Transformation of Archaean Lithospheric Mantle by Refertilization: Evidence from Exposed Peridotites in the Western Gneiss Region, Norway |
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Authors: | BEYER ELOISE E; GRIFFIN WILLIAM L; O'REILLY SUZANNE Y |
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Institution: | 1 ARC NATIONAL KEY CENTRE FOR GEOCHEMICAL EVOLUTION AND METALLOGENY OF CONTINENTS, DEPARTMENT OF EARTH AND PLANETARY SCIENCES, MACQUARIE UNIVERSITY NSW 2109, AUSTRALIA
2 CSIRO EXPLORATION AND MINING, NORTH RYDE NSW 2113, AUSTRALIA |
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Abstract: | Orogenic peridotites occur enclosed in Proterozoic gneissesat several localities in the Western Gneiss Region (WGR) ofwestern Norway; garnet peridotites typically occur as discretezones within larger bodies of garnet-free, chromite-bearingdunite and are commonly closely associated with pyroxenitesand eclogites. The dunites of the large Almklovdalen peridotitebody have extremely depleted compositions (Mg-number 9293·6);the garnet peridotites have lower Mg-number (90·691·7)and higher whole-rock Ca and Al contents. Post-depletion metasomatismof both rock types is indicated by variable enrichment in thelight rare earth elements, Th, Ba and Sr. The dunites can bemodelled as residues after very high degrees (>60%) of meltextraction at high pressure (57 GPa), inconsistent withthe preservation of lower degrees of melting in the garnet peridotites.The garnet peridotites are, therefore, interpreted as zonesof melt percolation, which resulted in refertilization of thedunites by a silicate melt rich in Fe, Ca, Al and Na, but notTi. Previous ReOs dating gives Archaean model ages forthe dunites, but mixed Archaean and Proterozoic ages for thegarnet peridotites, suggesting that refertilization occurredin Proterozoic time. At least some Proterozoic lithosphere mayrepresent reworked and transformed Archaean lithospheric mantle. KEY WORDS: Archaean mantle; Proterozoic mantle; Western Gneiss Region, Norway; mantle metasomatism; garnet peridotite |
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Keywords: | : Archaean mantle Proterozoic mantle Western Gneiss Region Norway mantle metasomatism garnet peridotite |
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