The late-stage evolution of oceanic gabbros - Combined experimental and in-situ isotope study on gabbros of the ODP Legs 118/176 drilled at the Southwest Indian Ridge

西南印度海岭735B孔（118和176段）的辉长岩是ODP （Ocean Drilling Program）迄今为止钻探的最长的海底下地壳连续剖面。大约25%的岩心受到晚期岩浆作用的强烈影响，导致富铁（辉长铁）和富硅（斜长花岗岩）成分作为端元。为了全面了解深海地壳中正在进行的晚期岩浆过程，我们提出了一种新的方法，通过在SWIR钻探的~ 1500 m长的天然辉长岩的实验和分析研究相结合。在三个实验子项目中，我们试图澄清(1)典型晚期岩浆系统的相关系和相组成，(2)液体不混溶是否是一个重要的晚期岩浆过程，(3)渗透晚期熔体如何影响刚刚凝固的正常辉长岩。在我们的实验中，将特别注意氧逸度和水活度，因为这些挥发物被认为在岩浆晚期活动中起主导作用。由于最近讨论了岩浆晚期过程是否也可能是深海地壳在高温下热液循环的结果，我们试图对735B辉长岩的晚期阶段进行原位Sr同位素分析，以澄清这些流体的性质，即它们是岩浆还是海水影响的。

Gabbroic rocks from Hole 735B at the Southwest Indian Ridge (SWIR; Legs 118 and 176), represent the longest continuous section of in-situ oceanic lower crust ever drilled by ODP (Ocean Drilling Program). About 25% of the core is strongly influenced by late-stage magmatic processes leading to Ferich (ferrogabbros) and Si-rich (plagiogranites) compositions as endmembers. For a comprehensive understanding of the late magmatic processes ongoing in the deep oceanic crust, we present here a new approach, by combining experimental and analytical investigations in natural gabbros from the ~ 1500 m long section drilled at SWIR. In three experimental subprojects we attempt to clarify (1) the phase relations and phase compositions in a typical late-magmatic system, (2) whether liquid immiscibility is an important late-magmatic process, and (3) how percolating late-stage melts influence the just solidified normal gabbro. Particular attention will be given to the oxygen fugacity and the water activity in our experiments, since these volatiles are regarded to play a dominant role during the late-magmatic activity. Since it has been recently discussed whether magmatic late-stage processes can also be the result of hydrothermal circulation in the deep oceanic crust at very high temperatures, we attempt to perform in-situ Sr isotope analyses of late-stage phases in the 735B gabbros for clarifying the nature of these fluids, i.e., whether they are magmatic or seawater-influenced.