High-pressure and high-temperature metamorphism of the mafic and ultramafic Lac Espadon suite, Manicouagan imbricate zone, eastern Grenville Province, Quebec
R. Cox et A. Indares, High-pressure and high-temperature metamorphism of the mafic and ultramafic Lac Espadon suite, Manicouagan imbricate zone, eastern Grenville Province, Quebec, CAN MINERAL, 37, 1999, pp. 335-357
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.