We show that recalescence, or spontaneous reheating of a cooling material due to rapid release of latent heat, can occur during disequilibrium crystallization of depolymerized Mg-rich melts. This can only happen at fast cooling rates, where the melt becomes undercooled by tens to hundreds of degrees before crystallization begins. Using a forward-looking infrared (FLIR) camera, we documented recalescence in pyroxene (Fe, Mg)SiO3 and komatiite lavas that initially cooled at 25–50 °C s–1. Local heating at the crystallization front exceeds 150 °C for the pyroxene and 10 °C for komatiite and lasts for several seconds as the crystallization front migrates through. We determined the latent heat release by differential scanning calorimetry to be 440 J g–1 for pyroxene and 275 J g–1 for komatiite with a brief power output of ∼100 W g–1 or ∼300 MW m–3. Recalescence may be a widespread process in the solar system, particularly in lava fountains, and cooling histories of mafic pyroclasts should not be assumed a priori to be monotonic.Molten materials, from magma oceans to lava droplets, crystallize when they are cooled at slow to moderate rates (Fig. 1A, path 1). Latent heat released during crystallization typically slows, but does not halt, monotonic cooling. During rapid cooling, molten materials can become supercooled, i.e., they can exist below their liquidus without immediately crystallizing. These supercooled liquids can undergo rapid disequilibrium crystallization at temperatures far below those of the liquidus but still above those of the glass transition (Fig, 1A, path 3; Kirkpatrick, 1975). If latent heat is released faster than it can be removed by radiation or conduction, the material can spontaneously heat up through a phenomenon known as recalescence (Fig. 1A, path 2; Fig. 1B). At the highest cooling rates, the liquid will quench to glass, which retains the amorphous structure of the liquid but lacks its mobility (Fig. 1A, path 4).Recalescence has long been known in iron and effectively limits the minimum grain size achievable in steel production (Yokota et al., 2004). Recalescence occurs in poor glass-forming liquids such as the alumina-yttria-lanthana system (e.g., Tangeman et al., 2007) and has been observed in levitated Mg2SiO4 liquids, where container-less synthesis allows rapid undercooling without crystallization (Tangeman et al., 2001). The latter example is the only reported experimental observation we could find of recalescence in silicate melts, as most experimental cooling-rate studies are conducted at cooling rates that are too slow for latent heat to produce net heating; instead, cooling rates are simply buffered (e.g., Lofgren and Russell, 1986; Longhi, 1992; Vetere et al., 2013). However, two studies suggest that recalescence took place in natural silicate melts; recalescence was proposed as an explanation for the irregular thermal histories recorded at the base of basaltic lava flows (Keszthelyi, 1995) and, over a much longer time scale, magma heating through the release of latent heat from crystallization has been inferred to explain data from plagioclase-hosted melt inclusions in andesitic lavas, which show increasing temperatures at decreasing pressures as magma ascends toward the surface and degasses (Blundy et al., 2006).Polymerized silicate melts, including window glass and rhyolitic lavas, can quench to glass easily without requiring rapid cooling as indicated by the dense obsidian cores of some thick and slow-cooling rhyolite flows (e.g., Fink, 1983), which prevents the release of significant latent heat and makes recalescence impossible. In general, more depolymerized melts are poorer glass-formers and are more likely to undergo recalescence during rapid disequilibrium crystallization. This suggests that ultramafic lavas such as komatiites, which were more common early in Earth history (Arndt et al., 2008), may undergo this process, which would affect both their thermal and rheological history during emplacement.Such considerations also extend to extraterrestrial environments. Depolymerized mafic lavas cover much of the lunar nearside as well as parts of every terrestrial planet, and mafic (and possibly ultramafic) lavas have been observed erupting on Jupiter's moon Io (e.g., McEwen et al., 1998). We conducted a series of experiments to investigate dynamic crystallization at large degrees of undercooling for two depolymerized silicate compositions, a simple pyroxene (Fe0.39Mg0.59SiO3.00) and a more complex komatiite (Ca0.18Mg0.46Fe0.17Al0.22Ti0.01Si0.91O3.00), for which we had previously determined thermal diffusivity to high temperature (Hofmeister et al., 2014; Sehlke et al., 2020), and we documented recalescence in both lavas.Starting glasses were synthesized from oxide and carbonate powders with repeated cycles of fusion in a Pt90Rh10 crucible, splat-quenching on a copper plate, and grinding to ensure homogeneity.We performed quantitative observations using a tripod-mounted FLIR Systems® T650sc with a 640 × 480 sensor array looking vertically downwards toward the sample from a distance of ∼1 m. We melted a few grams of pyroxene glass in a Pt90Rh10 crucible in a muffle furnace at 1590 °C and then placed it onto a graphite plate kept at ∼550 °C with a hot plate to reduce heat flow out of the base of the crucible.Chips of ∼25–50 mg were heated above their liquidus and then cooled to room temperature in a Netzsch® 404F1 Pegasus differential scanning calorimeter. Heat flow was converted to a quantitative measurement of isobaric heat capacity (CP) by running a series of three experiments under identical temperature-time programs including heating at a constant rate, an isothermal dwell at high temperature, and cooling at a constant rate. The first experiment involved a blank (empty pan), the second a sapphire standard (Ditmars et al., 1982), and the third the material to be analyzed. Full details of experimental conditions and observed heat flow peaks are given in Table S1 in the Supplemental Material1.Initial observations of recalescence were made during synthesis of some pyroxene melts [(Fe, Mg)SiO3], when the crucible was removed from the furnace at ∼1600 °C and placed on a copper plate. During cooling, nucleating crystals appeared brighter than the surrounding melt. As they grew, the advancing crystallization fronts remained brightest, crystal interiors were less bright, and uncrystallized melt was the least bright (Fig. 2; Video S1). These initial observations were recorded with a phone camera, which allowed only qualitative assessment of recalescence due to automatic brightness adjustments. We performed quantitative observations using a forward-looking infrared (FLIR) camera with an assumed emissivity of 0.95.On cooling from 1590 °C, at ∼30 °C s–1, crystallization of Fe0.4Mg0.6SiO3 liquid begins at ∼1110 °C, which is ∼370 °C below the liquidus temperature of 1480 °C (Muan and Osborn, 1956). Averaging over the whole base of the crucible (∼10 cm2), the observed temperature increase during crystallization was ∼100 °C, and it took ∼2.5 s to attain the thermal peak (Fig. 1B). Crystallization and heating can be seen migrating across the melt volume together (Video S2). The hottest part of the image is always the crystallization front, where the latent heat is actually being released. The crystals are therefore always warmer than the melt because the crystallization front has already moved through them. Examining a 3 × 3 pixel spot (∼1 mm2 in our setup), reheating to T >1270 °C occurred in ∼1 s (Fig. 1B). Recovered samples show the growth of needle-like spinifex-textured bronzite (Fe0.20Mg0.82Si0.98O3) with interstitial, iron-rich pyroxene crystals ranging in composition from ferrosilite (Fe0.92Mg0.10Si0.97O3) to ferrohypersthene (Fe0.74Mg0.25Si0.99O3); this range probably resulted from variable local Mg-depletion following early bronzite crystallization (Fig. 3; Table S1).Upon cooling of komatiite liquid from ∼1590 °C, the sample quenched to glass. Starting instead with the crucible at ∼1450 °C and cooling initially at ∼50 °C s–1, crystallization began at ∼1080 °C. Averaging over the base of the crucible, cooling paused for ∼2 s and then resumed at ∼15 °C/min (Fig. 1B). In a 3 × 3 pixel spot, ∼10 °C reheating occurred in ∼0.5 s. When viewed as the temperature difference between different video frames, newly formed crystals are ∼30 °C hotter than uncrystallized melt, and crystallization mostly proceeded from the crucible wall to the interior of the melt (Fig. 1H). Recovered samples show small chrome spinel crystals surrounded by a dendritic intergrowth of aluminous, Mg-rich pigeonite (Ca0.15Fe0.14Mg0.59Al0.10Si0.90O3) and aluminous augite (Ca0.25Fe0.17Mg0.38Al0.11Si0.91O3) (Fig. 3). Komatiite lavas typically crystallize olivine first and often display spinifex texture with interstitial plagioclase and aluminous clinopyroxene (Shore and Fowler, 1999), but cooling rates in our experiments were fast enough to crystallize two pyroxenes instead in a metastable manner.We also investigated crystallization using differential scanning calorimetry (DSC) to demonstrate that recalescence also occurs in melt quantities that are smaller by orders of magnitude and to quantify the heat flows involved. Samples were heated to a fully molten state at ∼1500 °C and then cooled at controlled rates of 50 °C min–1 or 100 °C min–1 to 500 °C, which is well below their glass transition temperature (Tg). For pyroxene melt that was cooled at ∼50 °C min–1, two distinct crystallization peaks were seen at 1316 °C and 1264 °C (Fig. 4). During cooling, the enthalpy of crystallization appears as an increase in apparent heat capacity because the calorimeter must remove both the sensible and latent heat components.Cooled at ∼100 °C min–1, a large peak was seen at 1313 °C with a smaller second peak at 1273 °C. Examination of recovered samples indicates crystallization of bronzite (Fe0.22Mg0.84Si0.97O3) of a similar composition but much larger size than was observed in the FLIR experiment, with small ferrosilite crystals (Fe0.94Mg0.05Si0.99O3) and exsolution of silica-rich melt globules (∼97 wt% SiO2) interspersed within a more iron-rich, glassy matrix (Fig. 3). We interpret the first DSC peak as recording bronzite crystallization and the second as recording oxide growth. The total latent heat release is 472 J g–1 at 100 °C/min and 418 J g–1, 439 J g–1, and 484 J g–1 in three experiments at 50 °C min–1.For komatiite melt cooled at 50 °C min–1, two distinct crystallization peaks were seen at 1139 °C and 986 °C (Fig. 4). Cooled at ∼100 °C min–1, the first peak was at ∼1125 °C while the second peak occurred at ∼1075 °C. Examination of samples recovered indicates crystallization of forsteritic olivine needles (Fe0.21Mg1.76Si1.00O4) that in places adopt a graphic texture; numerous small (∼2 µm) magnetite crystals are concentrated on olivine faces, and there is a matrix of ∼10-µm-sized dendritic aluminous augite (Ca0.30Fe0.19Mg0.23Al0.26Si0.92O3) similar in composition to the interstitial glass (Table S1). X-ray diffraction (XRD) analysis suggests the proportions of crystalline phases are ∼55 wt% forsterite, ∼40 wt% augite, and ∼5 wt% magnetite. We interpret the larger, higher temperature DSC peak as recording olivine crystallization and the subsequent peak as recording augite growth. The ΔHxtal for komatiite liquids was −233 J g–1 to −293 J g–1, which is lower than for the pyroxene liquids, because komatiitic liquids are more polymerized.Our observations of reheating in excess of 100 °C during spontaneous crystallization of depolymerized mafic melts have several implications for both terrestrial and planetary volcanology.Indirect evidence for recalescence occurring in nature comes from observations of temperature fluctuations at the base of a basaltic lava flow at Kīlauea volcano, Hawaiʻi (Keszthelyi, 1995). Our observations of temperature differences of up to ∼100 °C on a millimeter scale (Fig. 2) suggest that thermal imaging of basaltic lava flows using hand-held or tripod-mounted FLIR cameras needs to be conducted with millimeter-scale spatial resolution to assess true temperature fluctuations. Due to safety considerations, field-based temperature measurements of active lava flows and lakes are typically recorded from a distance that provides meter- to decimeter-scale rather than millimeter-scale spatial resolution (e.g., Harris et al., 2005; Spampinato et al., 2008; Harris, 2013), which may result in averaging cooler melt and hotter crystals within a single pixel and systematic overestimation of the temperature of the liquid phase.In practice, radiative cooling is fast, and overestimating the melt temperature in a lava flow is unlikely. Wright and Flynn (2003) obtained FLIR images of pahoehoe flows at Kīlauea with ∼4 mm spatial resolution, probably the highest to date, and found that the highest temperature pixel was only 1094 °C, which is substantially cooler than temperatures inferred from the rheological behavior of Hawaiian lavas forming pahoehoe lobes (Sehlke et al., 2014). In a normal lava flow, each part of the flow surface only gets to cool once. In contrast, active lava lakes continually expose new batches of fresh, hot lava at the surface (e.g., Tilling, 1987). However, this lava may also cool too quickly for recalescence to occur, and active lava lakes are typically very difficult to approach closely enough to ensure millimeter-scale pixel sizes.An alternative approach is to use numerical models of cooling and latent heat release, based on kinetic studies of crystal nucleation and growth rates, to predict recalescence (Keszthelyi, 1995). Thermal models of cooling lava that incorporate latent heat of crystallization as an “effective heat capacity” term, as is typically adopted for lava flows and cooling plutons (e.g., Nabelek et al., 2012; Harris, 2013), prohibit recalescence and may inaccurately capture the thermal history of rapidly cooling lava bodies.Droplets erupted in lava fountains can cool much more rapidly than larger bodies. Lava fountains on Earth typically involve tholeiitic basalts at shield volcanoes such as Kīlauea volcano (Eaton and Murata, 1960; Wolfe et al., 1987). Moitra et al. (2018) modeled cooling of basaltic pyroclasts and calculated cooling rates through 700 °C (∼Tg) of ∼3 °C s–1, 30 °C s–1, and 300 °Cs–1 for clast diameters of 30 mm, 3 mm, and 0.3 mm, respectively, which suggests that coarse ash and small lapilli will typically cool at rates that are consistent with recalescence in mafic melts. Volcanic glass spherules on the Moon are mostly <1 mm in size, but the larger spherules often contain acicular to fibrous crystals (Rutherford and Papale, 2009), textures consistent with rapid disequilibrium crystallization, and perhaps with recalescence (Fig. 3).Active lava fountain events were observed on Jupiter's moon Io in November 1999 by NASA's Galileo mission (McEwen et al., 2000) and using ground-based telescopes over a 25 yr period (Davies, 1996; Stansberry et al., 1997; de Kleer et al., 2019). These “outburst” eruptions have timescales similar to those of terrestrial events (hours to days). Ionian lavas were estimated to erupt at high temperatures, between 1200 and 1700 °C, based on observations by the Near-Infrared Mapping Spectrometer (NIMS) on the Galileo spacecraft (McEwen et al., 1998; Davies et al., 2000). Such high temperatures suggest mafic to ultramafic lava compositions such as komatiites.Keszthelyi et al. (2007) modeled the thermal history of lava droplets on Io and predicted that 0.1 mm and 1 mm droplets would cool by ∼650°C and ∼200°C in 1 s. However, droplets were assumed to quench to glass in the models and were therefore unable to recrystallize and release heat during crystallization. Slightly larger droplets would cool in the ∼50°Cs-1 range of our cooling experiments, and they should recalesce. In this case, the additional latent heat released will contribute to the overall thermal flux of the fountain but will not be accompanied by higher peak temperatures because recalescence is limited to subliquidus temperatures (Fig. 1). Recalescence would raise the temperatures of the hottest components, which are derived from model fits to observational data, closer to actual lava eruption temperatures. Hence, we would be closer to understanding the composition of silicate lavas erupting on Io.We thank Jerry Beeney from FLIR systems (https://www.flir.com) for assisting with video acquisition, and Paul Carpenter for assistance with microprobe analysis. We thank Ashley Davies and an anonymous reviewer for comments that improved the manuscript. Funding for this work was provided by NASA grants NNX12AO44G and 80NSSC19K1010.

中文翻译：

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结晶熔岩的自发重新加热

我们表明，在解聚的富镁熔体的不平衡结晶过程中，可能会发生由于潜热的快速释放而导致的冷却材料的重新发光或自发重新加热。这只能发生在快速冷却速度下，在结晶开始之前，熔体会过冷数十到数百度。使用前视红外 (FLIR) 相机，我们记录了辉石（Fe、Mg）SiO3 和科马提岩熔岩的再辉，最初冷却温度为 25–50 °C s–1。辉石结晶前沿的局部加热超过 150 °C，科马提岩超过 10 °C，并随着结晶前沿迁移而持续几秒钟。我们通过差示扫描量热法确定辉石的潜热释放为 440 J g-1，科马提石为 275 J g-1，短暂的功率输出为~100 W g-1 或~300 MW m-3。再辉可能是太阳系中的一个普遍过程，尤其是在熔岩喷泉中，不应先验地假设基性火山碎屑的冷却历史是单调的。从岩浆海洋到熔岩滴的熔融材料在缓慢冷却至中等速率（图 1A，路径 1）。结晶过程中释放的潜热通常会减慢但不会停止单调冷却。在快速冷却过程中，熔融材料会变得过冷，即它们可以存在于液相线以下而不会立即结晶。这些过冷液体可以在远低于液相线温度但仍高于玻璃化转变温度的温度下经历快速不平衡结晶（图 1A，路径 3；柯克帕特里克，1975 年）。如果潜热释放的速度快于辐射或传导的去除速度，该材料可以通过称为再辉的现象自发升温（图 1A，路径 2；图 1B）。在最高冷却速率下，液体将淬火成玻璃，它保留了液体的无定形结构但缺乏流动性（图 1A，路径 4）。人们早就知道铁的再辉，并有效地限制了可达到的最小晶粒尺寸钢铁生产（横田等人，2004 年）。再辉发生在较差的玻璃形成液体中，例如氧化铝-氧化钇-氧化镧系统（例如，Tangeman 等人，2007 年），并在悬浮的 Mg2SiO4 液体中观察到，其中无容器合成允许快速过冷而不会结晶（Tangeman 等人，2007 年） ., 2001)。后一个例子是我们在硅酸盐熔体中发现的重新发光的唯一报道的实验观察，因为大多数实验冷却速率研究都是在冷却速率太慢而潜热无法产生净热量的情况下进行的；相反，冷却速率只是缓冲（例如，Lofgren 和 Russell，1986 年；Longhi，1992 年；Vetere 等人，2013 年）。然而，两项研究表明，在天然硅酸盐熔体中发生了再辉；重新辉光被提议作为在玄武岩熔岩流底部记录的不规则热历史的解释（Keszthelyi，1995），并且在更长的时间范围内，通过结晶释放潜热的岩浆加热已被推断为解释来自安山岩熔岩中以斜长石为主体的熔体包裹体，随着岩浆向地表上升和脱气，显示温度升高，压力降低（Blundy 等，2006）。聚合硅酸盐熔体，包括窗玻璃和流纹岩熔岩在内，可以很容易地淬火成玻璃，而不需要快速冷却，正如一些厚的和缓慢冷却的流纹岩流的致密黑曜石核所表明的那样（例如，芬克，1983），这可以防止大量潜热的释放，并使不可能再发光。一般来说，更多解聚的熔体是较差的玻璃形成体，并且在快速不平衡结晶过程中更可能发生再辉。这表明在地球历史早期更常见的超镁铁质熔岩（如科马提岩）（Arndt 等人，2008 年）可能会经历这一过程，这将影响它们在就位期间的热和流变历史。这些考虑也扩展到外星环境. 解聚的镁铁质熔岩覆盖了月球近侧的大部分以及每个类地行星的一部分，已经观察到在木星卫星 Io 上喷发的镁铁质（也可能是超镁铁质）熔岩（例如，McEwen 等，1998）。我们进行了一系列实验来研究两种解聚硅酸盐组合物，一种简单的辉石 (Fe0.39Mg0.59SiO3.00) 和一种更复杂的科马提石 (Ca0.18Mg0.46Fe0.17Al0.22Ti0.01Si0 .91O3.00），我们之前已经确定了高温的热扩散率（Hofmeister 等人，2014 年；Sehlke 等人，2020 年），并且我们记录了两个熔岩中的再辉。起始玻璃由氧化物和碳酸盐粉末合成在 Pt90Rh10 坩埚中反复熔化，在铜板上快速淬火，并研磨以确保均匀性。我们使用安装在三脚架上的 FLIR Systems® T650sc 和 640 × 480 传感器阵列进行定量观察，从 1 m 的距离垂直向下看样品。我们在马弗炉中的 Pt90Rh10 坩埚中在 1590°C 下熔化了几克辉石玻璃，然后将其放置在保持在约 550°C 的石墨板上，并带有热板，以减少从坩埚底部流出的热量。约 25–50 mg 的碎片在其液相线以上加热，然后在 Netzsch® 404F1 Pegasus 差示扫描量热仪中冷却至室温。通过在相同的温度-时间程序下运行一系列三个实验，包括以恒定速率加热、在高温下等温停留和以恒定速率冷却，将热流转化为等压热容 (CP) 的定量测量。第一个实验涉及一个空白（空盘），第二个是蓝宝石标准（Ditmars 等，1982），第三个是要分析的材料。实验条件和观察到的热流峰的全部细节在补充材料 1 的表 S1 中给出。在合成一些辉石熔体 [(Fe, Mg)SiO3] 期间，当坩埚在∼1600 °C 并放置在铜板上。在冷却过程中，成核晶体看起来比周围的熔体更亮。随着它们的生长，前进的结晶前沿保持最亮，晶体内部不太亮，未结晶的熔体最不亮（图 2；视频 S1）。这些最初的观察是用手机摄像头记录的，由于自动亮度调整，这仅允许对重新发光进行定性评估。我们使用假定发射率为 0.95 的前视红外 (FLIR) 相机进行了定量观察。从 1590 °C 冷却后，在~30 °C s-1 时，Fe0.4Mg0.6SiO3 液体的结晶开始于~1110 ° C，比 1480°C 的液相线温度低 370°C（Muan 和 Osborn，1956）。在坩埚的整个底部（~10 cm2）上平均，在结晶过程中观察到的温度升高为~100°C，并且需要~2.5 秒才能达到热峰值（图 1B）。可以看到结晶和加热一起在整个熔体体积中迁移（视频 S2）。图像中最热的部分始终是结晶前沿，这里实际上释放了潜热。因此晶体总是比熔体热，因为结晶前沿已经穿过它们。检查 3 × 3 像素点（在我们的设置中为~1 mm2），在~1 秒内重新加热至 T > 1270 °C（图 1B）。回收的样品显示了针状刺状古铜矿 (Fe0.20Mg0.82Si0.98O3) 的生长，其间质富铁辉石晶体的组成范围从硅铁矿 (Fe0.92Mg0.10Si0.97O3) 到超铁 (Fe0.74Mg0O3) .25Si0.99O3)；这个范围可能是由于早期青铜矿结晶后的局部镁消耗变化所致（图 3；表 S1）。将科马提石液体从约 1590°C 冷却后，样品淬火成玻璃。取而代之的是坩埚在~1450°C 开始并在~50°C s-1 开始冷却，结晶在~1080°C 开始。在坩埚底部取平均值，冷却暂停约 2 秒，然后以约 15°C/分钟的速度恢复（图 1B）。在 3 × 3 像素点中，约 10 °C 的再加热发生在约 0.5 秒内。从不同视频帧之间的温差来看，新形成的晶体比未结晶的熔体高约 30°C，结晶主要从坩埚壁到熔体内部进行（图 1H）。回收的样品显示小的铬尖晶石晶体被铝、富镁变辉石 (Ca0.15Fe0.14Mg0.59Al0.10Si0.90O3) 和铝辉石 (Ca0.25Fe0.17Mg0.38Al0.11Si0.90O3) 的枝晶共生包围. 3). 科马提岩熔岩通常首先结晶橄榄石，并经常显示带有间隙斜长石和铝质单斜辉石的刺状结构（Shore 和 Fowler，1999），但是我们实验中的冷却速度足够快，可以使两种辉石以亚稳态的方式结晶。涉及的热流。样品在约 1500 °C 下加热至完全熔融状态，然后以 50 °C min-1 或 100 °C min-1 的受控速率冷却至 500 °C，这远低于其玻璃化转变温度 (Tg)。对于在约 50 °C min-1 下冷却的辉石熔体，在 1316 °C 和 1264 °C 处可以看到两个不同的结晶峰（图 4）。在冷却过程中，结晶焓表现为表观热容的增加，因为量热计必须同时去除显热和潜热分量。冷却至 100 °C min-1，在 1313 °C 处出现一个大峰，在 1273 °C 处出现较小的第二个峰。对回收样品的检查表明，具有相似成分但尺寸比 FLIR 实验中观察到的尺寸大得多的亚铜矿 (Fe0.22Mg0.84Si0.97O3) 结晶，具有小的铁硅酸盐晶体 (Fe0.94Mg0.05Si0.99O3) 和二氧化硅的外溶- 富熔体小球（~97 wt% SiO2）散布在更富铁的玻璃状基质中（图 3）。我们将第一个 DSC 峰解释为记录古铜矿结晶，将第二个峰解释为记录氧化物生长。在 50 °C min-1 的三个实验中，总潜热释放为 472 J g-1 在 100 °C/min 和 418 J g-1、439 J g-1 和 484 J g-1。对于科马提石熔体冷却至 50 °C min-1，在 1139 °C 和 986 °C 处看到两个不同的结晶峰（图 4）。在 ~100 °C min-1 下冷却，第一个峰在~1125°C，而第二个峰出现在~1075°C。对回收样品的检查表明，橄榄石橄榄石针状晶体 (Fe0.21Mg1.76Si1.00O4) 在某些地方采用图形纹理；许多小的（~2 µm）磁铁矿晶体集中在橄榄石表面，并且有一个~10-µm 大小的树枝状铝辉石 (Ca0.30Fe0.19Mg0.23Al0.26Si0.92O3) 矩阵，其成分与间隙玻璃相似（表 S1）。X 射线衍射 (XRD) 分析表明结晶相的比例为~55 wt% 镁橄榄石、~40 wt% 辉石和~5 wt% 磁铁矿。我们将更大、更高温度的 DSC 峰解释为记录橄榄石结晶，并将随后的峰解释为记录辉石生长。科马提岩液体的 ΔHxtal 为 -233 J g-1 至 -293 J g-1，低于辉石液体，因为科马提质液体更容易聚合。我们对解聚基性熔体自发结晶过程中再加热超过 100 °C 的观察对陆地和行星火山学都有几个意义。自然界中发生再辉的间接证据来自对底部温度波动的观察夏威夷基拉韦厄火山的玄武岩熔岩流 (Keszthelyi, 1995)。我们对毫米尺度上高达 100°C 的温差的观察（图 2）表明，使用手持或三脚架安装的 FLIR 相机对玄武岩熔岩流进行热成像需要以毫米尺度的空间分辨率进行评估真实的温度波动。出于安全考虑，活动熔岩流和湖泊的基于现场的温度测量通常是从提供米到分米尺度而不是毫米尺度空间分辨率的距离记录的（例如，Harris 等人，2005 年；Spampinato 等人，2008 年；Harris , 2013)，这可能会导致平均单个像素内较冷的熔体和较热的晶体，并系统地高估液相的温度。实际上，辐射冷却速度很快，并且不太可能高估熔岩流中的熔体温度。Wright 和 Flynn (2003) 获得了基拉韦厄 pahoehoe 流的 FLIR 图像，空间分辨率约为 4 mm，可能是迄今为止最高的，并且发现最高温度像素仅为 1094 °C，这比根据形成 pahoehoe 裂片的夏威夷熔岩的流变行为推断的温度要低得多（Sehlke 等人，2014 年）。在正常的熔岩流中，流动表面的每个部分只会冷却一次。相比之下，活跃的熔岩湖不断地在地表暴露出新一批的新鲜、热熔岩（例如，Tilling，1987）。然而，这种熔岩也可能冷却得太快而无法再发光，而且活跃的熔岩湖通常很难接近足够接近以确保毫米级像素大小。另一种方法是使用冷却和潜热释放的数值模型，基于关于晶体成核和生长速率的动力学研究，以预测再发光（Keszthelyi，1995）。冷却熔岩的热模型，将结晶潜热作为“有效热容”项，正如熔岩流和冷却岩体通常采用的那样（例如，Nabelek 等人，2012 年；Harris，2013 年），禁止再发光，并且可能不准确地捕捉快速冷却熔岩体的热历史。熔岩喷泉中喷出的液滴可以更快地冷却比更大的身体。地球上的熔岩喷泉通常涉及盾形火山（如基拉韦厄火山）的拉斑玄武岩（Eaton 和 Murata，1960 年；Wolfe 等人，1987 年）。莫伊特拉等人。(2018) 模拟了玄武岩火山碎屑的冷却，并计算了 700 °C (∼Tg) 的冷却速率为 ∼3 °C s–1、30 °C s–1 和 300 °Cs–1，对于直径为 30 mm 的碎屑，3分别为 mm 和 0.3 mm，这表明粗灰分和小火山灰通常会以与镁铁质熔体中的再辉相一致的速率冷却。月球上的火山玻璃小球大多小于 1 毫米，但较大的球粒通常包含针状至纤维状晶体（卢瑟福和帕帕莱，2009 年），质地与快速不平衡结晶一致，可能还具有再发光（图 3）。 美国宇航局于 1999 年 11 月在木星的卫星 Io 上观察到活跃的熔岩喷泉事件伽利略任务（McEwen 等人，2000 年）和使用地面望远镜超过 25 年（Davies，1996 年；Stansberry 等人，1997 年；de Kleer 等人，2019 年）。这些“爆发”喷发的时间尺度类似于地球事件的时间尺度（数小时到数天）。根据伽利略航天器上的近红外测绘光谱仪 (NIMS) 的观测结果，估计爱奥尼亚熔岩在 1200 至 1700 °C 的高温下喷发（McEwen 等人，1998 年；Davies 等人，2000 年）。如此高的温度表明从基性到超基性的熔岩成分，如科马提岩。Keszthelyi 等人。(2007) 模拟了 Io 上熔岩液滴的热历史，并预测 0.1 毫米和 1 毫米的液滴将在 1 秒内冷却 ~650°C 和 ~200°C。然而，模型中的液滴被假定为淬火成玻璃，因此在结晶过程中无法重结晶和释放热量。在我们的冷却实验中，稍大的液滴会在 50°Cs-1 的范围内冷却，并且它们应该会重新发光。在这种情况下，释放的额外潜热将有助于喷泉的整体热通量，但不会伴随更高的峰值温度，因为再辉仅限于亚液相线温度（图 1）。再辉会提高最热组件的温度，这是从模型拟合到观测数据得出的，更接近实际的熔岩喷发温度。因此，我们将更接近于了解 Io 上喷发的硅酸盐熔岩的成分。我们感谢 FLIR 系统 (https://www.flir.com) 的 Jerry Beingey 协助进行视频采集，以及 Paul Carpenter 协助进行微探针分析。我们感谢 Ashley Davies 和一位匿名审稿人对改进手稿的评论。这项工作的资金由 NASA 赠款 NNX12AO44G 和 80NSSC19K1010 提供。我们感谢 Ashley Davies 和一位匿名审稿人对改进手稿的评论。这项工作的资金由 NASA 赠款 NNX12AO44G 和 80NSSC19K1010 提供。我们感谢 Ashley Davies 和一位匿名审稿人对改进手稿的评论。这项工作的资金由 NASA 赠款 NNX12AO44G 和 80NSSC19K1010 提供。