Clinopyroxene partition coefficient

Figure 11. The clinopyroxene-liquid partition coefficient for 4+ ions entering the M2-site shown as a function of the ionic radins of the trace cation. Changes in clinopyroxene composition along a solid solntion lead to small changes in the dimensions of M2 (ro Jw 2>), which can lead in turn to changes in the relative fractionation between 4+ ions of similar ioiuc radii, such as and Th" (shown as vertical lines). We contrast the partitioning behavior of a diopside-rich clinopyroxene = 1 044 A) and a...

Fitting 71 Djh values (27 from their study and 44 from the literature) and subsequently excluding 5 outliers, Landwehr et al. (2001) derived the following expression for Th partitioning between clinopyroxene and silicate melt as a function of temperature, pressure, crystal chemistry and the molar MgMi partition coefficient ... 

The denotes molar, rather than weight fraction, partition coefficient. The X terms denote the cation molar fractions of Ca, Al and Mg, while the X terms denote the molar fraction of diopside and enstatite components in clinopyroxene. Note that this expression contains no explicit P-f dependence. 

Orthopyroxene has a Vl-fold Ml site and a Vl-fold M2 site. Both are predominantly filled by Mg and Fe. The smaller Ml site shares many characteristics with the clinopyroxene Ml site. It is therefore reasonable to assume that no U-series cations, including Pa (see above) enter that site. We will confine our discussion to the octahedral M2, which is smaller than the equivalent (Vni-fold) clinopyroxene site, even after allowing for the different coordination number. Consequently most of the U-series elements have very low orthopyroxene-melt partition coefficients. 

Argon partition coefficients for olivine have recently been determined by Brooker et al. (1998). Their measured Z)at values are around 10 , which is higher than measured for clinopyroxene, but similar to the estimated values for orthopyroxene. We propose a value... 

Brooker RA, Wartho J-A, Carroll MR, Kelley SP, Draper DS (1998) Preliminary UVLAMP determinations of argon partition coefficients for olivine and clinopyroxene grown from silicate melts. Chem Geol 147 185-200... 

Foley SF, Jackson SE, Fryer BJ, Greenough JD, Jenner GA (1996) Trace element partition coefficients for clinopyroxene and phlogopite in an alkaline lamprophyre from Newfoundland by LAM-ICP-MS. Geochim Cosmochim Acta 60 629-638... 

Green TH, Blundy JD, Adam J, Yaxley GM (2000) SIMS determination of trace element partition coefficients between garnet clinopyroxene and hydrous basaltic liquids at 2-7.5 GPa and 1080-1200°C. Lithos 53 165-187... 

Table 2. Experimentally determined mineral/melt partition coefficients (x 10 ) for U, Th, and Ba in clinopyroxene and garnet and calculated bulk partition coefficients (xlO ) for a garnet peridotite source.

Figure 4.11 Monte-Carlo simulation (100 trials) of error propagation for La/Yb fractionation in residual melts by clinopyroxene-garnet removal from a basaltic parent magma (see text for parameter description and distributions used). Top mineral-liquid partition coefficients for La and Yb. Bottom variations of the La/Yb ratio as a function of the fraction F of residual melt.

From the concentration of each element in the liquid and in the source, we can retrieve the degree of melting and the residual mineralogy. We assume that the liquid contains 676 ppm Ni, 426 ppm Cr, 0.763 ppm Yb and 0.1 ppm Rb, whereas its source composition y vector is (2500, 1500, 0.2, 0.01) in ppm. We will test the assumption that the residuum is composed of olivine and clinopyroxene with the partition coefficients given above. Phase abundances Jt will be ordered as liquid, olivine and clinopyroxene. Let us compute, as an example, the element in the third row and second column of the matrix A... 

A basalt contains 150 ppm Ni, 100 ppm Sr, 3 ppm Yb, and 10 ppm Rb. Calculate the concentration of each element after removal of 20 percent of a cumulate containing 30 percent olivine, 20 percent clinopyroxene and 50 percent plagioclase in the residual liquid and in the average cumulate. Assume the partition coefficients given in Table 9.6. 

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