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Relationship between melange fabrics of accretionary complex and relative convergence along the plate boundary

增生杂岩混杂组构与沿板块边界相对汇聚的关系

基本信息

批准号：
06640585
负责人：
KIMURA Gaku
金额：
$ 1.34万
依托单位：
Osaka Prefecture University, College of Integrated Art and Sciences
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

项目摘要

Systematic changes in fabrics of melanges have been detected in rocks of the Shimanto Belt, Japan. Several shear indicators : including S-C structures, Riedel shears and folds, in the melanges indicate consistent sense of shear both in outcrop and microscopic scales. The deformation mechanisms, independent particulate flow and pressure solution, suggest that the deformation started under unlithified condition and progressed through lithification due to strain hardening.After lithification, cataclastic deformation occurred locally but most of the earlier deformation features are preserved. This process appears to have taken place along the decollement beneath the off-scraped accretionary prism. Sinistral reverse sense of shear is observed in the Campanian melange, whereas a dextral reverse sense of shear is preserved in the Early Eocene melange in the Shimanto Belt. This change in fabric is interpreted to be linked to a change in relative convergence between the subducting and overriding plates.Three different plate models have been proposed for the Late Cretaceous to Early Tertiary western Pacific margin :1) subduction of the Kula-Pacific ridge along the continental margin,2) subduction of the Pacific Plate since 85 Ma, and3) subduction of the aborted Kula-Pacific ridge after 43 Ma.The obseved change in fabric of melange is consistent only with the third model, which predicts a change in relative convergence from sinistral to dextral at the appropriate time.

在日本岛东带的岩石中发现了岩石结构的系统变化。混杂岩中的S-C构造、Riedel剪切和褶皱等剪切指标在露头和微观尺度上显示出一致的剪切意义。独立颗粒流动和压力溶解的变形机制表明，变形开始于非岩化状态，并由于应变硬化而在岩化过程中进行。岩化作用后，局部发生碎裂变形，但大部分早期变形特征得以保留。这一过程似乎发生在脱落的吸积棱镜下的滑脱处。坎帕系混杂岩为左旋反向剪切，石曼托带早始新世混杂岩为右旋反向剪切。构造上的这种变化被解释为与俯冲板块和上覆板块之间相对收敛的变化有关。对于晚白垩世至早第三纪西太平洋边缘，提出了3种不同的板块模式：1)库拉-太平洋脊沿大陆边缘俯冲，2)85 Ma以来太平洋板块俯冲，3)43 Ma后库拉-太平洋脊中止俯冲。观察到的混杂物结构的变化仅与第三个模型相一致，该模型预测在适当的时间相对收敛从左旋到右旋的变化。