A Stable Isotopic Study Of Seawater Interaction With The Lower Ocean Crust, ODP Hole 735B

科学摘要：根据该奖项，PIs提议研究亚特兰蒂斯滩ODP站点735B最深处一公里岩芯样品中的氧和氢同位素，这是现有最深的海底辉长岩穿透。pi还将分析脉状矿物和整个岩石中的锶同位素，以补充稳定同位素测量。这些分析的目的是确定大块辉长岩剖面是否在18O年枯竭，就像热液活动缓冲海水d18O的模型所预测的那样，或者大块辉长岩是否在18O年富集，就像在一些推断的缓慢扩张的蛇绿岩中那样。最后一种可能性是，海水相互作用的信号随着地壳深度的增加而减弱，正如在Troodos蛇绿岩中观察到的那样，pi将试图验证这种特殊的假设。大块d18O值将对735b类物质俯冲后的地幔效应产生影响。第二个重要目标是确定海水在多大程度上参与了735B辉长岩的高温变形带，以及晚期岩浆流体（富氧化物和/或富硅）是否也参与了变形。此外，pi将评估脆性断层作为流体主要管道的程度。这部分研究对流体进入深海地壳的途径具有重要意义。研究的最终目的是测量岩心下部1 km处次生矿脉和长英质矿脉的d18O、D/H和锶同位素值。这一点很重要，因为这些脉体影响了剖面的整体组成，也因为脉体记录了下地壳与循环海水和晚期岩浆流体之间的相互作用。

Science Summary: Under this award, the PIs propose to study oxygen and hydrogen isotopes in samples from the deepest one km. of core from ODP site 735B on Atlantis Bank, the deepest penetration of seafloor gabbros in existence. The PIs will also analyze strontium isotopes in vein minerals and whole rocks to complement the stable isotope measurements. The purpose of these analyses is to determine whether the bulk gabbro section is depleted in 18O, as expected in models in which seawater d18O is buffered by hydrothermal activity, or whether instead the bulk gabbro is enriched in 18O as it is in some inferred slow-spreading ophiolites. A final possibility is that the signal of seawater interaction diminishes with depth in the crust as observed in the Troodos ophiolite and it is this particular hypothesis that the PIs will try to test. The bulk d18O values will have implications for mantle effects after subduction of 735B-like materials. A second important objective is to determine to what extent seawater was involved in high temperature deformation zones in the 735B gabbros, and whether late stage magmatic fluids (oxide-rich and/or silica-rich) were also involved in the deformation. In addition, the PIs will evaluate the extent to which brittle faults served as major conduits for fluids. This part of the study has important implications for fluid pathways into the deep ocean crust. A final objective of the study is to measure the d18O, D/H, and strontium isotope values of secondary mineral veins and felsic veins in the lower one km of the core. This is important because these veins affect the bulk composition of the section, and also because the veins document the interaction between the lower crust and circulating seawater and late magmatic fluids.