Tectono-Thermal Evolution of Late Mesozoic Extensional Granite Domes in Southern Mongolia and the Sino-Mongolian Border Region: Constraints from Low-Temperature Thermochronology

The South Mongolia–Central Mongolia border region is a significant area for the development of extensional tectonics in Northeast Asia. The formation and thermal evolution of Mesozoic granite domes in this region provide key insights into the mechanisms and dynamics of regional extension. This study combines low-temperature thermochronology techniques, including apatite fission-track dating, zircon (U-Th)/He dating and ⁴⁰Ar-³⁹Ar dating to analyze the tectonothermal evolution of three granite domes (Hannuula, Nartyn, and Altanshiree) across South Mongolia and adjacent areas. The results indicate that the ages of apatite fission-track dating from the ductile shear zones of these domes are (104.9±5.8)Ma, (101.3±5.5) Ma, (110.7±6.2) Ma, and (110.1±7.4) Ma, The zircon (U-Th)/He ages are(123.4±7.4)Ma and (123.7±7.4) Ma; biotite ⁴⁰Ar/³⁹Ar ages are (123.9±0.9) Ma and (121.3±1.4) Ma; and K-feldspar ⁴⁰Ar/³⁹Ar ages are (122.2±1.2) Ma and (122.3±0.8) Ma. Thermal history modeling reveals that all three domes underwent significant uplift during the Late Mesozoic with three distinct uplift phases: ① moderate uplift between 133 and 125 Ma. ② rapid uplift from 125 to 123 Ma, and ③ slow uplift from 123 to 100 Ma. The uplift of the domes is closely linked to regional magmatism and extensional tectonics. Early magmatic intrusions heated the crust, reducing lithospheric strength and inducing dome uplift, while regional extension during the later stages promoted rapid uplift. Furthermore, the uplift events are consistent with other extensional events associated with metamorphic core complexes in Northeast Asia during the Early Cretaceous. Lithospheric extension triggered by the collapse of the Mongol-Okhotsk Ocean and the rollback of the subducted Pacific Plate likely played a key role in driving the uplift of these granite domes.