Major and trace element profiles of clinopyroxene grains in oceanic gabbros from ODP Hole 735B have been investigated by a combined in situ analytical study with ion probe, and electron microprobe. In contrast to the homogeneous major element compositions, trace elements (REE, Y, Cr, Sr, and Zr) show continuous core to rim zoning profiles. The observed trace element systematics in clinopyroxene cannot be explained by a simple diffusive exchange between melts and gabbros along grain boundaries. A simultaneous modification of the melt composition is required to generate the zoning, although Rayleigh fractional crystallization modelling could mimic the general shape of the profiles. Simultaneous metasomatism between the cumulate crystal and the porous melt during crystal accumulation is the most likely process to explain the zoning. Deformation during solidification of the crystal mush could have caused squeezing out of the incompatible element enriched residual melts (interstitial liquid). Migration of the melt along grain boundaries might carry these melt out of the system. This process named as synkinematic differentiation or differentiation by deformation (Natland and Dick, 2001, doi:10.1016/S0377-0273(01)00211-6) may act as an important magma evolution mechanism in the oceanic crust, at least at slow-spreading ridges.

Numbers of ions were calculated on the basis of six O, and assume two cations on T site, Al (IV) and Al (VI) denote the Al in T and M1 site, respectively

Supplement to: Gao, Yongjun; Hoefs, Jochen; Hellebrand, Eric; von der Hand, Anette; Snow, Jonathan E (2007): Trace element zoning in pyroxenes from ODP Hole 735B gabbros: diffusive exchange or synkinematic crystal fractionation? Contributions to Mineralogy and Petrology, 153, 429-442