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Granite genesis is crucial to understanding the evolution of continental crust, yet many concerns about granite genesis remain not well answered, such as whether I-type granite contains metasedimentary components, what controls granite compositional diversity, and how granitic plutons are constructed. To explore these issues, we conducted a detailed study on the two-mica plagiogranite, tonalite, and biotite plagiogranite units of the Wujinxia composite pluton in the eastern Qilian orogen, NE Tibetan Plateau. These units comprise two-mica plagiogranite, tonalite (with diorite enclave), and biotite plagiogranite. Zircon U–Pb data reveal that three granitic units formed at ~ 487 Ma, ~ 464 Ma, and ~ 430 Ma, respectively. Magmatic and xenocrystic garnet were identified from the tonalite and biotite plagiogranite, respectively. The two-mica plagiogranite, tonalite, and biotite plagiogranite all belong to low-K series rocks (K2O/Na2O = 0.10–0.26), and were derived from deep crustal sources mainly consisting of juvenile mafic rocks, with involvement of minor metasedimentary rocks in the magma sources of the two-mica plagiogranite and tonalite. The diorite enclave within the tonalite was probably derived from an enriched mantle-derived basaltic magma. Mineral compositions, thermobarometric calculations, and whole-rock geochemical data indicate that the low-K intrusive units of the Wujinxia composite pluton resulted from multiple magmatic systems at different depths. The results suggest that I-type granites can contain metasedimentary components by partial melting of a mixed crustal source, and high-Mn content helps the preservation of high-Ca garnet within such rocks. For a composite pluton spanning a large compositional variation, its compositional diversity is jointly controlled by magma source composition, melting condition and thermal evolution of individual magma pulses, and the resulted assembly style during pluton construction. [ABSTRACT FROM AUTHOR]

The possibility that the Proto‐Tethys Ocean may have undergone intra‐oceanic subduction during ocean closure remains poorly constrained due to a lack of geological evidence for a mature intra‐oceanic arc. Here we present new geochemical and geochronological data for potential arc‐related volcanic rocks adjacent to the accretionary complex and forearc basin in the North Qaidam collisional belt, northern Tibetan Plateau. The volcanic rocks are dominated by foliated basalt, andesite, tuff, and minor dacite with zircon U‐Pb ages ranging from 517 to 497 Ma. They show distinctive geochemical characteristics and can be subdivided into three groups: island‐arc intermediate‐basic volcanic rocks, back‐arc basin basalts (BABB), and dacites with intra‐oceanic arc affinity. The island‐arc volcanic rocks have variable εNd(t) values (+1.6 to +7.5) that decrease northward and were generated by partial melting of depleted mantle wedge modified by hydrous fluid and sediment melt. The BABBs have high εNd(t) values (+5.3 to +6.6) and formed through the melting of MORB‐like mantle, whereas the nearby dacites have positive εNd(t) values (+1.9 to +3.6) similar to the surrounding island‐arc volcanic rocks and were derived from partial melting of intra‐oceanic arc crust as a result of BABB underplating. Integrated analysis of the spatial‐temporal distribution of these volcanic rocks and the reconstructed intra‐oceanic arc‐trench system confirms the existence of the earliest Phanerozoic intra‐oceanic arc formed in response to north‐directed intra‐oceanic subduction. This unrecognized subduction of the Proto‐Tethys Ocean in the North Qaidam belt initiated at ca. 530 Ma, matured ca. 520 Ma, and terminated by ca. 480 Ma. Plain Language Summary: Closure of an ocean basin is achieved through subduction of oceanic lithosphere at a continental margin or in an intra‐oceanic setting. Identification and structure of subduction‐related magmatic rocks are critical for fully understanding the complex processes associated with ocean closure and the paleotectonic framework. Geological mapping and geochemical analyses of the Tanjianshan Group in the North Qaidam collisional belt, northern Tibetan Plateau were undertaken. Results demonstrate the presence of relics of the earliest Phanerozoic intra‐oceanic arc and an associated complete arc‐trench system, generated by previously unrecognized intra‐oceanic subduction far from microcontinents that are now adjacent. This study reveals the entire evolution of a missing intra‐oceanic subduction system within the Proto‐Tethys Ocean, which started ca. 530 Ma, matured ca. 520 Ma and ended ca. 480 Ma. Key Points: Relics of the earliest Phanerozoic intra‐oceanic arc discovered in North Qaidam collisional beltProto‐Tethys Ocean in North Qaidam belt experienced north‐directed intra‐oceanic subductionIntra‐oceanic subduction started at ca. 530 Ma and lasted until ca. 480 Ma [ABSTRACT FROM AUTHOR]

The Central Qilian terrane (CQT) of the northern Tibetan Plateau played a key role in the tectonic evolution of the Proto‐Tethyan Ocean in the Tethysides, but its formation and tectonic attribution have been hotly debated. Here, we report the discovery of eclogites and HP mafic granulites in the Beidahe Complex of the western CQT. These occur as blocks of various sizes within a sequence of metavolcanic–sedimentary rocks, exhibiting typical a 'block‐in‐matrix' and thrust imbrication structure. The eclogite facies metamorphic rocks preserve distinct mineral assemblages and textures corresponding to prograde, peak, and retrograde metamorphism. By combining phase equilibrium modelling with SHRIMP and LA‐ICPMS U–Pb dating of metamorphic zircon, sphene, and rutile, the Late Neoproterozoic–Cambrian (c. 553–516 Ma) eclogite facies peak with low thermal gradients of 10–14°C/km, Cambrian (c. 515–506 Ma) post‐peak decompression and Ordovician (c. 495–455 Ma) cooling histories for these metabasic rocks have been restored. These constitute hairpin‐type clockwise pressure–temperature–time (P–T–t) paths depicting in detail the sequence of deep subduction and subsequent exhumation in Central Qilian during the Late Neoproterozoic to Early Palaeozoic. Our new findings suggest that the CQT represents a Japan‐type arc‐accretionary system that formed as a result of the North Qilian oceanic plate, one of the major branches of the Proto‐Tethys Ocean, being subducted southward. Eclogites in the Beidahe Complex in western CQT offer the earliest (c. 553 Ma) metamorphic record of subduction in the Qilian orogen, indicating that the North Qilian Ocean commenced subducting southward prior to the Late Neoproterozoic. [ABSTRACT FROM AUTHOR]

The Qilian orogenic belt in the northern Tibetan plateau connects the Altaids to the north with the Tethyan orogenic system to the south and occupies a key tectonic position in the evolution and assembly of Asia. The belt contains a wide range of subduction–accretion-related petrotectonic units. The Early–Middle Devonian Laojunshan conglomerate, deposited unconformably upon Cambrian–Silurian strata along the northern margin of the North Qilian terrane, contains a record of the late Paleozoic tectonism of the Qilian orogen. Its provenance and tectonic setting are critical in understanding not only the tectonic evolution of Tibetan plateau, but Paleozoic global reconstructions as well. The composition of clastic conglomerates and heavy mineral assemblages of sandstones suggests that coeval mafic, felsic, metamorphic, and sedimentary rocks were the main sources. The geochemistry of volcanic clasts and paleocurrent and paleogeographic data suggest derivation from subduction–accretion complexes in the North Qilian terrane. The geochemistry of siltstones and mudstones indicates that the Laojunshan conglomerate was derived from an arc and accumulated in an active continental margin. Geochemical data of granitoid clasts suggest that they were derived from Ordovician–Silurian subduction-related magmatic rocks. Mafic and ultramafic clasts, chromite, and magnetite decrease upwards in the stratigraphy whereas metamorphic, sedimentary and granitoid clasts, and garnet increase. These data imply that mafic rocks were the predominant source during initial deposition. Regional studies suggest that the North China plate subducted southwards and produced subduction-related arc magmatism along the southern margin of the North Qilian terrane during the Early–Middle Devonian. Therefore, we interpret the Laojunshan conglomerate as a fore-arc basin fill. [ABSTRACT FROM AUTHOR]

The timing and magnitude of upper crustal deformation in the northern Tibetan Plateau are important for testing models of plateau uplift and for understanding Cenozoic environmental variations and monsoon evolution in central and eastern Asia. Most published studies focus on the upward and outward growth of the northern Tibetan Plateau, whereas its tectonic, vertical-axis rotation history has received less attention. Here we evaluate paleomagnetic data from six stratigraphic sections in the northeastern Qaidam Basin of China, revealing a phase of clockwise rotation from ca. 20–11 Ma followed by counterclockwise rotation from ca. 11–5 Ma. We propose that differential crustal shortening and right-lateral shear drove early to middle Miocene clockwise rotation, whereas eastward flow of the Tibetan asthenosphere induced the post-middle Miocene counterclockwise rotation. These processes coincide with increased activity of first-order strike-slip faults in the northeastern plateau, emphasizing the important role of strike-slip faults in accommodating crustal deformation in northern Tibetan Plateau during the late Cenozoic. • First rotation analysis of the NE Qaidam Basin under a newly revised age model. • Sliding window averages indicate CW followed by CCW rotations. • Crustal differential shortening and asthenospheric processes contribute to basin rotation. [ABSTRACT FROM AUTHOR]

The Tibetan region underwent diachronous differential rises during the Cenozoic era. Its elevation history is critical for understanding the processes of mountain building, and for evaluating its climatic effects on atmospheric circulations. However, knowledge of paleoenvironment and paleoelevation in different geological domains of the Tibetan Plateau is still limited. Here we provide chronology of lacustrine deposits of the Upper Dingqing Formation in the Lunpola Basin in Central Tibet, which yields a middle Miocene age (15–12 Ma). Both stable isotope and palynological records indicate a climatic transition at ∼13.8 Ma marked by a change towards a cooler and drier climate after the Middle Miocene Climate Transition driven by global climatic cooling. Pollen and spore assemblages suggest that the vegetation was dominated by mixed coniferous–broadleaved forest with some grasslands. New palynological elevation reconstructions constrained by the co-existence approach yield a maximum paleo-elevation of 3100–3600 m (average 3350 m) of the Lunpola Basin, which was consistent with a maximum elevation of 3400 m based on floating-leaf plants. Our new data do not support previous views that the Lunpola Basin achieved its current elevation as early as the late Eocene or early Oligocene, but instead we suggest there has been a rise of up to 1200 m since 12 million years ago. Our results bring new light on both the paleoenvironmental reconstructions and the paleo-elevation estimates of the Lunpola Basin, Central Tibet. • Mid-Miocene age (15–12 Ma) of the upper Dingqing Formation in Central Tibet. • Climatic shifted to a cooler/drier climate after ca.13.8 Ma in Central Tibet. • The vegetation was dominated by mixed coniferous–broadleaved forest at 15–12 Ma. • The Lunpola Basin only attained a maximum elevation of 3400 m in the middle Miocene. [ABSTRACT FROM AUTHOR]

Considerable debate exists regarding how the East Asian summer monsoon (EASM) varied over the late Miocene, limiting our ability to understand the long-term evolution and forcing of this system. Much understanding of EASM variation over the late Cenozoic is based on loess magnetic susceptibility (χ lf) records from the Chinese Loess Plateau (CLP). During Pliocene-Quaternary times, χ lf decreases from southeast to northwest across the CLP, consistent with the modern monsoonal climate pattern. However, the χ lf records over the late Miocene show different patterns, with lower values on the central CLP sandwiched between higher values of the eastern and western CLP, a pattern inconsistent with predictions based on monsoon climate. Here we propose a hypothesis to explain this conundrum, and advance knowledge of late Miocene EASM variations. As with other parts of the CLP, high late Miocene χ lf values on the western CLP were caused by increases in the ultrafine ferrimagnetic grain content. However, we argue that part of the ultrafine ferrimagnetic grain increase on the western CLP was due to detrital input derived from eroding surface soil cover on the uplifting bounding mountains of the northeastern Tibetan Plateau and western Qinling. Loess provenance data and independent evidence regarding uplift timing of the northeastern Tibetan Plateau support our hypothesis. We propose that the eastern CLP χ lf more faithfully reflects EASM intensity; indeed, eastern CLP χ lf data show relatively low values over the late Miocene, indicating a weak EASM, consistent with inferences from marine sediments. Therefore, our work reconciles conflicting evidence regarding late Miocene EASM intensity and deepens our understanding of the underlying monsoon forcing mechanisms. We conclude that global climate, instead of Tibetan uplift, is the major mechanism driving EASM precipitation evolution over the late Miocene. [ABSTRACT FROM AUTHOR]