통가열도 남쪽지역에서 채취된 암석들에 대한 성인론

Abstract

We report whole-rock geochemical data of volcanic rocks dredged from the active submarine volcanoes (TA15, 16, and 19), located near Ata island, which marks the southern part of the Tonga arc. The seamounts have basal diameters of 9-13 km with summits of 350-740 m below sea level. Collected lava samples show a wide compositional variation of low-K tholeiitic series from basalt to dacite, indicating a fractional crystallization of olivine, orthopyroxene, clinopyroxene, and plagioclase. Petrogenesis of the southern Tonga arc can be explained by a three-component mixing including a depleted mantle wedge, a mixed sediment melt of Louisville seamount chain (LSC) materials and pelagic sediment (PS), and a fluid originated from the dehydration of the altered oceanic crust (AOC). Our geochemical modeling suggests that the mafic magmas from the study area might be generated by 10-20% partial melting of a depleted mantle component which is metasomatized by ~ 1% sediment melt of LSC and PS mixture in the proportion of 40:60 and ~ 1% AOC fluid, while Volcano V and Monowai, located further south near present LSC-Tonga trench intersection, were generated by 15-25% partial melting of a depleted mantle, metasomatized by ~ 1.5% sediment melt (90:10 mixture of LSC and PS) and ~ 0.5% AOC fluid. It is well matched with the study of Timm et al. (2013) reported that LSC implication is stronger in Volcano V and Monowai than those in Ata.