The effect of crystallization time on plagioclase grain shape in dolerites

Holness, Marian B. (2014) The effect of crystallization time on plagioclase grain shape in dolerites. Contributions to Mineralogy and Petrology, 168 (5). pp. 1-19. ISSN 0010-7999 (Print) 1432-0967 (Online) DOI


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The average aspect ratio of plagioclase, measured in thin section, varies systematically through dolerite sills, with a symmetrical “M”-shaped profile observed in sills thinner than ~200 m. Thicker sills show the same marginal reversal at the base, but average aspect ratios appear to continue increasing towards the top, creating an “S”-shaped profile. A distorted “M”-shaped profile is visible in the stratigraphic variation of plagioclase average aspect ratios in the prehistoric Makaopuhi lava lake, with the centre of the “M” in the olivine-enriched horizon close to the base of the lake. Higher overall values of average aspect ratio are observed in thin sills compared to thicker sills, demonstrating that the plagioclase in more slowly crystallized bodies is more equant than that in more rapidly crystallized bodies. There is a strong correlation between the plagioclase average aspect ratio in the central parts of the sills and the crystallization time calculated using a simple one-dimensional thermal model assuming conductive cooling. The cause of the marginal reversals in average aspect ratio is not well understood, but may result from early grain impingement in the developing crystal mushy layer.

Item Type: Article
Uncontrolled Keywords: 2014AREP; IA68;
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
07 - Gold Open Access
Journal or Publication Title: Contributions to Mineralogy and Petrology
Volume: 168
Page Range: pp. 1-19
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 06 Feb 2015 17:41
Last Modified: 16 Feb 2015 18:25

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