Meso-Cenozoic Evolution of Mountain Range - Intramontane Basin Systems in the Southern Siberian Altai Mountains by Apatite Fission-Track Thermochronology

Abstract

The Altai Mountains form the northern part of the Cenozoic Central Asian intracontinental orogenic system that developed as a far-field effect of ongoing India-Eurasia convergence. Our study focuses on the southern Siberian Altai Mountains where basement rocks for apatite fission-track (AFT) analysis were sampled. These rocks are mainly Paleozoic granitoids that currently outcrop in several high mountain ranges along reactivated transpressive Paleozoic fault zones. These ranges are in most cases thrust systems adjacent to lacustrine intramontane basins. We present AFT results from the Chuya and Kurai ranges (3 samples) that are thrust over Late Cenozoic sediments of the Chuya-Kurai Basin and from the Shapshal range (4 samples) east of the Dzhulukul Basin. In addition, 5 samples were collected along a transect west of aforementioned study areas in the low-elevation areas of the Siberian Altai or Gorny Altai. Apparent AFT ages were found to be Mesozoic (roughly ranging between 180 and 80 Ma) and AFT length distributions show signs of thermal track fading (mean track lengths vary between 11.3 and 14.1 µm). AFT age and length data were modelled and thermal histories for the different sample sites reconstructed. These yield a two- to three-stage evolution: Late Jurassic-Cretaceous rapid basement cooling, a prolonged period of Late Cretaceous to Paleogene-Neogene stability, and a possible Late Cenozoic cooling to ambient temperatures.