Thermal evolution of upper crustal magmatic systems from the Sierra de Velasco, NW Argentina

Abstract

Detailed mapping of the Huaco intrusive Complex in NW Argentina documents a shift in the emplacement style of successive magma additions in an upper crustal environment as the system evolves thermally. The units of the Huaco intrusive complex exhibit a change from a tabular to funnel-shaped subhorizontal body (Huaco unit) with stoping and brittle fracturing as main emplacement mechanisms, to a cylindrical body (Sanagasta unit), emplaced in a heated host rock which shows local ductile behaviour. As the system cools, the youngest intrusion (La Chinchilla unit) emplaces again as a subhorizontal tabular to funnel-shaped body. Furthermore, magmatic fabrics recorded a regional strain field that changed from a SW-NE to WSW-ENE shortening, as well as boundary strain increments and stress reorientation. Our results demonstrate that the evolution of magma chambers involves the emplacement of magma batches in a stiff crust, changing its thermal conditions and maturing the system for following intrusions. The latter ascend as visco-elastic elongated bodies using the same magmatic plumbing system, leading to a shift in the emplacement style. The described evolution is similar to that reported for the contemporaneous San Blas intrusive Complex located in the same range. This allows us to affirm that these processes are recurrent in the upper crustal section, and that the thermal and rheological conditions of the crust are locally modified by the formation and evolution of long-lived magma reservoirs.