Mesozoic Thermo-Tectonic Evolution of the Western Altai Orogenic Belt (NW China): Insights from Low-Temperature Thermochronology

Abstract

The Meso-Cenozoic tectonic activities of the Central Asian Orogenic Belt (CAOB) played an important role in controlling the present-day topography of Central Asia. The Altai orogenic belt is a key component in the southern CAOB; so far, there is still a lack of sufficient constraints on the time and mechanism of its tectonic reactivation since the Mesozoic. In this contribution, we present new zircon and apatite (U-Th)/He and apatite fission track thermochronological data from granitoid samples in the Habahe area, western Altai orogenic belt. Therein zircon (U-Th)/He ages range from ~230 to ~238 Ma, apatite fission track central ages are ~140–157 Ma, and apatite (U-Th)/He ages vary from ~134 to ~149 Ma. Based on the associated thermal history modeling results, the Habahe area underwent a moderate cooling during the Late Triassic to Middle Jurassic (~230–170 Ma) with a cooling rate of ~0.8–1.1℃/Ma and a subsequent moderate to slightly rapid cooling stage during the Middle Jurassic to Early Cretaceous (170–130 Ma) with a cooling rate of ~1.5–2.3℃/Ma. We propose that this prolonged cooling stage occurred under a long-lasting contractional tectonism in the western Altai throughout the early Mesozoic, which was produced by multiplate convergence in East Asia during this period, mainly including the consumption of the Mongol-Okhotsk Ocean in the northeast and the Meso-Tethys Ocean in the south. The region experienced rather limited Late Cretaceous-Cenozoic cooling and exhumation due to insufficient reactivation and weak surficial erosion.