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Antarctic subglacial properties impact geothermal heat, subglacial sedimentation, and glacial isostatic adjustment; critical parameters for predicting the ice sheet's response to warming oceans. However, the tectonic architecture of the Antarctic interior is unresolved, with results dependent on datasets or extrapolation used. Most existing deterministic suggestions are derived from qualitative observations and often presented as robust results; however, they hide possible alternative interpretations. Using information entropy as a measure of certainty, we present a robust tectonic segmentation model generated from similarity analysis of multiple geophysical and geological datasets. The use of information entropy provides us with an unbiased and transparent metric to communicate the ambiguities from the uncertainties of qualitative classifications. Information theory also allows us to test and optimise the methods and data to evaluate how choices impact the distribution of alternative output maps. We further discuss how this metric can quantify the predictive power of parameters as a function of regions with different tectonic settings.

During the Eocene-Oligocene transition, the meridional overturning circulation underwent large changes, associated with the geological evolution of Southern Ocean gateways. These are crucial for the Cenozoic climate transition from Greenhouse to Icehouse, but their dynamics still remain elusive. We demonstrate, using an idealised eddying ocean model, that the opening of a gateway leads to an abrupt onset of a vigorous, deep-reaching, meridional overturning circulation. This meridional overturning circulation has a maximum transport for a shallow gateway, and decreases with further deepening of the gateway. This abrupt change in the meridional overturning circulation can be explained through the ability with which standing meanders – turbulent features located downstream of the gateway – can induce deep vertical heat transport at high latitudes where bottom waters are produced. Our results demonstrate the crucial role of turbulent processes, associated with tectonic evolution, in setting the strength of the global ocean’s deep-reaching meridional overturning circulation.

Ambiguity over the Eocene opening times of the Tasman Gateway and Drake Passage makes it difficult to determine the initiation time of the Antarctic Circumpolar Current (ACC). If the Tasman Gateway opened later than Drake Passage, then Australia may have prevented the proto-ACC from forming. Recent modelling results have shown that only a relatively weak circumpolar transport results under Eocene surface forcing. This leads to warm and buoyant coastal water around Antarctica, which may impede the formation of deep waters and convective processes. This suggests that a change in deep water formation might be required to increase the density contrast across the Southern Ocean and increase circumpolar transport.Here we use a simple reduced gravity model with two basins, to represent the Atlantic and the Pacific. This fixes the density difference between surface and deep water and allows us to isolate the impact of deep water formation on circumpolar transport. With no obstacle on the southern boundary the circumpolar current increases its transport from 82.3 to 270.0 Sv with deep water formation. Placing an Antipodean landmass on the southern boundary reduces this transport as the landmass increases in size. However, circumpolar flow north of this landmass remains a possibility even without deep water formation. Weak circumpolar transport continues until the basin is completely blocked by the Antipodes. When the Antipodes is instead allowed to split from the southern boundary, circumpolar transport recovers to its unobstructed value. Flow rapidly switches to south of the Antipodes when the gateway is narrow.

The existence of mantle plumes was first proposed in the 1970s to explain intra-plate, hotspot volcanism, yet owing to difficulties in resolving mantle upwellings with geophysical images and discrepancies in interpretations of geochemical and geochronological data, the origin, dynamics and composition of plumes and their links to plate tectonics are still contested. In this Review, we discuss progress in seismic imaging, mantle flow modelling, plate tectonic reconstructions and geochemical analyses that have led to a more detailed understanding of mantle plumes. Observations suggest plumes could be both thermal and chemical in nature, can attain complex and broad shapes, and that more than 18 plumes might be rooted in regions of the lowermost mantle. The case for a deep mantle origin is strengthened by the geochemistry of hotspot volcanoes that provide evidence for entrainment of deeply recycled subducted components, primordial mantle domains and, potentially, materials from Earth’s core. Deep mantle plumes often appear deflected by large-scale mantle flow, resulting in hotspot motions required to resolve past tectonic plate motions. Future research requires improvements in resolution of seismic tomography to better visualize deep mantle plume structures at smaller than 100-km scales. Concerted multi-proxy geochemical and dating efforts are also needed to better resolve spatiotemporal and chemical evolutions of long-lived mantle plumes. Mantle plumes are an integral aspect of Earth’s convection system, yet, difficulty in imaging mantle upwellings led to controversies surrounding their origin, dynamics and composition. This Review synthesizes geophysical, geodynamic and geochemical constraints on mantle plumes and their importance in the Earth system.

Australia, and East Gondwana more broadly, host extensive Paleozoic–Mesozoic sedimentary basins with thick siliciclastic sequences. These sediments were for the greater part transported by large-scale fluvial systems; however, the spatial and temporal patterns of sediment dispersal remain poorly understood. We investigate the provenance of rift strata in the Mentelle Basin, Western Australia, which were deposited during the Late Jurassic–Early Cretaceous breakup of India from Australia-Antarctica. Monazite U–Pb and zircon U–Pb–Hf isotopic signatures suggest that the Upper Jurassic–Lower Cretaceous syn-rift sediments were supplied predominately by a transcontinental river system draining sediments from interior regions of East Antarctica to the northern Gondwanan passive margin. This fluvial system was focused within the developing rift between India and Australia-Antarctica. Provenance of the transgressive marine post-breakup strata reflects a transition to a proximal sediment source and marks the end of the transcontinental fluvial system after the final breakup of India from Australia-Antarctica in the Valanginian (~136 Ma). Statistical comparison of detrital zircon spectra of Mentelle Basin syn-rift strata with other Australian Paleozoic–Mesozoic rift strata located along our proposed transport route suggests that the transcontinental fluvial pathway was active since the Late Paleozoic. We infer that this fluvial system was one of the principal modes of siliciclastic sediment delivery to rift and passive margin basins of western Australia.

Large igneous provinces (LIPs) typically form in one short pulse of ∼1–5 Ma or several punctuated ∼1–5 Ma pulses. Here, our 25 new 40Ar/39Ar plateau ages for the main construct of the Kerguelen LIP—the Cretaceous Southern and Central Kerguelen Plateau, Elan Bank, and Broken Ridge—show continuous volcanic activity from ca. 122 to 90 Ma, a long lifespan of >32 Ma. This suggests that the Kerguelen LIP records the longest, continuous high-magma-flux emplacement interval of any LIP. Distinct from both short-lived and multiple-pulsed LIPs, we propose that Kerguelen is a different type of LIP that formed through long-term interactions between a mantle plume and mid-ocean ridge, which is enabled by multiple ridge jumps, slow spreading, and migration of the ridge. Such processes allow the transport of magma products away from the eruption center and result in long-lived, continuous magmatic activity.

Beneath the ice of East Antarctica lies a continent that is likely to be as geologically complex as its neighbors in Gondwana. An improved model of the heterogeneous lithosphere is required to progress research on Antarctica's tectonic evolution and support interdisciplinary studies of cryosphere and solid Earth interaction. We make use of multiple data sets, which were updated following the field campaigns and compilations of the International Polar Year of 2007/2008. Seismic tomography results, gravity anomalies, and surface elevation are used in a novel method, which combines spatial multivariate data to map possible boundaries as projected likelihood functions. Six multivariate combinations are tested and compared with sparse geological observations in East Antarctica. The resulting lithospheric domain boundaries contribute to our understanding of the deep continental structure. New boundaries are suggested in the interior, and models agree with likely surface expressions of crustal tectonic boundaries exposed along the coast.

We present GlobSed, a new global 5‐arc‐minute total sediment thickness grid for the world's oceans and marginal seas. GlobSed covers a larger area than previously published global grids and incorporates updates for the NE Atlantic, Arctic, Southern Ocean, and Mediterranean regions, which results in a 29.7% increase in estimated total oceanic sediment volume. We use this new global grid and a revised global oceanic lithospheric age grid to assess the relationship between the total sediment thickness and age of the underlying oceanic lithosphere and its latitude. An analytical approximation model is used to mathematically describe sedimentation trends in major oceanic basins and to allow paleobathymetric reconstructions at any given geological time. This study provides a much‐needed update of the sediment thickness distribution of the world oceans and delivers a model for sedimentation rates on oceanic crust through time that agrees well with selected drill data used for comparison.

Subglacial and ice-sheet marginal sedimentary basins have very different physical properties to crystalline bedrock and, therefore, form distinct conditions that influence the flow of ice above. Sedimentary rocks are particularly soft and erodible, and therefore capable of sustaining layers of subglacial till that may deform to facilitate fast ice flow downstream. Furthermore, sedimentary rocks are relatively permeable and thus allow for enhanced fluid flux, with associated impacts on ice-sheet dynamics, including feedbacks with subglacial hydrologic systems and transport of heat to the ice-sheet bed. Despite the importance for ice-sheet dynamics there is, at present, no comprehensive record of sedimentary basins in the Antarctic continent, limiting our capacity to investigate these influences. Here we develop the first version of an Antarctic-wide spatial database of sedimentary basins, their geometries and physical attributes. We emphasise the definition of in-situ and undeformed basins that retain their primary characteristics, including relative weakness and high permeability, and therefore are more likely to influence ice sheet dynamics. We define the likely extents and nature of sedimentary basins, considering a range of geological and geophysical data, including: outcrop observations, gravity and magnetic data, radio-echo sounding data and passive and active-source seismic data. Our interpretation also involves derivative products from these data, including analyses guided by machine learning. The database includes for each basin its defining characteristics in the source datasets, and interpreted information on likely basin age, sedimentary thickness, surface morphology and tectonic type. The database is constructed in ESRI geodatabase format and is suitable for incorporation in multifaceted data-interpretation and modelling procedures. It can be readily updated given new information. We define extensive basins in both East and West Antarctica, including major regions in the Ross and Weddell Sea embayments and the Amundsen Sea region of West Antarctica, and the Wilkes, Aurora and Recovery subglacial basins of East Antarctica. The compilation includes smaller basins within crystalline-bedrock dominated areas such as the Transantarctic Mountains, the Antarctic Peninsula and Dronning Maud Land. The distribution of sedimentary basins reveals the combined influence of the tectonic and glacial history of Antarctica on the current and future configuration of the Antarctic Ice Sheet and highlights areas in which the presence of dynamically-evolving subglacial till layers and the exchange of groundwater and heat with the ice sheet bed are more likely, contributing to dynamic behaviour of the Antarctic Ice Sheet.

Sea‐floor spreading at slow rates can be accommodated on large‐offset oceanic detachment faults (ODFs), that exhume lower crustal and mantle rocks in footwall domes termed oceanic core complexes (OCCs). Footwall rocks experience large rotation during exhumation, yet important aspects of the kinematics ‐ particularly the relative roles of solid‐block rotation and flexure ‐ are not clearly understood. Using a high‐resolution numerical model, we explore the exhumation kinematics in the footwall beneath an emergent ODF/OCC. A key feature of the models is that footwall motion is dominated by solid‐block rotation, accommodated by the non‐planar, concave‐down fault interface. A consequence of this fault shape is that curvature measured along the ODF is representative of a neutral stress configuration, rather than a ‘bent one. Instead, it is in the subsequent process of ‘apparent unbending that significant flexural stresses are developed in the model footwall. The brittle strain associated with apparent unbending is produced dominantly in extension, beneath the OCC, consistent with earthquake clustering observed in the Trans‐Atlantic Geotraverse at the Mid‐Atlantic Ridge.

We present an updated oceanic crustal age grid and a set of complementary grids including spreading rate, asymmetry, direction, and obliquity. Our data set is based on a selected set of magnetic anomaly identifications and the plate tectonic model of Muller et al. (2019, 10.1029/2018TC005462 ). We find the mean age of oceanic crust is 64.2 Myr, slightly older than previous estimates, mainly due to the inclusion of pockets of Mesozoic aged crust in the Atlantic and Mediterranean and improvements to the Jurassic Pacific triangle. This older crust is partly compensated by additional Cenozoic‐aged back‐arc basin crust not included in previous models. The distribution of spreading modes based on area of preserved crust is relatively equal between slow (20–55 mm/yr) and fast (75–180 mm/yr) spreading systems at 33% and 39%, respectively. Crust transitional between fast and slow, or intermediate systems (55–75 mm/yr), cover 20% of the preserved ocean floor with much smaller proportions of crust formed at ultraslow (5%) and super‐fast (3%) spreading systems. Slow and intermediate spreading systems exhibit the most stable behavior in terms of spreading asymmetry and obliquity, with the widest distribution of obliquities occurring at ultraslow spreading systems, consistent with present‐day observations. Our confidence grid provides a complementary resource for nonexperts to identify those parts of the age grid that are least well constrained. Our grids in 6, 2, and 1 arc min resolution as well as our python workflow, isopolate, used to compute our data sets are freely available in online repositories and on the GPlates data portal.

East Antarctica remains one of the few continental regions on Earth where an understanding of the origin and causal processes responsible for topographic relief is largely missing. Low‐temperature thermochronology studies of exposed Precambrian basement revealed discrete episodes of cooling and denudation during the Paleozoic-Mesozoic; however, the significance of these thermal events and their relationship to topography across the continental interior remains unclear. Here we use zircon and apatite (U‐Th)/He thermochronology to resolve the low‐temperature thermal evolution of a poorly exposed section of East Antarctic basement in the Bunger Hills region and gain insights into the chronology and style of landscape evolution across East Antarctica. Thermal history modeling results indicate that Precambrian basement in the Bunger Hills region experienced a distinct cooling episode during the Late Paleozoic-Triassic, which we relate to ~2-4 km of regional exhumation associated with intracontinental rifting, followed by a second episode of localized cooling and ≤1 km exhumation during the Late Jurassic-Cretaceous separation of India from East Gondwana. These findings, combined with existing thermochronological and tectonic evidence, support a continent‐scale denudation event associated with uplift and exhumation of large sections of Precambrian basement during Late Paleozoic-Triassic Pangea‐wide intracontinental extension. By contrast, continental extension associated with the Jurassic-Cretaceous breakup of East Gondwana resulted in significant denudation only locally in regions west of the Bunger Hills. We propose that the combined effects of these Paleozoic-Mesozoic tectonic events had a profound impact on the topography across the East Antarctic interior and influenced the long‐term landscape evolution of East Antarctica.

The Southern Ocean is a key player in the climate, ocean, and atmospheric system. As the only direct connection between all three major oceans since the opening of the Southern Ocean gateways, the development of the Southern Ocean and its relationship with the Antarctic cryosphere has influenced the climate of the entire planet. Although the depths of the ocean floor have been recognized as an important factor in climate and paleoclimate models, appropriate paleobathymetric models including a detailed analysis of the sediment cover are not available. Here we utilize more than 40 years of seismic reflection data acquisition along the margins of Antarctica and its conjugate margins, along with multiple drilling campaigns by the International Ocean Discovery Program (IODP) and its predecessor programs. We combine and update the seismic stratigraphy across the regions of the Southern Ocean and calculate ocean-wide paleobathymetry grids via a backstripping method. We present a suite of high-resolution paleobathymetric grids from the Eocene-Oligocene Boundary to modern times. The grids reveal the development of the Southern Ocean from isolated basins to an interconnected ocean affected by the onset and vigor of an Antarctic Circumpolar Current, as well as the glacial sedimentation and erosion of the Antarctic continent. The ocean-wide comparison through time exposes patterns of ice sheet development such as switching of glacial outlets and the change from wet-based to dry-based ice sheets. Ocean currents and bottom-water production interact with the sedimentation along the continental shelf and slope and profit from the opening of the ocean gateways.

The final lithospheric breakup of the Australian‐Antarctic rift system remains controversial due to sparse geological constraints on the nature of the basement along the ocean‐continent transition (OCT) zones. We present new interpretations of multichannel seismic reflection transects and new petrological data of dredged mantle rocks along the East Antarctic margin (Seamount B, offshore Terre Adelie). By combining both data sets, we show that a 50–100 km wide domain of cold and fertile subcontinental mantle was exhumed along the magma‐poor Antarctic margin. This study represents only the second locality, along with the Iberia‐Newfoundland margins, where the importance of exhumed mantle domains along OCTs can be clearly identified. The dredged peridotites preserve characteristics similar to mantle xenoliths found in syn‐ to post‐rift volcanism at the eastern end of the Australian margin (Victoria and Tasmania), indicating the exhumation of fertile subcontinental mantle during rifting between Australia and Antarctica. Seamount B represents the initial stages of exhumation of cold subcontinental lithosphere along an OCT during rifting. This thick mantle domain was likely affected by melt impregnation at high pressure (8 kbar), leading to the formation of plagioclase‐pyroxenites. The combination of continental rifted blocks, a wide domain of volcanic‐poor subcontinental mantle and (ultra‐) slow spreading is analogous to OCTs from the Jurassic Western Tethys and Iberia‐Newfoundland rifted margins. Additionally, evidence of melt stagnation at high pressure suggests that magmatism along the Australian‐Antarctic rifted margins was sufficient to form magnetic anomalies that can be used as isochrons despite their formation in lithosphere other than mature, steady‐state ocean crust.

Northeast Asia underwent widespread rifting and magmatic events during the Cenozoic. The geodynamic origins of these tectonic events are often linked to Pacific plate subduction beneath Northeast Asia. However, the Japan Sea did not open until the late Oligocene, tens of millions of years after Pacific Plate subduction initiation in the Paleocene. Moreover, it is still not clear why the Baikal Rift Zone extension rate increased significantly after the late Miocene, while the Japan Sea opening ceased at the same time. Geodynamic models suggest these enigmatic events are related to the rapidly-aging Pacific Plate at the trench after Izanagi–Pacific spreading ridge subduction. Subduction of the young Pacific Plate delayed the Japan Sea opening during the Eocene while advection of the old Pacific Plate towards the trench increases seafloor age rapidly, allowing the Japan Sea to open after the early Miocene. The Japan Sea opening promotes fast trench retreat and slab stagnation, with subduction-induced wedge zone convection gradually increasing its extent during this process. The active rifting center associated with wedge zone convection upwelling also shifts inland-ward during slab stagnation, preventing further Japan Sea spreading while promoting the Baikal Rift Zone extension. Our geodynamic model provides a good explanation for the temporal-spatial patterns of the Cenozoic tectonic and magmatic events in Northeast Asia.

The first dredge samples recovered from the Batavia Knoll in the eastern Indian Ocean demonstrate it is a rifted continental fragment that now lies submerged in 2 km of water between the Perth Abyssal Plain and Wharton Basin, ∼1600 km offshore Western Australia. This knoll is the second microcontinent to have been discovered in this region, lying ∼180 km to the NE of Gulden Draak Knoll; both knolls rifted from the Indian margin at c. 104–101 Ma during the breakup of East Gondwana. Dredged rocks include granite, granodiorite, charnockite and quartz-rich pegmatite, preserving igneous microstructure and biotite-schlieren. The composite nature of many samples suggests derivation from a felsic igneous complex. This basement is at least partly covered by Late Cretaceous sedimentary strata. Zircon grains from five representative granitoid samples primarily display modified oscillatory zoning and U-Pb data that spread along concordia over ∼50–70 m.y., suggesting protracted magmatism and Pb-loss during the latest Neoproterozoic–early Cambrian (c. 580–530 Ma). Despite the span in U-Pb zircon ages, the primary igneous populations exhibit a relatively narrow range of initial Hf isotopic ratios (Hfi = 0.281290–0.281814; eHfi = − 41.40 to − 23.32). This evolved nature of the Hf signature suggests derivation of melts from ancient crust (TDM2 = 4.05–2.92 Ga) with very limited juvenile input. Plate models based on sparse paleomagnetic data imply significant relative motion between India and Australia during the late Neoproterozoic–Cambrian. We suggest the new isotopic data from the Batavia Knoll granitic rocks, coupled with other regional geological constraints, are consistent with magmatic intrusion and subsequent disturbance of U-Pb systems along a late Neoproterozoic–Cambrian sinistral strike-slip margin related to Gondwana assembly.

Volcanism associated with the Kerguelen Large Igneous Province is found scattered in southwestern Australia (the ca 136 to ca 130 Ma Bunbury Basalts, and ca 124 Ma Wallaby Plateau), India (ca 118 Ma Rajmahal Traps and Cona Basalts), and Tibet (the ca 132 Ma Comei Basalts), but apart from the ∼70 000 km2 Wallaby Plateau, these examples are spatially and volumetrically minor. Here, we report dredge, geochronological and geochemical results from the ∼90 000 km2 Naturaliste Plateau, located ∼170 to ∼500 km southwest of Australia. Dredged lavas and intrusive rocks range from mafic to felsic compositions, and prior geophysical analyses indicate these units comprise much of the plateau substrate. 40Ar/39Ar plagioclase ages from mafic units and U–Pb zircon ages from silicic rocks indicate magmatic emplacement from 130.6 ± 1.2 to 129.4 ± 1.3 Ma for mafic rocks and 131.8 ± 3.9 to 128.2 ± 2.3 Ma for silicic rocks (2σ). These Cretaceous Naturaliste magmas incorporated a significant component of continental crust, with relatively high 87Sr/86Sr (up to 0.78), high 207Pb/204 Pb ratios (15.5–15.6), low 143Nd/144Nd (0.511–0.512) and primitive-mantle normalised Th/Nb of 11.3 and La/Nb of 3.97. These geochemical results are consistent with the plateau being underlain by continental basement, as indicated by prior interpretations of seismic and gravity data, corroborated by dredging of Mesoproterozoic granites and gneisses on the southern plateau flank. The Cretaceous Naturaliste Plateau igneous rocks have signatures indicative of extraction from a depleted mantle, with trace-element and isotopic values that overlap with Kerguelen Plateau lavas reflect crustal contamination. Our chemical and geochronological results therefore show the Naturaliste Plateau contains evidence of an extensive igneous event representing some of the earliest voluminous Kerguelen hotspot magmas. Prior work reports that contemporaneous correlative volcanic sequences underlie the nearby Mentelle Basin, and the Enderby Basin and Princess Elizabeth Trough in the Antarctic. When combined, the igneous rocks in the Naturaliste, Mentelle, Wallaby, Enderby, Princess Elizabeth, Bunbury and Comei-Cona areas form a 136–124 Ma Large Igneous Province covering >244 000 km2.

A new method for modeling heat flux shows that the upper crust contributes up to 70% of the Antarctic Peninsula's subglacial heat flux and that heat flux values are more variable at smaller spatial resolutions than geophysical methods can resolve. Results indicate a higher heat flux on the east and south of the Peninsula (mean 81 mW m−2) where silicic rocks predominate, than on the west and north (mean 67 mW m−2) where volcanic arc and quartzose sediments are dominant. While the data supports the contribution of heat-producing element-enriched granitic rocks to high heat flux values, sedimentary rocks can be of comparative importance dependent on their provenance and petrography. Models of subglacial heat flux must utilize a heterogeneous upper crust with variable radioactive heat production if they are to accurately predict basal conditions of the ice sheet. Our new methodology and data set facilitate improved numerical model simulations of ice sheet dynamics.

We present highlights of the first multibeam and bottom sampling survey surrounding the UNESCO World Heritage listed Heard and McDonald Islands (HIMI), conducted in the HIMI Marine Reserve InnerMarine Zone. These insular shelf data reveal that persistent eastward flowing currents and retreating glaciers drive patterns of sediment distribution. Sedimentary bedform directionality, corroborated by drifter data, suggest that the prevailing energy in this region dominates from west to east, and is deflected in an anticlockwise direction around Heard Island, causing sediment deposition to be concentrated on the eastern (downcurrent) side of the islands. Sediment bedform morphology likely mirrors the eastward flowing Antarctic Circumpolar Current and oscillating east!west tidal currents. Thick sediment accumulations north of Heard Island may be related to deglaciation since the Last Glacial Maximum. Sample sites on the northern down-current side of Heard Islands and on the western up-current side of the McDonald Islands contain a diverse range of taxonomic groups compared to all other sample sites. Benthic specimens obtained in rock dredges and sediment grabs show a range of invertebrate species that are likely endemic to the HIMI region.

Bubble emission mechanisms from submerged Large Igneous Provinces (LIPs) remains enigmatic. The Kerguelen Plateau, a LIP in the southern Indian Ocean, has a long‐sustained history of active volcanism and glacial/interglacial cycles of sedimentation, both of which may cause seafloor bubble production. We present the results of hydroacoustic flare observations around the under‐explored volcanically‐active Heard Island and McDonald Islands on the Central Kerguelen Plateau. Flares were observed with a split‐beam echosounder and characterized using multi‐frequency decibel differencing. Deep‐tow camera footage, water properties, water‐column δ3He, sub‐bottom profile, and sediment δ13C and δ34S data were analyzed to consider flare mechanisms. Excess δ3He near McDonald Islands seeps, indicating mantle‐derived input, suggests proximal hydrothermal activity; McDonald Islands flares may thus indicate CO2, methane, and other minor gas bubbles associated with shallow diffuse hydrothermal venting. The Heard Island seep environment, with sub‐bottom acoustic blanking in thick sediment, muted 3He signal, and δ13C and δ34S fractionation factors, suggest Heard seeps may either be methane gas (possibly both shallow biogenic methane and deeper‐sourced thermogenic methane related to geothermal heat from onshore volcanism) or a combination of methane and CO2, such as seen in sediment‐hosted geothermal systems (Procesi et al., 2019). These data provide the first evidence of submarine gas escape on the Central Kerguelen Plateau and expand our understanding of seafloor processes and carbon cycling in the data‐poor southern Indian Ocean. Extensive sedimentation of the Kerguelen Plateau and additional zones of submarine volcanic activity mean additional seeps or vents may lie outside the small survey area proximal to the islands. Science Foundation Ireland Australian Antarctic Science Program Australian Research Council Australian Government

The roles of plate tectonic or mantle dynamic forces in rupturing continental lithosphere remain controversial. Particularly enigmatic is the rifting of microcontinents from mature continental rifted margins, with plume-driven thermal weakening commonly inferred to facilitate calving. However, a role for plate tectonic reorganisations has also been suggested. Here, we show that a combination of plate tectonic reorganisation and plume-driven thermal weakening were required to calve the Batavia and Gulden Draak microcontinents in the Cretaceous Indian Ocean. We reconstruct the evolution of these two microcontinents using constraints from new paleontological samples, 40Ar/39Ar ages, and geophysical data. Calving from India occurred at 101–104 Ma, coinciding with the onset of a dramatic change in Indian plate motion. Critically, Kerguelen plume volcanism does not appear to have directly triggered calving. Rather, it is likely that plume-related thermal weakening of the Indian passive margin preconditioned it for microcontinent formation but calving was triggered by changes in plate tectonic boundary forces.

The Perth Abyssal Plain (PAP), located offshore southwest Australia, formed at the centre of Mesozoic East Gondwana breakup and Kerguelen plume activity. Despite its importance as a direct and relatively undisturbed recorder of this early spreading history, sparse geophysical data sets and lack of geological sampling hamper our understanding of the evolution of the PAP. This study combines new bathymetric profiles across the PAP with petrographic and geochemical data from the first samples ever to be dredged from the flanks of the Dirck Hartog Ridge (DHR), a prominent linear bathymetric feature in the central PAP, to better constrain the formation of the early Indian Ocean floor and the influence of the Kerguelen plume. Seafloor spreading in the PAP initiated at ~ 136 Ma with spreading observed to occur at (half) rates of ~ 35 mm/yr. Changes in spreading rate are difficult to discern after the onset of the Cretaceous Quiet Zone at ~ 120 Ma, but an increase in seafloor roughness towards the centre of the PAP likely resulted from a half-spreading rate decrease from 35 mm/yr (based on magnetic reversals) to ~ 24 mm/yr at ~ 114 Ma. Exhumed gabbro dredged from the southernmost dredge site of the DHR supports a further slowdown of spreading immediately prior to full cessation at ~ 102 Ma. The DHR exhibits a high relief ridge axis and distinctive asymmetry that is unusual compared to most active or extinct spreading centres. The composition of mafic volcanic samples varies along the DHR, from sub-alkaline dolerites with incompatible element concentrations most similar to depleted-to-normal mid-ocean ridge basalts in the south, to alkali basalts similar to ocean island basalts in the north. Therefore, magma sources and degrees of partial melting varied in space and time. It is likely that the alkali basalts are a manifestation of later excess volcanism, subsequent to or during the cessation of spreading. In this case, enriched signatures may be attributed tectonic drivers and melting of a heterogeneous mantle, or to an episodic influence of the Kerguelen plume over distances greater than 1000 km. We also investigate possible scenarios to explain how lower crustal rocks were emplaced at the crest of the southern DHR. Our results demonstrate the significance of regional tectonic plate motions on the formation and deformation of young ocean crust, and provide insight into the unique DHR morphology.

Long-term variations in eustatic sea level in an ice-free world, which existed through most of the Mesozoic and early Cenozoic eras, are partly driven by changes in the volume of ocean basins. Previous studies have determined ocean basin volume changes from plate tectonic reconstructions since the Mesozoic; however, these studies have not considered a number of important elements that contribute to ocean basin volume, such as regional differences in sedimentation, or uncertainties within the plate tectonic model itself, such as spreading asymmetries and the incomplete representation of back-arc basins in the Mesozoic. Additionally, studies on long-term changes in sea level related to the extension and rifting of passive margins have not been performed on a global-scale and likely significantly underestimated the influence of this process. In order to improve reconstructions of sea level on geologic time scales and assess the uncertainty in deriving the volume of ocean basins based on a global plate kinematic model, we investigate the influence of back-arc basins, spreading asymmetry, large igneous provinces (LIPs), sediment thickness, and passive margins on ocean basin volume since 200 Ma. We find that less-constrained plate tectonic elements, such as the presence of back-arc basins or spreading asymmetry, may contribute up to ~120 m or ~150 m to sea level respectively. Changes in the sea level related to sedimentation and LIPs are respectively ~75–165 m and ~45 m. Changes in sea level associated with passive margin formation are almost negligible at present day, though were much larger in the Cretaceous, and the assumed sedimentation style strongly influences the rate and magnitude of sea-level change. We incorporate predictions for these components during times where ocean basins are predominantly synthetic reconstructions and find that sea level driven by fluctuating ocean basin volume has changed by ~200 m since the Jurassic, which is comparable to previous estimates. Our revised estimates will need to be combined with other processes driving long-term sea-level change, including mantle convection-driven dynamic topography and glacio-eustasy for constructing a complete eustatic sea-level curve. Understanding and quantifying the uncertainties in the volume of ocean basins has implications for modelling subduction flux, the oceanic carbon cycle, and heatflow, and is important for exploring Earth's evolutionary cycles, especially during times in the geologic past where much of the ocean basin history has been lost.

The motion of diverging tectonic plates is typically constrained by geophysical data from preserved ocean crust. However, constraining plate motions during continental rifting and the breakup process relies on balancing evidence from a diverse range of geological and geophysical observations, often subject to differing interpretations. Reconstructing the evolution of rifting and breakup between Australia and Antarctica epitomizes the challenges involved in creating detailed models of Pangea breakup. In this example, differing degrees of emphasis on and alternative interpretations of offshore geophysical data, in particular magnetic anomalies and seismic reflection profiles, and onshore geological data, lead to starkly contrasting views of how the continents were configured at the onset of Mesozoic rifting. Here, we critically review reconstructions of rifting and breakup in the light of all available geological and geophysical data, including magnetic anomalies, fracture zones, conjugate crustal domains, amounts of continental extension, continental geology, plate boundary locations, break-up ages and stratigraphy. We identify the most viable plate tectonic reconstructions both with and without the input of the oldest, more controversial magnetic anomaly interpretations, and discuss implications for reconstructions of other margin pairs. Our analysis highlights key discrepancies between reconstructions based solely on geological piercing points, and those based on a range of constraints. These insights provide a powerful framework for reducing the range of viable models for Australian-Antarctic rifting, and provide key lessons for future efforts aimed at constraining pre- and syn-rift plate tectonic reconstructions. © 2018 Elsevier B.V. S.E.W. and R.D.M. were supported by ARC grants DP130101946 and IH130200012 . J.M.W. was supported by ARC grant DE140100376 . J.A.H was supported under Australian Research Council ‘s Special Research Initiative for Antarctic Gateway Partnership SR140300001 . S.E.W. and J.M.W. were supported by ARC grant DP180102280.

Global plate reorganization events (GPREs) can have profound impact on plate velocities, climate and the biotic cycle but the timing and triggers for GPREs remain debated. The timing and causes of the mid-Cretaceous GPRE, one of only two GPREs since the breakup of Pangea, remains poorly constrained because it occurred during the Cretaceous Normal Superchron. Here, we provide a new plagioclase 40Ar/39Ar age of Ma (2σ) at DSDP site 256 along the world's clearest curved fracture zones in the Wharton Basin, off NW Australia. Using Monte Carlo simulations, we compute that the mid-Cretaceous GPRE commenced at Ma (95% confidence). The mid-Cretaceous GPRE was associated with a significant plate deceleration (minimum ∼26%), similar to the Eocene GPRE, implying that this process is fundamental to plate reconfigurations. We propose that the mid-Cretaceous GPRE was caused by slab-breakoff and cessation of the south-dipping subduction zone in the Mesotethys Ocean at ca. 111 Ma. Ultimately, we posit that subduction zone initiations and cessations are the primary triggers for both post-Pangean GPREs and that top-down processes may be the fundamental drivers for GPREs.

Ocean-floor plateaus are not voluminous lava flows from central volcanoes as thought, but anomalously thick oceanic crust, suggest magnetic anomaly patterns from the Shatsky Rise, in the northwestern Pacific Ocean.

Analysis of dredged samples from the Gulden Draak Knoll demonstrates that it is a submarine rifted continental fragment that lies at the boundary between the western Perth Abyssal Plain and Wharton Basin, Indian Ocean. The Knoll comprises a granulite facies basement, including pelitic paragneiss and mafic orthogneiss, with a Cambrian granite inferred to intrude the other rocks. Boulders and cobbles of felsic gneiss with Mesoproterozoic and Cambrian protolith ages were also sampled likely reflecting a complex basement to variable sedimentary and volcanic rocks. The U–Pb isotopic system in the Archean and Mesoproterozoic zircon is significantly disturbed, reflecting Cambrian orogenesis that affected all samples. The protolith to garnet–sillimanite–biotite paragneiss has a maximum deposition age of 1163 ± 24 Ma and includes older detrital zircon grains with populations at c. 2.65 Ga and between 1.4 and 1.1 Ga. A younger population in this sample is interpreted as a mix of newly grown metamorphic zircon and isotopically reset zircon, implying that the granulite facies metamorphism occurred at c. 511 ± 5 Ma. Protracted Cambrian orogenesis is indicated by a metamorphic age in the mafic orthogneiss of 530 ± 6 Ma and isotopic disturbance shortly following emplacement of granite (c. 540 Ma with zircon ages disturbed to 509 ± 7 Ma) and the protolith to the felsic orthogneiss (c. 528 Ma with zircon ages disturbed to 510 ± 3 Ma). Xenocrystic zircon grains in the Cambrian rocks include Archean (c. 2839 ± 9 Ma) and Mesoproterozoic (1230–1370 Ma) populations also isotopically disturbed during Cambrian orogenesis. Igneous Cambrian zircon grains have less radiogenic Hf-isotope compositions (Hfi = 0.281821–0.281367) than Mesoproterozoic xenocrysts (Hfi = 0.282267–0.281993), indicating limited involvement of the Mesoproterozoic crust in granite production. A more likely source includes Archean crust represented by xenocrysts with Hfi = 0.281399–0.280863. The Gulden Draak Knoll is reconstructed in Gondwana (‘Leeuwin’ full-fit model) along strike of a major structure termed the Indo–Australo–Antarctic Suture (IAAS), recently mapped from geophysical interpretations in Wilkes Land, Antarctica. New isotopic data suggest that basement rocks from the Gulden Draak Knoll have affinity to crust exposed either side of the IAAS. Determining if this structure is a suture zone sensu stricto remains to be tested.

Oceanic fracture zone traces are widely used in studies of seafloor morphology and plate kinematics. Satellite altimetry missions have resulted in high-resolution gravity maps in which all major fracture zones and other tectonic fabric can be identified, and numerous scientists have digitized such lineaments. We have initiated a community effort to maintain low-cost infrastructure that allows seafloor fabric lineaments to be stored, accessed, and updated. A key improvement over past efforts is our processing software (released as a GMT5 supplement) that allows for semiautomatic corrections to previously digitized fracture zone traces given improved gridded data sets. Here we report on our seafloor fabric processing tools, which complement our database of seafloor fabric lineations, magnetic anomaly identifications, and plate kinematic models.

Tectonic plate and lower-mantle motions are often considered independent. Plate tectonic reconstructions reveal long-lived interactions between mantle plumes and mid-ocean ridges that imply feedback between plate boundaries and the deep mantle.

The most poorly exposed and least understood Gondwana-forming orogen lies largely hidden beneath ice in East Antarctica. Called the Kuunga orogen, its interpolation between scattered outcrops is speculative with differing and often contradictory trends proposed, and no consensus on the location of any sutures. While some discount a suture altogether, paleomagnetic data from Indo-Antarctica and Australo-Antarctica do require 3000–5000 km relative displacement during Ediacaran-Cambrian Gondwana amalgamation, suggesting that the Kuunga orogen sutured provinces of broadly Indian versus Australian affinity. Here we use compiled data from detrital zircons offshore of East Antarctica that fingerprint two coastal subglacial basement provinces between 60 and 130°E, one of Indian affinity with dominant ca. 980–900 Ma ages (Indo-Antarctica) and one of Australian affinity with dominant ca. 1190–1140 and ca. 1560 Ma ages (Australo-Antarctica). We combine this offshore compilation with existing and new onshore U-Pb geochronology and previous geophysical interpretations to delimit the Indo-Australo-Antarctic boundary at a prominent geophysical lineament which intersects the coast east of Mirny at ~94°E.

Starkly contrasting tectonic reconstructions have been proposed for the Late Cretaceous to mid Eocene (~ 85–45 Ma) evolution of the southwest Pacific, reflecting sparse and ambiguous data. Furthermore, uncertainty in the timing of and motion at plate boundaries in the region has led to controversy around how to implement a robust southwest Pacific plate circuit. It is agreed that the southwest Pacific comprised three spreading ridges during this time: in the Southeast Indian Ocean, Tasman Sea and Amundsen Sea. However, one and possibly two other plate boundaries also accommodated relative plate motions: in the West Antarctic Rift System (WARS) and between the Lord Howe Rise (LHR) and Pacific. Relevant geologic and kinematic data from the region are reviewed to better constrain its plate motion history during this period, and determine the time-dependent evolution of the southwest Pacific regional plate circuit. A model of (1) west-dipping subduction and basin opening to the east of the LHR from 85–55 Ma, and (2) initiation of northeast-dipping subduction and basin closure east of New Caledonia at ~ 55 Ma is supported. West-dipping subduction and basin opening were not driven by convergence, as has previously been proposed. Our plate circuit analysis suggests that between at least 74 Ma and subduction initiation at ~ 55 Ma there was little net relative motion between the Pacific plate and LHR

The oldest known rocks in Tasmania occur in the Proterozoic Rocky Cape Group, a ∼10 km thick quartzarenite-siltstone-pelite-dominated succession, previously constrained to have been deposited between 1450 Ma and 750 Ma. The Rocky Cape Group contains the enigmatic fossil Horodyskia (‘string of beads’) and has the potential to place Tasmania within supercontinent reconstructions. Detrital zircon and authigenic monazite grains dated via U–Pb laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) analysis yield a deposition window between c. 1450 Ma (youngest zircon populations) and c. 1330 Ma (oldest authigenic monazite population) for the ∼9 km thick lower-middle units (Pedder River Siltstone, Lagoon River Quartzite, Balfour Subgroup which hosts Horodyskia, Detention Subgroup). The upper units (∼1 km) include the Irby Siltstone, which is younger than c. 1310 Ma; this unit is likely separated from both the lower-middle units and the overlying c. 1900 Ma grains were identified. Authigenic monazite age distributions are complex, with multiple age domains within most samples. The common Pb corrected 206U/238Pb ages, defined by oldest grains in each sample, identify three statistically significant groups: (1) 1358–1292 Ma (inclusive of two sigma errors) (Lagoon River Quartzite and Pedder River Siltstone), (2) 1283–1239 Ma (Cowrie Siltstone and Balfour Subgroup), and (3) 1085 ± 9 Ma (Detention Subgroup). We suggest monazite was precipitated during episodic fluid flow events at these three stages in various parts of the basin. The original source for REE-bearing fluids could be detrital monazite, which is rarely preserved, and/or organic matter from the interbedded carbonaceous shales. The Rocky Cape Group has a shared provenance with the higher-grade metasediments (Surprise Bay and Fraser formations) of nearby King Island; the newly derived depositional ages also overlap and support the correlation of these rock associations. On the basis of current datasets, there are no obvious correlations that can be made with Mesoproterozoic basins preserved in mainland Australia. Instead, an overlap in the timing of deposition, similarities in detrital zircon signatures and analogous depositional environment suggests the c. 1.45–1.37 Ga upper Belt-Purcell Supergroup (Missoula and Lemhi groups) of western North America constitutes a plausible correlation with the Tasmanian Mesoproterozoic succession. If the (unexposed) Palaeoproterozoic basement of Tasmania correlates with the Transantarctic Mountains region of East Antarctica as previously proposed, we suggest that the overlying Mesoproterozoic sequences were deposited during rifting of the supercontinent Nuna, between proto-Australia (including the Mawson craton of Antarctica) and Laurentia as predicted by the most recent palaeogeographic reconstructions. Both the Tasmanian and western Laurentian packages were affected by episodic post-depositional fluid flow events between c. 1.35 and 1.05 Ga, possible thermotectonic imprints of the subsequent assembly of Rodinia.

Reconstructing the opening of the Labrador Sea and Baffin Bay between Greenland and North America remains controversial. Recent seismic data suggest that magnetic lineations along the margins of the Labrador Sea, originally interpreted as seafloor spreading anomalies, may lie within the crust of the continent–ocean transition. These data also suggest a more seaward extent of continental crust within the Greenland margin near the Davis Strait than assumed in previous full-fit reconstructions. Our study focuses on reconstructing the full-fit configuration of Greenland and North America using an approach that considers continental deformation in a quantitative manner. We use gravity inversion to map crustal thickness across the conjugate margins, and assimilate observations from available seismic profiles and potential field data to constrain the likely extent of different crustal types. We derive end-member continental margin restorations following alternative interpretations of published seismic profiles. The boundaries between continental and oceanic crust (COB) are restored to their pre-stretching locations along small circle motion paths across the region of Cretaceous extension. Restored COBs are fitted quantitatively to compute alternative total-fit reconstructions. A preferred full-fit model is chosen based on the strongest compatibility with geological and geophysical data. Our preferred model suggests that (i) the COB lies oceanward of magnetic lineations interpreted as magnetic anomaly 31 (70 Ma) in the Labrador Sea, (ii) all previously identified magnetic lineations landward of anomaly 27 reflect intrusions into continental crust, and (iii) the Ungava fault zone in Davis Strait acted as a leaky transform fault during rifting. This robust plate reconstruction reduces gaps and overlaps in the Davis Strait and suggests that there is no need for alternative models proposed for reconstructions of this area including additional plate boundaries in North America or Greenland. Our favored model implies that break up and formation of continent–ocean transition (COT) first started in the southern Labrador Sea and Davis Strait around 88 Ma and then propagated north and southwards up to onset of real seafloor spreading at 63 Ma in the Labrador Sea. In the Baffin Bay, continental stretching lasted longer and actual break up and seafloor spreading started around 61 Ma (Chron 26).

We present a new, 5 min sediment thickness grid for the Australian-Antarctic region (60 E–155 E, 30 S–70 S). New seismic reflection and refraction data have been used to add detail to the conjugate Australian and Antarctic margins and intervening ocean floor where regional sediment thickness patterns were poorly known previously. On the margins, sediment thickness estimates were computed from velocity-depth functions from sonobuoy/refraction velocity solutions ground-truthed against seismic reflection data. For the Southeast Indian Ridge abyssal plains, sediment thickness contours from Geli et al. (2007) were used. The new regional minimum sediment thickness grid was combined with the global National Geophysical Data Center (NGDC) sediment grid to create an updated global grid. Even using the minimum estimates, sediment accumulations on the extended Australian and Antarctic continental margins are 2 km thicker across large regions and up to 9 km thicker in the Ceduna Basin compared to the global NGDC compilation of sediment thickness data.

The seafloor within the Perth Abyssal Plain (PAP), offshoreWestern Australia, is the only section of crust that directly records the early spreading history between India and Australia during the Mesozoic breakup of Gondwana. However, this early spreading has been poorly constrained due to an absence of data, including marine magnetic anomalies and data constraining the crustal nature of key tectonic features. Here, we present new magnetic anomaly data from the PAP that shows that the crust in the western part of the basin was part of the Indian Plate—the conjugate flank to the oceanic crust immediately offshore the Perth margin, Australia. We identify a sequence of M2 and older anomalies in the west PAP within crust that initially moved with the Indian Plate, formed at intermediate half-spreading rates (35 mm/yr) consistent with the conjugate sequence on the Australian Plate. More speculatively, we reinterpret the youngest anomalies in the east PAP, finding that the M0-age crust initially formed on the Indian Plate was transferred to the Australian Plate by a westward jump or propagation of the spreading ridge shortly afterM0 time. Samples dredged from the Gulden Draak and Batavia Knolls (at the western edge of the PAP) reveal that these bathymetric features are continental fragments rather than igneous plateaus related to Broken Ridge. These microcontinents rifted away from Australia with Greater India during initial breakup at ~130Ma, then rifted from India following the cessation of spreading in the PAP (~101–103Ma).

Published plate tectonic models for the Australian-Antarctic plate pair imply geologically improbable scenarios at either, or both, ends of the Cretaceous rift and spreading system. Controversy also exists around the location of and motion at the plate boundary extending west of Australia-Antarctica, through the Kerguelen Plateau region. We present a plate tectonic model of relative motions among India, Australia and Antarctica from the onset of continental rifting to the establishment of rapid seafloor spreading, at ~43 Ma. The model conforms to a wide range of geological/geophysical evidence and reconstructs the formation of both the western Kerguelen region and the eastern Tasman region. The incorporation of spatio-temporally continuous plate boundaries reveals the presence of a plate boundary beneath the contiguous Central Kerguelen Plateau and Broken Ridge for ~65 million years. To investigate the relationship between the plate boundary system and the Kerguelen plume we test three alternative absolute reference frames. Using a fixed hotspot reference frame, the Indian Ocean mid-ocean ridge system remains within 500 km of the Kerguelen plume, while the proximity of the plate boundaries and the plume is more variable with a moving hotspot reference frame. Proximity between the plume, plate boundaries, and the Central Kerguelen Plateau/Broken Ridge for ~65Myrs, suggests that these specific features were not formed by a single, short-lived (5–10 Myr) pulse of magmatic activity, but rather by a ~25 Myr period of relatively high magma flux followed by ~40 Myr period of lower volume magmatic activity, an interpretation not excluded by the relatively sparse dredge and drill ages.

Published models for the Cretaceous sea!oor-spreading history of East Gondwana result in unlikely tectonic scenarios for at least one of the plate boundaries involved and/or violate particular constraints from at least one of the associated ocean basins. We link East Gondwana spreading corridors by integrating magnetic and gravity anomaly data from the Enderby Basin off East Antarctica within a regional plate kinematic framework to identify a conjugate series of east-west-trending magnetic anomalies, M4 to M0 (~126.7–120.4 Ma). The mid-ocean ridge that separated Greater India from Australia-Antarctica propagated from north to south, starting at ~136Ma northwest of Australia, and reached the southern tip of India at ~126 Ma. Sea!oor spreading in the Enderby Basin was abandoned at ~115 Ma, when a ridge jump transferred the Elan Bank and South Kerguelen Plateau to the Antarctic plate. Our revised plate kinematic model helps resolve the problem of successive two-way strike-slip motion between Madagascar and India seen in many previously published reconstructions and also suggests that sea!oor spreading between them progressed from south to north from 94 to 84 Ma. This timing is essential for tectonic !ow lines to match the curved fracture zones of the Wharton and Enderby basins, as Greater India gradually began to unzip from Madagascar from ~100 Ma. In our model, the 85-East Ridge and Kerguelen Fracture Zone formed as conjugate !anks of a "leaky" transform fault following the ~100Ma spreading reorganization. Our model also identi"es the Afanasy Nikitin Seamounts as products of the Conrad Rise hotspot.