Other
Scientific paper
Nov 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983e%26psl..65..303e&link_type=abstract
Earth and Planetary Science Letters, Volume 65, Issue 2, p. 303-310.
Other
3
Scientific paper
A modified AEI-IM20 ion microprobe has been used to measure 87Sr/86Sr ratios in carbonates. A suite of carbonates with varying major elements (Ca, Mg, Fe, Mn) was studied at low and high (M/ΔM ⋍ 3000) mass resolution to determine the types and intensities of molecular species isobaric with Sr peaks; Sr data collected at low mass resolution must be corrected for Ca2 and CaMgO species. Rb/Sr ratios are extremely low, and correction for 87Rb is not required (< 0.1‰ of 87Sr).
Usable Sr isotopic data may be obtained from calcite given Sr >= 400 ppm, and for Sr > 5000 ppm a precision of ~ +/- 1‰ (+/- 0.0007) in 87Sr/86Sr (2σ mean) can be achieved under optimum conditions. The corrections for Ca2 and CaMgO are smaller than the within-run precision in calcite, but in dolomite the correction for CaMgO is + 1.5%. Mass fractionation corrections to 87Sr/86Sr (based on 86Sr/88Sr = 0.1194) are typically +8 to +10‰. Good agreement between ion probe and solid source mass spectrometer results was found for calcites of known Sr isotopic composition: ST4a (~ 400 ppm Sr), average ion probe 87Sr/86Sr = 0.7267 +/- 0.0015, solid source 87Sr/86Sr = 0.72680 +/- 0.00008 [14]; JCG36 (~ 6000 ppm Sr), average ion probe 87Sr/86Sr = 0.7056 +/- 0.0009, solid source 87Sr/86Sr = 0.70588 +/- 0.00009 [16]; JCG44 (~ 6000 ppm Sr), average ion probe 87Sr/86Sr = 0.7057 +/- 0.0006, solid source 87Sr/86Sr = 0.70540 +/- 0.00008 [16]. The ability of the ion microprobe to measure 87Sr/86Sr for 10-μm spots in calcite was used: (1) to measure variation in 87Sr/86Sr of ~ 0.01 on a centimetre scale in a hydrothermally altered basalt from the Isle of Skye, northwestern Scotland; and (2) to determine the Sr isotopic composition of tiny (< 35 μm) calcite grains in a veined mantle lherzolite from Bultfontein, South Africa. Because of calcite's ubiquitous occurrence in many parageneses this technique may offer many opportunities for the measurement of fine scale heterogeneities in 87Sr/86Sr.
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