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Representative figures from different communities studying volcanoes. Left, archetypical mantle-focused subduction cartoon with an "emoji volcano" that only alludes to a shallower magmatic system. Right, archetypical upper crust-focused subduction volcano cartoon, with a "disembodied volcano", disconnected from the deeper magma source region
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Decades of study on volcanic arcs have provided insight into the overarching processes that control magmatism, and how these processes manifest at individual volcanoes. However, the causes of ubiquitous and dramatic intra-arc variations in volcanic flux and composition remain largely unresolved. Investigating such arc-scale issues requires greater...
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The thermal structure of the Tibetan plateau—the largest orogenic system on Earth—remains largely unknown. Numerous avenues provide fragmentary pressure/temperature information, both at the present (predominantly informed though geophysical observation) and on the evolution of the thermal structure over the recent past (combining petrological, geoc...
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... However, Calbuco volcano is monotonously andesitic throughout its entire volcanic history ( Fig. 10C; Mixon et al., 2021), and Villarrica has erupted only basaltic andesitic to andesitic magma following the local LGM (Moreno and Clavero, 2006;Lohmar et al., 2012). Some have suggested that mantle melt production and flux into the lower crust modulates how transcrustal magma plumbing systems operate in the Cascade arc (Till et al., 2019). Higher mantle melt flux into the base of a plumbing system-as at Calbuco and Villarrica volcanoes-could prevent cooling, stalling, and differentiation to produce significant amounts of silicic melt (Mixon et al., 2021). ...
Mocho-Choshuenco volcano (39.9°S, 72.0°W) produced ∼75 explosive eruptions following retreat of the >1.5-km-thick Patagonian Ice Sheet associated with the local Last Glacial Maximum (LGM, from 35 to 18 ka). Here, we extend this record of volcanic evolution to include pre- and syn-LGM lavas that erupted during the Pleistocene. We establish a long-term chronology of magmatic and volcanic evolution and evaluate the relationship between volcanism and loading/unloading of the Patagonian Ice Sheet via twenty-four 40Ar/39Ar and two 3He age determinations integrated with stratigraphy and whole-rock compositions of lava flows and glass compositions of tephra. Our findings reveal that the edifice is much younger than previously thought and preserves 106 km3 of eruptive products, of which 50% were emplaced immediately following the end of the penultimate glaciation and 20% after the end of the LGM. A period of volcanic inactivity between 37 and 26 ka, when glaciers expanded, was followed by the eruption of incompatible element-rich basaltic andesites. Several of these syn-LGM lavas dated between 26 and 16 ka, which crop out at 1500−1700 m above sea level, show ice contact features that are consistent with emplacement against a 1400- to 1600-m-thick Patagonian Ice Sheet. Small volume dacitic eruptions and two explosive rhyolitic eruptions dominate the volcanic output from 18 to 8 ka, when the Patagonian Ice Sheet began to retreat rapidly. We hypothesize that increased lithostatic loading as the Patagonian Ice Sheet grew prohibited dike propagation, thus stalling the ascent of magma, promoting growth of at least three discrete magma reservoirs, and enhancing minor crustal assimilation to generate incompatible element-rich basaltic andesitic to dacitic magmas that erupted between 26 and 17 ka. From an adjacent reservoir, incompatible element-poor dacites erupted from 17 to 12 ka. These lava flows were followed by the caldera-forming eruption at 11.5 ka of 5.3 km3 of rhyolite from a deeper reservoir atop which a silicic melt lens had formed and expanded. Subsequent eruptions of oxidized dacitic magmas from the Choshuenco cone from 11.5 to 8 ka were followed by andesitic to dacitic eruptions at the more southerly Mocho cone, as well as small flank vent eruptions of basaltic andesite at 2.5 and 0.5 ka. This complex history reflects a multi-reservoir plumbing system beneath Mocho-Choshuenco, which is characterized by depths of magma storage, oxidation states, and trace element compositions that vary over short periods of time (<2 k.y.).
... Such variability complicates risk mitigation strategies for communities living near active arc volcanoes given the variety of hazards associated with impending eruptions of an indeterminate nature [1,2]. The driving forces behind intra-arc diversity are largely attributed to variations in crustal properties and mantle flux [3,4]. Deciphering the relative importance of contributing factors by geography is best resolved by integrating datasets of detailed studies on individual volcanoes with regional arc-scale findings of a multi-disciplinary nature. ...
Intra-arc diversity in volcanic activity and composition is ubiquitous, but its underlying causes remain largely unresolved in many settings. In this work, we examine such variability in the Grenadines archipelago, southern Lesser Antilles arc. Here, juxtaposed volcanic centres exhibit eruptive longevities and chemistries distinct from northern counterparts in the same arc. Our goal is to explain this deviation by investigating variations in magmatic processes using petrological data from erupted crustal xenoliths and lavas, and interpreting these findings within the context of the archipelago’s tectonic history and geophysical structure. Textural analyses of xenoliths reveal crystallization over a wide range of pressure–temperature–melt composition conditions in the crust. Mineral phases display discrete compositional trends pointing towards significant inter-island variability in underlying plumbing systems. The geochemical variety of erupted magmas is reminiscent of the entire arc. We speculate that the Grenadines represents the early onset of subduction forming the modern-day Lesser Antilles arc. Extrusive volcanism initiated as submarine activity. Subsequent uplift eroded the original topography of these volcanic centres following the eventual cessation of volcanism in the Neogene. The positioning of the Grenadines on an elevated platform provides rare modern insight into early arc crust formation not commonly preserved in established active arcs.
... The relative importance of spatial versus temporal controls on the evolution of the lithosphere is a fundamental question in oceanic and continental arc systems, influencing magma geochemistry from deep source regions to final emplacement or eruption levels (e.g., Hildreth and Moorbath, 1988;de Bremond d'Ars et al., 1995;Kay and Kay, 1994;Cecil et al., 2018;Till et al., 2019;Schwartz et al., 2021). Arc magmas inherit compositional features from the underlying basement, which can include crust, mantle lithosphere, sediments, fluids, and astheno spheric mantle components, in varying proportions across-strike or along-strike of the arc (e.g., Kistler and Peterman, 1973;Hildreth and Moorbath, 1988;Chapman et al., 2017). ...
Although subduction is a continuous process, arc system behavior is non-steady-state, leading to uncertainty surrounding the composite spatial and temporal evolution of transcrustal arc magma plumbing systems. This study integrates field, geochronologic, and geochemical data sets from the central Sierra Nevada arc section to investigate the extent to which spatial inheritance is recorded in arc geochemical compositions, and how these signals may be modified by dynamic arc behaviors through time, from arc-wide flare-ups, migration, and crustal thickening to regional magma focusing. Geochemical patterns across Mesozoic arc rocks characterize persistent spatial signals of inheritance, whereas geochemical trends during Cretaceous arc activity provide the temporal component of simultaneous dynamic processes. Distinct bulk-rock isotopic signals define each of the three Mesozoic magmatic flare-ups, which, during Cretaceous arc magmatism, is coupled with eastward arc migration. Additionally, Cretaceous magmatic and tectonic thickening doubled the thickness of arc crust, and magmatism was focused toward a central zone, culminating in the formation of the ∼1100 km2 Tuolumne Intrusive Complex. During magma focusing, temporal signals of magma mixing outweighed the previously pervasive signal of spatial inheritance. Distinct dynamic behaviors effectively primed the arc by the Late Cretaceous, generating transcrustal hot zones of increased magma mixing, recycling, long-term storage, and homogenization. Non-steady-state behavior in the Sierra Nevada resulted in mountain building and voluminous continental crust formation by transforming the physical, thermal, and chemical properties of the lithosphere over tens of millions of years.
... Volcanic island arcs, such as the Lesser Antilles arc (LAA), may show large alongstrike variability in their eruptive frequencymagnitude relationships, crustal structure, geochemistry, seismicity, and isotopic signatures (Wadge, 1984;Hildreth and Moorbath, 1988;Schlaphorst et al., 2016;Melekhova et al., 2019;Cooper et al., 2020). The proposed mechanisms for such stark changes include different melt flux from the mantle ("melt flux"; Schlaphorst et al., 2018;Till et al., 2019;Cooper et al., 2020), chemically distinct mantellic melts (Pichavant et al., 2002), contrasting crustal differentiation mechanisms (Tamura et al., 2016), and shifts in wedge thermal structure (Turner et al., 2016). These processes can all modulate the thermal-chemical architecture of subvolcanic magma plumbing systems (Castruccio et al., 2017;Giordano and Caricchi, 2022), and subsequently the chemical and physical properties of magma via phase equilibria (Müntener and Ulmer, 2018). ...
Volcanoes exhibit a wide range of eruptive and geochemical behavior, which has significant implications for their associated risk. The suggested first-order drivers of intervolcanic diversity invoke a combination of crustal and mantle processes. To better constrain mantle-crustal-volcanic coupling, we used the well-studied Lesser Antilles island arc. Here, we show that melt flux from the mantle, identified by proxy in the form of boron isotopes in melt inclusions, correlates with the long-term volcanic productivity, the volcanic edifice height, and the geophysically defined along-arc crustal structure. These features are the consequence of a variable melt flux modulating the pressure-temperature-composition structure of the crust, which we inverted from xenolith mineral chemistry. Mafic to intermediate melts reside at relatively constant temperature (981 ± 52 °C; 2σ) in the middle crust (3.5−7.1 kbar), whereas chemically evolved (rhyolitic) melts are stored predominantly in the upper crust (<3.5 kbar) at maximum depths that vary geophysically along the arc (6−15 km). Our findings are applicable worldwide, where we see similar correlations among average magma geochemistry, eruptive magnitude, and rate of magma input.
... This kinematic framework is consistent with along-strike segmentation of Quaternary volcanic vents (Guffanti and Weaver, 1988;Wells et al., 1998). Topography mirrors diverse crustal geophysical signals associated with current magmatism in the Cascades arc (e.g., isostatic residual gravity, seismic tomography, heat flux, crustal rotation; Till et al., 2019;O'Hara et al., 2020), so mountain building likely reflects crustal thickening associated with magmatic intrusions that define long wavelength topography (Perkins et al., 2016), as well as background tectonic strain field. ...
The morphology and distribution of volcanic edifices in volcanic terrains encodes the structure and evolution of underlying magma transport as well as surface processes that shape landforms. How magmatic construction and erosion interact on long timescales to sculpt these landscapes, however, remains poorly resolved. In the Cascades arc, distributed volcanic edifices mirror long-wavelength topography associated with underlying crustal magmatism and define the regional drainage divide. The resulting strong along- and across-arc modern precipitation gradients and extensive glaciation provide a natural laboratory for climate-volcano interactions. Here, we use 1,658 volcanic edifice boundaries to quantify volcano morphology at the arc-scale, and reconstruct primary edifice volumes to create first-order estimations of Cascades erosion throughout the Quaternary. Across-arc asymmetry in eroded volumes, mirroring similarly asymmetric spatial distribution of volcanism, suggests a coupling between magmatism and climate in which construction of topography enhances erosion by orographic precipitation and glaciers on million-year timescales. We demonstrate with a coupled landscape evolution and crustal stress model that mountain building associated with magmatism and subsequent orographically-induced erosion can redistribute surface loads and direct subsequent time-averaged magma ascent. This two-way coupling can thus contribute to Myr-scale spatial migration of volcanism observed in the Cascades and other arcs globally.
... Thus, a decrease in magma flux should result in cooler temperatures and enhanced fractionation at depth, leading to deeper early fractionation pressures, deeper plagioclase stability, and thus increased seismic Moho depths. In this model, the flux of magma to arc crust is inversely correlated with Moho depth and exerts a strong control on the petrologic and thermal structure of the arc crust (cf., Till et al., 2019). Long-term estimates of magmatic fluxes in modern arcs appear to broadly support this inverse relationship between magma flux and crustal thickness: in comparison to continental arcs, island arcs are characterized by both thinner crust and also elevated average (felsic) magmatic fluxes of at least 60-80 km 3 /km/Myr (Jicha & Jagoutz, 2015)-rates that are matched in continental arcs only during magmatic flare-up events (Ducea et al., 2017;Paterson & Ducea, 2015). ...
During the differentiation of arc magmas, fractionating liquids follow a series of cotectics, where the co‐crystallization of multiple minerals control the melt compositional trajectories, commonly referred to as liquid lines of descent (LLD). These cotectics are sensitive to intensive properties, including fractionation pressure and melt H2O concentration, and changes in these variables produce systematic differences in the LLDs of arc lavas. Based on a compilation of experimental studies, we develop two major element proxies that exploit differences in LLDs to constrain the fractionation conditions of arc magmas. Near‐primary fractionating magmas evolve along the olivine‐clinopyroxene cotectic, which is pressure‐sensitive. We use this sensitivity to develop a proxy for early fractionation pressure based on the normative mineral compositions of melts with 8 ± 1 wt.% MgO. Fractionation in more evolved magmas is controlled by the clinopyroxene‐plagioclase cotectic, which is strongly sensitive to magmatic H2O contents. We use this relationship to develop an H2O proxy that is calibrated to the normative mineral components of melts with 2–4 wt.% MgO. These two proxies provide new tools for estimating the variations in pressure and temperature between magmatic systems. We applied these proxies to compiled major element data and phenocryst assemblages from modern volcanic arcs and show that in island arcs early fractionation is relatively shallow and magmas are dominantly H2O‐poor, while continental arcs are characterized by more hydrous and deeper early fractionation. These differences likely reflect variations in the relative contributions of decompression and flux melting in combination with distinct upper plate controls on arc melt generation.
... However, data sources and uncertainty associated with each estimate were not discussed. Based on the correlation between long seismic phase velocities and crustal heat flow, Till et al. (2019) suggest that crustal seismic structure and heat flow are primarily controlled by magmatic processes and advection of heat occurring in the upper mantle/deepest crust. They also argued that the flux of mantle-derived basalt varies by a factor of two along strike in the Quaternary Cascades. ...
The iconic volcanoes of the Cascade arc stretch from Lassen Volcanic Center in northern California, through Oregon and Washington, to the Garibaldi Volcanic Belt in British Columbia. Recent studies have reviewed differences in the distribution and eruptive volumes of vents, as well as variations in geochemical compositions and heat flux along strike (amongst other characteristics). We investigate whether these along-arc variations manifest as variations in magma storage conditions. We compile available constraints on magma storage depths from InSAR, geodetics, seismic inversions, and magnotellurics for each major edifice, and compare these to melt inclusion saturation pressures, pressures calculated using mineral-only barometers, and constraints from experimental petrology. The availability of magma storage depth estimates varies greatly along the arc, with abundant geochemical and geophysical data available for some systems (e.g. Lassen Volcanic Center, Mt. St. Helens), and very limited data available for other volcanoes, including many which are classified as “very high threat” by the USGS (e.g., Glacier Peak, Mt. Baker, Mt. Hood, Three Sisters). Acknowledging the limitations of data availability and the large uncertainties associated with certain methods, available data is indicative of magma storage within the upper 15 km of the crust (~2 ± 2 kbar). These findings are consistent with previous work recognising barometric estimates cluster within the upper crust in many arcs worldwide. There are no clear offsets in magma storage between arc segments that are in extension, transtension or compression, although substantially more petrological work is needed for fine scale evaluation of storage pressures.
... Wall et al. (2018) noted that the waxing and waning eruptive output of andesitic volcanoes in the Cascades over the Pleistocene reflects variability in the thermal energy delivered from the mantle at subduction zones, rather than cyclic surficial loading and unloading imposed by climate variability. Variability in magma compositions and eruptive rates along the Cascades volcanic arc was also shown by Till et al. (2019) to predominantly be related to variations in the flux of basalt into the crust. ...
One of the fundamental questions that underpins studies of the interactions between the cryosphere and volcanism is: do causal relationships exist between the ice volume on a volcano and its eruption rate? In particular, it is critical to determine whether the decompression of crustal magma systems via deglaciation has resulted in enhanced eruption rates along volcanic arcs in the middle to high latitudes. Evidence for such a feedback mechanism would indicate that ongoing glacier retreat could lead to future increases in eruptive activity. Archives of eruption frequency, size, and style, which can be used to test whether magma generation and eruption dynamics have been affected by local ice volume fluctuations, exist in the preserved eruptive products of Pleistocene-Holocene volcanoes. For this contribution, we have reviewed time-volume-composition trends for 33 volcanoes and volcanic groups in arc settings affected by glaciation, based on published radiometric ages and erupted volumes and/or compositions of edifice-forming products. Of the 33 volcanic systems examined that have geochronological and volumetric data of sufficient resolution to compare to climatic changes since ∼250 ka, increases in apparent eruption rates during post-glacial periods were identified for 4, with unclear trends identified for a further 12. Limitations in the geochronological and eruption volume datasets of the case studies make it difficult to test whether apparent eruption rates are correlated with ice coverage. Major caveats are: 1) the potential for biased preservation and exposure of eruptive materials within certain periods of a volcano’s lifespan; 2) the relative imprecision of geochronological constraints for volcanic products when compared with high-resolution climate proxy records; 3) the reliance on data only from immediately before and after the Last Glacial Termination (∼18 ka), which are rarely compared with trends throughout the Pleistocene to test the reproducibility of eruptive patterns; and 4) the lack of consideration that eruption rates and magma compositions may be influenced by mantle and crustal processes that operate independently of glacial advance/retreat. Addressing these limitations will lead to improvements in the fields of geochronology, paleoclimatology, and eruption forecasting, which could make valuable contributions to the endeavours of mitigating future climate change and volcanic hazards.
... Thermal and physical models point these regions (the so-called 'deep crustal hot zones') as the main place where arc magmas accumulate, differentiate and segregate from their source 10 . Magma production in the mantle and deep transfer processes are also increasingly thought to control the recharge and evolution of shallow magma chambers and ultimately volcanic activity 11,12 . Here, we take advantage of the intense activity of Tungurahua stratovolcano (Ecuador) between 1999 and 2016, and the evidence from large-scale syn-eruptive uplift of the edifice for continuous replenishment of the shallow magma chamber 13,14 , to constrain the compositional structure of the deep magma source by means of isotope analysis. ...
Arc volcanism arises from the release of fluids from the descending slab, which enables melting in the mantle wedge by lowering the solidus temperature. Metasomatism—compositional alteration by fluids—of the mantle is known to have an important role in magma production in volcanic arcs over long spatial and temporal scales. However, the episodic eruption of individual arc volcanoes is generally thought to be regulated primarily by the evolution and recharge of crustal magma reservoirs, with no established link to mantle processes. Here we show a link between eruptive activity in the 1999–2016 eruption sequence of Tungurahua volcano in Ecuador and small-scale metasomatism of the magma source. From high-resolution time series of the Pb and Sr isotopic composition of ashes, we determine that during the eruption sequence, the average rate of magma production varies logarithmically with the degree of source metasomatism, and that the sequence ended because of the exhaustion of the metasomatized source during its final weeks. Such an association points to mantle metasomatism over short spatial and temporal scales regulating magma production and ultimately eruptive activity of Tungurahua volcano. The influence of metasomatism on individual eruptions has been recognized for basaltic shield volcanoes, but our findings suggest that it is also a plausible mechanism to produce long-lasting eruptions at andesitic arc volcanoes.
... Volatiles also lower the solidus temperature of the mantle, which causes the mantle to melt, causing potentially hazardous eruptions along volcanic arcs (1)(2)(3). However, the fundamental controls on melt genesis and arc position at the surface remain debated, falling into two end-member hypotheses (4). In the first hypothesis, deep processes in the slab and mantle wedge dominate variations in magmatism, with slab devolatilization and mantle wedge thermal structure playing key roles (5). ...
Volatiles expelled from subducted plates promote melting of the overlying warm mantle, feeding arc volcanism. However, debates continue over the factors controlling melt generation and transport, and how these determine the placement of volcanoes. To broaden our synoptic view of these fundamental mantle wedge processes, we image seismic attenuation beneath the Lesser Antilles arc, an end-member system that slowly subducts old, tectonized lithosphere. Punctuated anomalies with high ratios of bulk-to-shear attenuation (Q κ −1 /Q μ −1 > 0.6) and V P /V S (>1.83) lie 40 km above the slab, representing expelled fluids that are retained in a cold boundary layer, transporting fluids toward the back-arc. The strongest attenuation (1000/Q S~2 0), characterizing melt in warm mantle, lies beneath the back-arc, revealing how back-arc mantle feeds arc volcanoes. Melt ponds under the upper plate and percolates toward the arc along structures from earlier back-arc spreading, demonstrating how slab dehydration, upper-plate properties, past tectonics, and resulting melt pathways collectively condition volcanism.
