The Sierra de Macon, Plutonic expression of the Ordovician magmatic arc, Salta Province Argentina

Abstract

The Macon granitoids are part of a tonalite/diorite granodiorite suit. Their trace elements place these rocks in the volcanic arc field. They have distribution patterns similar to those observed for rocks from Choschas, Taca Taca, Chuculaqui, and Quebrada de Batin. Macon rocks show strong enrichment of elements such as K, Rb, Th, and light REEs, which suggests crustal participation associated with the arc source. 87Sr/86Sri and (143Nd/144Nd)i isotopic ratios of two samples are compatible with arc-related rocks. Their calculated age of 482.7 Ma is consistent with other ages determined for the Ordovician western Puna eruptive belt (Faja Eruptiva de la Puna Occidental). This belt is made up of a set of granitoids, characteristic of the northern part of the Puna of Catamarca that, together with similar exposures of Salta and the Chilean region near the border with Argentina, suggests a meridian strike. The Ordovician ages and arc characteristics of the Sierra de Macon rocks, at the eastern extreme of the belt, incorporate them into this igneous province. This significantly increases the width of the Sierra de Macon igneous province to as much as 150 km at this latitude.