Geochemical characteristics, formation age, and mechanism of the cold volcano at Muji travertine, Xinjiang

This study presents the first systematic investigation of the rock geochemistry, hydrogeochemistry, geochronology, and formation mechanisms of the calcareous travertine-type cold volcano at Muji, Xinjiang. The Muji cold volcano is composed predominantly of travertine, which exhibited light rare earth element enrichment relative to heavy rare earth elements. The δ13C values range from 7.1‰ to 11.1‰, while δ18O values span from −12.3‰ to −7.8‰, classifying it as hypogean travertine. CO2 primarily originates from carbonate rock decarbonation, with a portion derived from the mantle. Water samples collected from the crater show HCO3-Ca and HCO3-Ca·Mg hydrochemistry types. U-Th dating of calcite indicates the Muji cold volcano formed between approximately 6.3 and 2.7 ka BP. The morphology and distribution pattern of the cold volcanoes are primarily controlled by hydrostatic pressure and the southwest boundary fault of the Muji Basin. Hydrostatic pressure of groundwater determines the growth height of the cones. The bead-like distribution orientation of the volcanic cones and the major axis direction of the elliptical contour lines of the cones align with the strike of the southwest boundary fault of the Muji Basin, indicating significant control by this fault.