THE LATE ARCHEAN RECORD: A PUZZLE IN CA. 35 PIECES

Abstract

The global Archean record preserves ca. 35 large cratonic fragments and a less well defined number of smaller slivers. Most Archean cratons display rifted margins of Proterozoic age and therefore are mere fragments of supercratons, which are defined herein as large ancestral landmasses of Archean age with a stabilized core that on break-up spawned several independently drifting cratons. The tectonic evolution of individual Archean cratons, such as the Slave craton of North America or the Kaapvaal craton of southern Africa, should therefore always be considered in the context of their ancestral supercratons. This is particularly true for many of the smaller cratons, which are too limited in size to preserve the complete tectonic systems that led to their formation. These limitations not only apply to the crustal geology of Archean cratons but also to their underlying lithospheric mantle keels. If these keels are Archean in age, as their broad correlation with ancient surface rocks suggests, they also are rifted and drifted remains of larger keels that initially formed below ancestral supercratons. The study of Archean cratons and their lithospheric keels should thus be global in scope.