Collaborative Research: The Crystal Chemistry of Rock-Forming Chlorite

变质岩石学的一个主要目标是了解变质过程中结晶条件（温度、压力、体积组成、挥发性组分的化学活性等）之间的相互关系。虽然绿泥石是一种常见的造岩变质矿物，其组成和晶体结构被认为与这些结晶条件有关，但还没有对绿泥石进行结构研究，以确定岩石学因素如何影响其结构。在这个项目中，单晶x射线衍射方法将被用来检查一系列特征良好的绿泥石。除了Plumbago钚组外，所有样品都含有石墨，因此铁的氧化态受到限制。缅因州的变质长岩片岩具有以下特征：(1)地层压力接近3.5 kbar, (2) Al饱和，(3)中至高Mg2+含量，(4)不同的地层温度。为了进行比较，我们选择了缅因州的一套从变质的普拉姆戈镁质到超镁质的岩体，因为它富含镁，但不饱和铝。此外，一个更富铁的套件将被检查。在进行化学分析后，比较各品位内和品位间绿泥石晶体的结构精密度。研究结果将有助于确定Al， Mg， Fe2+和空位如何分布在绿泥石的不同结晶位置，作为结晶压力和温度和绿泥石组成的函数。这些结果将有助于解释为什么变质绿泥石的允许成分范围有相对明显的成分界限。此外，对阳离子排序中涉及的变量的理解可以提供对限制Ti， Fe3+, Mn, Ni， Cr等取代的控制的额外理解。主要目的是了解这些因素如何影响或控制亚氯酸盐中八面体薄片和2:1层之间的氢键。最重要的是，这些数据将消除之前试图建立与天然岩石直接相关的绿泥石热力学溶液模型的临时方面。

Guggenheim and Guidotti0308588 and 0308546A major goal of metamorphic petrology is to understand the interrelationships among the crystallization conditions (temperature, pressure, bulk composition, chemical activities of volatile constituents, etc.) during metamorphic processes. Although chlorite is a common rock-forming metamorphic mineral believed to have a composition and crystal structure that relates to these conditions of crystallization, no structural studies of chlorite have been made to identify how petrologic factors affect the structure.In this project, single-crystal X-ray diffraction methods will be used to examine suites of well-characterized chlorite. For each suite except the Plumbago pluton suite, all samples contain graphite, so that the iron oxidation state is constrained. The metapelitic schists to be examined from Maine will have the following characteristics: (1) formation pressures at near 3.5 kbar, (2) Al saturated, (3) intermediate-to-high Mg2+-contents, and (4) varying formation temperatures. For comparison, a suite from the metamorphosed Plumbago mafic to ultramafic pluton in Maine, is selected because it is Mg-rich, but not Al-saturated. In addition, a more Fe-rich suite will be examined. After chemical analyses are made, structure refinements of chlorite crystals within each grade and between grades will be compared.The results of the study will help determine how Al, Mg, Fe2+, and vacancies are distributed in the various crystallographic sites of chlorite as a function of the pressure and temperature of crystallization and chlorite composition. These results will help to explain why there are relatively sharp compositional boundaries for the permissible composition range for metamorphic chlorites. In addition, an understanding of the variables involved in cation ordering may provide additional understanding of the controls limiting Ti, Fe3+, Mn, Ni, Cr, etc. substitutions. A major objective is to understand how these factors affect or control hydrogen bonding between the octahedral sheet and the 2:1 layer in chlorite. Most importantly, these data will eliminate the ad hoc aspect to previous attempts to formulate thermodynamic solution models for chlorite that are directly relevant to natural rocks.