TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

3.4.6.1 Partition coefficients for DSM plagioclase crystals
I used equation 3.2 and the parameterizations of Blundy and Wood [11, 12] to
calculate D values for Sr, Y, Ba, La, Ce, Nd, and Sm. (see Table 3.4). I assumed
a crystallization temperature of 1190 ◦ C to calculate D values. The validity of
this assumption was examined using the MELTS program [2, 55] to determine
the temperature at which plagioclase arrives on the liquidus during crystallization
of a typical Detroit Seamount tholeiitic basalt. I input Detroit Seamount tholei-
itic basaltic glass compositions reported by Huang et al. [72] into the MELTS
program. During equilibrium crystallization of the lowest MgO glass from Site
1203 (Unit 3), plagioclase appeared on the liquidus at 1170 ◦ C, at at 1190 ◦ C from
the highest MgO glass from Site 1203 (top of Unit 18), and at 1200 ◦ C from the
highest MgO glass from Site 884 (Unit 10). The use of 1170 ◦ C vs. 1200 ◦ C in D
calculations yields < 4% differences in trace element concentrations of parent liq-
uids, which is within the analytical error for my analyses. The effects of pressure
on plagioclase D values are not well documented for most elements, and where
they were documented for DSr by Vander Auwera et al. [137] they were negligible.
I used a crystallization pressure of 0.001 kbar for D calculations. I assume the
strain compensated (i.e., strain free) partition coefficient D 2+
0 in plagioclase is best
approximated by DCa (c.f., [12]), and to estimate DCa I used equation 3.1 and the
“a” and “b” constants reported for Ca by Bindeman et al. [7]. Estimation of D 3+
0
is less straightforward. I assumed D 3+
0 to be ∼ 7.5% of D 2+
0 , which was derived
from experimental data reported in Blundy [9]. I used equation 3.1 and the “a”
and “b” constants reported for Ti by Bindeman et al. [7] to estimate DTi
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