Fabric-based criteria to distinguish tectonic from sedimentary melanges in the Shimanto accretionary complex
Fabric-based criteria to distinguish tectonic from sedimentary melanges in the Shimanto accretionary complex
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基于组构的标准来区分四万十增生杂岩中的构造与沉积混杂岩
DOI：
10.1016/j.tecto.2011.10.018
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发表时间：
2012
期刊：
影响因子：
2.9
通讯作者：
Yuzuru Yamamoto
中科院分区：
文献类型：
--
作者：
Taro Maeda;Euichi Hirose;Yoshito Chikaraishi;Masaru Kawato;Kiyotaka Takishita;Takao Yoshida;Heroen Verbruggen;Jiro Tanaka;Shigeru Shimamura;Yoshihiro Takaki;Masashi Tsuchiya;Kenji Iwai;Tadashi Maruyama;Yuzuru Yamamoto
基于磁化率各向异性 (AMS) 的组构分析提供了区分日本西南部屋久岛第三纪四万十增生杂岩中的构造与沉积混杂岩的标准。沉积混杂岩的特征是与压实和成岩作用相关的织物叠印。这种混杂岩的磁性椭球体代表了解理/层理平行的磁性叶理，类似于附近岩石中的连贯沉积层所获得的结果。构造混杂岩和构造形成的双相结构的特征是晶粒旋转，即晶粒短轴围绕平行于 S 平面和 C 平面之间的交点以及铅笔解理长轴（垂直于剪切方向）的轴旋转。与沉积混杂岩相比，构造混杂岩和复式结构获得的AMS数据显示出较弱的磁片理，Kmax（最大磁化率）轴平行于S面和C面与铅笔解理长轴的交点，Kmin（最小磁化率）轴呈围绕Kmax的环带分布。这些对比鲜明的组构发展路径可能反映了沉积物沉积、埋藏、增生和隆起的整个历史过程中混杂岩形成的不同阶段。沉积混杂岩可能被强烈压实，因为它们是在沉积后不久形成的。相比之下，构造混杂岩和复式结构包含剪切诱发的组构，因为它们是在相对较晚的阶段发育的，一旦沉积物被充分压实，这种组构就可能在接近最大埋藏深度的水平上发育。
Fabric analyses based on the anisotropy of magnetic susceptibility (AMS) provide a criterion with which to distinguish tectonic from sedimentary mélanges in the Tertiary Shimanto accretionary complex, Yakushima Island, SW Japan. Sedimentary mélanges are characterized by fabric overprinting associated with compaction and diagenesis. The magnetic ellipsoids for such mélanges represent a cleavage/bedding-parallel magnetic foliation, similar to that obtained for coherent sedimentary layers in nearby rocks. The tectonic mélanges and tectonically formed duplex structure are characterized by grain rotation, whereby the grain short-axis is rotated about axes oriented parallel to the intersection between S- and C-planes and the long axis of pencil cleavage, perpendicular to the shear direction. The AMS data obtained for tectonic mélanges and duplex structure show a less intense magnetic foliation compared with the sedimentary mélanges, with Kmax(the maximum magnetic susceptibility) axes oriented parallel to the intersection between S- and C-planes and the long axis of pencil cleavage, and Kmin(the minimum magnetic susceptibility) axes showing a girdle distribution about Kmax. These contrasting paths of fabric development may reflect different stages of mélange formation during the overall history of sediment deposition, burial, accretion, and uplift. Sedimentary mélanges are likely to be strongly compacted, given that they formed soon after sedimentation. In contrast, tectonic mélanges and duplex structure contain a shear-induced fabric because they develop at a relatively late stage, once the sediments have been sufficiently compacted for such a fabric to develop, possibly at levels near the maximum burial depth.