ATMOSPHERIC CONTAMINATION - A POSSIBLE SOURCE FOR HEAVY NOBLE-GASES IN BASALTS FROM LOIHI SEAMOUNT, HAWAII

Re‐evaluation of available noble gas data obtained from the glassy rims of basalts from Loihi Seamount, Hawaii, shows that contamination of magmas prior to eruption, by addition of a significant component of atmosphere‐derived heavy noble gases, is a plausible explanation for the observed atmosphere‐like isotopic compositions of Ne, Ar, Kr, and Xe. The most likely source for the atmospheric component is interaction of the magma with seawater carrying dissolved atmosphere‐derived noble gases. The possibility of a significant atmospheric component in Loihi samples suggests that the observed heavy noble gas compositions may not be representative of the mantle source of Loihi magmas. While leaving open the question of the noble gas composition in the source region, atmospheric contamination provides a valid alternative to the interpretation that the mantle source region of Loihi magmas has an atmosphere‐like noble gas composition. Copyright 1990 by the American Geophysical Union.