2:45 PM - 3:00 PM
[SVC30-05] A parametric study of thermal evolution of upper crustal magma chambers through andesitic melt intrusion: application to the NE Japan arc
Keywords:magma chamber, thermal evolution, magma intrusion rate, magma effusion rate
In order to place active volcanoes in Japan in the process of thermal evolution, we conducted a parametric study of magma chamber evolution based on a previous model (Annen, 2009). The rapid cooling of magma in the cold upper crust at a depth of 5 km limited the minimum rate and duration of magma injection to form a magma chamber: 0.5 km3/yr in 200 years, 0.1 km3/y in 1300 years, and 0.01 km3/yr in 20,000 years for the for accumulation of 100 km3 eruptable magma. The magma accumulation rate was initially slow and rapidly increased with the accumulation/injection ratio reaching 1. The ratio even exceeded 1.0 owing to the contribution of crustal melting. Here, the sill diameter was assumed to be 10 km, a typical caldera size in the NE Japan arc (Yoshida, 2020). The diameter significantly affected the calculation as the magma thickness is inversely proportional to the square of the sill radius. Once a magma chamber with a diameter of 10 km is formed, its thermal lifetime is long due to the slow heat conduction in the crust. It takes ~10,000 years to cool down below the solidus temperature. The long-lived magma chamber may be juvenilized by injections of new hot magma and become eruptable in hundreds to thousands of years.
Compilation of the Geological Survey of Japan database on the quaternary volcanoes in Japan revealed that the magma effusion rates are negatively correlated with the preceding eruption interval. The present thermal evolution model showed that the higher magma intrusion rate results in a higher average effusion rate, presenting an interpretation of the observed negative correlation. The previously proposed minimum intrusion rate required for the magma ascent through the cold crust, 0.01 km3/yr (Menand, 2015), led to the effusion rate 1 order of magnitude higher than the observed value, suggesting that the initial condition of the present calculation, i.e., the magma supply rate from the lower crustal hot zone to the upper crust, should be optimized to explain the geological observation.
Compilation of the Geological Survey of Japan database on the quaternary volcanoes in Japan revealed that the magma effusion rates are negatively correlated with the preceding eruption interval. The present thermal evolution model showed that the higher magma intrusion rate results in a higher average effusion rate, presenting an interpretation of the observed negative correlation. The previously proposed minimum intrusion rate required for the magma ascent through the cold crust, 0.01 km3/yr (Menand, 2015), led to the effusion rate 1 order of magnitude higher than the observed value, suggesting that the initial condition of the present calculation, i.e., the magma supply rate from the lower crustal hot zone to the upper crust, should be optimized to explain the geological observation.