Breaking of Henry's law for sulfide liquid-basaltic melt partitioning of Pt and Pd
Mingdong Zhang1,2,3, Yuan Li4,5
1State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 510640, Guangzhou, China.
Abstract:
Platinum group elements are invaluable tracers for planetary accretion and differentiation and the formation of PGE sulfide deposits. Previous laboratory determinations of the sulfide liquid-basaltic melt partition coefficients of PGE ([Formula: see text]) yielded values of 102-109, and values of >105 have been accepted by the geochemical and cosmochemical society. Here we perform measurements of [Formula: see text] at 1 GPa and 1,400 °C, and find that [Formula: see text] increase respectively from 3,500 to 3.5 × 105 and 1,800 to 7 × 105, as the Pt and Pd concentration in the sulfide liquid increases from 60 to 21,000 ppm and 26 to 7,000 ppm, respectively, implying non-Henrian behavior of the Pt and Pd partitioning. The use of [Formula: see text] values of 2,000-6,000 well explains the Pt and Pd systematics of Earth's mantle peridotites and mid-ocean ridge basalts. Our findings suggest that the behavior of PGE needs to be reevaluated when using them to trace planetary magmatic processes.
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