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Geology Of Sierra De La Ventana – Argentina

International - Date: November, 2010, May 2012 and 2013

The Sierra de la Ventana Fold Belt (SVFB), in Argentina, is the westernmost extension of the South African Cape Fold Belt (CFB). Together they comprise a ca. 2,000 Km long fold-and-thrust belt, formed as a result of convergent tectonic processes that occurred along the southwestern margin of Gondwana during the Paleozoic (Gondwanides orogeny).

The SVFB is a set of elongated, NNW-SSE trending hills with arched sigmoidal shape, about 180 km long and 40 km wide, surrounded by Meso-Cenozoic deposits. It is constituted by Paleozoic siliciclastic sequences, divided into: the ca. 2,800 m thick Cambro-Ordovician Curamalal and Ventana Groups and the ca. 3,800 m thick Carboniferous-Permian Pillahuincó Group. The two former are mostly constituted by quartzites with minor pelites and conglomerates, overlying a Precambrian basement outcrops to the W. The Pillahuincó Group is composed by diamictites, pelites and feldspar-rich sandstones deposited at a low-angle unconformity. This sequence stratigraphy is very similar to the Cape and Lower Karoo sequences of South Africa.

All groups are metamorphosed at low greenschist facies during deformational phase D1 that generated the major system of northeast-verging tight to isoclinal folds with subordinated NW-SE reverse faults with top to NE movement. The basement is also affected by the faults that play a major role on the development of the fold system. This D1-fabric is attributed to a SW-NE compression with a minimum calculated shortening of ca. 27%. Minor NE-SW oriented faults occur cutting all other structures and are related to a D2-deformational phase due to a NW-SE shortening. Whether these phases are progressive is still a matter of debate.

In this project, we did the geological mapping of the NW-sector of the SVFB seeking more information concerning the stratigraphy and kinematic evolution of this part of the belt, in order to propose a unified tectonic and paleogeographic model comparing with the CFB.

The participants of this project are: Renata Schmitt (UFRJ – Brazil), Felipe Nepomuceno (UFRJ-Brazil), Rodolfo de Paula (UFRJ-Brazil), André Assis (UFRJ-Brazil), Renata Tomezzoli (UBA- Argentina), Leandro Cesar Gallo (UBA-Argentina), Guadalupe Arzádun (UBA-Argentina).