Alteration_Mass_Balance

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Unformatted text preview: Al2O3 Fe2O3(T) MnO MgO CaO Na2O K2O TiO2 P2O5 LOI Total Ba Sr Y Sc Zr Wednesday, 15 August, 12 29833 Fresh 2.90 69.11 12.67 3.3 0.064 1.36 5.03 2.74 1.57 0.234 0.04 4.61 100.7 104 132 7 16 65 29835 Altered 3.23 50.4 11.42 19.32 0.02 0.92 0.76 0.93 2.39 0.254 0.02 11.61 98.04 101 76 5 21 58 Alteration and Mass Balance • During alteration of a parent rock (e.g., fresh or least altered) to a daughter rock (e.g., altered rock) two things occur: • Mass and volume changes (i.e., changes in the size of the system). • Elemental changes (i.e., losses and gains of elements). Wednesday, 15 August, 12 Elemental Gain Original Size of System Fresh Rock Altered Rock Elemental Loss Wednesday, 15 August, 12 Elemental Gain Original Size of System Fresh Rock Altered Rock Elemental Loss Can’t look at raw data! Must correct for mass variations! Wednesday, 15 August, 12 Gresens’ (1967) Method • This is the seminal paper on mass-volume-elemental change during alteration and metamorphism. • Based on initial study of metasomatism in metamorphic petrology but has been the roots to the study of elemental mass change in alteration and metamorphism. • Still one of the best, and most quantitative methods of calculating mass and elemental change. Wednesday, 15 August, 12 Gresens’ (1967) Method • ! ! ! ! Relevant equations: ! ! ! ! ! ! ! [ f v ( p / p ) x − x ] = Δx i… (1) ! ! ! B ! ! ! A ! ! B i A i Where: fv = volume factor of rock A (protolith) to that of rock B (altered rock) – i.e. volume variation during alteration pB, pA = densities (specific gravity) or rocks A (fresh) and B (altered) XiB, XiA = weight fractions of element i in rocks, B (altered) and A (fresh), respectively ΔXi = absolute change in element i Wednesday, 15 August, 12 Gresens’ (1967) Method • If we assume that an element is immobile (e.g., Al2O3, Zr, etc.) we can calculate a volume factor as follows: !! • ! ! ! ! ! Then we can calculate elemental changes using the previous equation: ! [ f v ( p / p ) x − x ] = Δx i… (1) Wednesday, 15 August, 12 B A B i A i Gresens’ (1967) Method • In general, we take equation (1) for our data and input hypothetical fv and calculate ΔXi for a series of elements, to create a series of linear equations. • Plotting these linear equations results in a series of lines for each element. • Where a group of these lines intersect the ΔXi = 0 axis, or close to it, means that these elements were immobile during metasomatism. • We can then read off the fv graphically from this point.! ! ! ! ! • fv is then substituted into equation (1) for other “mobile” elements to calculate elemental change. Wednesday, 15 August, 12 From Gresens (1967) Wednesday, 15 August, 12 400 300 gains/losses (g/100g) 200 100 0 0 0.2 0.4 0.6 0.8 1 -100 -200 -300 -400 fv Wednesday, 15 August, 12 1.2 1.4 1.6 1.8 2 SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 Gresens’ (1967) Method • An alternative method is to assume certain elements are immobile (i.e., T...
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This document was uploaded on 03/06/2014 for the course ES 4502 at Memorial University.

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