Melt–peridotite reaction recorded in the chemistry of spinel and melt inclusions in basalt from 43°N, Mid-Atlantic Ridge

Compositions of spinel and glassy melt inclusions in primitive olivine (Fo89.3–91) 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 TiO2 (2.6–4.1 wt%), and Group-II melt inclusions show significant enrichment in SiO2 (54.6–58.4 wt%), TiO2, Na2O and K2O, 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.