The viscous-brittle transition of crystal-bearing silicic melt: Direct observation of magma rupture and healing
The viscous-brittle transition of crystal-bearing silicic melt: Direct observation of magma rupture and healing
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DOI：
10.1130/g3914.1
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发表时间：
2012-07-01
期刊：
影响因子：
5.8
通讯作者：
Burlini, L.
中科院分区：
文献类型：
--
作者：
Cordonnier, B.;Caricchi, L.;Burlini, L.
岩浆可以流动或破裂，这取决于它们的变形速率。这种粘性和脆性行为之间的转变控制了火山爆发的风格。虽然硅酸盐熔体的脆性破坏的特点是合理的，晶体的粘-脆性转变的影响尚未受到约束。在这里，我们研究的影响，悬浮晶体的机械故障的岩浆使用扭转实验进行的温度（600-900摄氏度），应变速率（10（-4）-10（-1）秒（-1）），和围压（200-300兆帕）有关的火山系统。我们提出了一个关系，预测的临界应力和相关的应变率在岩浆失败的晶体分数的函数。此外，结果表明，当晶体存在时，在较低的应力和应变速率下发生粘性到脆性的转变。含晶岩浆脆性破裂过程中形成的裂缝起源于熔融相，这使得气体逸出，从而降低气体超压。这些脱气途径愈合在相对较短的时间尺度上，由于在深度的高围压，突出的可能性，连贯的熔岩可能实际上是愈合的部分脱气岩浆包裹，经历了许多周期的断裂和愈合。
Magmas may flow or break depending on their deformation rate. The transition between such viscous and brittle behavior controls the style of volcanic eruptions. While the brittle failure of silicate melts is reasonably well characterized, the effect of crystals on the viscous-brittle transition has not yet been constrained. Here we examine the effect of suspended crystals on the mechanical failure of magmas using torsion experiments performed at temperatures (600-900 degrees C), strain rates (10(-4)-10(-1) s(-1)), and confining pressures (200-300 MPa) relevant for volcanic systems. We present a relationship that predicts the critical stress and associated strain rate at which magmas fail as a function of crystal fraction. Furthermore, the results demonstrate that the viscous to brittle transition occurs at lower stresses and strain rates when crystals are present. The fractures formed during brittle failure of crystal-bearing magma originate in the melt phase, which enables gas to escape, and hence to reduce gas overpressure. These degassing pathways heal on relatively short time scales owing to the high confining pressure at depth, highlighting the possibility that coherent lavas may actually be the healed remains of partially degassed magma parcels that have undergone many cycles of fracturing and healing.