Tectonic incorporation of the upper part of oceanic crust to overriding plate of a convergent margin: An example from the Cretaceous-early Tertiary Mugi Melange, the Shimanto Belt, Japan

摘要

A tectonic melange exposed on land is examined to reveal relationships between melange formation, underplating, and deformation mechanisms, focusing on the deformation of basaltic rocks. The studied Mugi Melange of the Shimanto Belt is composed of a shale matrix surrounding various blocks of sandstone, pelagic sediments, and basalts. The melange was formed during Late Cretaceous to early Tertiary times in a subduction zone under P-T conditions of 150-200 degrees C and 6-7 km depth as estimated from vitrinite reflectance and quartz veins fluid inclusions. The melange represents a range of deformation mechanisms, pressure solution with micro-scale cataclasis in the shale matrix, brittle tension cracking in the blocks, and ubiquitous strong cataclasis in the basal portion of basaltic layers. The cataclastic deformation in the basalts suggests a breakage of a topographic high in the seismogenic depth. (c) 2005 Elsevier B.V. All rights reserved.