Argon argon dating problems
In the minerals from Mauna Kuwale sporadic occurrences of inclusions have been noted in biotites and hornblendes, and crushing of the mineral releases the excess radiogenic argon.
The determination of the age of such a material would give an old age, and thus account for the anomalies found.
As part of his seminal work on excess argon, Dalrymple (1969) dated 26 historical lava flows with K-Ar to determine whether excess argon was present.
Of the 26 lava flows that were sampled and analyzed, 18 of them gave expected results. Eight rocks yielded unrealistic dates, which were either too old because of the presence of excess 40Ar (5 of them) or too young (negative ages) because of the presence of excess 36Ar (3 of them).
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 quantity of potassium in a rock or mineral is variable proportional to the amount of silica present.