Osmium mass balance in peridotite and the effects of mantle-derived sulphides on basalt petrogenesis

摘要: Analyses of enriched mantle (EM)-basalts, using lithophile element-based isotope systems, have long provided evidence for discrete reservoirs with variable composition. Upon partial melting, the reservoir imparts its isotopic fingerprint upon melt produced. However, it has increasingly been recognised that may not be simple to delimit these previously well-defined reservoirs; “mantle zoo” contain more than envisaged. Here we demonstrate a model varying contributions from two populations compositionally distinct sulphides can readily account observed heterogeneities in Os systematics such basalts without additional reservoirs. Osmium elemental and analyses individual sulphide grains separated spinel lherzolites Kilbourne Hole, New Mexico, USA exist terms both Re–Os textural relationship co-existing silicates. One population, rounded morphology, is preserved silicate typically possesses high [Os] low [Re] unradiogenic, sub-chondritic 187 Os/ 188 attributable term isolation low-Re environment. By contrast, irregular-shaped sulphides, along grain boundaries, possess [Os], higher wider range of, but generally supra-chondritic ([Os] 6 1–2 ppm, 0.3729; this study). This population thought represent metasomatic sulphide. Uncontaminated phases negligible (<100 ppt) therefore composition dominated by volumetrically insignificant 37 ppm; During early stages interstitial are mobilised incorporated into melt, adding their radiogenic signature. Only when armoured within silicates exposed through continued melting will enclosed add unradiogenic aggregate melt. Platinum-group element data whole rocks also consistent scenario. The sequence (i) addition all sulphide, followed (ii) incorporation small amounts thus EM-basalts worldwide need