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全球性的，通常用橄榄岩和/或变形辉长岩中的晶体学择优取向（CPO）来解释。虽然这个模型可能足以在洋中脊的快速扩展，在缓慢扩展环境中的变形带来了水化和矿物学的根本变化，改变了弹性特性。在这里，它建议进行中子和同步辐射衍射研究CPO在一套样品从亚特兰蒂斯地块的镁铁质-超镁铁质岩石，获得基本的洞察大洋基底在缓慢扩展的环境中的岩石物理性质。亚特兰蒂斯地块是在IODP 357考察期间钻探和取芯的，回收的岩石被认为是一个理想的测试案例，因为它通过钻探地点网络进行了出色的暴露和结构控制。原岩矿物和蚀变产物的弹性常数预测弹性的增加，因此，地震各向异性与变形和水化。这一预测与地震学研究的观测结果相反，地震学研究指出，缓慢扩张的地壳比正常或快速扩张的环境中观察到的各向异性要低。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.