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Upper-amphibolite facies partial melting of paragneisses from the Epupa Complex,NW Nambia,and relations to Mesoproterozoic anorthosite magmatism.
Brandt, S. and Klemd, R. (2008) Upper-amphibolite facies partial melting of paragneisses from the Epupa Complex,NW Nambia,and relations to Mesoproterozoic anorthosite magmatism. Journal of Metamorphic Geology, 26 (9). pp. 871-893. DOI 10.1111/j.1525-1314.2008.00793.x.
Full text not available from this repository.Abstract
The evolution of the mineral assemblages and P-T conditions during partial melting of upper-amphibolite facies paragneisses in the Orue Unit, Epupa Complex, NW Namibia, is modelled with calculated P-T-X phase diagrams in the Na(2)O-CaO-K(2)O-FeO-MgO-Al(2)O(3)-SiO(2)-H(2)O system. The close concordance of predictions from the phase diagrams to petrographic observations and thermobarometric results documents that quantitative phase diagrams are suitable to explain the phase relationships in migmatitic upper-amphibolite facies low- and medium-pressure metapelites, which occur in many high-grade metamorphic terranes worldwide. Different mineral assemblages in the migmatitic metapelites of the Orue Unit reflect regional discrepancies in the metamorphic grade: in a Northern Zone, early biotite-sillimanite-quartz assemblages were replaced via melt-producing reactions by cordierite-bearing assemblages. In a Southern Zone, they were replaced via melt-producing reactions by garnet-bearing assemblages while cordierite is restricted to rare metapelitic granofelses, which preserve Grt-Sil-Crd-Bt peak assemblages. Peak-metamorphic conditions of 700-750 degrees C at 5.5-6.7 kbar in the Southern Zone and of similar to 750 degrees C at 4.5 kbar in the Northern Zone are estimated by integrating thermobarometric calculations with data from calculated mineral composition isopleths. Retrograde back-reactions between restite and crystallizing melt are recorded by the replacement of garnet by biotite-sillimanite and/or biotite-muscovite intergrowths. Upper-amphibolite facies metamorphism and partial melting (c. 1340-1320 Ma) in the rocks of the Southern Zone of the Orue Unit, which underwent probably near-isobaric heating-cooling paths, are attributed to contact metamorphism induced by the coeval (c. 1385-1319 Ma) emplacement of the Kunene Intrusive Complex, a huge massif-type anorthosite body. The lower-pressure metapelites of the Northern Zone are interpreted to record contact metamorphism at an upper crustal level.
Document Type: | Article |
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Keywords: | contact metamorphism geothermobarometry metapelite migmatite phase diagrams nw namibia intrusive complex reaction textures kunene complex western angola pelitic rocks pb ages u-pb garnet granulites |
Research affiliation: | Kiel University |
Refereed: | No |
Date Deposited: | 12 Jan 2012 05:58 |
Last Modified: | 23 Sep 2019 21:48 |
URI: | https://oceanrep.geomar.de/id/eprint/15829 |
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