The thermal impact by the accommodation of mafic melts within the central basement complex of the Sierra de San luis: constraints from numeric modelling.

STEENKEN, A., LÓPEZ DE LUCHI, M.G., SIEGESMUND, S., WEMMER, K.,

La Plata

Congreso; 16 Congreso Geologico Argentino; 2005

Asociación Geologica Argentina, INREMI

The description of the thermal aureole in the vicinity of the mafic and ultramafic intrusions within the Pringles Metamorphic Complex using a finite-difference approximation simulation code indicates the requirement of a large near surface seated heat source in order to explain the widespread distribution of the observed granulite facies metamorphism. This heat source is most likely related to the large positive gravimetric anomalies that have been previously interpreted as been generated from mafic rocks. Simulation runs indicate that the injection of mafic melts was not a single event but rather a long-lasting episode of continuous magma supply and storage in order to fulfil the by geochronological dating constrained timeframe of magmatic and high-temperature metamorphic processes. Moreover, the sporadic emplacement of one short-living magma chamber will hardly account for the extension of high-grade metamorphic rocks. Apart from high-grade metamorphism those magma chambers provide the proportional melts for the Famatinian higher crustal granitoids. The heat input of the mafic melts on the lower crust is sufficient to account for the widespread migmatisation of the basement. Segregation of those crustal melts and mixing process with the more mafic melts led to the formation of the contemporary sheet-like intrusions. An important issue of our results is that both tonalite to monzogranite magmas might be produced as a result of a process of mafic magma additions to the deposits of the closing ?Pringles? back arc basin (cf. Steenken et al., 2004) and that in our case there is no need to invoke a stage of crustal thickening related to continental collisions to produce felsic granitoids which agrees with both the chemistry and the crystallization ages of the Ordovician granitoids of the Pringles Complex.