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In geological history, volcanism is closely related to the deposition of many black shales. However, the specific mechanism between volcanism and the deposition of black shales is still unclear. The black shales developed in the Chang 7 Member of the Yanchang Formation in the Ordos Basin are considered the most important hydrocarbon source rocks in Central China. The shales are deposited by frequent volcanic activities and preserved by extremely rich volcanic ash layers, making them an excellent example when investigating the influence of volcanism on the deposition of black shales. In this paper, petrographic, mineralogical, and geochemical analyses of three typical tuff and black shale segments of the Chang 7 Member were carried out. The productivity indicators [total organic carbon (TOC), P/Al, Ni/Al, and Cu/Al], redox indicators (V/Al, Mo/Al, U/Al and U/Th), and clastic influx indicators (Ti/Al and ƩREE) of the shales basically increased together in the longitudinal direction, and a relatively good positive correlation existed between P/Al, Ni/Al, Cu/Al, V/Al, Mo/Al, U/Al, U/Th, Ti/Al, ƩREE, and TOC. This finding indicated that the development of the Chang 7 black shales is the result of a combination of high primary productivity, anoxic conditions, and increased clastic influx. Considering that increased clastic influx may dilute organic matter, many phosphate nodules represented high productivity above the volcanic ash layers, and anoxic conditions are likely to be the result of a large amount of organic matter degradation indicated by the covariations of TOC versus P/Al and TOC versus Ba/Al. Therefore, the Chang 7 black shales in this study may be mainly controlled by the increased primary productivity. In addition, compared with the Weathering Index of Parker of background shales (not the contact clip or tuff layer), that of the black shales was significantly reduced after tuff deposition. On the contrary, the clastic influx indicators, redox indicators, productivity indicators of black shales significantly increased. This finding suggested that a series of environmental effects, such as enhanced weathering of terrestrial sources, increased clastic influx, anoxic water, and productivity bloom, was likely caused by volcanic activity. Considering that hydrothermal activity at the same time as volcanism may not cause productivity bloom, the nutrients (P/Al and Fe/Al) of the Chang 7 tuffs were significantly depleted, and the total sulfur content of black shales was much higher than that in ordinary freshwater sedimentation. Therefore, this paper reviewed and proposed the volcanism hypothesis model of the Chang 7 black shales. Volcanism generates large amounts of SO2 and volcanic ash. SO2 forms large areas of acid rain and accelerates terrigenous weathering with an increase in the lake land-based sources of debris and nutrient supply, while volcanic ash is decomposed and releases nutrients. These phenomena lead to biological productivity bloom and massive accumulation of organic matter, which in turn results in lake water anoxia and the eventual formation of black shales. [ABSTRACT FROM AUTHOR]

There are widespread Late Mesozoic volcanic rocks in the Great Xing'an Range, Northeast China. However, the precise age data and tectonic evolution are still controversial. In this paper, a suite of intermediate-felsic volcanic rocks and mafic volcanic rocks have been recognized in the Daheishan of the northern Great Xing'an Range. Zircon U–Pb dating constrains two groups of the crystallization ages at 129 Ma (dacite) and 124–127 Ma (rhyolite, rhyodacite and andesite), respectively. They all have magmatic zircon geochemical characteristics, including systematic positive Ce anomalies, weak negative Eu anomalies, and high Th/U ratios (average 0.84). The intermediate-felsic volcanic rocks show crustal signatures with high K2O (1.91–7.57 wt% and low MgO (0.19–2.78 wt%) contents. The zircon εHf(t) values mostly range from + 4.7 to + 10.2, with dominant two-stage model ages (TDM2) of 530–878 Ma. Therefore, combined with previous data, the mantle-derived mafic melts may have triggered partial melting of the juvenile lower crust to produce intermediate-felsic magmas, and the source rock is considered to be an amphibolite. In addition, the trace element data of the volcanic rocks display arc-like signatures. The published and our geochronological data indicate that these Late Mesozoic volcanic rocks in the Great Xing'an Range were mainly formed in the Early Cretaceous with a peak range of 124–133 Ma. The large-scale Early Cretaceous volcanic rocks in the Great Xing'an Range were formed in an active continental margin setting related to the subduction of the Paleo-Pacific Ocean. [ABSTRACT FROM AUTHOR]

This paper aims to analyze the deformation characteristics and constrain the deformation time of the Gudonghe ductile shear belt in the Yanbian area, NE China, the eastern segment of the Central Asian Orogenic Belt. Two stages of ductile deformation have been identified according to the macro- and micro-fabric characteristics. The NWW-trending D1 deformation, with pervasive dextral shearing and extensional features as indicated by shear folds and δ-porphyroclasts, occurred in the Early–Middle Triassic Yongxin pluton based on zircon U–Pb age of 246–236 Ma and previously published geochronological data, and the foliation was cut by an undeformed igneous rock of ~ 226 Ma; therefore, the D1 deformation time in the Gudonghe ductile shear belt is limited to the 236–226 Ma. The NE-trending D2 deformation event occurred in the Early Jurassic Baijin pluton. The S–C fabrics and σ-porphyroclasts in the D2 deformation stage show a pervasive sinistral shearing and were formed in a compression setting. Two deformed granites in the D2 deformation stage have a weighted mean age of 197 Ma, while the syn-tectonic granitic vein during the D2 deformation stage has a weighted mean age of 184 Ma. The undeformed granites, which intruded into the Early Jurassic Baijin pluton, have a weighted mean age of 179 Ma. Therefore, the D2 deformation of the Gudonghe ductile shear belt occurred during 184–179 Ma. Considering the regional tectonic evolution and the structural features of the Gudonghe ductile shear belt, the D1 deformation event could be related to the Middle–Late Triassic post-orogenic collapse after the closure of the Paleo-Asian Ocean, while the D2 deformation was formed in a compressional setting and was related to the onset of westward-directed subduction and accretion of the Paleo-Pacific Ocean in the Early Jurassic. [ABSTRACT FROM AUTHOR]

Permian magmatism occurred widely in the Tarim basin and adjacent areas of NW China, resulting in the emplacement of numerous carbonatite plutons and alkaline rock intrusions, which are likely to have been derived from mantle sources. In addition, at least one large igneous province (LIP) can be recognized in NW China; namely, the ca. 270–290 Ma Tarim LIP, and it can be inferred that the peak age of magma activity is ~ 280 Ma. Therefore, the mantle plume is limited spatially within southern Tianshan and the Tarim Basin and temporally in the Early Permian. Age and field evidence suggest a spatial and temporal relationship between the carbonatites and alkaline rocks within the Tarim LIP, and their genesis is related to the Tarim mantle plume. In this paper, we direct our attention to the mineral assemblages that are related to carbonatites and alkaline rocks which host REE deposits (Wajilitag, Boziguoer) in the northern Tarim Craton. Alkaline rocks typically are related to rifts and/or extensional tectonics, and we suggest that these magmatic and metallogenic events occurred during an extensional regime, possibly related to the Tarim mantle plume event that affected much of South Tianshan during the Permian. [ABSTRACT FROM AUTHOR]

The mechanics of crustal growth in the Altaids during the Phanerozoic is still not well understood. This paper reports new geochronological, geochemical, and isotopic data from Paleozoic adakitic intrusions in the Dananhu arc in the Chinese Eastern Tianshan with the aim of better understanding the specific mechanisms of crustal growth. Our new LA-ICPMS U–Pb zircon age data show that four phases of adakitic intrusions formed at 410–413 Ma, 385–387 Ma, 335 Ma, and 313–311 Ma. Combined with previous data of ours and from the literature, there were seven phases of adakitic intrusions from the Silurian to early Permian. All these adakitic intrusions have distinctive geochemical-isotopic signatures with high Na and Al, high Sr, low Yb and Y, high Sr/Y and (La/Yb)N values, relatively high MgO contents and Mg numbers (Mg# = 41–70), high abundances of compatible elements (Cr = 1.66–46.30 ppm, Ni = 2.40–26.96 ppm), and positive high εHf (t) (+ 7.1 to + 15.6) and a TDM (Ma) range from 325 to 670 Ma. These adakitic intrusions were associated with essential Cu polymetallic mineralization in the Dananhu arc. The above chemical data and relations indicate that the processes of oceanic slab melting generated these adakitic rocks. Our new geochronological, geochemical and isotopic data, integrated with the geology of the Dananhu intra-oceanic arc, lead us to conclude that multiphase of hot/young oceanic crust subduction and melting generated the massive crustal growth in the Silurian–early Permian. Our results indicate that the magmas were derived by slab melting of hot/young oceanic crust, which was one of the most critical mechanisms of continental crustal growth in the Paleozoic accretionary orogen of the Altaids. [ABSTRACT FROM AUTHOR]

Determining the age and petrogenesis of the Mesozoic magmatic rocks may provide crucial evidence regarding the tectonic setting and evolution of the North China Craton (NCC). In this paper, we present new zircon U–Pb ages and geochemical data for bimodal volcanic rocks from Zhuozi area in the eastern Yinshan belt, NCC, to discuss their petrogenesis and tectonic implications. The volcanic rock suite consists of basalts, rhyolites, and trachytes. According to the results of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), the rhyolitic and trachytic rocks have zircon U–Pb ages of 136.9 ± 0.8 Ma and 134.0 ± 1.7 Ma, respectively, representing their eruption ages. The basalts are enriched in large-ion lithophile elements (LILE; Ba, Rb, Sr, and Th) and light rare-earth elements (LREE), and are relatively depleted in high field strength elements (HFSE; Nb, Ta, and Ti). In addition, the basalts are characterized by high fractionations of rare-earth elements (REE), with (La/Yb)N = 24.87–42.85. These features suggest that they were derived from low-degree partial melting of enriched lithospheric mantle metasomatized by subduction-related components. The rhyolitic rocks have low mean Al2O3 (12.26 wt%) and TiO2 (0.14 wt%) contents and Mg# (14.92) values, with relatively low total REE abundances. They have high alkali and Zr, Ce, Y, and Nb contents and high Ga/Al ratios, with notably positive Pb and negative Sr, Ba, and Eu anomalies observed in the primitive mantle-normalized trace element diagram. These features indicate that the rocks exhibit characteristics of A1-type granite and likely derived from the partial melting of a crustal source. The trachytic rocks are show moderate trace elements and SiO2, MgO, Fe2O3T, and TiO2 contents. They were possibly generated by fractional crystallization of the underplating basaltic magmas and assimilated minor crustal materials. The geochemical characteristics, in combination with the regional geology, suggest that the bimodal volcanic rocks formed in an intraplate extensional setting likely associated with the retreat of the subducted Paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

The beginning of the Late Paleozoic Ice Age was characterized by localized events with small ice depocenters occurring in South America and a series of cyclic shallow-water limestones in far-field regions, in late Visean to Serpukhovian. This paper documents two topmost Visean–Serpukhovian sections in Guangxi, South China: a stromatolite-bearing deep-water succession in Helv village and a shallow-water succession in Dujie village. Seventeen microfacies types have been recognized and grouped into six microfacies associations. The vertical evolution of the microfacies associations from deep-water to shallow-water depositional environments in both sections indicate a major relative sea-level fall in the latest Visean. The repetitive successions comprising different morphological stromatolites in Helv section and the cyclic alternation of subtidal and peritidal facies in Dujie section imply high-frequency sea-level fluctuations during latest Visean to Serpukhovian, most likely eustatic in origin. The carbon isotope data of Dujie limestone exhibit a pronounced positive δ13C excursion with ± 4.3‰ in the peritidal deposits. This shift is interpreted as the result of enhanced organic carbon burial in other regions and depletion of the ocean in light carbon. The widespread coeval cyclicity occurring in settings in South China, Western Europe, and North America is most likely the results of glacio-eustatic sea-level fluctuations, possibly with local influences of tectonic movements. This pattern is interpreted to represent the expression of the onset of the major glaciation during the LPIA in low-latitudinal successions. [ABSTRACT FROM AUTHOR]

The origin and the Precambrian tectonic evolution of the Alxa Block have not been well studied, largely due to widespread desert coverage and a lack of high-resolution geochronological data. This paper reports zircon U–Pb ages and Hf isotopic data for the Langshan Group in the northeastern Alxa Block. Detrital zircons from the Langshan Group mainly provide U–Pb ages between ca. 2000 Ma and 1100 Ma, suggesting that their provenance was dominated by late Palaeoproterozoic to Mesoproterozoic rocks, which yield two main peak ages at 1592 Ma and 1745 Ma. These zircons possess εHf (t) values between − 15 and + 8, implying the derivation of their precursor magmas from old crust and juvenile materials. Zircon U–Pb dating yields ages of 898 ± 4 Ma and 808 ± 4 Ma for the granite cobbles in coarse conglomerate in the Fourth Formation and the diorite intruding into the Second Formation of the Langshan Group, which constrains the depositional age of the main part of the Langshan Group to between 898 and 804 Ma. Our data show that the Langshan Group was probably deposited in an intra-continental rift basin and originated from recycled orogens. The geochronology and palaeocurrent data indicate that the North China Craton (NCC) could not have provided source materials for the Langshan Group. Instead, the Langshan Group shares a similar origin and detrital zircon age spectrum with the Beishan Complex in the South Beishan Collage. Combining these findings with published data, we propose that the Alxa Block was not a part of the NCC during the Neoproterozoic but a Precambrian micro-continent block. The Alxa Block recorded footprints that are related to the late amalgamation of the Rodinia supercontinent and the initial breakup. We suggest that the Alxa Block laid between Australia and Laurentia in the Rodinia supercontinent during the Neoproterozoic. [ABSTRACT FROM AUTHOR]

The Hegenshan–Heihe Suture (HHS) is an important suture zone between the Xing'an and Songliao–Xilinhot blocks in the eastern Central Asian Orogenic Belt (CAOB). Many studies have examined the northern and southern parts of this suture zone, but the middle segment remains under-researched and controversial. This paper presents new research into Permian felsic rocks along the middle segment of the HHS, including alkaline granites, rhyolites, and granodiorites. Zircon U–Pb dating of these rocks yielded precise Permian ages of 300.4 ± 2.5, 292.8 ± 2.7, and 293.1 ± 2.2 Ma. The alkaline granites and the rhyolites are A-type rocks that were derived from lower crustal protoliths, with the melting of these protoliths caused by asthenospheric upwelling associated with lithospheric delamination. In comparison, the granodiorites are I-type granites were generated from a mantle-derived magmatic source. The petrogenesis of these granites also involved the assimilation of sedimentary rocks and fractional crystallization. This Permian magmatism occurred during post-collisional extension following the amalgamation of the Xing'an and Songliao–Xilinhot blocks. [ABSTRACT FROM AUTHOR]

Development of fan deltas alongside intrabasinal structural highs has been overlooked compared to those forming on basin margins. However, these fan deltas may provide important clues regarding the tectonic and climatic controls on deposition during rift development. This paper documents fan delta deposition alongside an intrabasinal structural high within the Early Cretaceous Xiagou Formation of the Jiuquan Basin, China, using subsurface geological and geophysical data. Deposits observed in drill core support fan delta deposition occurring almost exclusively through subaerial and subaqueous gravity flows. Subsurface mapping reveals a consistent decrease in the areal extent of fan deltas from lowstand to highstand system tracts, suggesting that deposition alongside the structural high is sensitive to lake-level changes. The temporal and spatial distribution of the fan deltas display retrogradational stacking patterns, where fan deltas exhibit a decreasing lateral extent up-sequence until fan delta deposition terminated and was replaced by deposition of fine-grained lacustrine deposits. The retrogradational stacking patterns observed alongside the intrabasinal structural high are not observed in fan deltas along the basin margin in the lower parts of the Xiagou Formation. Subsidence profiles also show differential subsidence across the basin during the earliest stages of this formation, likely resulting from border fault movements. These data suggest that non-uniform stacking patterns in the lower parts of the Xiagou Formation reflect basin-scale tectonic movements as the dominant control on synrift deposition patterns. However, later stages of Xiagou Formation deposition were characterized by uniform subsidence across the basin, and uniform retrogradational stacking patterns for fan deltas alongside the intrabasinal structural high and border fault. These observations suggest that basin-scale tectonic movements played a relatively limited role in controlling sediment deposition, and imply a potential change to regional-scale processes affecting fan delta deposition during later synrift stages. Climate change is favored here as the region-scale control on the uniform retrogradational fan delta stacking patterns. This assertion is supported by pollen assemblages, isotope signatures, and organic geochemical analyses, which collectively suggest a change from a humid to semi-arid environment during later synrift stages. We suggest that variations in stacking patterns between different fan delta systems can provide insights into the basin- and regional-scale processes that control rift basin deposition. [ABSTRACT FROM AUTHOR]

The dynamic mechanism for destruction of the North China Craton (NCC) has been extensively discussed. Numerical simulation is used in this paper to discuss the effect of mantle upward throughflow (MUT) on the lithospheric heat flux of the NCC. Our results yield a three-stage destruction of the NCC lithosphere as a consequence of MUT variation. (1) In Late Paleozoic, the elevation of MUT, which was probably caused by southward and northward subduction of the paleo-Asian and paleo-Tethyan oceans, respectively, became a prelude to the NCC destruction. The geological consequences include a limited decrease of the lithospheric thickness, an increase of heat flux, and a gradual enhancement of the crustal activity. But the tectonic attribute of the NCC maintained a stable craton. (2) During Late Jurassic-Early Cretaceous, the initial velocity of the MUT became much faster probably in response to subduction of the Pacific Ocean; the conductive heat flux at the base of the NCC lithosphere gradually increased from west to east; and the lithospheric thickness was significantly decreased. During this stage, the heat flux distribution was characterized by zonation and partition, with nearly horizontal layering in the lithosphere and vertical layering in the underlying asthenosphere. Continuous destruction of the NCC lithosphere was associated with the intense tectono-magmatic activity. (3) From Late Cretaceous to Paleogene, the velocity of MUT became slower due to the retreat of the subducting Pacific slab; the conductive heat flux at the base of lithosphere was increased from west to east; the distribution of heat flux was no longer layered. The crust of the western NCC is relatively hotter than the mantle, so-called as a ‘hot crust but cold mantle’ structure. At the eastern NCC, the crust and the mantle characterized by a ‘cold crust but hot mantle.’ The western NCC (e.g., the Ordos Basin) had a tectonically stable crust with low thermal gradients in the lithosphere; whereas the eastern NCC was active with a hot lithosphere. The numerical results show that the MUT is the main driving force for the NCC destruction, whereas the complex interaction of surrounding plates lit a fuse for the lithospheric thinning. [ABSTRACT FROM AUTHOR]

The Beishan and East Tianshan Orogenic Collages in the southernmost Central Asian Orogenic Belt (CAOB) record the final stages of evolution of the Paleo-Asian Ocean. These collages and their constituent arcs have an important significance for resolving current controversies regarding their tectonic setting and age, consequent accretionary history of the southern CAOB, and the closure time of the Paleo-Asian Ocean. In this paper, we present our work on the southern Mazongshan arc and the northern Hongyanjing Basin in the Beishan Orogenic Collage (BOC), and our comparison with the Bogda arc and associated basins in the East Tianshan Orogenic Collage. Field relationships indicate that the Pochengshan fault defines the boundary between the arc and basin in the BOC. Volcanic rocks including basalts and rhyolites in the Mazongshan arc have bimodal calc-alkaline characteristics, an enrichment in large ion lithophile elements such as Rb, Ba, and Pb and depletion in high field-strength elements (e.g., Nb and Ta), which were probably developed in a subduction-related tectonic setting. We suggest that these bimodal calc-alkaline volcanic rocks formed in rifted arcs instead of post-orogenic rifts with mantle plume inputs. By making detailed geochemical comparisons between the Mazongshan arc and the Bogda arc to the west, we further propose that they are similar and both formed in arc rifts, and helped generate a Carboniferous archipelago of multiple arcs in the southern Paleo-Asian Ocean. These data and ideas enable us to postulate a new model for the tectonic evolution of the southern CAOB. [ABSTRACT FROM AUTHOR]

This paper investigates kerogen carbon isotopes, the difference between carbonate and kerogen carbon isotopes (Δ13Ccarb-kero = δ13Ccarb − δ13Ckero) and the difference between carbonate and n-C19 alkane compound-specific carbon isotopes (Δ13Ccarb- n-C19 = δ13Ccarb − δ13C n-C19) during the Permian–Triassic transition at Meishan, South China. The results show that kerogen carbon isotopes underwent both gradual and sharp shifts in beds 23–25 and 26–29, respectively. The differences between carbonate and organic carbon isotopes, both the Δ13Ccarb-kero and Δ13Ccarb- n-C19, which are mainly affected by CO2-fixing enzyme and pCO2, oscillated frequently during the Permian–Triassic transition. Both the variations of Δ13Ccarb- n-C19 and Δ13Ccarb-kero coupled with the alternation between cyanobacteria and green sulfur bacteria indicated by biomarkers. The episodic low values of Δ13Ccarb- n-C19 corresponded to episodic blooms of green sulfur bacteria, while the episodic high values of Δ13Ccarb- n-C19 corresponded to episodic blooms of cyanobacteria. The relationships between the variation of carbon isotopes and biota show that the microbes which flourished after the extinction of macroorganism affected the carbon isotope fractionation greatly. Combining the carbon isotope compositions and the pattern of size variation of the conodont Neogondolella, this paper supposes that anoxia of the photic zone at bed 24 was episodic and it would be caused by the degradation of terrigenous organic matters by sulfate reducing bacteria in the upper water column. Considered together with results from previous research, the high resolution variation of the biogeochemistry presents the sequence of the important geo-events during the Permian–Triassic crisis. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the application of an airborne gravity survey to sedimentary basin analysis. Using high-precision airborne gravity data constrained by drilling and seismic data from the Bohai Bay Basin in eastern China, we interpreted faults, structural elements, sedimentary thickness, structural styles and local structures (belts) in the central area of the Basin by the wavelet transform method. Subsequently, these data were subtracted from the Bouguer gravity to calculate the residual gravity anomalies. On this basis, the faults were interpreted mainly by linear zones of high gravity gradients and contour distortion, while the sedimentary thicknesses were computed by the Euler deconvolution. The structural styles were identified by the combination of gravity anomalies and the local structures interpreted by the first vertical derivative of the residual gravity. The results showed evidence for seven faults, one sag and ten new local structure belts. [ABSTRACT FROM AUTHOR]

Deserts and sandylands that are located in the semi-arid and arid regions in the middle latitudes of the Northern Hemisphere are usually regarded as environmentally sensitive change belts which respond to global climatic change. In northern China, activation or immobilization of sand dunes is mainly influenced by humid and dry variation and is related to stronger or weaker Asian monsoons. In this paper, the history of Holocene millennial-scale climatic and environmental change is reconstructed by the systematic analysis of the geochemical element contents and parameters, along with the OSL and C chronologies, from the different lithologies of the palaeosol-aeolian sand sequence in the south-eastern Mu Us Desert, northern China. Our results indicate that the region was dominated by a dry climate with intensive aeolian activity before 7.2 ka BP, and there was an optimal humid climate and fixed desert in 7.2-4.6 ka. Afterwards, the dune fields became mobile again as the effective humidity declined. Additionally, six dry events were discovered with times of ~7.2, 7.0-6.8, 6.6-5.7, 4.6-4.1, 3.7-3.5, and 3.3-2.5 ka, which were not only coincident with the intervals of millennial-scale weaker Asian summer monsoons, but also accordant with the cold events evidenced in the ice cores and deep-sea deposits of the high latitudes in the Northern Hemisphere. In general, the Holocene climatic and environmental changes had the characteristics of the 'monsoonal mode' and 'abrupt millennial-scale oscillation' in the Mu Us Desert. [ABSTRACT FROM AUTHOR]

The Early Paleozoic Wuyi-Yunkai fold belt of South China represents a major orogenic belt in East Asia; however, its formation is not well understood. This paper evaluates the origins of the Neoproterozoic-Early Paleozoic basin and the southern margin of the South China Block (SCB) based on a compilation of the spatiotemporal evolution of the Late Neoproterozoic-Early Paleozoic strata and their depositional environments. These data are combined with high-resolution structural, geochronologic, metamorphic and petrologic data that are published from the region. A new model of a retroarc thrust wedge/foreland basin system is proposed for the succession based on the following: (1) the nature of the basal unconformity, (2) the wedge-shaped basin-fill geometry bounded by the mountain belt to the south, (3) basinward propagation of the thrust-front with time and (4) the presence of a typical underfilled stratigraphic trinity of the foreland basin. The proposed model suggests two major cycles of evolution of the retroarc thrust wedge/foreland basin system (<725-<635 and ca. 564-446 Ma), which record two periods of northwestward subduction of the oceanic slab beneath the southern margin of the SCB. Terrane accretion is inferred to have taken place during the late stage of these cycles. [ABSTRACT FROM AUTHOR]

Meso-Cenozoic extensional structures are important for understanding the tectonics of the Chinese Central Asia. This paper presents a systematic investigation on the Meso-Cenozoic extensional structures in the Northern Tarim Basin. Close interpretations of seismic data reveal that the Meso-Cenozoic extensional structures were widely developed in the Northern Tarim Basin. These extensional structures are regionally composed of many small normal faults, which usually group into left- or right-step en echelon and form several transtensional fault zones. Combinations of normal faults in profile become small graben-horst or staircase-like cross-sections. Based on the areal distribution, structural style, combination relationship, formation and evolution time, and formation mechanism of the extensional structures, we found that the Meso-Cenozoic extensional structures in Northern Tarim Basin can be classified into two conjugate normal fault systems, which were formed separately in Jurassic-Early Cretaceous and Late Cretaceous-Neogene. The former is likely associated with the stress relaxation after a collisional orogeny accompanied with a certain degree of anticlockwise rotation of the Tarim block relative to the South Tianshan; the latter is possibly induced by the east by south tectonic escape of the Tarim block with a certain degree of clockwise rotation relative to the South Tianshan triggered by the far-field effect of the Himalayan orogeny. [ABSTRACT FROM AUTHOR]

This paper describes an olistostrome formation and accompanied bimodal volcanic rocks occurring in the Baiyanggou area, south of Bogda Shan. The main lithotectonic units consist of olistostrome, volcanic rocks and turbidite. The olistostrome is tectonically underlain by Upper Carboniferous limestone and sandstone along a NEE-trending detachment fault. Paleo-growth fault is locally observed. The olistostrome unit includes plenty of blocks of limestone, sandstone, rhyolite and volcaniclastic rocks, and a matrix of graywacke. Limestone blocks are dated as Pennsylvanian-Bashkirian in age by the coral and brachiopod fossils that are extensively recognized in the Upper Carboniferous strata. The volcanic unit consists of pillowed and massive basalt and rhyolite, the latter occur as an 8- to 10-meter-thick layer above the olistostrome unit. The turbidite unit is mainly composed of chert, siliceous mudstone and sandstone, within which the Bouma sequence can be locally recognized. Meter-wide gabbro and diabase dykes intrude these three units. Geochemically, rhyolites are characterized by high ACNK value of >1.1, depletion of Ba, Nb and Sm, and enrichment in Rb, Th and Zr. Basaltic rocks are rich in KO, they show a LREE-enriched pattern and depletion in Ba, Nb and Zr, and enrichment in Ti, Ce and Hf, similar to continental rift-type tholeiite series. A gabbro porphyrite intruding the olistostrome was dated at 288 ± 3 Ma by a sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb method, and a rhyolite at 297 ± 2 Ma by a laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS) zircon U-Pb method. The Baiyanggou olistostrome and accompanying bimodal volcanic series are linked to an extensional setting that developed in the south of the Bogda Shan. Several lines of evidence, e.g. occurrence of large-scale strike-slip shear zones, large number of mantle-derived magmatic rocks and available geochronological data, demonstrate a significant geodynamic change from convergence to extension in the Chinese Tianshan belt, even in the whole Central Asian Orogenic Belt. The extension in the Chinese Tianshan belt is initiated at ca. 300 Ma, i.e. around Carboniferous-Permian boundary times, and the peak period of intra-plate magmatism occurred in the interval of 300-250 Ma. [ABSTRACT FROM AUTHOR]

The Yanshan thrust belt (YTB) is located at the northern edge of the North China plate. Because of the intense thicking and subsequent delamination of the lithosphere in north China, geologists have been focused on the Late Mesozoic deformation in the Yanshan belt. The Yanshan belt has been regarded as part of a stable craton from the Proterozoic to the early Mesozoic. In this paper, the authors present that the Yanshan area was deformed during the early Mesozoic. This deformation could be related to ocean basin closure along the northern margin of North China, or related to the collision between the north China and Yangtze Plates along the Qinling-Dabie ultrahigh pressure belt. Three stages of early Mesozoic deformation are identified in the eastern Yanshan at Lingyuan County. The first stage is characterized by westward thrusting (D1), the second stage comprises a top-to-east thrust system (D2), and the third stage comprises extensional gravity-induced collapse and landsliding (D3). The timing of these evens is constrained by both the crosscutting relationships of faults and the isotopic dating of volcanic rocks and gravels. The D1 and D2 events took place in the Late Triassic and Early Jurassic, whereas D3 event occurred at the end of the Middle Jurassic. The Dengzhangzi formation was deposited during the D1–D2 period and recorded a rapid uplift, erosion, and deposition sequence. These early Mesozoic contractional deformations in the YTB were probably related to the closure of ancient Asian ocean and ancient Qinling ocean. The later crustal extension was caused by gravitational collapse of the eastern China plateau during early Mesozoic. [ABSTRACT FROM AUTHOR]

The lacustrine source rocks of the upper member of the lower Ganchaigou Formation ( E 3 2 ) in the Yingxi area are considered to be important source rocks in the Qaidam Basin in northwestern China. In this study, we investigated the organic geochemical characteristics of the source rocks by selecting representative samples of the Eocene lacustrine succession spanning 200 m. The results show that the source rock quality is at a fair to good level, and the organic matter (OM) is in the immature–low-maturity stage. The OM originated from plankton/algae and bacteria, with a fluctuating input of terrigenous plants. The source rocks were deposited in a reducing saline-hypersaline environment, with water-column stratification associated with a variable chemocline related to a fluctuating salinity. The vertical variability of the OM abundance is accompanied by simultaneous changes in the source of the OM and the lake water environment parameters, which is caused by the oscillations between drier and wetter conditions in inland Asia in the Late Eocene. The drier periods had strong evaporation and low fluvial input, which facilitated the formation of widespread water anoxia and enhanced OM preservation, while the wetter periods had higher fluvial input and moderate OM preservation conditions because the higher sedimentation rate led to a strong terrestrial dilution effect, which in turn limited the accumulation of OM. [ABSTRACT FROM AUTHOR]

Eastern Tianshan is an important nickel ore belt in China, in which large to middle-sized magmatic Ni–Cu sulfide deposits occur spatially in the eastern part. The Baixintan magmatic Ni–Cu sulfide deposit is an important discovery in the western part of Eastern Tianshan, which provides an ideal target to track the evolution of the magmatic mineralization system in this part. The Baixintan intrusion is composed of the northeastern mafic units and the southwestern mafic–ultramafic units. The olivine Fo contents of the Baixintan intrusion range from 81.12 to 84.46 mol.%. Numerical calculations yield a parental magma composition with 9.14 wt.% MgO. The Rayleigh simulation using olivine Fo and Ni contents shows that the parental magma of the Baixintan intrusion has experienced ~ 2% olivine crystallization, and then evolved magma became sulfide-saturated. Calculations by the mass-balance R factor equation using PGE data indicate that the formation of the mafic and mafic–ultramafic units of the Baixintan intrusion resulted from multiple influxes of magmas. The Baixintan intrusion is highly comparable with those mafic–ultramafic intrusions that host large magmatic Ni–Cu sulfide deposits in the eastern part of Eastern Tianshan. The mafic–ultramafic intrusions in the western part of Eastern Tianshan should be carefully evaluated for the potential of hosting large magmatic Ni–Cu deposits. [ABSTRACT FROM AUTHOR]

The final closure of oceans in accretionary orogens is a transformative process for continental crustal growth. The geodynamic mechanism is still controversial. This study synthesizes the Permo-Carboniferous tectono-stratigraphy, detrital zircon U–Pb dating and magmatism in the Junggar terranes to determine their interlinkage during ocean closure. The tectono-stratigraphy shows a transition from a late Mississippian regressive to an early Pennsylvanian transgressive and late Pennsylvanian transgressive–regressive sequences controlled by the basin-bounding transtensional faults. Detrital zircon U–Pb chronology displays a change of the provenance area from distant in the late Mississippian to more proximal in the Pennsylvanian. The magmatism indicates that the late Mississippian island-arc volcanic successions, related to subduction, progressively gave way to early Pennsylvanian magmatic activity indicative of regional asthenosphere upwelling, which suggests back-arc basins opened since ~ 319 Ma. The termination of the subduction is constrained by A-type granite plutons (~ 307 Ma). The Junggar terranes changed from an active back-arc basin behind an active subduction zone (319–307 Ma), to a post-subduction back-arc basin that continued to extend in 307–290 Ma. This back-arc basin extension is synchronous with voluminous Pennsylvanian–early Permian granite emplacement in both West Junggar and East Junggar blocks. Asthenospheric upwelling in the back-arc area was triggered by subduction, but continued after subduction had ceased. Transfer of juvenile magma to the crust was enhanced by crustal thinning, high thermal gradient, decompression melting and magma pathways along strike-slip faults. The prolonged back-arc setting provided a mechanism for rapid continental crust generation in the Paleozoic southwestern part of Central Asian Orogenic Belt. [ABSTRACT FROM AUTHOR]

The Luobei Complex in Northeast (NE) China lies in the northern Heilongjiang Complex and comprises a sequence of low-temperature–high-pressure metamorphic rocks distributed along the N–S-oriented suture zone between the Jiamusi and Songliao blocks. However, the timing of formation and tectonic setting of the Luobei Complex remain poorly constrained. Here, we present petrological, geochronological, and geochemical data for metasedimentary rocks from the Luobei Complex to elucidate its origin and tectonic setting. The Luobei Complex is characterised by the occurrence of serpentinite, blueschist, greenschist, amphibolite, and marble, which form lenses or interlayers in a matrix of two-mica schist, albite schist, quartz schist, and granitic gneiss. Zircon U–Pb dating of four metasedimentary rocks yields consistent Late Triassic maximum depositional ages (ca. 214 Ma). Detrital zircons from the Luobei Complex yield ages ranging from 1889 to 202 Ma, with age peaks at 504, 350, 265, and 214 Ma. The ages prior to 350 Ma exist in both the Jiamusi Block and the Central Asia Orogenic Belt (CAOB), indicating that the syn-deposition of Luobei Complex, meanwhile, the lack of ages younger than 350 Ma suggests that the Jiamusi Block rifted eastward from the CAOB. Geochemical data indicate that the studied metasedimentary rocks were formed in a continental island arc setting. These results, together with the Early Jurassic metamorphism reported by previous studies, constrain the timing of final collision to Late Triassic–Early Jurassic after subduction of the Jiamusi Block beneath the Songliao Block. Combining our new results with previous findings, we propose a new tectonic model: (1) during the latest Carboniferous to Late Triassic, the Jiamusi Block rifted from the CAOB as a result of Mongol–Okhotsk oceanic plate subduction; and (2) during the Late Triassic and Early Jurassic, the Jiamusi Block was reunited with the Songliao Block, and the Heilongjiang Complex formed, as a result of Paleo-Pacific plate subduction. [ABSTRACT FROM AUTHOR]

Although China is well-endowed with tungsten deposits, while the tungsten resources in the Central Asian Orogen Belt (CAOB) are rarely reported. Recently, many W-skarn deposits have been discovered in the East Tianshan, but the source and evolution of the mineralising fluids are poorly understood. The Xiaobaishitou W(–Mo) deposits are hosted by carbonaceous limestone or banded crystalline limestone in the Mesoproterozoic Jianshanzi Formation, which is intruded by Triassic biotite monzogranite. The deposit comprises garnet-dominated prograde skarn and retrograde skarns followed by oxides (scheelite–cassiterite–magnetite), sulphides (quartz–molybdenite–bismuthinite–pyrite–chalcopyrite–sphalerite–galena), and carbonate stages. The types of fluid inclusions are composed of liquid-rich aqueous, vapour-rich aqueous, aqueous carbon-dioxide, and daughter mineral-bearing inclusions. The homogenization temperatures of fluid inclusions change from > 400 °C in garnet, through > 380 °C in epidote and 310–280 °C in scheelite, to 280 °C in quartz and 220 °C in calcite indicating a complex magmatic-hydrothermal process. The δ18Owater values varied from + 6.1 to + 8.4‰ in garnet, + 5.2 to + 7.4‰ in epidote, + 2.0 to + 3.0‰ in quartz, to − 0.7 to − 0.1‰ in calcite. The corresponding δD values are − 95 to − 71‰ in garnet, − 84 to − 80‰ in epidote, − 115 to − 90‰ in quartz and − 101 to − 89‰ in calcite. Both O and H isotopic compositions show the mineralisation fluids are originated from deep-sourced magmatic fluids. The δ13CCO2 values in the calcite range from − 7.8 to − 7.7‰, which is characteristic of magmatic fluids interacting with reduced carbon from metamorphic rocks. The δ34S values of hydrothermal fluids range from + 4.5 to + 5.1‰, and 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of sulphide are 18.072–18.664, 15.566–15.708, and 38.245–38.658, respectively, representing a mixed characteristic of magmatic and sedimentary sulphur. Considering the coexisting of L-type and V-type inclusions in the scheelite, we proposed that pH increase caused by fluid boiling may be the major cause for the precipitation of scheelite at the Xiaobaishitou deposit. [ABSTRACT FROM AUTHOR]

The Huangtan (including Jinling) Au–Cu–Zn deposit is an auriferous volcanogenic massive sulfide (VMS) deposit discovered in East Tianshan, Central Asian Orogenic Belt. The deposit is hosted in volcanic breccia and tuff of the Silurian Hongliuxia Formation. The ore bodies consist of concordant massive sulfide lenses and discordant sulfide veins. Chalcopyrite Re–Os dating constrained the age of mineralization in the Huangtan deposit at 432 Ma. Quartz and barite host abundant liquid-rich, liquid-only and minor vapor-rich aqueous fluid inclusions. The fluid inclusions in barite from the exhalative–sedimentary units mainly have homogenization temperatures at 140–260 °C, and calculated salinities of 3–9 wt% NaCl equiv.; Those values are at 120–300 °C, and 1–9 wt% NaCl equiv. for varieties in quartz from the vein ores and alteration assemblages. Fluid inclusions extract from pyrite have 3He/4He ratios of 0.929–1.374 Ra, 40Ar/36Ar of 388–520, and 40Ar/4He of 0.355–0.836. The quartz and barite yielded δ18O values of 7.4‰ to 10.1‰ and the δDV-SMOW values of the fluid inclusions in the quartz and barite range from − 69 to − 42‰. The He–Ar and H–O isotopes imply that the ore-forming fluids were derived from a magmatic source with the addition of deeply circulating seawater. The δ34SV-CDT values of pyrite and chalcopyrite range from − 2.0 to 1.5‰, and those of barite samples range from 24.1 to 24.8‰, which indicates that sulfur was derived from magmatic sulfur, and was subjected to fractionation between sulfide and sulfate. Linked to the ore geology, geochronology data, isotope compositions and fluid inclusions obtained in this study with those of previously published adjacent VMS deposits in the Kalatag area suggest that the Huangtan deposit and adjacent VMS deposits formed in the same metallogenic system. [ABSTRACT FROM AUTHOR]

As a portion of the Central Asian Orogenic Belt (CAOB), the Beishan Orogen is key to the evolution of the Paleo-Asian Ocean (PAO). The Mazongshan ophiolitic mélange in central Beishan Orogen comprises peridotite, gabbro, dolerite, anorthosite, massive and pillow basalt, and chert and turbiditic mudstone. Its age and tectonic environment remain controversial, which seriously affects the understanding of the tectonic evolution of the CAOB and PAO. Geochemical results demonstrated that gabbros could be divided into two distinct groups. Group A was enriched in both large ion lithophile elements (LILE) and high field strength elements (HFSE) and had high total rare earth element (REE) concentrations with the light REE (LREE) distinctly enriched relative to heavy REE (HREE), showing geochemical characteristics of oceanic island basalt (OIB). Group B has enriched LILE but flat HFSE patterns with LREEs slightly depleted relative to HREEs, which was similar to the patterns of normal mid-ocean ridge basalt (N-MORB). Basalts and peridotites displayed consistent geochemistry of MORB. Negative εSr(t) (− 44.89 to − 33.45) and positive εNd(t) (2.21 to 3.29) values of Group A indicated mantle origin. Gabbro and dolerite from Group A yielded a U–Pb age of 420 ± 2 Ma and 414 ± 3 Ma, respectively, but gabbro from Group B and tuff yielded a U–Pb age of 486 ± 15 Ma and 425 ± 6 Ma. The anorthosite dykes were formed approximately during 370 ± 5 Ma. These results demonstrate that the Mazongshan ophiolite represents relicts of the Ordovician–Devonian Paleo-Asian oceanic crust formed in the mid-ocean ridge and oceanic plateau environments. [ABSTRACT FROM AUTHOR]

The Manzhouli–Xin Barag Right Banner area, located in the southwestern Erguna Massif, is characterized by the distribution of a large volume of Mesozoic volcanic rocks and many polymetallic deposits. However, the tectonic setting of this area during the Late Mesozoic remains controversial. In this study, zircon U–Pb ages range from 142.8 ± 1.8 to 140.4 ± 1.6 Ma for the alkali basalt from the Meiletu Formation and 140 ± 0.9 Ma for alkaline rhyolites from the Baiyingaolao Formation, forming a bimodal volcanic rock assemblage. The initial 87Sr/86Sr ratios range from 0.705365 to 0.705674, and the εNd(t) values vary from + 0.55 to + 1.47. The alkaline rhyolites show εHf(t) values ranging from + 5.3 to + 8.6, corresponding to TDM1 and TDM2 ages in the range of 0.48–0.58 Ga and 0.64–0.86 Ga, respectively. Combined with the major and trace element compositions, the Meiletu alkali basalts are characterized by Nb enrichment (averaging 23.6 ppm) and were derived from partial melting of metasomatized subcontinental lithospheric mantle and underwent moderate fractional crystallization of minerals (e.g. olivine, clinopyroxene, apatite, and plagioclase). The alkaline rhyolites show A1-type granite affinity and originated from partial melting of the mafic lower crust accompanied by fractional crystallization. This suite of bimodal volcanic rocks was mainly dominated by the Mongol–Okhotsk tectonic regime, and the Erguna Massif was in a back-arc extensional setting triggered by slab rollback during the Early Cretaceous. [ABSTRACT FROM AUTHOR]

The Archean Kongling tonalite–trondhjemite–granodiorite (TTG) rocks and Neoproterozoic Huangling granodiorite–monzogranite–tonalite complex occupy the core of the Huangling anticline of the northern Yangtze Craton, South China. These Precambrian felsic rocks have provided crucial clues for understanding the earliest crustal growth in South China. This study presents a set of new zircon U–Pb geochronological and Lu–Hf isotopic data, and whole-rock geochemical data for the mafic dykes, predominantly intruding the Kongling TTG package in the northern Huangling anticline. Our data show that the dykes might be geochemically subdivided into Groups 1 and 2. Group 1 is characterized by low Al2O3, Na2O + K2O, Mg#, Th/Ta, and Sm/Yb but high FeOt and TiO2. In contrast, the Group 2 samples are marked by higher Al2O3, Mg#, Th/Ta, and Sm/Yb but lower FeOt and TiO2. The Group 1 dykes are inferred to be of Paleoproterozoic origin. Group 2 has zircon U–Pb ages of ~ 800 Ma but distinct εHf(t) values among the rock samples, ranging from − 0.3 to − 31.5 and indicating the Neoproterozoic lithospheric mantle being heterogeneous. The Paleoproterozoic Group 1 mafic dykes originated from an enriched and dry lithospheric source. The Neoproterozoic Group 2 mafic dykes were generated by an enriched lithosphere that was modified by slab-released fluid. In addition, a tonalite sample from the southern Huangling anticline is dated at ~ 815 Ma, and has the εHf(t) values ranging from − 19.8 to + 6.9. The wide εHf(t) range suggests the mixing between an enriched lithosphere with a less enriched source. Our data, along with the coeval mafic rocks in NW South China, North Laurentia, and South Australia, indicate that the Neoproterozoic mafic dykes and tonalite in the Yangtze interior are most likely the products in the supra-subduction setting along the Rodinia margin. [ABSTRACT FROM AUTHOR]

Many silicic plutonic rocks of the Late Permian Emeishan large igneous province (ELIP) are spatially and temporally related to oxide ore-bearing layered mafic–ultramafic intrusions. Their association suggests that there may be a petrogenetic link between the two rock types where the layered intrusion represents the cumulate portion of the magma system and the silicic rocks are the residual liquid portion. An alkali feldspar syenite collected in close spatial association with the Hongge-layered mafic–ultramafic intrusion yielded a weighted-mean zircon U–Pb age of 261.5 ± 2.4 Ma with a corresponding weighted-mean εHf(t) value of + 6.5 ± 0.5. The Hongge syenite is alkalic, metaluminous, and ferroan and somewhat similar to other A-type granitoids of the ELIP but, it is composed of ~ 90 vol% alkali feldspar. The rocks have initial 87Sr/86Sr ratios of 0.70570 and 0.70515 and εNd(t) values of − 0.3 and + 1.4. Rhyolite-MELTS and isotopic modeling indicate that the Hongge syenite is likely produced by crystal accumulation of a residual silicic liquid derived from a mafic parental magma that experienced localized crustal contamination during emplacement. Moreover, the age, location, and composition of the Hongge syenite suggests that it is the uppermost portion of the Hongge-layered intrusion and is representative of the residual silicic liquid of the mafic magmas that form the plagioclase-rich cumulate gabbros of the upper zone. [ABSTRACT FROM AUTHOR]

Recent breakthroughs in petroleum exploration suggest that the Linhe depression in the Hetao Basin in central and western Inner Mongolia has undergone multi-stage Meso-Cenozoic tectonic events and possesses considerable exploration potential. However, structural deformation sequences and the genesis of oil-bearing structures in the basin are still poorly understood. Analyzing the deformation sequences of structural styles can improve the understanding of the basin history and regional tectonic evolution, and is essential for targeting potential traps. In this study, we interpreted 2D seismic profiles, drilling, and well-logging data, and outcrops to elucidate structural styles, tectonic evolution, and temporal distribution characteristics of styles with the assessment of potential petroleum traps in the Linhe Depression, Hetao Basin. We identified four structural styles and sequences with fault associations in the Linhe Depression, namely, NE-striking normal faults (D1), inversion fault-folds (D2), NE-NNE-striking dextral strike-slip faults and normal faults (D3), and near-E-W-striking sinistral strike-slip faults (D4). Analysis of syn-sedimentary normal faults and the cross-cutting relationship of faults and sedimentary strata indicate that D1, D2, D3, and D4 occurred during the Early Cretaceous, Late Cretaceous to Early Eocene, Middle Eocene to Neogene, and Quaternary, respectively. The temporal development of structural styles promoted the formation, re-construction, and finalization of structural traps, while fault geometry and fluid potential influenced the dominant petroleum migration directions. It is shown that the hydrocarbon generally migrated from the northwestern sag to the southeastern slope during the peak hydrocarbon expulsion period in the Neogene. Traps of inversion anticlines and numerous fault blocks developed in the Cretaceous and Paleogene strata are identified as the most favorable trap types. The traps on the slope were produced by numerous NNE-NE-striking faults, and the dominant migration direction implies that hydrocarbons were available to fill the traps. [ABSTRACT FROM AUTHOR]

The Songliao Basin is the largest Early Cretaceous lacustrine rift basin of northeast China and hosts tremendous conventional and unconventional petroleum resources. However, the distribution of shale oil is not well constrained, as production from source rock reservoirs requires certain thermal maturity cut-offs (vitrinite reflectance of > 0.8%Rr). In this study, the thermal maturity of the Qiangshankou Formation along the Southern Uplift and in the Central Depression of the Songliao Basin was evaluated by combining traditional and advanced petrographic and geochemical maturity proxies with clay mineralogical investigations. The Qingshankou Formation is one of the major source rocks of the region, but previous studies encountered difficulties in obtaining reliable maturity data, mainly due to strongly shifted Tmax values. Equally, Tmax determined during this study showed apparent shifting likely caused either by retained solid bitumen or by variations in kerogen type. In contrast, the measured vitrinite reflectance shows a reliable depth trend, meeting the shale oil cut-off maturity of 0.8%Ro at a drilling depth of ~ 2300 m, which is only reached in the Central Depression of the basin. The vitrinite reflectance trend is supported by changes in clay mineralogy, such as the progressing ordering of I/S mixed layers ("Reichweite"), increasing illitization, decreasing detrital kaolinite and correspondingly increasing authigenic chlorite contents. Maturity-related biomarker proxies are only partly valid; while the methylphenanthrene index (MPI-1) and the trimethylnaphthalene ratio (TNR-1) show reliable maturity trends even over short depth intervals, other established proxies (e.g. based on alkylbiphenyls) proved insensitive to changes from immature to peak oil mature and are, therefore, not recommended for further use in studies on Qingshankou Fm. shales. In summary, the combination of various maturity parameters improves the understanding of shale oil distribution in the central Songliao Basin, providing valuable insights for studies on similar unconventional targets in the region. [ABSTRACT FROM AUTHOR]

The Manzhouli–Xin Barag right banner are located in the southwest of the Ergun Massif (NE China), the tectonic evolution of these areas are still controversial. In this study, a series of rocks comprising rhyolites (LA–ICP–MS U–Pb zircon ages of 206 ± 2 Ma and 195 ± 2 Ma), granodiorites (196 ± 1 Ma and 190 ± 1 Ma), and monzogranites (206 ± 5 Ma and 196 ± 1 Ma) are newly identified. Whole-rock major and trace element analyses show that these felsic rocks and granites belong to the metaluminous to peraluminous, high-K calc-alkaline series, and can be classified as I-type granites. The zircon in-situ Lu–Hf isotope analyses on rhyolite, granodiorite, and monzogranite, yielded the εHf(t) values that are ranging from of 9.7–12.1, and two-stage model age are in the range of 0.5 Ga to 0.6 Ga, εHf(t) values of 4.4–7.5, 0.8–1.0 Ga, εHf(t) values of 6.0–10.5, 0.6–0.9 Ga, respectively. The whole-rock Sr–Nd isotope analyses on rhyolite, granodiorite, and monzogranite, yielded lower initial 87Sr/86Sr ratios (ISr) of 0.703374–0.703586, 0.704503–0.704577, 0.704936–0.704379, with medium εNd(t) values of 4.32–4.38, 1.54–2.96, − 0.68 to 2.73, respectively, suggesting that they are derived from the partial melting of a juvenile depleted lower crust. They all show enrichment in the large ion lithophile elements (e.g., Rb, Ba, and K) and depletion in the high field strength elements (e.g., Nb, Ta, and Ti), indicating that they are generated in an Andean-type arc setting and are metasomatized by subduction-slab released fluids or melts with minor crustal contamination. Mainly three magmatic phases: ca. 283–225 Ma, ca. 225–166 Ma, and ca. 166 Ma–114 Ma are identified in the Ergun Massif, and above Late Triassic to Early Jurassic magmatic rocks are related to the second phase, which attribute to the Mongol–Okhotsk ocean southward subduction and lateral crustal growth. [ABSTRACT FROM AUTHOR]

Sedimentological and zircon U–Pb–Hf isotopic analyses of the Carboniferous strata in the Bainaimiao arc belt (BAB) provide provenance information for the northern margin of the North China Craton (NCC). The late Carboniferous strata in the eastern BAB were dominantly shallow marine carbonate-clastic deposits. Detrital zircon data show that: (1) sandstone from lower Sidaozhangpeng Formation displays two major age peaks of 369 Ma and 2522 Ma, with εHf (t) values of − 25.9 to − 20.4 and 2.2–6.4, respectively; (2) sandstone from upper Sidaozhangpeng Formation shows a significant age peak at 384 Ma, with εHf (t) values of − 25.3 to − 14.5. Determination of detrital zircon parent rock types based on trace element proxies suggests that the protolith rock types consist of felsic (73%) and mafic rocks (22%), with minor alkaline rocks (5%), implying a continental arc setting. The U–Pb–Hf dating of the Carboniferous strata in the western and eastern BAB shows different provenances: the Carboniferous sediments in the western BAB were derived from early Paleozoic magmatic rocks, micro-block (Hunshandake Block) and the NCC basement; the provenances of the Carboniferous strata from the eastern BAB were mainly local Devonian magmatic rocks, with subordinate input of the Neoarchean NCC basement rocks. The early Paleozoic zircon grains recorded by the early Devonian rhyolitic tuff and late Carboniferous sandstone indicate that the early Paleozoic arc magmatic activities also occurred in the eastern BAB. [ABSTRACT FROM AUTHOR]

The Permian–Triassic extinction was the largest Phanerozoic mass extinction event, yet its ultimate causes remain unresolved. Ocean redox conditions, global warming, and carbon cycle perturbations owing to massive volcanism and their inter-relationships are keys to resolve the origins of this event. We here assess such relationships using a method to obtain an instantaneous stratigraphic response from high-resolution (millennial-scale) records of carbonate-δ13C and pyrite framboid size distributions across the Permian–Triassic boundary (PTB) at Meishan, China. We report two gradual long-term negative δ13C shifts before and after the PTB. Late Permian ocean redox conditions varied through three successive oxic–dysoxic, dysoxic–euxinic, and high-frequency euxinic stages. Oxic and high-frequency euxinic events occurred in the early Griesbachian and middle Griesbachian, respectively. The short-term euxinia events were not associated with the negative δ13C excursions. Siberian volcanism could have produced large light-carbon inputs, global warming, and low-oxygen conditions at intermediate ocean depths, but it may not directly drive high-frequency euxinia across the PTB. Long-term dysoxia and occasional euxinia well before the PTB stressed mobile macroorganisms and caused gradual extinction before the major extinction event. High-frequency latest Permian euxinia reduced overall biotic adaptability, and caused the initial rapid mass extinction. Increasing temperatures and other deleterious environment factors then reinforced the extinction process. Oxic conditions contributed to biotic recovery immediately after the mass extinction in the early Griesbachian. Further millennial-scale dysoxic/euxinic alternations in the middle Griesbachian would have prolonged Early Triassic biotic recovery. [ABSTRACT FROM AUTHOR]

The Solonker Belt is an important tectonic unit of the Central Asian Orogenic Belt in Inner Mongolia, China and the sediments in the Solonker Belt record the paleogeographic evolution of the Paleo-Asian Ocean. This study characterizes the spatial distribution of the lithofacies and lithofacies associations, and environment variations in the Mandula Basin. The Upper Carboniferous to Lower Permian Amushan Formation shows typical features of slump deposits occurred in the lower slope environments. The Lower to Middle Permian Baotege Formation develops the channelized lobes, channel–levee–overbank, and hemipelagic/pelagic deposits that are formed in the base of slope to basin floor environments. The Lower to Middle Permian Dashizhai Formation represents volcanic edifice and volcaniclastic aprons in the basin floor. The Middle Permian Zhesi Formation includes the shallow water reefs, deep-water biogenetic limestones, and volcaniclastic aprons developed in the abyssal slopes of the volcanic edifice. The sedimentary facies in the Mandula Basin constitute two depositional systems: the continental slopes adjacent to marginal carbonate platform and the volcaniclastic aprons associated with volcanic edifice in the basin floor. The Mandula Basin is an extensional deep-water basin and akin to the marginal sea of an ocean. [ABSTRACT FROM AUTHOR]

The Paleoproterozoic Jiao-Liao-Ji Orogenic Belt provides key evidence of evolution from an early rift-basin (or back-arc basin) to final collision of the Longgang block (Eo-Meso Archean granitic gneiss) and the Nangrim block in the Liaodong peninsula, northeastern North China Craton. A structural investigation of schists and phyllites in the Langzishan Formation of the North Liaohe Group reveals two new major structures: (1) a sub-horizontal nappe on Meso-Archean granitic gneiss belonging to a ~ 1.95–1.9 Ga Paleoproterozoic D1-2 fold-thrust system produced by terminal collision; From the south basin to the north basement, the metamorphic gradient transferred from greenschist facies metamorphism into amphibolite facies produced by crustal thickening in the Paleoproterozoic orogenesis; the intensity of deformation was also increasing from south to north, the pure shearing style changed into simple shearing. (2) A metamorphic core complex (The Gongchangling metamorphic core complex) formed during Cretaceous extension and doming enabled delamination and diapiric rise and exhumation in the core complex. This extensional-delamination event affected a wide area of the orogenic belt, as part of the delamination of the northeastern half of the North China Craton. This is the first example of the Paleoproterozoic thrust-nappe tectonics exhumed and preserved by Cretaceous diapirism in northeast China. [ABSTRACT FROM AUTHOR]

The scale and extent of isotopic heterogeneities in the Paleo-Asian oceanic mantle remain poorly constrained. Here, we report Os isotopic data for mantle peridotites from the Paleozoic Gangou and Kumishi ophiolites, which are preserved in the western Chinese Tianshan sutures (Xinjiang, China) and considered to sample the Paleo-Asian oceanic upper mantle. These heavily serpentinized peridotites display positive correlations between Al2O3, Ti, and Yb contents, indicating variable degrees of melt extraction from fertile mantle sources. However, enriched light rare-earth element patterns in the peridotites are inconsistent with simple residues of partial melting, thus reflecting the effect of post-melting melt percolation. Peridotites from both ophiolites show wide variation of Os isotopic compositions, several of which are characterized by highly unradiogenic 187Os/188Os values (0.117–0.118), reflecting Proterozoic melt depletion. Such feature is common in modern oceanic peridotites and most Phanerozoic ophiolites, meaning that Os-isotopically ultradepleted domains should be widespread in the Paleo-Asian oceanic mantle. The overall similarity of Os-isotope distribution between the Paleozoic Tianshan ophiolites and modern oceanic peridotites suggests that they derive from the same heterogeneous upper mantle reservoir. This might support the hypothesis that isotopically ultradepleted domains are inherent components of the convecting upper mantle and have not been sufficiently homogenized by convection. Alternatively, Re-depletion ages (TRD) for these ancient domains are broadly coincident with the major peaks in crustal zircon ages that are thought to reflect episodes of continental crust growth in the adjacent Yili–Central Tianshan microcontinents. This suggests that the ultradepleted mantle domains in some of the Tianshan ophiolites may derive from ancient subcontinental lithospheric mantle, which detached and were exhumed to form the substrate of ocean basins. [ABSTRACT FROM AUTHOR]

The timing of the amalgamation of the Xing'an and Songliao–Xilinhot blocks in the eastern Central Asian Orogenic Belt has long been the subject of debate. To explore this question, we studied a suite of late Carboniferous mafic to felsic intrusive rocks in the central Great Xing'an Range, NE China. These rocks yielded late Carboniferous zircon U–Pb isotopic ages of 320–300 Ma. The felsic monzogranites and granodiorites are strongly peraluminous with high A/CNK ratios (≥ 1.1), and they have signatures transitional between I- and S-type granites. Their geochemical characteristics suggest a magmatic source in a heterogeneous juvenile crust that included both clay-rich pelitic material and metabasalt. On the other hand, the intermediate biotite granodiorites have characteristics that suggest a dual magmatic source involving both mantle material and crustal contributions. The mafic gabbros were derived from the partial melting of mantle materials including both spinel and garnet lherzolite. The upwelling of the asthenospheric mantle contributed greatly to the formation of these magmas, with the upwelling as a result of the delamination of dense lithosphere and/or previously trapped mafic slabs. The petrology, geochemical signatures, field characteristics, and rock associations of the late Carboniferous mafic to felsic intrusive rocks imply that they formed in a post-collisional extensional tectonic setting that developed after the amalgamation of the Xing'an and Songliao–Xilinhot blocks and closure of the Nenjiang Ocean between them. Considering that the tectonic setting during the early Carboniferous was one of regional subduction, our data constrain the amalgamation of the Xing'an and Songliao–Xilinhot blocks and the closure of the Nenjiang Ocean to the early late Carboniferous. [ABSTRACT FROM AUTHOR]

The coefficient of friction is a parameter of the mechanical state which has an important role in the shear failure of rock in the fields of earth sciences. In order to analyze the influence of temperature and pore pressure on the coefficients of friction between solid and gouge, data from studies carried out in both China and international contexts are applied, analyzed and discussed. The survey results show that the coefficient of friction mainly depends on the pore pressure, pressure and temperature. Under the supercritical water state, the framework of silicate minerals might be substantially disintegrated, which suggests a possible change in the frictional resistance from stick slip to stable sliding. The temperature range of 300–450 °C could constitute as the critical threshold for shear failure to collected rocks (i.e., gabbro gouge, pyroxene gouge, gabbro solid, biotite gouge, structured gouge, granitic mylonite, mylonite, plagioclase gouge, granite gouge, pre-fractured granite, westerly granite). [ABSTRACT FROM AUTHOR]

Late Quaternary paleoclimate records from arid regions help us understand the response of ecological systems to natural climate change to place recent changes in a longer-term perspective. In this research, a biogeochemical analysis of a sediment core from Lake Ebinur, Xinjiang, allowed us to infer the climate and environmental changes in the late Quaternary in arid northwestern China. The combined lipid biomarkers and bulk biogeochemical properties (TOC, δ13Corg) revealed moderately wet conditions from 34 to 28 ka, favoring the growth of terrestrial vegetation. The subsequent period from 28 to 13 ka was dominated by aquatic plants, algae and microbes, indicating cold and dry conditions. Ameliorated regional moisture conditions were deduced from the higher carbon preference index (CPI) and from δ13Corg values from 13 to 3.6 ka. The optimum climate conditions occurred from 9 to 5 ka. Several climatic events also exist in the Lake Ebinur records with a wide distribution into other regions. Our biogeochemical-based paleoclimate and paleoenvironmental reconstruction is generally synchronous with sedimentary records from mid-latitude Eurasia and the NGRIP ice core record, which probably has a certain linkage with the 45°N summer insolation. We propose that summer insolation conditions in the northern hemisphere might have an impact on the climate and environmental changes in arid northwestern China in the late Quaternary. [ABSTRACT FROM AUTHOR]

Evidence for the Jurassic–Cretaceous Yanshan Movement (Orogeny) was first identified in the Jingxi Basin, a part of the Yanshan fold-and-thrust belt (YFTB) along the northern margin of the North China Craton. The disconformity or angular unconformity within the Jurassic volcano-sedimentary successions in the basin was interpreted to have resulted from a period of incipient shortening during the Yanshan Movement, commonly known as event A. However, the absolute ages of both event A and associated Jurassic units remain controversial. Here, we present the results of zircon U–Pb geochronology for volcanic and clastic rocks from the Jurassic units in the Jingxi Basin. The results provide better constraints on the depositional ages of formations in the basin: (1) Early-to-early Middle Jurassic (175–167 Ma) for the Nandaling Formation; (2) middle Middle Jurassic for the Yaopo Formation; (3) late Middle Jurassic for the Longmen Formation; (4) early Late Jurassic for the Jiulongshan Formation; and (5) late Late Jurassic (157–149 Ma) for the Tiaojishan Formation. Stratigraphic and geochronological correlations indicate that the Jiulongshan Formation and the Tiaojishan Formation are of different depositional ages in different regions. The Longmen Formation in the Jingxi Basin is equivalent to the Haifanggou Formation in the eastern YFTB. Two sedimentary cycles separated by a sedimentary hiatus, shown as disconformity and local angular unconformity, have been identified in the Jurassic sequences of the YFTB. Depositional ages of the rocks above and below the disconformity, which lies between the Yaopo and Longmen formations in the Jingxi Basin, constrain the timing of event A to 167 ± 2 Ma (late Middle Jurassic). This event is the first phase of shortening deformation in eastern China induced by the paleo-Pacific plate subduction. We propose that the shortening period was relatively transient, in contrast to previous suggestions of long-duration shortening. [ABSTRACT FROM AUTHOR]

The southwest margin of the Yangtze Block underwent multiple tectonic events including the collision between the Yangtze and the South China Plate, Caledonian folding and uplift of South China, subduction of the western Pacific Plate, and Cenozoic continental escape during the Indo–Asia collision. The structural framework and tectonic evolution of the area are currently unclear. Through field petrologic and structural studies, microstructures within the deformed units, and estimates of the temperature of deformation, we constrain the conditions of deformation and further classify at least four-stage deformation. The first stage involved northeastward thrusting that produced folds, mylonites, and dynamically recrystallized quartz and calcite. Electron backscatter diffraction data indicate that deformation during this event occurred at < 400 °C, corresponding to a depth of ~ 10 km. The second stage of deformation involved uplift, extension, and the generation of a domal structure. During the third event, high-angle normal faults formed within the cover sequence that surrounds the dome. The fourth stage of deformation occurred in the Cenozoic and involved motion along sinistral and dextral strike–slip faults, which cut structures that formed during the previous stages of deformation. The first deformation event was related to Triassic N–S collision with the Indochina block; the second and third stages resulted from far-field compression related to westward subduction of the paleo-Pacific plate; and the fourth event was related to displacement along the Ailaoshan Red-River strike–slip fault. The dome in the study area represents a transitional structure between a metamorphic core complex and a gneissic dome, which we refer to as structural doming. [ABSTRACT FROM AUTHOR]

We present a series of images from the aeromagnetic data observed in South China areas, and reveal the detailed structures of the South China Block. By using lateral variation of the aeromagnetic anomalies, we characterize individual geological blocks and suggest the deep boundaries of the blocks. The Yangtze Block and Jiangnan orogenic belt are characterized by low aeromagnetic anomalies, whereas high values of the aeromagnetic anomaly are observed in the Cathaysia Block. The boundary between the Yangtze and Cathaysia blocks, which remains unclear to date, can be plotted along the large magnetic gradients. The high magnetic anomalies significantly relate to volcanic distributions in South China areas. These aeromagnetic observations seem to be useful to investigate the intracontinental tectonic evolution in this region. [ABSTRACT FROM AUTHOR]

The Qilian Orogen in the northern margin of the Tibetan Plateau is the northernmost of the Tethyan domain. Abundant ophiolites record the closure of an early Tethyan ocean and amalgamations between micro-continents of North China, Qaidam, and Tarim. The Muli arc–ophiolite complex in the western segment of the South Qilian belt represents remnants of the Proto-Tethyan oceanic lithosphere. It comprises serpentinite, dunite, cumulate gabbro, basalt, plagiogranite, and chert, which are in tectonic contact with Upper Ordovician turbidites. Basalts have typical subduction-related calc-alkaline geochemical affinity, representing portions of an island arc. Geochemical results for plagiogranites and spinels from serpentinite indicate that the Muli arc–ophiolite complex represents a super-subduction zone (SSZ)-type ophiolite. U–Pb zircon data indicate formation associated with southward subduction of the Proto-Tethys Ocean during a short interval between 539 and 522 Ma. Results of petrology, geochemistry, and zircon U–Pb dating demonstrate that granitoids intruded into this complex are Middle to Late Ordovician (470–450 Ma) products of subduction-related arc magmatism. Voluminous Late Ordovician–Early Silurian rocks include deep-water marine siliciclastic and volcaniclastic turbidites and abundant volcanic arc rocks located to the south of the Muli arc–ophiolite complex, whereas fluvial coarse-grained sandstones and conglomerates unconformably overlie the Cambrian–Middle Ordovician ophiolite–arc systems in the eastern South Qilian belt. This indicates that closure of the Proto-Tethys Ocean was diachronous during the early Paleozoic. [ABSTRACT FROM AUTHOR]

The Changning-Menglian Belt in western Yunnan, China, has been considered for decades as a remnant of Paleo-Tethys in this region. However, the understanding of the geological evolution of the belt remains sketchy and incomplete. As a significant component of the stratigraphic successions in the eastern part of the belt, the siliciclastic Nanduan Formation preserved essential information of the developing history of the belt. Petrologic studies of the formation show that it was deposited in a neritic environment. The increase of mudstone beds and decrease of grain size of sandstones upwards suggest a gradual deepening of sedimentary environment. Petrographic and geochemical characteristics of sandstones show that they were derived from mature continental provenance and deposited in a passive continental margin setting. Detrital zircon ages of the formation range from 362 to 3685 Ma. The youngest detrital zircon age (362.2 ± 5.5 Ma) confines the deposition age of the sandstones to being younger than the latest Devonian. Dominant age populations of ca. 950 Ma and ca. 550 Ma can be correlated with the magmatic events that occurred in Eastern Ghats-northern Prince Charles (India–Antarctica) (ca. 950 Ma) and Pan-African orogens (Australia–India) (ca. 550 Ma), which are considered, therefore, to be the main provenance of the Nanduan Formation. These results let us consider that the Nanduan Formation and the underlying Lancang Group were formed on the margin of the Baoshan-Shan Block (therefore, autochthonous), and the Carboniferous‒Permian limestones of seamount resemblance, the oceanic bedded cherts, and basic and ultra-basic igneous rocks in the central zone of the belt are overthrusted slices (allochthonous). [ABSTRACT FROM AUTHOR]

The Helanshan Tectonic Belt and its environs within the northwestern Ordos Terrane, western North China Craton, have been envisaged as aulacogen or plate boundary separating the Alxa Massif from the Ordos Block during Cambrian. However, it conflicts with geological and geophysical facts. This study presents integrated stratigraphic, sedimentary and geochronological data from the Cambrian strata in the northwestern Ordos Terrane to constrain the Cambrian tectonic evolutionary process of the western North China Craton. The Cambrian successions comprise, in ascending order, evaporite platform facies, restricted-open platform facies and evaporite platform facies, featuring a vertical transgression–regression sequence. An eastward-shoaling paleogeography was documented, evidenced by shallow-water dolomite layers enriched in the east and the detritus derived from northeast. Ages of detrital zircons span from 2566 to 1649 Ma with predominant two peaks around 2500 and 1850 Ma, suggesting these Cambrian detritus were sourced from the Archean–Paleoproterozoic rocks in the Yimeng highland. Comparable fossil associations and unified paleogeography system supported that there was no Cambrian plate boundary in the northwestern Ordos Terrane, implying the Alxa Massif was part of the North China Craton during the Cambrian. The westward-deepening facies differentiation with low-angle topography contradicts with the tectonic model of "Helan aulacogen". In combination with the relatively low subsidence rate and rare magmatic–metamorphic activities, we argue that the Cambrian shallow marine system in the western North China Craton was the continent-ward extension of passive continental margin basin system related to the spreading of the Paleo-Asian Ocean. [ABSTRACT FROM AUTHOR]

The Tethys Himalaya sedimentary sequence (THS) is characterized by N-S trending extensional rifts (NSTR) and the North Himalayan gneiss domes (NHGD). The Cuonadong dome, as one of the NHGD, is located at the N-S trending Cuona rift in the eastern part of the Tethys Himalaya. The dome had undergone four major deformation events: D1, characterized by top-to-S thrust resulting in N-S shortening and vertical thickening; D2, characterized by vertical thinning and N-S extensional deformation; D3, approximately E-W extensional deformation associated with intrusion of leucogranites; and D4, late collapse structural deformation around the core of the Cuonadong dome. There are numerous granitic dykes at the contact zone between the granite and surrounding rocks in the middle unit of the Cuonadong dome. Field observations show that granite intrusion occurred in part synchronously with D3, E-W extensional deformation. U-Pb-zircon dating shows that the granite crystallization took place at ca. 17.5-15.6 Ma, while muscovite Ar-Ar geochronological data from the deformed pegmatite and mylonitic schist in the Cuonadong dome show that the onset of the E-W extensional deformation is between 16.5 and 14.8 Ma, and suggesting that granite intrusion was synchronous with the E-W ductile extensional deformation in the Cuonadong dome, southern Tibet. Combined with previously published ages of the South Tibetan Detachment System (STDS), our study shows that granite intrusion was at least locally contemporaneous with both the E-W and N-S extensional deformation, especially with the E-W extension. [ABSTRACT FROM AUTHOR]

The cycling of various isomorphs of authigenic silica minerals is a complex and long-term process. A special type of composite quartz (Qc) grains in tuffaceous shale of Permian Lucaogou Formation in the sediment-starved volcanically and hydrothermally active intracontinental lacustrine Santanghu rift basin (NW China) is studied in detail to demonstrate such processes. Samples from one well in the central basin were subject to petrographic, elemental chemical, and fluid inclusion analyses. About 200 Qc-bearing laminae are 0.1-2 mm and mainly 1 mm thick and intercalated within tuffaceous shale laminae. The Qc grains occur as framework grains and are dispersed in igneous feldspar-dominated matrix, suggesting episodic accumulation. The Qc grains are bedding-parallel, uniform in size (100 s µm), elongate, and radial in crystal pattern, suggesting a biogenic origin. Qc grains are composed of a core of anhedral microcrystalline quartz and an outer part of subhedral mega-quartz grains, whose edges are composed of small euhedral quartz crystals, indicating multiple episodic processes of recrystallization and overgrowth. Abundance of Al and Ti in quartz crystals and estimated temperature from fluid inclusions in Qc grains indicate that processes are related to hydrothermal fluids. Finally, the Qc grains are interpreted as original silica precipitation in microorganism (algae?) cysts, which were reworked by bottom currents and altered by hydrothermal fluids to recrystalize and overgrow during penecontemporaneous shallow burial. It is postulated that episodic volcanic and hydrothermal activities had changed lake water chemistry, temperature, and nutrient supply, resulting in variations in microorganic productivities and silica cycling. The transformation of authigenic silica from amorphous to well crystallized had occurred in a short time span during shallow burial. [ABSTRACT FROM AUTHOR]

The South China Sea (SCS) is one of the classical example of a non-volcanic passive margin situated within three tectonic plates of the Eurasian, Indo-Australian and Philippine Sea plate. The development of SCS resulted from interaction of various types of plate boundaries, and complex tectonic assemblage of micro blocks and accretionary prisms. Numerous models were proposed for the formation of SCS, yet none can fully satisfy different aspects of tectonic forces. Temporal and geographical reconstruction of Cretaceous and Cenozoic magmatism with the isochrones of major basins was conducted. Our reconstruction indicated the SE margin of Asia had gone through two crustal thinning events. The sites for rifting development are controlled by localized thermal weakening of magmatism. NW-SE extension setting during Late Cretaceous revealed by magmatism distribution and sedimentary basins allow us to allocate the retreated subduction of Pacific plate to the cause of first crustal thinning event. A magmatic gap between 75 and 65 Ma prior to the initiation of first basin rifting suggested a significant modification of geodynamic setting occurred. The Tainan basin, Pearl River Mouth basin, and Liyue basins started to develop since 65 Ma where the youngest Late Cretaceous magmatism concentrated. Sporadic bimodal volcanism between 65 and 40 Ma indicates further continental extension prior to the opening of SCS. The E-W extension of Malay basin and West Natuna began since late Eocene followed by N-S rifting of SCS as Neotethys subducted. The SCS ridge developed between Pearl River Mouth basin and Liyue basin where 40 Ma volcanic activities concentrated. The interaction of two continental stretching events by Pacific followed by Neotethys subduction with localized magmatic thermal weakening is the cause for the non-volcanic nature of SCS. [ABSTRACT FROM AUTHOR]

Hosted by volcaniclastics of the Carboniferous Dahalajunshan Formation, the Songhu iron deposit is located in the central segment of the Awulale metallogenic belt, Chinese Western Tianshan. Mineralization and alteration are structurally controlled by orogen-parallel NWW-striking faults. Integrating with mineralogical and stable isotopic analyses based on paragenetic relationships, two types of iron mineralization have been identified. The deuteric mineralization (Type I) represented by brecciated, banded, and disseminated-vein ores juxtaposed with potassic-calcic alteration in the inner zone, which was formed from a magmatic fluid generated during the late stages of regional volcanism. In contrast, the volcanic-hydrothermal mineralization (Type II) is characterized by hydrothermal features occurring in massive and agglomerated ores with abundant sulfides, and was generated from the magmatic fluid with seawater contamination. Two volcaniclastic samples from the hanging and footwall of the main orebody yield zircon U-Pb ages of 327.8 ± 3.1 and 332.0 ± 2.0 Ma, respectively, which indicate Middle Carboniferous volcanism. Timing for iron mineralization can be broadly placed in the same epoch. By reviewing geological, mineralogical, and geochemical features of the primary iron deposits in the Awulale metallogenic belt, we propose that the two types of iron mineralization in the Songhu iron deposit are representative regionally. A summary of available geochronological data reveals Middle-Late Carboniferous polycyclic ore-related volcanism, and nearly contemporaneous iron mineralization along the belt. Furthermore, petro-geochemistry of volcanic-volcaniclastic host rocks indicates that partial melting of a metasomatized mantle wedge under a continental arc setting could have triggered the continuous volcanic activities and associated metallogenesis. [ABSTRACT FROM AUTHOR]