks have close genetic association with the largest Mo-(Au-Ag) polymetallic mineralization belt in China. In the present study, zircon U-Pb ages and elemental and Sr-Nd-Pb isotopic geochemistry are reported for two representative granite plutons (Heyu and Lantian) exposed in the eastern Qinling terrane. Granitoid rocks from both plutons are metaluminous to weakly peraluminous and are classified as I-type granite with formation ages of 145 ~ 135 Ma and 150 Ma, respectively. These rocks are characterized by adakite-like affinity without significant Eu anomalies. Both plutons have relatively high initial 87Sr/86Sr ratios ranging between 0.7063 and 0.7109 and variable εNd(t) values of – 29.2 to – 6.5. Their Pb isotopic compositions are comparable to those of old high-grade metamorphic basement rocks from the North China Craton but are different from those of country rocks from the Xiong'er and Taihua groups. These features indicate genesis via reworking of the lower crust beneath North China and partial involvement of juvenile crustal material to different extents. Occurrences of ca. 1000-Ma-old inherited zircon in the Lantian granites imply the contribution of the Qinling Group in North Qinling to the magma source(s). This magmatism occurred intensively in a transitional setting from compression to extension and was likely induced by lithosphere thinning and asthenosphere upwelling beneath eastern China during the Cretaceous. [ABSTRACT FROM AUTHOR]

The Qinling orogen is a key area for understanding the processes of subduction and collision between the South China Block (SCB) and North China Block (NCB). The Wuguan Complex, distributed along the southern margin of the Shangdan suture zone, can provide important constraints on the age of collision between NCB and SCB and the tectonic evolution of the Qinling orogen in Late Paleozoic. Detrital zircons from meta-sedimentary rocks of the Wuguan Complex in the Danfeng-Shangnan area have an age spectrum with two main peaks at ~448 Ma and ~819 Ma, and two subordinate peaks at ~938 and ~1440 Ma, respectively, and are interpreted to have been derived from the North Qinling terrane (NQT). The petrographic and geochemical characteristics of the meta-sedimentary rocks indicate that they were deposited in a fore-arc basin along the southern margin of the NQT. The youngest detrital zircons yield a weighted mean age of 378 ± 3 Ma, indicating that the fore-arc deposition was continuing at least to this time, which implies that the Paleo-Qinling Ocean between the NCB and SCB was not finally closed until at least the late Devonian. In combination with regional data, we propose that sedimentary rocks of the Wuguan Complex might once have been a sequence of late Ordovician to late Devonian strata with intercalated mafic rocks, which has been dismembered by the later tectonic activity. It was metamorphosed during northward subduction of the Paleo-Qinling Ocean at ca. 320 Ma, and slowly cooled through ca. 350°C at ca. 247 Ma (muscovite 40Ar/39Ar age). It has recorded the detailed processes of subduction and collision between the NCB and SCB. [ABSTRACT FROM AUTHOR]

The central Great Xing'an Range contains widespread exposures of Mesozoic igneous rocks, yet the origin of its Late Mesozoic volcanic rocks has long been controversial. They are composed of andesite, trachyte, trachyandesite, trachydacite, rhyolite, and minor basaltic andesite. The intermediate rocks are enriched in large ion lithophiles and light rare earth elements (LILEs and LREEs) and are depleted in high field strength elements (HFSEs) such as Nb, Ta, and Ti, with positive εHf(t) values (+6.2 to +13.4) and Hf single-stage model ages (TDM1 = 556–227 Ma). This indicates that they were derived from the partial melting of a mantle wedge that was modified by previously subducted slab-derived fluids was likely introduced with limited crustal contamination. The felsic rocks show positive εHf(t) values (+4.3 to +10.2) and Hf two-stage model ages (TDM2 = 910–544 Ma), with more enrichment of LILEs and LREEs and more depletion of HFSEs and negative Eu anomalies. This indicates that felsic rocks were mainly derived from partial melting of Neoproterozoic accreted quartz-amphibolite facies mafic crust. We summarise the geochronological and Hf-Nd isotope data for Mesozoic igneous rocks within the central Great Xing'an Range (CGXR), the northern Xing'an block (NXB), and the Erguna block (EB), with the aim of constraining the geochronological framework for Mesozoic volcanism and comparing the growth of continental crust. The evolution of Late Mesozoic magmatism in the three areas reached its climax ~125 Ma ago. Our data, together with regional isotope evidence, suggest that crustal accretion of the CGXR occurred during the Neoproterozoic–Phanerozoic. However, that of the EB occurred during the Meso- to Neoproterozoic. The EB exhibits more lateral and vertical heterogeneities and ancient continental crust than the CGXR and NXB in the northern magma source region. [ABSTRACT FROM AUTHOR]

We present new zircon U-Pb and Hf isotopic as well as whole-rock geochemical data for volcanic rocks from the eastern margin of the Xing’an Massif, Northeast China, in order to further our understanding of the suture location between the Xing’an and Songnen-Zhangguangcai Range massifs. Zircon secondary ion mass spectrometry U-Pb dating indicates that the volcanic rocks formed during the Early-Middle Ordovician (473-463 Ma). Compared with the coeval Moguqi basalts (rare earth element [REE] = 171-183 ppm; εHf(t) = +0.3 to +2.7; TDM1 = 1074-977 Ma), the Duobaoshan andesites exhibit lower overall REE abundances (109-131 ppm) with relatively high heavy REE contents, stronger high-field-strength element depletion, higher εHf(t) values (+13.0 to +14.8), and much younger TDM1 ages (559-484 Ma). This suggests that the primary magma for the andesites was generated by the partial melting of a relatively depleted mantle wedge that was metasomatized by subduction-related fluids. The primary magma for the basalts in the Moguqi area was probably derived from the partial melting of a relatively enriched lithospheric mantle that was also modified by fluids sourced from a subducted slab. These interpretations suggest that the andesites in Duobaoshan formed in a newly accreted island arc setting, whereas the coeval basalts in Moguqi formed along an active continental margin. We therefore attribute the Early-Middle Ordovician volcanism along the eastern margin of the Xing’an Massif to the northwestward subduction of the Nenjiang-Heihe oceanic plate beneath the Xing’an Massif. Furthermore, considering coeval igneous activity in the southern parts of the Xing’an Massif, we suggest that a magmatic arc existed along the margin of the Xing’an Massif in the early Palaeozoic (490-420 Ma). We conclude that the location of the suture between the Xing’an and Songnen-Zhangguangcai Range massifs runs from Airgin Sum, via south of Xilinhot, to Ulanhot, Moguqi, Nenjiang, and finally Heihe. [ABSTRACT FROM AUTHOR]

The Ningwu Volcanic Basin (NVB), located in the Lower Yangtze Metallogenic Belt, is characterized by the widespread occurrence of porphyritic iron-ore deposits. These deposits are clustered in three areas within the basin: the northern, central, and southern districts. Our study shows that the differences are existed in geochemistry of the rocks and the mineralization of the deposits among these three districts. Though results of Sr-Nd isotopes indicate that the parental magma of the sub-volcanic rocks in NVB were derived from EMI and EMII, however, the sub-volcanic rocks from the northern and southern districts have higher εNd(t) values (t = 130 Ma) and lower initial 87Sr/86Sr ratios (t = 130 Ma) than those from middle district. The rocks from northern and southern districts are similar to EMI in geochemistry; in contrast, rocks from the middle district are close to EMII. Meanwhile, the deposits from different districts show some differences in mineralization. The magnetites from the northern ore deposits are rich in Cu, Mo, Zn, and Mg and poor in Ca, Al, and Ti, which probably indicates that the magnetites from the northern ore deposits closer to hydrothermal genesis than to magmatic genesis, but the magnetites from the centre are closer to both magmatic and hydrothermal geneses. Based on the fact that a part of the sub-volcanic rocks is closer to EMI and another part to EMII in geochemistry, we suggested that the incorporation of the lower and upper crustal materials into the source regions of the sub-volcanic rocks has taken place by different manner and processes. Integrated with analysis of the tectonic evolution of NVB, we come to the conclusion that the sub-volcanic rocks have recorded the geochemical imprints of the subduction of Yangtze block towards North China block during Indosinian Period and the delamination of the lower crust of Yangtze block during Yanshanian Period. [ABSTRACT FROM AUTHOR]

Stone coal is defined as a combustible, low-heat value, high-rank black shale of early Paleozoic (in a few cases, Permian) age, widely distributed in southern China. Attention has been focused on stone coals because (1) they can be used as fuel energy (for power plants and daily use in some villages) mainly in southern China; (2) they are enriched in critical elements and are currently industrially (economic extraction of V) and agriculturally (such as Se) utilized or have such a great potential (e.g. Au, platinum group elements, Mo, and Ni); (3) they are the sources for some toxic elements that have caused environmental pollution (e.g. SO2 emission during their combustion) and endemic diseases such as selenoisis and fluorosis; and (4) they can provide useful information for geological events and regional geological setting (e.g. hydrothermal activities). This article reviews stone coal’s definition; occurrence and distribution; petrologic properties, mineralogy, and geochemistry; adverse impacts on environment and human health; and by-products of critical elements as well as major challenges remaining from point of view of determining element enrichment mechanisms, utilization of critical elements, and control of toxic elements released during stone coal utilization. [ABSTRACT FROM AUTHOR]

We report zircon U-Pb geochronologic and geochemical data for the post-collisional volcanic rocks from the Batamayineishan (BS) Formation in the Shuangjingzi area, northwestern China. The zircon U-Pb ages of seven volcanic samples from the BS Formation show that the magmatic activity in the study area occurred during 342-304Ma in the Carboniferous. The ages also indicate that the Palaeo-KaramailiOcean had already closed by 342Ma. Moreover, the volcanic rocks also contained 10 inherited zirconswith ages ranging from 565 to 2626 Ma, indicating that Precambrian continental crust or microcontinents with accretionary arcs are two possible interpretations for the basement underlying the East Junggar terrane. The sampled mafic-intermediate rocks belong to the medium-K to high-K calc-alkaline and shoshonitic series, and the formation of these rocks involved fractional crystallization with little crustal contamination. These Carboniferous mafic-intermediate rocks show depletions in Nb and Ta and enrichments in large ion lithophile elements (e.g. Rb, Ba, U, and Th) and light rare earth elements. The low initial 87Sr/86Sr values (0.7034-0.7042) and positive εNd(t) values (+2.63 to +6.46) of these rocks suggest that they formed from depleted mantle material. The mafic-intermediate rocks were most likely generated by 5-10% partial melting of a mantle source composed primarily of spinel lherzolite withminor garnet lherzolite that had been metasomatized by slab-derived fluids and minor slab melts. In contrast, the felsic rocks in the BS Formation are A-type rhyolites with positive εNd(t) values and young model ages. These rocks are interpreted to be derived from the partial melting of juvenile basaltic lower crustal material. Taken together, the mafic-intermediate rocks formed in a post-collisional extensional setting generated by slap breakoff in the early Carboniferous (342-330 Ma) and the A-type rhyolites formed in a post-collisional extensional setting triggered by the upwelling asthenosphere in the late Carboniferous (330-304 Ma). [ABSTRACT FROM AUTHOR]

Voluminous Neoproterozoic mafic–ultramafic, felsic, and alkaline intrusions are found in the northern Yangtze Block, South China. Here, we present whole-rock major and trace element, and Sr–Nd isotopic compositions, together with zircon U–Pb ages, for syenite and gabbro samples from the Shuimo–Zhongziyuan alkaline intrusive complex in the Micang Mountains region at the northwestern margin of the Yangtze Block. Zircon U–Pb dating yields crystallization ages for the Na- and K-rich Shuimo syenites of 869 ± 4 (MSWD = 0.85, 2σ) and 860 ± 5 Ma (MSWD = 0.47, 2σ), respectively, and for the Zhongziyuan gabbros of 753 ± 4 Ma (MSWD = 0.23, 2σ), indicating that the syenites and gabbros represent different stages of magmatism. The syenites include both Na- and K-rich types and have high values of the Rittman index (σ), and high SiO2and Na2O + K2O contents. These syenites are enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE), but depleted in high-field-strength elements (HFSE), with high (La/Yb)Nvalues and small negative and positive Eu anomalies (Eu/Eu* = 0.74–1.17). In contrast, the gabbros have lower SiO2and Na2O + K2O contents, are only slightly enriched in LREEs, are enriched in LILE but depleted in HFSEs, and have small negative and positive Eu anomalies (Eu/Eu* = 0.86–1.37). The syenites have low initial87Sr/86Sr (0.703340) andɛNd(t) values (+1.9 to +7.7). The gabbros have relatively high initial87Sr/86Sr (0.703562–0.704933) and positiveɛNd(t) values (+1.6 to +4.5). These data suggest that the syenites and gabbros are isotopically similar and were largely derived from melts of depleted mantle. The syenites underwent significant fractional crystallization and small amounts of crustal contamination during magma evolution. In contrast, the gabbros were formed by partial melting (>15%) of a garnet lherzolite source and might also have experienced crustal assimilation. Taking into account the geochemical signatures and magmatic events, we propose that the Shuimo syenites formed in an intra-arc rifting setting, however, the Zhongziyuan gabbros were most likely produced in a subduction-related, continental margin arc setting during the Neoproterozoic, thus suggesting that the alkaline intrusive complex were formed by the arc-related magmatism in the Micang Mountains. [ABSTRACT FROM PUBLISHER]

Mesozoic granitic intrusions are abundant in the South China Block (SCB). Understanding the generation of these granitic intrusions is important to better constrain tectonic regimes and mineralization processes. We studied the Weishan pluton, one of the largest Mesozoic composite granitic complexes in Hunan Province, to probe the relationship between multiple magma processes and tectonic events induced by plate interactions. The samples can be classified into three groups. Group 1 is highly fractionated and weakly peralumious, with flatter REE patterns and more negative Eu, Ba, Sr, P, and Ti anomalies compared with other groups. Group 2 is peralumnious-metaluminous while Group 3 is peraluminous, but with higher MgO, FeO, εNd(t), and lower initial87Sr/86Sr in Group 2 than in Group 3. Whole-rock and biotite compositions from all groups define a good linear trend, with Group 1 and Group 2 samples defining two mixing end-members. Single-grain mica Rb-Sr isochron and LA-ICP-MS zircon U-Pb ages show that Group 1 formed at ca. 240–230 Ma, Group 2 at 220–215 Ma, and Group 3 during two episodes at 210–205 Ma and 185 Ma. Integrated geochemical studies suggest that precursor magmas of the three groups were emplaced under oxidizing conditions at relatively low temperatures (<830°C). These magmas were mainly derived by partial melting of Palaeoproterozoic psammites but subsequently differentiated by fractional crystallization, crustal contamination, and remelting. Considering regional tectonothermal events, it is proposed that the oldest Group 1 granitic melts were derived by low-degree partial melting of thickened Palaeoproterozoic psammitic materials during prograde metamorphism due to the collision of the Indochina Block (ICB) and the SCB. The slightly younger Group 2 granitic melts were generated by further partial melting in response to stress relaxation in the post-collision stage and conductive heating from underplating mafic magma. The youngest Group 3 melts represent remobilized buoyant magma pulses supplied from a mushy Group 2 magma source accompanying regional reheating, possibly associated with the uplift of the SCB following its deep subduction during the Dabie orogeny and the subduction of the Palaeo-Pacific oceanic plate beneath the Eurasia plate, respectively. [ABSTRACT FROM AUTHOR]

Extensive magmatism occurred in southeast China during Late Jurassic time, forming large-scale granitic and volcanic rocks associated with non-ferrous, rare earth and rare, radioactive metal deposits. The Shuikoushan Pb–Zn–Au orefield is a typical example located in Hunan Province. This study reports LA-ICP-MS zircon U–Pb ages, whole-rock chemistry, and Sr–Nd–Pb isotopic compositions, andin situHf isotopic geochemistry of zircons from the Laomengshan rhyodacite in the Shuikoushan Pb–Zn–Au orefield. Zircon U–Pb dating yields a weighted average age of 156.7 ± 1.6 Ma for the intrusion of the rhyodacite. The rhyodacite samples are mainly shoshonitic series, having metaluminous to weakly peraluminous A/CNK values ranging from 0.96 to 1.09, with moderately high magnesium content (Mg# = 42.4–47.5). Samples display high (87Sr/86Sr)ivalues (0.71165–0.71176), lowεNd(T) values (−10.7 to −10.3), old Nd model ages (TDM = 1.73–1.86 Ga), and relatively homogeneous Pb isotopic compositions [(206Pb/204Pb)i = 18.365–18.412, (207Pb/204Pb)i = 15.663–15.680, and (208Pb/204Pb)i = 38.625–38.666]. The zircons exhibit enrichedεHf(T) values (−16.22 to −9.86) and old two-stage Hf model ages (TDM2 = 1.82–2.22 Ga). All the above data indicate that the Laomengshan rhyodacite originated from melting Palaeoproterozoic basement, perhaps contaminated by subordinate mantle melts. Intense extension and thinning of the continental lithosphere during Late Jurassic time resulted in melting of upwelling asthenosphere, and mafic mantle melts interacted with and melted Palaeoproterozoic lower crust, thus forming the Laomengshan rhyodacite. [ABSTRACT FROM PUBLISHER]

Abundant crude oil and CO2gas coexist in the fourth member of the Upper Cretaceous Quantou reservoir in the Huazijing Step of the southern Songliao Basin, China. Here, we present results of a petrographic characterization of this reservoir based on polarizing microscope, X-ray diffraction, fluid inclusion, and carbon–oxygen isotopic data. These data were used to identify whether CO2might be trapped in minerals after the termination of a CO2-enhanced oil recovery (EOR) project, and to determine what effects might the presence of CO2have on the properties of crude oil in the reservoir. The crude oil reservoir in the study area, which coexists with mantle-derived CO2, is hosted by dawsonite-bearing lithic arkoses and feldspathic litharenites. These sediments are characterized by a paragenetic sequence of clay, quartz overgrowth, first-generation calcite, dawsonite, second-generation calcite, and ankerite. The dawsonite analysed during this study exhibits δ13 C (Peedee Belemnite, PDB) values of −4.97‰ to 0.67‰, which is indicative for the formation of magmatic–mantle CO2. The paragenesis and compositions of fluid inclusions in the dawsonite-bearing sandstones record a sequence of two separate filling events, the first involving crude oil and the second involving magmatic–mantle CO2. The presence of prolate primary hydrocarbon inclusions within the dawsonite indicates that these minerals precipitated from oil-bearing pore fluids at temperatures of 94–97°C, in turn suggesting that CO2could be stored as carbonate minerals after the termination of a CO2-EOR project. In addition, the crude oil in the basin would become less dense after deposition of bitumen by deasphalting the injection of CO2gas into the oil pool. [ABSTRACT FROM AUTHOR]

A Neoarchaean sanukitoid pluton that was intruded into the base of the Guyang greenstone belt in the Yinshan Block of the North China Craton hosts a number of hornblendite enclaves. Geochemically, the pluton is characterized by high MgO, Mg#, Cr, Ni, large-ion lithophile element (LILE), and heavy rare earth element (HREE) contents and low TiO2and high-field strength element (HFSE) contents, and has relatively low Sr/Y ratios and negative Eu anomalies. Whole-rock Sr–Nd isotopic analyses indicate that it has εNd(t) values of +1.4 to +2.0. These geochemical and isotopic characteristic suggest that the sanukitoid was formed under a low-pressure and high-temperature environment by slab melting and assimilation of hornblendite enclaves. The hornblendite enclaves show high MgO, Mg#, Cr, and Ni contents, high and variable K2O, LREE, and Th contents, enrichment in LILEs and LREEs, and depletion in HFSEs. They have high Y contents and relatively low Sr/Y values, strongly negative Eu anomalies, and whole-rock εNd(t) values of +1.0 to +1.9. The geochemical and isotopic characteristics indicate that these enclaves might have been derived from a mixed source of an enriched mantle, metasomatized by melts expelled from subducted sediments in a high-temperature, low-pressure environment. To explain these characteristics, a ridge subduction model is proposed for the formation of the sanukitoid and hornblendite in the Yinshan Block in the Neoarchaean. [ABSTRACT FROM AUTHOR]

Zircon U–Pb geochronological and geochemical analyses are reported for a suite of the middle Silurian volcanic rocks from northern West Junggar (NW China), southern Central Asian Orogenic Belt (CAOB), with the aim to investigate the sources, petrogenesis, and tectonic implications. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb analysis from an andesite yielded a concordant weighted mean206Pb/238U age of 429 ± 3 Ma, indicating the presence of middle Silurian volcanic rocks in northern West Junggar. The andesite is tholeiite series and characterized by minor variations in compositions (SiO2 = 55.68–59.17 wt.%, Al2O3 = 14.56–17.7 wt.%, TiO2 = 0.55–1.23 wt.%, Na2O + K2O = 3.46–7.16 wt.%, and P2O5 = 0.15–0.37 wt.%), with wider MgO content (2.18–6.48 wt.%) and Mg# (57.4–77.9). All andesitic rocks are enriched in large-ion lithophile elements (LILEs; e.g. Rb, Ba, K, and Th) and light rare earth elements (LREEs), but strongly depleted in some high field strength elements (HFSEs; e.g. Nb, Ta and Ti), with slight negative Eu anomalies (Eu/Eu* = 0.8–1). These features suggest that the andesitic magmas were derived from 2–8% partial melting of a garnet lherzolite depleted mantle source with subducted sediments metasomatized by slab-derived fluids. Combining the current study with those data in existing literature, we conclude that the middle Silurian volcanic rocks formed in an intra-oceanic subduction setting during consumption of the Irtysh–Zaysan Ocean, and further confirm the eastern extension of the early Palaeozoic Boshchekul–Chingiz volcanic arc of East Kazakhstan in China. [ABSTRACT FROM AUTHOR]

The Yinshan Block, part of the Neoarchaean basement of the Western Block of the North China Craton, is composed of granite–greenstone and granulite–charnockite complexes. We report research on a suite of charnockites from the granulite–charnockite complex and characterize their geochemistry, zircon U–Pb geochronology, and Hf isotopic composition. The charnockites can be divided into intermediate (SiO2 = 59–63 wt.%) and silicic (SiO2 = 69–71 wt.%) groups. U–Pb zircon data yield protolith formation ages of 2524 ± 4 Ma, 2533 ± 15 Ma, followed by metamorphism at 2498 ± 3 Ma, 2490 ± 11 Ma, respectively, for these groups. Although the intermediate charnockites are characterized by higher Al2O3, TiO2, Fe2O3T, MnO, MgO, CaO, P2O5, K2O, Sr, and ΣREE content than the silicic charnockites, the ages and Hf isotopic composition of zircons and REE patterns of both intermediate and silicic charnockites are remarkably consistent, which indicates that they are genetically related. These charnockites are predominantly metaluminous to slightly peraluminous, calc-alkalic to calcic, and magnesian – characteristics generally related to a subduction setting. High-Sr + Ba granites with low K2O/Na2O characteristics, shown by these charnockites, imply a mixture of mafic and felsic magmas generated from an enriched mantle + lower crust. High MgO, Ni, Cr and Mg#, low K2O/Na2O, and metaluminous to slightly peraluminous natures imply that the source rocks most likely were amphibolites. Coeval calc-alkaline magmatism and high-T granulite-facies metamorphism under low-H2O activity in the area lead us to propose a model involving mid-ocean ridge subduction within a Neoarchaean convergent margin. The arc-related rocks accreted along the continent margin, and became a barrier when the lithospheric mantle ascended through the slab window. Melt derived from the decompressing mantle mixed with melt derived from the overlying, juvenile lower crust melt, which was warmed and metamorphosed by the ascending lithospheric mantle. [ABSTRACT FROM AUTHOR]

Recently, many Mo deposits genetically related to emplacement of Early Cretaceous granites have been found in the Dabie–Qinling belt. A typical intrusion that combines magmatism and metallogenesis, the Bao'anzhai granite, yields a zircon238U–206Pb age of 123.2 ± 1.1 Ma and a molybdenite Re–Os isochron age of 122.5 ± 2.7 Ma. This granite is characterized by high silica and alkali, but low Mg, Fe, and Ca. It is enriched with light rare earth elements (REEs) and large-ion lithophile elements (LILEs, Rb, K, Th, U) but depleted of heavy REEs, high field strength elements (HFSEs, Nb, Ta, Ti, and Y), and Sr. This high-K granite has medium initial87Sr/86Sr ratios (0.706518–0.707116) and low initial Pb isotopic ratios [(206Pb/204Pb)i, 16.423–16.699; (207Pb/204Pb)i, 15.285–15.345; (208Pb/204Pb)i, 37.335–37.633], and is characterized by low ϵNd(t) and ϵHf(t) values (−14.92 to −14.22 and −21.67 to −19.19, respectively). These data indicate that this pluton is a high-K calc-alkaline fractionatedI-type granitite. It was generated by partial melting of the Yangtze lower crust, which is probably similar to Neoproterozoic TTG-like magmatic rocks at the north Yangtze Block under a non-thickened lower crust environment (<35 km). The ores also have low radiogenic Pb isotopes (206Pb/204Pb, 16.592–17.674;207Pb/204Pb, 15.300–15.476;208Pb/204Pb, 37.419–37.911) and low Re content in molybdenite (5.693–10.970 ppm), suggesting a crustal magmatic source for the metallogenic minerals in the Mo deposit. [ABSTRACT FROM AUTHOR]

The Palaeo-Tethyan tectonic evolution of central Tibet remains a topic of controversy. Two Permian to Late Triassic arc-like volcanic suites have been identified in the eastern Qiangtang (EQ) block of north-central Tibet. Three competing models have been proposed to explain the formation of these volcanic suites, with two models involving a single stage of long-lived subduction but with opposing subduction polarities, while the other model involves a two-stage subduction process. Here, we present new whole-rock geochemistry, including Sr–Nd isotope data, for late Permian felsic volcanics of the Zaduo area. These volcanics are mainly low to middle K calc-alkaline felsic tuffs and rhyolites with SiO2concentrations up to 73 wt.%. In primitive mantle-normalized diagrams, the volcanics are typified by large ion lithophile element enrichment and high-field-strength element (e.g. Nb, Ta, P, and Ti) depletion, with slightly negative Eu anomalies. They have initial Sr ratios (87Sr/86Sr)iof 0.70319–0.70547, and ϵNd(t) values of +3.4 to +3.5, suggesting derivation by the partial melting of a depleted mantle wedge, followed by assimilation of crustal material. The available geochemical data indicate the presence of two distinctive igneous evolution trends within the Permian to Late Triassic volcanics of the EQ block, consistent with a two-stage subduction model. Permian to Early Triassic arc-like volcanics are formed during northward (present-day orientation) subduction, whereas the Late Triassic volcanics are related to southward (present-day orientation) subduction of mafic crust of the Garze–Litang Ocean. [ABSTRACT FROM PUBLISHER]

Volcanic rocks in the Middle–Lower Yangtze River Valley (MLYRV) constitute a bimodal magmatic suite, with a significant compositional gap (between 50% and 63% SiO2) between the mafic and felsic members. The suite is characterized by a relatively wide spectrum of rock types, including basalts, trachytes, and rhyolites. The basaltic rocks have low-to-moderate SiO2contents of 46.00–50.01%, whereas the trachytes and rhyolites possess SiO2contents in the range of 63.08–77.61%. Rocks of the bimodal suite show moderate enrichment of LILEs, negative Nb, Ta, and Ti anomalies, and are significantly enriched in LREEs. The basalts were most likely generated by parental mafic magmas derived from enriched lithospheric mantle with minor assimilation of crustal materials involving coeval crystal fractionation during magma evolution. The results of energy-constrained assimilation and fractional crystallization simulations demonstrate that the felsic magma was produced by the mixing of 5–20% lower crustal anatectic melts with an evolved mafic magma (∼48% SiO2) and accompanied by extensive clinopyroxene, plagioclase, biotite, and Fe–Ti oxide fractionation. Our model for the genesis of felsic rocks in bimodal suites is different from the traditional models of crustal melting and fractional crystallization or assimilation–fractional crystallization of basaltic liquids. [ABSTRACT FROM AUTHOR]

Post-orogenic mafic rocks from Northeast China consist of swarms of dolerite dikes. We report a new U–Pb zircon age, as well as whole-rock geochemical and Sr–Nd–Hf isotopic data. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb zircon analysis yielded an age of 210.3 ± 1.5 million years (i.e. Triassic) for these mafic dikes. Most Dalian mafic rocks exhibit low K2O + Na2O contents, and span the border between alkaline and calc-alkaline rock associations in the total alkali–silica diagram. The investigated dikes are also characterized by relatively high (87Sr/86Sr)i ratios (0.7061–0.7067) and negative ϵNd (t) (−4.7 to −4.3) and ϵHf (t) values (−4.1 to −1.1), implying that they were derived from an enriched lithospheric mantle source. The mafic dikes are characterized by relatively low MgO (4.65–5.44 wt.%), Mg# (41–44), and compatible element content [such as Cr (89.9–125 ppm) and Ni (56.7–72.2 ppm)], which are the features of an evolved mafic magma. No evidence supports the idea that the mafic rocks were affected by significant assimilation or crustal contamination during emplacement. We conclude that the dolerites formed in a post-orogenic extensional setting, related to lithospheric delamination or ‘collapse’ of the Central Asian Orogenic Belt (CAOB), also termed the Xingmeng Orogenic Belt in China. [ABSTRACT FROM AUTHOR]

The Liziyuan gold deposit, located on the northern margin of the western Qinling orogen (WQO), consists of five mineralized sites hosted by metavolcanic rocks, and one hosted by the Tianzishan monzogranite. Orebodies mainly occur as lenticular veins along NW-striking dextral ductile strike–slip shear zones. Major wall rock alteration includes silicification, pyritization, and carbonation, progressively increasing in intensity towards the orebodies. Ore minerals are dominated by pyrite, galena, and chalcopyrite; the major gangue minerals are quartz and calcite. Native gold is present chiefly as separate phases in sulphide and quartz microfractures. We recognize four stages of mineralization: (I) pyrite-quartz, (II) native gold-chalcopyrite-pyrite-quartz, (III) pyrite-freibergite-galena-quartz-carbonate, and (IV) carbonate stages. Fluid inclusion petrography and microthermometric results suggest that three types of primary fluid inclusions (carbonic, CO2–H2O, and aqueous) are present in the deposit. Microthermometric data and Laser Raman analyses indicate that the ores were deposited from moderate temperature (240–280°C), low salinity (0.5–9.1 wt.% NaCl equiv.) H2O–NaCl–CO2–(CH4) fluids. The common coexistence of aqueous, CO2–H2O, and carbonic inclusions indicates the trapping of heterogeneous immiscible fluids. Trace elements in mineralized quartz and carbonate veins suggest that the ore-forming fluids were mainly produced by prograde metamorphism of the upper crust. The calculated and δD values are 1.8–3.8‰ and –77‰ to –75‰, respectively, for quartz from stage II and –8.5‰ to –6.6‰ and –72‰ to –71‰ for calcite from stage III, implying that the ore-forming fluids were metamorphic in origin and evolved by late-stage mixing with meteoric water. Pyrite and galena have δ34S values of 3.9–8.5‰ with a pronounced mode at 5–8‰. Such relatively homogeneous sulphur isotopic compositions are consistent with orogenic gold deposits throughout the world, indicating that the sulphur was mainly sourced from reduced metamorphic fluids. The Liziyuan gold deposit can be grouped with other orogenic gold deposits that have similar characteristics. Geological observations and available isotopic ages suggest that the Liziyuan lode mineralization was related to the Indosinian orogenesis of the Qinling belt. Triassic continental collision caused crustal thickening, dextral ductile shearing, and greenschist facies metamorphism throughout the orogen. Due to the intensive deformation and metamorphism, crustal rocks released copious fluids that evidently mobilized and extracted ore elements along their flow pathways. The ductile shear zone in the Liziyuan mining area provided regions of low mean stress and high permeability, and thus appeared to be preferential channels for precipitation of the ore-forming fluids. As highly charged fluids migrated into the high permeability shear zones, rapid changes in physicochemical conditions resulted in sulphide precipitation and gold mineralization. [ABSTRACT FROM PUBLISHER]

Late Mesozoic granitoid plutons of four distinct ages intrude the lower plate of the Hohhot metamorphic core complex along the northern margin of the North China craton. The plutons belong to two main groups: (1) Group I, deformed granitoids (148 and 140 Ma subgroups) with high Sr, LREE, and Na2O, low Y and Yb contents, high Sr/Y and La/Yb ratios, weak or no Eu anomalies, low Rb/Ba ratios, similar initial 87Sr/86Sr values (0.7064–0.7071) and low Mg# (<37 mostly, 100 × molar MgO/MgO + FeO t ); (2) Group II, non-deformed granitoids (132 and 114 Ma subgroups) with low Sr, relatively low Na2O, high Y and Yb contents, pronounced negative Eu anomalies, high Rb/Ba ratios, and initial 87Sr/86Sr values (0.7098–0.7161). The two groups share geochemical similarities in ϵNd(t) (–11.3 to –15.4) and T DM2 ages (1.85–2.18 thousand million years) as well as Hf isotopic ratios in zircons. Geochemical modelling (using the MELTS code) suggests that similar sources but different depths of magma generation produced the early, high-pressure low-Mg adakitic granitoids and late, low-pressure granitoids with A-type characteristics. The early granitoids likely represent a partially melted, deep-seated, thickened lower continental crust that involved a minor contribution from young materials, whereas the later group partially melted at shallower depths. This granitic magmatic evolution coincided with the tectonic transition from crustal contraction to extension. [ABSTRACT FROM AUTHOR]

The Tarim block, one of the largest cratons in China, records an important part of the Proterozoic crustal evolution of the Earth. Many previous studies have focused on the Neoproterozoic magmatism and tectonic evolution of this block in relation to the break-up of Rodinia, although relatively little is known about its earlier tectono-magmatic history. In this article, we present detailed petrographic, geochronologic, whole-rock geochemical, and in situ zircon Hf isotope data for the pre-Neoproterozoic Xishankou granitoid pluton (XBP), one of several blue quartz-bearing granitoid intrusions well exposed in the Quruqtagh area, and discuss these intrusions in terms of their tectonic environment. Zircon LA-ICP-MS dating indicates that gneissic quartz diorite and granodiorite of the XBP crystallized at 1934 ± 13 and 1944 ± 19 Ma, respectively. Both underwent metamorphism essentially coeval with emplacement, a time that is compatible with the globally distributed 2.1–1.8 Ga crustal amalgamation during formation of the supercontinent Columbia. Petrographic and geochemical evidence suggest that the XBP is a continental-arc-type granite and may have been generated by the partial melting of Archaean thickened lower crust; this would suggest that the northern Tarim block was a continental-type arc at ca. 1940 Ma. Our new data, together with previous regional geological studies, indicate that a series of Palaeoproterozoic (ca. 2.0–1.8 Ga) tectono-magmatic events occurred in the northern Tarim attending the assembly of Columbia. [ABSTRACT FROM AUTHOR]

Post-orogenic mafic dikes are widespread across eastern Shandong Province, North China Craton, eastern China. We here report new U–Pb zircon ages and bulk-rock geochemical and Sr–Nd–Pb isotopic data for representative samples of these rocks. LA-ICP-MS U–Pb zircon analysis of two mafic dike samples yields consistent ages of 118.7 ± 0.25 million years and 122.4 ± 0.21 million years. These Mesozoic mafic dikes are characterized by high (87Sr/86Sr) i ranging from 0.7082 to 0.7087, low ϵNd(t) values from −17.0 to −17.5, 206Pb/204Pb from 17.14 to 17.18, 207Pb/204Pb from 15.44 to 15.55, and 208Pb/204Pb from 37.47 to 38.20. Our results suggest that the parental magmas of these dikes were derived from an ancient, enriched lithospheric mantle source that was metasomatized by foundered lower crustal eclogitic materials prior to magma generation. The mafic dikes underwent minor fractionation during ascent and negligible crustal contamination. Combined with previous studies, these findings provide additional evidence that intense lithospheric thinning beneath eastern Shandong occurred at ∼120 Ma, and that this condition was caused by the removal/foundering of the lithospheric mantle and lower crust. [ABSTRACT FROM PUBLISHER]