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550551552553554555556557558559560561562563564565566567568569570571572573574575AppendixA1. Perple_X CalculationsThe phase relations of eight typical WGR quartzofeldspathic gneisses (Table A1) weredetermined using Perple_X [Connolly and Petrini, 2002] and the activity models listedin Table A2. All the bulk compositions were simplified to the Na 2 O–CaO–K 2 O–MgO–FeO–MnO– Al 2 O 3 –TiO 2 –SiO 2 –H 2 O system. The exclusion of some components (e.g.,Cr) and the absence of some components from solid solution models (e.g., K 2 O inamphibole) means that the calculations only approximate natural rocks and minerals.K 2 O poses perhaps the greatest problem of this type because neglecting the presence ofK 2 O in amphibole means that the stability of K-white mica is overemphasized. Theamount of H 2 O was fixed to stabilize the existing mineral assemblage. CO 2 wasneglected principally because even for a CO2 = 0.5, a key equilibrium like <strong>titanite</strong> +anorthite + H 2 O = rutile + quartz + grossular expands <strong>titanite</strong> stability <strong>by</strong> only 0.2 GPa;for other equilibria, such as <strong>titanite</strong> + zoisite = rutile + quartz + grossular + H 2 O, theaddition of CO 2 moves the stability field of <strong>titanite</strong> to lower pressure.A2. Titanite Zr Analyses <strong>by</strong> Electron ProbeMeasurements were made using a Cameca SX-100 operated at 15 kV, 200 nA, a 5 µmspot, and using Probe for EPMA software (Table A3). Aggregate x-ray counts from 5spectrometers (4 LPET and one PET) were collected for 200 seconds on the Zr K α peakand 100 seconds off peak on both sides of the peak. A linear background extrapolationwas used to determine net (peak–background) Zr K α intensity. Zr metal was used aprimary standard and the natural <strong>titanite</strong> reference material BLR was used to assessaccuracy. The Zr content of BLR reported <strong>by</strong> Mazdab [2009] is 1300 ppm <strong>by</strong> EPMA,1470 ppm <strong>by</strong> solution <strong>ICP</strong>-MS, and 1830 ppm <strong>by</strong> INAA. We obtained values of 1496–33
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