In situ U-Pb SIMS (IN-SIMS) micro-baddeleyite dating of mafic rocks: Method with examples

An in situ U-Pb SIMS (IN-SIMS) method to date micro-baddeleyite crystals as small as 3 mu m is presented with results from three samples that span a variety of ages and geologic settings. The method complements ID-TIMS geochronology by extending the range of dateable crystals to sizes smaller than can be recovered by physical separation. X-ray mapping and BSE imaging are used to locate target grains in thin section, followed by SIMS analysis on a CAMECA ims 1270, using the field aperture in the transfer column to screen out ions from host phases. Internal age precisions for the method are anticipated to range from 0.1% for Precambrian rocks to 3-7% for Phanerozoic rocks. Results establish a 2689 +/- 5 Ma age for mafic dikes in the Wyoming craton, USA, a 1540 +/- 30 Ma age for a subaerial lava flow from the Thelon Basin of northern Canada, and a 457 +/- 34 Ma age for mafic dikes in the platform sequence of southeastern Siberia. The method is ideal for relatively non-destructive dating of small samples such as extraterrestrial rocks and precious terrestrial samples. (C) 2010 Elsevier B.V. All rights reserved.