Evolution of exhumationand erosion in western west gondwanaland as recorded by detrital zircons of late Neoproterozoic and Cambrian sedimentary rocks of NW and Centraal Argentina.

Abstract

The evolution of the provenance areas for Late Neoproterozoic,Cambrian and Early Ordovician sedimentary and meta-sedimentaryrocks of north central and northwest Argentina is discussed using 123maximum ages of detrital zircons from 42 samples from this andpreviously published studies. Most detrital zircon ages fall into twogroups: 1,200–900 Ma and 670–545 Ma. These ages are essentiallyidentical for the non- to very low grade metamorphic lateNeoproterozoic to Early Cambrian Puncoviscana Formation and thelow to high grade metamorphic rocks of Eastern Sierras Pampeanas.Hence, both units are related to similar provenance areas at thesame time of sedimentation. The time span from zirconcrystallization in the Earth’s crust to exhumation and erosion may bevery long. This is important when determining maximum ages ofsedimentary rocks. Variation of zircon maxima may also beinfluenced by concurrent sedimentary cover of proposed provenanceareas. For the late Mesoproterozoic to early Neoproterozoic zirconage group, an active mountain range of the southwest BrazilianSunsás orogen is the most probable provenance area. The younger,late Neoproterozoic zircons are related to the continuouslydeveloping mountains of the Brasiliano orogen of southwest and southcentral Brazil. Young zircons, up to 514 Ma, from fossil-bearingPuncoviscana and Suncho Formation outcrops are related to late EarlyCambrian volcanism contemporaneous with sedimentation. Thissituation continues through the Late Cambrian to the EarlyOrdovician, but the Sunsás orogen provenance diminishes as possibleRío de la Plata craton origins become important.Keywords West Gondwanaland – Neoproterozoic – Cambrian – Detrital