Cooling history of the CretaceousTokigranite in theeastern Sanyo Belt, Central Japan

Abstract

The cooling history of the Crateceous Toki granite, exposed in the eastern Sanyo Belt, Central Japan, was constructed from various geochronological data. The granite yields K-Ar biotite ages of 74 ± 2to72 ± 2Ma (± and K-Ar hornblende ages of 75 ± 4to74 ± 4Ma, which are concordant with a previously reported Rb-Sr whole-rock isochron age. Fission-track ages of zircon and apatite in the granite give ages 73 ± 3to64 ± 3Ma and 40 ± 4to37 ± 4 Ma, respectively. These above thermochronological data suggests two distinctive cooling stages for the Toki granite; 1) a first rapid cooling stage in which the granitic magma was cooled to the temperature of host rock soon after intrusion at depths of 5–7 km in the upper crust, and 2) second slow cooling stage (7–9±C/m.y.) associated with the uplift and subsequent erosion of the granite intrusion after ~ 70 Ma. © 2012, Japan Association of Mineralogical Sciences. All rights reserved.