Sulphur and Cu-Fe-Ni sulphides can record partial melting events and aspects of the reaction between depleted mantle and mafic melts. The incompatible nature of sulphur in mantle melting processes is demonstrated by a positive correlation between A12O3and S in massive peridotites sampled at some distance from pyroxenite layers. Extrapolation of this correlation yields 220 ppm S in the mantle source of the Lanzo massif, which agrees well with the composition of the convecting asthenospheric mantle. In contrast, Pyrenean lherzolites have been contaminated at the base of the sub-continental lithosphere and have slightly higher S contents (up to 390 ppm S). Refractory rocks (harzburgites and dunites) are characterized by a heterogeneous distribution of sulphur and sulphide grains. Some samples are distinctly enriched in S (up to 210 ppm) with respect to the Al vs. S partial melting trend. This enrichment suggests additional precipitation of sulphides from the tholeiitic melt which has circulated by porous flow within the refractory rocks. Pyroxenite layers, which are interpreted as crystalline segregates deposited by tholeiitic melts, are moderately enriched in 5 (< 1300 ppm) relative to the surrounding peridotites. Higher sulphur contents (up to 2000 ppm) characterize a late generation of alkali basalt-related amphibole-rich veins from the Eastern Pyrenean massifs. A process of in situ sulphide liquid immiscibility can account for the precipitation of sulphur in melt-filled cracks. Cu/S ratios are of use for discriminating between tholeiite- and alkali basalt-related melt percolation. All the rocks (lherzolites, harzburgites, dunites, or pyroxenites) which equilibrated with tholeiitic melts have high Cu/S ratios (0·1–0·4). Moreover, the variations in modal compositions of sulphides testify to strong Ni-Fe exchanges between tholeiite-filled cracks and wall rocks. In contrast, those rocks which have equilibrated with alkali basalts have low Cu/S ratios (0·05). Persistence and/or precipitation of sulphur at each stage in the evolution of orogenic peridotite massifs show that basaltic melts may become saturated with respect to sulphur before any fractional crystallization in the crust, in strong agreement with conclusions based on the study of MORB.

EXPLOR_STEP=$WICRI_ROOT/Wicri/Terre/explor/NickelMaghrebV1/Data/France/Analysis

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{{Explor lien
   |wiki=    Wicri/Terre
   |area=    NickelMaghrebV1
   |flux=    France
   |étape=   Analysis
   |type=    RBID
   |clé=     ISTEX:B387FFEE46EEAE5962A2C75C016FE17208050F33
   |texte=   Sulphide Petrology and Sulphur Geochemistry of Orogenic Lherzolites: A Comparative Study of the Pyrenean Bodies (France) and the Lanzo Massif (Italy)
}}