Clinopyroxenes trace elements

Figure 50 Garnet and clinopyroxene trace-element compositions (normalized to primitive mantle), together with their calculated whole-rock compositions (from modal data). Data sources 77 and 29 are rutile-free eclogites from Udachnaya, Siberia (Jacob and Foley, 1999) KEC80-A-2 is a high-Nb-mtile eclogite from Koidu, Sierra Leone...

Blundy JD, Dalton JA (2000) Experimental comparison of trace element partitioning between clinopyroxene and melt in carbonate and silicate systems and implications for mantle metasomatism. Contrib Mineral Petrol 139 356-371... 

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... 

Hauri EH, Wagner TP, Grove TL (1994) Experimental and natural partitioning of Th U Pb and other trace elements between garnet clinopyroxene and basaltic melts. Chem Geol 117 149-166 Hazen RM, Finger LW (1979) Bulk Modulus-volume relationship for cation-anion polyhedra. J Geophys Res 84 6723-6728... 

Schmidt KH, Bottazzi P, Vannucci R, Mengel K (1999) Trace element partitioning between phlogopite, clinopyroxene, and leucite lamproite melt. Earth Planet Sci Lett 168 287-299 Shaimon RD (1976) Revised effetive ionic radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Cryst A32 751-767... 

We have already noted that the double conversion from activity ratio to weight concentration ratio implicit in trace element geochemistry may involve complexities that must be carefully evaluated in the interpretation of natural evidence. Let us consider, for instance, the distribution of Ni between clinopyroxene and silicate liquid. Eigure lO.lOA shows the effect of temperature on the conven-... 

In contrast to the case for whole rocks, the linear regression method for residual clinopyroxenes can be applied to non-modal batch melting. The basic equation for the variation of a trace element in cpx during non-modal batch melting has been given in Eq. (7.56). We can obtain the following linear relationship from Eq. (7.56) (Zou, 1997) ... 

Although scattered, major and trace element variations for the Vulsini rocks define overall trends that support an evolution dominated by fractional crystallisation starting from different types of parental melts. Holm et al. (1982) suggested that the evolution of HKS magmas was dominated by fractional crystallisation with separation of olivine and clinopyroxene in the mafic range, and of variable proportions of clinopyroxene, leucite, pla-... 

Fractional crystallisation has been dominated by separation of various proportions of clinopyroxene and olivine in the mafic magmas, and of cli-nopyroxene and feldspars in the felsic melts. These generated decrease in ferromagnesian elements (FeO, MgO, Ni, Co, Cr, etc.) and increase in incompatible elements (e.g. Th, Ta, Nb, REE), with ongoing evolution. In contrast, ratios of incompatible trace elements were not affected by fractionation processes, and can be used to infer compositions of mantle-equilibrated melts. 

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). 

Hendricks, R. C. Dahl, P. S. (1987) Trace-element partitioning between coexisting metamorphic garnets and clinopyroxenes crystal field, compositional, and thermal controls. Geol. Soc. Amer., Ann. Meet., Abstr., 19, 700. 

Most trace elements have values of D< C 1, simply because they differ substantially either in ionic radius or ionic charge, or both, from the atoms of the major elements they replace in the crystal lattice. Because of this, they are called incompatible. Exceptions are trace elements such as strontium in plagioclase, ytterbium, lutetium, and scandium in garnet, nickel in olivine, and scandium in clinopyroxene. These latter elements acmally fit into their host crystal structures slightly better than the major elements they replace, and they are therefore called compatible. Thus, most chemical elements of the periodic table are trace elements, and most of them are incompatible only a handful are compatible. 

Figure 21 Abundances of lithophile trace elements normalized to PM values in clinopyroxene, orthopyroxene, olivine, and spinel separated from a peridotite from the Ronda massif (Garrido et al., 2000). Normalizing values after...

Rivalenti G., Mazzucchelli M., Vannucci R., Hofmann A. W., Ottolini L., Bottazzi P., and Obermiller W. (1995) The relationship between websterite and peridotite in the Balmuccia peridotite massif (NW Italy) as revealed by trace element variations in clinopyroxene. Contrib. Mineral. Petrol. 121, 275-288. 

Vanned R., Shimizu N., Bottazzi P., OttoliniL., Piccardo G. B., and Rampone E. (1991) Rare earth and trace element geochemistry of clinopyroxenes from the Zabargad perido-tite-pyroxenite association. J. Petrol. (Orogenic Iherzolites and mantle processes), 244- 255. 

Clinopyroxene shows a range of REE patterns from extremely enriched to very depleted TREE signatures (Figure 22). Noncratonic peridotites are subdivided on the basis of clinopyroxene REE patterns into LREE-depleted (type lA) and LREE-enriched (type IB Menzies, 1983 Figure 17). LREE-enriched type IB pyroxenes are the norm in most suites. LREE-depleted varieties are relatively scarce. Very few clinopyroxenes show simple LREE-depleted REE patterns that can be interpreted solely in terms of melt depletion, i.e., LREE depletion, fiat, unfractionated MREE-HREE patterns (e.g., UM-6 or 2905 Eigure 22). For peridotites that do have LREE-depleted clinopyroxenes, a correlation of HREE with other incompatible trace elements (e.g., yttrium, strontium, zirconium) in xenoliths suites worldwide requires fractional melting to be the principal means of depletion in the mantle (Norman, 2001). 

FREE enrichment in clinopyroxene is widely linked to metasomatism by either silicate melts or carbonatitic fluids, usually via cryptic (in the sense of no new phase being introduced) metasomatism, although there is a strong possibility that the diopside itself could have precipitated from the melt. This is strongly favored for much of the ubiquitously FREE-enriched diopside found in cratonic peridotites (Figure 17) which are not in trace-element equilibrium with their coexisting garnets and for which equilibrium melts for the diopside closely resemble kimberlite (Simon et al., 2003). 

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