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Evolution andine et raccourcissement au niveau de Cusco (13°-16°S) , Pérou : Enregistrement sédimentaire, chronologie, contrôles paléogéographiques, évolution cinématique

Abstract : A synthesis of the geologic research undertaken in the Andes of Cusco area is presented. The area lie between the NE boundary of the Western Cordillera and the SW one of the Eastern Cordillera forming the NW extremity of the Altiplano. The interpretative model which results of this study is of major importanc for the understanding of the geodynamic evolution of the Andes during Mesozoic and Cenozoic. Structural, sedimentological and petrologic data are discussed. The geodynamic evolution is controlled during paleozoic and meso--cenozoic times by a paleogeographic limit between two different kind of substratum which are in contact along a boundary corresponding to the Abancay defiexion and the Cusco-Puno threshold.The Permo-Trias represents the transition between an Hercynian regime and the Andean one. The major features of the Permo-Triassic basin are inherited structures which furtherly controlled all the Andean evolution. The area of Cusco is characterized by more than 10.000 m of Tertiary continental Red Beds which overlie marine and continental sequences of Cretaceous-PaIeocene age. These Red Beds were deposited in synorogenic basin during the Andean deformation in compressive setting. Strike-slip motions occur between 50 and 44?My along the Cusco-Puno threshold and near the NE boundary of the South-Peruvian Mesozoic basin, and result with the transtensive opening of the RedBeds basins and the deposition of the San Jeronimo Group in the Cusco, Sicuani,Ayaviri and Puno areas and possibly as far as Northern Bolivia, and representing the first settlement of the wide Altiplanic basin. A major change in stress regime occur at about 43-40 My leading to the compressive closure of the Red Beds basin and the beginning of the conglomeratic Anta sedimentation (Inca 1 tectonic event). The boundary between the Red Beds basin and the Western Cordillera, becomes a left lateral strike slip limit as shown by the evolution of the Oligo-Miocene basins. These left lateral displacement are in good agreement with the explicative model for the Bolivian Orocline. During that time (Qechua tectonic episodes) the Neogene basins were elosed in compressive tectonic regime. Geochronologic data suggest that the magmatic activity was more or less continuous since Eocene (48 My) times. However the spatial distribution of the magmatism was subject to strong variations. The quantification of the deformation shows that the amount of shortening obtained using surface geologic data cannot explain the crustal thickness observeed using geophysical data. A model involving the emplacement of continental material by underthrusting and tectonic erosion of continental crustal slivers in the subduction zone by is proposed in order to explain the volume excess. The plate kinematic seems to exercise an influence on the Andean geodynamic evolution, particularly through the event calendar, but the major control of the deformational patterns are the main paleogeographic boundaries.
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Submitted on : Tuesday, September 14, 2010 - 5:17:44 PM
Last modification on : Thursday, November 19, 2020 - 3:54:26 PM
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  • HAL Id : tel-00517507, version 1

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Victor Carlotto Caillaux. Evolution andine et raccourcissement au niveau de Cusco (13°-16°S) , Pérou : Enregistrement sédimentaire, chronologie, contrôles paléogéographiques, évolution cinématique. Géologie appliquée. Université Joseph-Fourier - Grenoble I, 1998. Français. ⟨tel-00517507⟩

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