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- Title
Primary Arc Basalts from Daisen Volcano, Japan: Equilibrium Crystal Fractionation versus Disequilibrium Fractionation during Supercooling.
- Authors
TAMURA, Y.; YUHARA, M.; ISHII, T.
- Abstract
Daisen volcano, southwest Japan, has been thought to be an exclusively dacitic volcano, lavas having trace element patterns with a garnet signature. We studied the basalts at the western foot of the volcano and made two unexpected findings. (1) The homogeneity of 87Sr/86Sr in Daisen basalts (Sr isotopic variability ≤0·0003) contrasts with great variations in basalts from nearby monogenetic fields. Moreover, the basalts and dacites from Daisen volcano have the same 87Sr/86Sr and 143Nd/144Nd, indicating that these rocks have a close genetic relationship. The calculated primary basaltic magma of Daisen volcano suggests a segregation depth of ∼60 km (∼18 kbar), and higher Sm/Yb ratios in the Daisen basalts relative to NE Japan arc basalts suggest that the segregation took place between the garnet and spinel peridotite stability fields. (2) The effects of fractional crystallization were distinguished from those produced by supercooling on the basis of olivine morphology and chemical relationships between olivines and host basalts. Supercooled magmas become magnesian through fractionation of iron-rich olivines and are seemingly anomalous because they contain iron-rich olivines despite their magnesian bulk-rock chemistry.
- Subjects
DAISEN (Japan); JAPAN; BASALT; IGNEOUS rocks; FLOOD basalts; SPILITES
- Publication
Journal of Petrology, 2000, Vol 41, Issue 3, p431
- ISSN
0022-3530
- Publication type
Article
- DOI
10.1093/petrology/41.3.431