The provenance of the Lower Palaeozoic Balcarce Formation (Tandilia System, Buenos Aires, Argentina).

ZIMMERMANN, U.; SPALLETTI, L.

La Plata

Congreso; XVI Congreso Geológico Argentino; 2005

ABSTRACT Provenance studies on Lower Paleozoic rocks from the Balcarce Formation revealed for the main facies, relatively poorly sorted quartz-arenites, a rifted margin mainly fed by old upper crustal material. The sources were sedimentary, probably magmatic, but, significantly, of metamorphic origin. However, in the eastern part of the basin, large amounts of tourmaline and Ti-rich heavy minerals were introduced into the detrital fraction. This is one of the few differences in the overall provenance. Provenance studies on rutile are in progress. At this stage of our research, geochemical data combined with petrographic results exclude as sources the underlying rocks of the Cerro Negro Formation and the Sierras Bayas Group. Kaolinite-rich rocks are intercalated, especially in the eastern part of the basin. Preliminarily, we interpret these rocks as highly altered volcanic deposits, supported by a first petrographic result. Geochemically, these deposits indicate a provenance from oceanic island arcs or volcanic arcs in general. However, possible sources for the influence of volcanic ashes during the Lower Paleoozic are not clear at this stage of our research.