(Table 2) Chlorine geochemistry and mineralogy of altered oceanic crust samples@en

Bulk chlorine concentrations and chlorine stable isotope compositions were determined for hydrothermally altered basalt (extrusive lavas and sheeted dikes) and gabbro samples (n = 50) from seven DSDP/ODP/IODP drill sites. These altered oceanic crust (AOC) samples span a range of crustal ages, tectonic settings, alteration type, and crustal depth. Bulk chlorine concentrations range from < 0.01 wt.% to 0.09 wt.%. In general, higher chlorine concentrations coincide with an increase in temperature of alteration and amphibole content. d37Cl values of whole rock AOC samples range from -1.4 to +1.8 per mil. High d37Cl values (>=~0.5 per mil) are associated with areas of higher amphibole content. This observation is consistent with theoretical calculations that estimate amphibole should be enriched in 37Cl compared to co-existing fluid. Negative to near zero d37Cl values are found in areas dominated by clay minerals. Chlorine geochemistry is a rough indicator of metamorphic grade and mineralogy. AOC is a major Cl host in the subducting oceanic lithospheric slab. Here we show that bulk chlorine concentrations are ~3 times higher than previous estimates resulting in a greater contribution of Cl to the mantle.我们对取自7个深海钻探计划（Deep Sea Drilling Project, DSDP）/大洋钻探计划（Ocean Drilling Program, ODP）/综合大洋钻探计划（Integrated Ocean Drilling Program, IODP）钻孔站位的热液蚀变玄武岩（喷出熔岩与席状岩墙）及辉长岩样品（共50件）测定了其总氯浓度与氯稳定同位素组成。该批蚀变洋壳（altered oceanic crust, AOC）样品覆盖了不同地壳年龄、构造环境、蚀变类型及地壳深度区间。总氯浓度范围为<0.01 wt.%至0.09 wt.%，总体而言，氯浓度越高，往往对应蚀变温度升高与角闪石含量增加。全岩蚀变洋壳样品的δ³⁷Cl值区间为-1.4至+1.8 ‰，其中高δ³⁷Cl值（≥~0.5 ‰）与角闪石含量较高的区域显著相关，这一观测结果与理论计算结果一致——相较于共存流体，角闪石应富集³⁷Cl。以黏土矿物为主的区域则呈现δ³⁷Cl负值至接近零的数值。氯地球化学可作为变质程度与矿物组成的粗略指示指标，而蚀变洋壳是俯冲洋岩石圈板块中氯的主要赋存载体。本研究表明，总氯浓度约为此前估算值的3倍，这意味着氯对地幔的贡献较以往认知更大。