Proterozoic-style intracratonic orogens and basins: extension, sedimentation, magmatism

Abstract

Early Precambrian greenstone belts (Chapter 10) are relatively uniform and lithologically “simple”, with a limited selection of rock types. This is the consequence of less diversified early crustal evolution, as well as deep erosion that has progressively removed the more varied upper levels and exhumed the lower levels. The predominantly greenschist-metamorphosed greenstone belts rest on or border older, high-grade metamorphosed “basement complexes” (Chapter 14) and had likely been initiated by rifting under conditions of the then prevalent mantle plume events (Groves et al., 2005). However, neither the distinct stages of rifted margin development as apparent in the geologically younger systems (Chapter 12), nor the metallogenesis resulting from interaction of the early stages of “greenstone” evolution with the old basement, are emphasized in the literature. They, however, exist even in the oldest juvenile greenstone belts, although as an exception, in the form of the mature “pre-greenstone” association of quartz arenites or conglomerates, carbonates, possible evaporites, terrigenous detrital sediments, interspersed with at least partly subaerial basalt flows and sometimes rhyolitic ignimbrites (e.g. Thurston and Chivers, 1990). By the Proterozoic (or even earlier as in the Kaapvaal Craton; Tankard et al., 1982) the frequency and, especially, preservation of the intracratonic rock- and oreforming environments, sustained by development of sublithospheric mantle and repeated extension of the continental crust combined with periodic influx of mantle-generated magmas from depth, have increased considerably.