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1. chinaXiv:202106.00106 [pdf]

A fragment of Argoland from East Gondwana in the NE Himalaya

Ji’en Zhang; Wenjiao Xiao; John Wakabayashi; Brian F Windley; Chunming Han
Subjects: Geosciences >> Geology

Previous studies have concluded that a Trans-Tethyan oceanic subduction zone existed prior collision of India-Eurasian plates, between which the ocean lacked intervening continental slivers. In contrast, we present first geological evidence of Early Cretaceous shortening and Late Jurassic alkali magmatism constraining that the Longzi block, an extensive (>450 km E-W by ca. 130 km N-S) tract of the NE Himalaya is such a continental sliver. The Longzi block records overturned south-vergent folds in Triassic to Lower Cretaceous strata intruded by 136-123 Ma mafic, dioritic, and dacite dikes, constraining Early Cretaceous shortening. The shortening demonstrates the NE Himalayan locating in a compressional setting, rather than an extensional Indian passive continental margin at that time. Triassic strata of NW Australian affinity and Late Jurassic rocks sourced from north India record pre-rifting history. Rifting evidence includes 152.8 Ma alkali intrusive rocks, a Late Jurassic unconformity, and rapid changes in sediment thickness and apparent water depth of deposition recorded in Upper Jurassic strata. The rifting event is coeval with 152-155 Ma oceanic crust in the NE Indian Ocean and a Late Jurassic submarine escarpment with 1200 m of sediments offshore of NW Australia. These data may reflect rifting of the westernmost Argoland continent in NE Himalaya from East Gondwana, followed by collision with a N-dipping Trans-Tethyan intra-oceanic subduction zone in the Early Cretaceous, long before terminal continent-continent collision. The Mesozoic rifting-collision in the Himalayan region unambiguously presents archipelagic paleogeography in eastern Neotethyan, which underwent Cenozoic two-stage Indian-Eurasian collisional processes.

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