Emplacement of the Renca Batholith, Sierras de San Luis, Argentina: an anisotropic ballooning pluton

LOPEZ DE LUCHI, MÓNICA; RAPALINI, AUGUSTO; ROSSELLO, EDUARDO; GEUNA, SILVANA

No Informado

Congreso; Northeastern Section - 36th Annual Meeting of Geological Society of America; 2001

Magneticand rock fabrics are used in order to constrain the emplacement of the zonedelliptical Late Devonian Renca Batholith (Sierra de San Luis, Argentina) whichis mainly made up by ferrimagnetic porphyric granodiorites (Unit 1) andparamagnetic equigranular monzogranites (Unit 2). Magnetic foliation can bedirectly related to the mesoscopic foliation in Unit 1, the steep to verticalfoliation results from a combination of both magmatic and locally hightemperature solid state flows. K »O is measured both in kynematic indicatorsand in AMS data with a distribution of magnetic foliation planes generallysub-vertical. The fabric is parallel to the external and internal boundaries ofthe ring-like Unit 1, the X-Y plane of the enclaves, synplutonic dykesattitude. These internal features are concordant with the ductile aureole thatdeveloped by meso- and micro-folding of the regional NNE S2/S3 of the Ordovicianmetamorphic country rocks. AMS allows to infer proximity to the roof zone fromthe concentric subhorizontal foliations and gently plunging lineations in Unit2. K close to O, oblate magnetic ellipsoids, weak lineation and concentricfoliation, indicate a ballooning type process, related with magma pressure.However, the ellipsoidal shape of the body would point to a preferred directionof extension that would be in agreement with some far-field influence ofregional structures active during the batholith construction. The regionalstrain field at 400 Ma is related with NNE dextral shear-zones that arerecognized towards the west of the area. Those zones could both promote orchannalize the ascent of the first melts and control the final expansion as theresult of the emplacement of the central monzogranites