The Role Of Inherited Tectono-sedimentary Architecture In The Development Of The Central Andean Mountain Belt: Insights From The Cordillera De Domeyko

摘要

The structure of the Cordillera de Domeyko is dominated by a number of elongated N-S-trending basement ridges. These ridges were uplifted by steep reverse N-S faults that deformed the Mesozoic-Cenozoic cover. The vergence of the fault system varies along strike, conferring an apparent doubly vergent "pop-up" geometry to the axial zone. Two Mesozoic pre-compressional extensional events were recorded in the area. New structural data presented in this paper indicate that most of the generated NS-trending thrusts and related folds were controlled by the inversion of the pre-existing Mesozoic extensional faults. Thin-skin structures in the Mesozoic-Cenozoic cover are genetically linked to major basement upthrusts, which could be interpreted as basement short-cuts formed during inversion rather than as uplifted blocks associated with major Cenozoic strike-slip faults. Growth-strata geometries date the beginning of the Andean compressional event, which generates the Chilean Precordillera, as far back as 90 Ma ago; the resulting structural architecture is strongly controlled by inherited pre-Andean extensional structures. The association of porphyry intrusives with major reverse faults suggests that the emplacement of the Eocene-Oligocene porphyry Cu-Mo deposits in Northern Chile can be explained by an oblique-inversion Tectonics Model. The upper Eocene-lower Oligocene giant porphyry copper bodies (Chuquicamata, La Eseondida, El Salvador) located in the Cordillera de Domeyko show an adakitic affinity. This magma affinity, together with structural evidence presented in this work, indicates that porphyry emplacement occurred at the end of the basement-involved contractional stage that generates the anomalous thickened crust needed to generate these magmas. This tectonic evolution is coherent with the existence of a flat-slab subducting beneath the Central Andes (22°-26° S) during early Cenozoic, that will also produce the eastward migrating of the compressional regime in the upper plate since Late Cretaceous.