The Mojotoro granitic porphyry (Salta): An intrusive roaf or a dike in the Pampean Cycle?

Abstract

The Mojotoro porphyritic granite is located close to the city of Salta (24°47´44,9"S - 65°21´35,9"W, 1304 m.a.s.l.), at Cerro Mojotoro in the Eastern Cordillera. The pluton is emplaced in the Puncoviscana Formation (late Precambrian-early Cambrian), a lithological unit composed mainly of greenish pelites. The Puncoviscana Formation is covered unconformably by Cambrian quartzites of the Meson Group. Stratigraphic relationships of the granite indicate a Pampean age and emplacement during the Tilcaric orogenic phase. Petrographically it is a porphyritic granite with K-feldspar phenocrysts accompanied by quartz, plagioclase and biotite. The rock is strongly altered by sericitization, kaolinization, and limonitization. Likewise, the granite exhibits recrystalized spherules, fluid inclusions and granophyric fragments, indicative of shallow emplacement, with fast intergrowth of quartz in a mass of K-feldspar hypersolvus. Low magnetic susceptibility, with values of 0.11x10-3 SI, is typical of cortical granite that was formed from a metasedimentary protolith.