COLLABORATIVE RESEARCH: The Role of Exsolution Lamellae in the Rates and Mechanism of Dissolution of Plagioclase Feldspare

斜长石是自然界中丰富的原生矿物，是非碳酸盐体系中钙、钠的重要来源。斜长石富钙相和富钠相(出溶片层)的两相共生是斜长石的共同特征，但很少有人研究它们在斜长石溶解速率、化学计量学和溶解机理中的作用。拟议的合作研究的目标是(I)确定出溶片层对斜长石的速率和化学计量比的影响，(2)确定优先风化的片层相对使用诸如X射线光电子能谱(XPS)等表面敏感光谱收集的数据的解释的影响；和(3)研究从具有良好特征的分水岭实验室收集的斜长石样品中，出溶相在优先释放钙方面的潜在作用。主要调查人员之间的合作将结合实现这些目标所需的专门知识和设施。溶解实验将在pH为4的条件下进行，使用批量pH恒定器、流过细胞和柱式反应容器，使用具有和不具有出溶片层的内容物范围内的斜长石样品。此外，来自分水岭实验室的斜长石样品将用于表征和溶解研究，以评估出溶薄片在自然系统中的潜在作用。反应矿物的表面将用扫描电子显微镜(SEM-EDX)、X射线光电子能谱(XPS)和高分辨电子显微镜(HRTEM-EDX、HRTEM-ED)进行表征。这项研究的结果将被用来模拟斜长石的溶解速度和化学计量比，作为含和不含出溶相的矿物中AN含量的函数。将在实验室和分水岭风化环境中验证关于斜长石溶解机制和溶解过程中Ca相对于Si和Na的优先释放的假设。

Plagioclase feldspars are abundant primary minerals in nature and represent an important source of Ca and Na in noncarbonate systems. Two phase intergrowths of calcic and sodic rich phases (exsolution lamellae) are common features in plagioclase feldspars, yet few studies have evaluated their role in the rates, stoichiometry and mechanisms of plagioclase dissolution. The objectives of the proposed collaborative study are to (i) determine the effects of exsolution lamellae on the rates and stoichiometry of plagioclase feldspars, (ii) determine the effect of preferentially weathered lamellar phases on the interpretation of data collected using surfaced sensitive spectroscopies such as x-ray photoelectron spectroscopy (XPS) and (iii) examine the potential role of exsolved phases in preferential release of Ca from plagioclase samples collected from well characterized watershed laboratories. Collaboration among the principal investigators will combine expertise and facilities necessary to accomplish these objectives. Dissolution experiments will be conducted at pH 4 using batch pH stat, flow through cell, and column reaction vessels using plagioclase samples over a range of an contents with and without exsolution lamellae. In addition, plagioclase samples from watershed laboratories will be used in characterization and dissolution studies to evaluate the potential role of exsolution lamellae in natural systems. The surfaces of reacted minerals will be characterized using scanning electron microscopy (SEM-EDX), x-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM-EDX, HRTEM-ED). Results from this study will be used to model the rate and stoichiometry of plagioclase dissolution as a function of An content in minerals with and without exsolved phases. Hypotheses concerning the mechanisms of plagioclase dissolution and the preferential release of Ca relative to Si and Na during dissolution will be tested for both laboratory and watershed weathering environments.