Meso-Cenozoic building of the northern Central Asian Orogenic Belt: Thermotectonic history of the Tuva region

摘要

The Tuvinian andWest-Sayan mountain ranges form part of the Central Asian Orogenic Belt (CAOB); more specifically, they align along the Altai–Sayan–Hangay zone. Its Precambrian–Paleozoic basement has been subjected to Mesozoic and Cenozoic tectonic reactivation. Two north-south transects across the mountain belts and intervening basins of Tuva were sampled for apatite fission-track (AFT) thermochronology in order to elucidate the thermal history of the Tuvinian basement in relation to the Mesozoic and Cenozoic reactivation of the CAOB. Most AFT ages are Late Cretaceous and range between 55 and 115 Ma. Mean lengths of confined fission tracks are relatively long with most values between 13 and 14 μm. Thermal history modeling shows a rapid Late Jurassic–Cretaceous cooling for the sampled Tuvinian crystalline rocks, related to exhumation of the Paleozoic basement. This exhumation is possibly related to the building and subsequent orogenic collapse of the Mongol–Okhotsk orogen that formed between the Siberian and North China–Mongolian (Sino-Korean or Amurian) continental blocks during the Late Mesozoic. Far-field effects of this orogeny and its collapse, might have affected the Baikal, Altai and Sayan units of the Central Asian Orogenic Belt, including the Tuvinian basement. Also, at the Mesozoic southern Eurasian margin, growth of the Asian continent continued and several collision–accretion events asserted distal tectonic influence into the CAOB. After a Paleogene period of stability, thermal history models for some samples hint at a renewed period of basement cooling during the Neogene. In support of this Neogene event, a single sample from the main West Sayan fault zone contains an apatite populationwith ~2Ma reset AFT ages. This is interpreted in the framework of ongoing building of themodern Central Asian orogens and associated fault movements and exhumation of the basement, presumably related with the ongoing India–Eurasia convergence.