Intraplate Volcanism Research Articles

Late Cenozoic intraplate volcanism as a trigger for hydrothermal venting in the Arctic southwestern Eurasia Basin

Intraplate volcanism has occurred for the last 35 million years within Northeast Atlantic and Arctic margins, including the western Barents Sea, Svalbard, and northern Greenland. Earlier studies have suggested that some of this volcanism might be sourced from nearby mid-ocean ridges. However, legacy data does not reveal correlations between the sporadic volcanism, despite comparable setting, ages, and compositions of basalts across the area. Here, we utilize a compilation of geophysical data to document late Cenozoic intraplate volcanism affecting the northeastern Yermak Plateau and southwestern Eurasia Basin located north of Svalbard. The identified seabed and subsurface features include volcanic (Mound-A) and hydrothermal vent systems (Tayrona Vent) formed approximately 10 and 2.6 million years ago, respectively. These intraplate volcanic products are coincident in age and origin with observed hydrothermal systems on Svalbard and Northeast Atlantic. We propose that these magmatic features are the result of intraplate volcanism associated with seismic and thermal anomalies in the mantle beneath northern Svalbard.

Recycled Oceanic Crust in the Source of the Intraplate Changbaishan‐Tianchi Volcano, China/North Korea

AbstractContinental intraplate volcano is an ideal probe to unravel the composition and structure of the deep Earth. The intraplate Changbaishan‐Tianchi volcano was one of the most hazardous eruptions on the Earth's planet. The long‐term activity of this volcano from the Pleistocene to 946 CE has erupted materials with a broad compositional range from basalt to rhyolite, which are expected to be associated with the continuous northeastward subduction of the Pacific plate, but the magma source remains controversial. In this paper, we present a comprehensive data set of in situ zircon Hf and O isotope data, combined with whole‐rock element and Sr‐Nd‐Pb isotope compositions, for selected eruptions of the Changbaishan‐Tianchi volcano, aiming to provide new insights into their magma source and the associated geodynamics. Radiogenic isotopic ratios and incompatible trace element compositions indicate that the erupted volcanic rocks at different stages, although with a varied differentiation degree, were derived from a common magma source characterized by a mixture of DM and EM1 end‐members. Zircon Hf and O isotopes are both relatively homogeneous for different lithologies and eruption stages, with the εHf(t) values varying between −5 and +5, and δ18O values between 3.58‰ and 5.97‰. Modeling of source mixing indicates that high‐temperature altered oceanic crust materials are an important component in the source of Changbaishan‐Tianchi volcano, likely derived from an ancient stagnant slab that has been reactivated by the subduction of the Pacific plate. This study demonstrates that the recycling of deeply subducted oceanic crust is potentially an important source and trigger for continental intraplate volcanism.

Two Mechanisms Generating Intraplate Volcanism in Southeast Asia: Insights From Mantle Transition Zone Discontinuities

AbstractDetermining the mechanisms responsible for intraplate volcanism ‐ such as slab devolatilization melting versus active mantle plumes ‐ remains a challenge. The greater South China Sea (SCS) region has experienced extensive intraplate Cenozoic volcanism across areas including Hainan, Southeast Indochina, northern Borneo, the northern SCS, and the post‐spreading SCS basin. The prevalence of volcanism distributed widely across this region prompts fundamental questions about the key geodynamic processes driving such diverse magmatic activities. In this study, we elucidate the mantle transition zone (MTZ) discontinuities in this region using SS precursors, which helps to overcome the sparse seismic coverage due to its predominantly oceanic setting. We collected over 16,000 high‐quality seismograms that sample the upper mantle and MTZ beneath this region from global earthquakes and stations. After correcting for the effects of shallow crustal variations and upper mantle heterogeneity on traveltimes of SS phases and their precursors, we unveil lateral variations in the MTZ boundaries (d410 and d660) and intricate features of the mid‐MTZ reflectors (S520S). Significant MTZ thinning and normal S520S waveforms beneath Hainan provide compelling evidence for mantle upwelling through the MTZ. Conversely, the evident splitting of S520S beneath the northern SCS, Southeast Indochina, and northern Borneo, all characterized by stagnant subducted slabs, indicates that the volcanism in these regions likely originated from a mechanism distinct from the active upwelling beneath Hainan. Dehydration melting attributed to devolatilizing stagnant slabs in the MTZ is a potential cause for Cenozoic volcanism in these regions.

Mantle deformation in the highly oblique indo-burma subduction system inferred from shear wave splitting measurements

We utilized shear wave splitting analysis of teleseismic SKS, SKKS, and PKS phases to infer upper mantle deformational fabrics across a substantial area of Southeast Asia, where splitting measurements were previously limited. We used newly available permanent and temporary broadband seismic networks deployed across the Indo-Burma subduction zone and the eastern Indochina peninsula. The resulting 492 well-constrained splitting and 654 null measurements from 185 stations reveal clear large-scale patterns in the mantle deformational fabrics in response to the highly oblique active subduction and a large transform plate boundary. We identified two distinct domains of mantle deformation fabrics in the western Burma microplate and the eastern Indochina peninsula. In the former, trench parallel N-S fast polarization directions with an average lag time (δt) of 1.9 s are observed beneath the Indo-Burman Ranges. We suggest the observed splitting is partly due to anisotropy in the sub-slab region and relates to shear induced by the north moving Indian plate. The lithospheric fabric within the Indo-Burman Ranges and underlying subducting slab fabric contribute to produce the observed average δt of 1.9 s. The δt value decreases to an average of 1.0 s towards the back-arc until we reach the dextral Sagaing fault. In the second domain, starting approximately 100 km east of the Sagaing fault, we observe a consistent E-W fast direction with an average δt of 1.10 s in the eastern Shan-Thai and Indochina blocks. We interpret the E-W fabric as due to the deformation associated with the westward spreading of the Hainan mantle plume, possibly driven by overriding plate motion. Low velocities in the shallow mantle and late Cenozoic intraplate volcanism in this region support the plume-driven asthenospheric flow model in the Indochina peninsula. The sudden transition of the fast polarization direction from N-S to E-W along the eastern edge of the Burma microplate indicates the Sagaing fault acts as a mantle flow boundary between the subduction dominated trench parallel flow to the west and plume induced asthenospheric flow to the east. We also observed no net splitting beneath the Bengal basin which is most likely due to the presence of frozen vertical fabric resulting from the Kerguelen plume activity during Early Cretaceous.

A Displaced Lower Mantle Source of the Hainan Plume in South China Revealed by Receiver Function Imaging of the CEArray

AbstractWe analyzed 49,592 teleseismic receiver functions (RFs) recorded by 278 CEArray stations to image the mantle transition zone (MTZ) beneath the South China Block to understand the origins of deep velocity anomalies and their potential links to subduction and intraplate volcanism. We employed a fast‐marching method and a high‐resolution 3‐D velocity model (FWEA18) derived from full waveform inversion in computing P‐to‐S conversion times to better image the 410‐ and 660‐km discontinuities. Our results indicate that the common‐conversion‐point stacking of RFs using 3‐D conversion times yielded better migration images of the two discontinuities. The images revealed a slightly depressed 410‐km with a few small uplifted patches, and showed that the 660‐km beneath the western Yangtze Craton is depressed by 10–25 km, which is likely caused by the stagnant Paleo‐Pacific slab. The 660‐km beneath the southern Cathaysia Block has a 5–15 km high plateau with a topographic low at its central part. The lateral dimension of the topographic low is ∼150 km and is located beneath the central Pearl River Mount Basin near Hong Kong. We speculate that the topographic low occurs within the Hainan plume with a temperature excess of ∼300–400 K and is caused by the garnet phase transition. The displaced deep plume enters the MTZ and spreads nearly horizontally at the base. The plume evolves into two channels with a minor one toward the northeast and a major one toward the southwest, which keep moving upward to the 410‐km. The southwest channel is likely the source that feeds the Hainan volcanoes.

Insights into the development of small-volume long lava flows: A case study of the Coalstoun Lakes Volcanic Field, southeast Queensland, Australia

Long lava flows exceeding 50 km in length are usually produced during large-volume flood basalt eruptions (>100 to 10,000 km3) but can also occur from small to moderate-volume (<30 km3) basaltic eruptions in continental intraplate monogenetic volcanic fields. Eruptive volume, therefore, is not an a priori barrier to producing long lava flows. Key factors that promote long lava flows include efficient lava transport systems that minimise heat loss, long-lived and sustained effusion rates to maintain flow advancement, and lava flow across low topographic gradients (<1°-10°) with minimal topographic barriers.Here, we focus on an anomalously young and poorly studied basaltic monogenetic volcanic field in southeast Queensland, Australia, that formed part of the broader intraplate volcanism in eastern Australia since the Late Cretaceous. The Coalstoun Lakes Volcanic Field (CLVF) comprises three lava fields: the Barambah Basalt Flow Field, the Deep Creek Flow Field and the Hunters Hill Flow Field. Basalt from the Barambah Basalt Flow Field has been redated here by Ar40/Ar39 analysis of groundmass material, yielding a weighted mean age of 0.520 ± 0.016 Ma. The Barambah Basalt Flow Field contains most of the eruptive volume and has advanced up to 165 km from the vent. The Hunters Hill and the Deep Creek flow fields are comparatively smaller in volume and have advanced ∼30 and ∼ 20 km from the vent, respectively. Lava tubes are only known from proximal regions and do not appear to be a significant factor in promoting long run-out in the CLVF. Flow confinement and utilisation of existing drainage networks are features of both lava flow fields, and advancement down the sand-based and ephemeral Burnett River significantly promoted long run-out despite low topographic gradients.New whole-rock geochemical data on our CLVF samples indicates that all lavas are hawaiites, a common feature of other Quaternary long lava flows globally. Overall, there is some compositional variation, but a cryptic zonation is readily apparent in trace element abundances, which helps to further distinguish the flow fields as the products of separate but closely spaced eruptions. The combination of field and geochemical data indicates that the long lava flow of the Barambah Basalt Flow Field resulted from a sustained and relatively low effusion eruption, creating a pāhoehoe flow field that continuously advanced across the landscape, utilising a drainage system that guided lava flow and helped to circumvent any topographic barriers.

Evidence for long-lived (>100 Myr) continental intraplate volcanism: Mongolia since the last ocean closure

Since the closure of the Mongol-Okhotsk Ocean in the Mesozoic, Mongolia has been in an intraplate tectonic setting; the nearest plate boundary being ∼3,000 km to the east, at the active Pacific subduction front. Throughout this time, Mongolia has experienced magmatism in the form of distinctive, small-volume volcanic fields dispersed along the central and eastern parts of the country. On the basis of geochemical, isotopic, palaeomagnetic and zircon data, the magmatism can be discriminated from preceding post-collisional magmatism. Gradual change from a lithospheric to an asthenospheric mantle source suggests lithospheric delamination occurred beneath Mongolia, starting at ∼140 Ma and terminating at ∼107 Ma. Accordingly, the onset of intraplate magmatism is set at 107 Ma. Regardless of the spatial and temporal occurrence and evolution of the intraplate magmatism in Mongolia, the geochemistry of the resultant volcanic rocks throughout time remains remarkably similar, although the cause of magmatism has been much debated.Through evaluation of available K-Ar and Ar-Ar data from the literature, along with newly-obtained data from three different volcanic fields, we have identified that the intraplate volcanism in Mongolia has been near-continuous since its onset, with hiatuses of only <6 Myr. Since 35 Ma, hiatuses have reduced to <1 My. In light of these findings, we re-evaluate the various models that have been proposed for the origins of this long-lived volcanism and suggest the cause of magmatism results from asthenospheric upwellings initiated by a delamination event in the Mesozoic, but have been prolonged by enhanced mantle flow relating to northward progression of India, the closure of Neo-Tethys, and ultimately the Indo-Asian collision. This example of intraplate magmatism is one of the longest-lived volcanic intraplate regimes on Earth that does not appear to relate to a geophysically-recognisable high heat-flux mantle plume.

Petrogenesis of volcanic rocks from the Quaternary Eifel volcanic fields, Germany: detailed insights from combined trace-element and Sr–Nd–Hf–Pb–Os isotope data

Quaternary rocks from the East and West Eifel volcanic fields in western Germany are a key suite of intraplate volcanic rocks that can provide insights into volcanism of the Central European Volcanic Province (CEVP) and into continental intraplate volcanism in general. We present a comprehensive dataset for Eifel lavas including isotope as well as major and trace element data for 59 samples covering representative compositions of the different volcanic fields. In line with previous studies, the lavas are all SiO2-undersaturated, alkaline-rich and mainly comprise primitive basanites, melilitites, and nephelinites (Mg# ≥ 57). Geochemical compositions of samples from both volcanic subfields display distinct differences in their trace-element as well as radiogenic isotope compositions, largely confirming previous subdivisions. Coupled trace-element and radiogenic Sr–Nd–Hf–Pb–Os isotope compositions can now provide firm evidence for spatially heterogeneous mantle sources and compositionally distinct magmatic pulses. Within the West Eifel Field, Sr–Nd–Pb isotope compositions of the younger (≤80 ka), ONB-suite (olivine-nephelinite-basanite) are similar to FOZO (FOcal ZOne) or the EAR (European Asthenospheric Reservoir) and resemble compositions that have been previously reported from plume-sourced ocean island basalts (OIB). In marked difference, older (700 Ma to 80 ka) volcanic rocks from the F-suite (Foidite) in the West Eifel field and from the entire east Eifel Field tap a more enriched mantle component, as illustrated by more radiogenic Sr isotope (86Sr/87Sr up to 0.705408) and variable Pb isotope compositions (206Pb/204Pb = 18.61–19.70, 207Pb/204Pb = 15.62–15.67 and 208Pb/204Pb = 38.89–39.76). Combined trace-element compositions of ONB-suite samples are in good agreement with results from batch melting models suggesting a hybrid composition of Eifel magmas formed through mixing 10% of a FOZO-like melt with 90% of a DMM-like melt, similar to melts from the Tertiary HEVF. However, radiogenic Sr–Nd–Pb isotope compositions of F-suite and EEVF and some ONB lavas require the admixture of melts from lithospheric mantle sources. Elevated Nb/Ta and Lu/Hf ratios in combination with variable 187Os/188Os ratios can now demonstrate the presence of residual carbonated eclogite components, either in the lithosphere or in the asthenospheric mantle. Finally, by combining geochemical and temporal constraints of Tertiary and Quaternary volcanism it becomes evident that CEVP volcanism in central and western Germany has resulted from compositionally distinct magmatic pulses that tap separate mantle sources. Although the presence of a mantle plume can neither be fully confirmed nor excluded, plume-like melt pulses which partially tap carbonated eclogite domains that interact to variable extents with the lithosphere provide a viable explanation for the temporal and compositional cyclicity of CEVP volcanism.

The crust-mantle velocity structure beneath the Wudalianchi-Erkeshan-Keluo volcanic belt by joint inversion of receiver functions and ambient noise

The Wudalianchi-Erkeshan-Keluo (WEK) volcanic belt is a significant component of intraplate volcanism in Northeast China and is composed of the Wudalianchi, Erkeshan, and Keluo volcanic clusters. Using joint inversion of receiver functions and ambient noise, we construct a high-resolution 3-D S-wave velocity model of the WEK volcanic belt and its adjacent region, taking advantage of a deployed dense seismic array around this volcanic belt. There is a prominent low-velocity anomaly at 8–15 km depth beneath the Wudalianchi volcanic cluster, suggesting the presence of a crustal magma chamber. Low-velocity anomalies are also observed at 30–35 km depth beneath the Erkeshan volcanic cluster and 30–40 km depth beneath the Keluo volcanic cluster, resulting in discontinuous velocity structures at the Moho discontinuity. We further find a distinct low-velocity anomaly in the uppermost mantle beneath the WEK volcanic belt. Combined with previous geophysical and geochemistry studies, we propose a magma system scenario for the WEK volcanic belt. The upwelling molten material from the asthenosphere accumulated in the uppermost mantle and the magma chamber was formed, which provided the same uppermost mantle magma sources for the WEK volcanic belt.

Continental Hotspots Tracks From an Analysis of GOCE Gravity Gradients Data

AbstractThis study aims to detect residual thermal anomalies along the path of a hotspot beneath the continental lithosphere using gradiometry data. We calculate perturbations in gravity vectors and gradients by employing a simple thermal anomaly model. The results highlight that the horizontal components of Bouguer gravity gradients, sensitive to source structure and elongation, exhibit substantial magnitudes, exceeding current detection levels. To improve signals from sources of different sizes and orientations, we apply a filtering approach involving wavelet transforms and rotated local frames. We also assess the impact of lateral crustal variations on the gravity field by introducing random density anomalies and a seismic crustal model, testing the method's ability to distinguish between these anomalies and thermal sources. Using Gravity field and steady‐state Ocean Circulation Explorer satellite data, we generated scale‐orientation diagrams aiming to identify signals aligned with the direction of plate movement and with a spatial scale of a few hundred kilometers (scale of the plumes). Maps of filtered Bouguer gravity gradients aligned with hotspot trajectories are generated for all continental hot plumes, with the position and the age of the intraplate volcanism to support the interpretation. While we do not show a clear signal in regions that are too tectonically complex or with lateral variations in the crust or at the lithospheric boundary correlated with the hotspot trace, we found observed signals with expected sign and amplitude over Hoggar, Tibesti, Darfour and Cameroon tracks in Africa and over Iceland and Jan Mayen in Greenland. However, determining corresponding mass source depths remains a complex task.

Stratigraphy, geochronology, geochemistry and Nd isotopes of the Ouarzazate Group, Anti-Atlas, Morocco: Evidence of a Late Neoproterozoic LIP in the northwestern part of the West African Craton

In the eastern and central Anti-Atlas of Morocco, the Late Neoproterozoic Ouarzazate Group (OG) forms a ∼ 2 km-thick section of volcano-sedimentary rocks deposited during intermittent magmatic activity, spanning a time period between 590 and 540 Ma. In the eastern Anti-Atlas, the stratigraphy of the OG, termed IMS (Imiter Mine succession), includes four units that reflect a gradual change from fluvial to lacustrine depositional sedimentary environments. In the central Anti-Atlas, the deposition of the OG occurs within a caldera environment, consisting of five units referred to as BMS (Bou Azzer Mine succession). UPb dating on zircon from the rhyolite lava flow at the top of the IMS constrains the latest lava flow of the IMS to 570.7 ± 2.1 Ma. In the Bou Azzer inlier, the stratigraphically correlated basal andesite and top dacite lava flows were emplaced at 590.6 ± 4.2 Ma and 555.9 ± 20.4 Ma, respectively, suggesting that the OG was constructed through successive pulses within a long-lived magmatic episode. The magmatic rocks display geochemical signatures typical of continental arc magmas, including high-K calc-alkaline to shoshonite composition, enrichment in LILE, and negative Nb, Sr, Ti and P anomalies. Nd isotopes indicate that magmas supplying the plumbing systems of the IMS and BMS constitute transitional products resulting from a combination of orogenic and intraplate volcanism, involving deep crustal recycling. The compositions of these magmas evolved through processes of crustal contamination, bulk assimilation, and minor fractional crystallization of the parent melt. High εNd values of the BMS rocks argue for a juvenile origin, whereas lower εNdt recorded in the IMS likely reflect old crustal protoliths and an overall less contribution of juvenile material in their source. The magmatic rocks of the OG are interpreted as products of a large igneous province (LIP) developed by a post-collisional delamination model that initiated tens of millions of years after the subduction-collision process stage of the Pan-African orogeny in the northwestern part of the West African Craton (WAC).

Experimental melting of phlogopite websterite in the upper mantle between 1.5 and 4.5 GPa

Abstract Reaction experiments have confirmed that phlogopite websterite can be formed by interaction of peridotite with hydrous alkaline or silica-rich melts. Phlogopite websterites commonly occur as xenoliths in orogenic and intraplate volcanism but do not receive much attention. We have experimentally investigated the melting behaviour of a phlogopite websterite at 1.5 GPa (1050–1300 °C), 3.0 GPa (1100–1500 °C), and 4.5 GPa (1200–1500 °C) to contribute to understanding the sources of ultrapotassic rocks that occur in different settings. The solidus temperature rises with increasing pressure, bracketed between 1050 and 1100 °C at 1.5 GPa, 1100 and 1150 °C at 3.0 GPa and between 1200 and 1250 °C at 4.5 GPa. At 1.5 GPa, phlogopite websterite melts incongruently to form olivine and melt, whereas orthopyroxene, garnet and melt are formed at 3.0 and 4.5 GPa. The transition of orthopyroxene from reactant to product with increasing pressure results in changes in the SiO2-content of melts. The experimental melts reach a maximum K2O content when phlogopite is consumed completely at temperatures ~150 °C above the solidus. The melting reactions are similar to those of phlogopite lherzolite, but the low-Al2O3 starting materials result in lower Al2O3 in the melt than in melts of phlogopite lherzolite. Comparison with natural ultrapotassic rock compositions reveals that the sources of ultrapotassic rocks in convergent settings may be dominated by phlogopite websterite, phlogopite lherzolite and phlogopite harzburgite. Sources of ultrapotassic rocks in intraplate settings are more likely to include phlogopite clinopyroxenite ± CO2 and K-richterite. In all melting experiments on phlogopite-bearing rocks, K2O from phlogopite passes into the melt, and hence the highest K2O contents in ultrapotassic rocks must be an indication of the minimum stoichiometric coefficient of phlogopite in the reaction. In cases where phlogopite websterite or phlogopite lherzolite is identified as the source, the minimum modal percentage of phlogopite in the source can be inferred from the highest K2O content. When applied to the Milk River minettes and New South Wales leucitites, the estimated modal proportion of phlogopite in the sources is greater than 20 wt.%. Phlogopite can survive the subduction process and melt later in the post-collisional environment, whereas thermal perturbations are necessary to trigger melting of phlogopite-bearing assemblages at the base of the lithosphere in intraplate settings.

An ongoing lithospheric dripping process beneath northeast China and its impact on intraplate volcanism

Abstract Unique intraplate volcano eruptions and westward volcano migration since the Oligocene have been observed in northeast China, where an overriding continental zone is tectonically controlled by the subduction of the northwestern Pacific plate and the opening of Japan Sea. Interestingly, these intraplate magmatic events occur around a subsiding basin (the Songliao Basin), but no volcanic activity has been observed within the Songliao Basin. The geodynamic mechanism responsible for these volcanoes remains unclear. To address the geodynamic process beneath northeast China, we conducted numerical models constrained by data from regional reconstruction and seismic and volcanic studies. The vertical velocity field of mantle convection and lithospheric partial melting structures derived from our models show that mantle upwelling and melting centers migrate from east to west in northeast China with the westward propagation of the sub-horizontal slab in the transition zone, leading to the observed volcano migration. Also, with the subduction retreat of the northwestern region of the Pacific plate and the opening of the Japan Sea, significant lithospheric thickness differences developed between the Changbaishan-Mudanjiang region and the Songliao Basin, leading to lithospheric unstable dripping. This dripping structure prevents the partial melting of the lithosphere but facilitates the subsidence of the Songliao Basin. Moreover, the lithospheric dripping model successfully predicts upper mantle structures consistent with the proposed tomography model, the observed Moho depth, and surface topography variations. Thus, lithospheric dripping induced by lithospheric thickness differences and the retreating subduction of the Pacific slab provides a robust mechanism for the unique geodynamic processes in northeast China.

Strong seismic anisotropy due to upwelling flow at the root of the Yellowstone mantle plume

Abstract The Yellowstone region (western United States) is a commonly cited example of intraplate volcanism whose origin has been a topic of debate for several decades. Recent work has suggested that a deep mantle plume, rooted beneath southern California, is the source of Yellowstone volcanism. Seismic anisotropy, which typically results from deformation, can be used to identify and characterize mantle flow. Here, we show that the proposed plume root location at the base of the mantle is strongly seismically anisotropic. This finding is complemented by geodynamic modeling results showing upwelling flow and high strains in the lowermost mantle beneath the Yellowstone region. Our results support the idea that the Yellowstone volcanism is caused by a plume rooted in the deepest mantle beneath southern California, connecting dynamics in the deepest mantle with phenomena at Earth's surface.

The Magmatic Patterns Formed by the Interaction of the Hainan Mantle Plume and Lei–Qiong Crust Revealed through Seismic Ambient Noise Imaging

Magmatism on continental lithospheres induced by mantle plumes is more complex compared to oceanic intraplate volcanism owing to the heterogeneous nature of continental crustal and lithospheric structures. Substantial evidence points to the deep-oriented Hainan mantle plume beneath the Lei–Qiong region, the southernmost of the South China block. In this study, we present a detailed shear wave velocity model of the crust and uppermost mantle in the Lei–Qiong volcanic region, derived from 3-year seismic data (2016–2018) from 34 stations and the use of the ambient noise tomography method. An evident columnar low-velocity anomaly was imaged in the crust and uppermost mantle beneath the Wushi Sag (WSS), Beibu Gulf, potentially suggesting that the center of either one branch or the entirety of the Hainan mantle plume impacts the crust here. This low-velocity anomaly is overlaid by a local Moho deepening, indicative of underplating beneath the existing crust. The Maanling–Leihuling Volcanic Field (MLVF) in northern Hainan Island, previously considered the center of the hotspot, does not exhibit such distinct velocity anomalies. Instead, subtle lower crustal anomalies beneath the MLVF are linked with the upper mantle low-velocity zone beneath the WSS. Additionally, the high-conductivity bodies beneath the MLVF indicate lateral magma transport. Earthquake swarms and deep-seated seismic events beneath the WSS further support the presence of magmatic processes. This study indicates that in the Lei–Qiong region, the interaction of the continental crust with the mantle plume centered in the WSS results in magma exhibiting both vertical ascent and lateral migration, leading to a dual low-velocity shear wave pattern in the upper crust, which significantly influences the surface volcanic activity.

Mid-Jurassic volcanism at Bokhara River and insights into metasomatism in the lithospheric mantle of the Thomson Orogen, eastern Australia

Eastern Australia is covered by extensive, thick regolith, which obfuscates much of its basement geology, making geological sampling difficult. The Bokhara River diatremes erupted through the Thomson Orogen in eastern Australia and are covered by ∼300 m of Cretaceous regolith cover. Hitherto, these diatremes have only been characterised by magnetic anomaly surveys and private exploration drilling. The melts were assumed to be leucititic, owing to their proximity to Miocene leucitite centres to the south, while their position along the Cosgrove hotspot track led to the assumption that the diatremes erupted at ca 20 Ma. However, whole-rock chemistry shows that the diatremes are basanites and, according to 40Ar/39Ar dating, erupted during the mid-Jurassic (ca 180 Ma; estimated by reproducible slightly discordant ages), substantially older than the assumed age and coincident with widespread Mesozoic flood basalts across Gondwana. The basanites entrained abundant mantle material during accent, which contaminated the basanite with ∼12.8 wt% xenocrystic material. The xenoliths are all fertile spinel lherzolites with Mg# 87–89, CaO 2.64–5.90 wt% and Al2O3 2.87–3.83 wt% that have been cryptically metasomatised by a mafic silicate melt, which resulted in chromatographic rare-earth element patterns. This demonstrates that mantle metasomatism occurred during the Mesozoic in this part of eastern Australia, revealing another expression of intraplate volcanism prior to Australia rifting away from Gondwana. The identification and characterisation of this Jurassic volcanism hosting evidence for mantle metasomatism suggest that intraplate volcanism and mantle metasomatism are synonymous within orogenic eastern Australia, and not restricted to the Cenozoic.

How to build a habitable planet: an interview with Charles H. Langmuir.

Earth is the only known habitable planet in the solar system. Understanding how Earth developed its unique habitability has been the frontier of Earth sciences and has become one of the main themes of current deep-space explorations. What are the decisive factors that led to a habitable planet? What is the role of solid Earth processes in the origin of life and in modulating the surface environment? Are Earth's habitability studies relevant to current challenges that human beings face? These questions have attracted the interest of both scientists and the public alike. NSR spoke to Prof. Charles H. Langmuir from Harvard University in the USA, who is a solid Earth geochemist who carries out research on diverse aspects of the plate tectonic geochemical cycle, including ocean ridges, convergent margins and intraplate volcanism. Prof. Langmuir is the author of the book How to Build a Habitable Planet (www.habitableplanet.org), one of the best Earth science books published in 2012.

Focused Mantle Upwelling Beneath the Southeastern Asian Basalt Province Revealed by Seismic Surface Wave Tomography

AbstractFollowing the termination of seafloor spreading in the South China Sea (SCS) basin, abundant intraplate volcanism widely spreads in the Indochina block, SCS basin, and Leiqiong area, forming the Southeastern Asian Basalt Province (SABP). The geodynamic origin of the SABP has long been enigmatic and debated. Here, we present a high‐resolution 3‐D upper mantle S‐wave velocity model in the region by conducting earthquake‐based surface wave tomography with seismic data collected across Southeast Asia. The resultant images depict a plume‐like structure beneath the central area of the SABP, characterized by a continuous, sub‐vertical low‐velocity column in the upper mantle. Our new findings, combined with previous geochemical and geodynamic evidence, suggest that the extensive post‐spreading intraplate volcanism within the SABP is likely induced by this focused mantle upwelling, which could be further traced down to the core‐mantle boundary as inferred by existing global velocity models.

Four distinct pulses of volcanism built the Melanesian Border Plateau: Implications for oceanic mid-plate superstructure formation

The ocean basins contain numerous volcanic ridges, seamounts and large igneous provinces (LIPs). Numerous studies have focused on the origin of seamount chains and LIPs but much less focus has been applied to understanding the genesis of large volcanic structures formed from a combination or series of volcanic drivers. Here we propose the term Oceanic Mid-plate Superstructures (OMS) to describe independent bathymetric swells or volcanic structures that are constructed through superimposing pulses of volcanism, over long time periods and from multiple sources. These sources can represent periods when the lithosphere drifted over different mantle plumes and/or experienced pulses of volcanism associated with shallow tectonic drivers (e.g. plate flexure; lithospheric extension). Here we focus on the Melanesian Border Plateau (MBP), one example of an OMS that has a complex and enigmatic origin.The MBP is a region of shallow Pacific lithosphere consisting of high volumes of volcanic guyots, ridges and seamounts that resides on the northern edge of the Vitiaz Lineament. Here we reconcile recently published constraints to build a comprehensive volcanic history of the MBP. The MBP was built through four distinct episodes: (1) Volcanism associated with the Louisville hotspot likely generating Robbie Ridge and some Cretaceous seamounts near the MBP. (2) Construction of oceanic islands and seamounts during the Eocene when the lithosphere passed over the Rurutu-Arago hotspot. (3) Reactivation of previous oceanic islands/seamounts and construction of new volcanos in the Miocene when the lithosphere passed over the Samoa hotspot. (4) Miocene to modern volcanism driven by lithospheric deformation and/or westward entrainment of enriched plume mantle due to toroidal mantle flow driven by the rollback of the Pacific plate beneath the Tonga trench. The combination of these processes is responsible for ∼222,000 km2 of intraplate volcanism in the MBP and indicates that this OMS was constructed from multiple volcanic drivers.

Origin of Early Cretaceous mafic volcanic rocks from the Erlian Basin west of the Great Xing’an Range of North China: Implications for the tectono-magmatic evolution of East Asia

Early Cretaceous intraplate volcanic rocks are widespread in NE Asia, but their origin remains controversial. This work presents zircon U-Pb ages, whole-rock element and Sr-Nd isotope data for mafic volcanic rocks from the Erlian Basin, a wide rift basin in NE Asia. There were two episodes of Early Cretaceous mafic volcanism in the Erlian Basin, and the eruptions show contrasting geochemical compositions. The early mafic volcanic rocks, with U-Pb ages of ca. 140−135 Ma, show slightly depleted Sr-Nd isotope compositions (ISr(t) = 0.7042−0.7052; εNd(t) = +0.82 to +3.0) and arc-like trace-element compositions, which are derived from subduction-related fluid/melt metasomatized lithosphere mantle. The late mafic volcanic rocks (dated at ca. 125 Ma) have enriched Sr-Nd isotopes (ISr(t) = 0.7055−0.7077; εNd(t) = −0.50 to −2.67) and oceanic-island basalt (OIB)-like trace-element compositions, revealing the metasomatism of melts from crustal materials and asthenosphere mantle. The two types of mafic volcanic rocks may record the interactions of the mantle and melts from the subducted paleo-Pacific oceanic slab at different depths. The landward-then-oceanward migration pattern of the Mesozoic volcanism from NE Asia can be explained by the flat subduction and subsequent slab roll-back of the Paleo-Pacific Ocean, consistent with migration patterns from the North China Craton and South China Block, implying similar Jurassic−Cretaceous subduction evolution along the entire East Asia margin. Some Late Jurassic to Early Cretaceous dates from east Mongolia and the southern margin of the Erlian Basin diverge from this trajectory. In combination with previous studies, we suggest that the Early Cretaceous pervasive intraplate volcanism in the Erlian Basin and adjacent areas of NE Asia mainly resulted from the slab roll-back of the Paleo-Pacific Ocean with a combined effect from the post-collision extension of the Mongol-Okhotsk orogen.