9504167 Hanan Hanan is the PI on this request for 12 months of support for each of two years for postdoctoral Magenheim to prefect the technique of measuring chlorine isotopes in basalts. With this technique Magenheim will determine the effects of assimilation of oceanic crust on chlorine isotopes and evaluate the contribution of hotspots in chlorine isotopes in MORBs. This may be useful in determining the amount of crust that has been recycled into the mantle. It could also be used to determine what part of the subducted crust is returned to the surface in back-arc volcanism. This is an emerging technique that Magenheim was instrumental in developing and which has great potential for telling us about major geological processes. This project is part of the RIDGE initiative (Ridge Interdisciplinary Global Experiment). ***