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

科罗拉多州里科的一套侵入岩中记录了衡量热液蚀变岩石反应进展程度的“标尺”。随着系统热源的接近，裂变径迹局部退火度增加，全岩氧同位素比值系统地降低。在远离热源的区域，岩石中蚀变产物的数量减少。在更靠近系统中心的地方，反应物矿物完全反应，但产物的矿物学在空间上随水热系统中位置的变化而变化。产物绿泥石和斜长石的组成随离热源的距离而变化，但功能不同。但斜长石中Al、Si的有序度随交换斜长石的AN值而变化。这里提出的研究将利用磷灰石和锆石中裂变径迹的部分退火度来限制水热系统的持续时间。RICO岩石中矿物-矿物反应和氧同位素交换的动力学模型可以用不同的反应进度标尺和裂变径迹年代学进行检验。这些数据将为热水-岩石相互作用的动力学约束的适用性提供一个独特的指示：一个提供真实时间测量的指示。

"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.