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

根据该奖项，PI计划研究最深1公里处样品中的氧和氢同位素。这是迄今为止海底辉长岩穿透深度最深的一次。PI还将分析矿脉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，以确定是否散装辉长岩部分耗尽18 O，预期在模型中，海水d18 O缓冲热液活动，或是否相反，散装辉长岩富含18 O，因为它是在一些推断的缓慢蔓延的蛇绿岩。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少，正如在特罗多斯蛇绿岩中观察到的那样，这正是PI将试图测试的特定假设。体d18 O值将有意义的地幔效应后，俯冲的735 B类物质。第二个重要目标是确定海水在多大程度上参与了735 B辉长岩的高温变形区，以及后期岩浆流体（富含氧化物和/或富含二氧化硅）是否也参与了变形。此外，PI将评估脆性断层作为流体主要通道的程度。这部分研究对进入深海地壳的流体通道具有重要意义。研究的最后一个目标是测量d18 O，D/H，和锶同位素值的次生矿脉和长英质脉在较低的1公里的核心。这一点很重要，因为这些矿脉影响了剖面的整体成分，也因为矿脉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.