Early Precambrian basic rocks of Greenland and Scotland

Abstract

Early Precambrian basic rocks in Greenland and Scotland comprise suites with a wide range of ages, compositions and metamorphic grade, and include plutonic, hypabyssal and volcanic types. The two provinces are conventionally considered to have been originally part of the same craton, and contiguous with the Nain Province of eastern Labrador before the opening of the North Atlantic (Bridgwater et al, 1973, 1978; Korstgård et al, 1987). The Archaean Craton from southern West Greenland to the Lewisian of Scotland comprises a high-grade gneiss complex (Bridgwater et al, 1976; Park and Tarney, 1987a). The development of the best preserved and most extensive part of the craton in West Greenland has been described by several authors (e.g. Bridgwater et al, 1976; Myers, 1976; Kalsbeek, 1981; McGregor et al, 1986). The craton is bounded to the north and south by the Proterozoic Nagssugtoqidian and Ketilidian mobile belts respectively (Figure 11.1) (Allaart, 1976; Escher et al, 1976; Korstgård, 1979a). The composite lithostratigraphic units of these early Precambrian terranes include a wide spectrum of basic lithologies ranging from early Archaean to early Proterozoic. The Archaean Complex of East Greenland, on the other hand, contains relatively few basic units and the craton is dissected by the Ammassalik Proterozoic mobile belt (Chadwick et al, 1989). Abundant high-grade metasedimentdominated supracrustal belts in the centre of the mobile belt (Hall et al, 1989) are probably also early Proterozoic. Reworked Precambrian gneisses also occur sporadically throughout the rest of Greenland (Figure 11.1) and often include supracrustal and intrusive basic units (Andersen and Pulvertaft, 1986; Kalsbeek, 1981; Kalsbeek and Taylor, 1985a; Kalsbeek et al, 1984; Mengel, 1983a, b; Hansen et al, 1987). However, they have been less extensively studied than those of southern West Greenland.