Research in Geochemistry - The Chile Ridge

Emily Klein and her graduate students, in collaboration with J. Karsten (U. of Hawaii) have recently completed two mapping and sampling cruises to the Chile Ridge. The Chile Ridge is unique in the current plate configuration because it is the only place where an actively spreading mid-ocean ridge is being subducted, at the Chile Trench. Our geochemical investigation included the analysis of major elements, trace elements and Sr, Nd, Pb and He isotope ratios in the recovered lavas. Lavas recovered closest to the trench were found to display trace element and isotopic systematics unlike any ocean ridge basalts recovered to date which show affinities with lavas from arc or back-arc environments. This refutes the long-held view that ocean ridge and arc magmas are recognizably distinct and calls into question the common practice of using diagnostic trace element variations to establish the provenance of ancient lava suites. The anomalous geochemistry of these samples, coupled with their unusual tectonic setting lead us to speculate, corroborated by our isotopic results, that the two factors may be linked and that ridge subduction may commonly be associated with contamination of the mantle with material derived from the downgoing slab.

Selected Publications

Klein, E.M. and Karsten, J.L. (1995) Ocean ridge basalts with convergent margin geochemical affinities from the southern Chile Ridge, Nature, 374, 52-57.

Sturm, M., Klein, E., Graham, D. and Karsten, J. Age constraints on crustal recycling to the mantle beneath the southern Chile Ridge: He, Sr, Nd and Pb isotope systematics, J. Geophys. Res., 104, 5097-5114, 1999.