Journal of Petrology | Volume 37 | Number 2 | Pages 235-260 | 1996
© Oxford University Press 1996
research-article |
Significance of MORB-derived Amphibolites from the Aracena Metamorphic Belt, Southwest Spain
1DEPARTAMENTO DE GEOLOGÍA, UNIVERSIDAD DE HUELVA, CAMPUS DE LA RÍBIDA 21819 HUELVA, SPAIN
2SCOTTISH UNIVERSITIES RESEARCH AND REACTOR CENTRE, EAST KILBRIDE GLASGOW G75 0QU, UK
Received January 23, 1995; Revised typescript accepted September 11, 1995
ABSTRACT
The Aracena metamorphic belt, in the southwest Iberian Massif, is characterized by the presence of MORB-derived amphibolites and continental rocks deformed and metamorphosed during the Hercynian orogeny. Geochemical relationships of these amphibolites indicate the existence of a multiple fractionation process from a set of parental magmas, implying the existence of a multi-chamber system beneath the ridge where the basalt protolith was extruded. Neodymium isotopic ratios are typical of MORB, and oxygen isotopes indicate that these amphibolites have been derived from the uppermost part of the oceanic crust. Thermal evolution, revealed from the study of chemical variations in the amphibole chemistry, is interpreted as resulting from subduction in a low-pressure regime in which the thermal structure of the continental hanging-wall played an important role. This continental wall was previously heated by subduction of a slab window resulting from migration of a triple junction along the continental edge during plate convergence. Three petrologic arguments support this tectonic model. These are: (1) the low-pressure inverted metamorphic gradient 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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