Trace element distribution in eclogites and their clinopyroxene/garnet pair; a case study from Soazza (Switzerland)

REE abundances have been determined in six samples of metabasites from the Pennidic Adula nappe in the Soazza area, Mesolcina Valley, Switzerland, ranging from eclogite to symplectitic garnet amphibolite to epidote amphibolite. The REE patterns do not vary significantly and indicate a common origin for these rocks as 'normal' MORB. The two main eclogitic phases, clinopyroxene and garnet, have been analysed for REE and other trace elements. The incorporation of these elements in structural sites of these two minerals is in accordance with an evaluation of site geometry, ionic radius and charge balance, and is therefore dependent on the major element composition of the host minerals. The change in clinopyroxene/garnet partition coefficients for HREE is particularly associated with the T of equilibration of the pair.