Eclogite and garnet pyroxenite from Stor Jougdan, Seve Nappe Complex, Sweden: implications for UHP metamorphism of allochthons in the Scandinavian Caledonides
2016 (English)In: Journal of Methamorphic Geology, Vol. 34, no 2, 103-119 p.Article in journal (Refereed) Published
Ultrahigh-pressure metamorphism (UHPM) has recently been discovered in far-travelled allochthons of the Scandinavian Caledonides, including finding of diamond in the Seve Nappe Complex. This UHPM of Late Ordovician age is older and less recognized than that in the Western Gneiss Region of southwestern Norway, which was related to terminal collision between Baltica and Laurentia. Here we report new evidence of UHPM in the Lower Seve Nappe, recorded by eclogite and garnet pyroxenite from the area of Stor Jougdan in northern Jämtland, central Sweden. Peak-metamorphic assemblage of eclogite, garnet + omphacite + phengite + rutile + coesite? yields P–Tconditions of 2.8–4.0 GPa and 750–900 °C, constrained by conventional geothermobarometry and thermodynamic modelling in the NCKFMTASH system. The prograde metamorphic evolution of the eclogite is inferred from inclusions of zoisite and amphibole in garnet, which are stable at lower pressure, whereas the retrograde evolution is recorded by formation of diopsidic clinopyroxene + plagioclase symplectites after omphacite, growth of amphibole replacing these symplectites, and of titanite around rutile. In garnet pyroxenite the peak-metamorphic assemblage consists of garnet + orthopyroxene + clinopyroxene + olivine. P–T conditions of 2.3–3.8 GPa and 810–960 °C have been derived based on the conventional geothermobarometry and thermodynamic modelling in the CFMASH and CFMAS systems. Retrograde evolution has been recognized from replacement of pyroxene and garnet by amphibole. The results show that eclogite was metamorphosed during deep subduction of continental crust, most probably derived from the continental margin of Baltica, whereas the origin and tectonic setting of the garnet pyroxenite is ambiguous. The studied pyroxenite/peridotite of Baltican subcontinental affinity could have been metamorphosed as a part of the subducting plate and exhumed due to the downward extraction of a forearc lithospheric block.
Place, publisher, year, edition, pages
2016. Vol. 34, no 2, 103-119 p.
eclogite–garnet pyroxenite;subduction–exhumation;Swedish Caledonides;ultrahigh-pressure allochthons
Geology Other Earth and Related Environmental Sciences
Research subject Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
IdentifiersURN: urn:nbn:se:uu:diva-271063DOI: 10.1111/jmg.12173ISI: 000369864800001OAI: oai:DiVA.org:uu-271063DiVA: diva2:891076
FunderThe Crafoord FoundationThe Royal Swedish Academy of Sciences, 007Swedish Research Council, 2012-4441