The limits of 3 distinct upper Palaeozoic to lower Mesozoic tectono-stratigraphic zones of the ancestral Pacific margin of Gondwana in southern South America are documented. These are: a fore-arc region consisting in part of ‘oceanic’ components; a magmatic arc that is coincident with Carboniferous to Triassic continental sedimentation; and a back-arc region comprising the upper Palaeozoic epicratonic sequences of the ‘Samfrau Geosyncline’. These zones, traceable 2300 km from 29–56°S (Cape Horn), document the semi-continuous subduction of the ancestral Pacific floor from the Middle Devonian to the Triassic. Between 29°S and 37°S the palaeo-subduction zone was roughly coincident with the present Pacific coast line. Between 37°S and Cape Horn, the subduction zone migrated progressively westward as an ‘Alaskan’ style accretionary prism grew to a width of 250 km. While in the northern sector, Jurassic are intrusions are coincident with the upper Palaeozoic are intrusions, in the S they intruded the upper Palaeozoic to lower Mesozoic accretionary prism 200 km W of their Palaeozoic equivalents. No post middle Palaeozoic ‘sutures’ have been identified in southern South America. Hence, there is no evidence of late Palaeozoic, Mesozoic, or Cenozoic accretion of discrete microplates.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.