University of Texas at El Paso DigitalCommons@UTEP Open Access Theses & Dissertations 2013-01-01 Olivine Ca Content Measured By ICP-OES To Estimate P-T Bradley Benavides University of Texas at El Paso, [email protected] Follow this and additional works at: https://digitalcommons.utep.edu/open_etd Part of the Geology Commons Recommended Citation Benavides, Bradley, "Olivine Ca Content Measured By ICP-OES To Estimate P-T" (2013). Open Access Theses & Dissertations. 1584. https://digitalcommons.utep.edu/open_etd/1584 This is brought to you for free and open access by DigitalCommons@UTEP. It has been accepted for inclusion in Open Access Theses & Dissertations by an authorized administrator of DigitalCommons@UTEP. For more information, please contact [email protected]. OLIVINE CA CONTENT MEASURED BY ICP-OES TO ESTIMATE P-T BRADLEY D. BENAVIDES Department of Geological Sciences APPROVED: Jasper Konter, Ph.D., Chair Elizabeth Anthony, Ph.D. Lawrence Ellzey, Ph.D. Benjamin Flores, Ph.D. Dean of the Graduate School OLIVINE CA CONTENT MEASURED BY ICP-OES TO ESTIMATE P-T by BRADLEY D. BENAVIDES, B.S. THESIS Presented to the Faculty of the Graduate School of The University of Texas at El Paso in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Department of Geological Sciences THE UNIVERSITY OF TEXAS AT EL PASO December 2013 ABSTRACT Ca is a trace element in olivine and its concentration is pressure and temperature dependent, providing a rare opportunity to estimate pressure conditions at which mantle-derived rocks (xenoliths) last equilibrated. This P-T dependence has previously been calibrated for mantle xenoliths, and we applied this technique to samples from Jasper Seamount (Jasper Seamount), an oceanic intraplate volcano (OIV) off the coast of the Baja California Peninsula of Mexico. Preliminary compositions for xenoliths from this location appear to define a magmatic plumbing system that features magma storage near the bottom of the crust. A more detailed analysis of the samples is required to better estimate P-T conditions, and this is normally achieved with electron microprobe measurements of Ca content in olivine, and Mg and Fe in orthopyroxene and clinopyroxene (Köhler and Brey, 1990). In order to assess and improve precision, O'Reilly et al. (1997) used proton microprobe and electron microprobe data to obtain Ca concentrations for two samples and compared them to compositional estimates from isotope dilution. The results show that isotope dilution yields the highest precision, while the electron microprobe achieves 1% precision, and the proton microprobe yields the worst precision (2.7%). It was found that Ca is strongly correlated with temperature and poorly correlated with pressure, requiring high-precision Ca concentrations to minimize the error on P- T estimates. In this study, the capabilities of ICP-OES to determine the concentration of Ca of a well-studied Kilbourne Hole xenolith (KH7) have been evaluated. Precise ICP-OES concentrations of Fe, Mg, and Ni were also determined, and these were tested as potential internal standards using electron microprobe concentrations of these elements and the ratio of Ca to one of these elements. The best precision was found to result from measuring Ca/Mg iii ratios, with a given Mg concentration from a different technique. A gravimetrically prepared UTEP Fake Olivine Standard (UFOS) was subsequently measured, having a composition that is close to Jasper Seamount xenoliths. The new Ca/Mg technique was then applied to the xenoliths of Jasper Seamount, bracketed with UFOS measurements for a secondary correction that also includes a drift correction. Jasper Seamount samples define a similar temperature range as was previously found, and overlapping with other OIVs. Pressure estimates only yield values outside of the calibrated range of the applied geothermobarometer, which may result from partial re-equilibration of mineral compositions, alteration of the samples on the seafloor, or by unintentionally including small inclusions of clinopyroxene in the bulk dissolution of olivine. iv TABLE OF CONTENTS Page ABSTRACT.......................................................................................................................................iii TABLE OF CONTENTS.......................................................................................................................v LIST OF TABLES..............................................................................................................................vii LIST OF FIGURES ............................................................................................................................ix LIST OF GRAPHS..............................................................................................................................x Chapter 1. INTRODUCTION .........................................................................................................................1 2. ANALYTICAL BACKGROUND........................................................................................................2 3. GEOLOGIC BACKGROUND .........................................................................................................3 4. TECHNIQUE DEVELOPMENT......................................................................................................8 4.1 Pilot study.................. ..................................................................................................8 4.2 Analysis-(ICP-OES) .......................................................................................................9 4.3 Analysis- (Electron Microprobe) ................................................................................10 5. SAMPLE DESCRIPTION AND PREPARATION .............................................................................13 6. RESULTS.............................. ....................................................................................................14 6.1 Pilot Study Results and Expected Precision ...............................................................14 6.2 Results for Jasper Seamount .....................................................................................15 7. DISCUSSION.............................................................................................................................16 7.1 Ca in Olivine and Extreme Pressures..........................................................................16 7.2 Temperature Estimates at Fixed Pressure ..................................................................17 8. CONCLUSIONS.........................................................................................................................19 REFERENCES .................................................................................................................................21 APPENDIX A. FIGURES ..................................................................................................................23 APPENDIX B. ELECTRON MICROPROBE ELEMENTAL MAPS.........................................................28 APPENDIX C. TABLES....................................................................................................................42 APPENDIX D. GRAPHS..................................................................................................................70 v CURRICULUM VITA.......................................................................................................................78 vi LIST OF TABLES Table 1..........................................................................................................................................42 Table 2. ........................................................................................................................................42 Table 3..........................................................................................................................................43 Table 4..........................................................................................................................................43 Table 5..........................................................................................................................................44 Table 6..........................................................................................................................................45 Table 7..........................................................................................................................................54 Table 8..........................................................................................................................................54 Table 9..........................................................................................................................................55 Table 10........................................................................................................................................55 Table 11........................................................................................................................................56 Table 12........................................................................................................................................57 Table 13........................................................................................................................................58 Table 14........................................................................................................................................59