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Radiometric dating of young MORB using the 40 Ar‐ 39 Ar incremental heating method
Author(s) -
Duncan R. A.,
Hogan L. G.
Publication year - 1994
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/94gl01375
Subject(s) - radiogenic nuclide , basalt , mantle (geology) , geology , radiometric dating , geochemistry , seafloor spreading , mineralogy , geophysics
Determination of reliable crystallization ages by K‐Ar methods for young (<1 Ma), fresh basalts from the seafloor has been frustrated by several effects. The small amounts of radiogenic 40 Ar developed over these timescales in such low‐K rocks are difficult to resolve from predominantly atmospheric 40 Ar. An additional concern is that mantle‐derived 40 Ar may not be totally outgassed when magmas quench at seafloor hydrostatic pressures. We have developed a successful strategy for partially separating atmospheric from radiogenic 40 Ar in 40 Ar‐ 39 Ar incremental heating experiments on mid‐ocean ridge basalts, from the East Pacific Rise near the Clipperton Fracture Zone. Pre‐heating samples to 400°C removes surficial atmospheric 40 Ar, while subsequent heating at 600°–1000°C produces favorable proportions of radiogenic 40 Ar. Experiments using “zero‐age” glassy and holocrystalline samples show that mantle‐derived 40 Ar is retained only in the outermost few cm of rapidly cooled pillow basalts.