Experimental Investigation of Chlorine Substitution into Calcic Amphiboles

研究结果将有助于进一步认识海水与海洋地壳岩石的相互作用、富氯流体在深部地壳岩石矿物学变化中的作用以及与矿物形成相关的流体组成等基本过程。富氯角闪石已经在广泛的地质环境中被观察到，但对它们是如何形成的知之甚少。本研究的重点是通过实验研究氯在常见的造岩矿物角闪孔和含氯卤水之间的分配。校准角闪孔中氯的浓度如何随宿主角闪孔的组成（如其铁含量）和周围盐水的氯含量变化，使地质学家能够确定曾经与角闪孔接触但不再存在的流体的氯含量。该项目的重要成果将是确定角闪孔中哪些成分变量对控制其吸收氯的能力最重要，并量化氯在矿物和流体之间的分布。该研究项目将通过检查文献中提出的一些晶体化学相关性，提供一些关于氯取代角闪孔的成分控制的第一批实验数据。将研究四种具体的相关性：(i)在八面体位置（即Fe#）用Fe2+取代Mg，并确定Cl含量是否随Fe#线性变化，（ii）在A晶体位置上K的占位，（iii）四面体Al取代Si， （iv）八面体Fe3+取代八面体Al。这些组成变量将主要使用角石铁-pargasite和hastingsite进行研究。这两种化合物在自然界中都有很高的氯含量，并且可以合成出足够大小的化合物，用于常规的电子探针分析。一组补充实验将在不同类型和不同Cl浓度的盐水中合成角闪石，以确定在给定的压力、温度和温度下，角闪石中获得的最大Cl含量或饱和水平。oxygen-fugacity条件。本研究的结果将有助于我们理解哪些组成变量是控制氯在角闪孔中取代的最重要因素，并量化钙质角闪孔和环境盐水之间氯的分配。这些信息可应用于地质科学的各个领域，包括海水-岩石相互作用、与cl -交代有关的流体中的氯浓度、盐溶液在形成高品位变质岩中的作用，以及描述产生重要经济矿床的流体特征。

The results from this study should provide insights into such basic processes as the interaction of seawater with oceanic crustal rocks, the role of chlorine-rich fluids in producing mineralogical changes in deep-crustal rocks, and the compositions of fluids associated with ore-mineral formation. Chlorine-rich amphiboles have been observed in a wide range of geological settings yet little is known about how they form. The focus of this proposal is to investigate experimentally the partitioning of chlorine between the common rock-forming mineral amphibole and chlorine-bearing brines. Calibrating how the concentration of chlorine in the amphibole varies with both the composition of the host amphibole (such as its iron content) and the chlorine content of the ambient brine permits geologists to determine the chlorine content of fluids that were once in contact with the amphibole but are no longer present. Important outcomes from this project will be to identify what compositional variables in the amphibole are most important in controlling its ability to incorporate chlorine, and quantifying the distribution of chlorine between mineral and fluid. This research project will provide some of the first experimental data on the compositional controls on the substitution of chlorine into amphibole by examining some of the crystal-chemical correlations that have been proposed in the literature. Four specific correlations will be investigated: (i) substitution of Fe2+ for Mg at octahedral sites (i.e., the Fe#) and determining whether or not the Cl content varies linearly with the Fe#, (ii) occupancy of K at the crystallographic A site, (iii) substitution of tetrahedral Al for Si, and (iv) substitution of octahedral Fe3+ for octahedral Al. These compositional variables will be studied primarily using the amphiboles ferro-pargasite and hastingsite, both of which have been observed with high Cl contents in nature and which can be synthesized with sufficient size for routine electron microprobe analysis. A complementary set of experiments will be done where amphiboles are synthesized in brines of varying types and Cl concentration in order to determine the maximum Cl content, or saturation level, obtained in the amphibole at a given set of pressure?temperature?oxygen-fugacity conditions. The results of this study should improve our understanding of what compositional variables are most important in controlling the substitution of Cl into amphibole and quantify the partitioning of Cl between calcic amphiboles and an ambient brine. This information has applications to diverse areas in the geological sciences, including seawater-rock interaction, chorine concentration in fluids associated with Cl-metasomatism, the role of saline solutions in forming high-grade metamorphic rocks, and characterizing fluids that yield economically important deposits.