Platinum Group Element Analysis of Komatiites

University Of Chicago, Chicago IL

Investigators

Abstract

Humayun EAR-0106974 To better understand the mantle geochemistry of platinum group elements (PGE) and the information returned by 186Os-187Os isotopic studies, we propose to determine the PGE abundances of a global suite of komatiites by a precise isotope dilution ICP-MS technique. Based on results in this lab, this analytical technique has been successfully applied for the determination of PGEs in komatiites. Proposed localities include komatiites from the following greenstone belts: Barberton (S. Africa); Kamennoozero, Vetreny, Onega (Baltic Shield); Belingwe (S. Africa); Abitibi (Canada); Kambalda (Australia); and Gorgona (Caribbean). All samples are available in collections held by us, or will be generously provided from other geochemical studies, particularly previous Os isotopic studies. These include both alumina-depleted and alumina-undepleted komatiites, and both chondritic and suprachondritic initial gamma-187Os-bearing komatiites. Our intellectual goals for the proposed study are to: 1. Focus on establishing the rules of PGE behaviour during the extremely high degrees of partial melting experienced by komatiites, and establish a framework for future work that would include picritic lavas and primary basaltic melts; 2. Determine the PGE composition of Archean crustal materials, which are possible sources of subducted crust for Phanerozoic flood basalts and OIB lavas; 3. Study the PGE composition of each komatiite source region, presumably the Archean lower mantle, for clues to its heterogeneity, with implications for mantle dynamics in the Archean; and 4. Search for evidence of core-mantle interaction in Archean plumes, including evidence for secular changes in such outer core derived signatures. Successful completion of this project will enable us to determine whether this approach can be applied to better understand mantle processes in source regions sampled by picrites and primary basalts, and thereby extend our framework to include a larger spatiotemporal sampling of the mantle. This project also supports the continued US visit of Russian geochemist, Igor Puchtel, the holder and dedicated student of an extensively studied suite of four komatiite localities in the Baltic Shield previously inaccessible to non-Russian scientists.