Understanding felsic veins in gabbros drilled by IODP at Atlantis Bank (Southwest Indian Ridge): Formation, metamorphism, and their role as multifunctional pathways for fluid and mass transfer

了解 IODP 在亚特兰蒂斯浅滩（西南印度洋中脊）钻探的辉长岩中的长英质脉：形成、变质作用及其作为流体和质量传递多功能途径的作用

• 批准号: 408055224
• 负责人: Professor Dr. Jürgen Koepke
• 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: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/408055224?language=en
• 关键词: Understanding; felsic; veins; gabbros; drilled

Typical lower crust from slow-spreading mid-ocean ridges, covering about one third of our planet, consists of gabbro which is cut by numerous cm- to dm-sized veins of evolved rocks, so-called "felsic veins". Their mode of formation and their role during hydrothermal alteration of the crust is only poorly investigated. An IODP Expedition drilled recently at Site 1473 on top of the Atlantis Bank (Southwest Indian Ridge, SWIR) into the lower crust, encountering ~ 790 m of massive gabbro, cut by nearly 400 felsic veins, comprising ~1.5% of the drill core, varying in composition from diorites to trondhjemites. The rocks from Hole U1473A offer the unique opportunity for a profound and comprehensive investigation of felsic veins cutting gabbros in slow-spread oceanic crust. The proposed project focusses on three main scientific targets:(1) The objective of theme 1 is to test the model of formation of the felsic veins in Hole U1473A. Do they represent the solidification of melts generated as very last step of MORB differentiation, or are they generated by partial melting of gabbros by percolating fluids, or by liquid immiscibility in an evolved MORB system? Our methodological approach to prove this is bulk rock geochemical analysis, geochemical modeling, and by an experimental simulation of partial melting. (2) Theme 2 focuses on the nature of the transition between latest magmatic processes and the first imprint of hydrothermal activity, which has also the potential to trigger magmatic processes. This theme includes the important question, how deep does water penetrate down oceanic detachment faults. This has broader implications also for the rheology of the just accreted "solid" crust. Key for unravelling these poorly investigated issues in the magmatic-to-metamorphic regime during accretion/uplifting of slow-spread oceanic crust lies in the careful investigation of high-temperature amphiboles, and their inherent information on formation temperature, as well as in the accurate estimation of the wet solidus temperature of the specific, often evolved gabbros from Hole U1473A.(3) Basis of theme 3 is the observation that the felsic veins are much more altered than the host gabbros and that the metamorphic assemblages in the felsic veins suggest varying metamorphic conditions from high temperatures (higher amphibolite facies) down to low temperatures (sub-greenschist facies).These observations raise the questions: what is the role of the felsic veins in the metamorphic development during the hydrothermal cooling of the crust and which are the amounts of fluids and masses transferred along these veins? Key approaches for this topic are the careful analysis of fluid bearing minerals (amphiboles, apatite), accurate temperature estimations by geothermometry in combination with the analysis of the local metamorphic equilibria, estimating the flux of seawater-derived fluids by Sr and oxygen isotope analysis, and thermodynamic computations.

典型的下地壳来自慢慢的中山脊，覆盖了我们星球的大约三分之一，由Gabbro组成，Gabbro由许多CM至DM大小的进化岩石静脉切割，所谓的“羊绒脉”。他们的形成方式及其在地壳的热液改变过程中的作用只有很少研究。最近在Atlantis Bank（Southwest Indian Ridge，Swir）顶部的1473号现场钻探的IODP探险中，遇到了约790 m的巨大Gabbro，切成了近400张毛绒静脉，其中包括约1.5％的钻头核心，从Diorites到Trondhjemites的组合物中有差异。孔U1473A的岩石为对慢速海洋外壳中的gabbros割断gabbros的深刻而全面的研究提供了独特的机会。拟议的项目重点介绍了三个主要科学目标：（1）主题1的目的是测试孔U1473a中长毛静脉形成的模型。它们是否代表了MOLTS产生的熔化，作为MORB分化的最后一步，还是通过渗透流体或通过进化的MORB系统中的液体不混溶而产生的Gabbros产生？我们证明这是大量岩石地球化学分析，地球化学建模以及通过部分熔化的实验模拟的方法学方法。 （2）主题2的重点是最新岩浆过程与水热活动的第一个烙印之间的过渡性质，这也有可能触发岩浆过程。这个主题包括一个重要的问题，水如何深入海洋脱离断层。这也对公正的“固体”地壳的流变性具有更大的影响。在积聚/升高过程中，在岩浆到超态性方面进行这些不当调查的问题的关键在于仔细研究高温片剂的固有信息，以及它们对地层温度的固有信息，以及它们对特定的iSPRETIOS的精确估计，通常从特定的固体温度估算，通常是从u1的特定固体温度估算的（3）。 that the felsic veins are much more altered than the host gabbros and that the metamorphic assemblages in the felsic veins suggest varying metamorphic conditions from high temperatures (higher amphibolite facies) down to low temperatures (sub-greenschist facies).These observations raise the questions: what is the role of the felsic veins in the metamorphic development during the hydrothermal cooling of the地壳，沿这些静脉传递的流体和质量的数量是什么？该主题的关键方法是对流体轴承矿物质（过木，磷灰石）的仔细分析，通过地热学通过地热测定法的准确温度估计，并结合对局部变质平衡的分析，估计了SR和氧气分析和热动力学计算的海水衍生流体的通量。