Postcollisional exhumation history of the Tanzawa Tonalite Complex, inferred from (U-Th)/He thermochronology and fission track analysis

Yamada, Kunimi; Tagami, Takahiro*

We performed new thermochronometry for the Tanzawa Tonalite Complex to investigate the exhumation history caused by arc-arc collision. Typical (U-Th)/He ages were 2.0 0.2 Ma on apatite and 3.3 0.2 Ma on zircon and 4.5 to 6.9 Ma on zircon using the fission-track method. The exhumation rate has been calculated to be 0.5 to 1.5 mm/yr from 7 to 3.3 Ma, 2 mm/yr from 3.3 to 2.0 Ma and 0.8 mm/yr from 2.0 to 0 Ma with an assumed geothermal gradient of 40C/km. The exhumation rate has not changed significantly despite the simultaneous tectonic changes around the Tanzawa Mountains after 7 Ma.