PROTEROZOIC MOUNT ISA SYNTHESIS

P.G. Betts & R.J. Armit

PGN Geoscience

Section II: Eastern Australian Proterozoic correlations

Proterozoic Mount Isa Synthesis

Page ii Section II: Eastern Australian Proterozoic Correlations

Proterozoic Mount Isa Synthesis SECTION II: EASTERN AUSTRALIAN PROTEROZOIC CORRELATIONS

Table of Contents INTRODUCTION...... 1 ARCHITECTURAL CONTEXT OF THE CORRELATIONS ...... 3 CONTINENTAL CRATONIC ELEMENTS ...... 3 North Australian Craton ...... 3 South Australian Craton...... 3 West Australian Craton...... 4 RECONSTRUCTION ARCHITECTURES ...... 4 TECTONIC EVOLUTION OF THE AUSTRALIAN CONTINENT...... 6 AMALGAMATION OF THE NORTH AUSTRALIAN CRATON (CA 1870–1820 MA)...... 6 Mount Isa Inlier...... 6 Correlations with the Gawler Craton ...... 8 Correlation with the Arunta Inlier-Tanami Province ...... 9 Kimberley Craton–Pine Creek Inlier ...... 9 Interior of the North Australian Craton...... 10 Tectonic Interpretation ...... 10 COLLISION OF THE WEST AND NORTH AUSTRALIAN CRATONS (CA 1820–1790 MA).....11 Basin Development ...... 11 Collision between the West Australian Craton and the Central Australian Craton...... 12 Tectonic Interpretation ...... 12 LEICHHARDT SUPERBASIN DEVELOPMENT (CA 1790–1760 MA)...... 13 Mount Isa Inlier...... 13 Leichhardt Superbasin correlations ...... 14 Orogenesis in Central Australia...... 14 Tectonic Interpretation ...... 15 WONGA EXTENSION EVENT (CA 1760–1740 MA)...... 16 Mount Isa Inlier...... 16 Basin Development in the continent interior...... 17 Plate margin magmatism...... 17 Tectonic Interpretation ...... 17 MID BASIN INVERSION (CA 1740–1725 MA)...... 18 Mount Isa Inlier...... 18 Kimban Orogeny and Strangways Event ...... 19 Tectonic Interpretations...... 19 CALVERT SUPERBASIN I (ca 1725–1690 Ma) ...... 21 Calvert Superbasin correlations...... 22 Kimban Orogeny/Strangways Event (continued)...... 23 Tectonic Interpretation ...... 23 CALVERT SUPERBASIN II (ca 1690–1670 Ma) ...... 25 Correlations...... 26 Plate Margin tectonism ...... 26

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Tectonic Interpretation ...... 27 ISA SUPERBASIN (ca 1670–1645 Ma)...... 28 Mount Isa Inlier...... 28 Lower Isa Superbasin correlations...... 29 Tectonic Interpretation ...... 30 RIVERSLEIGH EVENT (CA 1645–1630 MA) ...... 31 Upper Isa Superbasin correlations...... 31 Accretion in Central Australia...... 32 Tectonic Interpretation ...... 32 ISA SUPERBASIN (CA 1630–1595 MA)...... 32 EARLY ISAN OROGENY (CA 1620–1570 MA)...... 33 CORRELATED OROGENIC EVENTS...... 34 Chewings Orogeny...... 34 Olarian Orogeny...... 34 Painter Orogeny...... 35 Wartakan Orogeny...... 35 Kararan Orogeny...... 35 Ewamin Orogeny ...... 36 EVIDENCE FOR PLATE BOUNDARIES DURING THE ISAN OROGENY ...... 36 St Peter Suite Magmatic arc (Gawler Craton) ...... 36 Musgrave Magmatic arc ...... 37 Forest Home Suite...... 37 LATE ISAN OROGENY (CA 1550–1500 MA) ...... 38 CORRELATED OROGENIC EVENTS...... 39 Jana Orogeny...... 39 Late Orogenic A-type Granites...... 39 DRIVING OROGENESIS...... 41 Plume modified orogeny...... 41 Continental collision between the Gawler Craton and the North Australian Craton ...... 42 East-west shortening followed by transpression...... 42 SUMMARY ...... 43 REFERENCES ...... 44

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Table of Figures

Figure 1: Location of central and eastern Australian Proterozoic Inliers overlain on a total magnetic intensity image of Australia (Geoscience Australia)...... 1 Figure 2: Time-Space plot of Palaeo-Mesoproterozoic eastern Australian terranes displaying the tectonic regimes along with the sedimentary, igneous and metamorphic events recorded across the terranes...... 2 Figure 3: Geodynamic evolution of ca 1870–1830 Ma Eastern Proterozoic Australia...... 6 Figure 4: East-west gravity modeling across the Mount Isa Inlier indicating an easterly dipping suture between the Davenport/Tennant Creek and Mount Isa Inlier...... 8 Figure 5: Geodynamic evolution of ca 1820–1795 Ma Eastern Proterozoic Australia...... 11 Figure 6: Geodynamic evolution of ca 1790–1760 Ma Eastern Proterozoic Australia...... 13 Figure 7: Geodynamic evolution of ca 1760–1740 Ma Eastern Proterozoic Australia...... 16 Figure 8: Geodynamic evolution of ca 1735–1725 Ma Eastern Proterozoic Australia...... 18 Figure 9: Geodynamic evolution of ca 1725–1690 Ma Eastern Proterozoic Australia...... 21 Figure 10: Geodynamic evolution of ca 1690–1670 Ma Eastern Proterozoic Australia...... 25 Figure 11: Geodynamic evolution of ca 1660–1645 Ma Eastern Proterozoic Australia...... 28 Figure 12: Geodynamic evolution of ca 1645–1630 Ma Eastern Proterozoic Australia...... 31 Figure 13: Geodynamic evolution of ca 1620–1570 Ma Eastern Proterozoic Australia...... 33 Figure 14: Geodynamic evolution of ca 1550–1500 Ma Eastern Proterozoic Australia...... 38

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Page vi Section II: Eastern Australian Proterozoic Correlations

INTRODUCTION The absence of exposed post-1850 Ma plate boundaries in the Mt Isa Inlier has made the geodynamic context, in which the inlier has evolved, subject to much speculation and debate. There has been a recent trend away from intraplate tectonic models that were popular in the 1980s and early 1990s. These models have given way to interpretations which mainly involve plate tectonics processes. Many interpretations of the tectonic context of the inlier have relied on regional correlations with other geological provinces such as the Curnamona Province, Gawler Craton, Georgetown Inlier, and Arunta Block (Figures 1, 2).

This report summarises the tectonic context of the Mount Isa Inlier from the perspective of major tectonic events of Proterozoic Australia between ca 1870–1500 Ma. The evolution of the continent is broken into discrete time slices which pertain to the evolution of the Mount Isa Inlier.

Figure 1: Location of central and eastern Australian Proterozoic Inliers overlain on a total magnetic intensity image of Australia (Geoscience Australia).

Page 1 Proterozoic Mount Isa Synthesis

Figure 2: Time-Space plot of Palaeo-Mesoproterozoic eastern Australian terranes displaying the tectonic regimes along with the sedimentary, igneous and metamorphic events recorded across the terranes.

Page 2 Section II: Eastern Australian Proterozoic Correlations ARCHITECTURAL CONTEXT OF THE CORRELATIONS CONTINENTAL CRATONIC ELEMENTS

North Australian Craton

The North Australian Craton (Myers & others, 1996) extends across large tracts of Queensland, Northern Territory and Western Australia. The northern boundary of the craton is defined by the coastline of Australia. However, it is probable that the craton extends across the Torres Strait and forms the Precambrian basement beneath the Papua New Guinea highlands. The southern boundary is defined by the Musgrave Block and the Paterson Orogen. The eastern boundary is delineated by the Terra Australis Orogen (Cawood, 2005). There are numerous geological provinces which comprise the North Australian Craton, and these provinces preserve a geological evolution from the Late Archaean to the Mesoproterozoic (Cawood & Korsch, 2008). Major geological provinces include the Archaean to Paleoproterozoic cratonic blocks of the Kimberley Craton and Rum Jungle Province, as well as numerous buried cratons which have been delineated using continental scale geophysical datasets.

These cratonic blocks are separated by orogenic systems which evolved during ca 1850–1500 Ma. They include: the Halls Creek, King Leopold, and Top End orogens in the northwest, the Mount Isa, Georgetown, and Coen inliers in the east, and the Tanami Province and Arunta Inlier in the south. In addition to the cratonic basement and orogenic systems, an extensive basin system covering old Archaean cratonic blocks developed across a large portion of the craton during ca 1850–1600 Ma. Some of the more prominent basins include the Kimberley, Victoria River, McArthur Basins, and the extensive basin systems preserved in the Mount Isa and Georgetown inliers (Jackson & others, 2000). This basin system can be correlated with contemporary basins in the Curnamona Province (Giles & others, 2004; Conor & Priess, 2008; Gibson & others, 2008). This suggests that the Curnamona Province, which has previously been assigned to the South Australian Craton, may in fact belong to the North Australian Craton.

South Australian Craton

The South Australian Craton encompasses large regions of southern Australia, and includes Archaean crust, Paleoproterozoic and Mesoproterozoic orogenic systems. Geological provinces that comprise the South Australian Craton include the Archaean nucleus of the Gawler Craton (Daly & others, 1998; Hand & others, 2007; Payne & others, 2009), the Nawa Terrane, and the Coompana Block, which straddle the South Australian and Western Australian borders. The Curnamona Province was also considered part of the South Australian Craton in the original craton nomenclature of Myers & others (1996). However, subsequent reconstructions also consider the Curnamona Province as the southeastern margin of the North Australian Craton (Giles & others, 2004; Betts & Giles, 2006; Cawood & Korsch, 2008). An implication of this is that the South Australian Craton was not a coherent Page 3 Proterozoic Mount Isa Synthesis cratonic entity for much of the Paleoproterozoic. Rather, it is likely that it formed by gradual continental growth along the southern margin of the Australian continent during the Paleoproterozoic (Betts & Giles, 2006). Its outline as suggested by Myers & others (1996) (including the Curnamona Province) probably reflects Late Mesoproterozoic modification (e.g., Giles & others, 2004), rather than the original architecture. The present day boundary of the South Australian Craton covers Neoproterozoic to Cretaceous sedimentary basins which have been inferred from geophysical and sparse drill hole data. The South Australian Craton is delineated by the Musgrave Block in the north, the Neoproterozoic to Cambrian terranes of the Delamerian Orogen and Lachlan Orogen (Terra Australis Orogen) in the east, and the Albany Fraser orogenic system in the west. Although, the southern margin of the craton is defined by the Australian continental margin, it has long been recognised that rocks of the southern Gawler Craton correlate with rocks of Terre Adélie and the King George V Land in Antarctica (Fanning, 1995; Peucat & others, 1999; Fitzsimons, 2003), as well as the Miller and Shackleton ranges in the Trans Antarctic Mountains (Goodge & others, 2001; Betts & others, 2008; Payne & others, 2009). Together, the Gawler Craton and temporal rocks in Antarctica form the Mawson continent (Fanning, 1995; Payne & others, 2009).

West Australian Craton

The West Australian Craton (Myers & others, 1996) comprises the Archaean Yilgarn and Pilbara cratons, which are separated by the Paleoproterozoic rocks of the Capricorn Orogen (ca 1850–1810 Ma) (Myers & others, 1996). The southern boundary of the craton is defined by the Mesoproterozoic rocks of the Albany–Fraser Orogen and the western boundary by the N-S trending Neoproterozoic Pinjarra Orogen (Cawood & Korsch, 2008). The Mesoproterozoic Paterson Orogen defines part of the northern boundary. The remainder of the West Australian Craton’s margin is hidden beneath Neoproterozoic to Phanerozoic sedimentary basins (e.g., Officer Basin). The Archaean components of the West Australian Craton evolved independently until they eventually amalgamated during continental collision associated with the Paleoproterozoic Capricorn Orogeny (Cawood & Tyler, 2004). Thereafter the Western Australian Craton has remained relatively intact with only minor modifications and reworking during subsequent tectonic events (e.g., Paterson Orogeny).

RECONSTRUCTION ARCHITECTURES There are two architectural reconstruction models for the Australian continent during the Paleoproterozoic and the Mesoproterozoic. One model assumes that the Palaeo-Mesoproterozoic geological elements are essentially in the same position today as they were in the past and all interpretations were formed in this context (e.g. Wade & others, 2006; Gibson & others 2008). The other model requires a 50–55° rotation of the South Australian Craton (Gawler Craton and the Curnamona Province) about a euler pole located in the McArthur Basin (Wingate & Evans, 2003; Giles & others, 2004). These two very different models could impact markedly on the outcomes of

Page 4 Section II: Eastern Australian Proterozoic Correlations many tectonic/geodynamic reconstructions for the Mount Isa Inlier between ca 1850–1500 Ma. In this report we favour the rotation of the South Australian Craton because it is palaeomagnetically constrained, and provides a reconstruction architecture which allows the development of a holistic tectonic evolution of the Australian continent between ca 1870–1500 Ma. In addition, this rotation model is consistent with palaeomagnetic data which connects Australia–East and Antarctica–Laurentia as part of the Supercontinent Columbia (Betts & others, 2008).

In this section of the report we correlate the geology of the Mount Isa Inlier and major tectonic events with the surrounding geological provinces and use these relationships to constrain a geodynamic model.

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TECTONIC EVOLUTION OF THE AUSTRALIAN CONTINENT AMALGAMATION OF THE NORTH AUSTRALIAN CRATON (CA 1870– 1820 MA)

Figure 3: Geodynamic evolution of ca 1870–1820 Ma Eastern Proterozoic Australia.

Mount Isa Inlier

About 1870–1840 Ma widespread orogenesis, magmatism and high temperature-low pressure metamorphism occurred across large areas of the North Australian Craton (Betts & others, 2002). The temporal distribution of the orogenesis has been used to ascribe tectonic models that involve largely intraplate processes (e.g., Etheridge & others, 1987).

Plate tectonic models are considered herein to describe the distribution of orogenic events. This interval in evolution of the Australian continent was a period of rapid continental amalgamation in

Page 6 Section II: Eastern Australian Proterozoic Correlations which three major orogenic systems were active contemporaneously. This coincides with continental accretion during formation of the supercontinent Columbia (Nuna) (Rogers & Santosh, 2002).

In the Mount Isa Inlier, this period of continental collision is characterised by extensive greenschist to amphibolite facies metamorphism, preserved in the central to western parts of the Inlier, and poly- deformation which was associated with the Barramundi Orogeny (ca 1860–1850 Ma) (Etheridge & others, 1987). Geophysical modelling and interpretations suggest that the Mount Isa Inlier is bound by continental sutures to the east and west. Seismic data and gravity forward models indicate a west- dipping high density zone separating the Numil terrane to the east, from the Mount Isa basement terranes to the west. This zone is imaged in deep seismic refraction data which shows a prominent west-dipping high velocity zone extending to the Moho. This dipping zone is interpreted to be a suture zone. The geometry of the suture zone becomes shallower in the southern part of the inlier. The transition from a relatively steep dipping zone to a relatively shallow-dipping one is coincident with a deep-seated NE trending fault which is prominent in gravity data. This structure has been interpreted as a crustal tear in which there was a marked change in the geometry of the subducting slab and consequently the developed suture zone.

The western boundary of the Mount Isa Inlier is defined by an abrupt change in the strike of the dominant structural grain from N-S within the inlier to NW west of the inlier. This boundary is interpreted as a suture between the Tennant Creek/Davenport Province and the basement terranes of the Mount Isa Inlier. It is located west of the Mount Isa Fault Zone (Bierlein & Betts, 2004) and divides the Ardmore-May Downs from the Mount Oxide and the Leichhardt River domains. Gravity modelling suggests that this interface dips moderately to the east. This suture is thought to define a boundary between a continental ribbon, composed of the basement terranes of the Mount Isa Inlier, and the eastern margin of the North Australian Craton (Figure 3).

The Kalkadoon Batholith (ca 1850 Ma) forms a prominent north-trending belt of granitoids which display arc-like affinities (McDonald & others, 1997; Bierlein & Black, 2004) and possibly represent the remnants of a continental magmatic arc (ribbon). The basement to this arc accreted to the North Australian Craton during the Barramundi Orogeny (ca 1870–1850 Ma). It would appear, based on temporal relationships, that deformation during the Barramundi Orogeny recorded the collision of the Mount Isa basement with the North Australian Craton. Emplacement of the Kalkadoon arc following the Barramundi Orogeny recorded continued subduction-related magmatism until at least ca 1850 Ma. This suggests that west-dipping subduction, to the east of the inlier, continued until at least ca 1850 Ma and was eventually terminated by amalgamation of the Numil terrane and Mount Isa basement.

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Figure 4: E-W gravity modelling across the Mount Isa Inlier indicating an easterly dipping suture between the Davenport/Tennant Creek Province and Mount Isa Inlier.

Correlations with the Gawler Craton

The Donington Suite (ca 1850 Ma), which is preserved in the eastern Gawler Craton, forms a prominent 600km north-trending belt of granitoids (Hand & others, 2007) that correlate temporally with the Kalkadoon Batholith. In the reconstruction of Giles & others, (2004), the Donington Suite continued into the Mount Isa Inlier. The Donington Suite has an elevated incompatible element signature and Nd (1850Ma) values between –2 and –4, and Hf (1850Ma) values between –4 and 5.3. This suite was derived from the fractionation of mafic crust which has been contaminated by Archaean crust (Hand & others, 2007; Reid & others, 2008). Reid & others, (2008) argued, based on the absence of subduction characteristics of the magma that the Donington Suite could have formed in a continental back-arc region. An alternative interpretation is that the wide range of radiogenic isotope values reflects mixing of Archaean and juvenile magma sources. In either situation, magmatism occurred proximal to a plate margin (Figure 5).

Following emplacement of the Donington Suite, the eastern Gawler Craton underwent an episode of compressional orogenesis during the Cornian Orogeny (ca 1850–1845 Ma) (Reid & others, 2008).

Page 8 Section II: Eastern Australian Proterozoic Correlations This event was characterised by northwards transport and development of non-coaxial folds. The Cornian Orogeny is defined by a clockwise P-T path with peak metamorphic granulite facies conditions of 730°C and 6kbars (Reid & others, 2008) succeeded by decompression, associated with south-block-down extension. The Cornian Orogeny (ca 1850–1845 Ma) is correlated with the collision between Mount Isa and the Numil terrane because both events postdate emplacement of the Kalkadoon Batholith and Donington Suite batholiths.

The N-NNW trending Kalinjala Shear Zone extends for several hundreds of kilometres from the southern Gawler Craton. It defines the suture between the Archaean nucleus of the Gawler Craton (Sleaford Complex) and the continental ribbon (comprising the Donington Suite and Corny Point Paragneiss (ca 1960–1920 Ma: Zang & Fanning, 2003). This Kalinjala Shear Zone is stitched by Wallaroo Group metasedimentary rocks (ca 1790–1740 Ma) and in turn reworked during the Kimban Orogeny (ca 1740–1690 Ma: Vassallo & Wilson, 2002). The Kalinjala Shear Zone possibly correlates with the boundary between the Mount Isa Inlier and the Tennant Creek/Davenport Province or the suture defined by the Willowra Gravity Ridge (Willowra Lineament). This boundary reflects the collision between the Aileron Province of the northern Arunta Inlier (Central Australian Craton) and the Tanami Province (North Australian Craton).

Correlation with the Arunta Inlier-Tanami Province

Collision between the Aileron Province (Arunta Inlier) and the Tanami Province is thought to have occurred pre- ca 1840 Ma because the turbiditic succession of the Landers Package (Killi Killi Formation) occurs in both the Aileron and the Tanami provinces (Goleby & others 2009). Seismic reflection data indicate that this collision is characterised by a "crocodile" structure that formed in response to a combination of obduction and subduction of oceanic lithosphere (Goleby & others, 2009). This suture defines a rapid change in crustal thickening from ~35–42 km in the Tanami Province to ~60 km beneath the central Australian Craton (Aileron Province), which coincides with the Willowra Gravity Ridge (Willowra Lineament) (Goleby & others, 2009).

Kimberley Craton–Pine Creek Inlier

During ca 1870–1860 Ma, turbidites of the Tikalara Metamorphics were deposited within an ocean island arc setting, outboard of the western margin of the North Australian Craton (Sheppard & others, 2001). Deposition of these turbidites was approximately contemporaneous with the emplacement of the Paperbark Granite Suite at ca 1865 Ma, and regional high temperature, low pressure metamorphism associated with the Hooper Orogeny (Tyler & others, 1999). The Dougall Suite (ca 1850 Ma) comprises tonalites and trondjemites which were emplaced in an Island arc (Tickalara arc) setting with the subduction zone dipping SE beneath the Island arc (Sheppard & others, 1999). Arc terranes were accreted to the North Australian Craton during the Halls Creek Orogeny (ca 1850 Ma).

Page 9 Proterozoic Mount Isa Synthesis

Turbidites of the Hooper Complex (ca 1875–1865 Ma), Dougall Suite, Paperbark Granites, and the Tickalara Metamorphics collided with the North Australian Craton (Sheppard & others, 1999).

The Halls Creek Orogeny is characterised by poly-deformation which during this time involved early recumbent folding, later overprinted by upright folds (Bodorkos & others, 1999). Peak high temperature metamorphic conditions of 700–800˚C were attained during this time (Bodorkos & others, 1999). The expression of the Halls Creek Orogen in the adjacent Pine Creek Inlier is the Top End Orogeny (ca 1861–1847 Ma), which is characterised by greenschist to granulite facies metamorphism synchronous with tight to close upright folding (Carson & others, 2008).

Interior of the North Australian Craton

The Pine Creek Inlier, Tennant Creek-Davenport Province, and Tanami Province all encompass deposition of a dominantly siliciclastic sedimentary succession during ca 1870–1850 Ma. This deposition was accompanied by extensive emplacement of granitoids and predominantly mafic rocks. Bagas & others (2010a) proposed a continental back-arc setting for deposition of the ca 1865 Ma Stubbins Formation in the Tanami Province. Furthermore, it is likely that most of the interior of the North Australian Craton occupied a continental back-arc region leading up to amalgamation of the Kimberley Craton, Mount Isa basement terranes, and Central Australian Craton.

Tectonic Interpretation

During ca 1870–1840 Ma the largest continental collision event in the geological evolution of the Australian continent occurred. Collisional tectonics involved the amalgamation of Archaean cratons, continental ribbons, and possible arc terranes. The collision is recorded over a large area of the continent. This ca 1870–1840 Ma collisional event records the formation of the Supercontinent Columbia in which Australia and Laurentia were contiguous during ca 1850–1660 Ma.

Page 10 Section II: Eastern Australian Proterozoic Correlations COLLISION OF THE WEST AND NORTH AUSTRALIAN CRATONS (CA 1820–1790 MA)

Figure 5: Geodynamic evolution of ca 1820–1790 Ma Eastern Proterozoic Australia.

Basin Development

Following accretion, basins continued to develop throughout the North Australian Craton. The Strzelecki Volcanics and bimodal granulites of the Ongeva Package in the eastern Arunta Inlier were deposited over (ca 1810–1800 Ma) (Bagas & others, 2010). Deposition in the Tanami Province was characterised by emplacement of the felsic volcanic rocks and siliciclastic successions of the Ware Formation (Bagas & others, 2010). In the Tennant Creek/Davenport Province, sandstone dominated successions of the Lower Tomkinson Creek Group and Hatches Creek Group (ca 1820–1800 Ma) were deposited. This period of basin development was accompanied by extensive bimodal volcanism,

Page 11 Proterozoic Mount Isa Synthesis associated with the eruption of the Epenarra Volcanics, Treasure Volcanics, and Arabulja Volcanics. Basin development was also coincident with dolerite sill emplacement (Claoue-Long & others, 2008b).

Collision between the West Australian Craton and the Central Australian Craton

During ca 1810–1795 Ma, a major continent to continent collision event occurred and evidence for it is preserved in the Rudall Complex at the northern margin of the West Australian Craton. This event is characterised by intense poly-deformation, isoclinal folding and E to NE thrust stacking during the Yupungku Orogeny (Smithies & Bagas, 1997; Bagas. 2004). The Rudall Complex records a decompressive clockwise P-T evolution path with peak metamorphic conditions reaching medium pressure granulite facies (12kbars; 800°C) (Clarke & others, 1986). Granites in the Rudall Complex were emplaced between ca 1810 Ma and 1765 Ma (Bagas, 2004).

During this interval the Mount Isa Inlier was relatively quiescent with emplacement of the Yeldham and Little Toby granites.

Tectonic Interpretation

This episode defines the final amalgamation of major crustal fragments of Paleoproterozoic Australia (Figure 5).

Page 12 Section II: Eastern Australian Proterozoic Correlations LEICHHARDT SUPERBASIN DEVELOPMENT (CA 1790–1760 MA)

Figure 6: Geodynamic evolution of ca 1790–1760 Ma Eastern Proterozoic Australia.

Mount Isa Inlier

The tectonic evolution of the Mount Isa Inlier during ca 1790–1750 Ma is characterised by development of the Leichhardt Superbasin. In the Leichhardt River Domain, basin development was characterised by deposition of the Mount Guide Quartzite (marine) and Leander Quartzite followed by eruption of voluminous continental tholeiitic basalt in a major rift axis (Wilson & others, 1984; O'Dea & others, 1997b). Basaltic magmatism extended beyond the rift axis and is preserved in the Century and Mount Oxide Domains. Deposition of these successions occurred during E-W crustal extension (O'Dea & others, 1997b). The Leichhardt River Domain is interpreted as a remnant continental rift axis. Basaltic magmatism was followed by deposition of the mainly siliciclastic Myally Subgroup during N-S extension (O’Dea & others, 1997b). In the Mary Kathleen, Mitakoodi and Page 13 Proterozoic Mount Isa Synthesis

Canobie Domains, the sedimentary and volcanic successions deposited into the Leichhardt Superbasin include the Magna Lynn Metabasalt, Argylla Formation, Bulonga Volcanics (ca 1780–1760 Ma) and the overlying basaltic successions of the Marraba Volcanics. Normal fault activity in the Mitakoodi Domain and Mary Kathleen Domain controlled the architecture of the Ballara Quartzite (Williams, 1989) and Mitakoodi Quartzite (Potma & Betts, 2006). This activity correlates with the extension during the deposition of the Myally Subgroup in the Leichhardt Domain. Rift related sedimentation and volcanism was followed by sag-phase sedimentation in which the mostly carbonate upper Quilalar Formation (Western Mount Isa Inlier) and Corella Formation (Eastern Mount Isa Inlier) were deposited up until about 1740Ma when the Wonga and Burstall granites were emplaced.

Leichhardt Superbasin correlations

Sedimentary successions in the Leichhardt Superbasin can be correlated with sedimentary successions in the McArthur Basin and on the Gawler Craton. In the McArthur Basin are the lower Redbank Package, and the basaltic Seigel Volcanics (ca 1790 Ma). Basaltic magmatism was followed by deposition of the Sly Creek Sandstone and lower Redbank Package, including the Rosie Creek Sandstone and the stromatolitic and oolitic dolomites, sandstone, shale, and siltstone of the McDermott Formation. In the Gawler Craton, the Myola Volcanics, the Broadview Schist and the Price Metasediments (ca 1790 Ma) were deposited. In the Peake and Denison Inlier, northern Gawler Craton, basin development was accompanied by emplacement of the Wirriecurrie Granite (ca 1790 Ma), followed by extrusion of the bimodal Tidnamurkana Volcanics (ca 1775 Ma), and deposition of clastics in the Peake Metamorphics (Betts & Giles, 2006). These packages may have formed part of a more extensive basin system over a large area of the Gawler Craton and may have included part of the Hutchison Group, along with a sedimentary succession deposited throughout the Nawa terrane in the northwest of the craton (Payne & others, 2006). Sedimentation in the Pine Creek Inlier is recorded in sandstone, siltstone, and dolomite of the Tolmer Group.

Orogenesis in Central Australia

The Arunta Inlier records an episode of orogenesis at ca 1790 Ma termed the Yambah Event (Betts & Giles, 2006; Cawood & Korsch, 2008). This event is characterised by poly-deformation involving W- SW vergent thrusting followed by late orogenic shortening which resulted in N-S and SE oriented folding (Collins & Williams, 1995). Peak high temperature, low pressure granulite facies metamorphic conditions were reached during this event (Norman & Clarke, 1990). The Yambah Event temporally overlaps with the Yapungku Orogen in the Rudall Complex, and possibly represents an along strike continuation of the same orogenic system (Betts & others, 2008, in press). The distal effects of the Yambah Event were recorded by hydrothermal activity possibly associated with greenschist facies metamorphism (Pietsch & Edgoose, 1988), movement along Au-bearing shear zones (Rasmussen &

Page 14 Section II: Eastern Australian Proterozoic Correlations others, 2006) in the Pine Creek Inlier, and crustal shortening in the Tennant Creek Block (Claoue-Long & others, 2008b).

Tectonic Interpretation

Accretion or collision along the southern margin of the Australian continent ca 1780–1770 Ma is recorded in the Arunta Inlier (Yambah Event) and the distal effects are recorded in the plate interior. Large areas of the eastern parts of the continent experienced crustal extension and extensive bimodal volcanism during ca 1780–1760 Ma (Figure 6). The extent and volume of continental tholeiitic basaltic magmatism suggests that parts of the North Australian Craton approached continental break-up (e.g., along the Leichhardt Rift) which is now preserved in the Leichhardt River Domain (O'Dea & others, 1997b). The temporal overlap with accretion along the southern margin of the Australian continent suggests that roll-back was not the driver for extension in the overriding plate. Alternatively, the Yambah Event was localised along the Arunta Inlier (e.g., accretion of an oceanic ridge or plateau). Roll-back of a north-dipping subduction zone continued to the south, and drove extension in the overriding plate.

Page 15 Proterozoic Mount Isa Synthesis WONGA EXTENSION EVENT (CA 1750–1740 MA)

Figure 7: Geodynamic evolution of ca 1760–1740 Ma Eastern Proterozoic Australia.

Mount Isa Inlier

About 1750–1740 Ma, the Mount Isa Inlier underwent a N-S crustal extension event, termed the Wonga Event (Holcombe & others, 1991). The Wonga Event is best recorded in the Mary Kathleen Domain where a mid-crustal extensional detachment developed and the extensive Wonga and Burstall suite granites were emplaced at mid-crustal levels (Holcombe & others, 1991) at about 1740 Ma. This terminated deposition of the Corella Formation. High temperature, amphibolite facies conditions were attained during the Wonga Event (Holcombe & others, 1991). Extensional gneissic domes (metamorphic core complexes) also developed in the Kuridala-Selwyn Domain (e.g., Double Crossing Metamorphics). The felsic Mount Fort Constantine Volcanics were erupted in the Canobie Domain.

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Basin Development in the continent interior

Basin development at this time is recorded in the Pine Creek Inlier, Tennant Creek-Davenport Province, Gawler Craton and McArthur Basin, and is characterised by syn-extensional basal mainly clastic successions overlain by post-extensional mainly carbonate successions.

Basin development in the Tennant Creek-Davenport Province resulted in deposition of sandstone, dolostone, limestone, and siltstone of the upper Tomkinson Creek Group. On the Gawler Craton deposition occurred of the fine grained, shallow marine, sedimentary succession and rhyolites of the Wallaroo Group and Moonabie Volcanics (Daly & others, 1998) in the east and the Moondrah Gneiss in the Nawa terrane in the north (Payne & others, 2008). These successions formed an extensive cover sequence which appears to blanket the suture between the North Australian Craton and the Archaean nucleus of the Gawler Craton.

Plate margin magmatism

In the Arunta Inlier a series of temporally overlapping mainly felsic plutonic suites were emplaced during the ca 1760–1750 Ma Inkamilla Igneous Event (Scrimgeour, 2003; Betts & Giles, 2006). The magmas emplaced during the Inkamilla Igneous Event include volumetrically low calc-alkaline- trondhjemitic (CAT) plutons, and the Main Group granites (Zhao & McCulloch, 1995). The CAT plutons were emplaced in the southern Arunta Inlier and have strong geochemical affinities with arc magmas (Foden & others, 1999; Zhao & McCulloch, 1995). The Main Group Granites have formed by partial melting of older island arc intrusions from the Yambah Event (Zhao & McCulloch, 1995).

Tectonic Interpretation

Betts & Giles (2006) interpreted the geochemical response of the CAT granites to approximate the position of a north dipping subduction zone. The subduction zone would have been located outboard of the southern Arunta Inlier. The model preferred here differs from that presented in Betts & Giles (2006) as the subduction zone occurred outboard of the Gawler Craton, rather than between the Gawler Craton and North Australian Craton (Figure 7). The basins developed in the interior of the North Australian Craton have been interpreted as a series of interconnected continental back-arc basins which initiated in ca 1790 Ma and continued to evolve until ca 1735 Ma (Giles & others, 2002). Considering this tectonic model, crustal extension in the overriding plate (North Australian Craton) was most probably driven by roll-back of the subducting slab. Magmatism occurred in response to elevated geothermal gradients and crustal melting of the extended lithosphere.

Page 17 Proterozoic Mount Isa Synthesis MID BASIN INVERSION (CA 1740–1725 MA)

Figure 8: Geodynamic evolution of ca 1740–1725 Ma Eastern Proterozoic Australia.

Mount Isa Inlier

Following deposition of the Quilalar Formation, a depositional hiatus occurred between ca 1735– 1725 Ma west of the Kalkadoon-Leichhardt Domain (Jackson & others, 2000)). In the Mount Oxide, Leichhardt River and Century domains, this hiatus is coincident with a transient inversion of the Leichhardt Superbasin which resulted in development of localised folding associated with E-W to ENE- WSW shortening (Derrick, 1982; Betts, 1999). To the east, deposition of the Staveley Formation continued in the Marimo-Staveley and Doherty-Fig Tree domains. Page 18 Section II: Eastern Australian Proterozoic Correlations In the McArthur Basin the Settlement Creek Dolerite was emplaced at ca 1730 Ma. A basin inversion event in the McArthur Basin is characterised by a depositional hiatus within the Redbank Package. Inversion was followed by deposition of the Wununmantyala Sandstone and lithic and dolomitic sandstone of the Wollogorang Formation (Bull & Rogers, 1996).

Kimban Orogeny and Strangways Event

During ca 1735–1715 Ma, large tracts of the southern Australian continent were undergoing orogenesis and subsequent crustal shortening. In the Gawler Craton, this event is termed the Kimban Orogeny (Daly & others, 1998; Hand & others, 2007). The Kimban Orogeny affected the entire Gawler Craton and is considered to be a response to N-NE dipping subduction, outboard of the western Gawler Craton and southern Arunta Inlier. Metamorphic conditions, associated with the Kimban Orogeny, vary from greenschist to granulite facies (Hand & others, 2007; Dutch & others, 2008) with peak granulite facies (10kbar, 750°C) in the Eyre Peninsula. Dutch & others, (2008) showed that the P-T path for the Kimban Orogeny was strongly decompressive with a clockwise trajectory. Deformation associated with the Kimban Orogeny is dominated by sinistral transpressional tectonism along crustal-scale shear zones (e.g., Kalinjala Mylonite, Tallacootra Shear Zone) (Stewart & others, 2009). Extensive regions of Archaean rocks and the Donington Suite (ca 1850 Ma) were reworked by an early phase of sheath folding and later overprinted by upright folding (Vassallo & Wilson, 2001; 2002). The syn-tectonic Middle Camp Granite (ca 1725 Ma) and Moody Suite (ca 1715 Ma) granites were emplaced in the eastern parts of the Gawler Craton.

The Strangways orogenesis Event (ca 1735–1715 Ma) occurred in the Arunta Inlier (Moller & others, 2003; Claoue-Long & others, 2008a). This event was characterised by several deformations and involved kilometre-scale, sheath-like folds formed during east-over-west shearing associated with E-W to NE-SW crustal shortening (Goscombe, 1991; Collins & Shaw, 1995). High grade gneiss formed during this event was deformed by upright folds with a near vertical, N-S trending foliation (Hand & others, 1999). The Strangways Event is characterised by protracted granulite facies metamorphic conditions between ca 1735 Ma (M1) (Moller & others, 2003; Claoue-Long & others, 2008a) and at least ca 1715 Ma. The metamorphic grade associated with the Strangways Event decreases to greenschist facies to the northwest (Scrimgeour & Raith, 2001). High heat producing granites (e.g., Wuluma and Elkedra granites) were emplaced at ca 1725 Ma which was roughly synchronous with metamorphism in this region (Lafrance & others, 1995; Page & Sun, 1996).

The Strangways Event is characterised by greenschist facies metamorphism and the development of regional NW trending folds in the Tennant Creek-Davenport Province (Claoue-Long & others, 2008b).

Tectonic Interpretations

Page 19 Proterozoic Mount Isa Synthesis

The interval ca 1735–1725 Ma records a period of orogenesis along the southern margin of the Australian continent in response to north-dipping subduction outboard of the Gawler Craton and Arunta Inlier. The interior basins of the North Australian Craton underwent basin inversion and/or depositional hiatus most likely as stresses were transmitted into the continental interior (Figure 8). Following orogenesis, subduction roll-back led to renewed extensional basin development and heralded the onset of deposition in the Calvert Superbasin during ca 1725–1690 Ma (Jackson & others, 2000).

Page 20 Section II: Eastern Australian Proterozoic Correlations CALVERT SUPERBASIN I (ca 1725–1690 Ma)

Figure 9: Geodynamic evolution of ca 1725–1690 Ma Eastern Proterozoic Australia.

Following the mid-basin inversion, renewed basin development occurred across central and eastern Australia during ca 1725–1690 Ma. In the Mount Isa Inlier, this basin is termed the Calvert Superbasin (Jackson & others, 2000) where onset of sedimentation is marked by eruption of the Peters Creek Volcanics in the Camooweal-Murphy Domain (Page & Sweet, 1998). This was followed by fluvial sedimentation of the Bigie Formation (Big Supersequence) and bimodal volcanism (Fiery Creek Volcanics) (Page & others, 2000) between ca 1720–1710 Ma (Jackson & others, 2000; Page & Sweet, 1998). These successions were deposited during approximately NW-SE extension with SE thickening of half graben structures in the Mount Oxide, Century, and Leichhardt River domains (Betts

Page 21 Proterozoic Mount Isa Synthesis

& others, 1999). The Fiery Creek Volcanics are coeval with the ca 1710 Ma Weberra Granite (Betts & others, 1999; Neumann & others, 2009b).

The deposition of feldspathic and lithic sandstone, ferruginous mudstone and pebbly sandstone of the Mount Albert Group occurred in the Kalkadoon, the Mary Kathleen, and the Marimo domains at ca 1710 Ma (Foster & Austin, 2008). Deposition of the sandstone, siltstone and phyllite of the Staveley Formation occurred in the Marimo Domain (Foster & Austin, 2008).

Calvert Superbasin correlations

Basins that can be correlated with the Calvert Superbasin are preserved in the Curnamona Province, Georgetown-Yambo-Coen Inliers, Gawler Craton and McArthur Basin. In the Curnamona Province basin development occurred in the Olary Domain and the Broken Hill Domain where the Willyama Supergroup was deposited (Willis & others, 1983). Basin development through ca 1720–1715 Ma in the Olary Domain is characterised by deposition of dominantly clastic successions of the Curnamona Group, in a shallow marine environment (Conor & Preiss, 2008). The Olary Domain records a depositional hiatus during ca 1715–1690 Ma. Coincident with this hiatus was a period of sedimentation in the Broken Hill Domain during ca 1710–1700 Ma. Clastic successions of the intensely metamorphosed Clevedale Migmatite, Thorndale Composite Gneiss, and Thackaringa Group were deposited in a shallow marine environment (Conor & Preiss, 2008). Hypersaline conditions were prevalent during deposition of the Clevedale Migmatite (Conor & Preiss, 2008). Overlying the Thackeringa Group is the mainly turbiditic Broken Hill Group, which hosts the giant Broken Hill Pb-Zn- Ag deposit. An extensional tectonic setting has been proposed for the deposition of the lower packages of the Willyama Supergroup (Conor & Preiss, 2008).

Extensional basin development was accompanied by significant felsic magmatism during ca 1720– 1690 Ma. In the Olary Domain A-type Basso Suite volcanic units and subvolcanic granite sills were emplaced into the Curnamona Group ca 1720–1710 Ma (Conor & Preiss, 2008). Contemporaneous with the Basso Suite was emplacement of the I-type Poodla Hill Granite at ca 1720 Ma (Conor & Preiss, 2008). Mafic magmatism during this interval is preserved as the Montstephen Metabasalt member, although in general there is a paucity of mafic magmatism (Conor & Preiss, 2008). In the Broken Hill Domain, syn-extensional magmatism is preserved as orthogneiss within the stratigraphic pile. These orthogneiss are both volcanic and intrusive in origin (Page & others, 2005; Vassallo & Wilson, 2002), and include the S-type Alma Gneiss (ca 1705 Ma).

Temporal equivalents of the Calvert Superbasin stratigraphy exist in the McArthur Basins (upper Tawallah Group). This group consists of the upper parts of the Wollogorang Formation, Warramana Sandstone, trachyte and latite flows, tuff, tuffaceous and lithic sandstone, siltstone of the Gold Creek Volcanics, as well as the felsic volcanic Hobblechain Rhyolite and the Pungalina Member on the Page 22 Section II: Eastern Australian Proterozoic Correlations northern margin of the Murphy Tectonic Ridge. These rocks were probably deposited in a similar extensional setting to their equivalents in the Mount Isa Inlier (Jackson & others, 2000). The lower part Pungalina Member contains pebble to boulder conglomerate, deposited in a fluvial to alluvial environment. In contrast, lithic arenite, ferrugenous sandstone and mudstone of the Warramana Member, to the northwest, were deposited in a shallow marine environment. Synchronous with sedimentation was emplacement of the Settlement Creek Volcanics, which are now considered to reflect shallow level granite emplacement over an extensive area of the McArthur Basin ca 1730– 1720 Ma.

In the Pine Creek Inlier, the NE trending Arnhem Dyke array was emplaced at ca 1725 Ma (Golberg, 2010). Orientation of this feature is consistent with the NW-SE extension, in the Mount Isa Inlier at this time.

About 1720–1690 Ma the Einasleigh Metamorphics, Bernecker Creek, and Daniel Creek Formations were deposited in the Georgetown Inlier (Black & others, 2005; Withnall & others, 1997). The rock packages are dominated by fine grained clastic and calcsilicate successions that have been variably metamorphosed. This indicates that these sediments were deposited in a significantly different depositional environment when compared with the Big Supersequence. It is most likely that these sediments were deposited in a deep marine environment. This suggests that the Georgetown Inlier occupied a position of deeper basin subsidence during the period related the formation of the Calvert Superbasin. Granites were emplaced between ca 1705–1695 Ma (Withnall & others, 1997).

In the Gawler Craton, deposition of sandstone, interbedded siltstone and rhyolite-rhyodacite of the Labyrinth Formation and quartzite, conglomerate, sandstone, siltstone and minor basalt occurred during ca 1725–1715 Ma (Daly & others, 1998). These packages temporally overlap with the waning stages of the Kimban Orogeny and possibly represent foreland or intra-orogenic basins.

Kimban Orogeny/Strangways Event (continued)

About 1720–1690 Ma the Kimban Orogeny was characterised by upright folding, and the emplacement of syn-tectonic magmas of the Middle Camp Granite (ca 1725 Ma) and Moody Suite (ca 1715 Ma) (Hand & others, 2007; Daly & others, 1998). The Engenina Adamellite was emplaced in the northern Gawler Craton at ca 1690 Ma (Betts & others, 2003). The Strangways Event was characterised by continued granulite facies metamorphism, which prevailed until the termination of the event at ca 1690 Ma, when syn-extensional mafic dykes were emplaced (Claoue-Long & others, 2008a). At ca 1710 Ma the I-type Devils Suite Granites and lamprophyre were emplaced into the Tennant Creek-Davenport Province (Claoue-Long & others, 2008b).

Tectonic Interpretation

Page 23 Proterozoic Mount Isa Synthesis

Tectonic activity between ca 1720–1690 Ma was dominated by extensional basin development throughout large areas of the Australian Continent (Figure 9). This period of basin development overlaps with the waning stages of the Kimban Orogeny and the Strangways Event. Either compressional stresses were not transmitted into the interior of the continent or other far-field stresses influenced extensional tectonics (e.g., rifting between Australia and Laurentia), or the arrival of a ca 1725 Ma mantle plume in Arnhem land (Goldberg, 2010). These interpretations remain highly speculative.

Page 24 Section II: Eastern Australian Proterozoic Correlations CALVERT SUPERBASIN II (ca 1690–1670 Ma)

Figure 10: Geodynamic evolution of ca 1690–1670 Ma Eastern Proterozoic Australia

Renewed deposition during development of the Calvert Superbasin is characterised by fluvial to shallow marine sedimentation of the Surprise Creek Formation and Torpedo Creek Quartzite between ca 1690–1670 Ma. A NNE-SSW extension was inferred from shear zones developed in the mid-crust in the Sybella Domain (Gibson & others, 2008) and the activity on NW trending normal faults in the northern Kalkadoon-Leichhardt Domain (Myally sub-basin). The emplacement of the Sybella Granite (ca 1675–1670 Ma) was considered to have been synchronous with the development of the metamorphic core complex in the Sybella Domain (Gibson & others, 2006). The extrusion of the Carters Bore Rhyolite (Sybella Domain) occurred at ca 1680–1675 Ma (Page & others, 2000), and is coeval with emplacement of the Sybella Granite in a developing metamorphic core complex (Gibson

Page 25 Proterozoic Mount Isa Synthesis

& others, 2008). This is correlated with a depositional hiatus in the western fold belt. Also, in the regions to the east of the Kalkadoon-Leichhardt Domain there was a depositional hiatus.

Correlations

In the Curnamona Province, mainly pelitic successions of the Broken Hill Group were deposited in the Broken Hill Domain (Conor & Preiss, 2008). The Broken Hill Group is essentially absent in the Olary Domain, supporting the interpretation that the group was deposited in east-thickening half graben (Conor & Preiss, 2008). The Broken Hill Group was deposited in a shallow marine shelf environment (Stevens & others, 1988). After deposition of the Broken Hill Group, a depositional hiatus occurred between 1680–1670 Ma (Conor & Preiss, 2008). Thereafter, deposition of pelitic and psammitic units of the Sundown Group (Broken Hill Domain) and Saltbush Group (Olary Domain) occurred at ca 1670 Ma (Page & others, 2005).

Contemporaneous with the Broken Hill Group was bimodal volcanism and felsic and mafic intrusions. These intrusions are typically parallel with lithological boundaries which suggest that they either represent basaltic lavas or dolerite sills within the Broken Hill Group. Mafic bodies are not present in the overlying Sundown Group. Amphibolite sills of the Lady Louise Suite were emplaced at ca 1685 Ma in the Olary Domain (Conor & Preiss, 2008). The Georgetown Inlier recorded a period of bimodal magmatism between ca 1690–1670 Ma (Black & others, 1998; Withnall & others, 1997). In the McArthur Basin, ca 1690–1670 Ma basin development is characterised by a clastic succession in shallow marine and fluvial environments (upper Parsons Range Group and Rorruwuy Sandstone). The Oenpelli Dolerite (ca 1690 Ma) was intruded in the Pine Creek Inlier.

Plate Margin tectonism

In the western and central Gawler Craton, a suite of high potassium, alkali-calcic and magnesian and moderately peraluminous granitoids were emplaced at ca 1670 Ma (Tunkillia Suite) in a continental back-arc setting (Payne & others, 2009). This suggests the Gawler Craton was positioned proximal to a plate margin at this time. Similarly, the Albany Fraser Belt records a period of quartzite, sandstone, dolostone, conglomerate, phyllite, pelitic and psammitic schist of the Mount Barren Group. Betts & Giles (2006) suggested that these rocks record sedimentation in a continental back-arc basin. Felsic and mafic granulites, felsic gneiss, gabbro and metagabbro, amphibolite, microgranite, and pegmatite Dalyup Gneiss was emplaced along the eastern margin of the Yilgarn Craton margin at ca 1690 Ma (Nelson & others, 1995).

Basin development in the southern Arunta Inlier is recorded in the Madderns Package, which comprises quartzo-feldspathic gneiss, amphibolite, and felsic orthogneiss and manganiferous and calc-silicate meta-sedimentary successions. This package is preserved in the Warumpi Terrane, which may have been outboard of the Australian continent at ca 1690 Ma (Scrimgeour & others, 2005). Page 26 Section II: Eastern Australian Proterozoic Correlations Tectonic Interpretation

Large regions of the continent were experiencing extensional tectonism which resulted in deposition of dominantly fluvial sedimentary successions in the central and northern parts, whilst deeper water sedimentation occurred in the Curnamona Province and Georgetown Inlier (Figure 10). Eastern and northeastern parts of the continent underwent extensive bimodal magmatism which was coincident with a depositional hiatus. Thermal buoyancy associated with voluminous magmatism may have been responsible for regional uplift and/or erosion of a basinal succession in eastern parts of the continent.

Extensional tectonism may have been driven by roll-back of a north-dipping subduction zone. Felsic magmatism occurred in proximal back-arc regions in the Gawler Craton, and bimodal magmatism and back arc basin (?) development occurred along the eastern margin of the Yilgarn Craton. The increased subsidence along the eastern parts of the continent may reflect the later stages of continental rifting which culminated in the break-up between Australia and Laurentia (Betts & others, 2003).

Page 27 Proterozoic Mount Isa Synthesis ISA SUPERBASIN (ca 1670–1645 Ma)

Figure 11: Geodynamic evolution of ca 1670–1645 Ma Eastern Proterozoic Australia.

Mount Isa Inlier

Between ca 1660–1595 Ma an extensive basin system developed throughout the Mount Isa Inlier. This basin system marks the transition from extensional basin systems to sag-phase sedimentation interrupted by intermittent basin reactivation (Scott & others, 1998). The basin system is termed the Isa Superbasin. Onset of the Isa Superbasin is recorded by deposition of the lower Mount Isa Group between ca 1660–1650 Ma in the Leichhardt River Domain. The lower Mount Isa Group comprises the Warrina Park Quartzite, Moondarra Siltstone, Breakaway Shale, Native Bee Siltstone, Urquhart Shale, Spear Siltstone, Kennedy Siltstone, and Magazine Shale. Equivalent successions of the lower McNamara Group (Gunpowder Creek Formation, Paradise Creek Formation, and Esperanza Formation) were deposited in the Century, Mount Oxide, and Ardmore domains. In the far east of the Page 28 Section II: Eastern Australian Proterozoic Correlations inlier, sedimentation is recorded by deposition of the upper Soldier Cap Group (Mt Norna Quartzite and Toole Creek Volcanics) in the Soldiers Cap Domain, and the Answer Slates in the Marimo and Kuridala-Selwyn domain.

Lower Isa Superbasin correlations

Widespread post-extensional basin development occurred over large tracts of the Australian continent between ca 1660–1650 Ma. In the McArthur Basin the base of the Isa Superbasin is defined by marine and fluvial sandstone of the Masterton Sandstone (Southgate & others, 2000) and deposition of fluvial deposits of the upper Fish Creek Formation proximal to the Murphy Tectonic Ridge. Shallow marine dolostone, mudstone, sandstone in the lower Umbolooga Subgroup and siltstone and mudstone of the Slippery Creek Siltstone member (Habgood Group) were also deposited during this interval. In the Tennant Creek-Davenport Province quartz arenite, dolostone, mudstone and minor conglomerate of the Namerinni Group were deposited between ca 1660–1650 Ma.

Shallow marine pelitic successions of the Strathearn Group (Olary Domain) and the Paragon Group (Broken Hill Domain) define the onset of post-rift sedimentation in the Curnamona Province (Conor & Preiss, 2008). In the Georgetown Inlier, the Dead Horse Metabasalt (ca 1660 Ma), was emplaced (Withnall & others, 1997; Baker & others, 2010). This was followed by deposition of mudstone successions of the Corbett Formation and mudstone and siltstone successions of the Lane Creek Formation (Withnall & others, 1997). The Cobbold Metadolerite formed extensive sills throughout the Etheridge Group up to the top of the Lane Creek Formation and is dated at ~1655 Ma (Black & others, 1998).

The Yaya Package (ca 1660–1650 Ma) (southern Arunta Inlier) comprises a pelite, psammite, and calc-silicate succession and was deposited in the Warumpi Province, which at this time is interpreted to have lain to the south of the North Australian Craton. In the central Gawler Craton, shale-dominated successions intercalated with rhyodacite-basalt, quartzite, and conglomerate of the Tarcoola Formation were deposited in a fluvial to marginal marine setting at ca 1650 Ma (Daly & others, 1998).

Orogenic events at this time are very few, with the exception of a ca 1660 Ma high temperature, low pressure (900°C, 10kbars) event recognised in drill core in the western Gawler Craton (Hand & others, 2007). This event is termed the Ooldean Event but its significance and extent is relatively unknown.

Page 29 Proterozoic Mount Isa Synthesis

Tectonic Interpretation

Onset of the Isa Superbasin and correlated sedimentary packages define a change from rift-related sedimentation of the Calvert Superbasin to sag-phase sedimentation. This transition is interpreted to mark the opening of a small ocean basin along the eastern margin of the Australian continent, which developed as Australia and Laurentia drifted apart at ca 1660 Ma (Betts & others, 2003). Australia was considered to have occupied the lower plate and underwent continent wide thermal subsidence in response to continental break-up, whereas Laurentia occupied the upper plate and underwent regional uplift, deposition hiatus and erosion (Rainbird & others, 2003; Thorkelson & others, 2001). The developed ocean must have been relatively small as palaeomagnetic data suggest that Australia and Laurentia occupied similar positions at ca 1740 Ma (Betts & others, 2008) and ca 1590 Ma (Payne & others, 2009).

Along the southern margin of the Australian continent subduction continued (Figure 11). The polarity of the subduction zone has been debated. Scrimgeour & others (2005) proposed a south-dipping subduction zone/slab, which is supported by magnetotelluric data in the Arunta Inlier (Selway & others, 2009). In contrast, Betts & Giles (2006) suggested that a long lived north-dipping subduction zone may explain the link between tectonism at the plate margin and the evolution of basins in the continent’s interior. For the interval ca 1660–1650 Ma, little evidence exists to support plate margin influence on basin evolution. This has been attributed to a transient period of south-dipping subduction in which little stress was transmitted from the southern margin, which lead to accretion of the Warumpi Terrane at ca 1640 Ma (Scrimgeour & others, 2005). The major tectonic driver for this period of basin development was most probably the break-up of Australia from Laurentia at ca 1660 Ma.

Page 30 Section II: Eastern Australian Proterozoic Correlations RIVERSLEIGH EVENT (CA 1645–1630 MA)

Figure 12: Geodynamic evolution of ca 1645–1630 Ma Eastern Proterozoic Australia.

The ca 1650–1630 Ma tectonic evolution of the Mount Isa Inlier is characterised by deposition of the upper McNamara Group in the Century Domain and Murphy-Camooweal Domain (Loretta, River, Term supersequences) (Page & others, 2000; Southgate & others, 2000; Scott & others, 1998) (Upper Isa Superbasin). Following the Riversleigh Formation (Riversleigh Supersequence) basin inversion along E-W to E-NE faults in the northern Murphy-Camooweal Domain is evident in the seismic reflection data (McConachie & others, 1993; Southgate & others, 2000). In the Soldiers Cap Domain, high temperature metamorphic foliations developed in the middle crust (Rubenach & others, 2008; Rubenach in pmd*CRC I7 Project Team, 2008, appendix 1). This event was considered to be an early phase of the Isan Orogeny by the pmd*CRC I7 Project Team (2008, p28).

Upper Isa Superbasin correlations

Page 31 Proterozoic Mount Isa Synthesis

In the McArthur Basin cyclic dolostone, mudstone, and sandstone of the Umbolooga Subgroup, and stromatolitic dolostone, dolomitic siltstone, sandstone, and pyritic-carbonaceous shale of the Batten Subgroup were deposited. These sedimentary packages correlate with the Yarawoi Formation, Conway Siltstone, and Vaughton Formation in the western McArthur Basin. In the Broken Hill Domain, Ehlers & Nutman (1997) dated migmatitic melts at ca 1640 Ma which suggests a high temperature metamorphic foliation. Page & others, (2005) refuted this interpretation and argued this date represents a mixing age, rather than a metamorphic age. A ca 1630 Ma high temperature prograde metamorphic event was inferred from detrital zircons in modern drainage patterns (Belasouva & others, 2006) and may be related to slightly younger ca 1620–1610 Ma monazite growth associated with pre-Olarian Orogeny extension (Forbes & others, 2007).

Accretion in Central Australia

A significant accretionary event occurred in the southern Arunta Inlier and was associated with the docking of the Warumpi Terrane onto the southern margin of continent at ca 1640 Ma during the Leibig Event (Scrimgeour & others, 2005). The Leibig Event is characterised by peak metamorphic conditions of >800◦C and 9–10 kbars and a near-isothermal decompression P-T path. The Leibig Event deformed and metamorphosed the sedimentary succession of the Yaya Package, which was deposited approximately 20 million years earlier. Synchronous with the Leibig Event was the emplacement of orthopyroxene and olivine norite, gabbro-norite, diorite, porphyritic biotite granite, anorthosite and calc-silicate rock of the Andrew Young Igneous Complex (ca 1640 Ma), and emplacement of the granitoids of the Mount Webb Granite (ca 1640 Ma).

Tectonic Interpretation

Accretion of the Warumpi Terrane onto the southern margin of the Australian continent (Figure 12) is a basin inversion event in the interior basins of the North Australian Craton and is coincident with a major inflection in the Australian Polar Wander Path (Idnurm, 2000). It is also coincident with Pb-Zn mineralisation in the McArthur Basin.

ISA SUPERBASIN (CA 1630–1595 MA) The uppermost successions of the McNamara Group (Lawn, Wide, and Doom super sequences: Isa Superbasin) were deposited in the Century and Camooweal-Murphy domains between ca 1620– 1595 Ma (Page & others, 2000; Southgate & others, 2000; Scott & others, 1998). In the Tommy Creek Domain fine grained, clastic sediments of the Milo beds were deposited In the Arunta Inlier equivalent successions of the Iwupataka Package (ca 1615 Ma), which comprises amphibolite-facies quartz-muscovite schist, calc-silicates and amphibolites deposited in transtensional basins (Scrimgeour & others, 2003).

Page 32 Section II: Eastern Australian Proterozoic Correlations EARLY ISAN OROGENY (CA 1620–1570 MA)

Figure 13: Geodynamic evolution of ca 1620–1570 Ma Eastern Proterozoic Australia.

Interpretations that the Isan Orogeny (ca 1620–1500 Ma) represents a single protracted episode of crustal shortening are probably misleading. The Isan Orogeny is likely to represent multiple superimposed orogenic events during ca 1620–1500 Ma. The first stages of the Isan Orogeny are characterised by approximately N-S to NW-SE crustal shortening. This deformation is associated with peak metamorphic conditions at ca 1600–1570 Ma. This episode of crustal shortening is recognised over a wide area of the eastern and central parts of the Australian continent (Betts & others, 2009).

Page 33 Proterozoic Mount Isa Synthesis CORRELATED OROGENIC EVENTS Large tracts of central and eastern Australia underwent a period of orogenesis (Figure 13) which can be temporally correlated with the Isan Orogeny (ca 1600–1570 Ma). Terranes which preserve this history include the Arunta Inlier (Chewings Orogeny), Curnamona Province (Olarian Orogeny), Gawler Craton (Kararan Orogeny), Mount Isa Inlier (Isan Orogeny), and Georgetown Inlier (Jana Orogeny) (Cihan & others, 2006; Collins & others, 1995; Hand & others, 2007; Daly & others, 1998; Forbes & others, 2004, 2007; Gibson & others, 2008; Hand & others, 2007; Rubatto & others, 2001

Chewings Orogeny

The Chewings Orogeny (Collins & Shaw, 1995) was preserved in the eastern Arunta Inlier and is characterised by early thin skinned deformation and nappe formation during north-directed thrusting (Teyssier & others, 1988). Nappes were overprinted by upright, shallowly plunging folds with approximately E-W trending axial traces (Collins & Shaw, 1995), which were then intruded by the 1603±17 Ma Ormiston Granite (Collins & Shaw, 1995). The timing of peak granulite facies metamorphism was constrained by U-Pb geochronology of zircon and monazite populations which yield ages of ca 1587–1557 Ma (Rubatto & others, 2001; Vry & others, 1996).

Olarian Orogeny

The Olarian Orogeny is well preserved along the southern margin of the Curnamona Province and is tightly constrained at ca 1600–1590 Ma (Page & others, 2005). Post-orogenic granites of the Mundi Suite were emplaced into this poly-deformed terrane at ca 1590 Ma (Page & others, 2005). The oldest foliation in the province was dated, using U-Pb SHRIMP analysis on metamorphic monazites within inclusion trails in garnets. These monazites yield dates between ca 1620–1610 Ma and have been interpreted by Forbes & others (2007) to indicate a period of pre-orogenic crustal extension.

Initial crustal shortening and peak granulite to amphibolite facies metamorphism occurred during lateral translations of the Willyama Supergroup associated with the development of shallowly inclined to recumbent, non-cylindrical, folds and nappes (Clarke & others, 1986; Forbes & Betts, 2004; Forbes & others, 2004; Gibson & Nutman, 2004; Laing & others, 1978; Marjoribanks & others, 1980). The regional transport direction was approximately south-over-north and occurred along high- temperature shear zones (Forbes & Betts, 2004; Ganne & others, 2005). Subsequent folding was characterised by thick skinned deformation and the development of upright to steeply inclined N to NE trending folds (Wilson & Powell, 2001). The timing of upright folding was constrained by emplacement of the Mundi Mundi Suite Granites (ca 1596–1591Ma) in the Broken Hill Block (Page & others, 2005), and the Bimbowrie Suite S-type granites in the Olary Domain. Recent metamorphic monazite geochronology suggests that deformation may have lasted until about 1550 Ma (Rutherford & others, 2007).

Page 34 Section II: Eastern Australian Proterozoic Correlations Painter Orogeny

The Mount Painter Inlier, preserved in the northern Curnamona Province underwent a period of crustal shortening between ca 1592–1575 Ma (Oglivie, 2006; Armit & others unpubl. data). Deformation is constrained by the detrital zircon populations of ca 1592 Ma in the Freeling Heights Quartzite and emplacement of the late to post-orogenic Mt Neill Granite into the upper crust at ca 1575 Ma. Peak metamorphic conditions, associated with the Painter Orogeny, reached mid-amphibolite facies (Armit, 2007). Initial crustal shortening was characterised by development of recumbent folds which formed during N-S shortening.

Wartakan Orogeny

The Wartakan Orogeny is an orogenic event which affected the southern Gawler Craton between ca 1610–1590 Ma (Stewart & Betts, 2010). This event is sparsely preserved due to the limited exposure in the southern Gawler Craton. The Wartakan Orogeny is characterised by movement along major shear zones and tectonic switches from crustal shortening to crustal extension (Stewart & Betts, 2010). The initial stages of the Wartakan Orogeny involved E to NE ductile thrusting of St Peter Suite arc terrane over older Archaean and Paleoproterozoic basement. This resulted in exhumation of arc related granites of the St Peter Suite. A switch in the regional stress fields to NW-SE directed shortening led to folding and tear faulting of the existing structures. This was followed by a switch to an extensional regime in which the principal extension direction rotated from E-W to WNW-ESE during emplacement of the Hiltaba Granites and extrusion of the Gawler Range Volcanics at ca 1590–1580 Ma (Stewart & Betts, 2010). The transition to crustal extension coincided with the interaction of a mantle plume beneath the Gawler Craton continental lithosphere. This event most likely correlates with the Olarian Orogeny in the Curnamona Province.

Kararan Orogeny

Following emplacement of the Gawler Range Volcanics, the northern Gawler Craton underwent an episode of crustal shortening which effected largely buried terranes between ca 1585–1540 Ma (Betts & Giles, 2006; Hand & others, 2007). This event has been termed the Kararan Orogeny. U-Pb SHRIMP analysis of metamorphic zircons from drill hole samples in the Coober Pedy Ridge and the Mabel Creek Ridge (Daly & others, 1998; Fanning & others, 2007; Hand & others, 2007) indicate that peak high temperature metamorphic conditions (1000MPa/800oC) occurred at ca 1585 Ma (Hand & others, 2007). The orogen was characterised by isoclinal nappes and E-W trending thrusts and reverse faults, adjacent to the orogenic front (Coober Pedy Ridge), and overprinted by N-S trending upright to inclined folds (Betts, 2000).

Page 35 Proterozoic Mount Isa Synthesis

Ewamin Orogeny

In northeastern Queensland, an episode of N-S crustal deformation is recorded in the Georgetown, Coen, Yambo and Dargalong inliers between ca 1625–1500 Ma (Black & others, 1979, 1998, 2005; Cihan & others, 2006; Hills, 2004; Withnall, 1996). The oldest fabric is preserved as inclusion trails in metamorphic porphyroblasts and yields EPMA dates on monazite of ca 1625 Ma (Cihan & others, 2006). The earliest phases of N-S crustal shortening and peak amphibolite facies metamorphism of the Etheridge Group have been termed the Ewamin Orogeny (Davis, 1996; Withnall, 1996). Deformation is characterised by the development of meso-scale recumbent to shallowly inclined isoclinal folds with approximately E-W trending axial traces. Rb-Sr total rock isochrons of 1570 ± 20 Ma (Black & others, 1979) were considered to constrain metamorphism associated with the Ewamin Orogeny. This age is indistinguishable from ca 1585 Ma SHRIMP U-Pb ages of metamorphic zircons in the Dargalong and Yambo inliers (Blewett & others, 1998). The Langlovale Group lies unconformably on the Etheridge Group and has been interpreted to post-date the Ewamin Orogeny (Withnall, 1996)

EVIDENCE FOR PLATE BOUNDARIES DURING THE ISAN OROGENY

Several studies have suggested that the Isan Orogeny was driven by distal forces associated with plate boundaries. Plate boundary locations have been largely based on arc-related magmatic suites. These rocks have been identified in the southern Gawler Craton as the St Peter Suite (Swain & others, 2008), in the Musgrave Block (Wade & others, 2006), and in the Georgetown Inlier (Champion, 1991).

St Peter Suite Magmatic arc (Gawler Craton)

The St Peter Suite comprises ca 1620–1610 Ma intermingled granite, tonalite, granodiorite, diorite, and gabbro (Swain & others, 2008) preserved as triangular block bounded by shear zones in the southern Gawler Craton. Swain & others (2008) interpreted the suite to have formed by fractionation of chemically enriched mantle metasomatised by slab-derived fluids or silica-rich melts. Felsic to intermediate magmatic compositions display calc-alkaline affinities with εNd(1620) values that are relatively juvenile, varying between –0.8– +3.7 and depleted mantle model ages (TDM) between 2106–1802 Ma (Swain & others, 2008). These ages are relatively young in the context of Proterozoic Australia. Swain & others (2008) proposed that the St Peter Suite formed outboard of the Gawler Craton on the overriding plate of south-dipping subduction zone and was accreted to the southern Gawler Craton during collision of East Antarctica (Mawson Continent) and the Gawler Craton, although Betts & others (2009) reinterpreted the suite to represent a continental arc emplaced into Archaean crust in the overriding plate of a north-dipping subduction zone.

Page 36 Section II: Eastern Australian Proterozoic Correlations Musgrave Magmatic arc

Intensely deformed granulite to amphibolite facies felsic orthogneisses from the Musgrave Province, which were emplaced between ca 1590–1550 Ma (Camacho & Fanning, 1995; Wade & others,

2006), are characterised by relatively juvenile εNd(1550) values between –1.2– +0.9 and depleted mantle model ages (TDM), which vary between 2120–1920 Ma (Wade & others, 2006). The felsic component of this suite is relatively juvenile, negative εNd(1550) values (–1.2) may have been contaminated by evolved Archaean or Paleoproterozoic crust (Wade & others, 2006). The felsic rocks do not contain zircon populations older than 1590 Ma (Camacho & Fanning, 1995) and this was interpreted by Wade & others, (2006) to reflect slab sediment contamination rather than crustal assimilation during subduction. Wade & others (2006) interpreted these arc-related rocks to be located outboard along the northern margin of the Gawler Craton. In contrast, Betts & others (2009) speculated that the arc was positioned along the western margin of the Gawler Craton and is the along strike equivalent to the St Peter Suite. The arc was subsequently reworked into the Musgrave Province during the ca 1300–1100 Ma Musgravian Orogeny.

Forest Home Suite

The remnants of a potential magmatic arc are preserved as a series of small trondhjemitic I-type plutons of the Forest Home Supersuite, Georgetown Inlier. This suite was emplaced into the Etheridge Group between ca1560–1545 Ma (Black & Withnall, 1993; Champion, 1991), and is characterised by relatively juvenile –0.1 εNd(1550) values and a depleted mantle model age (TDM) of 1880 Ma (Black & McCulloch, 1990). Hf isotope analysis of zircons collected during a terrane-chron study (stream sediments) also shows a juvenile response from ca 1550 Ma zircon populations (Murgulov & others, 2007), interpreted to be sourced from the Forest Home Suite. Hf TDM model ages vary from 1605–3270 Ma, indicating an Archaean crustal component in addition to the significant juvenile mantle component (Murgulov & others, 2007). Champion (1991) argued that the Forest Home Supersuite displayed geochemical affinities with subduction related magmas and this was interpreted by Betts & others (2002) and Betts & Giles (2006) to indicate a west-dipping subduction zone outboard of the Georgetown Inlier at ca 1550 Ma.

Page 37 Proterozoic Mount Isa Synthesis LATE ISAN OROGENY (CA 1570–1500 MA)

Figure 14: Geodynamic evolution of ca 1570–1500 Ma Eastern Proterozoic Australia.

The second stage of the Isan Orogeny (ca 1550–1500 Ma) was characterised by 90o shift to approximately E-W to ESE-WNW crustal shortening and a change to thick skinned deformation, dominated by upright folds and reverse and strike-slip fault activity during retrograde metamorphic conditions. The waning stages of the orogeny were characterised by emplacement of voluminous A- and I-type granites into the eastern parts of the Inlier between ca 1545–1500 Ma (Wyborn, 1998).

Page 38 Section II: Eastern Australian Proterozoic Correlations CORRELATED OROGENIC EVENTS

Unlike, the early Isan Orogeny, this episode of crustal shortening was restricted to the Mount Isa Inlier, the McArthur Basin and the Georgetown Inlier to the east (Blenkinsop, 2008; Betts & others, 2009; Blewett & Black, 1998; Withnall, 1996; Withnall & others, 1988, 1997) (Figure 14).

Jana Orogeny

In the Georgetown Inlier, U-Pb SHRIMP geochronology indicates that there was a major metamorphic event at ~1560 Ma associated with growth of new zircon in the metamorphic rocks and granite genesis (Black & others, 1998, 2005). This event is termed the Jana Orogeny and has been equated with the development of open to locally isoclinal upright folds and dome and basin fold interference pattern s(Withnall, 1996; Withnall & others, 1988, 1997). It was succeeded by an episode of exhumation involving the removal of approximately 12km of upper crustal rocks involving about 4kbars of isothermal decompression in the eastern parts of the inlier (Boger & Hansen, 2004). In the western part of the inlier the Croydon Volcanic Group (ca 1550 Ma) was erupted unconformably onto the upper Etheridge Group and Langlovale Group (Withnall, 1996; Withnall & others, 1997). Cihan & others (2006) dated a flat-lying foliation interpreted to define an orogenic collapse event using EPMA on monazite, which yielded an age of ca 1555 Ma.. This event may equate to retrograde metamorphism described by Bell & Rubenach (1983) and Reinhardt & Rubenach (1989). Subsequent E-W shortening in the Georgetown Inlier (Hills, 2004) probably postdates the Langlovale Group and Croydon Volcanic Group, although it appears not to have effected the latter. This deformation may have occurred between ca 1542–1530 Ma based on EPMA geochronology of monazites (Cihan & others, 2006) and U-Pb SHRIMP geochronology of syn-tectonic pegmatites (Hills, 2004).

Late Orogenic A-type Granites

In the Mount Isa Inlier, the waning stages of the Isan Orogeny were characterised by the emplacement of a suite of TTG-granites, and A- and I-type syn-orogenic granites and granodiorites throughout the eastern parts of the inlier between ca 1545–1500 Ma (Betts & others, 2009 and references therein). Betts & others (2007) proposed that these granites formed part of a larger belt of A- and I-type granites that extended from the Gawler Craton, through the central and northern Curnamona Province, and into the eastern Mount Isa Inlier. In the Gawler Craton, this episode of magmatism is termed the Hiltaba Granite Suite and along with its coeval Gawler Range Volcanics were emplaced with a footprint that exceeds 600km diameter between ca 1595–1575 Ma. Magmatism was principally felsic with a minor and volumetrically small mafic component. Magmatism in the central and northern Curnamona Province was bimodal (Benagerie Volcanics) (Robertson & others, 1998; Williams & others, 2009). The Benagerie Volcanics are not exposed but have been intersected in drill holes. Regional aeromagnetic data suggest that the Benagerie Volcanics occur over an area of 20,000km2, although total volume estimates exceed 23,000km3 (Williams & others, 2009). The Page 39 Proterozoic Mount Isa Synthesis

Benagerie Volcanics comprise A-type porphyritic rhyolite, rhyodacite, trachyte, andesite, and altered basalt (Teale & Flint, 1993). The felsic volcanic component yields a U-Pb SHRIMP extrusion age of 1580 ± 2 Ma (Fanning & others, 1998). Similar A-type and I-type granites of the Mount Painter and Mount Babbage inliers in the northern Curnamona Province were emplaced between ca 1585–1555 Ma (Elburg & others, 2001; Neumann & others, 2009c; Teale, 1993).

In the reconstruction of Giles & others (2004), the spatial and temporal distributions of A-type magmatism suggest that emplacement occurred along a curvilinear belt which became progressively younger to the north. Betts & others (2007) proposed that this belt formed a 1,500km segment of a continental hot spot track which formed in response to about 1.5cm southward migration of eastern Mesoproterozoic Australia over a stationary plume (Betts & others, 2007). The systematic decrease in the width of the hot spot track from about 500km in the Gawler Craton to about 80km in the Mount Isa Inlier reflected the transition from plume head to plume tail interaction with the continental lithosphere. The existence of this inferred hotspot was supported by regional palaeomagnetic data, which show that the A-type magmatic belt occurred on a similar trajectory path as that defined by the apparent polar wander path of the North Australian Craton between ca 1640–1590 Ma.

Additional evidence for plume-related emplacement of the Mesoproterozoic granites of eastern Australia includes:

a) Elevated eruption and emplacement temperatures of magmatism in the Gawler Craton, Curnamona Province, and the eastern Mount Isa Inlier. For example, temperatures exceeded 1000oC based on pyroxene geothermometry and phase equilibria in the upper Gawler Range Volcanics (Creaser & White, 1991); and 800–900oC emplacement of the A-type granites in the Mount Painter Inlier based on Zirconium saturation temperatures (Stewart & Foden, 2001).

b) Sm-Nd data from the Hiltaba Suite and Gawler Range Volcanics suggest derivation from

continental crust, with negative εNd(1592 Ma) values varying depending on the age of the continental crust in which the granites were emplaced (Betts & others, 2009 and references therein). However, mafic components of the province are characterised by a much more

juvenile εNd(1592 Ma) response with mafic rocks of the lower Gawler Range Volcanics yielding

values of –6.92 to +2.5 and εHf(1592 Ma) of –6.7 to +7.4 (Fricke, 2006). Extensively altered mafic to ultramafic alkaline dykes, which intruded into the Roxby Downs Granite, display Sm-

Nd analysis of εNd(1590 Ma) values of +0.1 to +4.0 with the highest values recorded in the least altered dykes (Johnson & McCulloch, 1995).

Page 40 Section II: Eastern Australian Proterozoic Correlations DRIVING OROGENESIS

A number of mechanisms have been proposed as drivers for the widespread 1600–1500 Ma orogenesis and are summarised here.

Plume modified orogeny

Betts & others (2009) proposed a tectonic model that attempted to reconcile the distribution of plate margin magmatism with a hotspot track extending from the Gawler Craton to the eastern Mount Isa Inlier. The model considered that a N to NE dipping subduction zone migrated over an oceanic plume (during roll back), or a mantle plume arrived adjacent to or beneath a north-dipping subduction zone along the southwestern margin of the Gawler Craton. The onset of the plume is marked by the cessation of plate margin magmatism and a 10–15 Ma hiatus in magmatism in the Gawler Craton. Interaction of the plume and the subduction zone resulted in flat subduction, stalling of the subduction zone, and switching off the arc (Betts & others, 2009). This resulted in transfer of compressional stresses into the interior of the continent and drove far-field orogenesis, characterised by N-S shortening, up to 2,000km into the continental interior between 1600–1590 Ma. At ca 1600–1595 Ma, the plume switched from the down-going plate to the overriding plate by thermally eroding the flat slab or migrating through a slab window. The plume head interacted with the continental lithosphere beneath the Gawler Craton resulting in voluminous A-type granite emplacement (Hiltaba Granites) and the extrusion of the Gawler Range Volcanics in an extensional tectonic regime. Renewed crustal N-S crustal shortening (Kararan, Painter, Isan, Ewamin) was related to accretion along the southern margin of the continent, perhaps the accretion of the Coompana Block (Betts & Giles, 2006; Payne & others, 2009). Betts & others (2009) explained the 90o shift in the regional shortening direction in the Georgetown Inlier and Mount Isa Inlier to reflect the distal effects of collision between Australia and Laurentia outboard of the Australian continent (Betts & others, 2002). West-dipping subduction associated with this event is indicated by the emplacement of the Forest Home Suite. Palaeomagnetic data suggest that the positioning of Australia and Laurentia did not shift significantly between ca 1740 Ma (Betts & others, 2008) and ca 1595 Ma (Payne & others, 2009). This indicates that any ocean between Australia and Laurentia must have been small, or alternatively the collision occurred between the combined Australia and Laurentia continents, and a yet to be identified crustal fragment to the northeast (e.g., South China Block; Li & others, 1995). Nevertheless, the suture associated with this collision is located east of the Georgetown Inlier. The plume modified subduction model proposed by Betts & others (2009) assumed a 550 counterclockwise rotation between the South Australian Craton and the North Australian Craton (Giles & others, 2004).

Page 41 Proterozoic Mount Isa Synthesis

Continental collision between the Gawler Craton and the North Australian Craton

Wade & others (2006) proposed a tectonic model in which orogenesis in the North Australian Craton was driven by continental collision between the Gawler Craton and the North Australian Craton between ca 1590–1550 Ma. This model was largely derived by the recognition of ca 1590–1560 Ma arc-related magmas in the Musgrave Block. These magmas were interpreted to have formed at the northern margin of the Gawler Craton, which lay in the overriding plate of a south-dipping subduction zone. A- type and I-type magmatism throughout the Gawler Craton between ca 1600– 1580 Ma most probably occurred in a continental back-arc environment. This model assumes no rotation between the Gawler Craton and the North Australian Craton. Swain & others (2008) built on the model set by Wade & others (2006) and suggested a south-dipping subduction zone to the south of the Gawler Craton. The St Peter Suite formed outboard of the Gawler Craton and accreted to the Gawler Craton when the Gawler Craton and East Antarctica collided during the Wartakan Orogeny.

There are several geodynamic issues related to this model of Wade & others (2006) and Swain & others (2008).

a) The Swain model requires continental collision between the Gawler Craton and East Antarctica, for which there is no evidence. Correlations between the southern Gawler Craton and Terra Adelie suggest that the two continents were connected since at least 1740 Ma.

b) There is no evidence for a suture between the St Peter Suite and the central Gawler Craton.

c) There is no evidence for collision between the Western Gawler Craton and the eastern Yilgarn Craton as required by the Wade & others (2006) model.

d) Arc-related magmatism continued until ca 1560 Ma, post-dating ca 1600–1580 Ma deformation in which the Gawler Craton and the North Australian Craton collided.

e) Crustal shortening is dominantly recorded in the down-going plate, which is opposite to modern analogues such as the Himalaya and the European Alps.

f) The Wade/Swain model cannot explain the pre-1600 Ma correlations which exist between the Curnamona Province and the Mount Isa Inlier.

East-west shortening followed by transpression

Gibson & others (2008) proposed a model for orogenesis associated with the Isan Orogeny beginning at ca 1640 Ma, which was contemporaneous with the collision of the Warumpi Terrane along the southern margin of the Arunta Inlier (Scrimgeour & others, 2005). This event was/can be correlated with thin skinned deformation in the Curnamona Province and the Mount Isa Inlier. Basins

Page 42 Section II: Eastern Australian Proterozoic Correlations that formed contemporaneously and subsequent to this episode of crustal shortening (e.g., Upper McNamara Group) were considered to have been deposited in an orogenic foreland setting. The main phase of the Isan Orogeny (ca 1620–1575 Ma) evolved in an E-W shortening regime and was driven by a component of crustal reworking in central Australia (Chewings Orogeny) and the northern Gawler Craton (Kararan Orogeny). This was associated with a component of continental reactivation between the Mawson Continent (South Australian Craton and East Antarctica). This phase of deformation is recorded in thick skinned crustal shortening and strike-slip faulting. Gibson & others (2008) speculated that the major tectonic driver was the accretion of the conjoined Georgetown– Mojave crustal blocks at some time between 1640–1600 Ma, implying a continental suture between ca 1640–1600 Ma.

The model of Gibson & others, (2006) fails to consider:

a) the development of magmatic arcs on the southern margin of the Gawler Craton (St Peter Suite) and in the Musgrave Block (Wade & others, 2006); b) the development of the early phase of thin skinned deformation associated with the Ewamin Orogeny which can be correlated with the apparently separated Mount Isa Inlier and Curnamona Province; and c) the distribution of strain and metamorphic grade in the Georgetown Inlier which decreases toward the proposed suture zone between the Mount Isa Inlier and Georgetown Inlier.

SUMMARY

The Mount Isa Inlier was subjected to approximately 350 million years of continuous tectonic activity which included several orogenic cycles and major episodes of basin development. For most of the evolution of the Inlier, tectonic activity was located in a far-field back arc region and the evolution of the inlier reflects the distal tectonic forces imposed from the plate margins. For the majority of the era between ca 1850–1500 Ma, the Australian continent faced a large oceanic basin to the south. This margin was dominated by convergence. Basin development between ca 1800–1660 Ma was controlled by a combination of subduction, roll-back and break-up of the Australian and Laurentia continents to the east. Transient episodes of accretion and orogenesis along the convergent plate margin correlate with episodes of basin inversion and depositional hiatus (e.g., Kimban Orogeny and post-Leichhardt Superbasin inversion). The transition from extensional basins to post-extensional basins at ca 1650 Ma coincides with the break-up of Australia and Laurentia (Isa Superbasin phase). The reactivation of the Isa Superbasins was also driven by tectonism along the southern margin of the continent (e.g., accretion of the Warumpi Terrane). Moreover, this time interval between ca 1620– 1500 Ma is dominated by orogenesis. This protracted orogenic evolution resulted from complex interactions along convergent southern and eastern margins of the continent. Plate margin activity was further complicated by the onset of a mantle plume along the southern margin of the continent Page 43 Proterozoic Mount Isa Synthesis

(Gawler Craton) and the migration of Australia above the plume which occurred contemporaneously with orogenesis.

Despite the absence of post-1850 Ma plate margins in the Mount Isa Inlier, the tectonic history reflects the distal effects of activity along two plate margins. The Inlier is unique in that it records a comprehensive Paleoproterozoic basin evolution and Mesoproterozoic poly-orogenic evolution.

REFERENCES

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