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首页> 外文期刊>Contributions to Mineralogy and Petrology >Diffusion-controlled development of silica-undersaturated domains in felsic granulites of the Bohemian Massif (Variscan belt of Central Europe)
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Diffusion-controlled development of silica-undersaturated domains in felsic granulites of the Bohemian Massif (Variscan belt of Central Europe)

机译：波西米亚地块（中欧瓦里斯坎带）长英质花岗岩中硅欠饱和畴的扩散控制发展。

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摘要

Plagioclase rims around metastable kyanite crystals appear during decompression of high-pressure felsic granulites from the high-grade internal zone of the Bohemian Massif (Variscan belt of Central Europe). The development of the plagioclase corona is a manifestation of diffusion-driven transfer of CaO and Na2O from the surrounding matrix and results in isolation of kyanite grains from the quartz- and K-feldspar-bearing matrix. This process establishes Si-undersaturated conditions along the plagioclase–kyanite interface, which allow crystallization of spinel during low-pressure metamorphism. The process of the plagioclase rim development is modeled thermodynamically assuming local equilibrium. The results combined with textural observations enable estimation of equilibration volume and diffusion length for Na and Ca that extends ～400–450 and ～450–550 μm, respectively, around each kyanite crystal. Low estimated bulk diffusion coefficients suggest that the diffusion rate of Ca and Na is controlled by low diffusivity of Al across the plagioclase rim.
机译：在从波希米亚地块（中欧的瓦里斯卡纳地带）的高品位内部区域内的高压长丝质粒岩减压过程中，出现了亚稳蓝晶石晶体周围的斜长石边缘。斜长石电晕的发展是CaO和Na2 从周围基质中扩散驱动转移的一种表现，并导致蓝晶石颗粒与石英和钾长石基质分离。这个过程沿着斜长石-蓝晶石界面建立了硅不饱和条件，这使尖晶石在低压变质过程中结晶。斜长边发展的过程是在热力学上模拟局部平衡的。结果与组织学观察相结合，可以估算在每个蓝晶石晶体周围分别延伸〜400-450和〜450-550μm的Na和Ca的平衡体积和扩散长度。估计的较低的体扩散系数表明，Ca和Na的扩散速率受Al跨斜长石边缘的低扩散率控制。

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