Evolución magmática y relaciones regionales de los complejos eruptivos de La Esperanza, prov. de Río Negro

RAPELA, C.W.; LLAMBÍAS, E.J.

Revista Asociación Geológica Argentina

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 1985 vol. 40 p. 4 - 25

0004-4288

The magmatic characteristics and evolution of the eruptive sequences in a sector of the Northpatagonian Massif recently mapped in detail (Llambías and Rapela, 1984) are described within the context of the Upper Palaeozoic Andean magmatism. Major arid trace (Rb, Sr, Ba, Zr) elements were determined in all units of both La Esperanza Plutonic Complex (hornblende-biotite granodiorites and biotite granites—Cycle 1) and the Das Lomas Plutonic-Volcanic Complex (dacitic and rhyolitic ignimbrites and high silica leucogranites and ignimbrites-Cycle II). Both complexes are mostly composed by high-K calcalkalic associations showing metaluminous to peraluminous transitions. Nevertheless, mildly peralkaline compositions, acmite normatives, were found in the final magmatic episodes of the cycle II, represented by leucogranites and associated dykes. Four main magmatic episodes with distintive chemical trends that show an overall increasing acidity and alkalinity were recognized within each complex. Clear consanguineity relationships relate rocks of a given petrographic unit but the trends of the different units of a complex do not follow a co-linear pattern. Each complex appear then to be composed by several progresively more acidic magmatic pulses emplaced at epizonal levels (Cycle 1) and subvolcanic to surface levels (Cycle II) during a period of time not yet well established. The chemical evolution of the eruptive sequences of the Northpatagonian Massif resembles closely those described for the Upper Palaeozoic magmatism of the Frontal Cordillera Magmatic Belt and the Sanrafaelino Pampeano geological province. These results allow to define a single and extensive province, the Cuyano-Northpatagonian Magmatic Province, which shows a remarkable geographical continuity. Its petrological, geochemical arid ore deposit characteristics are compared with those of the Pampean Ranges and some circumpacific mesozoic batholiths.