The behaviour of platinum-group elements in petrogenetic processes: a case study from the seaward-dipping reflector sequence (SDRS), Southeast Greenland volcanic rifted margin

The concentration of the platinum-group elements were determined in mantle-derived volcanic rocks from the seaward- dipping reflector sequence (SDRS) along the southeast Greenland margin in order to determine the geochemical behaviour of these elements during petrogenetic processes. Major, trace, and rare earth element relations and results of trace element modelling have been taken in consideration to constrain and qualify the behaviour of PGE during formation and differentiation of mantle-derived melts. This contribution evaluates the effects of S-saturation and - undersaturation of a magma on the geochemical behaviour of the PGE during magma generation and magma evolution. It is demonstrated that geometrical (shape of melting regime), chemical (Fe-contents of the melts) and physical factors (degree of partial melting, p/T-variations) have a pronounced effect on the S-saturation of generated melts and therefore on the PGE systematics of magmas. The fractionation of the PGE during partial melting is inferred to be a consequence of the incompatible behaviour Pt and Pd in S- undersaturated melts, whereas the behaviour of Ir, Ru, and Rh indicates that these elements are compatible in at least one mantle phase, possibly spinel or PGE alloys. ... mehrPlatinum and Pd behave incompatibly during magma evolution in S- undersaturated magmas. As soon as the magmas reach S- saturation, Pt and Pd behave highly compatibly and becoming effectively depleted in the magmas through partitioning into sulphides which segregated. In contrast, the elements Ir, Ru, and Rh behave compatibly during magma evolution in S- undersaturated as well as in S-saturated magmas. Spinel and Ir- Ru alloys are inferred to be the most likely candidates to be responsible for the compatibility of these elements.