Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Abstract Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Palme, H. Search for Related Content GeoRef GeoRef Citation

Platinum-Group Elements in Cosmochemistry

^* Institut für Geologie und Mineralogie, Universität zu Köln
Zülpicherstrasse 49b, 50674 Köln, Germany
E-mail: herbert.palme{at}uni-koeln.de

View larger version (22K): [in this window] [in a new window]   FIGURE 1 Reduction potentials (µO2) of PGE oxides and FeO as a function of temperature. Data are for equilibrium between pure oxide and pure metal. The reduction potential indicates the thermodynamic stability of oxides compared to metals. The most noble metal is Pt. Its oxide is the least stable of all PGE oxides. FIGURE ADAPTED FROM O'NEILL ET AL. (1995), UPDATED BY J. BRENAN (PERSONAL COMMUNICATION)

View larger version (54K): [in this window] [in a new window]   FIGURE 2 Results of condensation calculations. Fractions of PGE condensed at a given temperature are shown (at 10-4 atm). Five PGE condense in alloy with W, Mo and Re, but Pd condenses with Fe-Ni alloy. ADAPTED FROM CAMPBELL ET AL. 2001

View larger version (41K): [in this window] [in a new window]   FIGURE 3 CI-chondrite-normalized pattern of nanometre-sized alloys of refractory metals, compared with single-phase condensation calculations. Terrestrial PGE nuggets never contain Mo and W. RMN, refractory metal nugget. FIGURE ADAPTED FROM EISENHOUR AND BUSECK (1992)

View larger version (106K): [in this window] [in a new window]   FIGURE 4 Opaque assemblage in an Allende Ca, Al-rich inclusion. Bright spots are Os-Ru alloys with up to 80% Os. On the left side are Ir-rich alloys. Grey phase is Fe-Ni metal with some Pt; the dark phases are powellite, scheelite and V-magnetite. FROM BISCHOFF AND PALME (1987)

View larger version (55K): [in this window] [in a new window]   FIGURE 5 The absolute and relative abundances of PGE in chondritic meteorites are variable, certainly beyond analytical uncertainties, which are only a few percent. Each colour designates a different meteorite. Elements are arranged in order of increasing volatility (decreasing condensation temperatures) from left to right, with Pd, the most volatile PGE, at the extreme right. FIGURES ADAPTED FROM HORAN ET AL. (2003)

View larger version (43K): [in this window] [in a new window]   FIGURE 6 Experimental determination of Pd solubility in silicate melts. A strong decrease in solubility with decreasing oxygen fugacity is observed. In the lower diagram, the contributions of various Pd species to the total number of dissolved Pd ions are indicated. Reversals with high Pd in the initial silicates are indicated. Oxygen fugacity buffers: MH, magnetite-hematite; QFM, quartz-fayalite-magnetite; IW, iron-wüstite. An-Di, anorthite-diopside. FIGURE MODIFIED FROM BORISOV ET AL. (1994)

View larger version (50K): [in this window] [in a new window]   FIGURE 7 Impact melts from bore holes drilled in winter through a thick ice cover on the 320 m deep Clearwater East Lake, marking a 20 km diameter impact crater in Quebec (Canada). The difference in Ir and Os abundances between meteorites and the Canadian Shield basement is four orders of magnitude. FIGURE ADAPTED FROM PALME ET AL. (1978)

View larger version (38K): [in this window] [in a new window]   FIGURE 8 Ir anomaly at a terrestrial K/T section in the Raton basin (Colorado, USA). The strong decrease in angiosperm pollen (solid black circles) coincides exactly with the Ir anomaly (light blue histogram), reflecting severe changes in the environment exactly at the time of Ir delivery. MODIFIED FROM ORTH ET AL. (1981)