Shield Volcano Research Articles

Numerical simulation of open channel basaltic lava flow through topographical bends

In this study, we utilised computational fluid dynamics to investigate the behaviour of open-channel basaltic lava flows navigating bends on shield volcanoes. Our focus was on understanding the relationship between flow velocity, rheology, and bend geometry. Employing a simple Force Balance Model (FBM), which considers the equilibrium between hydrostatic pressure and centrifugal force, we accurately approximated the changes in the height of the lava’s free surface through various bend geometries. Our analysis includes examining the influence of channel depth, width, and bend radius on the flow, revealing that variations in these parameters significantly affect the flow’s vertical displacement. Additionally, the bend sector angle emerged as a critical factor, indicating a minimum angle necessary for the flow to fully develop before exiting the bend.Further, we assessed the applicability of the Shallow Water Equations (SWE) for modelling the inertial displacement of the lava flow in bends, finding a good fit. The study extended to comparing the FBM’s predictions of the tilt angle of the flow’s free surface with the SWE results, showing notable agreement under specific conditions, particularly at a bend angle of 90 degrees. The impact of fluid density was also considered, revealing that density is a contributing factor to the development of the wetted line in the bend, a factor that is not captured by the simple FBM model. Finally, we explored different rheologies akin to natural lava flows, such as viscoplastic flow, and determined that factors like yield stress, consistency index, and power law index have a small impact on the flow behaviour in a steady-state condition within a bend.

Seismo‐Acoustic Characterization of the 2018 Sierra Negra Caldera Resurgence and Fissure Eruption in the Galápagos Islands

AbstractThe 2018 eruption of Sierra Negra volcano, Galápagos, Ecuador has provided new insights into the mechanisms of caldera resurgence, subsidence, and fissuring at basaltic shield volcanoes. Here, we integrate local (∼0.4 km) seismo‐acoustic records and regional (∼85 km) infrasound array data to present new observations of the 2018 Sierra Negra eruption with improved time and spatial resolutions. These observations include: air‐to‐ground coupling ∼2 hr before the time of the eruption onset, migration of the infrasound tremor from 22:54 June 26 to 12:31 June 27 UT (all times in UT), and persistent infrasound detections during the weeks between 5 July and 18 August from an area that does not coincide with the previously documented eruptive fissures. We interpret air‐to‐ground coupling as infrasound tremor generated in the nearby fissures before the main eruptive phase started, although ambiguity remains in interpreting a single seismic‐infrasonic sensor pair. The progressive location change of the infrasound tremor agrees with the migration of the eruption down the north flank of Sierra Negra at a rate of ∼0.15 ± 0.04 m/s. The weeks‐long persistent detections coincide with a region that has thermal anomalies, co‐eruptive deformation, lava fields, and geological features that could be interpreted as multiple lava tube skylights. Our observations and interpretations provide constraints on the mechanisms underlying fissure formation and magma emplacement at Sierra Negra.

Volcano-tectonic controls on the morphology and volcanic rift zone configuration on Bioko Island (Equatorial Guinea) derived from TanDEM-X data

The morphology of the shield volcanoes on Bioko, a volcanic island in central Africa, is controlled both by tectonic and volcanic processes, but the complex interplay of these regional and local mechanisms is poorly understood. Using a TanDEM-X digital elevation model, we are able to create an inventory of 436 vents and monogenetic cones, and over 1330 structural elements and lineaments, and perform a comprehensive morphological and geospatial analysis. We provide detail on the general geomorphology of Bioko Island, and describe its flat top, apical graben-like structures, and the setting of the structural inventory created. Based on vent density and lineament mapping, we are able to identify volcanic rift zones that are governed by vent clustering and the asymmetry of associated monogenetic cones. Specifically, we find that eruption vents are not only clustered but aligned and follow the principal NE-SW axis, although we also highlight evidence for complex structures such as side-stepping alignments and en échelon patterns indicative of strike-slip contributions to the volcano-tectonic fabrics. We discuss possible volcano-tectonic and regional tectonic contributors, such as the Cameroon Volcanic Line and intersecting fracture zones, as well as gravity-tectonic processes dominant at Bioko Island. In this view, our results are relevant for understanding the past and recent volcanic activity and discuss the influence of regional and local volcano-tectonic architectures.

A Geodetically Constrained Petrogenetic Model for Evolved Lavas from the January 1997 Fissure Eruption of Kīlauea Volcano

Abstract Magmatic systems below volcanoes are often dominated by partially crystalline magma over the long term. Rejuvenation of these systems during eruptive events can impact lava composition and eruption style—sometimes resulting in more violent or explosive activity than would be expected, as was the case at Fissure 17 during Kīlauea’s 2018 eruption. Here, we explore how the crystallinity of unerupted intrusion magmas affect hybrid magma compositions and petrological signatures by constructing phase-equilibria models to evaluate mineral and melt compositions of low-MgO lavas erupted along the East Rift Zone of Kīlauea volcano on 30 to 31 January 1997 (Episode 54, Fissures A-F). We then compare calculated mixing proportions and petrologically derived magma volumes to GPS-based geodetic inversions of ground deformation and intrusion growth in an attempt to reconcile geodetic and petrologically estimated magma volumes. Open-system phase-equilibria thermodynamic models were used to constrain the composition, degree of differentiation, and thermodynamic state of a rift-stored, two pyroxene + plagioclase saturated low-MgO magma body immediately preceding its mixing with high-MgO recharge and degassed drainback (lava lake) magma from Pu‘u‘ō‘ō‘, shortly before fissure activity within Nāpau Crater began on 29 January 1997. Mixing models constructed using the Magma Chamber Simulator reproduce the mineralogy and compositions of Episode 54 lavas within uncertainties and suggest that the identity of the low-MgO magma body may be either variably differentiated remnants of un-erupted magmas intruded into Nāpau Crater in October 1968, or another spatially and compositionally similar magma body. We find that magmas derived from a single, compositionally stratified magma emplaced beneath Nāpau Crater in 1968 can mix with mafic Kīlauea magmas to reproduce average Episode 54 bulk lava, mineralogy and mineral compositions without necessitating the interaction of multiple, low-MgO rift-stored magma bodies to produce Episode 54 lava compositions. Further, by constructing phase equilibria-based mixing models of Episode 54, we can better define the pre-eruptive state of the magmatic system. The resultant mineral assemblages and compositions are consistent with the possibility that the now-fractionated, rift-stored magma body was compositionally stratified and ~ 40% to 50% crystalline at the time of mixing. Finally, we estimate the volume of the low-MgO magma body to be ~7.51 Mm3. Phase-equilibria model results corroborate field and geochemical relationships demonstrating how shallow intrusions at intraplate shield volcanoes can crystallize, evolve, and then be remobilized by new, later batches of mafic magma. Most notably, our MCS models demonstrate that the pre-eruptive conditions of an intrusive body may be recovered by examining mineral compositions within mixed lavas. Discrepancies between the geodetic constraints on volumes of stored rift versus newly intruded (recharge) magma and our best-fit results produced by MCS mixing models (which respectively are mmafic:mlow-MgO ≈ 2 vs. mmafic:mlow-MgO ≈ 0.75) are interpreted to highlight the complex nature of incomplete mixing on more localized scales as reflected in erupted lavas, compared to geodetically constrained volumes that likely reflect large spatial scale contributions to a magmatic system. These dissimilar volume relationships may also help to constrain eruptive versus unerupted volumes in magmatic systems undergoing mixing. By demonstrating the usefulness of MCS in modeling past eruptions, we highlight the potential to use it as a tool to aid in petrologic monitoring of ongoing activity.

Review: Andesitic aquifers—hydrogeological conceptual models and insights relevant to applied hydrogeology

Research on the hydrogeology of andesitic volcanic aquifers in subduction areas is reviewed. Andesitic aquifers are of high interest in volcanic arc islands and subduction zones, where they constitute a strategic water resource. This review gathers a compilation of worldwide results and case studies to propose a generic hydrogeological conceptual model (GHCM). It is based on the geological conceptual model splitting the volcanic edifice, from upstream to downstream, into central, proximal, medial and distal zones. In this geological structure, the GHCM identifies where the main aquifer types (fractured lava, pyroclastic flows, and the volcano-sedimentary basins downstream) and the typical aquitards (lahars, fine pyroclastic falls and surges, indurated pyroclastic flow, and weathered rocks) are structured and organized. To integrate the evolution of volcanoes and some specific volcanic activities, a specific GHCM for old andesitic volcanoes or andesitic shield volcanoes is detailed. The paper also describes how the GHCM results are of use to hydrogeologists in terms of scale (from the lithological units to the regional scale), to effectively site water wells, and to sustainably manage groundwater resources in such aquifers. Among these various scales, the volcanic “flank continuum” is presented as the most adapted to support groundwater resources management. Several ways to improve this GHCM are suggested, notably to better consider the geological complexity of these aquifers.

Tracing the Origin and Magmatic Evolution of the Rejuvenated Volcanism in Santa Clara Island, Juan Fernández Ridge, SE Pacific

Oceanic intraplate volcanoes sometimes experience late-stage eruptive activity known as rejuvenated volcanism, and contrasting interpretations for its petrogenesis depend on the compositional characteristics. In the Juan Fernández Ridge (JFR), a volcanic chain approximately 800 km in length emplaced on the Nazca Plate, some subaerial occurrences of rejuvenated volcanism have been recognized on the Robinson Crusoe and Santa Clara Islands, both part of the same deeply eroded shield volcano complex. This study aims to understand the origin and magmatic evolution of rejuvenated volcanism on Santa Clara Island, emplaced after ~2.15 Ma of quiescence above the shield sequence, mainly via the analysis of unpublished geochemical and isotopic data. Field reconnaissance identified two nearly coeval rejuvenated sequences on Santa Clara Island: Bahía W (BW) and Morro Spartan (MS), both formed by basanitic and picro-basaltic lava flows with brecciated levels and local intercalations of sedimentary and pyroclastic deposits. In comparison to the chemical signature of the preceding shield-building stage (comprised mainly of basalts and picrites), the two rejuvenated sequences exhibit a notable enrichment in incompatible elements, but the Sr, Nd, and Pb isotopes are very similar to the FOZO mantle endmember, with an apparent additional contribution of HIMU and EM1 components. The geochemistry of lavas revealed the involvement of various processes, including contamination by ultramafic xenoliths, high-pressure fractional crystallization of olivine and clinopyroxene, and potential partial assimilation of oceanic lithospheric components. While the oceanic lithosphere has been considered as a potential source, the isotopic data from Santa Clara lies outside of the mixing curve between depleted mantle (DM, here represented by the North Chile Rise and the East Pacific Rise) and the previous shield stage, suggesting that a lithospheric mantle is not the primary source for the rejuvenated stage volcanism. Therefore, we favor an origin of the rejuvenated volcanism from the mantle plume forming the JFR, supported by similarities in isotopic signatures with the shield stage and high values of 208Pb/204Pb (only comparable to San Félix—San Ambrosio in the vicinity of JFR), implying the presence of a regional source with radiogenic 208Pb/204Pb isotope ratios. In addition, isotopic variations are subparallel to the mixing line between HIMU and EM1 components, whose participation in different proportions might explain the observed trends. In conclusion, we propose that the source of the rejuvenated volcanism on Santa Clara Island is a heterogeneous mantle plume, the same one that fed the shield stage. The rejuvenated volcanism is derived from a secondary melting zone away from the main axis of the plume.

The Nieve volcanic cluster: A Pliocene - Pleistocene lava dome cluster in the Michoacán-Guanajuato volcanic field (México)

The Nieve monogenetic volcanic cluster is located in the central–eastern region of the Michoacán–Guanajuato volcanic field, along the Huiramba fault zone, a relay ramp in the Morelia–Acambay fault system produced by oblique north-northwest transtension. This volcanic cluster includes at least 17 middle Pliocene to late Pleistocene lava domes, two small shield volcanoes, and two scoria cones. Between 4 and 3.8 Ma, two effusive eruptions built two small shield volcanoes overlying one another, with a magma volume of 3.93 km3. Between 2.9 Ma and 21.4 ka, 17 lava domes and two scoria cones were emplaced on the flanks of these volcanoes. The entire cluster resulted in a total erupted volume of 17 km3, covering an area of 326 km2 and reaching a thickness of emplaced volcanic material of 1200 m, resulting in a magma eruption rate equivalent to 0.004 km3/ka. All the rocks associated with this cluster are within a relatively restricted range in composition, between 53.9 and 64.2 wt% SiO₂, from andesite enriched in silica to basaltic andesite. The presence of intrusive-rock xenoliths and xenocrysts with dissolution textures reveals that assimilation processes modified the magmas. Based on the regional geological record, we suggest that the establishment of the Nieve volcanic cluster has been controlled by tectonic structures and the basement of the region, which has allowed the chemical evolution of these magma batches that probably had sources in at least two deep reservoirs as reflected by the Nb/Th versus Ta/U ratio.

Laser In Situ U–Pb Isotope Dating of Carbonate Rocks in Weijia Guyot in the Western Pacific Ocean and Its Geological Significance

Shallow-water carbonate rocks constitute a crucial component of large guyots, arising in distinct environments and harboring valuable insights into the evolutionary stages of seamount islands as well as the tectonic conditions of the underlying oceanic plate. Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS) was used to conduct in situ U–Pb isotope dating of carbonate minerals with low uranium content collected from Weijia Guyot. This dating approach yielded crucial evidence for the vertical development of the seamount. Our study indicates that shallow-water carbonate rocks in Weijia Guyot had a temporal range between 91 My and 137 My. The carbonate rocks underwent two growth phases, Hauterivian to Barremian and Cenomanian to Turonian, with a hiatus of approximately 20 My. Since the Hauterivian age, the shield volcano of Weijia Guyot is essentially complete, with its seamount top exposed at or near sea level and receiving its first stage of shallow-water carbonate sedimentation. Based on the dating of both shallow-water carbonate rocks and hawaiite within the Weijia Guyot, it is inferred that approximately 10 My elapsed from shield-building volcanism to late alkalic volcanism. During the Turonian age, the main reason for the second phase of shallow-water carbonate rocks in the seamounts was the regional tectonic uplift triggered by the drift of the Weijia Guyot along with the Pacific Plate toward the Society hotspot.

Single-crystal 40Ar/39Ar dating of the Montagna Grande-Monte Gibele trachytic shield volcano, Pantelleria (Strait of Sicily rift zone), Italy

Montagna Grande and Monte Gibele represent the northwestern and southeastern portions of a shield volcano (hereafter “MGV”) located entirely within the Cinque Denti caldera structure on Pantelleria. The Cinque Denti caldera formed during the 45.7 ± 1.0 ka eruption of the pantelleritic Green Tuff. Subsequent isostatic compensation was achieved by the eruption within the caldera of ∼3 km3 of trachyte lavas that comprise the MGV and are thought to represent renewed tapping of the Green Tuff magma reservoir. The time interval between the eruption of the Green Tuff and the MGV trachytes has not been well constrained, with previous KAr ages from alkali feldspar yielding ages between 44 ± 8 and 28 ± 16 ka. In this study we report the results of new single-crystal anorthoclase incremental heating and total fusion 40Ar/39Ar ages collected from three trachyte lava flows collected at different sites and at different stratigraphic heights that provided ages of 26.2 ± 2.0, 22.5 ± 0.8 ka, and 22.3 ± 2.8 ka (uncertainties at 2σ). The results indicate that there was a repose period of up to ∼20,000 years between the eruption of the caldera-forming ignimbrite and the caldera-filling trachytes. The timing of our oldest dated sample is coincident with renewed basaltic volcanism in the northwest part of the island at ∼28 ka and suggests that the eruption of the trachyte was promoted by mafic recharge. We briefly review the petrogenetic processes operative in the reservoir during the repose period. Modelling of the thermal and compositional evolution of the fractionating system indicates an eruption rate of 7.5 × 10−4 km3/yr over the ∼4 ka eruption period.

Emplacement and flow dynamics in a small volcanic dyke swarm: The example of Mount Calanna (Etna, Italy)

The emplacement mechanism and flow dynamics of small dyke swarms associated with monogenetic eruptive centres are less well studied than those of large swarms associated with shield volcanoes and flood basalts. This is due to their limited exposure and ease of reworking by later events. However, the study of small dykes helps to better constrain the forces controlling dyke propagation and thus reconstruct the emplacement history of the volcanic system. This study presents a multidisciplinary analysis of Mount Calanna (Mount Etna, Italy) where we sampled a total of 11 dykes among the two groups: 1) sub-vertical dykes from the lower part of the system, and 2) sub-horizontal dykes from the upper part. To infer the magma flow direction, we used Anisotropy of Magnetic Susceptibility (AMS) and compared the results to the Shape Preferred Orientation (SPO) of the plagioclase crystal fabric. To quantify the relative timing of dyke emplacement, and to characterise the magma plumbing system, we also used the palaeomagnetic and geochemical signature of the sampled dykes.The fabric analysis highlights a NE-SW flow direction in the sub-vertical dykes, and a NE-SW and NW-SE direction in the sub-horizontal dykes. Dykes emplaced at the lowest levels in the swarm show sub-vertical to inclined magma flow, whereas those towards the top of the Mount Calanna show inclined to sub-horizontal flow. The combined structural and geochemical analyses suggest the Mount Calanna swarm is a coherent intrusive complex associated with a phase of activity of Ancient Alkaline centre (AAC), with Mount Calanna representing an example of the uppermost portion of a shallow plumbing system in which intrusion orientations are controlled by regional tectonics.

Analysis of faults and pit chains in Noctis Labyrinthus: Implications for early extension and possible magmatic plumbing

Noctis Labyrinthus has been a region of disputed origin due to its complexity and poor understanding of how various processes and mechanisms may have combined to form it. The surface is an integrated record of intensive tectonic activity expressed by a multiple extended sets of dip-slip faults oriented in different directions, and thought to have acted on this region over its history. These faults are always coalescent to pits and pit chains displaying a complicated geological history in the region. To understand this geological history, we mapped the surface features in Noctis Labyrinthus using the High-Resolution Stereo Camera (HRSC) onboard Mars Express ND2 nadir channel basemaps, and we adapted the Digital Terrain Map (DTM) from the Mission Experiment Gridded Data Record (MEGDR) of Mars Orbiter Laser Altimeter (MOLA) onboard Mars Global Surveyor (MGS) for the topography. We have investigated the spatial distribution and trend of fault systems, the pit chains' morphology, and the correlation between these two types of features. Our results show three fault systems: i) NS and NNE-SSW, ii) EW and ENE-WSW, and iii) NNW-SSE and NW. The analysis of the faults trending, cross-cutting correlation and the superimposition led to identify multiple intersections between these faults that have been alongside with the reactivations of some inherited faults. We interpreted the first system of fault to be related to coeval lateral extension, generated by regional stress tensor, which is probably related to the slight bending of Valles Marineris within two phases of bidirectional extension. The second system of faults has been generated by the radial oblate stress tensor related to the formation of the small shield volcanoes in Syria Planum. However, the third system is likely related to the external driving process, probably in the Tharsis province. We classified pits in four evolutionary stages based on their morphometric attributes. We believe that the formation of the pit chains in Noctis Labyrinthus is related to a surface collapse after a pressure drop related to the magma chamber deflation associated with Syria Planum volcanic province. We propose a deformational model based on early extension and magmatic plumbing as driving processes for the formation of Noctis Labyrinthus.

Geological history of the Atira Mons large shield volcano, Beta Regio, Venus.

Atira Mons is a large (∼300,000 km2) low-relief (1.8 km) shield volcano, with individual flows extending up to ∼700 km from the central caldera. It is located about 3000 km NW from the major plume center Beta Regio. Detailed mapping of the flows (at 1:500,000 scale, 10x more detailed than previous mapping) has identified fifty-three flow units which are grouped into eleven packages. Flow units are distinguished based on radar brightness, topography, morphology, continuity, structural modification, and sources, while flow packages group flows with clear stratigraphic relationship affinity.Cross-cutting relationships indicate a complex and multi-episodic eruption history with provisional identification of six mapped stages. The most voluminous flows are concentrated in the early stages, while the younger pulses, with a few exceptions, are shorter and less voluminous. A central caldera hosts the youngest volcanism with flows breaching its eastern side. Multiple stages of caldera collapse are indicated.The volume of the volcano is estimated using various methods and yields values range from ∼47,000 to ∼270,000 km3. The larger estimates are consistent with that of the magma volume of Large Igneous Provinces (LIP) on Earth. An appropriate terrestrial analogue is the Benham Rise Oceanic LIP in the western margin of the Philippine Sea, and particularly the Apolaki Caldera, which is the world's largest known basaltic caldera with a diameter of ∼150 km.

Seismicity under a Dormant Volcano: Unveiling Active Crustal Faulting beneath Piton des Neiges, La Réunion

ABSTRACT Volcanic environments are commonly associated with seismic activity. The two prominent shield volcanoes of La Réunion island—Piton des Neiges and Piton de la Fournaise, exhibit sustained seismic activity. Whereas the seismicity at Piton de la Fournaise is tied to its volcanic activity, the seismic activity beneath Piton des Neiges, which has been dormant for 27,000 yr, remains poorly understood. The occurrence of earthquakes under the north flank of Piton des Neiges, often felt by the population, led to the deployment of several seismic stations in the area since 2012. In this study, we employ template matching and double-difference relocation techniques to construct a high-resolution catalog of the region. Our results reveal that the seismicity observed under Piton des Neiges is primarily concentrated on a northeast-dipping fault located in the oceanic crust beneath the volcanic edifice. Analysis of focal mechanisms indicates that this structure operates as a reverse fault. In the vicinity of this primary fault, we also identify secondary seismicity clusters with similar orientation and focal mechanisms. The region has experienced continuous seismicity since 1999, with occasional periods of increased swarmlike activity in 2011 and 2018. These fluctuations in seismicity rate do not correlate with markers of deep magma transfers often observed before eruptions at the Piton de la Fournaise volcano. Beyond the crustal faults highlighted in this study, it is noteworthy that the majority of earthquakes in northern La Réunion island exhibit consistent reverse focal mechanisms. These observations suggest that seismic events may not be driven by deep magmatic activity but, rather, result from regional tectonic stress and edifice loading on pre-existing faults.

A Global Survey of Gravitationally Deformed Volcanoes on Venus

AbstractGravitational instabilities can develop at volcanoes of any size and in any geological setting and can lead to various types of volcano deformation, ranging from small‐scale landslides on the flanks of the edifice to large, deep‐seated sector collapses. As volcanoes grow, they impose an increasing load on the underlying basement, which can result in styles of gravitational deformation where the edifice sags or spreads outward under its own weight. In this study, we utilize our previously developed global catalog of volcanoes on Venus to analyze a subset of edifices that appears to have undergone gravitational deformation. We identify 162 volcanoes that display morphological evidence for gravitational deformation and classify them into four main categories based on associated deformational structures: landsliding, sector collapse, spreading, and sagging. Landsliding of volcano flanks or full sector collapse are the most common and geographically widespread deformational styles on Venus, and account for ∼64% of our data set. Edifices exhibiting structures linked to volcano spreading and sagging are relatively rare; nonetheless, we note for the first time on Venus the presence on a shield volcano of flank terraces, structures linked to sagging. We find that deformed volcanoes are distributed globally, are found at a range of elevations, are spatially proximal to a variety of tectonic structures, and are associated with various crustal thickness values, which together suggest that there are numerous drivers of volcano deformation on Venus.

PALEOVOLCANIC KARING RECONSTRUCTION IN THE MERANGIN JAMBI UNESCO GLOBAL GEOPARK TERRITORY BASED ON PETROLOGICAL AND GEOCHEMICAL APPROACH

The presence of lava and pyroclastic sequences in the Karing River on the Merangin Jambi UNESCO Global Geopark territory provides information about the existence of ancient volcanoes. The absence of confirmed rock formations from the distribution of volcanic rock products that have been mapped nationally and also the shape of this ancient volcanic body, is an important reason for this research to be carried out using a petrological approach using petrography and XRF gochemical methods. Petrographic analysis is an appropriate method to determine the mineralogy consist, textures and particular textures, rock structures that are confirmed from field data. Meanwhile, a geochemical approach is used to determine rock oxide compounds. This method aims to reconstruct the shape and type of volcanoes. Research data shows that there are four lava sequences, with Sequence 1 having an entablature structure, Sequence 2 and Sequence 3 having a flow structure, and Sequence 4 having a vesicular-flow structure. The petrography results show that Sequence 1 and Sequence 2 are composed of phenocrysts and microliths of plagioclase, olivine, clinopyroxene, orthopyroxene. Meanwhile, in Sequence 3, hornblende is present, and in Sequence 4, the mineral olivine is absent. The results of geochemical analysis from the four lava sequences are in basalt rocks with 40%-50% Silica content, Calk-alkali basalt magma series, petrogenesis interpreted from the convergence of oceanic subduction beneath continent. The pyroclastic rocks found at the bottom of the lava sequence are evidence of the stratigraphic structure that makes up a volcano originating from the Karing Paleovolcanic, while the pyroclastic rocks found at the top of the lava sequence are believed to originate from other ancient volcanic eruptions. With the stratigraphy composed of lava and pyroclastic sequences, it can be concluded that this ancient volcano is a strato volcano type which is relatively sloping and almost resembles a shield volcano.

Volcanosedimentary fill of the early Cretaceous Yingcheng formation and response to the end of continental rifting in the Songliao Basin: Constraints from well SK-2, northern Xujiaweizi fault depression

Well SK-2 of the International Continental Scientific Drilling Project (ICDP) obtained continuous core samples with a length of 365.32 m in the Early Cretaceous Yingcheng Formation, showing a stratigraphy of interbedded rhyolites and coarse clastic rocks in the Xujiaweizi fault depression. The Yingcheng Formation in well SK-2 is divided into three sequences. Sequences 1 (S1) and 3 (S3) consist of coarse clastic rocks, and four types of conglomerate lithofacies are identified. The conglomerate lithofacies of S1 is characterized by gravity flows. In comparison, the conglomerate lithofacies of S3 is characterized by a progradational braided channel, reflecting a proximal provenance and a shallowing upward setting. Sequence 2 (S2) rocks are rhyolites, and geochemical analysis shows these to have mainly originated from the middle-upper crust. On the basis of volcanic rocks in wells Shengshen 2–1 and Shengshen 203 and seismic profiles crossing these wells, we identify two types of volcanic edifices: stratovolcanoes in the east and shield volcanoes in the west. The Early Cretaceous strike-slip faults, including the Xuzhong and Xudong faults, play an important role in controlling this area. In comparison with extensive, dark, and fine-grained clastic rocks of the Shahezi Formation, the felsic and coarse clastic rocks of the Yingcheng Formation in well SK-2 mark a sedimentary response to strike-slip tectonics and indicate the ending fault movement of the Xujiaweizi fault depression, and perhaps even the end of the Early Cretaceous Songliao Basin rifting stage.

Petrogenesis of the Hoy lava field, a long-lived continental mafic volcanic province in eastern Australia

Small-scale continental basaltic fields can erupt with little warning and bring deep undegassed magmas to the surface rapidly. To explore the lifetime, petrogenesis and plumbing system architecture feeding such basaltic lava fields and compare them with large-scale shield volcanoes, we have focused on the Hoy lava field, central Queensland, Australia. 40Ar/39Ar geochronology, elemental and isotopic whole-rock geochemistry and mineral chemistry on selected Hoy samples reveal long-lived volcanism of ca 50 Ma and magma storage at mantle depths, notably different from the comparatively short duration (3–5 Myr) and crustal magma storage depths of shield volcanoes. In this study, four Hoy lava-field eruptive intervals spanning ca 50 Ma were investigated: 67.5 ± 0.3 Ma, 32.3 ± 0.6–31.6 ± 0.7 Ma, 21.9 ± 0.5 Ma and 18.1 ± 0.3 Ma. In all four eruptive events, samples are porphyritic alkali basalts and trachybasalts (11.41–6.45 wt% MgO) with incompatible element concentrations and Sr–Nd–Pb isotope ratios dominantly derived from a metasomatised sub-continental lithospheric mantle (SCLM) source with an enriched mantle I (EMI) signature. Complex crystal populations show major- and trace-element variations reflecting fractional crystallisation, magma recharge, magma mixing and mantle xenocryst entrainment. Clinopyroxene–melt thermobarometry indicates magma storage in SCLM reservoirs at ∼30–47 km depths. The nearby larger but shorter-lived (3–5 Myr) Buckland central volcano has similar source compositions; however, magma storage is limited and concentrated in the crust, resulting in increased crustal contamination. The results suggest that basaltic centres of contrasting scale and longevity are linked to distinct magma production mechanisms, fluxes, ascent and differentiation.

Pleistocene to Holocene volcanism in the Canadian Cordillera

The Canadian Cordillera hosts numerous Pleistocene and Holocene volcanoes and volcanic deposits, including a number of volcanoes that have erupted within the last several hundred years. The nature and composition of volcanic edifices and deposits are diverse and dictated by the complex configuration of tectonic plates along the western margin of British Columbia and the thermal structure of the underlying mantle. Our modern knowledge of these is built upon more than a century of field- and increasingly, laboratory-based studies. We recognize five distinct volcanic domains within the Cordillera that are distributed across British Columbia, the Yukon Territory, and easternmost Alaska. These include the Wrangell Volcanic Belt, the Northern Cordilleran Volcanic Province, the Anahim Volcanic Belt, the Wells Grey-Clearwater Volcanic Field, and the Garibaldi Volcanic Belt representing the northern extension of the Cascade Volcanic Arc. Volcanism in the Canadian Cordillera spans the full range of explosive to effusive behaviours, encompasses the suite of common volcanic chemical compositions (alkaline to calc-alkaline and nephelinite to peralkaline rhyolite), and is expressed by long-lived stratovolcanoes, shield volcanoes, and calderas, as well as shorter-lived tephra cones and associated lava flows. The range in tectonic settings (subduction to extension), eruption environments (subaerial–subaqueous–cryospheric), and topographic variability make volcanism within the Canadian Cordillera as diverse as anywhere on Earth, yet it is also the least studied. Here, we summarize the current state of knowledge concerning volcanism within the Canadian Cordillera and conclude with thoughts on research areas that merit further effort, namely glaciovolcanism and volcanic hazards.

Age, duration and spatial distribution of ocean shields and rejuvenated volcanism: Fuerteventura and Lanzarote, Eastern Canaries

Fuerteventura and Lanzarote form the oldest emerged part of the Eastern Canary Islands archipelago. Geologically, they can be considered a single edifice, constituting a continuous volcanic ridge extending 250 km from SW to NE. This study completes the dating and the determination of the magnetic stratigraphy of the shields and the rejuvenated volcanism of Fuerteventura and Lanzarote, refining the volcanic stratigraphy and cartography. The new unspiked K–Ar ages and magnetostratigraphy of Fuerteventura and Lanzarote indicate that these islands developed patterns similar to those of the Central and Western Canary Islands, building adjacent and successively superimposed basaltic shield volcanoes during the Miocene, between 20.19 ± 0.30 and 6.30 ± 0.11 Ma. The overlay of post-Miocene rejuvenated volcanism hinders determination of the extent and interrelationship of the shields. These materials constitute only a small fraction by volume but cover a large part of the islands. Despite this, it is confirmed that the disposition of the shields is opposite to the insular progression induced by the hotspot, suggesting the presence of some SW–NE propagation volcanic front or fracture to explain its direction of development. Supplementary material: A description of the K–Ar method is available at https://doi.org/10.6084/m9.figshare.c.6641464

Global geological mapping of Venus and the twenty-first-century legacy of William Smith: identification of challenges and opportunities for future research and exploration

Abstract Geological mapping principles have been applied across planet Earth since William Smith's initial 1815 map. During the Space Age, these principles were applied to smaller moons and planets, appropriately adjusted for remote conditions and data, and revealing ‘one plate planets’ recording Earth's missing chapters. Yet what of Venus, Earth's ‘twin’, shrouded in opaque clouds? How can these geological mapping principles be applied to address fundamental questions of planetary history? We outline how Venus's geological mapping over the last 35 years has proceeded towards a successively integrated more global picture that has revealed a surface and history unlike Earth or the smaller planetary bodies! The current 1 : 10 M global geological map documents geological units that all formed in the last c. 20% of Venus's history. The oldest, Fortunian, involved intense deformation and building of thicker crust (tessera). The Guineverian featured near-global emplacement of vast volcanic plains. The Atlian saw prominent rift zones and large shield volcanoes. The three major phases of activity provide a basis for assessing the geological, atmospheric and geodynamical processes operating earlier in Venus's history that led to the preserved record, raising a series of questions to be investigated in the coming decade by an international armada of Venus missions.