The Musgrave Province is a Paleo- to Mesoproterozoic crystalline basement terrain that extends across the common borders of South Australia, Western Australia and the Northern Territory.

Age of major events

• Formation of oceanic crust of the Mirning Ocean at ~1950–1900 Ma (only preserved in the isotopic record).
• Subduction-related magmatism, volcanism and sedimentation in oceanic arc environments: formation of the ~1700–1500 Ma protoliths of the Birksgate Complex and the ~1610–1540 Ma Warlawurru Supersuite.
• Successive magmatism and sedimentation: ~1480–1440 Ma mafic orthogneisses, ~1400 Ma Papulankutja Supersuite, ~1400 Ma metasediments, ~1345–1290 Ma Wankanki Supersuite and ~1340–1270 Ma Wirku Metamorphics (Ramarama Basin).
• Granite intrusions of the Pitjantjatjara Supersuite, associated with deformation and amphibolite to granulite facies metamorphism during the ~1220–1120 Ma Musgrave Orogeny.
• Giles Event: ultramafic–mafic–anorthositic intrusions of the Giles Suite (including the Alcurra Dolerite); granite intrusions and bimodal volcanics of the Warakurna Supersuite; and deposition of sediments of the Bentley Supergroup in the Bentley Basin (including the Ngaanyatjarra Rift) at ~1085–1030 Ma.
• Emplacement of Amata Dolerite dykes between ~825–760 Ma (equivalent to the Gairdner Dolerite).
• Sediment deposition in the Centralian Superbasin from ~850 Ma to ~540 Ma over a largely buried Musgrave Province basement.
• Petermann Orogeny (~630–520 Ma): intracratonic crustal shortening and deformation leading to large-scale exhumation of the Musgrave Province from beneath the Centralian Superbasin along bivergent thrust systems. Associated with the development of internal, sediment-filled pull-apart basins (Levenger and Moorilyanna grabens) as well as development of nappe complex along northern province margin accompanied by synorogenic sedimentation in the adjacent Amadeus Basin.
• Alice Springs Orogeny (~450–300 Ma): Fault reactivation and further exhumation of the Musgrave Province. Significant fluid flow and associated epidote–quartz alteration along fault zones. Uplift-related synorogenic sedimentation in the adjacent Officer and Amadeus basins.

Prospect commodities

Ni, Co, Cu, PGE, Cr, V, Ti, Au, Ag, Pb, Zn, REE, U, graphite, gemstones, construction material (road base), groundwater.

Major exploration models

• Magmatic nickel-copper sulphides and PGE
• Stratiform chromite cumulates
• Stratiform vanadiferous titanomagnetite cumulates
• Laterite nickel-cobalt deposits
• VHMS and hydrothermal gold veins in volcano-sedimentary rocks
• VHMS and SEDEX in metamorphosed basement rocks

Summary geology

The Musgrave Province covers an area of approximately 120,000 km², straddling the border between South Australia, the Northern Territory and Western Australia. It is a Proterozoic lithospheric domain that largely lacks evidence of Archean provenance, in contrast to the surrounding basement provinces of the West, North and South Australian cratons (WAC, NAC and SAC, respectively). The Musgrave Province consists mainly of reworked remnants of Paleo- to Mesoproterozoic oceanic crust modified by intra-oceanic subduction processes.

The origin of the Musgrave Province goes back to c. 1.95–1.9 Ga, when rifting and sea floor spreading initially formed juvenile oceanic crust of the Mirning Ocean. This early crust-forming event is only preserved in the isotopic record of the Musgrave Province but not in its rock record. Probably none of this early crust has survived later reworking that successively formed more differentiated felsic crust by subduction-related intra-oceanic recycling of the older primitive oceanic crust. However, a c. 1920 Ma orthogneiss from the northern margin of the Gawler Craton has a trace element profile consistent with derivation through limited fractionation of an E-MORB like magma, perhaps reflecting an extensional environment marking the ocean-continent transition on the edge of the Gawler Craton towards the nascent Mirning Ocean.

The oldest known rocks of the Musgrave Province in South Australia belong to the Paleo- to Mesoproterozoic Birksgate Complex. These rocks consist of felsic to minor mafic gneisses with igneous intrusive, volcanic, volcaniclastic and, less commonly, sedimentary precursors that probably formed in oceanic arc environments. Within these rocks, igneous zircon populations of inferred proximal intra-provincial magmatic arc origin, i.e. zircons not derived as detritus from more distant Archean cratonic sources, document more or less continuous felsic magmatic arc activity between c. 1.7 and c. 1.5 Ga, with a frequency peak around 1.6 Ga. Similar igneous rocks of the c. 1610–1540 Ma Warlawurru Supersuite form the oldest components in the western Musgrave Province. Igneous protoliths typically have calc-alkaline affinities and trace element tectonic discrimination plots as well as juvenile isotopic compositions suggest that the protoliths to the Birksgate Complex formed in a volcanic arc setting and record formation of juvenile crust by construction of successive oceanic arcs.

Minor localised early Mesoproterozoic magmatism was recorded in form of c. 1480–1440 Ma mafic orthogneisses in the central part of the Musgrave Province and by felsic gneisses of the c. 1400 Ma Papulankutja Supersuite in its western part. Metasediments with a c. 1400 Ma depositional age were reported to occur in the eastern Musgrave Province but their extent is poorly known.

In the western Musgrave Province, a younger suite of calc-alkaline granitoids, the Wankanki Supersuite, intruded and crystallised between c. 1345 to 1290 Ma during the Mount West Orogeny. Near synchronously, a sedimentary package composed mostly of paragneisses and termed the Wirku Metamorphics, were deposited in the Ramarama Basin between c. 1340 and 1270 Ma. Currently there is no evidence that these units are present within the South Australian portion of the Musgrave Province.

The above rocks were subsequently deformed and metamorphosed at amphibolite to granulite facies during the province-wide c. 1220–1120 Ma Musgrave Orogeny. Large volumes of predominantly felsic magma intruded during this orogeny and have been grouped into the Pitjantjatjara Supersuite. This magmatism is isotopically juvenile and reflects crustal thinning, possibly due to lithospheric delamination and asthenospheric upwelling processes following earlier accretionary activity.

The Musgrave Orogeny was followed by the c. 1085–1030 Ma Giles Event, which includes the mafic-ultramafic layered to massive Giles Suite intrusions, dykes of the Alcurra Dolerite, granites and bimodal volcanics of the Warakurna Supersuite, and associated rift sediments of the Bentley Supergroup/Bentley Basin. The Giles Event has been interpreted to form part of the Warakurna Large Igneous Province, which affected much of central and western Australia.

The Giles Event was followed by dyke intrusions of the c. 825–760 Ma Amata Dolerite, a correlative of the Gairdner Dolerite that intruded the Gawler Craton in central South Australia, marking the beginning of the break-up of the Rodinia supercontinent. This time also marks the onset of sediment deposition in the Centralian Superbasin, on top of the older rocks of the Musgrave Province, which was largely buried beneath this subsiding Neoproterozoic basin during the time interval c. 850–540 Ma.

The c. 630–520 Ma Petermann Orogeny was a major intracratonic crustal shortening event, which resulted in the reactivation of several crustal-scale east-west trending shears, faults and thrusts and was accompanied by the development of widespread mylonitic shear fabrics and the extensive formation of pseudotachylite veins. The transpressional tectonics led to the exhumation of the Musgrave Province from beneath the Centralian Superbasin. Coeval with the Petermann Orogeny was the development of the Levenger and Moorilyanna grabens, which were infilled with coarse clastic sediments derived from the locally exposed Musgrave Province basement. At around the same time, north-directed thrusting and uplift led to the development of a basement-cored nappe complex at the northern margin of the Musgrave Province, accompanied by synorogenic molasse-like foreland sedimentation in the adjacent Amadeus Basin.

During the c. 450–300 Ma Alice Springs Orogeny internal east-trending structures were reactivated across large parts of the Musgrave Province, including the Woodroffe Thrust in the central-northern part of the province, and the Marryat, Coglin, Echo, De Rose and Wintiginna faults in its eastern part. Apatite fission track and (U-Th)/He apatite and zircon analysis indicate that two discrete cooling events recorded in the eastern Musgrave Province, one at c. 450–400 Ma and one at c. 310–290 Ma, represent uplift associated with the Alice Springs Orogeny.

There is also evidence for reactivation of the Munyarai – Everard thrust system along the southern margin of the Musgrave Province, where basement was thrust southward over Neoproterozoic and early to mid‑Paleozoic sediments of the Officer Basin causing synorogenic deposition of Devonian sediments. Synorogenic deposition associated with uplift of the Musgrave Province during the Alice Springs Orogeny is also recorded for the Amadeus Basin. Furthermore, deformation of the Cambrian sediments of the Levenger and Moorilyanna grabens also occurred during the Alice Springs Orogeny. Substantial epidote and silica alteration occurring along structures in the eastern Musgrave Province has been linked with fluid flow facilitated by fault reactivation during the Alice Springs Orogeny.

Following the Alice Springs Orogeny, the Musgrave Province has undergone at least one phase of intensive deep weathering and erosion prior to the deposition of clastic sediments of the Mesozoic Eromanga Basin along its eastern margin. Intense chemical weathering of these sedimentary deposits as well as the basement rocks resulted in a deep weathering profile that can reach up to 90 m below the present-day surface. The typically composite weathering profiles are characterised by kaolinisation and mottled or varicoloured, pallid, ferruginous or siliceous zones. Multiple phases of post-Mesozoic dominantly siliceous and ferruginous induration led to the formation of widespread silcrete and ferruginous duricrust.

During the early Paleogene, rivers incised up to 70 m into the older cover sediments and the basement rocks. The channels were subsequently filled during two distinct phases of fluvial sedimentation: first in the Eocene-Oligocene, followed by a second fluvial phase in the Early to Late Pliocene. These fluvial periods are separated by a marginal marine to estuarine interval deposited during the Late Miocene to Early Pliocene. In the Quaternary, the onset of aridity, with episodes of alluvial and aeolian activity, resulted in today’s landscape with the formation of alluvial plains, sand plains and aeolian dunes and dunefields.

The Musgrave Province is still tectonically active with several significant earthquakes occurring in the region in the past 40 years. In 1986 a 6.0 magnitude earthquake produced a 13 km long fault scarp with a maximum throw of 0.6 m along the Marryat Fault zone. More recently, the community of Ernabella (Pukatja) recorded two magnitude 5.7 earthquakes in both 2012 and 2013.

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