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

MACCHIOLI GRANDE, M.; ALASINO, P. H.; ROCHER, S.; LARROVERE, M. A.; URAN, G. M.; REINOSO CARBONELL, V.; MORENO GUZMÁN, G.

JOURNAL OF STRUCTURAL GEOLOGY

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2019 vol. 118 p. 1 - 20

0191-8141

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