Palaeoproterozoic to Mesoproterozoic Geology of North Queensland

Other Proterozoic Inliers – Yambo•Yambo Metamorphic Group– Divided into 13 metamorphic units– High-grade metasedimentary and meta-igneous rocks– Sedimentary protoliths inferred to be fine-grained siliciclastic rocks– Isotopic constraints (Blewett et al., 1998)• Mafic granulite – zoned zircon with an age of 1586±4Ma interpreted to bean igneous age• Sericite-garnet gneiss – igneous zircon modified by metamorphismgives an age of 1585±6Ma• Granodioritic gneiss; rims at 1576±5Ma and cores at 1581±8Ma and1636±13Ma• Mylonitic granitic gneiss with a complex spectrum of zircon ages; rimsat 1579±4Ma (metamorphic age) and youngest group of cores 1642±7MaNote again that these are orthogneisses and ages probably reflect anatexisand peak of metamorphism – therefore original age of paragneisses isstill unknown