R6: Plutonic rocks, volcanic rocks and subduction factory

[R6P-02] Formation of upper-most crust in volcanic belt: Example for Cretaceous volcano–plutonic complex, Hyogo Prefecture, southwest Japan

*Masaaki OWADA¹, Shunsuke Fukuda¹, Atsushi Kamei² (1. Yamaguchi University, 2. Shimane University)

Keywords:Late Cretacous, Volcano-plutonic complex, volcanic front, Tholeiitic seriese

A volcano–plutonic complex is an important magmatic body to understand for the formation of upper-most crustal processes in terms of its magmatic histories, geochronology, and geochemical investigations along volcanic belts. There are many volcano–plutonic complexes during the Cretaceous and Paleocene Tertiary in the southwest Japan. Cretaceous Volcanic tuff and welded tuff layers with 74 Ma by zircon Fission Track dating are underlain by Himeji City and Kakogawa City, Hyogo Prefecture, and are intruded by the Ohfuji-yama granodiorite (biotite K–Ar age, 77 Ma), andesitic dike, and quartz diorite dike. All intrusive rocks geochemically show tholeiitic compositions. Considering constituent rock types with their geochemical signatures, the volcano–plutonic complex in this area was situated in the volcanic front and formed an upper-most crust during the Late Cretaceous.