COMPATIBILITY OF RHENIUM IN GARNET DURING MANTLE MELTING AND MAGMA GENESIS

Measurements of the partitioning of rhenium (Re) between garnet and si licate liquid from 1.5 to 2.0 gigapascals and 1250 degrees to 1350 deg rees C show that Re is compatible in garnet. Oceanic island basalts (O IBs) have lower Re contents than mid-ocean ridge basalt, because garne t-bearing residues of deeper OIB melting will retain Re. Deep-mantle g arnetite or eclogite may harbor the missing Re identified in crust-man tle mass balance calculations. Oceanic crust recycled into the upper m antle at subduction zones will retain high Re/Os (osmium) ratios and b ecome enriched in radiogenic Os-187. Recycled eclogite in a mantle sou rce should be easily traced using Re abundances and Os isotopes.