Journal of Chromatography & Separation Techniques
Open Access

Pb baddeleyite geochronology by the thermal extraction-thermal ionization mass spectrometry, a new method for dating Proterozoic large igneous provinces

International Summit on Current Trends in Mass Spectrometry

July 13-15, 2015 New Orleans, USA

Anil Kumar1, E. Nagaraju1, D. Srinivasa Sarma1, DonaldW. Davis2

Posters-Accepted Abstracts: J Chromatogr Sep Tech

Abstract :

The ability to easily obtain precise (~0.1%) age determinations on mafic rocks can facilitate identification of contemporaneous magmatic events across continents and hence open new avenues of research investigations related to large scale mantle processes. We present high precision Pb age determinations on baddeleyite (ZrO2), a common accessory mineral in mafic rocks using thermal extraction-thermal ionization mass spectrometer (TE-TIMS). Replicate analyses of twelve preheated (at 1250 °C) and silica embedded baddeleyite grains from the Paleoproterozoic Phalaborwa carbonatite using this procedure have yielded a 207Pbâ??206Pb weighted mean age of 2060.3 ± 0.4 Ma, consistent with previously reported 207Pbâ??206Pb ages for this carbonatite occurrence determined by the conventional Uâ??Pb isotope dilution-thermal ionization mass spectrometry (ID-TIMS) technique. Fourteen baddeleyite fractions from a large Paleoproterozoic Nâ??S striking mafic dyke swarm in the Dharwar craton yielded a 207Pbâ??206Pb weighted mean age of 2215.9 ± 0.3 Ma, also consistent with previously determined conventional ages. All data were corrected for mass fractionation of 0.18%/amu as determined previously on zircon. Both data sets scatter outside measurement errors, implying an external 2 sigma error of 0.055% in the case of the carbonatite and 0.043% for the mafic dyke, which we suggest represents the reproducibility of the fractionation correction. Our results demonstrate that thermal extraction 207Pbâ?? 206Pb ages are comparable with the conventional Uâ??Pb ages in both accuracy and precision. This new procedure does not need ultra-clean laboratory conditions (<1pg procedure blanks), a prerequisite for conventional high precision Uâ??Pb geochronology, and hence can be easily practised in most TIMS isotope geochemistry laboratories.