Early Precambrian basic rocks of the USA

Abstract

Early Precambrian basic rocks occur throughout a large part of the USA. Archaean complexes outcrop in two major provinces, one forming the southwestern tip of the Superior Province in northern Minnesota and Wisconsin, and the other comprising the Wyoming craton, outcropping in the mountain ranges of Wyoming and its neighbouring states. Both of these provinces have significant plutonic, hypabyssal and volcanic basic components, ranging in age from early to late Archaean. In addition, early to mid-Proterozoic hypabyssal basic intrusions occur in virtually all of the Archaean cratonic regions, while early to mid-Proterozoic metavolcanic suites occur throughout western central USA. This chapter aims to catalogue and review the most important basic units and to highlight their lithological and geochemical characteristics. We draw attention to the petrological differences and similarities between the various units, and summarise some of the tectonic interpretations which can be drawn from them. -from Authors