Cuencas triásicas del Oeste argentino: origen y evolución

L.A. SPALLETTI

Abstract


The Triassic basins of western Argentina and northern Patagonia are located along fhe Pacific margin of Southwest Gondwana. They are narrow and elongated depressions oriented NW-SE, floored by a thick continental crust composed of Precarnbrian and Lower Palaeozoic magmatic rocks, and an Upper Palaeozoic plutonic-volcanic complex (Gondwana Magmatism). These basins are associated with the Choiyoi Magmatic Province, the Central Patagonian Batholith and the Comallo Volcanic Complex.

For the Triassic of western Argentina the following stages are recognised: Barrealian (Early to Mid Triassic), Cortaderitian (Mid to early Late Triassic) and Florian (Late Triassic). During the Barrealian severa1 passive rfts are opened (Ischigualasto - Villa Unión, Marayes, Las Salinas - Beazley, Cuyo and the short-lived San Rafael basins). They are characterised by a synrift phase related to the activity of the main fracture systems along the active flank of the half-grabens, high accommodation space and frequent coarsegrained sediment supply (usually vocaniclastic) from the active margins. Intercalations of basic lava flows are common. In the Cortaderitian protracted extension, maximum regional development of the Triassic bgsins occurred. Most basins were controlled by thermal-tectonic subsidence. High accommodation space, limited coarse-grained cbntributions and high lacustrine base levels are the more characteristic conditions for basin sedimentary infill. In the Florian stagelthe Ischigualasto-Villa Unión, the Marayes and the Cuyo basins are characterised by fluvial-dominated red-bed successions, related to a transtensional stage of evolution. Several half-grabens (Malargüe, Paso Flores and Chacaico) are opened as precursors of the Neuquén Basin. In northwestern Patagonia, the combInation between regional strike-slip displacement along the Gastre Fault System and protopacific subduction, causes the development of the arc magmatism represented by the Central Patagonian Batholith and the thick volcano-sedimentary Comallo complex.


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