"Secret of the Temple of Doom: A Tale of Subduction and Exhumation, Western Gneiss Region, Norway"

Dr. Rebecca A. Jamieson Professor Emeritus Department of Earth and Environmental Sciences Dalhousie University

B.Sc. Dalhousie 1974; Ph.D. Memorial 1979, Professor of Earth Sciences, Dalhousie, 1979-2016

Research Interests: Metamorphic geology, orogenic tecctonics, and related fields

Study Areas: Western Gneiss Region (Norway), Appalachians (Nova Scotia & Newfoundland), Grenville Orogen (Ontario), Himalaya-Tibet

Approach: Integration of various field and petrological methods (including P-T-t-d paths) with quantitative models of orogenic processes

Title: Secrets of the Temple of Doom: A Tale of Subduction and Exhumation, Western Gneiss Region, Norway

Rebecca A. Jamieson¹, Luke Hilchie^1,2 & Ben Myrer^1,3

¹Department of Earth Sciences, Dalhousie University, Halifax, NS, B3H 4R2 <beckyj@dal.ca>; ²Earthbound Eyes Consulting, Scient Analytics; ³Marine Geomatics, COGS, Lawrencetown, NS

Abstract: The Western Gneiss Region (WGR) of Norway preserves large tracts of ultra-high-pressure (UHP) metamorphic rocks formed in subducted Baltican crust during the Scandian (late Devonian) phase of the Caledonian orogeny. In the Nordøyane UHP domain, the deepest and hottest part of the WGR, coesite and microdiamond are locally preserved in eclogite-facies assemblages. Along the north coasts of the islands of Haramsøya and Flemsøya, rafts of mafic eclogite within migmatitic orthogneisses are surrounded by dioritic “melt envelopes” containing abundant eclogitic enclaves and xenocrysts. At Arhaugen, in an outcrop informally referred to as the “Temple of Doom”, intensely recrystallised eclogite with a steep lineation is separated from the adjacent melt envelope by a dioritic dyke that is highly contaminated with partly digested eclogitic material. The dioritic matrix consists largely of zoned plagioclase, quartz, biotite, hornblende, scapolite, and ilmenite/titanite, and contains abundant xenocrysts including embayed and fragmented garnet and spongy clinopyroxene-plagioclase intergrowths. Coesite is present in garnet xenocrysts from both the dyke and the adjacent melt envelope, but has not yet been found in situ in the adjacent eclogite bodies. The coesite-hosting xenocrysts differ in texture, composition, and inclusion assemblages from garnets in the adjacent eclogites, and also record higher PT conditions. We conclude that the xenocrysts were not derived from the spatially associated eclogite bodies. By implication, their dioritic hosts were not locally derived but must have originated from a different, deeper, source. The results from this study are integrated with a numerical model for the tectonic evolusion of the Western Gneiss Region (Butler et al., Lithosphere, 2015) to shed some light on where and when melting may have taken place, and to assess its possible effects on the exhumation of UHP rocks in western Norway.

Butler, J.P, Beaumont, C. & Jamieson, R.A. (2015) Paradigm lost: Buoyancy thwarted by the strength of the Western Gneiss Region (U)HP terrane, Norway. Lithosphere, 7, 379-407; doi:10.1130/L426.1.