Significance of MORB-derived Amphibolites from the Aracena Metamorphic Belt, Southwest Spain |
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| Authors: | CASTRO ANTONIO; FERNANDEZ CARLOS; DE LA ROSA JESUS D; MORENO-VENTAS IAKI; ROGERS GRAEME |
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| Institution: | 1DEPARTAMENTO DE GEOLOGA, UNIVERSIDAD DE HUELVA, CAMPUS DE LA RBIDA 21819 HUELVA, SPAIN
2SCOTTISH UNIVERSITIES RESEARCH AND REACTOR CENTRE, EAST KILBRIDE GLASGOW G75 0QU, UK |
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| Abstract: | The Aracena metamorphic belt, in the southwest Iberian Massif,is characterized by the presence of MORB-derived amphibolitesand continental rocks deformed and metamorphosed during theHercynian orogeny. Geochemical relationships of these amphibolitesindicate the existence of a multiple fractionation process froma set of parental magmas, implying the existence of a multi-chambersystem beneath the ridge where the basalt protolith was extruded.Neodymium isotopic ratios are typical of MORB, and oxygen isotopesindicate that these amphibolites have been derived from theuppermost part of the oceanic crust. Thermal evolution, revealedfrom the study of chemical variations in the amphibole chemistry,is interpreted as resulting from subduction in a low-pressureregime in which the thermal structure of the continental hanging-wallplayed an important role. This continental wall was previouslyheated by subduction of a slab window resulting from migrationof a triple junction along the continental edge during plateconvergence. Three petrologic arguments support this tectonicmodel. These are: (1) the low-pressure inverted metamorphicgradient of amphibolites of the oceanic domain; (2) the high-temperature-low-pressure metamorphism of the continental hanging wall; (3)the early intrusion of boninites into the continental domain.
*Corresponding author. |
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