La prolongación austral de las Sierras Pampeanas en la provincia de La Pampa: evidencias geofísicas y geológicas.

DELPINO, S., FERRACUTTI, G., KOSTADINOFF, J. Y BJERG, E.A.

Revista de la Asociación Geológica Argentina

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 2005 vol. 60 p. 535 - 551

0004-4822

 In Valle Daza, outcrops of gabbros and leucocratic granites with associated pegmatite’s allow the distinction of two metamorphic events, whose characteristics are: a) ductile deformation in high or superior to amphibolite facies, responsible of the NNE-SSW foliation and the transformation of gabbros into granoblastites and amphibolites and granites and pegmatites into protomylonites and mylonites, and b) fragile-ductile deformation at low temperature, leading to retrogradation of high grade paragenesis into medium to high greenschist facies.Significant gravimetric (diameter 30 km and +15 mGal amplitude) and magnetometric anomalies (diameter 20 km and 250 nT maximum value) in the study area are the result of large volumes of high density mafic rocks. The mafic and granitic rocks outcropping in the western part of Sierra de Lonco Vaca share very similar petrologic and structural characteristics to those occurring in Valle Daza. The Sierra de Lonco Vaca is located at the northern sector of a series of gravimagnetometric anomalies bearing the same orientation as the regional foliation (NNE-SSW), with remarkable local anomalies at Estancia El Coya and El Durazno localities. From north to south, the outcrops of clinopyroxenic granoblastites and amphibolites at Lonco Vaca, Valle Daza and Estancia Santa Maria are coincident with gravimagnetometric anomalies. Our results indicate that the tectono-metamorphic events recognized in La Pampa province can be correlated with the F3 (S3-M3) and F4 (M4) events recognized in the Central Block of the Sierras de San Luis. Both regions share other common features as is the case of discontinuous gravimagnetometric anomalies trending NNE-SSW, coincident with regional belts of ductile deformation dipping ESE and with WNW vergence. Structural, petrologic and geophysical correlations established in the present contribution are in favor of the hypothesis postulating the extension of the Sierras Pampeanas into the central portion of La Pampa province.