Abstract

SRUOGA, Patricia et al. La Peligrosa caldera (47°15´ 5,71°40´W): A key event in the siliceous province of Chon Aike. Rev. Asoc. Geol. Argent. [online]. 2010, vol.66, n.3, pp.368-376. ISSN 0004-4822.

In the area located between Ghío lake and sierra Colorada, in Cordillera Patagónica Austral, the Late Jurassic El Quemado Complex is represented by vent-facies of pyroclastic and lava origin. A reconstruction of the volcanic architecture has been carried out based on the integrated study of the lithofacies and the structures. Four ignimbritic units and one rhyolitic lava unit have been recognized, mainly controlled by NNW trending transtensional faults. The evolution of the La Peligrosa Caldera is modellized in three stages:1) pre-collapse, when a precursory downsag-piecemeal subsidence took place, related to a dilatational zone which become the caldera 2) collapse, when the emplacement of large volume crystal-rich ignimbrites and megabreccias occurred under a progressive subsidence controlled by a transtensional regime with a NE direction of extension and 3) post-collapse, when the lava flows and associated domes were emplaced, controlled by oblique extension conditions with a NW direction of extension. The caldera development was accompanied by a remarkable change from transtension to oblique extension, which may represent an important variation in the deformation conditions during Jurassic time. The La Peligrosa Caldera may be considered as a key event to understand the eruptive mechanisms of the flare-up volcanism in the Silicic Chon Aike Province.

Keywords : Cordillera Patagónica Austral; Jurassic; Caldera; Ignimbrites; Transtension.

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