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

测量热液蚀变岩石中反应进展程度的“尺度”已经在科罗拉多州Rico的一套侵入岩中被记录下来。与热源的接近程度有关，裂变径迹部分退火程度增大，全岩氧同位素比值减小。在区域外围，离热源越远，岩石蚀变产物数量越少。靠近系统中心的地方，反应物反应完全，但产物的矿物学随热液系统中位置的变化而在空间上有所不同。产品绿泥石和斜长石的组成是可变的，但在功能上与热源的距离无关。然而，斜长石中Al、Si的有序程度随交换斜长石的An值而变化。本文提出的研究将利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。利用不同的反应过程尺度和裂变径迹年代学，可以检验Rico岩石中矿物-矿物反应和氧同位素交换的动力学模型。这些数据将为热液水岩相互作用动力学约束的适用性提供一个独特的指示：提供一个真实的时间度量。

"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.