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Examining multiple tectonic scenarios using numerical modelling: Halls Creek Orogen, east Kimberley

Sep 02, 2016

Fariba Kohanpour, Weronika Gorczyk, Mark Lindsay, Sandra Occhipinti

The tectonic setting of most Australian orogenic systems during the Proterozoic is intensely debated and multiple scenarios are often proposed. Tectonic models ranging from intra-cratonic to plate margin settings have been suggested to explain how Australian Archean nuclei were welded together. The Halls Creek Orogen (HCO) is a well-preserved and well-exposed Paleoproterozoic orogenic belt in the east Kimberley, northern Australia, which can provide some insight into the assembly of the Diamantina Craton during Nuna Supercontinent amalgamation. Despite the relative abundance of rock exposure, this is an example of where controversy remains as to how the Orogen developed. The 1865 Ma Tickalara Metamorphics seem to be a key unit within the central zone of the Halls Creek Orogen in helping resolve the controversy. The formation of the protoliths to the Tickalara Metamorphics, and other sedimentary and igneous rocks of central zone have been described as either forming in: (1) an ensialic marginal basin located closer to the margin of Kimberley Craton; or (2) an oceanic island arc setting above an easterly dipping subduction zone outboard of Kimberley Craton (Sheppard et al., 1999) (Fig.1);
Fig. 1. Possible tectonic settings for development of the Tickarala Metamorphics (from Sheppard et al., 1999): (a) in an ensialic marginal basin; or (b) in an oceanic island arc setting.

The two plausible tectonic scenarios of the Halls Creek Orogen are examined through 33 2D thermo-mechanical-petrological numerical experiments based on I2VIS code. The initial constraints for model setup aim to best represent the tectonic environment for the protoliths to the Tickalara Metamorphics as either ocean-continent subduction (Fig. 2a) or intra-ocean subduction (Fig. 2b).

Fig. 2. Initial geodynamic model setup for two tectonic scenarios: (a) continental active margin; (b) intra-ocean subduction.

With this approach we were able to execute experiments with specific physical parameters that resemble the geological conditions prior to the collision of the Kimberley and North Australian Cratons. The experiments were run, and the results are remarkably consistent with the geology observed in the Halls Creek Orogen, and indicate that the ensialic marginal basin scenario is the more likely. The basin scenario is validated using a range of measures, and is most consistent with the observed geology, structure and P-T-t paths determined in other metamorphic studies. Examining these models reveals processes which led to the generation of key lithological units and major structures, along with sources of magmatism and development of metamorphic conditions that occurred during the tectonic evolution of the Halls Creek Orogen (Fig.3). More details on the experimental set-up and analysis of results can be viewed here.

Fig. 3. (a-b) Representative snapshots of numerical models showing the major lithological units found in the Halls Creek Orogen; (c-d) Second invariant of strain rate as a proxy for major structures; (e) P-T paths from several locations using markers shown in a) and b).

Fariba’s PhD research is supported by MRIWA Project M465 “Deep crustal-scale structure, geological evolution and multi-commodity prospectivity analysis in the Halls Creek Orogen, Kimberley region, Western Australia” and was recently presented at the Australian Earth Sciences Convention 2016 in Adelaide, Australia. We would like to thank the Geological Survey of Western Australia, Panoramic Resources and MRIWA for their support.