The Sierra de Calalaste in Northwestern Argentina, a counterpart of the peri-Gondwanan Ellsworth Terrane in the northern Appalachians?

ESCAYOLA M. P.; VAN STAAL C. R.; DAVIS W.; ROGERS N.

Toronto

Congreso; AGU Meeting Toronto; 2009

AGU - GAC - MAC

The Ellsworth terrane, coastal Maine, is one of a number of fault-bounded blocks that occur along the eastern margin of Ganderia, a peri-Gondwanan terrane that underlies the bulk of the central part of the northern Appalachians. The Ellsworth block is considered part of the Ganderia microcontinent based on its geological history during the Early Paleozoic lithological characteristics and abundance of Early Cambrian detrital zircon. U-Pb zircon geochronology of rhyolitic schists indicates that both the Ellsworth schists (508 pm 0.8 Ma) and overlying Castine volcanics (503 pm 2.5 Ma) are middle Cambrian in age. The rhyolitic tuffs are  interlayered with lava flows of enriched MORB affinity. The epsilon Nd (500) is depleted + 5.8 to +7.5, and Pb isotopic composition is unradiogenic to relatively enriched. Serpentinezed ultramafic sheets and massive sulfide deposits are present. The geologic, geochemical and isotopic characteristics of the bimodal volcanic sequences led recent workers to interpret the Ellsworth terrane as the remnants of a proto-oceanic rift system. The occidental sector of Puna in NW Argentina contains Cambrian to Ordovician magmatic associations distributed in two belts, the Occidental Eruptive Belt and the Oriental Eruptive Belt. Bimodal, basalts and rhyolites of the Occidental eruptive belt correspond to subalkaline, tholeiitic, low-K  sequences developed in a suprasubduction zone environment. The Sierra de Calaste Ranges of the Occidental Eruptive Belt comprise a sequence of metaquarzites, rhyolitic flows and tuffs, mafic gabbroic rocks and some serpentinezed ultramafic sheets. Small massive sulfide deposits are locally also present. U-Pb zircon ages on rhyolites are Upper Cambrian (495 pm 3Ma). Their epsilon Nd values are +4 to+7. Pb isotopic compositions are unradiogenic. The rocks are interpreted to belong to a rift setting similar to that proposed for the  Ellsworth terrane, which is nearly coeval in age. Recent reconnaissance fieldwork  highlight strong similarities between the Sierra de Calalaste rocks and the Ellsworth terrane. A prominent NNE-SSW shear zone, named the Tipa Shear Zone is a major terrane boundary between the Western Pampia and the Famatina terranes and could represent an older terrane boundary that accommodated the separation of Ganderia or an along strike-equivalent (Carolinia?) from Gondwana. We believe that the Ellsworth terrane and the Calaste Ranges, are pieces of a related proto-oceanic setting developed along the western margin of Gondwana during the Middle to Late Cambrian immediately before Ganderia detached from the Gondwanan margin.