Origin of high-magnesian andesites in the Setouchi volcanic belt, southwest Japan, I. Petrographical and chemical characteristics
Abstract
High-magnesian andesites of middle Miocene age occur in southwest Japan, forming an obvious volcanic belt. These andesites have low FeO*/MgO ratios (0.546-0.931), and are rich in Ni (101-312 ppm), Co (30.0-45.1 ppm), and Cr (208-756 ppm). They are relatively aphyric (phenocrysts <10 vol.%), and the phenocrysts of magnesian olivine (∼Fo 88) are in equilibrium with the host high-magnesian andesite magmas on the basis of the Fe-Mg exchange partitioning. These features suggest that the high-magnesian andesites are not differentiated or accumulative; they appear to represent primary andesites generated in the upper mantle. These southwest Japanese high-magnesian andesites are rich in incompatible elements, and show light rare earth enrichment relative to boninites, suggesting that the former is derived from a less depleted mantle source than the latter.
- Publication:
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Earth and Planetary Science Letters
- Pub Date:
- September 1982
- DOI:
- 10.1016/0012-821X(82)90008-5
- Bibcode:
- 1982E&PSL..60..293T