Volcanic Structures Research Articles

Reassessing the paleointensities of three Quaternary volcanic structures of the -Michoacán-Guanajuato Volcanic Field (Mexico) through a multimethodological analysis

An approach that has acquired popularity in the last decade to ensure the quality of paleointensity determinations is the use of multimethodological analysis, especially when comparing intensity values obtained by methods with different physical bases such as the conventional Thellier-type experiments against the Shaw-family methods and the most recent multispecimen protocol. This research presents the reevaluation of the intensities of three monogenetic volcanic structures: the Rancho Seco and Jabalí cones and lavas, and the Malpaís Prieto fissure lava flow, all located in the Michoacán-Guanajuato volcanic field (central Mexico). This analysis is accompanied by an exhaustive study of rock-magnetic properties to obtain a complete characterization of the magnetization carriers and a better understanding of the intensity results. The three volcanic structures have previously published intensity data; one of them was obtained with the original Shaw method that nowadays is considered unreliable due to the absence of monitoring of thermal alteration during the experiment. The quality of the previously published data is discussed to be compared to our intensity values, which were obtained employing Thellier-type methods and the multispecimen protocol (MSP). A good concordance was found for the data obtained by more than one methodology for samples from the Jabalí volcano and the Malpaís Prieto lava flow, obtaining average intensity values of 43.7 ± 5.1 μT and 47.8 ± 3.1 μT, respectively. However, a difference of almost 30 μT was found between our MSP results (50.9 ± 2.8 μT) and previously published data using the IZZI method (20.0 ± 1.4 μT) for Rancho Seco volcano. An attempt was made to clarify this controversial result with the support of stepwise susceptibility against temperature curves analysis and the results obtained from a set of samples treated with the Tsunakawa-Shaw paleointensity method. The results obtained indicate that the low paleointensity values are associated with the thermal alteration of the magnetic mineralogy of the samples.

Sr isotope variations in Oligocene–Miocene and modern biogenic carbonate formations of Koko Guyot (Emperor Seamount Chain, Pacific Ocean)

The Hawaiian–Emperor Seamount Chain, a major topographic feature of the Pacific Ocean floor, is composed of seamounts capped with fossil coral reef deposits that originally formed close to sea level but are now covered by hundreds of meters of water owing to prolonged subsidence. These fossil reef deposits are important archives of paleoenvironmental change and yield information on the subsidence history of the seamounts. We studied the Sr isotope compositions of Oligocene–Miocene coral reef limestone from Koko Guyot in the southern Emperor Seamount Chain to assess the dynamics of the subsidence. The ages of the studied samples containing coral fragments established by Sr isotope stratigraphy vary from 26.3 to 20.1 Ma. In contrast, the youngest samples (15.3 Ma), which were deposited in water depths of >120 m, are barren of corals and are composed exclusively of bryozoans and coralline algae. The subsidence rate of the Koko Guyot volcanic structure was not constant over time. Integration of our new data with the results of previous studies reveals that the subsidence rate was 0.046 ± 0.005 mm/yr during the first 25–30 Myr (from 49–44 to 20 Ma). During this period, Koko Guyot was in a bathymetric interval favorable for coral reef development, and its subsidence was compensated by rapid vertical growth of the reef. Subsequently, the subsidence rate decreased to an average value of 0.019 ± 0.003 mm/yr from 20 to 15 Ma. The decrease in the rate of bottom subsidence coincided with unfavorable environmental conditions for coral reef development, leading to the disappearance of corals. The average subsidence rate has been 0.015 ± 0.002 mm/yr since 15 Ma, comparable to the present-day subsidence rate. We also analyzed the stable Sr isotope ratios (δ88/86Sr) of warm-water coral samples formed at 25–20 Ma (0.32‰ ± 0.1‰), as well as carbonate of large benthic foraminifera, coralline algae, and other non-coral species for the period 20–15 Ma (0.10‰ ± 0.09‰). We suggest that the large difference in carbonate δ88/86Sr between 25–20 and 20–15 Ma corresponds to a difference in the fractionation factor caused by environmental and benthic community change.

Fracture Structures in and Around Hakone Volcano Revealed by Dense Seismic Observations

Preexisting fracture systems, including old fissures, dikes, and microfractures in the caldera, are possibly used as channels for magma and hydrothermal fluid intrusions during an eruption. To reveal such a fracture system in the Hakone volcano, we used the fuzzy c-means method to perform clustering on S-wave splitting analysis results. The results show that the fracture system in the Hakone caldera can be divided into two clusters (A and B) or four clusters (A1, A2, B1, and B2). In the central cone vicinity, craters or dikes corresponding to the compressive axis of the regional stress field are dominant, whereas the fault systems with the best orientation to the regional stress field develop around the central cone. Cluster B1 can be explained by the northwest–southeast alignment of micro cracks or dikes corresponding to the direction of maximum horizontal pressure of the regional stress field. The others are likely explained by fault fracture zones, which have an optimal orientation for regional stress fields, or by the alignment of micro cracks affected by the local stress field. Cluster B2 suggests the existence of fracture zones of the Tanna and Hirayama fault systems, which cross the Hakone volcano from north to south. Clusters A1 and A2 are possibly explained by the conjugate system of B2. However, the alignment of micro cracks generated by the local stress field or old volcanic structures can also be a cause of the clusters.

Deformation Styles and Multi-Stage Evolution History of a Large Intraplate Strike-Slip Fault System in a Paleozoic Superimposed Basin: A Case Study From the Tarim Basin, NW China

The complex deformation styles of large intraplate strike-slip fault systems in the multi-stage superimposed basin are hot topics worldwide. This article proposes structural models and evolution processes for such strike-slip fault systems in the Tarim Basin based on high-resolution 3D seismic data and deep wells. Our analyses reveal that strike-slip fault in the Tarim Basin formed with different structural styles in five tectonic layers from the Sinian to the Permian that accompanies the Sinian rift systems and uplift, the Lower–Middle Cambrian reversed faults and salt tectonics, the Ordovician fault-karst systems, the Silurian to the Carboniferous en-echelon transtensional faults, and the Permian volcanic structures. Influenced by the multi-tectonic layers and complex evolution history, the strike-slip faults performed as multi-layer flower structures and various fault types. The evolution history of paleo-uplifts also influenced the distribution characteristics of strike-slip faults, such as X, diamond, and V shapes in the Tabei uplift and T shapes in the Tazhong uplift. The strike-slip faults formed in late Cambrian stage were associated with unconformities, inverted structures, and growth strata in deep layers. The different tectonic evolution models of the Tabei and the Tazhong uplift were built, which shows pre-existing structures, the lithological combinations from the rift basin to the marine basin, and the change of regional tectonic stress from the Cambrian to Permian are controlling factors of the strike-slip fault systems. These models provide a new interpretation method for intraplate strike-slip fault systems worldwide.

Western flanks of the Central Asian late paleozoic continental rift system and uranium mineralization

Introduction. Available information on the occurrences of high alkaline magmatic rocks fixing the position of the western flanks of the southern branches (Gobi Altai and Gobi Tien-Shan) of the Central Asian Late Paleozoic continental rift system in the territory of the North-West of Chingiz (the eastern part of Central Kazakhstan), the Kendyktas-Chu-Ili-Bet-Pak-Dal uranium-bearing province of the Southern Kazakhstan and the Chatkal-Naryn zone of Tien-Shan (Uzbekistan) is reviewed. Data on the confinement of uranium mineralization to these occurrences and its paragenetic relationship with the Late Paleozoic alkaline volcanic-plutonic association is provided.Aim. To study the uranium mineralization of Late Paleozoic alkaline magmatism to clarify metallogenic representations and justify prospects for the ore-bearingness of the western flanks of the southern branches of the Central Asian continental rift system.Materials and methods. The largest part of materials was obtained in the process of geological surveys and prospecting works of various scales in the regions of Central Kazakhstan in the period 1965–1985 with the participation of the author. Published materials concerning the subdivision of magmatic formations in the uranium ore fields of Southern Kazakhstan and the Chatkal-Naryn zone were also used.Results. Subvolcanic bodies of comendites and small masses of alkaline granites of the Late Paleozoic were identified across the area of uranium ore occurrences in the South-Western Chingiz and some deposits of South Kazakhstan confined to Devonian volcanic structures, which indicates their relationship with the southern branches of the Central Asian continental rift system. Rare-metalalbite, uranium-phosphorus and uranium-molybdenum formations are confined to alkaline rocks. Rare-metal mineralization is closely associated with alkaline rocks, while uranium mineralization occurred after the introduction of the most recent microgabbrodiorite and lamprophyre dikes. Similar correlations of rare-metal and uranium mineralization with alkaline granites and of microgabbrodiorite and lamprophyre dikes are observed in the uranium deposits of the Chatkal-Naryn zone located among the early Permian bimodal trachybasalt-trachyolite formation.Conclusion. The establishment of ore mineralization on the western flanks of the Gobi Altai and Gobi Tien-Shan branches in the territory of Southern and Central Kazakhstan allows these areas to be distinguished as metallogenic zones, promising in terms of rare-metal and uranium mineralization.

Hotspot volcanism along a leaky fracture zone contributes the formation of the 85°E Ridge at 11°N latitude, Bay of Bengal

The 85°E Ridge is a prominent linear structure in the northeastern Indian Ocean. Its nature and origin are still controversial due to the coverage of thick Bengal Fan sediments. Here we present a newly collected 400-km-long 2-D seismic reflection profile which crosses the 85°E Ridge near 11°N and shows the basement morphology and internal structures of the ridge. The ridge has a thickened crust characterized by two basement highs rising up to ~2–3 km above the surrounding oceanic crust and a Moho depression with amplitude of ~3–4 km. Typical volcanic structures formed by hotspot volcanism are identified in the ridge. Deep-rooted faults played important roles in the formation of the 85°E Ridge. They acted as the preferred conduit for the upwelling of hotspot melts, but their syn- and post-volcanic reactivations induced the collapse of volcanic sequences and the relative uplift of the East Ridge. These observations support that the 85°E Ridge near 11°N having formed by hotspot magmatism drained along a leaky fracture zone. Combined with previous results, a new single-hotspot formation model of the 85°E Ridge is proposed, in which the entire 85°E Ridge was formed by a weak and pulsating mantle plume acting on the northward drifting Indian Plate. Its along-strike variations in location, morphology, and structure in different segments are interpreted to reflect different elastic strength of the oceanic lithosphere and the existence of a pre-existing fracture zone which laterally redistributed the shallow melts.

Gravity Forward and Inversion Modelling in Improving the Geology Model of the Flank Volcanic Structure

Cross-sections of volcanic structures are generally constructed using existing surface rock data. The detailed subsurface is not accessible because of a limited approach; as a result, precision is less accurate. Geophysical data obtained from surface gravity measurements will improve this phenomenon based on the response of density variation through forward and inverse modelling. The joint interpretation will make it possible to improve the subsurface model and to apply it in volcano deposits that experience a throw. Gravity data acquisition is 200 points over an area of 16 × 14 square kilometres. An anomaly study will focus on near-surface phenomena, where modelling shows that inversion needs to be enhanced by mesh refinement. In addition, forward modelling renders the model more realistic. The results show, the fault reaches a half km. It is not seen in the geology section, and the density variation shows 0.3 grams/cc. This density change is interpreted for the pyroclastic in the depression segment. Fumaroles may interpret as the water percolating pathway from the peak through the flank structure. The meteoric water flows inside the volcanic deposits and the fault plane is the ends of the meteoric water reaching the outside.

A Seismic Tomography, Gravity, and Flexure Study of the Crust and Upper Mantle Structure of the Emperor Seamounts at Jimmu Guyot

AbstractThe intraplate Hawaiian‐Emperor Seamount Chain has long been considered a hotspot track generated by the motion of the Pacific plate over a deep mantle plume, and an ideal feature therefore for studies of volcanic structure, magma supply, plume‐crust interaction, flexural loading, and upper mantle rheology. Despite their importance as a major component of the chain, the Emperor Seamounts have been relatively little studied. In this paper, we present the results of an active‐source wide‐angle reflection and refraction experiment conducted along an ocean‐bottom‐seismograph (OBS) line oriented perpendicular to the seamount chain, crossing Jimmu guyot. The tomographic P wave velocity model, using ∼20,000 travel times from 26 OBSs, suggests that there is a high‐velocity (>6.0 km/s) intrusive core within the edifice, and the extrusive‐to‐intrusive ratio is estimated to be ∼2.5, indicating that Jimmu was built mainly by extrusive processes. The total volume for magmatic material above the top of the oceanic crust is ∼5.3 × 104 km3, and the related volume flux is ∼0.96 m3/s during the formation of Jimmu. Under volcanic loading, the ∼5.3‐km‐thick oceanic crust is depressed by ∼3.8 km over a broad region. Using the standard relationships between Vp and density, the velocity model is verified by gravity modeling, and plate flexure modeling indicates an effective elastic thickness (Te) of ∼14 km. Finally, we find no evidence for large‐scale magmatic underplating beneath the pre‐existing crust.

The Ulandryk and related iron oxide-Cu-REE(-Au-U) prospects in the Russian Altai: A large emerging IOCG-type system in a Phanerozoic continental setting

The Ulandryk and related prospects in the Altaid orogenic belt (near the Russian-Mongolian border) comprise intense iron oxide (hematite), Cu, REE, and locally U mineralization and are estimated to contain in excess of 240 Mt iron oxide ores and 3.7 Mt copper. These prospects bear many signatures of the “classic” IOCG (-REE, U) deposits typical of Precambrian terranes but, in contrast, are situated in a Phanerozoic (Paleozoic) setting. They are related to the Early Devonian subvolcanic potassic granite stocks with transitional shoshonitic to A-type granite signatures suggesting a post-orogenic (post-collisional) setting, with some anorogenic (intracontinental to within-plate) affinity. The stocks have been intruded into a coeval local volcanic structure (a volcanic dome complicated by the central caldera) composed of Devonian trachyandesite, trachydacite, quartz latite, rhyolite, rhyolite-dacite, and dominant trachyrhyolite lavas, tuffs and subovolcanic porphyry intrusions.The granitic stocks are accompanied by magmatic and multi-staged hydrothermal breccias, zones of sodic (albite-quartz), potassic (quartz-K-feldspar), propylitic (quartz-albite-chlorite-amphibole) and dominant phyllic to carbonate-phyllic (quartz-sericite to quartz-sericite-carbonate) to possibly argillic (quartz-kaolinite) alteration, with intense development of hematite. Fluorite is also ubiquitous and locally abundant. The mineralization occurs in several wide (typically 60–100 m, up to 200 m) and extended (1.4–6 km) linear to arc-like paralleling steeply dipping zones of breccias surrounding the granite stocks, with the host rock and quartz fragments cemented by fine-grained quartz-hematite and coarser hematite (specularite) material. Copper-gold, REE, and locally U mineralization overprints hematite-rich zones. Wider quartz-sulfide stockworks with Cu-Au mineralization zones containing minor to trace hematite are also present. Quartz is generally abundant forming quartz-hematite veins, stockworks, and breccias (locally with crustiform texture), and zones of quartzite-like pervasive silicification (typically with sericite and clay minerals).Fluid inclusions in quartz contain daughter halite crystals and homogenize by halite dissolution after vapor bubble disappearance indicating a homogenous, high-salinity (35–45 wt%), Na-Ca-K-chloride, aqueous mineralizing fluid. The relatively low homogenization temperatures (∼200–260 °C) and generally subvolcanic-level pressure (∼0.2–0.5 kbar) conditions suggest a shallow level of mineralization possibly corresponding to an upper (to the uppermost) part of a vertically extended magmatic-hydrothermal system.

EVALUATION OF DEM DERIVED BY REPEAT-PASS X-BAND STRIPMAP MODE PAZ DATA

Abstract. This paper, presents the initial results of digital elevation model (DEM) extraction from PAZ Synthetic Aperture Radar (SAR) satellite images using repeat-pass interferometric analysis. We used a multi-temporal high-resolution strip-map mode X-band satellite image that has a single polarization. Five main classes, i.e., volcanic structures, agriculture, settlement, sand dune and plain bareland are considered depending on the structure of the region. Within the category, the coherence value and DEM value are evaluated. In the accuracy assessment analysis, a reference map produced from aerial photogrammetry is used. Additionally, global DEM TanDEM-X data is also tested in the study region. In the analysis, quality metrics, mean error (ME), root means square error (RMSE), standard deviation (STD), and the normalized median absolute deviation (NMAD) are used. The results showed that as the temporal baseline increases the coherence values and the quality of the DEM product decrease. The RMSE values range between 2.36 m to 7.09 m in different classes. The TanDEM-X data provided high accuracies over each class range from 0.88 m to 2.40 m. Since the study area is vulnerable to sinkhole formation, sinkhole-like signals were also observed in the interferograms obtained from different and sequential pairs. The high-resolution repeat-pass PAZ data pointed out its potential for interferometric products generation.

New insights into the Jurassic polyphase strain partition on the patagonian back-arc; constraints from structural analysis of ancient volcanic structures

Located in the western Northpatagonian region, Argentina, the Lower Jurassic Cañadón Chileno Complex (CCHC) provides a remarkable opportunity to assess the roles of pre-, syn-, and post-eruptive faulting in felsic diatremes complexes evolution. The structural analyses of fractures, dikes, and folds allow recognition of the occurrence of four different strain partitions (SP1-SP4) developed during the Lower to Middle Jurassic. Recognized strain configurations show equivalent temporal and structural relationships throughout the Jurassic back-arc system of Patagonia and contemporary basins of southern South America. The stratigraphical criteria allow inferring an Upper Sinemurian to Lower Pliensbachian time interval for the initial strain configurations (SP1, SP2, and SP3). WNW, NNE, and NE-oriented extensional phases were defined and correlated with adjoining areas. Particularly, the third strain partition phase is characterized by a significant transpressive deformation. A NE contractional episode characterizes the post-eruptive deformation stage (SP4) during the Bajocian to Callovian interval. Tectonic interpretations were elaborated concerning subduction dynamics, continental drift, and rotation that controlled the regional and local stress configuration throughout the Jurassic Period of Patagonia and central Argentina.

On the possible role of magmatism in the atasu type strathiform mineralization (Central Kazakhstan)

Purpose. Studying the geological features of large industrial Atasu type ore objects. Methodology. Critical analysis of literature and stock materials, comparative analysis of geological factors characteristic of stratiform ores, stages and peculiarities of formation depending on the processes of volcanism, analysis of the results of isotope dating of rocks. Findings. Participation of volcanism (magmatism) processes in forming deposits of ferromanganese and barite-polymetallic ores of the Atasu type was minimal. It was expressed only in the development of a dissected pre-Famennian paleorelief favorable for the accumulation of metal-bearing silts and in the development of local hydraulic seals, which made it possible for the metal-bearing waters to circulate. Magmatic formations are protrusions of more ancient pre-Famennian Givetian-Franian volcanic structures. Originality. The pre-ore age of subvolcanic intrusions partially confirmed by the results of determining the absolute age, from the samples taken in the quarry of the Ushkatyn deposit that amounted to 373 4 million years, which corresponds to the middle of the Frasnian stage. The presence of three Atasu type ferromanganese deposits in the amagmatogenic Aidagarly graben-syncline also confirms this hypothesis. The genesis of deposits of the Atasu type is considered as sedimentary-hydrothermal one, associated with the processes of diagenesis and catagenesis. Practical value. Predicting the possibility of finding deposits of the Atasu type in graben-synclines throughout the entire area of the Devonian volcano-plutonic belt.

Semi-Automated Inversion-Specific Data Selection for Volcano Tomography

Active seismic experiments allow reconstructing the subsurface structure of volcanoes with unprecedented resolution and are vital to improve the interpretation of volcanic processes. They require a quality assessment for thousands of seismic waveforms recorded at hundreds of stations in the shortest amount of time. However, the processing necessary to obtain reliable images from such massive datasets demands signal processing and selection strategies specific to the inversions attempted. Here, we present a semi-automated workflow for data selection and inversion of amplitude-dependent information using the original TOMODEC2005 dataset, recorded at Deception Island (Antarctica). The workflow is built to tomographic techniques using amplitude information, and can be generalised to passive seismic imaging. It first selects data depending on standard attributes, like the presence of zeroes across all seismic waveforms. Then, waveform selections depend on inversion-specific attributes, like the delay of the maximum amplitude of the waveform or the quality of coda-wave decays. The automatic workflow and final visual selections produce a dataset reconstructing anomalies at a node spacing of 2 km, imaging a high-attenuation anomaly in the centre of the Deception Island bay, consistent with previously-published maps. Attenuation models are then obtained at a node spacing of 1 km, highlighting bodies of highest attenuation scattered across the island and a NW-SE trend in the high-attenuation anomaly in the central bay. These results show the effect of the local extension regime on volcanic structures, providing details on the eruptive history and evolution of the shallow magmatic and hydrothermal systems. The selection workflow can be easily generalised to other amplitude-dependent tomographic techniques when applied to active seismic surveys. Image improvements from the original dataset are minor when selecting data using standard attributes, like signal-to-noise ratios. Tomographic maps become drastically more stable and consistent between different frequencies and resolutions when data selection targets attributes specific to the inversion.

Magnetometric Surveys for the Non-Invasive Surface and Subsurface Interpretation of Volcanic Structures in Planetary Exploration, a Case Study of Several Volcanoes in the Iberian Peninsula

Volcanoes are typical features of the solar system that offer a window into the interior of planets. Thus, their study can improve the understanding of the interiors and evolution of planets. On Earth, volcanoes are monitored by multiple sensors during their dormant and active phases. Presently, this is not feasible for other planets’ volcanoes. However, robotic vehicles and the recent technological demonstration of Ingenuity on Mars open up the possibility of using the powerful and non-destructive geophysical tool of magnetic surveys at different heights, for the investigation of surfaces and subsurfaces. We propose a methodology with a view to extract information from planetary volcanoes in the short and medium term, which comprises an analysis of the morphology using images, magnetic field surveys at different heights, in situ measurements of magnetic susceptibility, and simplified models for the interpretation of geological structures. This methodology is applied successfully to the study of different examples of the main volcanic zones of the Iberian Peninsula, representative of the Martian intraplate volcanism and similar to Venus domes, as a preparatory action prior to the exploration of the rocky planets’ surfaces.

3D imaging of the subsurface electrical resistivity structure in West Bohemia/Upper Palatinate covering mofettes and Quaternary volcanic structures by using Magnetotellurics

The region of West Bohemia and Upper Palatinate belongs to the West Bohemian Massif. The study area is situated at the junction of three different Variscan tectonic units and hosts the ENE-WSW trending Ohře Rift as well as many different fault systems. The entire region is characterized by ongoing magmatic processes in the intra-continental lithospheric mantle expressed by a series of phenomena, including e.g. the occurrence of repeated earthquake swarms and massive degassing of mantle derived CO2 in form of mineral springs and mofettes. Ongoing active tectonics is mainly manifested by Cenozoic volcanism represented by different Quaternary volcanic structures. All these phenomena make the Ohře Rift a unique target area for European intra-continental geo-scientific research. With magnetotelluric (MT) measurements we image the subsurface distribution of the electrical resistivity and map possible fluid pathways. Two-dimensional (2D) inversion results by Muñoz et al. (2018) reveal a conductive channel in the vicinity of the earthquake swarm region that extends from the lower crust to the surface forming a pathway for fluids into the region of the mofettes. A second conductive channel is present in the south of their model; however, their 2D inversions allow ambiguous interpretations of this feature. Therefore, we conducted a large 3D MT field experiment extending the study area towards the south. The 3D inversion result matches well with the known geology imaging different fluid/magma reservoirs at crust-mantle depth and mapping possible fluid pathways from the reservoirs to the surface feeding known mofettes and spas. A comparison of 3D and 2D inversion results suggests that the 2D inversion results are considerably characterized by 3D and off-profile structures. In this context, the new results advocate for the swarm earthquakes being located in the resistive host rock surrounding the conductive channels; a finding in line with observations e.g. at the San Andreas Fault, California.

Kernel Analyses of Volcanic Vent Distribution: How Accurate and Complete are the Objective Bandwidth Selectors?

Kernel Density Estimation is a powerful tool that can be used to extract information about the underlying plumbing system in zones of distributed volcanism. Different approaches concerning the form in which this tool should be applied, however, exist on the literature. One of those approaches sustains that an unbiased selection of a parameter known as the bandwidth is preferable to other alternatives because it reduces biases on the analysis. Nevertheless, there are more than 30 different forms in which a bandwidth can be “objectively” selected, therefore questioning the meaning of “objectivity” on the selection of a method used for its calculation. Furthermore, as shown in this work, the range of allowed “objective” choices of the bandwidth is not much different from a typical range that could be selected subjectively. Consequently, instead of focusing on the question of “what is the best method?” it is shown here that a more informative approach is to focus on the questions of “what are the special values of different methods, and what are their several advantageous applicabilities?”. The benefits of this shift in approach are illustrated with application to three locations of volcanic interest that have a previously well-constrained volcanic structure.

Laser induced 3D porous graphene dots: Bottom-up growth mechanism, multi-physics coupling effect and surface wettability

One-step conversion of three-dimensional (3D) porous laser-induced graphene (LIG) from carbon precursors opens a facile way to prepare graphene-related materials. Herein, a series of dots is fabricated by CO2 laser irradiation of polyimide (PI, Kapton) films to investigate the in-situ growth mechanism of LIG. Complex phase transitions combined with various physical fields lead to morphologic changes from mastoid to volcanic structure. The cross-section profile varying with laser parameters are fitted to measure the physical characteristics (e.g., top/bottom width, depth, and tilt angle) under Gauss energy distribution. With considering the highly localized heating effect and non-uniform thermal stress, a coupled physical field is established to theoretically analyze the temperature, thermal stress and deformation distribution. The micro-scale spatial effects such as nucleation, growth, escape and explosion of bubbles in the air flow field are responsible for the 3D porous structure of LIG. Inspired by the “lotus effect”, a superhydrophobic dot matrix is manufactured with static contact angle of 151.5 ± 1.3° and roll-off angle of 15.7 ± 1.2°, laying a foundation for large-scale production of LIG.

First characterization of the volcanism in the southern Mozambique Channel: Geomorphological and structural analyses

The southern part of the Mozambique Channel is characterized by a cluster of isolated seamounts, including the Bassas da India atoll and Europa Island, ranging in latitude from 20°S to 22°S and from 38° to 40° in longitude, and located at the Rovuma-Lwandle plate boundary. Only Cenozoic carbonate platforms have previously been studied in this region, with very little work done on the volcanic history. We confirm here the volcanic nature of the basement of the Bassa da India/Europa complex by providing important constraints on the setting of this hitherto poorly understood volcanism.Recent bathymetric surveys and dredging operations allowed us to map and date these seamounts, comprising, from west to east, the Hall Bank, the Jaguar Bank, Bassas da India, Ptolemee, and Europa. In addition, we discovered, to the south of Bassas da India, two large new polygenetic volcanic edifices, Pamela Seamount 1 (PS1) and Pamela Seamount 2 (PS2), showing heights and diameters of up to 900 m and 13 km, respectively. Mapping and statistical analysis carried out revealed that the volcanic structures of the Bassas da India/Europa complex are organized along two main alignments with different stages of development: (i) a NE-SW volcanic alignment characterized by volcanic ridges up to 700 m in height, comprising small individual volcanic cones; and (ii) a NW-SE volcanic alignment in which many large and well-developed individual volcanic cones can be found. From this distribution of the volcanism, we suggest that the large volcanic edifices of the Bassas da India/Europa complex were fed by long-lived magma systems, repeatedly supplied from deep magma reservoirs through a significant network of dykes and faults, with lateral injections of magma guided by a dense network of faults allowing magma to reach the surface along rift-zones. 40Ar/39Ar dating confirms that the volcanism covers a period from the Oligo-Miocene to the Pleistocene, and probably extends to the present day. The two volcanic alignments are also consistent with the tectonic features already recognized for the region and are spatially superimposed by active seismicity. Magma ascent is strongly controlled by large pre-existing crustal structures.

Tectonic evolution, volcanic features and geochemistry of the Paleoproterozoic Salla belt, northern Fennoscandia: From 2.52 to 2.40 Ga LIP stages to ca. 1.92–1.90 Ga collision

This study adapts the LIP and mantle plume model for magmatic events in the northern Fennoscandian Shield at 2.51–2.49 Ga and 2.45–2.44 Ga, corresponding globally to the Mistassini LIP and Matachewan LIP systems in the Superior craton. We propose a new model for the Salla belt, where the 2.45–2.44 Ga represents the plume arrival, and both radiating swarm and the circumferential stages. Associated 2.45–2.43 Ga layered intrusions and granites form intrusions ringing the plume centre close to the present NNW part of Fennoscandia.In the Salla belt, the subaerial magmatism of the Sumi system (Salla group) initiated at ca. 2.45–2.44 Ga and followed by volcanism of the subaqueous to subaerial Sariola system (Kuusamo group) at ca. 2.43 to 2.40 Ga. A more primitive magmatic stage at 2.43–2.40 indicates a final gravitational collapse of the LIP mantle plume. Calc-alkaline to tholeiitic affinities indicate that volcanism resulted from the content of the core-related fluids in the plume heads. Enriched in LILE elements with negative Nb and Ta anomalies compared to primitive mantle, suggest continental crustal contamination in a within-plate plume-driven rift setting. Volcanic structures indicate lava cooling, gas expansion and escape processes, and vapor differentiation processes and devolatilization of lava, which are suggestive of continental flood basalts and/or pahoehoe-type lava flows.Based on our structural-tectonomagmatic model, shield-wide systems suggest a correlation of the Seidorechka formation in the Imandra–Varzuga Belt and the upper part of the Sumi sequence within the Lekhta and Shombozero Belts with the 2.45–2.44 Ga Salla group Sumi volcanics in the Salla belt. In addition, the volcanics of the Sariola system (Kuusamo group) are correlated with the Vetreny Belt, the Kairala–Noukajärvi–Aapajärvi formations in Kuolajärvi, and the Polisarka formation in the Imandra–Varzuga Belt. The most peripheral part of the Lapland foreland fold and thrust belt (1.92–1.90 Ga) includes the Salla belt, where E–W contraction first led to E-vergent thrusting followed by a thick-skinned tectonic style with reverse faults and long-wavelength folds.

Trends in volcano seismology: 2010 to 2020 and beyond

Volcano seismology has been fundamental to our current understanding of crustal magma migration and eruption. The increasing availability of portable seismic networks with the creative use of seismic sources and ambient noise has led to a better understanding of the volcanic structure of many volcanoes and is producing increasingly detailed images of the volcanic subsurface. The past decade (2010-2020) has seen advances in our understanding of seismic sources under and surrounding volcanoes through precise locations, and through analysis of source mechanisms from seismic signals that are more varied and smaller in magnitude, reaching beyond traditional techniques. In tandem with continued research on fundamental physics-based understanding of volcano-seismic sources, new advances in computational analyses including machine learning methods will push our understanding of volcanic processes into the future. Incorporation of multidisciplinary geophysical observations (especially infrasound) has become commonplace, and our understanding of infrasound propagation and sources will feed back into our ability to monitor ongoing eruptions and surficial mass movements. Open-source codes will permit widespread evaluation and adoption of new methodologies for volcano-seismic analysis and inversion. Combined with quantitative and conceptual source models using improved structural constraints, these new methodologies will better characterize the range of volcano-seismic signal evolution scenarios and hold promise for creating better short-term forecasts. Finally, permanent instrumentation is available on an expanding range of volcanoes, and open data policies are increasingly making these data available to the scientific community in near real time.