The Dynamics of Mantle-melt Extraction Systems: A Field and Theoretical Approach

该奖项由2009年美国复苏和再投资法案（公法111-5）资助。该项目由地球科学部的岩石学地球化学和构造学项目共同支持，并由国际科学与工程办公室（非洲，近东和南亚项目）赞助。这一研究举措旨在研究在摩洛哥壮观的超镁铁岩-贝尼布塞拉超镁铁岩-的起源中，聚焦熔体渗滤的作用，该超镁铁岩的起源深度超过150公里。超镁铁岩体侵入低密度大陆地壳的构造背景，横跨大陆盾，裂谷系统，碰撞造山带，岩浆弧的大量的各种各样的记录。这些天体是有趣的和地球动力学上的重要，因为它们的密度比它们的寄主岩石高300-500 kg/m3。了解它们的就位机制是了解它们起源的关键。详细的现场观察和地球化学数据的贝尼Boussera超镁铁质岩已被用来推断，这些机构中的一些公里规模的熔体渗透功能，将是本项目的重点。最近提出了一种新的侵位机制，即上地幔中的聚焦流产生重力不稳定性，导致高密度地幔岩侵位到低密度地壳序列中。该模型预测：a）许多下地壳超镁铁岩体是到达上地幔的千米级熔体通道; B）上地幔内部的受限熔体渗流触发了整个熔体提取系统的显著垂直运动，影响了局部地幔对流模式。研究计划将把联合收割机广泛的实地测绘与详细的结构和组构分析、岩石学、地球化学以及同位素指纹分析结合起来。它还将结合地质约束的传质模型，以提供熔体渗流区的动态的见解。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This project is co-supported by the Petrology & Geochemistry and Tectonics programs of the Division of Earth Sciences, and sponsored also by the Office of International Science and Engineering (Africa, Near East, And South Asia Program). This research initiative is designed to study the role of focused melt percolation in the origin of a spectacular ultramafic massif in Morocco, the Beni Boussera ultramafite, that records a depth of origin in excess of 150 km. Intrusions of ultramafic bodies into the lower density continental crust have been documented for a large variety of tectonic settings spanning continental shields, rift systems, collisional orogens, and magmatic arcs. These bodies are intriguing and geodynamically significant because they are denser by 300-500 kg/m3 than their host rocks. Understanding their emplacement mechanism is key to their origin. Detailed field observations and geochemical data of the Beni Boussera ultramafic massif have been used to infer that some of these bodies are composed of km-scale melt percolation features that will be the focus of this project. A new emplacement mechanism has been recently proposed whereby focused flow in the upper mantle produces gravitational instabilities resulting in the emplacement of high-density mantle rocks into low-density crustal sequences. This model predicts that a) many lower crustal ultramafic bodies are km-scale melt channels that reach into the upper mantle and b) confined melt percolation within the upper mantle triggers significant vertical movement of the entire melt extraction systems, influencing local mantle convection patterns. The research plan will combine extensive field mapping with detailed structural and fabric analyses, petrology, geochemistry as well as isotopic fingerprinting. It will also be combined with geologically constrained mass transfer modeling to provide insights on the dynamics of melt percolation zones.