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The connection between the Ordovician bentonites on the southern margin of the Ordos Basin and the Early Palaeozoic volcanic rocks of the North Qinling Orogenic Belt is crucial for understanding the subduction and collisional closure of the Shangdan Ocean during the Early Palaeozoic. This paper investigates zircon U–Pb ages, geochemistry and Lu–Hf isotopic compositions of zircons in the Upper Ordovician Zhaolaoyu Formation bentonites located on the southern margin of the Ordos Basin. U–Pb dating of zircon indicates a coeval age of 453.3 ± 1.4 Ma (MSWD = 0.99), which represents the crystallisation age during the Late Ordovician Katian stage. The bentonites exhibit higher SiO2 (57.94–77.95 wt.%) and Al2O3 (9.21–14.33 wt.%), classifying them within the low‐potassium alkali basalt to medium‐potassium calc‐alkaline series. The parent rock of the bentonites is likely intermediate to felsic volcanic rocks. The rare earth element partitioning curves of the bentonites are right‐dipping, with a more pronounced negative Eu anomaly (δEu = 0.48–0.67). The zircons in the bentonites yield two‐stage model ages ranging from 546 to 956 Ma, along with εHf(t) values between 5.56 and 13.55. These results indicate that the bentonites are products of volcanic arc magma formed in a subduction–collision environment. The interbedded bentonites in the Upper Ordovician limestones of the southern margin of the Ordos Basin may be associated with the northward subduction of the Shangdan Oceanic crust, reflecting the subduction and consumption of the Proto‐Tethys Ocean along the southern margin of the North China Block. [ABSTRACT FROM AUTHOR]

The North Tianshan Accretionary Complex represents a Late Palaeozoic suture between the Junggar Terrane and the Yili Block. We report detrital zircon U–Pb dating and Hf isotope results for a sandstone from the Lower Carboniferous Anjihai Formation in the northern margin of the Yili Block, to reveal the geochronological framework of the northern Yili Block, and discuss the subduction process of the North Tianshan Ocean (NTO). The detrital zircon ages were divided into 2 clusters, namely, the Precambrian and Palaeozoic ones. The Palaeozoic age group can be further divided into 3 subgroups, that is, 472–461 Ma, 448–423 Ma, and 406–335 Ma, with peaks at 465, 436, and 346 Ma, respectively. All the Palaeozoic zircons have oscillatory zoning textures and high Th/U ratios, showing an igneous provenance. The zircon Ti‐temperatures are between 584 and 809 °C, suggesting that their source rocks were I‐ or S‐type granitic rocks. In addition, most of the Palaeozoic zircons have positive εHf(t) values, indicating that the source rocks of the Palaeozoic zircons are derived from not only Mesoproterozoic continental crust but also involved depleted mantle components, which matched well with the Hf isotopic signatures of magmatic rocks from the northern Yili Block. Based on the regional geology, these zircons were thought to be sourced from magmatic rocks that were related to the subduction of the NTO. Taking into consideration the Middle–Late Ordovician arc‐type granitoids in the Wenquan area, we conclude that the northern margin of the Yili Block was a unified active continental margin in the Palaeozoic, and the subduction of the NTO started at least from the Middle Ordovician. [ABSTRACT FROM AUTHOR]

A suite of granitic gneisses has been identified in the Hatu area, eastern segment of the East Kunlun Orogen. Zircon U-Pb dating of granitic gneisses indicates magmatic crystallization at 895.4 ± 9.3 Ma. However, some zircons yield a metamorphic age of 433.8 ± 6.2 Ma. When taken together, these data reveal that the Early Neoproterozoic granites experienced Early Paleozoic metamorphism. The granitic gneisses are characterized by high contents of SiO2, Al2O3, and K2O + Na2O and low concentrations of TiO2, MnO, and CaO. The petrochemical character (average A/CNK = 1.09 and average A/NK = 1.42) and the mineral assemblages suggest that the granites are of S type and peraluminous. The chondrite-normalized rare earth element patterns of the samples show enrichment of light rare earth elements ((La/Yb) N = 13.84) and moderate negative Eu anomalies (δEu = 0.60). The primitive-mantle-normalized trace element diagrams show an enrichment of Rb and Th and a depletion of Ta, Nb, Sr, P, and Ti. The granitic gneisses have features of crust-derived and typical continent-continent syn-collisional granites. All the above characteristics suggest that the Paleoproterozoic Baishahe Formation probably served as the source rocks and that the granitic gneisses were generated by partial melting of the metasedimentary material related to crustal thickening. They also reveal a collision between the micro-block in the Early Neoproterozoic in response to the assembly of the supercontinent Rodinia in East Kunlun. [ABSTRACT FROM AUTHOR]

The Buqingshan Tectonic Mélange Belt in the south margin of the East Kunlun Orogen, located in west section of Buqingshan-A'nyemaqen Suture Zone, is one of the key areas to understand continental tectonics and continental dynamics of China. This paper reports zircon U-Pb dating results and geochemistry of the Manite granodiorite (rock mass) in the Buqingshan Tectonic Mélange Belt. Zircons from the granodiorite show oscillatory zoning structures and relatively high Th/U ratios, indicating that they are magmatic zircons. Zircon LA-ICP-MS U-Pb dating for the Manite granodiorite yields ages of 487 ± 11 Ma (MSWD = 2.3) and 479 ± 2 Ma (MSWD = 0.56), implying that the Manite granodiorite were formed in the Late Cambrian to Early Ordovician. Geochemical analyses show that the rocks have high contents of SiO2 (66.06 wt.%-68.60 wt.%) and Al2O3 (14.84 wt.%-16.54 wt.%), and low alkaline (6.17 wt.%-7.43 wt.%), belonging to the middle-K calc-alkaline series. The A/CNK (Al2O3 /(CaO + Na2O + K2O)) ratios are 1.02-1.15, indicating that the granodiorite is weakly peraluminous. The contents of rare earth elements (REEs) are lower (89.64-130.41 ppm), with weakly negative to weakly positive Eu anomalies ( δEu = 0.83-1.12). The primitive mantle-normalized trace elements are characterized by evidently negative anomalies of Nb, Ta, P, Hf, Ti, etc., and positive anomalies of Th, La, Nd, Zr, Eu, etc. Moreover, the rocks show features of typical I-type granite. This leads us to conclude that the Manite granodiorites is derived from the partial melting of crust and formed in an island-arc environment. Combined with previous studies, we believe that the subduction of the Proto-Tethyan Ocean in the Buqingshan area was ongoing during 487 to 479 Ma and formed island-arc-type granites represented by the Late Cambrian to Early Ordovician Manite granodiorite. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Qushi'ang granodiorite (QSG) is located at the central east of the ophiolitic melange belt in the East Kunlun Orogenic Belt (EKOB) in the northern margin of the Qinghai-Tibetan Plateau. LA-MC-ICP-MS zircon U-Pb dating suggests that the granodiorite and mafic microgranular enclaves (MMEs) crystallized 246.61±0.62 and 245.45±0.9 Ma ago, respectively. Granodiorite, porphyritic diorite, and MMEs are metaluminous and medium-K calk - alkaline series, with island-arc magma features, such as LILE enrichment and HFSE depletion. The porphyritic diorite has high Cr (13.50 ppm to 59.01 ppm), Ni (228.53 ppm to 261.29 ppm), and Mg# (46-54). Granodiorite and porphyritic diorite have similar mineral compositions and evolved major and trace elements contents, particularly Cr and Ni, both of which are significantly higher than that in granites of the same period. The crystallization age of MMEs is close to that of granodiorite, and their major and trace elements contents are in-between porphyritic diorite and granodiorite. The results suggest that the original mafic magma, which was the product of mantle melting by subduction process, intruded into the lower crust (Kuhai Rock Group), resulting in the formation of granodiorite. Countinous intrusion of mafic magma into the unconsolidated granodiorite formed MMEs and porphyritic diorite. The granodiorite reformed by late-stage strike-slip faulting tectonic event indicates that the strike-slip fault of Middle Kunlun and the collision of the Bayanhar block with East Kunlun were later than 246 Ma. Therefore, the formation of the QSG not only indicates the critical period of evolution of East Kunlun but also represents the tectonic transition from oceanic crust subduction to slab breaking. [ABSTRACT FROM AUTHOR]

This study focuses on the zircon U-Pb geochronology and geochemistry of the Bairiqiete granodiorite intrusion (rock mass) from the Buqingshan tectonic mélange belt in the southern margin of East Kunlun. The results show that the zircons are characterized by internal oscillatory zoning and high Th/U (0.14-0.80), indicative of an igneous origin. LA-ICP-MS U-Pb dating of zircons from the Bairiqiete granodiorite yielded an age of 439.0 ± 1.9 Ma (MSWD = 0.34), implying that the Bairiqiete granodiorite formed in the early Silurian. Geochemical analyses show that the rocks are medium-K calc-alkaline, relatively high in Al2O3 (14.57-18.34 wt%) and metaluminous to weakly peraluminous. Rare-earth elements have low concentrations (45.49-168.31 ppm) and incline rightward with weak negative to weak positive Eu anomalies (δ5Eu = 0.64-1.34). Trace-element geochemistry is characterized by negative anomalies of Nb, Ta, Zr, Hf and Ti and positive anomalies of Rb, Th and Ba. Moreover, the rocks have similar geochemical features with adakites. The Bairiqiete granodiorite appears to have a continental crust source and formed in a subduction-related island-arc setting. The Bairiqiete granodiorite was formed due to partial melting of the lower crust and suggests subduction in the Buqingshan area of the Proto-Tethys Ocean. [ABSTRACT FROM AUTHOR]

The article discusses a study to describe the fossil characteristics and compares these samples with Neocalamites fossils identified before for the classification, evolution, and plant geography of Neocalamites fossils. Topics discussed include the preservation of Neocalamites as trunk fossils in argillaceous siltstone, the length of Neocalamites trunk, and the identification of Neocalamites fossils from the Upper Triassic Daheba Formation in the West Qinling strata in China.

The article presents a study which discusses understanding of the possible progressive evolution process of supra-subduction zone (SSZ) forearc magmas for Acite ophiolite. Topics discussed include geochemistry of oceanic crust rocks, tectonic evolution history of a proto-tethys, and classification of calcic-alkaline basaltic andesites (CABs) having higher silicon oxide contents.

The article presents a study which discusses magma mixing and mingling for Xiangjiananshan Granitic batholith at eastern area of the East Kunlun Orogenic Belt. Topics discussed include occurrence of complicated tectono-magma events in the East Kunlun Orogenic Belt (EKOB), granitic intrusions, and presence of mafic microgranular enclaves (MMEs).