4.1 The Kerguelen-Broken Ridge Sector
 A plate tectonic reconstruction for the rifting and early spreading between Australia and Antarctic needs to provide a reasonable model for the timing and kinematics of the formation of the basement in the Central Kerguelen-Broken Ridge and Diamantina Zone/Labuan Basin sectors of the margin. Our new rigid plate tectonic reconstruction model (1) does not involve any unlikely tectonic motion, or large-scale deformation of oceanic or continental crust, and (2) provides a detailed model for the formation of the poorly constrained Kerguelen sector of the Australian-Antarctic margin, and in particular the Labuan Basin and the Diamantina Zone.
 The southernmost part of the Labuan Basin (also known as the Shackleton Basin, Figure 1) is morphologically different to the northern parts of the basin and is characterized by dipping reflectors [Stagg et al., 2004]. There is no clear boundary between this basin and the Labuan Basin to the north. The basement and overlying sediments are generally unfaulted, with the basement morphology consistently smooth and flat.
 In our model, the basement of the Princess Elizabeth Trough and the Shackleton Basin formed between 136 and 115 Ma due to seafloor spreading between India and Antarctica, with the Antarctic flank underlying the Princess Elizabeth Trough where Mesozoic anomalies have been interpreted [Gaina et al., 2007; Murakami et al., 2000].
 Our tectonic reconstruction shows the northern Labuan Basin and the Diamantina Zone formed as one basin between 108 and 43.8 Ma, in agreement with previous interpretations that these features were once continuous [Beslier et al., 2004; Chatin et al., 1998; Gladczenko and Coffin, 2001; Munschy, 1998; Stagg et al., 2004]. Both the Diamantina Zone and the Labuan Basin exhibit two structurally different provinces: one comprising tilted fault blocks separated by south to southwest dipping faults, and the other characterized by elongated basement highs that are larger and more dome shaped [Munschy, 1998]. South to southwest dipping faults separating predominantly northeast oriented basement highs are consistent with the NW-SE oriented transtensional motion in our model.
 A number of different models have been proposed for the formation of the ~600 km wide combined Labuan Basin-Diamantina Zone, including ultra-slow seafloor spreading [Cande and Mutter, 1982], diffuse deformation (50–55 Ma, 65–78 Ma) of pre-existing oceanic crust [Munschy, 1998], crustal extension between 130 and 95 Ma and mantle unroofing between 95 and 84 Ma [Rotstein et al., 1991], amagmatic extension between ~83 and 43 Ma [Tikku and Cande, 2000], a combination of extended Kerguelen Plateau material and oceanic crust [Gladczenko and Coffin, 2001], and progressive south to north extension with a central extrusive zone between the pre-Albian and Campanian [Borissova et al., 2002].
 Whether the crust within the Labuan Basin and Diamantina Zone is predominantly oceanic [Gladczenko and Coffin, 2001] or continental is disputed [Borissova et al., 2002]. Our model is more consistent with the oceanic crust formed under slow seafloor spreading conditions. The composition of the alkaline basalts dredged from both the Labuan Basin and the Diamantina Zone indicates small amounts of melting [Chatin et al., 1998] and continental rocks have been sampled from the Labuan Basin, although these were originally interpreted as ice-rafted debris [Montigny et al., 1993].
 In our model, the western Labuan Basin/northern Diamantina Zone formed between ~108 and 83.5 Ma during relative Australian-Antarctic motions that were moderately oblique to the trend of the mid-ocean ridge. During this period, we model the Australian-Antarctic plate boundary to run through the CKP, resulting in the formation of the majority of the crust underlying the CKP. This continuation of the plate boundary from the Labuan Basin to beneath the CKP is supported by the observation that the tilt-block morphology of the Labuan Basin extends onto the Kerguelen Plateau [Rotstein et al., 1991].
 We model the formation of the eastern Labuan Basin/southern Diamantina Zone between 83.5 Ma and 43.8 Ma during locally more oblique extensional conditions. During this period, relative motion between Australia and Antarctica resulted in ~250 km of extension and 180 km of strike-slip motion in the easternmost Diamantina Zone, progressing to ~240 km of purely strike-slip motion beneath the northernmost CKP. This phase of motion matches well with the ~120 km width of the eastern Labuan Basin.
 For the period between 83.5 Ma and 43.8 Ma, our reconstructions model more strike-slip motion than the reconstruction of Tikku and Cande  but do not require major strike-slip motion between Tasmania and Australia that seems unlikely in the light of aeromagnetic data over the Bass Basin and onshore geology for southeastern Australia [Cayley, 2011; Cayley et al., 2002]. A long-standing problem with plate tectonic reconstructions of Australia-Antarctica is the placement of a plate boundary through the Kerguelen region between 95 Ma and ~43 Ma. Magnetic anomaly interpretations from the Bight/Wilkes Land sector of the conjugate Australian-Antarctic margin clearly show continuous, albeit slow, relative motion of these two plates throughout this period. There are structures that can be interpreted as paleoplate boundaries in the SKP and southern CKP. However, there is a striking absence of evidence for this relative motion, in the form of rifts, strike-slip boundaries, etc., in the Central Kerguelen/Broken Ridge sector of the margin. This has lead to the proposal that there simply was no [Rotstein et al., 2001] or minimal [Tikku and Cande, 2000] relative motion at this section of the margin. However, as discussed in more detail earlier, minimizing/removing relative motion leads to kinematic reconstructions with unlikely plate boundary configurations in the eastern Indian Ocean [Rotstein et al., 2001] or geologically improbable continental deformation in the Tasmanian/Cape Adare region [Tikku and Cande, 2000].
 Our approach to modeling the formation of crust between Australia and Antarctica explicitly breaks the ocean floor into discrete, rigid blocks and does not take into account the possibility of diffuse deformation. It is likely that the thicker, rheologically weaker Kerguelen Plateau/Broken Ridge regions were not affected by diffuse deformation and rather experienced focused deformation similar to that observed at the Chagos Bank [Henstock and Minshull, 2004]. Likely examples of this focussed deformation exist on the SKP, e.g., the 75°E and 77°E Grabens—prominent N-S trending features crossing the Central and Southern Kerguelen Plateaux that formed between 72 Ma and 64 Ma and record small amounts of extensional (~5 km) and strike-slip (~3 km) motion [Rotstein et al., 1991]. However, it is possible that diffuse deformation affected the thinner Diamantina Zone/Labuan Basin rather than relative motion being focused at a discrete plate boundary.
 Our reconstruction predominantly models the formation of oceanic crust beneath the Kerguelen Plateau prior to, or contemporaneously with the formation of the Kerguelen Plateau. The age of the underlying ocean crust is compatible with igneous basement ages from the Kerguelen Plateau Sites 749—110 Ma [Whitechurch et al., 1992] and 750—112 Ma [Coffin et al., 2002], but not with the 119 Ma basement age from Site 1136 [Coffin et al., 2002; Duncan, 2002] which lies on crust we model to have formed between 108 and 115 Ma (compare the reconstructions in Figure 4 at 115 Ma and 108 Ma). In our model, the Southern Perth spreading corridor forms between 136 and 115 Ma, followed by the spreading corridor beneath the Southern Kerguelen Plateau at 115–108 Ma. A better match between the age of the underlying ocean floor from the plate tectonic model and the 119 Ma igneous basement age may be achieved, however, if the Southern Kerguelen corridor formed first, prior to 119 Ma and the South Perth corridor second after ~119 Ma. Additional data from the Perth Abyssal Plain are required to test this scenario, which would require a different plate boundary configuration, and possible additional ridge jump.
4.2 Hot Spot-Triple Junction Relationship
 A possible relationship between volcanic plateaus and triple-junctions has long been observed, for example for the Shatsky Rise [Nakanishi et al., 1999], Agulhas Plateau [Gohl and Uenzelmann-Neben, 2001; Tucholke et al., 1981], and Mozambique Ridge [Gohl and Uenzelmann-Neben, 2001]. Our plate reconstructions allow us to investigate the relationship between the locations of the Indian-Australian-Antarctic triple-junction with that of the Kerguelen plume (Figure 4), although we note that the exact location of the reconstructed triple junction remains poorly constrained and may have varied through time. From ~136 Ma to 108 Ma, the triple junction between India-Australia-Antarctica moved as a result of India's relative motion away from both Australia and Antarctica at an average rate of ~79 km/Myr (~1500 km; Figure 4). During this period, seafloor spreading in the Perth and Enderby Basins resulted in movement of the MOR toward the reconstructed position of the Kerguelen plume for all reference frames considered, although the Mu93 model results in the most consistent proximity between the Kerguelen plume and the mid-ocean ridge system and Indian-Australian-Antarctic triple junction.
 The two ridge jumps, at 115 Ma of the Enderby MOR and at 108 Ma of the Perth MOR, were substantial and westward and resulted in fragments of continental crust being rifted from the Indian passive margin (the Elan Bank at 115 Ma [Gibbons et al., 2012] the Gulden Draak Knoll and Batavia Knoll at 108 Ma [Gibbons et al., 2012; Williams, 2011]) and likely at least some portion of the Southern Kerguelen Plateau [Operto and Charvis, 1995]. Both these ridge jumps are consistent with the hypothesis of Müller et al.  that plate boundaries jump toward hot spots, resulting in the formation of micro-continents. At 108 Ma, following the ridge jump the Mu93 modeled location of the Kerguelen hot spot is closest to the Indian-Australian-Antarctic triple junction (also see Figure S6). It should be noted that the inferred hot spot tracks all fit poorly with the Ninetyeast Ridge and the Kerguelen Plateau. The model providing the closest match is the Mu93 fixed hot spot model. This result indicates that individual plume motions coupled with moving hot spot reference frames should be used with some caution when reconstructing individual plumes and interrogating their position relative to reconstructed plate tectonic features. This is particularly applicable for the Kerguelen plume, where considerably different hot spot motions are estimated from models with different buoyancy parameters, for example Doubrovine et al.  and Steinberger and Antretter .
 Between 108 and 43 Ma, the Indian-Australian-Antarctic triple-junction progressed much more slowly to the NW (~1000 km) at a rate of 15 km/Myr (Figure 4). This slow motion reduced the distance between the location of the Indian-Australian-Antarctic triple junction and the reconstructed ON05 position of the plume to within ~100 km by 43.8 Ma. Overall, during this period, the triple-junction remains roughly equidistant to the Mu93 and ON05 reconstructed Kerguelen plume locations (Figure 4). The slow progression of the triple-junction location (and by implication the locations of the Indo-Australian-Antarctic plate boundaries) during this period, particularly compared with the rapid motion in the preceding period, suggests a strong preference for the triple-junction to remain near to the Kerguelen plume.
4.3 Triple Junction-Plateau Relationship
 The Southern Kerguelen Plateau, Central Kerguelen Plateau, and Broken Ridge are each proposed to have formed rapidly over short (~5–10 million year) periods, approximately 120–110 Ma, 105–100 Ma, and 100–95 Ma, respectively [Coffin et al., 2002]. Based on our plate tectonic constraints, we propose an alternative scenario for the Central Kerguelen Plateau/Broken Ridge that conforms to the known history for the Eastern Indian Ocean and the Tasmanian/Cape Adare region and implies continued relative transtensional motion in the Central Kerguelen/Broken Ridge sector between ~100 and 43 Ma. To reconcile our model with the absence of rift or strike-slip features in the northern CKP that could have connected the Diamantina Zone/Labuan Basin to the Indian Ocean spreading centers, we propose ongoing, variable flux magmatism in this region which has overprinted the evidence of much of the paleoplate boundary. This scenario requires variable magma output rates over extended time periods, a scenario supported by the geodynamic models of Lin and van Keken .
 We propose that the Central Kerguelen Plateau and Broken Ridge formed as the result of interaction between continued Kerguelen plume-related volcanism, and the Indian-Australian-Antarctic triple junction and Australian-Antarctic plate boundary, over a period of approximately 65 Ma, from ~108 Ma to ~43 Ma (Figure 4), with the majority of the joint plateau formed during initial phase of magmatism between 108 and 83 Ma, followed by lower volume building until ~43 Ma. Episodic magma fluxes exploited this interaction to build the CKP/Broken Ridge volcanic edifice over ~65 Myr, an ongoing process that resulted in the masking of rift or strike-slip features formed as a result of Australian-Antarctic relative plate motions. Our model is consistent with the available basement ages available from the CKP (100.4 Ma ODP Site 1138 and 83.7–84.8 Ma ODP Site 747) and Broken Ridge (94.5–95.1 Ma ODP Sites 1141 and 1142). These relatively sparse data have previously been interpreted to indicate formation of the plateaux over a shorter time span but do not discount the possibility of more gradual accretion of crust over longer time spans, albeit possibly at lower volumes.
 Alternative models have been necessary to explain the formation of the Kerguelen Plateau, and other onshore and marine LIPs, by variable magma output rates over tens of millions of years. Proposed mechanisms have included multiple plume sources, a single, but dismembered plume [Coffin et al., 2002] or the development of secondary instabilities due to the interaction between thermal and compositional variations [Lin and Van Keken, 2005].
 Our proposed model for the formation of the CKP/Broken Ridge matches variable flux plume models such as Lin and van Keken  by requiring variable magma output volumes over longer periods at a relatively stationary location. Continued proximity of the Central Kerguelen Plume to the Indian-Australian-Antarctic triple junction over the ~65 Myr period may also have aided the construction of the extensive CKP/Broken Ridge from lower volume and/or variable rates of magma output. This long period of construction is not inconsistent with the formation of sedimentary basins on the Central Kerguelen Plateau as the slow rates of magmatism would only have affected small regions of the CKP at a time, with other regions quiescent and able to subside and accumulate sediment.
 The best studied example of a LIP formed through the interaction of a plume and a triple-junction is the Shatsky Rise, located in the northwest Pacific [e.g., Hilde et al., 1976; Larson and Chase, 1972; Nakanishi et al., 1999]. Like the Central Kerguelen Plateau/Broken Ridge, this large oceanic plateau does not appear to have formed rapidly from short-lived ~1–5 Myr episodes of voluminous volcanism. Subsidence rates observed from DSDP and ODP sediment data on the Shatsky Rise are difficult to reconcile with the rapid emplacement of the plateau by a high-temperature plume [Ito and Clift, 1998]. Sager et al.  proposed sustained episodic volcanism over approximately 20 Ma (chron M20 to M1), with decreasing volumes of magma and plume triple-junction interaction forming the three spatially separated plateaux of the Shatsky Rise and the volumetrically smaller, linear Papanin Ridge—a model that fits with the variable flux plume model of Lin and van Keken . This interpretation is strongly supported by the clear age progression of the Shatsky Rise toward the northeast [Nakanishi et al., 1999]. Unfortunately, the basement volcanics of the Central Kerguelen Plateau/Broken Ridge were emplaced during the Cretaceous Quiet Zone, when there was an absence of magnetic reversals, so such a clear age progression is not apparent. In any case, it is unlikely that such a clear age progression would affect the CKP/Broken Ridge due to the nature of the underlying plate boundary. An ultra-slow spreading transtensional plate boundary lay under the CKP/Broken Ridge, in contrast to the normal mid-ocean ridge underlying the Shatsky Rise.
 There are significant differences between the morphology of Central Kerguelen Plateau/Broken Ridge and the plateaux of the Shatsky Rise. The Shatsky Rise exhibits a more rugged topography compared to the CKP and comprises three, relatively small, rugged, spatially separated plateaux, while the CKP is a single, very large, relatively smoother, plateau. Nevertheless, both these LIPs exhibit variable magma flux over millions of years, Shatsky over ~20 Myr and the CKP over ~65 Myr. Although the absolute timescales differ, for both of these LIPs, the initial magma flux appears to have been higher, followed by lower volumes, which appear to cease in the Shatsky Rise case but which have continued to the present-day in the case of the Kerguelen plume.