Abstract
The uplift history of south-eastern Tibet is crucial to understanding processes driving the tectonic evolution of the Tibetan Plateau and surrounding areas. Underpinning existing palaeoaltimetric studies has been regional mapping based in large part on biostratigraphy that assumes a Neogene modernization of the highly diverse, but threatened, Asian biota. Here, with new radiometric dating and newly collected plant-fossil archives, we quantify the surface height of part of the south-eastern margin of Tibet in the latest Eocene (∼34 Ma) to be ∼3 km and rising, possibly attaining its present elevation (3.9 km) in the early Oligocene. We also find that the Eocene–Oligocene transition in south-eastern Tibet witnessed leaf-size diminution and a floral composition change from sub-tropical/warm temperate to cool temperate, likely reflective of both uplift and secular climate change, and that, by the latest Eocene, floral modernization on Tibet had already taken place, implying modernization was deeply rooted in the Palaeogene.
Highlights
The Tibetan Plateau today has an average elevation of more than 4.5 km spread over an area of ~2.5 million km2 and, together with the adjacent Himalaya and Hengduan mountain systems (Fig. 1), form the Himalaya-Tibet Edifice (HTE), the most prominent orographic feature on Earth
We find that the Eocene-Oligocene transition in southeastern Tibet witnessed leaf size diminution and a floral composition change from sub-tropical/warm temperate to cool temperate, likely reflective of both uplift and secular climate change, and that by the latest Eocene floral modernization on Tibet had already taken place implying modernization was deeply-rooted in the Paleogene
Using Climate Leaf Analysis Multivariate Program (CLAMP) we find that MK3 assemblage yields a mean annual air temperature (MAAT) of 17.8 ± 2.3 °C, with a warm month mean air temperature (WMMAT) of 28.1 ± 2.8 °C and a cold month mean air temperature (CMMAT) of 4.8 ± 3.6 °C (Table 1)
Summary
The Tibetan Plateau today has an average elevation of more than 4.5 km spread over an area of ~2.5 million km and, together with the adjacent Himalaya and Hengduan mountain systems (Fig. 1), form the Himalaya-Tibet Edifice (HTE), the most prominent orographic feature on Earth. The presence of a high PTH in the Paleogene challenges numerous molecular phylogenetic studies that link biotic diversification to a Neogene uplift of the Tibetan Plateau [8,9,10]. This PTH, made up of the Lhasa and Qiangtang terranes (Fig. 1), hosted two major mountain systems. The Lhasa Terrane had a high (~4.5 km) southern flank at 56 Ma in the form of the Andes-like Gangdese Arc highlands [11] that pre-dated the rise of the Himalaya [7] and was separated from the Qiangtang Terrane uplands (the elevation of which is loosely constrained but may have been >4 km [11]) by an East-West trending elongate lowland along the Bangong–Nujiang suture, represented in part today by the Nima and Lunpola Basins. The palaeoelevation histories of the floors of these basins are poorly quantified, but the inferred lowland floor could have persisted below ~3 km until as recently as the early Miocene [12, 13]
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