Experimental Investigation into Interaction between Amphibole and Highly Saline H2O–NaCl–KCl Fluid at 750°C, 700 MPa: Implications to Alkaline Metasomatism of Amphibole Rocks

IF 1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
L. I. Khodorevskaya, D. A. Varlamov, O. G. Safonov
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引用次数: 0

Abstract

The paper presents experimental data on the interaction of amphibole with NaCl–H2O and (K, Na)Cl–H2O solutions at varying salt content. When interacting with H2O–NaCl fluid, amphibole remains the predominant mineral in all experiments, and the newly formed minerals are Na-phlogopite, plagioclase, and nepheline/sodalite. At \({{a}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}\) > 0.6, the amphibole melts. When amphibole interacts with H2O–NaCl–KCl fluid at \({{X}_{{{{{\text{H}}}_{2}}{\text{O}}}}}\) < 0.40 and ХKCl/(ХKCl + ХNaCl) in the fluid, defined as ХNaCl = 0.506 – 0.84ХKCl, the amphibole is replaced by the association of nepheline with sodic plagioclase, sodalite, and biotite. At ХKCl/(ХKCl + ХNaCl) > 0.3, nepheline, sodalite, and plagioclase become unstable, K-feldspar is formed, and biotite, clinopyroxene, and amphibole remain stable. At ХKCl/(ХKCl + ХNaCl) > 0.5, the association Cpx + Bt + Kfs + Grt (grossular–andradite) is stable. Thus, grossular–andradite garnet is an indicator of a high potassium activity in the fluid, whereas nepheline testifies that the sodium activity was high. Na → K exchange is typical of the amphibole and biotite, and Ca → Na exchange occurs in the clinopyroxene, and all of these minerals (but neither nepheline nor garnet) remain generally stable within a wide range of the K/Na ratio in the fluid. Clinopyroxene in the experiments spans Ca–Fe–Mg compositions with a varying, sometimes high, Al content, and the amphiboles belong to the pargasite–hastingsite series. With an increase in \({{a}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}\) (\({{X}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}\) > 0.57), i.e., a decrease in the gross salinity of the fluid, melts are generated, and their composition varies from trachyte to phonolite. An increase in the ХKCl/(ХKCl + ХNaCl) ratio in the fluids leads to a decrease in alumina content of the melts. An increase in the total salinity of the fluid leads to an increase in the content of potassium in the melt and a decrease in the content of chlorine in it. The experiments have shown that interaction between amphibole and fluids containing high NaCl and KCl concentrations results in mineral associations typically produced by alkaline metasomatism of amphibole-bearing rocks and concomitant HCl enrichment in the fluid phase. The substitution of highly saline fluids for highly acidic ones leads to the leaching of Ca, Mg, Fe from the metamorphic rocks, and the transport and redeposition of these components. It follows that significant removal of FeO, MgO, CaO from rocks is sometimes a consequence of the interaction of the host rocks with saline aqueous solutions.

Abstract Image

750°C, 700 MPa条件下角闪孔与高盐H2O-NaCl-KCl流体相互作用的实验研究:对角闪孔岩石碱性交代作用的启示
本文给出了不同含盐量下闪孔与NaCl-H2O和(K, Na) Cl-H2O溶液相互作用的实验数据。当与H2O-NaCl流体相互作用时,角闪孔仍是主要矿物,新形成的矿物有钠云母、斜长石和霞石/钠云母。网址:\({{a}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}\) &gt;0.6,角闪孔融化。当角闪孔与H2O-NaCl-KCl流体在\({{X}_{{{{{\text{H}}}_{2}}{\text{O}}}}}\) &lt;0.40和ХKCl/(ХKCl + ХNaCl),定义为ХNaCl = 0.506 - 0.84ХKCl,闪孔被霞石与钠质斜长石、钠长石和黑云母的组合所取代。网址:ХKCl/(ХKCl + ХNaCl) &gt;0.3,霞石、钠长石、斜长石变得不稳定,钾长石形成,黑云母、斜辉石、角闪石保持稳定。网址:ХKCl/(ХKCl + ХNaCl) &gt;0.5, Cpx + Bt + Kfs + Grt (grossular-andradite)的组合是稳定的。因此,榴辉石石榴石是流体中钾活性高的指示物,而霞石则证明流体中钠活性高。角闪洞和黑云母中存在典型的Na→K交换,斜辉石中存在Ca→Na交换,这些矿物(霞石和石榴石除外)在较大的K/Na比值范围内保持稳定。实验中的斜辉石由Ca-Fe-Mg组成,Al含量不同,有时含量很高,角闪石属于寄生石系列。随着\({{a}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}\) (\({{X}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}\) &gt;0.57),即流体的总盐度降低,产生熔体,其组成从粗叶岩到phonolite不等。流体中ХKCl/(ХKCl + ХNaCl)比值的增加导致熔体中氧化铝含量的降低。液体总盐度的增加导致熔体中钾含量的增加和氯含量的减少。实验表明,角闪洞与含高NaCl和KCl浓度的流体之间的相互作用导致矿物组合,通常由含角闪洞岩石的碱性交代和伴随的流体相HCl富集产生。高盐流体取代高酸性流体,导致变质岩中Ca、Mg、Fe的浸出及其输运和再沉积。由此可见,岩石中FeO、MgO、CaO的显著去除有时是寄主岩石与含盐水溶液相互作用的结果。
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
Petrology
Petrology 地学-地球科学综合
CiteScore
2.40
自引率
20.00%
发文量
27
审稿时长
>12 weeks
期刊介绍: Petrology is a journal of magmatic, metamorphic, and experimental petrology, mineralogy, and geochemistry. The journal offers comprehensive information on all multidisciplinary aspects of theoretical, experimental, and applied petrology. By giving special consideration to studies on the petrography of different regions of the former Soviet Union, Petrology provides readers with a unique opportunity to refine their understanding of the geology of the vast territory of the Eurasian continent. The journal welcomes manuscripts from all countries in the English or Russian language.
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