Deciphering the tectonic history of the Musgrave Block to assist mineral explorers and regional synthesis programs

An ARC Discovery funded project - LP0560887

Project Investigators

Project Collaborators

Doctor Peter Betts (Monash University)

Doctor Bruce Schaefer (Monash University)

Project Details

Why are the Musgraves important?

The investigation of the Musgrave Block is highly pertinent for the two reasons:

• Firstly it links the northern Australian Craton and the Gawler Craton in southern Australia, and therefore understanding the timing and manner of its formation has critical significance for understanding the tectonic evolution of Proterozoic Australia as a whole.
• Secondly it is highly prospective with intense greenfields exploration currently focused over the entire region of the Musgrave Block, with companies concentrating on scouring the ultramafic Giles complex for Nickel deposits.

The aim of this project is to develop an integrated framework that describes the tectonic evolution of the latest Palaeo-to-Mesoproterozoic Musgrave Block in southern Central Australia.

Project Background

Until relatively recently, interpretations on the evolution of Proterozoic Australia have strongly favoured its evolution as a single intact piece of crust, dominated by intraplate tectonism.

These "stabilist" ideas incorporated crust forming processes to be dominated by processes such as vertical accretion involving underplating, and extensional tectonic processes driven by mantle plumes and delamination.

However, recent geochemical and isotopic studies within central Australian terranes such as the Arunta Inlier are recognising, albeit in a somewhat cryptic way, evidence that "dynamic" plate margin processes were in operation within Proterozoic Australia. Limited outcrop and restricted access has hindered previous studies of the entire Musgrave Block, however there has been growing evidence that plate margin processes have been responsible for crustal growth of at least part of the Musgraves.

Existing "stabilist" models view the Musgrave Block as a continuation of the Albany-Fraser mobile belt, formed during the reworking of older continental material during the assembly of Australian cratons at ~1300-1100. This is seen as to be linked to the formation of Rodinia. However, geochronological studies on felsic gneisses situated in the northern and western Musgrave Block indicate that these felsic gneisses represent older crustal material (~1580-1550 Ma), and have geochemical affinities that support the notion of a subduction-related crust-forming event at this time. Outcrop of this older, possibly subduction-related felsic gneiss, is relatively extensive, and is discontinuously scattered along along the length of the Musgrave Block.

In addition to these granulitic felsic gneisses, ~1075 Ma Alcurra dyke swarm alludes to older subduction related processes. Epsilon Nd analyses of the Alcurra dyke swarm give values indicative of subcontinental lithosphere contaminated by subducted sediment (Fig. 4). Sm-Nd isochrons of the Alcurra dykes give ages of c.1600 Ma, perhaps indicating that the modification of the lithospheric mantle through subduction may have occurred at this time.

Preliminary work on the metasediments from the eastern Musgrave Block have constrained their minimum depositional age to ~1400 Ma. The presence of zircon ages unusual to Australia but common in North America has implications for Proterozoic reconstructions of Australia involving the Musgrave Block.

Aims of this project

This project will investigate:

• the timing and spatial distribution of the tectonic events in the Musgrave Block (i.e. Musgravian and Petermann Orogenies)
• the tectonic settings of the major magmatic systems (Basement felsic gneisses and the Kulgera Dyke Swarms)
• the origin of the metasedimentary rock systems within the block
• the evolution of the lithospheric mantle through the history of the Musgrave block (tectonic and geochemical classification of the Giles Complex and temporally coincident dyke swarms)

These observations will ultimately lead to a reconstruction of the tectonic and magmatic processes involved in the formation of the Mesoproterozoic Musgrave Block.

Musgraves sub-projects

Crustal setting and structural evolution of the 1080 Ma Giles Complex, Musgraves province WA-SA-NT: insights from regional geophysical datasets.

Complex strain evolution and age of mylonites, Western Musgraves, WA.

Isotopic, geochemical and petrogenic approaches to terrane analysis and Proterozoic reconstruction in the Musgrave Block.

Tectonic linkages between the Musgrave Block and North Australian Craton: correlations, event chronology, and tectonothermal regimes.

Structural and metamorphic evolution of rocks in the Mann Ranges, central Musgrave Block.

Age and nature of orogenesis in the southern Latitude Hills, WA