|Title:||In situ U‐Pb SIMS (IN‐SIMS) micro‐baddeleyite dating of mafic rocks: Method with examples|
|Authors:||K.R. Chamberlain, A.K. Schmitt, S.M. Swapp, T.M. Harrison, N.Swoboda‐Colberg, W.Bleeker, T.D. Peterson, C.W. Jefferson, and A.K. Khudoley|
|Publication:||Precambrian Research, v. 183, p. 379‐387.|
An in situ U‐Pb SIMS (IN‐SIMS) method to date micro‐baddeleyite crystals as small as 3 µm 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.