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Connelly 2006
Connelly, J.N. (2006). Improved dissolution and chemical separation methods for Lu-Hf garnet chronometry. Geochemistry Geophysics Geosystems 7: doi: 10.1029/2005GC001082. issn: 1525-2027.

Garnet-based Lu-Hf geochronology using conventional (HF-HNO3) dissolution methods may be compromised by full or partial digestion of Hf-rich zircon inclusions. This study integrates two complimentary methods to substantially reduce zircon digestion while assuring complete digestion of garnet and sample-spike equilibration. Handpicked garnet fractions are heat treated to >1000¿C in an evacuated silica glass ampoule to anneal zircon inclusions and then dissolved with 12 M HCl at 210¿C and cold 28 M HF. Analyses of heat-treated garnet (and their high-temperature breakdown products orthopyroxene-spinel-quartz) from Gore Mountain, New York, demonstrate the method is capable of complete dissolution of garnet and routinely achieving sample-spike equilibration. Independent analyses of annealed and unannealed zircons dissolved by HCl -- cold HF demonstrate the benefit of heat treatment prior to dissolution. Analyses of zircon-rich garnets from peletic paragneisses of Labrador, Canada, show the potential of this method by returning Lu-Hf ratios commensurate with the degree of heat treatment. Finally, a complementary chemical separation method for Lu and Hf is presented that supports analysis of garnet by MC-ICP-MS.

BACKGROUND DATA FILES

Abstract

Keywords
Geochemistry, Radiogenic isotope geochemistry, Geochronology, Radioisotope geochronology, Mineralogy and Petrology, Pressure-temperature-time paths
Journal
Geochemistry Geophysics Geosystems
Publisher
American Geophysical Union
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