We reconstruct the rise of a segment of the southern flank of the Himalaya-Tibet orogen, to the south of the Lhasa terrane, using a paleoaltimeter based on paleoenthalpy encoded in fossil leaves from two new assemblages in southern Tibet (Liuqu and Qiabulin) and four previously known floras from the Himalaya foreland basin. U-Pb dating of zircons constrains the Liuqu flora to the latest Paleocene (ca. 56 Ma) and the Qiabulin flora to the earliest Miocene (21-19 Ma). The proto-Himalaya grew slowly against a high (~4 km) proto-Tibetan Plateau from ~1 km in the late Paleocene to ~2.3 km at the beginning of the Miocene, and achieved at least ~5.5 km by ca. 15 Ma. Contrasting precipitation patterns between the Himalaya-Tibet edifice and the Himalaya foreland basin for the past ~56 m.y. show progressive drying across southern Tibet, seemingly linked to the uplift of the Himalaya orogen.

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Mesozoic strata of the Hoh‐Xil‐Songpan‐Ganzi complex in northern Tibet are exposed in a vast (> 370,000 km2) triangle‐shaped orogenic belt bound by the Longmen Shan thrust belt in the east, the Kunlun terrane and North China block in the north, and the Qiangtang terrane and Yidun arc in the south. These strata consist of Middle–Upper Triassic submarine fan and deep marine facies rocks that were deposited in the Paleo‐Tethys Ocean. Late Triassic–Early Jurassic contractional deformation in the eastern Hoh‐Xil‐Songpan‐Ganzi complex marks the demise of the Paleo‐Tethys Ocean basin and the accretion of the Gondwana‐derived Qiangtang terrane to Eurasia. We conducted geological mapping, regional stratigraphic analyses, and U‐Pb geochronology of detrital zircons (n = 4128) on the Mesozoic sequences exposed in the Hoh‐Xil‐Songpan‐Ganzi complex, Kunlun terrane, and Qiangtang terrane. We identify for the first time marine silciclastic sandstone and shale of Jurassic age in the northwestern Hoh‐Xil‐Songpan‐Ganzi complex that unconformably overlie Upper Triassic turbidites. Zircon age data indicate that the Middle–Upper Triassic marine gravity‐flow deposits of the Hoh‐Xil‐Songpan‐Ganzi complex were shed from the North and South China blocks, and Middle–Late Triassic ultrahigh‐pressure Qinling–Dabie orogenic belt, as well as the Kunlun and Qiangtang terranes. In addition, the detrital zircon results suggest vast sediment source to sink distances (>1500 km) for the Middle–Upper Triassic Hoh‐Xil‐Songpan‐Ganzi strata, which is consistent with tectonic models for the Paleo‐Tethys Ocean basin that incorporate significant components of horizontal tectonic transport like opening of large back‐arc basins in response to oceanic slab rollback.