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Journal of Petrology | Volume 44 | Number 6 | Pages 1145-1162 | 2003
© Oxford University Press 2003

High-Temperature Metamorphism and the Role of Magmatic Heat Sources at the Rogaland Anorthosite Complex in Southwestern Norway

MATHIAS WESTPHAL1,*, JOHN C. SCHUMACHER1,{dagger} and STEFAN BOSCHERT2

1 INSTITUT FÜR MINERALOGIE, PETROLOGIE UND GEOCHEMIE DER UNIVERSITÄT FREIBURG IM BREISGAU, ALBERTSTRASSE 23B, D-79104 FREIBURG, GERMANY
2 KRISTALLOGRAPHISCHES INSTITUT, DER UNIVERSITÄT FREIBURG IM BREISGAU, D-79104 FREIBURG, GERMANY

Present address: Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK. E-mail: j.c.schumacher{at}bris.ac.uk

The Rogaland complex covers ~1000 km2 in southwestern Norway and consists mainly of anorthosite massifs and the layered Bjerkreim–Sokndal lopolith (BSL). These rocks intrude charnockitic migmatites containing intercalated marbles and garnetiferous migmatites. High-temperature mineral isograds (pigeonite, osumilite and orthopyroxene) in the metamorphic basement are subparallel to and increase in grade towards the intrusive complex. P–T estimates from the country rocks show a roughly linear increase in temperature towards the BSL consistent with the distribution of isograds. The peak P–T conditions at 20 and 2·5 km from the contact at ~5 kbar range from 700 to >1000°C. Field relations and age determinations link the high-T metamorphism and the magmatism. The two-dimensional thermal modelling indicates that heat from a single magmatic cooling unit is not sufficient to produce the array of isograds and the peak metamorphic temperatures. Two magmatic episodes separated by ~3 Myr, however, can account for the high-temperature metamorphism. In this model, the emplacement and crystallization of the anorthosite produces a regional thermal gradient (from 750 to 600°C). After a brief hiatus a second, smaller body (BSL) provides an additional thermal input that results in an array of high-temperature isograds and country-rock temperatures >1000°C.

KEY WORDS: Rogaland; UHT; thermal model; osumilite


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Home page
 Geological Society, London, Special PublicationsHome page
A. Moller, P. J. O'Brien, A. Kennedy, and A. Kroner
Linking growth episodes of zircon and metamorphic textures to zircon chemistry: an example from the ultrahigh-temperature granulites of Rogaland (SW Norway)
Geological Society, London, Special Publications, January 1, 2003; 220(1): 65 - 81.
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