Investigation of the inert gas content of Hawaiian inclusions that exhibit anomalous ages

Abstract

An investigation was made of the inert gas content of Some mineral inclusions from volcanic rocks. Potassium-argon dating of these inclusions has shown that they contain radiogenic argon in excess of that predicted by geochronological methods. Inclusions from Hualalai (Hawaii), Salt Lake Crater (Oahu), dredged from the Puna Rift east of Kilauea (Hawaii), and from Bultfontein, Republic of South Africa were examined. Specimens investigated were dunite nodules and separated grains of olivine, mica, pyroxene, and feldspar. Existing gas extraction and mass spectrographic equipment was modified to allow helium analysis, and also to make the entire gas analysis more rapid and convenient. A technique was developed for the analysis of potassium in olivine by flame photometry. The results from this study indicate that a similarity exists in helium-to-argon ratios found in inclusions from different sources and that the absolute inert gas content varies significantly within individual samples. The excess argon found in the deep ocean tholeiite cautions against the use of similar samples for potassium-argon dating. This study reaffirms the theory that the excess radiogenic argon found in some minerals is held in fluid inclusions and that these minerals do not yield consistent or significant ages.