A geochemical approach to the characterization of a hidden magmatic arc: The source of the Goonoo Goonoo Mudstone, eastern Australia

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Abstract
The chemical composition of a stratigraphically controlled sequence of volcanic conglomerate clasts in the Palaeozoic forearc sequence of the New England Fold Belt has been used to deduce characteristics of their source. Basaltic lithologies are absent, and compatible element concentrations indicate that the suite has undergone low pressure fractionation, producing a continuum from andesite to rhyolite. A discrimination diagram based on immobile elements from modern arc lavas, originally constructed for basaltic rocks, can be used for intermediate rocks and shows that the clasts were derived from a calc‐alkaline volcanic arc. A new plot utilizing Ce/Y v. Sr/Y distinguishes between volcanic arc rocks erupted through oceanic, continental and thinned continental crust. This plot shows that the magmatic arc bordering the forearc basin in New England was floored by thin continental crust (intermediate in thickness to oceanic and continental crust), in accord with a significant proportion of granitic and recycled sedimentary clasts. The use of conglomerate clasts in provenance determination avoids the problems inherent in other methods such as component mixing (bulk sediment chemistry) and modification or destruction of diagnostic phases (petrographic techniques).