Mesozoic tectonic and topographic evolution of Central Asia and Tibet: a preliminary synthesis

During the Late Palaeozoic–Mesozoic, Central Asia and Tibet were affected by several geodynamic episodes that induced either large-scale compression or widespread extension. The Late Palaeozoic final amalgamation of the Central Asian Orogenic Belt, the accretion of the Cimmerian blocks, the closure of the Mongol–Okhotsk Ocean and the accretion of the Neocimmerian blocks set the structural pattern of the continent. This Mesozoic tectonic heritage plays a first-order role in the localization and evolution of the Tertiary deformation of the continent. Similarly, large-scale Mesozoic topographic features are still preserved in Central Asia, where they form a non-negligible part of the present-day topography. This work aims at providing an overview of the major tectonic events that affected Central Asia and Tibet during the Late Palaeozoic and Mesozoic periods. The general topographic evolution of the continent is also described together with the accompanying climatic changes through time.

Mesozoic-Cenozoic tectonothermal evolution of the eastern part of the Tibetan Plateau (Songpan-Garzê, Longmen Shan area): insights from thermochronological data and simple thermal modelling

We present a synthesis of the tectonic and thermochronological evolution of the Eastern Tibet since the Triassic. The long-term cooling histories obtained on magmatic and metamorphic rocks of the South Songpan-Garzê, Kunlun and Yidun blocks are similar showing a very slow and regular cooling during Late Jurassic and Cretaceous, confirming the suspected lack of major tectonic events between c. 150 and 30 Ma. The exhumation linked to the Tertiary growth of the Tibetan Plateau initiated around 30 Ma and concentrates at the vicinity of the major tectonic structures. Exhumation rates increased again from about 7 Ma in the Longmen Shan.

To interpret this very slow cooling rate between Late Jurassic and Early Cenozoic from granites of this area, we use a simple 1D thermal model that takes into account the thermal properties of both sediments and crust. The results suggest that: (1) high temperature (500 °C) can be kept over a long period of time; (2) during Cretaceous, cooling is mostly controlled by the thermal properties of sediments of continental origin; and (3) the initial Late Triassic rapid cooling rate was caused by the large thermal contrast between the granite body and the sedimentary rocks rather than by a high exhumation rate.