The Significance of Granophyric and Myrmekitic Textures in the Lundy Granites

D. Shelley
Department of Geology, University of Liverpool1
1Present Address: Dept. Geol., Univ. Canterbury, Christchurch, New Zealand.

Summary: Zonal myrmekitic and granophyric intergrowths in plagioclase and K-feldspar phenocrysts are described. There are two such zones in the feldspars of the Late Granite, G2, but only one in the Early Granite, G1. The zonal granophyric intergrowths are the end-product of the replacement of myrmekitic plagioclases by K-feldspar. Transitional stages of this replacement, which took place in the solid state, are represented in numerous examples. The zones of myrmekite, which also represent growth in the solid state, occur between zones of magmatic plagioclase, which is oscillatory-zoned. It is concluded that the granites evolved at depth under the influence of at least three phases of volcanic activity. Each of these phases resulted in the partial melting of the country rocks with subsequent magmatic crystallization, followed further, under the slow cooling conditions, by extensive reaction in the solid state. During each of the final two phases, some of the granite was intruded as a crystal mush to form G1 and G2, in which the phenocrysts retain evidence of their evolution at depth whilst the ground-mass gives evidence of the final magmatic crystallization.

Mineralogical Magazine; March 1966 v. 35; no. 273; p. 678-692; DOI: 10.1180/minmag.1966.035.273.03
© 1966, The Mineralogical Society
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