Phosphorus zoning reveals dendritic architecture of olivine

Abstract

Quantitative spot analyses were acquired with the JEOL JXA-8500F field-emission gun electron probe micro-analyzer of the University of Hawaii – Manoa over two sessions. Olivine was analyzed during the first session with an electron beam tuned at 20 keV, 50 nA and 10 µm probe diameter. The elements were acquired using five analyzing crystals as followed: one LiFH for Cr and Ni, one LiF for Fe and Mn, one PETJ for Ca and Ti, one PETH for P, and two TAPJ crystals for Al, Si and Mg. The standards used were Verma garnet for Mn, San Carlos olivine USNM 111312/444 for Fe, Si, Mg and Ni, sphene glass for Ti, chromite USNM 117075 for Al and Cr, and fluor-apatite USNM 104021 for Ca and P. The on-peak and off-peak counting times were each 20 s for Si, Al and Mg, 30 s for Mn, Ti and Ni, 35 s for Fe, Ca and Cr, and 70 s for P. The off-peak correction method was linear for major elements and exponential for trace elements Ti, Al, Cr and P, using Probe for EPMA software. Detection limits are in the range 0.005 – 0.01 wt%. Precision and accuracy (1) are 0.4 – 2 % for major elements (reported in weight percent oxide), 3 – 5 % for minor elements (Ca, Mn and Ni – reported in µg/g) and 20 – 70 % for trace elements (Al, P, Ti, and Cr – reported in µg/g in Table DR1), based on repeated analyses of San Carlos olivine standard (USNM 111312/444). Matrix glasses and melt inclusions were analysed during the second session with a beam tuned at 15 keV, 15 nA and 10 µm probe diameter. Elements were acquired using one LiFH for Ti and Cr, one LiF for Fe and Mn, one PETH for Ca and K, and two TAPJ crystals for Mg, Al, Na and Si (Na measured first). The standards were Verma garnet for Mn, Kakanui augite USNM 122142 for Al, Fe, Si, Mg and Ca, sphene glass for Ti, chromite USNM 117075 for Cr, Amelia albite for Na, and orthoclase OR-1 for K. The on-peak and off-peak counting times were 30 s for all elements. Detection limits for Cr2O3 and S are 0.02 wt%. Precision is better than 1% for all elements (1), except Na and K (<3%). Accuracy (1) is better than 5 % for all elements.