Neoproterozoic to Lower Palaeozoic successions of the Tandilia System in Argentina: implication for the palaeotectonic framework of southwest Gondwana

UDO ZIMMERMANN, DANIEL G. POIRÉ, LUCÍA GÓMEZ PERAL

International Journal of Earth Sciences

Springer Berlin / Heidelberg

Lugar: Berlin; Año: 2011 vol. 2-3 p. 489 - 510

1437-3262

ABSTRACT The Cryogenian-Ediacaran to Lower Palaeozoic successions of the Tandilia System (Sierras Bayas Group and Cerro Negro Formation) in central-eastern Argentina is exceptional because of its unmetamorphosed and nearly undeformed character, the absence of any identified glacial deposit, the absence of rift-drift and collision related tectonic expressions and the extraordinary provenance trend. We could decipher a dramatic change in the basin evolution from small-scale depositional areas during the Neoproterozoic to a larger basin related to an active continental margin throughout the Cambrian. The base of the succession is represented by relatively immature detrital material of alkaline composition (Villa Mónica Formation). Towards the top of this formation, detrital material is well sorted and strongly reworked, but reflects only the local rock record. The clastic deposition is interrupted by diagenetic overprinted dolomites. The unconformable overlying Cerro Largo Formation is composed of mature quartz-arenites, which reworked the Cryogenian Villa Mónica Formation and/or mainly felsic granitic and metamorphic basement material of slightly larger variety, the dominant alkaline geochemical signature disappears. Based on diagentic, petrographic and sedimentological data, we interpret the unconformity to represent a long time of erosion. The Cerro Largo Formation is Ediacaran in age and shows a transition to the mudstones and heterolithic facies of the Olavarría Formation. The top of the Sierras Bayas Group is represented by limestones of the Loma Negra Formation, which are discordantly overlain by Lower Palaeozoic Cerro Negro Formation. The latter displays detrital material related to a continental volcanic arc, mafic source and a felsic source. Several arc-related geochemical proxies (Th/Sc < 0.8; Zr/Sc < 10; La/Sc < 2; Ti/Zr > 20) are abundant in the rocks of the Cerro Negro Formation and point to such a source for the detrital record. The occurrence of syndepositional pyroclastic beds and the absence of any volcanic detritus in the underlying rocks allow proposing that the Cerro Negro Formation is related to the southern active continental margin fringing Gondwana (?Terra Australis Orogen?) as a retro-arc or retro-arc foreland basin. The basin evolution differs therefore substantially from others in the region and shall not be used for correlation.