Reaction Lengths and Reaction Rates in Metamorphic Rock Systems Using Isotopic and Age Zoning in Garnet Porphyroblasts

9805218德保罗这项拟议的研究旨在确定(1)在500至700摄氏度之间变质岩中矿物-流体交换反应的速率，以及(2)在这些条件下变质过程中保持化学“平衡”的长度尺度。该方法包括测量变质岩中石榴石斑岩的锶、钕和氧同位素组成，并结合对整个岩石和基质样品进行类似的同位素测量。同位素测量将与矿物主要元素组成的电子探针研究相辅相成。这项研究将对层状变质岩中的样品进行研究，选择这些地点是因为它们具有能够确定流体-岩石系统的“平衡长度”或“反应长度”的特性。野外场地所需的特征是：(1)具有不同初始锶同位素比值和不同Rb/Sr比值的层间岩性；(2)丰富的大型石榴石斑岩，适合于对核心、边缘和中间带进行同位素分析的显微取样；以及(3)相对较新的变质作用时代。在阿尔卑斯山、佛蒙特州、加利福尼亚州和阿拉斯加州发现了合适的露头。

9805218 DePaolo The proposed research is designed to determine (1) the rates of mineral-fluid exchange reactions in metamorphic rocks at temperatures between 500 and 700 C and (2) the length scales over which chemical "equilibrium" is maintained during metamorphism under these conditions. The approach involves measurements of Sr, Nd and O isotopic compositions of garnet porphyroblasts from metamorphic rocks, combined with similar isotopic measurements of whole rock and matrix samples. The isotopic measurements will be supplemented with electron microprobe studies of major element compositions of minerals. The study will be made on samples from layered metamorphic rocks, the localities chosen specifically because they have characteristics which allow determination of the "equilibration length" or "reaction length" of the fluid-rock system. The required characteristics of the field sites are: (1) interlayered lithologies with different initial Sr isotope ratios and different Rb/Sr rations; (2) abundant large garnet porphyroblasts suitable for microsampling of core, rim, and intermediate zones for isotopic analyses; and (3) a relatively recent age of metamorphism. Appropriate outcrops have been identified in the Alps, Vermont, California and Alaska.