PUNA GRANITIC PLUTONISM AS POSSIBLE NORTHERN CONTINUATION OF THE LATE PALEOZOIC–EARLY TRIASSIC MAGMATIC ARC FROM THE FRONTAL CORDILLERA, ARGENTINA

Along the Argentinian Andes at 29º - 30º 30´S one of the most representative characteristics of the Gondwana Cycle is the voluminous and widespread Late Paleozoic to Early Triassic magmatism Frontal Codillera´s Colangüil granits and Choiyoi volcanics. A preliminary result on current research in the Puna of Salta has allowed identify contemporaneous magmatic rocks with similar chemical and petrographic characteristics.

Granitoids are widely exposed and crop out from the western side of the salar de Arizaro to the granite León Muerto in Catamarca province. They are calc-alkaline granitoids that compositionally plot in the granodiorite and tonalite fields with subordinate gabbro-dioritic and granitic facies. Their Ar/Ar age has been calculated as 252.2 ± 7.9 Ma. However, there is a second type of plutons, typically fine-grained and with granophyric textures, often with a pinkish colour, consistent with intrusion to shallower levels. These two different suites of granitoids plutons are representing different tectonic phases.

The geochemical signature of the first one shows La/Yb ratios of only 11.75 to 16.2 indicative of fractionation of pyroxene and/or amphibole. The slightly higher La/Sm ratios (3 to 6.46) could be attributed to relatively low pressure crystal fractionation and some low normalized abundance of conservative elements (Ta, Nb, Hf and Zr) can be explained by influence of a volcanic arc. Trace elements abundances show a pattern that could be interpreted as a typical subduction related calc-alkaline orogenic suite. The second plutonic suite with bodies of leucogranite is progressively more siliceous and chemically displays a calc-alkaline trend with an important withinplate component.

Therefore, the ages, chemistry, petrography and geographical distribution of the Late Paleozoic–Early Triassic magmatic rocks of the Puna show such a striking similarity with those of the southern Colangüil Batholiths and Choiyoi province in frontal Cordillera of Argentina that points out the possibility that both magmatic provinces could be distal expressions of the same mega-orogenic event.