R. Kretz et al., Approaches to equilibrium in the distribution of trace elements among the principal minerals in a high-grade metamorphic terrane, J METAMORPH, 17(1), 1999, pp. 41-59
X-ray fluorescence, instrumental neutron activation, and particle-induced X
-ray emission methods were used to determine the distribution of numerous t
race elements among garnet (Grt), Ca-pyroxene (Cpx), hornblende (Hbl), biot
ite (Bt), plagioclase (Pl) and K-feldspar (Kf) in a high-grade metamorphic
terrane within the Grenville Province of the Canadian Shield. Results are p
resented as distribution formulae, e.g.
Sr: Kf 1.1 Pl 16 Hbl 2.2 Cpx 1.0 Pt 1.2 Grt
Sc: Hbl 1.1 Cpx 1.0 Crt 7.8 Bt 22 Pl 2.6 Kf
V: Hbl 1.15 Bt 2.07 Cpx 6.0 Crt (1.4% CaO) > l (Pl, Kf)
Zn: Bt 1.6 Hbl 1.62 Cpx 2.9 Grt 10 Pl
Ga: Bt 1.2 Hbl 1.2 Pl 2.5 Cpx 1.3 Grt
where numbers are distribution ratios, e.g. ppm Sr in Hbl/ppm Sr in Cpx = 2
.2. Examples of inter-element similarities and differences are (a) both Rb
and Cs are concentrated in biotite relative to K-feldspar, but for Rb the r
atio is 2.3 and for Cs it is 16, (b) the distribution formulae for seven la
nthanides are similar except for the position of garnet, e.g.
Ce: Hbl 2.7 Cpx 2.8 Pl 1.1 Bt 11 Kf 16 Grt
Yb: Grt 2.8 Hbl 2.7 Cpx 9 Pl 1.0 Bt 7 Kf
and (c) all of Sr, eight lanthanides, Zr, V and Cr are concentrated in horn
blende relative to Ca-pyroxene by a factor that lies in the narrow range of
2.2-3.1. There is a larger variation (departure from the mean) in some dis
tribution ratios than in others. Thus the mean ratios (Hbl/Cpx) for each of
six elements and in parentheses the percentage relative standard deviation
are Zn 1.62 (8.6), V 2.38 (12), Cr 2.42 (18), Sr 2.7 (28), Pa 2.9 (36) and
Ni 1.66 (38). We suggest that variation of this kind is the result of diff
erences from place to place in the magnitude of deformation and recrystalli
zation (which facilitated the rearrangement of atoms), combined with rates
of lattice and crystal-boundary diffusion that are unique for the various e
lements, thus permitting some trace elements to approach equilibrium more c
losely than others.