La Provincia Pegmatítica Pampeana. II: Metalogénesis de sus distritos económicos

GALLISKI M. A.

Revista de la Asociación Geológica Argentina

Instituto Salesiano de Artes Gráficas

Lugar: Buenos Aires; Año: 1994 vol. 49 p. 113 - 122

0004-4822

ABSTRACT. The Pampean Pegmatitic Provine. Metallogeny of its economic fields. The total population of graniticpegmatites of the Sierras Pampeanas defines a pegmatitic province integrated by orogenic and post-orogenic fields. The formerare aligned in N-S belta, with muscovite class pegmatites generally westward of a rare element pegmatitic belt of LCTpetrogenetic family. The muscovite class pegmatite fields are found in rocks with medium grade Barrovian-type metamorphismand do not show apace-time relationships with granitoids; its K-Ar ages range from Upper Precambrian to Lower Silurian. Theorogenic rare element pegmatite fields are placed in an Abukuma-type metamorphic belt, in upper greenschists to loweramphibolite facies rocks. Many pegmatites are deformed with boudinage or disarmonic folding. The parental intnisives aresmall-sized, heterogeneous, strongly peraluminous two mica granitoids. They have alSr/86Sr ratios: 0.71 and are considered tobe S(+I) types. The ages of the granites and associated pegmatite swarms are Cambrian to Ordovician. The post-orogenicpegmatites and granites intrude the previously uplilted and eroded Famatinian orogen. The pegmatites are ovoidal zonedbodies, void of deformation, contained in, or neer, their cogenetic granitos. They contrast geochemically with the LCT family,because they have higher K and F contenta, and almost lack Li-minerals. The parental intrusives form composite batholithsconstituted by peraluminous, high K-calcalkaline granitoids, that have greater F/OH ratios than the orogenic ones; their REEpattems are similar to the NYF signatures. The most likely source for them is of A(+S) provenance. The ages of this suite areclase to 330 Ma. The most probable tectonic setting, in which the Pampean Pegmatitic Province developed, is related to aPhanerozoic continent-centinent collision. The LCT pegmatites were formed during pre to syn-collisional tectonic stages at theaxil of a turbiditic prism. The mixed signature pegmatite-granite systems were originated within an intraplate setting at thewaning stage of a post-collision subduction regime.