QUANTIFYING PGES IN THE CHICXULUB IMPACT BASIN

The platinum group elements (PGEs: Ru, Rh, Pd, Os, Ir, Pt) have been identified as geologically important indicators of mechanisms such as planetary differentiation, core signatures in plume volcanism, and understanding the effects of meteorite/asteroid impacts. PGEs have the ability to identify the type of impactor as they are elevated yet have variable ratios in different bolide families. International Ocean Discovery (IODP) expedition 364 retrieved 835 m of core from the Chicxulub impact structure, including the critical Cretaceous-Paleogene (K-Pg) boundary in Core 40. This a transitional unit defined as 1G, which bridges the upper peak ring material below to the post impact sediments above. It is hypothesized that the PGE-signature of the impactor will be at the highest concentrations within this layer (if they have not been redistributed elsewhere), as at other K-Pg boundary sections worldwide. The global boundary layer signified by PGE enrichment indicates that the Chicxulub impact was a global catastrophic event. At the impact site, it has been demonstrated that the heat generated was intense enough to initiate hydrothermal systems that caused remobilization of material and secondary mineralization. Comparing section 1G to other lithologies recovered from Expedition 364, as well as data from the K-Pg boundary gathered from different locations, may reveal the local and global extent of PGE distribution. For this study, samples were digested and the PGEs separated via a cation exchange method. Analyses were conducted via standard addition using high resolution ICP-MS, which allows for the quantification of monoisotopic Rh, but we did not quantify Os due to its volatility during sample dissolution. Results show that the PGEs are at low abundances (mid ppt to low ppb) in this boundary layer, although they do show slight enrichments in distinct zones. Notably the slight PGE enrichments correlate with Cr as measured at the top and bottom of section 1G, and a general depleted nature dominates the central mudstone portion. Other samples containing secondary sulfide minerals, as well as impact melt, are being processed for analysis. It is hoped that this analytical campaign will determine the location of the most enriched PGEs, the extent of remobilization, and potentially identification of the impactor type.