Collaborative Research: Magma Dynamics in Sill and Dike Systems - Constraints From Magnetic Fabrics and Paleomagnetism in the Karoo Large Igneous Province

大陆地壳中的岩浆转移是需要解决的一级问题，以了解岩浆系统如何在时间和空间中运作。这在大火成岩省的情况下尤其重要，从地质学上讲，大量岩浆在相对较短的时间内（大约100万年）从源头移动到地球表面。磁组构技术，如磁化率各向异性法，在约束流动几何和运动学方面取得了成功。然而，这种方法的许多方面仍然是模棱两可的。例如，没有令人满意的解释说明磁性片理平行于岩壁的情况，而应该模拟流动方向的磁性线理却垂直于岩壁边界。本研究项目通过结合图像分析、电子背散射衍射、非滞后剩磁各向异性等独立方法，确定矿物结构和岩浆流动参数，解决了这些问题。六个对照实验专门研究了给料和非给料岩脉之间磁性结构的差异，单畴磁铁矿颗粒对磁化率各向异性的可能贡献以及层状形成过程在矿物结构发育中的重要性。实验的自然实验室目标是南非的Karoo大火成岩省，该地区除了可用的连续钻孔岩心外，还具有良好的地图，特殊的暴露。该项目将由南伊利诺伊大学、圣罗斯学院和新墨西哥大学组成的一个美国研究小组与来自罗德大学和地球科学委员会的南非科学家合作开展。该研究将为目前确定岩浆流动方向最常用的磁化率各向异性技术提供理论背景和验证。它将确定磁化率各向异性技术可以和应该使用的界限。这项调查的结果将使更广泛的社区能够将这项技术应用于许多其他地质环境，并对其结果的重要性有更大的信心。虽然该项目侧重于一种岩浆系统（贫硅岩浆），但其结果很可能在富硅系统中有更广泛的应用。这一研究将对火成岩岩石学和火山群落产生重大影响，因为岩浆转移仍然是这些学科的关键问题之一。该项目要求研究生和本科生广泛参与国际研究，并努力扩大代表性不足的群体参与地球科学。美国国家科学基金会国际科学与工程办公室（近东和南亚项目）和美国国家科学基金会地球科学部（构造项目和地球物理项目）支持这项研究。

Magma transfer in the continental crust is a first order problem that needs to be addressed to understand how magmatic systems operate through time and in space. This is particularly important in the case of Large Igneous Provinces in which large volumes of magma have moved from the source to the surface of the Earth in, geologically speaking, relatively short times (approximately 1 million years). Magnetic fabric techniques, such as the Anisotropy of Magnetic Susceptibility method, have been successful in constraining flow geometry and kinematics. However, numerous aspects of this approach are still ambiguous. For example, no satisfactory explanation accounts for cases where the magnetic foliation is parallel to a dike wall and yet the magnetic lineation, which is supposed to mimic the flow direction, is perpendicular to the dike boundary. This research project addresses these issues by combining several independent methods (image analysis, Electron BackScatter Diffraction, Anisotropy of Anhysteretic Remanent Magnetism) to determine the mineral fabric and magma flow parameters. Six controlled experiments specifically investigate differences in magnetic fabrics between feeder and non-feeder dikes, the possible contribution of single domain magnetite grains to Anisotropy of Magnetic Susceptibility and the importance of layering-forming processes in development of mineral fabric. The natural laboratory targeted for the experiments is the Karoo Large Igneous Province in South Africa, a region with well-mapped, exceptional exposures in addition to available continuous borehole cores. The project will be carried out by a U.S. research team from Southern Illinois University, College of Saint Rose, and University of New Mexico in partnership with South African scientists from Rhodes University and the Council for Geoscience.This study will provide the theoretical background and validation for the technique Anisotropy of Magnetic Susceptibility that is currently the most often used to determine magma flow direction. It will define the boundaries within which the Anisotropy of Magnetic Susceptibility technique could and should be used. The results of this investigation will enable the broader community to apply this technique to many other geological settings with greater confidence regarding the significance of its results. Although the project focuses on one type of magmatic system (silica-poor magmas), it is very likely that the results will have broader applications to silica-rich systems. This research will considerably impact the igneous petrology and volcanic community because magma transfer is still one of the key questions in these disciplines. The project involves extensive graduate and undergraduate participation in international research and makes efforts to broaden participation of underrepresented groups in the Earth Sciences. The NSF Office of International Science and Engineering (Near East and South Asia Program) and the NSF Earth Sciences Division (Tectonics Program and Geophysics Program) are supporting this research.