2:45 PM - 3:00 PM
[SMP43-05] Depth distribution and fluid saturation of the fossil calderas and their relations with geofluid activities at NE Japan
Keywords:Fossil caldera, Geofluid, Melt inclusion, Arc magma
Melt inclusions in quartz obtained from these calderas are low-alkaline rhyolite, and its major and trace element compositional trends can be explained by fractionation of plagioclase±quartz. Entrapment pressure of melt was estimated from the pressure dependency of eutectic composition of plagioclase–quartz, and are 30–300 MPa, indicating the depth of magma chamber at 1–11 km. The H2O contents of the melt inclusion are 2.8–5.5 wt%, with <38 ppm of CO2. The pressure–H2O content relations are close to solubility curve of H2O in rhyolite melt, indicating that melt was water-saturated at least at the depth range of 1–6 km.
The depth distribution of magma chambers (1–11 km) and depth of water-saturation (1–6km) corresponds to a low Vs, Vp and high Poisson‘s ratio region (5–10 km) and seismic reflectors (2–5 km), respectively. Therefore, these regions are expected to be a geofluid reservoir consists of tonalitic plutonic rocks. Earthquake swarms occur beneath Shiraswa and Fukano calderas at the depth of 7–12 km, indicating that supply of geofluid under these tonalite fluid reserviors.