11:30 AM - 11:45 AM
[MIS08-04] Igneous activities of the Paleo-Kuril forearc induced by Izanagi-Pacific ridge
The shoshonitic associations occur as sills and pillow lavas. They can be divided into two groups in petrography and geochemistry. The Group 1 has higher Mg# (Mg/[Mg+Fe]) than the Group 2, which is in contrast relatively differentiated. The Group 1 mainly occurs as sills intruded into lower part of the Nemuro Group whereas the Group 2 occurs as pillow lavas and sills mainly into mid- to upper sequences of the Nemuro Group (70-54 Ma), some of which are erupted over unconsolidated sediments (i.e. interpillow sediments). It is possible to consider the Group 2 shoshonites are formed by fractional crystallization of phenocrysts in the Group 1. The adakitic association can be seen in the lowermost part of the Nemuro Group.
Here, we provide the new tectonic model for elucidating the forearc volcanism in the Paleo-Kuril Arc. Our model suggest that the adakitic igneous activity was caused by approaching of Izanagi-Pacific ridge to the Paleo-Kuril trench.