New SHRIMP age constraints on the timing and duration of magmatism and sedimentation in the Mary Kathleen Fold Belt, Mt Isa Inlier, Australia

Abstract

Paleoproterozoic magmatic rocks from the Mary Kathleen Fold Belt of the Mt Isa Inlier record different magmatic textures and variations in tectonic strain associated with extension and the development of crustal-scale detachment zones. New SHRIMP U–Pb zircon geochronology for magmatic rocks, combined with field relationships, refine the duration of this extension to between 1780 and 1740 Ma. The initial stages of this tectonomagmatic event are coincident with mafic magmatism, basin formation and rapid sedimentation of the ∼1780–1765 Ma Myally Supersequence of the Leichhardt Superbasin in the adjacent Leichhardt River Fault Trough. The Ballara Quartzite and Corella Formation represent a period of sag-phase sedimentation during the later part this event, and facies models, sequence-stratigraphic interpretations and detrital-zircon geochronology data confirm the time equivalence of these units to the Quilalar Supersequence of the Leichhardt River Fault Trough. These correlations permit the Eastern and Western Successions of the Mt Isa Inlier to be correlated from 1780 Ma. Locally, the Corella Formation is intruded by 1740 Ma granites, suggesting that at least the lower parts of this package were deposited during the 1780–1740 Ma extensional event. By linking deep-crustal extension processes in the Mary Kathleen area with near-surface basin formation in the adjacent Leichhardt River Fault Trough, it is possible to develop crustal-scale architecture models that provide insights into the development and migration of ore-bearing fluids.