Growth of the Southern Patagonian Andes (46?53°S) and Their Relation to Subduction Processes

GHIGLIONE, MATIAS; RAMOS, VICTOR; CUITIÑO, JOSÉ IGNACIO; VARBERÓN, VANESA

Growth of the Southern Andes

Springer

Año: 2016; p. 201 - 240

The Cretaceous-Cenozoic evolution of the Southern Patagonian Andes isone of the most prominent examples of coupling between subduction processesand climatic, magmatic, deformational, and sedimentary events. Three orogenic andmagmatic cycles can be particularly related to processes in the subduction zone(1) Late Cretaceous closure of the Rocas Verdes marginal basin, (2) Paleogenecollision of the Farallón-Aluk seismic ocean ridge, and (3) Miocene subduction ofthe Chile seismic ridge beneath South America. Andean orogenic growth startedduring Late Cretaceous times, in a tectonic scenario that included the Rocas Verdesback-arc oceanic basin, widening from 49°S toward the south. The Andean segmentsouth of 49°S experienced a strong Cenomanian?Santonian deformational eventduring the closure of the back-arc basin and progressive subduction of its oceanfloor. The final closure produced the Coniacian?Santonian exhumation of theSarmiento Ophiolitic Complex and propagation of the orogenic front toward theforeland. The second cycle, during Paleogene deformation, coincided with anEocene volcanic arc gap, and seems to be related to the Fallarón-Phoenix seismicridge collision. The resulting slab window produced OIB volcanic plateaux representedby the Chile Chico and Posadas Basalts, erupted in the foothills andretroarc. The third cycle of accelerated Andean uplift started during the Oligocene,as a consequence of orthogonal and fast subduction of young lithosphere, while theChile seismic ridge between Antarctica and Nazca was approaching the trench.Kinematic plate reconstructions show that at approximately 14?18 Ma the Chileoceanic ridge entered the South America trench and migrated northward from 53°Sto its present-day position at 46°S. The early Miocene ridge collision and resulting slab window produced an extensive OIB magmatism between 10 and 3 Ma inextra-Andean Patagonia. The space-time unraveling of tectonic uplift is well knownfrom geochronometers, and shows a migration from the basement domain to theexternal fold and thrust belt accompanied by lower Miocene synorogenic sedimentation.Orogenic growth led to middle Miocene rain shadow in the foothills,followed by the late Miocene?Pliocene desertification of Patagonia.