SHRIMP U-Pb monazite dating of 1600-1580 Ma amphibolite facies metamorphism in the southeastern Mt Isa Block, Australia

Abstract

SHRIMP U-Pb monazite dates of ca 1600-1580 Ma are reported from three samples taken from the southeastern margin of the Proterozoic Mt Isa Block. The samples include an upper amphibolite facies paragneiss and a pegmatite from the host sequence of the Cannington Ag-Pb-Zn deposit and a middle amphibolite facies metasediment from the Soldiers Cap Group near Maronan station. These dates are interpreted to represent the timing of amphibolite facies metamorphism at the southeastern margin of the Mt Isa Block. They are in accordance with the results of earlier SHRIMP U-Pb zircon and 40Ar/39Ar dating, which suggested that metamorphism in the southeastern Mt Isa Block occured approximately 50 million years earlier than metamorphism in the western Mt Isa Block. This challenges the common perception of orogeny in the Mt Isa Block in which 'peak metamorphism', and the deformation events associated with it, can be correlated across the entire terrane.