Crustal history of the Mesoproterozoic basement of the San Rafael Block (Mendoza).

CINGOLANI CARLOS; ABRE PAULINA; URIZ NORBERTO

San Miguel de Tucumán

Congreso; XX Congreso Geológico Argentino; 2017

The present isotopic data arethe result of a study of basement rocks of the San Rafael Block, located at theMendoza Province, Argentina. Two areas were sampled, the type section of the CerroLa Ventana Formation known as Leones-Ponón Trehué-La Estrechura regionand ductile-deformed rocks of the ElNihuil Mafic Unit. The Rb?Sr, Sm?Nd, Pb?Pb, and U?Pb methodologies wereapplied in order to constrain the basement age, tectonic history and to discussrelationships with equivalent Mesoproterozoic units located along the Cuyaniaterrane in the proto-Andean Gondwana margin. The Rb?Sr isochron yielded an ageof 1148 ± 83 Ma, with initial ratio of 0.70292 indicative of a slightly evolvedMesoproterozoic source. The Sm?Nd isochron indicates an age of 1228 ± 63 Ma,whereas TDM ages ranges between 1.23?1.64 Ga with εNd in between−0.94 and +4.7 recording a source less evolved than CHUR for the time ofcrystallization. In Pb/Pb diagrams the samples plot similarly to rocks from thebasement of Cuyania terrane. Zircon U?Pb data obtained from tonalitic facies (Leones River type section) yielded acrystallization age of 1214.7 ± 6.5 Ma (ID-TIMS). In situ U?Pb (LA-ICP-MS) zircon data carried out at two differentlaboratories on tonalitic orthogneisses (ElNihuil Mafic Unit) record an intercept at 1256 ± 10 Ma plotted in a concordiadiagram, whereas in a Tera-Wasserburg diagram the age is of 1222 ± 6.9 Ma.Therefore, a Mesoproterozoic age for the basement of the San Rafael Block ishere confirmed; this ca. 1.2 Ga ageis found elsewhere within the Cuyania allochthonous terrane.