Low‐grade metamorphism in the Palaeozoic sequences of the Townsville hinterland, northeastern Australia

Abstract

The transition from diagenesis to low‐grade metamorphism for the Ordovician ‐ Early Carboniferous sequences of the Burdekin and Clarke River Basins and the Broken River ‐ Camel Creek region is characterised by b ‐cell dimension and Kübler Index (KI = illite crystallinity) of K‐white micas, clay‐mineral assemblages and conodont colour alteration index (CAI). Data indicate that: (i) there is a regional metamorphic pattern characterised by anchizonal conditions, with consistently higher grade in the Camel Creek region (or Subprovince); (ii) anomalies are explicable in terms of location relative to areas of differing intensity of deformation (e.g. the Ruxton Formation) and inferred greater depth of burial (e.g. southern versus northern outcrop tracts of Quinton Formation); (iii) the regional pattern in the Broken River ‐ Gray Creek area shows general alignment with the regional grain; (iv) there is a generalised north to south increase in CAI for the Broken River region (‘Top Hut’ to Broken River, 6), with higher values towards the Montgomery Range intrusions; (v) in the Burdekin Basin, there arehigher CAI values north of Mt Podge and ‘Star’, and lower values (