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TitleParameterizations of calcic clinopyroxene - melt trace element partition coefficients
AuthorBédard, J H
SourceGeochemistry, Geophysics, Geosystems (G3) vol. 15, no. 2, 2014 p. 303-336, Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20130359
Mediapaper; on-line; digital
File formatpdf
Subjectsgeochemistry; mineralogy; igneous and metamorphic petrology; clinopyroxene; trace element analyses; trace element geochemistry; trace elements; lattice spacings
Illustrationstables; plots
ProgramGEM: Geo-mapping for Energy and Minerals, PGE/Base Metals - Victoria Island (NWT and Nunavut)
Released2014 02 06
AbstractSemi-empirical parameterizations of the values and trends of variation of Nernst trace element partition coefficient data for Ca-rich clinopyroxene (cpx/liquidD) are provided, applicable mainly to common terrestrial magmatic suites. cpx/liquidD data for most trace elements show significant variability which cannot be neglected when modeling melting and crystallization. Compilation and interpretation of partitioning data show that the influence of pressure on cpx/liquidD is strong for many elements, particularly Na and Sr, which increase steadily as pressure rises, and most high-field strength elements, which decrease with increasing pressure. Most cpx/liquidD values increase as the temperature decreases, as wt% melt MgO, MgO# (MgO/MgO+FeOtotal), CaO and FeO contents drop, as cpx molar mg# (Mg/Mg+Fetotal) decreases, and as wt% melt SiO2 and Na2O+K2O increase. For some elements a diffuse positive correlation is seen with increasing cpx wollastonite content and melt Al2O3. No clear trends are seen for variations of cpx/liquidD against melt H2O. For mafic melts, many elements show well-defined trends of cpx/liquidD increase as the clinopyroxene tetrahedral Al-content (cpx Aliv) increases. Many cpx/liquidD are well correlated against cpx/liquidDTi, and many ¿near-neighbour¿ elements show good cpx/liquidD intercorrelations (e.g. Zr-Hf, U-Th, Nb-Ta, La-Ce, Yb-Lu). Cpx/liquidD profiles calculated from parameterizations against several input variables can be used to constrain the way D values change during melting or crystallization. Cpx/liquidD for the rare earth elements were fit to the lattice strain model to derive fits that closely reproduce the parabolic cpx/liquidDREE profile shapes (REE=rare earth elements). These fits indicate that cpx/liquidDHREE for melts more evolved than picritic basalts cannot be modeled assuming that all REE are in octahedral coordination in a single M2 site, but also require sixfold partitioning into an M1 site for Lu, Yb, Tm and Er.
Summary(Plain Language Summary, not published)
Experimental partitioning data for trace elements between clinopyroxene and melt are compiled and parameterized. This will facilitate quantitative modeling of trace elements in igneous rocks.

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