An almandine garnet isograd in the Rogers Pass area,British Columbia: The nature of the reaction and an estimation of the physical conditions during its formation期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

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An almandine garnet isograd in the Rogers Pass area,British Columbia: The nature of the reaction and an estimation of the physical conditions during its formation

Authors:	J W Jones

Institution:	(1) Department of Geology, University of Calgary, T2N 1N4 Calgary 4, Alberta, Canada

Abstract:	In the Rogers Pass area of British Columbia the almandine garnet isograd results from a reaction of the form: 5.31 ferroan-dolomite+8.75 paragonite+4.80 pyrrhotite+3.57 albite+16.83 quartz+1.97 O₂=1.00 garnet+16.44 andesine+1.53 chlorite+2.40 S₂+1.90 H₂O+10.62 CO₂. The coefficients of this reaction are quite sensitive to the Mn content of ferroan-dolomite.Experimental data applied to mineral compositions present at the isograd, permits calculation of two intersecting P, T equilibrium curves. P=29088–39.583 T is obtained for the sub-system paragonite-margarite (solid-solution), plagioclase, quartz, ferroan-dolomite, and P=28.247 T–14126 is obtained for the sub-system epidote, quartz, garnet, plagioclase. These equations yield P=3898 bars and T=638° K (365° C). These values are consistent with the FeS content of sphalerite in the assemblage pyrite, pyrrhotite, sphalerite and with other estimates for the area.At these values of P and T the composition of the fluid phase in equilibrium with graphite in the system C-O-H-S during the formation of garnet is estimated as: $P_{{\text{H}}_{\text{2}} {\text{O}}} = 3138$ bars, $P_{{\text{CH}}_{\text{4}} } = 570$ bars, $P_{{\text{H}}_{\text{2}} {\text{S}}} = 180$ bars, $P_{{\text{CO}}_{\text{2}} } = 6$ bars, $P_{{\text{H}}_{\text{2}} } = 3$ bars, $f_{{\text{O}}_{\text{2}} } = 10^{ - 31.2}$ bars, $f_{{\text{S}}_{\text{2}} } = 10^{ - 3.2}$ bars, $f_{{\text{CO}}} = 10^{ - 1.7}$ bars, $f_{{\text{SO}}_{\text{2}} } = 10^{ - 8.3}$ , bars, $f_{{\text{SO}}_{\text{3}} } = 10^{ - 20.7}$ bars.

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