Polarity and Timing of the Deformation Along the Jinsha Suture Zone (Yushu Area, Northeastern Tibet) Special Section: Advances in tectonic evolution and geodynamics of the Central Asian Orogenic Belt

1. Introduction“Pre-collisional” tectonics of Tibet, defined as the tectonics preceding the collision of India with Asia in theearly Cenozoic, are increasingly regarded as a major component of the buildup of the present Tibetan plateau(Kapp & DeCelles, 2019; Murphy et al., 1997). From the Paleozoic to the Mesozoic, the continental terranescomposing Tibet, that is, the North-Qiangtang, South-Qiangtang, and Lhasa terranes (Figure 1a), together withother micro-continents such as the Tarim, Qaidam, North and South China, Yidun, Sibumasu, and Indochinablocks, drifted from Gondwana and were accreted together to form the southern margin of Asia (B. Huanget al., 2018). The oceanic basins (Proto-Tethys, Paleo-Tethys, and Meso-Tethys) separating the main blocks wereprogressively subducted (Figure 1b). Each of these subductions and suture accretions represented major tectonicevents at the Asian scale (Jolivet, 2017; Metcalfe, 2021). Among them, the closure of the Paleo-Tethys ocean,which resulted in the amalgamation of the Qiangtang terranes and the formation of the huge Songpan-Ganzeaccretionary wedge, has received much attention in the past two decades highlighting various reactivations (e.g.,Kapp et al., 2000, 2003; Pullen et al., 2008; Roger et al., 2000, 2003, 2008).Abstract The Tibetan Plateau was formed by intense Cenozoic shortening (up to 1,100 km) of a composite“proto-Tibet,” itself the product of a long Paleozoic and Mesozoic history of accretion of Gondwana-derivedcontinental fragments and volcanic arcs against the Asian continental margin. The difficult access and thescarcity of outcrops have long limited the possibilities of studying these Mesozoic suture zones in the heartof the Plateau. In this work, we present new U-Pb and 40Ar/ 39Ar ages from the highly deformed units of theYushu mélange, along the Jinsha Suture in the northeastern Qiangtang terrane. Early Triassic (c. 253 Ma) toMiddle Jurassic ages (c. 165 Ma) complement the existing data set and help to refine the chronology of thePaleo-Tethyan oceanic subductions which have structured the northeastern part of the Qiangtang terrane. TheYushu mélange records at least three successive tectono-magmatic events. The opening of a back-arc basinduring the northward Paleo-Tethyan subduction along the Longmu Co-Shuanghu Suture during Early to MiddleTriassic; then its closure during the southward subduction of the Songpan-Ganze Ocean along the Jinsha Suturein Late Triassic. Finally, a shortening phase relat