The development of thin thrust sheets and basement-cover sandwiches in the southern part of the Rinkian belt, Umanak district, West Greenland

Abstract

At the southern margin of the Rinkian belt, West Greenland, it can be demonstrated that the Lower Proterozoic Marmorilik Marble Formation, which was deposited unconformably on a gneiss basement, has been squeezed and stretched into a thin recumbent syneline and overridden by the basement over an area of more than 1000 km2. Aseeond supracrustal cover unit, seen now as a thin mylonitic biotite schist horizon, occurs at a slightly higher structural level, and marks the site of another thrust along which the gneiss basement has overridden its supracrustal cover. The demonstration that a superficially simple sequence consisting of concordant layers of different gneiss types and supracrustal rocks is in faet a pile ofthrust sheets, has important implications for the interpretation of both West Greenland and other Precambrian areas.