Alteration_Mass_Balance

Alteration_Mass_Balance

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Unformatted text preview: iO2, Al2O3, Zr, Nb, REE) and assume that no mass change - > ΔXi = 0, and calculate fv from equation (3). • Then substitute the average fv calculated from immobile elements into equation (1) for the other elements to calculate mass changes. • Plot mass changes on bar plots. Wednesday, 15 August, 12 Buttercup Hill: Epidote-Quartz Alteration 10 6 4 Total S H2O CO2 P2O5 K2O Na2O CaO MgO MnO Fe2O3 -2 Al2O3 0 TiO2 2 SiO2 Absolute Gains/Losses (g/100g) 8 -4 -6 -8 Data from Lesher et al. (1986) Wednesday, 15 August, 12 Gresens’ (1967) Method • Presentation of data often requires g/100g presentation of gains/ losses – just remove 100 from the front of equation (1). • Very rigorous but often time-consuming, requires good sampling and stratigraphic control, etc. • Not good for large datasets but can be extrapolated if a key group of samples has mass/gain calculated. • Programs: NewGres (Leitch and Lentz, 1994), etc. Wednesday, 15 August, 12 Grant’s (1986) Method • Grant (1986) simplified the calculations of Gresens (1967) by creating the isocon diagram. • Method involves plotting the elements in a fresh rock (x-axis) against those in an altered rock (y-axis). • • Immobile elements lie upon a line of equal concentration or “isocon” Elements above or below isocon represent mass gains and losses, respectively. Wednesday, 15 August, 12 Isocon Diagram 10000 1000 Mo/Ma = 1 element gain element loss 1 a= o /M M Ca (altered) 100 10 1 .1 .01 .001 .001 Wednesday, 15 August, 12 .01 .1 1 10 Co (least altered) 100 1000 10000 Grant’s (1986) Method • Grant (1986) proposed the following that: • Where: • CiA, CiO = concentrations in the altered and fresh rocks, respectively • • MA, MO = masses of the fresh and altered rocks, respectively ΔCi = mass change of element i during the alteration process Wednesday, 15 August, 12 Grant’s (1986) Method • Grant (1986) proposed the following that: • In the case where elements have not been mobile (i.e., mass conservation) then ΔCi = 0 and the above equation reduces to: • This is a linear equation through the origin in which the slope is proportional to the mass change during the alteration – this is the mass factor and can be applied to calculate mass changes for other mobile elements. Wednesday, 15 August, 12 Grant’s (1986) Method • We can rearrange the latter equation to get: • By comparing the concentration of an immobile element from the fresh and altered rock we can calculate the mass factor. For example, use Al2O3altered/Al2O3fresh (or Zr, Nb, Ti, etc.), or linear regression through all isocon points. • If MO/MA > 1 = system has lost mass, MA/MO < 1 = system has gained mass. M Ol M bC - A C i O = DC i ....... (7) M M O A i Wednesday, 15 August, 12 A Isocon Diagram 10000 1000 Mo/Ma = 1 element gain element loss 1 a= o /M M Ca (altered) 100 10 1 .1 .01 .001 .001 Wednesday, 15 August, 12 .01 .1 1 10 Co (least altered) 100 1000 10000 Isocon Diagram 1000 Ca (altered) 10...
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This document was uploaded on 03/06/2014 for the course ES 4502 at Memorial University.

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