Big difference in 87Sr/86Sr ratios of basalt and basin water: higher 87Sr/86Sr ratios in plagioclase

摘要

We analyzed the 87Sr/86Sr ratios of basaltic rocks and basin water in Xuyi,China,and found a big difference,which may challenge conventional wisdom on the contribution of basalt weathering in end-member analysis.Results of an in-house weathering experiment suggest that rainwater and dust are not responsible for the difference.By isolating the major minerals in basalt,we found that plagioclase has much higher 87Sr/86Sr ratios than bulk basalt and basin water,which might explain the difference in 87Sr/86Sr ratios of basalt and basin water.We infer that low-temperature hydrothermal alteration increased the 87Sr/86Sr ratios of plagioclase.Future analyses of end-member contribution in a mixed-rock basin should take into account that basin water and plagioclase have higher 87Sr/86Sr ratios than basaltic rocks.