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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Thermal weakening of the carbonate basement under Mt. Etna volcano (Italy):Implications for volcano instability
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Thermal weakening of the carbonate basement under Mt. Etna volcano (Italy):Implications for volcano instability

机译：Mt下碳酸盐地下室的热弱化。埃特纳火山（意大利）：对火山不稳定的影响

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The physical integrity of a sub-volcanic basement is crucial in controlling the stability of a volcanic edifice. For many volcanoes, this basement can comprise thick sequences of carbonates that are prone to significant thermally-induced alteration. These debilitating thermal reactions, facilitated by heat from proximal magma storage volumes, promote the weakening of the rock mass and likely therefore encourage edifice instability. Such instability can result in slow, gravitational spreading and episodic to continuous slippage of unstable flanks, and may also facilitate catastrophic flank collapse. Understanding the propensity of a particular sub-volcanic basement to such instability requires a detailed understanding of the influence of high temperatures on the chemical, physical, and mechanical properties of the rocks involved. The juxtaposition of a thick carbonate substratum and magmatic heat sources makes ML Etna volcano an ideal candidate for our study. We investigated experimentally the effect of temperature on two carbonate rocks that have been chosen to represent the deep, heterogeneous sedimentary substratum under Mt Etna volcano. This study has demonstrated that thermal-stressing resulted in a progressive and significant change in the physical properties of the two rocks. Porosity, wet (i.e., water-saturated) dynamic Poisson's ratio and wet Vp/Vs ratio all increased, whilst P- and S-wave velocities, bulk sample density, dynamic and static Young's modulus, dry Vp/Vs ratio, and dry dynamic Poisson's ratio all decreased. At temperatures of 800 ℃, the carbonate in these rocks completely dissociated, resulting in a total mass loss of about 45% and the release of about 44 wt% of CO_2. Uniaxial deformation experiments showed that high in-situ temperatures (>500 ℃) significantly reduced the strength of the carbonates and altered their deformation behaviour. Above 500 ℃ the rocks deformed in a ductile manner and the output of acoustic emissions was greatly reduced. We speculate that thermally-induced weakening and the ductile behaviour of the carbonate substratum could be a key factor in explaining the large-scale deformation observed at Mt Etna volcano. Our findings are consistent with several field observations at Mt. Etna volcano and can quantitatively support the interpretation of (1) the irregularly low seismic velocity zones present within the sub-volcanic sedimentary basement, (2) the anomalously high CO_2 degassing observed, (3) the anomalously high Vp/Vs ratios and the rapid migration of fluids, and (4) the increasing instability of volcanic edifices in the lifespan of a magmatic system. We speculate that carbonate sub-volcanic basement may emerge as one of the decisive fundamentals in controlling volcanic stability.
机译：火山地下层的物理完整性对于控制火山岩的稳定性至关重要。对于许多火山而言，该地下室可能包含较厚的碳酸盐序列，这些碳酸盐序列易于发生明显的热诱导变化。来自近端岩浆储存空间的热量促进了这些使人衰弱的热反应，促进了岩体的减弱，并因此可能促进了建筑物的不稳定性。这种不稳定性会导致重力缓慢扩散，并导致不稳定侧面连续滑移，并且还可能导致灾难性的侧面崩溃。要了解特定的次火山基底对这种不稳定性的倾向，需要详细了解高温对所涉及岩石的化学，物理和机械特性的影响。稠密的碳酸盐岩层和岩浆热源的并置使得ML Etna火山成为我们研究的理想选择。我们通过实验研究了温度对两种碳酸盐岩石的影响，这些碳酸盐岩石被选作代表埃特纳火山下的深层非均质沉积基质。这项研究表明，热应力导致两块岩石的物理性质发生了逐渐的显着变化。孔隙率，湿（即水饱和）动态泊松比和湿Vp / Vs比均增加，而P波和S波速度，大块样品密度，动态和静态杨氏模量，干Vp / Vs比和干动态泊松比均下降。在800℃的温度下，这些岩石中的碳酸盐完全解离，导致总质量损失约45％，释放出约44 wt％的CO_2。单轴变形实验表明，较高的原位温度（> 500℃）会显着降低碳酸盐的强度并改变其变形行为。在500℃以上，岩石会发生延性变形，从而大大降低了声发射的输出。我们推测，热致弱化作用和碳酸盐岩基质的延性行为可能是解释在埃特纳火山观察到的大规模变形的关键因素。我们的发现与山顶的一些实地观察一致。埃特纳火山（Etna volcano）可以定量地解释（1）亚火山沉积基底内存在的不规则低地震速带，（2）观察到异常高的CO_2脱气，（3）异常高的Vp / Vs比和快速的流体的运移，以及（4）岩浆系统寿命中火山建筑物的不稳定性增加。我们推测，碳酸盐岩下火山岩基底可能成为控制火山岩稳定性的决定性基础之一。

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