J. C. Ely

Signatures of the highly siderophile elements in the SNC meteorites and Mars: a review and petrologic synthesis

We have evaluated the highly siderophile element (HSE) signatures of the martian (SNC) meteorites using new and literature data. These Ir and Os concentrations correlate with the Mg# [molar Mg/(Mg+Fe)], Cr and Ni, suggesting that olivine or chromite acts as a host for compatible siderophiles. Our analysis agrees with others who have suggested that the martian mantle has chondritic relative abundances of siderophiles. We also agree that, unlike the Sr and Nd isotopic systems, there is no evidence from Os isotopes for crustal assimilation. Comparisons of the siderophile element ratios of ALH 84001 to younger SNCs give no indication of a change in the martian siderophile element pattern over time. D 2002 Published by Elsevier Science B.V.

Quantifying the platinum group elements (PGEs) and gold in geological samples using cation exchange pretreatment and ultrasonic nebulization inductively coupled plasma-mass spectrometry (USN-ICP-MS)

Abstract A method for analyzing low abundances of the platinum group elements (PGEs) and gold has been developed using cation exchange chromatography and ultrasonic nebulization inductively coupled plasma mass spectrometry (USN-ICP-MS). Ultrasonic nebulization increases sensitivity over regular pneumatic nebulization so that resolvable signals above background are possible in the fg/g range. Small sample sizes (≤250 mg) and low volumes of reagents produce procedural blank levels below the detection limit for Ru, Pd and Ir, in the fg/g range for Rh and in the low pg/g range for Pt and Au. Heterogeneous PGE and Au distributions in geological samples are avoided by a rigorous homogenization/rehomogenization procedure. The reference material UMT-1, which contains rock concentrations of the PGEs and Au at the low ng/g levels, monitored recoverability. Interferences of HfO+ and TaO+ on Ir, Pt and Au were not seen in the analyses of UMT-1 because Hf and Ta have low abundances in this reference material. However, these interferences are acute for silicate rocks, even after cation exchange chromatography. Isotope dilution cannot be adapted to this method for Ir and Pt because two interference-free isotopes are not available. An external calibration method has been developed for the accurate and precise determination of the PGEs and Au in rocks with low abundances of Hf and Ta (

Using platinum-group elements to investigate the origin of the Ontong Java Plateau, SW Pacific

Fractionated basalts (4.5–8.9 wt.% MgO) from the islands of Malaita and Makira (San Cristobal) in the Solomon Islands represent outpourings of magma that formed the Ontong Java Plateau (OJP), SW Pacific. The origin of the OJP is explored by examining platinum-group element (PGE: Ru, Rh, Pd, Ir, Pt) abundances in these basalts. On Makira, mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs) are occasionally intercalated within the stratigraphic sequence of the OJP—the OIBtype basalts could be representative of the plume tail sequence and the MORB-type flows may be an indication of heterogeneity within the OJP source. Partial melting models indicate that the MORB-type basalts were generated from a source dominated by upper mantle material. However, they suggest that the OJP basalts and the OIB-type basalts were not generated from an exclusively upper mantle source. Our illustrative modeling shows the range of PGE compositions in these plume-generated basalts are best generated from a hybrid source that incorporates 0–0.5 wt.% of outer core material, 50% depleted upper mantle and 50–49.5% lower (primitive) mantle. D 2002 Elsevier Science B.V. All rights reserved.