Evolution du régime tectonique de l'Altiplano et de la cordillère orientale des Andes de Bolivie du miocène supérieur à l'actuel : un effet des forces de gravité et des forces aux limites

Content Provider	Semantic Scholar
Author	Lavenu, Alain Mercier, Jacques Louis
Copyright Year	1991
Abstract	Evolution of the tectonic regime of the Alti lano Bolivian Andes from upper Miocene to Present-day: an e Ii and the eastern Cordillera of the ect of the gravitational body forces and the boundary forces. The Bolivian Andes are located above a 300 dipping segment of the Andean subduction zone. They are characterized by a large subsident sedimentary basin bounded by faults, by a rapid change in the structural trend of the Andean belt which corresponds to the Arica-Santa Cruz elbow-line and a talc-alkaline Cenozoic to Present volcanism. This paper addresses the changes in the tectonic regime of the Bolivian Altiplano and Eastern Cordillera since the Upper Miocene. During the uppermost Miocene (7-8 Ma) this region is submitted to a NE-SW trending compression. Durjng the Pliocene (6 to 3 Ma), the High Andes are submitted to an E-W trending extension. During the uppermost Pliocene-lower Pleistocene (= 3-2 Ma) an E-W trending compression affects this region. Yet, some faults exhibit kinematics which are in agreement with a N-S shortening. It has not been possible to demonstrate a clear chronology between these two N-S and E-W trending shor-tenings. Finally, during the mid-late Pleistocene and Present-day, the High Andes are submitted to a N-S to NNE-SSW trending extension while the Sub-andean lowlands are submitted to an E-W trending compression. These changes in the tectonic regimes are interpreted as resulting from a balance between boundary forces due to the slab push on the Andean lithosphere and body forces due to the high topography, the crustal thickness and the low density mantle beneath. In this mode1 it is considered that the lithospheric horizontal maximum stress (oHmax), trending E-W approximately parallel to the convergence, is fairly constant and that the vertical stress (ozz) increases with the topography. Concerning the Quaternary-Present day tectonic regime, in the Sub-andean lowlands, tectonics are compressional: oHmax is a1 and ozz is 03. In the High Andes, the ozz value increases with the topography and becomes a1 ; thus oHmax becomes a2 and the minimum horizontal stress (oHmin), orthogonal to aHmax, becomes a3 allowing extension to occur in a N-S trending direction. Supposing that the rheology of the Andean lithosphere has not significantly changed since 5 Ma, as the altitude of the Andes above sea level has not significantly changed since the Upper Miocene, variations of the magnitude of the boundary forces are necessary to explain the changes in the Andean tectonic regime. Magnitude decreased during the Pliocene to permit an E-W trending extension and increased during the Upper Pliocene-lower Pleistocene to permit an E-W trending compression. It is surmised that such changes are related to changes in the dip-angle of the subducting slab during time.
Starting Page	21
Ending Page	55
Page Count	35
File Format	PDF HTM / HTML
Volume Number	6
Alternate Webpage(s)	http://horizon.documentation.ird.fr/exl-doc/pleins_textes/cahiers/geodyn/41473.pdf
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article