Permalink : http://hdl.handle.net/2115/20424

JaLCDOI : 10.14943/gbhu.70.1

Many researchers have studied the thermal state of the crust and the upper mantle and its tectonic implications in Hokkaido, Japan. Terrestrial heat flow data have revealed the following characteristic features: (1) High heat flow (84〜125 mW/m2) is observed in the backarc side of the volcanic front, while low heat flow (< 42 mW/m2) is observed in the forearc side, showing the typical thermal aspects of the island arc. (2) The central axis zone of Hokkaido (the Kamuikotan and Hidaka metamorphic belts) shows relatively low heat flow (42〜80 mW/m2). The low heat flow zone extends for Sakhalin. (3) Extremely low (25〜34 mW/m2) and high (125 〜210 mW/m2) heat flow is distributed locally on the Ishikari-Tomakomai low land and its neighbor on the west, respectively. Based on the heat flow data and other geophysical data, such as the seismic velocity structure, aeromagnetic data, and so on, the Curie point depth, the solidus temperature depth, temperature at the Moho, and the mantle heat flow have been estimated. The estimated thermal structure implies the temperature of the lower crust comes to the solidus temperature beneath the backarc side of Hokkaido. The result is well supported by the electrical resistivity soundings: the low resistive layer (10~40 ohm-m) develops in the lower crust and is ascribed to the effect of partial melting of the crustal rocks.