Early Cenozoic Tectonics of the Tibetan Plateau

Geological mapping at a scale of 1:250000 coupled with related researches in recent years reveal well Early Cenozoic paleo‐tectonic evolution of the Tibetan Plateau. Marine deposits and foraminifera assemblages indicate that the Tethys‐Himalaya Ocean and the Southwest Tarim Sea existed in the south and north of the Tibetan Plateau, respectively, in Paleocene‐Eocene. The paleo‐oceanic plate between the Indian continental plate and the Lhasa block had been as wide as 900km at beginning of the Cenozoic Era. Late Paleocene transgressions of the paleo‐sea led to the formation of paleo‐bays in the southern Lhasa block. Northward subduction of the Tethys‐Himalaya Oceanic Plate caused magma emplacement and volcanic eruptions of the Linzizong Group in 64.5–44.3 Ma, which formed the Paleocene‐Eocene Gangdise Magmatic Arc in the north of Yalung‐Zangbu Suture (YZS), accompanied by intensive thrust in the Lhasa, Qiangtang, Hoh Xil and Kunlun blocks. The Paleocene‐Eocene depression of basins reached to a depth of 3500–4800 m along major thrust faults and 680–850 m along the boundary normal faults in central Tibetan Plateau, and the Paleocene‐Eocene depression of the Tarim and Qaidam basins without evident contractions were only as deep as 300–580 m and 600–830 m, respectively, far away from central Tibetan Plateau. Low elevation plains formed in the southern continental margin of the Tethy‐Himalaya Ocean, the central Tibet and the Tarim basin in Paleocene‐Early Eocene. The Tibetan Plateau and Himalaya Mts. mainly uplifted after the Indian‐Eurasian continental collision in Early‐Middle Eocene.