Groundwater Flow, Normal Fault Block Motion, and Brine Evolution Within the Rio Grande Rift System, New Mexico: Implications for Potassium Metasomatism

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It is now well established that potassic hydrothermal alteration of igneous and sedimentary rocks is intimately associated with extensional tectonics and the evolution of regional groundwater flow systems within continental rift basins. While the paleohydrology of compressional tectonic systems has received considerable attention in the literature in recent years, the hydrodynamics of extensional terrains remains poorly understood in a quantitative sense. Little is know, for example, about the effects of listric fault block motion, the relative importance of different fluid flow inducing mechanisms, and the evolution of brines on basin hydrodynamics. In this proposal a methodology is presented for investigating crustal scale groundwater flow within continental rift basins using mathematical modelling. The approach will be used to study the giant potassium anomaly within the Rio Grande Rift system near Socorro, New mexico, a site where sufficient geologic and hydrologic data are available to evaluate the utility of the analysis. Finite element models of hydrothermal fluid flow brine evolution, and the kinematics of normal fault block motion will be constructed along cross-sectional transects through the rift. Special emphasis will be place on assessing the hydrologic connection between shallow (0-5 km) and deep (5-15 km) flow systems as well as the relative importance of compaction-, topography-, density-, and seismogenically-induced groundwater motion. The quantitative results will be compared with observed potassic hydrothermal alteration of igneous and sedimentary rocks within the Rio Grande Rift system in cooperation with Dr. Charles Chapin, Director of the New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico.