First U-Pb detrital zircon ages from the Los Morteritos Unit (El Gigante Metamorphic Complex), Sierras Pampeanas, Argentina: new insight into the early Paleozoic evolution of SW Gondwana

Abstract

The El Gigante Metamorphic Complex, in the homonymous range (Sierras Pampeanas, Argentina), consists of three lithostratigraphic units that, from bottom to top, are: Quebrada Grande (Mesoproterozoic protoliths), Loma Cortada (Ediacaran-early Cambrian sedimentary protoliths), and Los Morteritos (middle to late Cambrian protoliths), all reworked by the Famatinian orogeny. This study reports the first U–Pb detrital zircon data from a quartz–micaceous schist of the Los Morteritos Unit, which shows two main Mesoproterozoic peaks (~1350 and ~1070 Ma) and minor Cambrian ages. This pattern suggests a recycling of the underlying units and a minor contribution from the early Cambrian Pampean basement. The graphite-rich rocks, along with an abundance of carbonate protoliths, isotopic data, and detrital zircon evidence, support a correlation of the Los Morteritos Unit with other units of the westernmost Sierras Pampeanas. They correspond to sedimentary successions deposited in a low-energy, distal environment, belonging to a mixed carbonate–siliciclastic platform developed at the SW Gondwana margin in the middle to late Cambrian (ca. 525-490 Ma).