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Origin and Evolution of Ureilite Vein Metal – Fe, Ni, Co and Ni­Isotope Systematics of Ureilite Vein Metal and Ureilite Silicates

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Origin and Evolution of Ureilite Vein Metal – Fe, Ni, Co and Ni­Isotope Systematics of Ureilite Vein Metal and Ureilite Silicates Origin and evolution of ureilite vein metal – Fe, Ni, Co and Ni­isotope systematics of ureilite vein metal and ureilite silicates Dissertation zur Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakultäten der Georg-August-Universität zu Göttingen vorgelegt von Dipl.-Min. Aron D. Gabriel aus Berlin Göttingen 2009 1 D 7 Referentin/Referent: Prof. Dr. Andreas Pack Korreferentin/Korreferent: Prof Dr. Addi Bischoff Tag der mündlichen Prüfung: 2 Table of Contents 1 Introduction........................................................................................................................ 8 1.1 What are meteorites?.................................................................................................. 8 1.2 Weathering and shock................................................................................................. 8 1.3 Meteorite classification ............................................................................................. 10 1.3.1 Chondrites .......................................................................................................... 10 1.3.2 Achondrites ........................................................................................................ 16 1.3.3 Primitive Achondrites......................................................................................... 19 2 The ureilite group............................................................................................................. 20 2.1 Introduction............................................................................................................... 20 2.2 Mineralogy................................................................................................................. 20 2.2.1 Silicates............................................................................................................... 20 2.2.2 Vein material ...................................................................................................... 22 2.2.3 Spherule inclusions in olivine............................................................................. 23 2.3 Ureilite bulk rock chemistry....................................................................................... 24 2.3.1 Lithophile elements............................................................................................ 24 2.3.2 Siderophile elements.......................................................................................... 25 2.3.3 Rare Earth Elements (REE) ................................................................................. 25 2.3.4 Noble gases ........................................................................................................ 27 2.3.5 Oxygen isotopes ................................................................................................. 27 2.3.6 Carbon isotopes.................................................................................................. 28 2.3.7 Ureilite formation age and cosmic ray exposure age ........................................ 29 2.3.8 The 60Fe‐60Ni short‐lived isotope chronometer ................................................. 30 2.4 Ureilite genesis .......................................................................................................... 32 3 2.4.1 Parent body composition................................................................................... 32 2.4.2 Thermal history of ureilites................................................................................ 33 2.4.3 Igneous processes on the ureilite parent body.................................................. 34 2.4.4 Reduction on the ureilite parent body............................................................... 35 3 Goals of this study............................................................................................................ 38 4 Thermodynamics.............................................................................................................. 39 4.1 Theoretical background............................................................................................. 39 4.2 Gibbs free energy of reaction.................................................................................... 41 4.3 Activity coefficients of Fe, Co and Ni in Fe‐Co‐Ni metal............................................ 42 4.4 Activity coefficients of Fe2SiO4 in olivine................................................................... 45 4.5 Activity coefficients of Ni2SiO4 and Co2SiO4 in olivine............................................... 47 4.6 Comparison of the regular solution model with Hirschmann’s model ..................... 49 5 Mass balance calculations................................................................................................ 52 5.1 Mass balance calculations of the UPB’s core ............................................................ 52 5.2 Model of the UPB core formation process................................................................ 53 6 Sampling........................................................................................................................... 60 6.1 Allan Hills 84136 (ALH84136) .................................................................................... 60 6.2 Allan Hills 77257 (ALHA77257) .................................................................................. 61 6.3 Dar al Gani 340 (DaG340) .......................................................................................... 61 6.4 Elephant Moraine 87517 (EET87517)........................................................................ 62 6.5 Elephant Moraine 96042 (EET96042)........................................................................ 62 6.6 Elephant Moraine 96331 (EET96331)........................................................................ 63 6.7 Kenna ......................................................................................................................... 63 6.8 Graves Nunataks 95205 (GRA95205) ........................................................................ 64 6.9 Lewis Cliff 85440 (LEW85440) ................................................................................... 64 7 Sample preparation and analytical procedures............................................................... 65 4 7.1 Sample preparation ................................................................................................... 65 7.2 Electron microprobe measurements......................................................................... 65 7.2.1 Measurements at the Institute of mineralogy in Cologne................................. 65 7.2.2 Measurements at the University of Göttingen .................................................. 66 7.2.3 The Co‐problem.................................................................................................. 67 7.3 Laser‐ablation‐ICP‐MS measurements of silicates .................................................... 69 7.4 Ni‐Isotope analyses.................................................................................................... 74 8 Results .............................................................................................................................. 76 8.1 Data of individual ureilites......................................................................................... 76 8.1.1 ALH84136 ........................................................................................................... 76 8.1.2 ALHA77257......................................................................................................... 80 8.1.3 DaG340............................................................................................................... 84 8.1.4 EET87517............................................................................................................ 87 8.1.5 EET96042............................................................................................................ 91 8.1.6 EET96331............................................................................................................ 95 8.1.7 GRA95205........................................................................................................... 99 8.1.8 Kenna................................................................................................................ 103 8.1.9 LEW85440......................................................................................................... 106 8.2 Ni and Co in ureilite silicates ................................................................................... 110 8.3 Ni and Co in vein metal............................................................................................ 114 8.4 Ni‐isotope data ........................................................................................................ 116 9 Discussion....................................................................................................................... 118 9.1 Thermodynamic equilibrium between vein metal and ureilite olivine................... 118 9.1.1 Calculation of Fe‐Ni and Fe‐Co‐exchange equilibrium temperatures.............. 118 9.1.2 Equilibration temperatures for ALH84136....................................................... 120 9.1.3 Equilibration temperatures for EET96331 ....................................................... 121 5 9.1.4 Is ureilite olivine and vein metal in equilibrium?............................................. 121 9.2 Relation
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