Magma distribution across ridge-axis discontinuities on the East Pacific Rise from multichannel seismic images

Abstract

Detailed studies of the morphology of the East Pacific Rise axis have shown that its linearity is disrupted by many small but distinct non-transform offsets, including overlapping spreading centres (OSCs) and deviations from axial linearity (devals), which display variable geochemical signals1–9. Using multichannel seismic reflection profiling, we have mapped the distribution of a bright, shallow reflector that Detrick et al.10 have associated with an axial magma chamber. We have found that it is neither continuous across the 9°03' OSC6, nor separated into two parallel bodies2, and that its lateral offset does not conform to that of the topographic offset associated with the 9° 17' deval. These observations provide important insight into a causative relationship between morphological and petrological segmentation in this region of the East Pacific Rise, and we speculate that the discontinuities may be the morphological response to fluctuations in the spatial pattern of magma delivery.