EarthRef.org Digital Archive (ERDA) -- Excess Argon in submarine pillow basalts from Hawaii

Description
Submarine samples of historical age sometimes reveal ages that are much older. For example, lavas that formed pillow basalts less than 10,000 years ago on the northeast ridge of the Kilauea volcano in Hawaii have ages reported up to 43 Myr. As is shown is this diagram, the measured apparent ages increase significantly from the core to the glassy pillow rims. This systematic can be explained by the entrapment of initial or excess argon, inherited from the mantle source that formed these magmas. Improper outgassing under high hydrostatic pressures is normally assumed to be the cause for this entrapment. The outer parts of the pillow basalts show this entrapment more distinctly because they quenched to volcanic glass in the submarine environment and thus had less time to equilibrate with the Argon in the Earth's atmosphere. The inner cores of the pillows took longer to cool and solidify and thus had more time to outgas and equilibrate. Modified after Dalrymple & Moore 1968.

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