The Liquiñe Ofqui fault zone: A major Cenozoic strike-slip duplex in the southern Andes

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Available from: Hervé F., Oct 02, 2015
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    • "The regional tectonic setting has been described by López- Escobar et al. (1995), Lavenu and Cembrano (1999), and Ortiz et al. (2003). The Central Southern Volcanic Zone (CSVZ) of the Southern Andes runs NNE for approximately 1000 km along the socalled Liquiñe-Ofqui Fault Zone (with a dextral strike-slip motion) (Cembrano and Herve, 1993; Lavenu and Cembrano, 1994; López- Escobar and Moreno, 1994). Its northern sector is offset by the Gastre Fault Zone, trending N60W and running parallel to the Villarrica-Quetrupillán-Lanín alignment (Moreno, 1974; Cembrano and Moreno, 1994; Ortiz et al., 2003). "
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    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 Fault Zone.
    Full-text · Article · Oct 2013 · Journal of South American Earth Sciences
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    • "Between 40 and 43 30 0 S the Somuncura plateau is composed of Late Oligocene to Early Miocene succession of mafic lavas that has been linked to a hot spot impacting against the base Fig. 2. Main contractional features of the retroarc fold and thrust belts in the Southern Andes. Note a differential progression of the fold and thrust belt along latitude, between areas where contraction was absorbed in the drainage divide surroundings and areas where deformation advances hundred kilometers from the trench (based on Ramos, 1989; Cembrano and Hervé, 1993; Kozlowski et al., 1993; Manceda and Figueroa, 1995; Coutandt et al., 1999; Kraemer et al., 2002; Cobbold and Rossello (2003); Ghiglione et al., 2009; Zamora Valcarce et al., 2006; Giambiagi et al., 2008). "
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    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.
    Full-text · Article · Dec 2011 · Journal of South American Earth Sciences
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    • "The CBVF lays about 400 km eastward of the current Peru–Chile Trench, where the Nazca Plate is subducting beneath the South American Plate at a rate of 9 cm per year, with a moderate oblique component (Hervé et al., 2000). This oblique convergence induces a dextral stress along the active volcanic arc, activating the Liquiñe– Ofqui fault system (Cembrano and Hervé, 1993). The current subducting plate is relatively young, ∼10 Ma, (the actual age of the Nazca plate now entering the Chile trench at the latitudes 41° to 43°S is 15–20 Ma) making it light and buoyant. "
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    ABSTRACT: The Crater Basalt Volcanic Field (CBVF) in northern Patagonia (˜42°S, Chubut province) is located 400 km eastward of the current Peru Chile Trench and to the southwest of the Meseta de Somuncura, in a back-arc position in the extra-Andean Patagonia. The CBVF lava flows cover glaciation related terraces and present stream valleys. The occurrence of CBVF is related with the Gastre Fault System (GFS), a very significant tectonic feature about 40 km wide. The CBVF volcanics cover a surface of ˜700 km2, occurring mainly as lava flows and scoria cones. CBVF volcanics have relatively high contents of MgO (6 9 wt.%), Cr (136 289 ppm) and Ni (25 198 ppm), and classify as alkali basalts, basanites and trachybasalts. Geothermometry indicates a crystallization temperature of ˜1140 °C and a fO2 of - 1.0 1 to 0.0 (log FMQ units). The petrographic and geochemical characteristics of CBVF products suggest that the magma originated from a garnet-bearing lherzolite mantle source with asthenospheric characteristics, as a result of decompression, partial melting and ascent. These melts would have risen through a system of deep faults like the Gastre Fault System, following the last Quaternary glacial event.
    Full-text · Article · Jul 2006 · Journal of Volcanology and Geothermal Research
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