Iron isotope and trace metal variations during mantle metasomatism: In situ study on sulfide minerals from peridotite xenoliths from Nograd-Gomor Volcanic Field (Northern Pannonian Basin)

Sulfides from lherzolite and wehrlite xenoliths from the Nograd-Gomor Volcanic Field (NGVF), located in the Northern Pannonian Basin, were studied to understand the behavior of chalcophile and siderophile elements during mafic melt - peridotite interaction. We applied in situ methods to analyze the major and trace elements, as well as Fe isotope compositions of sulfide minerals. Sulfides are more abundant in wehrlites (similar to 0.03 vol%) and are often enclosed in silicates, whereas in lherzolites, they are scarcer (similar to 0.01 vol%) and predominantly interstitial. Monosulfide solid solution and pentlandite are the most common sulfide phases in the lherzolite xenoliths, whereas in wehrlite xenoliths it is pyrrhotite and chalcopyrite. Consequently, wehrlitic sulfides show higher bulk Fe and Cu but lower bulk Ni and Co contents compared to the lherzolitic sulfides. Trace elements with both chalcophile and siderophile character (Ge, Se, Te, and Re) show lower, whereas highly chalcophile elements (Zn, Cd, Sb, and Tl) show higher concentrations in wehrlitic sulfides compared to lherzolitic ones. Highly siderophile elements show no systematic difference between the sulfides of the two xenolith series, which suggests moderate enrichment in these elements in wehrlite bulk rocks due to their higher sulfide content. Sulfide delta Fe-56 signature indicates variable isotopic composition both in lherzolites (delta Fe-56: -0.13 to +0.56 parts per thousand) and wehrlites (delta Fe-56: -0.20 to +0.84 parts per thousand) relative to the terrestrial mantle (delta Fe-56: +0.025 +/- 0.025 parts per thousand; Craddock et al., 2013). However, irrespectively of the xenolith lithology, there is a significant difference between the delta Fe-56 of sulfides from the two sampling localities: NTB /North/: vary from -0.20 to +0.04 parts per thousand and NME /South/: vary from +0.56 to +0.84 parts per thousand. This suggests that the Fe isotopic ratios of sulfides are not modified by the wehrlitization process. Difference in sulfide delta Fe-56 between the two xenolith localities is probably because of the higher, isotopically heavier (delta Fe-56: from +1.28 to +1.60 parts per thousand; Ciazela et al., 2019) chalcopyrite content in sulfides from the NME xenoliths compared to those from the NTB xenoliths irrespectively to their lithology. Our results also indicate sulfide and chalcophile element enrichment resulting from metasomatism in the subcontinental lithospheric mantle. We suggest that this process affected the regional metal distribution and has implications for global metal mass balance within the subcontinental lithosphere. (C) 2021 The Authors. Published by Elsevier B.V.

Automated summary

Sulfides from lherzolite and wehrlite xenoliths in the Nograd-Gomor Volcanic Field were studied to understand the behavior of chalcophile and siderophile elements. Significant differences were found in the composition and distribution of sulfides between the two xenolith types, suggesting enrichment of sulfides and chalcophile elements in the subcontinental lithospheric mantle due to metasomatism.