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Crustal anatexis and melt extraction during deformation in the restitic xenoliths at El Joyazo (SE Spain)

Published online by Cambridge University Press:  05 July 2018

B. Cesare
Affiliation:
Dipartimento di Mineralogia e Petrologia, Università di Padova, Corso Garibaldi 37, 1-35137 Padova, Italy
E. Salvioli Mariani
Affiliation:
Istituto di Petrografia, Università di Parma, Viale delle Scienze 78, 1-43100 Parma, Italy
G. Venturelli
Affiliation:
Istituto di Petrografia, Università di Parma, Viale delle Scienze 78, 1-43100 Parma, Italy

Abstract

The dacite of El Joyazo contains abundant metapelitic xenoliths. These can be divided into two main types: garnet-biotite-sillimanite and spinel-cordierite xenoliths. In the xenoliths the widespread occurrence of rhyolitic glass as interstitial films, foliation-parallel layers and primary melt inclusions in all mineral phases indicates that these assemblages developed in the presence of a melt phase, i.e. during anatexis. The composition of the interstitial glass is comparable to that of the melt inclusions, suggesting that melt was locally produced. Phase equilibria indicate that anatexis occurred at P-T conditions of 5–7 kbar and 850±50°C.

Several microstructural lines of evidence show that melt extraction was assisted by deformation during foliation development, and that on the scale of the xenoliths (up to 50 cm) melt escaped mainly by flow along foliation planes. The development of a syn-anatectic foliation also suggests that metapelitic rocks were involved in high-grade metamorphism and partial melting prior to fragmentation and dispersion in the host dacite.

Mass balance calculations, based on the chemical composition of interstitial glass and melt inclusions in minerals, the bulk xenoliths and representative samples of potential pelitic sources support a model wherein the xenoliths represent restites after the extraction of 30 to 55 wt.% melt from graphitic metapelite protoliths similar to the rocks constituting the surrounding Alpujarride metamorphic complex.

Type
Petrology
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1997

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