Re-Os dating of sulphide inclusions zonally distributed in single Yakutian diamonds: Evidence for multiple episodes of Proterozoic formation and protracted timescales of diamond growth

摘要

The timing of diamond formation in the Siberian lithospheric mantle was investigated by Re-Os isotope dating of sulphide inclusions from eclogitic and lherzolitic diamonds from the Mir, 23~(rd) Party Congress and Udachnaya kimberlite pipes in Yakutia. The diamonds contained multiple sulphide inclusions distributed over their core-to-rim zones. Cathodoluminescence, carbon isotope and nitrogen aggregation studies demonstrate that the diamonds are zoned and that the distinct zones are associated with different diamond growth episodes. There are coherent relationships between carbon isotope composition, nitrogen concentration and aggregation state of the diamond hosts, and major and trace element compositions, Re-Os compositions and initial Os isotope ratios of the included sulphides. This suggests that the different diamond and sulphide populations formed at different times from fluids/melts with different chemical compositions. Based on the Re-Os isochron ages and the nitrogen aggregation states we conclude that the sulphides are co-genetic with their diamond hosts.The ages obtained for the different diamond populations demonstrate two major periods of Yakutian diamond formation for both eclogitic and lherzolitic suites, i.e., ~2.1-1.8Ga (Mir, 23~(rd) Party Congress and Udachnaya) and ~1.0-0.9Ga (Mir and ~(23)rd Party Congress). These two episodes correspond to major tectono-magmatic events: collision between the different terranes of the Siberian Craton during the formation of the Palaeoproterozoic supercontinent ~2.0-1.8Ga and accretion leading to formation of the supercontinent Rodinia ~1.1Ga.Importantly, Re-Os isotope dating demonstrates that some single diamonds have protracted timescales of growth with different ages associated with core and rim zones. Zoned single eclogitic crystals from Mir and ~(23)rd Party Congress in the current study crystallised over intervals that were irresolvable (<200Ma) up to ~1Ga apart.The very radiogenic initial Os isotope ratios of the eclogitic and lherzolitic sulphides (~(187)Os/~(188)Os=0.14-2.22) imply incorporation of radiogenic Os from subducted oceanic lithosphere, a conclusion that is also supported by the anomalously light carbon isotope compositions of some diamonds. Subducted lithosphere is therefore considered a significant component in Proterozoic diamond formation beneath the Siberian Craton.