Investigation of High Precision Os Measurements on Lavas From Iceland and the Austral Islands

Northwestern University, Evanston IL

Investigators

Abstract

Brandon EAR-0000908 Recent work has shown that coupled enrichments in 186Os/188Os and 187Os/188Os for some Hawaiian lavas is consistent with the hypothesis of core-mantle interaction within the Hawaiian plume source. If this is correct, then these are perhaps the most robust geochemical data to date, that show some plumes originate in the D" region of the deepest part of the mantle. Alternatively, these data could instead be consistent with entrainment of ancient recycled crust provided certain conditions hold. As a further test of these hypotheses, high precision 186Os/188Os and 187Os/188Os data for lavas from Iceland and the Austral Islands will be obtained. These two suites are ideal for subsequent testing of the roles of core-mantle interaction and ancient crustal recycling in generating radiogenic Os compositions in plumes because of the following. Seismic evidence suggests that Iceland plume originates from D" just above the core-mantle boundary. It is a high 3He hotspot with active volcanism in a relatively fixed position for at least 60 million years. Taken together, these observations support a deep mantle origin for the Iceland plume where core-mantle interaction may occur. Some Austral Islands lavas have 187Os/188Os that are too high to be produced by reasonable models for entrainment of outer core into plume sources. Therefore, the these lavas can be used to make a rigorous test of the role of ancient crustal recycling for potentially producing radiogenic 186Os/188Os in plume-derived lavas. The ultimate result of this study will be to provide a greater understanding of the significance of chemical exchange between the outer core and plume sources, the role of crustal recycling to produce Os isotopic signatures in plumes, and the use of coupled enrichments of 186Os/188Os and 187Os/188Os to constrain the depths of origin of plumes.