Shallow Magma Reservoir Research Articles

Pulsatile extractions of Lower Cretaceous silicic volcanic plumbing system beneath the Baiyunzhang and Lianhuashan basins, eastern Guangdong: silicic magma evolution and related mineralization

Highly differentiated magmas are closely related to the formation of tin deposits. The Lianhuashan Basin and Baiyunzhang Basin, surrounded by multiple coeval tin deposits, developed various types of volcanic and subvolcanic rocks. The diagenetic connections between different types of rocks within the two basins provide new insight into the evolution of the silicic magma systems and the impact of highly differentiated magmas on tin mineralization. Both basins have consistent zircon U–Pb ages (143–138 Ma) and similar whole-rock Nd isotopes ( ε Nd ( t ) = −5.7 to −3.4) and zircon Hf–O isotope ranges ( ε Hf ( t ) = −9.0 to −2.5; δ 18 O = 5.1–7.9), suggesting that both basins originate from the same deep-level magma reservoir, followed by different degrees of crystal differentiation and several episodes of crystal–melt separation in their respective shallow-level magma reservoirs. The multiple pulses of magma extraction eventually produced different volcanic rocks (granite porphyry and rhyolite porphyry), whereas the remaining crystal mush consolidated in situ to form quartz monzonite porphyry. Further studies show that the tectonic regime changed from a compressive to an extensional environment at c . 140 Ma. Consequently, mantle-derived magmas with low oxygen fugacity injected shallow magma reservoirs that were able to evolve to a high degree of differentiation through multiple recharge, thus favouring the formation of the Sn deposit.

Satellite Geodesy Unveils a Decade of Summit Subsidence at Ol Doinyo Lengai Volcano, Tanzania

AbstractThe processing of hundreds of Synthetic Aperture Radar (SAR) images acquired by two satellite systems: Sentinel‐1 and COSMO‐SkyMed reveals a decade of ground deformation for a ∼0.5 km diameter area around the summit crater of the only active carbonatitic volcano on Earth: Ol Doinyo Lengai in Tanzania. Further decomposing ascending and descending orbits when the appropriate SAR data sets overlap allow us to interpret the imaged deformation as ground subsidence with a significant rate of ∼3.6 cm/yr for the pixels located just north of the summit crater. Using geodetic modeling and inverting the highest spatial resolution COSMO‐SkyMed data set, we show that the mechanism explaining this subsidence is most likely a deflating very shallow (≤1 km depth below the summit crater at the 95% confidence level) magma reservoir, consistent with geochemical‐petrological and seismo‐acoustic studies.

Changes in the magmatic plumbing system associated with the Gotemba sector collapse at Mount Fuji, Japan

It is well known that magmatic plumbing systems change over time, but there is much debate as to why and how. We studied volcanic ejecta continuously deposited in an outcrop at Kagosaka Pass at the eastern base of Mount Fuji to investigate the factors responsible for changes in the magmatic plumbing system. The sample consisted of pyroclastic sediments from explosive eruptions for approximately 3000 y, which sandwiched the time of the Gotemba sector collapse at approximately 2500 BP. Chemical analyses of whole rocks, minerals, and matrix glasses, as well as mode measurements of glass and bubbles, were performed on samples collected from approximately 30 layers; significant changes were observed before and after the collapse. For example, before and after the collapse, matrix glass area increased around 60% to over 80% and anorthite content (Ca / (Ca + Na) * 100) of phenocryst plagioclase decreased from over 80 to below 65. For a period after the collapse, possibly hundreds of years, the plagioclase and olivine phenocrysts exhibited characteristics indicative of crystallization at low temperatures and pressures, and the pyroclast matrix became highly vitreous. Eruptions with ejecta of these characteristics continued more than a dozen times, lasting about 500 years. In addition, the trend in the distribution of the bulk rock chemical composition changed significantly, showing a differentiation trend with only plagioclase and clinopyroxene crystal separation. An investigation using the MELTS software revealed that the phenomenon of direct eruptions from deep magma chambers to the surface, bypassing shallow magma reservoirs, continued for several hundred years after the collapse. This can be interpreted as a decrease in confining pressure associated with the collapse, facilitating the eruption of magma from the depths. Furthermore, based on an examination of the water content in the magma during this period, we posit that the trigger for the rise of magma from the deep magma chamber of Mount Fuji is the acquisition of excess pressure by the injection of magma from a deeper level.

Precise dating of large flank collapses by single-grain 40Ar/39Ar on pyroclastic deposits from the example of Flores Island (Azores)

Large-scale flank collapses are one of the main hazards associated with the evolution of volcanic islands. Precisely dating such events is critical to evaluate the frequency of destabilization episodes and further assess the triggering mechanism(s) associated with internal and/or external factors, such as volcano dynamics, regional tectonics, and global paleoclimatic changes. Here, we constrain the age of a pumice-rich pyroclastic deposit exposed on the eastern flank of Flores Island (Azores), which we interpret as a co-blast deposit generated by a major flank collapse that destroyed the whole western flank of the former volcanic edifice. Twelve single-grain 40Ar/39Ar analyses, performed on 250–500 µm anorthoclase feldspars (mean K/Ca close to 5) with our high-sensitivity multi-collector NGX mass spectrometer, provide a robust weighted mean age of 1.32 ± 0.01 Ma for this eruption. This new age is consistent with previous K/Ar data bracketing the flank collapse between 1.30 ± 0.04 and 1.18 ± 0.09 Ma, and indicates that this event occurred at the end of the main construction phase of the volcano. The explosion produced pumice-rich layers preceded by a lahar as attested by a polygenetic mudflow deposit underlying the dated deposit. From the geochemistry of lavas erupted just before and after the collapse, we speculate upon the possible role of magmatic processes on flank destabilization. We propose a first hypothesis where differentiation in a shallow magma reservoir could have favored edifice inflation, ground shaking, and flank failure, triggering a decompression-induced violent eruption. Overall, our study shows that high-sensitivity mass spectrometers have now reached analytical performances allowing to measure precisely and accurately ages on relatively small and moderately K-rich single feldspars, which is of the utmost importance for dating heterogeneous blasts and tephra deposits that may have been induced by large-scale flank collapses during the late Quaternary.

Petrological and geochemical insights into the magma plumbing system of the Daliuchong dacite eruption, Tengchong Volcanic Field, SW China

The formation of highly evolved, dacitic magmas has been attributed to various processes, including crystal fractionation, partial melting of overlying crust, and/or assimilation of crustal material into an evolving magma chamber. These processes are undoubtedly primary processes involved in the formation of dacites, but they may not be the only mechanism involved in the formation of high-silica dacites. For instance, mafic magma replenishment has been proposed as an additional mechanism but has not been assessed, and thus, its role has not been well-constrained. The Daliuchong volcano is the result of one of the largest eruptive events within the Tengchong Volcanic Field (TVF) in southwest China during the Early-Middle Pleistocene. Here, we conducted detailed mineral textures, mineral chemistry, and geochemical studies on Daliuchong pyroclastic rocks to explore the pre-eruptive storage conditions and evolution processes of the magma. The Daliuchong pyroclastic rocks are dacitic in composition. The samples show porphyritic textures characterized by phenocrysts of plagioclase, amphibole, clinopyroxene, orthopyroxene, and Fe-Ti oxides. Additionally, two distinct types of glomerocryst are identified: a gabbroic glomerocryst containing plagioclase + clinopyroxene + orthopyroxene ± Fe-Ti oxides assemblage and a dioritic glomerocryst containing plagioclase + amphibole ± pyroxene ± Fe-Ti oxides assemblage. Both phenocryst and glomerocryst show rich micro-textures. The Daliuchong dacite exhibits bulk compositional heterogeneity. Analysis of bulk-rock data suggests that this heterogeneity may arise from both the differentiation of the dacite itself and the injection of mafic magma. The compositional similarity between the Daliuchong dacite and experimentally produced partial melts of metamorphic basalt supports that the Daliuchong dacite was predominantly formed through the partial melting of the mafic lower crust. Thermobarometry estimation indicates that clinopyroxenes with high Mg# crystallized at 560–870 MPa, whereas amphibole and clinopyroxenes with low Mg# crystallized at 185–300 MPa. Based on the observed phase relations and the calculated crystallization conditions, we propose that during the differentiation of the Daliuchong dacite, heterogeneous dacitic magma formed by partial melting accumulated in a deep magma reservoir (21–32 km) before subsequently ascending toward shallower depths. Crystallization of plagioclase, amphibole, Fe-Ti oxides, and small amounts of pyroxene and apatite occurred at a shallower depth (7–10 km). The presence of coarse-sieve texture, fine-sieve texture, and oscillatory zoning with high amplitude in plagioclase suggests intermittent injection of mafic magma into the shallow magma reservoir, with the eruption of dacitic magma occurring after the final mafic magma replenishment. The petrological evidence above advocates that primitive magma replenishment could have been involved in the formation and triggered the eruption of dacite in the Daliuchong volcano.

The magma plumbing system of the potentially hazardous Laoguipo volcano in the Tengchong Volcanic Field, SW China

The Late Pleistocene-Holocene Laoguipo volcano in the Tengchong Volcanic Field (TVF), southwestern China, displays significant geochemical and geophysical anomalies characteristics. Here we present petrographic observations, mineral chemistry, bulk rock geochemistry, thermobarometry, and thermodynamic simulation to evaluate the crystallization conditions and pre-eruptive magmatic processes occurring within the magma plumbing system. This study reveals the existence of two magma reservoirs beneath the Laoguipo volcano. The deep magma reservoir is composed of basaltic trachyandesite (SiO2 = 54–57 wt%), which is located at 15–19 km depths with 1087–1160 °C, 1.5–2 wt% H2O content, oxygen fugacity of ΔNNO+1 (Ni-NiO buffer), melt viscosity of 101.7–102.6 Pa·s, and density of 2.5–2.6 g/cm3. The formation of the deep magma reservoir is attributed to the 31% mass fractional crystallization of primitive basalt in the TVF. The shallow magma reservoir is composed of trachyte (SiO2 = 63–64 wt%), which is located at 6–11 km depths with 780–825 °C, 5.9–6.5 wt% H2O content, oxygen fugacity of ΔNNO+1 (Ni–NiO buffer), melt viscosity of 103.9–104.8 Pa·s, and density of 2.2–2.3 g/cm3. The shallow magma reservoir formed after the basaltic trachyandesite had assimilated 19% mass of the upper crustal material and fractionated 41% mass of the crystals. This study suggests that the shallow trachyte magma reservoir is being heated by the ascending deep basaltic trachyandesite magma, resulting in crystal dissolution, remobilization of crystal mush, and magma convection, which may be the main factors responsible for the geochemical and geophysical anomalies characteristics. The Laoguipo volcano is forming a mature magma plumbing system, which is of significance for forecasting future volcanic eruptions.

Evidence of a Shallow Magma Reservoir Beneath Askja Caldera, Iceland, From Body Wave Tomography

AbstractIn August 2021, Askja caldera switched to reinflation following ∼40 years of continuous deflation that was first measured some 20 years after its last eruption in 1961. Various lines of evidence, including from geodetic modeling, suggest that both the deflation and reinflation events are related to a shallow magma body. To better understand the subsurface plumbing system, we derive P‐wave velocity (Vp), S‐wave velocity (Vs), and Vp/Vs models of the mid‐upper crust by leveraging a new local earthquake traveltime data set. A cylindrical low‐velocity zone, ∼3 km wide and extending to ∼8 km below sea level (bsl), was imaged beneath the caldera. Within it, two distinct lower velocity and higher Vp/Vs anomalies are illuminated, one centered at ∼0.5 km and the other at ∼6 km bsl. The shallower anomaly lies directly beneath the zone of uplift and is likely associated with the current reinflation event.

The Subsurface Structure of the Kīlauea Caldera Before Its 2018 Collapse Inferred From Ground Magnetic, SP, and Temperatures Anomalies

AbstractThe 2018 crisis of Kīlauea volcano stands as a major event in its evolution with a large down‐rift effusive eruption that drained a shallow magma reservoir at the summit. The characterization of such active magmatic systems and associated hazardous events remains a necessity and a challenge. The summit area is hydrothermally active and strongly altered as indicated by geological mapping. A unique data set of geophysical measurements was collected around Halemaʻumaʻu crater before its collapse. Magnetic data are interpreted here in combination with geological information, temperature anomalies at the surface, self‐potential measurements, and a model of electrical conductivity. 3D forward modeling shows that the main magnetic dipole‐like anomaly observed around the crater is not only caused by the crater topography but suggests the presence of an important volume of weakly magnetic material beneath the crater, which may be caused by higher temperature and/or hydrothermal alteration. 3D inversion of the data allows us to explore the first order geometry of the magnetic structures. We complement this inversion with 2D forward modeling in order to refine the geometry of major structures. This study shows the presence of major geological structures in the 2018 collapsed area that may have been associated with mechanical weaknesses and could have played a role in the geometry of the collapse. Therefore, mapping magnetic anomalies and monitoring their temporal evolution are of great interest for constraining the nature and mechanical properties of the underlying formations and their temporal evolution in order to help predict future behavior.

Geophysical imaging of the active magmatic intrusion and geothermal reservoir formation beneath the Corbetti prospect, Main Ethiopian Rift

SUMMARY Silicic volcanic complexes in the Main Ethiopian Rift (MER) system host long-lived shallow magma reservoirs that provide heat needed to drive geothermal systems. Some of these geothermal systems in Ethiopia appear to be suitable for green and sustainable electricity generation. One such prospect is located at the Corbetti volcanic complex near the city of Awassa. High-resolution imaging of the subsurface below Corbetti is of imminent importance, not only because of its geothermal potential, but also due to reported evidence for an ongoing magmatic intrusion. In this study, we present a new subsurface 3-D electrical conductivity model of Corbetti obtained through the inversion of 120 magnetotelluric stations. The model elucidates a magmatic system under Corbetti and reveals that it is linked to a magma ponding zone in the lower crust. Magma is transported through the crust and accumulates in a shallow reservoir in form of a magmatic mush at a depth of $\gtrapprox 4\, {\rm km b.s.l.}$ below the caldera. The imaged extent and depth of the shallow magma reservoir is in agreement with previous geodetic and gravimetric studies that proposed an ongoing magmatic intrusion. Interpreting our model with laboratory-based conductivity models for basaltic and rhyolitic melt compositions suggests that Corbetti is seemingly in a non-eruptible state with ∼6–16 vol. per cent basaltic melt in the lower crust and ∼20–35 vol. per cent rhyolitic melt in the upper crust. With these observations, Corbetti’s magmatic system shares common characteristics with volcanic complexes found in the central MER. Specifically, these volcanic complexes are transcrustal two-stage magmatic systems with magma storage in the lower and upper crust that supply heat for volcano-hosted high-temperature geothermal systems above them. According to the presented subsurface model, a cross-rift volcano-tectonic lineament exerts first-order controls on the magma emplacement and hydrothermal convection at Corbetti. Our study depicts hydrothermal convection pathways in unprecedented detail for this system and helps identify prospective regions for future geothermal exploration. 3-D imaging of both the Corbetti’s magmatic and associated geothermal systems provides key information for the quantitative evaluation of Corbetti’s geothermal energy potential and for the assessment of potential volcanic risks.

Miocene Volcanism in the Slovenský Raj Mountains: Magmatic, Space, and Time Relationships in the Western Carpathians

The Miocene volcanic-intrusive complex in the Slovenský Raj Mountains, middle Slovakia, comprises a swarm of subalkaline basalts and basaltic andesites with alkaline basalts, trachybasalts and basaltic trachyandesites. Basaltic to doleritic feeder dykes and sporadic hyaloclastite lavas are exposed in contact with the Triassic Bódvaszilas Formation of the Silica Nappe. The primary clinopyroxene, plagioclase, and Fe-Ti oxide assemblage also contains calcite spheroids inferred to represent carbonatitic melt. These spheroids are associated with subsolidus chlorite, actinolite, magnetite, titanite, calcite, and epidote. Micropoikilitic clinopyroxene, albite, and Ti-magnetite formed due to rapid quenching. There was an incorporation of host rock carbonate during the eruption. The erupted products are the result of magmatic differentiation of the parental basaltic tholeiitic magma with a redox of ∆QFM = +1 to +3, affected by varying degrees of 0%–50% fractionation and the assimilation of carbonate material in a shallow magmatic reservoir. REE geochemistry shows N-MORB-like type patterns with both LaN/YbN and LaN/SmN < 1 at near constant Eu/Eu* (~0.9). This is supported by εNd(t=13 Ma) values of +8.0 to +7.4 determined from the basaltic rocks. The REE values can be modeled by 1% fractional melting of garnet peridotite mixed with 7% melting of spinel peridotite of PM composition (1:9 proportions). SIMS and LA-ICP-MS U/Pb analysis of zircons yields a concordant age of 12.69 ± 0.24 Ma and a 13.3 ± 0.16 Ma intercept (Serravallian) age. The Middle Miocene volcanic activity was related to subduction-collision processes along the boundary of the Cenozoic ALCAPA (Alps–Carpathians–Pannonia) microplate and the southern margin of the European plate.

Melt extraction and mineralization: A case study from the Shuangjianzishan supergiant Ag-Pb-Zn deposit (208 Mt), Inner Mongolia, NE China

The supergiant Shuangjianzishan (SJZ) Ag-Pb-Zn deposit is in the southern segment of the Great Hinggan Range (SGHR), northeast China. Previous studies suggest the ore-forming material and fluid originated from the magmatic system, and the mineralization age was consistent with the diagenetic age. However, the relationship between granitic magmatism and mineralization is still unclear in the SJZ. In this study, C-H-O-He-Ar and in-situ S-Pb isotope analyses were conducted to determine the sources of ore-forming fluids and metals, which were combined with geochemistry data of SJZ granitoids from previous studies to constrain the relationship between the magmatism and the mineralization. The C-H-O-He-Ar-S-Pb isotopic compositions suggested the SJZ ore-forming material and fluids were derived from a magmatic source, which has mixed a small amount of mantle-derived materials. In addition, the disseminated sulfide from the syenogranite has comparable S-Pb isotopic composition with the sulfide minerals from ore veins, suggesting that the generation of the SJZ ore-forming fluids has a close relationship with the syenogranite magmatism. Combining with the geochemical characters of the syenogranite, the authors proposed that the mantle-derived fingerprint of the SJZ ore-forming fluid might be caused by the parent magma of the syenogranite, which was derived from partial melting of the juvenile lower crust, and underwent the residual melts segregated from a crystal mush in the shallow magma reservoir. The extraction of the syenogranite parent magma further concentrated the fertilized fluids, which was crucial to mineralization of the SJZ Ag-Pb-Zn deposit.©2023 China Geology Editorial Office.

Magmatic connectivity among six Galápagos volcanoes revealed by satellite geodesy

Shallow magmatic reservoirs that produce measurable volcanic surface deformation are often considered as discrete independent systems. However, petrological analyses of erupted products suggest that these may be the shallowest expression of extensive, heterogeneous magmatic systems that we show may be interconnected. We analyse time series of satellite-radar-measured displacements at Western Galápagos volcanoes from 2017 to 2022 and revisit historical displacements. We demonstrate that these volcanoes consistently experience correlated displacements during periods of heightened magma supply to the shallow crust. We rule out changes in static stress, shallow hydraulic connections, and data processing and analysis artefacts. We propose that episodic surges of magma into interconnected magmatic systems affect neighbouring volcanoes, simultaneously causing correlations in volcanic uplift and subsidence. While expected to occur globally, such processes are uniquely observable at the dense cluster of Western Galápagos volcanoes, thanks to the high rate of surface displacements and the wealth of geodetic measurements.

A shifty Toba magma reservoir: Improved eruption chronology and petrochronological evidence for lateral growth of a giant magma body

Polycyclic caldera complexes hold clues to understanding why some magmatic systems develop into supersized magma bodies and how they can recover to produce several caldera-forming eruptions. However, the geologic records of the transitions between successive caldera events are very often inaccessible due to limited preservation of eruptive products of inter-caldera activity, prompting the search for alternative archives of magma evolution such as accessory minerals. Here we applied multiple geochemical tools to study one of the most active caldera centres of the Quaternary, the Toba caldera complex in Sumatra (Indonesia), which produced at least four caldera-forming eruptions in the last 1.6 My, including the iconic Youngest Toba Tuff at 74 ka. We combined feldspar 40Ar/39Ar and zircon U–Pb geochronology of proximal pyroclastic deposits with glass and mineral chemistry of both the tuffs and distal marine tephra to revise the eruption chronology of Toba, obtaining new eruption ages of 1417 -31/+14 ka (zircon) or 1339 ± 39/39 ka (plagioclase, internal/full external 2σ uncertainty) for the Haranggaol Dacite Tuff, 783.81 ± 0.85/1.32 ka (sanidine) for Oldest Toba Tuff, and 503.61 ± 1.36/1.50 ka (sanidine) for Middle Toba Tuff. Isotope dilution thermal ionisation mass spectrometry (ID-TIMS) U–Pb crystallisation ages, trace element contents and Hf isotopic ratios of zircons illuminate changes in the shallow magma reservoir which saw near-continuous zircon crystallisation over 1.6 My. Prolonged build-ups to each eruption with highly scattered zircon trace element compositions reflect a complex, heterogeneous character of the shallow reservoir, without a clear temporal trend or indications of the eruption trigger. In contrast, hafnium isotopes in zircon display a pronounced shift towards unradiogenic values immediately after the OTT caldera collapse, followed by a gradual recovery to a baseline value of εHf = -7 at the time of YTT eruption, interpreted as a reflection of the shift in magma reservoir position corresponding to change in the character of assimilated crust. We can show in unprecedented detail how a large caldera collapse affects magma geochemistry; however, identification of patterns in the behaviour of the Toba system and making geochemistry-based predictions about its future development remain a challenge.

Does a Shallow Magma Reservoir Exist in the Wudalianchi Volcanic Field? Constraints From Magnetotelluric Imaging

AbstractWe obtain new images of the 3D resistivity structure of the Wudalianchi volcanic field (WVF). No low‐resistivity structure is found beneath Laoheishan and Huoshaoshan volcanoes in the WVF, which challenges the hypothesis of one or more magma reservoirs in the upper crust of this region. We observe a low‐resistivity body beneath Weishan volcano; however, estimated magma emplacement rates conflict with the observed volume of that body. Due to the relatively low geothermal gradient and surface heat flow in the area, magma would cool rapidly and could not be sustained for a long time unless new magma was regularly introduced into the system, but our observations do not support this scenario. We suggest that the magma in the WVF mainly originates from the mantle or the base of the crust with little crustal residence, and that the low‐resistivity body in the upper crust is likely due to saline aqueous free fluids.

Mafic magma recharge triggered eruption of a long-lived shallow silicic magma reservoir beneath a submarine volcano from the southwestern Okinawa Trough

Abundant submarine volcanoes have been identified in the southwestern Okinawa Trough, yet the duration of shallow magma reservoirs and processes driving their eruptions remains unclear. Here, the texture and in situ element compositions of orthopyroxene and magnetite in the dacite and mafic magmatic enclaves (MMEs) from the FDV-1 submarine volcano were investigated to decipher the duration of pre-eruption shallow silicic magma storage and eruption triggering processes. Both unzoned and zoned orthopyroxene phenocrysts were observed in the host dacite. The rims of zoned and unzoned orthopyroxene have similar compositions with Mg# from 49 to 55, Cr = 2.31–9.26 μg/g, V = 54.10–137 μg/g, and Ni = 16.44–21.19 μg/g, and they are in equilibrium with the rhyolitic matrix, which is consistent with growth in the shallow silicic magma reservoir. In contrast, the high Mg# cores (Mg# = 63–79) in the zoned orthopyroxenes are in equilibrium with basalt, with significant enrichment in Cr (1092–1737 μg/g), Ni (106–181 μg/g), and V (183–295 μg/g), which indicates a recycled (antecryst) origin by mafic magma recharge and magma mixing. Furthermore, the timescales from FeMg interdiffusion in orthopyroxene phenocrysts suggest that the magma mixing is approximately 600 years before eruption. Correspondingly, the shallow silicic magma reservoir beneath the submarine volcano is longevity. The presence of bubble and V-depleted magnetite aggregates in the MMEs suggests that volatile-saturated and oxidized mafic magma recharges into the shallow silicic magma chamber. Moreover, the distinct contents of relatively fast-diffusing Ni in magnetite between the MMEs and host dacite suggest that the mafic magma injection into the silicic magma reservoir and formation of the MMEs must have occurred over very short timescales (< 24 h) before the eruption to inhibit complete re-equilibration. Therefore, this last mafic magma recharge induces destabilization of the long-lived shallow silicic magma reservoir and leads to the dacitic magma eruption.

Long-term volcano evolution controlled by lateral collapse at Antuco volcano, southern Andes, Chile

Beyond the catastrophic environmental effects of large (>1 km3) volcanic landslides, their impact on underlying magmatic systems remains unclear. Chemical variations in post-collapse volcanic products, alongside dramatic eruptive behaviour transitions reported from several volcanoes, imply that surface unloading directly influences subsurface magmatic processes. By combining petrologic data with magma ascent models, we track the post-collapse (<7 ka) magmatic system evolution of Antuco volcano (Chile). During the pre-collapse period, low-explosivity eruptions were sourced from a hotter and deeper storage region. However, the landslide-induced unloading and decompression reactivated a pre-existing, shallower, silicic magma reservoir, favouring more explosive activity. The pre-collapse conditions were restored after edifice regeneration over a few thousand years. Since shallow magma reservoirs are common beneath volcanoes (e.g. in Etna, Villarrica, or Fuji), similar responses could follow future lateral collapses. These findings are relevant when assessing volcanic hazards at gravitationally unstable or collapsed volcanoes on a hundred- to thousand-year timescale.

Conductivity distribution beneath Socompa volcano, northwestern Argentina, from 3-D magnetotelluric characterization

The Socompa volcano is one of the Holocene volcanoes of the Central Volcanic Zone of the Andes. Given that it records effusive activity after 5910 YBP and that recent studies reveal unrest associated with the uplift of its edifice, it is considered an active volcano. With the aim of explaining new features that provide information about the nature of its state, here we present a geoelectric structures model of the subsurface of Socompa volcano obtained with the magnetotelluric method. One of the main features defined by the 3-D model is a body with an electrical resistivity value lower than 10 Ωm between 2 and 7 km depth and located below the volcanic edifice. This body, interpreted as the magmatic heat source of the volcano, is connected to a shallow and thick high conductive layer that covers the surrounding area. Our results highlight a possible shallow magma reservoir below the Socompa volcano and an associated -active or not- hydrothermal system.

Geochemical constraints on the evolution of the magmatic system leading to catastrophic eruptions at Aira Caldera, Japan

Caldera-forming eruptions of Aira volcano at 30 ka were among the most explosive eruptions in Japan during the late Pleistocene. In this study, new data on whole-rock major and trace elements, Sr–Nd–Pb isotopes, and 238U-230Th disequilibrium were obtained for representative volcanic products of caldera-forming and pre-caldera eruptions (31–90 ka) to acquire insights on the evolution of the felsic magma system leading to catastrophic eruptions. Voluminous rhyolitic pumices from the caldera-forming eruptions at 30 ka and rhyolitic lavas and pumices of the younger pre-caldera eruptions (31–36 ka) have similar Sr, Nd, and Pb isotopic compositions, and differ from those of dacitic and rhyolitic pumices produced by eruptions at 90 and 60 ka, respectively. These three types of felsic magmas are considered to have formed by partial melting of hornblende gabbroic rocks with distinct isotopic compositions in the middle-lower crust. Most felsic products from the pre-caldera and caldera-forming eruptions are in secular 238U-230Th equilibrium, suggesting that the original magmas were generated > ∼ 400 ka and existed as long-lived crystalline mush in the deep hot crust. Felsic magmas originating from the deep crustal mush zones ascended to form the shallow felsic magma system, which was replaced by a new one after the explosive eruptions at 90 and 60 ka. The voluminous rhyolitic magmas for the caldera-forming eruptions accumulated in a shallow magma reservoir between 60 and 30 ka. Rhyolitic magmas with compositions similar to those of the voluminous magmas erupted catastrophically at 30 ka began to erupt effusively at 36 ka and 33 ka as lava flows with significant 238U-230Th disequilibrium, suggesting that these magmas were generated in the deep crust much later than the other main rhyolitic magmas. The effusive magma eruptions presumably resulted from the relatively low content of dissolved H2O in the melt due to the low crystallinity because of the shorter residence time in the shallow felsic magma system.

The mechanism responsible for the geochemical diversity of the Putuoshan volcanic-plutonic complex and its implications for the late Mesozoic crustal evolution of the Cathaysia Block, Southeast China

Essential mechanisms for the geochemical diversity observed in a silicic igneous rock association, which is of paramount importance for understanding the differentiation and growth of continental crust, remain highly controversial. Here the issues are explored by comparing the Late Cretaceous intrusions (minor-phase miarolitic alkali-feldspar granite and main-phase alkali-feldspar granite) and coeval volcanic rocks (rhyolite and rhyodacite) within the Putuoshan (PTS) volcanic-plutonic complex in the coastal area of southeast (SE) China. Zircon UPb ages indicate that the rhyolite, rhyodacite, minor-phase granite and the previously studied main-phase granite are nearly contemporaneous (ca. 98–94 Ma), but the coexisting dacites are obviously earlier at ca. 160 Ma. The dacites show adakitic geochemical characteristics and extremely enriched NdHf isotopic compositions with Paleoproterozoic model ages, suggesting their derivation from remelting of Paleoproterozoic basement rocks in a thickened lower crust. In contrast, the coexisting Late Cretaceous volcanic and intrusive rocks have comparable and relatively depleted NdHf isotopic compositions. Our data, combined with previous studies suggest that parental magmas of these Late Cretaceous magmatic rocks were derived from partial melting of juvenile crust with varying degrees of involvement of mantle-derived melts, and the observed compositional variation are mainly controlled by crystal-melt segregation and rejuvenation of crystal mush facilitated by recharge of hot mafic magmas in the shallow magma reservoir. The Jurassic and Late Cretaceous magmatic rocks within the PTS complex were generated in an advancing subduction compressive regime and a retreating subduction extensional regime of the paleo-Pacific plate, respectively. The gradually increasing tectonic extension during the Cretaceous due to slab rollback and the induced underplating of depleted mantle-derived magmas not only gave rise to the continental rejuvenation of SE China but also are the main driving mechanism of this Late Cretaceous long-lived transcrustal magma system.

Earthquake-Triggered Crustal Shear Velocity Change at the Erupting Turrialba Volcano

ABSTRACT Monitoring variations in seismic velocities surrounding active volcanoes provides insights into crustal deformation caused by eruptions and earthquakes. Turrialba volcano in Costa Rica has been erupting sporadically since 2010 and experienced a local seismic swarm in 2016, including the Mw 5.5 Capellades earthquake. It is thus an ideal natural laboratory to study crustal velocity changes associated with a seismic event at an active volcano. We use seismic noise-generated surface waves to characterize emergent upper crustal velocity variations following the earthquake sequence off the flank of the volcano. Our study highlights a rapid velocity drop immediately following the earthquake implying widespread damage and/or a readjustment of local stress. From the frequency dependence of surface waves, we find that the depth over which the velocities vary is localized to the upper ∼2.5 km of the crust, coinciding with the depth extent of the Capellades earthquake aftershock sequence as well as the shallow magma chamber feeding the Turrialban eruption. From the areal extent of the velocity decrease, crustal variations are likely tied to both damage following the seismic sequence and the evolution of the shallow magma reservoir feeding Turrialba.