Breaking of Henry’s law for sulfide liquid–basaltic melt partitioning of Pt and Pd
Mingdong Zhang, Yuan Li
Abstract
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 ( $${D}_{PGE}^{SL/SM}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mrow> <mml:mi>D</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>P</mml:mi> <mml:mi>G</mml:mi> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>S</mml:mi> <mml:mi>L</mml:mi> <mml:mo>/</mml:mo> <mml:mi>S</mml:mi> <mml:mi>M</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> ) yielded values of 10 2 –10 9 , and values of >10 5 have been accepted by the geochemical and cosmochemical society. Here we perform measurements of $${D}_{Pt,\,Pd}^{SL/SM}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mrow> <mml:mi>D</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>P</mml:mi> <mml:mi>t</mml:mi> <mml:mo>,</mml:mo> <mml:mspace/> <mml:mi>P</mml:mi> <mml:mi>d</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>S</mml:mi> <mml:mi>L</mml:mi> <mml:mo>/</mml:mo> <mml:mi>S</mml:mi> <mml:mi>M</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> at 1 GPa and 1,400 °C, and find that $${D}_{Pt,\,Pd}^{SL/SM}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mrow> <mml:mi>D</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>P</mml:mi> <mml:mi>t</mml:mi> <mml:mo>,</mml:mo> <mml:mspace/> <mml:mi>P</mml:mi> <mml:mi>d</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>S</mml:mi> <mml:mi>L</mml:mi> <mml:mo>/</mml:mo> <mml:mi>S</mml:mi> <mml:mi>M</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> increase respectively from 3,500 to 3.5 × 10 5 and 1,800 to 7 × 10 5 , 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 $${D}_{Pt,\,Pd}^{SL/SM}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mrow> <mml:mi>D</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>P</mml:mi> <mml:mi>t</mml:mi> <mml:mo>,</mml:mo> <mml:mspace/> <mml:mi>P</mml:mi> <mml:mi>d</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>S</mml:mi> <mml:mi>L</mml:mi> <mml:mo>/</mml:mo> <mml:mi>S</mml:mi> <mml:mi>M</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> 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.