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The mid-Cretaceous Langshan Formation, which crops out on the north Lhasa subterrane, central Tibet, is composed of a thick carbonate sequence with local volcanic rock and sandstone interlayers. In this study, we present data from the Asuo area, including fossil assemblages within carbonates, detrital zircon U–Pb ages of sandstone interlayers, zircon U–Pb ages and whole-rock geochemistry of andesite interlayers within the Langshan Formation to provide new constraints on the tectonic evolution of north Lhasa subterrane. The fossil assemblage indicates that the Langshan Formation was deposited on a carbonate platform at water depths of approximately 0–50 m during the late Albian to early Cenomanian period. The volcanic rock interlayers (111–109 Ma) primarily consist of high-K calc-alkaline andesites/dacites (SiO2: 56.48–67.03 wt. %; Mg#: 42.5–58.9). These andesites exhibit limited evidence of significant modification by crustal contamination. The high Mg# values and arc-like trace element signatures suggest that the andesites may have resulted from partial melting of the mantle wedge induced by fluids derived from a subducted slab. Furthermore, the lithic fragments within the sandstone interlayers predominantly exhibit characteristics of "recycled orogen" and "arc orogen," indicating that the sandstone was derived from recycled ancient strata and a few magmatic arc materials. Considering the regional paleogeographic context, the carbonate accumulation of the Langshan Formation appears to have occurred nearly simultaneously with a period of high-flux magmatism, long-term slow tectonic subsidence, and the closure of the Meso-Tethys Ocean. The arc–arc "soft" collision provides a plausible mechanism to explain the widespread and rapid accumulation of thick carbonates in collision settings. It also accounts for the presence of magmatic rocks with enhanced mantle contributions on both sides of the north Lhasa subterrane. [ABSTRACT FROM AUTHOR]

• A new Neoproterozoic stratum is determined in North Lhasa terrane. • The stratum is an intercontinental rift sedimentation (∼875 Ma). • Detrital zircons of the stratum exhibit both Australian and Indian characteristics. • North Lhasa originated from Western Australia. • North Lhasa experienced the Precambrian evolution of "rift–drift–emplacement". Constraining the origin and Paleogeographic positions of ancient continental fragments plays a crucial role in reconstructing and validating supercontinent cycles. The Lhasa terrane in southern Tibet is the key to revealing the early formation and evolution of the Himalayan–Tibetan orogen. Although previous origin models of the Lhasa terrane are supported by Phanerozoic evidence, Precambrian geological records have not been comprehensively considered. The U–Pb age and Hf isotope data on detrital zircons from newly discovered Precambrian basement in the North Lhasa terrane define two distinctive age populations of ca. 1170 Ma with ε Hf (t) values identical to the coeval detrital zircons from Western Australia, and ca. 950 Ma with a similar ε Hf (t) range to the contemporaneous detrital zircons from South Qiangtang and Tethyan Himalaya terranes. The ca. 1170 Ma detrital zircons were most likely derived from Western Australia, whereas the ca. 950 Ma detrital zircons might have been sourced from the norther Indian margin. Compiled detrital zircon data shows that in the early Neoproterozoic, the affinity between northern Lhasa and Western Australia decreased, while the predilection between northern Lhasa and northern India increased. Combined with ca. 930–870 Ma rift, ca. 870–700 Ma arc igneous rocks and ∼650 Ma high-pressure granulites, we propose that the North Lhasa terrane was a ribbon continent that rifted from Western Australia in the early Neoproterozoic (ca. 930–870 Ma), drifted westward along the northern edge of Rodinia in the middle Neoproterozoic (ca. 870–700 Ma), and was emplaced in the Northern East African Orogen during the late Neoproterozoic (∼650 Ma). [ABSTRACT FROM AUTHOR]

To determine the Late Palaeozoic evolution of the Lhasa terrane, we report the results of field mapping, petrological and fossil investigations, and U–Pb dating of detrital zircon grains (n = 474) from lower-greenschist-facies clastic rocks of the Lagar Formation in the Baruo area, Tibet. Our results indicate that the Lagar Formation was deposited during the Late Carboniferous to Early Permian in a shallow-marine environment on the northern margin of Gondwana. Glacial marine diamictites are common within the Lagar Formation and record glaciation of Gondwana during the Late Palaeozoic. Moreover, the detrital materials of the Lagar formation originated mostly from the collision orogenic belt. The ages of detrital zircon grains from the Lagar Formation make up five main groups with ages of 410–540 Ma, 550–650 Ma, 800–1100 Ma, 1600–1800 Ma, and 2300–2500 Ma, which display three characteristic age peaks at ~1150, 2390 and 2648 Ma. We tentatively suggest that the Lhasa terrane was a shallow-marine basin under the influence of the Gondwanan glaciation during the Late Carboniferous–Early Permian. [ABSTRACT FROM AUTHOR]

The timing and mechanisms of collapse of the middle and western segments of the Lhasa–Qiangtang orogenic belt in central Tibet are poorly constrained. Here, we report whole-rock geochemical, and zircon U–Pb age and Hf-isotopic data for the Asa-intrusive rocks located at the southern edge of the northern Lhasa subterrane. The Asa-intrusive rocks include the Namujeler granite porphyry (NGP), the Gernicamdro granodiorite porphyry (GGDP), and the Neeze granodiorite porphyry (NGDP). The NGP and GGDP have adakitic geochemical characteristics, such as high Sr (317–511 ppm), Sr/Y (57.8–96.8), and (La/Yb)N (13.1–16.0), and low Y (4.68–5.49 ppm) and heavy rare-earth element contents (e.g., 0.44 ≤ Yb ≤ 0.57 ppm). In situ zircon U–Pb dating of three samples yielded Late Cretaceous ages (NGP = 88.7 Ma; GGDP = 89.7 Ma; NGDP = 90.1 Ma). Zircon εHf(t) values vary over a wide range (NGP = − 11.5 to + 9.3; GGDP = + 4.6 to + 7.6; NGDP = − 21.2 to + 7.6). Our results suggest that the Asa adakitic rocks (NGP and GGDP) are most likely generated by partial melting of thickened mafic lower crust under a garnet-bearing amphibolite facies. The presence of the Asa adakitic rocks indicates that the crust beneath the Lhasa–Qiangtang collision zone had experienced thickening and the crustal thickness remains quite large (> 40 km) at ca.90 Ma. On the basis of evidence from the Asa-intrusive suite and coeval igneous rocks, along with some stratigraphic and tectonic constraints, we proposed that the middle and western segments of the Lhasa–Qiangtang orogenic belt was collapsed by lithospheric delamination during the early Late Cretaceous (ca. 94–82 Ma), and the thickened lithospheric keel did not delaminate as a wholly, it delaminated piece by piece. From east to west, the time of the lithospheric delamination is getting younger. [ABSTRACT FROM AUTHOR]

• A New Precambrian basement has been identified in Asa region, southern Tibet. • The emplacement age of gabbro intrusions in this basement is ca. 875 Ma. • These gabbro intrusions were formed in an intercontinental rift environment. • The North Lhasa terrane may originate from Australia. Due to the less exposure of Precambrian basement, the origin of ancient continental blocks in the Tibetan plateau and their paleogeographic locations in the Rodinia supercontinent remain enigmatic. Here we first report the newly identified Precambrian basement from the Asa region of the North Lhasa terrane (NL), southern Tibet. The zircon U–Pb age and whole-rock geochemical data on gabbro intrusions (known as Tugu gabbros) in this basement reveal an important tectonic evolution process of continental-oceanic transition experienced by the North Lhasa terrane in the early Neoproterozoic (ca. 900–875 Ma), which may be the prelude to the disintegration of Rodinia in China. Tugu gabbros (ca. 876–874 Ma) belong to the series of sub-alkaline tholeiitic basalt and have N-MORB geochemical affinities. In combination, the high (87Sr/86Sr) i ratios (0.709–0.711), positive ε Nd (t) values (2.8–3.9) and the relatively young Nd isotopic pattern age (t DM C = 1.2–1.3 Ga) indicate that it came from a depleted mantle source and were formed in an intercontinental rift environment on the northern margin of Rodinia. According to previous studies and data provided herein, the era and nature of Precambrian magmatic-metamorphic records in North and South Lhasa terranes cannot be compared, suggesting these may have been two separate terranes in the Precambrian. We propose that the South Lhasa terrane (SL) originated from India, while the North Lhasa terrane may originate from Australia. After splitting from Australia at ca. 930–875 Ma, the North Lhasa terrane continued to drift westward owing to the break-up of Rodinia. During the process of drifting, the North Lhasa terrane received sedimentary input from India and developed Andean-type arc magmatism with the influence of oceanic subduction on the northwest margin of supercontinent. [ABSTRACT FROM AUTHOR]

As a part of the Bangong-Nujiang suture, the Shiquanhe-Namco ophiolite mélange belt (SNM), together with the Bangong-Nujiang ophiolite mélange belt (BNM), records the evolutionary history of the Mesotethys. In terms of the closure of the Mesotethys, previous sedimentological research has focused on the BNM, while the SNM remains insufficient. On the basis of detrital zircon dating and sedimentologic data, in this study, we determined the existence of Aptian deep-marine turbidites in the Zhongcang and Lhakorco areas of the SNM. Sandstone petrographic and detrital zircon analysis combine to show that the Zhongcang turbidites provide records of the recycled from the accretionary complex and Triassic-Jurassic strata in the southern Qiangtang margin, with the minor addition of Qiangtang magmatic arc rocks, while sediments in the Lhakorco turbidites were derived mainly from recycled orogen source and Late Jurassic-Early Cretaceous magmatic arc in the Lhasa Terrane. Further analysis suggests that the Aptian turbidites were deposited in a deep-marine oceanic basin of Mesotethys and this oceanic basin prevented Qiangtang-derived sediments transported onto the Lhasa terrane. The Mesotethys experienced diachronic closure from east to west during the Early Cretaceous, and the final closure was most likely completed along the SNM after Aptian. • Discovery of the Aptian deep-marine fan turbidities in SNM • Featuring the Aptian Qiangtang and Lhasa source separation along SNM • Implications for diachronous closure of the Mesotethys [ABSTRACT FROM AUTHOR]

Intra-oceanic subduction is a fundamental process on Earth, the study of which can improve understanding of plate tectonic processes and the history of continental growth. Several studies of the intra-oceanic subduction of the Meso-Tethys Ocean have been published in recent years, particularly relating to the Bangong–Nujiang suture zone (BNSZ) and the Shiquanhe–Nam Tso mélange zone (SNMZ) in central Tibet. Here, we report newly discovered occurrences of Jurassic diorite (161.2–160.6 Ma) and plagiogranite (161.0 Ma) from the western part of the central SNMZ. The diorite samples have moderate SiO 2 and high MgO contents and Mg# values; high Ba/Th and Ba/La ratios; low K 2 O, TiO 2 , and REE contents; low (La/Yb) N , (La/Sm) N , and Th/Yb ratios; and positive ε Hf (t) values, similar to high-Mg diorite formed by partial melting of a subduction-modified mantle wedge. The plagiogranite intrudes gabbro of the ophiolite suite and has high SiO 2 and Na 2 O contents; low Al 2 O 3 , K 2 O, P 2 O 5 , TiO 2 , and total REE contents; and clear negative Eu anomalies, similar to shear-related oceanic plagiogranite, which can be formed by partial melting process of gabbro in the high temperature shear zone near the expansion center. The formation processes of Asa high-Mg diorite and shear-related plagiogranite are consistent with initial subduction within the Meso-Tethys ocean. Based on these data and those for sedimentary and Jurassic magmatic rocks of the region, we propose that, during subduction, the Northern Lhasa terrane was formed from a collage of oceanic island arcs, oceanic plateaus, and accretionary complexes. • Intermediate-acid magmatism in the SNMZ, central Tibet. • High-Mg diorites and shear-type plagiogranite with Late Jurassic ages (161–160 Ma). • The Jurassic intra-Meso-Tethys oceanic subduction event (165–160 Ma). • The generation of the Northern Lhasa terrane by accretion of intra-oceanic arcs. [ABSTRACT FROM AUTHOR]