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How deceptive are microstructures in granitic rocks? Answers from integrated physical theory, phase equilibrium, and direct observations
Contributions to Mineralogy and Petrology ( IF 3.5 ) Pub Date : 2018-07-20 , DOI: 10.1007/s00410-018-1488-8
M B Holness 1 , J D Clemens 2 , R H Vernon 3
Affiliation  

In this contribution, we address the vexed question of the extent to which microstructures in granitic rocks reflect their igneous histories or have been masked by later events. The previous works have tended to address the problem either using theoretical or modelling considerations, or by interpretation of observed microstructures. Here, we use an approach that integrates the theory of microstructural development and the results of experimental phase-equilibrium studies with direct observation of natural examples on a variety of scales. We show that the predictions of the theoretical and experimental approaches agree perfectly with the mesoscopic and microscopic evidence from granitic rocks themselves. Our conclusion is that although, in many cases, granitic rock microstructures have been modified by near-solidus reactions and crystallisation, in the absence of tectonic deformation the fundamental elements of their igneous heritage remain intact. This means that it is perfectly in order to infer aspects of crystallisation sequences, magmatic reactions, and magma flow through careful microstructural observations. Thus, our answer to the question of how deceptive granitic textures are is, in most instances, ‘not very’. However, some undeformed plutons have undergone fluid-driven alteration, and others have been affected by contact metamorphism. Thus, each case should be examined on its own merits.

中文翻译:

花岗岩中的微观结构有多具有欺骗性?来自综合物理理论、相平衡和直接观察的答案

在这篇文章中,我们解决了花岗岩中的微观结构在多大程度上反映了其火成历史或被后来的事件掩盖的棘手问题。以前的工作倾向于使用理论或建模考虑,或通过对观察到的微观结构的解释来解决该问题。在这里,我们使用一种方法,将微观结构发展理论和实验相平衡研究的结果与各种尺度的自然实例的直接观察相结合。我们表明,理论和实验方法的预测与花岗岩本身的介观和微观证据完全一致。我们的结论是,尽管在许多情况下,花岗岩微观结构已被近固相线反应和结晶改变,但在没有构造变形的情况下,其火成岩遗产的基本元素仍然完好无损。这意味着它非常适合通过仔细的微观结构观察来推断结晶序列、岩浆反应和岩浆流的各个方面。因此,在大多数情况下,我们对花岗岩纹理的欺骗性如何这一问题的回答是“不太好”。然而,一些未变形的岩体经历了流体驱动的蚀变,而另一些则受到了接触变质作用的影响。因此,每个案件都应根据其本身的优点进行审查。
更新日期:2018-07-20
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