Potassium dating

The potassium-argon method is attractive for dating volcanics since it can be applied to rocks of Pleistocene age and older, thus encompassing important periods of general volcanic activity.However it has been found that dates obtained on whole rocks and on included minerals frequently show gross discordances.Rock samples are recorded, marked, sealed and kept free of contamination and excessive heat on the way to the lab.The rock samples are crushed, in clean equipment, to a size that preserves whole grains of the mineral to be dated, then sieved to help concentrate these grains of the target mineral.In order to establish this dating method in this application an attempt has been made to trace the sources of the anomalies.To illustrate these efforts, dating results from a rhyodacite of Mauna Kuwale, Oahu, Hawaii, are reported.The method relies on satisfying some important assumptions: Given careful work in the field and in the lab, these assumptions can be met.The rock sample to be dated must be chosen very carefully.

The site also must be geologically meaningful, clearly related to fossil-bearing rocks or other features that need a good date to join the big story.This mineral sample is then baked gently overnight in a vacuum furnace.These steps help remove as much atmospheric Ar from the sample as possible before making the measurement.K-Ar analyses cost several hundred dollars per sample and take a week or two.A variant of the K-Ar method gives better data by making the overall measurement process simpler.

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