Chemical characteristics and geological implication of plagioclase in CA Seamount basalts from the Middle Pacific

doi:10.3969/j.issn.1001-909X.2017.02.003

Abstract

Abstract: Chemical composition of plagioclase phenocryst zone, plagioclase crystallite and silicate of basalts in CA Seamount (sample CAD21), was examined using EPMA method and X-Ray fluorescence spectrometry (XRF) on basis of petrography. The basalts of CA Seamount are intraplate basalts formed by the activity of mantle plume. The core and the edge of zones of plagioclase phenocrysts show nonsequence optical extinction phenomenon, indicating a discontinuous zoning structure. The sequence of zones is labradorite to bytownite from edge to core, showing a normal zoning in the process of magmatic evolution. Such a phenomenon is constrained by melt composition and temperature-pressure condition. Average temperatures of plagioclase phenocrysts are 1 281 ℃(temperature of magmatic source),1 198℃(temperature of magmatic chamber) and 1 071 ℃(temperature of magmatic exhalation) respectively. The small temperature difference indicates a rapidly eruption process, in accord with the formation and eruption characteristics of oceanic island basalt magma.

Key words: CA Seamount, basalt, plagioclase, zoning, crystallization temperature

CLC Number:

P588.14⁺⁵

HE Xin, SUN Guo-sheng, CHU Feng-you, WANG Chun-guang, JIN Rui-xiang, LI Yang, ZHAN Nai-chen, LIU Shi-wei, SUN Jiu-da. Chemical characteristics and geological implication of plagioclase in CA Seamount basalts from the Middle Pacific[J]. Journal of Marine Sciences, 2017, 35(2): 23-32.

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