Pyroclastic Research Articles

Geochemical characteristics and mapping of Reşadiye (Tokat-Türkiye) bentonite deposits using machine learning and sub-pixel mixture algorithms

Reşadiye bentonite deposits, which play a significant role in Türkiye's bentonite production, are situated in Central Anatolia. Geochemical, mineralogical, and remote sensing data have been integrated to map the spatial distribution of clay minerals in the bentonite deposits and argillic areas. It is hypothesized that the bentonite samples occurred by the in-situ diagenetic alteration of rhyolite-dacite, trachyte, and andesite/basaltic andesitic composition pyroclastic rocks (ash-flow tuff). Biotite, clinoptilolite, calcite, dolomite, K-feldspar, opal-CT, quartz, and clay minerals are detected in most bentonite samples. The clay patterns determined in the bentonite samples in the X-ray diffraction (XRD) diagrams were 12.3–12.6 Å and were interpreted as being rich in Na-smectites. Mineral mapping in these deposits is essential for mining operations since the high-grade bentonite deposits can be affected by the other clay, gang, and ore minerals they contain in addition to the smectite. The sample spectra measurements matched montmorillonite and kaolin/smectite spectra. This study tests support vector machine (SVM) and artificial neural network (ANN) machine learning and MTMF subpixel algorithms in lithology and mineral mapping in Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite data. It combines the power of subpixel unmixing algorithms to determine the distribution of clay and high-grade bentonites in argillic areas discriminated by machine learning. The results showed that the SVM algorithm can map better than ANN for argillic areas. Additionally, the distribution of high-grade bentonite and kaolin/smectite bearing sites in the study area is discriminated by the mixture-tuned matched filtered (MTMF) spectral classification method. As a result, this study shows that remote sensing studies can be utilized for the exploration and monitoring of high-grade bentonite sites during and/or post-mining operations.

Investigating the Dynamic Creep and the Tensile Performance of Zeolitic Tuff-modified Warm Asphalt Mixtures

Aims This research investigates the effect of adding natural Jordanian Zeolitic tuffs to the SUPERPAVE asphalt mixture at the dynamic creep and the indirect tensile performance. Background Rutting and fatigue are considered the most common types of distress that affect pavements all over the world. Many factors can affect these properties, such as different aggregate properties, asphalt grades, and properties, as well as the type and amount of the mineral filler. Mineral fillers play an important role in enhancing the asphalt mixtures' performance by filling the voids in the mixture besides improving the cohesion of the binder as it has a small weight in addition to a very large surface area. Generally, the powder of limestone is the most used type of filler. However, studies showed that many materials could also be used as mineral fillers successfully. The focus of this study is using natural Jordanian Zeolitic tuff as a mineral filler. Jordanian zeolitic tuff mainly consists of Phillipsite, chabazite, and faujasite, which are considered the most abundant Zeolitic tuff minerals. The pyroclastic material is widely distributed in the Badia region of northeast Jordan. Zeolitic tuffs are located in Jabal Aritayn (30km northeast of Azraq), Tlul AlShahba (20 km east of Al Safawi), Tal Al-Rimah (35 km northeast of Al Mafraq), and other small deposits in central and south Jordan. Objectives The aim of this research was to study the impact of Zeolitic tuffs on overall Superpave asphalt mixture performance. Methods The specimens were prepared using the optimum asphalt content obtained by the SUPERPAVE method. Dynamic Testing System DTS-16 was used to apply both dynamic creep and indirect tensile tests that give a good idea about the rutting and fatigue behavior of asphalt mixtures. Both tests were conducted at 25 °C. Results The Zeolitic tuffs modified asphalt mixtures have lower accumulated strains and higher creep stiffness compared to the control mixture. Subsequently, the indirect tensile test results showed that the modified asphalt mixtures have a higher resilient modulus than the control asphalt mix. Generally, using Zeolitic tuffs as a modifier of asphalt mixtures enhanced the rutting and fatigue resistance. The results showed that asphalt mixtures fortified with 25% Zeolitic tuffs emerged as the best contenders for rutting resistance. Also, mixtures enriched with 50% Zeolitic tuffs stood out in fatigue resistance performance. Conclusion The best dynamic creep performance was by adding 25% Zeolitic tuffs by the mineral filler mass, while the best resilient modulus was by adding 50% Zeolitic tuffs by the mineral filler mass. Other The overarching goals encompass understanding the dynamic creep behavior of Zeolitic tuff-infused asphalt blends, deciphering its indirect tensile performance, pinpointing the ideal replacement ratio for mineral fillers, and drawing a performance comparison between WMA and conventional Hot Mix Asphalt (HMA) compositions.

First evidence of Pinaceae and Fagaceae in the fossil wood record of the České středohoří Mts. (Czech Republic): A comprehensive study of fossiliferous sites in pyroclastic rocks surrounding the late Oligocene Milá stratovolcano

A comprehensive anatomical and mineralogical study of fossil wood fragments from fields in the vicinity of Bečov and Břvany villages (NW Bohemia, Czech Republic) indicates that Taxodioxylon gypsaceum (Cupressaceae s.l.) predominates, but also identifies another coniferous wood: Pinuxylon parryoides (Pinaceae) and three angiosperms Quercoxylon böckhianum, Castanoxylon bavaricum and Lithocarpoxylon sp. (all Fagaceae). This paper therefore presents the first occurrence of Pinaceae and Fagaceae fossil wood in the volcanic rocks of the České Středohoří Mts. as well as its youngest palaeobotanical record in general, late Oligocene in age (26.56 ± 0.38 Ma). The samples were buried by alkaline pyroclastic deposits and were mineralized by carbonates. Two distinct depositional processes burying the fossil woods were identified. Closer to the vent, the woods occur in a near-vent pyroclastic fall deposits of the former pyroclastic cone, whereas more distant sites consist of pyroclastic flow deposits. Carbonate mineralization mostly consists of dolomite, but subordinate amounts of magnesite (likely the first time this is documented in fossil wood) as well as calcite and siderite are present. Only one sample collected in the same area, bearing clear signs of riverbed transport (Lithocarpoxylon sp.), was perfectly silicified, but its origin remains unclear.

Self-Calibrated Laser-Induced Breakdown Spectroscopy for the Quantitative Elemental Analysis of Suspended Volcanic Ash.

Real-time analysis of fine ash in volcanic plumes, which represent magma fragments expelled from the crater during explosive eruptions, is a valuable tool for volcano monitoring and hazard assessment. To obtain the chemical characterization of the juvenile pyroclastic material emitted in volcanic plumes, many analytical techniques can be used. Among them, laser-induced breakdown spectroscopy (LIBS) is the one that can most easily be adapted to advanced applications in extreme environments. In this paper, LIBS experiments based on self-calibrated approaches are used to determine the elemental composition of suspended volcanic ash. To simulate the conditions of dispersed volcanic ash in the atmosphere, different sizes of volcanic ash samples are suspended in the air by laser-induced shockwaves in a dedicated chamber, and a parametric study is carried out to establish the optimal experimental conditions for recording usable plasma emission spectra for each ash size. The quantitative analysis is performed using a self-calibrated analytical method, including calibration-free LIBS, which is based on the calculation of the spectral radiance of a uniform plasma in local thermodynamic equilibrium. The method accounts intrinsically for self-absorption since it modifies the intensity of spectral lines and thus leads to an underestimation of the elemental fraction. An intensity calibration of the spectra based on the measurements of Fe lines intensities was also used in this work to deduce the apparatus response from the spectrum itself and avoid the use of standard calibration lamps. Results demonstrate the potential of real-time measurements of elemental fractions in volcanic ash with good agreement with the literature composition.

Pyroclastic component influence on the weathering indices assessment in marine sediments – Lessons from Upper Ordovician of the Baltic Basin

The chemical weathering indices of the sediments can serve as tools for estimating the intensity of weathering in the sediment source rock area and its changes in response to the dynamic interplay of climate, tectonics, and bioevolution. The siliciclastic terrigenous component, comprising sediment particles formed during weathering, carries information regarding weathering. Nevertheless, the presence of volcanic material with silicate composition in the sedimentary record can introduce bias to the weathering estimate by incorporating pyroclastic material that has not undergone weathering but is susceptible to diagenetic alteration. Therefore, a comprehensive understanding of the nature and significance of the volcanic component in sediments is imperative for accurately interpreting weathering derived from sedimentary successions. Our study focuses on investigating the presence of the volcanic component and its influence on weathering indices calculation in the Upper Ordovician sedimentary succession of the Baltic Basin. The results from geochemical massbalance mixing modelling reveal that volcanic material is not confined solely to discrete altered volcanic ash beds (bentonites), and a substantial amount of volcanic material is dispersed or re-deposited into the host rock. Within the interval containing discrete bentonite beds, the volcanic component in the carbonate host rock sections ranges from 50% to 90%, and significantly impacts the terrigenous fraction weathering index calculations. This underscores the necessity of considering the nature and significance of the volcanic component when interpreting geochemical-mineralogical signals.

Penelusuran sisa-sisa Kerajaan yang hilang dibalik Letusan Gunung Tambora di Situs Doro Bente

The archaeological research in the Tambora Peninsula was initiated by the National Archaeological Research Center in 2006, and from 2008 onwards, it was continued by the Archaeological Office in Denpasar-Bali until 2021. Numerous archaeological pieces of evidence have been successfully excavated from Mount Tambora's pyroclastic material. Recent research has been focused on the Doro Bente Site on the Teluk Saleh Peninsula. The research aims to understand the sequence of historical events on settlement centers based on artifact evidence resulting from the eruption of Mount Tambora in 1815. The study employs qualitative, descriptive methods, and a geoarchaeological approach. Data acquisition involves excavation, surveys, and literature studies. Stratigraphic analysis is conducted to identify sediment matrices and understand the deposition sequence. Excavation activities have uncovered significant artifacts such as ceramic fragments, pottery, animal bones, and shell fragments. Micro-scale deposition chronology in excavation box B28U18 indicates that the three lower layers, the oldest, were deposited in a marine environment, followed by five layers of pyroclastic material from the 1815 eruption of Mount Tambora. The geographical factors and available natural resources make Sumbawa Island a focal point for Chinese and European attention from the 13th to the 19th centuries AD.

Hydrologic remobilisation of tephra‐fall deposits: A sedimentological analysis throughout fluvio‐lacustrine systems of North‐West Patagonia

AbstractThis paper explores the response to Holocene ash inundation in different sub‐environments of two fluvio‐lacustrine systems, Las Piedritas and Totoral, focussing on the processes of volcaniclastic remobilisation. Sediment cores and outcrops were used to recognise three deposit types, noting how some differ from lahars, through sedimentological and stratigraphic analysis: (1) thick, laterally discontinuous, pumice‐dominated deposits occur overlying alluvial plain and lower terrace surfaces across both watersheds; (2) chaotic, extremely poorly sorted and matrix‐supported beds composed of both epiclastic and pyroclastic material occur as two conspicuous deposits at Las Piedritas outcrops, in a low‐gradient confined channel setting; and (3) layers with an exclusively pyroclastic composition and no flow sedimentary structures or fragment roundness were found draping each of the two chaotic intervals and intercalating with the background sediment in Las Piedritas prodelta. Thick pumice packages capping the floodplains resulted from the overflow of streams carrying a floating pumice load. Due to its positive buoyancy, the pumice is transported as a slowly moving overlying mantle without mixing with the streamflow. The disorganised pattern and poor sorting of the matrix‐rich polymictic beds are consistent with laminar, gravity‐driven, high‐concentration flows. They constitute secondary lahars, originating upstream from large run‐off processes that reworked a pyroclastic substrate. The lack of reworking features in the vitric‐rich units identified in the lake core retrieved from Las Piedritas prodelta, as well as the continuous and widespread occurrences of those interbedded in upstream outcrops, indicate an airfall origin. No reworked tephra unit is recognised in the prodelta sediment record, although various deposits from the hydrologic remobilisation of airfall tephra are found along the subaerial portion of both watersheds. Apparently, large amounts of flotation‐remobilised tephra were retained on the delta plain, while another considerable fraction would have been carried away from the creek mouth under the influence of dominant regional winds.

Detection of pyroclastic material and deformation of the lava dome in Mt. Sinabung with multi-temporal analysis (2010-2020)

The persistent eruptions of Mt. Sinabung resulted in the lava dome’s deformation and blanketed the surrounding area with pyroclastic material. This research focused on determining the changes in Mt. Sinabung during the prolonged eruptions from 2010-2020. A total of 22 volcanic ash samples were collected following a 1x1 km grid interval spread over from the East to South slope of Mt. Sinabung. The studied area is the most affected by the volcanic eruption. Digital elevation models from the shuttle radar topographic mission and sentinel-1 were utilized to monitor deformations of the lava dome and the distribution of pyroclastic material on Mt. Sinabung. Sentinel Application Platform and Google Earth Engine were used as the main tools in multi-temporal digital elevation model (DEM) data processing. The eruption of Mt. Sinabung from 2010 to 2020 changed the height from 2,460 m to 2,404.3 m and created a new crater (5.35 ha). The lava dome volume from 2010 to 2020 is about 2,308,041 m3 and has collapsed to produce pyroclastic material which deposits to the surrounding area of Mt. Sinabung during the eruption. The distribution of pyroclastic material increased from 2010 to 2019, covered up an area of 103.27 ha (2010), 846.48 ha (2013), 1,029.74 ha (2016), 1,235.97 ha (2017) and 1,463.62 ha (2019). The thickness of the pyroclastic material deposits at Mt. Sinabung until 2020 varied from 13,24 cm to 219 cm. The findings from this study can be used as a reference for observing topographic changes due to volcanic activities and drawing a mitigation and contingency plan for a volcanic disaster program in the active volcanic region of Indonesia.

Mapping of volcanic soil chemical properties with digital soil mapping after the prolonged eruption of Mt. Sinabung (2013-2020)

Volcanic soils in Indonesia cover an area of about 5.4 million ha and around 2.7 million ha in Sumatra. The prolonged eruptions of Mt. Sinabung in North Sumatra from 2013 to today eject pyroclastic materials, which blanketed and altered the soil surface. As a result, volcanic soil formed from these pyroclastic deposits. This study aims to map the chemical properties of volcanic soils after the prolonged eruption of Mt. Sinabung from 2013-2020. Thirty-four soil samples were collected at a depth of 0-20 cm according to the grid sampling system with an interval of 1x1 km covering an area of about 4,500 ha. Regression kriging (RK) was applied to predict the soil’s chemical properties and distribution spatially. The soil samples were air dried, sieved, and analyzed to determine soil pH (H2O and KCl), available, potential and retention P, organic carbon, total nitrogen, cation exchange capacity (CEC), and exchangeable basic cations. Soil pH (H2O) ranges from very acidic to neutral (4.14-6.52) and very acidic to acidic pH (KCl) (3.89-5.26), low to very high available-P (3.46-382.01 ppm), potential-P very low to very high (3.76-230.26 mg 100g-1), P-retention is categorized as very high (90-99%). The organic Carbon range from low to very high (1.73-13.05%), low to high total nitrogen (0.13-0.60%), low to high cation exchange capacity (11.78-97.71 cmolc kg-1), and exchangeable base cations are categorized as high with K values (1.60-2.98 cmolc kg-1). Na (3.72-7.45 cmolc kg-1) and Mg (5.79-12.15 cmolc kg-1) were categorized as high and Ca very low (0.039-0.157 cmolc kg-1). The estimated area of soils with pH between 4 and 5 is about 424.85 ha, and soils with pH between 5 and 6 covered an area of approximately 3,964.81 ha. Our findings suggest that persistent eruptions of Mt. Sinabung supply new plant nutrition, which can enrich and increase soil fertility in the future.

Tracing sulphur dioxide in volcanic deposits and ash emission during the 2019 Sinabung eruptions

Sulphur dioxide (SO2) emissions from Mt. Sinabung eruption were quantified in time series for 2019. Both pyroclastic materials and gas or aerosol ejected during volcanic eruption contain sulphur as sulphate salt deposits coating volcanic ash grains or gasses. Sulphur dioxide from the eruption will directly impact the surrounding area. Spectral from satellite optical sensors can be used to monitor and measure SO2 gas near real-time after an eruption. The distribution of SO2 column density in the atmosphere was tracked using the Sentinel-5P satellite. Regression kriging (RK) is applied to predict the spatial distribution of sulphur. The area under study is located in a radius of 3 to 7 km from the eruptive center, covering an area of about 4,517 ha. A total of 51 soil samples and volcanic ash were collected from 0- 20 cm soil depth based on a 1x1 km grid interval. All samples were air- dried, sieved, and analyzed for pH, sulphate, and total SO3 using XRF. The Google Earth Engine (GEE) platform was also used to process Sentinel-5P satellite imagery to determine the number and distribution of SO2 column density in the atmosphere during 2019. The pH of the ash is very acidic to neutral (3.56 - 6.55), while soils are considered acidic to neutral (4.67 - 6.52). The available sulphate content in soil ranges from 0 to 303.39 ppm and 0 to 142.47 ppm in volcanic ash samples. SO2 content in ash ranges from 0 to 16.53% and 0 to 3.71% in soils. Sentinel-5P satellite image spectral data shows that SO2 is concentrated mainly in the southern region, with the highest level occurring in August 2019. This study can serve as one of the volcanic mitigation programs and forecast the distribution of SO2 in an active volcanic region of Indonesia.

The architecture of basalt reservoirs in the North Atlantic Igneous Province with implications for basalt carbon sequestration

Abstract Offshore CO 2 sequestration in basaltic formations of the North Atlantic Igneous Province may allow permanent storage of large volumes of CO 2 through rapid carbonate mineralization. Characterizing the internal architecture of such reservoirs is key to assessing the storage potential. In this study, six photogrammetry models and three boreholes on the Faroe Islands have been used to characterize the internal lava sequence architectures as a direct analogue to potential offshore North Atlantic Igneous Province storage sites. The studied formations are dominated by c. 5 to 50 m thick simple and compound lava flows, with drill core observations documenting a transition from pāhoehoe moving towards ‘a’ā lava flow types interbedded with thin (<5 m thick) volcaniclastic rock units. The identification of flow margin breccias is potentially important as these units form excellent reservoirs in several other localities globally. Stacked, thick simple flows may present sealing units associated with dense flow interiors. Connected porous and permeable lava flow crusts present potential reservoirs; however, the degree of secondary mineralization and alteration can alter initially good reservoir units to impermeable barriers for fluid flow. Large-scale reservoir volumes may be present mainly within both vesicular, fractured pāhoehoe and brecciated flow margins of transitional simple lava flows.

Geology, geochemistry, mineralization and fluid inclusion characteristics of the SW of Hormuz Island banded iron formations, southern Iran

The Hormuz Island banded iron formations (HIBIFs) are situated at the Zagros Folded Zone in southern Iran. The BIFs occur intercalated with the Neoproterozoic Hormuz series, an evaporite and siliciclastic succession with pyroclastic rocks, and were deposited on the continental rift margin of the Arabian plate. The HIBIFs are banded rocks consisting of the alternation of dark Fe-rich and reddish-brown Si-rich layers, and belong to oxide facies iron formations. The post-Archean Australian shale normalized rare earth elements and yttrium patterns of HIBIFs have the characteristics of both hydrothermal solutions and seawater. The sharp positive Eu anomaly (2.10–6.90) may be inherited from high-temperature hydrothermal solutions, while slightly negative Ce anomalies (0.57–0.82) are inherited from seawater. The homogenization temperature and salinity of primary fluid inclusions range from 180.7 to 474.3°C and from 2.24 to 12.85 wt% NaCl, respectively, which suggests that intermediate- to high-temperature hydrothermal fluids and seawater contributed to the formation of the HIBIFs. The Eu/Sm and Sm/Yb ratios in BIFs are between the values of hydrothermal fluids and seawater. In summary, all geological and geochemical data suggest that the HIBIFs are a post-great oxidation event iron formation pulse at the end of the Ediacaran period. However, this is actually not similar to Neoproterozoic syn-glacial iron formations. Instead, this is a new occurrence of iron formation in an overlooked/understudied time period when either global or local conditions were conducive to iron deposition. The iron deposition on Hormuz Island does not appear to be triggered by fluctuating atmospheric oxygen or sea-level variations, but instead may be related to syn-basinal volcanism in the active continental rift margin environment in anoxic submarine condition. Thematic collection: This article is part of the Geochemical processes related to mined, milled, or natural metal deposits collection available at: https://www.lyellcollection.org/topic/collections/geochemical-processes-related-to-mined-milled-or-natural-metal-deposits

Marine Geological Studies of the Bay of Naples (Southern Tyrrhenian Sea, Italy): Revised Applications of the Seismo-Stratigraphic Concepts and Evolving Technologies to a Late Quaternary Volcanic Area

Marine geological studies of Naples Bay are discussed and reviewed, focusing on the application of the seismo-stratigraphic concepts to a Late Quaternary volcanic area. The Naples Bay represents an active volcanic area in which the interactions between volcanic and sedimentary processes controlled a complex stratigraphic architecture during the Late Quaternary period. While the volcanic processes took place in correspondence with the activity of the Somma–Vesuvius, Campi Flegrei Ischia, and Procida volcanic complexes, the sedimentary processes were controlled by the fluvial processes in the Sarno-Sebeto coastal plain and by the tectonic uplift in correspondence with the Sorrento Peninsula’s structural high Key geophysical and stratigraphic studies of the three active volcanic complexes are revised and discussed. The seismo-stratigraphic concepts applied in the geological interpretation of seismic profiles of Naples Bay are reviewed and discussed: here, the classical concepts of seismic and sequence stratigraphy have been successfully applied, but only partly, due to the occurrence of several buried volcanoes and volcanic seismic units and tephra layers, calibrated by gravity cores.

Estimation of groundwater recharge from groundwater level fluctuations and baseflow rates around Mount Meru, Tanzania

Estimating groundwater recharge, direct runoff and baseflow is essential for understanding groundwater resource availability and managing groundwater systems. This study estimates groundwater recharge, direct runoff and baseflow on two slopes of Mount Meru: the northern and southern slopes using the water-table fluctuation (WTF) method and baseflow separation technique. High-frequency groundwater level measurements in five shallow wells over three hydrological years from 2018 to 2021 were analysed, while streamflow data in four gauging stations over nine hydrological years from 2010 to 2019 were used. The results of the WTF method show that the aquifer undergoes an average recharge of 544 mm/year and 90 mm/year on the south-western and north-eastern slopes, respectively. On average, this recharge is about 53% and 13% of the annual rainfall on each slope. The baseflow results show that the aquifer on the south-eastern and north-western slopes recharges an average of 88 mm/year and 54 mm/year, respectively, which is on average about 12% and 7% of annual rainfall, respectively. In general, the high recharge on the south-western slope is attributed to the high rainfall, and the high hydraulic conductivity and high hydraulic diffusivity of the pyroclastic deposits compared to the debris avalanche deposits on the north-eastern slope. In addition, debris avalanche deposits show homogeneous recharge conditions, while pyroclastic deposits show heterogeneous recharge conditions. The WTF method can be useful to identify areas of preferential recharge so that preferential groundwater flow paths can be mapped for focused recharge of surface runoff during the rainy season.

Insights on the Permian tuff beds from the Saint-Affrique Basin (Massif Central, France): an integrated geochemical and geochronological study

The Permian marks the transition between the end of the accretion of the supercontinent Pangea and the beginning of its dislocation. In the Eastern Pangea intertropical domain (i.e. the present-day Western Europe), the late-Paleozoic (i.e. uppermost Carboniferous–Permian) history remains poorly constrained due to the lack of precise radiometric data. This is particularly true for Permian basins from the southern part of the French Massif Central, making it difficult to determine correlations between basins and therefore robust timings and constraints on the environmental and climate events described in these basins, and to compare them with the larger-scale settings. This article focuses on the Saint-Affrique Basin, via an integrated petrological, geochemical and geochronological study of eight of the volcanic-ash levels interbedded in the sedimentary succession. It highlights the existence of two different groups of felsic volcaniclastic rocks. The first group, located at the base of the basin and attributed to the Stephanian continental stage, is related to a late-orogenic volcanic setting and corresponds to calc-alkaline trachy-andesitic tuffites that could not be dated due to the lack of volcanic zircon. The second group, located towards the top of the succession, is composed of calc-alkaline dacitic ash beds and tuffites yielding Kungurian ages, i.e. late early Permian (Cisuralian, 283.5±0.6 to 273.01±0.14Ma), and are attributed to a post-orogenic deposition setting. These ages show that the sedimentary filling of the basin is younger than hitherto expected (i.e. Artinskian, 290.1±0.26 to 283.5±0.6Ma). The elemental geochemistry, the presence of inherited detrital zircons and the Hf signatures of the volcanic ones indicate the involvement of an old (Proterozoic and older) basement in the magma genesis; this crustal contribution becomes more prominent towards the top of the sedimentary succession.

Radiocarbon dating, eruptive dynamics, and hazard implications of four Holocene Plinian-type eruptions recorded in Manizales city, Colombia

Urban centers settled under the influence of volcanic activity are common in the Colombian Andes, particularly those such as Manizales city (ca. 400,000 inhabitants) and other smaller towns on the western flank of the Central Cordillera. Several pumice-rich tephra layers widely dispersed beneath the city suggest multiple Plinian-type eruptions have occurred nearby. From this geological record, the four youngest, thickest, and most persistent layers in the region are the most representative of this activity. This work uses mapping, physical descriptions, radiocarbon dating, and calculation of physical parameters to: (1) define and characterize the tephra sequence, (2) determine the age of the eruptions, (3) define the source and eruptive dynamics associated with each of the events, and (4) give insights into the volcanic hazard for Manizales city. The deposits were named in this study as Lower Manizales (Lm), Middle-lower Manizales (Mlm), Middle-upper Manizales (Mum) and Upper Manizales (Um) tephra layers, together forming the “Manizales tephra sequence”. Mapping of the deposits revealed the lower layer originated from the little known Plazuela volcano (~ 15 km east of Manizales), while the others originated in the Cerro Bravo volcano (~ 25 km east of Manizales). The radiometric analysis indicates that the lowest tephra layer originated at 7879.5 ± 55.5 cal. years BP, while the three overlying layers were deposited at 7730 ± 55 cal. years BP, 5294 ± 19 cal. years BP, and 2759 ± 20 cal. years BP. All of these deposits were formed by Plinian-type eruptions, with column heights varying between 18 and 29 km. The minimum tephra volume emitted by each eruption was between 0.21 and 0.38 km3, and the emission rate 21.6 × 107 kg/s for the Lm layer, 3.38 × 107 kg/s for the Mlm layer, 6.27 × 107 kg/s for the Mum layer, and 5.16 × 107 kg/s for the Um layers. The results suggest that the region is strongly threatened by pyroclastic falls associated with several active volcanoes located in the Central Cordillera.

Extending the mid-18th century eruptive record of the Cordón Caulle Volcanic Complex (40,5° S) through the study of three lake sedimentary sequences

The research focuses on the characterization of a tephra level extracted from sedimentary sequences obtained from three lacustrine environments from the northern Patagonia Andean range to define the volcano of origin. The dating of the tephra level corresponds to the mid-18th century but there is no scientific record nor geological evidence of this event. The sediment sequences were collected from lakes Nahuel Huapi, Moreno Oeste, and Tonček, in northern Patagonia, located downwind from the Cordón Caulle Volcanic Complex (CCVC), the potential source, at 45, 86, and 95 km respectively. These environments are frequently impacted by tephra falls from different sources in the Southern Volcanic Zone. Particle morphology, glass and mineral chemistry, together with textural analysis, provided a detailed characterization of the tephra layer recovered at each site. This characterization allowed the association of the tephra material with the CCVC predominantly, with minor Osorno volcano contributions. Historical records of both volcanic systems included eruptions in the mid-18th century (1759 CE and 1752–1796 CE, respectively). Hence, the characterization and the comparison with historical records of volcanic eruptions let us conclude that the tephra is composed of materials dispersed by CCVC in the nearby lakes, whereas contributions from Osorno volcano are observed in environments to the south of the study site, during the mid-18th century. The study demonstrates the potential of this type of detailed characterization in lake sequences to develop and support increasing research on historical volcanic records, helping to improve the knowledge of the volcanic hazard of a region.

Discovery of Pseudomorph Scapolite and Diagenetic Indication from the Permian Volcaniclastic Rocks in Western Sichuan (SW China)

Volcaniclastic rocks are important unconventional oil and gas reservoirs from which it is difficult to determine the protolith due to strong metasomatic alteration. Intensive alteration has occurred in much of western China, but few robustly documented examples are known from which to assess the alteration processes. Further recognition from the petrological and mineralogical record is essential to quantify the diagenetic environment, the degree of alteration, and its impacts. Permian volcanic rocks are widely developed in the western Sichuan Basin (southwestern China), with a thickness of more than 200 m. The thickness of volcaniclastic rocks in the Permian Emeishan Basalt Formation is up to 140 m, with a 5600~6000 m burial depth. In this study, we demonstrate an approach to recognizing hydrothermal alteration by the occurrence of scapolite megacryst mineral pseudomorphs (SMMPs) in Permian volcaniclastic rocks in the Sichuan Basin (southwestern China). The results show that SMMPs in the Permian volcaniclastic rocks in the western Sichuan Basin mainly occur in the lower part of the Permian basalts as intragranular minerals and rock inclusions. Scapolite is transformed into quartz and albite, and only the pseudomorph is preserved, indicating secondary hydrothermal fluid metasomatic alteration. Scapolite is formed after microcrystalline titanite and is the product of the high-temperature pneumatolytic metasomatism of plagioclase from the mafic protolith during the post-magmatic stage. The mixing of meteoric water and barium-rich hydrothermal fluid leads to the precipitation of barite; additionally, the pores are filled with barite and halite after the alteration of scapolite. The silicification and hydrothermal dissolution of scapolite and the albitization of sodium-rich matrix minerals increase the pore volume, which is conducive to the later recharge by hydrothermal fluids. The discovery of SMMPs can serve as an indicator of the high-temperature pneumatolytic metasomatism and mixing of meteoric water and deep hydrothermal fluid.

Geologic evidence that volcanic lightning promotes life on Earth

Large quantities of fixed nitrogen found in ash and pyroclastic deposits confirm suspicions about a likely source of life’s earliest building blocks.

Geochronology and geochemistry of the Gréixer rhyolitic caldera complex: Implications on Permo-Carboniferous magmatism (South-Central Pyrenees, NE Spain)

The Gréixer Rhyolitic Complex is one of the most important manifestations of the post-Variscan Permo-Carboniferous volcanism of the Catalan Pyrenees. This volcanic complex is represented by a > 800 m thick, > 12 km wide, intra-caldera succession, mostly composed of strongly-welded, lava-like rheomorphic rhyolitic pyroclastic rocks. Previous studies have attributed a Lower Permian age to this caldera complex and interpreted it as having resulted from the gravitational collapse of a central volcanic edifice after a large-volume explosive event, mostly represented by widespread extra-caldera pyroclastic deposits (the Castellar de n'Hug Ignimbritic Member), which was radially emplaced from the caldera structure. However, new stratigraphic, structural, geochemical, and geochronological data reveal that this co-genetic relationship between the inferred intra- and extra-caldera deposits does not exist. On the contrary, each of these two successions of pyroclastic deposits resulted from a different volcanic event, which had occurred within a time span of 15 Ma. Moreover, the geochemical signature of these volcanic rocks shows a different magma source for each case, with a clear crustal origin for the Gréixer Rhyolitic Complex and a mixed mantle-crustal origin for the Castellar de n'Hug Ignimbrite Member. The apparent stratigraphic correlation between both successions is the result of the Alpine tectonics, which put together different late and post-Variscan Permo-Carboniferous rocks that had originated in different areas and at different times.