Age and associated stress field of the Miocene Tochihara Rhyolites using dikes in the Daigo Town, Northeast Japan

Abstract

The Neogene paleostress field around the Tanakura Fault Zone was investigated by fault analysis, such as mesoscale fault analysis and fault shear sense analysis. Since it is usually unknown when each fault was formed, these analyses are difficult to determine the age of paleostress field of the results. In this study, we studied rhyolite dikes of the Neogene Tochihara Rhyolites to obtain data of paleostress and its age. Age of Tochihara Rhyolites magmatism was constrained by zircon U-Pb dating, and paleostress field was revealed by analysis of dikes. The paleostress field revealed by analysis of the rhyolite dikes suggests a normal-faulting stress regime with a WNW-ESE-trending σ₃-axis, while zircon U-Pb dating of a rhyolite dike yielded a Miocene age of 17.2±0.2 Ma (2σ). The results show that the Tochihara Rhyolites were erupted under WNW-ESE extension when the Tanakura Basin began to form at ca. 17 Ma. These data provide clues to the development of the Tanakura Basin and the Neogene kinematic history of the Tanakura Fault Zone.