Tonga Kermadec Research Articles

Large Earthquakes in Subduction Zones around the Polar Regions as a Possible Reason for Rapid Climate Warming in the Arctic and Glacier Collapse in West Antarctica

A correlation is observed between changes in the level of Earth’s seismic activity and increments of the atmospheric methane concentration over the past 40 years. Trigger mechanisms are proposed for methane emissions and glacier collapse in polar regions. These mechanisms are due to deformation waves caused by large earthquakes in subduction zones located near the polar regions: the Aleutian and Kuril–Kamchatka subduction zones, closest to the Arctic, and the Antarctica–Chilean and Tonga–Kermadec–Macquarie subduction zones. Disturbances of the lithosphere are transmitted over the distances of 3000–4000 km and more at a speed of about 100 km/year. Additional associated stresses come to the Arctic and Antarctica several decades after the occurrence of large earthquakes. In the Arctic zone, additional stresses affect the low-permeability structure of gas bearing sedimentary strata, causing increased methane emission and climate warming. In West Antarctica, deformation waves could trigger the acceleration and intensive collapse of West Antarctic glaciers, which has been observed since the 1970s. These waves are also capable of activating dormant volcanoes located under the sheet glaciers of West Antarctica, leading to an increase in heat flux, to the melting of ice at the glaciers’ base, and to their accelerated sliding towards the ocean, as is happening with the Thwaites Glacier.

Trigger Mechanisms of Gas Hydrate Decomposition, Methane Emissions, and Glacier Breakups in Polar Regions as a Result of Tectonic Wave Deformation

Trigger mechanisms are proposed for gas hydrate decomposition, methane emissions, and glacier collapse in polar regions. These mechanisms are due to tectonic deformation waves in the lithosphere–asthenosphere system, caused by large earthquakes in subduction zones, located near the polar regions: the Aleutian arc, closest to the Arctic, and the Antarctica–Chilean and Tonga–Kermadec–Macquarie subduction zones. Disturbances of the lithosphere are transmitted over long distances (of the order of 2000–3000 km and more) at a speed of about 100 km/year. Additional stresses associated with them come to the Arctic and Antarctica several decades after the occurrence of seismic events. On the Arctic shelf, additional stresses destroy the microstructure of metastable gas hydrates located in frozen rocks at shallow depths, releasing the methane trapped in them and leading to filtration and emissions. In West Antarctica, these wave stresses lead to decreases in the adhesions of the covered glaciers with underlying bedrock, sharp accelerations of their sliding into the sea, and fault occurrences, reducing pressure on the underlying rocks containing gas hydrates, which leads to their decomposition and methane emissions.

Deep‐Ocean Circulation in the Southwest Pacific Ocean Interior: Estimates of the Mean Flow and Variability Using Deep Argo Data

AbstractThe spatial structure and time variability of the global deep‐ocean circulation are poorly understood due to limited sampling below 2,000‐m depth. A Deep Argo array deployed in 2016 has significantly increased oceanic measurements from the ocean surface to near the sea floor in the Southwest Pacific Basin interior. Deep Argo profiles collected between 2016 and 2019 show that 4.3–4.7 Sv between 1,500 and 4,800 m, relative to 4,800 m, of the Deep Western Boundary Current flowing along the Tonga Kermadec Ridge is redirected southward over the abyssal plain between the Tonga Kermadec Ridge and the East Pacific Rise. The southward recirculation of the Deep Western Boundary Current exhibits seasonality that may be influenced by Ekman pumping.

Chapter 2 Geodynamics of the SW Pacific: a brief review and relations with New Caledonian geology

Abstract The SW Pacific region consists of a succession of ridges and basins that were created by the fragmentation of Gondwana and the evolution of subduction zones since Mesozoic times. This complex geodynamic evolution shaped the geology of New Caledonia, which lies in the northern part of the Zealandia continent. Alternative tectonic models have been postulated. Most models agree that New Caledonia was situated on an active plate margin of eastern Gondwana during the Mesozoic. Extension affected the region from the Late Cretaceous to the Paleocene and models for this period vary in the location and nature of the plate boundary between the Pacific and Australian plates. Eocene regional tectonic contraction included the obduction of a mantle-derived Peridotite Nappe in New Caledonia. In one class of model, this contractional phase was controlled by an east-dipping subduction zone into which the Norfolk Ridge jammed, whereas and in a second class of model this phase corresponds to the initiation of the west-dipping Tonga–Kermadec subduction zone. Neogene tectonics of the region near New Caledonia was dominated by the eastwards retreat of Tonga–Kermadec subduction, leading to the opening of a back-arc basin east of New Caledonia, and the initiation and southwestwards advance of the New Hebrides–Vanuatu subduction zone towards New Caledonia.

How to Create New Subduction Zones: A Global Perspective

The association of deep-sea trenches—steeply angled, planar zones where earthquakes occur deep into Earth’s interior—and chains, or arcs, of active, explosive volcanoes had been recognized for 90 years prior to the development of plate tectonic theory in the 1960s. Oceanic lithosphere is created at mid-ocean ridge spreading centers and recycled into the mantle at subduction zones, where down-going lithospheric plates dynamically sustain the deep-sea trenches. Study of subduction zone initiation is a challenge because evidence of the processes involved is typically destroyed or buried by later tectonic and crust-forming events. In 2014 and 2017, the International Ocean Discovery Program (IODP) specifically targeted these processes with three back-to-back expeditions to the archetypal Izu-Bonin-Mariana (IBM) intra-oceanic arcs and one expedition to the Tonga-Kermadec (TK) system. Both subduction systems were initiated ~52 million years ago, coincident with a proposed major change of Pacific plate motion. These expeditions explored the tectonism preceding and accompanying subduction initiation and the characteristics of the earliest crust-forming magmatism. Lack of compressive uplift in the overriding plate combined with voluminous basaltic seafloor magmatism in an extensional environment indicates a large component of spontaneous subduction initiation was involved for the IBM. Conversely, a complex range of far-field uplift and depression accompanied the birth of the TK system, indicative of a more distal forcing of subduction initiation. Future scientific ocean drilling is needed to target the three-dimensional aspects of these processes at new converging margins.

Lithium isotope variations in Tonga–Kermadec arc–Lau back‐arc lavas and Deep Sea Drilling Project (DSDP) Site 204 sediments

AbstractLithium isotopes have been identified as a promising tracer of subducted materials in arc lavas due to the observable variations in related reservoirs such as subducting sediments and altered oceanic crust. The Tonga–Kermadec arc–Lau back‐arc provides an end‐member of subduction zones with the coldest thermal structure on Earth. Reported here are Li isotope data for 14 lavas from the arc front and 7 back‐arc lavas as well as 12 pelagic and volcaniclastic sediments along a profile through the sedimentary sequence at DSDP Site 204. The arc and back‐arc lavas range from basalts to dacites in composition with SiO2 = 48.3–65.3 wt% over which Li concentrations increase from 2 ppm to 16 ppm. Li/Y ratios range from 0.08 to 0.77 and from 0.24 to 0.65 in the arc and back‐arc lavas, respectively. The majority of the lavas have δ7Li that ranges from 2.5 ‰ to 5.0 ‰ with an average of (3.6 ±0.7) ‰, similar to that reported from other arcs and there is no distinction between the arc front and back‐arc lavas. The pelagic sediments have variable Li concentrations (33–133 ppm) and δ7Li that ranges from 1.2 ‰ to 10.2 ‰ while the volcaniclastic sediments have an even greater range of Li concentrations (3.6–165 ppm) and generally higher δ7Li values (8–14 ‰). However, δ7Li in the lavas does not correlate with commonly used trace element ratio or isotope signatures indicative of slab‐derived fluids or the sediments. This is probably because the range of δ7Li in the lavas and sediments overlap. Calculated sediment mass‐balance models require significantly more sediment than previous estimates based on Th–Nd–Be isotopes. This may indicate that a sizeable proportion of the total Li budget in the lavas is provided by Li‐enriched fluids from the subducting sediments and/or altered oceanic crust.

Magneto-biostratigraphic constraints of the Eocene micrite–calciturbidite transition in New Caledonia: tectonic implications

ABSTRACTWe conducted an integrated magneto-biostratigraphic study of a 37 m-thick composite section exposed at two sites near Nouméa (New Caledonia). The section contains a transition from pelagic micrite to terrigenous-rich calciturbidites. This transition, observed regionally in coeval records of New Caledonia, marks a shift from pelagic sedimentation on a stable continental submarine plateau to turbidite deposition indicating development of a slope in a convergent tectonic regime. The studied section spans magnetic polarity Chrons C22r to C20r, calcareous nannofossil zones CNE5 to CNE10, and radiolarian zones RP9 to RP11 (49.5 to c. 44 Ma), and the micrite–turbidite transition occurred around 45.3 Ma (early middle Eocene). This transition could be the onshore correlative of a regional switch from tectonic extension to compression, which has been inferred from analysis of new seismic profiles acquired for the Tasman–northern Zealandia area, and that has been interpreted as precursor of the Tonga–Kermadec subduction initiation.

Sourcing of Miocene accretionary lapilli on ‘Eua, Tonga; atypical dispersal distances and tectonic implications for the central Tonga Ridge

ABSTRACTVolcaniclastics hosting accretionary lapilli on the Tonga Ridge were sourced from the remnant Lau Ridge, prior to Lau back-arc basin opening. For the ‘Eua occurrences, an atypical dispersal distance of not less than 70 km is estimated, partly arising from the anomalous easterly position of ‘Eua. Dispersal within ocean-surface pyroclastic density currents is supported but strike-slip movement in a fault zone south of ‘Eua, post-middle Miocene but pre-ridge-splitting, can account for part of the dispersal distance by vertical axis block rotation, a tectonic process common on the southern Tonga–Kermadec–Hikurangi trend. In this model, the volcano which sourced the ‘Eua tephra was on a subjacent block, rather than the block which hosts ‘Eua. After deposition but prior to the opening of the Lau Basin, the accretionary lapilli on ‘Eua became displaced by block rotation c. 40 km towards the Tonga trench and away from source.

Upper- and mid-mantle interaction between the Samoan plume and the Tonga–Kermadec slabs

Mantle plumes are thought to play a key role in transferring heat from the core–mantle boundary to the lithosphere, where it can significantly influence plate tectonics. On impinging on the lithosphere at spreading ridges or in intra-plate settings, mantle plumes may generate hotspots, large igneous provinces and hence considerable dynamic topography. However, the active role of mantle plumes on subducting slabs remains poorly understood. Here we show that the stagnation at 660 km and fastest trench retreat of the Tonga slab in Southwestern Pacific are consistent with an interaction with the Samoan plume and the Hikurangi plateau. Our findings are based on comparisons between 3D anisotropic tomography images and 3D petrological-thermo-mechanical models, which self-consistently explain several unique features of the Fiji–Tonga region. We identify four possible slip systems of bridgmanite in the lower mantle that reconcile the observed seismic anisotropy beneath the Tonga slab (VSH>VSV) with thermo-mechanical calculations.

Present-day stress field in subduction zones: Insights from 3D viscoelastic models and data

3D viscoelastic FE models were performed to investigate the impact of geometry and kinematics on the lithospheric stress in convergent margins. Generic geometries were designed in order to resemble natural subduction. Our model predictions mirror the results of previous 2D models concerning the effects of lithosphere-mantle relative flow on stress regimes, and allow a better understanding of the lateral variability of the stress field. In particular, in both upper and lower plates, stress axes orientations depend on the adopted geometry and axes rotations occur following the trench shape. Generally stress axes are oriented perpendicular or parallel to the trench, with the exception of the slab lateral tips where rotations occur. Overall compression results in the upper plate when convergence rate is faster than mantle flow rate, suggesting a major role for convergence. In the slab, along-strike tension occurs at intermediate and deeper depths (>100km) in case of mantle flow sustaining the sinking lithosphere and slab convex geometry facing mantle flow or in case of opposing mantle flow and slab concave geometry facing mantle flow. Along-strike compression is predicted in case of sustaining mantle flow and concave slabs or in case of opposing mantle flow and convex slabs. The slab stress field is thus controlled by the direction of impact of mantle flow onto the slab and by slab longitudinal curvature. Slab pull produces not only tension in the bending region of subducted plate but also compression where upper and lower plates are coupled. A qualitative comparison between results and data in selected subductions indicates good match for South America, Mariana and Tonga–Kermadec subductions. Discrepancies, as for Sumatra–Java, emerge due to missing geometric (e.g., occurrence of fault systems and local changes in the orientation of plate boundaries) and rheological (e.g., plasticity associated with slab bending, anisotropy) complexities in the models.

Middle Ordovician disorganized arc rifting in the peri-Laurentian Newfoundland Appalachians: implications for evolution of intra-oceanic arc systems

The Annieopsquotch Accretionary Tract comprises a tectonic collage of Ordovician peri-Laurentian terranes that formed during closure of Iapetus Ocean and imbricated beneath the composite margin of Laurentia. New zircon U–Pb geochronological data ( n = 8) for felsic volcanic rocks representing three distinct tectonostratigraphic units (the Mary March Brook group, the Buchans Group and the Red Indian Lake Group) indicate deposition over a short interval between 465 and 462 Ma. These tectonostratigraphic units are characterized by submarine mafic and felsic magmatism, and sedimentation typical of intra-oceanic arc systems. New and compiled whole-rock geochemical ( n = 315) and Sm–Nd isotopic ( n = 33) data for mafic and felsic volcanic rocks indicate that these tectonostratigraphic units formed in tholeiitic island arc to calc-alkaline arc settings. Isotopic (ε Nd −11.2 to +6; T DM 1.0–2.4 Ga) and zircon inheritance data (0.5–3.4 Ga) are consistent with presence of Laurentian continental crust in the basement. Relationships within and between these and adjacent tectonostratigraphic units in the Annieopsquotch Accretionary Tract suggest that they represent imbricated slices of a submarine arc that experienced disorganized arc rifting, similar to sectors of the modern Tonga–Kermadec and Izu–Bonin–Mariana arcs. The recognition of disorganized spreading in the Annieopsquotch Accretionary Tract has significant implications for along-strike correlations within the Appalachian orogen, as the nature of the arc systems is expected to differ significantly along-strike. The presence of a clear isotopic and inheritance signature of peri-Laurentian continental crust within the Annieopsquotch Accretionary Tract submarine arc system is consistent with the discoveries of older arc and continental basement in modern intra-oceanic arc systems. Supplementary materials: Geochronological analytical procedures and data, summary of geochemical data and isotopic data are available at http://www.geolsoc.org.uk/SUP18860 .

Seismic stratigraphy and paleogeographic evolution of Fairway Basin, Northern Zealandia, Southwest Pacific: from Cretaceous Gondwana breakup to Cenozoic Tonga–Kermadec subduction

AbstractWe present the first comprehensive seismic‐stratigraphic analysis of Fairway Basin, which is situated on the rifted continent of Zealandia in the Tasman Sea, southwest Pacific, between Australia and New Caledonia. The basin is 700 km long, 150 km wide, and has water depths of 500–3000 m. We describe depositional architecture and paleogeographic evolution of this basin. Basin formation was concurrent with two tectonic events: (i) Cretaceous rifting during eastern Gondwana breakup and (ii) initiation and Cenozoic evolution of Tonga–Kermadec subduction system to the east of the basin. To interpret the basin history we compiled and interpreted 2D seismic‐reflection profiles and make correlations with DSDP boreholes and the geology of New Caledonia. Five seismic‐stratigraphic units were defined. The deepest and oldest unit, FW3, folded and faulted can be correlated with volcaniclastic sediments and magmatic rocks in New Caledonia that are associated with Mesozoic Gondwana margin subduction. Alternatively, given the basin location 200–300 km west of New Caledonia and inboard of the ancient plate boundary, the unit could have formed as Gondwana intra‐continental basin with no known correlative. The overlying unit FW2b records syn‐rift deposition, probably associated with Cretaceous Gondwana breakup. Subaerial erosion supplied terrigenous sediment into the deltas in the northern part of the basin, as suggested by the truncation surfaces on the basement highs and sigmoid reflector geometries within unit FW2b respectively. Above, unit FW2a records post‐rift sedimentation and passive subsidence as the Tasman Sea opened and the Fairway Basin drifted away from Australia. Subsidence led to the flooding of the basement highs and burial of wave‐cut surfaces. Eocene compressive deformation resulted in minor folding and tilting within the Fairway Basin and was associated with the formation of many diapiric structures. The top of unit FW2 is an extensive unconformity that is associated with erosion and truncation on surrounding ridges. Above this unconformity, unit FW1b is interpreted as a turbidite system sourced from topography created during the Eocene tectonic event, which we interpret as being related to Tonga–Kermadec subduction initiation. Pelagic carbonate sedimentation is now prevalent. Unit FW1a has progressively draped the basin during Oligocene to Pleistocene subsidence. Many small volcanic cones were erupted during this final phase of subsidence, either as a delayed consequence of subduction initiation, or related to Tasmantid and Lord Howe hotspot trails. The northern Fairway Ridge remains close to sea level and its reef system continues to supply carbonate detrital sediments into the basin, most likely during sea‐level lowstands. Fairway Basin contains a nearly continuous record of tectonic and paleoclimatic events in the southwest Pacific since Cretaceous time. Its paleogeographic history is a key piece in the puzzle for understanding patterns of regional biodiversity in the southwest Pacific.

Trace element systematics of pyrite from submarine hydrothermal vents

Submarine hydrothermal sulfide ores occur at mid-ocean ridges, intra-oceanic arcs and in back-arc basins associated with host rocks of highly variable composition. Pyrite is the dominant sulfide mineral in most samples presented within this study, and thus the trace element composition of pyrite may reflect the different metal sources and precipitation processes. Here, we report on a systematic study of minor and trace element contents in pyrite from active and inactive submarine hydrothermal vent fields at different plate-tectonic settings including the Indian and Mid-Atlantic Ridges, the Tonga–Kermadec intra-oceanic arc, the Lau back-arc and the central Okinawa Trough. Our results show that the trace element contents of pyrite from different locations vary significantly but for most elements without any systematic correlation to the concentration in the magmatic host rocks. Only As appears to be depleted in pyrite from ultramafic-hosted vent systems that are affected by serpentinization. These As depleted pyrites preferentially host Au 0 micro- or nano-particles. Bismuth is enriched in pyrite from hydrothermal systems that contain a sedimentary component and micro-inclusions of sphalerite are either due to fluid–sediment interaction or phase-separated fluid venting. Pyrites from individual locations have highly variable concentrations of elements like Au, Co, Cu, Se, Mo, Ag and Sb that are most likely related to fluid evolution and changes in fluid composition. Sub-seafloor hydrothermal fluid–seawater mixing influences the distribution of Au, Co, Cu, Se and Mo in pyrite. Elements like Au, Ag, Sb and Pb often have a characteristic affinity to As, while Cd correlates closely with Zn. A magmatic volatile contribution to the Hine Hina hydrothermal system may result in the precipitation of Cu-enriched pyrite. Our results show that the concentrations of most trace metals in pyrite are a function of the physicochemical parameters of the fluid phase rather than a reflection of the magmatic host rock composition.

Use of ancient wave-ravinement surfaces to determine palaeogeography and vertical crustal movements around New Zealand

Wave-ravinement (shallow marine erosion) surfaces are formed during landwards migration of the shoreline due to rising relative sea level. They can be preserved if subsequently buried by sediment, and are easily identifiable on seismic reflection data. We present two examples from New Zealand's north-western offshore frontier region where these surfaces, despite a diachronous nature, represent sequence stratigraphic and geomorphic markers that are used to constrain regional palaeogeography and tectonic history. Thermal subsidence that followed the break-up of Gondwana led to the landwards migration of shorelines across the then-emergent Challenger Plateau and formation of a prominent Late Cretaceous–Eocene wave-ravinement surface. In the Reinga Basin, subsidence of uplifted land areas that had previously emerged during Cenozoic initiation of Tonga–Kermadec subduction was similarly accompanied by formation of transgressive wave-ravinement surfaces. Wave-ravinement surfaces serve as useful proxies for palaeo-sea level and, as the above two examples show, they are powerful tools for characterising regional deformation, uplift and subsidence histories and tectonic influence on relative base level fluctuations (changes in shoreline position). The study of these and other remarkable palaeo-sea-level markers around New Zealand and in the circum-Pacific region provides a different perspective on constraining vertical crustal movements associated with major tectonic events.

Hafnium isotope evidence for slab melt contributions in the Central Mexican Volcanic Belt and implications for slab melting in hot and cold slab arcs

This study presents evidence that Quaternary frontal arc calc-alkaline lavas from Central Mexican Volcanic Belt (CMVB) contain contributions from partial melts of the subducting garnet-bearing eclogitic oceanic crust and sediment, based on chemical and Hf–Nd isotope data. The CMVB includes both calc-alkaline lavas with arc-type trace element patterns such as aqueous fluid mobile element enrichments and high field strength element depletions; and “high-Nb” alkaline lavas with trace element patterns similar to ocean island basalts. The two types of lavas are closely related geographically and temporally. Distinct from the high-Nb lavas, the calc-alkaline lavas show trends toward higher 176Hf/177Hf and 143Nd/144Nd ratios coupled with lower Lu/Hf. The high Hf–Nd isotope ratios fingerprint contributions of subducted basaltic ocean crust, while the correlation with low Lu/Hf indicates melting in the presence of residual garnet, which reflects conversion of the subducted oceanic crust to eclogite. Isotopic and chemical mass balance considerations indicate that the slab melts are ~80% basaltic oceanic crust and ~20% subducted sediment. The calc-alkaline lavas have higher SiO2 at a given Mg# compared to the high-Nb alkaline lavas, also reflecting melt contributions from the subducted slab.A survey of global arc lavas shows that calc-alkaline lavas with low Lu/Hf ratios, reflecting melting in the presence of residual garnet and preferential mobilization of Hf over Lu from the subducted slab, are generally associated with hot slab conditions. These include arcs where young (<30Ma old) ocean crust is subducted (e.g. Mexican Volcanic Belt, Cascades, Austral Andes, Luzon, Setouchi), where slab tearing occurred and hot asthenospheric mantle could upwell through the slab window (e.g., western Aleutians, Sunda, southern Scotia), and where oblique or slow subduction leads to higher slab temperatures (e.g. Lesser Antilles, western Aleutians). In some of these hot slab arcs, where low Lu/Hf ratios are coupled with high Nd–Hf isotope ratios, slab melt contributions are dominated by partial melts from the subducted oceanic basalt (e.g., Mexican Volcanic Belt, Aleutians and Cascades). In other hot slab arcs, low Lu/Hf ratios are coupled with low Nd–Hf isotope ratios, reflecting slab contributions dominated by sediment melts (e.g. Setouchi, Lesser Antilles, Luzon, Sunda, and southern Scotia). Arcs associated with colder subducted oceanic crust (e.g. Izu–Bonin–Marianas, Tonga–Kermadec, central and northern Scotia) erupt lavas with high Lu/Hf along with high Hf–Nd isotope ratios, similar to mid-ocean ridge basalts, thus they lack the signature of residual garnet as well as significant slab melt input.

Potential field and bathymetric investigation of the Monowai volcanic centre, Kermadec Arc: implications for caldera formation and volcanic evolution

The dynamics of caldera formation are affected by internal factors, such as magma chamber structure and properties and regional tectonic stresses. Understanding their interrelationship is important for assessing volcanic hazard and reconstructing the evolution of a volcano. The Monowai volcanic centre, located at the Tonga–Kermadec Arc, is a basaltic–andesitic submarine stratovolcano and caldera. Recent surveys have shown that it is active, but little is known about its structure and evolution. Here we present a combined analysis of swath bathymetry and potential field data from Monowai, acquired during cruise SO215 on the R/V Sonne, in 2011 April–June. The Monowai caldera is associated with a 20–25 mGal Bouguer gravity anomaly high and a broad positive magnetic anomaly. Short-wavelength magnetic anomalies of up to +1400 and −800 nT are observed along the caldera rim and on the summit of Monowai cone. Inversion of the Bouguer gravity anomaly data shows that the caldera high is caused by a buried dense body with density contrast of up to +450 kg m−3 with respect to the surrounding arc crust. The body has a volume of ∼250 km3 and is divided into a main unit extending from 3 to 6 km depth and a shallower ring structure that underlies the rim of Monowai caldera. We estimate the density of the body to be 2650–2850 kg m−3, suggesting a mafic composition. The ring structure is interpreted as set of ring dykes and the main unit as a solidified or partly solidified magma chamber system (the Monowai pluton). The observed magnetic anomalies are consistent with pluton intrusion within the Bruhnes magnetic polarity. Analysis of the swath bathymetry data shows that Monowai is located in a 20-km-wide graben, part of an en-echelon, left-stepping horst and graben system that spans the length of the arc and backarc. The Monowai caldera is elongated perpendicular to the direction of rifting, suggesting that it is affected by the regional stress regime. Geomorphological analysis suggests that the caldera was created by repeated collapse of a single caldera structure and that its complex shape and multiple ring faults can be attributed to prolonged activity and multiple cycles of inflation and collapse. We propose a multiphase evolution of the Monowai volcanic centre comprising initial magma emplacement and crustal inflation; magma chamber evacuation and caldera collapse; caldera resurgence and mass waisting; southward migration of the eruptive vent; and formation of Monowai cone. It remains unclear whether the current eruption at the Monowai cone is fed directly from a small underlying magma chamber, or laterally from the Monowai pluton. Observation of radial fissure ridges on its flanks suggests that a shallow magma body may have been recently emplaced beneath the summit causing inflation and the formation of extensional cracks. The summit appears unstable and may be prone to lateral or vertical collapse. Therefore, the region remains a potential source of regional volcanic and tsunami hazard.

Erratum: Louisville seamount subduction and its implication on mantle flow beneath the central Tonga–Kermadec arc

Nature Communications 4: Article number: 1720 (2013); Published: 16 April 2013; Updated: 8 January 2014. Table 1 was inadvertently omitted during the production of this Article, and should have been referred to in the fourth paragraph of the ‘Geological and geochemical background’ section of the Results, as follows: ‘Sr and Pb isotopic compositions of lavas from ‘U’, ‘V’, Monowai and Ata are generally more radiogenic than Pacific and Indian MORB (Table 1, Fig.

Geometry of the subducting Pacific plate since 20 Ma, Hikurangi margin, New Zealand

Evolution of slab geometry beneath the North Island, New Zealand, has been investigated using a combination of published arc-type volcanic ages and earthquake locations in the subducting Pacific plate. Arc-front volcanoes migrated SE by 150 km in the last 8 myr subparallel to the present active arc. Migration of the arc is interpreted to mainly reflect slab rollback along the Tonga–Kermadec subduction system changing to fixed hinge slab steepening beneath the central North Island. The strike of the Pacific plate beneath the North Island, imaged by Benioff zone seismicity (50–200 km) and positive mantle velocity anomalies (200–600 km), is parallel to the NE–SW trend of arc-front volcanism. Arc parallelism since 16 Ma indicates that the strike of the subducting plate beneath the North Island was constant over this time interval, in contrast to clockwise vertical-axis rotations of ≥50° of the overriding plate over the same period along the eastern and southern Hikurangi margin. Acceleration of arc-front migration rates (from c . 4 to c . 18 mm a −1 ), eruption of high-Mg# andesites, increasing eruption frequency and size, and uplift of the overriding plate indicate an increase in the hydration, temperature and size of the mantle wedge beneath the central North Island from c . 7 Ma.

Seismic stratigraphic record of transition from Mesozoic subduction to continental breakup in the Zealandia sector of eastern Gondwana

The southwest Pacific between Australia, New Zealand and New Caledonia is a block of continental crust, Zealandia, that moved away from Australia and Antarctica after a long period of subduction beneath eastern Gondwana. We use >100,000line-km of seismic-reflection profiles to identify intra-continental basins related to the Gondwana active margin, overlain with erosional unconformity by retrogradational strata. We interpret this regional-scale first-order unconformity, the Eastern Gondwana Composite Surface, and seismic-stratigraphic megasequence pattern to represent the transition from subduction to continental breakup and separation of eastern Gondwana. Rocks that make up the lower seismic-stratigraphic megasequence (Zealandia-3, Permian to Early Cretaceous) have been drilled near New Zealand and can be correlated with Murihiku Supergroup rocks. Farther north on the Lord Howe Rise, we correlate this megasequence with Triassic to Jurassic rocks of the Clarence-Moreton Basin of eastern Australia. We reinterpret the Fairway–Aotea Basin to be underlain by a wedge of Zealandia-3 deposits thrust in a retro-arc-like foreland basin that was active immediately prior to breakup. The lower rift and retrogradational megasequence (Zealandia-2, Late Cretaceous to Eocene) we correlate with the Pakawau and Kapuni Groups of Taranaki Basin, New Zealand, and the “Formation à charbon” and “phtanites” of New Caledonia. The boundary with the shallowest megasequence (Zealandia-1, Late Eocene to present) is the “Eocene–Oligocene Unconformity”, which is primarily overlain by pelagic carbonate rocks. This regional unconformity likely represents the onset of the modern Tonga–Kermadec subduction system.

Louisville seamount subduction and its implication on mantle flow beneath the central Tonga–Kermadec arc

Subduction of intraplate seamounts beneath a geochemically depleted mantle wedge provides a seldom opportunity to trace element recycling and mantle flow in subduction zones. Here we present trace element and Sr, Nd and Pb isotopic compositions of lavas from the central Tonga-Kermadec arc, west of the contemporary Louisville-Tonga trench intersection, to provide new insights into the effects of Louisville seamount subduction. Elevated (206)Pb/(204)Pb, (208)Pb/(204)Pb, (86)Sr/(87)Sr in lavas from the central Tonga-Kermadec arc front are consistent with localized input of subducted alkaline Louisville material (lavas and volcaniclastics) into sub-arc partial melts. Furthermore, absolute Pacific Plate motion models indicate an anticlockwise rotation in the subducted Louisville seamount chain that, combined with estimates of the timing of fluid release from the subducting slab, suggests primarily trench-normal mantle flow beneath the central Tonga-Kermadec arc system.