• Schmidt, Gerhard

Abstract

(1) The Ir/Rh mass ratio in chondrite groups, melt samples from impact craters and the Earth's mantle exogenic contribution ("late veneer") is a reliable indicator of the relative formation distance to the sun (2) refractory element ratios correlate roughly with Є100Ru values (3) platinum group elements show decreasing solar system normalized abundances with increasing condensation temperatures (4) there is a continuous decrease of abundances with decreasing volatility as measured by the condensation temperature (5) more reduced materials like enstatite and ordinary chondrites have lower Ir/Rh values compared to more oxidized and volatile-rich materials such as carbonaceous chondrites that formed at greater heliocentric distance (6) the Earth's mantle has the lowest Ir/Rh mass ratio, an indication that the formation of the "late veneer" has its origin more close to the sun than enstatite chondrites. It is also possible that projectiles from impact craters on Earth (e.g., Clearwater East, however controversial discussed [see Schmidt 2019 Meteoritical Society Meeting 2019, Japan] because of relatively high Cr contents in melt samples which would argue against an iron projectile if Cr were of meteoritic origin) have their origin in the innermost solar system beneath Sun and Earth. Abundances of Os, Ir, Ru, Pt, Rh (monoisotopic element), Pd, Re and Au (monoisotopic) in impact melt samples and terrestrial rock samples were obtained by neutron activation analysis (NAA) at the Institute for Nuclear Chemistry in Mainz. The element concentrations were determined by using a nickel sulfide fire assay collection procedure on homogenized sample powders (nugget effect!). The NAA procedure involved two irradiations: a short irradiation for Rh and a 12 hrs irradiation for Os, Ir, Ru, Pt, Pd, Re and Au. The nineteen monoisotopic elements As, Rh, Co, Au, Na, F, I, Sc, etc. are difficult to analyse with mass spectrometry. On the other hand, it is desirable to analyse samples using different analytical methods. High-quality data of Rh, Ir etc. from various planetary materials (meteorites, mars, moon, impact melts, asteroid sample return missions, environmental samples, etc.) should be obtained by neutron activation analysis and at the Heidelberg ion microprobe. High quality data especially of the monoisotopic element Rh, Ru and Ir might answer fundamental questions of cosmochemistry and contribute to our understanding of the origin of the solar system and the processes involved in the formation and unique composition of planetary bodies.

Topics

• impedance spectroscopy
• nickel
• melt
• Platinum
• mass spectrometry
• iron
• activation
• refractory
• spectrometry
• neutron activation analysis