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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: EpidoteQuartz 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 timeconsuming, 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 (xaxis) against
those in an altered rock (yaxis). •
• 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.
 Fall '12
 DrPiercey

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