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Paper No. 9
Presentation Time: 11:00 AM

STRUCTURAL AND GEOPHYSICAL ESTIMATES OF SHORTENING OF THE ANDEAN FORELAND THRUST BELT AT 35°S: IMPLICATIONS FOR ANDEAN STRUCTURE AND PRE-ANDEAN HISTORY


MESCUA, José F., Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, CCT Mendoza, CONICET, Av. Ruiz Leal s/n, Parque General San Martín, Mendoza, 5500, Argentina, GIAMBIAGI, Laura B., Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, CCT, Parque San Martin s/n, Mendoza, 5500, Argentina, TASSARA, Andrés, Departamento de Ciencias de la Tierra, Universidad de Concepción, Victor Lamas 1290, Concepción, 5500, Chile and RAMOS, Víctor A., Laboratorio de Tectónica Andina, CONICET - Universidad de Buenos Aires, Ciudad Universitaria. Pab.II, Buenos Aires, C1428EHA, Argentina, jmescua@mendoza-conicet.gob.ar

The Andean foreland thrust belt at 35ºS is characterized by a thick-skinned structure in which basement reverse faults transfer displacement to a Mesozoic sedimentary cover. Deformation commenced in the Early Miocene, and advanced from west to east consistently with an evolution governed by critical wedge theory. Different structural models have been proposed for this thrust-belt, depending on the interpretation of the main structures as inverted Mesozoic normal faults, newly-formed Andean thrusts or both.

We compare the shortening estimates from balanced cross-sections built using these different structural models with an estimate derived from a crustal model based on an extensive compilation of geophysical data.

Structural modeling constrains shortening between 23 km, for an inversion model with subordinate thrusts, and 35 km for a model based on Andean thrusting. On the other hand, the shortening calculated with the geophysical model varies greatly depending on the initial (pre-deformation) crustal thickness (T0) used. For T0 < 36 km, the calculated shortening is higher than 95 km, which is clearly too large with respect to structural estimates. Values of shortening in the range of the structural estimates are obtained with T0= 39-40 km. Taking into account the pre-Andean history of the region, this implies a complex crustal geometry before Andean deformation started, with thickened regions (probably a relict of the Late Paleozoic San Rafael orogeny) in the west, and a normal/thin crust in the east formed during Mesozoic extension related to the Neuquén basin development.

Finally, we compare the regional trends of maximum crustal thickness and structurally derived shortening between 33º30’S and 36ºS. Our results indicate that the pre-existing normal faults have played an important role in the Andean deformation at 35ºS, either through fault inversion or controlling the dip of Andean thrusts.

Session No. 368

T208. Hinterland, Retroarc Fold- Thrust Belt, and Foreland Systems (Posters)
Wednesday, 30 October 2013: 9:00 AM-6:30 PM
Hall D (Colorado Convention Center)
Geological Society of America Abstracts with Programs. Vol. 45, No. 7, p.825
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