Late Mississippian-Pennsylvanian extensional deformation along the SW Gondwana margin: Insight from the San Rafael Basin, western Argentina

The retro-arc San Rafael Basin (34 degrees SL) records a long-term history of its varied filling. This is the reason why it has been approached by several studies from many disciplines. However, its origin has been a controversial issue until now. There exists an agreement about its development during the latest Mississippian-Early Pennsylvanian ages, coetaneous with the sedimentation of the El Imperial Formation. The generation of this basin took place afterward the Chanic Orogeny and before the San Rafael orogeny. Although there is consensus about an extensional setting controlled the basin's inception, no crustal deformation corroborates this tectonic regime. This contribution is a first attempt to present geological and structural field evidence supported by preliminary kinematic analysis. From these new field observations, an NNE-SSW extensional deformation coetaneous to the deposition of the lower Member of the El Imperial Formation was recognized in the area near the confluence of the Atuel river and Aisol stream. Consequently, our data are following the previous hypothesis of an extensional origin for the San Rafael retro-arc basin.