40Ar/39Ar studies of deep-sea igneous rocks |
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| Authors: | David Seidemann |
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| Institution: | Department of Geology and Geophysics. Yale University, New Haven, CT 06520, U.S.A. |
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| Abstract: | An attempt to date deep-sea igneous rocks reliably was made using the 40Ar/39Ar dating technique. It was determined that the 40Ar/39Ar incremental release technique could not be used to eliminate the effects of excess radiogenic 40Ar in deep-sea basalts. Excess 40Ar is released throughout the extraction temperature range and cannot be distinguished from 40Ar generated by 40K decay. The problem of the reduction of K-Ar dates associated with sea water alteration of deep-sea igneous rocks could not be resolved using the 40Ar/39Ar technique. Irradiation induced 39Ar loss and/or redistribution in fine-grained and altered igneous rocks results in age spectra that are artifacts of the experimental procedure and only partly reflect the geologic history of the sample. Therefore, caution must be used in attributing significance to age spectra of fine grained and altered deep-sea igneous rocks. Effects of 39Ar recoil are not important for either medium-grained (or coarser) deep-sea rocks or glasses because only a small fraction of the 39Ar recoils to channels of easy diffusion, such as intergranular boundaries or cracks, during the irradiation. |
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