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The 1.85 Ga Sudbury Igneous Complex (SIC), Ontario, Canada, is an intrusive...
The 1.85 Ga Sudbury Igneous Complex (SIC), Ontario, Canada, is an intrusive complex representing a crystallized melt sheet formed during a bolide impact. The SIC has been extensively studied due to its rich endowment in magmatic sulfide ores (Ni-Cu-PGEs). In this study, primary melt inclusions hosted in cumulus apatite within three mafic units of the SIC (gabbro, norite and sublayer quartz diorite) are used to decipher the physical and chemical characteristics of the evolving melt sheet as it crystallized. The compositions of coeval melt inclusions show 2 distict types: (1) SiO 2-rich, ranging from tonalitic to granodioritic in composition (60 -70 wt% SiO 2, up to 11 wt% eO); and(2) Fe-rich with syenogabbroic to essexitic to alkali gabbroic compositions (27-49 wt% SiO2, 16-44 wt% FeO). The liquids are interpreted to represent the products of immiscibility (c.f.Skaergaard Intrusion[1]). D Fe-rich melt/Si-rich melt values range between ~0.7 and ~2 with the exception of V and Co that partition more strongly into the Fe-rich melt (D > 4). Microthermometry shows that complete melting of the inclusion contents occurs at ~1100°C, with homogenization (i.e., minimum trapping T; by bubble contraction) between ~1230 and 1300° C, confiming that apatite is an early liquidus phase in melt and trapped melt over a range of temperatures.Preliminary melt inclusion analyses suggest that the earliest melt phase of the SIC, as represented by sublayer quartz diorite, was enriched in Ni and Cu, up to an order of magnitude higher than those liquids trapped in the units stratigraphically higher in the SIC, and may reflect loss of these metals to early sulfide liquids. The results of this study may lead to the development of parameters that enhance exploration success in mafic-ultramafic systems where post-magmatic processes have severely limited the application of bulk rock chemistry in understanding their petrogenesis.
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