Temperature-dependent distribution of Cr between olivine and pyroxenes in lherzolite xenoliths

✍ Scribed by R. L. Hervig; J. V. Smith

• Publisher: Springer
• Year: 1982
• Tongue: English
• Weight: 646 KB
• Volume: 81
• Category: Article
• ISSN: 0010-7999
• DOI: 10.1007/bf00371295

✦ Synopsis

The temperature effect on the exchange reaction CrzO3(ol)=Cr203(px) was studied for coexisting olivine and both clino and ortho pyroxenes. The distribution of Cr between olivine and clinopyroxene in 31 coarse garnet lherzolites and 10 porphyroclastic garnet lherzolites from kinberlites, and in 17 coarse spinel lherzolites from basalts, obeys a van't Hoff relation (c.f. Stosch 1981 ) with the Wells two-pyroxene temperature: T(Kelvin) = 8,787 On Dcr + 2.87) where Dcr (cpx/ol) = wt. % Cr (clinopyroxeue)/Cr (olivine). An analogous exchange for olivine and orthopyroxene with 0.7-1.6 wt.% Al~O3 in 41 garnet lherzolites from kimberlites shows considerable scatter about the following relation: T(Kelvin) = 5,540/(ln Dcr + 1.86) where OCr (opx/ol) = wt. % Cr (orthopyroxene)/Cr (olivine). Spinel lherzolites and a garnet lherzolite from the Malaita aln6ite do not obey the second relation. For orthopyroxene with 2.5-5.1 wt.% A1203, Dcr(opx/ol) is 1.7 to 3 times highcr, and for 0.1 wt.% A120 3 is 2 times lower than for the garnet lherzolites. Experimental calibration is needed, especially to check the possible effect of A1 on Dc~(Opx/ol ).