Evidence for the granulite-granite connection: Penecontemporaneous high-grade metamorphism, granitic magmatism and core complex development in the Liscomb Complex, Nova Scotia, Canada

Abstract

Upper amphibolite-granulite facies gneisses and granites of the Liscomb Complex (Nova Scotia, Canada), which are exposed in a core complex within the Cambro-Ordovician Meguma Group of southern Nova Scotia, yielded concordant U-Pb zircon/monazite ages of 377 ± 2 and 374 ± 3 Ma, respectively. Geochronological and geochemical data suggest a single Devonian high-grade metamorphic event, which generated the granitic magma by partial melting of the fertile Liscomb gneisses at a depth of ∼30 km. The melting was also synchronous with an extensional event during which the gneisses were uplifted in a core complex associated with the intrusion of granitoids to a depth of ∼10 km. Subsequently, the gneisses and granites underwent rapid exhumation before the deposition of unconformably overlying late Fammenian rocks at ∼364 Ma. These events took place during terminal stages of the Acadian Orogeny and the onset of extensional tectonics in Atlantic Canada during the Middle-Late Devonian. The close temporal and spatial association of Liscomb gneisses/granulites and granites, their major and trace element compositions, and their overlapping isotopic characteristics confirm the hypothesis that high-grade metamorphism and generation of granitic melt are complementary processes. As the Liscomb granites are of similar age, mineralogy and chemistry to the voluminous granitoid plutons found throughout the Meguma Terrane, a similar process is indicated for the rest of the terrane. © 2005 Elsevier B.V. All rights reserved.