Neoproterozoic A-type magmatism in the Western SierrasudPampeanas (Argentina): evidence for Rodinia break-up alonguda proto-Iapetus rift?

摘要

A-type orthogneisses of mid Neoproterozoic age (774 ± 6 Ma,udU-Pb SHRIMP zircon age), are reported for the first time fromudthe Grenvillian basement of the Western Sierras Pampeanas inudArgentina. These anorogenic meta-igneous rocks represent theudlatest event of Rodinia break-up so far recognized in Grenvillianudbasement exposures across Andean South America. Moreover,udthey compare well with A-type granitoids and volcanic rocksudalong the Appalachian margin of Laurentia (Blue Ridge), thusudadding to former evidence that the Western Sierras PampeanasudGrenvillian basement was left on the conjugate rifted margin ofudeastern Laurentia during Rodinia break-up and the consequentudopening of the Iapetus ocean.