Late Jurassic extensional tectonics in south-western Mendoza province, Argentina

MESCUA, J. F.; GIAMBIAGI, L. B.; BECHIS, F.

Niza, Francia

Simposio; VII International Symposium on Andean Geodynamics; 2008

IRD

Several studies have addressed the control of pre-existing structures in the Andean deformation in south western Mendoza (e.g. Manceda and Figueroa, 1995; Giambiagi et al., 2003). They have shown that knowledge of the pre-Cenozoic geologic history is needed to understand the processes involved in the formation of the Andes.    Based on the existence of an unconformity between the Oxfordian Auquilco Formation and the Kimmeridgian Tordillo Formation in some localities, early studies of the Neuquen Basin suggested an orogenic phase (Stipanicic and Rodrigo, 1970; Davidson and Vicente, 1973). Later studies in northern Mendoza (Sanguinetti and Ramos, 1993; Cegarra and Ramos, 1996; Giambiagi et al., 2003) proposed an extensional setting for this period, whereas in Chile regional extension is well documented (Vergara et al., 1995; Charrier, 2007). Nevertheless, it is generally assumed that extension in southern Mendoza was over by the late Early Jurassic (Legarreta and Gulisano, 1989; Gulisano and Gutiérrez Pleimling, 1995; Vergani et al., 1995; Ramos, 1999; Legarreta and Uliana, 1999). As shown above, observations in southern Mendoza support the existence of an extensional tectonic setting for the Kimmeridgian in this region. The region affected by Kimmeridgian extensional processes in Argentina would extend, at least, from 32º30’ S (Aconcagua region) to 36º S. The unconformities observed between Oxfordian and Kimmeridgian deposits in some localities of southwest Mendoza (e.g. Río Salado, Dajczgewand, 2002) could be related to tilting and erosion associated with this extension. Vergani et al. (1995) interpreted that extensional fault-controlled subsidence was restricted to the Late Triassic- Early Jurassic in the Neuquén Basin. Based on data collected south of 36ºS, they suggest that the high rates of subsidence in Late Jurassic and Early Cretaceous times are due to relaxation of in-plane stresses with a NW-directed σ3. On the other hand, in south-western Mendoza, activity of normal faults would have taken place at least during the Kimmeridgian. Available data from limited measurements of minor faults coeval with the deposition of the Tordillo Formation suggest that this extension had a NW direction. Major Early Jurassic NNW-trending normal faults are interpreted to be reactivated with an oblique normal sense.