Peridotites from a ductile shear zone within back‐arc lithospheric mantle, southern Mariana Trench: Results of a Shinkai 6500 dive
Peridotites from a ductile shear zone within back‐arc lithospheric mantle, southern Mariana Trench: Results of a Shinkai 6500 dive
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DOI：
10.1029/2008gc002197
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发表时间：
2009-05
期刊：
影响因子：
3.7
通讯作者：
K. Michibayashi;Y. Ohara;R. Stern;Patricia Fryer;Jun-Ichi Kimura;Miki Tasaka;Y. Harigane;Teruaki Ishii
中科院分区：
文献类型：
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作者：
K. Michibayashi;Y. Ohara;R. Stern;Patricia Fryer;Jun-Ichi Kimura;Miki Tasaka;Y. Harigane;Teruaki Ishii
马里亚纳南部前弧的两个南北断层带记录了至少 20 公里的左旋位移。作为 2006 年 R/V Yokosuka 巡航的一部分，我们使用潜水器 Shinkai 6500（YK06‐12 Dive 973）检查了其中一个断层带（西圣罗莎岸断层）从 6469 米到 5957 米水深的朝东斜坡。样品显示糜棱岩、碎斑岩和粗糙、中等变形的次生纹理。橄榄岩内橄榄石的晶体择优取向表现出典型的[100](010)模式，织物强度从具有粗糙次生结构的岩石到糜棱岩逐渐降低。因此，取样的橄榄岩代表了上覆板块岩石圈地幔内的延性剪切带。橄榄岩的暴露可能与俯冲板块的撕裂有关，此前根据测深和地震活动推断。此外，虽然潜水地点位于靠近马里亚纳海沟的前弧，但采样的橄榄岩中的尖晶石成分与马里亚纳海槽后弧的尖晶石成分相当，表明弧后盆地地幔沿着西圣罗莎浅滩断层暴露。
Two N–S fault zones in the southern Mariana fore arc record at least 20 km of left‐lateral displacement. We examined the eastward facing slope of one of the fault zones (the West Santa Rosa Bank fault) from 6469 to 5957 m water depth using the submersible Shinkai 6500 (YK06‐12 Dive 973) as part of a cruise by the R/V Yokosuka in 2006. The dive recovered residual but still partly fertile lherzolite, residual lherzolite, and dunite; the samples show mylonitic, porphyroclastic, and coarse, moderately deformed secondary textures. Crystal‐preferred orientations of olivine within the peridotites show a typical [100](010) pattern, with the fabric intensity decreasing from rocks with coarse secondary texture to mylonites. The sampled peridotites therefore represent a ductile shear zone within the lithospheric mantle of the overriding plate. Peridotites were probably exposed in association with a tear in the subducting slab, previously inferred from bathymetry and seismicity. Furthermore, although the dive site is located in the fore arc close to the Mariana Trench, spinel compositions within the sampled peridotites are comparable to those from the Mariana Trough back arc, suggesting that back‐arc basin mantle is exposed along the West Santa Rosa Bank fault.