Xuan Yang1,2, Chengsheng Chen2*, Yunpeng Wang2*, Zheng Zhou3
1. State Key Laboratory of Deep Earth Processes and Resources, Guangzhou institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
2. University of Chinese Academy of Sciences, Beijing, 100049, China
3. Lancaster University, Lancashire, LA1 4YW, United Kingdom
Abstract：Noble gas isotopes are robust tracers for tracking subsurface fluid migration and evolution within sedimentary basins due to their inherent chemical inertness. Bounded by the South Tianshan Orogen to the north and the West Kunlun Orogen to the south, the Southwest Tarim Depression comprises two major secondary structural units: the Southwest Sag and the Makit Slope. Previous studies have identified both mantle-derived and crustal signals in the Southwest Tarim Depression (Li et al., 2022), yet the specific fluid mechanisms remain poorly constrained.
The Mazatagh Structural Belt lies at the junction between the southern Bachu Uplift and the Makit Slope, hosting the large Hetian He-rich gas field. Its surface uplift underwent synchronic and equal-amplitude deformation coeval with the West Kunlun Orogen, which may be attributed to crustal basement weakening triggered by residual rigid Permian mantle plume heads at depth (Li et al., 2024a; Li et al., 2024b).
To clarify the genetic linkage between the formation of He-rich gas reservoirs and two phases of tectonic events in this area, and to determine whether mantle-derived fluid signals are preserved within crustal fluid-enriched zones across the Southwest Tarim Depression, a total of 19 natural gas samples were collected from separate blocks along the Mazatagh Thrust Fault Zone, with additional comparative samples acquired from 2 gas wells in the Rastagh Structural Belt. All gas samples were recovered from Ordovician–Carboniferous reservoirs consisting of carbonate rocks interbedded with sandstones. The results of this study are expected to provide direct geochemical constraints on fluid mixing and transport processes and their tectonic controls in the southwestern Tarim Basin.
