The down-hole magmatic-metamorphic evolution in basalts and gabbros monitored by Fe-Ti oxides: A complete section of Superfast Spreading Crust at IODP Site 1256D

IODP多次巡航使命“超快速扩展地壳”任务成功地将上大洋地壳的一个完整部分钻到下面的辉长岩中（1256 D站点;赤道东太平洋; 15 Ma地壳形成于东太平洋隆起）。恢复的岩石，现在代表了第一个参考剖面通过快速扩张的上洋壳，揭示了岩浆和变质过程之间的复杂相互作用：初级结晶;低温和高温蚀变;接触变质;部分熔融/同化;岩浆混合。整个剖面的岩相学记录表明，所有的过程都涉及到铁钛氧化物的形成或反应，因此，它可以被用作监测快速扩张洋壳的岩浆变质演化的不同阶段的合适的代理。因此，我们计划对1256 D地壳剖面中的铁钛氧化物进行详细的微区分析研究。为了评价温度-氧逸度的历史，应将电子探针数据应用于改进的Fe-Ti氧化物热氧气压计。铁同位素的原位分析将提高我们对热液循环和原始岩浆过程之间相互作用的理解。为了限制岩浆房和轴向高温热液系统之间的导电边界层中的条件，计划使用富含氧化物（富铁钛）辉长岩作为起始材料进行实验研究，以确定结晶过程中的温度、氧化还原条件和挥发性活动。这种演变的组合物被解释为代表一个关键的岩性之间的岩浆和热液系统的过渡。

The IODP multi-cruise mission Superfast Spreading Crust drilled successfully a complete section of the upper oceanic crust into the underlying gabbros (Site 1256D; eastern equatorial Pacific; 15 Ma crust formed at the East Pacific Rise). The recovered rocks, now representing the first reference profile through fast-spreading upper oceanic crust, reveal a complex interaction between magmatic and metamorphic processes: Primary crystallization; low- and high-temperature alteration; contact-metamorphism; partial melting/assimilation; magma mixing. The petrographic record of the whole section reveals that all processes involve the formation of, or the reaction with, Fe-Ti oxides, which can consequently be used as suitable proxies for monitoring the different stages in the magmatic-metamorphic evolution of fast-spreading oceanic crust. Therefore, we plan a detailed microanalytical study on the Fe-Ti oxides in 1256D crustal section. Electron microprobe data should be applied to an improved Fe-Ti oxide thermooxybarometer in order to evaluate the temperature-oxygen fugacity history. In-situ analysis of iron isotopes should improve our understanding of the interplay between hydrothermal circulation and primary magmatic processes. To constrain the conditions prevailing in the conductive boundary layer between the magma chambers and the axial high-temperature hydrothermal systems, an experimental study using very oxide-rich (Fe-Ti-rich) gabbros as starting material is planned to determine temperatures, redox conditions and volatile activities prevailing during crystallization. Such evolved compositions are interpreted as representing a key lithology at the transition between magmatic and hydrothermal systems.