Volcanic Cones Research Articles

Stratovolcanoes on the Chilean-Bolivian border as geoatraction

The cluster of stratovolcanoes located on the Chilean-Bolivian border, in the Western Cordillera, is composed of typical, for that part of the Central Volcanic Zone in the Andes, volcanic landforms. The highest volcano is the Nevado Sajama (6,542 m a.s.l.), apparently extinct. The other: Parinacota (6,336 m a.s.l.), Pomerape (6,222 m a.s.l.), Acotango (6,052 m a.s.l.) and Cerro Quisiquisini (5,542 m a.s.l.) were all active in both the Pleistocene and the Holocene. Recently, only the Guallatiri Volcano (6,071 m a.s.l.) is still active. The summits of these mountains are covered with permanent snow or ice caps. On the slopes, there are post-glacial valleys,rocks glaciers and debris avalanches. In the vicinity of volcanic cones, active fumaroles occur, along with hot springs, geysers and high-mountain peat bogs (bofedales), in addition to one of the highest in the world mountain lakes – the Lago Chungará (4,520 m a.s.l.). The unique landform is a huge debris avalanche and was formed during the eruption of the Parinacota Volcano. Small villages settled by Aymara Indians and their cultural monuments complete the extraordinary landscape of the Altiplano Plateau. The values of biotic nature are also unique and deserving of protection on both sides of the state border. Moreover, these sites have been registered into the UNESCO World Heritage List. Modest accommodation facilities located off the main roads satisfy the qualified tourists interested in volcanology. The authors describe the grueling trekking trails, the climbing routes leading to the summits of volcanoes and the other geoattractions, accessible for ordinary hikers.

Using fallout 137Cs and OSL as sediment tracers in badlands: a case study of Tepezalá volcano (Central Mexico)

ABSTRACT Badlands are dynamic landforms that cause soil loss over extensive areas. In this study, we analyze recent sediment mobilization in a badland area by using a novel approach that integrates fallout 137Cs and optically stimulated luminescence (OSL). We assess how erosion and sediment storage operate over the Tepezalá volcano, a tephra cone located in central Mexico. We analyzed a set of sediment samples extracted from the surface of an altitudinal sequence with different land uses to explore how landscape management practices relate to erosion and, depth profiles from local sinks, to detect patterns of sediment mobilization and sedimentation. We compared 137Cs and OSL results with reference values to evaluate whether erosion or deposition is predominant and to assess how deep the erosive processes in the landscape are. Results from fallout 137Cs values indicate that in those badlands with implemented actions to mitigate erosion, sediment is retained. The high luminescence values show that the edaphic soil has been flushed away, and subsoil crops out in some of the sampled sites. For the case of depth profiles, maximum values of 137Cs coincide with high luminescence values, suggesting that in such sites, the sediment was mobilized during rapid incision episodes that caused widespread erosion of the landscape. We detected at least three episodes of rapid incision in 10 years of sediment record. We propose that using 137Cs and OSL together can provide valuable information of the sediment transport in settings dominated by fast erosion as do occur for the case of badlands.

Physical modeling of magma chamber of slamet volcano by means of satellite gravimetric data

Slamet Volcano (3,432 m) is the highest volcano in Central Java, Indonesia, with a weak explosive type of eruption compared to other active volcanoes. Designing the magma chamber model may help reveal the characteristics of Slamet Volcano. The modelling uses the gravimetric satellite data from GGMplus, which is best in spatial resolution compared to other satellite data, i.e. 220 m. Data processing begins with Bouguer correction and terrain correction and has resulted in complete Bouguer anomalies data, with values ranging from 11.068 – 117.451 mGal. Further, residual Bouguer anomalies data were obtained after data reduction to the horizontal surface and removal of regional anomalies data, to obtain values ranging from -67.569 – 38.808 mGal. The residual anomaly contour map shows the lowest anomalous value is under the volcanic cone at positions of 109.21967° E and 7.24281° S which is estimated to be the location of the magma chamber of Slamet Volcano. However, the inversion modeling resulting from the residual Bouguer anomalies data shows that the magma chamber of Slamet Volcano can be observed clearly at positions of 109.22053° E and 7.24719° S. The location of the magma chamber is not perfectly vertical under the volcanic cone but has a slight slope. The obtained model of the magma chamber has a relatively small volume and shallow depth, i.e. about 1 – 4 km. The obtained physical parameters of the magma chamber impact the characteristics of the eruption of Slamet Volcano which tend to be weak explosive.

Evolution of magma supply system beneath a submarine lava dome after the 7.3-ka caldera-forming Kikai-Akahoya eruption

Kikai caldera in SW Japan, which is a submarine volcano, has undergone repeated caldera-forming eruptions. After the 7.3-ka caldera-forming Kika-Akahoya eruption, basaltic and rhyolitic subaerial eruptions occurred at Inamura-dake, Iwo-dake and Showa-Iwojima volcanic centers on the caldera rim. Fumarole activity still continues at Iwo-dake. Recent submarine surveys have revealed that a 600 m high central lava dome grew inside the Kikai caldera, with a volume of 32 km3. In addition, several satellite volcanic cones formed to the east and the west of this central lava dome. These features inside the submarine caldera would postdate the 7.3-ka Akahoya eruption. However, the formation mechanism of these submarine volcanic edifices is yet to be well understood. Here we present the whole-rock and mineral chemistry of dredged rocks from the central lava dome and satellite volcanic cones inside the submarine caldera. The results are used to constrain magmatic conditions that formed these submarine volcanic edifices. Most rhyolites from the central lava dome and the western satellite volcanic cones are compositionally distinct from those of the Akahoya eruption and the old Iwo-dake volcanic stage (5.2–3.9 ka) rhyolites. Instead, the chemical compositions of these submarine rhyolites overlap with those of the volcanic products of the young Iwo-dake, which is active since 2.2 ka. The compositional similarity suggests that the central lava dome tapped the same magma supplying the young Iwo-dake volcanism. By contrast, the dredge samples from the eastern satellite volcanic cones exhibit binary chemical trends: one group having chemical composition that overlaps with those of the young Iwo-dake rhyolites; the other group being chemically similar to the rhyolites from the old Iwo-dake and the Akahoya eruption. The magma temperature estimated from Fe-Ti oxide thermometry (922 °C on average) is almost equal to those estimated for subaerially erupted rhyolites at Iwo-dake during the young Iwo-dake volcanic stage and the Showa-Iwojima eruption in 1934–1935. The oxygen fugacity estimated from Fe-Ti oxygen barometry is 0.8 log unit higher than Ni-NiO buffer (NNO + 0.8), on average, which is lower than that estimated for the subaerially erupted rhyolites. A magmatic hygrometer estimated H2O content of the melt ranging 2.2–3.5 wt%. Polybaric crystallization from H2O-saturated melts may have occurred beneath the submarine lava dome at depths of 2–4 km. These results suggests that a separate magma supply system with basaltic and rhyolitic magmas may exist beneath the submarine central lava dome and that underlying basaltic magma, such as that beneath Iwo-dake and Showa-Iwojima, may have heated rhyolitic magmas stored at depths of 2–4 km. Additionally, the lack of mafic enclaves, which are by contrast commonly observed in the subaerially erupted rhyolites at Iwo-dake and Showa-Iwojima on the caldera rim, implies that direct interaction between basaltic and rhyolitic magmas is limited beneath the center of the submarine caldera.

Evolution Magmatism of Nagasari Volcano Dieng, Central Java, Indonesia

Nagasari Volcano, part of the Dieng volcanic complex, is one of the unique volcanoes in Central Java. Around this volcano grow eruption craters, volcanic cones, and pyroclastic flow ridges. There were several 14 eruption centers around Mount Nagasari, so it is necessary to know the development of magmatism evolution. The aims of the research to determine the evolutionary development of magmatism. The methodology used is geological mapping and petrographic analysis. The observations of rocks found in the study area include andesite lava, lapilli-tuff, fallen pyroclastic breccias, and flow pyroclastic breccias. Meanwhile, geological mapping and petrographic observations of volcanic rock samples show that the evolution of magmatism in the study area from the oldest to the youngest is basaltic magma that formed Prau Volcano in the pre-caldera period. On the other hand, magmatism in the post-caldera I period was of the type of pyroxene andesite forming the Gembol to Jimat Volcano group. In contrast, in the post-caldera II period, the hornblende-biotite andesite group formed the Dieng Kulon to Kendil group.

Syn‐rift volcanism in the Barmer Basin: An intra‐basin extrusive complex at the northern limit of the Deccan volcanic province in India

The Raageshwari Volcanic Formation (RVF) is a volcanic complex in the southern part of the Barmer Basin, NW India, localized around a large rift centre horst block, the Central Basin High. The RVF comprises an initial sequence of acid igneous rocks, which are of ignimbritic origin, termed the Agni Member, overlain by a stacked sequence of basaltic lava flows interbedded with subordinate pyroclastic deposits, the Prithvi Member. Seismic data confirms that the volcanic complex has a conical overall geometry and a layered internal structure produced by successive and extensive flows of basalt and ignimbrite, very similar to that observed in the main Deccan lava outcrops along the western margin of India. U–Pb zircon ages near the top of the Agni Member in the Raageshwari‐26 well give an age of 68+/−2 Ma for a tephrite pyroclastic unit, whilst Ar–Ar analysis of a distal basalt containing phenocrysts of biotite from the Saraswati‐4 well gave an older robust Ar–Ar plateau age of 73.7 ± 1.4 Ma. A typical Deccan age of 67.9 ± 1.7 Ma was obtained from the isolated unaltered basaltic andesite in well NE‐South‐1. Due to depositional on‐lap onto the Central Basin High, the overlying alluvial Dandlawas and Fatehgarh formations are absent on the crest of the Central Basin High and Barmer Hill Formation lake sediments rest directly on the basalts. This relationship indicates that the volcanic cone was a structural or topographic high during deposition onto which the Fatehgarh and Barmer Hill formations lake sediments eventually on‐lapped. The RVF of the Barmer Basin along with the Deccan volcanics in the Cambay Basin, Narmada Rift and in Saurasthra are all developed within fault‐bounded rift basins, in which deep seated faults extend beneath the Deccan volcanic sequence. They are associated with thermal anomalies and thinned continental crust and the presence of a linear low velocity zone at ~100 km depth in the upper mantle region beneath the Barmer and Cambay basins. This is interpreted to be the position of the “conduit” through which plume head material passed through the upper mantle before arriving at the base of the Indian lithosphere. The RVF therefore appears to be an early eruption of differentiated ultrabasic magma from a shallow, secondary magma chamber produced by partial crustal melting.

Developing an integrated approach based on geographic object-based image analysis and convolutional neural network for volcanic and glacial landforms mapping.

Rapid detection and mapping of landforms are crucially important to improve our understanding of past and presently active processes across the earth, especially, in complex and dynamic volcanoes. Traditional landform modeling approaches are labor-intensive and time-consuming. In recent years, landform mapping has increasingly been digitized. This study conducted an in-depth analysis of convolutional neural networks (CNN) in combination with geographic object-based image analysis (GEOBIA), for mapping volcanic and glacial landforms. Sentinel-2 image, as well as predisposing variables (DEM and its derivatives, e.g., slope, aspect, curvature and flow accumulation), were segmented using a multi-resolution segmentation algorithm, and relevant features were selected to define segmentation scales for each landform category. A set of object-based features was developed based on spectral (e.g., brightness), geometrical (e.g., shape index), and textural (grey level co-occurrence matrix) information. The landform modelling networks were then trained and tested based on labelled objects generated using GEOBIA and ground control points. Our results show that an integrated approach of GEOBIA and CNN achieved an ACC of 0.9685, 0.9780, 0.9614, 0.9767, 0.9675, 0.9718, 0.9600, and 0.9778 for dacite lava, caldera, andesite lava, volcanic cone, volcanic tuff, glacial circus, glacial valley, and suspended valley, respectively. The quantitative evaluation shows the highest performance (Accuracy > 0.9600 and cross-validation accuracy > 0.9400) for volcanic and glacial landforms and; therefore, is recommended for regional and large-scale landform mapping. Our results and the provided automatic workflow emphasize the potential of integrated GEOBIA and CNN for fast and efficient landform mapping as a first step in the earth's surface management.

Modelling Erosion and Floods in Volcanic Environment: The Case Study of the Island of Vulcano (Aeolian Archipelago, Italy)

The re-mobilization of volcaniclastic material poses a hazard factor which, although it decreases with time since the last eruption, remains present in the hydrographic basins of volcanic areas. Herein, we present the results of the numerical modelling of erosive phenomena of volcanic deposits, as well as of flooding in the volcanic area. The proposed approach includes runoff estimation, land use analysis, and the application of hydraulic and erosion modelling. It exploits the Iber software, a widely used and validated model for rainfall-runoff, river flooding, and erosion and sediment transport modelling. The methodology was applied to the Island of Vulcano (Italy), known for the erosion phenomena that affect the slopes of one of its volcanic cones (La Fossa cone). The rainfall excess was calculated using a 19-year dataset of hourly precipitations, and the curve number expressed by the information on soil cover in the area, derived from the land cover and land use analysis. The erosion and flow models were performed considering different rainfall scenarios. Results show a particularly strong erosion, with thicknesses greater than 0.4 m. This is consistent with field observations, in particular with some detailed data collected both after intense events and by long-term observation. Results of the hydraulic simulations show that moderate and torrential rainfall scenarios can lead to flood levels between 0.2 and 0.6 m, which mostly affect the harbours located in the island’s inhabited area.

Lava fountain jet noise during the 2018 eruption of fissure 8 of Kīlauea volcano

Real-time monitoring is crucial to assess hazards and mitigate risks of sustained volcanic eruptions that last hours to months or more. Sustained eruptions have been shown to produce a low frequency (infrasonic) form of jet noise. We analyze the lava fountaining at fissure 8 during the 2018 Lower East Rift Zone eruption of Kīlauea volcano, Hawaii, and connect changes in fountain properties with recorded infrasound signals from an array about 500 m from the fountain using jet noise scaling laws and visual imagery. Video footage from the eruption reveals a change in lava fountain dynamics from a tall, distinct fountain at the beginning of June to a low fountain with a turbulent, out-pouring lava pond surrounded by a tephra cone by mid-June. During mid-June, the sound pressure level reaches a maximum, and peak frequency drops. We develop a model that uses jet noise scaling relationships to estimate changes in volcanic jet diameter and jet velocity from infrasound sound pressure levels and peak frequencies. The results of this model indicate a decrease in velocity in mid-June which coincides with the decrease in fountain height. Furthermore, the model results suggest an increase in jet diameter, which can be explained by the larger width of the fountain that resembles a turbulent lava pond compared to the distinct fountain at the beginning of June. The agreement between the infrasound-derived and visually observed changes in fountain dynamics suggests that jet noise scaling relationships can be used to monitor lava fountain dynamics using infrasound recordings.

Long-term change of the eruption activities of Sakurajima volcano, Japan, inferred from the fallout tephra deposits

Stratigraphic analysis of fallout tephra deposits in and around a volcano provides a framework for understanding the long-term temporal change in the volcano’s activities. Here, we reconstruct the evolution of the volcanic activities of Sakurajima volcano based on reconstructed tephra stratigraphy by original field surveys, compilations of geological and archeological data, and new 14C dating. We define three eruption stages of Stage 1 (30–24 ka), Stage 2 (12.8–4.8 ka), and Stage 3 (4.5 ka–present), based on a major hiatus and shifting of the volcanic centers. Stages 2 and 3 are further subdivided according to the predominant mode of volcanic activity. Revised distribution of tephra deposits indicates that a total of 14.5 km3 (5.8 km3 dense rock equivalent) of fallout tephra has erupted from Sakurajima. Among them, Stage 2a (13–8 ka) produced the largest volume of tephra fallout deposits, suggesting that Sakurajima peaked in magma discharge during Stage 2a (2.9 km3/kyr) and then decreased rapidly toward Stage 2b (8–4.8 ka; 0.07 km3/kyr). The eruption of large-volume tephra deposits in Stage 2a, followed by the development of a thick volcanic ash layer in Stage 2b, indicates the eruption style shifted from explosive pumice eruptions in Stage 2a to ash-producing Vulcanian activity in Stage 2b, with decreasing magma discharge rate. Thick volcanic ash deposits covered by several fallout tephra deposits during Stage 3 also reflect a shift in activity from repeated Vulcanian explosions with lava effusions in Stage 3a (4.5–1.6 ka) to predominantly pumice eruptions during the historical period (Stage 3b) with an increasing magma discharge rate. The case study of Sakurajima presented here demonstrates that the combined analysis of the distribution, stratigraphy, and age of pumice fall layers with the lava and pyroclastic cone deposits on the volcanic edifice is a powerful tool for deciphering the growth history of complex stratovolcanoes.

Improved High‐Resolution Bathymetry Map of Tamu Massif and Southern Shatsky Rise and Its Geologic Implications

AbstractThe formation and geology of oceanic plateaus are incompletely understood, in part because geophysical data are sparse and of low density. This paper presents an improved high‐resolution bathymetry map for southern Shatsky Rise, by combining newly acquired multibeam bathymetry data from several cruises and by filling in gaps in multibeam coverage with the SRTM15+ global bathymetry model. This map provides important insights on the evolution of Shatsky Rise from plateau forming, to post‐plateau secondary volcanism, to sedimentation, erosion, and sedimentary mass wasting. Tamu Massif is segmented by several subdued bathymetric troughs that divide the massif flanks into smaller rises. The segmentation pattern suggests Tamu Massif was built by a series of eruptions along a jumping triple junction. The distribution of secondary volcanic cones is non‐uniform, with most occurring on the southern and eastern flanks. Most of these secondary cones occur as short chains that parallel nearby magnetic lineations, suggesting control by spreading ridge parallel faults. These results suggest the evolution of Shatsky Rise was largely controlled by spreading ridges during its active volcanic phase. Numerous escarpments were identified around the plateau, a majority of which parallel bathymetry contours, suggesting these features developed because of differential subsidence of the rise massifs. The map reveals widespread mass wasting and downslope sediment movement, shifting sediment distribution and changing the surface morphology. Improved topography improves our understanding of the evolution of Shatsky Rise and emphasizes the importance of bathymetry data in deciphering the geodynamic evolution of large igneous provinces.

Hazardous Changes in Soil CO2 Emissions at Vulcano, Italy, in 2021

AbstractThe La Fossa volcano on the Island of Vulcano, Italy, showed signs of more energetic fumarolic–solfataric activity during 2021. Several increases in volcanic gas emissions and seismicity, namely, “crisis,” punctuated the passive degassing at Vulcano that had ensued after the last 1888–1890 vulcanian eruption. Most of the gases (i.e., up to 90%) were emitted at the crater cone while the diffuse degassing of CO2 at Vulcano Porto accounted for more than 10% of the volcanic emissions. Two anomalous degassing zones at the base of the volcanic cone (i.e., Palizzi and Faraglione) showed notable changes in the gas output during the volcanic crisis. In these zones, increases of soil CO2 flux (φCO2) had several practical implications other than of volcanological interest, owing to the risk related to people's exposure to volcanic gas emissions. The results of this study reveal variations of the average φCO2 from 74 g m−2 d−1 during September 2021 to 370 g m−2 d−1 in November 2021, which were 27% and 538% higher than the statistical background since 1988 (φCO2 ≈ 58 g m−2 d−1), respectively. These observations helped in volcanic surveillance at Vulcano. The soil CO2 partitioning determined using both φCO2 and carbon isotope measurements, helped track changes in the volcanic CO2 output from 9.97 · 104 to 101.15 · 104 kg d−1. Estimates for volcanic CO2 suggest that the instability of a magmatic body caused a transition from background fumarolic–solfataric activity toward an unrest event after September 2021.

Identification and Geomorphometric Characterization of Volcanic Cones in the Marius Hills, the Moon

AbstractInvestigation of the detailed geological characteristics of lunar volcanic cones can peer into their formation and emplacement processes, thus deepening our understanding of pyroclastic eruptions on the Moon. In this work, we focus on the Marius Hills region (centered at 13°N, 55°W), a volcanic plateau in south Oceanus Procellarum, which hosts the most abundant volcanic cones on the Moon, along with other volcanic features. The range of volcanic features indicates various eruption styles and complicated sequences of regional magmatic activities. Based on the SLDEM2015 topography data, with assistance from other multisource topography and image data sets, we identified 360 known and suspected volcanic cones and 22 volcanic domes in the Marius Hills. Following detailed morphological characterizations, the volcanic cones show various morphology types, including C‐shaped, elliptical‐shaped, elongated‐shaped, irregular‐shaped, and rounded‐shaped. The cones (median basal width ∼2.7 km, height ∼115 m, and volume 0.25 km3) contain summit pit craters (15%; median width ∼358 m), exhibiting smaller basal widths and summit pit crater widths compared with lunar mare domes. The mean slope (3.5°–15.6°) and rock abundance (0.3%–3.8%) of volcanic cones in Marius Hills are larger than those of the mare dome, suggesting different eruption mechanisms. Marius Hills cones also show larger basal widths and smaller height/width ratios than terrestrial volcanic cones, which are attributed to multiple factors, including subaerial environment, volatile content of the magma, eruption rate, and lava viscosity.

Growth and evolution of NE Australian continental crust interpreted from complex melting-hybridization histories of northern Queensland granulite xenoliths

During active tectonic processes the lower continental crust plays a major role in the development and evolution of the overlying crustal column. The lower crust is heavily influenced by influx of mafic magma from the mantle and extraction of more felsic magma to the shallower crust. Evidence of such interactions are preserved in residues after melting that are rarely brought to the surface as suites of granulite-facies, lower-crustal xenoliths.Here we investigate the petrology, geochemistry and petrochronology of a set of granulite xenoliths from the Pleistocene Hill 32 volcanic cone that has intruded through the geologically complex Georgetown Inlier, north Queensland, which has experienced multiple magmatic-tectonic events since the Paleoproterozoic. Petrochronology constrains the temperature in the Pleistocene lower crust to above the closure temperature of U-Pb in apatite (350–550°C) and rutile (∼400–500°C), which define an eruption age for Hill 32 at 1.6±0.1 Ma, and below the closure temperature of titanite (up to 800°C), which gives an age of 219±4 Ma. The samples contain petrographic and petrochronological evidence of recrystallisation and melt extraction at >900°C, conditions able to reset U-Pb systematics in zircon. The zircons give U-Pb ages consistent with the timing of the Permo-Triassic New England orogeny, indicating zircon recrystallisation/regrowth coeval with major felsic magmatism in the upper crust at that time. U-Pb in zircon records minor preservation of earlier events. While, εHf indicates mixing between Proterozoic to Archean precursor crust with juvenile mantle-derived magma, which provided both heat and radiogenic Hf. The samples are interpreted to be the product of melt-precursor rock hybridisation followed by melt extraction in the lower crust that represents a critical and rarely observed component of crust formation processes.

Airborne data processing and 3D modeling of magnetic structures between Nador region and the Chaffarine Islands: Geological significances

The Cap of Trois Fourches-Nador-Chaffarine Islands zone (CTF-N-CI) located in the Moroccan Oriental Rif is recognized by Neogene-Quaternary volcanic outcrops. Those later formed volcanic cones and are considered the main source of the huge Nador magnetic anomaly. This study aims to enhance the magnetic context using geophysical techniques and identify the geometry of magnetic sources by performing 3D modeling using Talwani method. We have achieved the following findings: (1) The elaborated residual magnetic map (Rs) that shows three aligned magnetic anomalies. They are oriented W-E and register a maximum intensity of 380 nT. Applying reduction to the pole to (RTP) the Rs map makes the anomalies on the top of their body sources. Thus, we have found that those anomalies have resulted essentially from the Gourougou volcano and Chaffarine Islands volcanoes outcropping in the study area. Except for the middle Pm anomaly, which is related to volcanic rocks of the Kariate Arekmane drillhole. (2) Performing horizontal derivative (HD) technique leads to establishing the edges of the source bodies. Hence, the inversed map of the magnetization distribution proves that the three bodies are homogeneous and probably splintered from a unique mass. (3) The downward up continuation (DC) to different heights (from 500 to 2000 m) indicates the source's depth. Thus, we have demonstrated that the common source could reach 0.6 km of altitude. (4) Finally, we have constructed a 3D Talwani model of the volcanic edifices. The released 3D model demonstrates that the anomalies are related to a very extensive mass of 80 km in length, 20 km in width, 1.3 km in thickness. This model supports that the Neogene-Quaternary volcanism of the study area was fissural and related to the W-E fracture zone of up to 80 km in length. This volcanism was also affected by the sinistral Nekor fault, which probably made the Trois Fourches Cap body isolated from the other volcanic edifices.Previously mentioned elements probably prove the simultaneous establishment of this large magnetic structure. Moreover, they emphasize the crucial role of the magmatic phenomena which occurred in Northeastern Morocco at the beginning of the Messinian.

An insight into the evolution of the lithospheric mantle of south Saharan metacraton: Mantle xenoliths from Jabal Eghei Volcanic Complex, Libya

Mantle xenoliths from a Pliocene (∼2 Ma) pyroclastic cone of the Jabal Eghei Volcanic Complex (south Libya) are studied for unravelling depletion-, deformation- and metasomatic events within this part of the Saharan Metacraton. The xenoliths are fertile Cpx-rich spinel lherzolites texturally distinguished into protogranular (hereafter: undeformed – UX) and porphyroclastic/equigranular (deformed – DX) types. The extent of depletion is estimated at 5–10% (olivine-spinel compositions) and 3–13% (HREE contents in clinopyroxene) of melt extraction; all parameters of depletion indicate that the UX are slightly more depleted than the DX. Calculated equilibrium temperatures range 800–1100 °C and generally overlap with temperatures obtained for other xenolith suites in Libya and for other off-cratonic xenoliths worldwide. The temperature estimates for the UX are slightly higher (857–1091 °C) than those for the DX (800–923 °C) and the former xenolith types are better equilibrated. The studied xenoliths exhibit evidence of stealth (high abundances of modal Cpx in some samples) and cryptic metasomatism (LREE-enriched patterns on whole-rock and Cpx REE diagrams) with metasomatic agents most likely akin to alkaline mafic melts similar in composition to host magmas. The study provides a simplified 2D model assuming that: a) the Jabal Eghei lithospheric mantle was roughly stratified with more depleted undeformed peridotite in deeper and less depleted deformed peridotite in shallower regions, b) in the Miocene, normal faulting caused ductile and brittle deformations in the lower and the upper parts of the lithosphere, respectively, and produced small-scale mafic alkaline melts that moved upward and metasomatized the overlying mantle, and c) the advancing extension produced mafic alkaline magma that captured xenoliths and brought them to the surface.

Concealed anatomy and new geological features beneath desert areas of NW India – Constrained from high resolution aero-geophysical data

The vast swathe of area in the Trans-Aravalli region between the western part of the South Delhi Fold Belt and eastern part of the Barmer basin, north-western India exhibits limited geological information due to thick sand cover of the Thar Desert. The present study is to unravel the hidden architecture of the above area using recently acquired high-resolution aero-magnetic data. Here, our interpreted results brought out a buried ring structure in the northern part and NW-SE trending constellation of linear magnetic highs in the southern part. Considering the regional geological milieu, our study correlates the buried ring structure with a possible remnant volcanic cone of the Neoproterozoic silicic Malani Large Igneous Province. Secondly, the significant NW-SE trending linear magnetic highs in the south possibly represents a humongous dyke swarm activity, facilitated by the intricate network of fractures. The orientation of these magnetic linear are conspicuously similar with the Deccan linked Sarnu-Dandali dykes and regional Barmer-Cambay rift system. The northwestern portion of study area displays high magnetic and gravity responses of long wavelength features indicating crustal heterogeneity. The study for the first time documents two concealed structures, which may hold a link of Neoproterozoic Malani and Mesozoic Deccan magmatic pulses.

Morphometric Analysis of Mount Ararat (Eastern Anatolia, Türkiye)

In this study, the morphometric characteristics of Mount Ararat which is a strato-volcano are analyzed. Türkiye’s highest Mountain, Mount Ararat, is located in Eastern Anatolia. The Mountain takes the shape of two major volcanic cones after 2500 m height; these volcanic cones are named Greater Mount Ararat (5137 m) and Little Mount Ararat (3896 m). In this study, relief morphometry, basin morphometry, and drainage characteristics are morphometrically analyzed with Geographic Information Systems (GIS) using 10x10 m resolution Digital Elevation Model (DEM). According to the analysis results, there is an increase in the elevation on the high and steep slopes of the main cone and the slope values increase up to 56° in some locations towards the summit. On the other hand, according to the aspect analyses, 19.9% of slope faces are north-east direction, 14.7% of the slopes are north-direction, 9.4% are northwest, 9.8% are west, 10.7% are southeast, and 16.4% of the slopes are east direction. These results support the fact that Mount Ararat extends in NW-SE direction and is formed on the basis of a fault line in this direction. According to the grouping made by the altitude ranges analysis, the decrease in the rate of elevation belts starting from the slopes of the mountain towards the top confirms the structure of volcanic cone. Elevation differences in relative relief analyses range between 0 and 1141 m and this value increases to 1141 m on the slopes surrounding the summit. The cone structure of Mount Ararat was prominent in transverse and longitudinal profile analyses.

Transition to magma-driven rifting in the South Turkana Basin, Kenya: Part 1

Characterization of the role of magma in driving rift basin evolution is fundamental to our understanding of how extensional plate boundaries develop. Here, we examine patterns of normal faulting, volcanism and magmatism in the South Turkana Basin, Kenya, to test how magmatism has impacted the Quaternary evolution of this system. Utilizing high-resolution, single-channel reflection seismic data and radiocarbon-dated cores, we estimate that shallow Holocene normal faulting accounts for 3.5–5.8 mm a −1 of extension, consistent with estimates farther south in the Suguta Basin. Spatial fault patterns show that extension in the Holocene is concentrated along a c. 20 km wide intra-rift fault network, aligning with the axial volcano, South Island. We suggest that up to 85% of Late Quaternary regional extension is accommodated within an axial magmatic segment rather than on the border fault system responsible for the original basin architecture. Axial extension increases towards South Island, highlighting magmatism as crucial in driving recent shallow upper crustal faulting in the South Turkana Basin. Below this zone of extensional faulting, geochemical evidence supports a developed magma plumbing system that broadly parallels equivalent axial magmatic systems within the Main Ethiopian Rift. Overall, our data support a recent (Mid- to Late Pleistocene) transition to magma-driven axial extension in the Lake Turkana rift. Supplementary material: Supplementary text and the fault, volcanic cone and radiocarbon age data utilized in this study are available at https://doi.org/10.6084/m9.figshare.c.6026624

Variability of East Asian winter monsoon during Middle–Late Holocene: A study based on a crater lake on Jeju Island, South Korea

Understanding the natural variability of the East Asian monsoon (EAM) system, mainly consisting of summer and winter monsoons, is essential to predict future climate changes that will influence agricultural and industrial activities in the highly populated region. To date, the variability of the East Asian winter monsoon (EAWM) and its controlling factors is still unclear in downwind areas that experience the Siberian High, mostly due to the lack of a high-resolution winter monsoon index. Based on the correlation between diatom variations in a volcanic cone of Jeju Island, South Korea, with past regional climate changes (e.g., temperature, dust, and sea ice) and solar activity, in this study, we evaluated the changes in the climate from the sum of acidophilous species (SAS), known to be mainly controlled by the pH of the prevalent water pool, and inferred that the SAS increased during the cold and dry periods (e.g., Little Ice Age and Dark Age Cold Period). Furthermore, millennial-timescale fluctuation in the detrended SAS during the past 8000 years, with peaks at ~500, 1500, 3000, 5600, 6600, and 7600 cal yr B·P., corresponded to the ice-rafted events reported from studies conducted on subpolar ocean sediments and solar activity. In this study, we suggest that, historically, high-latitude climate change driven by solar activity has controlled the EAWM; additionally, we support the application of the SAS in Jeju Island as a high-resolution EAWM index.