Geology of the double Mer White Hills and surrounding region, Grenville Province, eastern Labrador

Abstract

The Double Mer White Hills map area is located in the Grenville Province, easrem Labrador. Major rock groups recognized are orthogenesis, metasedimentary gneiss, granitoid plutons, granulite facies rocks, gabbroid intrusions and the post-Crenvillian Double Mer Formation. The dioritic to granitic orthogenesis and the dominantly pelitic to psammitic metasedimentary gneiss, are interpreted as representatives of a sedimentary-plutonic terrane that was subjected to severe tectonothermal activity at ea. J.65 Ca. The granitoid plutons are either the less deformed parts of the orthogenesis or slightly younger granitoid plutons. Corona-textured gabbroid intrusions generally can be assigned to the ea. 1.4 Ca Michael gabbro, but probably include remnants of the ea. 1.65 Ca Ad/avik intrusive Suite. The Double Mer Formation consists of terrigenous redbeds confined to a post-Crenvillian halfgraben. The map area includes parts of three major crustal segments, the Trans-Labrador batholith and the Croswater Bay and Lake Melville terranes. These are lithologically and structurally distinct regions with a zonal metamorphic patternfrom greenschistfacies in the northwest to granulite facies in the southeast. The deepest level rocks exposed were metamorphosed to about 9-10 kb and 800°C. Metamorphism terminated with Crenvillian orogenesis, involving uplift of deeper level metamorphic rocks from the south, and slicing of the region into thrustbound lithotectonic terranes. Prospects for mineralization of economic interest, which appear low, are confined to minor copper staining associated with pyritic metasedimentary gneiss.