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

科学摘要：根据这一奖项，私人投资机构建议研究最深一公里处样品中的氧和氢同位素。从亚特兰蒂斯岸上的ODP735B站获得的岩心，是现存海底辉长岩最深的穿透。PIS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块状辉长岩段是否像海水d18O被热液活动缓冲的模型中所预期的那样在18O处亏损，或者相反地，块状辉长岩是否像某些推断的缓慢扩张的蛇绿岩中那样，在18O处富含18O。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，正如在特罗多斯蛇绿岩中观察到的那样，而PI将试图验证这一特殊的假设。在735B类物质俯冲后，d18O值将对地幔效应产生影响。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的主要管道的程度。该研究的这一部分对流体进入深海地壳的路径具有重要意义。这项研究的最终目标是测量岩芯下部1公里处次生矿脉和长英脉的d18O、D/H和锶同位素值。这一点很重要，因为这些矿脉影响着剖面的整体成分，也因为这些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.