Sieve-textured plagioclase in volcanic rocks produced by rapid decompression
Sieve-textured plagioclase in volcanic rocks produced by rapid decompression
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发表时间：
2007
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SrnpHnN T. NBr;Anr MoNrANrA
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作者：
SrnpHnN T. NBr;Anr MoNrANrA
不平衡结构，特别是斜长石的粗筛结构在造山火山岩中很常见。这些结构通常被解释为岩浆混合的结果，但它们也可能发生在快速减压的过程中，此时热损失相对于上升速率来说是很小的。为了验证这一假设，我们在安山岩上进行了高压活塞缸实验。实验从12千巴开始，然后以2千巴、4千巴和6千巴的增量进行等温压力释放，在斜长石中产生了与许多火山岩非常相似的筛状结构。因此，筛状结构斜长石的存在不应作为岩浆混合的先验证据。许多火山系统可能经历类似于本研究模拟的减压条件，减压被认为是产生这种纹理的简单机制，因为它不需要增加热量或质量。快速减压也可能与岩浆混合一起起作用。
Disequilibrium textures, particularly the coarse sieve texture ofplagioclase, are common in orogenic volcanic rocks. The textures are usually interpreted as resulting from magma mixing, but they may occur by rapid decompression, where heat loss is minor relative to the ascent rate. We conducted high-pressure piston-cylinder experiments on an andesite to test this hypothesis. Experiments starting at 12 kbar, followed by isothermal pressure release in increments of 2, 4, and 6 kbar, produce sieve textures in plagioclase very much like those in many volcanic rocks. Therefore, the presence of sieve-textured plagioclase should not be taken as a priori evidence for magma mixing. Many volcanic systems probably experience conditions of decompression similar to those simulated in this study, and decompression is considered to be a simple mechanism to produce such textures, as it requires no addition of heat or mass. Rapid decompression may also operate in conjunction with magma mixing.