Formation - exhumation history of the Carboniferous Axi epithermal gold deposit in the Chinese Western Tianshan based on zircon U-Pb and pyrite Re - Os geochronology, and (U-Th)/He zircon - apatite thermochronometry

Abstract

The Central Asian Orogenic Belt (CAOB) represents a Late Paleozoic archipelago. Yet the crustal growth, reworking and exhumation of individual microcontinental massifs remain poorly constrained. Here, we utilize the Axi epithermal deposit to examine continental preservation and exhumation of CAOB in the Chinese Western Tianshan. Zircon U-Pb dating and geochemistry demonstrate that the andesitic host rock formed by incremental addition of magma in an Andean-type magmatic arc setting at 362, 354 and 342 Ma. Pyrite Re-Os data and textural evidence reveal two mineralization events at 355 and 332 Ma. Zircon (U-Th)/He data reveal temperatures of ∼180 °C until 317.8 ± 9.8 Ma, which is interpreted to record the timing of exhumation of the andesite and gold orebodies prior to their burial by Carboniferous aged sediments. Further sedimentary concealment continued until the Late Mesozoic, when the system was re-exhumed between 148.6 ± 8.6 and 120.0 ± 13 Ma at a rate of ∼9.8 m/Ma as shown by apatite (U-Th)/He data . Collectively, the geo-/thermochronology demonstrates that the Chinese Western Tianshan records the transition from compressional to extensional tectonism during the Late Paleozoic and the Late Mesozoic. The shallow epithermal mineralization was protected from erosion by post-mineralization deposition. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6640014