Depth of oceanic-crust underplating in a subduction zone: Inferences from fluid-inclusion analyses of crack-seal veins
Depth of oceanic-crust underplating in a subduction zone: Inferences from fluid-inclusion analyses of crack-seal veins
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DOI：
10.1130/g19885.1
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发表时间：
2003-11-01
期刊：
影响因子：
5.8
通讯作者：
Ikesawa, E
中科院分区：
文献类型：
--
作者：
Matsumura, M;Hashimoto, Y;Ikesawa, E
在陆地上的增生混杂岩中分析了裂缝封闭脉中的流体包裹体。 I 脉包裹体见于混杂岩砂岩块颈部，11 脉包裹体发育于逆冲断层下方的页岩中，逆冲断层切割混杂岩。对矿脉 I 内包裹体的压力和温度估计表明，在大约 92-144 MPa 的流体压力下，裂缝在大约 125-195 ℃ 的温度下被封闭。矿脉 11 形成于裂缝中，这些裂缝可能是在逆冲断层冲破洋壳并进入混杂岩时造成的损坏区中打开的；这些静脉含有在大约 135-245 摄氏度、大约 107-149 MPa 的流体压力下捕获的流体包裹体。深度（类似于海底以下 4-6 公里）和温度估计与沉积岩内的地震滑脱下降到海洋基底的条件一致，因此洋壳的薄层位于上盘下方。这样的下降地点就是现代南海海槽孕震带的上倾极限。
Fluid inclusions in crack-seal veins are analyzed in accreted melange now on land. The vein I inclusions are observed in the necked parts of sandstone blocks in melange, and the vein 11 inclusions developed in shale below the thrust fault, which cuts the melanges. The pressure and temperature estimations from the inclusions within vein I show that the cracks were sealed at similar to125-195 degreesC under similar to92-144 MPa of fluid pressure. Vein 11 formed in cracks that might have opened in a damage zone caused by the thrust fault as it broke through oceanic crust and into the melange; these veins contain fluid inclusions trapped at similar to135-245 degreesC under similar to107-149 MPa of fluid pressure. The depth (similar to4-6 km below the seafloor) and temperature estimates are consistent with the conditions where an aseismic decollement within sedimentary rocks steps down into the oceanic basement, so that a thin section of oceanic crust underplates in the hanging wall. Such a step-down site is the updip limit of the seismogenic zone in the modern Nankai Trough.