Dynamics of gas-driven eruption on Ceres as a probe to its interior
Dynamics of gas-driven eruption on Ceres as a probe to its interior
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DOI：
10.1016/j.icarus.2023.115533
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发表时间：
2023-03
期刊：
影响因子：
3.2
通讯作者：
K. Yumoto;Yuichiro Cho;T. Koyaguchi;S. Sugita
中科院分区：
文献类型：
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作者：
K. Yumoto;Yuichiro Cho;T. Koyaguchi;S. Sugita
黎明使命观察到的谷神星上局部明亮矿床的矿物学表明，它们是富含盐水的冰火山成因。根据矿床的形态观察，提出了爆发式和喷溢式两种喷发方式。由于火山喷发的方式和速度是由管道内气体膨胀的程度控制的，因此可以根据对谷神星上局部沉积物的观测来限制内部水环境，如气体浓度和温度。然而，这些属性控制喷发方式和速度的方式是复杂的。从地下储层上升的低温岩浆由于水的沸腾和溶解气体的出溶而获得浮力，这是由于谷神星表面附近减压到极低的压力。气-熔偏析也会影响动力学。因此，目前还没有完全了解谷神星的内部环境如何影响冰火山活动的上升动力学，并随后控制喷发的风格（爆炸与溢出）和速度。为了解决这个问题，我们开发了一个一维稳态两相流模型的上升动力学的气体驱动的低温岩浆的谷神星的条件下，同时考虑水沸腾和气体出溶。我们发现，喷发的速度和爆炸性强烈控制由以下三个参数，其特征的低温岩浆环境谷神星的内部：（a）导管传导性（CC; rc 2/μ，其中r是导管半径和μ是岩浆粘度），（B）溶解气体浓度c 0，和（c）岩浆库温度T0。我们的模型结果表明，低CC总是导致溢出或低爆炸性喷发。当C 0或T0足够高时，较高的CC允许爆发性喷发。这些依赖关系可以概括为以下CC-c 0-T0条件下的四种喷发模式。(1)喷出驱动的爆发喷发（X1型）发生在富含挥发分的岩浆中（CC ≥ 10− 3 m2/（Pa·s），CO2含量为0.1wt%）。(2)沸腾驱动的爆炸喷发（X2型）发生在温暖的岩浆（CC = 10− 3 m2/（Pa·s），CO2的c 0 = 0.1wt%，和高T0）中。(3)粘度引起的喷溢喷发（F1型）发生在狭窄的通道和/或高粘度岩浆（CC = 10− 3 m2/（Pa·s））。(4)低产气量喷发（F2型）发生在低温和低挥发性岩浆（CC ≤ 10− 3 m2/（Pa·s），CO2的c 0 ≤ 0.1wt%，T0低）。我们的模型预测，爆炸性喷发需要c 0 <$0.5wt%的CO2或T0 <$−5°C才能达到喷发速度<$30 m/s，这是基于谷神星上一些大光斑的大小提出的。这种富含气体或温暖的岩浆条件不太可能通过浅地壳内的平衡来实现。因此，我们的研究结果表明，岩浆需要从更深的地下供应。与此相反，低速渗出的盐水也提出了基于对谷神星上的陨石的形态分析。我们的研究结果表明，岩浆的盐水溢出是粘性的，并通过一个狭窄的管道输送到表面，或者他们是从水库平衡的浅地壳内的环境材料的来源。由于Occator陨石坑中光斑的喷发起源与小管道一致，因此喷发的性质可能不一定排除最近谷神星内部相对高挥发性或温暖的岩浆。这些结果表明，光斑存款的形态特征可以放置重要的限制谷神星的内部条件时，相关的喷发风格/速度是已知的。我们的...
The mineralogy of localized bright deposits on Ceres observed by the DAWN mission suggests their brine-enriched cryovolcanic origin. Based on the morphological observations of these deposits, explosive and effusive styles have been proposed for their eruption. Because volcanic eruption style and velocity are controlled by the extent of gas expansion inside the conduit, constraints on the internal aqueous environment, such as gas concentration and temperature, could be placed based on the observations of localized deposits on Ceres. However, the way these properties control the eruption style and velocity is complex. Cryomagma ascending from a subsurface reservoir gains buoyancy due to both boiling of water and exsolution of dissolved gas, owing to decompression to the extremely low pressure near the Ceres surface. Gas–melt segregation should also affect the dynamics. Thus, it is not yet fully understood how the internal environment of Ceres affects the ascent dynamics of cryovolcanism and subsequently controls the styles (explosive versus effusive) and velocities of eruptions. To address this problem, we developed a one-dimensional steady-state two-phase flow model for the ascent dynamics of gas-driven cryomagma under the conditions of Ceres taking both water boiling and gas exsolution into account. We found that the velocity and explosivity of an eruption are strongly controlled by the following three parameters, which characterize the cryomagmatic environment of Ceres's interior: (a) conduit conductivity (CC;rc2/μ, wherercis the conduit radius andμis the magma viscosity), (b) dissolved gas concentrationc0, and (c) magma reservoir temperatureT0. Our model results reveal that low CC always leads to effusive or low-explosivity eruptions. Higher CC allows explosive eruption when eitherc0orT0is sufficiently high. These dependences can be summarized as four modes of eruption under the following CC-c0-T0conditions. (1) Exsolution-driven explosive eruptions (X1 type) occur with volatile-rich magma (CC ≳ 10−3m2/(Pa·s) andc0≳ 0.1 wt% of CO2). (2) Boiling-driven explosive eruptions (X2 type) occur with warm magma (CC ≳ 10−3m2/(Pa·s),c0≪ 0.1 wt% of CO2, and highT0). (3) Viscosity-induced effusive eruptions (F1 type) occur with a narrow conduit and/or high-viscosity magma (CC ≲ 10−3m2/(Pa·s)). (4) Low-gas-production-induced effusive eruptions (F2 type) occur with low-temperature and low-volatile magma (CC ≳ 10−3m2/(Pa·s),c0≪ 0.1 wt% of CO2, and lowT0). Our model predicts that eitherc0≳ 0.5 wt% of CO2orT0≳−5°C is required for explosive eruptions to achieve eruption velocities ≳30 m/s, which has been proposed based on the size of some large faculae on Ceres. Such gas-rich or warm magma condition is unlikely to be achieved by equilibrium within the shallow crust. Thus, our results suggest that magma needs to be supplied from a deeper subsurface. In contrast, low-velocity effusion of brines has also been proposed based on morphometric analyses of evaporites on Ceres. Our results show that magma of such brine effusions is viscous and transported to the surface through a narrow conduit or they are sourced from reservoirs equilibrated to the ambient material within the shallow crust. Because the effusive eruption origin of faculae in the Occator crater is consistent with small conduits, the effusive nature may not necessarily rule out relatively high-volatile or warm magma inside Ceres in the recent past. These results show that the morphometric properties of facula deposits can place important constraints on the internal conditions of Ceres when the relevant eruption style/velocity is known. Our …