25. VELOCITY BEHAVIOR OF LOWER CRUSTAL AND UPPER MANTLE ROCKS FROM A FAST-SPREADING RIDGE AT HESS DEEpl
25. VELOCITY BEHAVIOR OF LOWER CRUSTAL AND UPPER MANTLE ROCKS FROM A FAST-SPREADING RIDGE AT HESS DEEpl
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25. 赫斯深部快速扩张海脊的下地壳和上地幔岩石的速度行为
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
N. Christensen
中科院分区：
文献类型：
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作者：
G. Iturrino;D. Miller;N. Christensen
在海洋钻探计划第 147 段期间回收的下地壳和上地幔样品，在高达 600 MPa 的围压下测量了地震速度。将西南印度洋中脊孔 735B 和蛇绿岩数据进行的孔隙度和密度系统比较表明，橄榄岩更强烈的蛇纹石化作用和更普遍的绿片岩蚀变是赫斯深部辉长岩的特征。 Leg 147 样品的蛇纹石化程度和橄榄石与斜方辉石的比例控制着上地幔岩石的密度趋势。压缩波和剪切波速度显示出由优选矿物和微裂纹方向引起的几种类型的地震各向异性。辉长岩样品的特征是定向斜长石和橄榄石，而蛇纹石化橄榄岩则显示出优选的水平微裂纹方向。剪切波分裂已被记录并归因于优选的矿物取向。在赫斯深部样本中观察到的蛇纹石化程度可能是下地壳-上地幔边界反射率的一个重要因素。辉长岩样品显示出比高度蛇纹石化的上地幔岩石更低的泊松比。
Seismic velocities have been measured at confining pressures as high as 600 MPa for lower crustal and upper mantle samples recovered during Ocean Drilling Program Leg 147. A comparison of porosity and density systematics with Southwest Indian Ridge Hole 735B and ophiolite data illustrates the more intense serpentinization of peridotites and more pervasive greenschist alteration characterizing the gabbros from Hess Deep. The degree of serpentinization and the olivine:orthopyroxene ratio of the Leg 147 samples control the density trends of the upper mantle rocks. The compressional- and shear-wave velocities show several types of seismic anisotropy caused by preferred mineral and microcrack orientations. Gabbroic samples are characterized by oriented plagioclase and olivine whereas the serpentinized peridotites show preferred horizontal microcrack orientation. Shear-wave splitting has been recorded and is attributed to preferred mineral orientation. The degree of serpentinization observed in the Hess Deep samples can be a significant factor in the reflectivity of the lower crust-upper mantle boundary. Gabbroic samples show lower Poisson's ratios than the highly serpentinized upper mantle rocks.