Documentation of a 1450 Ma contractional orogeny preserved between the 1850 Ma Sudbury impact structure and the 1 Ga Grenville orogenic front, Ontario, Canada

Abstract

A 1453–1445 Ma contractional deformation event is documented in rocks of the Early Proterozoic Huron Supergroup at the southeastern boundary between the Hudsonian craton to the northwest and an Early to Middle Proterozoic granitoid suite that forms the northeasternmost recognized extension of the Transcontinental Proterozoic Provinces. Detailed structural mapping, quartz c-axis fabrics, and grain-shape analysis indicate that four major orogenic phases have affected the area: (1) the Penokean orogeny, which predated the 1850 Ma Sudbury impact event, (2) ca. 1750 Ma granite plutonism, (3) ca. 1450 Ma orogenic events, and (4) the ca. 1000 Ma Grenvillian orogeny. The Murray fault zone, which likely accommodated considerable ductile displacement during the Penokean orogeny, underwent only brittle deformation during the younger orogenies. The previously undocumented Long Lake fault represents the northern limit of significant ductile south-over-north reverse thrusting during 1453–1445 Ma deformation. The effect of the Grenvillian orogeny in this area appears to have been minor. No deformation features could be linked to the intrusion of the ca. 1750 Ma granitoid suite.