Seismic evidence for uniform crustal accretion along slow-spreading ridges in the equatorial Atlantic Ocean

The crustal accretion along mid-ocean ridges is known to be spreading-rate dependent. Along fast-spreading ridges, two-dimensional sheet-like mantle upwelling creates relatively uniform crust. In contrast, the crust formed along slow-spreading ridges shows large along-axis thickness variations with thicker crust at segment centres, which is hypothesised to be due a three-dimensional plume-like mantle upwelling or due to focused melt migration to segment centres. Using wide-angle seismic data acquired from the equatorial Atlantic Ocean, here we show that the crustal thickness is nearly uniform (similar to 5.5 km) across five crustal segments for crust formed at the slow-spreading Mid-Atlantic Ridge with age varying from 8 to 70 Ma. The crustal velocities indicate that this crust is predominantly of magmatic origin. We suggest that this uniform magmatic crustal accretion is due to a two-dimensional sheet-like mantle upwelling facilitated by the long-offset transform faults in the equatorial Atlantic region and the presence of a high concentration of volatiles in the primitive melt in the mantle.

Automated summary

Using wide-angle seismic data from the equatorial Atlantic Ocean, this study shows that the crustal thickness is nearly uniform across five crustal segments formed at the slow-spreading Mid-Atlantic Ridge. The crust is predominantly of magmatic origin, likely due to a two-dimensional sheet-like mantle upwelling facilitated by long-offset transform faults and a high concentration of volatiles in the mantle.