Collisional and collapse processes of reef-seamount complex

我们通过野外和显微镜检查确定了筑波石灰岩内部普遍存在的结构破坏。我们的研究表明，石炭-二叠纪筑波石灰岩在七步地体中的碰撞和吸积可以用Sano和Kanmera(1991)的工作假说得到最满意的解释。筑海石灰岩的碰撞和吸积事件的序列概括如下：位于海山上的筑海造山体侵入海沟区，沿着外沟坡的正断层使造造物分裂并产生断层诱导的断裂，造山体及其基座和崩塌块内部结构的大规模破坏，崩塌产物的楔形向沟内移动及其与楔形物质的混合，崩塌产物的移位及其与沟槽填充沉积物的混合，碰撞产物与沟槽填充沉积的剥离增生，并将它们并入增生构造。这些事件都发生在早、中侏罗世早期。值得注意的是，造山体的玄武岩基座也参与了碰撞坍塌事件。除了筑波石灰岩外，还研究了秋吉地体中的晚古生代石灰岩。虽然还需要进一步的检查，但这些石灰岩的内部结构破坏也很普遍。我们的全部结果表明，Sano和Kanmera(1991)提出的工作假说适用于另一种大洋石灰岩，在吸积构造中具有重要的意义。

We identified the prevailing internal textural destruction in the Tsukumi Limestone through the field and microscopic examinations. Our research revealed that the collisional and accretion of the Carboniferous-Permian Tsukumi Limestone in the Chichibu terrane is most satisfactorily explained by the working hypothesis by Sano and Kanmera(1991). The sequence of the collisional and accretionary events of the Tsukumi Limestone is summarized as follows ; encroachment of the Tsukumi oceanic buildup resting on a seamount into a trench area, split of the buildup by normal faults along the outer trenchslope and generation of fault-induced fractures, large scale collapse of the buildup along with its pedestal and internal textural destruction of the collapse blocks, trenchward-movement of a wedge of the collapse products and their intermixing with the wedge, displacement of the collapse products and their mixing with trench-fill sediments and offscraping accretion of the collisional products fogether with the trench-fill sediments and their incorporation into an accretionary prism. All these events took place in early Early to early Middle Jurassic time. Worthy to note is that the basaltic pedestal of the buildup was also involved into the collisional collapse events.Addition to the Tsukumi Limestone, the late Paleozoic limestones in the Akiyoshi terrane were examined. Though the further examination is needed, internal textural destruction is also widespread in these limestones. The results imply that their accretion can be explained by the collisional collapse model avobe described.The whole of our results mean that the working hypothesis proposed by Sano and Kanmera(1991) is applicable to another accreted oceanic limestones and is ot great significance in the accretion tectonics.