Laser Ablation ICP-MS of Siderophile and Chalcophile Elements in Mid-Oceanic Ridge Glasses

1. Laser Ablation ICP-MS of Siderophile and Chalcophile Elements in Mid-Oceanic Ridge Glasses Evelyn Martinique Mervine Dartmouth College July 29th, 2005 Mentor: Dr. Vincent Salters, Geochemistry

2. Outline • Goals of the Study • Background • Sample Selection and Analysis • Data • Conclusions • Acknowledgements

3. Goals of the Study • Develop technique for measuring siderophile and chalcophile elements in glasses • Compare LA-ICP-MS with traditional ICP-MS • Examine residual aprons • Study how siderophile and chalcophile elements behave during crystal fractionation

4. Background: Goldschmidt’s Classification of the Elements • Atmophile: • Noble gases • Covalently-bonded gases • Siderophile: • Metals near and including iron in the periodic table • Transition metals • Exhibit metallic bonding • Chalcophile: • Elements that bond to S, Se, Te, Sb, and As • Tend to form covalent bonds • Lithophile: • Elements which typically bond to oxygen in silicates and oxides • Tend to form ionic bonds

5. Background:Why Study Siderophile and Chalcophile Elements? • Scientists do not understand the behavior of most siderophile and chalcophile elements well • Can compare behavior of siderophile and chalcophile elements during magma genesis with the well-known behavior of major and other trace elements • What these elements may tell us: • Oxidation state of the mantle • Behavior of sulfur during magma genesis • Composition of the Earth’s core

6. Sample Selection • Mid-Atlantic Ridge Glasses • On loan from Smithsonian’s Volcanic Glass Collection • Thirty samples, divided into two suites of fifteen • Each suite represents samples related through crystal fractionation • Indian Ridge Glasses • Already at the lab • Used for method development

7. Analysis • Glass chips mounted in epoxy on a slide • Slide polished to reveal flat glass surface • Slide placed in sample holder • Laser beam fired on sample, ablates sample • Sample flows to the Finnigan ICP-MS, which ionizes the sample • Elemental concentrations measured by separating ions based on mass in a magnetic field and counting them 4 mm Laser Holes Mass Spectrometer Laser

8. Analysis:What We Learned • Blank Levels • Concentration Levels • Length of measurements • Track vs. spot analysis • LA-ICP-MS data is comparable to solution ICP-MS data • Firing on residual aprons does not affect data quality Residual Apron Laser Hole

9. Data:Elements Measured in This Study Table Source: http://ruby.colorado.edu/~smyth/G30103.html = Elements analyzed in this study

10. Example: Incompatible Element Negative Slope Data: Concentrations • Incompatible elements • Preferentially included in the melt over the crystalline phase • Decrease with increasing MgO content • Compatible elements • Preferentially included in the crystalline phase over the melt • Increase with increasing MgO content • MgO concentration is inversely proportional to amount of crystal fractionation Example: Compatible Element Positive Slope

11. Data: Crystal Fractionation Trends Copper (Cu) • Cu is compatible • Pb and Zn are incompatible Zinc (Zn) Lead (Pb)

12. Data: Crystal Fractionation Trends By comparing the slopes of the elements plotted against MgO, can determine relative compatibilities Highly Incompatible: Mo, Pb, Pd, Zn Incompatible: Ga, Se, Cd, Co Compatible: Ni, Cu Insufficient Data: Ag, Re

13. Conclusions • Were able to determine concentrations of many siderophile and chalcophile elements in mid-ocean ridge glasses using LA-ICP-MS • LA-ICP-MS data is comparable to ICP-MS data • Firing on residual aprons does not affect data quality • Chalcophile Cu seems to behave compatibly • Chalcophile Zn and Pb seem to behave incompatibly

14. Acknowledgements • Thanks to Vincent Salters, Roy Odom, Michael Bizimus, Munir Humayun, and everyone else in Geochemistry • Thanks to Pat Dixon, Gina LaFrazza, Stacy Vanderlaan, and Sarah Mullins in the Center for Integrating Research and Learning • Thanks to NSF, NHMFL