A review about the mechanisms associated with active deformation, regional uplift and subsidence in southern South America.

ANDRÉS FOLGUERA A,; GIANNI, G; SAGRIPANTI, L; ROJAS VERA, E

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2015 vol. 1 p. 1 - 20

0895-9811

A broadrange of processes act and acted simultaneously during the Quaternary producingrelief in the Andes and adjacent foreland zone, from the Chilean coast, wherethe Pacific ocean floor is sinking beneath the South American border, to theBrazilian and Argentinean Atlantic platform area. This picture shows to becomplex and responds to a variety of processes that just start to be recentlyconsidered. The Geoid reflects an important change at 35ºS along the Andes thatcould be indicating the presence of dynamic forces pushing up the continent inthe Southern Central and Patagonian Andes due to a strong asthenosphericdynamics that is absent in the north. On the other hand, mountains created in theAtlantic passive margin setting, along a vast section of the Bazilian Atlantic coastand regions located inland seem to be created at the area where the forearcregion eastwardly shifts at a similar rate than the westward advancingcontinent, and therefore can be considered as relatively stationary anddynamically sustained by a perpendicular-to-the-margin asthenospheric flow. Onthe other hand, the orogenic processes associated with the eastern Andes showto be highly active at two particular areas: The Subandean region, where thetrench is stationary and at the Pampean flat subduction zone to the south, wherea shallower geometry of the Nazca plate creates particular conditions fordeformation and rapid propagation of the orogenic front creating a high-amplitudeorogen. To the south, crustal seismicity develops mainly on the western Andeanslope indicating that retroarc orogenic activity is inhibited at the retroarczone and replaced by synthetic-to-the-subduction zone thrusts. This isexplained by the rain fall pattern that changes at these latitudes  and could be determining subcritical conditionson the Chilean Andean slope. In the southern Central and Patagonian Andes, mountain(orogenic) building processes are attenuated, becoming dominant othermechanisms of exhumation such as the i) impact of mantle plumes originated inthe 660 km mantle transition, ii) the retirement of ice-masses from the Andes afterthe Pleistocene producing an isostatic rebound, iii) the dynamic topographyassociated with the opening of asthenospheric windows during the subduction ofthe Chile ridge and slab tearing processes,  iv) the subduction of oceanic plateaux linkedto transform zones and v) the accretion of oceanic materials beneath theforearc region. Additionally and after last geodetic studies, vi) exhumationdue to co-seismic and post-seismic lithospheric stretching associated with largeearthquakes along the subduction zone, also shows to be a factor associatedwith exhumation that needs to be further considered as an additional mechanism fromthe Chilean coast to the western retroarc area.