Identifying Laurentian and SW Gondwana sources in the Neoproterozoicto Early Paleozoic metasedimentary rocks of the Sierras Pampeanas:Paleogeographic and tectonic implications

Abstract

The provenance of Neoproterozoic to Early Paleozoic sedimentary rocks in the Sierras Pampeanas has beenestablished using U–Pb SHRIMP age determination of detrital zircons in twelve metasedimentary samples,with supplementary Hf and O isotope analyses of selected samples. The detrital zircon age patterns show thatthe western and eastern sectors of the Sierras Pampeanas are derived from different sources, and were juxta-posed during the Early Cambrian‘Pampean’collision orogeny, thus defining initiation of the supercontinentstage of southwestern Gondwana. The Western Sierras Pampeanas (WSP), which extend northwards to thesouthern Puna (Antofalla) and the Arequipa Massif (Peru), constitute a single large continental basement ofPaleoproterozoic age—the MARA block—that was reworked during the Grenvillian orogeny. The MARA blockprobably extends eastwards to include the Río Apa block (southern Brazil), but in this case without aMesoproterozoic overprint. Detrital zircons from the WSP and Antofalla yield age peaks between 1330 and1030 Ma, remarkably similar to the range of ages in the Grenville province of eastern Laurentia. The WSPNeoproterozoic sedimentary cover to this basement shows the same 1330–1030 component, but also includesimportant 1430–1380 Ma zircons whose juvenile Hf and O isotopic signatures strongly suggest derivationfrom the Grenville and the Southern Granite–Rhyolite provinces of eastern Laurentia. In contrast the EasternSierras Pampeanas metasedimentary rocks have a typically bimodal detrital zircon pattern with peaks atca. 1000 and 600 Ma, which respectively indicate sources in the Natal–Namaqua belt and the East African orogenand/or the Dom Feliciano belt of SE Brazil and Uruguay. Sedimentary rocks in the Eastern Sierras Pampeanas andPatagonia deposited during the Late Early Cambrian–Early Ordovician interval, after the Pampean orogeny, havedetrital patterns common to many sectors along the Terra Australis orogen, reflecting increasingly dominantinput to the Paleozoic basins from the Neoproterozoic to Early Cambrian orogenic belts of the Gondwana margin.