Meso–Cenozoic exhumation and preservation of rare metal deposits in the eastern Tibetan Plateau, Southwest China: Insights from fission track thermochronology

Abstract

The eastern part of the Songpan–Garze–Tianshuihai orogenic belt (E-SGTOB) is a significant source of pegmatitic rare metal resources. Serving as a critical stress release zone and tectonic transfer corridor in the eastern Tibetan Plateau, the E-SGTOB has experienced multiple periods of thrust nappe formation, uplift, and exhumation, accompanied by extensive strike-slip and thrust fault development during the Meso–Cenozoic era. These complex geological processes have profoundly influenced the formation, evolution, and spatial distribution of mineral resources in the region. However, research on the exhumation history and preservation conditions of rare metal deposits in this area remains limited. To clarify the impact mechanisms of the tectonic evolution of the Tibetan Plateau on the formation and preservation of rare metal deposits, this study reconstructs the cooling history of the Jiajika and Ke’eryin deposits via apatite fission track (AFT) dating and examines the uplift–exhumation processes of the E-SGTOB. The main research findings are as mentioned. (i) The AFT ages of Jiajika and Ke’eryin samples range from 84.12 Ma to 61.27 Ma and from 23.27 Ma to 9.29 Ma, respectively. (ii) Thermal modeling reveals two notable stages of rapid exhumation in the E-SGTOB during the Meso–Cenozoic era. The first stage, during the Late Cretaceous (ca. 90–60 Ma), involved significant exhumation in the Jiajika area, with an average cooling rate of ∼ 3.3 °C Ma⁻¹. However, AFT data from the Ke’eryin deposit show no evidence of this thermal event, suggesting that Late Cretaceous exhumation was spatially restricted. The second stage, from the Neogene to the present (<25 Ma), was characterized by intense tectonic activity in the eastern Tibetan Plateau due to the far-field effects of the India–Eurasia continental collision. During this period, the pegmatite-type rare metal deposits of the E-SGTOB were extensively exhumed to surface levels. The cooling rate in the Ke’eryin area exceeded 4.6 °C Ma⁻¹, considerably higher than the 2.2 °C Ma⁻¹ observed in the Jiajika area. (iii) The preservation of deposits in the E-SGTOB was jointly constrained by the regional tectonic evolution of the Tibetan Plateau and local tectonic patterns of the eastern Tibetan Plateau. After the completion of the Indosinian orogeny and before the Neogene period (∼25 Ma), the long-term tectonic stability in the Tibetan Plateau created a favorable condition for the preservation of deposits. After the Neogene (25–0 Ma) and during the late Himalayan orogeny, amidst intense tectonic activity, the rare metal deposits located in the regions of weak deformation with a low exhumation rate or in highly hidden geological settings exhibited favorable preservation conditions.