Magmatic Heat Source of the Bajawa Geothermal Field, Central Flores, Indonesia

Abstract

Numerous cinder cone alignments are obsenled in the Bajawa geothermal field, central Flores Island, eastern Indonesia. They are considered as post caldera cones of the Sajawa caldera. Sajawa caldera is a sort of a small rifi valley where fragmentary caldera walls are not closed and elongated north-south, indicating a dike-shaped magma chamber. This reflects lefilateral shear derived from the collision of the Australia continent. Four major geothermal system in the study area, Mataloko, Nage, Wolo Bob0 and Mengeruda derive their heat h m the Bajawa caldera magma system. Although the majority of volcanic rocks in the study area are basaltic and tholeiitic, the Bajawa caldera magma system is andesitic and calcalkaline. Chemical compositions of the calderafonning tuff and post-caldera cones show little vadation. This suggests a homogeneous, dikeshaped magma chamber beneath Bajawa caldera. Buoyancy of the calc-alkaline Baja wa caldera magma system may cause high-level intrusion. Petrology indicates that a depth of the magma genesis is also as shallow as 10 km.