Other
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.516h&link_type=abstract
Meteoritics, vol. 30, no. 5, page 516
Other
1
Chromium, Eucrites, Lanthanum, Murchison, Partial Melting, Scandium, Sioux County, Vanadium
Scientific paper
Scandium, V, and Cr are depleted in eucrites compared to other lithophile refractory trace elements, and, therefore, understanding these depletions is important to deciphering the origin of eucrites. Previously, we have reported Sc partitioning experiments relevant to eucrite petrogenesis [1] and V concentrations in partial melts of the Murchison chondrite [2]. The Sc experiments indicated that eucrites such as Sioux County were generated by about 20% partial melting of a source whose residual phases were dominated by olivine. Additionally, our V analyses of the Murchison glasses were very similar to those measured for the Sioux County eucrite. This was particularly gratifying, since the major element concentrations of our 1180 degrees C Murchison glass were also very similar to those of eucrites [3]. Because the solid residua of the Murchison experiments were also dominated by olivine, there was apparent qualitative agreement between the inferences from both Sc and V. Previously, Sc partition coefficients for olivine and pyroxene at 1190-1200 degrees C have allowed us to model eucrite petrogenesis by assuming that eucrites such as Sioux County are simple partial melts [1]. Newly acquired V partition coefficients (Table 1) allow us to perform a similar calculation for V (Table 2). Vanadium analyses were corrected for Ti interference, and the similarity of partition coefficients from different experiments gives us confidence in the results. In addition, lnD versus 1/T regressions give good fits with r^2 > 0.99. Thus, partial melting models may be tested, using our experimental partition coefficients, by independently modeling Sc and V depletions. The assumptions necessary may be summarized: Eucrites such as Sioux County are produced by equilibrium partial melting of a source region and this source has approximately CM chondrite relative abundances of refractory lithophile elements. With this proviso, we have a system of four equations and four unknowns: one equation specifying X(sub)ol + X(sub)pyx + X(sub)sp+ X(sub)liq = 1 and three mass balance equations, one for Sc/La (or V/La), and one each for Mg/Al and Cr/Al. The equations and the numerical values of constants are input into Mathematica [4], which then solves the system of equations and unknowns. The results of the Sc and V calculations are quite consistent. Both require about 20% partial melting and both have residues dominated by olivine. Thus, simple partial melting is sufficient to explain depletions of Cr, V, and Sc in primitive eucrites. References: [1] Paslick C. et al. (1990) LPS XXI, 936-937. [2] Jones J. H. et al. (1994) LPS XXV, 639-640. [3] Jurewicz A. J. G. et al. (1993) GCA, 57, 2123-2139. [4] Wolfram S. (1991) Mathematica: A System for Doing Mathematics by Computer, p. 961, Addison-Wesley, New York. Table 1,showing V in phases from chondrite partial melting experiments, appears here in the hard copy. Table 2, showing the results of partial melting calculation, appears here in the hard copy.
Hanson B. Z.
Houston Jones Jane
Jurewicz Amy J. G.
Mittlefehldt Dave W.
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