Quantitative laser-induced breakdown spectroscopy of potassium for in-situ geochronology on Mars

• Published in: Spectrochimica Acta Part B: Atomic Spectroscopy
• Main Authors: Stipe, Christopher B., Guevara, Edward, Brown, Jonathan, Rossman, George R.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2012
• Subjects: Laser-induced breakdown spectroscopy; Geochronology; K–Ar dating; Potassium; Mars; Iceland
• Online Access: https://doi.org/10.1016/j.sab.2012.04.010

Laser-inducedbreakdownspectroscopy is explored for the development of an in-situ K–Ar geochronology instrument for Mars. Potassium concentrations in standard basaltic glasses and equivalent rock samples in their natural form are quantified using the potassium doublet at 766.49 and 769.90 nm. Measurement precision varies from 0.5 to 5.5 (% RSD) over the 3.63% to 0.025% potassium by weight for the standard samples, and little additional precision is achieved above 20 laser shots at 5 locations. For the glass standards, the quantification limits are 920 and 66 ppm for non-weighted and weighted calibration methods, respectively. For the basaltic rocks, the quantification limits are 2650 and 328 ppm for the non-weighted and weighted calibration methods, respectively. The heterogeneity of the rock samples leads to larger variations in potassium signal; however, normalizing the potassium peak by base area at 25 locations on the rock improved calibration accuracy. Including only errors in LIBS measurements, estimated age errors for the glasses range from approximately ± 30 Ma for 3000 Ma samples to ± 2 Ma for 100 Ma samples. For the basaltic rocks, the age errors are approximately ± 120 Ma for 3000 Ma samples and ± 8 Ma for 100 Ma samples. © 2012 Elsevier. Received 30 December 2011. Accepted 24 April 2012. Available online 3 May 2012. The authors would like to thank Niels Oskarsson of the Institute of Geosciences at the University of Iceland for sharing the BIR-1 rock sample, Steve Wilson of the U.S.G.S. for the BCR-2 and NKT-1 samples, and Photon Machines, Inc. for the use of their equipment and for thoughtful discussions. This work was funded by the Keck Institute for Space Studies (Award# 9900600 to Caltech), the Seattle University Faculty Sabbatical Program, and the Welch Fund for Undergraduate Research.