Chlorine in oceanic intraplate basalts: Constraints on mantle sources and recycling processes

Submarine volcanic glass data from different hotspot regions indicate that the Cl inventory and the Cl/K ratios of the mantle are variable. The majority of hotspot lavas have higher Cl/K ratios than depleted mid-oceanic-ridge basalts, consistent with the presence of recycled crustal components in the mantle-plume sources of hotspots. Enriched mantle sources (EM1 and EM2) have relatively low Cl/K ratios, suggesting significant devolatilization of the subducted sedimentary material. Lavas from HIMU-type hotspots (high mu, mu = U-238/Pb-204) have the highest but variable Cl/K, most likely due to the presence of recycled altered oceanic lithosphere in their source. Near-ridge hotspots show correlations between Cl/K ratios and radiogenic isotopes, supporting mixing between plume and depleted upper-mantle material. The variable Cl/K ratios in the HIMU-type magmas and the low Cl/K ratios in the EM-type magmas suggest that the quantity of Cl recycled into the mantle via subduction is not uniform.