Model of layered pattern formation in binary igneous systems

IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
Jade Ghaoui , Ivan L'Heureux
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引用次数: 1

Abstract

Centimeter to meter-scale repetitive patterns in composition and texture are sometimes observed in igneous systems. Examples are found in layered intrusions and multi-shelled orbicular granites. These patterns may result from the action of nonlinear self-organization processes in which the interplay between crystallization dynamics, diffusion and thermal conduction causes mineral and crystal size segregations. These mechanisms are analogous to the ones underlying the formation of Liesegang bands and lead to comparable features, such as a geometric progression of the band positions and the presence of doublets. We present here a comprehensive one-dimensional numerical model of Liesegang pattern formation process from binary eutectic melts in igneous systems. The model incorporates nucleation, growth and Ostwald ripening and is applied to both the layered intrusion and the orbicular granite configuration with appropriate simple geometries and cooling boundary conditions. The emergence of cyclic layering is described in terms of two key parameters that control the pattern formation: the scaled latent heat of crystallization (Stefan number) and the ratio of the thermal diffusivity to a characteristic diffusion coefficient (Lewis number). It is found that, in intrusions, a banding pattern compatible with the Liesegang spacing law is generated when the Stefan number is large and the Lewis number small, in agreement with previous studies. For orbicular granites with low Lewis number, we show that the band thickness and the crystal size increase with distance from the rim to the core, in agreement with the observations of Zhang and Lee (2020). This suggests that the pattern progresses inwards from the outer boundary, rather than from a colder core, thus supporting the conceptual model reported in Zhang and Lee (2020). Moreover, the results for both geometries indicate that ripening plays an important role in the formation of realistic patterns.

二元火成岩系统层状图案形成模式
在火成岩系统中,有时可以观察到厘米到米尺度的成分和结构的重复图案。在层状侵入体和多壳圆形花岗岩中发现了这样的例子。这些图案可能是由于非线性自组织过程的作用,其中结晶动力学,扩散和热传导之间的相互作用导致矿物和晶体尺寸的分离。这些机制类似于lieesegang带形成的机制,并导致类似的特征,例如带位置的几何级数和双重态的存在。本文建立了火成岩体系中二元共晶熔体形成列色岗图案过程的一维综合数值模型。该模型结合了成核、生长和奥斯特瓦尔德成熟,适用于层状侵入岩和具有适当简单几何形状和冷却边界条件的圆形花岗岩结构。循环分层的出现是根据控制图案形成的两个关键参数来描述的:结晶的尺度潜热(Stefan数)和热扩散系数与特征扩散系数的比值(Lewis数)。研究发现,在侵入体中,当Stefan数较大,Lewis数较小时,会产生符合lieesegang间距规律的带状图,这与前人的研究结果一致。对于低Lewis数的圆形花岗岩,我们发现从边缘到核心的距离增加能带厚度和晶体尺寸,这与Zhang和Lee(2020)的观测结果一致。这表明该模式从外部边界向内发展,而不是从较冷的核心开始,从而支持Zhang和Lee(2020)报告的概念模型。此外,两种几何形状的结果表明,成熟在真实感图案的形成中起着重要作用。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Solid Earth Sciences
Solid Earth Sciences GEOSCIENCES, MULTIDISCIPLINARY-
CiteScore
3.60
自引率
5.00%
发文量
20
审稿时长
103 days
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