Simple magma supply geometry inferred beneath a segment of the Mid-Atlantic Ridge

Abstract

The petrological characteristics of axial basalts along the global mid-ocean ridge system shed light on the processes of magma supply involved in the formation of ocean crust. Several models of magma supply1–4 predict regular patterns of chemical variation along the strike of mid-ocean ridge axes. Here we present chemical data from closely spaced samples of axial basalts from the Mid-Atlantic Ridge, between the Rio Grande and Moore fracture zones at ∼26° S. This segment of the ridge is far from active hotspots and erupts normal mid-ocean-ridge basalt. The samples show regular patterns of chemical variation along the ridge axis, indicating systematic and correlated differences in depth and extent of partial melting and extent of shallow fractionation. These patterns support the existence of a deep central supply system but preclude along-axis melt migration and the presence of large well-mixed chambers below this segment of the southern Mid-Atlantic Ridge.