Journal of Volcanology and Geothermal Research最新文献

{"title":"Interflow and intraflow boles, and potential pitfalls in bole-based geology and stratigraphy of continental flood basalts","authors":"Hetu Sheth ,&nbsp;Anmol Naik ,&nbsp;Janisar M. Sheikh ,&nbsp;Alok Kumar","doi":"10.1016/j.jvolgeores.2025.108460","DOIUrl":"10.1016/j.jvolgeores.2025.108460","url":null,"abstract":"<div><div>Boles are weathered, clayey to silty horizons separating successive continental flood basalt (CFB) lava flows. They are found in many CFB provinces, being exceedingly common in the Deccan Traps. Most commonly red, but also often in brown, orange, green and other colours, boles are commonly viewed as “interflow” beds that formed between CFB eruptions. However, whereas some boles can be palaeosols developed on weathered flow tops, indicating an eruptive hiatus, they can also be alteration products of volcanic ash beds, interflow sediments, glassy tops and bases of basalt flows, and flow-top and flow-bottom breccias of rubbly pāhoehoe and ‘a‘ā lava flows. Individual boles may form by one or more of these mechanisms, and we show examples of these. More important, we present varied evidence that even many interflow boles have formed <em>after</em> their overlying flows, out of sequence, with some boles forming long after the entire CFB event. A fundamental principle of geology – the principle of superposition – would be incorrect when applied to these boles. Many interflow boles, contrary to their standard interpretation, do not represent eruptive breaks. Adding to the complexity, we show that many boles have formed <em>within</em> individual CFB lava flows. We present examples of such “intraflow” boles, formed as altered glassy rinds of small-scale compound pāhoehoe lobes, between the entablature and colonnade tiers of sheet lobes, within the entablatures of sheet lobes, within the massive cores of sheet lobes (sometimes more than one boles), and in random (including subvertical) orientations within sheet lobes. Our new observations highlight the complexity of boles, and the potential pitfalls in bole-based interpretations of CFB geology and stratigraphy. Alteration of volcanic glass to palagonite (hydrated glass), and further to clay minerals, is the key process in bole formation, whether interflow or intraflow.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"469 ","pages":"Article 108460"},"PeriodicalIF":2.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145468848","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Magmatic plumbing system through shallow sills characterization in a sector of Guaymas rift basin, Gulf of California","authors":"Cristian Alejandro Gallegos-Castillo,&nbsp;Mario González-Escobar,&nbsp;Antonio González-Fernádez","doi":"10.1016/j.jvolgeores.2025.108499","DOIUrl":"10.1016/j.jvolgeores.2025.108499","url":null,"abstract":"<div><div>We interpret eleven two-dimensional multichannel seismic reflection profiles across the Northern Trough of the Guaymas Basin, grouped into three sectors: north, intermediate, and south. Using seismic facies and geometry, we map and correlate sills across adjacent seismic profiles. Three intrusion series are defined in the north and intermediate sectors (deep, middle, and shallow), and a 3D visualization derived from the 2D interpretations is used to illustrate spatial distribution and emplacement trends. In the north sector, located toward the northwest, deep sills redistribute magma upward into the shallow series, together with intrusive series that enter from the northeast and are interpreted to be associated with the Guaymas Transform Fault. Emplacement steps upward and propagates toward the southwest, and there is an increase in shallow-series emplacement along the northwest–southeast direction toward the axial trough, although coverage limits prevent tracking this trend farther. In the intermediate sector, southeast of Isla Tortuga, two intrusive series converge from opposite directions: one from the northeast margin, likely related to the transform system, and one from the southwest, likely from the Isla Tortuga side. Petrographic inspection and whole-rock geochemistry of IODP Expedition 385 sills from Guaymas basin, compared with Isla Tortuga lavas, reveal comparable inherited anomalies consistent with an arc-derived parental magma, suggesting that the island and basin sills may be connected in the subsurface by a common plumbing system. Along the axial system, long complexes of shallow intrusions are more common toward the northwest, whereas deeper and larger intrusions occur toward the southeast. This contrast matches sector-scale differences in sediment delivery, with thicker terrigenous input favoring deeper emplacement, and thinner cover favoring shallower levels. Finally, the close spacing of profiles in the north sector enabled sill correlation and definition of a coherent, stepped emplacement pattern; in the intermediate sector, the shorter lateral extent of individual bodies limited correlation across adjacent 2D profiles, but the emplacement trend could still be tracked, clarifying the magmatic plumbing architecture of the Northern Trough.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"469 ","pages":"Article 108499"},"PeriodicalIF":2.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145618214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Empirical drag coefficients for in-flight volcanic bombs: A novel application of aerospace techniques to volcanic hazards","authors":"A. Sork ,&nbsp;P. Kreit ,&nbsp;D. Banerjee ,&nbsp;M. Sellier ,&nbsp;B. Kennedy ,&nbsp;L. Watson ,&nbsp;R. Fitzgerald ,&nbsp;F. McIntyre ,&nbsp;K. Tsunematsu","doi":"10.1016/j.jvolgeores.2025.108484","DOIUrl":"10.1016/j.jvolgeores.2025.108484","url":null,"abstract":"<div><div>Volcanic ballistic projectiles (VBPs) are a dangerous near-vent hazard. Physics-based models are often used to estimate potential impact locations to help reduce risk to nearby people and environment. Drag is an essential model component, but many VBPs, especially molten VBPs (bombs), are irregular in shape and their drag behaviour has not previously been quantified.</div><div>We measure 3D-printed models of in-flight Strombolian bomb shapes in a wind tunnel to quantify drag effects in terms of drag coefficient (C_D) and Reynolds number (<em>Re</em>). Tests were performed on static models across increasingly oblique angles to the air flow, and on dynamically rotating models across increasing spin frequencies. The model size and air speeds tested here correspond with <em>Re</em> values 9.3 × 10⁴ to 1.2 × 10⁶, encompassing the laminar-turbulent flow transition into the supercritical <em>Re</em> regime (which occurs at ∼2.5 × 10⁵ for spheres).</div><div>We find rounded and bilobate shapes have distinctly different drag behaviour. The C_D of bilobate shapes varies significantly with changes in orientation (0.29-0.41 head-on, 0.64-0.88 broadside). The C_D of rounded shapes varies little with changes in orientation (0.2-0.4 head-on, 0.33-0.44 broadside), lower than the range for bilobate shapes at both head-on and broadside. The average C_D of a rotating model approaches its broadside static C_D. We compare results to in-flight observations where spin is commonly observed and conclude that the broadside C_D is most applicable for use in scenario modelling. For Strombolian VBPs at supercritical Reynolds number, we therefore recommend a C_D range of 0.33-0.88 and propose a new methodology for physics-based models which accounts for relationships between size, shape, Reynolds number, and C_D.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"469 ","pages":"Article 108484"},"PeriodicalIF":2.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145428793","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Emplacement mechanism of volcanic debris avalanche deposits: Insight from inter- and intrablock-matrix characterization at Quevar Volcanic complex, Argentina","authors":"E. Bustos ,&nbsp;G. Norini ,&nbsp;M. Arnosio ,&nbsp;W. Báez ,&nbsp;L. Capra","doi":"10.1016/j.jvolgeores.2025.108494","DOIUrl":"10.1016/j.jvolgeores.2025.108494","url":null,"abstract":"<div><div>Compound volcanoes are inherently unstable landforms prone to recurrent collapses driven by both internal and external factors, undergoing multiple failure -regrowth episodes during their evolution. While large-scale collapses dramatically reshape volcanic landscapes, small-volume events also play a key role in modifying volcanic morphology. The Quevar 1 deposit, located in the Quevar Volcanic Complex (Argentine Puna), represents a small-scale volcanic debris avalanche deposit (VDAD) formed by the gravitational collapse of an unaltered dacitic lava dome. This study combines digital elevation model (DEM) analysis, granulometry, and scanning electron microscopy to reconstruct the emplacement dynamics of Quevar 1. The deposit is monolithological, composed exclusively of Quevar Dacite, and displays features typical of a rock rotational slide evolving into a debris avalanche, including a curved main scarp, and abrupt confinement against paleotopography, consistent with a short-runout collapse likely triggered by post-eruptive seismic shaking. Grain-particle variations indicate shear-driven particle segregation. The axial zone has a smaller mean particle size, poorer sorting, higher matrix content, and the smallest maximum block size. Voids indicate high-velocity point-to-point impacts, possibly linked to higher axial velocities, with subtle scratches and fractures. The marginal zone is characterized by larger clasts and better sorting. In this area and in the basal region fractures, lips, striations, staircase geometry reflect lateral friction at the margins and base, indicating prolonged particle–particle interactions under a frictional-elastic regime and high stress. The Interblock matrix shows greater transport influence, whereas the intrablock matrix preserves confined shear and in situ fragmentation. The absence of hydrothermal alteration, pyroclastic deposits, and water-related facies, combined with morphological evidence, supports interpretation of Quevar 1 as a structurally controlled slope failure, dominated by gravitational forces. These findings underscore the diversity of failure mechanisms in composite volcanoes and emphasize the importance of tectonic triggers in generating small-scale VDADs.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"469 ","pages":"Article 108494"},"PeriodicalIF":2.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145571554","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Time–Frequency characterization of microearthquakes based on Convolutional Neural Networks and explainability models","authors":"Fernando Lara ,&nbsp;Román Lara-Cueva ,&nbsp;Felipe Grijalva ,&nbsp;Ana Zambrano","doi":"10.1016/j.jvolgeores.2025.108485","DOIUrl":"10.1016/j.jvolgeores.2025.108485","url":null,"abstract":"<div><div>Given the potential destructiveness of volcanic eruptions, the study of volcanic microearthquakes is a key tool for improving our understanding of the relationship between a volcano and its environment. In the last decade, Convolutional Neural Networks (CNN) have shown great potential for the automatic classification of microearthquakes. However, one major limitation is their “black box” nature, it is often unclear which features drive their decisions. In this work, we propose the use of Explainability Models in conjunction with CNNs and two novel Time–Frequency representations: Adaptive Superlets (ASLT) and Spectrogram-based Periodogram with Window Switching (SPWS). The aim of this paper is to extract the Time–Frequency features leveraged by CNNs for microearthquake classification. This could be used to increase the reliability of CNN-based recognition systems and to identify possible new Time–Frequency characteristics that identify microearthquakes. This proposal verifies the frequency bands for Long Period (LP), Volcano Tectonic (VT), Tectonic (TC), and Tremor (TR) microearthquakes. Moreover, this could be useful for identifying frequency components that can be used to distinguish between LP and VT events and to determine the starting point of overlapping events within the same detection window.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"469 ","pages":"Article 108485"},"PeriodicalIF":2.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145520680","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Remote sensing of surface thermal anomalies on the Reykjanes Peninsula, SW-Iceland from 2016 to 2023, preceding and coinciding with recent volcanic unrest","authors":"P. Muanza ,&nbsp;I. Jónsdóttir ,&nbsp;T. Thórdarson ,&nbsp;G. Einarsson ,&nbsp;S. Kristinsson","doi":"10.1016/j.jvolgeores.2025.108482","DOIUrl":"10.1016/j.jvolgeores.2025.108482","url":null,"abstract":"<div><div>This study investigates geothermal surface activity across four of the six recognized geothermal systems on the Reykjanes Peninsula in southwest Iceland Reykjanes, Krýsuvík, Miðdalur, and Grændalur using satellite-derived Land Surface Temperature (LST) data from Landsat 8 and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) spanning 2016 to 2023. These sites were selected to represent diverse geothermal behaviors and to maximize temporal data availability under cloud-free conditions. Thermal imagery was acquired from consistent seasonal windows each year to reduce the effects of atmospheric and solar variability. The temporal and spatial evolution of thermal anomalies was analyzed to monitor surface-level geothermal changes, with anomalies defined relative to site-specific thermal baselines. In addition, Moderate Resolution Imaging Spectroradiometer (MODIS) data and ground-based temperature measurements including drone thermal imagery were used at selected sites to validate the satellite-derived LST, enhancing the overall reliability of the findings. Results show heterogeneous thermal responses across the four fields: Reykjanes exhibits persistent LST anomalies potentially linked to shallow magmatic inputs and anthropogenic geothermal operations; Krýsuvík shows episodic thermal peaks coinciding with recent periods of regional volcanic unrest; while Miðdalur and Grændalur display gradually declining thermal signatures and shrinking anomaly extents. These patterns are interpreted as indicative of varying geothermal dynamics and system maturity. The study demonstrates the effectiveness of integrating multi-sensor remote sensing with field validation for long-term geothermal monitoring in tectonically active regions and highlights the importance of interannual consistency and baseline referencing in detecting subtle geothermal changes.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"469 ","pages":"Article 108482"},"PeriodicalIF":2.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145468681","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Volatile emissions from Deccan volcanic eruptions and their effects on climate across the K-Pg boundary","authors":"Ritwick Sen ,&nbsp;Margherita Polacci ,&nbsp;Margaret Hartley ,&nbsp;Mike Burton ,&nbsp;Saibal Gupta","doi":"10.1016/j.jvolgeores.2025.108493","DOIUrl":"10.1016/j.jvolgeores.2025.108493","url":null,"abstract":"<div><div>The Deccan Volcanic Province (DVP) hosts approximately one million km³ of basaltic lava, emplaced over a period of about one million years across the Cretaceous-Palaeogene (K-Pg) boundary associated with the major extinction event ∼66 Ma ago. This review synthesises the current state of knowledge of DVP pre-eruptive magmatic volatile (H₂O, CO₂, S, Cl, F) contents gleaned from direct measurements of melt inclusions, trace element proxies, and equilibrium melt calculations. Most direct volatile measurements are from Western Ghats tholeiites, with limited data available for the minor picritic, alkaline, carbonatitic, and silicic lithologies across other DVP sub-provinces. Western Ghats eruption geochronology and palaeotemperature trends across the K-Pg boundary suggest that the peak in lava extrusion rate was decoupled from the phase of maximum volatile emissions. Resolving this temporal incongruence will require improved constraints on magma volatile contents; emission timelines and fluxes; the extent of stratospheric injection; and passive emissions from magmatic intrusions; as well as geochronological and volumetric data across different DVP formations and sub-provinces. Volatile emissions from DVP eruptions induced sustained climatic perturbations lasting ∼1 Myr across the K-Pg boundary, in contrast to the temporally constrained abrupt changes triggered by the Chicxulub impact at the K-Pg boundary. We outline the outstanding challenges in deploying geochemical approaches to obtain DVP magma volatile contents, and offer potential future directions to estimate the climatic impact of DVP eruptions.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"469 ","pages":"Article 108493"},"PeriodicalIF":2.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145571552","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Seismic activities at Kikai Caldera, Japan, detected using distributed acoustic sensing via seafloor telecommunication cables","authors":"Masaru Nakano ,&nbsp;Tomoya Nakajima ,&nbsp;Eiichiro Araki ,&nbsp;Hiroko Sugioka ,&nbsp;Aki Ito ,&nbsp;Hiroyuki Matsumoto ,&nbsp;Takashi Yokobiki ,&nbsp;Takashi Tonegawa ,&nbsp;Shigeaki Ono","doi":"10.1016/j.jvolgeores.2025.108498","DOIUrl":"10.1016/j.jvolgeores.2025.108498","url":null,"abstract":"<div><div>Kikai Caldera, located south of Kyushu Island, Japan, experienced a devastating eruption at 7.3 ka, and volcanic activities have continued at volcanic islands located on the caldera rim. Recent surveys have revealed that the huge lava dome situated at the center of the caldera formed after the 7.3 ka eruption. However, the current activities of the caldera are not well understood because of the difficulties in monitoring submarine volcanoes. Seismic observations obtained using distributed acoustic sensing (DAS) could resolve this issue. DAS can realize real-time seafloor seismic observations by using seafloor fiber-optic cables. We carried out seismic observations around Kikai Caldera using DAS via existing telecommunication cables connecting the islands around the caldera rim. We determined the hypocenters of detected earthquakes by semblance analysis of DAS strain records. Because the waveforms were not well coherent even for DAS observations at a channel spacing of about 50 m, we used the envelope of strain records to compute the semblance. Some of the earthquakes were located beneath the caldera dome at depths between 0 and 15 km. This finding implies that volcanic activity is ongoing beneath the caldera, but there is no immediate sign of an impending eruption because of the small number of detected events. Continuous observations using DAS are crucial for monitoring the activity of such remote volcanoes on the seafloor.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"469 ","pages":"Article 108498"},"PeriodicalIF":2.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145618213","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"One eruption, three separate vent areas: The case of the La Alberca-Joya Blanca monogenetic complex, Valle de Santiago area, Michoacán-Guanajuato Volcanic Field (Mexico)","authors":"Elizabeth Rangel-Granados ,&nbsp;Juan Enrique Suárez-Jiménez ,&nbsp;Claus Siebe ,&nbsp;Nanci Reyes-Guzmán ,&nbsp;Marie-Noëlle Guilbaud ,&nbsp;Mélida Pilar Schliz-Antequera","doi":"10.1016/j.jvolgeores.2025.108495","DOIUrl":"10.1016/j.jvolgeores.2025.108495","url":null,"abstract":"<div><div>The La Alberca-Joya Blanca monogenetic complex is located in the Valle de Santiago area of the Michoacán-Guanajuato Volcanic Field, within the Trans-Mexican Volcanic Belt. Field, stratigraphic, geochronological, petrographic, and geochemical evidence reveals that the complex formed ∼22,000 yr B.P. during a brief single eruptive period that involved magmatic, phreatic, and phreatomagmatic activity at three distinct vent areas. The erupted magma was basaltic trachy-andesitic and ascended through secondary fractures associated with the NNW-SSE-trending Tzitzio-Valle de Santiago fault zone. The eruption began at two vent areas (Vents #1 and #2), aligned E-W and located 1.6 km apart. Vent #1 produced Hawaiian-Strombolian activity that formed scoria-spatter mounds and lava flows (La Alberca mounds). At Vent #2, the eruption began with a phreatic phase that generated a mud deposit, which was followed by Hawaiian-Strombolian eruptions that built a scoria-spatter cone and emitted lava flows (La Alberca cone). While both vent areas remained active, new activity took place at a third vent (Vent #3) located 1.6 km south of Vent #1. At this site, phreatomagmatic explosions formed a tuff cone (Joya Blanca), driven by interactions between ascending magma and a shallow perched aquifer hosted within Middle Pleistocene lava flows. As the external water source was depleted, the eruption shifted to a Strombolian phase that produced a scoria mound located within the tuff cone's crater. Then, activity at Vents #1 and #3 ceased, and eruptive focus moved back to Vent #2, where the initially magmatic eruption that was building the La Alberca cone transitioned into a brief but intense phreatomagmatic phase, leading to the formation of a maar (Joya La Alberca) in approximately 4 to 10 days. This phreatomagmatic activity was sustained by groundwater sourced from a highly permeable fractured aquifer hosted within the same Middle Pleistocene lava flows. This final phreatomagmatic phase involved a relatively small magma volume (1.2–1.9 × 10⁶ m³) and required a groundwater flux ranging from 0.6 to 1.8 m³/s to achieve a water/magma ratio of 0.1–0.3. Such a flux correlates with cold and humid climatic conditions prevailing during the Late Pleistocene in the Valle de Santiago region, when annual precipitation was over 1000 mm.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"469 ","pages":"Article 108495"},"PeriodicalIF":2.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145571553","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Insights into the petrogenesis of alkalic, shonkinitic magmas from the Adel Hill Volcanic Field, Montana","authors":"C.L. McLeod ,&nbsp;M.L. Lytle ,&nbsp;T.J. Cracas ,&nbsp;K.L. Brown ,&nbsp;B.J. Shaulis ,&nbsp;M. Loocke","doi":"10.1016/j.jvolgeores.2025.108496","DOIUrl":"10.1016/j.jvolgeores.2025.108496","url":null,"abstract":"<div><div>Shonkinites are rare alkali-rich igneous rocks found in the geological record from the Precambrian to the Eocene. This study investigates the Upper Cretaceous shonkinites from the Adel Hills Volcanic Field (AHVF), central Montana. The AHVF shonkinites are porphyritic with large, euhedral to subhedral phenocrysts of diopside that exhibit sector zoning. Other major mineral phases include plagioclase, sanidine, and secondary zeolites. Minor and accessory phases identified with SEM-EDS include magnetite, apatite, rare ilmenite and pyrite, and secondary calcite. Bulk rock SiO₂ ranges from 47 to 49 wt% with Na₂O + K₂O varying from 5.50 to 7.34 wt% within that silica range. Normalized bulk trace elements indicate LILE enrichment and Nb<img>Ta depletion, consistent with a volcanic arc setting. Bulk rock, diopside, and apatite chondrite-normalized REE signatures collectively exhibit a limited range of Eu anomalies (Eu/Eu* from 0.92 to 1.33). High-resolution elemental mapping of sector-zoned diopsides reveals that Si and Mg-enrichment is accompanied by Al, Ti, Na, and Cr-depletion within {−111} faces. In symmetrically equivalent prism sectors, Al, Ti, Na, and Cr enrichment with correlated depletions in Si and Mg is documented. This is interpreted to result from low degrees of undercooling during crystallization (ΔT = 13-25 °C). The lack of dendritic patterns at the Al sector boundaries further supports this. Apatite trace element chemistries are consistent with crystallization from mafic, alkali-rich melts while accompanying Ce/Ce* vs. Eu/Eu* systematics are consistent with formation in a hydrous, moderately oxidizing magmatic environment in which plagioclase crystallization was suppressed. Petrogenesis of the AHVF shonkinites is inferred to have occurred in a contractional tectonomagmatic setting in which variably metasomatized, heterogeneous mantle lithosphere experienced low degrees of partial melting. This occurred prior to the collapse of the Cordilleran fold and thrust belt and subsequent lithospheric extension in the middle Eocene-early Miocene.</div></div>","PeriodicalId":54753,"journal":{"name":"Journal of Volcanology and Geothermal Research","volume":"469 ","pages":"Article 108496"},"PeriodicalIF":2.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145618216","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}