The Ordovician syntectonic pluton El León, southwestern end of the Cordón de Lila, Antofagasta Region, Chile.

Abstract

The El León pluton, located in the Cordón de Lila in the Precordillera of the Antofagasta region, Chile, is an intrusive body emplaced in the famatinian magmatic arc in the southwestern margin of Gondwana during the Darriwilian (Middle Ordovician). It has a strong magmatic foliation and it is has a granodioritic composition that is coarse grained in its central part and fine grained in its borders. It contains metric and decametric fringes of mylonitic rocks. Aditionally it develops a contact metamorphic aureole in its country rock and it was intruded in the mesozone. There was collected ca. 400 structural data from magmatic and mylonitic foliations inside the pluton. There was established that the general trend of the magmatic foliation is N77E and the shear sense from S-C foliations and mica-fish in the mylonites is normal-sinistral. By means of the analysis of microstructures and their associated deformation mechanisms it has established a continuous deformation sequence that started with magmatic deformation followed by submagmatic and solid-state deformations. The latter begun at high temperatures and was followed by low temperatures. An important magmatic stoping occurred during the plutonic emplacement. Besides, the development of high temperature mylonites, the sinmagmatic character of the deformation and a shear subvertical-sinistral component is compatible with a descending piston mechanism model. Its deformation is asigned to the compressive Guandacol tectonic phase in the Cordón de Lila.