Mafic Enclaves Reveal Multi-Magma Storage and Feeding of Shangri-La Lavas at the Nevados de Chillán Volcanic Complex

Abstract

The Nevados de Chillán Volcanic Complex is one of the most active of the Southern Volcanic Zone. It is formed by NW-SE-aligned eruptive centers divided into two subcomplexes, namely Cerro Blanco (basaltic andesitic) and Las Termas (dacitic), and two satellite cones (to the SW and NE of the main alignment). Our study of the Shangri-La volcano, which is located between the two subcomplexes, in alignment with the satellite cones, and which produced dacitic lavas with basaltic andesitic enclaves, sheds light on the compositional and structural diversity of the volcanic complex. Detailed petrography along with mineral chemistry allows us to suggest partial hybridization between the enclaves and the host lavas and that mixing processes are related to the generation of the Shangri-La volcano and to other volcanic products generated in the complex. This is supported by mixing trends between the enclaves and the most differentiated units from Las Termas. We argue the presence of two main magma storage areas genetically related to crustal structures. A dacitic reservoir (~950 °C) is fed along NW-SE structures, whereas a deeper mafic reservoir (>1100 °C) utilizes predominantly NE-SW structures. We suggest that the intersection between these sets of structures facilitates magma ascent and controls the Nevados de Chillán plumbing system dynamics.