Abstracts
Summary
In Labrador, the northerly-trending zonesof the Churchill Province are truncated at their southern margin by rocks of the Labrador Orogen within the Grenville Province. Churchill Province rocks locally extend into the Grenville Province where they are grada-tionally reworked. This paper describes thegeology of the central part of the Churchill Province (the Rae Province) in a 3700 km2 area lying astride the Grenville Front.
The eastern part of the area, the Ormadomain, consists of supracrustal rocks intruded by, and infolded into, orthogneiss. The supracrustal unit is dominated by maficvolcanic and pelitic rocks with subordinate psammite, felsic volcanic rocks, quartzite and conglomerate. The orthogneiss unit consists of foliated to gneissic tonalité andgranodiorite. Both units are intruded by aplutonic suite of granite, diorite and gabbro.U-Pb zircon geochronology of four tonalité samples indicates that the majority of orthogneiss in the Orma domain was empiaced in the Late Archean (2682-2675 Ma). These data confirm earlier ideas that parts of the Rae Province consist of reworked Archean crust. U-Pb results of both zircon and titanite analyses from the same samples indicate a Labradorian Pb-loss, but show no influence by either the Hudsonian or Grenvillian orogenies on the U-Pb isotopic systematics.
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