Mantle compositional control on the extent of mantle melting, crust production, gravity anomaly, ridge morphology, and ridge segmentation: a case study at the Mid-Atlantic Ridge 33–35°N

Abstract

Abstract Mantle temperature variation and plate spreading rate variation have been considered to be the two fundamental variables that determine the extent of mantle melting and ocean crust production. Along the length of a ∼200 km portion of the Mid-Atlantic Ridge (MAR) between the Oceanographer (35°N) and Hayes (33°N) transforms, the mantle potential temperature is the same, the plate spreading rate is the same, but the extent of mantle melting and crustal production vary drastically. In addition to the typical crustal thickness variation on ridge segment scales at the MAR, i.e. thicker at segment centers and thinner at segment ends, there exist between-segment differences. For example, the ∼90 km long segment OH-1 is magmatically robust with a central topographic high, thick crust, and a large negative gravity anomaly whereas the ∼45 km long segment OH-3 is magmatically starved with a deep rift valley, thin crust and a weak negative gravity anomaly. We demonstrate that the observed differences in the extent of mantle melting, melt production and crustal mass between segments OH-1 and OH-3 are ultimately controlled by their fertile mantle source compositional difference as reflected by the lava compositional differences between the two segments: >70% of OH-1 samples studied (N=57) are enriched MORB with [La/Sm]N>1, but >85% of OH-3 samples studied (N=42) are depleted MORB with [La/Sm]N