Composition and classification of Paleozoic flysch mudrocks of eastern Australia: Implications in provenance and tectonic setting interpretation
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The mudrock suites of Paleozoic flysch sequences of eastern Australia can be characterised on the basis of the relative abundances of phyllosilicates and tectosilicates (mainly feldspar and quartz). A mudrock maturity index is defined as the ratio of total phyllosilicates to phyllosilicates + feldspar + quartz. Mudrocks are classified into tectic, phyllo-tectic and phyllic types, on the basis of increasing maturity. Based on studied examples of eastern Australia, preliminary characteristics of mudrocks of various tectonic settings are identified. Oceanic island arc mudrocks are of the tectic type, characterised by high feldspar and low phyllosilicate content. They are derived from calc-alkaline andesitic rocks of the magmatic arc. Mudrocks of the continental island arc and active continental margins (Andean type and strike-slip basins) are characterised by a higher phyllosilicate content and are mainly phyllo-tectic in type. Passive margin mudrocks are of the phyllic type, characterised by extremely high phyllosilicate and low feldspar contents, suggesting their recycled nature. Mudrock maturity is accompanied by an increase in the K2O/Na2O ratio from oceanic island arc to continental island arc and active continental margin to passive margin type mudrocks. © 1985.
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