Mid-Proterozoic evolution of the eastern Grenville Province, Canada

Abstract

Geological investigations in the eastern Grenville Province during the last decade have resulted in: (i) recognition of a 1710–1620 Ma Labradorian Orogeny, (ii) increased knowledge of a Middle Proterozoic anorogenic event, (iii) identification of Grenvillian plutonism, (iv) recognition and delineation of Grenvillian lithotectonic terrenes, (v) development of models linking mid-Proterozoic eastern Laurentia and Baltica. The concept of a major 1710–1620 Ma orogenic event within the eastern Grenville Province, involving mainly clastic sedimentation followed by calc-alkaline to alkali-calcic plutonism and the emplacement of layered gabbronorite to monzonite complexes, is now well established. The 1450–1250 Ma Middle Proterozoic anorogenic event resulted in the emplacement of anorthosite-granite massifs, hypabyssal mafic intrusions, alkalic felsic magmatism and rift-related mafic volcanism and associated terrestrial sedimentation. These rocks are part of a more widespread anorogenic event that extended across the southern parts of Laurentia and Baltica. Geochronological studies have confirmed that Grenvillian plutonism occurred in the southern part of the eastern Grenville Province between 1130–1000 Ma and 966–956 Ma. Several distinct lithotectonic terranes are now recognized in the eastern Grenville Province. The exterior terranes are regions of structural telescoping, but retain elements of structural and lithological continuity with the foreland. Several large, lobate allochthonous terranes are present south of the exterior terranes. Away from their margins, the allochthonous terranes were not greatly modified during Grenvillian orogenesis, suggesting that they overthrust and buried the exterior terranes, but remained at high crustal levels themselves. Continued studies have affirmed mid-Proterozoic correlations between eastern Laurentia and Baltica. Structural trends and thrust directions in eastern Labrador differ from the remainder of the Grenville Province, and provide geological support for paleomagnetic models advocating rotation and collision of Baltica with eastern Laurentia.

Key Words:

• Mid-Proterozoic
• Grenville Province
• Labradorian Orogeny
• Laurentia
• Baltica
• Grenvillian