Geochemical variation of the Late Cretaceous-Paleogene granitoids across the Ehime-Hiroshima-Shimane transect, Japan

Abstract

Geochemical and geomagnetic character of the Late Cretaceous-Paleogene granitic batholith was examined at N-S transect across the city of Hiroshima. The granitoids are mostly biotite granite in composition, but granodiorite predominates in the Takanawa Peninsula. Their magnetic susceptibility is the highest in the Sanin belt, but becomes lower of the ilmenite-series to the south and lowest in the southernmost Ryoke belt. The granitoids are most sodic in the Sanin belt and potassic in the Sanyo and Ryoke belts, which may reflect igneous and sedimentary source rocks, respectively. The alumina saturation index (A/CNK) is above 1.0, i.e., peraluminous, but never exceeding 1.1 for S-type granite. Rb and Pb replacing K are the least in the Sanin belt but the highest in the Ryoke and southern Sanyo belts. High-Sr granitoids and adakite of the northern Kyushu and the Kinki district were not found in the studied regions. Zircon saturation temperatures in the average of the studied granitoids are the highest of 753 o C in the Ryoke belt, because granodiorite predominates here.