Petrogenesis of Granitic Rocks in the Hisakajima Island, Goto Archipelago, Southwestern Japan: A Geochemical Study

Abstract

Whole-rock chemical compositions including rare earth elements for the granitic rocks from the Hisakajima Island, Goto Archipelago, southwestern Japan were measured in order to constrain their origin and petrogenesis. The granites were divided into two types—a granodioritic group (GD) and a high Fe/Mg ratio granitic group (HFG). The granitic magma was formed by the upwelling of high-temperature mantle material, which might be related to the extension of the Japan Sea around the Middle Miocene. The origin of the GD magma was attributed to the mantle material, while the origin of the HFG magma was attributed to partial melting of the crust by upwelling of the high-temperature mantle. The amount of rare earth elements revealed the secondary addition of light rare earth elements through hydrothermal processes for the granites. Chondrite normalized rare earth element patterns revealed that the HFG rocks were not well differentiated.

Keywords

• granite
• Goto Islands
• southwestern Japan
• rare earth elements