Exhumation of Jiajika lithium deposit in the eastern Tibetan Plateau: Insights from low-temperature thermochronology of the JJK scientific drilling borehole

Abstract

The Jiajika lithium deposit, located on the southeastern Songpan-Ganze orogenic belt in the Tibetan Plateau, is one of China's largest and most significant lithium deposits. Previous studies mainly focused on this deposit's petrography, geochemistry, and geochronology. However, its exhumation, thermal evolution, and implication for ore-deposit preservation remain enigmatic due to the scarcity of low-temperature thermochronology studies. Here, we perform the detailed low-temperature thermochronological methods including Zircon (U-Th)/He, Apatite Fission-Track, and Apatite (U-Th)/He on fifteen successive core samples from our 3000 m Jiajika scientific drilling borehole. Combined with the regional tectonic evolution, we suggest that the Jiajika area underwent three stages of rapid cooling: (1) middle Cretaceous (∼120–88 Ma); (2) Late Eocene (∼43–30 Ma); (3) since Early Miocene (∼18–14 Ma). These rapid cooling episodes are probably associated with the Cretaceous collision between the Lhasa and Qiangtang terranes, the Eocene crustal thickening in the central and north Tibetan Plateau affected by India-Asia collision, and Miocene activity of the Xianshuihe Fault and/or drainage erosion, respectively. Further, assuming a geothermal gradient of 30 ± 2 °C/km, we estimate the exhumation thickness of the Jiajika area up to ca. 3.5 ± 1 km since ∼ 120 Ma, of which the middle Cretaceous exhumation accounts for a major proportion, nearly ∼ 2.7 ± 0.6 km.