Experimental Investigation of Chlorine Substitution into Calcic Amphiboles

从这项研究的结果应该提供洞察等基本过程，如海水与海洋地壳岩石的相互作用，富氯流体在深地壳岩石中产生矿物学变化的作用，以及与成矿流体的成分。富含氯的角闪石已经在广泛的地质环境中被观察到，但对它们如何形成却知之甚少。 本研究的重点是实验研究氯在常见造岩矿物角闪石和含氯卤水之间的分配。 校准角闪石中氯的浓度如何随宿主角闪石的组成（如其铁含量）和环境盐水的氯含量而变化，允许地质学家确定曾经与角闪石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石中哪些成分变量在控制其结合氯的能力方面最重要，并量化矿物和流体之间氯的分布。 本研究项目将通过研究文献中提出的一些晶体化学相关性，提供有关氯取代成闪石的成分控制的一些第一批实验数据。 将研究四种特定的相关性：（i）Fe 2+在八面体位点（即，Fe#），并确定Cl含量是否随Fe#线性变化，（ii）K在晶体学A位的占有率，（iii）四面体Al对Si的取代，以及（iv）八面体Fe 3+对八面体Al的取代。这些组成变量将主要使用角闪石铁钠闪石和黑锰矿进行研究，这两种化合物在自然界中都观察到具有高的Cl含量，并且可以合成为具有足够的尺寸用于常规电子探针分析。 一组互补的实验将在不同类型和Cl浓度的盐水中合成角闪石，以确定最大的Cl含量，或饱和度，在给定的一组压力下在角闪石中获得？温度？氧逸度条件 这项研究的结果应该提高我们的理解，什么成分变量是最重要的控制氯角闪石的替代和量化的钙角闪石和周围的盐水之间的Cl的分区。 这些信息在地质科学的各个领域都有应用，包括海水-岩石相互作用、与Cl-交代作用相关的流体中的氯浓度、盐溶液在形成高级变质岩中的作用，以及表征产生经济上重要的矿床的流体。

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.