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Studies on Oman Meteorites Studies on Oman Meteorites Inauguraldissertation der Philosophisch-naturwissenschaftlichen Fakultät der Universität Bern vorgelegt von Ali Faraj Ahmed Al-Kathiri von Oman Leiter der Arbeit: PD Dr. Edwin Gnos Dr. Beda Hofmann Institut für Geologie, Universität Bern Studies on Oman Meteorites Inauguraldissertation der Philosophisch-naturwissenschaftlichen Fakultät der Universität Bern vorgelegt von Ali Faraj Ahmed Al-Kathiri von Oman Leiter der Arbeit: PD Dr. Edwin Gnos Dr. Beda Hofmann Institut für Geologie, Universität Bern Von der Philosophisch-naturwissenschaftlichen Fakultät angenommen Der Dekan Bern, 9. Februar 2006 Prof. Dr. P. Messerli Acknowledgments I thank to the Swiss National Foundation for funding this project (grants 2100-064929 and 200020-107681) and the Ministry of Commerce and Industry of the Sultanate of Oman for assistance and permitting fieldwork in Oman. Special thanks to the following: All my family members and relatives for their patience and the love they gave me through the period of my study. His Highness Maqbool Bin Ali Sultan, Minister of Commerce and Industry, for his support and granting me a study leave to conduct my PhD thesis at the University of Bern. Drs. Beda Hofmann and Edwin Gnos for their direct supervision and their unlimited scientific and technical assistance. They are also thanked for their transfer of knowledge and experience through the period of my PhD study and during the meteorite search campaigns. Prof. Martin Engi for his scientific guiding and supervision. His is thanked for his care, hospitality and creating very friendly working atmosphere. Akram Al-Muraza, Khalid Al-Rawas, and Sami Al-Zubaidi and all my colleagues from the Ministry of Commerce and Industry, Salalah, for their logistic and administrative support during the project. Dr. Hilal Al-Azri, Directorate general of Minerals, Ministry of Commerce and Industry, Muscat, for his support in initiating the project, and permission to search for meteorite in Oman. Prof. Tjerk Peters for presenting the research proposal to the Ministry of Commerce and Industry to initiate a joint Omani-Swiss meteorite search project and his recommendation to include me as member of the search team. Dr. Timothy Jull, NSF lab, University of Arizona, for providing the 14C terrestrial ages of a large number of meteorites recovered during the joint Omani-Swiss meteorite search project including those used for the study of weathering of meteorites from Oman. Prof. Otto Eugster for his noble gas isotope measurements and his field support during one meteorite search campaign in Oman. Prof. Urs Krähenbühl for his chemical analyses on the iron meteorite Shisr 043 and the lunar meteorite SaU 169, and his field support during one meteorite search campaign in Oman. Dr. Kees Welten for his determination of the cosmic ray exposure age for the Shisr 043 iron meteorite. V Manuel Eggimann and Dr. Sylvio Lorenzetti for their assistance and joining us during various periods of meteorite search in Oman. Profs. Rainer Wieler and Ingo Leya, Dr. Salim Al-Busaidi, Ali Al-Rajihi, Mohamed Al-Batashi, Dr. Niklaus Waber, Mohamed Ishaq, Jürg Bühler, Lorenz Moser and Mark Hauser for joining us during some meteorite searching periods. Ulli Linden and Werner Zaugg for passing on their computing experience and helping whenever it is needed. Vreni Jakob and Jürg Megert for preparing petrographic thin sections of the meteorites recovered during our search program, and Ruth Mäder for analysis of water content in meteorites. Peter Vollenweider for making additional photographs of meteorites used in this study. Isabelle Jobin, Sarah Antenen, Barbara Grose and Brigitte Schneiter for always having been very helpful with any administrative work or question during my stay in Bern. Many thanks to all professors, assistants, post doctors, colleges and employees at the Institute of Geological Science and the Museum of Natural History at Bern for their hospitality and kind help. VI Abstract A large number of meteorites have been recovered during the joint Omani-Swiss meteorite search project (2001-2005). This made meteorites from Oman available to scientists around the world as well as to Omani researchers and students to perform scientific research on different aspects of the science of meteoritics. This PhD thesis consists of five independent sections prepared for publication in peer- reviewed journals, in which I am the first author in the first three papers and a co-author in the last two papers. During this PhD thesis most of the work was directed to study the terrestrial weathering of meteorites, starting in the field by measuring fragmentation, dispersion of fragments on the soil and taking soil samples to compare the effect of soil chemistry on the meteorites. At the University of Bern sample preparations were done on a large number of meteorites and soil samples for chemical analysis and petrographic investigations. In addition, studies were also performed on rare and unique meteorites such as the KREEP-rich lunar meteorite SaU 169, the only iron meteorite so far found in Oman (Shisr 043) and the Martian meteorite SaU 094. Results from the weathering study showed that the chemical composition of the desert soil in the interior of Oman is very homogeneous and the influence of soil geochemistry on meteorite weathering can therefore be assumed to be nearly constant over the whole study area. The investigation of weathering-related parameters (fragmentation, dispersion of fragments on the soil, alteration mineralogy, color of powdered meteorites, bulk chemistry) as a function of 14C terrestrial ages showed an accumulation of Sr, Ba and H2O, and a loss of S with increasing terrestrial age. Fast iron metal oxidation is correlated with rapid rates of water absorption. The slower oxidation of troilite releases sulfate, allowing the steady precipitation of Ba and Sr sulfates over time. Cementation of pores with weathering products gradually decreases the weathering rate over time, however the rate of purely physical weathering will remain constant. Meteorite powders exhibit a color change as a function of weathering grade. Fresh unweathered meteorites have a dark grey color, with increasing amounts of weathered metal and troilite, the powder commonly grades to dusky brown, grayish brown, moderate brown, and finally light brown for strongly weathered meteorites. The local surface topography (hard/soft soil, depressions and small hills) also has a marked influence on the weathering of meteorites. The iron meteorite Shisr 043 is a single mass not paired with any of the other eight known iron meteorites from the Arabian Peninsula. Based on the mean kamacite bandwidth and the chemical composition of the meteorite it is classified as a medium octahedrite belonging to the chemical group IIIAB. Cosmic ray exposure data yielded an age of 290 ± 20 Ma, and a terrestrial age of <10,000 years. Sayh al Uhaymir 169 is the first known KREEP-rich lunar meteorite. The study on the regolith part of the lunar meteorite showed that it contains clasts of Ti-poor to Ti-rich basalts, gabbros to granulites, and regolith breccias, and that the regolith formed in two stages. The younger regolith additionally contains a highland gabbronorite clast with anorthite An96-97, forsteritic (Fo85) and fayalitic (Fo12) mineral clasts, and impact melt shards. Based on the regolith chemistry, the comparison of Fe-Ti-Th-K concentrations with remote sensing data from the lunar surface, the KREEP clast contained in the regolith, and the volcanic clast types and its TiO2 content, the regolith source area can be assigned to the vicinity of the Apollo 12 and 14 landing sites. In combination with data on the impact melt part of SaU 169 the complex history of the VII meteorite could be reconstructed registering impact events on the Moon at 3909 ± 13 Ma, ~2800 Ma, ~200 Ma, <340000 years, and a delivery to Earth <10000 years ago. Sayh al Uhaymir 094 is classified as a strongly-shocked melanocratic olivine-porphyric Martian rock belonging to the shergottite group with affinities to lherzolitic shergottites. Its model composition is very similar to the Dar al Gani 476/489/670/735/876 shergottites from the Libyan Desert. The meteorite is now recognized to be paired with SaU 005/008/051/060/090/120/125/130/131/150 making it the largest known strewnfield produced by a Martian meteorite. All meteorites found during this project were classified using optical methods and electron microprobe. These results are listed in the appendix 1. VIII Contents Page Acknowledgements V Abstract VII Contents IX Introduction 1 Meteorites 1 Meteorite searching in Oman 2 Aims of the project 3 Importance of meteorite finds during this project for Oman 3 Geology of the searched area 3 Meteorite finds 5 Soil samples 6 PhD thesis content 8 Section 1 8 Section 2 8 Section 3 9 Section 4 10 Section 5 10 Appendices 11 References 11 Section 1: Weathering of meteorites from Oman: Correlation of chemical 13 and mineralogical weathering proxies with 14C terrestrial ages and the influence of soil chemistry Abstract 13 Introduction 13 Geology of the interior Oman desert 14 Characterization of meteorite collection surfaces and climatic conditions 14 Samples and methods 15 Results 19 Effects of weathering measured in the field: Fragmentation, fragment 19 dispersion, aeolian abrasion Terrestrial ages of meteorites from Oman 20 Meteorite powder color and weathering grade 20 Mineralogy of weathering products 20 Chemistry of meteorite alteration 22 Correlation of weathering
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