Lord Howe Rise Research Articles

Odontanthias grahami Randall & Heemstra, a junior synonym of Anthias xanthomaculatus Fourmanoir & Rivaton (Teleostei: Serranidae: Anthiadinae)

Although previously classified in the genus Pseudanthias Bleeker, 1871, the holotype of Anthias xanthomaculatus Fourmanoir & Rivaton, 1979 from New Caledonia was recently shown to be a juvenile specimen of the genus Odontanthias Bleeker, 1873, and possibly conspecific with Odontanthias grahami Randall & Heemstra, 2006 from eastern Australia. Meaningful comparison with the latter species was problematic as it was known only from four adult specimens. Recent collection of a size series of six specimens from the Lord Howe Rise confirms that the two nominal species are conspecific. Odontanthias grahami is therefore placed in the synonymy of A. xanthomaculatus.

Detrital zircons in Triassic–Cretaceous sandstones, Clarence-Moreton Basin, eastern Australia: speculations upon Australia and Zealandia provenances

Detrital zircon U–Pb age patterns in sandstones from the Triassic–Cretaceous Clarence-Moreton Basin, eastern New South Wales and Queensland, unexpectedly reveal sediment sources overwhelmingly dominated (>70%) by Precambrian–Cambrian zircons, with virtually no input, as was anticipated, from the nearby Carboniferous, Permian or Triassic magmatic arcs and contemporary accretionary wedge associated with the New England Orogen. Some rare, youngest zircons (<5%) are mostly contemporaneous with the estimated depositional age. The older, reworked zircon populations can only be acquired by postulating either (1) an Australian provenance by long overland sediment pathways from the interior to the west, during one or more transport cycles, perhaps from within the Thomson Orogen, and then bypassing or crossing the New England Orogen without any local contribution from that sector or (2) a North Zealandia provenance with a shorter transport distance from a postulated basement block to the east, within the Northern Lord Howe Rise and Kenn Plateau. This would comprise late Mesoproterozoic (1200–1000 Ma) and late Neoproterozoic–Cambrian (700–500 Ma) igneous and metamorphic complexes, similar to that proposed in South Zealandia. KEY POINTS Triassic to Jurassic Clarence-Moreton Basin sedimentary rocks have provenances unlike their hinterland time-correlates in New South Wales and Queensland. The latter better share similarities with those in Murihiku Terrane, North Island, New Zealand. The provenance of Clarence-Moreton sediments is similar to that of time-correlates in New Caledonia, and it is postulated that they share a source region on the northern Lord Howe Rise or Kenn Plateau.

Origin and Composition of Ferromanganese Deposits of New Caledonia Exclusive Economic Zone

Located in the South-West Pacific, at the northern extremity of the mostly submerged Zealandia continent, the New Caledonian Exclusive Economic Zone (EEZ) covers 1,470,000 km² and includes basins, ridges and seamounts where abundant ferromanganese crusts have been observed. Several investigations have been conducted since the 1970s on the nature and composition of ferromanganese crusts from New Caledonia’s seamounts and ridges, but none have covered the entire EEZ. We present data from 104 ferromanganese crusts collected in New Caledonia’s EEZ during twelve oceanographic cruises between 1974 and 2019. Samples were analysed for mineralogy, geochemical compositions, growth rates, and through a statistical approach using correlation coefficients and factor analysis. Crust thicknesses range from 1 mm to 115 mm, with growth rates between 0.45 mm/Ma and 102 mm/Ma. Based on textures, structures, discrimination plots, and growth rates, we distinguish a group of hydrogenetic crusts containing the highest mean contents of Co (0.42 wt%), Ni (0.31 wt%), and high contents of Mo, V, W, Pb, Zn, Nb, from a group of hydrothermal and/or diagenetic deposits showing high mean contents of Mn (38.17 wt%), Ba (0.56 wt%) and low contents of other trace metals. Several samples from this later group have exceptionally high content of Ni (0.7 wt%). The data shows that crusts from the southern part of the EEZ, notably seamounts of the Loyalty Ridge and the Lord Howe Rise, present high mineral potential for prospectivity owing to high contents of valuable metals, and constitute a great target for further investigation.

Neogene Mass Accumulation Rate of Carbonate Sediment Across Northern Zealandia, Tasman Sea, Southwest Pacific

AbstractSediment mass accumulation rate (MAR) is a proxy for paleoceanographic conditions, especially if biological productivity generated most of the sediment. We determine MAR records from pelagic calcareous sediments in Tasman Sea based on analysis of 11 boreholes and &gt;3 million seismic reflection horizon picks. Seismic data from regions of 10,000–30,000 km2 around each borehole were analyzed using data from International Ocean Discovery Program Expedition 371 and other boreholes. Local MAR was affected by deepwater currents that winnowed, eroded, or deposited seafloor sediment. Therefore, it is necessary to average MARs across regions to test paleoceanographic and productivity models. MARs during the Miocene Climate optimum (18–14 Ma) were slightly lower than Quaternary values but increased on southern Lord Howe Rise at 14–13 Ma, when global climate became colder. Intensification of the Indian and East Asian monsoons at ∼8 Ma and ∼3.6 Ma approximately corresponds to the start and end, respectively, of the Biogenic Bloom, which had MARs at least double Quaternary values. On northern Lord Howe Rise, we recognize peak MARs at∼7 Ma and ∼5 Ma. There is no correlation between Neogene MAR and ocean pH or atmospheric CO2 concentration. Neogene MARs are on average higher than Quaternary values. We posit that future long‐term productivity in the southwest Pacific could be higher than Quaternary values, but new computer models that can fit our observations are required to test this hypothesis.

Stratigraphy around the Cretaceous-Paleogene boundary in sediment cores from the Lord Howe Rise, Southwest Pacific

Abstract During Deep Sea Drilling Project (DSDP) Leg 21, Cenozoic and latest Cretaceous sediments were recovered at Site 208 on the Lord Howe Rise, Southwest Pacific. We provide new biostratigraphic, magnetostratigraphic and chemostratigraphic data from Site 208 to constrain the stratigraphy around the Cretaceous-Paleogene (K-Pg) boundary and to determine the depth of the K-Pg boundary more precisely. Biostratigraphic data from calcareous nannofossils indicate a near-continuous succession of sediments from the mid-Maastrichtian (Late Cretaceous) to lowermost Thanetian (Paleocene) at depths of 540–590 m below seafloor (mbsf). The biostratigraphic data suggest that the K-Pg boundary corresponds to a siliceous claystone at the base of an interval of silicified sediments (576.0–576.8 mbsf). Carbonate carbon isotopic composition (δ13Ccarb) reveals a negative shift across this interval, which is consistent with global patterns of δ13C across the K-Pg boundary. Osmium concentration and Os isotopic composition (187Os/188Os) can also be used to identify the K-Pg boundary interval, as it is marked by a peak in Os concentration and a drop in 187Os/188Os values to 0.12–0.15, both of which are the result of the Chicxulub impact event. Our 187Os/188Os data show trends similar to those of coeval global seawater with the lowest value of 0.12–0.16 in the siliceous claystone (576.8 mbsf). However, the concentration of Os is low (&amp;lt;80 pg g−1) in this sample, which suggests that this siliceous claystone was deposited around the K-Pg boundary but may not include the boundary itself. Although the sedimentary record across the K-Pg interval at Site 208 may not be completely continuous, it nevertheless captures a time interval that is close to the Chicxulub impact event.

Biotic Response to Early Eocene Warming Events: Integrated Record From Offshore Zealandia, North Tasman Sea

AbstractEnvironmental and biotic responses to early Eocene hyperthermal events in the southwest Pacific are critical for global paleoclimate reconstructions during Cenozoic greenhouse intervals, but detailed multidisciplinary studies are generally missing from this time and location. Eocene carbonate sediments were recovered during International Ocean Discovery Program Expedition 371 at Site U1510 on southern Lord Howe Rise in the Tasman Sea. Part of the Early Eocene Climatic Optimum (EECO; 53.26–49.14 Ma) and superimposed hyperthermal events have been identified based on refined calcareous nannofossil biostratigraphic data and carbon stable isotope records on bulk sediment and benthic foraminifera. Four negative carbon isotope excursions (CIEs) associated with negative oxygen isotope excursions are recognized within the EECO. Comparison with a global compilation of sites indicates these CIEs correlate to the K event (Eocene Thermal Maximum 3), and tentatively to the S, T, and U events. Sediments with a high carbonate content throughout the EECO provide an excellent opportunity to examine these CIEs, as carbonate dissolution often impacts correlative records elsewhere. Benthic foraminifera and calcareous nannoplankton taxa indicative of warm waters are most abundant during the K event, the most prominent hyperthermal of the EECO. Eutrophication of surface waters during the K event did not lead to increased trophic conditions at the seafloor, whereas a coupled response is observed during smaller hyperthermals. The biotic turnover sheds new light on the paleoenvironmental consequences of hyperthermal events.

Calcareous nannoplankton response to early Eocene warmth, Southwest Pacific Ocean

Episodes of pronounced climatic warming in the early Eocene (56–48 Ma) provide insights into how biological systems might respond to future climate changes. Eocene climate reconstructions for the Southwest (SW) Pacific have proved challenging due to some disparities between geochemical proxy-based estimates for sea temperatures and estimates derived from climate models. Changes in marine phytoplankton populations through the early Eocene provide a means to evaluate model and proxy-based approaches and also reveal how climatic changes affected the ocean ecosystem. This study documents early to middle Eocene calcareous nannofossil assemblages from legacy Deep Sea Drilling Project (DSDP) sites in the SW Pacific. We integrate nannofossil assemblage changes with foraminiferal-based stable isotopes and other microfossil data to provide updated age models for DSDP Sites 207 (Lord Howe Rise) and 277 (Campbell Plateau), and to infer past environmental change through the early to mid-Eocene in the SW Pacific. Although these sites record a short hiatus in the earliest Eocene, deposition resumed by ~54 Ma, prior to the onset of the Early Eocene Climate Optimum (EECO). Both sites show an increase in warm-water taxa from the onset of the EECO until approximately 50.5 Ma. Abundance of warm-water taxa was higher (~23%) at the EECO onset at the more northerly Site 207 and increased only slightly to ~27%, whereas at Site 277 warm-water taxa comprised only ~3% at the EECO onset but increased to ~31% by 50.5 Ma. Cool-water taxa at both sites were present in very sparse numbers (<3%) through much of the EECO and only began to increase in abundance after 50 Ma, concomitant with a decrease in warm-water taxa. These results are similar to other mid-latitude sites in the SW Pacific and Indian Ocean, including mid-Waipara River (Canterbury Basin, New Zealand) and ODP Site 762 (Exmouth Plateau), and indicate assemblages during the EECO are best described as warm temperate. Benthic δ18O records from both sites show good agreement with nannofossil trends and, despite the possibility of recrystallization at Site 277, sea surface temperatures (SSTs) indicated by planktic foraminifera also imply warm temperate conditions. This suggests that a warm proto-East Australian Current extended to at least 55°S during the EECO, displacing the proto-Tasman Front southward, which migrated northward after termination of the EECO possibly due to expansion of a proto-Ross Sea Gyre.

Thin-sectioned otoliths reveal extended longevity of southern boarfish (Pentaceros richardsoni) and are used to investigate inter-oceanic differences in length and age structure and growth

The age and growth of southern boarfish (Pentaceros richardsoni) was determined from samples collected by deep-sea trawlers over the Lord Howe Rise region in the Tasman Sea and Walters Shoal region in the south-west Indian Ocean. The number of growth (opaque) zones counted in whole otoliths and in thick sections (450 μm) of otoliths were lower than the counts of opaque zones in thin-sections (300 μm) of otoliths. Visual analyses and modelling of the trends in marginal increments on thin-sections of otoliths show that opaque zones are formed annually. The maximum ages determined for female and male P. richardsoni of 41 and 60 years respectively, greatly exceed the estimate of 14 years previously determined for this species based on counts of opaque zones in whole otoliths and the 2–8 years for its congener Pentaceros wheeleri from the North Pacific Ocean (NPO). The high maximum age for P. richardsoni and corresponding low natural mortality rates parallel those of Pentacerotids in coastal waters of southern Australia. Trends in the growth of P. richardsoni from the Tasman Sea demonstrate that this species exhibits rapid growth in the first 4–5 years of life with little or no subsequent growth throughout the remainder of their protracted life, which is analogous to other Pentacerotids. The truncation of the lengths and ages of P. richardsoni from the Walters Shoal suggests that the population of this species in these waters has experienced greater fishing mortality than the populations over the Lord Howe Rise region in the Tasman Sea, which is also confirmed by the far higher total mortality estimates in the former region. These findings for P. richardsoni, and the knowledge that P. wheeleri populations in the NPO have still not recovered from sustained, high fishing mortalities in the late 1960s to mid-1970s should inform the management strategies for P. richardsoni in the Southern Hemisphere.

Bayesian trans-dimensional full waveform inversion: synthetic and field data application

SUMMARYSeismic full waveform inversion (FWI) is a state-of-the-art technique for estimating subsurface physical models from recorded seismic waveform, but its application requires care because of high non-linearity and non-uniqueness. The final outcome of global convergence from conventional FWI using local gradient information relies on an informative starting model. Bayesian inference using Markov chain Monte Carlo (MCMC) sampling is able to remove such dependence, by a direct extensive search of the model space. We use a Bayesian trans-dimensional MCMC seismic FWI method with a parsimonious dipping layer parametrization, to invert for subsurface velocity models from pre-stack seismic shot gathers that contain mainly reflections. For the synthetic study, we use a simple four-layer model and a modified Marmousi model. A recently collected multichannel off-shore seismic reflection data set, from the Lord Howe Rise (LHR) in the east of Australia, is used for the field data test. The trans-dimensional FWI method is able to provide model ensembles for describing posterior distribution, when the dipping-layer model assumption satisfies the observed data. The model assumption requires narrow models, thus only near-offset data to be used. We use model stitching with lateral and depth constraints to create larger 2-D models from many adjacent overlapping submodel inversions. The inverted 2-D velocity model from the Bayesian inference can then be used as a starting model for the gradient-based FWI, from which we are able to obtain high-resolution subsurface velocity models, as demonstrated using the synthetic data. However, lacking far-offset data limits the constraints for the low-wavenumber part of the velocity model, making the inversion highly non-unique. We found it challenging to apply the dipping-layer based Bayesian FWI to the field data. The approximations in the source wavelet and forward modelling physics increase the multimodality of the posterior distribution; the sampled velocity models clearly show the trade-off between interface depth and velocity. Numerical examples using the synthetic and field data indicate that trans-dimensional FWI has the potential for inverting earth models from reflection waveform. However, a sparse model parametrization and far offset constraints are required, especially for field application.

Continental-scale geographic change across Zealandia during Paleogene subduction initiation

Abstract Data from International Ocean Discovery Program (IODP) Expedition 371 reveal vertical movements of 1–3 km in northern Zealandia during early Cenozoic subduction initiation in the western Pacific Ocean. Lord Howe Rise rose from deep (∼1 km) water to sea level and subsided back, with peak uplift at 50 Ma in the north and between 41 and 32 Ma in the south. The New Caledonia Trough subsided 2–3 km between 55 and 45 Ma. We suggest these elevation changes resulted from crust delamination and mantle flow that led to slab formation. We propose a “subduction resurrection” model in which (1) a subduction rupture event activated lithospheric-scale faults across a broad region during less than ∼5 m.y., and (2) tectonic forces evolved over a further 4–8 m.y. as subducted slabs grew in size and drove plate-motion change. Such a subduction rupture event may have involved nucleation and lateral propagation of slip-weakening rupture along an interconnected set of preexisting weaknesses adjacent to density anomalies.

Neogene-Quaternary architecture and sedimentary processes on an isolated carbonate-fed deep-water basin (Fairway Basin, Southwest Pacific)

The Fairway Basin is an intracratonic deep-water basin inherited from cretaceous rifting, perched between the Lord Howe Rise and the New Caledonia Basin in the Southwest Pacific. Its originality lies in its atypical present-day physiography and its carbonate-dominated sedimentary setting since the Miocene. Although very limited well controls are available, its overall structure, seismic stratigraphy and architecture are relatively well known. However, little is known on the detailed sedimentary processes controlling its recent infill. Its remote location from any major clastic sediment sources provides a great setting to study deep-water carbonate sedimentary processes. In this paper, we propose a detailed analysis of surface morphologies based on existing multibeam and subbottom echosounding data together with an analysis of the Neogene to Quaternary basin-fill based on seismic reflection data. This allows us to discuss active sedimentary processes, notably gravity flow processes which are thought to be active since the Middle Miocene. These processes are evidenced by both surface and subsurface features, such as submarine canyons, channels and lobes, composite scarps and mass transport deposits (MTDs). In the northern part of the basin, a 400 km-long axial turbidite system is developed close to the Lansdowne Bank, a partly drowned isolated carbonate platform, where present-day sediment remobilisation seems to be essentially sourced from intra-slope instabilities. These reworked sediments extend over an area of 16,000 km2. Along with this axial turbidite system, seismic data show two main mass transport complexes (covering an area of ca 20% of the basin's surface) originating from the slopes of the basin. The potential triggering mechanisms of MTDs of the northern complex might be directly attributed to overloading and high slope values of the Lansdowne Bank area (>1.5°). For the southern complex, surface slope values are lower (<1.4°), and the role of fluid migration and escape is discussed. The Fairway Basin indeed shows strong evidences for fluid generation (e.g. polygonal faulting, pockmarks, presence of a widespread Opal-A/Opal-CT diagenesis-related bottom simulating reflectors) and fluid overpressures.

Crustal Structure Across the Lord Howe Rise, Northern Zealandia, and Rifting of the Eastern Gondwana Margin

AbstractDuring the Late Cretaceous, the fragmentation of eastern Gondwana led to the formation of the narrow eastern Australian margin and the wide Lord Howe Rise during the opening of the oceanic Tasman Basin. To provide crustal‐scale constraints on this margin, a 680‐km‐long, east‐west oriented refraction transect with 100 ocean bottom seismometers was acquired from the Tasman Basin to the Lord Howe Rise. After traveltime tomographic inversion of the first refracted arrivals and reflected arrivals from the Moho, the final P wave velocity model reveals strong variations in crustal thickness. The Tasman Basin is floored by a two‐layered and 7‐km‐thick oceanic crust. To the east, the Middleton Basin separates the Dampier Ridge, with 16‐km‐thick continental crust, from the Lord Howe Rise, where the extended continental crust is 20–23 km thick. Below the Middleton Basin, Moho reflections are recorded at the base of 7‐km‐thick crust. The velocity gradient of this two‐layer crust suggests an oceanic origin for the Middleton Basin. Our results show no clear evidence for mantle exhumation or a sizable igneous intrusion within three separate and relatively narrow (&lt;70 km) necking zones. The northwestern Zealandia margin thus appears to be magma poor and, despite the considerable width of this margin (&gt;1,000 km), the lack of evidence for mantle exhumation, the evidence for oceanic crust under the Middleton Basin, and the narrow necking zones combine to suggest that northern Zealandia is not a hyperextended margin.

Modelling and visualising distributed crustal deformation of Australia and Zealandia using GPlates 2.0

The recently released GPlates 2.0 software (www.gplates.org) provides a framework for building plate motion models including distributed extension and compression, driven by the motions of the surrounding rigid plate interiors, with constraints assimilated from well and seismic data. Here we present a regional deforming plate model for Australia and Zealandia. It captures the progressive extension of all Australian continental margins, starting with the Jurassic extension of the northwest shelf, and the Cretaceous extension of the southern and eastern Australian margins. The model also includes the extension of the Lord Howe Rise and southern Zealandia in the mid- to Late Cretaceous and the subsequent complex compressional deformation of New Zealand since the early Miocene. The model enables the time-dependent computation of crustal stretching factors for passive margins, as well as compression factors for orogenic regions. The thinning/thickening can be tracked by points distributed within a deforming mesh, either by starting with an assumed initial stretching factor or by applying an iterative approach in estimating initial crustal thicknesses to account for present-day constraints. The latter is suitable for basins, while the former is more applicable for orogens, where the present-day crustal thickness is not a reliable indicator of total crustal thickening due to the effects of erosion. Modelled crustal stretching factors can also be ground-truthed with independently derived stretching factors from strain rate inversion of stratigraphic sequences from well data or forward models of tectonic subsidence. The model can be combined with estimates of mantle-driven dynamic topography through time to generate basement subsidence or uplift models that include isostatic and dynamic components, serving as boundary conditions for basin and source-to-sink sediment transport models to provide improved constraints for resource exploration.

Geophysical and geological characterisation of dredge locations from RV Southern Surveyor voyage ss2012_v06 (ECOSATI): hotspot activity in northern Zealandia

In October-November 2012 a geophysical mapping and dredging campaign in the eastern Coral Sea was conducted on the RV Southern Surveyor during voyage ss2012_v06 (ECOSATI). Part of this campaign was focussed in northernmost Zealandia where volcanic seamounts and uplifted portions of the Lord Howe Rise were targeted to determine the age and location of the northern portion of the Lord Howe Seamount Chain. Geophysical and geological analysis of the dredge sites from the southernmost South Rennell Trough and Chesterfield Plateau confirm the extension of the Lord Howe Seamount Chain ~200 km northward than previously identified, with an age-progression extending to ~27-28 Ma. These new samples, together with previously published samples from the youngest part of the chain, show consistency with both Indo-Atlantic and Pacific hotspots. The average magma flux rate of the Lord Howe hotspot is estimated at 0.4 m3/s, which is similar to the rates of crustal production at the South Rennell Trough, A peak in magmatism along the trail in the late Oligocene may be related to a slowdown in the motion of the Australian plate sometime between 27-23 Ma. The results of the geophysical and geological sampling and estimates of magma flux from the Lord Howe Seamount Chain will assist in thermal history modelling in the sedimentary basins of northern Zealandia and will help provide a geological framework for frontier resource exploration in this region.

First Australian records of Ethusina (Crustacea: Decapoda: Ethusidae) and additional records from New Zealand

Deep water ethusid crabs, genus Ethusina, are confirmed for the first time from Australia, with additional distribution records from New Zealand waters. Prior to the present study, Ethusina was reported from Australia on the basis of a single unidentified species from southwestern Australia. Four species are reported herein: Ethusina castro Ahyong, 2008, E. ciliacirrata Castro, 2005, E. robusta (Miers, 1886), and E. rowdeni Ahyong, 2008. Ethusina castro, previously known only from the female holotype from northern New Zealand is reported for the first time from eastern Australia, the Lord Howe Rise and Monowai Caldera, including the first known males. Ethusina ciliacirrata, described from Vanuatu, is confirmed from the Coral Sea and southwestern Australia. Ethusina rowdeni, from New Zealand, and the widespread E. robusta are recorded for the first time from Australia.

Physical properties and seismic-reflection interpretation of bathyal marine sediments affected by carbonate and silica diagenesis in the Tasman Sea

ABSTRACTDiagenesis of calcareous and siliceous sediments in northern Zealandia produces characteristic seismic reflections that are a valuable tool for constraining paleoenvironmental and tectonic history. We correlate Deep Sea Drilling Program (DSDP) borehole lithology changes with seismic reflectivity to characterise distinct diagenetic horizons. An increase in reflectivity in calcareous Paleocene to Miocene age sediments marks the depth that ooze alters to chalk. Predominantly occurring at c. 300 m below the seafloor on the Lord Howe Rise, variations are observed in the New Caledonia Trough, and in the Eocene in the Southern Lord Howe Rise due to changes in sediment composition. Paleocene–Eocene silica-rich sediments undergoing diagenesis produced distinct negative–positive polarity paired reflections from unaltered and altered sediments, respectively. Sediments undergoing diagenesis range in age from Paleocene to Miocene, indicating that overburden thickness and temperature are the main controlling factors for the onset of diagenesis, whereas the diagenetic potential of sediments is controlled by composition and burial conditions.

大陸の分裂・沈降は地球史に何をもたらしたか？：ロードハウライズ掘削プロジェクトを例として

大陸の分裂・沈降は地球史に何をもたらしたか？：ロードハウライズ掘削プロジェクトを例として

Regional volcanism of northern Zealandia: post-Gondwana break-up magmatism on an extended, submerged continent

Abstract Volcanism of Late Cretaceous–Miocene age is more widespread across the Zealandia continent than previously recognized. New age and geochemical information from widely spaced northern Zealandia seafloor samples can be related to three volcanotectonic regimes: (1) age-progressive, hotspot-style, low-K, alkali-basalt-dominated volcanism in the Lord Howe Seamount Chain. The northern end of the chain ( c. 28 Ma) is spatially and temporally linked to the 40–28 Ma South Rennell Trough spreading centre. (2) Subalkaline, intermediate to silicic, medium-K to shoshonitic lavas of &gt;78–42 Ma age within and near to the New Caledonia Basin. These lavas indicate that the basin and the adjacent Fairway Ridge are underlain by continental rather than oceanic crust, and are a record of Late Cretaceous–Eocene intracontinental rifting or, in some cases, speculatively subduction. (3) Spatially scattered, non-hotspot, alkali basalts of 30–18 Ma age from Loyalty Ridge, Lord Howe Rise, Aotea Basin and Reinga Basin. These lavas are part of a more extensive suite of Zealandia-wide, 97–0 Ma intraplate volcanics. Ages of northern Zealandia alkali basalts confirm that a late Cenozoic pulse of intraplate volcanism erupted across both northern and southern Zealandia. Collectively, the three groups of volcanic rocks emphasize the important role of magmatism in the geology of northern Zealandia, both during and after Gondwana break-up. There is no compelling evidence in our dataset for Late Cretaceous–Paleocene subduction beneath northern Zealandia.

A new deep-water species of Myopiarolis Bruce, 2009 (Crustacea: Isopoda: Serolidae) from New Zealand waters

Myopiarolis tona sp. nov. is described from the Challenger Plateau, southern Lord Howe Rise and the west coast of the North Island, New Zealand at depths of 634-1250 m. M. tona sp. nov. can be identified by the prominent posteriorly directed dorsal nodule on fused pereonites 5-7. There are nine species in four genera of the cold-water, epibenthic family Serolidae recorded from New Zealand waters, three species of Myopiarolis Bruce, 2009, one undescribed species of Acutiserolis Brandt, 1988, four of Brucerolis Poore and Storey, 2009 and the monotypic Spinoserolis Brandt, 1988.

Triassic–Jurassic granites on the Lord Howe Rise, northern Zealandia

We present U–Pb zircon ages from a phosphate-cemented pebbly sandstone dredged from the central Lord Howe Rise and a 97 Ma rhyolite drilled on the southern Lord Howe Rise. Four granitoid pebbles from the sandstone give U–Pb ages in the range 216–183 Ma. Most detrital zircons in the bulk sandstone are also Late Triassic–Early Jurassic, but subordinate populations of Late Cretaceous and Precambrian zircons are present. The pebbly sandstone's highly restricted Late Triassic–Early Jurassic zircon population indicates the nearby occurrence of underlying basement plutons that are the same age as parts of the I-type Darran Suite, Median Batholith of New Zealand and supports a continuation of the Early Mesozoic magmatic arc northwest from New Zealand. Zircon cores from the southern Lord Howe Rise rhyolite do not yield ages older than 97 Ma and thus provide no information about older basement.