Hydration fronts penetrate 50–135 μm into glassy rhyolite embayments hosted in quartz crystals from the Mesa Falls Tuff in the Yellowstone Plateau volcanic field. The hydration fronts occur as steep enrichments that reach 2.4 ± 0.6 wt% H2O at the embayment opening, representing much higher values than interior concentrations of 0.9 ± 0.2 wt% H2O. Molecular water accounts for most of the water enrichment. Water speciation indicates the hydration fronts comprise absorbed meteoric water that modified the original magmatic composition of the rhyolitic glass. We used finite difference diffusion models to demonstrate that glass rehydration was likely produced over a few decades as the ignimbrite cooled. Such temperatures and time scales are consistent with rare firsthand observations of decadal hydrothermal systems associated with cooling ignimbrites at Mount Pinatubo (Philippines) and the Valley of Ten Thousand Smokes (Alaska).Volcanic glasses rehydrate when exposed to moisture. Rehydration is a diffusion-limited process that produces concentration gradients of water that become enriched at interfaces exposed to water. The shape and magnitude of water enrichment in a concentration gradient are functions of many variables, including water diffusivity, water solubility, glass composition, temperature, and time. Archaeologists were the first to exploit this relationship, using the thickness of hydration rinds on obsidian artifacts to establish the age of burial (e.g., Friedman and Smith, 1960; Liritzis and Laskaris, 2011). Geoscientists subsequently recognized that rehydration of natural glasses provides opportunities to reconstruct past geologic processes related to climate, hydrology, topography, tectonics, and volcanology (e.g., Cassel and Breecker, 2017; Mitchell et al., 2018; Hudak et al., 2021; McIntosh et al., 2022).The use of rehydrated glass in volcanology requires careful assessment of water abundance and speciation because all volcanic glasses contain water. The source of water in volcanic glass may be primary magmatic, secondary meteoric, secondary marine, or combinations thereof. Magmatic melts contain dissolved water, with values commonly ranging between 0.1 and ~6 wt%. Dissolved magmatic water occurs as two separate species, molecular water and hydroxyl (Stolper, 1982). During eruption, both species of primary magmatic water exsolve during degassing, but they may also be partially preserved in erupted material by rapid ascent and quenching. The molecular water and hydroxyl preserved in erupted products record past volcanic processes because their relative proportions are controlled by intrinsic thermodynamic properties and kinetics. In contrast, low-temperature rehydration of rhyolite glass occurs almost entirely by diffusive absorption of molecular water. The resulting rehydration fronts occur as oversteepened, “S-shaped” concentration gradients (Anovitz et al., 2008; Hudak and Bindeman, 2020). The unique S-shaped form of the gradients is produced by the self-dependence of water diffusivity, meaning higher water concentration produces higher diffusion rates (Ni and Zhang, 2008). Information about water abundance, distribution, and speciation can consequently help to untangle the record of competing geologic processes preserved in volcanic glasses.We discovered S-shaped enrichments of molecular water in rhyolitic glasses preserved within quartz-hosted embayments from the Mesa Falls Tuff, Yellowstone Plateau volcanic field, western United States (Fig. 1A). Embayments are glass-filled channels that tunnel into crystal interiors (Figs. 1B and 1C). The crystal host partially shields the entrapped melt from subsequent modification, with exchange only allowed via the embayment “mouth” at the crystal's surface. During eruptive degassing, diffusion-limited loss of H2O and CO2 from embayments produces negative concentration gradients that can be used for geospeedometry of volcanic decompression rates (e.g., Humphreys et al., 2008; Myers et al., 2018). Quartz-hosted embayments from the Mesa Falls Tuff preserve negative CO2 concentration gradients, indicating slow decompressive ascent rates of 10–3.4 ± 0.5 MPa s–1 (Befus et al., 2023). Contrary to expectation, H2O gradients increase toward the embayment mouth. In this study, we demonstrate that positive concentration gradients of H2O in Mesa Falls fall deposit embayments were produced by diffusion-limited addition of meteoric water over a period of years to decades in response to a hydrothermal system that was established following deposition of the Mesa Falls ignimbrite. Our work suggests that embayment glasses, already a significant avenue for research because they track syneruptive decompression, also present opportunities to constrain the posteruptive history of volcanic deposits.Quartz crystals were handpicked from gently crushed pumice lapilli and loose bulk aggregate from a Mesa Falls pyroclastic fall deposit (44.122°N, 111.441°W). At this location, the fall deposit is directly overlain by ~10 m of Mesa Falls ignimbrite produced from the same eruption. Quartz crystals with glassy embayments were mounted in Crystalbond (Aremco), oriented, and ground and polished to produce a wafer of doubly exposed, doubly polished embayment glass. We analyzed 40 embayments in 39 quartz crystals.The embayments were analyzed by Fourier transform infrared spectroscopy (FTIR) using the synchrotron-source infrared Beamline 1.4 at the Advanced Light Source, Berkeley, California. The exceptional brightness and ~3 μm diffraction-limited spot size of the synchrotron allowed us to collect high-resolution transects of each embayment during ~60 h of continuous beamtime. Absorbances at 3500 and 2350 cm–1 were converted to volatile concentrations of total H2O and CO2 using the Beer-Lambert law and a representative rhyolite density of 2300 g L–1. We used a molar absorption coefficient of 1214 L cm–1 mol–1 for CO2 after Behrens et al. (2004) and a speciation-dependent coefficient for H2O that varied between ~60 and ~80 L cm–1 mol–1 (see Supplemental Material1). Molecular H2O was calculated using absorbance at 1630 cm–1 and converted into concentration using an absorption coefficient of 55 L cm–1 mol–1 (Newman et al., 1986). Sample thicknesses, ranging from ~30 to 160 μm, were measured in multiple spots along the embayment length using a petrographic microscope equipped with a linear drive encoder. Thickness uncertainties ranged up to 6 μm, and we used that 2σ uncertainty to establish error bars for volatile data.Mesa Falls Tuff embayments preserve concentration gradients of H2O and CO2. CO2 contents follow standard diffusion-limited gradients that decrease toward the embayment mouth (Supplemental Material). The form of the decreasing CO2 was produced during eruptive decompression, and it was not altered by rehydration (Befus et al., 2023). The distribution of H2O is similar across all embayments. Embayment interiors preserve flat, consistent H2O concentrations ranging from 0.72 ± 0.10 to 1.04 ± 0.10 wt%. These interior concentrations are composed of both hydroxyl and molecular H2O in roughly equal proportion (54% ± 10%). Those relatively uniform interior concentrations reflect equilibrium speciation during cooling from magmatic temperatures. The interiors ramp into steep, S-shaped rehydration fronts in the final 50–135 μm closest to the embayment mouth (Fig. 2). Rehydration fronts are enriched up to 1.73 ± 0.06–3.17 ± 0.10 wt% H2O. Most of the water in those enrichments occurs as molecular H2O (82% ± 5%). Such high molecular H2O is a disequilibrium speciation produced by low-temperature rehydration.The diffusion-limited form of the rehydration fronts in the Mesa Falls pyroclastic fall embayments can be used as a geospeedometer, one that presents the opportunity to extract the cooling time scale of the subsequent landscape-altering Mesa Falls ignimbrite. Geospeedometers exploit some geochemical signatures of the time scale of a volcanic process (e.g., Wallace et al., 2003; Lavallée et al., 2015). Here, time-temperature information is preserved in the S-shaped rehydration fronts, which are superimposed upon concentration gradients originally produced during volcanic decompression. To model the rehydration process, we assumed the relatively flat, consistent H2O gradients in the embayment interiors represent the initial condition for rehydration. The one-dimensional (1-D) finite-difference script, its description, and boundary conditions are provided in the Supplemental Material.The diffusivity of H2O in rhyolite glass (DH2O) expected in a cooling ignimbrite is one variable that must be established. Both archaeologic and volcanic research concurs that DH2O is ~10–23.5 ± 0.5 m2 s–1 in dry rhyolite glass at ambient conditions at Earth's surface (~0.1 wt% H2O; Liritzis and Laskaris, 2011; Giachetti et al., 2020). It is also accepted that DH2O will increase with increasing temperature and/or increasing water concentration. In experiments, >400 °C, DH2O increases linearly with H2O contents up to 1.8–2 wt% (Ni and Zhang, 2008; Coumans et al., 2020). The proportionality becomes exponential as water contents increase further (Zhang and Ni, 2010). It is the exponential relationship that produces the S shapes observed here, as well as those described in Yellowstone perlites and hydrothermal experiments (Bindeman and Lowenstern, 2016; Hudak and Bindeman, 2020). We suggest the formulation by Ni and Zhang (2008) is the best available approach for modeling DH2O in rhyolite glasses <400 °C, although their work specifically constrained diffusivity across the interval of ~400 to ~1600 °C (Ni and Zhang, 2008). Extrapolating the data presented by Ni and Zhang (2008) down from 400 °C to 0 °C reveals two important results: (1) It maintains the appropriate Arrhenian form, and (2) it predicts H2O diffusivity of 10−23 to 10−24 m2 s–1 at ambient conditions, coinciding with expectation (e.g., Giachetti et al., 2020; Fig. S1).We emphasize that rehydration modeling does not produce unique solutions but instead matches with observed concentration gradients as joint time-temperature-diffusivity combinations. We assumed the pyroclastic fall cooled to ambient temperatures during deposition, and that no rehydration occurred in the eruption column. We have no direct constraints on the emplacement temperature or cooling rate of the Mesa Falls ignimbrite. Matrix and embayment glasses have not altered to clays, nor have the rhyolite glasses lost alkalis. No columnar alteration was observed (e.g., Self et al., 2022). Together, the absence of those alteration features suggests limited temporal exposure to fluids >100 °C. Diffusivity is better constrained than cooling rate, so we treated the time-temperature path as the primary unknown in our model.We first calculated the time-temperature path for a cooling ignimbrite using a 1-D finite-difference thermal conductivity model. Conductive cooling presented a cooling time scale for the ignimbrite of ~40 yr to return to 5 °C. To establish this time scale, we modeled cooling of a 10-m-thick, crystal-rich rhyolitic ignimbrite as a single sheet. The ignimbrite was emplaced on top of a 5 m fall deposit initially at 5 °C. Bulk porosity (vesicles and interparticle space) was assumed to be 60% for all deposits (e.g., Karstens et al., 2023). Density and thermal conductivity of the solids were assumed to be 2600 kg m–3 and 1.6 W m–1 K–1 (Sass et al., 1988), respectively, with the effects of porosity accounted for using the model of Bagdassarov and Dingwell (1994). Specific heat was from Lavallée et al. (2015). This model inherently simplifies the cooling system by neglecting liquid and gas flow, the temperature dependence of thermodynamic properties, and possible changes in porosity.We focused on the form of the time-temperature path for material at ~1 m depth within the pyroclastic fall deposit where our samples were collected (Fig. 3B; Fig. S2). Conductive cooling predicts that the samples warmed rapidly in the first months after ignimbrite deposition. After reaching maximum temperatures between 150 °C and 250 °C, samples likely then cooled along an exponentially decreasing trend for the subsequent decades (Fig. 3C). Conductive cooling models have been shown to well approximate the time-temperature paths directly observed in some cooling ignimbrites following their historic eruptions (Riehle et al., 1995; Keating, 2005). When water sourced by precipitation or groundwater transports significant amounts of heat by liquid or vapor flows, cooling can be either faster or slower than the conductive limit depending on position within the ignimbrite (Randolph-Flagg et al., 2017). Here, we neglected cooling by precipitation because it would affect the upper parts of the ignimbrite, and the subsurface under the fall deposits would not reach the boiling temperature of water.The Mesa Falls ignimbrite erupted to produce the Henrys Fork caldera at 1.300 ± 0.001 Ma (Rivera et al., 2016). The eruption age represents the maximum diffusive time scale permitted for meteoric rehydration. The region's alpine, glacial-interglacial climate has been largely consistent since 1.3 Ma. Past climate supplied ample meteoric waters produced by orographic precipitation during cold winters and cool summers (seasonal range of ~–10 °C to ~10 °C; Licciardi and Pierce, 2018). H2O diffusivity during cold rehydration has been estimated to be ~10–23.5 ± 0.5 m2 s–1 (see Giachetti et al., 2020, and references therein), but modeling cold rehydration since the eruption at 1.3 Ma produced enrichments that extend <20 μm into embayments (Fig. S1). Cold rehydration therefore would require impermissibly long diffusive time scales ranging from 10 to 100 m.y. to reproduce the observed gradients.Rehydration fronts must have been generated by much higher diffusivity. We propose the embayment glasses were instead rehydrated after the ignimbrite transformed the extant cold hydrologic system into a high-temperature hydrothermal system. By analogy, we introduce the Valley of Ten Thousand Smokes, Alaska. The Griggs expedition first reached Novarupta in 1916, 4 yr after its caldera-forming eruption. They christened a nearby valley as the Valley of Ten Thousand Smokes because “the whole valley as far as the eye could reach was full of hundreds, no thousands—literally tens of thousands—of smokes curling up from the fissured floor.” The Valley of Ten Thousand Smokes hydrothermal system remained active for ~100 yr (Griggs, 1922; Hogeweg et al., 2005). Year-to-decade hydrothermal systems have been also observed in pyroclastic density current deposits at Mount Pinatubo, Philippines (e.g., Self et al., 2022).Geospeedometry modeling recovered the penetration distance, enrichment, and S-shaped forms of the observed rehydration fronts in the ~40 yr permitted by conductive cooling (Figs. 3D and 3E). Modeling also demonstrated how variations in ignimbrite character can each influence rehydration. Whereas sample depth and ignimbrite thickness were directly measured, emplacement temperature is unknown. Our observations generated model results that suggest emplacement at 400–450 °C, coinciding with published estimates for unwelded rhyolitic ignimbrites (Figs. 3D and 3E). Equally good fits to the data can be produced at higher temperatures, but only if the ignimbrite cooled faster than expected from pure end-member conductive cooling. More rapid cooling could be produced by effects of latent heat of vaporization. The paleoclimate of the Yellowstone region likely supplied ample groundwater and percolating precipitation to cycle through the cooling ignimbrite and its substrate.Embayments have a relatively simple geometry that can only be modified across the spatially limited, unprotected mouth. Glass will consequently be preserved in embayments much longer than other glasses in the same environment. Glass preservation, and its use, is also improved because embayment glasses are commonly dense, which reduces complications associated with vesiculation. Embayment-hosted crystals are emplaced instantaneously by volcanic eruptions that tend to have tight geochronologic constraints. Taken together, glassy embayments may be an as-of-now untapped record for paleoclimate and archaeology that could preserve information in deposits where no other glass remains because of age or other glass degradation processes.This research used resources of the Advanced Light Source, a U.S. Department of Energy Office of Science User Facility under contract no. DE-AC02-05CH11231. This research was made possible by grants from the National Science Foundation to K. Befus and M. Manga (grants EAR 2015255 and EAR 2042173, respectively). Reviews by Thomas Giachetti and Iona McIntosh improved this manuscript.

中文翻译：

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再水化的玻璃海湾记录了黄石火凝结岩的冷却过程


水化锋面渗透到黄石高原火山区梅萨瀑布凝灰岩石英晶体中的玻璃状流纹岩海湾中 50-135 微米。水化锋面呈陡峭富集状态，在海湾开口处达到 2.4 ±0.6 wt% H2O，比内部浓度 0.9 ±0.2 wt% H2O 高得多。分子水占富集水的大部分。水形态表明水化前沿包含吸收的大气水，改变了流纹岩玻璃的原始岩浆成分。我们使用有限差分扩散模型来证明，随着火凝灰岩冷却，玻璃再水化可能在几十年内产生。这样的温度和时间尺度与皮纳图博山（菲律宾）和万烟谷（阿拉斯加）与冷却火凝结物相关的十年热液系统的罕见第一手观察结果一致。火山玻璃在暴露于湿气时会重新水化。再水化是一种扩散限制过程，会产生水的浓度梯度，并在暴露于水的界面处富集。浓度梯度中水富集的形状和幅度是许多变量的函数，包括水扩散率、水溶性、玻璃成分、温度和时间。考古学家是第一个利用这种关系的人，他们利用黑曜石文物上水化外皮的厚度来确定埋葬年龄（例如，Friedman 和 Smith，1960 年；Liritzis 和 Laskaris，2011 年）。地球科学家随后认识到，天然玻璃的再水化提供了重建过去与气候、水文、地形、构造和火山学相关的地质过程的机会（例如，Cassel 和 Breecker，2017 年；Mitchell 等人，2017 年）。, 2018;胡达克等人，2021； McIntosh 等人，2022）。在火山学中使用再水化玻璃需要仔细评估水丰度和形态，因为所有火山玻璃都含有水。火山玻璃中的水源可以是原生岩浆、次生陨石、次生海洋或其组合。岩浆熔体含有溶解水，其含量通常在 0.1 至 6 wt% 之间。溶解的岩浆水以两种不同的形式出现，即分子水和羟基水（Stolper，1982）。在喷发过程中，两种原生岩浆水在脱气过程中都会溶出，但它们也可能通过快速上升和淬火而部分保留在喷发物质中。喷发产物中保留的分子水和羟基记录了过去的火山过程，因为它们的相对比例受到内在热力学性质和动力学的控制。相比之下，流纹岩玻璃的低温再水化几乎完全通过分子水的扩散吸收发生。由此产生的再水化前沿表现为过度陡峭的“S 形”浓度梯度（Anovitz 等人，2008 年；Hudak 和 Bindeman，2020 年）。独特的 S 形梯度是由水扩散率的自相关性产生的，这意味着较高的水浓度会产生较高的扩散速率（Ni 和Zhang，2008）。因此，关于水丰度、分布和物种形成的信息可以帮助解开火山玻璃中保存的竞争地质过程的记录。我们在黄石梅萨瀑布凝灰岩石英海湾内保存的流纹岩玻璃中发现了分子水的 S 形富集美国西部高原火山场（图1A）。 海湾是玻璃填充的通道，通向水晶内部（图 1B 和 1C）。晶体主体部分地保护了截留的熔体免于随后的改性，仅允许通过晶体表面的海湾“口”进行交换。在喷发脱气过程中，水和二氧化碳从海湾的扩散限制损失产生负浓度梯度，可用于火山减压速率的地球速度测量（例如，Humphreys等人，2008年；Myers等人，2018年）。梅萨瀑布凝灰岩的石英海湾保留了负二氧化碳浓度梯度，表明减压上升速率为 10–3.4 ± 0.5 MPa s–1（Befus 等人，2023 年）。与预期相反，H2O 梯度向海湾口方向增加。在这项研究中，我们证明了梅萨瀑布瀑布沉积海湾中 H2O 的正浓度梯度是通过在数年至数十年的时间内有限扩散的大气水产生的，以响应梅萨瀑布沉积后建立的热液系统火凝灰岩。我们的工作表明，海湾玻璃已经是一个重要的研究途径，因为它们跟踪协同爆发减压，也提供了限制火山沉积物后爆发历史的机会。石英晶体是从轻轻压碎的浮石和来自梅萨瀑布火山碎屑落下的松散散装骨料中手工挑选出来的沉积物（44.122°N，111.441°W）。在此位置，瀑布沉积物直接被同一次喷发产生的约 10 米的梅萨瀑布火凝灰岩覆盖。将具有玻璃湾的石英晶体安装在 Crystalbond (Aremco) 中，进行定向、研磨和抛光，以生产双重曝光、双重抛光的湾玻璃晶片。 我们分析了 39 种石英晶体中的 40 个凹坑。这些凹坑是使用加州伯克利高级光源公司的同步加速器源红外光束线 1.4 通过傅里叶变换红外光谱 (FTIR) 进行分析的。同步加速器卓越的亮度和 ~3 μm 衍射极限光斑尺寸使我们能够在 ~60 h 的连续光束时间内收集每个海湾的高分辨率横断面。使用比尔-朗伯定律和 2300 g L-1 的代表性流纹岩密度，将 3500 和 2350 cm–1 处的吸光度转换为总 H2O 和 CO2 的挥发浓度。根据 Behrens 等人的研究，我们使用了 1214 L cm–1 mol–1 的 CO2 摩尔吸收系数。 (2004) 和 H2O 的形态依赖系数在 ~60 和 ~80 L cm–1 mol–1 之间变化（参见补充材料 1）。使用 1630 cm–1 处的吸光度计算 H2O 分子，并使用 55 L cm–1 mol–1 的吸收系数转换为浓度（Newman 等人，1986）。使用配备线性驱动编码器的岩相显微镜，沿海湾长度在多个点测量样品厚度，范围为约 30 至 160 μm。厚度不确定性范围高达 6 μm，我们使用 2σ 不确定性来建立挥发性数据的误差线。梅萨瀑布凝灰岩海湾保留了 H2O 和 CO2 的浓度梯度。 CO2 含量遵循标准的扩散限制梯度，该梯度朝海湾口递减（补充材料）。减少的二氧化碳的形式是在喷发减压过程中产生的，并且不会因补水而改变（Befus et al., 2023）。所有海湾的水分布相似。海湾内部保持平坦、一致的 H2O 浓度，范围为 0.72 ± 0.10 至 1.04 ± 0.10 wt%。 这些内部浓度由羟基和分子 H2O 组成，比例大致相等 (54%±10%)。这些相对均匀的内部浓度反映了从岩浆温度冷却过程中的平衡形态形成。在最接近海湾口的最后 50-135 μm 处，内部斜坡进入陡峭的 S 形再水化前沿（图 2）。再水化前沿富集至 1.73 ± 0.06–3.17 ± 0.10 wt% H2O。这些浓缩物中的大部分水以分子 H2O 的形式存在（82% ± 5%）。这种高分子H2O是低温再水化产生的不平衡形态。梅萨瀑布火山碎屑落湾中再水化前沿的扩散限制形式可以用作地球速度计，它提供了提取水化冷却时间尺度的机会。随后的景观改变了梅萨瀑布的熔岩。地球速度计利用火山过程时间尺度的一些地球化学特征（例如，Wallace 等人，2003 年；Lavallée 等人，2015 年）。在这里，时间-温度信息被保存在S形再水化前沿中，这些前沿叠加在火山减压过程中最初产生的浓度梯度上。为了模拟再水化过程，我们假设海湾内部相对平坦、一致的 H2O 梯度代表了再水化的初始条件。补充材料中提供了一维 (1-D) 有限差分脚本、其描述和边界条件。冷却凝灰岩中预期的 H2O 在流纹岩玻璃 (DH2O) 中的扩散率是必须确定的一个变量。考古学和火山研究都一致认为，在地球表面环境条件下，干流纹岩玻璃中的 DH2O 约为 10–23.5 ± 0.5 m2 s–1（约 0.5 m2 s–1）。1 wt% H2O； Liritzis 和 Laskaris，2011； Giachetti 等人，2020）。人们还认为，DH2O 会随着温度的升高和/或水浓度的增加而增加。在实验中，>400 °C，DH2O 随 H2O 含量线性增加，最高可达 1.8–2 wt%（Ni 和Zhang，2008；Coumans 等，2020）。随着含水量进一步增加，比例呈指数变化（Zhang 和 Ni，2010）。正是指数关系产生了此处观察到的 S 形状，以及黄石珍珠岩和热液实验中描述的 S 形状（Bindeman 和 Lowenstern，2016；Hudak 和 Bindeman，2020）。我们建议 Ni 和Zhang (2008) 的公式是在 <400 °C 的流纹岩玻璃中模拟 DH2O 的最佳可用方法，尽管他们的工作特别限制了 ~400 至 ~1600 °C 范围内的扩散率（Ni 和Zhang, 2008） ）。将 Ni 和Zhang (2008) 提供的数据从 400 °C 外推到 0 °C 揭示了两个重要结果：(1) 它保持了适当的阿伦尼式形式，(2) 它预测 H2O 扩散率为 10−23 到 10−在环境条件下为 24 m2 s–1，与预期一致（例如，Giachetti 等人，2020；图 S1）。我们强调，再水化模型不会产生独特的解决方案，而是与观察到的浓度梯度相匹配，作为联合时间-温度-扩散率组合。我们假设火山碎屑在沉积过程中冷却到环境温度，并且喷发柱中没有发生再水化。我们对梅萨瀑布火凝灰岩的就位温度或冷却速率没有直接限制。基质和海湾玻璃没有变成粘土，流纹岩玻璃也没有失去碱。未观察到柱状蚀变（例如，Self 等人，2022）。 总之，这些改变特征的缺失表明有限的时间暴露于>100°C的液体。扩散率比冷却速率受到更好的约束，因此我们将时间-温度路径视为模型中的主要未知数。我们首先使用一维有限差分热导率模型计算冷却凝灰岩的时间-温度路径。传导冷却呈现出熔结矿冷却至 5 °C 所需的约 40 年时间。为了建立这个时间尺度，我们将 10 米厚、富含晶体的流纹岩熔结岩的冷却模拟为单片。最初在 5 °C 下将火凝灰岩放置在 5 米高的坠落沉积物顶部。所有沉积物的体积孔隙率（囊泡和颗粒间空间）假设为 60%（例如，Karstens 等人，2023）。固体的密度和导热系数假设分别为 2600 kg m–3 和 1.6 W m–1 K–1（Sass 等人，1988），并使用 Bagdassarov 和 Dingwell 模型考虑了孔隙率的影响（1994）。比热来自 Lavallée 等人。 （2015）。该模型通过忽略液体和气体流动、热力学性质的温度依赖性以及孔隙率可能的变化，从本质上简化了冷却系统。我们重点关注火山碎屑沉积物内约 1 m 深度的材料的时间-温度路径形式我们收集样本的地方（图 3B；图 S2）。传导冷却预测样品在熔凝结沉积后的头几个月内迅速升温。在达到 150 °C 至 250 °C 之间的最高温度后，样品可能在接下来的几十年中沿着指数下降趋势冷却（图 3C）。 传导冷却模型已被证明可以很好地近似在历史性喷发后的一些冷却熔结岩中直接观察到的时间-温度路径（Riehle 等人，1995 年；Keating，2005 年）。当来自降水或地下水的水通过液体或蒸汽流传输大量热量时，冷却速度可能比传导极限更快或更慢，具体取决于火凝灰岩内的位置（Randolph-Flagg 等，2017）。这里，我们忽略了降水冷却，因为它会影响熔凝结岩的上部，而瀑布沉积物下的地下不会达到水的沸点。梅萨瀑布熔凝结岩在1.300 ± 0.001 Ma时喷发，产生亨利斯福克破火山口。 （里维拉等人，2016）。喷发年龄代表了大气再水化所允许的最大扩散时间尺度。自1.3 Ma以来，该地区的高山、冰期-间冰期气候基本保持一致。过去的气候在寒冷的冬季和凉爽的夏季提供了由地形降水产生的充足的大气水（季节范围为〜10°C至〜10°C；Licciardi和Pierce，2018）。冷补液期间的 H2O 扩散率估计为 ~10–23.5 ± 0.5 m2 s–1（参见 Giachetti 等人，2020 年以及其中的参考文献），但自 1.3 Ma 喷发以来的冷补液模拟产生了延伸 <20 的富集度μm 进入海湾（图 S1）。因此，冷再水化需要 10 至 100 m.y 的超长扩散时间尺度。重现观察到的梯度。再水合前沿一定是由更高的扩散率产生的。我们建议，在熔结岩将现有的冷水文系统转变为高温热液系统后，海湾玻璃被重新水化。 以此类推，我们介绍一下阿拉斯加的万烟谷。格里格斯探险队于 1916 年首次到达诺瓦鲁普塔，即火山喷发 4 年后。他们将附近的一个山谷命名为“万烟谷”，因为“整个山谷放眼望去，充满了成百上千——实际上是数万——从裂缝的地面上袅袅升起的烟雾。”万烟谷热液系统保持活跃约 100 年（Griggs，1922；Hogeweg 等，2005）。在菲律宾皮纳图博山的火山碎屑密度流沉积物中也观察到了年至十年的热液系统（例如，Self等人，2022）。地球速度测量模型恢复了所观察到的再水化的渗透距离、富集度和S形形式传导冷却允许的约 40 年锋面（图 3D 和 3E）。建模还证明了凝灰岩特性的变化如何影响再水化。虽然直接测量了样品深度和熔凝结厚度，但安放温度未知。我们的观察产生的模型结果表明就位温度为 400–450 °C，与已发表的未焊接流纹岩熔结岩的估计值一致（图 3D 和 3E）。在更高的温度下也可以得到同样良好的数据拟合，但前提是熔凝结块的冷却速度比纯端件传导冷却的预期要快。通过汽化潜热的作用可以产生更快速的冷却。黄石地区的古气候可能提供了充足的地下水和渗透降水，以在冷却的熔凝岩及其基质中循环。海湾具有相对简单的几何形状，只能在空间有限、未受保护的河口进行修改。 因此，玻璃在海湾中的保存时间比相同环境中的其他玻璃要长得多。玻璃的保存及其使用也得到了改善，因为海湾玻璃通常很致密，这减少了与水泡相关的并发症。海湾中的晶体是由火山喷发瞬间形成的，而火山喷发往往具有严格的地质年代学限制。总而言之，玻璃海湾可能是迄今为止尚未开发的古气候和考古记录，它可以在由于年龄或其他玻璃降解过程而没有其他玻璃残留的沉积物中保存信息。这项研究使用了先进光源的资源，美国能源部科学用户设施办公室，合同号： DE-AC02-05CH11231。这项研究是通过国家科学基金会向 K. Befus 和 M. Manga 的资助（分别为 EAR 2015255 和 EAR 2042173）而得以实现的。 Thomas Giachetti 和 Iona McIntosh 的审阅改进了这份手稿。