Magma Migration Research Articles

Permutation entropy variations in seismic noise before and after eruptive activity at Shinmoedake volcano, Kirishima complex, Japan

Permutation entropy (PE) is a complexity metric that encodes a time series into sequences of symbols and can be used to decipher between deterministic and stochastic behavior. This study investigates PE variations in seismic noise during three eruption cycles in 2011, 2017, and 2018 at Shinmoedake volcano, Japan. The volcano is monitored by a dedicated seismic network and by infrasound microphones that recorded continuously during the aforementioned eruptions. The frequency range 1–7 Hz was used in order to infer temporal changes of PE in seismic noise and minimize any human contributions. The results showed that PE values decreased before the occurrence of each eruption. By combining these results with other observations we can attribute this decrease in PE to two reasons: first, to the occurrence of volcanic tremor that is a deterministic signal, and second, to magma migration at shallower depth beneath Shinmoedake which can attenuate high-frequency seismic waves and thus result in a less stochastic signal. PE also exhibited a spike-like increase just before the onset of the three eruptions. In 2011 and 2017, this feature was probably associated with bubble growth and collapse due to the interaction between the aquifer and high temperature magma. In 2018 the aquifer had mostly evaporated; hence, the spike in PE values was likely generated by fracturing of solidified magma within the conduit as fresh magma was pushing its way upwards. These results show that PE is a potentially useful tool for monitoring seismic noise at volcanoes and can contribute toward forecasting volcanic eruptions in conjunction with other widely used methodologies.Graphical

Insights into the plumbing system of Colima Volcanic Complex from geophysical evidence

The Colima Volcanic Complex (CVC) consists of three stratovolcanoes: El Cántaro, Nevado de Colima and Volcán de Colima, aligned from north to south, with the same chronological order. It has been assumed that the magmatic system also has migrated in the same direction, with the surface trend of the volcanic edifices following the same pattern at depth. However, 3D inversion of gravimetric and aeromagnetic data, combined with spectral analysis (Werner deconvolution) give a detailed analysis of the CVC magmatic system, resulting in a new model of its geometry and migration, which takes into account the rifting process of the Colima Graben, and the separation of the Jalisco and Michoacán Blocks. The resulting fractures favor magma ascent through the western Michoacán Block boundary, which follows a NE-SW direction and gradually changing its angle, becoming more vertical close to Volcán de Colima. This research shows that the CVC magmatic system is best described as a Trans-crustal mush system, characterized by a zone of crystal rich magma storage located within the structural system. The direction of the magmatic migration at depth does not correspond to vertical ascent, illustrated by the lack of correlation with the volcanic edifices on the surface. Additionally, in the results it is possible to identify the separation between distinct phases of the magma, whereby the lower viscosity mobile phase is located in distinct zones within the upper crust, feeding the activity of Volcán de Colima.

Permian ridge subduction-related magmatism in the Eastern Tianshan: Implications for the evolution of the southern Altaids

Permian large-scale transcurrent tectonics and syn -kinematic ultramafic–felsic magmatism are prominent features in the Eastern Tianshan of the southern Altaids. However, the genetic relationship between coeval Ni Cu mineralized mafic-ultramafic intrusions and felsic intrusions, and the geodynamics of the region remains equivocal. To assess these topics and improve our understanding of this geologically complex and economically significant region, zircon Hf isotope and bulk-rock geochemical data from Permian granitoids along the Kanggur–Huangshan Shear Zone (KHSZ) in the Eastern Tianshan are determined and interpreted in the context of previous geochronological–geochemical data. The Kungurian Longdong (ca. 278 Ma) and Hongshi (ca. 273 Ma) granitoids are high-K, calc-alkaline, metaluminous to weakly peraluminous I-type granitoids, whereas the Capitanian Shuangchagoubei (ca. 262 Ma) granitoids are calc-alkaline, peraluminous, adakitic I-type granitoids. All of the granitoid samples are enriched in light rare earth elements and large ion lithophile elements (e.g., Rb, U, and K), and depleted in high field strength elements (e.g., Nb, Ta, and Ti), similar to arc magmas, indicating that subduction-related magmatism was still active in the late Permian. Taking into account the regional geology, and the presence of Permian high-temperature metamorphism, adakites, I-type granites, Alaskan-type Ni Cu sulfide and orogenic Au mineralization, and EW-trending N-MORB type gabbro and mélange along the KHSZ, we suggest that subduction of a spreading center during the Permian generated a slab window, allowing the upwelling of asthenospheric mantle. This permitted the generation and migration of mantle-derived magmas to shallower crustal levels along translithospheric faults (e.g., Kanggur and Yamansu faults), forming the mafic–ultramafic intrusions and associated Ni Cu sulfide deposits. The continuous migration of magma provided the necessary heat to induce partial melting of juvenile crust, generating the Permian high-K to calc-alkaline I-type granitoids. Ridge subduction-induced juvenile crustal reworking likely played a central role in the formation of the granitoids during the late Paleozoic accretionary orogenesis of the southern Altaids. • Subduction-related magmatism was active in the Eastern Tianshan in the late Permian. • Crustal growth and reworking processes must have occurred simultaneously in the Eastern Tianshan during the Permian. • Ridge subduction-induced juvenile crustal reworking likely played an important role in the formation of the granitoids in the southern Altaids.

Timing of Rhyolite Intrusion and Carlin-Type Gold Mineralization at the Cortez Hills Carlin-Type Deposit, Nevada, USA

AbstractCarlin-type gold deposits (CTDs) of Nevada are the largest producers of gold in the United States, a leader in world gold production. Although much has been resolved about the characteristics and origin of CTDs in Nevada, major questions remain, especially about (1) the role of magmatism, whether only a source of heat or also metals, (2) whether CTDs only formed in the Eocene, and (3) whether pre-Eocene metal concentrations contributed to Eocene deposits. These issues are exemplified by the CTDs of the Cortez region, the second largest concentration of these deposits after the Carlin trend.Carlin-type deposits are notoriously difficult to date because they rarely generate dateable minerals. An age can be inferred from crosscutting relationships with dated dikes and other intrusions, which we have done for the giant Cortez Hills CTD. What we term “Cortez rhyolites” consist of two petrographic-geochemical groups of siliceous dikes: (1) quartz-sanidine-plagioclase-biotite-phyric, high-SiO2 rhyolites emplaced at 35.7 Ma based on numerous 40Ar/39Ar dates and (2) plagioclase-biotite-quartz ± hornblende-phyric, low-SiO2 rhyolites, which probably were emplaced at the same time but possibly as early as ~36.2 Ma. The dikes form a NNW-trending belt that is ~6 to 10 km wide × 40 km long and centered on the Cortez Hills deposit, and they require an underlying felsic pluton that fed the dikes. Whether these dikes pre- or postdated mineralization has been long debated. We show that dike emplacement spanned the time of mineralization. Many of both high- and low-SiO2 dikes are altered and mineralized, although none constitute ore. In altered-mineralized dikes, plagioclase has been replaced by kaolinite and calcite, and biotite by smectite, calcite, and marcasite. Sanidine is unaltered except in a few samples that are completely altered to quartz and kaolinite. Sulfides present in mineralized dikes are marcasite, pyrite, arsenopyrite, and As-Sb–bearing pyrite. Mineralized dikes are moderately enriched in characteristic Carlin-type elements (Au, Hg, Sb, Tl, As, and S), as well as elements found in some CTDs (Ag, Bi, Cu, Mo), and variably depleted in MgO, CaO, Na2O, K2O, MnO, Rb, Sr, and Ba. In contrast, some high-SiO2 rhyolites are unaltered and cut high-grade ore, which shows that they are post-ore. Both mineralized and post-ore dikes have indistinguishable sanidine 40Ar/39Ar dates. These characteristics, along with published interpretations that other giant CTDs formed in a few tens of thousands of years, indicate the Cortez Hills CTD formed at 35.7 Ma. All Cortez-area CTDs are in or adjacent to the Cortez rhyolite dike swarm, which suggests that the felsic pluton that fed the dikes was the hydrothermal heat source. Minor differences in alteration and geochemistry between dikes and typical Paleozoic sedimentary rock-hosted ore probably reflect low permeability and low reactivity of the predominantly quartzofeldspathic dikes.Despite widespread pre-35.7 Ma mineralization in the Cortez region, including deposits near several CTDs, we find no evidence that older deposits or Paleozoic basinal rocks contributed metals to Cortez-area CTDs. Combining our new information about the age of Cortez Hills with published and our dates on other CTDs demonstrates that CTD formation coincided with the southwestern migration of magmatism across Nevada, supporting a genetic relationship to Eocene magmatism. CTDs are best developed where deep-seated (~6–8 km), probably granitic plutons, expressed in deposits only as dikes, established large, convective hydrothermal systems.

Vertical deformation partitioning across a collapsing large and hot orogen

AbstractFeaturing 3 000‐km‐long large and hot orogen, the Mantiqueira Province provides a rare opportunity to study the process of gravitational collapse at mid to deep crustal levels. Distinct but contemporary (~500 Ma) post‐collisional intrusions show structures and anisotropy of magnetic susceptibility (AMS) fabrics related to their emplacements, recording different flow patterns. In southern deep‐seated intrusions, ellipsoidal‐shaped roots with gabbroic‐to‐hybrid cores surrounded by granitic rocks show concentric patterns of AMS fabrics that cut across the NE‐trending regional foliation. In contrast, northern intrusions, exposed as the upper sections of batholith‐size bodies of coarse‐grained granite emplaced at the shallow to mid‐crust, show general NS‐trending magnetic fabrics roughly parallel to strike of the orogen and the regional foliation of host rocks. These contrasting magnetic patterns from shallow to deeper crust suggest vertical magma migration from the overthickened orogenic core to be emplaced across its thinner stretched flanks during the gravitational collapse of the orogenic edifice.

Zircon evolution from migmatite to crustally-derived granite: A case study of late Neoarchean migmatite in the Yishan area, western Shandong, North China Craton

Sequential changes in the texture, composition and U-Pb age of zircon from the late Neoarchean migmatites and related rocks in the Yishan area of western Shandong, eastern North China Craton, record the evolution of melt and magma from paleosome to crustally-derived granite. Zircon grains from the paleosome and metatexite have features of recrystallization, with narrow rims; those from leucosome have inherited cores and wide homogenous rims; those from diatexite preserve evidence of a complex evolution involving dissolution and growth, with the euhedral morphology of the rims, and the cross-cutting relationship between cores and rims, consistent with a magmatic origin. With the increase in melt content toward granite, the newly-grown zircon has clearer magmatic zoning and higher Th/U ratios. The low whole-rock Zr saturation temperatures (684–728 ℃) indicate that the diatexites, with abundant residual zircon, might be the product of low-temperature melting. The contemporaneous, crustally-derived granites, however, contain no or much less xenocrystic zircon and have high zircon saturation temperatures (740–868 ℃). Only at the higher temperature was sufficient partial melt produced to start the migration of magma out of the source region to form the granites. Anatectic (magmatic) zircons in diatexite commonly contain xenocrystic (residual) zircons, no matter how the magmatic system evolves further, the xenocrystic zircons in the anatectic (magmatic) zircons will still be retained. On the other hand, the crustlly-derived granites widely distributed in the area contain few residual zircons. Therefore, the crustally-derived granites widely distributed in western Shandong cannot form by further evolution of the diatexites, but require a higher degree of partial melting under higher temperature conditions. SHRIMP U-Pb zircon dating, combined with CL imaging, reveals that zircon crystals from the diatexites mostly are characterized by inherited cores with thick magmatic overgrowths, recording a regional anatectic event at ∼2.51 Ga. Residual source rock enclaves and xenocrystic zircons in the diatexites mostly have ages of ∼2.70 Ga and ∼2.53 Ga, suggesting that the diatexites were derived from Neoarchean continental crust.

Mid−late Neoproterozoic tectonic evolution of the northern margin of the Yangtze Block, South China, as constrained from the detrital zircon record

The northern margin of the Yangtze Block (NYB) experienced distinct tectono-magmatic evolution during the mid- and late-Neoproterozoic, as compared with the northwestern margins of the Yangtze Block (NWYB), although the geodynamic mechanism remains controversial. The South Qinling Belt (SQB), which forms the northernmost NYB, is a significant target for studying the Neoproterozoic tectonic evolution of the NYB. Here we present U-Pb geochronology and Lu-Hf isotopes of detrital zircons from clastic rocks belonging to the Yaolinghe and Wudangshan Groups in the SQB. The U-Pb ages reveal that the maximum depositional ages are respectively ca. 630 Ma and ca. 680 Ma for the Yaolinghe and Wudangshan Groups in the Ankang and Wudang Uplifts. Based on the compilation of U-Pb ages and Hf−Nd−O isotopic data as well as multidimensional scaling (MDS) analysis, clastic rocks of the Yaolinghe Group are suggested to be sourced mainly from the NWYB, whereas those of the Wudangshan Group were derived mostly from the NWYB and the NYB. The data compiled also indicate ca. 800−680 Ma northeastward migration of magmatism in response to slab rollback and ca. 680−600 Ma eastward migration of magmatism resulting from slab tearing. A tectonic model is proposed that envisages an arcuate subduction system around the Yangtze Block during the mid−late Neoproterozoic. The continuous slab rollback and slab tearing underneath the NYB resulted in an extensional environment at that time. The rocks in the NWYB underwent uplift and erosion, and the detritus was transported to the NYB. The new model can well account for the two distinct groups of volcanic rocks in the Yaolinghe Group.

Gravity Data Reveal New Evidence of an Axial Magma Chamber Beneath Segment 27 in the Southwest Indian Ridge

Hydrothermal systems are integral to mid-ocean ridge activity; they form massive seafloor sulfide (SMS) deposits rich in various metallic elements, which are potential mineral resources. Since 2007, many hydrothermal fields have been discovered along the ultraslow-spreading Southwest Indian Ridge (SWIR). The Duanqiao hydrothermal field is located at segment 27’s axis between the Indomed and Gallieni transform faults; tomography models reveal an obvious low-velocity anomaly beneath it, indicating a possible axial magma chamber (AMC). However, confirmation of an AMC’s existence requires further study and evidence. In this study, we first calculated the gravity effect to identify the heterogeneous distribution of crustal density beneath segment 27 and the surrounding area. Next, we used the gravity-inversion method to obtain the crustal density structure beneath the study area. The results indicate that a thickened crust and low-density crustal materials exist beneath segment 27. The low-density anomaly in the lower crust beneath the Duanqiao hydrothermal field suggests the existence of an AMC covered with a cold and dense upper crust. The density results identify several faults, which provide potential channels for magma migration. In addition, the melt migrates westward and redistributes laterally toward the segment’s western end. However, when migrating toward the segment’s eastern end, the melt is affected by a rapid cooling mechanism. Therefore, the segment’s ends present different density features and morphologies of nontransform discontinuities (NTDs).

Deformation and seismicity decline before the 2021 Fagradalsfjall eruption

Increased rates of deformation and seismicity are well-established precursors to volcanic eruptions, and their interpretation forms the basis for eruption warnings worldwide. Rates of ground displacement and the number of earthquakes escalate before many eruptions1–3, as magma forces its way towards the surface. However, the pre-eruptive patterns of deformation and seismicity vary widely. Here we show how an eruption beginning on 19 March 2021 at Fagradalsfjall, Iceland, was preceded by a period of tectonic stress release ending with a decline in deformation and seismicity over several days preceding the eruption onset. High rates of deformation and seismicity occurred from 24 February to mid-March in relation to gradual emplacement of an approximately 9-km-long magma-filled dyke, between the surface and 8 km depth (volume approximately 34 × 106 m3), as well as the triggering of strike-slip earthquakes up to magnitude MW 5.64. As stored tectonic stress was systematically released, there was less lateral migration of magma and a reduction in both the deformation rates and seismicity. Weaker crust near the surface may also have contributed to reduced seismicity, as the depth of active magma emplacement progressively shallowed. This demonstrates that the interaction between volcanoes and tectonic stress as well as crustal layering need to be fully considered when forecasting eruptions.

Seismicity during the recent activity (2009–2020) of Turrialba volcano, Costa Rica

Turrialba is a stratovolcano located at the easternmost part of the Costa Rican volcanic front. After remaining quiescent for more than a century, in 1996 it started to show signs of unrest, until a first phreatomagmatic explosion occurred on January, 2010. Since then, the activity evolved from phreatic to magmatic, in a series of distinct eruptive phases. In this paper, we investigate the seismic records that span the whole eruptive process (2010-present), in order to identify precursory signals and characterize the volcanic evolution. A long-term analysis was carried out based on the continuous records, as well as seismic catalogs (volcano-tectonic seismicity, harmonic tremor, etc.). In addition, the gradual character of the evolution of this eruption allowed for the analysis of independent precursory stages. Thus, we inspected in detail the most important of those periods, particularly, prior to the first 2010 phreatomagmatic eruption, and prior to the 2016 transition to an open vent system. Temporary tremor amplitude decreases were found to precede most of the eruptive phases. In total, 9 pre-eruptive tremor abatement periods were identified spanning several days (5–44), which often concurred with a decrease in the SO2 flux. The analysis of the volcano-tectonic seismicity highlights the migration of magma from a deep (6–10 km) reservoir beneath the neighboring Irazú volcano towards Turrialba volcano, especially between the years 2015 and 2016. This activity peaked on December 2016 when a Mw 5.5 earthquake took place between both volcanoes. Harmonic tremor episodes thrived in the later phase when the system finally opened (2017–2018). In the short-term, compounded tonal seismic signals were identified as precursor events, such as long-period events followed by harmonic tremor or by a multichromatic coda similar to tornillo-type events. The co-occurrence of tremor amplitude decreases and tonal seismic signals is interpreted to be caused by a sealing of the hydrothermal system, which blocked the circulation of fluids and permitted the resonances in the inner cavities. This process leaded to pressure accumulation and the consequent eruptions. Thus, trough a series of cycles of sealing and rupture the system of conduits gradually opened. The seismic characterization of this eruption constitutes insightful knowledge useful for monitoring and risk assessment purposes.

U–Pb geochronology of intrusive rocks of northwestern Mesa Central province and Sector Tansversal of Sierra Madre Oriental, Mexico: Time and space distribution of inland Cretaceous-Paleogene magmatism during Mexican orogeny

At the northwest of Mesa Central province and the Sector Transversal of Sierra Madre Oriental, Mexico, intrusive magmatic rocks that range compositionally from quartz-monzodiorites to monzonites crop out and mainly intrude continental and marine sedimentary sequences ranging from Lower Triassic to Upper Cretaceous in age. Detrital zircon ages from a host sandstone of the most western studied intrusive rock suggest that they derived from a basement similar in age to the Guerrero Terrane. U–Pb age obtained in zircons from intrusive rocks ranges from Late Cretaceous to Oligocene. The analysis of distribution in space and time of these intrusive rocks shows that at the interior of the continent: 1) there are more intrusive rocks of Upper Cretaceous ages than previously thought, and 2) there is a little or null presence of magmatism during Paleocene. These remarkable aspects do not support a model of magmatic migration since ∼110 Ma from the paleotrech of the western edge of North America, promoted by a change to a slab geometry subduction as has been previously proposed, and it appears that only after the re-establishment of magmatism during Eocene, age and geographic distribution fit within a model of magmatic migration. Therefore, alternative models should be proposed that better explain the distribution in space and time of these magmatic rocks based on subsequent geochemical and isotopic data.

Melt Migration in Crystal Mushes by Viscous Fingering: Insights From High‐Temperature, High‐Pressure Experiments

AbstractWe conducted experiments to study melt migration in crystal‐rich mushes, with application to magma ascent within transcrustal magma reservoirs. Mushes with crystal volume fractions of 0.59–0.83 were prepared by hot‐pressing crushed borosilicate glass mixed with different proportions of quartz sand particles. Each experimental sample comprises stacked disks of mush and soda‐lime glass, a proxy for crystal‐free magma. Samples were subjected to confining pressures of 100–300 MPa and a temperature of 900°C (above the glass transition temperatures of the borosilicate and soda‐lime glasses) for up to 6 h. The bottom and circumference of the mush and soda lime disks experience the confining pressure, but the top of the mush disks is at room pressure, resulting in a pore‐pressure gradient across the mush layer. Following cooling and decompression, we determined the area fraction and morphology of soda‐lime melt that migrated into the mush layer during experiments. Melt fraction is more strongly correlated to crystal fraction than pore‐pressure gradient, increasing with crystal fraction before sharply decreasing as crystal fractions exceed 0.8. This change at 0.8 coincides with the transition from crystals in the mush moving during soda‐lime migration to crystals forming a continuous rigid network. In our experiments, melt migration occurred by viscous fingering, but near the mobile‐to‐rigid transition, melt migration is enhanced by additional capillary action. Our results indicate that magma migration may peak when rigid mushes “unlock” to become mobile. This transition may mark an increase in magma migration, a potential precursor to volcanic unrest and eruption.

The fate of oceanic plateaus: subduction versus accretion

SUMMARYOceanic plateaus (or aseismic ridges) can be either subducted into the deep mantle, or accreted onto the overriding plate. Furthermore, some oceanic plateaus can change subduction mode from steep to flat-slab subduction. What factors control the fate of oceanic plateaus during subduction remain enigmatic. Here, we investigate the controls on these modes and their respective geological effects using 2-D thermomechanical simulations. We systematically examine the characteristics of an oceanic plateau (including crustal thickness and length), plateau-trench distance, convergence rate and eclogitization of the oceanic crust. Our models confirm that the size of the plateau and eclogitization are the main factors controlling the subduction characteristics. For the eclogite models, a relatively thin oceanic plateau (≤20 km thick) undergoes steep subduction, a moderate-scale plateau (25–30 km thick) favours flat-slab subduction and large-scale plateaus (≥35 km thick) are more susceptible to collide and accrete to the overriding upper plate. Eclogitization significantly reduces the formation chance and duration of flat-slab subduction. The switch from flat-slab to steep subduction occurs rapidly (<5 Ma), and the steepening occurs twice as fast as the flattening. The plateau-trench distance determines the location of the break-off, and shallow break-off (<300 km) of the frontal slab will significantly change the subduction pattern. Either fast convergence rates (≥8 cm yr−1) or overthrusting of the overriding plate promotes the formation of flat-slab subduction. The mode changed from flat-slab to steep subduction explains the landward migration of magmatism followed by a trenchward migration in Eastern China since the Mesozoic.

Monitoring magma migration at Mt. Etna using the Seismic Amplitude Ratio Analysis method

The Seismic Amplitude Ratio Analysis method (SARA) was applied to data recorded six days before the May 13, 2008 eruption of Mt. Etna to test its potential as a forecasting attribute. By using this method, the magma migration path, as well as the seismic migration, can be determined with the amplitude of continuous data recorded at least at one pair of stations from a seismic network near the eruption site. Due to the sudden changes in the seismic amplitude ratio calculated for each pair of stations, the seismic migration trend, as well as the magma path at depths, were detected before the main eruption. The start and end times of the seismic swarms were also determined. The standard practice to achieve similar results is to use volcanic tremors, which must be pre-selected thus reducing efficiency and increasing the time needed. By using the whole seismic signal, the method provides a simpler semi-automated alternative, especially for a seismic event or places where it is not possible to record tremors continuously. This simple method is useful to reduce uncertainties relative to hazardous magma propagation during volcanic unrest, as it helps improve the accuracy of locating seismic swarms and determining the direction of magma movement at depth before the eruption. We also analyzed the amplitude ratio trend using Mann-Kendall and Sen's estimator test. The results of these tests confirmed a positive and increasing trend from the day before the eruption in most pairs of stations.

The Hiccup of Villarrica volcano (Chile) during the 2015 eruption and its expression in LP activity and VLP ground motion

SUMMARY Volcano seismology is an essential tool for monitoring volcanic processes in the advent and during eruptions. A variety of seismic signals can be recorded at volcanoes, of which some are thought to be related to the migration of fluids which is of primary importance for the anticipation of imminent eruptions. We investigate the volcanic crises at Villarrica volcano in 2015 and report on a newly discovered very-long-period (VLP) signal that accompanies phases of periodic long period (LP) signal burst. Despite their low amplitude emergent character, we can locate the source region of the 1 Hz LP signals to the close vicinity of the volcano using a network-based correlation method. The source of the VLP signal with a period of about 30–100 s appears to locate in the vicinity of two stations a few kilometres from the summit. Both stations record very similar VLP waveforms that are correlated with the envelope of the LP bursts. A shallow magma reservoir was inferred by Contreras from surface deformation as the source of inflation following the eruption in 2015. Cyclic volume changes of 6 m3 in this reservoir at 3 km depth can explain the observed amplitudes of the vertical VLP signal. We propose that the LP signal is generated by the migration of gas or gas-rich magma that is periodically released from the inflating reservoir through a non-linear valve structure which modulates the flux, and thereby causes bursts of flow-related LP signals and pressure changes observed as VLP deformation. Our model predicts that the correlated occurrence of LP bursts and VLP surface motion depends on the intensity of the fluid flux. A weaker flux of fluids may not exceed the opening pressure of valve structure, and higher rates might maintain pressure above the closing pressure. In both cases, the VLP signal vanishes. Our observation provides constrains for models of fluid transport inside volcanoes. At Villarrica the VLP signal, and its relation to the LP activity, reveal additional information about fluxes in the magmatic reservoir that might aide forecasting of volcanic activity.

Rheological Controls on Magma Reservoir Failure in a Thermo‐Viscoelastic Crust

AbstractAs volcanoes undergo unrest, understanding the conditions and timescales required for magma reservoir failure, and the links to geodetic observations, are critical when evaluating the potential for magma migration to the surface and eruption. Inferring the dynamics of a pressurized magmatic system from episodes of surface deformation is heavily reliant on the assumed crustal rheology, typically represented by an elastic medium. Here, we use Finite Element models to identify the rheological response to reservoir pressurization within a temperature‐dependent Standard Linear Solid viscoelastic (“thermo‐viscoelastic”) domain. We assess the mechanical stability of a deforming reservoir by evaluating the overpressures required to initiate brittle failure along the reservoir wall, and the sensitivity to key parameters. Reservoir inflation facilitates compression of the ductile wall rock, due to the non‐uniform crustal viscosity, impacting the temporal evolution of the induced tensile stress. Thermo‐viscoelasticity enables a deforming reservoir to sustain greater overpressures prior to failure, compared to elastic analyses. High‐temperature (e.g., mafic) reservoirs fail at lower overpressures compared to low‐temperature (e.g., felsic) reservoirs, producing smaller coincident displacements at the ground surface. The impact of thermo‐viscoelasticity on reservoir failure is significant across a wide range of overpressure loading rates. By resisting mechanical failure on the reservoir wall, thermo‐viscoelasticity impacts dyke nucleation and formation of shear fractures. Numerical models may need to incorporate additional processes that act to promote failure, such as regional stresses (e.g., topographic and tectonic), external triggers (e.g., earthquake stress drops), or pre‐existing weaknesses along the reservoir wall.

Late Amazonian dike-fed distributed volcanism in the Tharsis volcanic province on Mars

Tharsis is the largest volcanic province on Mars and in the solar system. This region includes major volcanoes (Olympus Mons, Alba Mons, Arsia Mons, Pavonis Mons, and Ascraeus Montes) and hundreds of small volcanic cones and vents, whose origin is not yet fully understood. Although the main Tharsis' edifices plumbing system has been extensively studied, smaller volcanoes' origin remains unknown. The formation of those minor volcanic landforms may be related to the large volcanic edifices' evolution, and/or controlled by the fault systems through which magma migrates towards the Martian surface. In this study, we analyzed the central part of the Tharsis volcanic province using satellite images with a resolution of ~6 m/px from the Context Camera onboard the Mars Reconnaissance Orbiter (CTX/MRO). We identified and mapped 659 volcanic edifices >1 km in diameter. We analyzed (1) their spatial distribution, (2) alignment of summit craters, and (3) surface model ages derived from crater counting. We found that volcanic edifices are unevenly distributed across the Tharsis province and proposed that their formation is controlled by at least six individual magma-plumbing systems associated with major edifices: Olympus Mons, Alba Mons, Arsia Mons, Pavonis Mons, Ascraeus Mons, and Uranius Mons. Their summit alignment orientations indicate they were controlled by radial and circumferential dikes originated from magma sources beneath the six central volcanoes, either magma chambers in the crust or other magmatic underplates at the base of the crust. Volcano flanks of distributed volcanoes are of similar age or younger than the summit calderas of the associated central volcano indicating a common magmatic system. Magma migration and eruptions from distributed volcanoes may thus extend beyond the magma waxing periods when magma supply was high enough to sustain summit eruptions. The relatively young age of documented volcanic activity within the Tharsis province may imply recently active hydrothermal systems triggered by magma-water interaction.

A gravitational origin for volcano-tectonic faults in the Campi Flegrei caldera (southern Italy) inferred from detailed field observations

Faults in volcanic areas can have different origins and can form due to several volcano-tectonic processes. In this work, by means of detailed field observations, we analysed a fault array cutting through a recent pyroclastic succession in the Campi Flegrei caldera of southern Italy to investigate its origin. Geometric and kinematic data indicate that the fault array consists of steeply dipping faults with both normal and reverse senses of movement. Displacement data suggest that these faults with opposed kinematics acted together , in agreement with what was previously described from analogue and numerical experiments for faults formed in response to gravitational collapses in volcanic areas. By integrating these results with considerations of the recent volcano-tectonic evolution of the Campi Flegrei caldera, we propose a model in which the studied fault array developed to accommodate a gravitational collapse triggered by an underground magma migration predating the 1538 CE historical Monte Nuovo eruption. This work is, to our knowledge, the first thorough field description of faults developed to accommodate gravitational collapses in volcanic areas.

Bathymetry Based Modeling of Subaxial Magma Flows Under the Mid-Atlantic Ridge, 0 to 30° N

Fracture patterns of the Mid-Atlantic Ridge (MAR) provide evidence of tectonic forces related to divergence and magma upwelling at the ridge axis. In this study, we focus on the MAR from 0 to 30° N, where the N-S ridge exhibits slow spreading rates (2-4 cm/yr) and pronounced axial topography. Ridge segments and transform faults identified in bathymetry data were analyzed for strike orientation and axial depth profiles. Azimuths of transform faults and ridge segments exhibit increasing clockwise rotation with latitude, and all have left lateral displacement. Bathymetric sampling along ridge segments occurred at 9 km intervals with 20 km sampling radii, producing axial lithostatic pressure gradients. One-dimensional magma flows parallel to the ridge axis at 10 and 50 km depths were modeled using Darcy’s law based on published parameters and calculated gradients. Subaxial magma velocities of up to 4 cm/yr were predicted for horizontal flow at depth and are comparable in magnitude to upwelling rates in published literature. Average flow magnitudes (n = 422) within the melt generation region are predicted at 0.8 and 0.2 cm/yr for 10 and 50 km depths respectively. Flow velocities up to five times higher are expected with this model in the high-porosity boundary layer below the solidus. The Coriolis parameter would affect the movement of the flows predicted by our model and may be linked to rotational patterns observed at the MAR. Future research of magma migration below divergent margins would benefit from incorporating axial lithostatic load variations as a driver of flow.

Thermal and seismic precursors to the explosive eruption at La Soufrière Volcano, St. Vincent in April 2021

High temporal resolution, geostationary, thermal infrared data from the Advanced Baseline Imager combined with seismic data of La Soufrière Volcano, St. Vincent provide empirical insights into the volcanic processes and mechanisms that occurred from November 2020 until the explosive phase in April 2021. An overall increase in intensity of thermal output and seismicity are observed during the effusive phase; however, the intensity of the thermal data increased ∼20 days earlier than the seismicity. During the effusive phase, the daily radiant heat flux increased from 0.01 to >100 MW and the seismicity increased from 1 to 647 events. The climax of both records occurred during the explosive eruptions on April 9-14, 2021. Strong correlations are observed between these datasets in the weeks leading to the explosive eruptions. A significant (∼5 day) decrease in thermal and seismic activity is observed ∼12 days prior to the explosive phase, which could reveal a hiatus in magma migration prior to the eruption. Periods of decoupling between these datasets are also observed and are attributed to different mechanisms during the volcanic unrest. Occurrences with high seismicity and low heat flux may indicate deeper magmatic migration where no significant surface thermal response could be detected, for example. Recognizing correlations, or lack thereof, between high-temporal resolution thermal infrared and seismic data expands potential insights to subsurface volcanic processes by providing a second, complementary vantage. Such seismic-thermal analysis can improve our community's capability to monitor and evaluate new volcanic eruptions. Indeed, extensive seismic networks (local and regional) and multiple geostationary weather satellites now provide near global coverage. A similar analysis to our work at La Soufrière Volcano, St. Vincent is feasible, and should become routine, at other volcanoes worldwide using combined high-temporal, ground and orbital data where available. The 2022 eruption at Hunga-Tonga-Hunga-Ha'apai volcano, Tonga, illustrates the important potential for these high cadence data and subsequent analysis even at extremely remote volcanoes.