Elastic and electrical properties and permeability of serpentinites from Atlantis Massif, Mid-Atlantic Ridge
Elastic and electrical properties and permeability of serpentinites from Atlantis Massif, Mid-Atlantic Ridge
复制标题
DOI：
10.1093/gji/ggx341
复制
发表时间：
2017-11-01
影响因子：
2.8
通讯作者：
Roumejon, Stephane
中科院分区：
文献类型：
--
作者：
Falcon-Suarez, Ismael;Bayrakci, Gaye;Roumejon, Stephane
蛇纹岩橄榄岩与基性岩共存于多种海相环境中，包括俯冲带、大陆裂谷和洋中脊。远程地球物理方法对于区分它们和提高对海洋地壳的构造、岩浆和变质历史的理解至关重要。但是，蛇纹岩橄榄岩表现出广泛的物理性质，使这种区分复杂化。本文分析了国际海洋发现计划357考察期间在大西洋中脊亚特兰蒂斯地块南壁上采集的4个蛇纹岩橄榄岩样品的超声P波和s波速度（V-p, V-s）及其各自的衰减(Q(P)(-1)， Q(s)(-1))，电阻率和渗透率。测量是在加载-卸载应力路径（5-45 MPa）范围内进行的，使用类似于从海底钻取的原始岩心中水平提取的1.7厘米长，5厘米直径的样品。测量参数表现出不同程度的应力依赖性，但遵循相似的趋势。V-p、V-s、电阻率和渗透率具有良好的相互关系，而Q(p)（-1）和Q(s)（-1）之间的关系不太清楚。高蛇纹岩化超镁铁质基质（bbb50 ω m）与机械/地球化学蚀变（岩浆/热液驱动蚀变）域（< 20 ω m）的电阻率对比明显。这些信息与样品的弹性常数（V-p/V-s比和体积模量）一起，使我们能够推断出有关蛇纹石化程度和岩石蚀变状态的有用信息，并通过岩石学分析进行对比。该研究显示了将地震技术与可控源电磁测量相结合，在了解热液系统的构造岩浆过程和流体路径方面的潜力。
Serpentinized peridotites co-exist with mafic rocks in a variety of marine environments including subduction zones, continental rifts and mid-ocean ridges. Remote geophysical methods are crucial to distinguish between them and improve the understanding of the tectonic, magmatic and metamorphic history of the oceanic crust. But, serpentinite peridotites exhibit a wide range of physical properties that complicate such a distinction. We analysed the ultrasonic P- and S-wave velocities (V-p, V-s) and their respective attenuation (Q(p)(-1), Q(s)(-1)), electrical resistivity and permeability of four serpentinized peridotite samples from the southern wall of the Atlantis Massif, Mid-Atlantic Ridge, collected during International Ocean Discovery Program Expedition 357. The measurements were taken over a range of loading-unloading stress paths (5-45 MPa), using similar to 1.7 cm length, 5 cm diameter samples horizontally extracted from the original cores drilled on the seafloor. The measured parameters showed variable degrees of stress dependence, but followed similar trends. V-p, V-s, resistivity and permeability show good inter-correlations, while relationships that included Q(p)(-1) and Q(s)(-1) are less clear. Resistivity showed high contrast between highly serpentinized ultramafic matrix (> 50 Omega m) and mechanically/geochemically altered (magmatic/hydrothermal-driven alteration) domains (< 20 Omega m). This information together with the elastic constants (V-p/V-s ratio and bulk moduli) of the samples allowed us to infer useful information about the degree of serpentinization and the alteration state of the rock, contrasted by petrographic analysis. This study shows the potential of combining seismic techniques and controlled source electromagnetic surveys for understanding tectonomagmatic processes and fluid pathways in hydrothermal systems.