The crustal tongue melting model and the origin of massive anorthosites |
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| Authors: | JC Duchesne JP Liégeois J Vander Auwera & J Longhi |
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| Institution: | L.A. Géologie, Pétrologie et Géochimie, Universitéde Liège, B-4000 Sart Tilman, Belgium,;Department of Geology, Africa Museum, B-3080 Tervuren, Belgium, and, L.A. Géologie, Pétrologie et Géochimie, Universitéde Liège, B-4000 Sart Tilman, Belgium,;L.A. Géologie, Pétrologie et Géochimie, Universitéde Liège, B-4000 Sart Tilman, Belgium,;Lamont-Doherty Earth Observatory, Palisades, NY 10964, USA |
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| Abstract: | Recent detailed field studies in several anorthosite complexes have shown that anorthosites are frequently associated with weakness zones in the crust which may have favoured their emplacement at mid-crust levels. Recent experimental data have shown that the parent magma compositions of various anorthosite massifs lie on thermal highs in the relevant phase diagrams at 10–13 kbar, indicating that these magmas cannot be derived by fractionation of peridotitic mantle melts but by melting of gabbronoritic sources in the lower crust at 40–50 km depths. In the Sveconorwegian Province terne boundaries have been traced in deep seismic profiles to Moho offsets or to tongues of lower crustal material underthrust to depths higher than 40 km. In Southern Norway, we suggest that a lithospheric-scale weakness zone (the Feda transition zone?) has channelled the Rogaland anorthosites through linear delamination, asthenospheric uprise and melting of a mafic lower crustal tongue. |
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