The Haslingden Group is the oldest cover sequence in the Mount Isa Orogen; it is ca. 18 km thick and accumulated in the Leichhardt River Fault Trough (LRFT) between 1800 and 1710 Ma ago on ca. 1860 Ma-old continental crust. The volcano- sedimentary Haslingden Group has previously been interpreted as a single-stage rift sequence and an overlying sedimentary package, the Quilalar Formation, as the sag phase associated with subsequent thermal contraction of the lithosphere. Our preliminary work on the Haslingden Group suggests a more complex evolution involving at least two stages of rifting. This hypothesis will be evaluated by: i) constraining the stratigraphic evolution of the Haslingden Group through a detailed sedimentological/paleogeographical analysis including quantitative analysis of shallow marine sediments of probable tidal origin; ii) contrasting the stratigraphic evolution of the Haslingden Group with documented rift sequences in the geologic record; and iii) quantitatively modelling the subsidence history of the LRFT within the constraints of the stratigraphic analysis and the geochronological framework. An understanding of the stratigraphic evolution of the Haslingden Group will enhance the understanding of less well-exposed rifts such as the North Sea and Keweenawan Rifts and of rifts in general. The proposed study is part of a multidisciplinary investigation of the Mount Isa Orogen, including a structural analysis of the LRFT, by the Bureau of Mineral Resources, Australia. As part of this project we will be able to evaluate the evolution of the LRFT within its own tectonic context as well as within the framework of surrounding tectonic processes. The results of the analysis of the Haslingden Group will be integrated with ongoing structural-metamorphic, geochronologic, geochemical and sedimentological studies to formulate a comprehensive tectonic model for the Mount Isa Orogen. Subsidence modelling and integration of various disciplines in developing a tectonic model for the Mount Isa Orogen will be undertaken while the PI is on study leave at the BMR for the duration of 1988.
