TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

droplet, which generated a slurry as sample material was removed. The slurry was
removed using a micropipette and placed in a 3.5 mL Teflon beaker. The sample
was then subjected to a hotplate digestion with concentrated HF and HNO3.
Strontium was extracted using a scaled-down ion exchange column method. The
samples were run Re filaments with a TaF activator and 87 Sr/ 86 Sr ratios were
measured using a Finnigan Triton thermal ionization mass spectrometer (TIMS).
Davidson et al. [39] and Tepley et al. [135] provide more thorough discussions
about of the micro-Sr isotope method.
4.3.6 Choosing Partition Coefficients (D)
Blundy [9] noted that inversion of magma compositions from mineral data
using appropriate trace element D values is a robust means of estimating parent
magma compositions and suggested that trace element D values derived from
microbeam techniques were more accurate than those derived from bulk crystal-
matrix analyses. Blundy and Wood [10, 11] and Bindeman et al. [7] showed
that the dominant factors controlling the trace element D vaues for plagioclase
are An content and crystallization temperature. Bindeman et al. [7] applied this
relationship to a variety of major and trace elements and produced values for the
constants “a” and “b” in their Equation 2 (equation 4.1 below) for calculating
plagioclase partition coefficients via the expression:
RT ln(Di) = aXAn + b (4.1)
where R is the gas constant, T is temperature (Kelvin), i is the element of interest,
and XAn is the mole fraction of anorthite. Using equation 4.1, Ginibre et al.
[59] noted that temperatures in the range of 850-1,000 ◦ C had miniscule effect on
181