Experimental Investigation of Glaucophane Solid Solution with Several Calcic Amphiboles

这项建议是为了从实验上研究钠基角闪石蓝闪石和几种常见的钙质角闪石之间矿物固溶体组成的范围和性质。这些类型的钠钙角闪岩是世界各地观察到的典型的高压变质岩。虽然已经有经验观察到这种角闪石的成分变化与其构造环境有关，但这些成分变化还没有得到定量的校准。这项研究将有助于地质学家从钠钙角闪石的成分变化中确定造山带或俯冲带的压力-温度历史。本研究将重点研究透闪石-蓝闪石、镁闪石-蓝闪石和蓝闪石-蓝闪石化学体系中透闪石-蓝闪石、镁闪石-蓝闪石和蓝闪石-蓝闪石化学体系中的成分连接。这些成分连接构成了钠钙角闪岩中最常见的成分变化。透闪石-蓝闪石连接的混溶间隙的存在是从现场证据中很好地建立起来的，并得到了本实验室获得的初步实验数据的支持。目前提案的一个主要目标是尽可能准确地确定这种混溶间隙的位置，因为它对终端成员组分的热力学混合性质施加了严格的限制。混合间隙在温度-组成空间中的位置将通过使用各种方法的组成反转来确定，例如端元透闪石和蓝闪石沿混合间隙溶解成组分，以及可能通过最初均一的角闪石出溶来确定。还将沿着其他接合处寻找混溶间隙。对于正在研究的每个连接，将注意通过结合OH-拉伸区的红外光谱和使用适当大晶体的单晶结构精细化的键长与离子半径关系来确定长程和短程阳离子有序度的程度。从每个连接中选择的晶体将通过高分辨率电子显微镜进行检查，以证明存在可能导致一定程度的表观固溶体而不是真正的固溶体的链多重数故障。这项研究的信息可以用来校准钠钙角闪岩的成分随压力、温度和共存矿物组合的变化。反过来，这将是那些利用钠钙角闪石成分变化来确定增生带或碰撞带构造历史的人特别感兴趣的。这项提案包括为研究生和本科生提供资金。与当地一所高中合作，对选定的地球科学优等生的辅导将作为这一研究项目的一部分。

This proposal is to investigate experimentally the extent and nature of mineral solid solution compositions between the sodic amphibole glaucophane and several common calcic amphiboles. These types of sodic-calcic-amphiboles are typical of high-pressure metamorphic rocks observed around the world. Although there have been empirical observations relating compositional changes in such amphiboles to their tectonic settings, these compositional changes have yet to be calibrated quantitatively. The information obtained in this study will help geologists to determine the pressure-temperature history of orogenic belts or subduction zones from the compositional variations of sodic-calcic-amphiboles.This study will focus on the compositional joins tremolite-glaucophane, magnesiohornblende-glaucophane, and pargasite-glaucophane in the chemical system Na2O-MgO-CaO-Al2O3-SiO2-H2O. These compositional joins comprise the most common compositional variations in sodic-calcic-amphiboles. The presence of a miscibility gap for the tremolite-glaucophane join is well established from field evidence and supported by preliminary experimental data obtained in this lab. A major goal of the current proposal will be to define the location of this miscibility gap as accurately as possible because of the tight constraints that it places on the derived thermodynamic mixing properties of the end-member components. Location of the miscibility gap in temperature-composition space will be determined by compositional reversals using various methods, such as the dissolution of end-member tremolite and glaucophane to compositions along the miscibility gap and possibly by exsolution of initially homogeneous amphibole. Miscibility gaps will also be sought along the other joins. For each of the joins being studied, care will be taken to determine the extent of long- and short-range cation order by a combination of infrared spectroscopy in the OH-stretching region and the use of bond-length versus ionic-radius relationships from single-crystal structural refinements of suitably large crystals. Selected crystals from each join will be examined by high-resolution transmission electron microscopy to document the presence of chain-multiplicity faults that might induce a certain degree of apparent rather than true solid solution. The information from this study can be used to calibrate variations in the compositions of sodic-calcic-amphiboles with pressure, temperature, and coexisting mineral assemblage. This, in turn, will be of particular interest to those using variations in sodic-calcic-amphibole compositions to determine the tectonic history of accretionary or collision zones. This proposal includes funding for graduate and undergraduate students. In cooperation with a local high school, mentoring of selected Earth science honors students will be included as part of this research project.