[S-IT26] New perspectives on the geodynamics of East Asia

[SIT26-06] 三次元モデリングによるマリアンナ沈み込み帯の温度構造、スラブ変成作用と境界面地震

*季 頴鋒^1,2,3、吉岡 祥一^3,4 (1.中国科学院チベット高原地球科学卓越創新センター、2.中国科学院チベット高原研究所、3.神戸大学都市安全研究センター、4.神戸大学大学院 理学研究科 )

キーワード：熱構造、スラブ変成作用、境界面地震、マリアンナ、三次元モデリング

The Marina arc system represents a typical mode of intra-oceanic convergent boundary characterizing circum-Pacific subduction zones, together with the Izu-Bonin, Kuril and Tonga-Kermadec margins well known for the tectonically formed deep trenches. Active back-arc extension driven by hydrothermal mantle upwell comprises one of the significant features of Mariana caused by steep subduction. Previous studies document that the narrow subduction constrains the seismicity in Mariana to be less than M7. However, the subduction thermal regime remains still unclear in detail. Based on the 3-D thermal model constructed for Mariana, we found that the highly curved Mariana arc presenting such a particular tectonic setting caused by trench retreat produces a cold thermal structure beneath the central and northern Mariana influenced by an oblique subduction. The deep earthquakes (>100 km) are therefore frequently detected compared with the southern Mariana. The subducted Pacific plate entraining the oceanic crust components is calculated to obtain their pressure-temperature conditions for different petrological faces undergoing multiple phase transition including the paths from amphibolite to eclogite or harzburgite at a high temperature of >500 degrees in Celsius which is conjectured to facilitate the deep earthquakes at Mariana. The dewatered oceanic plate is expected to releases ample fluids for the backarc volcanism and hydrous circulation at Mariana mantle wedge. The 3-D temperature structure of Mariana obtained in this study sheds lights on regional earthquake genesis and slab metamorphism in such an intro-oceanic subduction system featured by deep events.