Cooling processes of a dolerite sill inferred from the variations in plagioclase aspect ratio, Atsumi District, north-eastern Japan.

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Bibliographic Details
Title:	Cooling processes of a dolerite sill inferred from the variations in plagioclase aspect ratio, Atsumi District, north-eastern Japan.
Authors:	Kondo, Kentaro¹ (AUTHOR), Hoshide, Takashi² (AUTHOR) hoshide@gipc.akita-u.ac.jp
Source:	Geosciences Journal. Apr2022, Vol. 26 Issue 2, p183-199. 17p.
Subject Terms:	Diabase, Heat convection, Plagioclase, Olivine, Zeolites, Crystallization
Geographic Terms:	Japan
Abstract:	The upper Kayaoka sheet in the Atsumi area, Northeast Japan, has an alkaline-basaltic composition. The modal olivine and Ni enrichment in the lower part of the sheet indicates the accumulation of early formed olivine crystals. Overall, the average aspect ratio of plagioclase increases from the central part of the sheet toward both the top and bottom margins. The average aspect ratios of plagioclase and calculated crystallisation times at each height of the sheet, except for the lowermost margin, are roughly plotted near the regression line drawn based on those from many sills in previous research. However, we observed that the average aspect ratios of plagioclase in some horizons of the central part of the sheet exhibit an offset from the regression line. The olivine analcite dolerite in the central part of the sheet is rich in zeolite amygdules and glassy mesostasis with a quench texture. These observations suggest that the cooling rate in the central part of the sheet was faster compared with assuming conductive cooling only. A plausible mechanism for the rapid cooling at the centre of the sheet is heat transport by the convection of seawater that has infiltrated the columnar joint. [ABSTRACT FROM AUTHOR]
Database:	Energy & Power Source

Description
Abstract:	The upper Kayaoka sheet in the Atsumi area, Northeast Japan, has an alkaline-basaltic composition. The modal olivine and Ni enrichment in the lower part of the sheet indicates the accumulation of early formed olivine crystals. Overall, the average aspect ratio of plagioclase increases from the central part of the sheet toward both the top and bottom margins. The average aspect ratios of plagioclase and calculated crystallisation times at each height of the sheet, except for the lowermost margin, are roughly plotted near the regression line drawn based on those from many sills in previous research. However, we observed that the average aspect ratios of plagioclase in some horizons of the central part of the sheet exhibit an offset from the regression line. The olivine analcite dolerite in the central part of the sheet is rich in zeolite amygdules and glassy mesostasis with a quench texture. These observations suggest that the cooling rate in the central part of the sheet was faster compared with assuming conductive cooling only. A plausible mechanism for the rapid cooling at the centre of the sheet is heat transport by the convection of seawater that has infiltrated the columnar joint. [ABSTRACT FROM AUTHOR]
ISSN:	12264806
DOI:	10.1007/s12303-021-0038-y