A Geochemical and Isotopic Study of the Magmatic-Hydrothermal Transition in the Lower Oceanic Crust

下洋壳岩浆-热液转变的地球化学和同位素研究

• 批准号: 9907070
• 负责人: Susan Humphris
• 金额: $ 19.46万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-09-01 至 2002-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9907070&HistoricalAwards=false
• 关键词: Geochemical; Isotopic; Study; Magmatic; Hydrothermal

The thermal structure of ocean crust along the mid-ocean ridge system is controlled by the balance between magmatic heat input from below and hydrothermal heat removal through circulating seawater. However, our knowledge of the magmatic-hydrothermal transition (MHT) is extremely limited. This proposal is aimed at providing a better understanding of mass and heat transport processes across the MHT and their geochemical consequences. We will examine rocks from the lower crust recovered from Ocean Drilling Program (ODP) Hole 735B on the Southwest Indian Ridge. We have preliminary evidence that this 1500 m deep borehole in the lower crust penetrates the MHT, and thereby provides an exciting opportunity to investigate mass transport between magma and hydrothermal fluids. Downhole variations in the mineralogical composition of rocks and fracture-filling veins suggest variable mineralization conditions, ranging from interaction of rocks with seawater-derived fluids shallow in the hole to impregnation of the rock with magmatic fluids exsolved from solidifying magmas in the deeper sections. We will use the chemical and isotopic compositions of minerals, in combination with fluid inclusion work, to distinguish between late-stage magmatic crystallization and mineralization in response to reaction with magmatic fluids and seawater-derived fluids. The distribution of mineralization types in the crust, variations in mineralization temperature and pressure, and observations on the relative timing of mineralization events, will provide us with new insights into the dynamics of the magmatic-hydrothermal transition.

洋中脊系统沿线洋壳的热结构受来自下方的岩浆热量输入和通过循环海水排出的热液热量之间的平衡控制。然而，我们对岩浆热液转变（MHT）的了解极其有限。 该提案旨在更好地了解 MHT 上的质量和热量传输过程及其地球化学后果。 我们将检查从西南印度洋中脊的海洋钻探计划 (ODP) 735B 孔中回收的下地壳岩石。 我们有初步证据表明，下地壳中这个 1500 米深的钻孔穿透了 MHT，从而为研究岩浆和热液之间的质量传输提供了令人兴奋的机会。 井下岩石和裂缝充填矿脉矿物成分的变化表明了不同的成矿条件，从岩石与孔内浅层海水衍生流体的相互作用到岩石被较深部分凝固岩浆排出的岩浆液浸渍。 我们将利用矿物的化学和同位素组成，结合流体包裹体工作，来区分晚期岩浆结晶和矿化，以响应与岩浆流体和海水衍生流体的反应。 地壳中矿化类型的分布、矿化温度和压力的变化以及对矿化事件相对时间的观测将为我们提供对岩浆-热液转变动力学的新见解。