A Chemical Investigation of Minerals in L-6 Chondritic Meteorites

AN ABSTRACT OF THE THESIS OF DAVID BALLANTYNE CURTIS for the DOCTOR OF PHILOSOPHY (Name of Student) (Degree) in Chemistry presented on October 30, 1973 (Major) (Date) Title: A CHEMICAL INVESTIGATION OF MINERALS IN L-6 CHONDRITIC METEORITES Abstract approved:Redacted for Privacy Roman A. Schmitt Major and minor minerals have been separated from three L-6 chondritic meteorites (Alfianello, Colby (Wiscon- sin), and Leedey). Olivine, hypersthene, diopside, feldspar, troilite, chromite, phosphate minerals, and metallic minerals were analyzed for major, minor and trace elements using instrumental neutron activation analysis and radiochemical neutron activation analysis techniques. Concen- trations df the following elements were determined in some or all of the minerals which were separated: Al, Na, Ca, K, Rb, Cs, Cr, V, Mn, Mg, Zn, Sc, Fe, Ni, Co, Au, Se, S, Cl, La, Ce, Nd, Sm, Eu, Tb, Tm, Yb, Lu. The major element abundances were used primarily to evaluate contamination between minerals. An attempt was made to quantify the cross contamination and correct the trace element abundances accordingly. The distribution of elements within minerals, the partitioning of elements between minerals, and the chemical- mineralogical relationships suggest that many minor and trace elements have been distributed in an orderly fashion in L-6 chondritic meteorites. The Rare Earth Elements (REE) have well defined differences in their absolute and relative abundances in the same minerals from the three meteorites. These chondrites were not in equilibrium with each other with respect to the REE. Neither heterogeneous distribution of accessory minerals nor variations in the absolute and relative abundances of REE in minerals from different meteorites can explain the subtle fractionation of REE between different L chondrites (Masuda et al., 1973). The differences in REE distributions in the same minerals from the three meteorites probably represent various degrees of attainment of equilibrium or equilibration under different physical-chemical conditions. The REE fractiona- tions between different meteorites probably pre-date the present chemical-mineralogical relationships. The relative abundances of Ni, Co, and Au in fine grained metallic minerals differ from the abundances of these elements in the bulk of the metallic phases. Differ- ences in the abundance of Ni can be attributed to various proportions of kamacite and taenite in the analyzed samples. Cobalt and Au abundances do not correlate with Ni; therefore, variations in the abundances of Co and Au are apparently not related to the relative proportions of the metallic minerals. The distribution of Ni and Co between non-metallic meteoritic minerals is different than the distribution between analogous terrestrial minerals. The abundances probably reflect equilibrium between metallic and non-metallic minerals. The last temperatures at which Ni was equili- brated between metal and olivine was calculated from per- tinent thermodynamic relationships. The calculated temperatures indicate that the last temperature of Ni equilibration in the three meteorites decreased in the following order: Colby > Alfianello > Leedey. Rubidium and Cs are concentrated in the feldspar minerals. Rubidium is uniquely associated with the feldspars within the sensitivity of the techniques. Cesium is nearly ubiquitous among the meteoritic minerals. Quantities of Cs in minerals other than feldspar probably reflect the pre- sence of Cs at grain boundaries and in interstitial sites. The Rb/Cs ratio in feldspars from all three meteorites vary considerably. This ratio may be an indicator of thermal events in the history of the meteorites in which Cs was volatilized to various degrees. The largest Rb/Cs ratio which has been identified in the whole rocks is nearly the same value as this ratio in the feldspar minerals. This may indicate that the interstitial Cs enriched phase is the volatile Cs component. If the Rb/Cs ratio is an indicator of some thermal event, the relative temperature in the three meteorites decreases in the following order: Leedey > Alfianello > Colby. This ordering of relative temperatures is reversed compared to the relative temperatures based on the equilibration of Ni between olivine and metallic minerals. The two temperature estimates may reflect the effective temperatures of two different thermal events in the petrogenesis of the three meteorites. Zinc and Mn have nearly identical geochemical affini- ties in these L-6 chondrites. There is no indication of the mechanism which depleted the abundance of Zn in ordi- nary chondrites relative to the abundance in C-1 carbona- ceous chondrites. A Chemical Study of the Minerals from L-6 Chondritic Meteorites by David Ballantyne Curtis A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy June 1974 APPROVED: Redacted for Privacy Professor of Chemistry Redacted for Privacy Chairman of the Department of Chemistry Redacted for Privacy Dean of Graduate School Date thesis is presented October 30, 1974 Typed by Dana Cramer for David Balantyne Curtis Dedicated to Susan I'm sorry she has to share my pain in order to share my joy. ACKNOWLEDGEMENTS I am greatly indebted to Professor R. A. Schmitt for showing a great deal of confidence in me from the first day I started until the final work was completed. Without his encouragement, I might never have done the job. Dr. Marvin Dudas and Dr. T. W. Osborn extended a great deal of their own ideas and advice to me. Dr. J. C. Laul was invaluable in helping me with the radiochemical proce- dure. I am deeply indebted to Dr. W. V. Boynton for inumerable clever suggestions, and a lot of pragmatic assistance. T. V. Anderson, W. Carpenter and the OSU reactor opera- tions crew were of great assistance in the irradiations at the Oregon State University Triga Reactor. Jerry Schlapper and Chester Edwards provided swift and courteous service in the use of the University of Missouri Reactor Facility. The OSU radiation safety personnel enabled me to carry out my work in a safe manner with a minimum of problems. David Hess was particularly helpful in this respect, as well as being extremely cooperative in every aspect of the work at the Radiation Center. Vern Smith was helpful daily in carrying out such a diversity of tasks that I could not itemize them. He deserves gratitude from everyone who works at the Radiation Center; including myself. This work was partially supported by a fellowship from Gulf General Atomic and partially supported by NASA Grant NGL-38-002-020 administered by Dr. R. A. Schmitt. Jean, Marj, and Phyllis are marvelous people. Nicole and Kristen enabled me to keep my perspective. TABLE OF CONTENTS Chapter Page I INTRODUCTION 1 II EXPERIMENTAL 6 Introduction 6 Mineral Separations 6 Elemental Analysis 11 III PRESENTATION AND EVALUATION OF RESULTS 14 Introduction 14 Pre-analysis Contamination and Leaching 14 Cross Contamination between Minerals 19 Elemental Abundances in Minerals from L-6 Chondritic Meteorites 32 Introduction 32 Aluminum and the Alkali Elements 35 Calcium 48 Chromium and Vanadium 50 Iron and Magnesium 61 Selenium and Sulfur 62 Chlorine 65 Nickel, Cobalt and Gold 65 Zinc 77 Manganese 80 Scandium 82 Rare Earth Elements 84 IV ELEMENT DISTRIBUTION IN L-6 CHONDRITIC METEORITES 99 Introduction 99 Partitioning of Trivalent Cations 109 Normalized Distribution Curves 109 Distribution Coefficients of Trivalent Cations between Coexisting Minerals 121 Pyroxenes 121 Olivine 125 Partitioning of Divalent Cations 127 Manganese and Zinc 127 Cobalt and Nickel 137 Fractionation of Alkali Elements in L-6 Chondritic Meteorites 144 Chapter Page V SUMMARY AND CONCLUSIONS 151 Bibliography 155 Appendix A 162 Appendix B 169 Appendix C 196 LIST OF TABLES Table Page 1 Elemental Abundances in Clerici Solution 15 2 Elemental Abundances in "Pure" Minerals from L-6 Chondritic Meteorites 23 3 Indicator Elements for Determination of the Abundances of Mineral Impurities in Separated 24 Samples 4 Estimated Contamination Between Phases 27 5 Elemental Abundances in Standard Rocks and Whole Meteorites 33 6 Corrected Major Element Abundances in Minerals from L-6 Chondritic Meteorites 36 7 Mass Balance for Minor and Trace Elements 38 8 Fraction of Minerals in Whole L-6 Chondrites 40 9 Estimates of Feldspar Contamination using Na, Al, and Rb as Tracers 42 10 Corrected Rubidium Abundances in Minerals from L-6 Chondritic Meteorites 44 11 Corrected Cesium Abundances in Minerals from L-6 Chondritic Meteorites 46 12 Corrected Potassium Abundances in Feldspar from L-6 Chondritic Meteorites 48 13 Calculated and Analyzed Abundances of Sc and Ca in Silicate Minerals 56 14 Corrected Chromium Abundances in Minerals from L-6 Chondritic Meteorites 58 15 Corrected Vanadium Abundances in Minerals from L-6 Chondritic Meteorites 60 16 Corrected Selenium Abundances in Minerals from L-6 Chondritic Meteorites 64 Table Page 17 Corrected Nickel Abundances in Minerals from L-6 Chondritic Meteorites 74 18 Corrected Cobalt Abundances in Minerals from L-6 Chondritic Meteorites 75 19 Corrected Gold Abundances in Minerals from L-6 Chondritic Meteorites 76 20 Corrected Zinc Abundances in Minerals from L-6 Chondritic Meteorites 78 21 Corrected Mn Abundances in Minerals from L-6 Chondritic Meteorites 81 22 Corrected Scandium Abundances in Minerals from L-6 Chondritic Meteorites 83 23 Average Values of REE Abundances from Three L-6 Chondritic Meteorites (normalized to 86 chondritic average)

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