The Difunta Correa metasedimentary sequence (NW Argentina): relict of a Neoproterozoic platform? — elemental and Sr-Nd isotope evidence
The Sierra de Pie de Palo (Western Sierras Pampeanas, Argentina) in the Andean foreland is mainly formed by a Mesoproterozoic basement and an Ediacaran metasedimentary cover referred to as the Difunta Correa metasedimentary sequence. The latter is key to understanding the characteristics of this region prior to the early Cambrian assembly of SW Gondwana. It is composed of low- to medium grade metamorphic rocks (metasandstones, mica-schists, Ca-pelitic schists, metaconglomerates, marbles and less abundant amphibolites) that can be grouped into four informal lithostratigraphic units. The chemical composition of these rocks allows to classify the siliciclastic protoliths as shales, Fe-shales and immature sandstones (wackes, sub-litharenites, litharenites and Fe-sandstones). The sediments were derived from an evolved felsic to intermediate continental source and were deposited on a continental passive margin overlaying a Mesoproterozoic basement that crops out at several places of the Western Sierras Pampeanas. Thick marine carbonate beds with seawater isotope composition, phosphatic clasts and the lack of contemporaneous, arc related igneous rocks, also support a passive margin sedimentation. Phosphatic clasts within metaconglomerates are described for the first time in the Sierras Pampeanas and were probably formed after an important Neoproterozoic glaciation (Marinoan). We further suggest, based on our data and previous works, that the passive margin probably belonged to the Paleoproterozoic MARA (acronym of Maz, Arequipa, Río Apa) continental block. MARA, which remained juxtaposed to Laurentia since the middle to late Mesoproterozoic orogenies until its eventual drifting in the late Neoproterozoic, finally accreted to SW Gondwana in early Cambrian times during the Pampean orogeny.