Structure and petrophysics of oceanic Crust and Lithosphere, Atlantis Massif. Study of cores from IODP Expedition 357 (CLAM)

地球海洋地壳和岩石圈的地震各向异性是在全球范围内观测到的，通常用橄榄岩和/或变形辉长岩的晶体学优先取向（CPO）来解释。虽然该模型可能适用于洋中脊的快速扩张，但缓慢扩张环境中的变形会带来水化和矿物学的根本变化，从而改变弹性特性。本文拟对来自亚特兰提斯地块基性-超基性岩石的一套样品进行CPO的中子和同步衍射研究，以获得慢扩张环境下大洋基底岩石物理性质的基本认识。亚特兰蒂斯地块是在IODP远征357期间钻探和取芯的，由于其良好的暴露和通过钻井点网络对结构的控制，所回收的岩石被认为是一个理想的测试案例。原岩矿物的弹性常数和蚀变产物的弹性常数预测了弹性的增加，从而预测了地震各向异性随变形和水化的增加。这一预测与地震学研究的观察结果相反，地震学研究指出，在缓慢扩张的地壳中，各向异性比在正常或快速扩张的环境中观察到的要低。分析和解释构造模型和地震观测之间的这种重要脱节是计划研究的主要动机。

Seismic anisotropy of the Earth´s oceanic crust and lithosphere is globally observed, and usually explained by crystallographic preferred orientations (CPO) in peridotites and/or deformed gabbros. While this model may be adequate for fast-spreading at mid oceanic ridges, deformation in slow-spreading environments brings about hydration and fundamental changes in mineralogy that alters elastic properties. Here it is proposed to conduct a neutron and synchrotron diffraction study of CPO in a suite of samples from the mafic-ultramafic rocks of Atlantis Massif, to gain fundamental insight in petrophysical properties of oceanic basement in a slow-spreading environment. Atlantis Massif was drilled and cored during IODP Expedition 357, and the rocks recovered are considered an ideal test case because of its excellent exposure and structural control through the network of drillsites. Elastic constants of the protolith minerals and those of the alteration products predict an increase of elastic and, thus, seismic anisotropy with deformation and hydration. This prediction is in contrast to observations made by seismological studies pointing to lower anisotropies of slow-spreading crust than those observed in normal or fast spreading environments. To analyze and explain this important disconnect between tectonic models and seismological observations is the main motive of the planned study.