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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

Fe-Ti 氧化物监测玄武岩和辉长岩的井下岩浆-变质演化：IODP 1256D 站点超快展布地壳的完整剖面

基本信息

批准号：
28854569
负责人：
Professor Dr. Francois Holtz, Ph.D.
金额：
--
依托单位：
Institut für Mineralogie
依托单位国家：
德国
项目类别：
Infrastructure Priority Programmes
财政年份：
2006
资助国家：
德国
起止时间：
2005-12-31 至 2011-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/28854569?language=en
关键词：
down hole magmatic metamorphic evolution

项目摘要

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.

IODP多次巡航任务超快速扩张地壳成功地将上洋地壳的完整剖面钻入下伏辉长岩（1256D地点；东赤道太平洋；15 Ma地壳形成于东太平洋隆起）。通过快速扩张的上洋地壳，这些岩石代表了第一个参考剖面，揭示了岩浆和变质作用之间复杂的相互作用：原生结晶；低温、高温蚀变；接触变质;部分熔融/同化;岩浆混合。整个剖面的岩石学记录表明，这些过程都涉及到铁钛氧化物的形成或与之反应，因此可以作为监测快速扩张海洋地壳岩浆变质演化不同阶段的合适指标。因此，我们计划对1256D地壳剖面的Fe-Ti氧化物进行详细的微量分析研究。为了评价铁钛氧化物热氧计的温度-氧逸度历史，应将电子探针数据应用于改进的铁钛氧化物热氧计。铁同位素的原位分析有助于我们了解热液循环与原生岩浆作用之间的相互作用。为了限制岩浆房和轴向高温热液系统之间导电边界层的条件，计划以富铁富钛辉长岩为起始材料进行实验研究，以确定结晶过程中普遍存在的温度、氧化还原条件和挥发性活动。这种演化的成分被解释为岩浆和热液系统过渡时期的关键岩性。