The Giles Complex, South Australia: mantle plume or SCLM source?

The Giles Complex of the Musgrave Block, Central Australia comprise a number of discrete layered ultramafic-mafic intrusions of Neoproterozoic age. These intrusives are considered to represent the remnants of a far more extensive Large Igneous Province (LIP), the ~1.08Ga Warakurna Province, which once covered much of central and western Australia[1]. Here we present 187Re-187Os isotopic data for transects across two of the larger cumulate bodies within the province, the Kalka and Gosse Pile intrusions. These bodies are dominantly comprised of pyroxenites and gabbros, with local picrites, websterites and anorthosites. Initial γOs values are typically close to chondritic, but do range to significantly subchondritic (γOs(i) = -13) with the most evolved being a websterite with (γOs(i) = +8.5). These data contrast with the relatively evolved lithophile isotope signatures recoded in the intrusions (ɛNd(i) ~ -1 to ~-5), which suggests that either the plume source contained a depleted component which was contaminated by continental crust,. Such a component could incorporate a significant SCLM contribution, however mixing models present non-unique solutions for primary vs SCLM Os. Alternatively, Nd and Os isotopes may be decoupled; or a third, highly speculative option, is that the Giles Complex is much younger than previously considered, resulting in higher γOs(i) values, which would suggest a greater crustal input, more in line with Nd isotope constraints. [1] Wingate, MTD, Pirajno, F and Morris, PA. 2004 Geology 32(2) 105-10