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The scientific question of precisely determining the northern boundary of the Qinling Orogenic Belt (QOB) with regard to the southern segment of the North China Craton (S-NCC) has been controversial and unresolved, as it is heavily covered by loess and lacks some geological evidence. In order to identify the concrete northern boundary of the QOB, this paper first reports the metabasalt discovered in the Qianhe River Basin in Northwestern China, on the foundation of petrography, mineralogy, geochronology and geochemistry analyses. Detailed regional geological survey presents that the Qianhe metabasalt (QMB) is in unconformable contact with the Mesoproterozoic Gaoshanhe Group. Moreover, there is the new laser ablation (LA) inductively coupled plasma mass spectrometry (ICP-MS) U-Pb dating for magmatic zircons that yielded a weighted mean age of 450 ± 9 Ma, revealing that the QMB occurred in the Late Ordovician rather than that in the Mesoproterozoic period as previously considered. Both major and trace elements show that the samples are characterized by the back-arc basin (BAB) basalt affinity. In addition, combined with the regional geology analysis, it stands to reason that the QMB is very similar to those of Ordovician Caotangou Group along the northern QOB (N-QOB). Accordingly, it is illuminated that the QMB belonging to the N-QOB, is more likely originated from the back-arc basin setting, and truly defines the QOB's northern boundary in this segment, which has prominent geoscientific significance for determining the tectonic boundary in the heavily loess-covered regions. [ABSTRACT FROM AUTHOR]

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]

Early Paleozoic magmatism in the West Kunlun Orogenic Belt (WKOB) preserves important information about the tectonic evolution of the Proto-Tethys Ocean. This paper reports whole-rock compositions, zircon and apatite U-Pb dating, and zircon Hf isotopes for the Qiaerlong Pluton (QEL) at the northwestern margin of WKOB, with the aim of elucidating the petrogenesis of the pluton and shedding insights into the subduction-collision process of this oceanic slab. The QEL is mainly composed of Ordovician quartz monzodiorite (479 ± 3 Ma), quartz monzonite (467–472 Ma), and syenogranite (463 ± 4 Ma), and is intruded by Middle Silurian peraluminous granite (429 ± 20 Ma) and diabase (421 ± 4 Ma). Zircon εHf(t) values reveal that quartz monzodiorites (+2.1 to +9.9) and quartz monzonites (+0.6 to +6.8) were derived from a mixed source of juvenile crust and older lower crust, and syenogranites (−5.6 to +4.5) and peraluminous granites (−2.9 to +2.0) were generated from a mixed source of lower crust and upper crust; diabases had zircon εHf(t) values ranging from −0.3 to +4.1, and contained 463 ± 5 Ma captured zircon and 1 048 ± 39 Ma inherited zircon, indicating they originated from enriched lithospheric mantle and were contaminated by crustal materials. The Ordovician granitoids are enriched in LILEs and light rare-earth elements, and depleted in HFSEs with negative Nb, Ta, P, and Ti anomalies, suggesting that they formed in a subduction environment. Middle Silurian peraluminous granites have the characteristics of leucogranites with high SiO2 contents (74.92 wt.%–75.88 wt.%) and distinctly negative Eu anomalies (δEu = 0.03–0.14), indicating that they belong to highly fractionated granite and were formed in a post-collision extension setting. Comparative analysis of these results with other Early Paleozoic magmas reveals that the Proto-Tethys ocean closed before the Middle Silurian and its southward subduction resulted in the formation of QEL. [ABSTRACT FROM AUTHOR]

Paleoproterozoic A-type granites are widely distributed in the southern margin of the North China Craton (SNCC), providing important information for understanding the Paleoproterozoic tectonic regimes in this area. This paper reports newly obtained whole-rock compositions and zircon U-Pb ages for the Tieluping syenogranite porphyry (TLP) and Huoshenmiao alkali granite porphyry (HSM) in the SNCC. Zircons from the TLP and HSM have U-Pb ages of 1 805 ± 12 and 1 792 ± 14 Ma, respectively. These ages are taken to date the emplacement of these intrusions. They had high total alkali contents (K2O + Na2O > 7.13 wt.%), with high 10 000 × Ga/Al ratios (3.06–3.41) and Zr + Y + Nb + Ce values (709 ppm–910 ppm) as well as high zircon saturation temperatures (864–970 °C), indicative of A-type granite affinities. High Y/Nb (1.75–3.32), Ce/Nb (7.72–9.72), and Yb/Ta (2.89–5.60) ratios suggested that TLP and HSM belonged to the A2-type granite. The negative whole rock εNd(t) values (−8.4 to −6.6) and negative zircon εHf(t) values (−15.9 to −6.3) confirmed that TLP and HSM were likely generated by the partial melting of an ancient continental crust. The εHf(t) (−7.4 to +4.0) values of inherited zircons in the TLP suggested that they were derived from the partial melting of Archean basement rocks. Considering the geochemical similarity of the 1.80 Ga A-type granitoids in the SNCC, we propose that the TLP and HSM were formed in a post-collisional regime that was likely associated with the break-off of the Paleoproterozoic subducted slab. Upwelling of the asthenosphere provided huge heat to generate the regional 1.80 Ga A-type granite in the SNCC. [ABSTRACT FROM AUTHOR]

This paper presents the results of mineralogical, geochemical, isotope, and geochemical (Sm–Nd) studies of siltstones from the upper Bystraya subformation of the Argun continental massif, as well as U–Pb dating of detrital zircon grains from them. The main goal of the research was to identify the main sources of clastic material, to reconstruct the paleogeodynamic environment of accumulation, and to constrain the lower age limit for the formation of terrigenous rocks of the upper Bystraya subformation. The mineralogical composition of the studied rocks indicates their accumulation in an environment associated with subduction processes. The trace element composition of siltstones from the subformation suggests the presence of rocks of mixed composition in the source area in terms of their silica content. Based on Sm–Nd isotope and geochemical data, it was established that the main sources of clastic material for siltstones of the stratigraphic unit were Paleoproterozoic rocks and (or) younger rocks whose formation is associated with the reworking of the Paleoproterozoic continental crust. Most of the zircons from the studied siltstone sample of the upper Bystraya subformation are Neo- and Paleoproterozoic in age. Their sources are probably Neo- and Paleoproterozoic igneous rocks widespread within the Argun massif in China. The ages of the youngest zircons (556 ± 9 and 566 ± 10 Ma) isolated from siltstones of the upper Bystraya subformation were used to constrain the lower limit of their accumulation at the middle Ediacaran. [ABSTRACT FROM AUTHOR]

This paper presents the zonal geochemistry and elasticity characteristics of gallium- and lithium-rich No. 6 coalbed in the Haerwusu mine and discusses interpretation methodologies of coal-hosted gallium and lithium resources using lab-measured samples and field-measured wireline logs. The results demonstrate that both coal-composition-based and elastic-parameter-based classifications yield similar results, categorizing the coalbed into subzones related to coal quality. Material compositions, elastic properties, critical metals, and host minerals exhibit zonal distribution characteristics within the ultrathick No. 6 coalbed. Three-class classifications significantly enhance correlations among host minerals, elastic parameters, and critical metals, albeit with differing trends among classes. In classes II and III (ultralow- and low-ash-yield coals), boehmite and kaolinite primarily host gallium and lithium, respectively. In class I (medium-ash-yield coal), gallium is associated with kaolinite, while lithium lacks specific mineral associations. Constrained by wireline logs, a rock physics modeling strategy is proposed to link mesoscale coal compositions to macroscale elastic responses. Moreover, explicit correlations between host minerals and critical metals are established, connecting macroscale elastic responses to microscale gallium and lithium enrichments and exploring interpretation methods of coal-hosted critical metals. Preferred lithium interpretation methods include compositional ternary plots and elastic parameter cross plots, while preferred gallium interpretation methods involve boehmite-gallium and elastic parameter-gallium fitting. These findings may contribute to understanding the enrichment mechanisms and interpretation technologies of coal-hosted critical metals in ultrathick low-rank coalbeds. [ABSTRACT FROM AUTHOR]

Post‐collisional magmatism contains important clues for understanding the reworking and growth of continental crust, as well as lithospheric delamination and orogenic collapse. Early Devonian magmatism has been identified in the North Qilian Orogenic Belt (NQOB). This paper reports an integrated study of petrology, whole‐rock geochemistry, Sm‐Nd isotope and zircon U‐Pb dating, as well as Lu‐Hf isotopic data, for two Early Devonian intrusive plutons. The Yongchang and Chijin granites yield zircon U‐Pb ages of 394–407 Ma and 414 Ma, respectively. Both of them are characterized by weakly peraluminous to metaluminous without typical aluminium‐rich minerals, LREE‐enriched patterns with negative Eu anomalies and a negative correlation between P2O5 and SiO2 contents, consistent with geochemical features of I‐type granitoids. Zircons from the studied granites display negative to weak positive εHf(t) values (–5.7 to 2.1), which agree well with those of negative εNd(t) values (−6.4 to −2.9) for the whole‐rock samples, indicating that they were derived from the partial melting of Mesoproterozoic crust. Furthermore, low Sr/Y ratios (1.13–21.28) and high zircon saturation temperatures (745°C to 839°C, with the majority being >800°C) demonstrated a relatively shallow depth level below the garnet stability field and an additional heat source. Taken together, the Early Devonian granitic magmatism could have been produced by the partial melting of ancient crustal materials heated by mantle‐derived magmas at high‐temperature and low‐pressure conditions during post‐collisional extensional collapse. The data obtained in this study, when viewed in conjunction with previous studies, provides more information about the tectonic processes that followed the closure of the North Qilian Ocean. The tectonic transition from continental collision to post‐collisional delamination could be constrained to ∼430 Ma, which is provided by the sudden decrease of Sr/Y and La/Yb ratios and an increase in zircon εHf(t) values for granitoids. A two‐stage tectonic evolution model from continental collision to post‐collisional extensional collapse for the NQOB includes (a) continental collision and crustal thickening during ca. 455–430 Ma, characterized by granulite‐facies metamorphism and widespread low‐Mg adakitic magmatism; (b) post‐collisional delamination of thickened continental crust and extensional collapse of orogen during ca. 430–390 Ma, provided by coeval high‐Mg adakitic magmatism, A‐type granites and I‐type granitoids with low Sr‐Y ratios. [ABSTRACT FROM AUTHOR]

Accurately determining the timing and mechanism of metallogenesis of ore deposits is essential for developing a robust genetic model for their exploration. In this paper, we analyze the formation conditions of cassiterite in five major deposits of southern Hunan Province, one of the most important tungsten-tin (W-Sn) provinces in South China, using a combination of cathodoluminescence imaging, in situ U-Pb geochronology, and trace-element concentration data. In situ cassiterite U-Pb geochronology constrains the main period of Sn mineralization to between 155.4 and 142.0 Ma, demonstrating a temporal and genetic relationship to silicic intrusive magmatism in the same area. Three stages of magmatic activity and metallogenic evolution are recognized: (1) Early Paleozoic and Triassic: the initial enrichment stage of tungsten and tin; (2) Jurassic: the metasomatic mineralization stage; and (3) Cretaceous: the magmatic-hydrothermal superposition stage. The cassiterite in these deposits takes four forms, i.e., quartz vein-type, greisen-skarn-type, greisen-type, and granite-type, representing a progression characterized by the increasing content and decreasing range of variation of high field strength elements (HFSEs), and reflecting a general increase in the degree of evolution of the associated granites. Rare earth element (REE) concentrations suggest that precipitation of cassiterite was insensitive to the redox state of the fluid and that precipitation of cassiterite in the southern Hunan Sn deposits did not require a high-fO2 environment. These findings provide new insights into tin mineralization processes and exploration strategies. [ABSTRACT FROM AUTHOR]

Guizhou Province of China is rich in shale gas resources. In recent years, important progress has been made in the exploration and development of shale gas in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in Zheng'an block in northern Guizhou, adjacent to Sichuan Basin. Due to the complex geological conditions and fragile ecological environment in the shale gas distribution area, serious environmental pollution risks may exist in shale gas exploitation. Therefore, this paper conducted element, hydrogen and oxygen isotope analyses for shale gas fracturing flowback/produced water of Well AY7-4 in Zheng'an block. The results showed that the contents of K, Na, Ca, Mg and NH+ 4 in the flowback/produced water of Well AY7-4 were very high, with an average of 118 mg/L, 7616 mg/L, 266 mg/L, 47 mg/L and 76 mg/L, respectively. The content of Na, Ca and Mg is similar to that of shale gas flowback/produced water in Weiyuan, but lower than that in Changning and Fuling. NH+ 4 content was similar to that in Changning, but much higher than that in Weiyuan. The average Cl content was 11605 mg/L, which was similar to that in Weiyuan, but lower than that in Changning and Fuling. The average Br content is 48 mg/L, slightly lower than that of Weiyuan, and about half of that of Changning and Fuling. Correspondingly, the Br/Cl value of Well AY7-4 is the lowest, reflecting its relatively low Br content. The average content of Li, B and Sr is 17 mg/L, 10 mg/L and 45 mg/L, respectively, which is similar to that of the Weiyuan, Changning and Fuling shale gas fields. The distribution model of Li and Sr is similar to that of Cl, Br and Na, but the B content and B/Cl value of Well AY7-4 are the lowest. The linear relationship between Br and Cl contents and between dD and d18O of flowback/produced water of Well AY7-4, freshwater used for hydraulic fracturing and hydraulic fracturing injected fluid indicates that flowback/produced water of Well AY7-4 is mainly the mixed product between low salinity injected fracturing fluid and high salinity brine retained in shale formation. The hydrogen and oxygen isotopic compositions gradually become heavier over time, indicating that the proportion of high salt end formation brine in flowback/produced water is increasing. The contents of Cl, Br, Na and NH+ 4 in the flowback/produced water of Well AY7-4 are far higher than the allowable discharge value, which is a potential environmental pollution risk and cannot be discharged directly. [ABSTRACT FROM AUTHOR]

Guizhou Province of China is rich in shale gas resources. In recent years, important progress has been made in the exploration and development of shale gas in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in Zheng'an block in northern Guizhou, adjacent to Sichuan Basin. Due to the complex geological conditions and fragile ecological environment in the shale gas distribution area, serious environmental pollution risks may exist in shale gas exploitation. Therefore, this paper conducted element, hydrogen and oxygen isotope analyses for shale gas fracturing flowback/produced water of Well AY7-4 in Zheng'an block. The results showed that the contents of K, Na, Ca, Mg and NH+ 4 in the flowback/produced water of Well AY7-4 were very high, with an average of 118 mg/L, 7616 mg/L, 266 mg/L, 47 mg/L and 76 mg/L, respectively. The content of Na, Ca and Mg is similar to that of shale gas flowback/produced water in Weiyuan, but lower than that in Changning and Fuling. NH+ 4 content was similar to that in Changning, but much higher than that in Weiyuan. The average Cl content was 11605 mg/L, which was similar to that in Weiyuan, but lower than that in Changning and Fuling. The average Br content is 48 mg/L, slightly lower than that of Weiyuan, and about half of that of Changning and Fuling. Correspondingly, the Br/Cl value of Well AY7-4 is the lowest, reflecting its relatively low Br content. The average content of Li, B and Sr is 17 mg/L, 10 mg/L and 45 mg/L, respectively, which is similar to that of the Weiyuan, Changning and Fuling shale gas fields. The distribution model of Li and Sr is similar to that of Cl, Br and Na, but the B content and B/Cl value of Well AY7-4 are the lowest. The linear relationship between Br and Cl contents and between dD and d18O of flowback/produced water of Well AY7-4, freshwater used for hydraulic fracturing and hydraulic fracturing injected fluid indicates that flowback/produced water of Well AY7-4 is mainly the mixed product between low salinity injected fracturing fluid and high salinity brine retained in shale formation. The hydrogen and oxygen isotopic compositions gradually become heavier over time, indicating that the proportion of high salt end formation brine in flowback/produced water is increasing. The contents of Cl, Br, Na and NH+ 4 in the flowback/produced water of Well AY7-4 are far higher than the allowable discharge value, which is a potential environmental pollution risk and cannot be discharged directly. [ABSTRACT FROM AUTHOR]

The Ordovician–Silurian bentonite is an ideal target for probing complex geological events such as biological extinction, glaciations, and volcanic events at that time due to its global distribution and multiple intercalary strata. In this paper, Late Ordovician–Early Silurian K–bentonites from the western segment of the South Dabashan are sampled for zircon U–Pb dating and geochemical analyses. A mean 441.4 ± 4.2 Ma zircon U–Pb age is obtained from the K–bentonite and is regarded as volcanic eruptive time. Geochemical data show characteristics of intermediate volcanic rocks and typical K–bentonites elsewhere. Chondrite–normalized REE+Y distribution patterns display LREE (light REE) enrichment and HREE (heavy REE) depletion with distinct negative Eu anomalies. Primitive mantle–normalized spider diagram shows similar concave-up patterns with relatively enriched LILE (Ba, U, and Pb), HFSE (Nb, Ta, Zr, and Hf) and distinctly depleted elements such as P, Sr and Ti, indicating these K–bentonites derive from high–K and alkaline primary magma and represent the product of within–plate volcanic eruption. High-frequent and periodic volcanic eruptions from the Yangtze block, its peripheral areas, and the southern margin of the North China block began with Early Ordovician and lasted to Late Silurian. In the Dabashan region, ca. 440–448 Ma K–bentonites may primarily originate from the within–plate volcanic setting, but volcanic ashes of ca. 450–460 Ma K–bentonites are perhaps island arc products connected with north–dipping continuous subduction of the Paleo–Qinling Ocean during Early Paleozoic. [ABSTRACT FROM AUTHOR]

Numerous Neoproterozoic granitic intrusions occur over a north-south distance of more than 700 km in the western Yangtze Block. In this paper, we use zircon U-Pb age, Lu-Hf isotopic, and whole-rock geochemical data to show that the Shimian granitic pluton, which was previously thought to be S-type granite in the area, is actually A-type granite. The selected fresh samples for this study are mainly porphyritic biotite monzogranites. They are weak peraluminous, A2-subtype granites, displaying high contents of SiO2 and K2O, low CaO, and Na2O, with the characteristics of high silica, rich potassium, and low sodium. They are enriched in incompatible trace elements, but low in trace elements compatible in mafic silicates and feldspars, and they are chemically characterized by having high REE and Ga abundances and low Al, Ni, Ba, Sr, and Eu abundances. The major and trace element behavior suggests that the granites underwent the process of advanced fractional crystallization and were likely generated by crustal partial melting. Zircon U-Pb age shows the Shimian granitic pluton was emplaced at 728 ± 20 Ma. The studied granites yield an average 176Hf/177Hf value of 0.282363 (εHf = 0.8) with a 94% confidence interval of 0.282334 to 0.282384 (εHf = −0.1 to 1.7), indicating that they are derived from the remelting of juvenile continental crust. We suggest that this newly identified A-type granite at Shimian, southwestern China, was more plausibly generated in an extensional setting as a result of slab window caused by ridge subduction, which can account not only for the formation of voluminous granitoids, but also for the basalts, boninitic pillow lavas, and SSZ-type ophiolites in western Yangtze Block. [ABSTRACT FROM AUTHOR]

Metal migration and precipitation in hydrothermal fluids are important topics in economic geology. The Hongling polymetallic deposit comprises one of the most important parts of the Huanggangliang–Ganzhuermiao polymetallic metallogenic belt, which is in eastern Inner Mongolia. Except for lead–zinc skarn, minor cassiterite in the skarn and disseminated W–Sn mineralization in granitic rocks have also been found. The dominant Sn–W mineralization is in the northern part of the deposit, occurring as disseminated wolframite and cassiterite in aplite hosted in Mesozoic granite porphyry. The aplite together with pegmatite K-feldspar–quartz comprises vein dikes hosted in the granite porphyry, providing evidence for the transition from melt to fluid. The veins, dikes, and Sn–W mineralization in the aplite provide an opportunity to investigate fluid exsolution and the mechanics of metal precipitation. Based on field observations, the micrographic and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) results of the vein dikes, chronology, and the whole-rock geochemistry of the host rock, together with the fluid inclusion results, this paper discusses the characteristics of the causative magma, the mechanics of fluid exsolution and W–Sn precipitation. Our results show that the causative magma is of highly fractionated A-type granite affinity and has an intrusive age of late Mesozoic (133.3 ± 0.86 Ma). The magmatic evolution during shallow emplacement led to immiscibility between highly volatile, high-silica, and W- and Sn-enriched melts from the parent magma, followed by fluid exsolution from the water-rich melt. The alkaline-rich fluid exsolution led to a change in the redox state of the magma and the chilling of the melt. Fluid boiling occurred soon after the fluid exsolution and was accompanied by the degassing of CO2. The boiling and escape of CO2 from the fluid led to changes in fluid redox and W and Sn precipitation; thus, the W and Sn mineralization are mostly hosted in causative intrusions or peripheral wall rocks, which can be used as indicators for Sn–W exploration in the area. [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 Pingbei area is the main accumulation area of oil and gas in the Xihu Sag. The phase characteristics of oil and gas in this area are complex, and the understanding of their genesis is still unclear. In this paper, based upon discussions of crude oil and natural gas geochemical data, integrated with local geological features, we discuss the sources, migration, and phase state characteristics of oil and gas in the Pingbei area of the Xihu Sag. The study results show that the crude oil and natural gas in the Pingbei area are coal-derived and the oil and gas produced by the humic organic matter during the mature stage. The oil and gas source correlation showed that crude oil and natural gas have good affinity with the Eocene Pinghu Formation (PH) coal-bearing source rocks. Crude oil has the characteristics of near-source accumulation and short-distance migration while natural gas is supplied from a dual source: the coal-derived hydrocarbon rocks of PH in the deep part of the study area, supplemented by the coal-derived hydrocarbon rocks of PH on the bottom of the slope, and adjacent hydrocarbon-bearing sub sag. The distribution characteristics and geochemical migration indices of hydrocarbon show that the oil generated from the hydrocarbon source rocks of PH in the deep Pingbei area mainly migrates vertically along the fault connecting the reservoir and the source rocks to the trap, where it accumulates, while the natural gas exhibits deep and large faults that mainly migrate vertically, supplemented by its lateral migration along the composite transport system composed of faults and sandstone layers in the slope zone. The whole area presents the phase characteristics of "upper oil and lower gas, west oil and east gas". The mechanisms of produced-exhausted and geochromatographic effects (PGE), as well as evaporative fractionation (EF) and phase-controlled migration fractionation (PMF), result in the obvious discrepancy of hydrocarbon's properties on the vertical profiles. [ABSTRACT FROM AUTHOR]

Lithium is one of the important strategic energy metals, which is in short supply in China. There are three major types of lithium deposits: brine and salt lake type, highly differentiated granite or pegmatite type, and carbonate-clay type. In recent years, some new types of lithium deposits have also begun to receive great attention and subject recent research. There are many crypto-explosive breccia pipe type deposits in the world, including copper, gold, lead, zinc, tungsten and tin deposits, but little is known about this type of lithium deposit. This paper introduces the latest research results of the Weilasituo Sn−Li−Rb polymetallic deposit in Inner Mongolia (NE China), which occurs in the middle-southern section of the Great Xing'an Range metallogenic belt. A remarkable feature of this deposit is the coexistence of various mineralization types, including granite type Rb and Sn−Zn, hydrothermal crypto-explosive breccia pipe type Li−Rb, quartz vein type Sn−Zn and sulfide vein type Pb−Zn−Ag mineralization. Among them, hydrothermal crypto-explosive breccia pipe type Li-Rb deposit is currently very rare at home and abroad, which is likely a new type of rare metal deposit that worthy of our attention. This paper systematically summarizes the geology, alteration and mineralization, geochemistry, isotopes and geochronology of the Weilasituo deposit, and establishes a new petrogenic and metallogenic model. [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]

Late Mesozoic mafic dykes, which are widely developed in the North Qinling Orogenic Belt (NQOB), include abundant geodynamic information. This paper describes the mafic dykes that intrude the Late Jurassic granite in the Dayu and Kuyu areas, and reports important petrological constraints for the late Mesozoic tectonic transition from compression to extension in the NQOB. Three zircon U–Pb results show that the minimum ages of the mafic dykes are 139.8 ± 1.4 Ma, 137.4 ± 1.7 Ma and 133.4 ± 0.9 Ma, indicating that the emplacement age of the Dayu and Kuyu mafic dykes is 140–133 Ma. Petrogeochemical analyses suggest that the mafic dykes belong to the high-K calc-alkaline shoshonite series with low SiO2 (46.93–56.73 wt%), MgO (1.88–9.10 wt%) and TiO2 (1.17–1.82 wt%), and high Al2O3 (13.98–17.46 wt%), TFe2O3 (7.81–10.92 wt%) and K2O (1.28–4.78 wt%). The mafic dykes are enriched in large ion lithophile elements (e.g. Rb, Ba, K, La, Sr) and depleted in high-field-strength elements (e.g. Nb, Ta, Zr, Ti). These samples have the right-sloping chondrite-normalised rare earth element patterns, which suggest light rare earth element enrichment and heavy rare earth elements depletion with no obvious Eu anomalies (δEu = 0.94–1.11). The ISr, εNd(t), εHf (t) and TDM2(crust) values are 0.7056–0.7060, −10.60 to −5.98, −14.1 to −2.8, and 1382.4 ± 25.1 to 2081.9 ± 47.6 Ma, respectively. Both elemental and isotopic geochemistry show that the formation of Dayu and Kuyu mafic dykes is due to the partial decompression melting of previously enriched lithospheric mantle during a delamination process. The mafic dykes have undergone fractionation crystallisation of Mg–Fe phase minerals during magma ascent, accompanied by some crustal contamination. Combined with the regional tectonic setting, we suggested that the NQOB experienced intra-continental extension during the Early Cretaceous. Early Cretaceous (140–133 Ma) mafic dykes have been discovered in the middle part of the North Qinling Orogenic Belt. The remote effect of the Paleo-Pacific Plate subduction has reached the middle of the North Qinling Orogenic Belt. The North Qinling Orogenic Belt entered the extensional stage in the Early Cretaceous (140–133 Ma). [ABSTRACT FROM AUTHOR]

The Central Asian Orogenic Belt (CAOB) is the world's largest accretionary orogenic belt, and its formation is related to the closure of the Paleo-Asian Ocean (PAO). However, the closure time and style of the PAO remain controversial. To address these issues, this paper presents zircon U-Pb dating, whole-rock geochemistry and zircon Lu-Hf isotope analyses of the volcanic rocks in the Faku-Kaiyuan area on the northern margin of the North China Craton. The results show that the Bachagou andesites formed in the Early Permian (287 ± 2 Ma), while the Chaijialing andesites and dacites formed in the Late Permian (253.3 ± 3.7 Ma) and Middle Triassic (244.3 ± 1.3 Ma), respectively. The Bachagou andesites and Chaijialing andesites are enriched in LILEs and LREEs and depleted in HFSEs and HREEs, indicating that they formed in the active continental margins. The Chaijialing dacites show similar geochemical signatures to adakite and formed in a syn-collisional setting. Geochemistry and isotopic analysis indicates that the Bachagou andesites were derived from a partial melting of the mantle wedge that was metasomatized by subduction fluids. The Chaijialing andesites were generated from a metasomatized mantle by slab-derived and sediment fluids. The Chaijialing dacites formed by a partial melting of thickened lower crust. Combined with previous research results, we can conclude that the Eastern PAO closed by a scissor-like movement from west to east during the Late Permian–Middle Triassic. [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]

A large number of Late Silurian–Early Devonian intrusive rocks are distributed in the central Beishan orogenic belt (BOB). Tectonic setting of these intrusive rocks is of great significance to the study of the subduction and accretion of the Paleo-Asian Ocean. Previous studies show that most of the intrusive rocks in this region are S-type or A-type granitoids. In this study, we firstly reported the Late Silurian–Early Devoniandia bases, granodiorites on the southside of the Baiyunshan ophiolitic mélanges belt, as a part of Hongliuhe-Xichangjing ophiolitic mélanges belt (HXOMB). Zircon LA-ICP-MS U-Pb dating yields emplacement ages between 418 and 397 Ma, REE distribution patterns exhibit enriched LREE and flat HREE in the diabases, the discriminant diagrams show that the diabases have geochemical characteristics of intraplate basalt. The granodiorites in this paper present more like S- and A-type granitoids reported, showing the geochemical characteristics of syn/post-collision granites. Actually, the bimodal magmatic rocks are developed during Late Silurian–Early Devonian on both sides of the HXOMB, which are related to the tectonic background of the post orogeny extension. The diabases are tholeiitic with relative strong depleted εHf(t) (+8.1 to +13.0), which are mainly from relative depleted mantle. The granodiorites are calc-alkaline with relative slightly depleted εHf(t) (+0.7 to +5.6) and the lower Mg# and MgO contents (34.6–36.9, 0.50 wt.%–1.19 wt.% respectively), reflecting the source characteristics of meta-basalt. Therefore, the remelting of juvenile crust may be the main way of continental crust accretion during Late Silurian–Early Devonian in the central BOB. [ABSTRACT FROM AUTHOR]

Dongcao muscovite granite, as the product of the second stage of the magmatic intrusion of the Ganfang composite pluton, is closely related to the mineralization of Li–Nb–Ta rare metals in the Yifeng area. This paper aims to discuss the diagenetic age, evolutionary process, and relationship with the rare metal mineralization of Dongcao muscovite granite by using petrographic, cassiterite U–Pb dating and geochemical analyses. Petrographic analysis shows that the lithology of the Dongcao muscovite granite is medium– to fine–grained muscovite monzogranite. The cassiterite U–Pb dating results show that the diagenetic age of the Dongcao muscovite granite is 139.7 ± 6.7 Ma, which is Early Cretaceous. The geochemical analysis indicates that the rock is characterized by high Si, abundant aluminum alkalis, low Ca and Fe, and low Mg, which indicates that this granite is a strongly peraluminous rock. Moreover, the Dongcao muscovite granite is enriched with Rb, U, Ta, Pb, P, and Hf and depleted of Ba, Sr, Ti, and rare earth elements (REEs), with a tetrad effect of REEs. Based on this analysis, the Dongcao muscovite granite is a highly differentiated granite that formed in the tectonic transition from continental collisional to post–collisional settings related to the subduction of the Paleo–Pacific plate. A high degree of crystallization differentiation occurred at the early stage of magmatic evolution, resulting in the initial enrichment of Li–Nb–Ta–Sn. The melt–fluid interaction in the late stage is significant to the high enrichment of Li–Nb–Ta–Sn until the final mineralization. [ABSTRACT FROM AUTHOR]

The Ailaoshan orogenic belt is one of the most significant orogenic belts in the southeastern margin of the Qinghai–Tibet Plateau. The widely developed magmatic rocks in this belt preserve the multi-stage tectonic evolution records of the South China Plate. As an important response to the Rodinia breakup tectonic event, the study of Neoproterozoic magmatic rocks in the area is of great significance for reconstructing the Neoproterozoic tectonic process of the Ailaoshan orogenic belt and the tectonic evolution of the South China Plate. Petrology, geochemistry, zircon U-Pb, and Lu-Hf isotopes of the Daping pluton in the Ailaoshan orogenic belt are studied in this paper. The Daping pluton is mainly divided into gabbros and granites. Gabbros and granites belong to the sub-alkaline series, which are relatively enriched in large ion lithophilic elements and depleted in high-field strength elements. The ΣREE contents of the gabbro are low with enrichment in LREEs and depletion in HREEs, and the degree of differentiation of light and heavy rare earth is low, with positive δEu and weak negative δCe anomalies. The ΣREE contents of the granite are low with enrichment in LREEs and depletion in HREEs, and the degree of light and heavy rare earth differentiation is high, with medium–weak negative δEu and weak positive δCe anomalies, suggesting an A2-type granite with A1-A2 transition characteristics. The weighted average age of the gabbro is 816.1 ± 4.1 Ma (MSWD = 0.11), with zircon εHf(t) values of −7.5–5.5. The magma source is a mixture of an ancient crust source and a new mantle source; the weighted average age of the syenogranite is 783.7 ± 8.1 Ma (MSWD = 1.4), with zircon εHf(t) values of −4.3–0.4. The magma source is mainly ancient crustal material (Ailaoshan Group), mixed with a small amount of mantle-derived material; the weighted average age of the monzogranite is 754.8 ± 6.1 Ma (MSWD = 3.0), with positive zircon εHf(t) values of 1.65–10.36. The magma source is a mixture of a large number of mantle-derived materials and a small number of crust-derived materials (Ailaoshan Group). The Daping pluton was formed in the transitional tectonic environment from post-collision to intraplate continental margin rift, corresponding to the Rodinia breakup process in the western margin of the South China Plate. [ABSTRACT FROM AUTHOR]

The Qushandao Granite, mainly composed of alkali‐feldspar granite, is situated in the eastern Zhejiang province of coastal southeast China. In this paper, we present whole‐rock geochemistry, zircon U–Pb geochronology, and Hf isotopes to constrain the age, magma sources, and geodynamic setting of the Qushandao Granite. LA‐ICP‐MS zircon U–Pb dating results revealed that the Qushandao Granite was emplaced in the Late Cretaceous (101–98 Ma). Geochemically, the Qushandao Granite exhibits relatively high silica and alkali contents, metaluminous to weakly peraluminous (A/CNK = 0.98–1.02), and low abundances of phosphorus, titanium, magnesium, and calcium. It is also characterized by enrichment in Rb, K, Th, and depletion in Nb, Ta, P, Ti, and Sr with moderately to weakly negative europium anomalies (Eu/Eu* = 0.71–0.87). Furthermore, the Qushandao Granite displays lower FeOT/MgO, 104 × Ga/Al, and Zr + Nb + Ce + Y values relative to typical A‐type granites. Therefore, we classify the Qushandao Granite as calc‐alkaline I‐type granite based on a synthesis of geological and geochemical characteristics. The Qushandao Granite shows variable zircon Hf isotopic compositions (εHf(t) = −7.6 to +2.3) and TDM2 model ages of 1.40–0.83 Ga with a mean value of 1.17 Ga. We argue that the Qushandao Granite was most likely generated by mixing of mantle‐derived mafic magma and crust‐derived felsic magma in the lower crust, and that it was formed during post‐collisional extension in the Late Cretaceous, related to the gradually increasing subduction angle of the Paleo‐Pacific plate. [ABSTRACT FROM AUTHOR]

Reconstructing the tectonic architecture of the southern Altaids is of great importance to piece together the continental growth history of the Central Asian continent. In this paper, we address the subduction‐accretion process of the Paleo‐Tianshan Ocean, one branch of the South Tianshan Ocean, in the southern Altaids, through a detailed geological and geochemical investigation of the Wulanmoren Accretionary Complex (WAC). The WAC is composed of ophiolitic mélanges, ocean plate stratigraphy mélanges, and turbiditic coherent units. In this study, we present key geological, petrological, and geochemical evidence indicating back‐arc and ocean island affinity of the igneous rocks of the WAC. Zircon U‐Pb dates of these rocks ages range between 380.2 ± 1.3 and 302.0 ± 5.3 Ma. The sedimentary matrix units of the mélanges were deposited in the Early Devonian (∼405 Ma) to the Late Triassic (∼222 Ma), rather than Silurian strata as previously thought. However, the ages of some detrital zircons in the sedimentary matrix are Precambrian, pointing to a complex evolution involving multiple ocean island terrains and island arcs of different ages that accreted from the mid‐Paleozoic to the Early Mesozoic. Plain Language Summary: Well‐exposed rock outcrops of the Wulanmoren Accretionary Complex (WAC) offer an ideal opportunity to solve the enigma of the evolutionary history of the Paleo‐Tianshan Ocean (PTO) of Central Asia. We report field observations, geochemistry, and geochronology of the WAC in the southern Altaids, pointing to multiple tectonic settings of ages spanning from the Early Devonian (∼405 Ma) to the Late Triassic (∼222 Ma). These reconstructions suggest closure time of the PTO occurred post‐Triassic. Based on detrital zircons provenance analysis, we propose a multi‐island ocean model to explain the tectonic evolution of the PTO in the time period studied. Key Points: The Wulanmoren Accretionary Complex was composed of ophiolitic mélanges, ocean plate stratigraphy mélanges, and coherent unitsThe Late Paleozoic MORB‐like and OIB‐type basalts, and ∼222 Ma coherent units indicate closure of the Paleo‐Tianshan Ocean occurred post‐TriassicThe southern Paleo‐Asian Ocean was an archipelago with several subduction systems which is similar to the modern southwest Pacific [ABSTRACT FROM AUTHOR]

Research on the mineralogical and geochemical characteristics of altered end-Guadalupian basaltic volcanoclastic rocks can increase the understanding of the alteration history of the overlying stratabound Nb(Ta)-Zr(Hf)-REY-Ga mineralization in the Late Permian coal-bearing sequences. In this paper, based on petrographic observations in addition to XRD, XRF, and ICP-MS analyses, we present and discuss in detail the relationships between primary and secondary minerals and outline the distribution of major and trace element chemistry in the middle/Late Permian basaltic volcaniclastics from the ELIP's zone, western Guizhou, southwest China. The primary clastic suite consists of plagioclase-group minerals, clinopyroxenes, feldspathoids, spinels, and basaltic glasses. Fragments of mafic and, less commonly, felsic and alkaline volcanic rocks are minor components of the studied samples. The alteration products are represented by various chlorite-group minerals (including abundant chamosite), quartz, calcite, albite, analcime, barite, and pyrite, along with relatively minor amounts of titanite, sanidine, magnetite, rutile, and copiapite. The mineralogical and geochemical characteristics of the studied volcaniclastics provide strong evidence correlating them with the high-Ti basalt group, widely distributed within the inner Emeishan large igneous province (ELIP) and coeval rift zone of the middle and outer ELIP. After deposition, the volcaniclastics reacted with complex solutions including heated meteoric waters and were periodically infiltrated by seawater and ascending hydrothermal fluids. As a result, the primary volcanic rocks partly lost alkalis, titanium, silica, and most of the trace elements. These elements, especially the incompatible elements, were probably enriched in the overlying tuffaceous and coal-bearing sequences in the middle and outer ELIP. • Primary and secondary minerals of Emeishan basaltic volcaniclastics were presented. • The volcaniclastics reacted with complex solutions from various sources. • The primary volcanic partly lost alkalis, Ti, Si, and most of the trace elements. • The lost elements were probably enriched in the overlying sediments. [ABSTRACT FROM AUTHOR]

The Carboniferous–Triassic period was an important stage of global sea–land transformation, with coal formation in the Carboniferous, biological extinction at the end of the Permian, and global drought in the Triassic. The MS-1 well in the Mosuowan High of the Junggar Basin is the deepest well drilled in Northwestern China. In this paper, we investigate the sedimentary environment and climate evolution of the Mosuowan area in the central Junggar Basin during the Late Carboniferous–Early Permian by the petrothermal, lipid biomarker, and isotopic composition of mud shale core samples, and explore the tectonic–climatic events and Central Asian orogenic belt evolution driving the sedimentary environment. The study shows that the organic matter from the Upper Carboniferous to the Lower Permian is at a mature stage, but biomarkers maintained the primary information although the organic matter was subjected to thermal evolution. In the late Carboniferous period (Tamugan Formation), the study area was a closed remnant sea with a relatively humid climate, triggering lush terrestrial vegetation and high organic carbon content in the sediments, which had the potential to evolve into natural gas. During the Xiazijie Formation of the Middle Permian, tectonic activity shifted to the subsidence period, and the salinity of the water decreased after a large input of fresh water. The lake basin area expanded, and the content of aquatic organisms continued to increase. As the Lower Permian stratigraphy is missing, this sea–land transition seems to jump. The low and upper Urho Formations of the Middle–Upper Permian are a deltaic foreland deposit, and geochemical indicators show an overall lake retreat process with a continuous increase in organic matter content of terrestrial origin. The lithologic assemblage of the Triassic Baikouquan Formation is braided river deltaic sedimentation with migration of deposition centers of the lake basin. In conclusion, the Late Carboniferous–Early Permian period was influenced by global changes, Paleo-Asian Ocean subduction, and continental splicing, which resulted in a continuous increase in terrestrial organic matter, water desalination, and oxidation-rich sediments in the Mosuowan region, but the P–T biological mass extinction event was not recorded. [ABSTRACT FROM AUTHOR]

The Kuqa Basin is an important potentially potash-bearing basin in China, and thick salt-bearing strata were deposited under the influence of multistage Tethyan transgression-regression cycles during the Eocene. At present, research on the process of potash formation in the Kuqa Basin has mostly focused on traditional salt mineralogy, whole-rock geochemistry, and evaporite sedimentary evolution characteristics. However, research on the original ore-forming parent fluid directly related to potash formation has not yet been carried out, directly hindering further evaluation of potash mineralization. Therefore, this paper takes the internal factors controlling potash formation as the starting point and analyzes the physical and chemical properties, such as the homogenization temperatures ( T h ) and chemical compositions, of primary halite fluid inclusions. A total of 220 T h data from fluid inclusions were obtained, and the temperatures ranged from 9.4 to 54.1°C, indicating a high-temperature brine environment conducive to the rapid deposition of the potash deposit. In total, 22 halite fluid inclusions were analyzed for chemical components. The highest KCl content reached 0.59%, which was higher than the lowest industrial grade of potassium-rich brine (0.5%), indicating that the brine experienced a high degree of evaporation and concentration during the salt-forming period and reached the potash precipitation stage. This paper provides quantitative data on the evolution of the sedimentary environment in the Kuqa Basin and supports future potash exploration. [ABSTRACT FROM AUTHOR]

The tectonic evolution of the Qinling orogen is key to understanding the process of convergence between the North China Block (NCB) and the South China Block (SCB). The Wuguan Complex and Liuling Group, situated along the southern margin of the Shangnan–Danfeng suture zone (SDSZ) between the North Qinling Terrane (NQT) and the South Qinling Terrane (SQT), are important indicators of the late Paleozoic tectonic evolution of the Qinling orogen. In this paper, the detrital zircon U–Pb geochronology and geochemical analysis of the Wuguan Complex and Liuling Group are carried out. Detrital zircons from two metasedimentary rock samples of the Liuling Group yield a major age peak at 460 Ma and two subordinate peaks at 804 Ma and 920 Ma, with a few older grains having formed between 1000–2549 Ma. One metasedimentary rock sample of the Wuguan Complex has a similar age spectrum as that of the Liuling Group, which shows the main age peak at 440 Ma and two subordinate peaks at 786 and 927 Ma, indicating all detrital zircon age results have the same source area. Geochemical analyses suggest that the sedimentary rocks of the Liuling Group and part of the Wuguan Complex were deposited in the tectonic setting of the continental island arc (CIA), while the geochemical characteristics of the other group of sedimentary rocks of the Wuguan Complex indicate the mixing of basic rock sources. The protolith of garnet amphibolite and hornblende schist, which were collected from the Wuguan Complex, were classified as andesite and basalt, with the nature of arc andesite and oceanic island basalt, respectively. In combination with regional data, we suggest that the Liuling Group and the Wuguan Complex were deposited in a fore-arc basin. Additionally, the Wuguan Complex was subsequently incorporated into the tectonic mélange by the northward subduction of the Paleo-Qinling Ocean. Zircons from the subduction-related metamorphic igneous rocks in the Wuguan Complex yielded a weighted mean age of 365 ± 19 Ma, indicating that the Paleo-Qinling Ocean between the SQT and NQT was still subducted at the end of Devonian. [ABSTRACT FROM AUTHOR]

Basaltic magmas can provide important information about mantle source nature, tectonic settings and tectonic evolution for a given terrain. This paper reports geology, petrography and geochemistry of whole-rock major and trace elements and Nd−Sr isotopes for a suite of garnet amphibolites from southeastern Wulan (Ulan), Quanji Massif, northwestern China. The garnet amphibolites were likely generated from basaltic lavas, associated with both paragneisses and orthogneisses of the lower Delingha Group. The basaltic protolith of these amphibolites can be broadly constrained to be formed at ∼2.33 Ga in an extensional setting post-collision. The geochemistry of amphibolites shows subalkaline and highly evolved characteristics. They display high-Fe low-Ti characteristics, with TFeO of 13.1 wt.%–17.9 wt.% and TiO2 of 1.42 wt.%–3.09 wt.% (in most samples TiO2 ⩽2.5 wt.%). The chondrite-normalized REE patterns show enrichment of LREE and LILE and the primitive-mantle-normalized incompatible element patterns display negative P, Ti, Nb−Ta and Zr−Hf anomalies. The (87Sr/86Sr), values of 0.697 8–0.712 3 and εNd(t) values of −2.81–5.08 respond to depleted mantle model ages (TDM) of 2.33–3.30 Ga. These suggest that the precursor magmas of the protolith of the garnet amphibolites were probably derived from the Early Paleoproterozoic depleted sub-continental lithospheric mantle that had been metasomatized by subduction-induced fluids and melts. The precursor basaltic magmas were contaminated by the older crustal components during magma ascending. This post-collisional basaltic magmatic event at ∼2.33 Ga in Quanji Massif thus enhanced the subduction shutdown or slowdown tectonic regime both in NW China and coevally with those plate tectonics in some important domains worldwide during the Early Paleoproterozoic. [ABSTRACT FROM AUTHOR]

The Zhashui-Shanyang ore cluster area is one of the most important gold polymetallic ones in northwestern China. The Qinglingou gold deposit is a newly discovered small-scale deposit in the Zhashui-Shanyang area. Gold mineralization closely related to acid intrusive rocks has been found for the first time in this area. In this paper, the geochronology, whole-rock geochemistry, and isotope signature of the granite porphyries in the deposit are studied. They are characterized by variable medium SiO2 (67.22–71.72 wt.%), high K2O + Na2O contents (6.54–10.34 wt.%), and variable Al2O3 (14.47–15.10 wt.%) values. The A/CNK ratios range from 0.90 to 1.23, and the A/NK ratios vary from 1.14 to 1.48. These rocks also contain biotite and amphiboles and are similar to peraluminous and high-K calc-alkaline I-type granites. The Qinglingou granite porphyries show relative enrichment of Rb, Th, and K, and depletion of Nb, Ta, P, Ti, and other high field strength elements. These porphyries are enriched in light rare earth elements relative to heavy rare earth elements with weak negative Eu anomalies (δEu = 0.63–0.89), which is interpreted to be the best age of crystallization of the Qinglingou porphyries. LA–ICPMS zircon U–Pb dating yields an age of 211 ± 1.2 Ma (n = 16, MSWD = 0.39). The close spatial relationship between the ore bodies and granite porphyry dikes indicates that this age may represent the metallogenic age in this area. The zircons have 176Hf/177Hf ratios ranging from 0.282625 to 0.282702, the εHf(t) values are near 0 and the two-stage zircon Hf model ages range from 1121 to 1296 Ma. These data indicate that the Qinglingou granite porphyries were derived from the interplay between mantle- and crustal-derived magmas. We therefore propose that there is potential gold in carbonate rocks at the periphery of porphyry-skarn copper-molybdenum deposits. [ABSTRACT FROM AUTHOR]

This paper studies the mineralization process and the ore-forming setting of the Kantian fluorite deposit in South China through the zircon U-Pb chronology, quartz Rb-Sr dating, whole rock geochemistry, H-O isotope and fluid inclusions. A mineralization model for the Kantian fluorite deposit is proposed as follows: The subduction of the Pacific plate during the late mid-Jurassic and late Jurassic led to the formation of several fault zones. As the subduction gradually decelerated and eventually ceased, continental extension and lithosphere thinning occurred, accompanied by upwelling of the asthenosphere. This asthenosphere upwelling facilitated melting of the lithospheric mantle, resulting in the ascent of magma into the lower crust. Consequently, the intrusion of magma into the lower crust caused substantial heat, triggering partial melting of the lower crust. The molten material then ascended along faults, generating a significant quantity of granites. During the Early Cretaceous period, the Yanshan cycle witnessed another notable phase of magmatic activity. The residual magmatic hydrothermal fluid from this period served as a source of heating, while the pre-existing fault structures provided favorable pathways and storage space. Atmospheric precipitation infiltrated into the depth along these faults, and the deep-seated residual magmatic hydrothermal fluid heated the infiltrated atmospheric water, inducing cyclic upwelling. The upward migration of hydrothermal fluid continuously extracted Ca and F elements from the granites. Ongoing interaction between the fluid and the surrounding rocks led to changes in pH, coupled with alterations in temperature and pressure, ultimately resulting in the precipitation of fluorite with associated alteration zones in the surrounding rocks. [Display omitted] • Ca and F element in the fluorite were derived through the surrounding rocks. • The ore-forming fluids belong to the NaCl-H 2 O system and exhibit characteristics of medium–low temperature, low salinity, and low density, and were derived from meteoric water. • The intrusion age of surrounding rock in Kantian fluorite deposit was 159.4 ± 2.2 Ma, and the ore-forming of fluorite was 135.6 ± 0.7 Ma. • The tectonic setting responsible for the diagenesis and mineralization processes is believed to be an intracontinental stretching environment associated with the subduction of the Pacific plate. The Yanshanian events have led to the development of South China as a unique granite province globally. Within South Jiangxi, numerous metallic and non-metallic deposits have a close association with Mesozoic granite formations. The Kantian fluorite deposit, a newly discovered non-metallic deposit in southern Jiangxi Province, is one such deposit that is linked to Mesozoic granites. The orebody at the Kantian fluorite deposit is identified as occurring in veined structures within the silicification fracture zone of Mesozoic granites, with strict control exerted by fault systems. Fluorite ore can be classified into two categories based on the amount of quartz and fluorite. The first category is the fluorite quartz type, which has a higher amount of quartz than fluorite. The second category is quartz fluorite type, which has more fluorite than quartz. Among these two categories, the quartz fluorite type is precipitated during the primary mineralization stage. Through the analysis of fluid inclusions within the fluorite, it was determined that the homogenization temperature is relatively low, ranging from 133 to 236℃. The fluid inclusions also display low salinity (0.18–3.39 wt% NaCl eqv.) and low density (0.75–0.96 g/cm3). Laser Raman spectroscopy revealed that the primary components of the fluid inclusions are H 2 O, with minor C 3 H 6. Isotope analysis indicated δD VSMOW values of fluorite ranging from −61.9 ‰ to −54.8 ‰ (average −59.8 ‰), while δ18O VSMOW values varied from 1.3 ‰ to 3.1 ‰ (average 2.0 ‰). This study presents chronological, petrological and geochemical data that suggest several processes. The metallogenic age is 135.6 ± 0.7 Ma. The mineralizing fluids were identified to the NaCl-H 2 O system, with heated meteoric water identified as the primary source; The ore-forming materials originated from the granite, and water–rock interactions are proposed as the primary mechanism for fluorite precipitation. Based on a tectonic setting characterized by stretching, which is closely linked to the subduction of the Pacific plate, we proposed a model for the Kantian fluorite deposit. [ABSTRACT FROM AUTHOR]

This paper presents first geochemical and Sm-Nd isotope-geochemical data on conditionally Vendian metasedimentary rocks of the Byrka Series of the Argun superterrane. Analysis of chemical composition of rocks made it possible to establish that sources of detrital material were both felsic and mafic rocks. This conclusion is consistent with the presence of felsic and mafic metavolcanic intercalations in sequences. The isotope-geochemical studies of metasedimentary rocks of the Byrka Series indicate that their source areas contained rocks with Paleoproterozoic Nd model age. The main sources of clastic material for metasedimentary rocks of the Byrka Series were likely Precambrian magmatic and metamorphic complexes located at the Argun superterrane, within Eastern Transbaikalia, and at the adjacent territory of China. [ABSTRACT FROM AUTHOR]

Late Mesozoic granites are present throughout the Jiaodong Peninsula in eastern China, but the petrogenesis of these granites, the magma sources, and the geodynamic setting of the magmatism remain unclear. This paper presents new zircon U–Pb geochronological and Lu–Hf isotopic and whole‐rock geochemical data for the Late Jurassic Queshan pluton in the Shandong Peninsula, an area that represents the boundary between the Jiaobei and Sulu ultrahigh‐pressure (UHP) terranes. Laser ablation–inductively coupled plasma–mass spectrometry zircon U–Pb dating yields Late Jurassic ages from 158 ± 1 to 153 ± 1 Ma for the pluton in addition to a small number of inherited zircons that yield ages that cluster at 2410, 1831–1776, 750, and 209–202 Ma. Zircons from different samples have similar 176Hf/177Hf values (0.281926–0.282255) and variably negative εHf (t) values that range from −26.5 to −15.1 (weighted mean of −22.9 ± 0.9). The corresponding two‐stage Hf model ages range from 2,869 to 2,154 Ma, with a weighted mean value of 2,645 ± 54 Ma. These data indicate that the magmas that formed the Queshan pluton were derived from multiple sources, including the lower crust of the North China (NCC) and Yangtze (YC) cratons, as well as collision‐related alkaline rocks. The whole‐rock geochemical compositions of the samples indicate that the granites are weakly peraluminous, are high‐K and calc‐alkaline with I‐type affinities, and have high contents of Sr, low contents of Y and Yb, high (La/Yb)N and Sr/Y values, and positive Eu anomalies (δEu = 1.20–1.65), indicating an adakitic affinity. This indicates that the Queshan granites formed from magmas generated by partial melting of a thickened region of the crust (>50 km) associated with eclogite, garnet amphibolite, or amphibolite residual material. The genesis of the Late Jurassic granites are also likely to have been influenced by the collisional orogeny between the NCC and YC and continued subduction of the Izanagi Plate. Thickening of the lower crust associated with this continental collisional event occurred before the magmatism, with further compression and thickening of the lower crust caused by the low‐angle subduction of the Izanagi Plate beneath northeastern China being the main geodynamic driver of the formation of the granites in this region. [ABSTRACT FROM AUTHOR]

Hainan Island is a key part of the eastern Tethyan region and contains detailed geological information that can enhance our understanding of the tectonic evolution of this region since the late Palaeozoic. In this paper, we report geochronological, geochemical, and Sr–Nd isotopic data for granitoids from Baomei and Chahe in the northern part of Hainan Island. Three new zircon U–Pb ages of 243.3 ± 1.7 Ma, 237.1 ± 5.1 Ma, and 257.0 ± 4.0 Ma were obtained for these granitoids. The late Permian Chahe granite (257 Ma) is weakly peraluminous to peraluminous, and has rare earth element patterns and Ga/Al and FeOT/MgO ratios typical of A‐type granites formed in an extensional tectonic setting. The Middle Triassic Baomei granitoids (243–237 Ma) are weakly peraluminous, and exhibit a negative correlation between P2O5 and SiO2, which is typical of I‐type granites. All the granitoids have EM II‐type‐enriched mantle Sr–Nd isotopic compositions, which indicate that they were derived from a mantle source that had experienced enrichment and metasomatism. Hainan Island was in an extensional tectonic setting from the late Permian to Middle Triassic when widespread A‐ and I‐type granites were generated. We speculate that Hainan Island was mainly affected by the Tethyan tectonic domain during the Permian–Triassic, which involved closure of the Palaeo‐Tethys Ocean, collision of the Indochina and South China blocks, and subsequent post‐collisional extension. [ABSTRACT FROM AUTHOR]

The Kelameili Ocean was one branch of the Palaeo‐Asian Ocean, the initiation and closure history of which remains elusive. Consequently, they hamper our understanding of the accretionary evolution of the southern Altaids. In this paper, we carried out field mapping and also geochronological and geochemical analyses on the Huangcaopo Group in the northern Harlik Mountains, NW China. Field investigation revealed that "block‐in‐matrix" structure develops with blocks of andesite, limestone, sandstone, and gabbro in matrices of turbidites. Combined with our recent work, our field investigation indicates that the Huangcaopo Group is the southern extension of the Kelameili accretionary complex. A gabbro block (19HAM057) was dated at 500 ± 4 Ma, its geochemical affinity was defined to be similar to arc magmatic rocks. Magmatisms represented by two gabbroic intrusions (19HAM057‐2 and 19HAM048) were dated at the latest Devonian (360 ± 5 Ma) and the latest Carboniferous (299 ± 4 Ma), respectively. Their geochemistry displays enrichments in light rare earth elements (LREE) and large ion lithophile elements (LILE), but depletions in high field strength elements (HFSE, especially Nb and Ta). And a younger gabbroic intrusion (19HAM052) yielded crystallization age of the latest Permian (254 ± 3 Ma), and its geochemistry also shows affinity to arc magmatism. The magmatism represented by the gabbro block (19HAM057) was coeval with the Zhaheba‐Aermantai ophiolite, indicating that it was the product of incipient arc magmatism following subduction initiation in the Kelameili branch of the Palaeo‐Asian Ocean. However, two episodes of gabbroic magmas (19HAM057‐2 and 19HAM048) that intruded the Kelameili accretionary complex from the latest Devonian to latest Carboniferous indicate southward rollback of the subducting Kelameili oceanic lithosphere and resulted in the development of a growing arc. Meanwhile, the youngest gabbroic intrusion (19HAM052) suggests that northward subduction of the Kelameili oceanic lithosphere may have at least lasted to the latest Permian, indicating that the closure of the Kelameili Ocean might have been later than the latest Permian, most likely in the early Triassic. Our new data provide further constraints on the initiation and closure history of the Kelameili Ocean, which shed light on the accretionary evolution of the Altaids. [ABSTRACT FROM AUTHOR]

It is difficult to date a brittle fault because of the absence of effective dating methods. Recently, calcite U-Pb dating has drawn the attention of many researchers and has been successfully applied to constrain the age of brittle deformation. The South China Block (SCB) has experienced multiphase deformations characterized by widespread brittle faults and folds, which has led to significant debate on the Mesozoic dynamic mechanism and deformational phases. A syn-faulting calcite vein that occurred in the Permian limestones of the Ningzhen Mountain region was analyzed using U-Pb dating and geochemistry techniques in this paper. The U-Pb dating results display multiphase activities with two mixed ages of 109.9±5.8 Ma (MSWD=46, n=231) and 117.2±2.4 Ma (MSWD=3.6, n=150). The age of 117.2±2.4 Ma likely represents the timing of the brittle faults. Trace elements and rare earth elements data indicate that these fault-related calcites are mainly derived from host limestones and unrelated to Cretaceous magmatic activity. These faults formed in a tectonic reactive period and dormant time of the adakitic magma in the Lower Yangtze region. [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]

The Shuangjianzishan vein-type Ag-Pb-Zn deposit in the southern Great Xing'an Range (GXR), NE China, is hosted in the slate of the Lower Permian Dashizhai Formation intruded by granite porphyry. In this paper, U–Pb zircon ages and bulk-rock and isotope (Sr, Nd, Pb and Hf) compositions are reported to investigate the derivation, evolution and geodynamic setting of this granite porphyry. It is closely associated with Pb-Zn-Ag mineralization in the southern GXR and contains important geological information relating to regional tectonic evolution. Laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) zircon U–Pb dating yields an emplacement age of 131 ± 1 Ma for the granite porphyry. Bulk-rock analyses show that the Shuangjianzishan granite porphyry is characterized by high Si, Na and K contents but low Mg and Fe contents, and that the enrichment of Zr, Y and Ga suggests an A-type granite affinity. Most of the studied samples have relatively low 87Sr/86Sr values (0.70549–0.70558), with positive ϵNd(t) (0.71–0.88) and ϵHf(t) (4.9–6.9) values. The Sr–Nd isotope modelling results, in combination with the young TDM2 ages of Nd and Hf (850–864 and 668–778 Ma, respectively), reveal that the Shuangjianzishan granite porphyry may be derived from the melting of mantle-derived juvenile component, with minor lower crustal components; this finding is also supported by Pb isotopic compositions. Considering the widespread presence of granitoids with coeval volcanic rocks and regional geology data, we propose that the Shuangjianzishan granite porphyry formed in a post-orogenic extensional environment related to the upwelling of asthenospheric mantle following the closure of the Mongol–Okhotsk Ocean. [ABSTRACT FROM AUTHOR]

The Permian Pingdiquan Formation (P 2 p) in Shishugou Sag, Junggar Basin, Northwest China, is a typical example of mixed sedimentary strata formed in a saline lacustrine environment, characterized by complex lithological assemblages and extensive distribution of organic-rich source rocks. To further investigate the differences in oil-source contribution and hydrocarbon generation characteristics of source rocks with different lithologies, studying the difference of their geochemical characteristics and the formation mechanism of organic-rich source rocks is the top priority. Based on a comprehensive analysis of lithologic types, geochemical characteristics, and hydrocarbon generation potential of source rocks using organic petrology, molecular geochemistry and element geochemistry, this paper reveals the formation background and organic matter enrichment mechanism of the P 2 p organic-rich source rocks. The results show that the mixed sedimentary rocks of the P 2 p were deposited under relatively arid and saline lacustrine conditions. Paleoclimatic conditions tended to be more arid and hydrothermal activity became more frequent during the sedimentation process from mudstone, dolomitic mudstone to argillaceous dolomite. Consequently, the water column salinity elevated, leading to an increased proportion of salt-tolerant green algae and slight salt-tolerant cyanobacteria compared to salt-intolerant algae. Frequent changes in paleoclimate and hydrothermal activity control the interbedding deposition of mudstone, dolomitic mudstone and argillaceous dolomite, and the resulting salinity fluctuations contribute to variations in the proportion of salt-tolerant and intolerant algae in source rocks with different lithologies. Furthermore, the source rocks within the mixed sedimentary strata (mudstone, dolomitic mudstone and argillaceous dolomite) all exhibit substantial hydrocarbon generation potential, and there exists heterogeneity among source rocks of the same lithology. The key factor influencing the development of these organic-rich source rocks is the enhancement of palaeoproductivity driven by volcanic activity. Additionally, the water stratification caused by saline water promotes anoxic water columns, also contributing to organic matter enrichment in the source rocks. • The paleoclimate and hydrothermal activity control the lithology and its composition. • The water column salinity controls the variation of algal composition in source rocks. • Volcanic activity promotes organic-rich source rock by controlling paleoproductivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • The paleoclimatic conditions during deposition control the development of gray sandstone in the red beds. • The uranium mineralization in the red beds exhibits a certain correlation with the inorganic redox reactions involving iron. • Some dark mudstones in the red beds undergo a significant uranium pre-enrichment during deposition. • The climatic alternations lead to a weak reducing capacity in the red beds, with uranium mineralization occurring in the interior of the basin. The search for uranium deposits in the red beds is currently a hotspot in China's sandstone-type uranium exploration efforts. The typical occurrence of uranium deposits is within gray sandstone layers amidst the red beds, where the distribution of these gray sand bodies dictates the presence of uranium deposits. Hence, delving into the genesis of gray sandstone within the red beds proves beneficial for both uranium exploration and unraveling the ore-forming mechanisms. However, there is currently significant controversy surrounding the genesis of gray sandstone in the red beds. This paper focuses on the typical uranium deposit in the red beds—the HLJ-DL uranium deposit in the southwestern part of the Songliao Basin. It investigates the genesis of gray sandstone within uranium-bearing rock series and its relationship with uranium mineralization. The lithology of representative drill cores, including the red sandstone for comparative study, is methodically examined, along with their elemental geochemistry as well as carbon and oxygen isotope characteristics. The petrological characteristics suggest that both the gray and red sandstone share similar compositions of clastic particles, indicating minimal influence of the source rock on the sandstone color. The gray sandstone displays comparable TOC content (averaging around 0.05 %) and δ18O PDB values (averaging around −16 ‰) to the red sandstone. However, it exhibits relatively higher δ13C PDB values (averaging −0.26 ‰), whereas the average δ13C PDB value for the red beds is −1.61 ‰. The data indicate that the gray sandstone is less affected by hydrothermal or hydrocarbon fluids. Compared to the red sandstone, which has relatively higher Cu/Al values (averaging 1.09) and Fe3+/Fe2+ ratios (averaging 3.37), the gray sandstone exhibits low Cu/Al values (averaging 0.44) and a low Fe3+/Fe2+ ratio (averaging 0.36), suggesting its formation in a relatively reducing environment. The reducing conditions necessary for the formation of gray sandstone may stem from the climate becoming relatively warm and humid, irrespective of whether it originates from the original sedimentary environment or is induced by the reducing pore water discharged from dark mudstones. The chemical weathering index of fine-grained sediments indicates that, the gray sandstones were commonly configured in relatively humid-warm climate with fairly low dissolved oxygen content in the bottom water. Additionally, the deposition of the uranium-bearing rock series experienced alternating climatic changes, rather than consistently being in a humid-warm climate. This resulted in the sand bodies with low TOC content, insufficient reducing potential, and uranium mineralization primarily occurring in the interior of the basin. Organic matter has a relatively weak control over uranium mineralization, whereas uranium mineralization shows a certain correlation with iron reduction. The ore-forming fluid was uranium-rich oxygenated atmospheric water. Dark-colored mudstones, formed under humid-warm climatic condition, contain relatively high TOC contents (avg. 0.43 %) and exhibit a strong reducing capacity. The reducing pore water in dark-colored mudstones excreted into the adjacent sandstones under compaction during the early diagenesis, is able to serve as a vital reducing agent in later-stage uranium mineralization. Additionally, certain dark-colored mudstones with high uranium content (up to 944 ppm) undergo significant uranium pre-enrichment, providing a partial uranium source for uranium mineralization. [ABSTRACT FROM AUTHOR]

This paper presents new zircon U-Pb geochronological, Hf isotopic and whole-rock geochemical data for the granitic plutons in the Xing'an Massif, Northeast China, to constrain the Late Mesozoic tectonic evolution of the Mongol-Okhotsk Ocean and the Paleo-Pacific Ocean. The zircon U-Pb ages indicate that the granitoids emplaced during the Late Jurassic-Early Cretaceous. The granodiorites show an adakitic affinity with high Sr/Y ratios and low Yb (< 1.30 μg/g) contents. The monzogranites exhibit high SiO2, low MgO contents, enrichment in LILEs (Rb, K, and Th), and depletion in HSFEs (Ta, Nb, Zr, P, and Ti). Petrological and geochemical features of these monzogranites suggest that they are highly fractionated I-type granitoids. In addition, the zircon εHf(t) values and two-stage model ages (TDM2) are in the range of +2.6 to +8.1 and 669-1011 Ma, respectively, indicating that primary magma was generated by partial melting of juvenile lower-crustal materials, and there was a significant crustal growth in the Phanerozoic in the Northeast China. Combined with the coeval granitoids widely exposed in the Xing'an Massif, we conclude that the Late Jurassic magma in Northeast China was generated in an extensional setting related to the closure of the Mongol-Okhotsk Ocean, but the Early Cretaceous magma was related to the subduction of the Paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

Geodynamic evolution in the late Paleozoic is significant for understanding the final amalgamation of the Central Asian Orogenic Belt (CAOB). No consensus has yet been reached regarding the late Paleozoic geodynamic evolution of the northern Great Xing'an Range (GXR) in northeastern China, the eastern CAOB. Furthermore, late Paleozoic syenogranite–diabase dyke association is present in the Xiaokele area in northern GXR. It provides an important opportunity to understand the nature of magmatism and the geodynamic evolution during this period. This paper presents new zircon U–Pb ages, zircon Hf isotopic compositions, and geochemical data of whole rocks for Xiaokele syenogranite and diabase. Zircon U–Pb dating suggests that the Xiaokele syenogranite (292.5 ± 0.9 Ma) and diabase (298.3 ± 1.5 Ma) were emplaced during the early Permian. The Xiaokele syenogranites have high SiO2 contents, low MgO contents, and enriched zircon εHf(t) values, suggesting that their primary magma was generated by the partial melting of the juvenile crustal material. The Xiaokele diabases have low SiO2 contents, high MgO contents, are enriched in large-ion lithophile elements, depleted in high-field-strength elements, and exhibit enriched zircon εHf(t) values. They derived from a lithospheric mantle source that had previously been metasomatized by slab-derived fluids. Combined with previous research results, we believe that the continent–continent collision between the Xing'an and Songliao blocks occurred during the late early Carboniferous – early late Carboniferous (330–310 Ma), and the two blocks were transformed into a post-collisional extensional setting during the latest Carboniferous – early Permian. [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]

The supercontinent Rodinia existed as a coherent large landmass from 900 to 750 Ma and is now dispersed over all current major continents. Controversy has long surrounded the reconstructions of the East Asian blocks in Rodinia, especially the South China craton and nearby microcontinents. The Central Qilian block is a Precambrian microcontinent in the early Paleozoic Qilian orogenic belt, which is located in the northeastern part of the Qinghai-Xizang (Tibet) Plateau and marks the junction of the North China, South China and Tarim cratons. The formation and tectonic affinity of the Precambrian basement in the Central Qilian block is unclear, which affects our understanding of the assembly of Rodinia. The Huangyuan Group and the Maxianshan Group crop out in the eastern part of the block and represent the lower part of the basement. In this paper, we present a systematic study of the petrology, whole-rock geochemistry, and geochronology of amphibolites and orthogneisses from the Huangyuan and Maxianshan Groups. The protolith of the amphibolites was tholeiitic and calc-alkaline gabbro or gabbroic diorite formed in a continental arc environment, with laser ablation-inductively coupled plasma mass spectrometry (LAICPMS) zircon U-Pb ages of 967-957 Ma, a wide range of eHf(t) values of -3.74 to +5.06 and TDM1 model ages peaking at 1470 Ma and 1607 Ma. Minor inherited zircon grains with older ages of 1207-1515 Ma were collected from the amphibolites. The primitive magma was derived from partial melting of a spinelfacies fertile (lherzolite) lithospheric mantle that was modified by fluids and melts from a subducted slab. Fractionation of olivine, Fe-Ti oxides and plagioclase played a dominant role in the magma differentiation for gabbroic rocks in the Huangyuan Group, while fractionation of olivine and clinopyroxene controlled differentiation to form Maxianshan Group gabbros. The protolith of orthogneisses includes weakly peraluminous I-type and A2-type granites with consistent LA-ICPMS zircon U-Pb ages of 963-936 Ma, a wide range of eHf(t) values of -3.86 to +6.15 and TDM2 model age peaks at 2001 Ma and 1772 Ma. A few inherited zircon grains yield ages of 1033-2558 Ma. The peraluminous I-type granites resulted from a low-pressure partial melting process and the peraluminous A-type granites were derived from a charnockite source heated by largescale magmatic underplating. Fractionation of plagioclase, biotite, and K-feldspar from the magma played the main role during the generation of the granitoids. The intrusion of these granites is related to a back-arc extension. It is inferred that the lower part of Precambrian basement of the Central Qilian block is composed mainly of early Neoproterozoic rock assemblages formed in a trench-arc-basin system during the assembly of the Rodinia supercontinent, with probable existence of late Paleoproterozoic to Mesoproterozoic continental nuclei. Combining our results with existing data, we identify a sequence of initial intra-oceanic subduction (ca. 1121-967 Ma) in front of a continental nucleus, continuous subduction of oceanic crust beneath the continental mass with formation of a mature continental arc and a back-arc basin (ca. 967-896 Ma) and continental rifting (

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]

Dolomite is the most important component of the prolific reservoirs in the Ma55 to Ma51 submembers of the Ordovician Majiagou Formation in the central Yishan Slope, Ordos Basin. However, the origins of the different types of dolomite are unclear because of the different diagenetic environments and complex diagenetic fluids. This paper mainly focuses on the diagenetic environment and diagenetic fluid associated with the dolomite. The petrographic features of the dolomite were studied on the basis of core observation and thin section identification. Geochemical characteristics were analyzed according to the O, C and Sr stable isotopes and major and trace elements. The results demonstrate that, petrographically, the dolomite can be divided into four types, namely, type 1, type 2, type 3 and type 4. Type 1 is mainly characterized by dolomite with gypsum and salt dissolution as well as breccia structures with no clay minerals filling between breccia clasts. Type 2 is characterized by powder-fine crystalline dolomite with apparent residual textures and residual intergranular and intercrystal pores. Type 3 is characterized by leopard limestone or dolomite with leopard textures and massive bioborings. Finally, type 4 is characterized by karst breccia dolomite with many fractures and caves filled by abundant terrigenous clay minerals. In combination with the petrographic data, analysis of the geochemical data reveals that the type 1 dolomite formed in an early near-surface diagenetic environment and the diagenetic fluid might have been early freshwater. Type 2 and type 3 dolomite formed in a shallow-burial diagenetic environment. The diagenetic fluid of type 2 dolomite might have been hypersaline brine that was influenced by freshwater, but that of type 3 dolomite might have been a mixed fluid consisting of seawater and freshwater, which was less saline than the type 2 dolomite fluid. Type 4 dolomite formed in an epidiagenetic near-surface environment and the diagenetic fluid might have been superficial freshwater carrying abundant terrigenous clay minerals. The study shows that the analysis of the diagenetic environment and fluid of dolomite has great significance for research on dolomite origins. The porosity and permeability values of the four types of dolostone reservoirs indicate that type 1 dolomite reservoirs are the best reservoir, type 2 dolomite reservoirs have good physical properties, type 4 dolomite reservoirs are relatively good reservoirs, and the worst reservoir is the type 3 dolomite reservoirs. [ABSTRACT FROM AUTHOR]

Several Palaeozoic ophiolitic mélanges distributed in the West Junggar, Xinjiang, are remnants of the Paleo‐Asian Ocean evolution. They are important keys for studying the component, tectonic evolution, and crust–mantle interaction of the Central Asian Orogenic Belt (CAOB). This paper presents petrology, zircon U‐Pb chronology, geochemistry, and Hf isotope data of mafic rocks from the Dalabute ophiolitic mélange, West Junggar. The zircon U‐Pb chronology data of gabbro in the Dalabute ophiolitic mélange can be divided into two groups. The first group magmatic zircons yield a weighted mean age of 389.7 ± 7.7 Ma. It suggests that gabbros of the Dalabute ophiolitic mélange were formed during the period of Early‐middle Devonian, which represents the main period that the Dalabute back‐arc ocean basin expanded. The second group inherited zircons with ages ranging from 910 to 975 Ma were interpreted as Neoproterozoic materials of basement entered its magmatic source. Geochemical characteristics show that the mafic rocks from the Dalabute ophiolitic mélange can be subdivided into alkaline and tholeiite series. Whole‐rock and Hf isotopic data indicate that alkaline basalts have the signatures of typical OIB and formed in the oceanic island or seamount settings related to mantle plume, which were most likely derived from an enriched mantle source. Besides, tholeiitic rocks exhibit the features of MORB and generated in an immature back‐arc basin in the supra‐subduction zone. Their magmas originated from a depleted mantle that had been metasomatized by subduction‐related fluids and contaminated by materials with crustal nature. Therefore, Dalabute ophiolites are supposed to be generated from a back‐arc oceanic basin, which is relate to intra‐subduction and with mantle plumes developed within it. These results jointly provide convincing evidence for the evolution and property of the Dalabute ophiolite in the West Junggar and further supply reference and base for reconstruct the evolutionary history of the CAOB. [ABSTRACT FROM AUTHOR]