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A Modeling Experiment in the Laboratory of Magma Mixing between Basaltic and Silicic Magmas and Its Application to the Tianchi Volcano, Changbai Mountain

Author: LiuQiang
Tutor: WeiHaiQuan
School: Institute of Geology of China Earthquake Administration
Course: Geochemistry
Keywords: Changbaishan Tianchi volcano Magma mixing Volatile Bubble Turn Simulation experiments
CLC: P588.1
Type: Master's thesis
Year: 2008
Downloads: 68
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Abstract

When mafic magma intrusion into acidic magma chamber already exists in the earth's crust, the temperature of the mafic magma the acidic magma temperature higher than that already exists in the magma chamber, according to the theory of heat transfer, mafic magma to begin convective heat transfer, cooling and crystallization. The intrusion of mafic magma density is greater than in the original magma chamber magma, the the acidic magma viscosity magma chamber is greater than the intrusion of mafic magma, mafic magma in the magma chamber resides down at the bottom of the original magma. Since the role of heat transfer, the bottom of the magma chamber mafic magma temperature decreased gradually began to crystallize volatiles dissolved in the magma, thus the original start from the magma in the form of bubbles dissolution. If these bubbles are stranded in the underlying mafic magma, mafic magma density will be reduced until it is lower than the density of the upper magma. Then two kinds of magma buoyancy effect occurs massive flip. If these bubbles are separated from the mafic magma and rise through the lower magma will be gathered to form a foam layer at the contact surface of the two layers of magma. By the bubble density of the composition of the foam layer to be smaller than the upper layer of the magma, the small bubbles in the foam layer will be gathered together in the form of a bubble column into the upper magma go, this case does not occur large-scale flip. Previous studies have shown that both the mixing process are likely to occur within the magma chamber, and field observations also found geological evidence. Massive flip corresponding mixed magma eruption, without massive flip corresponding Mature magma eruption was found in the wild contain new invasive magma. If the the mafic magma's viscosity is low enough, then the time will be less than the time due to the cooling of magma bubbles bubbles need to be separated from the magma can be seen through the model calculations. Under this condition, by the calculation of the model can be considered to not occur massive magma flip. However, if the cooling speed is faster or bubbles rise more slowly, the massive magma flip or happens. We have done a series of simulation experiments in the laboratory to explore the phenomenon of magma flipped. In the experiment, we through the electrolytic generation of the bubble to simulate the magma of bubbles generated in the cooling and crystallization process. Glass sink as the electrolyzer of the use of 500 mm × 200 mm × 300 mm (depth), a smooth surface, the pores of the nickel mesh is fixed at the bottom of the electrolytic cell, connected to the cathode of the DC power supply is used to generate the diameter at 30 - The platinum wire, the bubbles of 50 μm, to be connected to the anode of the DC power supply is also fixed in the electrolyzer. We use the combination of different viscosity and density of the solution, but the lower the density of the solution is always greater than the upper solution, the viscosity of the total is lower than the upper solution. The the electrolytic bubble generated initial diameter is the same, these bubbles will rise through the lower solution. In the the basic magma higher viscosity experiments, we observed a large-scale reversal and liquid mixing phenomenon occurs, and for the experiments with the lower viscosity values ??and not a large-scale reversal occurs, the bubbles gathered in the two liquid layers a contact surface is formed of a foam layer, and the small air bubbles formed in the bubble column from time to time to rise to the upper layer on the ground to. Why we can observe in the wild to the higher density of mafic magma intrusion to go to a less dense, more mature magma can be explained by the model calculations and laboratory simulation. Through theoretical analysis and laboratory simulation experiments to verify that we can see that: 1) large-scale magma flip usually accompanied by high cooling rate and the relatively high viscosity of mafic magma intruded into the saturated acidic magmatic volatiles. 2) If the acidic magma volatile unsaturated relatively poor, the compressibility of the magma, when the magma flip occurs before the increase in pressure caused by the expansion of the mafic magma may trigger volcanic eruptions. 3) If the viscosity of the magma of the lower group is low or the cooling rate is relatively low cases air bubbles easily separated from the magma out of the small bubble column, which will be formed in the junction surface of the two-magma. Magma mixing occurs in this form would not have happened a massive flip. These results are based on the on the basis of a simplified model of a two magmatic cooling crystallization. Bubbles flipped inhibition of magma from the magma separation can be seen from our experiments. Although these experiments can not simulate all the factors in the magmatic system and see the phenomenon than the parameters of our model complex, but is consistent with the model law. For example, in the experiment, if the viscosity of the supernatant liquid is large, then a contact surface of the two liquid layers to form a layer of foam layer, in the actual situation, however, the bubbles may be reabsorbed upper acidic magma, then you It does not form a bubble layer. But the aim of our study is to explore the conditions under which flip may occur due to air bubbles formed an obvious layer of foam, into the the acidic magma layer or re-absorption of acidic magma, the results are the same, the lower magma density remains unchanged, that is, the separation of bubbles from the lower magma with suppressed occurrence flip. Changbaishan Tianchi volcano field samples, all the key quantitative parameters is very difficult to determine, but there are many field observations illustrate the presence of magma mixing, and we can apply given the principle of Changbaishan Tianchi volcano further research.

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