A magnetic fabric study of the Renca Batholith, northern San Luis Province, Argentina

RAPALINI, A.E.; LÓPEZ DE LUCHI, M.; GEUNA, S. E.; ROSSELLO, E.

Rio de Janeiro

Congreso; 31st International Geological Congress; 2000

The Renca Batholith is a 19 km by 13 km ellipsoidal composite and zonalpluton exposed in the northeastern part of the Sierra de San Luis, Argentina. Aporphyroid granodiorite and monzogranite external zone (Unit 1) and an equigranularbiotite-muscovite monzo to leuco-monzogranite inner zone (Unit 2) constituteits principal units. It intrudes a medium-grade metamorphic basement composedof schists and micacites. In order to determine its geometry and conditions andprocesses involved in its emplacement, a multidisciplinary study has been startedon this magmatic unit. As part of the geophysical characterization, asystematic magnetic fabric study was carried out. Sixty sampling sites wereevenly distributed on most of the batholith. Two to five oriented cores werecollected at each site. Bulk susceptibility (K) and anisotropy of magneticsusceptibility (AMS) measurements were done on all specimens. K values indicatea bimodal distribution that correspond to Unit 1 (ferromagnetic) and Unit 2(paramagnetic). This match the magnetometric response of this body. Samedistribution is observed in the anisotropy degree, with higher values in the porphyroidgranitoid (Unit 1 ). The AMS has a predominantly foliated fabric, with adistribution of magnetic foliation planes generally sub-vertical and parallelto the boundaries of the ring-like Unit 1. Unit 2 shows less consistentorientation of these planes, which are frequently subhorizontal. The magneticfabrics of this body agree with other fabric parameters and are consistent witha model of radial stress produced on Unit 1 during emplacement of the centralUnit 2.