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The Ontong Java Plateau (OJP), Shatsky Rise (SR), and Kerguelen Plateau/Broken Ridge (KP/BR) represent three large igneous provinces (LIPs) located in oceanic settings. The basement lavas have been investigated through scientific ocean drilling and, in the case of the OJP, fieldwork on the emergent obducted portions of the plateau in the Solomon Islands. Such studies show that these three LIPs have very different characteristics. For example, the KP/BR still has an active hotspot, whereas the OJP and the SR do not. The OJP is remarkable in its compositional monotony across the plateau (the Kwaimbaita geochemical type), with minor compositional variation found at the margins (the Kroenke, Singgalo, and Wairahito types). Shatsky Rise shows more compositional variation and, like the OJP, has a dominant lava type (termed the "normal" type) in the early stages (Tamu Massif), but subsequent eruptions at the Ori and Shirshov massifs comprise isotopically and trace element enriched lavas, likely reflecting a change in mantle source over time. The KP/BR has highly variable basement lava compositions, ranging from lavas slightly enriched above that of normal mid-ocean ridge basalt in the northern portion (close to the South East Indian Ridge) to more enriched varieties to the south and on Broken Ridge, with a continental crust signature present in lavas from the southern and central KP/BR. The OJP and the KP/BR appear to have formed through punctuated magmatic events, whereas the SR was formed by one relatively long, drawn out event. The formation of oceanic LIPs has in many (but not all) cases been synchronous with oceanic anoxic events. This paper focuses on three oceanic plateaus to emphasize the debate surrounding the environmental impact such LIPs may have had, and also highlights the contributions of scientific ocean drilling to our knowledge of oceanic LIP formation and evolution. This new knowledge allows planning for future oceanic LIP drilling.

A compilation of foraminiferal stable isotope measurements from southern high latitude (SHL) deep-sea sites provides a novel perspective important for understanding Earth's paleotemperature and paleoceanographic changes across the rise and fall of the Cretaceous Hot Greenhouse climate and the subsequent Paleogene climatic optimum. Both new and previously published results are placed within an improved chronostratigraphic framework for southern South Atlantic and southern Indian Ocean sites. Sites studied were located between 58° and 65°S paleolatitude and were deposited at middle to upper bathyal paleodepths. Oxygen isotope records suggest similar trends in both bottom and surface water temperatures in the southern sectors of the South Atlantic and in the Indian Ocean basins. Warm conditions were present throughout the Albian, extreme warmth existed during the Cretaceous Thermal Maximum (early-mid-Turonian) through late Santonian, and long-term cooling began in the Campanian and culminated in Cretaceous temperature minima during the Maastrichtian. Gradients between surface and seafloor δ18O and δ13C values were unusually high throughout the 11.5 m.y. of extreme warmth during the Turonian-early Campanian, but these vertical gradients nearly disappeared by the early Maastrichtian. In absolute terms, paleotemperature estimates that use standard assumptions for pre-glacial seawater suggest sub-Antarctic bottom waters were ≥21 °C and sub-Antarctic surface waters were ≥27 °C during the Turonian, values warmer than published climate models support. Alternatively, estimated temperatures can be reduced to the upper limits of model results through freshening of high latitude waters but only if there were enhanced precipitation of water with quite low δ18O values. Regardless, Turonian planktonic δ18O values are ~1.5‰ lower than minimum values reported for the Paleocene-Eocene Thermal Maximum (PETM) from the same region, a difference which corresponds to Turonian surface temperatures ~6 °C warmer than peak PETM temperatures if Turonian and Paleocene temperatures are estimated using the same assumptions. It is likely that warm oceans surrounding and penetrating interior Antarctica (given higher relative sea level) prevented growth of Antarctic ice sheets at all but the highest elevations from the late Aptian through late Campanian; however, Maastrichtian temperatures may have been cool enough to allow growth of small, ephemeral ice sheets. The standard explanation for the sustained warmth during Cretaceous Hot Greenhouse climate invokes higher atmospheric CO2 levels from volcanic outgassing, but correlation among temperature estimates, proxy estimates of pCO2, and intervals of high fluxes of both mafic and silicic volcanism are mostly poor. This comparison demonstrates that the relative timing between events and their putative consequences need to be better constrained to test and more fully understand relationships among volcanism, pCO2, temperature ocean circulation, Earth's biota and the carbon cycle.

A high-resolution multibeam echosounder (MBES) dataset covering over 279,000 km2 was acquired in the southeastern Indian Ocean to assist the search for Malaysia Airlines Flight 370 (MH370) that disappeared on 8 March 2014. The data provided an essential geospatial framework for the search and is the first large-scale coverage of MBES data in this region. Here we report on geomorphic analyses of the new MBES data, including a comparison with the Global Seafloor Geomorphic Features Map (GSFM) that is based on coarser resolution satellite altimetry data, and the insights the new data provide into geological processes that have formed and are currently shaping this remote deepsea area. Our comparison between the new MBES bathymetric model and the latest global topographic/bathymetric model (SRTM15_plus) reveals that 62% of the satellite-derived data points for the study area are comparable with MBES measurements within the estimated vertical uncertainty of the SRTM15_plus model (± 100 m). However, > 38% of the SRTM15_plus depth estimates disagree with the MBES data by > 100 m, in places by up to 1900 m. The new MBES data show that abyssal plains and basins in the study area are significantly more rugged than their representation in the GSFM, with a 20% increase in the extent of hills and mountains. The new model also reveals four times more seamounts than presented in the GSFM, suggesting more of these features than previously estimated for the broader region. This is important considering the ecological significance of high-relief structures on the seabed, such as hosting high levels of biodiversity. Analyses of the new data also enabled sea knolls, fans, valleys, canyons, troughs, and holes to be identified, doubling the number of discrete features mapped. Importantly, mapping the study area using MBES data improves our understanding of the geological evolution of the region and reveals a range of modern sedimentary processes. For example, a large series of ridges extending over approximately 20% of the mapped area, in places capped by sea knolls, highlight the preserved seafloor spreading fabric and provide valuable insights into Southeast Indian Ridge seafloor spreading processes, especially volcanism. Rifting is also recorded along the Broken Ridge – Diamantina Escarpment, with rift blocks and well-bedded sedimentary bedrock outcrops discernible down to 2400 m water depth. Modern ocean floor sedimentary processes are documented by sediment mass transport features, especially along the northern margin of Broken Ridge, and in pockmarks (the finest-scale features mapped), which are numerous south of Diamantina Trench and appear to record gas and/or fluid discharge from underlying marine sediments. The new MBES data highlight the complexity of the search area and serve to demonstrate how little we know about the vast areas of the ocean that have not been mapped with MBES. The availability of high-resolution and accurate maps of the ocean floor can clearly provide new insights into the Earth's geological evolution, modern ocean floor processes, and the location of sites that are likely to have relatively high biodiversity.

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

We report new age determinations and compositions for rocks from 18 dredge hauls collected from eight submarine areas across Central Kerguelen Plateau (CKP). Sea knolls and volcanic fields with multiple small cones were targeted over a ∼125 000 km2 region that includes Heard and McDonald Islands. Large early Miocene (22–16 Ma) sea knolls rise from the western margin of the CKP and are part of a NNW–SSE line of volcanic centres that lie between Iles Kerguelen and Heard and McDonald Islands. These are probably related to hotspot activity now underlying the Heard Island area. We see evidence of much younger activity (5 Ma to present) in volcanic fields to the north of, and up to 300 km NE of, Heard Island. Compositions include basanite, basalt and trachybasalt, which are broadly similar to plateau lava flows from nearby Ocean Drilling Program Site 1138, lower Miocene lavas at Iles Kerguelen, dredged rocks from the early Miocene sea knolls, and Big Ben lavas from Heard Island. Geochemical data indicat...

We present 40Ar/39Ar age and geochemical (major and trace element and Sr–Nd–Hf–Pb isotope) data from submarine samples recovered from the basement of the Manihiki Plateau during the R/V Sonne research expedition SO193. The samples, predominately tholeiites, with minor occurrences of basaltic andesites and hawaiites, give a mean age of 124.6 ± 1.6 Ma from four different localities on the plateau. Based on TiO2 content, we define two groups of volcanic rocks that differ in trace element and isotopic compositions. Partial melting modeling suggests that the low-Ti group lavas were derived through large degrees of melting (c. 30%) of a peridotitic source at mantle potential melting temperatures of c. Tp = 1510 °C, more than 100 °C above the ambient mantle potential melting temperature. Since the primary water contents of both groups of lavas are low (0.1–0.3g wt.%) and the source is peridotitic, excess temperature is most likely the reason for the large degrees of melting producing the large volume of plateau basalts, consistent with the involvement of a mantle plume. The incompatible element contents of the low-Ti group lavas show a multistage history with enrichment in the most incompatible elements of a previously highly depleted source. They have isotopic compositions similar to enriched mid-ocean-ridge basalt (EMORB) and similar to the common focal zone (FOZO) component. The high-Ti group lavas have more enriched incompatible element compositions overall. Their isotopic compositions tend towards an enriched mantle (EMI)-type endmember, similar, although less extreme, than lavas from the Pitcairn Islands. The geochemistry of the Manihiki Plateau can best be explained by a plume containing three components: 1) a dominant peridotitic FOZO-type component, 2) delaminated EMI-type subcontinental lithospheric mantle (SCLM), and 3) a HIMU (recycled oceanic crustal)-type component possibly in the form of eclogite/pyroxenite. The similarity in age and geochemical composition of Manihiki, Hikurangi and Ontong Java basement lavas, including volcanism in some adjacent basins, suggests that the Greater Ontong Java Volcanic Event covered c. 1% of the Earth's surface with volcanism.

To show the structure of oceanic crust and Moho around the eastern Ogasawara Plateau, we have analyzed industry-standard two-dimensional multichannel seismic reflection data. To obtain improved velocity models, phase information of seismic signals was used for velocity analysis and velocity models for oceanic crust above Moho were determined. We apply this velocity analysis technique to seismic reflection data around the eastern Ogasawara Plateau, with the result of clear images of structures within oceanic crust and Moho. South of the Ogasawara Plateau, Moho deepens proximal to the Plateau. Moho distal to the Plateau is ca 7 km below sea floor (bsf), whereas it is ca 10 km bsf near the Plateau. The characters of oceanic crust and Moho differ significantly north and south of the Plateau. To the north, the structure of oceanic crust is ambiguous, the sea floor is shallower and less smooth, and Moho is discontinuous. To the south, structures within oceanic crust and Moho are imaged clearly, and the sea floor is deeper. A strong Moho reflection south of the Plateau might represent a sharp boundary between layered gabbro and peridotite. However, discontinuous Moho reflections north of the Plateau might represent rough topography because of intensive magmatism or a gradual downward increase in velocity within a thick Moho transition zone. A fracture zone north of the Plateau also appears to separate oceanic crust and Moho of different characters, suggesting vigorous magmatism between the Plateau and the fracture zone, and that the Ogasawara Plateau and the fracture zone influenced the genesis of oceanic crust and upper mantle. Differences in acoustic characteristics to the north and south of the Plateau are apparent in profiles illuminated by seismic attributes.

Oceanic Anoxic Events (OAEs) are geological time intervals characterized by extremely high burial rates of organic carbon that led to deposition of organic-rich “black shales” in the global ocean. It has been proposed that oceanic anoxic events are ultimately caused by massive volcanism associated with formation of large igneous provinces (LIPs) because of chronological similarities, but no general consensus has developed yet. To investigate the possibility of LIP volcanism instigating OAEs, we measured stable isotopic compositions of bulk organic carbon (δ13Corg) and lead (Pb) isotopic compositions in the silicate sediment fraction across the Bonarelli black shale (Italy), a type stratigraphic section for the end-Cenomanian OAE (OAE-2; 94 Ma). Ultra-high-resolution δ13Corg records determined every 1.5 mm capture a 3‰ sharp negative shift at the base of the Bonarelli. At the same stratigraphic level, Pb isotopic compositions in the silicate sediment fraction exhibit significant shifts toward characteristic values of volcanic rocks from contemporaneous LIPs (Caribbean and Madagascar flood basalts). These data suggest a rapid, substantial increase in the relative supply of silicate minerals from the two LIPs. Massive subaerial volcanism associated with LIP formation provides a simple explanation for these two isotopic geochemical signals via release of a huge amount of carbon dioxide (∼ 105 Gt CO2) and particulate materials into the atmosphere, which resulted in a rapid negative shift of δ13C in sea water and changes in Pb isotopic compositions in the silicate sediment fraction, respectively. We interpret that massive volcanism triggered significant climatic changes, inducing biotic crises and oceanic anoxia.

The Manihiki Plateau in the western equatorial Pacific Ocean is a Cretaceous Large Igneous Province. Several studies have proposed that the Manihiki Plateau was formed by the same mantle plume that formed the Ontong Java and Hikurangi plateaus ca. 125 Ma. Recent multibeam bathymetric surveys of the Manihiki Plateau reveal the morphology of the Danger Islands Troughs (DIT), Suvarov Trough, which are systems of deep troughs within the plateau. The troughs divide the Manihiki Plateau into three distinct provinces, the North Plateau, the Western Plateaus, and the High Plateau. The DIT between the High Plateau and Western Plateaus comprises four en echelon troughs. With one exception, all segments of the DIT are bordered by steep escarpments, to 1500 m high. The basins of the DIT are smooth. Elongated northeast-southwest–striking scarps are common in the southernmost DIT and at the junction between the DIT and Suvarov Trough. The features revealed by the new bathymetric data indicate that a sinistral strike-slip tectonic environment formed the DIT during the break-up into the Manihiki and Hikurangi plateaus, whereas the Suvarov Trough developed after the formation of the DIT.

A rich mosaic of disparate crustal types characterizes the Earth beneath the sea. Although “normal” oceanic crust approximately 7-km thick is by far the most prevalent, abnormally thick oceanic-type crust of large igneous provinces (LIPs) also forms a signifi cant component of the marine realm (e.g., Coffi n and Eldholm, 1994; Mahoney and Coffin, 1997; Saunders, 2005). Scientific ocean drilling has significantly advanced understanding of LIPs. Herein we focus on significant outcomes of ten LIP-dedicated expeditions between 1985 and 2000 and also highlight prospects for future drilling efforts. The ten expeditions include three to the volcanic margins of the North Atlantic Tertiary Igneous Province, four to the Kerguelen Plateau/Broken Ridge LIP in the Indian Ocean, two to the Ontong Java Plateau in the western equatorial Pacifi c Ocean, and one to the Chagos-Maldive-Laccadive Ridge and Mascarene Plateau in the Indian Ocean (Table 1). Complementary geophysical and/or onshore geological investigations have added signifi cant value to all of these expeditions.

Possibilities for the fate of oceanic plateaus at subduction zones range from complete subduction of the plateau beneath the arc to complete plateau–arc accretion and resulting collisional orogenesis. Deep penetration, multi-channel seismic reflection (MCS) data from the northern flank of the Solomon Islands reveal the sequence stratigraphy, structural style, and age of deformation of an accretionary prism formed during late Neogene (5–0 Ma) convergence between the 33-km-thick crust of the Ontong Java oceanic plateau and the 15-km-thick Solomon island arc. Correlation of MCS data with the satellite-derived, free-air gravity field defines the tectonic boundaries and internal structure of the 800-km-long, 140-km-wide accretionary prism. We name this prism the “Malaita accretionary prism” or “MAP” after Malaita, the largest and best-studied island exposure of the accretionary prism in the Solomon Islands. MCS data, gravity data, and stratigraphic correlations to islands and ODP sites on the Ontong Java Plateau (OJP) reveal that the offshore MAP is composed of folded and thrust faulted sedimentary rocks and upper crystalline crust offscraped from the Solomon the subducting Ontong Java Plateau (Pacific plate) and transferred to the Solomon arc. With the exception of an upper, sequence of Quaternary? island-derived terrigenous sediments, the deformed stratigraphy of the MAP is identical to that of the incoming Ontong Java Plateau in the North Solomon trench.

Large igneous provinces (LIPs) represent huge volumes of erupted and intruded magma and are exceptional volcanic events in Earth history. They were erupted over a brief period of geologic time. The volume of magma emitted during each individual eruption that makes up an LIP (frequently 103 to perhaps 104 km3) is also exceptional, and these form Earth's largest eruptions. LIPs occur on continental crust (flood basalt provinces) and in ocean basins (oceanic plateaus), and at the transition between continents and oceans (“volcanic-”divergent margins). Basaltic LIPs usually form within a geologically brief period of time, especially the climax, or peak, of volcanic output, which may be less than 1 million years in duration. The eruptions that form flood basalt provinces have been proposed as a cause of major environmental perturbations throughout much of Earth history, including mass extinctions. Pāhoehoe-type lavas dominate in flood basalt provinces, and eruptions are thought to have durations of decades to perhaps centuries. The huge flow fields of pāhoehoe lavas are dominated by sheet lobes in many provinces, as well as alternations with flow fields dominated by smaller inflated lava lobes. Vents are poorly known, but some, at least, were long fissure-type systems.

The Kerguelen hotspot (Indian Ocean) has produced basalt for …130 Myr, among the longest known volcanic records from a single source. New and published 40Ar/39Ar age determinations from the Kerguelen Plateau, Broken Ridge, Rajmahal Traps, and Bunbury basalts, and of Indian and Antarctic dikes help to document the hotspot’s history. Using radiometric dates and crustal structure determined from geophysical data and drilling results, we calculate the magmatic output of the Kerguelen hotspot through time. Output rates have varied in ways not predicted by current geodynamic models; maximum eruption volumes postdate the initial surface manifestation of the hotspot as well as break-up between Antarctica and India by ∶15 Myr, and magma output rates were high, as well as geographically diverse, over an interval of 25 Myr, from …120 to …95 Ma. We propose two alternatives to the standard mantle plume paradigm, one involving multiple plume sources, and another consisting of a single, but dismembered plume source.

Large igneous provinces (LIPs) are constructed when Two objectives of ODP Leg 183 were to sample the copious amounts of mantle-derived magma enter the submarine LIP in as many locations as possible to: (1) Earth’s crust in localized regions. Although the Kerguelen determine the temporal variation in magma production; Plateau and Broken Ridge are now submarine, they (2) constrain the origin and evolution of the volcanic formed as a contiguous, largely subaerial LIP during rocks forming the LIP. Studies of igneous basement Cretaceous time in the eastern Indian Ocean. Subrecovered during Leg 183 complement continuing studies sequently, they were separated by sea-floor spreading of the Cenozoic subaerial lavas that form the Kerguelen beginning in Middle Eocene time along the Southeast Archipelago. This volume includes a collection of papers Indian Ridge (SEIR; Fig. 1). The Kerguelen Archipelago that address these objectives by using data for lavas is a Cenozoic feature constructed on the Northern Kerforming the Kerguelen Plateau, Broken Ridge and Kerguelen Plateau (NKP; Fig. 1). Together with the guelen Archipelago. >82–38 Ma hotspot track formed by the Ninetyeast High-quality radiometric age determinations are critRidge, the Kerguelen Plateau, Broken Ridge and Kerical for understanding rates of LIP formation, their causguelen Archipelago represent >119 Myr of volcanism ative dynamic mantle processes, and their temporal that has been attributed to the Kerguelen mantle plume. relationships to potentially related environmental Although the igneous basement of the Kerguelen Plateau changes. Duncan employs the Ar/Ar technique to had been sampled at Sites 738, 747, 749 and 750 (Fig. determine ages at all of the ODP Leg 183 igneous 1) by Ocean Drilling Program (ODP) Legs 119 and 120, basement drill sites (Fig. 1). In general, ages young Leg 183 was the first leg dedicated to understanding the northwards on the Kerguelen Plateau, from >119 Ma origin and evolution of an oceanic LIP. Five sites (1136, at Site 1136 in the south to >34 Ma at Site 1140 in the 1137, 1138, 1139, 1140) penetrated igneous basement north. Emplacement of the conjugate Central Kerguelen of the Kerguelen Plateau, and at two sites (1141, 1142) Plateau (CKP) and Broken Ridge falls within an >5 Myr the first basement samples were obtained from Broken Ridge (Fig. 1). window from >100 to >95 Ma. An unanticipated result

We use multichannel seismic data, gravity, and subsidence modeling, in conjunction with plate reconstructions, to evaluate the crustal origin and composition of the Kerguelen Plateau. Predominantly oceanic crust of the southern and parts of the central Kerguelen Plateau appears to include continental fragments related to the breakup of India and Antarctica; these fragments may have been metamorphosed during emplacement of the main plateau. The upper crust is basaltic, the middle crust is intrusive mafic rock and intruded continental crust, and the lower crust is a plagioclase-rich metamorphic rock. The Labuan Basin crust is predominantly oceanic with stranded Kerguelen Plateau fault blocks. High-density lower crust in the Labuan Basin is probably composed of serpentinized peridotites formed during slow rifting and spreading. Plate reconstruction models indicate opening between eastern Broken Ridge and southern Kerguelen Plateau at ∼90 Ma, heralding the formation of the Labuan Basin and Diamantina Zone; crustal attenuation and slow accretion of oceanic crust continued until the Australian and Antarctic plates separated at CI8 time (∼40 Ma). Plate reconstructions of the free-air gravity field indicate that the Naturaliste Plateau fits against Antarctica and that Elan Bank and India were juxtaposed until ∼110 Ma. Both Naturaliste Plateau and Elan Bank are probable microcontinents. A ∼1 km positive residual depth anomaly in the oceanic basins adjacent to the plateau, along with the positive geoid anomaly centered beneath the northern Kerguelen Plateau, imply that the lithosphere is partially dynamically supported by an upwelling hot asthenosphere of the Kerguelen hot spot.

New marine geophysical data along the Macquarie Ridge Complex, the Australia-Pacific plate boundary south of New Zealand, illuminate regional neotectonics. We identify tectonic spreading fabric and fracture zones and precisely locate the Australia-Pacific plate boundary along the Macquarie Ridge Complex. We interpret a ∼5–10 km wide Macquarie Fault Zone between the two plates along a bathymetrie high that extends nearly the entire length of the Australia-Pacific plate boundary south of New Zealand. We conclude that this is the active Australia-Pacific strike-slip plate boundary. Arcuate fracture zones become asymptotic as they approach the plate boundary. A broad zone of less intense deformation associated with the plate boundary extends ∼50 km on either side of the Macquarie Fault Zone. Marine geophysical data suggest that distinct segments of the plate boundary have experienced convergence and strike-slip deformation, although teleseismic evidence overwhelmingly indicates strike-slip motion along the entire surveyed boundary today. The McDougall and southernmost Puysegur segments show no evidence for past underthrusting, whereas data from the Macquarie and Hjort segments strongly suggest past convergence. The present-day strike-slip plate boundary along the Macquarie Ridge Complex coincides with the relict spreading center responsible for Australia-Pacific crust in the region. Our conceptual model for the transition from seafloor spreading to strike-slip motion along the Macquarie Ridge Complex addresses the decreasing length of spreading center segments and spacing between fracture zones, as well as the arcuate bend of the fracture zones that become asymptotic to the current transform plate boundary.

Seafloor structure at the Macquarie Ridge Complex strongly influences the intensity and circulation pattern of ocean currents south of New Zealand. New marine geophysical data show heterogeneous sedimentary environments on Macquarie seafloor that reflect interaction of highly variable bathymetry with the Antarctic Circumpolar Current and north flowing Antarctic Bottom Water. Acoustic backscatter, bathymetry, and seismic reflection data collected aboard R/V Rig Seismic in 1994 show five bathymetrically constrained sedimentary provinces flanking the ridge complex: (1) northwest Macquarie hemipelagic drifts, (2) current-modified Solander submarine fan complex, (3) southwest Macquarie manganese nodule province, (4) Emerald Basin pelagic drift province, and (5) sediment-free oceanic crust related to the 53.5°S passage in the Macquarie Ridge Complex. The late Miocene-Pliocene opening of a 53.5°S passage in the ridge complex caused a major increase in the intensity of ocean current circulation, sediment reworking, and erosion in all sedimentary provinces.

We examine the early geological history of the southern Kerguelen Plateau (Indian Ocean) using ocean bottom seismometer ((ORS), multichannel seismic (MCS), and Ocean Drilling Program data. Velocity-depth models in the sedimentary Raggatt Basin are constrained by near-range OBS data (refractions and reflections, including multiples and converted shear waves) and migrated MCS data. The models elucidate the significance of Lower Cretaceous lava flows, Albian to Coniacian/Santonian terrestrial and terrigenous sediment, and Maastrichtian and Paleocene seismic sequences. The Albian/Aptian basaltic basement complex consists of an upper and a lower series. The upper series is characterized by average Vps of 4.6-4.7 km/s, an upward increase of intercalated terrestrial sediment and altered flowtops, and a concomitant decrease in flow thickness ; the lower series is marked by average Vps of 5.3-5.5 km/s, and contains thicker flows and less sediment. A volcanic center in the Raggatt Basin shows relatively low Vps (3.7-3.9 km/s for the upper series, 4.7-4.9 km/s for the lower series), and dipping reflections on the Raggatt Basin's flanks are also recorded as refractions. Terrestrial and terrigenous sediment of the Raggatt Basin, immediately overlying basement, is characterized by a seismic low-velocity layer with Vps ranging from 2.2-2.9 km/s and a thickness of greater than 1100 m in the central basin. Nearby source regions (e.g. Banzare Bank and other elevated areas south of the basin) account for a terrestrial and terrigenous sediment volume of approximately 12,500 km3, deposited over approximately 20 m.y. The depocenter of the Raggatt Basin began shifting in Santonian to early Maastrichtian time, and concluded by early late Paleocene time. (Résumé d'auteur)

The impact of volcanism on weather and climate is unequivocally documented by temporal correlations in both historical and prehistorical records. Although volcanic events have been traced far back in time, only Quaternary and Holocene records provide the detail and resolution necessary to address many otherwise ambiguous connections. Both observations and modeling suggest inherent relationships among the geosphere, hydrosphere, cryosphere, and atmosphere, setting the stage for various climate responses commonly incorporating complex feedback loop systems and their elusive dependence on proximity to thresholds. Furthermore, both volcanism and climate may trigger secondary phenomena of sometimes catastrophic nature. The cause-and-effect sequence is particularly intriguing, i.e., whether volcanism forces climate or changing climate forces volcanism or if, in fact, either or both can occur in nature. This overview is based on a number of studies that comprehensively address the overall theme (e.g., Cas and Wright, 1987; Sigurdsson, 1999; Robock, 2000; Schmincke, 2004; Oppenheimer, 2011; McGuire, 2012; Cashman and Sparks, 2013; and references therein).

Gondwana, with East Antarctica as its center, began to fragment during Late Triassic to Early Jurassic time. With the exception of the Permian or older convergent Pacific margin of the Antarctic Peninsula and Thurston Island, the margins of Antarctic are rifted or transform margins. The earliest seaway around the present-day margin of Antarctica developed during the Late Jurassic along the western part of Queen Maud Land of East Antarctica and may have included parts of the Weddell Sea margin of the Antarctic Peninsula. The next significant change occurred i­130 Ma, with the opening of the South Atlantic and rifting of India from East Antarctica. Circulation of deep water into the South Atlantic was blocked by the Falkland Plateau, and open, deep water circulation between India and Antarctica was blocked by Sri Lanka. The Falkland Plateau cleared the southern tip of Africa i­100 Ma, but circulation from the South Atlantic northward into the Central Atlantic probably did not begin until Santonian time. Slow spreading between Australia and Antarctica, and a complicated spreading regime between various New Zealand plates, may have opened a seaway as early as 80 Ma. However, major circulation was probably delayed until as late as 40 Ma, when Tasmania and the South Tasman Rise finally cleared north Victoria Land of East Antarctica. The final barrier to circumpolar circulation was in the region of southern South America and the northern Antarctic Peninsula. There, various continental fragments may have partially blocked Drake Passage until the Miocene. General cooling of the world's oceans accompanied early Tertiary opening between Australia and Antarctica and the later opening of Drake Passage.

Large igneous provinces (LIPs) are common on the Moon, Mars and Venus, and their presence, characteristics, and geologic and temporal settings offer a potentially important perspective for interpreting LIPs on Earth. On the Moon, shallow magma reservoirs and large shield volcanoes are unknown. The relatively low-density, thick anorthositic crust creates a density trap for rising basaltic magmas which are thought to collect in reservoirs at the base of the crust; reservoir overpressurization causes dikes to propagate to the surface. Dikes sufficiently large to reach the surface are likely to result in large-volume, high-effusion-rate eruptions; single eruptive phases are predicted theoretically and observed in the maria to be several hundred to over 10 3 km 3 . On Mars, massive shield volcanoes have formed on the stable lithosphere over hot spots lasting over a billion years; shield heights are up to 25 km above the adjacent plains. Volumes of single edifices are of the order of 1.5 x 10 6 km 3 , comparable to the total volumes of many basalt provinces on Earth. The impact cratering record on Venus suggests that Venus underwent rapid and massive planet-wide volcanic resurfacing about 300 m.y. ago, an event possibly related to the overturn of a depleted mantle layer resulting from the vertical accretion of a basaltic crust. This hypothesized event could be the equivalent of a planet-wide LIP and underlines the possibility of episodic and catastrophic LIPs throughout planetary history, resembling mantle overturn events proposed for Earth. The planetary record, in concert with the detailed examination of examples on Earth, can be of use in developing and testing models for the emplacement of LIPs, and may help to distinguish plate tectonic influences from those linked to deeper interior (mantle and core) processes.

Together with Iceland, the two giant oceanic plateaux, Ontong Java in the western Pacific and Kerguelen/Broken Ridge in the Indian Ocean, are accumulations of mafic igneous rock which were not formed by ‘normal’ seafloor spreading. We compare published geochronological, crustal structure, and subsidence results with tectonic fabric highlighted in new satellite-derived free-air gravity data from the three igneous provinces, and conclude that existing evidence weighs lightly against the Ontong Java and Kerguelen plateaux originating at a seafloor spreading centre.

Widespread basalts and rhyolites were erupted in Madagascar during the Late Cretaceous. These are considered to be related to the Marion hot spot and the breakup of Madagascar and Greater India. Seventeen argon-40/argon-39 age determinations reveal that volcanic rocks and dikes from the 1500-kilometer-long rifted eastern margin of Madagascar were emplaced rapidly (mean age = 87.6 +/- 0.6 million years ago) and that the entire duration of Cretaceous volcanism on the island was no more than 6 million years. The evidence suggests that the thick lava pile at Volcan de l'Androy in the south of the island marks the focal point of the Marion hot spot at approximately 88 million years ago and that this mantle plume was instrumental in causing continental breakup.

This article describes an innovative, hands-on approach to teaching customer service that was initiated at Purdue University's School of Consumer Sciences and Retailing in 1992. The course does not follow the structure of a traditional classroom setting. Instead, the customer service function from the business world is simulated for a university setting. Participants in the course are responsible for operating and managing a consumer hot line for their school so that feedback from students, faculty, and staff can be gathered. This feedback is subsequently processed with the help of a special computer program in order to obtain actionable information for university administrators. The implementation of this experimental course frequently proved to be a "sink-or-swim" (that is, problem-solving) experience. Therefore, in addition to a description of teaching method, course content, and evaluation, considerable attention is paid to the lessons learned from solving a number of unforeseen problems. These are especially relevant to marketing educators.

The Central Kerguelen Plateau (South Indian Ocean) is characterized by abundant north-south striking normal faults, which comprise two prominent north-south rifts known as the 77°E and 75°E grabens. The 77°E Graben is a well-defined structure which extends over some 800 km from the eastern margin of the Kerguelen Plateau to about 58.5°S. Over most of its length it is associated with a 10–30 km wide axial rift and with a 100–150 km wide uplift. The 75 °E Graben is less well documented, but the available data suggest that its dimensions and internal structure resemble that of the 77°E Graben. In the better documented 77°E Graben, six rift segments, 50–100 km long, are identified. Faulting is more developed at the northern and southern ends of the 77°E Graben, possibly resulting from the interaction with other rifts. To the north, the 77°E Graben abuts the highly faulted eastern margin of the Kerguelen Plateau and the northern part of an even larger rift zone, the Plate Boundary Rift Zone, which extends along the boundary with the Australian-Antarctic Basin. To the south, the 77°E Graben adjoins the northwestern end of the Southern Kerguelen Plateau Rift Zone. The 77°E and 75°E grabens, and the other rift zones on the Kerguelen Plateau, appear to have been formed at approximately the same time, between 72 and 60 Ma. They are all part of an important extensional phase which occurred in the region and mark the beginning of the process which led to the development of the Plate Boundary Rift Zone into the Southeast Indian Ridge, between 46 and 43 Ma. The north-south trend of the 77°E and 75°E grabens is different from that of the other rift zones, which are oriented northwest-southeast. This geometry suggests that some strike-slip motion may have occurred along the north-south trending grabens as a result of extension on the northwest-southeast trending rifts, particularly the Southern Kerguelen Plateau Rift Zone. However, since near-surface extension estimates for the Southern Kerguelen Plateau Rift Zone are small, the strike-slip motion along the 77°E Graben must be equivalently small. Also, the available seismic data from this graben do not show typical seismic characteristics of a strike-slip environment, such as zones of compression or flower structures. Thus the results of this work are inconsistent with any model for the development of the South Indian Ocean which requires significant amount of transform motion on the 77°E or 75°E grabens. Finally, the seismic data from this area provide a unique opportunity to compare rifting on an oceanic plateau environment with continental rifting. We find great similarities between the two processes, in the segmentation of the rifts, the asymmetric cross section, and the associated shoulder uplifts.

Early single-channel and recent multichannel seismic reflection data together reveal major tectonic events in the history of the Southern Kerguelen Plateau (SKP). The SKP was created by Early Cretaceous volcanism which was mainly subaerial. We estimate the age of the adjacent ocean basins to be similar to that of the plateau. Following termination of the main volcanism, the SKP began to subside and to accumulate sediment. A lower sedimentary megasequence was deposited at this time, primarily in depressions on the plateau. At about 88 Ma, tectonism affected the eastern Raggatt Basin; this tectonism may be related to faulting which created the steep eastern margin of the SKP. At about 72 Ma, predominant tectonic activity, characterized by widespread extension and uplift forming the tilted block morphology, occurred over large areas of the SKP. The extension centered along several NW-SE trending rift systems, in places creating well-preserved axial rifts. The largest structure of this kind, the Central SKP Uplift, lies along the center of the SKP; its relief increases from the southernmost part of the plateau toward the NW. The northernmost part of this uplift, the Banzare Bank, was elevated during rifting above sea level and was eroded. A second extensional structure, the SW Uplift, lies in the SW corner of the plateau, and other, smaller structures may also be present. The extension appears to have culminated in the initiation of the Southeast Indian Ridge at 43 Ma, but, at least in the Raggatt Basin, the two events were not continuous. Tectonic subsidence that was associated with the extension corresponds to deposition of a second megasequence, estimated to be about 1000 m thick on Banzare Bank. The subparallel trend of the rift systems on the SKP to the Southeast Indian Ridge and their timing suggest that the rearrangement of spreading in the South Indian Ocean at 43 Ma was not solely the result of the collision of India with Asia; it started earlier in association with other plate motions in the area.

[1] The Early Cretaceous Ontong Java Plateau (OJP) in the western equatorial Pacific, Earth's most voluminous large igneous province (LIP), is characterized by intrabasement seismic reflections. To investigate the nature of such reflections, we have analyzed new and all older multichannel seismic (MCS) reflection data from the OJP using an instantaneous phase velocity analysis technique and synthetic seismograms. Intrabasement reflections are most prevalent on the main OJP, especially on its crest. On MCS data, the reflections (1) are semicontinuous and subparallel to the top of igneous basement; (2) in places, have the opposite phase of seafloor reflections; and (3) have an average frequency of ∼20 Hz. We calculate synthetic seismograms using impedance contrasts between massive lava and pillow lava flows obtained from downhole logs at OJP scientific drill sites and show that these lithologies can produce intrabasement reflections similar to those observed in the MCS data. Alternatively, to evaluate the possibility of sediment/sedimentary rock interbeds causing the intrabasement reflections, we use published Early Cretaceous sedimentation rates determined from OJP drill sites and published estimates for the duration of massive OJP volcanism to calculate a range of possible sedimentary interbed thicknesses. The range proves to be below the detection limit of the MCS data. Therefore, we conclude that the intrabasement reflections arise from alternating relatively thin lava flows produced at low effusion rates and relatively thick massive flows generated at high effusion rates, both originating from vents and fissures on the OJP, probably on its crest.

During Cenozoic and late Mesozoic time, sediment accumulated in the Raggatt Basin on the southern Kerguelen Plateau. We describe the seismic stratigraphy of the Raggatt Basin, utilizing multichannel seismic (MCS) data obtained by the Bureau of Mineral Resources, Geology and Geophysics (Australia) and the Institut de Physique du Globe de Strasbourg (France). Seven major seismic stratigraphic sequences in the Raggatt Basin overlie a basement complex of Early Cretaceous age. The underlying basement complex is characterized by two types of seismic images: acoustic basement and a layered basement which includes dipping reflectors. The seismic stratigraphic sequences include terrestrial and shallow-water units K1 and K2 of Early to Late Cretaceous age, which fill depressions in the basement; a thick unit, K3, of Late Cretaceous to Paleocene age, which is of mixed shallow-water and open-marine facies and in places has a mounded (carbonate) upper surface; a depression-filling pelagic deposit, P1, of Late Cretaceous to Eocene age; a thick pelagic unit, P2, which is mainly Eocene in age; and two post-Eocene pelagic sequences, PN1 and NQ1, which are relatively thin and more limited in areal extent than the underlying sequences. Highlights in the geologic history of the Raggatt Basin include formation and erosion of the basement complex in a subaerial or shallow-water environment in Early Cretaceous time; differential subsidence, probably thermal in origin, and development of carbonate mounds and a major western boundary transform fault in Late Cretaceous time; renewed subsidence near the Cretaceous-Tertiary boundary possibly related to formation of the Labuan Basin/Diamantina Zone by sea-floor spreading; and vigorous Antarctic Circumpolar Current activity beginning by Oligocene time, probably related to the breakup of the northern Kerguelen Plateau and Broken Ridge.

Deep crustal reflections, appearing at two-way times of 6–20 s, are characterised by a low signal-to-noise ratio and a low-frequency content (~ 5–30 Hz). Optimising the visibility of these reflections requires that: 1. (1) the source energy be concentrated in this band; 2. (2) the receiver be as long as practically possible; 3. (3) the shot spacing be as snail as possible. An airgun array simulation program was used to investigate the effect of operating a 10-gun array at different depths. It predicted that the source energy could be enhanced at low frequencies by running the gun array at depths of up to 25 m, which would improve the signal-to-noise ratio for deep reflectors by a factor of 2 relative to the same array at 7.5 m depth at the expense of some loss of temporal resolution. The receiver length was limited to 4.4 km by the number of cable sections available and the maximum tension allowable in the cable. It was configured as 88 channels of 50 m length. To reduce the shot spacing, minimise the tow noise and reduce tension in the cable, the ship speed was reduced to 4 knots. A cable depth of 20 m was chosen to reduce sea state noise and keep the receiver ghost notch frequency outside the frequency band of interest. A variety of operational problems was encountered. Fish bites holed 50% of the total cable inventory and cable sections were damaged when they sank below their maximum rated depth after being holed. Shot-generated noise was the limiting factor in deep water. Despite these problems, useful data were obtained over the Lord Howe Rise, Dampier Ridge, Gippsland Basin margin and the deep abyssal plain and the survey demonstrated the use of an airgun array tuned for maximum energy.

[1] The Mesozoic Nauru Basin in the western Pacific was created by seafloor spreading in Late Jurassic and Early Cretaceous time and was subsequently affected by Early Cretaceous flood volcanism approximately contemporaneous with emplacement of the nearby ∼120 Ma Ontong Java Plateau (OJP). To investigate structure and stratigraphy of the basin, we completed a coincident multichannel seismic reflection (MCS) and refraction (sonobuoy) transect from the center of the Nauru Basin to the eastern flank of the OJP in 1998 aboard R/V Hakuho Maru. Along the transect we identify four segments of distinct crustal structure: C1, a thick igneous complex with no observable refractions; C2, basaltic sills and flows, C3, faulted sediment and rock near the flank of the OJP; and C4, the OJP. On data from seven sonobuoys we observe P-wave refraction arrivals with apparent velocities of ∼6.0 km/s in each segment except C1. Sonobuoy data from segment C1 show no refractions, a common phenomenon in the northern Nauru Basin. We consider that the structure in segment C1 is most representative of typical Nauru Basin crust, and we estimate the volume of the thick igneous complex from discrepancies between actual seafloor depths and those predicted by an age-depth model, which commonly exceed 1000 m. We selected an appropriate model by comparing observed seafloor depths at drill holes in the Mesozoic Pigafetta and East Mariana basins where Cretaceous igneous complexes are thin or absent. From an empirical density-velocity relation, we calculated a basalt loading factor of 780 m/s for subsidence of the Late Jurassic-Early Cretaceous oceanic crust. We then applied the factor to estimate the thickness of the younger Early Cretaceous igneous complex, using previous seismic reflection (Charcot 2), drilling (DSDP Site 462), and wide-angle seismic data from DSDP Site 462 as controls. We estimate that the igneous complex is thickest, ∼5500 m, in the center of the basin and that the total volume of the Early Cretaceous igneous complex is 3.3 × 106 km3.

[1] The southernmost portion of the Macquarie Ridge Complex (MRC) comprises the Hjort Ridge, Trench, and Plateau, the topographic expression of the Australian-Pacific plate boundary south of New Zealand. On the basis of marine geophysical (swath bathymetry/reflectivity, seismic reflection, gravity, magnetic) data, teleseismic data, and gravity modeling, we argue that the Australian plate is actively underthrusting the Pacific plate along the Hjort Trench, but self-sustaining subduction does not yet appear to have commenced. We interpret a crustal discontinuity in the Trench as a shallowly dipping thrust splay off a sub-vertical transform fault in the crest of the Hjort Ridge (Hjort Fault). The Hjort Fault separates oceanic crust generated at the Southeast Indian Ridge (SEIR crust), located to the south, from oceanic crust generated at the extinct Australian-Pacific spreading center located to the north (MRC crust). Oblique convergence on the transform has initiated a significant plate boundary decollement in the Trench, but our estimate of ∼50 km of underthrusting does not support the existence of an eastwardly dipping Australian slab below ∼20 km depth. For the length of the Hjort Ridge and Trench system, oblique convergence is partitioned between the decollement in the Trench and the Hjort Fault. South of 57.5°S, the trench decollement accommodates thrusting. North of 57.5°S, the boundary-parallel component of convergence becomes dominant, the Trench gradually shallows, and the trench decollement evolves into a low-angle, oblique-slip fault. The trench decollement and strike-slip system in the Hjort Ridge are structural boundaries that contain tectonic slivers of inferred SEIR crust of the western flank of the Hjort Ridge that currently belong to neither the Australian nor the Pacific plates.

The Australian-Pacific transform plate boundary fault zone along the Macquarie and McDougall segments of the Macquarie Ridge Complex (MRC), south of New Zealand, is characterized by dominantly normal faults and pull-apart basins, in apparent conflict with the regional transpressional tectonic setting. We propose that present-day curvature of the transform is inherited from a preexisting divergent plate boundary and that the overall extensional kinematics shown by faults along the main plate boundary trace and exposed on Macquarie Island result from local stresses related to right-lateral, right stepping, en echelon plate boundary faults and not to the current transpressional setting. Transpression along the Australian-Pacific transform plate boundary has resulted in uplift along the ?1500 km long Macquarie Ridge Complex. Macquarie Island, the only subaerial exposure of the complex, sits atop a ?5 km high, ?50 km wide submarine ridge of oceanic crust and lies ?4.5 km east of the major active plate boundary fault zone. Thus Macquarie Island and the surrounding seafloor provide a unique opportunity to study an active oceanic transform fault using complementary marine geophysical and land-based geological data. Mapping of recent faults affecting the topography of Macquarie Island shows that the island is extensively cut by high-angle normal faults forming pull-apart basins. Furthermore, evidence for reverse motion is rare. Using marine geophysical data, including swath bathymetry, reflectivity, and seismic reflection data, collected along the Australian-Pacific plate boundary north and south of the island, we have defined a 5–15 km wide plate boundary zone. A series of right stepping en echelon faults, within this zone, lies along the main plate boundary trace. At the right stepping fault terminations, elongate depressions (?10 km wide and 1.2 km deep) parallel the plate boundary, which we interpret as extensional relay zones or pull-apart basins. We propose that transpression is partitioned into en echelon strike-slip faults at the plate boundary and a convergent component that flexes the crust, causing the anomalous bathymetric ridge and trough morphology of the McDougall and Macquarie segments of the MRC.

Australia is an island nation with about two thirds of its jurisdiction underwater. On 25 May 2012, Australia instituted the Seas and Submerged Lands (Limits of Continental Shelf) Proclamation 2012, confirming areas of seabed where Australia has exclusive rights to explore and exploit marine resources. This proclamation follows recommendations by the Commission on the Limits of the Continental Shelf, a body established under the United Nations Convention on the Law of the Sea, confirming Australia's entitlement to extended continental shelf, i.e., that beyond 200 nautical miles from the coastline, of some 2.56 million square kilometers, excluding Australian Antarctic Territory [Symonds et al., 2009] (Figure 1a).

[1] The Ontong Java Plateau (OJP; see Figure 1a), in the western equatorial Pacific Ocean, is one of the largest oceanic plateaus on Earth, covering 1.86 million square kilometers—equivalent to roughly one third of the contiguous United States [Coffin and Eldholm, 1994]. This voluminous plateau is thought to have formed about 120 million years ago and to have caused significant global environmental changes; however, a consensus has not been reached on how the OJP formed. Competing theories include formation through a mantle plume, a meteor impact, and fast spreading ridges. Detailed knowledge of the OJP's crustal and upper mantle structure is necessary to help distinguish among existing models and to develop new models of how the OJP formed. Previous seismic studies acquired data by exploding charges at the ocean's surface and, through seismic analyses of travel times, deducing horizons of reflections and refractions below the ocean floor. However, most of these studies used relatively low energy shots and sparse source and receiver intervals and thus were unable to unambiguously determine the depth of the crust-mantle boundary.

At Elan Bank of the Kerguelen Plateau in the southeast Indian Ocean, Leg 183 of the Ocean Drilling Program recovered clasts of garnet-biotite gneiss in a fluvial conglomerate intercalated with basalt flows. U-Pb and Pb-Pb dates of zircons and monazites in these clasts and an overlying sandstone range from 534 to 2547 Ma, which is much older than the surrounding Indian Ocean seafloor. These dates show that old continental crust resides in the shallow crust of the oceanic Kerguelen Plateau and that the breakup of Gondwana dispersed continental fragments into the nascent Indian Ocean lithosphere.

Mesozoic and Cenozoic continental flood-basalt provinces, oceanic plateaus, oceanic basin flood basalts, and volcanic passive margins share geologic and geophysical characteristics that indicate an origin distinct from igneous rocks formed at mid-ocean ridges. Such characteristics of mafic large igneous provinces (LIPs) include (1) broad areal extent (>10^5 km^2) of basalts of similar age erupted over ~10^6 yr; (2) lower-crustal bodies characterized by Vp = 7.0–7.6 km·s^–1; (3) some component of intermediate and silicic volcanic rocks; (4) trace element, rare earth element, and isotopic signatures in flood basalts that are distinct from mid-oceanic-ridge basalts (MORBs); (5) thick (10s–100s of meters) individual basalt flows; and (6) long (?750 km) individual basalt flows. In addition, basaltic and gabbroic crustal sections of oceanic LIPs are two to five times thicker than those of “normal” oceanic crust, implying larger magma chambers than at typical mid-ocean ridges and, in the case of some continental flood basalts, resulting in layered intrusive complexes containing chromite. Lastly, some flood-basalt provinces are associated with kimberlites and other ultramafic volcanism. LIPs have formed, on average, every 10 m.y. since 250 Ma. However, despite the lower energy required to obduct relatively high standing oceanic LIPs in contrast to normal oceanic crust, only five obducted oceanic LIPs have been well documented in the Mesozoic and Cenozoic continental and island-arc geologic record. More ophiolite fragments may be obducted sections of volcanic passive margins and oceanic plateaus than we now suppose.

The origin of the submarine Naturaliste Plateau off the southwestern coast of Australia is controversial; previous work supports both oceanic and continental affinities for the basement to volcanic and sedimentary sequences. We report the first evidence of reworked Mesoproterozoic (ca. 1230-1190 Ma) continental crust, based on laser ablation-inductively coupled plasma-mass spectrometry analysis of zircons from granite and orthogneiss samples dredged from the southern margin of the plateau. Thermobarometry of peak metamorphic minerals and electron microprobe chemical dating of monazite reveal that these igneous rocks were metamorphosed to similar to 700 degrees C and similar to 6.5 kbar during the Cambrian Pinjarra Orogeny at ca. 515 Ma. These data confirm a continental origin for a significant swathe of the southern Naturaliste Plateau, and suggest that the protoliths may have affinities to Mesoproterozoic crust within the Albany-Fraser-Wilkes Orogen (Australia-Antarctica). The present Naturaliste Plateau basement beneath its volcanic carapace probably represents a middle- to lower-crustal extensional allochthon exhumed during Cretaceous hyperextensional breakup between Australia and Antarctica. Refereed/Peer-reviewed

© 2000 by the American Geophysical Union. Large Igenous Provinces (LIPs) constitute broad areas, > 10 5 km 2 , of mafic volcanic and plutonic rocks erupted over ~106 yr. Compared with plate dimensions, LIPs are smaller, localized features; they form both in plate interiors and at plate boundaries. LIPs originate in the mantle, via mass and energy transfer which acts both independently o￡ and in conjunction with, the wide-ranging upwellling systems producing new oceanic crust by sea floor spreading along the mid-oceanic ridge system. Plate tectonic theory does not readily explain the massive magmatism, which is most commonly attributed to mantle plumes. Most LIPs form in extensional oceanic or continental plate tectonic settings, suggesting a relationship with thinned lithosphere. Deformed LIP complexes in intraplate continental settings suggest formation throughout most of Earth history. The post-150 Ma LIP record reveals both many events and large melt volumes from 135-85 Ma, and a distinct decline since 50 Ma. These trends may reflect variations in mantle circulation and have links to global environmental change. Following formation, oceanic LIPs may be carried laterally by the plates to regions of plate convergence. Subsequent accretion of major LIPs into continental crust contributes episodically to continental growth.

The continental margin of East Africa began forming in the PermoCarboniferous with the development of rift basins, and extension occurred intermittently over 150 million years until the Late Jurassic initiation of sea floor spreading. The margin developed by a combination of extensional and transform tectonics that separated plates containing Africa, Madagascar-Greater India, South America, and Antarctica. A salient aspect of the pre-breakup stratigraphy of the rift basins is salt in isolated Tanzanian grabens, in the Somali Coastal Basin, and in offshore Madagascan basins. At the initiation of sea floor spreading, sedimentary facies changed throughout the rift and pull-apart basins from dominantly continental to marine. Volcanic activity and faulting occurred at the same time. Sea floor spreading ceased in the Western Somali Basin in the Early Cretaceous. Vigorous abyssal circulation along the East African margin probably commenced in the midCretaceous, and widespread regional volcanism occurred in the Late Cretaceous. Middle Jurassic through Holocene sediment thicknesses exceed 8 km in places along the margin.

The validity of two 40Ar/39Ar ages presented in our recent paper on the Manihiki Plateau ([Ingle et al., 2007][1]) is questioned by [Baksi (2008)][2]. We welcome the opportunity to clarify the strengths and weaknesses of the data underpinning these ages. Very little is known about the geochemistry

The large submarine Naturaliste Plateau (NP), lying off the southwestern tip of Australia, is a poorly known part of Australia’s offshore jurisdiction. Only two dredges, one from the northern margin and one from the southern margin, have recovered rocks from this feature, which is approximately the size of Tasmania. Based on the presence of distinctive 130 m.y. old basalts at Bunbury, on the adjacent coast of Western Australia, it has been claimed that the NP may form the easternmost part of the massive Kerguelen Plateau Large Igneous Province (LIP). In this case, the NP would be underlain by thickened oceanic-type crust, and dredged rocks will provide substantial spatial and age constraints on one of the largest LIPs on Earth. However, a recent Geoscience Australia assessment suggested that much of the NP may be underlain by continental rocks. A recently completed swath mapping and dredging cruise using R/V Southern Surveyor investigated the nature and origin of the NP. Pillowed, but often highly vesicular and autobrecciated basalts were sampled along the entire length of the S margin of the NP, and at several locations on its N and NW margins. Quartz + feldspar-phyric glassy rhyolitic lavas were present in several dredges with basalts, suggesting they are part of the same igneous event. Crustal rocks, including garnet-bearing gneisses and granitic rocks, were also dredged along the S margin, including at the most westerly extent of the NP. We will present new ageand geochemical data for the extensive volcanic rocks of the Naturaliste Plateau, and evaluate possible links with the Kerguelen plume.

Call me Moby. The dream of every marine acoustician and seismologist is to image the ocean, the seafloor, and the subseafloor from the perspective of a whale's ear or, if the abyss weren't utterly dark, a fish's eye. Peter Wille's ambitious and remarkable, yet idiosyncratic compilation of sound translated into visual images of the ocean realm is perhaps the next best thing. The meat of the volume and accompanying CD-ROM consists of 452 mostly fascinating, mostly color images, all helpfully indexed at the start of the book, representing the contributions of more than 120 scientists from 22 nations. Those latter two numbers produce shudders and tics, if not migraines, in anyone who's ever assembled a volume involving contributions from even an order of magnitude fewer contributors.

Earth history is punctuated by continents breaking apart and births of oceans, phenomena occurring today in places such as the high Arctic, East Africa/Red Sea, the Gulf of California, and the western Pacific near Papua New Guinea. The tectonic, magmatic, geodynamic, and sedimentary processes associated with continental rifting and breakup interact to produce a variety of margin styles of rifting and breakup, ranging from narrow to hyperextended margins, from weakly to strongly magmatic margins, and from sedimentstarved to thickly sedimented margins. The wide variety of styles has puzzled and inspired Earth scientists for generations, who have employed an increasingly diverse and sophisticated set of observational tools to investigate, and conceptual models to explain, continental rifting and breakup.

We use multichannel seismic reflection (MCS) and gravity data from the southern Izu-Bonin convergent plate margin to test for tectonic erosion. The Hahajima Seamount is a serpentinite seamount on the Izu-Bonin forearc. This serpentinite body likely originated from the mantle wedge beneath the Izu-Bonin arc, but it subsequently detached. MCS data and gravity modeling demonstrate that the Ogasawara Plateau on the incoming Pacific plate has been partly subducted beneath the Hahajima Seamount. Our analysis indicates that the Hahajima Seamount is a “rootless” serpentinite seamount, and the “root” of the serpentinite body was eroded during subduction of the western edge of the Ogasawara Plateau. Structural features of the Hahajima Seamount, the Ogasawara Plateau, and the Philippine Sea plate suggest that tectonic erosion, particularly basal erosion, has been occurring throughout this area.

Macquarie Island consists of uplifted oceanic crust, uniquely situated in the ocean basin where it formed, thus allowing onshore structures to be placed into their regional oceanic tectonic context. The Finch-Langdon fault, the most significant spreading-related structure on the island, juxtaposes upper-crust rocks against lower-crust and upper-mantle rocks. It consists of dominantly oblique strike-slip, northwest-, west-northwest–, and north-northeast–striking fault segments that bear hydrothermal mineralization indicative of faulting during seafloor spreading. Talus breccias and graywackes overlain by volcanic flows proximal to the fault indicate a long-lived submarine fault scarp that exposed diabase dikes and gabbros during volcanism. Swath reflectivity and bathymetry reveal ridge-parallel spreading fabric and perpendicular fracture zones, the closest 7 km east of the island. On the basis of field and swath data, we propose that this fault zone formed near the inside corner of a ridge-transform intersection and that structures on the island are conformable with those in the surrounding seafloor.

On 26 September 2003, a magnitude 8.0 earthquake, Earth's most powerful in 2.5 years, struck offshore Tokachi, Hokkaido, Japan, at 0450 local time. The hypocenter was at 40 km depth along the boundary of the Pacific and North American plates (www.jma.go.jp). The focal mechanism shows a reverse fault with a northwest-southeast compressional axis (P-axis) (see http://www.bosai.go.jp). Following the main shock, named “Heisei 15 Tokachioki-jishin,” seismic activity has continued in the region. As of 30 September, the largest aftershock was M7.1 on 26 September at 0608. Tsunamis were observed on the Pacific coast of Hokkaido and the Tohoku region, including waves of 1.2 m at Kushiro, 1.3 m at Urakawa, and 1.0 m at Hachinohe.

During a 44-day expedition on board the Australian vessel Rig Seismic, scientists collected new information on the morphology of the Macquarie Ridge Complex (MRC), located at the boundary between the Pacific and Australian plates. In the joint venture, funded by the U.S. National Science Foundation and Australian Geological Survey Organization (AGSO), investigators from the two countries studied deformation in the area along the MRC, which includes the site of the largest earthquake of the 1980s (May 23, 1989, Mω=8.2). The researchers acquired ∼160,000 km2 of HAWAII MR1 (HIG acoustic wide-angle imaging instrument, mapping researcher 1) side-scan sonar/bathymetry images and ∼7000 km of 8-channel seismic reflection data (Figure 1). In addition, three ∼400-km gravity transects of the MRC were completed across the morphologic ridge and trench system. The transects were augmented by 96-channel seismic reflection imaging across the morphologic ridge and trench system. Gravity and magnetic data were collected during the entire survey.

A study of five major basaltic provinces, including oceanic plateaus, volcanic passive margins, and continental flood basalts, shows that they are voluminous constructions of extrusive igneous rock underlain by intrusive rock. Crustal thickness ranges from 20 to 40 km, and lower crust is characterized by high (7.0-7.6 km/s) seismic velocities. Volumes and emplacement rates derived for two oceanic plateaus, the Ontong Java and Kerguelen-Broken Ridge, reveal short-lived pulses of increased global crustal production and suggest an origin involving the lower mantle. The Ontong Java rate of emplacement may have exceeded the contemporaneous global production rate of the entire mid-ocean ridge system. Despite the importance off large igneous provinces in studies of mantle dynamics and the global environment, scarce age and deep crustal data necessitate intensified efforts in seismic imaging and scientific drilling in a range of such features.