New insights into the Piedra de Afilar Formation, Canelones department of Uruguay: Very-low-grade metamorphism, pressure solution, and age

Abstract

A detailed microstructural, mineralogical, and geochronological study was carried out along a profile in the Piedras de Afilar Formation (PAF) at the González quarry and surroundings (Uruguay). Both the PAF and the Soca granite were affected by very-low-grade metamorphism and pressure-induced dissolution. These postdiagenetic processes resulted in intense corrosion and alteration indicated by sericitization, silicification, and crystallization of iron oxides. Major auto-metamorphism was identified between the intrusive gabbro and the PAF, with almost no effects on the wall rock. K-Ar ages of sericite indicate 609-604 Ma for the metamorphism and related pressure-solution in the PAF. This age is in agreement with the juxtaposition of the Edén or Nico Pérez terranes and the Piedra Alta Terrane along the Sarandí del Yí shear zone. K-Ar dating of the gabbro wall rock constrained a deposition age of the PAF between 1000 and ca. 734 Ma.