Arc and mantle detritus in the post-collisional, Lower Silurian Kabadah Formation, Lachlan Orogen, New South Wales

The Kabadah Formation outcrops in central New South Wales as a thrust package 66km long, interleaved with Lower Silurian Canowindra Volcanics and situated between the Junee-Narromine and Molong Volcanic Belts of the Ordovician Macquarie Arc. The Kabadah Formation contains Early Silurian corals and Llandovery graptolites. Its provenance is complex, with detrital fragments of mafic-intermediate volcanic rocks, free crystals of pyroxene, chromite and ultramafic clasts, detrital volcanic quartz, garnet, and clasts of welded S-type rhyolitic volcanic rocks; and rare clasts from uplifted fold-belt rocks (granite and metamorphosed and deformed sediments). The variety of these clasts suggests that the Kabadah Formation records the Benambran collision of the Macquarie Arc with Ordovician quartz-rich sedimentary rocks, with detritus also derived from coeval Early Silurian mafic and felsic magmatism. The major source of detritus was from the short-lived emergent Fifield arc that formed from the subduction of an older backarc basin. The Kabadah Formation accumulated in an upward-shallowing Early Silurian marine basin between phases of the Benambran Orogeny.