Crystallization history of granophyric intrusives from the Peruvian Coastal Batholith |
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| Authors: | MA Bussell |
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| Institution: | Department of Geography and Geology, Marlborough Building, Polytechnic of North London, 383 Holloway Road, London, N. 7. 6PN, UK |
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| Abstract: | In the Huaura centred complex, a component of the Coastal Batholith of Peru, water undersaturated granitic magma of the San Jeronimo suite rose from an environment of 4–7 kb pressure to be emplaced at pressures of ca. 0.5 kb. Within the suite, different magma compositions originated from the partial melting of contrasting quartz-rich and quartz-poor source rocks. Initially marginal crystallization resulted in granitic textures with early precipitation of plagioclase, quartz, magnetite, biotite and hornblende under relatively reducing conditions. Subsequent residual concentration of water and oxygen in the centre of the pluton gave rise to more oxidizing conditions and ultimately water saturation resulted in rupture of the pluton roof. The consequent quenching resulted in extensive development of granophyric textures in the residual magma. Distribution of Rb, Sr and major elements can be explained largely by fractionation of ca. 18 % of the observed phenocryst assemblage. Ba depletion and Rb enrichment with evolution of the magma suggest an important role for diffusive transfer during the late episode of granophyre crystallization. |
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