Pit craters are observed throughout the solar system, but are rarely seen forming. Here we document pit crater formation and characteristics following the 2011–2012 Cordón Caulle rhyolitic eruption using satellite and drone data with field observations. Syn-eruptive shallow intrusion (laccolith) uplift and subsequent subsidence at Cordón Caulle are found to be responsible for the creation of faults and fractures as well as at least 349 collapse pits. At Puyehue volcano, we measure nearly 35 m of subsidence within the 2.5 km wide summit caldera from 2016–2024 using digital elevation models leading to ring fractures and pit craters forming inside the caldera. Some pit craters may form from melting snow buried by tephra deposited during 2011–2012. This study offers a unique example of near real-time pit crater formation and evolution, which may be applied to better understanding these processes on Earth and other planetary bodies.

Understanding how magma storage architecture and mafic recharge control eruptive behaviour is essential for interpreting explosive volcanism in thickened continental crust. We investigate the 1993 sub-Plinian eruption (VEI 4) of Lascar volcano, Andean Central Volcanic Zone, Chile, to constrain its crustal plumbing architecture and elucidate the role of magma mixing and mafic recharge. We integrate field observations, petrography, bulk-rock and mineral chemistry, to characterize five distinct eruptive products of the 1993 eruption: white pumice, green pumice, black scoria, banded pumice, and dome lithics, that range from basaltic trachyandesites to dacites (56–64 wt.

Most eruptions tap magmas from a range of pressures and storage environments within the crust and potentially even in the mantle. In this context, early crystallizing phases, such as olivine, provide a unique perspective into the deeper parts of many eruptions. When considering large olivine populations, compositional spectra of those populations serve as proxies for the different batches of magma that constitute the sometimes complex assembly of an eruption. While major element compositions in olivine provide links to melt compositions, minor and trace elements fingerprint deviations from simple liquid lines of descent. Moreover, Fe-Mg isotope signatures demonstrate whether magmas equilibrated diffusively or whether some mineral zoning retains growth histories prior and during assembly. To reveal the full picture of the assembly of an eruption and potentially changes during the eruption it is essential to collect olivine “interviews” from a large population as they exit the volcano. Here I show that such magma assembly prior to eruption varies greatly from one eruption to the next and that simple monogenetic cones may contain much more complex histories as they quickly pass the crust and may extract crystal cargo from a variety of locations and conditions, while many volumetrically larger more long-lived systems retain a simpler story despite their polybaric magma storage.

The Ca-in-olivine geohygrometer, first calibrated in 2016 (Gavrilenko et al. J Petrol, 57(9):1811-1832, 2016a), has since been widely applied to diverse datasets, providing significant insights into magmatic H2O contents. Building on extensive experience with this method, this study reviews the application of this petrological tool, summarizing its key features, strengths, and limitations. Using a large dataset of olivine-hosted melt inclusions (MIs) from Klyuchevskoy volcano, we highlight the method's advantages and challenges, propose strategies for optimizing its use, and suggest potential improvements for Ca-in-olivine hygrometry. Applying the Ca-in-olivine geohygrometer to extensive MI datasets for a given arc volcano can reveal the H2O content variation during this magma evolution, showing magmatic H2O accumulation at greater depth due to incompatible H2O behavior, and then a degassing trend at shallow depth when H2O saturation is reached. While effective for evolved compositions (Fo < similar to 85), the method underestimates magmatic H2O content in primitive compositions (Fo > similar to 85). Based on the 1-atm and high-pressure experiments with Klyuchevskoy compositions, combined with secondary fluorescence modeling around olivine-hosted MIs, we suggest that refining current Ca partitioning models (olivine/melt) and routinely measuring CaO in host olivine for reported MIs can improve the method's accuracy and broaden its applicability in magmatic studies. These findings aim to enhance the accuracy and applicability of this technique in studying magmatic processes.

Magma mush systems are commonly invoked as the source from which crystal-melt segregation produces rhyolites, but these systems are rarely observed. The 2011-2012 VEI 4 eruption of Cord & oacute;n Caulle produced rhyolite lavas which scavenged basaltic enclaves. These enclaves contain interstitial glass similar to their host rhyolitic lava, suggesting that these enclaves offer a window into an active, shallow basaltic mush system. This mush was proposed as the source from which crystallization generates high-silica rhyolite in a single step. Here, we use rhyolite-MELTS to determine whether this is thermodynamically realistic. First, we use melt geobarometry to establish that enclave-derived pressures (similar to 25-200 MPa) are consistent with those previously determined for the lavas. We then simulate isobaric crystallization using a range of initial starting water concentrations to test if it is possible to generate rhyolites of the appropriate composition, assuming a starting composition which is the same as the basaltic enclave whole-rock. We find that it is possible to produce suitable rhyolitic compositions via fractional crystallization. We then explore the simulated physical consequences of crystallization and fluid exsolution. Lower water simulations (0.5-1.0 wt.% H2O) at pressures of 100-200 MPa produce changes in volume most consistent with pre-eruptive ground deformation signals. We determine the timescales of heat loss from the crystallizing basaltic magma to be similar to 8-25 ka, but it is plausible that heat loss occurred on the order of similar to 1-10 ka which is broadly consistent with repose times of the system. The application of rhyolite-MELTS to an actively monitored system offers multifaceted insights into the geochemical, thermal, and physical evolution of magmas.

The 2011–2012 eruption at Cordón Caulle, Chile offers an exceptional opportunity to investigate topographic evolution of a laccolith, lava flows, and tephra during and after rhyolitic eruptions using satellite TanDEM-X and Plèiades data. We find distinct phases: rapid surface uplift from the laccolith and tephra (June–August 2011) and lava (June 2011–March 2012), followed by a reduction in the elevation of the laccolith and tephra (up to 19 m yr−1) until February 2013, and slower subsidence of all deposits until 2019 (the most recent data). The spatial distribution of subsidence-to-uplift ratios shows different volcanic and geomorphological processes occurring (degassing, cooling, crystallization, lateral movement, compaction, erosion). Pre-eruptive river channels showed elevation increases of up to 10–50 m due to tephra deposition, but this tephra was largely removed within three to four years. This research shows the potential of repeating high-resolution remote sensing elevation data to elucidate volcanic landscape evolution and yields insights into the co- and post-eruptive evolution of deposits.

Eocene arc magmatism is recognized to be responsible for the great quantities of porphyry Cu and Carlin-type Au mineralization in the Great Basin. However, an enigmatic spatial discontinuity exists in the metallogenic character of these ore deposits, with Au and Cu being predominantly found in eastern Nevada and western Utah, respectively. This east- west variability can be explained by diverging magma-fluid evolutionary paths with reduced and oxidized end members producing the mineralization observed in eastern Nevada and western Utah. The agent of such divergence is hypothesized to be contamination via crustal material of markedly different redox conditions in the two regions. Here, we add to a basin-wide analysis of redox conditions of Eocene plutons associated with Au and Cu mineralization by analyzing sulfur speciation in Swales Mountain intrusive apatite that is present in different mineral associations. Micro X-ray absorption near edge structure (𝜇-XANES) data were collected on apatite at the Advanced Photon Source. Collected spectra indicate varied paleo-redox conditions of ~FMQ + 2 at the most oxidized and ~FMQ + 0.3 at the most reduced. Reduced S-XANES signatures, however, were increasingly more frequent when observed in evolved samples and textures. Swales Mountain apatite included within late-stage crystallizing phases, i.e., plagioclase, orthoclase, and quartz, tended to present reduced signatures. Some apatite also exhibit low intensity and unclear spectra owing to the fact that sulfide does not substitute into the apatite structure as readily as the sulfate ion. A regionally extensive, organic carbon-rich, deep marine shale, the Vinini Formation, is a potential reducing assimilant. When assuming a high magmatic S concentration (2000 ppm) and a low TOC of the Vinini Formation of 1 wt%, we calculate that a maximum assimilation of just ~5% is needed to achieve the observed oxygen fugacity change. Assuming lower S concentrations in the magma and higher TOC results in ~1% or less assimilation that is needed to account for the change in observed S speciation measured in apatite. We use these observations to argue for late late stage reduction of Swales Mountain plutons and to further provide evidence of reduced crustal contamination leading to the mineralization of Au in Eastern Nevada.

ABSTRACT This guide presents an eight-hour, in-person tour of intersecting geologic and human history in western Nevada, USA. A 25 megaton phreatomagmatic blast created a mile-wide (1.6-km-wide) maar, now filled by Soda Lake. The magnitude 7 Dixie Val- ley earthquake ripped along more than 45 km of the Stillwater Range front in 1954. The 12 kiloton Shoal nuclear test in 1963 created a 50-m-wide cavity in solid granite. This field trip generally follows the GSA guide published in GSA Field Guide 61 (available at https://pubs.geoscienceworld.org/gsa): Louie, J.N., and Ruprecht, P., 2021, The blast, the quake, and the bomb: A guide to high-energy events in western Nevada, USA, in Florsheim, J., Koeberl, C., McKay, M.P., and Riggs, N., eds., Field Excursions from the 2021 GSA Section Meetings: Geological Society of America Field Guide 61, p. 201–219, https://doi.org/10.1130/2021.0061(09).

In some ways, olivine has driven the evolution of the Solar System and likely beyond. As one of the earliest-crystallizing silicate minerals, olivine controls the initial chemical evolution of planet-wide magma oceans and individual lava flows alike. In solid aggregate form, it controls and records deformation of the mantle and smaller-scale intrusive complexes. The components of its crystal structure are mobile at high temperatures and their migration can be used to explore the timing of magmatic events. During chemical weathering, these olivine crystals capture carbon dioxide from the atmosphere as secondary minerals are formed. All of these processes take place not only on Earth, but also on other planetary bodies, making olivine ideally suited to shed light on both primordial planet-building processes and current-day volcanism and surface processes.

When magmas erupt at the surface, they may have undergone many changes since their inception. While olivine drives some of these changes through crystallization and fractionation, it also records the magma evolution via mineral chemistry and by trapping mineral and melt inclusions. Olivine is an effective recorder of intensive parameters, such as temperature and melt composition, and provides an outstanding petrological tool for constraining dynamic processes, such as ascent, mixing, and cooling. Olivine sheds light on magmatic puzzles that involve both mafic and more evolved magmas, with protracted and complex magmatic histories that often obscure earlier and deeper processes. This contribution summarizes the current state of how olivine helps reconstruct source-to-surface magma assembly through its chemistry, inclusions, and textures.

SUMMARY The 2011–2012 eruption at Cordón Caulle in Chile produced crystal-poor rhyolitic magma with crystal-rich mafic enclaves whose interstitial glass is of identical composition to the host rhyolite. Eruptible rhyolites are thought to be genetically associated with crystal-rich magma mushes, and the enclaves within the Cordón Caulle rhyolite support the existence of a magma mush from which the erupted magma was derived. Moreover, towards the end of the 2011–2012 eruption, subsidence gave way to inflation that has on average been continuous through at least 2020. We hypothesize that magma segregation from a crystal mush could be the source of the observed inflation. Conceptually, magma withdrawal from a crystal-poor rhyolite reservoir caused its depressurization, which could have led to upward flow of interstitial melt within an underlying crystal mush, causing a new batch of magma to segregate and partially recharge the crystal-poor rhyolite body. Because the compressibility of the crystalline matrix of the mush is expected to be lower than that of the interstitial melt, which likely contains some fraction of volatile bubbles, this redistribution of melt would result in a net increase in volume of the system and in the observed inflation. We use numerical modelling of subsurface magma flow and storage to show under which conditions such a scenario is supported by geodetic and petrologic observations.

Two distinct types of rare crystal-rich mafic enclaves have been identified in the rhyolite lava flow from the 2011–12 Cordón Caulle eruption (Southern Andean Volcanic Zone, SVZ). The majority of mafic enclaves are coarsely crystalline with interlocking olivine-clinopyroxene-plagioclase textures and irregular shaped vesicles filling the crystal framework. These enclaves are interpreted as pieces of crystal-rich magma mush underlying a crystal-poor rhyolitic magma body that has fed recent silicic eruptions at Cordón Caulle. A second type of porphyritic enclaves, with restricted mineral chemistry and spherical vesicles, represents small-volume injections into the rhyolite magma. Both types of enclaves are basaltic end-members (up to 9.3 wt% MgO and 50–53 wt% SiO 2 ) in comparison to enclaves erupted globally. The Cordón Caulle enclaves also have one of the largest compositional gaps on record between the basaltic enclaves and the rhyolite host at 17 wt% SiO 2 . Interstitial melt in the coarsely-crystalline enclaves is compositionally identical to their rhyolitic host, suggesting that the crystal-poor rhyolite magma was derived directly from the underlying basaltic magma mush through efficient melt extraction. We suggest the 2011–12 rhyolitic eruption was generated from a primitive basaltic crystal-rich mush that short-circuited the typical full range of magmatic differentiation in a single step.

At present, the Basin and Range of the western USA is arid, but geologic studies show evidence of past wetness. The timing of these wetter conditions reveals a close association with glacial conditions. This association has led to the hypothesis of a causal link between glacial climate and regional wetness, but poor age control on the onset of regional wetness thwarts a test of this hypothesis. Here we determine the start of the most recent interval of persistent wetness in the Mono Basin, which is a hydrologically closed depression that sits at the west-central edge of the Basin and Range. The most recent emergence of persistent wetness in the Mono Basin is stratigraphically correlated with the depositional age of Ash 19—a rhyolitic ash bed that represents the oldest tephra of the Wilson Creek Formation and one of the earliest-known products of explosive volcanic activity from the Mono Craters. We constrain the depositional age of Ash 19 by using the U/Th disequilibrium dating method to date carbonates that are younger and older than Ash 19. Our U/Th dating results show that Ash 19 was deposited before the formation of a cross-cutting carbonate bed dated to 69.2 ± 0.3 ka but after an underlying carbonate tufa dated to 67.4 ± 3.5 ka, which suggests that the start of wetness in the Mono Basin was contemporary with the inception of the Last Glaciation—the beginning of Marine Isotope Stage 4—at ca. 70 ka. This finding corroborates the hypothesis of a link between glacial climate and regional wetness.

Several mechanisms have been proposed to allow highly viscous silicic magma to outgas efficiently enough to erupt effusively. There is increasing evidence that challenges the classic foam-collapse model in which gas escapes through permeable bubble networks, and instead suggests that magmatic fracturing and/or accompanying localized fragmentation and welding within the conduit play an important role in outgassing. The 2011–2012 eruption at Cordón Caulle volcano, Chile, provides direct observations of the role of magmatic fractures. This eruption exhibited a months-long hybrid phase, in which rhyolitic lava extrusion was accompanied by vigorous gas-and-tephra venting through fractures in the lava dome surface. Some of these fractures were preserved as tuffisites (tephra-filled veins) in erupted lava and bombs. We integrate constraints from petrologic analyses of erupted products and video analyses of gas-and-tephra venting to construct a model for magma ascent in a conduit. The one-dimensional, two-phase, steady-state model considers outgassing through deforming permeable bubble networks, magmatic fractures, and adjacent wall rock. Simulations for a range of plausible magma ascent conditions indicate that the eruption of low-porosity lava observed at Cordón Caulle volcano occurs because of significant gas flux through fracture networks in the upper conduit. This modeling emphasizes the important role that outgassing through magmatic fractures plays in sustaining effusive or hybrid eruptions of silicic magma and in facilitating explosive-effusive transitions.

Abstract The conditions under which halogens partition in favor of an exsolved fluid relative to the coexisting melt are key for understanding many magmatic processes, including volcanic degassing, evolution of crustal melt bodies, and ore formation. We report new F, Cl, and Br fluid/melt partition coefficients for intermediate to silicic melts, for which F and Br data are particularly lacking; and for varying CO2- H2O contents to assess the efects of changing fluid composition (XH2O) on Br fluid/melt partitioning for the first time. The experiments were conducted at pressures 50–120 MPa, temperatures 800–1100 °C, and volatile compositions [molar XH2O = H2O/(H2O +CO2)] of 0.55 to 1, with redox conditions around the Nickel-Nickel Oxygen bufer (ƒO2 ≈ NNO). Experiments were not doped with Cl, Br, or F and were conducted on natural crystal-bearing volcanic products at conditions close to their respective pre-eruptive state. The experiments therefore provide realistic constraints on halogen partitioning at naturally occurring, brine-undersaturated conditions. Measurements of Br, Cl, and F were made by Secondary Ion Mass Spectrometry (SIMS) on 13 experimental glass products spanning andesite to rhyolitic compositions, together with their natural starting materials from Kelud volcano, Indonesia, and Quizapu volcano, Chile. Fluid compositions were constrained by mass balance. Average bulk halogen fluid/melt partition coefficients and standard deviations are: DCl fluid/melt = 3.4 (±3.7 1 s.d.), DFfluid/melt = 1.7 (±1.7), and DBrfluid/melt = 7.1 (±6.4) for the Kelud starting material (bulk basaltic andesite), and DCl fluid/melt = 11.1 (±3.5), DFfluid/melt = 0.8 (±0.8), and DBr fluid/melt = 31.3 (±20.9) for Quizapu starting material (bulk dacite). The large range in average partition coeficients is a product of changing XH2O, pressure and temperature. In agreement with studies on synthetic melts, our data show an exponential increase of halogen Dfluid/melt with increasing ionic radius, with partitioning behavior controlled by melt composition according to the nature of the complexes forming in the melt (e.g., SiF4, NaCl, KBr). The fundamental chemistry of the diferent halogens (differing ionic size and electronegativities) controls the way in which partitioning responds to changes in melt composition and other variables. Experimental results confirm that more Cl partitions into the fluid at higher bulk Cl contents, higher melt Na, higher fluid XH2O ratios, and lower temperatures. Bromine shows similar behavior, though it seems to be more sensitive to temperature and less sensitive to Na content and XH2O. In contrast, F partitioning into the fluid increases as the melt silica content decreases (from 72 to 56 wt% SiO2), which we attribute to the lower abundance of Si available to form F complexes in the melt. These new data provide more insights into the conditions and processes that control halogen degassing from magmas and may help to inform the collection and interpretation of melt inclusions and volcano gas data.

Olivine is an important mineral in mafic-ultramafic rocks and records various crustal and mantle processes in basaltic magma. Generally, phosphorus (P) is immobile in olivine and its zoning tends to record magmatic processes. In contrast, lithium (Li) is one of the most mobile elements in olivine and tends to be re-distributed by postcumulus to hydrothermal processes. This study reports coupled Li-P oscillatory and sector zoning in cumulus olivine (Fo > 80 mol%) from magmatic Ni-Cu deposits in northwest China. The close to 1:1 relationship between Li + Na cation and P cation in olivine suggests P substitutes for slowly diffusing Si at the tetrahedral site and Li (Na) substitutes for Mg at the octahedral metal site. The preservation of such coupled Li-P zoning suggests that the charge-balanced-controlled substitution of Li+P5+ for Mg2+Si4+, producing a member of the Li(Fe)PO4 structure, may cause sluggish Li diffusion in olivine. The Li-P zoning is uncorrelated to other elements (Fe, Mg, Cr, Al, Ca, Ti, V, Ni, Zn, Mn, Co, and Sc). The Ca abundances in cumulus olivine are significantly depleted relative to those in volcanic olivine and modeled for olivine using the rhyolite-MELTS program, whereas the Mg, Fe, Mn, Zn, Ni, and Co contents show no signs of depletion. The Cr and Al contents in high Fo olivine are lower than those in volcanic olivine with a similar Fo value. The depletions in Ca, Cr, and Al (both divalent and trivalent cations) have been attributed to post-crystallization re-equilibration processes. We suggest that the selective Ca-Cr depletion in olivine resulted from re-equilibration between olivine and clinopyroxene-orthopyroxene-spinel-melts at the postcumulus stage, whereas the Al content variation in olivine is likely controlled by olivine-spinel (pyroxene) re-equilibration. Olivine fractionation modeling results reveal that Co content in both olivine and sulfides changes slightly during evolution, whereas the olivine Ni/Co ratio decreases dramatically from 30 (at Fo90) to 4 (Fo80). These are consistent with the variation of Ni and Co contents in olivine from sulfide-barren rocks but cannot explain the strong positive Ni-Co correlation observed in olivine from the sulfide-bearing rocks. The considerable increase in the Ni/Co ratio in olivine coexisting with the high Ni tenor sulfide compared with the slight increase of the Ni/Co ratio in olivine coexisting with moderate-low Ni tenor sulfide strongly suggests that the Ni and Co contents and Ni/Co ratio in olivine from the mineralized rocks were the results of olivine-sulfide interaction. The olivine Fe/Zn and Mn/Zn ratios show little difference between sulfide-barren and sulfide-rich rocks, but these ratios decrease considerably with the decreasing Fo values. Overall, the study suggests that elements (Ca, Cr, Al, Mg, Fe, Ni, Co, Zn, etc.) diffuse faster than P have been re-distributed in cumulus olivine by re-equilibration processes, modifying the elemental content and inter-element ratios in olivine. The characteristics of the crystallization, particularly the source recorded in cumulus olivine, may be obscured and overprinted by postcumulus processes.