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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]

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]

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]

• 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]

The Eocene palaeogeomorphology and uplift process of the Central Tibetan Plateau including the Lhasa and Qiangtang terranes have been controversial. In this paper, we study Eocene rhyolites in Wuma area of the Northern Lhasa terrane on the Central Tibetan Plateau by zircon U-Pb dating, geochemistry, zircon Lu-Hf isotopes, and Sr-Nd isotopes. The results show that the ages of Wuma rhyolites are 40-39 Ma, and the petrogenesis of them is related to partial melting of lower crust. The La/Yb, Dy/Yb, Sm/Yb and zircon Eu/Eu* of lower-crust-derived intermediate-felsic magmatic rocks can well reflect crustal thickness and Moho depth. Based on statistics of intermediate-felsic magmatic rocks in the Central Tibetan Plateau at 47–37 Ma, we find that lower-crust-derived intermediate-felsic magmatic rocks of the Northern Lhasa terrane have lower La/Yb, Dy/Yb, Sm/Yb and zircon Eu/Eu* than those of the Southern-Central Lhasa and Qiangtang terranes, indicating that Northern Lhasa terrane had thinner crust than Southern-Central Lhasa and Qiangtang terranes during late Eocene. Further, according to Airy isostatic compensation, in which thick crusts correspond to high altitudes and thin crusts correspond to low altitudes, we speculate that the Northern Lhasa terrane had lower altitude, while the Southern-Central Lhasa and Qiangtang terranes had higher altitude during late Eocene; that is, the Central Tibetan Plateau had the late Eocene palaeogeomorphology of two mountains and one basin. In addition, through statistics of intermediate-felsic magmatic rocks in the Northern Lhasa terrane and near its suture zones on both sides since 100 Ma, we find that La/Yb, Dy/Yb and Sm/Yb of these intermediate-felsic magmatic rocks increase at 40-34 Ma, indicating that the crust of the Northern Lhasa terrane have thickened and the surface may have been uplifted during late Eocene. Based on that there are abundant late Eocene lower-crust-derived intermediate-felsic magmatic rocks in the Central Tibetan Plateau and the late Eocene palaeogeomorphology of Central Tibetan Plateau is two mountains and one basin, and other evidences, we speculate that the late Eocene uplift of Northern Lhasa terrane may have been related to lower crustal channel flow. [Display omitted] • The Wuma rhyolites in the Northern Lhasa terrane are Late Eocene (40–39 Ma). • The Wuma rhyolites are derived from partial melting of the lower crust. • Late Eocene topography of Central Tibetan Plateau is two mountains and one basin. • Lower crustal channel flow caused late Eocene uplift of Northern Lhasa terrane. [ABSTRACT FROM AUTHOR]