TY - JOUR
T1 - Mechanism of crystal redistribution in a sheet-like magma body
T2 - Constraints from the Nosappumisaki and other shoshonite intrusions in the Nemuro peninsula, Northern Japan
AU - Simura, Rayko
AU - Ozawa, Kazuhito
N1 - Funding Information:
We thank H. Nagahara, H. Iwamori, T. Koyaguchi, T. Fujii, and T. Kuritani for fruitful discussions. Comments from three reviewers—R. C. Kerr, O. Backmann, and R. A. Wieve—were very helpful in improving the manuscript. We thank R. C. Kerr for drawing our attention to the fluid dynamic instability in particle settling of highly concentrated suspensions. Editorial handling by D. Geist is greatly appreciated. R.S. is grateful to Hideto Yoshida for EPMA and XRF analyses. R.S. also thanks the people of Nemuro City, especially those of the Nemuro Fishery Laboratory, for providing housing in Nemuro, and those of the Preparative Office of the Nemuro Municipal Museum for providing access to some documents. This work was supported by the Japanese Society for the Promotion of Science for Japan Junior Scientists.
Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2006/9
Y1 - 2006/9
N2 - Processes of crystal separation in a magma heavily laden with crystals without phase change are investigated from observations on frozen magma systems: Nosappumisaki and other shoshonite intrusions in the Nemuro peninsula, Japan, for which the origin of the crystals and the initial conditions are well constrained. The Nosappumisaki intrusion is 120 m in thickness and extends for more than 1.5 km. It exhibits a wide range of lithological variation, principally as a result of crystal redistribution after intrusion. Crystals in each lithology can be clearly divided into two kinds according to their composition and texture: those present before the intrusion of the magma ('phenocrysts') and those that crystallized in situ after intrusion. From the vertical change in mode and size of 'phenocrysts', it is shown that (1) augite 'phenocrysts' were rapidly deposited, with little overgrowth after intrusion, by significant coagulation or clustering on a time-scale of more than a few years, and (2) plagioclase 'phenocrysts', definitely denser than the melt but concentrated in the upper level, floated by counter flow of massive deposition of augite 'phenocrysts'. These results indicate that in a magma heavily laden with crystals of a few millimeters in size (>20 vol. %), crystal-crystal and crystal-melt interaction play an important role in the separation of crystals from the host melt.
AB - Processes of crystal separation in a magma heavily laden with crystals without phase change are investigated from observations on frozen magma systems: Nosappumisaki and other shoshonite intrusions in the Nemuro peninsula, Japan, for which the origin of the crystals and the initial conditions are well constrained. The Nosappumisaki intrusion is 120 m in thickness and extends for more than 1.5 km. It exhibits a wide range of lithological variation, principally as a result of crystal redistribution after intrusion. Crystals in each lithology can be clearly divided into two kinds according to their composition and texture: those present before the intrusion of the magma ('phenocrysts') and those that crystallized in situ after intrusion. From the vertical change in mode and size of 'phenocrysts', it is shown that (1) augite 'phenocrysts' were rapidly deposited, with little overgrowth after intrusion, by significant coagulation or clustering on a time-scale of more than a few years, and (2) plagioclase 'phenocrysts', definitely denser than the melt but concentrated in the upper level, floated by counter flow of massive deposition of augite 'phenocrysts'. These results indicate that in a magma heavily laden with crystals of a few millimeters in size (>20 vol. %), crystal-crystal and crystal-melt interaction play an important role in the separation of crystals from the host melt.
KW - Crystal settling
KW - Magma chamber
KW - Nosappumisaki
KW - Plagioclase flotation
KW - Sill
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U2 - 10.1093/petrology/egl028
DO - 10.1093/petrology/egl028
M3 - Article
AN - SCOPUS:33747876398
VL - 47
SP - 1809
EP - 1851
JO - Journal of Petrology
JF - Journal of Petrology
SN - 0022-3530
IS - 9
ER -