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When the modern-like geomorphology and climate pattern of the Himalaya-Tibetan Plateau were established still remains unclear. In this study, we apply paired stable isotope compositions of carbonate (d18Oc) and leaf waxderived n-alkanes (d2Halk) from the upper Gazhacun Formation in the Namling Basin to reconstruct the middle Miocene elevation and climate of southern Tibet. Depositional age of the upper Gazhacun Formation has been precisely constrained to between 15.5 Ma and 15.1 Ma by zircon U-Pb ages of dacite interlayers. Paired carbonate derived d18Ow values (-17.9 ± 1.3‰ to -18.3 ± 1.3‰) and leaf-wax derived d2Hw values (-131.5 ± 20‰ to -145.7 ± 20‰) plot on or very close to the global meteoric water line suggesting that these samples experienced little evaporation enrichment and isotopic alternation. Based on these two independent proxies, paleoelevation estimates for the Namling Basin are consistently between 4.6+0.7/-0.8 km and 5.2+0.7/-0.8 km, supporting a high elevation for southern Tibet in the mid-Miocene. Integrated with published paleoelevation estimates for the Himalaya, central and northern Tibet in literature, a near-present elevation across the whole Himalaya-Tibetan Plateau has already been established since the middle Miocene (ca. 15 Ma). Besides, stable isotopic values across the Himalaya-Tibetan Plateau show that the d2Hw values gradually increase northward from the Himalaya to northeastern Tibet, quite similar to that of the present day. This pattern suggests that during the middle Miocene, the Himalaya-Gangdese system may have blocked southerly monsoonal moisture from reaching northern Tibet. Westerlies or local recycling of moisture might be the dominant moisture sources across northern Tibet, with enriched d18Ow and d2Hw precipitation values that could lead to erroneous paleoelevation estimates over central and northern Tibet. [ABSTRACT FROM AUTHOR]

The authors comment on a study focusing on the elevation of the India-Asia suture zone during mid-Cenozoic time and the evidence regarding it from Paleosols of Liuqu Conglomerate in China. Topics discussed include the stable isotopes used in the study, the paleoelevation history and geodynamic mechanism of the Himalayan orogen, and the use of plant megafossil leaves and tuffites in Liuqu Conglomerate to analyze geologic history.

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. [ABSTRACT FROM AUTHOR]