caa a22 4500 465791387 CHVBK 20180323112025.0 cr unu---uuuuu 170327e19900601xx s 000 0 eng 10.1007/BF00320969 doi (NATIONALLICENCE)springer-10.1007/BF00320969 An 40Ar/39Ar investigation of the contact effects of a dyke intrusion, Kapuskasing Structural Zone, Ontario [Elektronische Daten] A comparison of laser microprobe and furnace extraction techniques [J. Lee, T. Onstott, J. Hanes] An 40Ar/39Ar study on biotite and hornblende from baked tonalite gneiss adjacent to a 14-m-wide Kapuskasing dyke in the Chapleau Block of the Kapuskasing Structural Zone employed resistance-furnace step-heating, of bulk-mineral separates, single-grain laser step-heating, and laser spot dating of individual grains in thick section. All three methods yielded concordant results for the biotite, indicating that it has been uniformly overprinted at ca. 2.05 Ga. This date is probably a close estimate of the age of the dyke intrusion. The argon data from the hornblende are more difficult to interpret. All three methods suggest that the hornblende was partially overprinted and then affected by a later influx of excess argon from the external environment. Laser spot dates record an apparent age gradient, extending radially outward from ≈2.25 Ga in the grain cores to 2.4-2.7 Ga in the grain rims. Corresponding 37Ar/39Ar values show no systematic variation across the hornblende, although 38Ar/39Ar ratios display a similar pattern to the age distribution, with lower values in the cores than in the rims. The bulk separate and single grain step-heating spectra mimic a volume diffusion Ar-loss profile that would appear to be inconsistent with the laser-spot dates. Three possible interpretations to explain this apparent discrepancy may involve either experimental difficulties, an effective radius of diffusion which is much smaller than the actual grain radius, or an effective radius of diffusion that is of the order of the grain radius. It is clear that for the 40Ar/39Ar dating of samples that have experienced complex geologic histories, it is important to utilize both resistance-furnace and laser techniques. Springer-Verlag, 1990 Lee J. Department of Geological and Geophysical Sciences, Princeton University, 08544, Princeton, NJ, USA aut Onstott T. Department of Geological and Geophysical Sciences, Princeton University, 08544, Princeton, NJ, USA aut Hanes J. Department of Geological Sciences, Queen's University, K7L 3N6, Kingston, Ontario, Canada aut Contributions to Mineralogy and Petrology Springer-Verlag 105/1(1990-06-01), 87-105 0010-7999 105:1<87 1990 105 410 https://doi.org/10.1007/BF00320969 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00320969 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Lee J. Department of Geological and Geophysical Sciences, Princeton University, 08544, Princeton, NJ, USA aut NATIONALLICENCE 700 1- Onstott T. Department of Geological and Geophysical Sciences, Princeton University, 08544, Princeton, NJ, USA aut NATIONALLICENCE 700 1- Hanes J. Department of Geological Sciences, Queen's University, K7L 3N6, Kingston, Ontario, Canada aut NATIONALLICENCE 773 0- Contributions to Mineralogy and Petrology Springer-Verlag 105/1(1990-06-01), 87-105 0010-7999 105:1<87 1990 105 410 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer