| For geochemical analysis, a reference material is analyzed with samples to assure quality control. Deviations between Notre Dame results for the standard BHVO-1 and consensus values induced a study comparing all recent values for BHVO-1. Results indicate that consensus values for Rb, Y, Zr, Pb, and Th need to be modified. The following new values are suggested for each element: Rb: 9.3 ± 0.2 μg/g; Y: 24.4 ± 1.3 μg/g; Zr: 172 ± 10 μg/g; Pb 2.2 ± 0.2 μg/g; Th: 1.22 ± 0.02 μg/g.; Basalts from the Ontong Java and Kerguelen Plateaus (OJP and KP, respectively) were then analyzed for major, trace, platinum group elements (PGEs). The goal was to model the petrogenesis of these basalts in an effort to constrain source characteristics that are specific to the PGEs, such as an outer core signature. The model indicated that a small amount of core material (up to 1 wt %) must be added to a primitive mantle source in order to generate the highest PGE abundances of the OJP. Variations in the amount of core material and fractional crystallization can account for the PGE compositions of the basalts. Using estimates from sulfur models, the minimum temperature for the OR source was calculated to 1465–1515°C, which is comparable to other estimates (>1500°C). Models for the KP basalts also required a ∼1% core component, but were more complicated, requiring a resorption and fractional crystallization model to replicate all observed trace and PGE compositions and patterns.; The sulfur models employed during the PGE modeling were then analyzed in detail. The pressure-temperature model is only useful when the “A” term is positive in the equation governing sulfide saturation. In addition, magmas that have >10 wt % FeO and that are generated by >20% partial melting will not likely saturate with respect to sulfur. Thus, MORBs leave their source S-saturated and remain so until they reach the surface, whereas LIP magmas are S-undersaturated when they leave their source regions and are unlikely to become saturated during ascent. |
