Gondwana Research 24 (2013) 984–998

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GR focus review A reassessment of paleogeographic reconstructions of eastern Gondwana: Bringing geology back into the equation

L.T. White a,b,⁎, G.M. Gibson c, G.S. Lister b a Southeast Asia Research Group, Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey TW200EX, United Kingdom b Research School of Earth Sciences, Building 61, Mills Road, The Australian National University, Canberra 0200, Australia c Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia article info abstract

Article history: In recent years several tectonic reconstructions have been presented for Australia–Antarctica break-up, with Received 6 December 2012 each putting the Australian plate in a different location with respect to Antarctica. These differences reflect Received in revised form 14 June 2013 the different datasets and techniques employed to create a particular reconstruction. Here we show that Accepted 25 June 2013 some of the more recent reconstructions proposed for Australia–Antarctica break-up are inconsistent with Available online 1 July 2013 both our current knowledge of margin evolution as well as the inferred match in basement terranes on the fl fi Handling Editor: M. Santosh two opposing conjugate margins. We also show how these incorrect reconstructions in uence the t of the Indian plate against Antarctica if its movement is tied to the Australian plate. Such errors can have a major Keywords: influence on the tectonic models of other parts of the world. In this case, we show how the position of the Antarctic plate Australia plate can predetermine the extent of Greater India, which is (rightly or wrongly) used by many Australian plate as a constraint in determining the timing of India–Asia, or India–Island Arc collisions during the closure of Break-up Tethys. We also discuss the timing of Australia–Antarctica break-up, and which linear magnetic features Indian plate are a product of symmetric sea-floor spreading versus those linear magnetic features that result from rifting Paleogeography of a margin. The 46 Ma to 84 Ma rotational poles previously proposed for Australia–Antarctica break-up, and confined to transitional crust and the continent–ocean transition zone, more likely formed during earlier stages of rifting rather than during symmetric sea-floor spreading of oceanic crust. So rotation poles that have been derived from magnetic anomalies in such regions cannot be used as input in a plate reconstruction. A new reconstruction of the Australia–Antarctica margin is therefore proposed that remains faithful to the best available geological and geophysical data. © 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Contents

1. Introduction ...... 985 2. Geological Criteria used to evaluate reconstructions of eastern Gondwana ...... 985 2.1. Piercing points between the Australian and Antarctic plates ...... 985 2.2. Piercing points between the Indian and Antarctic plates ...... 986 3. Reconstructing eastern Gondwana before break-up ...... 986 3.1. Australia–Antarctica ...... 986 3.2. Impact of Australia–Antarctica (mis)fits on the Indian plate ...... 987 4. The initiation of sea-floor spreading between Australia and Antarctica ...... 989 4.1. The timing of break-up according to interpretation of sea-floor magnetic anomalies ...... 989 4.1.1. Australian margin ...... 989 4.1.2. Antarctic margin ...... 990 4.2. Stratigraphic record ...... 991 5. Comparison of Australia–Antarctica reconstructions at the time of break-up ...... 992 6. Reconstructing the South Tasman Rise ...... 993 7. Reconstructing Australia–Antarctica break-up: A clean slate ...... 994

⁎ Corresponding author at: Southeast Asia Research Group, Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey TW200EX, United Kingdom. Tel.: +44 1784 276638; fax: +44 1784 434716. E-mail address: [email protected] (L.T. White).

1342-937X/$ – see front matter © 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.gr.2013.06.009 L.T. White et al. / Gondwana Research 24 (2013) 984–998 985

8. Implications for basin evolution along Australia's southern margin ...... 996 9. Conclusions ...... 996 Acknowledgments ...... 996 References ...... 996

1. Introduction 2004), eventually resulting in sea-floor spreading between India, Australia and Antarctica (Norvick and Smith, 2001). A plate tectonic reconstruction of the Earth is reliant on a series of It therefore follows that many of the rocks will have similar char- choices. The choices refer to which data sources, reference frames acteristics across each margin. This is demonstrated in the geological and/or time-scales are adopted for a particular reconstruction observations (e.g. mapping, petrology, geochemistry and geochronol- (e.g. White and Lister, 2012). These choices ultimately explain why ogy) that have been conducted over several decades along each mar- one plate reconstruction is different from another. gin (c.f. Fitzsimons, 2003; Boger, 2011; Gibson et al., 2013; Veevers, In this paper, we review existing reconstructions of the Australian 2012 and references therein) (Fig. 1). So any given plate reconstruc- plate with respect to the Antarctic plate and show how it is possible tion should position the plates in a manner that is consistent with to arrive at very different conclusions regarding the position of the these observations. We therefore used the Pplates reconstruction Australian and Indian plates within Gondwana and after its dispersal. software developed at the Australian National University to test In particular, we show how the adoption of different datasets and the validity of published reconstructions by examining how they rotational poles influence the position of these plates in various position conjugate geological terrane boundaries and key piercing reconstructions. We further test which of the existing reconstructions points that occur along the margins. for the break-up of eastern Gondwana are the most geologically plausible, and use this framework to develop a new reconstruction 2.1. Piercing points between the Australian and Antarctic plates for the evolution of this margin. We chose to review the reconstructions of Australia–Antarctica The best piercing points for reconstructions of Gondwana are because there is contention as to which of the published models is near-vertical, planar structures of the same age such as dykes or faults the best representation of available geophysical and geological data that formed after Gondwana coalesced and before it dispersed (e.g. Tikku and Cande, 1999, 2000; Whittaker et al., 2007, 2008; (i.e. between ~750 Ma and ~165 Ma) (Reeves and de Wit, 2000). Müller et al., 2008; Tikku and Direen, 2008; Williams et al., 2011; For the Australian–Antarctic margin these include the correlation of: Gibson et al., 2013). Much of the disagreement centers on: (1) which (1) the Neoproterozoic proto–Darling Fault (Australia) with its pro- reconstruction provides the best paleogeographic fit between the posed extension to an unnamed fault beneath the Scott and Denman two continents (c.f. Powell et al., 1988; Williams et al., 2011; Gibson Glaciers (Antarctica) (Harris, 1995; Fitzsimons, 2003; Boger, 2011), et al., 2013), (2) establishing when sea-floor spreading began between (2) the Paleozoic Avoca–Sorell fault system (Australia) with the the two plates (c.f. Tikku and Direen, 2008; Direen, 2011; Direen et al., Leap Year or the Lanterman faults (Antarctica) (Gibson et al., 2011, 2012) and (3) which fracture zones are considered to be conjugates of 2013), and (3) the Coorong Shear Zone (Australia) with the Mertz one another during the computation of Euler poles (c.f. Whittaker et Shear Zone (Antarctica) (Gibson et al., 2013). The Mertz Shear Zone al., 2007, 2008; Tikku and Direen, 2008; Williams et al., 2011). We had previously been correlated with the Kalinjala Mylonite Zone in examine each of these issues individually, first by discussing the South Australia but this interpretation is now considered less likely background to each problem, and by showing graphical examples following the discovery of meso-Archean crust east of the Kalinjala and potential solutions to each issue. Mylonite Zone (Fraser et al., 2010), indicating that the edge of the Please note that all Era, Period, Epoch, Stage and magnetic Delamerian orogeny occurred much further east than earlier sup- isochron ages reported in this paper refer to those in the most recent posed (e.g. Di Vincenzo et al. 2007; Goodge and Fanning, 2010). Fur- internationally recognized geological time scale (Gradstein et al., ther supporting this revised interpretation is the observation that the 2012), unless otherwise specified. This was done by adjusting Coorong and Mertz shear zones both lie along strike of the George V the age from the various time scales used in different papers to Fracture Zone whose location is thought to have been predetermined Gradstein et al. (2012) geological and magnetic time scales. However, by these two opposing crustal-scale structures (Gibson et al., 2013) some workers did not report which time scale was adopted in their (Fig. 1). study, so we were unable to update a particular age to Gradstein et Several workers have proposed that particular outcrops or al. (2012). In these cases we report the ages as they were originally samples identified on each margin can be directly correlated, and ⁎ published and highlight them with a superscript asterisk ( ). therefore represent good piercing points for plate reconstructions. This includes the correlation of the Cape Hunter Phyllite (Antarctica) with the Price-Wangary Paragneiss (Australia), which are essentially 2. Geological Criteria used to evaluate reconstructions of the same age and have similar compositions (Oliver and Fanning, eastern Gondwana 1997)(Fig. 1). Glacial erratics from the Terre Adelie Craton are also strikingly similar in age and composition to the Gawler Range Australia was part of eastern Gondwana during the Jurassic to Volcanics (Peucat et al., 2002)(Fig. 1). These similarities provide fur- upper Cretaceous (Powell et al., 1980). The development of extensive ther support for the idea that the terranes that are exposed on either half graben systems in the Bight and Duntroon Basins at ~165– margin were once connected, but they should not be used as tie 144 Ma indicates that rifting had begun between what is now rec- points for plate reconstructions as they do not match the criteria for ognized as the Australian and Antarctic plates (Totterdell et al., piercing points specified in Reeves and de Wit (2000). This is because 2000; Totterdell and Bradshaw, 2004). Rifting was driven by the it is difficult, if not impossible to establish the precision of such corre- fragmentation of Gondwana, which resulted in a triple junction lations because the surface expression of a geological unit can be with arms extending between present-day India–Antarctica, India– quite extensive (particularly for a unit with a shallow dip), or because western Australia and southern Australia–Antarctica (McGowran, 1973; a unit might only be exposed in certain locations on either margin. Deighton et al., 1976; Hegarty et al., 1988; Stagg et al., 1990; Willcox The precision is even lower in the case of sampling sites of glacial and Stagg, 1990; Norvick and Smith, 2001; Totterdell and Bradshaw, erratics, which have clearly been transported after being exposed on 986 L.T. White et al. / Gondwana Research 24 (2013) 984–998

130°E 140°E

120°E 150°E

110°E 160°E CoSZ Tasmanides

New England

DF

100°E Fold Belt 170°E AF COB

Naturaliste FZ Leeuwin FZ Tasman 180°E 90°E FZ V George Sea

WSTR 30°S

ESTR Tasman FZ Tasman

Southern

Ocean FZ Balleny 40°S

Transitional crust 50°S Continent-Ocean Transition Zone COB PSFZ Undifferentiated Continental Crust Vincennes FZ

New England Fold Belt MSZ 60°S UF Terrains and/or Gondwana derived turbiditic sediments accreted 510-300 Ma

LYF ANT: Bowers Terrane LFZ AUS: Grampians-Stavely zone 70°S Reworked passive margin sediments (Ediacaran to Cambrian) ANT: Mawson Craton (Late Archean) Spreading Ridge AUS: Gawler Craton, Curnamona Province, Adelaide Supergroup

Coompana Block (undifferentiated Palaeo and Mesoproterozoic) 80°S Fault, Shear Zone or Fracture Zone (FZ)

Rayner Belt (990-900 Ma) Tie Point (Fault) ANT: Crohn Craton Albany-Fraser Belt (1330-1140 Ma) Gawler Range Volcanics (Aus.) / Moraine equivalents (Ant.) AUS: North Australian Craton Pinjarra Belt (1330-1140 Ma) Cambrian collisional belts (530-490 Ma) Price Wangary Paragneiss (Aus.) / Cape Hunter Phyllite (Ant.)

Fig. 1. Tectonic element map of Australia, Antarctica and the Southern Ocean showing the terrane and structural boundaries used here. The geological boundaries and structures were adapted from Harris (1995), Oliver and Fanning (1997), Yuasa et al. (1997), Tikku and Cande (1999), Peucat et al. (2002), Whittaker et al. (2007), Boger (2011) and Gibson et al. (2011). Abbreviations: FZ = fracture zone, DF = Darling Fault, CoSZ = Coorong Shear Zone, AF = Avoca Fault, MSZ = Mertz Shear Zone, LFZ = Lanterman Fault Zone, LYF = Leap Year Fault, UF = unnamed fault (underlying the Scott/Denman Glacier), COB (continent–ocean boundary), WSTR (West South Tasman Rise) and ESTR (East South Tasman Rise). The COB polygons were provided by colleagues at Geoscience Australia and are essentially the same as those shown in Direen et al. (2012). the surface. Given these limitations, none of these features were used Wilson, 2003; Lisker, 2004; Golynsky et al., 2005; Veevers and Saeed, as piercing points in the reconstructions presented in this paper. We 2008, 2009; Ferraccioli et al., 2011; Veevers, 2012). We have also instead used the position of terrane boundaries as per the maps of used the map/extent of Greater India as was proposed by Ali and Boger (2011) and Gibson et al. (2011; 2013) (Fig. 1) as the location Aitchison (2005) in the reconstructions of the Indian plate. and age of these terranes is relatively well known along the Australian and Antarctic coastlines, defined from studies by workers such as Oliver and Fanning (1997) and Peucat et al. (2002). 3. Reconstructing eastern Gondwana before break-up

2.2. Piercing points between the Indian and Antarctic plates 3.1. Australia–Antarctica

We also investigated how the position of the Indian plate in A significant amount of lithospheric stretching occurred before Gondwana can be influenced by reconstructions of the Australian Australia and Antarctica separated (Lister et al., 1986; Powell et al., plate with respect to Antarctica. To evaluate existing reconstructions 1988; Veevers and Eittreim, 1988; Lister et al., 1991; Sayers et al., of the fit of India with Australia and Antarctica we used a similar 2001; Totterdell and Bradshaw, 2004; Espurt et al., 2009, 2012). rationale as proposed above. That is, we used the position of conjugate This deformation cannot be accounted for in traditional reconstruc- terrane boundaries on the Indian and Antarctic plates as per Boger tions, as tectonic plates are treated as rigid blocks that are rotated (2011) to test which of the existing reconstructions produced the about the surface of the Earth. Nor can this deformation be quantified best fit. In this example we also used position of the Lambert Rift by using sea-floor magnetic anomalies as these are not produced in (Antarctica) with the Mahanadi Rift (India) and the Robert Glacier the earliest phases of continental rifting, or if they are, they are Rift (Antarctica) with the Pranhita–Godavari Rift (India) after the more likely magnetic anomalies associated with exhumed peridotites geological maps (not the reconstructions) of Harrowfield et al. (2005) (e.g. Sibuet et al., 2007). Tectonocists have therefore used the geom- and Veevers (2012). These represent Permian rift basins that were etry of bathymetric contours or the edge of the continent–ocean dissected when India and Antarctica broke apart. They are considered boundary to create “best-fit” rotation poles to account for the excellent piercing points for full-fit reconstructions of India and Antarc- crustal extension related to plate break-up (e.g. Carey, 1958; Sproll tica as the edges of the rifts are delineated by relatively steep faults and and Dietz, 1969; Powell et al., 1988), while some have also made an because the rocks from each basin are the same age on each margin attempt to restore the amount of stretch crust along the margin (Federov et al., 1982; Harris, 1994; Mishra et al., 1999; Boger and (e.g. Williams et al., 2011; Veevers, 2012). L.T. White et al. / Gondwana Research 24 (2013) 984–998 987 a 165 Ma: Powell et al. (1988) Though many of these reconstructions have not been adequately tested with geological data and others have been produced with paper “cut-outs” that do not account for distortion associated with projected two-dimensional plates being rotated around a sphere. We therefore propose that the most appropriate reconstructions of Australia and Antarctica's pre-rift fit will be those that most faithfully reposition the plates so that the conjugate geological terranes and structures (see Section 2) are aligned. In order to test this proposition we restored the position of the Australian plate with respect to Antarctica at ~165 Ma (Fig. 2a–c) and ~120 Ma (Fig. 2d–e) according to the Euler poles summarized in Supplementary File 1. We also com- pared several reconstructions of Australia and Antarctica at ~100 Ma (Supplementary File 2). b 165 Ma: Royer and Sandwell (1989) The best fit of geological terrane boundaries for the conjugate rift margins in Australia and Antarctica is obtained by the reconstructions of Powell et al. (1988) and Veevers and Eittreim (1988) (Fig. 2a, d, Sup- plementary File 2). The other reconstructions shift Australia further to the east with respect to Antarctica and this produces sub-optimal fits between the conjugate terranes (Fig. 2b, c, e and Supplementary File 2). These misfits are most likely produced by attempting to mini- mize the overlap of the South Tasman Rise and Victoria Land, as is shown in many of the 165 Ma–99 Ma reconstructions (Fig. 2 and Supplementary File 2). While the Powell et al. (1988) reconstruction has the best overall match of terrane boundaries between Australia and Antarctica, it does however have a greater overlap of the South Tasman Rise and Victoria Land relative to the reconstructions of c 165 Ma: Williams et al. (2011) Veevers and Eittreim (1988), Royer and Sandwell (1989), Müller et al. (2008), Williams et al. (2011) and Gibbons et al. (2012).

3.2. Impact of Australia–Antarctica (mis)fits on the Indian plate

The pre-rift fit of Australia with respect to Antarctica has significant implications for where other plates are positioned in reconstructions of Gondwana. We show here how some workers have rotated the Indian plate with respect to Australia in their reconstructions of Gondwana (e.g. Müller et al., 2008), whereas others have rotated India relative to Antarctica (e.g. Powell et al., 1988; Gibbons et al., 2012). If the Indian plate is rotated relative to the Australian plate, and Australia is rotated d 120 Ma: Powell et al. (1988) relative to Antarctica, then India's location will be influenced by where Australia is positioned with respect to Antarctica. As we have shown that there are considerable differences in where the Australian plate is positioned with respect to Antarctica (Fig. 2 and Supplementary File 2), it follows that there will be repercussions for the positioning of the Indian plate. This is highlighted if we use the Euler poles of Müller et al. (2008) to rotate India relative to Australia, and then rotate Australia relative to Antarctica according to the 165 Ma rotation pole proposed by: (1) Powell et al. (1988) (Fig. 3c); (2) Royer and Sandwell (1989) (Fig. 3d) and (3) Williams et al. (2011) (Fig. 3e) and compare how each of these reconstructions positions terrain boundaries and tie points between India and Antarctica. This comparison indicates that the best geological fits for India– e 120 Ma: Müller et al. (2008) Australia–Antarctica are obtained by using the Powell et al. (1988) and Royer and Sandwell (1989) Euler pole data (Fig. 3a–b). The Williams et al. (2011) “hybrid-pole” shifts Australia too far eastward with respect to Antarctica, so India is similarly shifted eastward, resulting in a large overlap between the Indian and Antarctic plates, as well as a significant misfit between the conjugate geological boundaries of India and Antarctica when using the Euler poles of Müller et al. (2008) for India's position relative to Australia (Fig. 3c).

Fig. 2. Reconstructions proposed by various workers for Australia's position relative to Antarctica at 165 Ma and 120 Ma. Reconstructions use the Euler poles of: (a) Powell et al. (1988); (b) Royer and Sandwell (1989), (c) Williams et al. (2011); (d) Powell et al. (1988) and (e) Müller et al. (2008). The best geological fit for both intervals is obtained using the Euler poles of Powell et al. (1988). 988 L.T. White et al. / Gondwana Research 24 (2013) 984–998

a b

Greater India* Greater India*

Australia rotated relative to Antarctica (Powell et al. 1988) Australia rotated relative to Antarctica (Royer and Sandwell 1989) India rotated relative to Australia (Müller et al. 2008) India rotated relative to Australia (Müller et al. 2008) c d

Greater India* Greater India*

Australia rotated relative to Antarctica (Williams et al. 2011) Australia rotated relative to Antarctica (Powell et al. 1988) India rotated relative to Australia (Müller et al. 2008) India rotated relative to Antarctica (Powell et al. 1988) e

Greater India* Continent-Ocean Transition Zone

Ediacaran-Cambrian collisional belt (550-520 Ma)

Maud-Natal Belt (1130-1060 Ma) Coats Land Block - folded basement and undeformed Mesoproterozoic volcanic rocks (1100 Ma)

Ediacaran collisional belt (580-550 Ma)

Reworked passive margin sediments (Ediacaran to Permian)

Fault / Shear Zone Current position of the Indus-Tsangpo Suture Zone rotated with India Current position of the Main Frontal Thrust rotated with India Australia rotated relative to Antarctica (Gibbons et al. 2012) India rotated relative to Antarctica (Gibbons et al. 2012)

Fig. 3. The effect of error propagation in a plate circuit (where one plate is rotated with respect to another). In this case, several Euler poles were used to rotate Australia with re- spect to Antarctica at 165 Ma (see Supplementary File 1). The Indian plate was rotated with respect to the Australian plate using the full-fit Euler pole of Müller et al. (2008) (Latitude: 11.8°/Longitude: −175.8°/Angle: 63.81°/Age: 136.2 Ma). The best geological fit is obtained for the Australian, Antarctic and Indian plates when using the Euler poles of (a) Powell et al. (1988). The other reconstructions (b–c) translate Australia further to the east and produce a poorer geological fit between India and Antarctica. The error prop- agation can be reduced if the Indian plate is rotated relative to Antarctica instead of being tied to the Australian plate using the poles of (d) Powell et al. (1988) and (e) Gibbons et al. (2012). In this case the best geological fit is again obtained with the Euler poles of Powell et al. (1988). Significant misfits are produced in the Gibbons et al. (2012) reconstruction. This also highlights how different Euler poles and plate circuits can influence impressions of the extent of Greater India.

Interestingly, rotating India relative to Australia according to the extends to the Wallaby–Zenith plateau (Fig. 3b–d). This has Müller et al. (2008) poles, means that the Greater India polygon of implications for establishing the timing of India–Asia collision or the Ali and Aitchison (2005) could be extended by ~50 km so that it accretion of island arcs to the northern margin of India as it moved L.T. White et al. / Gondwana Research 24 (2013) 984–998 989 northward towards Eurasia, providing that the position and shape of between 49.34 Ma and 42.30 Ma (chrons 22–20) (Weissel and Hayes, the ancient southern margin of Eurasia and/or Tethyan island 1971, 1972; Weissel et al., 1977). However, Cande and Mutter (1982) arcs could be accurately and precisely located. While numerous stated that chrons 22 to 19 of Weissel and Hayes (1972) were paleomagnetic studies have attempted to define the extent of the an- misinterpreted, and were, in fact, anomalies 34 to 20. This meant cient margins, they all result in a range of latitudes that effectively that sea-floor spreading must have initiated between Australia and demonstrate that the uncertainty of the results derived from this Antarctica by 84 Ma, but could have begun earlier (110–90 Ma) technique can be in the order of 1000 km. (Cande and Mutter, 1982). The need to extend Greater India is reduced if India is instead rotated This was contested by Veevers (1986), who proposed that chron relative to Antarctica according to the poles proposed by Powell et al. 34 of Cande and Mutter (1982) did not represent oceanic crust, (1988) (Fig. 3d) and Gibbons et al. (2012) (Fig. 3e). The best geological but represented a magnetic anomaly at the youngest edge of the fit is obtained with the Euler poles proposed by Powell et al. (1988) who continent–ocean boundary. Veevers (1986) calculated an age of rotate Australia with respect to Antarctica, and India with respect to 99 ± 5 Ma at the oldest edge of the continent–ocean boundary by ex- Antarctica (Fig. 3d). However, this reconstruction would mean that trapolating the spreading rate between it, and the oldest magnetic the northern extent of Greater India (as per Ali and Aitchison, 2005) anomaly (chron 34y). Several reconstructions adopted the 99 ± must be shortened slightly to remove its overlap with the Wallaby– 5 Ma age as the time when sea-floor spreading initiated (Powell et Zenith Plateau. Trimming this northern margin of Greater India would al., 1988; Veevers and Eittreim, 1988; Veevers et al., 1991). result in a younger age of India–Asia, or India-arc collision. However, Other workers considered that sea-floor spreading may have this again presupposes that the estimated shape of a continent can be begun earlier due to the interpretation of Mesozoic (“M-Series”) used as a constraint and then only if the position and extent of Eurasia anomalies south of the Eyre sub-basin and west of the Ceduna and the arcs can be established precisely. sub-basin (Stagg et al., 1990; Stagg and Willcox, 1992). Interpretation The fitoftheAli and Aitchison (2005) Greater India is essentially of these data indicated that sea-floor spreading between Australia perfect when using the Euler poles of Gibbons et al. (2012). However, and Antarctica could have occurred during the Hauterivian this also means that there is a significant misfit between the Indian– (134–130 Ma) west of the Ceduna sub-basin, and continued crustal Antarctic terrane boundaries (Fig. 3e). As the fit between Greater extension, or a second phase of sea-floor spreading produced the India and the Wallaby–Zenith Plateau is essentially perfect in Gibbons younger magnetic isochrons that are observed eastward. et al. (2012),wewonderiftheAli and Aitchison (2005) Greater India However, subsequent interpretations of magnetic and gravity data polygon was used as a constraint to fit India to Australia and Antarctica, indicated that the initiation of spreading was much younger (Tikku instead of using other data such as the position of conjugate geological and Cande, 1999). Tikku and Cande (1999) proposed that the edge terranes? In any case, this demonstrates that there is some uncertainty of the magnetic quiet zone was not a true magnetic isochron as it as to where the Indian plate is positioned with respect to Australia and resulted in an overlap between Tasmania, the South Tasman Rise Antarctica, and that there is some flexibility in defining the northern ex- and Wilkes Land. Tikku and Cande (1999) therefore tentatively pro- tent of Greater India if it cannot extend further than the Wallaby–Zenith posed that anomaly 34y (83.64 Ma) was the oldest possible magnetic Plateau (as proposed by Ali and Aitchison, 2005). Yet, the obvious geo- isochron between Australia and Antarctica. They also stated that the logical misfits highlight the importance of using geological observations anomalies 34y, 33o and 32y could have been falsely identified as to constrain interpretations of geophysical data. true magnetic anomalies, and thus that spreading perhaps did not As the best geological fit for India–Antarctica is obtained with the initiate until after 32y (71.45 Ma). pole of Powell et al. (1988), we used these to restore India relative to The assertion that spreading had begun by ~84 Ma was supported Antarctica and trimmed the northern extent of Ali and Aitchison's by the work of Sayers et al. (2001), who showed that the basement Greater India so that it does not extend further than the Wallaby– ridge complex in the Great Australian Bight was most likely Zenith Plateau. This polygon is provided as an ArcGIS shapefile for composed of serpentinized peridotite ridges and mafic magmatism those workers who are interested in investigating this subject further derived by mantle upwelling and limited partial melting. These (Supplementary File 3). magmas were said to cool during chron 34 (125.93–83.64 Ma), producing a distinctive magnetic anomaly that was unrelated to 4. The initiation of sea-floor spreading between Australia sea-floor spreading (Sayers et al., 2001). Later reconstructions of and Antarctica Australia–Antarctica break-up therefore used the 83.64 Ma age as the timing of the initiation of sea-floor spreading (e.g. Norvick and Rifting of Australia and Antarctica continued episodically from Smith, 2001) and interestingly this break-up age was the preferred ~165 Ma and eventually the lithosphere was stretched so much that age for break-up in the earlier reconstruction of Tikku and Cande subcontinental lithospheric mantle was exhumed before seafloor (2000). spreading initiated. The position of the plates during this time is poor- Other workers reverted to an older age for Australia–Antarctica ly constrained. The first appearance of true oceanic crust represents break-up in their reconstructions (Whittaker et al., 2007; Boger, an important component of reconstructions of Australia and Antarcti- 2011). Whittaker et al. (2007) proposed that break-up occurred at ca as the first oceanic fracture zones and magnetic anomalies on the 96 Ma* based on an extrapolation of the spreading rate between the sea-floor allow us to establish the position of the plates with respect oldest magnetic anomaly (chron 34: ~83.64 Ma) and the edge of to one another. However, there is considerable debate as to what the magnetic quiet zone, the same rationale adopted by Veevers represents the first oceanic crust (e.g. Sayers et al., 2001; Tikku and (1986). Tikku and Direen (2008) queried why Whittaker et al. Direen, 2008; Whittaker et al., 2008), so we have reviewed the (2007) adopted this age, as previous work clearly stated that the various arguments and the available data to help us produce a revised magnetic quiet zone was an inappropriate constraint on the timing reconstruction of the margin. of break-up. This was because: (1) on the Australian margin some of what had previously been interpreted as magnetic anomalies 4.1. The timing of break-up according to interpretation of sea-floor older than chron 20n(o) (43.43 Ma) were actually serpentinised magnetic anomalies peridotites and that chron 33n(o) (79.90 Ma) was the oldest true magnetic isochron (e.g. Tikku and Cande (1999); Sayers et al. 4.1.1. Australian margin (2001)) and; (2) investigations of the Antarctic margin showed that The earliest work on the magnetic isochrons between Australia true oceanic crust was erupted on the Antarctic Wilkes margin and Antarctica was taken to indicate that sea-floor spreading initiated between chron 32n(y) (71.45 Ma) and 33n(y) (74.31 Ma) (Colwell 990 L.T. White et al. / Gondwana Research 24 (2013) 984–998 et al., 2006). This means that the older Euler poles proposed by the Australian and Antarctic margins (Fig. 4). This shows that the Whittaker et al. (2007) could not have been picked from true mag- oldest end of chron 33n (79.90 Ma) is the oldest anomaly located in netic isochrons. Whittaker et al. (2008) responded by stating that oceanic crust along Australia's southern margin, and chron 34 their work presented an alternate hypothesis, where long symmetric (83.64 Ma), which is often taken as the timing of the initiation of magnetic anomalies were produced due to slow, relatively amagmatic sea-floor spreading, is entirely within the Australian continent– spreading. However, this reasoning was not adopted in subsequent ocean transition zone. Further to the east, the magnetic anomalies reconstructions produced by the same authors who reverted to a are younger according to Royer and Rollet (1997) (Fig. 5). Off the ~84 Ma break-up age (Müller et al., 2008; Williams et al., 2011). west coast of Tasmania, the oldest magnetic anomalies are chron Boger (2011), in a more recent reconstruction of Australia and 18n.2no (40.15 Ma) and chron 17n.3no (38.33 Ma). However, Royer Antarctica, adopted the 96 Ma* break-up age proposed by Veevers and Rollet (1997) also identified several other anomalies to the (1986). The adoption of a single age for break-up was later south of Tasmania and the South Tasman Rise that were at least as questioned by Direen (2011) who argued instead that the initiation old as 53.98 Ma (chron 24n.3no), and potentially as old as 69.27 Ma of sea-floor spreading between Australia and Antarctica was (chron 31no) (Fig. 5). diachronous as evidenced by information gleaned from deep-sea dredging and the interpretation of seismic reflection data. In discussing the idea of diachronous sea-floor spreading initiation fur- 4.1.2. Antarctic margin ther, Direen et al. (2012) reported that spreading was thought to The oldest continuous magnetic anomaly on the Antarctic margin have first occurred in the west, off the Naturaliste–Bruce Rise and is the youngest end of chron 21n (45.72 Ma) (Fig. 4). The majority of Bremer Basin (93–87 Ma: Beslier et al. (2004); Halpin et al. (2008)), older magnetic anomalies on the Antarctica margin are at least par- before progressing into the central Great Australian Bight tially, if not entirely within the continent–ocean transition zone (85–83 Ma), and then followed by separation in the western Bight (Fig. 4). This means that those anomalies that have been identified (~65 Ma), and the Terre Adelie–Otway region (~50 Ma) (Fig. 1). In within the transition zone cannot represent true magnetic isochrons view of this progressive development, Direen et al. (2012) stated produced during symmetric seafloor spreading, and thus cannot be that it is highly unlikely that the age of break-up can be defined used reliably if at all to calculate Euler poles for a plate reconstruction. using one isochron. Rather, in their view the age of break-up should Alternatively, the Geoscience Australia continent–ocean boundary be determined using all available (e.g. magnetic isochron picks, stra- may not be everywhere correct and need further refinement. Howev- tigraphy and the interpretation of reflection seismic data combined er, as this continent–ocean boundary is based on the interpretation of with petrographic information obtained from dredge samples and seismic reflection data from both the Australian and Antarctic drill holes). margins (it is similar to that shown in Direen et al., 2012 which was We investigated this issue further by plotting the magnetic anom- derived from most of the same sources) we are confident that this aly identifications of Whittaker et al. (2007) with Geoscience is the best estimation of the location of the continent–ocean bound- Australia's current estimate of the continent–ocean boundaries for ary and continental–oceanic transition zone.

a 200 km Magnetic Anomaly Age (Ma)

QZB QZB QZB 35°S 83.64Ma 83.64 83.64 71.45 Ma 79.90 Ma 79.90 79.90 53.98 Ma 71.45 71.45 45.72 Ma 69.27 69.27 43.43 Ma 33.71 Ma

62.22 62.22 115°E 140°E 33.71 Ma 53.98 53.98 28.28 Ma 31.03 Ma 40°S 45.72 45.72 28.28 Ma 33.71 Ma b 31.03 Ma 43.43 43.43 43.43 Ma 60°S 33.71 33.71 Ma 31.03 71.45 Ma 45.72 Ma 79.90 Ma 28.28 45.72 Ma 83.64 Ma Seamount B QZB 25.99 Linear magnetic 83.64 Ma 65°S features that may

have previously been 115°0'0"E mistaken for isochrons

200 km

110°E 150°E 130°E

Fig. 4. The magnetic isochron identifications of Whittaker et al. (2007) for the Australian and Antarctic margins plotted against the geological terrane boundaries shown in Fig. 1 for: (a) the Australian margin, and (b) the Antarctic margin. L.T. White et al. / Gondwana Research 24 (2013) 984–998 991

Antarctic plates — cf. Gaina et al., 2007; Jokat et al., 2010). This scenario 53.98 Ma also depends on competing hypotheses as to whether Australia– 40°S Antarctica rifting occurred symmetrically (e.g. Colwell et al., 2006; Direen et al., 2012) or if it involved an early phase of symmetric rifting, followed by asymmetric rifting prior to eventual sea-floor spreading (Espurt et al., 2012). However, further investigations as to the nature 40.15 Ma of stretching along the margin are required as the results of the Espurt

WSTR et al. (2012) model are dependent on the 84 Ma rotational pole pro- 68.27 Ma? posed by Whittaker et al. (2007) that has since been disproved (Tikku 38.33 Ma ESTR 59.28 Ma? and Direen, 2008; Direen et al., 2012; This Paper). A resolution to this 53.98 Ma 43.43 Ma problem is important, as it contradicts another interpretation that indi- 40.15 Ma cates that the evolution of the Australian–Antarctic margin during 38.33 Ma break-up was dominantly symmetrical (Direen et al., 2011, 2012). This 36.70 Ma 50°S said, it is possible that some sections of each margin developed due to 35.29 Ma symmetric rifting, and others due to asymmetric rifting where exhumed 33.71 Ma mantle is juxtaposed against sections of the upper plate along transfer 31.03 Ma 29.97 Ma 25.99 Ma faults on both the Australian and Antarctic margins (c.f. Fig. 3 of Lister 28.28 Ma 24.47 Ma et al., 1986). So a resolution to this issue will not be reached without 27.44 Ma 23.30 Ma 22.27 Ma studies of numerous sections along the Australian and Antarctic margins. 20.71 Ma 19.72 Ma 4.2. Stratigraphic record

The stratigraphic record indicates that there were successive phases of rifting and subsidence between Australia and Antarctica prior to continental break-up. Much of this work has focused on the geology of Australia's southern margin sedimentary basins, conducted 250 km by Geoscience Australia (and its predecessor organizations) over 60°S 140°E 150°E many years for the purpose of understanding the evolution of hydro- carbon systems. The stratigraphic record is generally divided into Magnetic Anomaly Age (Ma) several tectonic/temporal phases, yet it is also recognized that the 2.58 19.72 27.44 38.33 lithospheric thinning has been a progressive process from west to east (Deighton et al., 1976; Hegarty et al., 1988; Willcox and Stagg, 6.03 20.71 28.28 40.15 1990; Totterdell et al., 2000; Norvick and Smith, 2001; Direen et al., 11.65 21.16 29.97 43.43 2012). The extension between Australia and Antarctica led to a broad 15.16 22.27 31.03 45.72 zone of faults forming between the Australian and Antarctic plates. 16.72 23.30 33.71 53.98 This is commonly referred to as the Southern Rift System (SRS) 17.53 24.47 35.29 59.28 after Stagg et al. (1990, 2005). The SRS extends from Broken Ridge– Naturaliste Plateau and Kerguelen Plateau in the Indian Ocean to 18.52 25.99 36.70 68.27 the South Tasman Rise, south of Tasmania (Stagg et al., 1990, 2005; Direen et al., 2011). The earliest phase of rifting of this system is doc- Fig. 5. The age of the magnetic anomalies west and south of the South Tasman Rise as umented in the western Bight Basin in the Callovian (166–163 Ma) were interpreted by Royer and Rollet (1997). Their interpretation indicates that the and consisted of ~300 km of NW–SE directed extension (Willcox isochrons are N10 Ma younger than those that have been identified west of the George and Stagg, 1990; Totterdell et al., 2000; Norvick and Smith, 2001; V Fracture Zone, but also N10 Ma older than those identified west of the Tasman Fracture Zone. WSTR = West South Tasman Rise, ESTR = East South Tasman Rise. Blevin and Cathro, 2008). Rifting progressively moved eastwards, producing the Duntroon sub-basin and Otway and Gippsland basins during the Tithonian (152–145 Ma). As rifting was progressive The fact that linear magnetic features occur within the continental– along the margin, the structural style of the western Bight Basin had oceanic transition zone of both the Australian and Antarctic margins has changed to thermal subsidence by the Valanginian (139–134 Ma) been noted before (e.g. Tikku and Direen, 2008) and is usually attribut- while fluvio-lacustrine rift sedimentation continued until the ed to the presence of exhumed mantle rocks (Sayers et al., 2001)ashas Barremian (131–126 Ma) in the Duntroon sub-basin and the Otway been observed elsewhere wherever stretching occurs between two and Gippsland basins (Totterdell et al., 2000; Norvick and Smith, plates (e.g. Lister et al., 1986, 1991; Sutra and Manatschal, 2012). In 2001). the present instance, the mantle rocks were exhumed as elongate ridges A second phase of rifting (oriented NNE–SSW) began during the along different segments of the Australian and Antarctica plates Berriasian (145–139 Ma) and is observed in the western Otway (e.g. Niida and Yuasa, 1995; Yuasa et al., 1997; Sayers et al., 2001; Basin (Blevin and Cathro, 2008). This was associated with a period Direen et al., 2012). These belts of exhumed mantle material are mag- of slow movement between what were to eventually become the netic, so it is possible that earlier workers mistook the magnetic signals Australian and Antarctic plates (Norvick and Smith, 2001). This as symmetrical stripes that were produced due to sea-floor spreading. phase resulted in stress reorganization, the uplift in eastern Australia As these mantle rocks were exhumed due to symmetric (e.g. Direen et and different evolutionary paths of the southern margin basins al., 2012) or asymmetric stretching (e.g. Espurt et al., 2012) rather (Norvick and Smith, 2001). than symmetric sea-floor spreading, they cannot be used to constrain A third phase of rifting (oriented NNE–SSW) began in the the position of the Australian plate with respect to the Antarctic plate. Turonian (93.9 Ma) to Late Maastrichtian (66.0 Ma) and is observed This might also apply to other plates where there is contention as to in the Otway, Sorell and Bass basins (Blevin and Cathro, 2008). This what the oldest evidence of magnetic anomalies (e.g. the discrepancy phase of extension coincides with the cessation of spreading in the in ages of interpreted magnetic anomalies between the Indian and Tasman Sea, the onset of rapid northward motion of the Australian 992 L.T. White et al. / Gondwana Research 24 (2013) 984–998 plate (~45 Ma) and culminated in the final separation of Australia/ a South Tasman Rise and Antarctica at ~34 Ma (Totterdell et al., 2000; Norvick and Smith, 2001). It coincides with a major change in the pat- tern of sedimentation where a thin layer of marine/shelf carbonates was deposited between the Paleocene–Early Eocene and the Middle Eocene (McGowran, 1973) and it also corresponds with a period of mantle exhumation within the continent–ocean transition zone of the Australian plate from ~84 Ma to possibly 45 Ma, thus explaining the elongate magnetic anomalies that are exposed along the southern margin (Sayers et al., 2001) (e.g. Figs. 4, 5). This said, we must also consider that rifting, sedimentation style and sea-floor spreading were diachronous along the margin (Norvick and Smith, 2001; 84 Ma: Powell et al. (1988) & Veevers et al. (1991) Direen, 2011), and that changes in sedimentation style are not neces- sarily caused by tectonic forces and could instead reflect processes b such as subsidence and/or sea-level rise.

5. Comparison of Australia–Antarctica reconstructions at the time of break-up

As we showed that there were considerable differences in recon- structions of Australia and Antarctica at ~165 Ma, ~120 Ma and ~100 Ma (Fig. 2 and Supplementary Data 2), we consider it important to make another comparison at the time of break-up. We therefore compare several reconstructions of Australia relative to Antarctica at 84 Ma (Fig. 6), as this is the age that most workers consider when 84 Ma: Royer and Sandwell (1989) & Müller et al. (1997; 2008) sea-floor spreading began between the two continents. All of the 84 Ma reconstructions that are shown in Fig. 6 produce c an overlap of the Australian and Antarctic continent–ocean bound- aries along most of the margin. However, this makes no account for the amount of stretching anticipated to have occurred during rifting in order that subcontinental lithospheric mantle be exhumed along part of the Australian margin. This point aside, the models of Powell et al. (1988), Royer and Sandwell (1989) and Müller et al. (1997, 2008) all produce an overlap of the continent–ocean boundaries of Australian and Antarctic plates in the west, and would also give rise to an underlap of the plates in the east were it not for the South Tasman Rise. The importance of the South Tasman Rise in reconstruc- tions was first raised by Tikku and Cande (1999, 2000) (Fig. 6a–b) 84 Ma: Tikku and Cande (1999; 2000) who tried to resolve the underlap issue, although in doing so, they produced a significant overlap of the South Tasman Rise with Antarctica, d as was discussed by Gaina et al. (1998) and Whittaker et al. (2007) (Fig. 6c). The Tikku and Cande (1999, 2000) reconstructions also imply that the initial phase of spreading had a N–S orientation although this has been questioned by several workers because the orientation of the first formed extensional faults are interpreted to indicate that the ini- tial phase of spreading was oriented NNW–SSE (Willcox and Stagg, 1990). However, McClay et al. (2002) have shown that similar differ- ences between fault and stress orientation are generated in analog models, suggesting that the initial spreading direction proposed in these reconstructions could be valid. 84 Ma: Whittaker et al. (2007) Whittaker et al. (2007) tried to address this issue by rotating Australia with respect to Antarctica by matching the Leeuwin e (Perth) Fracture Zone (115°E, 37°S) on the Australian plate (Fig. 1) to what they referred to as the Perth South Fracture Zone, offshore Wilkes Land, Antarctica (110°E, 65°S) (Fig. 1). This resulted in a better fit between the west coast of Tasmania and north coast of Wilkes Land, and it ensured that the spreading direction was oriented NW–SE between ~95 Ma* and 53 Ma, thus matching what Willcox and Stagg (1990) had proposed from structural observations.

Fig. 6. Reconstructions comparing Australia's position relative to Antarctica at 84 Ma. Constructed using the Euler poles of: (a) Powell et al. (1988) and Veevers et al. (1991); 84 Ma: Williams et al. (2011) (b) Royer and Sandwell (1989) (which was adopted by Müller et al., 1997, 2008); (c) Tikku and Cande (1999; 2000);(d)Whittaker et al. (2007),and;(e)Williams et al. (2011). L.T. White et al. / Gondwana Research 24 (2013) 984–998 993

However, the Whittaker et al. (2007) reconstruction also shifted the prior to break-up. Gaina et al. (1998) also showed there was less Australian plate several hundred kilometers eastward with respect space for the two South Tasman Rise blocks in the Tikku and Cande to the reconstruction of Tikku and Cande (1999, 2000) (Fig. 6c–d). (1999) reconstruction (e.g. Fig. 7a–c) and therefore stated that partial This is because Tikku and Cande (1999, 2000) chose different fracture zones as conjugates. In their model the Leeuwin Fracture Zone was a conjugate of the Vincennes Fracture Zone (102°E, 63°S) instead of the a Significant overlap b Significant overlap Perth South Fracture Zone (Fig. 1). Whittaker et al. (2008) argued that of the STR at of the STR at 84 - 96 Ma 84 - 96 Ma fi Australian Australian their reconstruction (Whittaker et al., 2007) produced a better t, Plate Plate with no overlap between Tasmania/Tasman Rise and Cape Adare. Slight modifications to this reconstruction have also been proposed in Williams et al. (2011) and Gibbons et al. (2012). These later recon- structions do not rotate Australia as far south as in earlier reconstruc- WSTR tions (Tikku and Cande, 1999, 2000; Whittaker et al., 2007), and so ETP ETP there is less overlap between the South Tasman Rise and Wilkes Land when it is held fixed to the Australian plate. However these re- WSTR ESTR ESTR constructions still produce an overlap of the Australian and Antarctic continent–ocean boundaries west of Tasmania (Fig. 6e–f). We compared two of these reconstructions ((1. Tikku and Cande, 1999, 2000) and 2. (Whittaker et al., 2007)) to one another in an earlier paper (Gibson et al., 2013) to determine which one produced Antarctic Antarctic a better fit between conjugate onshore continental–scale faults. Plate Plate These continental–scale faults controlled the location and initiation c Significant overlap d Restoring the displacement of of oceanic fracture zone development and transfer fault propagation of the STR at the Colac-Rosedale Fault (CRF) during break-up (Gibson et al., 2013) as shown here in Fig. 6 with 84 - 96 Ma creates space for the STR the tie points and terrane boundaries discussed in Section 2. This test indicated that the Tikku and Cande (1999, 2000) reconstruction Australian Australian Plate produced a better geological fit. Though, other good geological fits Plate at 84 Ma are obtained in the reconstructions of Powell et al. (1988); ETP Veevers et al. (1991); Royer and Sandwell (1989) and Müller et al. ESTR (1997, 2008) and Tikku and Cande (1999, 2000) (Fig. 6a–c). In com- ESTR parison, the reconstructions of Whittaker et al. (2007), Williams et WSTR WSTR al. (2011) and Gibbons et al. (2012) all shift the Australian plate too far to the east, resulting in a poorer fit between the conjugate terrane ETP boundaries and transform faults (Fig. 6d–f). These misfits are also evident in the reconstructions presented in Whittaker et al. (in press). It is therefore apparent that some of the choices that were adopted in Antarctic Antarctic the reconstruction of Whittaker et al. (2007) were also carried over Plate Plate into these other reconstructions (Williams et al., 2011; Gibbons et al., e Restoring the displacement of There is no overlap of 2012; Whittaker et al., in press) which focused on the earlier aspects the Colac-Rosedale Fault (CRF) f the STR with Australia Australian and Antarctica at 45 Ma of Gondwana break-up (as was discussed earlier in Section 3 and creates space for the STR Plate shown in Figs. 2 and 3). and no need to invoke CRF

AustralianPlate 6. Reconstructing the South Tasman Rise ETP

ETP The South Tasman Rise and the East Tasman Plateau both form large submarine plateaux made up of continental crust (Exon et al., WSTR ESTR 1997; Royer and Rollet, 1997)(Fig. 1). Many workers recognize WSTR ESTR the issue of overlap between the South Tasman Rise and the reconstructed position of Australia and Antarctica and have proposed models to account for this by positioning the South Tasman Rise between western Tasmania and North Victoria Land (Stump et al.,

1986; Willcox and Stagg, 1990), or (2) south of Tasmania and east Antarctic Antarctic of North Victoria Land/Ross Sea Shelf (Grindley and Davey, 1982; Plate Plate Gray and Norton, 1988; Veevers and Eittreim, 1988; Lawver and Gahagan, 1994; Bernecker and Moore, 2003; Gibson et al., 2011). Fig. 7. Reconstructions of southeast Australia, East Antarctica and the South Tasman Other workers sub-divided the South Tasman Rise into western Rise (STR). Images (a–b) and (d–e) show Australia's position relative to Antarctica at and eastern segments (Exon et al., 1997; Royer and Rollet, 1997; 84 Ma according to Tikku and Cande (1999, 2000), while (c) shows how the Euler Gaina et al., 1998). Royer and Rollet (1997) considered that the west- poles proposed by Whittaker et al. (2007) position the two major plates. Note the fi ern segment was initially attached to Antarctica and was rifted from signi cant overlap of the East South Tasman Rise (ESTR) and West South Tasman Rise (WSTR) when using the Euler poles proposed for these microplates by (a) Royer this continent in the Late Paleocene/Early Eocene, while the eastern and Rollet (1997) and (b–c) Gaina et al. (1998).(d–e) The overlap at 84 Ma is reduced segment rifted off Tasmania and the East Tasman Plateau during the if Tasmania is translated along the Colac–Rosedale Fault (CRF), however, significant separation of Australia from Antarctica between chrons 33y and 30y overlaps of the continental fragments (as well as gaps) are still produced if we use (74.31 Ma and 66.40 Ma). However, Gaina et al. (1998) showed the poles for the WSTR and ESTR proposed by (d) Royer and Rollet (1997) or (e) Gaina et al. (1998). There is limited evidence available to support the existence that this reconstruction produced a gap between the eastern South of the Colac–Rosedale Fault. (f) So if it does not exist the STR can only be positioned Tasman Rise, the East Tasman Plateau, the Gilbert Seamount Complex between Tasmania and northern Victoria Land if Australia is only rotated with respect and the Lord Howe Rise when they were restored to their position to Antarctica to its position at 45 Ma (according to Tikku and Cande, 1999, 2000). 994 L.T. White et al. / Gondwana Research 24 (2013) 984–998 closing of embayments and the reduction of the size of the plateau to need of dividing it into smaller fragments with different movement account for crustal extension associated with rifting would produce a histories (e.g. Fig. 7a–d). This also ensures that the distinctive curved better fit. In addition, Gaina et al. (1998) proposed that the South shape of the southern edge of the South Tasman Rise continental Tasman Rise started moving slowly southward relative to Australia crust fits to the corresponding curved shape of the continental crust during the opening of the Tasman Sea thereby producing a rift between of northern Victoria Land, as was proposed as the best fit according Tasmania and the South Tasman Rise, and E–Wsea-floor spreading to the available gravity data (Gibson et al., 2011)(Fig. 7f). However, between the South Tasman Rise and the East Tasman Plateau. In their this does not preclude the possibility that the South Tasman Rise con- reconstruction, the eastern South Tasman Rise became attached to sists of two parts that had different “plate” motions. Australia shortly before chron 31y (68.37 Ma) and the west South Tasman Rise became fixed to the east South Tasman Rise at 40 Ma, after about 70 km of left-lateral strike-slip motion between the two 7. Reconstructing Australia–Antarctica break-up: A clean slate blocks (Fig. 7d–e). Yet, this still results in a significant overlap between Australia, Antarctica and the South Tasman Rise when using the terrane We have shown that reconstructions of the Australian plate rela- boundaries that we have adopted for this study (Fig. 1). tive to Antarctica are fraught with uncertainties, not least of which The over/underlaps of the continental fragments are perhaps why is the exact time sea-floor spreading began between the two conti- there has been a recent tendency to translate Australia further to the nents. The problem lies in establishing which isochrons are real, and east with respect to Antarctica (e.g. Whittaker et al., 2007; Müller et which are exhumed magnetized mantle rocks that are emplaced al., 2008; Williams et al., 2011; Gibbons et al., 2012) (Figs. 2 and 6 within the transitional zone between stretched continental and and Supplementary File 2). However, as we stated earlier, this east- oceanic crust. This problem is common to most other, if not all, ward shift is an untenable solution as it is done at the expense of a “rift–drift” margins around the world (e.g. between India and Antarc- significant misfit of the terranes on either side of the margin. One pos- tica c.f. Jokat et al. (2010), and the Atlantic opening: c.f. Sibuet et al., sible solution to this problem is to use the Euler poles that produce 2007; Sibuet and Tucholke, 2012; Sutra and Manatschal, 2012) and the best geological fit between Australia and Antarctica, and then to we are only beginning to understand the impact of these observations translate Tasmania and the South Tasman Rise N200 km to the east on existing plate reconstructions. with respect to Australia, thus ensuring that there is room for the Disparities between where the Australian plate has been posi- South Tasman Rise between Tasmania and Victoria Land (Fig. 7d–e). tioned with respect to the Antarctic plate (e.g. Figs. 2 and 6) have This idea was proposed by Stump et al. (1986) and Elliot and Gray ramifications for where other plates (e.g. India) and “microplates” (1992) who stated that during/after break-up, Tasmania was moved (e.g. the South Tasman Rise) were positioned in the past (Figs. 3 westward along the Colac-Rosedale Fault, and northern Victoria and 7). From these evaluations we have drawn attention to those Land moved southward along a postulated left-lateral strike-slip reconstructions that are most faithful to geological observations so fault (Fig. 7d–e). A similar idea was proposed in Betts et al. (2002) that these can be used as a framework to build more accurate who proposed that a left lateral strike-slip fault developed due to con- reconstructions of Gondwana, which is what we attempt here. tinued propagation of faults along Australia's southern margin associ- We produced a simplified reconstruction of Australia–Antarctica– ated with the rotation of Australia with respect to Antarctica during India break-up using the PaleoArc ArcGIS application developed by the early phases of break-up (see Fig. 20 of Betts et al., 2002). Howev- Cambridge Paleomap Services Ltd. and FrogTech Pty. Ltd. In this re- er, there is a potential problem with these interpretations, as no construction we rotated Australia with respect to a fixed Antarctica ~E–W trending structures are observed in the high-resolution aero- to the oldest identifiable isochron that extends along the margin magnetic data now available for Bass Strait (Direen and Crawford, (chron 21n — 45.72 Ma) according to the poles of Tikku and Cande 2003a, 2003b; Gibson et al., 2011). Casting further doubt on the exis- (1999, 2000). From this position, we rotated Australia about a pole tence of this structure are belts of greenstone and other correlative (Latitude: −25.153°/Longitude: −157.776°/Angle: 30.198°) between sequences that extend continuously across Bass Strait from northern 45 Ma and 165 Ma, before rifting began (Norvick and Smith, 2001; Tasmania into Victoria without any obvious offset or disruption Totterdell and Bradshaw, 2004). This ensures that (1) there was min- that might point to the presence of a strike-slip fault (Gibson et al., imal eastward or westward translation of Australia with respect to 2011). It follows that moving Tasmania along a strike-slip fault Antarctica; (2) the best geological fit was obtained between the two through the Bass Strait is not a justifiable option according to the plates at all times and; and (3) that there is sufficient room for part data currently available. This is not to say that: (1) Tasmania's posi- if not all of the South Tasman Rise between southern Tasmania and tion did not change at all during the evolution of the southern margin, northern Victoria Land. While this is perhaps an oversimplified histo- especially considering that there was some movement of Tasmania ry it at least remains faithful to the geological boundaries on either associated with the opening of the Bass Basin (e.g. Norvick and margin and means that we have not used any magnetic anomalies Smith, 2001; Veevers, 2012), or (2) that higher-resolution geophysi- that are located within the continent–ocean transition zone. cal datasets that are collected in the future (e.g. seismic tomograms) This reconstruction is also faithful to the idea that Coorong and will not delineate vertical ~E–W trending faults in the Bass Basin, in Mertz Shear Zones, and the Avoca and Lanterman and Leap Year which case the reconstructions will need to be revised. fault zones are conjugate structures on the Australian and Antarctic Earlier we discussed the problem of identifying magnetic iso- margins (Gibson et al., 2011, 2013). These relationships are shown chrons in the continent–ocean transition zone (e.g. Figs. 4, 5). Consid- at 165 Ma in Fig. 8a. The reconstruction also highlights how these ering the arguments presented above, it follows that Euler poles transfer faults are potentially the pre-cursors to the George V and derived from the older isochrons that were assumed to extend Tasman fracture zones that developed as oceanic transfer faults along the length of the margin are not appropriate constraints for after the plates had stretched further and finally began to separate the position of the Australian plate with respect to Antarctica. So we (Fig. 8a–f). Whether the (Mount) Darling Fault in Western Australia have ignored the previously published Euler poles derived from iso- and its unnamed conjugate on the Antarctic plate (Fig. 1) similarly chrons older than 46 Ma and have only rotated the Australian plate acted as transform faults during the evolution of the margin is less (with respect to Antarctica) back as chron 21n (45.72 Ma) for certain. This uncertainty stems from the fact that we do not observe which there is some certainty regarding its origin as a true magnetic any oceanic fracture zones developing along strike from these on- isochron produced during symmetric sea-floor spreading. If this is shore features in the reconstruction (Fig. 8a–f). However, the conju- done, then there is sufficient room to position the South Tasman gate terrane boundaries do match in this reconstruction, so it might Rise between Tasmania and northern Victoria Land without the simply mean that these faults did not influence the future location L.T. White et al. / Gondwana Research 24 (2013) 984–998 995

a b

165 Ma 125 Ma

c d

100 Ma 80 Ma

e f

45 Ma 0 Ma

Fig. 8. Revised reconstruction of Australia–Antarctica–India break-up from 165 Ma to the present. (a) Rifting between the three major plates begins at 165 Ma. Continued stretching led to the eventual break-up of India from Australia and Antarctica between (b) 125 Ma and (c) 100 Ma. Rifting continued episodically from west to east along the Australian mar- gin from (a) 165 Ma until approximately (d) 80 Ma, when the first magnetic isochrons were produced between the two plates. Seafloor spreading was very slow between (d) 80 Ma and (e) 45 Ma, but (f) Australia moved rapidly northwards after 45 Ma. A movie of this reconstruction can be viewed at 5 Ma increments (http://vimeo.com/ user18925575/gondwana). of the oceanic transfer faults as has been proposed further east example, if sea-floor spreading initiated at 50 Ma instead of 45 Ma. Al- (e.g. Gibson et al., 2011, 2013). ternatively, this gap could be a function of the simple rigid plate recon- We also propose another Euler pole (Latitude: 6.750°/Longitude: struction that we have shown that does not consider deformation of −135.300°/Angle: 22.800°) to restore the pre-break-up position of the South Tasman Rise, or the continental–oceanic crust surrounding it. the South Tasman Rise between 45 Ma and 140 Ma that is faithful to India's position in this reconstruction (Fig. 8) is reliant on the matching the terrane boundaries identified for Victoria, the South Euler poles for India's motion relative to Antarctica as per Patriat Tasman Rise and northern Victoria Land (Gibson et al., 2011). This and Ségoufin (1988) and Patriat (1987) (i.e. the same poles that Euler pole remains faithful to the idea that there was sinistral were adopted by White and Lister (2012)) between 0 Ma and displacement between the South Tasman Rise and Tasmania. However, 84 Ma and as per Powell et al. (1988) between 84 Ma and 165 Ma. this reconstruction also means that a small gap remains between the Further details are shown in Supplementary File 1. We also used the South Tasman Rise and northern Victoria Land. This could be modified version of Ali and Aitchison's (2005) Greater India polygon removed if the Australian plate was rotated further southward. For as was discussed in Section 3.2. These data ensure that there is a 996 L.T. White et al. / Gondwana Research 24 (2013) 984–998 good geological fit between the Australian, Antarctic and Indian when the plates are restored to their pre-break-up position. This is plates (Fig. 8f), and this will mean that equally good fits should be a major problem, and can have a flow-on effect to misfits with other obtained with the other major plates and microplates of Gondwana. plates if they are rotated relative to Australia (e.g. the Indian plate). In order to achieve an optimal continental fit we refrained from using We therefore went back to the basics, and presented a very simple any of the existing Euler poles previously proposed for Australia– reconstruction of the break-up of the Australian, Antarctic and Indian Antarctica break-up between 45 Ma and 165 Ma. We adopted this plates with the hope that this forms a framework for geologists and approach because we cannot be certain that any of the previously iden- geophysicists to build more detailed, but geologically feasible tified 45–84 Ma magnetic features are true isochrons as all occur within reconstructions of Gondwana. While geophysical data are often continental or transitional continental–oceanic crust (e.g. Figs. 2, 3). considered more quantitative when compared to geological data, Future workers may show that the continent–ocean boundaries that our review of existing reconstructions highlights that geological we have adopted in this study are inappropriate, and therefore justify data cannot be removed from the equation. the use of N46 Ma magnetic sea-floor anomalies. Supplementary data to this article can be found online at http:// While we did not want to advocate a discrete age for the initial dx.doi.org/10.1016/j.gr.2013.06.009. phase of seafloor spreading, we considered it important to try to show how the seafloor magnetic anomalies might have been generat- Acknowledgments ed after break-up between Australia and Antarctica. Synthetic iso- chrons were generated at 4 Ma increments with PaleoArc according Research support was provided by the Australian–Indian Strategic to the rotation poles for Australia and Antarctica between 84 Ma Research Fund “Towards a unified East Gondwanaland reconstruction and 0 (Fig. 8d–f) and the modern day geometry of the spreading and its implications for Himalayan Orogeny” and by a consortium of center (Fig. 1). This shows that magnetic isochrons may have oil companies that sponsor the South East Asia Research Group. developed at various places discontinuously along the margin G. M. Gibson publishes with permission from the CEO, Geoscience between 84 and 80 Ma (Fig. 8d). Spreading was very slow between Australia. Sam Hart is thanked for his efforts in developing the Pplates 80 Ma and 45 Ma (Fig. 8e), but the Australian plate moved rapidly code. Alan Smith and Lawrence Rush of Cambridge Paleomap Services northward after this time (Fig. 8f). While the geometries of the Ltd. are thanked for providing a copy of PaleoArc and instructions on synthetic isochrons are not perfect, they do match very closely to its use. We are grateful for discussions about the evolution of the the modern day fracture zone geometry and this gives us some southern margin with J. Totterdell, C. Mitchell and A. Stacey and for confidence about what is shown in the reconstruction, which can the insight and recommendations of Nick Direen and Steve Boger in be observed as a movie at 5 Ma increments (http://vimeo.com/ their reviews of the paper. user18925575/gondwana).

8. Implications for basin evolution along Australia's References southern margin Ali, J.R., Aitchison, J.C., 2005. Greater India. Earth-Science Reviews 72, 169–188. Bernecker, T., Moore, D.H., 2003. Linking basement and basin fill: implications for hy- Our new reconstruction shows that Australia–Antarctica rifting drocarbon prospectivity in the Otway Basin region. The APPEA Journal 43, 39–58. began in the west, and crustal extension would have propagated east- Beslier, M.O., Royer, J.Y., Girardeau, J., Hill, P.J., Boeuf, E., Buchanan, C., Chatin, F., Jacovetti, G., Moreau, A., Munschy, M., Partouche, C., Robert, U., Thomas, S., 2004. ward as the Australian plate rotated clockwise relative to the Antarctic Une large transition continent–ocean en pied de marge sud-ouest australienne: plate (Fig. 8a–c). This scenario is consistent with the pattern and timing premiers resultats de la champagne MARGAU/MD110. Bulletin Society Geologique of rifting in the sedimentary basins along Australia's southern margin, Francaise 175, 629–641. Betts, P.G., Giles, D., Lister, G.S., Frick, L.R., 2002. Evolution of the Australian lithosphere. where rifting and spreading began in the west, and propagated Australian Journal of Earth Sciences 49, 661–695. eastward (Halpin et al., 2008; Direen et al., 2012). Blevin, J., Cathro, D., 2008. Australian Southern Margin Synthesis. FrOG Tech Pty. Ltd., The reconstruction is also consistent with the structural evolution Canberra 104 (https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_ of the sedimentary basins and the Southern Rift System, where the DETAILS&catno=68892 (last accessed 7 November 2012)). Boger, S.D., 2011. Antarctica — before and after Gondwana. 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Veevers, J., 1986. Breakup of Australia and Antarctica estimated as mid-Cretaceous Lloyd White graduated with a BSc (Hons) from the (95 ± 5 Ma) from magnetic and seismic data at the continental margin. Earth University of NSW (2006), before briefly working for and Planetary Science Letters 77 (1), 91–99. Geoscience Australia (2006–2008) on various geological- Veevers, J.J., 2012. Reconstructions before rifting and drifting reveal the geological con- based projects. He later completed a PhD at the Australian nections between Antarctica and its conjugates in Gondwanaland. Earth-Science National University (ANU) (2008–2011), where he investi- Reviews 111, 249–318. gated the tectonic history of the Himalayan orogen. This Veevers, J., Eittreim, S., 1988. Reconstruction of Antarctica and Australia at breakup was followed by an Australian–Indian Strategic Research (95 ± 5 Ma) and before rifting (160 Ma). Australian Journal of Earth Sciences 35 Fund post-doctoral fellowship at ANU (2011–2012), and (3), 355–362. another post-doctoral fellowship with the Southeast Asia Veevers, J.J., Saeed, A., 2008. Gamburtsev subglacial mountains provenance of Perm- Research Group at Royal Holloway University of London ian–Triassic sandstones in the Prince Charles Mountains and offshore Prydz Bay: (2012–). His research interests revolve around structural ge- – – fi integrated U Pb and TDM ages and host rock af nity from detrital zircons. ology, geochronology and plate reconstructions and he is cur- Gondwana Research 14, 316–342. rently focusing on unraveling the tectonic history of SE Asia. Veevers, J.J., Saeed, A., 2009. Permian–Jurassic Mahanadi and Pranhita–Godavari Rifts of Gondwana India: provenance from regional paleoslope and U–Pb/Hf analysis of detrital zircons. Gondwana Research 16, 633–654. Veevers, J.J., Powell, C.McA, Roots, S.R., 1991. Review of seafloor spreading around Australia. I. Synthesis of the patterns of spreading. Australian Journal of Earth Sciences 38 (4), 373–389. George M. Gibson is a graduate of Edinburgh and Otago Weissel, J.K., Hayes, D.E., 1971. Asymmetric seafloor spreading south of Australia. universities with extensive research and leadership experi- Nature 231, 518–522. ence in the structure and tectonic evolution of Proterozoic Weissel, J.K., Hayes, D.E., 1972. Magnetic anomalies in the southeast Indian Ocean. orogenic belts, including Broken Hill and Mount Isa. His re- Antarctic Oceanology II: The Australian–New Zealand Sector. Antarctic Res. Ser, search interests lie in structural geology, geochronology 19, pp. 165–196. and tectonic analysis which have taken him to projects in Weissel, J.K., Hayes, D.E., Herron, E.M., 1977. Plate tectonics synthesis: the displace- Europe, Australia, New Zealand and Antarctica. He is cur- ments between Australia, New Zealand, and Antarctica since the Late Cretaceous. rently a theme leader (Geodynamics) in the International Marine Geology 25 (1–3), 231–277. Geological Correlation Program and for the previous four White, L.T., Lister, G.S., 2012. The collision of India with Asia. Journal of Geodynamics years served on various committees for the highly successful 56–57, 7–17. http://dx.doi.org/10.1016/j.jog.2011.06.006. 34th International Geological Congress (Brisbane, 2012). Be- Whittaker, J.M., Muller, R.D., Leitchenkov, G., Stagg, H., Sdrolias, M., Gaina, C., Goncharov, fore joining Geoscience Australia in 1995, he was employed A., 2007. Major Australian–Antarctic plate reorganization at Hawaiian-Emperor bend in the private and university sectors. time. Science 318 (5847), 83–86. http://dx.doi.org/10.1126/science.1143769. Whittaker, J.M., Muller, R.D., Leitchenkov, G., Stagg, H., Sdrolias, M., Gaina, C., Goncharov, A., 2008. Response to comment on “Major Australian–Antarctic plate reorganization at Hawaiian-Emperor bend time”. Science 321 (5888), 490d–d. http://dx.doi.org/ 10.1126/science.1157501. Whittaker, J.M., Williams, S.E., Müller, R.D., 2013. Revised tectonic evolution of the Gordon Lister is a Professor at ANU: PhD ANU (1975), lec- Eastern Indian Ocean. Geochemistry, Geophysics, Geosystems. http://dx.doi.org/ tured at Leiden University (1974–1979), Utrecht University 10.1002/ggge.20120 (in press). (1979–1984), Bureau of Mineral Resources (1984–1987), Willcox, J., Stagg, H., 1990. Australia's southern margin: a product of oblique extension. Columbia University, NY (1986), Professor of Earth Sciences, Tectonophysics 173 (1–4), 269–281. Monash University (1987–2003), and Research School Williams, S.E., Whittaker, J.M., Müller, R.D., 2011. Full-fit, palinspastic reconstruction of of Earth Sciences, ANU (2003–present). His research has the conjugate Australian–Antarctic margins. Tectonics 30 (6). http://dx.doi.org/ focused on structural geology and tectonics, computers in 10.1029/2011TC002912. the geosciences, and economic geology. His current research Yuasa, M., Niida, K., Ishihara, T., Kisimoto, K., Murakami, F., 1997. Peridotite dredged interests include seismotectonics and cellular automata, from a seamount off Wilkes Land, the Antarctic: emplacement of fertile mantle the role of extreme extension during mountain building, fragment at the early rifting stage between Australia and Antarctica during the argon geochronology and the 4D evolution of the planetary final breakup of Gondwanaland. The Antarctic Region: Geological Evolution and lithosphere. Processes. 725–730.