Thermal Alteration History of the Fenghuoshan Group, Hoh Xil Basin, Northern Tibetan Plateau: Insights From Clumped Isotope Thermometry

The carbonate clumped isotope (Delta(47)) thermometer has been widely used for paleoclimatic and paleo-elevation reconstructions in sedimentary basins. Its reliable use requires that carbonates are free from later diagenetic alteration and retain their depositional Delta(47) compositions, which is not always the case during the burial history of a basin. Therefore, identifying the alteration mechanisms that occurred during burial is essential for the correct interpretation of Delta(47) signatures. In this study, we used the Delta(47) thermometer to investigate possible carbonate alteration during burial of the Fenghuoshan Group (FHSG) in the Hoh Xil Basin, northern Tibetan Plateau, China. The Delta(47) temperatures [T(Delta(47))] of 30 carbonate samples through the similar to 4.5 km thickness of the FHSG range from 51 to 132 degrees C and exceed the surface temperature, implying the effects of thermal alteration on FHSG carbonates. The T(Delta(47)) values combined with the water-rock exchange model, indicating that the alteration occurred under closed burial conditions at low water:rock ratios. The solid-state reordering model fails to predict the Delta(47) values, even with a modified time-temperature history. In contrast, most measured Delta(47) values are in agreement with predictions from recrystallization models. Therefore, the proposed alteration scenario is that FHSG carbonates underwent progressive microscale recrystallization during deep burial and subsequent exhumation, during which process recrystallized carbonate equilibrated with ambient burial temperature and therefore modified Delta(47) values. This study highlights the potential of Delta(47) thermometry and related models for evaluating the burial history and diagenesis of carbonates in sedimentary basins.

Automated summary

This study investigated possible carbonate alteration during burial of the Fenghuoshan Group in the northern Tibetan Plateau, China using the Delta(47) thermometer. Results showed that carbonates underwent progressive microscale recrystallization during deep burial, modifying their Delta(47) values. While the solid-state reordering model failed to predict the Delta(47) values accurately, most measured values were in agreement with predictions from recrystallization models.