The aims of this research programme were twofold: to analyse the iron isotope compositions of metal grains from ordinary chondrite meteorites over a range of class and petrographic type to investigate redox reactions and thermal metamorphism during primitive planetesimal formation; and to analyse the iron isotope composition of secondary carbonate minerals in Martian meteorite ALH84001 to determine the formation temperature and thus constrain near surface conditions on early Mars. To analyse the iron isotope compositions of these materials it was necessary to develop a methodology using a Nu Plasma multi collector inductively coupled plasma mass spectrometer and a new technique for analysing natural iron-bearing samples without first purifying them by anion exchange chromatography. The purification process can cause fractionation within the sample which may mask small natural fractionation variations. The new methodology developed here yielded reproducible iron isotope ratios to within o.osroo (20) ensuring that small isotopic variations of (i56Fe -0.06roo to 0.3sroo were resolved during the analysis of the ordinary chondrite metal grains. The method for analysing samples containing matrix elements was successful and achieved an accuracy and precision comparable to pure analyte solutions for the analysis of the Martian carbonates. The analysis of the metal grains revealed a correlation between their iron isotope compositions and the redox and thermal metamorphism that these materials have experienced. The results indicate that the degree of iron isotope fractionation can be related to thermal metamorphism temperatures, except for metal grains from type 3 chondrites. This was interpreted as resulting from the type 3 chondrites not getting hot enough during thermal metamorphism to overprint the original igneous isotopic signatures. The a-rich carbonates in ALH84001 were petrographically characterised to place them within the known carbonate assemblage sequence which implied that the zoned carbonate deposition occurred during multiple phases. The zoned carbonates were then analysed for iron isotope composition and an isotopic fractionation variation for (i56Fe of -0.6%0 was determined relative to bulk Martian silicates. This indicated a formation temperature of approximately ±800( (20) and implied that liquid water was stable on or near the surface during this time.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:488641 |
| Date | January 2008 |
| Creators | Theis, Karen Julia |
| Contributors | Gilmour, J. D. |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://www.manchester.ac.uk/escholar/uk-ac-man-scw:163898 |
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