Constraints on the Duration of Water-Rock Interaction in the Rico Paleothermal Anomaly

在科罗拉多里科的一套侵入岩中，已经记录了测量热液蚀变岩中反应进展程度的“标尺”。裂变径迹部分退火的程度增加，整个岩石的氧同位素比值系统地减少作为接近系统的热源的函数。岩石中的蚀变产物在区域外围远离热源的地方数量减少。靠近系统的中心，反应物矿物完全反应，但产物的矿物学在空间上随热液系统中的位置而变化。产物长石和斜长石的组成是可变的，但不是功能上相对于距离热源。而Al、Si有序程度则随交换斜长石的An值而变化。这里提出的研究将使用磷灰石和锆石中裂变径迹的部分退火程度来限制热液系统的持续时间。矿物-矿物反应和氧同位素交换的动力学模型可以使用不同的反应进程尺度和裂变径迹年代学在Rico岩石中进行检验。这些数据将提供动力学约束对热液水-岩相互作用的适用性的独特指示：提供真实的时间测量的指示。

"Yardsticks" that measure the extent of reaction progress in hydrothermally altered rocks have been documented in a suite of intrusive rocks from Rico, Colorado. The degree of fission track partial annealing increases and the whole rock oxygen isotope ratios decrease systematically as a function of proximity to the system's heat source. The quantity of alteration products in the rocks decrease going away from the heat source in the peripheral portions of the district. Closer to the center of the system, reactant minerals are completely reacted, but the mineralogy of the products varies spatially as a function of position in the hydrothermal system. Compositions of product chlorite and plagioclase are variable but not functionally with respect to distance from the heat source. However, the degree of Al, Si order in the plagioclase varies with the An value of the exchanged plagioclase. The research proposed here will use the degree of partial annealing of the fission tracks in apatite and zircon to set constraints on the duration of the hydrothermal system. Kinetic models of mineral-mineral reactions and oxygen isotope exchange can be tested using the different reaction progress yardsticks and the fission track chronology in the Rico rocks. These data will provide a unique indication of applica- bility of kinetic constraints to hydrothermal water-rock inter- action: one that provides a real measure of time.