The use of dynamic reaction cell ICP mass spectrometry to facilitate Rb-Sr age determination
F. Vanhaecke, G. De Wannemacker, L. Balcaen, L. Moens, 2003. "The use of dynamic reaction cell ICP mass spectrometry to facilitate Rb-Sr age determination", Geochronology: Linking the Isotopic Record with Petrology and Textures, D. Vance, W. Müller, I. M. Villa
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By using a set of granitic whole rock samples, originating from the Regensburg Forest (Germany) and dated (approximately 350 Ma old) previously by means of thermal ionization mass spectrometry (TIMS), the capability of dynamic reaction cell (DRC) inductively coupled plasma mass spectrometry (ICPMS) for Rb-Sr age determination was demonstrated. With DRC-ICPMS, chemical separation of Sr from Rb during the sample pretreatment is no longer required as interference-free determination of the 87Sr/86Sr isotope ratio can be accomplished by monitoring the signals of the SrF+ adduct ions, formed as a result of the selective reaction between the Sr+ ions extracted from the ICP and the reaction gas CH3F. The mass discrimination was established to depend strongly on the matrix composition. This drawback could be overcome by using the United States Geological Survey reference material G-2 as an external standard. Results obtained by DRC-ICPMS (age and initial 87Sr/86Sr ratio) showed an excellent agreement with both (a) experimental values obtained by means of quadrupole-based and sector field ICPMS after isolation of Sr via cation exchange chromatography and (b) TIMS literature values. In addition, DRC-ICPMS offers a smaller combined uncertainty on the isotope ratio results as a result of (a) an improved internal isotope ratio precision (<0.1% RSD when also using Ne as an additional non-reactive collision gas) and (b) the fact that, in contrast to quadrupole-based and sector field ICPMS, no correction for the remaining overlap between the signals of 87Sr+ and 87Rb+ is required.
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Isotope geochemistry has produced many technical developments in the past decade or so that have revolutionized the potential information available on the tectonics of metamorphic belts from geochronology. These include the ability to date minerals and rocks on small spatial scales, scales that at last approach those from which other types of information — structural and petrological — are obtained. However, interpreting the new data, and their integration with the other datasets available, is not straightforward and requires careful chemical and textural observations that go hand-inhand with the geochronology. The increasing realization of the importance of this approach has led to a number of symposia at international conferences devoted to this topic in recent years. The set of papers in this book emanates from one such symposium and describes recent progress in integrating this new information with other datasets from metamorphic petrology on a mineral and sub-mineral scale.