See more from this Division: Topical Sessions
See more from this Session: Alpine Concepts in Geology and the Evolution of Geological Thought
Abstract:
Most gabbros included in the continental crust of the Alps display a Permian-Triassic age; they concentrate in the Austroalpine and Southalpine domains and are often intruded in metamorphic rocks deformed in HT and middle- to intermediate-P conditions. They are interpreted, with the contemporaneous metamorphism often developing in their country rocks, as the sign of a positive thermal anomaly associated to a lithospheric thinning, envisaged by some authors as the precursor of the continental rift leading to opening of the Ligure-Piemontese Alpine Ocean (DAL PIAZ et alii, 1977; LARDEAUX & SPALLA, 1991; SCHUSTER et alii, 2001; REBAY & SPALLA, 2001, SPALLA & GOSSO, 2003; MAROTTA & SPALLA, 2007; SPALLA & MAROTTA, 2007).
The Dent Blanche nappe is the portion of Austroalpine domain of the Western Alps containing the maximum density of Permian gabbros, mostly included within metagranitoids (Arolla gneisses); the main bodies are the Matterhorn and Mont Collon-Dent de Bertol (DAL PIAZ et alii, 1977; MONJOIE et alii, 2005), Sassa (DIEHL et alii, 1952, PENNACCHIONI & GUERMANI, 1993). The tectonic contact between gabbros and the country Arolla metagranitoids is marked by thick persistent mylonites. Polyphase Alpine deformation in the gabbros is highly hetherogeneous; the pre-Alpine and Alpine evolution of the Sassa gabbro complex reveals three Alpine deformation events, reconstructed by means of detailed structural mapping of foliation trajectories. Nearly undeformed hundred m-scale gabbro lenses, displaying only corona-type metamorphic reactions, manifest igneous emplacement meso- to micro-scale structures, related to accretion of the magma chamber (WIEBE & COLLINS, 1998).
See more from this Division: Topical Sessions
See more from this Session: Alpine Concepts in Geology and the Evolution of Geological Thought