TECTONICS, VOL. 29, TC5010, doi:10.1029/2009TC002543, 2010

Neoproterozoic rifting in the southern Georgina Basin, central Australia: Implications for reconstructing Australia in Rodinia

David C. Greene1 Received 29 May 2009; revised 25 January 2010; accepted 1 February 2010; published 17 September 2010.

[1] AsystemofnorthweststrikingNeoproterozoic 2005], and the Australia‐Mexico (AUSMEX) reconstruc- rift basins underlies Paleozoic strata in the southern tion suggests a connection between northeastern Australia Georgina Basin of central Australia. Normal faults and Mexico [e.g., Wingate et al.,2002;Pisarevsky et al., bounding these rift basins were selectively reactivated 2003, 2007]. Other reconstructions have matched Australia during the mid‐Paleozoic Alice Springs Orogeny and with Siberia [Sears and Price, 2000, 2003] and South China [Li et al., 1995; Li and Powell, 2001; Li et al., 2008] or have are now expressed as high‐angle reverse faults that rejected the Rodinia reconstruction entirely [e.g., Piper, invert the preexisting rift basins. Exhumed and eroded 2000, 2007]. rift basin remnants are present in the hanging wall of [3] One approach to evaluating these reconstructions is to the Oomoolmilla, Lucy Creek, Tarlton, and Toomba investigate structures that formed during the Neoproterozoic reverse faults, and rift basins may be preserved in breakup of Rodinia. Continental blocks that were adjacent the subsurface beneath the Toko Syncline and Burke prior to breakup should show similar timing of extension River Structural Belt. Rift basin fill indicates two peri- and rifting and also a matching geometry of the resulting ods of extension: a major rift‐forming episode between conjugate rifted margins. This paper summarizes field evi- approximately 700 and 650 Ma (coeval with Sturtian dence and geophysical interpretations indicating that a glacial deposits) and a second episode of extension system of northwest trending Neoproterozoic rift basins at approximately 600 Ma (coeval with Marinoan gla- underlies Paleozoic strata in the southern Georgina Basin of central Australia (Figure 2a). cial deposits). This northwest striking rift system in [4] This northwest trending rift system developed during central Australia supports results from other regions, two distinct phases of northeast directed extension along indicating that the Neoproterozoic continental margin the eastern margin of the North Australian Craton. The of Australia consisted of northwest striking rift seg- existence of this northwest striking rift system in central ments offset by northeast striking transform faults. Australia correlates with results from south Australia [e.g., Such a configuration is geometrically incompatible with Preiss, 2000; Li and Powell, 2001], indicating that the Neo- aLaurentiancontinentalmargin consisting of northeast proterozoic continental margin of Australia consisted of striking rift segments and conflicts with reconstructions northwest striking rift segments offset by northeast striking such as SWEAT and AUSWUS that match Australia transform faults (Figure 2c) rather than a proposed alterna- with western Laurentia in the Rodinia supercontinent. tive configuration of northeast striking rift segments offset Citation: Greene, D. C. (2010), Neoproterozoic rifting in the by northwest striking transforms (Figure 2b) [e.g., Shaw southern Georgina Basin, central Australia: Implications for et al., 1991; Myers et al., 1996; Veevers, 2000]. reconstructing Australia in Rodinia, Tectonics, 29, TC5010, [5] This study contributes to a more complete under- doi:10.1029/2009TC002543. standing of Neoproterozoic rifting in Australia during the breakup of Rodinia. Continental margins proposed to be conjugate to Australia at breakup (e.g., western Laurentia 1. Introduction or south China) must be geometrically compatible with the rift and transform geometry documented here. [2] Marked geologic similarities between Australia and western North America have lead to a number of proposed 2. Geologic Setting reconstructions of the Proterozoic supercontinent Rodinia (Figure 1). The southwest United States‐East Antarctica [6] The Georgina Basin (Figure 2) is a broad Neoproter- (SWEAT) hypothesis places Australia adjacent to Canada ozoic to Paleozoic intracratonic sedimentary basin that over- [e.g., Moores, 1991; Dalziel, 1991; Hoffman, 1991; Goodge lies the North Australian Craton in north central Australia et al., 2004, 2008], the Australia‐southwest United States [Dunster et al., 2007]. It is an erosional remnant of a series (AUSWUS) reconstruction matches Australia with the south- of interconnected basins termed the Centralian Superbasin western United States [e.g., Brookfield,1993;Burrett and [Walter et al., 1995] that developed in central Australia after Berry,2000;Karlstrom et al.,1999,2001;Fioretti et al., amalgamation of Proterozoic crustal elements between 1300 and 1000 Ma [Myers et al., 1996; Betts and Giles, 2006]. 1Department of Geosciences, Denison University, Granville, Ohio, USA. 2.1. Stratigraphy and Basin History

Copyright 2010 by the American Geophysical Union. [7] The Georgina Basin consists predominantly of Late 0278‐7407/10/2009TC002543 Neoproterozoic, Cambro‐Ordovician, and Devonian strata

TC5010 1 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

[9] In the Late Neoproterozoic, two successions of pre- dominantly immature, coarse, clastic sedimentary rocks were deposited in localized, fault‐bounded basins. The older succession (Aroota Group) consists of the Yardida Tillite and Mount Cornish Formation, which unconformably over- lie Yackah beds or crystalline basement. The units consist of up to 650 m of diamictite and siltstone, including boulder conglomerates with striated basement clasts up to 1 m in diameter [Freeman, 1986; Dunster et al., 2007]. These units are considered to be coeval with the Sturtian Glaciation and dated at ∼700–650 Ma [Preiss et al.,1978;Walter et al., 1995; Preiss, 2000; Kendall et al., 2006; Eyles et al., 2007]. [10] The younger Neoproterozoic succession (Keepera Group) consists of up to 1100 m of predominantly arkose and arkosic pebble to boulder conglomerate (Oorabra Arkose and Black Stump Arkose), overlain by a “cap carbonate” (Wonnadinna Dolostone). Locally derived basement clasts up to 1.5 m in diameter indicate high relief and a local source area [Freeman, 1986]. This succession is correlated with Elatina Formation glacial deposits in South Australia

Figure 1. Five proposed reconstructions of Australia and Laurentia in the Rodinia supercontinent, approximately 900 Ma: (a) Southwest United States‐East Antarctica (SWEAT); (b) Australia‐southwest United States (AUS- WUS); (c) Australia‐Mexico (AUSMEX); (d) Australia‐ Siberia‐Laurentia; (e) Australia‐south China‐Laurentia. ANT, Antarctica; AUS, Australia; LAU, Laurentia; SCH, South China; SIB, Siberia. Reconstructions modified from Wingate et al. [2002], Sears and Price [2003], and Li et al. [2008]. unconformably overlying Proterozoic crystalline basement (Figure 3) [Smith,1972].Athin(∼500 m) Cambro‐Ordovician platform succession in the central Georgina Basin thickens southward to up to 2200 m of predominantly lower Paleo- zoic strata in depocenters on the southern basin margin [Dunster et al., 2007]. Beneath the widespread Paleozoic strata, up to 1500 m of Late Neoproterozoic, predominantly coarse, immature, siliciclastic rocks are locally preserved in fault‐bounded basins and half grabens [Walter, 1980; Freeman, 1986; Walter et al., 1995; Kruse et al., 2002]. 2.1.1. Neoproterozoic Stratigraphy [8] The oldest sedimentary rocks exposed in the southern Georgina Basin are the Yackah beds, a locally preserved sandstone and dolostone unit with an estimated maximum thickness of 250 m [Walter et al., 1995; Dunster et al., 2007]. These rocks are correlated with the Heavitree Quartzite and Bitter Springs Formation of the Amadeus Basin to the south, considered to be ∼825–800 Ma [Zhao et al., 1994; Figure 2. (a) Generalized geologic map of Australia Walter et al., 1995]. The Yackah beds form the distal edge showing location of the Georgina Basin. Line marked TL of a southwestward thickening clastic and shallow marine indicates approximate location of Neoproterozoic continen- succession that was widely deposited across central Australia tal margin; areas to the east are presumed to have accreted on a low‐relief basement surface. The Yackah beds and during Paleozoic time. Box shows location of study area correlative units represent an early phase of broad subsidence illustrated in Figures 4 and 6. (b and c) Alternative inter- that initiated the Centralian Superbasin [Shaw et al., 1991; pretations of extension direction during Neoproterozoic Walter et al., 1995; Preiss, 2000]. rifting of Australia away from Rodinia. Evidence presented here supports northeast extension.

2 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

Figure 3. Lithostratigraphy of the southern Georgina Basin, with major tectonic events. Data from Ambrose et al. [2001], Kruse and Mohammed [2005], and Dunster et al. [2007].

[Preiss et al., 1978; Walter et al., 1995; Preiss, 2000] that 700 and 650 Ma and a second episode of extension at ap- are considered to be Marinoan in age. The exact age of proximately 600 Ma. Marinoan glacial strata in Australia is currently a matter of [12] Latest Neoproterozoic clastic sediments of the debate and may be either 635 Ma or approximately 580 Ma Mopunga Group (Figure 3) are more widespread, deposited [e.g., Calver et al., 2004; Kendall et al., 2006]. across an eroded, low‐relief surface overlying rifts and rift [11] These two Neoproterozoic successions were depos- shoulders [Ambrose et al., 2001]. ited locally in association with major basement faults. Both 2.1.2. Paleozoic Stratigraphy successions are wedge shaped in cross section, thinning and [13] Early Cambrian clastic sedimentary rocks (Shadow fining away from basement faults to pinch out beneath the Group), including the prominent ridge‐forming Mount Bald- widespread latest Neoproterozoic to Paleozoic strata of the win Formation, unconformably overlie Neoproterozoic strata. Georgina Basin. They are interpreted as glaciogenic sedi- These are interpreted as distal foreland basin deposits related ments that were deposited in developing Neoproterozoic rift to the Peterman Orogeny, which mainly affected the Mus- basins inboard of the Australian craton margin [e.g., Powell grave region to the southwest [Camacho et al., 1997; Haines et al., 1994; Preiss, 2000; Ambrose et al., 2001; Pisarevsky et al., 2001; Dunster et al., 2007]. et al., 2003]. These two successions indicate two distinct [14] Middle and Upper Cambrian strata (Narpa Group) periods of extension: a major rift‐forming episode between primarily represent deposition on a stable, broad marine carbonate platform. Deposition of sandstone and a hiatus

3 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010 in Late Cambrian time may reflect distal effects of the involving predominantly north‐south to northeast‐southwest Delamerian Orogeny [Ambrose et al., 2001]. This orogeny shortening, occurred at approximately 450–440 Ma (Rodingan caused extensive deformation in the Adelaide Rift Complex Movement), approximately 390–375 Ma (Pertnjara Move- [Preiss, 2000], but its effects in the Georgina Basin appear ment), and 330–320 Ma (Mount Eclipse Movement) and to be limited to minor uplift and reactivation of basement correlate with pulses of sedimentation in the adjacent faults [Ambrose, 2006]. Amadeus and Georgina basins [e.g., Haines et al., 2001; [15] Subsequent deposition of Ordovician siliciclastic Buick et al., 2008]. Deformation appears to have been most rocks (Toko Group) in a marine platform setting was ter- intense in the eastern Arunta Region, where amphibolite minated by uplift associated with the earliest phase of the facies metamorphism was accompanied by south vergent Alice Springs Orogeny. Synorogenic foreland basin sedi- thrusting and recumbent folding [Dunlap et al., 1995; Huston ments of the Dulcie Sandstone and Cravens Peak beds were et al., 2006]. In contrast, north of the eastern Arunta Region deposited in the Devonian, in association with a later phase along the present southern margin of the Georgina Basin, (Pertnjara Movement) of the Alice Springs Orogeny [Haines including the present study area, deformation was predom- et al., 2001; Maidment et al., 2007; Dunster et al., 2007]. inantly brittle in style, and preexisting major basement faults Significant erosion and basin unroofing across the southern were reactivated as high‐angle reverse faults. Georgina Basin occurred during the Carboniferous Mount 2.1.5. Structural Framework Eclipse Movement, the last phase of the Alice Springs [20] The southern Georgina Basin (Figure 4) was pri- Orogeny [Haines et al., 2001; Ambrose, 2006; Dunster et al., marily deformed during the Devonian Pertnjara Movement 2007]. of the Alice Springs Orogeny. Contractional deformation [16] The Georgina Basin is overlain to the east and south- resulted in reverse faulting, uplift, and tilting of basement‐ east by undeformed Jurassic and Cretaceous sedimentary cored blocks and in broad folds and monoclinal flexures in rocks of the Eromanga Basin. the overlying Paleozoic strata (Figure 5) [Simpson et al., 2.1.3. Larapinta Event 1985; Freeman,1986;Kruse et al.,2002;Dunster et al., [17] During the early Ordovician (∼480–460 Ma), sedi- 2007]. Devonian synorogenic sedimentation in the Dulcie mentary rocks of Neoproterozoic and Cambrian age in the and Toko synclines (which fold the Ordovician Toko Group eastern Arunta Region, on the southern edge of the Georgina and older rocks) occurred in foreland basins that devel- Basin, were metamorphosed to granulite facies at depths of oped on footwall blocks adjacent to major reverse faults 30–35 km and temperatures of ∼800°C [Mawby et al., 1999; (Oomoolmilla and Toomba faults, respectively) (Figure 4). Hand et al., 1999; Buick et al., 2001]. These rocks were Deformation decreased northward, and the central Geor- subsequently exhumed and juxtaposed against surrounding gina Basin consists of predominantly flat‐lying strata with Paleoproterozoic rocks of the Arunta Region during the subtle warps and local disturbances of bedding probably earliest phase of the Alice Springs Orogeny (Rodingan related to structures in the underlying basement [Kruse and Movement) between about 450 and 440 Ma [Scrimgeour Mohammed, 2005]. and Raith, 2001; Buick et al., 2005]. This highly localized [21]Duringcontractionaldeformation,normalfaultsbound- tectonic episode, termed the Larapinta Event, has been inter- ing Neoproterozoic rift basins were reactivated as high‐ preted to result from opening and subsequent closure of angle reverse faults, and much of the Paleozoic structure in a pull‐apart basin in a dextral strike‐slip fault system proba- the southern Georgina Basin is related to variable reacti- bly associated with development of the northwest trending vation of these underlying basement faults. Reverse faults Larapintine Seaway [Buick et al., 2005]. with uplifted Neoproterozoic rift basin fill exposed in the [18] Neither the exceptionally rapid subsidence of these hanging wall (e.g., Oomoolmilla, Lucy Creek, Tarlton, rocks to lower crustal depths nor their subsequent and equally Toomba, and Sun Hill faults) clearly demonstrate the inver- rapid exhumation are reflected in the adjacent Georgina sion of preexisting rift basins (Figures 4 and 5). Similar Basin, where coeval Ordovician siliciclastic rocks of the high‐angle reverse faults and monoclinal flexures exposed Toko Group were deposited in a marine platform setting in overlying Paleozoic strata (e.g., monoclines in the Lucy [Buick et al., 2005; Maidment et al., 2007]. The Ordovician Creek, Toomba, and Sun Hill fault zones, Pilgrim Fault in age of the Larapinta Event is not coincident with either the Burke River Structural Belt) indicate the location of earlier Neoproterozoic rifting in the Georgina Basin or the reactivated normal faults bounding subsurface rift basins main phase of block uplift and inversion in the Devonian. beneath the Paleozoic strata. It therefore appears that deformation associated with the [22] New field work, combined with existing regional Larapinta Event was sharply partitioned across the bound- mapping and drill hole data [Reynolds, 1965, 1968; Casey, ing shear zones and did not significantly affect rocks in the 1968; Senior, 1973; Blake et al., 1984; Simpson et al., 1985; Georgina Basin [Scrimgeour and Raith, 2001]. Freeman, 1986; Kruse et al., 2002; Greene, 2003], repro- 2.1.4. Alice Springs Orogeny cessed and reinterpreted seismic data [Harrison, 1979, 1980; [19] A series of intracratonic tectonic episodes in central Skilbeck and Lennox, 1984; Lodwick and Lindsay, 1990; Australia that occurred between Late Ordovician and Late Lechler and Greene,2006;Geoscience Australia, 2008] and Carboniferous time (∼450–300 Ma) are collectively known depth‐to‐basement estimates derived from regional gravity as the Alice Springs Orogeny [Shaw et al.,1992;Dunlap and aeromagnetic data [Tucker et al., 1979; Murray et al., et al.,1995;Haines et al.,2001;Buick et al.,2008].Distinct 1997; Milligan and Franklin, 2004; OZ SEEBASE™ Study, pulses of localized metamorphism, uplift and deformation, 2005; Dunster et al., 2007; Pierson and Greene, 2008],

4 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

Figure 4. Simplified geologic map of the southern Georgina Basin showing Neoproterozoic normal faults. Lines A, B, and C indicate locations of cross sections shown in Figure 5. Box shows location of Huckitta region illustrated in Figure 6. BR, Burke River Structural Belt; DS, Dulcie Syncline; LF, Lucy Creek Fault; OF, Oomoolmilla Fault; PF, Pilgrim Fault; SF, Sun Hill Fault; TF, Tarlton Fault; ToF, Toomba Fault; TL, approximate location of Neoproterozoic continental margin; TS, Toko Syncline. Modified from published mapping, see text for data sources.

Figure 5. Cross sections showing Neoproterozoic rift basins underlying Paleozoic sedimentary rocks of the southern Georgina Basin. Rift‐bounding normal faults were variably reactivated during the mid‐ Paleozoic Alice Springs Orogeny. Section locations indicated in Figure 4. Section A is based primarily on geologic mapping; sections B and C are based on interpretation of seismic and aeromagnetic data. Note that sections are of different scales. See text for data sources. MF, Mount Playford Fault.

5 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

Figure 6. Interpreted rift basins superimposed on simplified geologic map of the southern Georgina Basin showing Neoproterozoic normal faults. LinesA,B,andCindicatelocationsofcrosssections shown in Figure 5. BR, Burke River Structural Belt; DS, Dulcie Syncline; LF, Lucy Creek Fault; OF, Oomoolmilla Fault; PF, Pilgrim Fault; SF, Sun Hill Fault; TF, Tarlton Fault; ToF, Toomba Fault; TL, approximate location of Neoproterozoic continental margin; TS, Toko Syncline. allow regional mapping of the Neoproterozoic rift system ilarly oriented fault that truncates the Elua Range to the underlying the southern Georgina Basin (Figures 4 and 6). south form northeast striking step or transfer faults within the predominantly northwest trending regional fault systems 3. Neoproterozoic Rift Basins of the southern Georgina Basin. The Oomoolmilla Fault is significant as a particularly well‐exposed and relatively [23] The southwestern margin of the Georgina Basin in accessible example of a reverse fault that offsets Devonian the Huckitta region (Figure 7) is relatively well exposed strata and has Neoproterozoic rift facies sedimentary rocks in uplifted and tilted fault blocks [Freeman, 1986]. Good uplifted in the hanging wall (Figure 8). These relations indi- exposures at multiple structural levels along the Oomool- cate the Oomoolmilla Fault originated as a Neoproterozoic milla and Lucy Creek faults clearly demonstrate the rela- rift‐bounding normal fault and was subsequently reactivated tionship between mid‐Paleozoic contractional deformation as a reverse fault during the later phases of the Alice Springs and Neoproterozoic rift basins. These fault zones and asso- Orogeny, as detailed below. ciated stratigraphic and structural relations are described in [25] The Oomoolmilla Fault is 25 km in length, strikes detail below, based primarily on field mapping and outcrop N70°E, and dips approximately 70° south based on maxi- data, and are used as analog models for interpreting regional mum dip of overturned bedding in the adjacent footwall. structure. Structures increase in scale and complexity to The footwall of the fault consists of Upper Cambrian the southeast along the Georgina Basin margin but are less Arrinthrunga Formation that is folded upward from essen- well exposed, and seismic, aeromagnetic and gravity data tially flat lying at distances greater than 1 km from the fault become progressively more important in delineating sub- trace to vertical or overturned and dipping 70–80° south surface structures. adjacent to the fault (Figure 9). The hanging wall is pre- dominantly Proterozoic Jinka Granite, but steeply dipping 3.1. Oomoolmilla Fault Zone blocks of the overlying Neoproterozoic and Paleozoic strata [24] The Oomoolmilla Fault [Freeman, 1986] is a prom- are locally preserved as fault slivers or down‐folded ero- inent, northeast striking, steeply south dipping reverse fault sional remnants. In particular, a thick section of Neopro- that juxtaposes Proterozoic crystalline basement with Cam- terozoic Oorabra Arkose is exposed where the Oomoolmilla brian to Devonian sedimentary rocks of the Georgina Basin Fault cuts the Elua Syncline (Figures 7 and 9). to the north (Figure 7). The Oomoolmilla Fault and a sim-

6 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

Figure 7. Geologic map of the Huckitta region, southern Georgina Basin, modified from Freeman [1986]. Oomoolmilla and Lucy Creek‐Mount Playford fault systems were active as reverse faults dur- ing the mid‐Paleozoic Alice Springs Orogeny but expose Neoproterozoic rift basin fill in their hanging walls, indicating mid‐Paleozoic reactivation of preexisting rift‐bounding normal faults. Lines D and E indicate locations of cross sections shown in Figures 8 and 10, respectively. Box indicates location of Figure 9.

[26] Minimum vertical displacement on the Oomoolmilla Sandstone (Figure 7), indicating that latest displacement Fault is 1400 m based on stratigraphic offset (Figure 8), must be syn‐ or post‐Devonian. although total displacement has been estimated at approxi- 3.1.1. Hanging Wall Stratigraphy mately 3500 m by Freeman [1986], based on projecting [27] Distinctive Neoproterozoic rift facies strata are locally the dip of the basement/cover contact northward from the exposed in the hanging wall of the Oomoolmilla Fault. Elua Range. The Oomoolmilla Fault truncates and overprints The Mount Cornish Formation consists of up to 15 m of northwest trending folds in the early‐to‐late Devonian Dulcie diamictite and siltstone that are locally preserved in former

Figure 8. Cross section of the Oomoolmilla fault zone. Neoproterozoic arkosic conglomerate (Oorabra Arkose) in the hanging wall thins away from the fault, suggesting deposition in a rift basin adjacent to an active normal fault. Hanging‐wall‐up offset of Paleozoic strata indicates subsequent reverse reactivation during the Alice Springs Orogeny. Units as in Figure 7. Location of cross section shown in Figures 7 and 9.

7 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

Figure 9. (a) Aerial photograph of the Oomoolmilla fault zone. Proterozoic crystalline basement to the southeast is uplifted and juxtaposed against Cambro‐Ordovician strata of the Georgina Basin to the northwest. Siliceous dikes visible as northwest trending ridges in the Proterozoic basement are truncated by the fault zone. Overturned, southeast dipping Cambrian strata adjacent to the fault (gray color) indi- cates Paleozoic southeast‐up displacement on a southeast dipping reverse fault. Neoproterozoic Oorabra Arkose exposed in the hanging wall is interpreted as rift basin fill deposited adjacent to a Neoproterozoic normal fault that was subsequently reactivated during the Alice Springs Orogeny. Neoproterozoic strata are preferentially preserved in the core of the Elua Syncline and have been eroded from adjacent struc- turally higher areas of the hanging wall block. Line labeled D indicates the location of cross section D‐D′ shown in Figure 8. Air photo courtesy of Northern Territory Government. (b) Oorabra Arkose in out- crop, showing granite and quartz cobbles floating in massive, coarse‐grained, arkosic matrix.

8 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

Figure 10. Cross section of the Lucy Creek–Mount Playford fault system. Stratigraphic offset and monoclinal folding (Figure 11) indicates mid‐Paleozoic west up reverse displacement on both the Lucy Creek and Mount Playford faults. Neoproterozoic rift basin fill (Oorabra Arkose) in the hanging wall of the Lucy Creek Fault indicates that this was a Neoproterozoic rift‐bounding normal fault prior to reactivation during the mid‐Paleozoic Alice Springs Orogeny. Units as in Figure 7. Location of cross section shown in Figure 7. topographic lows on the bedrock surface [Freeman,1986]. 3.2. Lucy Creek Fault Zone Varves, dropstones, and striated basement surfaces indicate [31] The Lucy Creek and Mount Playford faults are a pair deposition concurrent with glaciation. The Mount Cornish of related, northwest striking, west‐side‐up reverse faults that Formation is correlated with the Sturtian Glaciation at 700– truncate the northeast end of the Jervois Range (Figures 7 650 Ma [Walter et al., 1995] and indicates the time of ini- and 10). The Lucy Creek Fault has a distinct linear trace tiation of the rift basin. visible in air photo and satellite imagery for a distance of [28] Spectacular cobble to boulder conglomerates of the greater than 75 km. Paleozoic stratigraphic offset and struc- late Neoproterozoic Oorabra Arkose are preserved in a tural expression are at a maximum in the Jervois Range and structural low in the core of the Elua Syncline (Figure 9), decrease northward into a sequence of minor faults, mono- unconformably overlying the Mount Cornish Formation. clines, and disturbed bedding that eventually terminates in a These rocks contain distinctive clasts up to 1.5 m in diam- series of northeast trending splays [Freeman, 1986]. eter that are derived from the adjacent granitic basement 3.2.1. Jervois Range Area [Freeman, 1986]. The Oorabra Arkose has been interpreted [32] The Lucy Creek and Mount Playford faults in the as glacial outwash sediments deposited in half grabens Jervois Range are steeply west dipping reverse faults, as [Freeman, 1986; Walter and Veevers, 2000]. It is correlated indicated by linear map traces, west‐side‐up stratigraphic with the Marinoan Glaciation [Walter et al., 1995] and is offsets, and the development of associated monoclinal folds thought to have been deposited at about 600 Ma. with steeply east dipping to locally overturned limbs [29] The Neoproterozoic Oorabra Arkose and Mount Cor- (Figures 7 and 10). A thin wedge of rift basin fill (Oorabra nish Formation are thickest adjacent to the Oomoolmilla Fault Arkose) is exposed in the hanging wall adjacent to the Lucy (estimated to be ∼500 m) and thin southeastward to pinch Creek Fault, overlain by Cambro‐Ordovician rocks [Freeman, out beneath the overlying Elyuah Formation (Figure 8) 1986]. [Freeman, 1986]. East of the Elua Syncline, the arkose and [33] The minimum vertical displacement on the Lucy overlying Paleozoic sedimentary rocks were mostly removed Creek Fault is about 700 m based on the stratigraphic jux- during erosion of the uplifted hanging wall block but are taposition of Neoproterozoic Elyuah Formation and Cam- locally preserved in down‐dropped slivers within the fault brian Red Heart Dolostone on the southern edge of the zone. range. Projecting the 10° average dip of exposed strata on 3.1.2. Summary and Interpretation Mount Playford into the fault zone suggests that actual [30] The Oorabra Arkose forms a northward thickening displacement may exceed 1000 m (Figure 10). Juxtaposition wedge of very coarse, locally derived, clastic sediments in of Cambrian Mount Baldwin Formation against Cambro‐ the hanging wall adjacent to the Oomoolmilla Fault. The Ordovician Tomahawk Formation across the Mount Play- Oorabra Arkose and Mount Cornish Formation have been ford Fault indicates about 1600 m of vertical displacement. interpreted as glaciogenic rift basin fill originally depos- [34] Prominent monoclines are developed in the ridge‐ ited in localized half grabens [Freeman, 1986; Walter and forming Mount Baldwin Formation adjacent to the trace of Veevers, 2000; Dunster et al., 2007]. In the Huckitta region, both the Lucy Creek and Mount Playford faults (Figure 11). the Oorabra Arkose was locally deposited and is only present These folds formed in the upthrown hanging walls of the in association with steeply dipping faults (Figure 7). These respective faults, and in both cases the stratigraphic offset relations are interpreted to indicate that the Oorabra Arkose requires that the monoclines be cut by the adjacent fault was originally deposited adjacent to a late Neoproterozoic, (Figure 10). These folds are characteristically kink‐like, southeast‐down, rift‐bounding normal fault that was reac- with planar limb segments separated by angular hinge tivated as the present Oomoolmilla southeast‐up reverse fault zones. Dip of the steep limb on the Lucy Creek monocline is during the mid‐Paleozoic Alice Springs Orogeny.

9 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

Figure 11. West‐up monocline in the hanging wall of the Lucy Creek Fault where it truncates the north end of the Jervois Range. View looking northwest. Folded strata exposed in hillside are sand- stones of the Cambrian Mount Baldwin Formation. Topographic relief is approximately 100 m.

45–60°NE, whereas in the Mount Playford monocline ments. Southeast of the Jervois Range, the surface expres- bedding is vertical to overturned. A broad anticline devel- sion of the Lucy Creek Fault is limited to a series of quartz oped in the hanging wall west of the Lucy Creek monocline veins that follow the trend of the fault. However, a promi- is characteristic of monoclines where the underlying fault nent aeromagnetic lineament indicates the trace of the fault surface is listric and is a geometric consequence of reverse at least as far as the Mount Cornish area, where the trace displacement on a curved fault surface [e.g., Stone, 1993]. trends more easterly and may connect with the Tarlton fault The field relations and structural geometries described here system. indicate that these are basement‐involved, fault‐generated [38] The Mount Playford Fault coincides with a prominent folds, with geometries and modes of formation very similar boundary between small wavelength magnetic anomalies to monoclines and thrust folds developed during Laramide characteristic of shallow or exposed crystalline basement intracontinental deformation in the western United States and areas to the northeast consisting of high amplitude long [e.g., Davis, 1978; Huntoon, 1993; Stone, 1993; Erslev and wavelength anomalies indicating more deeply buried base- Rogers, 1993; Bump, 2003; Erslev, 2005]. ment. Northwest of the Jervois Range, the magnetic linea- 3.2.2. Mount Cornish Area ment coincident with the Mount Playford Fault appears to [35] The Lucy Creek and Mount Playford faults continue curve into and terminate against the Lucy Creek Fault in a southward from the Jervois Range under Holocene cover to “J‐hook” relationship characteristic of younger‐against‐ the Mount Cornish area (Figure 7), as indicated by aligned older fracture terminations [e.g., Pollard and Aydin, 1988]. quartz veins and quartz breccia zones and a distinctive linear Southeast of the Jervois Range, the Mount Playford Fault discontinuity on aeromagnetic intensity maps [e.g., Freeman, continues as a prominent aeromagnetic boundary to the 1986; Kruse and Mohammed, 2005]. East of Mount Cornish, Mount Cornish area, where the trace appears to break up Neoproterozoic sedimentary rocks of the Mount Cornish into a series of northwest trending and west‐northwest Formation and Yackah beds are truncated by the northwest trending segments [Kruse et al., 2002]. trending Lucy Creek Fault, with poorly exposed Proterozoic 3.2.4. Timing of Reverse Faulting crystalline basement to the east (Figure 7). West‐down [39] The Lucy Creek and Mount Playford faults are syn‐ dip‐slip displacement is indicated by the juxtaposition of or post‐Ordovician in age, as the youngest exposed unit crystalline basement to the east with Neoproterozoic sedi- offset by these faults is the Cambro‐Ordovician Tomahawk mentary rocks to the west. Formation. These faults are part of a distinct phase of 3.2.3. Geophysical Expression basement‐cored uplifts on high‐angle reverse faults that [36] Both the Lucy Creek and Mount Playford faults are includes the Oomoolmilla and Toko faults, both of which prominently expressed as consistent linear discontinuities on deform early‐to‐late Devonian rocks. Reverse displacement aeromagnetic anomaly maps (Figure 12) [e.g., Teasdale and on the Lucy Creek and Mount Playford faults is therefore Pryer, 2002; Dunster et al., 2007]. As the sedimentary cover also interpreted as syn‐ or post‐Devonian and related to the rocks are nonmagnetic [Dunster et al., 2007], the magnetic later phases of the Alice Springs Orogeny. signal is derived primarily from lithologic and structural 3.2.5. Summary and Interpretation contrasts in the basement and indicates that these faults are [40] The Lucy Creek and Mount Playford faults are related significant basement structures. structures that together form the southwest edge of the Geor- [37] The Lucy Creek Fault northwest of the Jervois Range gina Basin in the Huckitta region. Both are northwest trend- is visible as a linear anomaly in the magnetic data for about ing, west‐up, reverse faults. Although the Mount Playford 40 km. As in its outcrop expression, the fault appears to Fault has less surface expression, it has substantially more merge into a diffuse system of northeast trending linea- Paleozoic offset.

10 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

Figure 12. Magnetic anomaly map of the southern Georgina Basin with locations of major Neopro- terozoic normal faults. Compare with geologic map of same area (Figure 4) and locations of inter- preted rift basins (Figure 6). PF, Pilgrim Fault; TL, approximate location of Neoproterozoic continental margin. Other faults as in Figure 4. Base map modified from OZ SEEBASE™ Study [2005].

[41] Geological and geophysical data indicate that the Lucy erosion was followed by widespread deposition of late Creek Fault is continuous southward from the Jervois Range Neoproterozoic through Cambrian sedimentary rocks of the to the Mount Cornish area. Apparent displacement on the Georgina Basin (Figure 13b). Contractional deformation fault in these two areas is, however, opposite in sense. In the during the Alice Springs Orogeny resulted in reactivation of Jervois Range west‐up displacement is clearly demonstrated the rift‐bounding normal fault as a reverse fault, forming the by the stratigraphic and structural relations, whereas in the Lucy Creek Fault (Figure 13c). Mount Cornish area, juxtaposition of Neoproterozoic sedi- [43] The deeper structural level in the Mount Cornish area mentary rocks against Mesoproterozoic crystalline basement exposes Neoproterozoic rift‐related sediments juxtaposed indicates west‐down displacement. These opposite offsets on against crystalline basement along an extensional fault with the same fault support a model in which an early west‐down Neoproterozoic, probably syn‐sedimentary, west‐side‐down normal fault was later reactivated as a west‐up reverse fault displacement. Subsequent mid‐Paleozoic west‐side‐up dis- (Figure 13). placement during reactivation as a contractional reverse fault [42] In this interpretation, the Lucy Creek Fault originally did not completely remove evidence of the early extensional developed as a steeply west dipping normal fault during component of deformation in this area. Structurally higher Neoproterozoic extension, forming a rift basin in which the levels in the northern Jervois Range expose younger late more wide‐spread Yackah beds were preserved from ero- Neoproterozoic and Paleozoic rocks that are recording sion, and the Mount Cornish Formation was subsequently only the mid‐Paleozoic west‐up contractional phase of deposited (Figure 13a). A second phase of extension resul- deformation. ted in renewed subsidence and deposition of the Oorabra [44] The Lucy Creek Fault formed first as a direct reac- Arkose, now locally preserved underlying hanging wall tivation of a preexisting listric normal fault. However, the rocks in the Jervois Range [Freeman, 1986]. A period of upper steeply dipping portion of this fault was poorly oriented

11 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

Figure 13. Conceptual model for the formation of reverse faults in the Huckitta region. (a) Neoproterozoic rifting and syn‐rift sedimentation. (b) Post‐rift erosion and regional sedimentation. (c) Paleozoic contractional reactivation of preexisting normal faults. Reverse faults (e.g., Oomoolmilla and Lucy Creek faults) initially form at a steep angle due to reactivation of the steeply dipping portion of a listric normal fault. Footwall shortcut faults (e.g., Mount Playford Fault) may form subsequently as splays that branch from the old fault and form new, lower‐angle thrusts [after Bump, 2003]. Figure 14. (a) View east at Tarlton fault zone, juxtaposing Paleozoic Georgina Basin strata (Pz) against Proterozoic for contractional reactivation, and with increasing strain the crystalline basement (pC). Note that fault displacement is Mount Playford Fault developed as a lower‐angle footwall basement‐up, opposite to the present topographic relief. shortcut fault that acted to decrease resistance to horizontal (b) View southeast along Tarlton fault zone. Low‐relief shortening (Figure 13c) [e.g., McClay, 1989; Bump, 2003]. plain on right (southwest) is underlain by Proterozoic base- [45] Thus, Neoproterozoic syn‐rift sediments in the ment. Low hills in center are formed by steeply west dipping Mount Cornish area preserve a record of early west down quartz veins that have intruded the fault zone. Prominent extensional faulting, whereas post‐rift strata in the Jervois scarp and darker hills on left (northeast) are capped by Range record only mid‐Paleozoic reverse displacement. Ordovician Carlo Sandstone of the Toko Group. (c) Con- Taken together, these structural relations indicate that the ceptual model for the formation of inverted topography Lucy Creek Fault formed by mid‐Paleozoic reactivation of a in the southern Georgina Basin. Reverse reactivation of Neoproterozoic, rift‐bounding normal fault. Neoproterozoic normal faults during the Alice Springs Orogeny results in stripping of Paleozoic cover from 3.3. Tarlton Fault Zone the uplifted hanging wall block. Relatively more rapid erosion of exposed crystalline basement in the hanging [46] The Tarlton fault zone [Kruse et al., 2002] (Figures 4 and 5) is a northwest striking fault zone, approximately wall block produces topographic inversion with structurally 40 km in exposed length, that juxtaposes Proterozoic crys- lower Paleozoic footwall rocks forming a fault line scarp talline basement on the west with flat‐lying Ordovician that stands topographically high relative to the Proterozoic strata of the southeastern Georgina Basin (Figure 14a). The basement. Tarlton Fault is located approximately 25 km southeast of

12 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010 the Lucy Creek Fault and appears to be a left‐stepping en dipping 40–70° west (Figure 5), with a vertical displacement echelon extension of that fault. of up to 6500 m [Harrison, 1979, 1980; Simpson et al., 1985; [47] In the Keepera Ridge area at the northern end of the Lechler and Greene, 2006]. A prominent footwall syncline, fault zone and in similar exposures to the north and south, the Toko Syncline, is discussed below. subcrop and rare outcrop of the Neoproterozoic Black 3.4.1. Timing Stump Arkose and Wonnadinna Dolostone locally overlie [53] Neoproterozoic clastic rocks and underlying crystal- crystalline basement adjacent to the fault [Kruse et al., line basement are thrust over steeply dipping Paleozoic strata, 2002]. Juxtaposition of Neoproterozoic units with Ordovi- including mid‐Devonian synorogenic sedimentary rocks (Cra- cian Kelly Creek Formation indicates greater than 3300 m vens Peak beds), that form the west limb of the Toko Syncline of total west‐up stratigraphic offset on two fault strands [Simpson et al., 1985]. Thus, west‐up reverse displacement (Figure 5). Paleozoic strata in the footwall adjacent to the occurred at least as late as the middle Devonian, coeval with Tarton Fault are steeply dipping and locally overturned and the later phases of the Alice Springs Orogeny. west dipping. 3.4.2. Hanging Wall Stratigraphy [48] The fault zone is intruded by multiple generations of [54] Coarse clastic rocks of Neoproterozoic age are mostly steeply west dipping quartz veins that form a perva- broadly exposed in the hanging wall of the Toomba Fault sively silicified, brecciated, and recemented zone in the crys- (Figures 4 and 5) and thicken eastward to greater than talline basement (Figure 14b). Quartz veins do not intrude 1000 m of strata adjacent to the fault [Simpson et al., 1985]. Paleozoic strata, indicating that veining is associated with an Extensive exposures of diamictite, shale, and siltstone of the early (Proterozoic or Neoproterozoic) phase of faulting. Sturtian age Yardida Tillite are preserved in a wide zone [49] West dipping bedding in Paleozoic footwall strata adjacent to the fault. These are unconformably overlain by and steeply west dipping quartz veins intruding the fault up to 700 m of arkose, pebbly arkose, and sandstone of the zone, together indicate that the Tarlton Fault is presently a Marinoan Black Stump Arkose that spreads more broadly to west dipping reverse fault, not an east dipping normal fault the west where it directly overlies crystalline basement as previously interpreted [Kruse et al., 2002; Dunster et al., [Shergold, 1985; Simpson et al., 1985]. 2007]. Relatively more rapid erosion of felsic crystalline [55] These stratigraphic relationships indicate two periods basement in the uplifted hanging wall block has resulted in of subsidence, with initial rifting and basin formation coeval topographic inversion, with structurally lower Paleozoic with Sturtian glacial deposits between 700 and 650 Ma and footwall rocks now forming a fault line scarp that stands a second phase of rifting and subsidence with increased topographically high relative to the Proterozoic basement basin size synchronous with Marinoan glacial deposits at (Figure 14c). approximately 600 Ma. Exposures of latest Neoproterozoic [50] Neoproterozoic rift basin fill (Black Stump Arkose Grants Bluff Formation overlying basement yet farther to and Wonnadinna Dolostone) exposed in the hanging wall of the west were probably deposited in a subsequent subsiding the Tarlton Fault indicates that Paleozoic west‐up reverse rift shoulder environment. faulting reactivated a preexisting west‐down Neoproterozoic 3.4.3. Summary and Interpretation rift‐bounding normal fault. [56] Juxtaposition of Neoproterozoic rocks with Devonian synorogenic sedimentary rocks across the west dipping 3.4. Toomba Fault Zone Toomba Fault indicates west‐up reverse faulting during [51] The Toomba fault zone on the southwestern edge of the later phases of the Alice Springs Orogeny. The east- the Georgina Basin (Figures 4 and 5) is a prominent north- ward thickening wedge of Neoproterozoic rift basin fill in west striking zone more than 200 km in length [Simpson the hanging wall block indicates that the Toomba Fault et al., 1985; Kruse et al., 2002]. The fault zone juxtaposes originated as a Neoproterozoic rift‐bounding normal fault. Paleozoic strata preserved in the Toko Syncline with Prote- Structural complexities in the fault zone likely result in part rozoic crystalline basement of the Arunta region and over- from reactivation of a preexisting segmented normal fault lying Neoproterozoic sedimentary rocks. The northern half system and in part from formation of new footwall cutoff of the fault zone is relatively well exposed, but to the south faults during Paleozoic contractional deformation. surface exposure is lost beneath sand dunes of the Simpson Desert and the fault is known primarily from seismic and 3.5. Rift Basins Underlying the Toko Syncline aeromagnetic data. [57] The Toko Syncline is a broad, asymmetric regional [52] The fault zone is complex in detail and consists of syncline with a steeply dipping to overturned western limb left‐stepping en echelon segments, with individual fault in the footwall of the Toomba Fault and a wide, gently segments dying out northward into monoclinal folds (e.g., dipping eastern limb (Figures 4 and 5). Outcrop and sparse Marqua and Cragie monoclines) [Simpson et al., 1985] as drill hole data indicate that the syncline is composed of displacement is transferred between segments (Figure 4). middle Cambrian through Devonian strata [Harrison, 1979, Multiple parallel and anastomosing fault strands result in 1980; Simpson et al., 1985]. The syncline plunges gently isolated blocks with anomalous orientations and structural to the southeast and Paleozoic units thicken into a deep levels within the fault zone. Stratigraphic offset indicates structural trough that may contain as much as 7500 m of west‐up, primarily dip‐slip displacement. Overturned, west Paleozoic strata [Harrison,1979,1980;Lodwick and Lindsay, dipping strata in the footwall and interpretation of seismic 1990]. A thick sequence (up to 8000 m) of Neoproter- profiles indicate that the Toomba Fault is a reverse fault ozoic sediments has been suggested to underlie Paleozoic

13 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010 strata in the southern part of the Toko Syncline based pri- [62] The Pilgrim Fault forms a major structural boundary marily on seismic and gravity data [Tucker et al., 1979; in the crystalline basement of the Mount Isa Inlier that was Harrison, 1980; Lodwick and Lindsay, 1990], although this active during the Mesoproterozoic Isan Orogeny [Blake interpretation has been disputed [e.g., Dunster et al., 2007] et al., 1984; Betts et al., 2006; Blenkinsop et al., 2008]. on the basis that low density and nonmagnetic granitoids in The Pilgrim Fault can be traced southward from the Mount basement may be mistaken for deep basin fill. Isa Inlier for at least 180 km as a zone of disturbance [58] Two separate Neoproterozoic rift basins are here and west‐up bedding offsets in Cambro‐Ordovician rocks interpreted to underlie the Toko Syncline (Figures 5 and 6) [Reynolds,1965;Casey,1968;Senior,1973;Blake et al., based on interpretation of a composite seismic line [Lechler 1984; Anderson et al., 2004]. In the Boulia region, a series and Greene, 2006] combined with depth‐to‐basement esti- of asymmetric synclines with steep west limbs dipping up mates derived from regional aeromagnetic and gravity maps to 60°E are developed east of the fault trace, whereas broad [Murray et al.,1997;Milligan and Franklin,2004;OZ west dipping panels are exposed west of the fault trace SEEBASE™ Study, 2005]. A prominent west dipping reflec- [Casey, 1968]. This geometry is typically associated with tor in seismic profiles [Harrison, 1979; Lechler and Greene, west up displacement on a west dipping reverse fault, where 2006] coincident with major discontinuities in aeromagnetic uplift and rotation on a listric fault surface results in back and gravity data indicate a west dipping normal fault and tilting of strata in the hanging wall and development of an associated basement trough underlying the eastern edge of asymmetric syncline in the footwall (e.g., Figure 13c) the Toko Syncline. A second rift basin is interpreted to [Stone, 1993; Bump, 2003]. This interpretation contrasts with underlie the axis of the Toko Syncline, based primarily on previous interpretations of the Pilgrim Fault as an east dipping aeromagnetic and gravity data. Regional geologic mapping normal fault [Casey, 1968], in which a significant phase of and seismic data show that Cambro‐Ordovician strata are post‐Ordovician extensional deformation would be implied. not significantly offset by the rift‐bounding faults underly- 3.7.1. Age Constraints ing the Toko Syncline, suggesting little or no reactivation [63] The youngest strata clearly offset by the Pilgrim Fault of these faults during the Alice Springs Orogeny. are the Cambro‐Ordovician Ninmaroo Formation [Casey, 1968; Blake et al., 1984], indicating that Paleozoic reactiva- 3.6. Sun Hill Fault tion of the fault must be syn‐ or post‐Ordovician. The struc- [59] The Sun Hill Fault (Figure 4), the next major fault tural style of the Pilgrim Fault is very similar to the Toomba east of the Toko Syncline, has exposures of Neoproterozoic Fault to the west, where syn‐orogenic deposition and defor- arkosic conglomerate (Sun Hill Arkose) in the hanging wall mation of middle Devonian Cravens Peak beds demonstrates and steeply dipping Cambro‐Ordovician strata in the foot- reverse faulting during the Alice Springs Orogeny [e.g., wall [Simpson et al., 1985], again indicating west‐up reac- Simpson et al.,1985;Haines et al.,2001;Dunster et al., tivation of a west dipping rift‐bounding normal fault. The 2007]. Other indications of the effects of the Alice Springs fault trace dies out to the northwest into a west‐up mono- Orogeny in the Burke River Structural Belt include an Early cline in Paleozoic strata. Devonian remagnetization event in Cambro‐Ordovician [60] Southwest of the Sun Hill Fault, the Marduroo 1 drill carbonates adjacent to the Pilgrim Fault [Anderson et al., hole penetrated approximately 800 m of clastic rocks that 2004] and uplift and denudation of the Mount Isa Block underlie flat‐lying Cretaceous cover and are tentatively during the Middle Carboniferous [Spikings et al., 1997]. On correlated with the Neoproterozoic Yardida Tillite [Senior, the basis of these observations, reverse reactivation of the 1973; Dunster et al., 2007]. These coincide with the west Pilgrim Fault is here interpreted to have occurred during edge of a northwest striking magnetic low and suggest the the later phases of the Alice Springs Orogeny, although the presence of another subsurface rift basin (Figure 6). available stratigraphic constraints allow for deformation as early as Early Ordovician. 3.7. Pilgrim Fault and the Burke River Structural Belt [64] Although there are no surface exposures of Neopro- terozoic strata in the hanging wall of the Pilgrim Fault, at [61] A major Neoproterozoic rift basin is here interpreted least three drill holes west of the fault zone are reported to to underlie Paleozoic strata in the Burke River Structural have penetrated Neoproterozoic clastic rocks [Senior, 1973; Belt at the southeastern edge of the Georgina Basin south Day et al., 1983; Draper, 2007]. of the Mount Isa Inlier (Figure 6). Paleozoic structures [65] Reactivation of the Pilgrim Fault caused the fault to and offset stratigraphy delineate a steeply dipping fault propagate into overlying Paleozoic strata, with resulting system, the Pilgrim Fault, that bounds the Burke River stratigraphic offset and surface expression serving to indi- Structural Belt [Blake et al., 1984; Casey, 1968]. The Pil- cate the presence of the subsurface fault. It is important to grim Fault coincides with the eastern boundary of prominent note, however, that the exact timing of reactivation is not gravity and aeromagnetic anomalies that indicate a deep directly relevant to the interpretation discussed here that a north‐south elongate subsurface basin [Tucker et al., 1979; Neoproterozoic rift basin is located in the subsurface of the Murray et al.,1997;Milligan and Franklin,2004;OZ Burke River Structural Belt west of the presently exposed SEEBASE Study, 2005; Pierson and Greene, 2008], here ™ Pilgrim Fault. interpreted as a subsurface analog of Neoproterozoic rift 3.7.2. Geophysical Expression basins exposed to the west in the hanging walls of the [66] The Pilgrim Fault coincides with the eastern boundary Toomba, Tarlton, and Lucy Creek faults. of prominent gravity and aeromagnetic anomalies [Tucker

14 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

Figure 15. Magnetic anomaly map of Australia with overlay showing major discontinuity that indicates approximate location of the Neoproterozoic continental margin (line marked TL). Georgina Basin rift sys- tem developed in the corner of a major embayment in the Neoproterozoic margin. Box shows location of study area illustrated in Figures 4 and 6. Base map is modified from the Magnetic Anomaly Map of Australia [Milligan and Franklin, 2004] and is copyright by Commonwealth of Australia–Geoscience Australia (2004). et al.,1979;Murray et al.,1997;Milligan and Franklin, SEEBASE™ Study, 2005], interpreted here as a Neoproter- 2004; Mackey et al.,1999a,1999b;Pierson and Greene, ozoic rift basin bounded to the east by the Pilgrim Fault 2008]. South from the Mount Isa Inlier discontinuous, (Figure 6). The rift basin trends N20°W, is at least 200 km patchy magnetic highs interspersed with lows merge into long by 40 km wide, and plunges to the south. The rift basin northwest trending, linear highs east of the fault trace, while is truncated to the south by a prominent northeast trending a single, large magnetic low is present west of the fault magnetic and gravity anomaly known as the Tasman Line (Figure 12) [Pierson and Greene, 2008]. Gravity data shows [e.g., Veevers, 2000; Milligan et al., 2003] that coincides broad linear bands roughly parallel to the magnetic signature with the eastern edge of exposed Proterozoic basement of but encompassing larger basement blocks. the North Australian Craton (Figures 2b and 15). [67] The Georgina Basin sedimentary rocks are magneti- 3.7.3. Northern Burke River Structural Belt cally transparent [e.g., Blake et al.,1984;Dunster et al., [69] The subsurface rift basin described above terminates 2007], and the magnetic anomaly pattern thus reflects a at its northern end at about 22°S latitude, near the southern combination of basement lithologic control and depth to edge of the exposed Mount Isa Inlier (Figure 6). In this area, basement [Mackey et al.,1999a,1999b;Seely and Keller, the trace of the Pilgrim Fault is locally indistinct as it crosses 2003]. The prominent contrast in texture as well as inten- from the east to the west side of the Burke River Structural sity across the mapped trace of the Pilgrim Fault indicates a Belt. change in depth to basement as well as a likely lithologic [70] Just north of 22°S latitude, a recent seismic line boundary in the underlying basement. [Geoscience Australia, 2008] images a gently west dipping [68] The geophysical data indicate a deep north‐south package of Cambrian and Ordovician strata that thicken elongate subsurface basin [e.g., Tucker et al.,1979;OZ westward across the northern Burke River Structural Belt to

15 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010 approximately 3000 m thick in the vicinity of the Pilgrim kilometers of structural relief are interpreted to bound Fault. The fault zone is imaged as an approximately 5 km basement‐cored uplifts [e.g., Huntoon,1993;Tindall and wide zone of distributed faulting that includes evidence of Davis, 1999; Marshak et al., 2000]. both extensional and contractional deformation, terminating [75] Where erosion on the Colorado Plateau has breached westward in a 2 km wide zone adjacent to Proterozoic monoclines and exposed sufficiently lower structural levels, basement in which there are no coherent reflectors, sug- such as in the Grand Canyon, it has been shown that these gesting the presence of steeply dipping bedding. monoclines are cored by reverse faults and that these [71] Overall, this seismic line is strikingly similar to reverse faults reactivate previous rift‐bounding normal faults seismic lines across the Toomba fault zone and Toko Syn- [Huntoon,1993;Timmons et al.,2001;Timmons and cline to the southwest [e.g., Lechler and Greene, 2006] and Karlstrom, 2007]. The primary difference between struc- supports a similar interpretation. The Pilgrim fault zone is tures in the Georgina Basin and the Colorado Plateau is in shown to be a steeply dipping zone with at least 3000 m of topographic expression. In the Colorado Plateau basement is syn‐ to post‐Ordovician west up displacement, juxtaposing not generally exposed and uplifts are indicated by broad Proterozoic crystalline basement against lower Paleozoic upwarps and bounding monclines in the overlying sedi- Georgina Basin strata. Contractional structures and indica- mentary cover rocks. In central Australia, extensive erosion tions of steeply dipping bedding within the fault zone are has breached the sedimentary cover and exposed crystalline consistent with mid‐Paleozoic contractional reactivation of a basement in the uplifted blocks. Because the felsic basement preexisting normal fault. In both the Toomba and Pilgrim was less resistant to erosion than quartz‐rich sedimentary fault zones, poor imaging of the fault zones makes direct cover rocks, an inverted topography has developed in central determination of the fault dip difficult (e.g., Figures 6 and 8) Australia, in which structurally high basement blocks are [Harrison, 1980; Geoscience Australia, 2008], but whereas generally topographically lower than surrounding areas the Toomba Fault is demonstrably west‐dipping based on (Figure 14c). outcrop data, the dip of the Pilgrim Fault in this area is [76] The timing of contractional reactivation and inversion ambiguous. in central Australia was distinctly different from that of 3.7.4. Summary and Interpretation Laramide deformation in the western United States. In central [72] The Pilgrim Fault originally formed as a Mesopro- Australia, reactivation occurred during the mid‐Paleozoic terozoic structural boundary within the Mount Isa Inlier. Alice Springs Orogeny, whereas in North America reacti- South of the Mount Isa Inlier in the southern Burke River vation occurred primarily during the Late Paleozoic Ancestral Structural Belt, the fault was reactivated in the Neoproter- Rocky Mountain and Cretaceous to Eocene Laramide oro- ozoic as a rift‐bounding normal fault or series of faults, and genies. However, the extensional fault systems that were reac- it is possible that the northern section was reactivated at this tivated are broadly synchronous [e.g., Prave, 1999; Timmons time as well. The Pilgrim Fault zone was reactivated again et al., 2001; Lund et al., 2003], having formed during a in the Paleozoic with regionally variable amounts of reverse prolonged period of rifting and continental extension asso- displacement. ciated with the Neoproterozoic breakup of Rodinia. [77] During subsequent intraplate deformation, far‐field 4. Tectonic Implications stresses related to tectonic conditions specific to each con- tinent determined the timing of reactivation. In both Australia 4.1. Reverse Faulting and Intraplate Orogeny and North America, however, a regional structural fabric [73] In the southern Georgina Basin, contractional defor- that has influenced all subsequent intracratonic deforma- mation during the mid‐Paleozoic Alice Springs Orogeny tion appears to have been established in the Neoproter- was characterized by basement block uplifts on high‐angle ozoic during the extension and breakup of Rodinia [Timmons reverse faults. These reverse faults are here interpreted to et al.,2001;Marshak and Paulsen,1996;Marshak et al., have developed by reactivation and structural inversion of 2000; Thomas, 2006]. preexisting rift‐bounding normal faults formed during Neo- proterozoic extension. 4.2. Neoproterozoic Rifting in Australia [74] Such fault‐bounded, basement‐cored uplifts formed and the Breakup of Rodinia by inversion of extensional fault systems are characteristic [78] Field and geophysical evidence summarized here of intraplate cratonic deformation in many parts of the world indicates that major reverse faults affecting Paleozoic rocks [e.g., Marshak and Paulsen, 1996; Timmons et al., 2001; in the southern Georgina Basin result from variable reacti- Gomez et al., 2000; Kley and Monaldi, 2002; Maystrenko et vation of underlying basement normal faults that bound al., 2003]. Reverse faults inverting extensional systems and Neoproterozoic rift basins. The likely extent of rift basins associated structures which formed during the Laramide associated with these known faults is shown in Figure 6. Orogeny in the western United States have been particularly Exposed Neoproterozoic rift basin fill in the hanging walls well studied and subsurface fault geometries are generally of at least six high‐angle reverse faults define rift basins up well known from seismic and drill hole data [e.g., Stone, to 110 km in length and 40 km in width. Structural and 1993; Mitra and Mount, 1998; Bump, 2003; Erslev, 2005]. geophysical data indicate subsurface rift basins underlying Structures in the southern Georgina Basin region most the Toko Syncline and Burke River Structural Belt that are closely resemble in scale and geometry structures developed on the order of 250 km in length and 50 km in width. Thus, on the Colorado Plateau, where reverse faults with a few a major system of northwest striking rift basins of Neo-

16 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010 proterozoic age underlies Paleozoic strata of the southern Georgina Basin. 4.2.1. Timing of Rifting [79] Rifting in central Australia occurred in two major phases: initial rift basin formation coeval with Sturtian glacial deposits between ∼700 and 650 Ma and renewed extension and subsidence coeval with Marinoan glacial deposits at approximately 600 Ma [Preiss et al., 1978; Walter et al., 1995; Preiss, 2000]. These phases of rifting are considerably younger than the 825–750 Ma age of mafic dikes and bimodal volcanism in Australia that are proposed to indicate a mantle superplume associated with the breakup of Rodinia [Wingate and Giddings, 2000; Li et al., 1999; Ernst et al., 2008]. Rifting in central Australia is, however, similar in age to major extensional events on the western margin of Laurentia [Lund et al., 2003] and in East Ant- arctica [Goodge et al., 2004, 2008]. In general, evidence from all continents suggests that the breakup of Rodinia was Figure 16. Mismatch of rift and transform segment orien- a complex and protracted process, involving multiple phases tations between Australia and Laurentia suggests that recon- of regional extension prior to final separation [Lund et al., structions such as SWEATandAUSWUSthatjoin 2003; Li et al., 2008]. Australia to western Laurentia cannot be correct, if Lauren- 4.2.2. Neoproterozoic Rifted Margin of Australia tia has northeast trending rift segments as shown. Mismatch [80] The Georgina Basin rift system developed in the cor- implies that either another continental block (e.g., South China ner of a major embayment in the margin of cratonic Australia. [Li et al., 2008]) was present between Australia and Laurentia This margin is defined by the eastern edge of exposed Archean or alternatively that the Laurentian margin consisted of and Proterozoic crystalline basement and has been referred to northwest trending rift segments with northeast trending as the Tasman Line [e.g., Walter et al., 1995; Li and Powell, transforms [e.g., Cecile et al., 1997; Lund, 2008]. Configu- 2001; Fioretti et al., 2005]. The boundary is poorly exposed ration of Laurentia modified from Karlstrom et al. [2001] at the surface but forms a major discontinuity on continent‐ and Sears and Price [2003]; Australia from Li and Powell scale magnetic and gravity anomaly maps (Figure 15) [e.g., [2001]. Murray et al., 1997; Milligan and Franklin, 2004] and is generally considered to approximate the Neoproterozoic con- interpreted as alternating rift and transform segments, although tinental margin of Australia (Figure 2) [Powell et al.,1994; there has been disagreement about whether the margin Myers et al., 1996; Burrett and Berry, 2000; Preiss, 2000; Li consisted of northeast striking rift segments offset by and Powell, 2001; Karlstrom et al., 2001; Li et al., 2008]. northwest striking transform faults (Figure 2b) [e.g., Shaw [81] Direen and Crawford [2003] have disputed this inter- et al., 1991; Powell et al., 1994; Myers et al., 1996; Veevers, pretation, arguing that in southern Australia the Tasman Line is 2000] or northwest striking rift segments offset by northeast formed by different ages and types of magnetic and gravity striking transform faults (Figure 2c) [e.g., Gibson, 1998; source anomalies and shows evidence of multiple deforma- Powell, 1998; Preiss, 2000; Li and Powell, 2001]. tional events. These characteristics are to be expected, however, [83] The Georgina Basin rift system is parallel to and at a Proterozoic craton margin with a long history of accretion forms a possible continuation of the northwest striking and deformation. A rifted craton margin forms a fundamental segment of the craton margin. Major northwest trending rift crustal boundary that will localize subsequent deformation, basins underlying the Toko Syncline and Burke River resulting in multiple reactivations and overprinted younger Structural Belt deepen to the southeast and are apparently deformational events contributing to the geophysical signature truncated by the northeast striking segment of the craton of the resulting boundary zone. Indeed, this is the case for the margin. These observations suggest that both the Georgina Georgina Basin rift system, in that the present geological Basin rift system and the adjacent northwest striking craton and geophysical signature of the Neoproterozoic rift basins margin developed due to northeast directed extension, with is primarily related to Paleozoic reactivation rather than to the northwest striking segment evolving into a rifted margin the original rifting event. The Neoproterozoic margins of and the northeast striking segment into a left‐lateral trans- Laurentia also show a similar pattern of younger terrane form boundary (Figure 2c). This is in accord with work in accretion overprinting an originally orthogonal rifted conti- southeast Australia and the Adelaide Rift Complex indi- nental margin, with resulting localization and reactivation of cating northeast directed extension during the Neoproter- preexisting structures [e.g., Thomas, 1991, 2006; Dickinson, ozoic [e.g., Preiss, 2000; Direen and Crawford, 2003] and 1977, 2004; Lund, 2008]. some previous tectonic interpretations [e.g., Li and Powell, [82] The Neoproterozoic continental margin of Australia as 2001]. delineated by basement exposures and prominent continent‐ [84] The intracratonic Georgina Basin rift system possibly scale geophysical anomalies consists of orthogonal northeast developed due to tip abandonment on the northwest propa- striking and northwest striking segments that have been gating rift segment, as active rifting shifted to the northeast

17 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

(Figure 2). The Georgina Basin rift system is, thus, similar Marshak and Paulsen, 1996; Karlstrom et al., 1999, 2001] in tectonic setting to other intracratonic rifts developed at rather than northeast striking transform faults as indicated rift‐transform segment boundaries, such as the Cambrian here. Similar problems arise with SWEAT reconstructions Mississippi Valley graben [Thomas, 1991] or the present‐day [Moores, 1991; Dalziel, 1991; Hoffman, 1991; Goodge et al., Gulf of Suez Rift [Khalil and Froitzheim,2001;Bosworth 2004, 2008], in which Australia is shifted northward relative et al., 2005]. to the Laurentian continental margin and matched with 4.2.3. Reconstructing Australia in Rodinia present‐day Canada. [85] The supercontinent Rodinia formed between about [87] The northwest striking rift segment configuration of 1300 and 900 Ma and broke up during a protracted series the Australian Neoproterozoic rifted margin can be more of rifting events between approximately 825 and 600 Ma easily accommodated by reconstructions such as AUSMEX [Pisarevsky et al., 2003; Li et al., 2008]. The position of [Wingate et al., 2002] that leave the margin conjugate to Australia within Rodinia continues to be a significant unknown, Australia unidentified or by reconstructions that place other and numerous potential positions and matches with features continental blocks such as Siberia [Sears and Price, 2003], on other continents have been proposed (Figure 1) [e.g., South China [Li and Powell, 2001; Li et al., 2008], or Rio de Moores, 1991; Karlstrom et al., 2001; Wingate et al., 2002; la Plata [Pisarevsky et al., 2003] adjacent to Australia. Sears and Price, 2003; Piper, 2007; Li et al., 2008]. Conti- [88] Alternatively, the geometric mismatch is resolved if nental margins proposed to match with Australia in recon- rift segments of the Laurentian margin are northwest trending structions of Rodinia should match the rift geometry and rather than northeast trending as generally assumed. Such timing outlined here. For example, as pointed out by Powell aconfiguration[e.g.,Cecile et al., 1997; Lund, 2008] would [1998], a Neoproterozoic Australian continental margin con- allow for permissible AUSWUS or SWEAT reconstructions. sisting of northwest striking rift segments with right‐stepping transform offsets (Figure 16) is not compatible with recon- [89] Acknowledgments. This research was supported by grants from structions of Rodinia such as AUSWUS that join Australia the Petroleum Research Fund and the Denison University Research Fund to a southwestern U.S. continental margin consisting of north- and was begun while a visiting researcher at the Australian National Uni- east striking, left‐stepping rift segments [e.g., Speed, 1994; versity. Generous logistical support was provided by Basil Tikoff, Lindsay Li and Powell,2001;Sears and Price,2003;Dickinson,2006]. Johannsen, and the Northern Territory Geological Survey. Tim Barton of Geoscience Australia provided reprocessed seismic data from the Toko [86] In addition, AUSWUS and similar reconstructions Syncline. I especially thank Jim Dunlap, Alfredo Camacho, and an anony- invoke northwest striking transform faults extending from mous reviewer for support, discussions, and suggestions at various stages in North America into central Australia [Brookfield, 1993; the project.

References Ambrose, G. J. (2006), Northern Territory of Australia, Buick, I. S., J. A. Miller, I. S. Williams, and I. Cartwright Casey, J. N. (1968), Boulia, Queensland, Geol. Ser. onshore hydrocarbon potential, 2006, Rec. 2006- (2001), Ordovician high‐grade metamorphism of a Explanatory Notes, Sheet SF/54-10, 30 pp., scale 003,North.Territ.Geol.Surv.,Darwin,North. newly recognized late Neoproterozoic terrane in 1:250,000, Bur. of Miner. Resour., Canberra. Territ., Australia. the northern Harts Range, central Australia, J. Meta- Cecile, M. P., D. W. Morrow, and G. K. Williams Ambrose, G. J., P. D. Kruse, and P. E. Putnam (2001), morph. Geol., 19,373–394, doi:10.1046/j.0263- (1997), Early Paleozoic (Cambrian to Early Devonian) Geology and hydrocarbon potential of the southern 4929.2001.00316.x. tectonic framework, Canadian Cordillera, Bull. Georgina Basin, Australia, APPEA J., 41, 139–163. Buick, I. S., M. Hand, I. S. Williams, J. Mawby, J. A. Can. Pet. Geol., 45, 54–74. Anderson, K. L., M. A. Lackie, D. A. Clark, and P. W. Miller, and R. S. Nicoll (2005), Detrital zircon prov- Dalziel, I. W. D. (1991), Pacific margins of Laurentia Schmidt (2004), Return to Black Mountain; palaeo- enance constraints on the evolution of the Harts and East Antarctica‐Australia as a conjugate rift magnetic reassessment of the Chatsworth and Nin- Range metamorphic complex (central Australia): pair; evidence and implications for an Eocambrian maroo Formations, western Queensland, Australia, Links to the Centralian Superbasin, J. Geol. Soc., supercontinent, Geology, 19, 598–601, doi:10.1130/ Geophys. J. Int., 157, 87–104, doi:10.1111/j.1365- 162, 777–787, doi:10.1144/0016-764904-044. 0091-7613(1991)019<0598:PMOLAE>2.3.CO;2. 246X.2003.02164.x. Buick, I. S., A. Storkey, and I. S. Williams (2008), Davis, G. H. (1978), Monocline fold pattern of the Col- Betts, P. G., and D. Giles (2006), The 1800–1100 Ma Timing relationships between pegmatite emplace- orado Plateau, Mem. Geol. Soc. Am., 151,215–233. tectonic evolution of Australia, Precambrian Res., ment, metamorphism and deformation during the Day, R. W., W. G. Whitaker, C. G. Murray, I. H. Wilson, 144, 92–125, doi:10.1016/j.precamres.2005.11.006. intra‐plate Alice Springs Orogeny, central Australia, and K. G. Grimes (1983), Queensland Geology: A Betts, P. G., D. Giles, G. Mark, G. S. Lister, B. R. Goleby, J. Metamorph. Geol., 26,915–936, doi:10.1111/ Companion Volume to the 1:2 500 000 Scale Geo- and L. Ailleres (2006), Synthesis of the Proterozoic j.1525-1314.2008.00794.x. logical Map (1975), Publ. 383, 194 pp., Geol. Surv. evolution of the Mt Isa Inlier, Aust. J. Earth Sci., 53, Bump, A. P. (2003), Reactivation, trishear modeling, of Queensland, Brisbane, Queensland, Australia. 187–211, doi:10.1080/08120090500434625. and folded basement in Laramide uplifts: Implica- Dickinson, W. R. (1977), Paleozoic plate tectonics and Blake, D. H., R. J. Bultitude, P. J. Donchak, L. A. tions for the origins of intracontinental faults, GSA the evolution of the Cordilleran continental margin, Wyborn, and I. G. Hone (1984), Geology of the Today, 13(3), 4–10, doi:10.1130/1052-5173(2003) in Paleozoic Paleogeography of the Western United Duchess‐Urandangi Region, Mount Isa Inlier, Queens- 013<0004:RTMAFB>2.0.CO;2. States: Pacific Section, edited by J. H. Stewart, C. H. land, Bull. 219, 96 pp., Geosci. Aust., Canberra. Burrett, C., and R. Berry (2000), Proterozoic Australia‐ Stevens, and A. E. Fritsche, Spec. Publ. Soc. Econ. Blenkinsop, T. G., C. R. Huddlestone‐Holmes, D. R. Western United States (AUSWUS) fit between Paleontol. Mineral., 7, 137–155. W. Foster, M. A. Edmiston, P. Lepong, G. Mark, Laurentia and Australia, Geology, 28,103–106, Dickinson, W. R. (2004), Evolution of the North Amer- J. R. Austin, F. C. Murphy, A. Ford, and M. J. doi:10.1130/0091-7613(2000)28<103:PAUSAF>2.0. ican Cordillera, Annu. Rev. Earth Planet. Sci., 32, Rubenach (2008), The crustal scale architecture of CO;2. 13–45, doi:10.1146/annurev.earth.32.101802.120257. the Eastern Succession, Mount Isa: The influence Calver, C. R., L. P. Black, J. L. Everard, and D. B. Dickinson, W. R. (2006), Geotectonic evolution of the of inversion, Precambrian Res., 163,31–49, Seymour (2004), U‐Pb zircon age constraints on late Great Basin, Geosphere, 2, 353–368, doi:10.1130/ doi:10.1016/j.precamres.2007.08.011. Neoproterozoic glaciation in Tasmania, Geology, 32, GES00054.1. Bosworth, P., W. Huchon, and K. McClay (2005), The 893–896, doi:10.1130/G20713.1. Direen, N. G., and A. J. Crawford (2003), The Tasman Red Sea and Gulf of Aden basins, J. Afr. Earth Sci., Camacho, A., W. Compston, M. McCulloch, and Line; where is it, what is it, and is it Australia’s Rodi- 43, 334–378, doi:10.1016/j.jafrearsci.2005.07.020. I. McDougall (1997), Timing and exhumation of nian breakup boundary? Aust. J. Earth Sci., 50(4), Brookfield, M. E. (1993), Neoproterozoic Laurentia‐ eclogite facies shear zones, Musgrave Block, central 491–502, doi:10.1046/j.1440-0952.2003.01005.x. Australia fit, Geology, 21,683–686, doi:10.1130/ Australia, J. Metamorph. Geol., 15,735–751, 0091-7613(1993)021<0683:NLAF>2.3.CO;2. doi:10.1111/j.1525-1314.1997.00053.x.

18 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

Draper, J. (2007), Georgina Basin; an early Palaeozoic Hand, M., J. Mawby, P. Kinny, and J. Foden (1999), brian Res., 160, 179–210, doi:10.1016/j.precamres. carbonate petroleum system in Queensland, APPEA J., U‐Pb ages from the Harts Range, central Australia: 2007.04.021. 47,107–126. Evidence for early Ordovician extension and con- Lodwick, W. R., and J. F. Lindsay (1990), Southern Dunlap, W. J., C. Teyssier, I. McDougall, and S. Baldwin straints on Carboniferous metamorphism, J. Geol. Georgina Basin: A new perspective, APEA J., 30, (1995), Thermal and structural evolution of the intra- Soc., 156, 715–730, doi:10.1144/gsjgs.156.4.0715. 137–148. cratonic Arunta nappe complex, central Australia, Harrison, P. L. (1979), Recent seismic studies upgrade Lund, K. (2008), Geometry of the Neoproterozoic and Tectonics, 14(5), 1182–1204, doi:10.1029/ the petroleum prospects of the Toko Syncline, Paleozoic rift margin of western Laurentia; implica- 95TC00335. Georgina Basin, APEA J., 19,30–42. tions for mineral deposit settings, Geosphere, 4, Dunster, J. N, P. D. Kruse, M. L. Duffett, and G. J. Harrison, P. L. (1980), The Toomba Fault and the west- 429–444, doi:10.1130/GES00121.1. Ambrose (2007), Geology and resource potential ern margin of the Toko Syncline, Georgina Basin, Lund, K., J. N. Aleinikoff, K. V. Evans, and C. M. Fanning of the southern Georgina Basin, Digital Inf. Pack- Queensland and Northern Territory, BMR J. Aust. (2003), SHRIMP U‐Pb geochronology of Neoproter- age DIP007,North.Territ.Geol.Surv.,Darwin, Geol. Geophys., 5, 201–214. ozoic Windermere Supergroup, central Idaho: Impli- North. Territ., Australia, Oct. Hoffman, P. F. (1991), Did the breakout of Laurentia cations for rifting of western Laurentia and Ernst, R. E., M. T. D. Wingate, K. L. Buchan, and Z. X. turn Gondwanaland inside‐out? Science, 252, synchroneity of Sturtian glacial deposits, Geol. Soc. Li (2008), Global record of 1600–700 Ma large 1409–1412, doi:10.1126/science.252.5011.1409. Am. Bull., 115(3), 349–372, doi:10.1130/0016- igneous provinces (LIPs): Implications for the recon- Huntoon, P. W. (1993), Influence of inherited Pre- 7606(2003)115<0349:SUPGON>2.0.CO;2. struction of the proposed Nuna (Columbia) and Rodi- cambrian basement structure on the localization Mackey, T. E., P. J. Gunn, A. J. Meixner, and D. H. nia supercontinents, Precambrian Res., 160,159– and form of Laramide monoclines, Grand Canyon, Blake (1999a), Springvale Interpreted Geology, 178, doi:10.1016/j.precamres.2007.04.019. Arizona, in Laramide Basement Deformation in scale 1:250,000, Aust. Geol. Surv. Organ., Canberra. Erslev, E. A. (2005), 2D Laramide geometries and kine- the Rocky Mountain Foreland of the Western Mackey, T. E., P. J. Gunn, A. J. Meixner, and D. H. matics of the Rocky Mountains, western U.S.A., in United States, edited by R. B. Chase and E. A. Blake (1999b), Boulia Interpreted Geology, scale The Rocky Mountain Region: An Evolving Litho- Erslev, Spec. Pap. Geol. Soc. Am., 280, 243–256. 1:250,000, Aust. Geol. Surv. Organ., Canberra. sphere, Geophys. Monogr. Ser.,vol.154,edited Huston, D. L., D. Maidment, and K. Hussey (2006), Maidment, D. W., I. S. Williams, and M. Hand (2007), by K. E. Karlstrom and G. R. Keller, pp. 7–20, Regional geology and metallogeny of the eastern Testing long‐term patterns of basin sedimentation AGU, Washington, D. C. Aileron and Irindina Provinces: A field guide, by detrital zircon geochronology, Centralian Erslev, E. A., and J. L. Rogers (1993), Basement‐cover Rec. 1448‐2177, 2006/13,44pp.,Geosci.Aust., Superbasin, Australia, Basin Res., 19,335–360, geometry of Laramide fault‐propagation folds, in Canberra. doi:10.1111/j.1365-2117.2007.00326.x. Laramide Basement Deformation in the Rocky Karlstrom, K. E., S. S. Harlan, M. L. Williams, J. McLelland, Marshak, S., and T. Paulsen (1996), Midcontinent U.S. Mountain Foreland of the Western United States, J. W. Geissman, and K.‐I. Ahall (1999), Refining fault and fold zones: A legacy of Proterozoic intra- edited by R. B. Chase and E. A. Erslev, Spec. Rodinia: Geologic evidence for the Australian‐ cratonic extensional tectonism? Geology, 24, 151– Pap. Geol. Soc. Am., 280, 125–146. western U.S. connection in the Proterozoic, GSA 154, doi:10.1130/0091-7613(1996)024<0151: Eyles, C. H., N. Eyles, and K. Grey (2007), Palaeocli- Today, 9(10), 1–7. MUSFAF>2.3.CO;2. mate implications from deep drilling of Neoprotero- Karlstrom,K.E.,K.‐I.Ahall,S.S.Harlan,M.L.Williams, Marshak, S., K. Karlstrom, and J. M. Timmons (2000), zoic strata in the Officer Basin and Adelaide Rift J. McLelland, and J. W. Geissman (2001), Long‐lived Inversion of Proterozoic extensional faults: An Complex of Australia: A marine record of wet‐ (1.8–1.0 Ga) convergent orogen in southern Laurentia, explanation for the pattern of Laramide and Ances- based glaciers, Palaeogeogr. Palaeoclimatol. its extensions to Australia and Baltica, and implications tral Rockies intracratonic deformation, United States, Palaeoecol., 248,291–312, doi:10.1016/j.palaeo. for refining Rodinia, Precambrian Res., 111,5–30, Geology, 28,735–738, doi:10.1130/0091-7613 2006.12.008. doi:10.1016/S0301-9268(01)00154-1. (2000)28<735:IOPEFA>2.0.CO;2. Fioretti, A. M., L. P. Black, J. Foden, and D. Visona Kendall, B. S., R. A. Creaser, and D. Selby (2006), Mawby, J., M. Hand, and J. Foden (1999), Sm‐Nd (2005), Grenville‐age magmatism at the South Re‐Os geochronology of postglacial black shales in evidence for high‐grade Ordovician metamorphism Tasman Rise (Australia): A new piercing point for Australia: Constraints on the timing of “Sturtian” in the Arunta Block, central Australia, J. Metamorph. the reconstruction of Rodinia, Geology, 33,769– glaciation, Geology, 34,729–732, doi:10.1130/ Geol., 17, 653–668, doi:10.1046/j.1525-1314.1999. 772, doi:10.1130/G21671.1. G22775.1. 00224.x. Freeman, M. J. (1986), Huckitta, Northern Territory, Khalil, S. M., and N. Froitzheim (2001), Tectonic evo- Maystrenko, Y., et al. (2003), Crustal‐scale pop‐up Geol. Map Ser. Explanatory Notes, Sheet SF53‐11, lution of the northwestern Red Sea‐Gulf of Suez rift structure in cratonic lithosphere; DOBRE deep seis- 58 pp., scale 1:250,000, North. Territ. Geol. Surv., system, Geol. Soc. Spec. Publ., 187,453–473, mic reflection study of the Donbas fold belt, Darwin, North. Territ., Australia. doi:10.1144/GSL.SP.2001.187.01.22. Ukraine, Geology, 31(8), 733–736, doi:10.1130/ Geoscience Australia (2008), The 2006 Mt Isa Seismic Kley, J., and C. R. Monaldi (2002), Tectonic inversion G19329.1. Survey (L180) [DVD], Canberra. in the Santa Barbara System of the central Andean McClay, K. R. (1989), Analogue models of inversion Gibson, G. M. (1998), Initiation of Rodinia breakup in foreland thrust belt, northwestern Argentina, Tecton- tectonics, in Inversion Tectonics, edited by M. A. Southeast Australia by SW‐NE extension; evidence ics, 21(6), 1061, doi:10.1029/2002TC902003. Cooper and G. D. Williams, Geol. Soc. Spec. Publ., from shear zone kinematics and dyke intrusion, Kruse, P. D., and L. C. Mohammed (2005), Geology of 44, 41–59. Geol. Soc. Aust., 50,37–38. the southern Georgina Basin, Northern Territory, 1st Milligan, P. R., and R. Franklin (2004), Magnetic Anomaly Gomez, F., W. Beauchamp, and M. Barazangi (2000), ed., geologic special, scale 1:500,000, North. Territ. Map of Australia, 4th ed., scale 1:5,000,000, Geosci. Role of the Atlas Mountains (northwest Africa) Geol. Surv., Darwin, North. Territ., Australia. Australia, Canberra. within the African‐Eurasian plate‐boundary zone, Kruse, P. D., A. T. Brakel, J. N. Dunster, and M. L. Milligan, P. R., P. Petkovic, and B. J. Drummond (2003), Geology, 28,775–778, doi:10.1130/0091-7613 Duffett (2002), Tobermory, Northern Territory, Potential‐field datasets for the Australian region: (2000)28<775:ROTAMN>2.0.CO;2. 2nd ed., Geol. Map Ser. Explanatory Notes, Sheet Their significance in mapping basement architecture, Goodge, J. W., P. Myrow, and I. S. Williams (2004), SF 53‐12,58pp.,scale1:250,000,North.Territ. in Evolution and Dynamics of the Australian Plate, Provenance of Neoproterozoic and lower Paleozoic Geol. Surv., Darwin, North. Territ., Australia. edited by R. R. Hillis and R. D. Muller, Spec. Pap. siliciclastic rocks of the central Ross Orogen, Ant- Lechler, A. R., and D. C. Greene (2006), Fault reactiva- Geol. Soc. Am., 372, 129–139. arctica: Detrital record of rift‐, passive‐, and active‐ tion during intracontinental deformation: The Toko Mitra, S., and V. S. Mount (1998), Foreland basement‐ margin sedimentation, Geol. Soc. Am. Bull., 116, Syncline and Toomba Fault, Georgina Basin, cen- involved structures, AAPG Bull., 82, 70–109. 1253–1279, doi:10.1130/B25347.1. tral Australia, Geol. Soc. Am. Abstr. Programs, Moores, E. M. (1991), SW US‐East Antarctica (SWEAT) Goodge, J. W., J. D. Vervoort, C. M. Fanning, D. M. 38, 5, 11. connection: A hypothesis, Geology, 19,425–428, Brecke, G. L. Farmer, I. S. Williams, P. M. Myrow, Li, Z. X., and C. McA. Powell (2001), An outline of the doi:10.1130/0091-7613(1991)019<0425:SUSEAS> and D. J. DePaolo (2008), A positive test of East paleogeographic evolution of the Australasian region 2.3.CO;2. Antarctica‐Laurentia juxtaposition within the Rodinia since the beginning of the Neoproterozoic, Earth Sci. Murray, A. S., M. P. Morse, P. R. Milligan, and T. E. supercontinent, Science, 321, 235–240, doi:10.1126/ Rev., 53,237–277, doi:10.1016/S0012-8252(00) Mackey (1997), Gravity anomaly map of the Austra- science.1159189. 00021-0. lian region, 3rd ed., scale 1:5,000,000, Geosci. Aust., Greene, D. C. (2003), Laramide‐style basement block Li, Z. X., I. Zhang, and C. McA. Powell (1995), South Canberra. faulting and fault inversion during the mid‐Paleozo- China in Rodinia: Part of the missing link between Myers, J. S., R. D. Shaw, and I. M. Tyler (1996), Tec- ic intraplate Alice Springs orogeny, Huckitta region, Australia‐East Antarctica and Laurentia? Geology, tonic evolution of Proterozoic Australia, Tectonics, Northern Territory, central Australia, Geol. Soc. 23,407–410, doi:10.1130/0091-7613(1995) 15(6), 1431–1446, doi:10.1029/96TC02356. Am. Abstr. Programs, 34(7), 344. 023<0407:SCIRPO>2.3.CO;2. OZ SEEBASE™ Study (2005), Public Domain Report Haines, P. W., M. Hand, and M. Sandiford (2001), Li, Z. X., X. H. Li, P. D. Kinny, and J. Wang (1999), to Shell Development Australia by FrOG Tech Pty Palaeozoic synorogenic sedimentation in central The breakup of Rodinia: Did it start with a mantle Ltd., 184 pp. and northern Australia: A review of distribution plume beneath south China? Earth Planet. Sci. Pierson, M. L., and D. C. Greene (2008), Geophysical and timing with implications for the evolution of Lett., 173, 171–181, doi:10.1016/S0012-821X(99) evidence for a Neoproterozoic rift basin underlying intracontinental orogens, Aust. J. Earth Sci., 48, 00240-X. the Burke River structural belt, eastern Georgina 911–928, doi:10.1046/j.1440-0952.2001.00909.x. Li, Z. X., et al. (2008), Assembly, configuration, and Basin, central Australia, Geol. Soc. Am. Abstr. Pro- breakup history of Rodinia: A synthesis, Precam- grams, 40(1), 68.

19 of 20 TC5010 GREENE: NEOPROTEROZOIC RIFTING CENTRAL AUSTRALIA TC5010

Piper, J. D. A. (2000), The Neoproterozoic superconti- and magnetics: Implication for hydrocarbon source Timmons, J. M., and K. E. Karlstrom (2007), Geologic nent: Rodinia or Palaeopangaea? Earth Planet. potential, AAPG Bull., 87(8), 1299–1321, doi:10.1306/ Map of the Butte Fault/East Kaibab Monocline Area Sci. Lett., 176, 131–146, doi:10.1016/S0012-821X 031903200198. Eastern Grand Canyon, Arizona, Monogr. 14, scale (99)00314-3. Senior, B. R. (1973), Machattie, Queensland, Geol. Ser. 1:24,000, Grand Canyon Assoc., Grand Canyon, Piper, J. D. (2007), The Neoproterozoic supercontinent Explanatory Notes, Sheet SG/54‐2,16pp.,scale Ariz. Palaeopangaea, Gondwana Res., 12,202–227, 1:250,000, Bur. of Miner. Resour., Canberra. Timmons, J. M., K. E. Karlstrom, C. M. Dehler, J. W. doi:10.1016/j.gr.2006.10.014. Shaw, R. D., M. A. Etheridge, and K. Lambeck (1991), Geissman, and M. T. Heizler (2001), Proterozoic Pisarevsky, S. A., M. T. Wingate, C. McA. Powell, Development of the late Proterozoic to mid‐Paleozoic, multistage (ca. 1.1 and 0.8 Ga) extension recorded S. Johnson, and D. A. Evans (2003), Models of intracratonic Amadeus Basin in central Australia: A in the Grand Canyon Supergroup and establishment Rodinia assembly and fragmentation, in Proterozoic key to understanding tectonic forces in plate interiors, of northwest‐ and north‐trending tectonic grains in East Gondwana: Supercontinent Assembly and Tectonics, 10(4), 687–721, doi:10.1029/90TC02417. the Southwestern United States, Geol. Soc. Am. Breakup, edited by M. Yoshida, B. F. Windley, and Shaw, R. D., P. K. Zeitler, I. McDougall, and P. R. Tingate Bull., 113, 163–180, doi:10.1130/0016-7606(2001) S. Dasgupta, Geol. Soc. Spec. Publ., 206, 35–55. (1992), The Palaeozoic history of an unusual intracra- 113<0163:PMCAGE>2.0.CO;2. Pisarevsky, S. A., M. T. D. Wingate, M. K. Stevens, tonic thrust belt in central Australia based on (super Tindall, S. E., and G. H. Davis (1999), Monocline devel- and P. W. Haines (2007), Palaeomagnetic results 40) Ar‐(super 39) Ar, K‐Ar and fission track dating, opment by oblique‐slip fault‐propagation folding; from the Lancer 1 stratigraphic drillhole, Officer J. Geol. Soc., 149,937–954, doi:10.1144/gsjgs. the East Kaibab Monocline, Colorado Plateau, Utah, Basin, Western Australia, and implications for 149.6.0937. J. Struct. Geol., 21, 1303–1320, doi:10.1016/S0191- Rodinia reconstructions, Aust. J. Earth Sci., 54, Shergold, J. H. (1985), Notes to accompany the Hay 8141(99)00089-9. 561–572, doi:10.1080/08120090701188962. River‐Mount Whelan Special 1:250 000 geologi- Tucker, D. H., B. W. Wyatt, E. C. Druce, S. P. Mathur, Pollard, D. D., and A. Aydin (1988), Progress in under- cal sheet, southern Georgina Basin, Rep. 251, and P. L. Harrison (1979), The upper crustal geology standing jointing over the past century, Geol. Soc. 47 pp., Bur. of Miner. Resour., Geol. and Geo- of the Georgina Basin region, BMR J. Aust. Geol. Am. Bull., 100,1181–1204, doi:10.1130/0016- phys., Canberra. Geophys., 4, 209–226. 7606(1988)100<1181:PIUJOT>2.3.CO;2. Simpson, C. J., J. H. Shergold, B. M. Radke, M. R. Veevers, J. J. (2000), Neoproterozoic‐Paleozoic Australia Powell, C. McA. (1998), Break‐up of Rodinia in Walter, G. E. Wilford, D. Green, and J. J. Draper and neighbours in Gondwanaland, in Billion‐Year Australia; implications for the western margin of (1985), Geology of the Hay River‐Mount Whelan Earth History of Australia and Neighbours in Gond- Laurentia, Geol. Soc. Am. Abstr. Programs, 30(7), 47. area, southern Georgina Basin, geological special, wanaland,editedbyJ.J.Veevers,pp.253–282, Powell, C. McA., W. V. Preiss, C. G. Gatehouse, B. Krapez, scale 1:250,000, Geosci. Aust., Canberra. GEMOC Press, Sydney, N. S. W., Australia. and Z. X. Li (1994), South Australian record of a Rodi- Skilbeck, C. G., and M. J. Lennox (Eds.) (1984), The Walter, M. R. (1980), Adelaidean and Early Cambrian nian epicontinental basin and its mid‐Neoproterozoic Seismic Atlas of Australian and New Zealand Sedi- stratigraphy of the southwestern Georgina Basin: breakup (approximately 700 Ma) to form the palaeo‐ mentary Basins,301pp.,EarthResour.Found., Correlation chart and explanatory notes, Rep. Pacific Ocean, Tectonophysics, 237,113–140, Univ. of Sydney, Sydney, N. S. W., Australia. 0084‐7100, Bur. Miner. Resour. Geol. Geophys. doi:10.1016/0040-1951(94)90250-X. Smith, K. G. (1972), Stratigraphy of the Georgina Basin, 214, BMR Microform MF92,21pp.,Aust.Geol. Prave, A. R. (1999), Two diamictites, two cap carbo- Bull. 111, 156 pp., Bur. of Miner. Resour., Geol. and Surv. Organ., Canberra. nates, two delta (super 13) C excursions, two rifts; Geophys., Canberra. Walter, M. R., and J. J. Veevers (2000), Neoproterozoic the Neoproterozoic Kingston Peak Formation, Speed, R. C. (1994), North American continent‐ocean Australia, in Billion‐Year Earth History of Australia Death Valley, Calif. Geol., 27, 339–342. transitions over Phanerozoic time, in Phanerozoic and Neighbours in Gondwanaland, edited by J. J. Preiss, W. V. (2000), The Adelaide geosyncline of Evolution of North American Continent‐Ocean Veevers, pp. 131–153, GEMOC Press, Sydney, South Australia and its significance in Neoprotero- Transitions, DNAG Continent‐Ocean Transect Vol- N. S. W., Australia. zoic continental reconstruction, Precambrian Res., ume, edited by R. C. Speed, pp. 1–86, Geol. Soc. of Walter, M. R., J. J. Veevers, C. R. Calver, and K. Grey 100,21–63, doi:10.1016/S0301-9268(99)00068-6. Am., Boulder, Colo. (1995), Neoproterozoic stratigraphy of the Centra- Preiss, W. V., M. R. Walter, R. P. Coats, and A. T. Wells Spikings, R. A., D. A. Foster, and B. P. Kohn (1997), lian Superbasin, Australia, Precambrian Res., 73, (1978), Lithological correlations of Adelaidean gla- Phanerozoic denudation history of the Mount Isa In- 173–195, doi:10.1016/0301-9268(94)00077-5. ciogenic rocks in parts of the Amadeus, Ngalia, and lier, northern Australia; response of a Proterozoic Wingate, M. T., and J. W. Giddings (2000), Age and Georgina basins, BMR J. Aust. Geol. Geophys., 3, mobile belt to intraplate tectonics, Int. Geol. Rev., palaeomagnetism of the Mundine Well dyke swarm, 43–53. 39, 107–124, doi:10.1080/00206819709465262. Western Australia; implications for an Australia‐ Reynolds, M. A. (1965), Springvale, Queensland, Geol. Stone, D. S. (1993), Basement‐involved thrust‐generated Laurentia connection at 755 Ma, Precambrian Ser. Explanatory Notes, Sheet SF/14‐14,16pp., folds as seismically imaged in the subsurface of the Res., 100,335–357, doi:10.1016/S0301-9268(99) scale 1:250,000, Bur. of Miner. Resour., Canberra. central Rocky Mountain foreland, in Laramide Base- 00080-7. Reynolds, M. A. (1968), Bedourie, Queensland, Geol. ment Deformation in the Rocky Mountain Foreland Wingate, M. T., S. A. Pisarevsky, and D. A. D. Evans Ser. Explanatory Notes, Sheet SG/54‐1,18pp., of the Western United States, edited by R. B. Chase (2002), Rodinia connections between Australia scale 1:250,000, Bur. of Miner. Resour., Canberra. and E. A. Erslev, Spec. Pap. Geol. Soc. Am., 280, and Laurentia: No SWEAT, no AUSWUS? Terra Scrimgeour, I., and J. Raith (2001), Tectonic and ther- 271–318. Nova, 14(2), 121–128, doi:10.1046/j.1365-3121. mal events in the northeastern Arunta Province, Teasdale, J., and L. L. Pryer (2002) Georgina 2002.00401.x. Rep. 12, 45 pp., North. Territ. Geol. Surv., Darwin, SEEBASE™ Project (and GIS), April‐May 2002, Zhao, J., M. T. McCulloch, and R. J. Korsch (1994), North. Territ., Australia. SRK Consulting Services report to Northern Territory Characterisation of a plume‐related approximately Sears, J. W., and R. A. Price (2000), New look at the Siber- Geological Survey, Rec. 2002‐004,North.Territ. 800 Ma magmatic event and its implications for ian connection; no SWEAT, Geology, 28, 423–426, Geol. Surv., Darwin, North. Territ., Australia. basin formation in central‐southern Australia, Earth doi:10.1130/0091-7613(2000)28<423:NLATSC>2.0. Thomas, W. A. (1991), The Appalachian‐Ouachita Planet. Sci. Lett., 121, 349–367, doi:10.1016/0012- CO;2. rifted margin of southeastern North America, Geol. 821X(94)90077-9. Sears, J. W., and R. A. Price (2003), Tightening the Soc. Am. Bull., 103,415–431, doi:10.1130/0016- Siberian connection to western Laurentia, Geol. 7606(1991)103<0415:TAORMO>2.3.CO;2. D. C. Greene, Department of Geosciences, Denison Soc. Am. Bull., 115(8), 943–953, doi:10.1130/ Thomas, W. A. (2006), Tectonic inheritance at a conti- University, Granville, OH 43023, USA. (greened@ B25229.1. nental margin, GSA Today, 16(2), 4–11, denison.edu) Seely, J. M., and G. R. Keller (2003), Delineation of doi:10.1130/1052-5173(2006)016[4:TIAACM]2.0. subsurface Proterozoic Unkar and Chuar Group sed- CO;2. imentary basins in northern Arizona using gravity

20 of 20