Spatial distribution of mercury in geothermal springs and its correlation with tectonic setting in the Bayan Har block of Tibetan Plateau, China

• Mercury concentrations in geothermal springs across the Bayan Har block showed significant higher levels along block boundary fault compared to intra-block region. • Deep fluids were likely the primary source of Hg in geothermal springs. • The regional tectonic regime plays a crucial role in controlling the migration and enrichment of Hg in geothermal system . Mercury (Hg) serves as a pivotal tracer in geothermal systems, elucidating both deep lithospheric processes and surficial environmental dynamics. Constraining the sources and distribution of Hg in hot springs as well as its behavior is essential for unraveling subsurface fluid-rock interactions and assessing potential environmental risks. However, the distribution patterns of Hg in geothermal systems, particularly in tectonically active regions, remain poorly understood. This research investigated the distribution of thermal Hg across the Baryan Har block within the Tibet Plateau, a region featured by intense tectonic activity. Through integrated geochemical analysis of 58 springs, we revealed spatial variations in dissolved Hg concentrations (0.51∼50.66 ng/L, with an exceptionally high value of 1100.5 ng/L), exhibiting relatively higher Hg enrichment in the springs along active fault boundaries (44.35±186.99 ng/L) than that in intra-block region (4.16±4.69 ng/L). Geochemical data suggested that non-geological factors (including atmospheric precipitation and anthropogenic activity) and water-rock interactions involving Hg-bearing minerals were not the primary factors influencing the observed Hg distribution. The positive correlation between Hg and chloride concentrations in springs near block boundary fault indicated that deep fluids might be a significant source of Hg. Additionally, the spatial correlation between Hg concentrations, shear strain rates, and heat flow further confirmed the impacts of tectonic regime on the migration and enrichment of Hg. This research underscores the significance of tectonic activity on governing Hg distribution in geothermal systems, providing a better understanding for the geochemical behaviors of Hg in tectonically active regions and its potential environmental implications.