Element Partitioning and Distribution Coefficients SERC Workshop 2010
Element Partitioning and Distribution Coefficients SERC Workshop 2010 Teaching Geochemistry Valerie Reynolds Colby College
Goals for this activity � Students learn how distribution coefficients are calculated, the conditions that influence partitioning behavior, and how to apply this knowledge when reading primary literature.
Audience �Junior-level undergraduate elective �Mineralogy prerequisite • Chemistry is a prerequisite for Mineralogy �May have had Petrology �Assignment is stand-alone exercise w/out discussion �Can be manipulated to suit different manuscript/chemical composition (e. g. , granite rather than basalt)
Higher Order Thinking Skills � Students learn how to read scientific literature with a critical mindset so they can evaluate the merit of the interpretation presented in the paper. Husch (1990)
Exercise Overview �Part I: Cationic Substitution • Mineralogy review �Part II: The Distribution Coefficient • Explore Kd via GERM �Part III: Application of Knowledge • Read manuscript that uses chemistry to interpret crystallization sequence
Part I: Cationic Substitution Students refresh Mineralogy concepts • • • Factors influencing cationic substitution Coordination #’s of elements in Earth’s crust Predict elemental substitutions Basalt, specifically • • • Given: Ni common trace element in basalt Review basalt mineralogy and element CN’s Predict for what/in what Ni substitutes
Part II: The Distribution Coefficient Geochemical Earth Reference Model • • GERM: (http: //earthref. org/GERM/) Provide specific instructions (Ni/olivine/basalt) • Range of Kds • How determined? • Links to references • Calculate Kd using mineral/matrix data • Compare with predicted results from Part I
Part III: Application of Knowledge � Use Georef to look up article • Husch J. M. (1990) Palisades sill: Origin of the olivine zone by separate magmatic injection rather than gravity settling. Geology 18, 699 -702. � Discussion of pyroxene vs olivine accumulation � Ni, Cr, and Sc � Timing of plagioclase crystallization Husch (1990)
Part III Cont’d �Summary • • and Discussion Students assigned in groups of ~3 Groups meet to discuss paper/answer questions Individuals write summaries Class Discussion
Student Feedback � � � Exercise led well into article material Guide questions appropriate Article at appropriate level Discussion particularly helpful Subsequent assignments have students develop the guide questions
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