Clinopyroxenes series

Mineral-Melt Partitioning ofU-Series Nuclides Clinopyroxene along mantle solidus... 

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. 

Wood BJ, Blundy JD, Robinson JAC (1999) The role of clinopyroxene in generating U-series disequilibrium during mantle melting. Geochim Cosmochim Acta 63 1613-1620 Zou H, Zindler A, Niu Y (2002) Constraints on melt movement beneath the East Pacific Rise from °Th- U disequilibrium. Science 295 107-110... 

Lundstrom CC, Shaw H, Ryerson F, Phinney D, Gill J, Williams Q (1994) Compositional controls on on the partitioning of U, Th, Ba, Pb, Sr and Zr between clinopyroxene and haplobasaltic melts implications for uranium series disequilibria in basalts. Earth Planet Sci Lett 128 407-423 Lnndstrom CC (2003) Uranium-series disequilibria in mid-ocean ridge basalts observations and models of basalt genesis. Rev Mineral Geochem 52 175-214... 

Dal Negro A., Carbonin S., Molin G. M., Cundari A., and Piccirillo E. M. (1982). Intracrystalline cation distribution in natural clinopyroxenes of tholeiitic, transitional and alkaline basaltic rocks. In Advances in Physical Geochemistry, vol. 1, S. K. Saxena (series ed.), New York Springer-Verlag. 

Variation of many major and trace elements in the Somma-Vesuvio rocks suggest that fractional crystallisation was a main mechanism in magma evolution. Different trends shown by the various rock series for both major and trace elements have been interpreted either to reveal the presence of different types of parental magma and/or to indicate fractionation dominated by different relative amounts of clinopyroxene and feldspar, possibly as a consequence of variable pressure during fractionation (Joron et al. 1987 Trigila and De Benedetti 1993). 

Only in calcic clinopyroxenes, in which Ca2+ ions completely fill the M2 sites and Fe2+ and other transition metal ions occur in the Ml sites alone, is ideal solution behaviour to be expected. This is because cation ordering is not possible in one-site atomic substitution in the pyroxene Ml site. Furthermore, there is an insignificant variation of the CFSE of Fe2+ across the diopside-hedenbergite series ( 5.5.3). 

Another example of an important effect of bulk composition on partitioning behavior is provided by uranium and thorium partitioning into clinopyroxene. The decay series is frequently used as an indicator of the nature and timescales of magmatic processes (e.g., Condomines et aL, 1981 McKenzie, 1985). The parent isotope... 

The experimental results obtained at the QFM buffer are listed in Table II. and type formulas for the various mineral series in Table III. Olivine and chrome spinel are the only crystalline phases which occur between 1240°C and 1179°C clinopyroxene and... 

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