Textural and mineralogical significance of the Granitic Xenoliths from the Central Volcanic Region, North Island, New Zealand
作者:
A. Ewart,
J. W. Cole,
期刊:
New Zealand Journal of Geology and Geophysics
(Taylor Available online 1967)
卷期:
Volume 10,
issue 1
页码: 31-54
ISSN:0028-8306
年代: 1967
DOI:10.1080/00288306.1967.10428183
出版商: Taylor & Francis Group
数据来源: Taylor
摘要:
Granitic boulders have been found at four localities in the central North Island: Mt Tarawera, Huka, Atiamuri, and Hinuera. They occur closely associated with the acid volcanic suite, in pumice breccias and associated water-laid deposits. Two distinct types of boulders are recognised, the true granodiorites of Tarawera and Huka, and those characteristically containing extensive graphic intergrowths, found at Atiamuri and Hinuera. Both types are characterised by a “high temperature” mineralogy, and are regarded as co-magmatic with the acid volcanic rocks of the region, and not part of the basement. The granodiorites are characterised by subhedral to euhedral zoned plagioclase, subhedral to euhedral embayed quartz, subhedral to interstitial sanidine, and the presence of biotite, hornblende, hypersthene, and magnetite. The granodiorites are considered to be representative of the magma from which they crystallised, but the second type show evidence of progressive potassium enrichment and are considered to be late-stage differentiates of their parent magma. Modal and chemical data are given.
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