Abstract
The Kushigatayama Group distributed in the central Koma Mountains, South Fossa Magna, was studied and found to consist mostly of resedimented volcaniclastics with both synvolcanic lavas, intrusions and post volcanic intrusions. The volcanic rocks are mostly tholeiitic basalt and andesite, and minor calc-alkaline hornblende andesite and dacite. Thickness of the Kushigatayama Group distributed in this region is calculated at ca. 11, 5000 m.Non-genetic facies were identified from field observations based on sedimentary structure and texture. Facies associations of single non-genetic facies show that the majority of the deposits are turbidites, debrites, subaqueous pyroclastic flow deposits and grain flow deposits. Primary volcanic rocks include lavas and syn-volcanic intrusions associated with hyaloclastite and/or peperite. Curviplanar euhedral volcaniclasts, isolated pillows and pseudo-pillows are predominant in the resedimented volcaniclastic deposits.Volcanic activity was dominanted by effusive eruptions of basalt and andesite, associated with lesser concurrent explosive eruptions of dacite of a distant source.
