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Date Permissions Signed
Date of Award
Master of Science (MS)
Hirsch, David M., 1969-
Burmester, Russell F.
Babcock, R. Scott (Randall Scott)
The nature of fluid movement through the lower crust during prograde metamorphism is an important but poorly understood part of the global H2O and CO2 cycles on this planet. A broad set of samples from some of the structurally deepest exposures of the Nason terrane in the Cascades crystalline core were used to evaluate fluid movement during peak amphibolite-grade metamorphism. XRF bulk-rock chemical analyses, T-X(CO2) pseudosections, and thin-section petrography were used to identify equilibrium fluid composition for the solid phases in each specimen; these span the gamut of X(CO2) values. The juxtaposition of gneiss and marble-lithologies with differing equilibrium fluid compositions-and the infiltration of fluids during prograde metamorphism resulted in the development of a trend in calculated equilibrium fluid composition across the study area. Linear regression analysis of the fluid chemical data suggests that time-averaged fluid flow throughout peak conditions in the study area occurred largely upward in the study area with a small horizontal component towards the northeast. Vectors fit to the trend of mean fluid composition in each marble body suggest that fluid flowed upward 75º±88º above horizontal 64º±35º (NE) for the LW Body and 70º±42º above horizontal with an azimuth 73º±34º (ENE) for the SS Body. This is in agreement with models in the current literature that suggest fluid movement under these conditions is governed by buoyancy forces in the crust, as opposed to meter- to kilometer-scale variations in permeability described by previous studies of aqueous fluid systems in the lower crust. This study embodies a new method that employs petrography, XRF analyses and thermodynamic modeling for the determination of fluid flow directions during metamorphism.
Western Washington University
North Cascades (B.C. and Wash.)
Copying of this thesis in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Ponshock, Perry M. (Perry Martin), "Sub-vertical fluid flow during prograde metamorphism in the Nason terrane, North Cascades crystalline core, Washington" (2011). WWU Masters Thesis Collection. 147.