An official website of the United States government
Abstract Magma‐water interaction can dramatically influence the explosivity of volcanic eruptions. However, syn‐ and post‐eruptive diffusion of external (non‐magmatic) water into volcanic glass remains poorly constrained and may bias interpretation of water in juvenile products. Hydrogen isotopes in ash from the 2009 eruption of Redoubt Volcano, Alaska, record syn‐eruptive hydration by vaporized glacial meltwater. Both ash aggregation and hydration occurred in the wettest regions of the plume, which resulted in the removal and deposition of the most hydrated ash in proximal areas <50 km from the vent. Diffusion models show that the high temperatures of pyroclast‐water interactions (>400°C) are more important than the cooling rate in facilitating hydration. These observations suggest that syn‐eruptive glass hydration occurred where meltwater was entrained at high temperature, in the plume margins near the vent. Ash in the drier plume interior remained insulated from entrained meltwater until it cooled sufficiently to avoid significant hydration.
more »
« less
Evaluating the Potential of Rhyolitic Glass as a Lithium Source for Brine Deposits
Abstract Lithium is an economically important element that is increasingly extracted from brines accumulated in continental basins. While a number of studies have identified silicic magmatic rocks as the ultimate source of dissolved brine lithium, the processes by which Li is mobilized remain poorly constrained. Here we focus on the potential of low-temperature, post-eruptive processes to remove Li from volcanic glass and generate Li-rich fluids. The rhyolitic glasses in this study (from the Yellowstone-Snake River Plain volcanic province in western North America) have interacted with meteoric water emplacement as revealed by textures and a variety of geochemical and isotopic signatures. Indices of glass hydration correlate with Li concentrations, suggesting Li is lost to the water during the water-rock interaction. We estimate the original Li content upon deposition and the magnitude of Li depletion both by direct in situ glass measurements and by applying a partition-coefficient approach to plagioclase Li contents. Across our whole sample set (19 eruptive units spanning ca. 10 m.y.), Li losses average 8.9 ppm, with a maximum loss of 37.5 ppm. This allows estimation of the dense rock equivalent of silicic volcanic lithologies required to potentially source a brine deposit. Our data indicate that surficial processes occurring post-eruption may provide sufficient Li to form economic deposits. We found no relationship between deposit age and Li loss, i.e., hydration does not appear to be an ongoing process. Rather, it occurs primarily while the deposit is cooling shortly after eruption, with δ18O and δD in our case study suggesting a temperature window of 40° to 70°C.
more »
« less
- Award ID(s):
- 1735512
- PAR ID:
- 10353457
- Date Published:
- Journal Name:
- Economic Geology
- Volume:
- 117
- Issue:
- 1
- ISSN:
- 0361-0128
- Page Range / eLocation ID:
- 91 to 105
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Models of subduction zone magmatism ascribe the andesitic composition of arc magmas to crustal processes, such as crustal assimilation and/or fractional crystallization, that basaltic mantle melts experience during their ascent through the upper plate crust. However, results from time series study of olivine-phyric high-Nb basalts and basaltic andesites from two monogenetic arc volcanoes (V. Chichinautzin and Texcal Flow) that are constructed on the ~45 km thick continental basement of the central Transmexican Volcanic Belt (TMVB) are inconsistent with this model. Instead, ratios of radiogenic isotope and incompatible trace elements suggest that these volcanoes were constructed through multiple individual melt batches ascending from a progressively changing mantle source. Moreover, the high Ni contents of the olivine phenocrysts, together with their high mantle-like 3He/4Heoliv =7-8 Ra with high crustal δ18O oliv = +5.5 to +6.5‰ (n=12) point to the presence of secondary ‘reaction pyroxenites’ in the mantle source that create primary silicic arc magmas through melt-rock reaction processes in the mantle [1, 2] . Here we present additional trace element concentration of the high-Ni olivines by electron microprobe (Mn, Ca) and laser-ablation ICPMS (Li, Cr and V) analysis in order to test this model. Olivine Li (2-7 ppm) and Mn (1170- 2810 ppm) increase with decreasing fosterite (Fo89 to Fo75), while Cr (29-364 ppm), V (4-11 ppm) and Ca (825-2390 ppm) decrease. Quantitative modeling shows that these trends in their entirety cannot be controlled by fractional crystallization under variable melt water H2O or oxygen fugacity (fO2), or co-crystallization of Cr-spinel. Instead, the variations support the existence of compositionally distinct melt batches during earliest melt evolution. Moreover, the trace element trends are qualitatively consistent with a model of progressive source depletion by serial melting (shown in olivine Ca, V and Cr) that is triggered by the repetitive addition of silicic slab components (shown by olivine Li). These findings suggest mantle source variations are not eliminated despite the thick crust these magmas pass during ascent. [1] Straub et al. (2013) J Petrol 54 (4): 665-701; [2] Straub et al. (2015) Geochim Cosmochim Acta 166: 29-52.more » « less
-
The origin of gaps or zoning in the composition of erupted products is critical to understanding how sub-volcanic reservoirs operate. We characterize the compositionally zoned magma that produced the 2053 ± 50 cal. yr BP Paso Puyehue Tephra from the Antillanca Volcanic Complex in the Andean Southern Volcanic Zone (SVZ). The 3.7 km3 Paso Puyehue Tephra is zoned from dacite (69 wt% SiO2) lapilli and ash comprising the lowermost 80% of the deposit that abruptly transitions upward into basaltic andesite scoria (54 wt% SiO2) making up the remaining ~20%. Variations in whole-rock, matrix glass, and mineral compositions through the deposit allow us to estimate pre-eruptive magma storage conditions and to develop a model of how this magma body was generated. Our findings suggest that amphibole-bearing basaltic andesitic magma stored at ~8.0 ± 1.3 km depth fractionally crystallized and cooled from 1048 ± 1.1 to 811 ± 28.6 ◦C under highly oxidizing conditions to produce silicic a melt that upon extraction and rise, pooled at ~6.4 ± 1.2 km depth at temperatures as low as 810 ◦C before eruption. MELTS models suggest that crystallization of a basaltic andesite parent magma with 4 wt% dissolved H2O can produce the dacite under conditions predicted by mineral thermobarometers with phase compositions comparable to those measured in minerals. Pervasive normal zoning at the rims of plagioclase crystals—most pronounced at the transition between dacite and basaltic andesite, and compatible vs. incompatible trace element concentrations, suggest that magma mixing was limited and likely occurred at the interface between the dacitic and basaltic andesitic magmas during ascent within the conduit upon eruption. Compositionally bimodal tephras are increasingly recognized throughout the SVZ with several interpreted to reflect basaltic recharge and mixing into extant rhyolitic reservoirs. In further contrast to other SVZ rhyolitic products, e.g., from the nearby Cord´on Callue and Mocho Choshuenco volcanoes, the Paso Puyehue magma was highly oxidized. This may reflect enhanced delivery of H2O from the subducting plate into the mantle wedge, which in turn may facilitate efficient extraction and separation of buoyant, low-viscosity rhyolitic melt from crystal-rich basaltic andesitic parent magmas and the co-eruption of both end members.more » « less
-
The Colorado Plateau, USA, is bordered by Pleistocene continental rift volcanism in New Mexico, Arizona, and Utah. While most of the eruptions have been basaltic, rhyolitic domes, tuffs, and lavas have been produced. On the western margin, where the Colorado Plateau meets the Basin and Range extensional province, the Black Rock Desert of central Utah hosts Pleistocene-Holocene bimodal basalt-rhyolite volcanic activity. The South Twin Complex consists of six rhyolites within a single basin erupted between 2.45 and 2.40 Ma, and they precede all Pleistocene basalts of the region. In this work, we share a new rhyolite eruptive stratigraphy based on high precision 40Ar/39Ar dates and examine the zircon crystal cargo from each eruptive center. The new eruption ages allow us to examine the spatial and temporal distribution of volcanism in the South Twin Complex, whereas the zircon crystal morphology, geochemistry, and U/Pb dating allow us to assess the conditions and timescales of silicic magma processes in the subvolcanic plumbing system. Our data suggest the plumbing system beneath the region experienced punctuated influxes of magma over a brief period of thousands to tens of thousands of years. Further, the timescales and patterns of silicic magma assembly and evolution of this small anorogenic region are similar to those observed within the voluminous Yellowstone province, suggesting that the volume of magmatic flux does not control magmatic evolution in intercontinental settings.more » « less
-
Explosive eruption jets rising through relatively shallow water layers form eruption columns that can deliver volcanic ash, gases, and entrained water to the atmosphere and ocean in sequence or simultaneously, depending on eruption source parameters (Gilchrist et al. 2023). Despite the mesospheric eruption column height of the January 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai (HTHH), the majority of erupted material was delivered to the surrounding seafloor via submarine pyroclastic density currents (PDCs). Deposits of HTHH show evidence of axisymmetric terraced deposits, which we show are linked to the mass eruption rate and dynamics of column collapse. We use scaled analog experiments on multiphase sand-water fountains injected into water layers of varying depth to model the collapse dynamics of shallow water eruption columns and to link fountain source conditions to deposit topography. The source strength of multiphase fountains predicts whether they collapse periodically or continuously via sedimentation waves with varying frequency and momentum. In turn, the frequency and momentum of sedimentation waves impacting the tank base determines whether ground-hugging gravity currents flowing out of the sedimentation wave impact zone are initially erosive or depositional. On the basis of experiments, we propose that syn-eruptive shallow submarine caldera deposits that show evidence of terracing and proximal scouring are linked to relatively strong eruption jets in the regime where the jet is in partial collapse or total collapse. In these regimes, the eruption jet collapses periodically as sedimentation waves that erode the deposit in the impact zone and transition into submarine PDCs that deposit the sedimentation wave mixture into regularly spaced terraces thereafter (Fig. 1, black boxes). In contrast, we expect weak eruption jets to occur in the total collapse regime where sedimentation waves descend in rapid succession and effectively supply submarine PDCs continuously which, in turn, build deposits lacking terraces (Fig. 1, blue box). For common values of caldera eruption source parameters, we link submarine PDC deposit morphology to eruption jet strength and plausible mass eruption rates.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5382/econgeo.4866
