Conodont geothermometry in Palaeozoic carbonate rocks of Tasmania and its economic implications

Abstract

Conodont colour alteration index (CAI) values from Early to Middle Palaeozoic marine carbonate rocks of the West Tasmania Terrane range from 1.5 to 8. Highest CAI values are found in hornfels adjacent to a Jurassic dolerite intrusion. CAI of 5 indicate temperatures of 300–480°C and are found either adjacent to Jurassic dolerite intrusions or in an arcuate belt around the west and northwest of the island rimming the Precambrian rocks of the Tyennan and Rocky Cape regions. CAI values of 1.5 are found in the southwest of the state and values of 2 are common in central southern Tasmania. Low vitrinite reflectance values from the unconformably overlying Late Carboniferous‐Late Triassic Parmeener Supergroup, suggest that the major heat input into the conodonts was in the Late Devonian‐Early Carboniferous associated with regional metamorphism and the widespread intrusions of granitoids. High CAI values are not due to thick overburden as these are very unlikely in many parts of Tasmania. It is probable that high ...