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Abstract

Chemical and mineralogical evidence is reported, first for mudrocks from the Mid-Permian–Mid-Triassic Maitai Group and, secondly, for Late Permian(?) mudrocks from the structurally underlying Patuki Melange. Weathering and alteration indices indicate increased source weathering and aluminosilicate input stratigraphically upwards in the Maitai Group. The Maitai Group exhibits an upward change from a relatively enriched continental magmatic arc source (and related country rocks) during the Late Permian, to a relatively depleted continental magmatic arc source (and related country rocks) during the Triassic. The melange mudrocks have a similar provenance to the Late Permian mudrocks of the Maitai Group. The melange mudrocks are, however, generally less altered, probably because of additional, local, ophiolite-related input. Red iron-rich mudrocks accumulated widely in two Triassic Maitai Group formations and also locally in the Patuki Melange. The iron oxide was derived by continental weathering under warm conditions, and then accumulated relatively slowly under oxidizing seafloor conditions. The chemical evidence, as a whole, indicates sources for all of the mudrocks similar to the Median Batholith and associated country rocks, or non-exposed equivalents along the SE Gondwana active continental margin. Accumulation took place during a change from an icehouse to a hothouse world.

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