INVESTIGADORES
DAVILA Federico Miguel
congresos y reuniones científicas
Título:
Late Paleozoic foreland development through western Argentina
Autor/es:
EZPELETA, M.; FEDERICO MIGUEL DAVILA; ASTINI, R. A.
Lugar:
Mendoza
Reunión:
Congreso; Gondwana 12; 2005
Resumen:
The Late Paleozoic history of western Argentina has been largely interpreted to evolve within a retroarc scenario, located between the Gondwanic arc to the west and the cratonic areas to the east. Two domains are recognized at ~29º based on paleogeographic reconstructions: the Río Blanco depozone (RBD≥5000m thick) to the west, located close to the tectonic loads, and the Paganzo depozone (PD≤1000m thick) located farther east from the hinterland, characterized by a broader depozone. The sedimentary history of these domains together with the volcanic and deformational features along- and across-strike allow us to propose an integrated basin evolution model for western Argentina. In the RBD, five thickening-upward megasequences (coined as MS 1, 2, 3, 4 and 5) separated by angular unconformities represent separate evolving stages. The MS 1 is represented by strongly cleaved 800-m thick, thin-bedded fine-grained succession, with few dropstones of the Agua de Lucho Fm. This interval correlates with lower Malimán Fm. to the south and is interpreted as early Carboniferous deltaic to submarine environments (Protocanites fauna & Archaeosigillaria Malimanium) unconformably laying on folded Ordovician rocks. MS 2 covers MS 1 in angular unconformity and is represented by a glaciomarine succession capped by fluvio-lacustrine beds (~2000-m thick) included in the Cerro Tres Cóndores Fm. The association Frenguellia-Paulophyton suggests a mid Late Carboniferous age. Possible correlatives to the south are the upper Cortaderas and lower Guandacol Fms. In angular unconformity overlies the MS 3, characterized by the 1000-m thick Punta del Agua Fm, composed of subaqueous volcano-sedimentary sequences. Radiometric data and NBG flora indicate a Late Carboniferous age. The MS 4 rests unconformably on a significant palerelief represented by MS2 & MS 3. It is composed of 1550-m thick fluvio-deltaic and coastal succession known as Río del Peñon Fm. Fm). A Late Carboniferous-earliest Permian age has been suggested on the basis of marine faunas and radiometric ages. This unit correlates with the Tupe Fm in PD. An Early-Middle Permian red interval represents MS 5 (>450 m) and has been mapped as Patquía Fm conformable above the Rio del Peñon Fm. In contrast, the PD shows three megasequences. Abrupt thicknesses and facies changes characterize the basal MS, represented in Famatina by the Agua Colorada Fm, onlapping a strong glacial paleorelief carved on folded Early Paleozoic substrates. >720-m matrix-rich conglomerates with frequent striated boulders and coarse sandy fluvial beds with paleocurrents to the west. A late Carboniferous (Namurian) age is suggested from palinological studies. Glacial features and age constraints allow a correlation with middle MS developed in the western RBD. 130-560-m thick lacustrine-fandeltaic successions with interbeded coal beds cover in various angular relationships the basal MS within PD, suggesting intra-Carboniferous deformation. Locally, middle MS onlaps cataclastic Ordovician granites and yields intraformational unconformities. Palinological data supports a Late Carboniferous-Permian age for this distinct synorogenic package which we propose to call Las Pircas Fm (LPF). This interval partly correlates with the Tupe and Lagares Fms. elsewhere in PD and with the MS 4 at the RBD. Colour and facies changes mark the beginning of upper MS, composed of fluvial, lacustrine and eolian strata, which represent the Early-Middle Permian red beds of the De La Cuesta-Patquía Fms (~600 m thick). This correlates with the Permian beds of MS 5 in hinterland areas. This MS contains proximal volcaniclastic rocks farther east. Contrasted stratigraphy and thicknesses between domains and intervening angular unconformities support different behaviours and dissimilar sedimentary and structural settings for both domains, which can be thought in a foreland framework. Whereas the RBD largely behaved as a flexural foredeep repeatedly evolving from underfilled to overfilled stages afterwards affected by folding, the PD partly represents forebulge-interbulge regions, eventually converted into a broken-foreland. Correlations show that during the Early Carboniferous sedimentation occurred only in the hinterland, whereas cratonward erosion and bypass could be related to a flexural upwarping that later served as glacial center. Episodic folding and exhumation within the hinterland contributed to tectonic condensation toward the arc. By contrary, most of the angular unconformities within the RBD seem local but are important in constraining the foredeep filling stages. Carboniferous arc-related volcaniclastics in the RBD (MS 3) indicate an eastward volcanic-arc broadening, supporting the onset of shallow subduction. Basement exposure, deformation and partitioning at the PD is recorded by the LPF and indicates a broken foreland basin stage, allowing to suggest a slab flattening. Later depocenter expansion by shallow lacustrine depositional systems and definitive lap-outs onto previous intermontane basement highs allow interpreting that dynamic subsidence controlled the accommodation space for Permian times.