Preservation of chemical residue-melt equilibria in natural anatexite: the effects of deformation and rapid cooling
Preservation of chemical residue-melt equilibria in natural anatexite: the effects of deformation and rapid cooling
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DOI：
10.1007/s00410-002-0405-2
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发表时间：
2003
影响因子：
3.5
通讯作者：
A. Berger;C. Rosenberg
中科院分区：
文献类型：
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作者：
A. Berger;C. Rosenberg
结合岩石学，结构和化学方法被用来解释部分熔融过程中的花岗闪长质片麻岩的接触晕的Bergell岩体（中央阿尔卑斯山）的化学交换和变形之间的关系。与大多数区域变质的正长岩不同，残余物和分离熔体之间的化学平衡是由几种元素实现和保持的，正如它们目前的分布所示。平衡涉及的主要和微量元素中的岩石形成的矿物和轻稀土元素（LREE），主要是在褐帘石托管。相对于LREE的平衡实现，因为褐帘石在水存在的熔融过程中具有反应行为，与磷钇矿的折射行为相反，磷钇矿的折射行为主要控制HREE的分布。白细胞体和残余物之间平衡的达到和保持需要特殊的边界条件。我们建议，熔体和残留物之间的平衡的实现是由变形促进，通过熔体存在颗粒流（即溶解容纳晶界滑动活动在部分熔融）的机制操作。显微结构的观察表明，熔体存在的颗粒流是在这些正长岩的主要变形机制。残余物-熔体平衡的保存被推断为由于接触变质条件下的快速冷却和固相线以下的变形的缺乏。
A combined petrologic, textural and chemical approach is used to interpret the relationship between chemical exchange and deformation during partial melting of a granodioritic gneiss in the contact aureole of the Bergell Pluton (Central Alps). In contrast to most regional metamorphic anatexites, chemical equilibrium between residue and segregated melt was attained and preserved by several elements, as shown by their present distribution. Equilibrium involved both the major and the trace elements hosted in the rock-forming minerals and the light rare earth elements (LREE), hosted primarily in allanite. Equilibrium with respect to LREEs was achieved because allanite had a reactive behaviour during water-present melting, in contrast to the refractive behaviour of xenotime, which mostly controls the distribution of the HREE's. The attainment and preservation of equilibrium between leucosome and residue requires peculiar boundary conditions. We propose that the achievement of equilibrium between melt and residue was promoted by deformation, operating via a mechanism of melt present granular flow (i.e. dissolution-accommodated grain-boundary sliding active during partial melting). Microstructural observations indicate that melt-present granular flow was the dominating deformation mechanism in these anatexites. The preservation of residue–melt equilibrium is inferred to result from rapid cooling under contact metamorphic conditions and from the lack of deformation below the solidus.