High-pressure and high-temperature metamorphism of the mafic and ultramafic Lac Espadon suite, Manicouagan imbricate zone, eastern Grenville Province, Quebec

The Lac Espadon suite (LES) of the Manicouagan Imbricate Zone (Quebec) is c omprised of layered mafic and ultramafic rocks, Labradorian in age (ca. 165 0-1630 Ma) that were variably deformed and metamorphosed under high-pressur e and high-temperature (high-PT) conditions during the Grenvillian Orogeny. Maximum P-T conditions of 780-930 degrees C at 16-19 kbar (high-T eclogite facies) are recorded in massive coronitic troctolite and hornblendite from the western part of the LES. In these rocks, metamorphic coronas of orthop yroxene, clinopyroxene and garnet have grown at the expense of igneous oliv ine and plagioclase. Relict plagioclase contains inclusions of kyanite and corundum, and garnet coronas locally preserve growth zoning. Deformed margi ns of the mafic rocks have granoblastic hydrous assemblages that are interp reted to have equilibrated during exhumation at ca. 700 degrees C at 10-12 kbar and then down to ca. 600 degrees C at 5 kbar (amphibolite-facies condi tions), suggesting a steep retrograde P-T path. Olivine gabbro from the eas tern part of the LES records peak conditions of 775-870 degrees C at 14.5-1 6.25 kbar. Granoblastic areas in the rock are partially hydrated and give c onditions of 760-820 degrees C at 12-14 kbar, suggesting a near-isothermal P-T trajectory. The P-T paths are compatible with structural evidence sugge sting tectonic exhumation of these rocks by northwesterly thrusting, with e xtension on top of the pile. The high-PT conditions and steep decompression paths recorded by the LES are similar to those in several adjacent and nea rby terranes, suggesting widespread tectonic exhumation of the lower crust in this area of the Grenville Province.