山口県後期白亜紀防府バソリスの三次元形態：地質・岩石と重力異常からの推定

Abstract

Geology, petrography, and gravity data have been used to determine the D geometry and emplacement mechanisms involved in the formation of the Late Cretaceous Hofu batholith. Grain size distributions and textures have been used to classify granites of the batholith into five lithofacies: coarse-, medium-, and fine-grained granites, porphyritic granite, and granodiorite. These granites are vertically stacked sheet-like bodies that were emplaced at a depth of < km, as determined from their intrusive relationships with surrounding volcanic rocks.The batholith is associated with a negative gravity anomaly, particularly the northern part of the intrusion that is bounded by the Fushinogawa-Oharako and Sabagawa faults. The batholith has an areal extent of km, with the base of the batholith estimated using a gravity data inversion to be at a depth of ca. to m, suggesting that the batholith is tabular. The fact that the deep parts of the batholith occur at depths of m near both faults suggests that the granite magma may have been transported along nearvertical fault-controlled conduits.