Development of high thermal gradients by coeval transpression and magmatism during the Variscan orogeny: insights from the Cap de Creus (Eastern Pyrenees)

摘要

The Cap de Creus massif in the Eastern Pyrenees is a fragment of the Variscan mid-crust. Geological mapping and meso- and micro-scale analysis of the relationships between fold structures, metamorphic mineral assemblages and fabrics affecting igneous bodies suggest the interaction of three processes: deformation, metamorphism and magmatism. Low pressure progade metamorphism grades laterally from greenschist to amphibolite facies over a distance of similar to5 km. Zones of intense metamorphism coincide with transpressional deformation and with the intrusion of small sheets of diorite and granitoid. Sillimanite schists and small migmatite pods are distributed around the small intrusions of basic-intermediate composition. The inferred maximum thermal gradient is >80 degreesC/km. This thermal pattern is similar to patterns observed in other Variscan massifs in the Pyrenees, where high metamorphic gradients are interpreted in different ways. In the NE Cap de Creus, the type and distribution of prograde metamorphism was caused, or at least enhanced, by the intrusion of diorites and granitoids. Alternatively, deformation developed at prograde conditions and synchronously with magmatism, displays a highly heterogeneous distribution, producing a sub-vertical zone of high strain that coincides with domains of highest grade metamorphism and igneous activity. This tons, of high strain, developed in a broad transpressive regime, could have favoured the injection of magmatic sheets from deep to mid-crustal levels. Progressive folding from prograde to retrograde metamorphic conditions might account for the narrowing of metamorphic zones. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 71]