[Show abstract][Hide abstract] ABSTRACT: The Southern Andes have been built through the stacking of crustal sheets in discrete periods during the last 100 My. The first important shortening took place in Late Cretaceous at the time of eastward arc expansions potentially linked to two areas of subducted slab shallowings of 200 and 800 km wide respectively. These shallowings have progressed to two smaller flat slabs in Eocene times, where rather anhydrous subducted slabs generated a discontinuous arc emplaced in the foreland area at the time of mountain building. Discrete segments of the former Late Cretaceous slab shallowings would have fallen down at this time producing early slab steepening settings where within-plate products and extensional basins developed such as in the southern Chubut Province. Then Late Oligocene times coincide with the final steepening of the broad Late Cretaceous to Eocene shallow subduction zone with the emplacement of voluminous volcanic plateaux in central Patagonia and extensional basins in the hinterland zone. Lately a long quiescence period was interrupted by the development of three Miocene shallow subduction settings more than 400 km long each, evidenced by arc expansions and associated with Andean construction. Most of these areas were extensionally reactivated in the last 5 My at the time of retraction and steepening of formerly shallow subduction zones, being associated with voluminous mantle derived materials and shallow asthenospheric injection. While some of these shallow subduction configurations could be explained by subduction of highly buoyant oceanic lithosphere related to seismic ridges, in particular those of the Aluk/Farallones and Chilean ridges, other mechanisms remain more speculative. The alternation of shallow subduction zones and their steepening in the last 100 My in the Southern Andes explain location and timing of main magmatic fluxes in the arc and retroarc areas, as well as the presence of coeval foreland mountain systems east of the Main Andes.Highlights► The construction of the southern Andes is linked to shallow subduction settings. ► There are fast migrations/expansions of arc-derived rocks towards the foreland. ► The mountain building phases are related with expansion/migration of the arc. ► Subduction of buoyant oceanic seismic ridges is the main controlling factor.
Journal of South American Earth Sciences 12/2011; 32(4):531-546. · 1.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report data from a radon survey conducted at Villarrica volcano.
Measurements have been obtained at selected sites by
E-PERM® electrets and two automatic stations utilizing
DOSEman detectors (SARAD Gmbh). Mean values for Villarrica are 1600
(±1150) Bq/m3 are similar to values recorded at
Cerro Negro and Arenal in Central America. Moderately higher emissions,
at measurement sites, were recorded on the NNW sector of the volcano and
the summit, ranging from 1800 to 2400 Bq/m3. These
measurements indicate that this area could potentially be a zone of
flank weakness. In addition, the highest radon activities, up to
4600 Bq/m3, were measured at a station located near the
intersection of the Liquiñe-Ofqui Fault Zone with the Gastre
Journal of South American Earth Sciences 10/2013; · 1.53 Impact Factor
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