Melt-peridotite reaction recorded in the chemistry of spinel and melt inclusions in basalt from 43oN Mid Atlantic Ridge

Compositions of spinel and glassy melt inclusions in primitive olivine (Fo 89.3-91) from basalt AII32 D11-177 at 43°N, Mid-Atlantic Ridge fall into two principal groups. The dominant (~90%) Group-I spinel and melt inclusions have typical MORB compositions. In contrast, Group-II Cr-spinels are strongly enriched in TiO 2 (2.6-4.1 wt%), and Group-II melt inclusions show significant enrichment in SiO 2 (54.6-58.4 wt%), TiO 2, Na 2O and K 2O, whereas their CaO contents (9.3-11.1 wt%) are unusually low. Group-II melts are also remarkable in crystallizing high-Mg orthopyroxene (Mg 91). These mineral associations and melt compositions are unusual for MORB, and are interpreted to result from interaction between MORB-like melts and harzburgitic peridotite at low pressure.