Fluid inclusion and isotopic constraints for fluid evolution in the Ordovician veins in Central Tarim, NW China

摘要

Barite, anhydrite, fluorite, calcite and quartz are found filling factures in Central Tarim. Modem brines have δ18O values from -1.5 to +1.4‰, and 87Sr/86Sr from 0.71026 to 0.71109. Hydrothermal barite veins show an average δ18O value of 12.0‰ and precipitated at～142°C from a solution with a δ18O of～1.80‰ and a 87 Sr/86Sr of ～0.7090. Subsequently, the solution was cooled by mixing with meteoric water, resulting in a δ18O of- 1.60‰. Anhydrite and fluorite veins have lower homogenization temperatures and show much higher 87Sr/86Sr ratios (0.70912 to 0.71036) than barite and bulk limestone, but are closer in composition to modem brines, suggesting more radiogenic Sr contribution from clastic rocks in the west to the Central Tarim during cooling. Calcite veins were precipitated under a wide temperature range and show variable 87Sr/86Sr ratios.Quartz veins were likely not in oxygen isotopic equilibrium with the mineralizing fluid.