Reconnaissance geochronology and geochemistry of the Mont-Tremblant gneiss of the Morin terrane, Grenville Province, Québec

摘要

The Mont-Tremblant gneiss is a granulitefaciesnquartzofeldspathic orthogneiss unit innMorin terrane of the southwestern GrenvillenProvince. These gneisses are the oldest rocks innthe Morin terrane and country rocks to intrusionsnof the 1.15 Ga anorthosite- mangeritecharnockite-ngranite (AMCG) suite. ThenMont-Tremblant gneiss may also be basementnto the Grenville Supergroup, but until now itnhas not been directly dated. Sensitive highresolutionnion microprobe–reverse geometryn(SHRIMP-RG) geochronology of zirconnfrom two penetratively deformed samples ofnMont-Tremblant gneiss yields igneous ages ofn1324 ± 38 Ma and 1333 ± 32 Ma (2 ), and onensample shows metamorphic zircon growthnduring the Shawinigan orogeny at 1159.4 ±n15.6 Ma. Geochemically, Mont-Tremblantngneiss samples are calc-alkaline, granitic, andnshow hallmarks of an evolved arc environment.nThese characteristics are consistentnwith the Mont-Tremblant gneiss being correlativenwith the Geon 14 Lacoste and Bondynsuites in the Central Metasedimentary Beltnof Québec to the west, but contrast with thenmore juvenile tonalitic Geon 14 calc-alkalinensuites in the Adirondack Highlands and othernGrenville outliers in the Appalachian Mountains.nThis transition may refl ect differences innthe lithosphere along strike of the Laurentiannmargin during Geon 14 subduction.