Effect of anorthite on granite phase relations: Experimental data and models

IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
Michel Pichavant , Catherine Weber , Arnaud Villaros
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引用次数: 7

Abstract

New experimental data on the effect of anorthite (An) on liquidus phase equilibria in the system Qz–Ab–Or are presented. The data were obtained for 5 wt% An added to variable Qz/Ab/Or compositions at 300 MPa and under H2O-saturated conditions. Crystal–liquid equilibria were determined for 13 synthetic glass compositions made from gels in experiments performed between 660 and 750 °C in cold-seal pressure vessels. Forward and reversal experiments were systematically conducted on each composition to demonstrate equilibrium. A total of 51 charges was examined. Three crystalline phases, quartz, alkali feldspar and plagioclase appear on the H2O-saturated liquidus surface. The determined minimum liquidus 5 wt% An “piercing” point (39% Qz, 33% Ab, 28% Or) is shifted away from the Ab apex toward the Qz–Or sideline when compared with the An-free 300 MPa H2O-saturated minimum. This shift is of the same type as that observed at 100 MPa in the same system and at 200 MPa in a rhyolitic system. The new experimental results are used to test both empirical and thermodynamic models for silicic magmas. Empirical models reproduce reasonably well the new experimental data, although more sophisticated calculations schemes appear to be required to improve their accuracy. The new experimental results in the haplogranodiorite system are not well reproduced with the model of Holland and Powell (2001), mainly because plagioclase stability appears greatly enhanced in the model. Rhyolite-MELTS satisfactorily reproduces the Qz-, Pl- and Af-liquid phase equilibria, but model H2O solubilities are significantly lower and crystallization temperatures higher than in experiments.

钙长石对花岗岩相关系的影响:实验数据和模型
给出了钙长石(An)对Qz-Ab-Or体系液相相平衡影响的新实验数据。在300 MPa和水饱和条件下,在不同的Qz/Ab/Or组合物中添加5 wt%的a,获得了数据。在660 - 750°C的冷密封压力容器中,测定了由凝胶制成的13种合成玻璃组合物的晶体-液体平衡。系统地对每种成分进行了正向和反转实验,以证明平衡。共审查了51项指控。水饱和液质表面呈现石英、碱长石和斜长石三种晶相。测定的最小液相线5 wt% An“穿刺”点(39% Qz, 33% Ab, 28% Or)从Ab顶点向Qz - Or边线偏移,与无An的300 MPa h2o饱和最小液相线相比。这种位移与同一体系在100mpa和流纹岩体系在200mpa时观察到的位移类型相同。新的实验结果用于验证硅质岩浆的经验模型和热力学模型。经验模型相当好地再现了新的实验数据,尽管似乎需要更复杂的计算方案来提高其准确性。Holland and Powell(2001)的模型不能很好地再现单长花岗闪长岩系统的新实验结果,主要原因是斜长石的稳定性在模型中得到了极大的增强。流纹岩熔体令人满意地再现了Qz-、Pl-和af -液相平衡,但模型水溶解度明显低于实验,结晶温度明显高于实验。
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
Comptes Rendus Geoscience
Comptes Rendus Geoscience 地学-地球科学综合
CiteScore
2.80
自引率
14.30%
发文量
68
审稿时长
5.9 weeks
期刊介绍: Created in 1835 by physicist François Arago, then Permanent Secretary, the journal Comptes Rendus de l''Académie des sciences allows researchers to quickly make their work known to the international scientific community. It is divided into seven titles covering the range of scientific research fields: Mathematics, Mechanics, Chemistry, Biology, Geoscience, Physics and Palevol. Each series is led by an editor-in-chief assisted by an editorial committee. Submitted articles are reviewed by two scientists with recognized competence in the field concerned. They can be notes, announcing significant new results, as well as review articles, allowing for a fine-tuning, or even proceedings of symposia and other thematic issues, under the direction of invited editors, French or foreign.
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