Other
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28r.320b&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 320
Other
Oxidation, Synchrotron, Trace Elements, X-Ray Techniques
Scientific paper
Introduction: The oxidation state of minor and trace elements in minerals from planetary materials can be used to directly probe the oxygen fugacity of the environment from which the minerals formed. For example, on the basis of existing oxygen fugacity determinations it has been suggested that the parent bodies of chondrites were > 30 km in diameter [1]. Petrogenetic models generally assume oxygen fugacities based on indirect evidence. The x-ray microprobe offers the capability to determine oxidation states for a large suite of elements in individual coexisting phases in conventional rock thin sections using the microXANES (X-ray Absorption Near Edge Structure) technique. Recent Results: Initial research has concentrated on transition metals particularly Cr. The results on Cr oxidation state for olivine and pyroxene from mare basalts 15555 [2] showed that olivine contains predominately divalent Cr while pyroxene accommodates Cr mainly in trivalent state. Similar results for olivine from kimberlitic diamonds showed a mixture of the two states [3]. These results suggest that the terrestrial olivine crystallized in a more oxidizing environment than the lunar olivine and that divalent chromium is a ubiquitous component of olivine crystallized under reducing conditions. Calibration of the method in terms of oxygen fugacity requires the analysis of synthetic olivine crystallized from melts of appropriate composition at controlled fO(sub)2 [4]. MicroXANES analyses of Fe surprisingly suggested that Fe in plagioclase from lunar anorthosite 15415 is more oxidized than that in plagioclase from Stillwater anorthosites and shergottites [5]. Recently, iron oxide specimens were analyzed, specifically, magnetite (Fe3O4), hematite (Fe2O3) and altered magnetites (i.e., magnetites suspected of containing substantial alteration to hematite). The results showed that the altered magnetites are roughly equal mixtures of magnetite and hematite [6]. Future Research: The work on lunar olivines in lunar basalts is being extended to lunar olivines in highlands rocks. Oxygen fugacities of the early lunar magmas will be compared with those of the latter mare systems. Determinations of Cr oxidation state in olivine from carbonaceous meteorites are also being pursued but the Cr content of olivine from primitive meteorites is close to current detection limit with microXANES (about 10 ppm). MicroXANES will also provide valuable information on the oxidation states of transition elements in primitive interplanetary dust particles (IDPs). Preliminary results on one IDP indicated that Fe was in both the divalent and trivalent states and the shape of the spectrum is inconsistent with an oxide host. This technique will also be useful in estimating magnetite content in heated IDPs. Iron oxidation states of SNC meteorites and other achondrites will be valuable in constraining the oxygen fugacity of igneous planetary systems. Measurements of Ti^3+, Ti^4+, V^2+ and V^3+ in the constituent phases of CAIs will help to constrain the chemical history of materials that formed in the early solar nebula. The next generation synchrotron source, the Advanced Photon Source at Argonne National Laboratory, will be available for use by planetary scientists in 1996 and will extend these techniques to 1 ppm detection limits and 1 micrometer spatial resolution. References: [1] Rubin A. E. et al. (1988) In Meteorites and the Early Solar System, 488-511. [2] Sutton S. R. et al. (1993) GCA, 57-2, 461-468. [3] Sutton S. R. et al. (1993) LPS XXIV, 1383- 1384. [4] Hanson B. Z. and Delano J. W. (1992) LPS XXIII, 481- 482. [5] Delaney J. S. et al. (1992) LPS XXIII, 299-300. [6] Sutton S. R. et al. (1993) LPS XXIV, 1385-1386.
Bajt Saa
Smith Joseph V.
Sutton Richard S.
No associations
LandOfFree
X-Ray Absorption Spectroscopy Determination of Oxidation States does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with X-Ray Absorption Spectroscopy Determination of Oxidation States, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and X-Ray Absorption Spectroscopy Determination of Oxidation States will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1072850