K/Ar and 40Ar/39Ar analyses of meltrock from the Acraman impact structure, Gawler Ranges, South Australia

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Authors:Baldwin, S. L.; McDougall, I.; Williams, G. E.
Author Affiliations:Primary:
Australian National University, Research School of Earth Sciences, Canberra, Australia
University of Adelaide, Australia
Volume Title:Australian Journal of Earth Sciences
Source:Australian Journal of Earth Sciences, 38(3), p.291-298. Publisher: Blackwell, Melbourne, Victoria, Australia. ISSN: 0812-0099
Publication Date:1991
Note:In English. 32 refs.; illus. incl. 4 tables, sketch map
Summary:Two samples of devitrified meltrock from the Acraman site consist primarily of albite (Ab99) microlites in a hematitic devitrified matrix of cloudy K-feldspar (Or97) and quartz, considered to be likely low-T authigenic phases. Conventional K/Ar, 40Ar/39Ar total fusion and integrated apparent ages for both samples agree within analytical uncertainty. Based on apparent ages that are least affected by diffusional loss, a minimum estimate for the age of the meltrock is approx 450 m.y., late Ordovician. This is regarded as a minimum age for the impact event; however, these results do not provide an unequivocal test of the hypothesis that the ejecta blanket in the late Proterozoic Bunyeroo formation and Rodda Beds is uniquely linked to the Acraman impact structure. [R.L.O.]
Subjects:Absolute age; Ar-40/Ar-39; Argon; Dates; Delamerian Orogeny; Impactites; Impacts; Isotopes; K/Ar; Lower Paleozoic; Metamorphic rocks; Noble gases; Ordovician; Paleozoic; Radioactive isotopes; Sampling; Stable isotopes; Upper Ordovician; Australasia; Australia; South Australia; Acraman Structure; Gawler Ranges
Abstract Numbers:93M/3269
Record ID:1994036353
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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