NO EVIDENCE FROM MULTICHANNEL REFLECTION DATA FOR A CRUSTAL MAGMA CHAMBER IN THE MARK AREA ON THE MID-ATLANTIC RIDGE

THE role of crustal magma chambers in the construction of oceanic crust along the slowly spreading Mid-Atlantic Ridge (MAR) is still highly disputed1. Some investigators have argued for small, short-lived crustal magma bodies2, whereas others have postulated the presence of permanent reservoirs centred between ridge offsets, which expand and contract in response to a fluctuating magma supply3. Thermal modelling4,5, detailed seismic refraction experiments at several different locations along the MAR6-9, and micro-earthquake10,11 and teleseismic-source mechanism studies12 preclude the existence of large, steady-state magma chambers under the entire MAR rift valley; however, smaller, localized crustal magma bodies could be present, at least intermittently. Here we use multichannel seismic reflection profiles to look for evidence of a crustal magma chamber along the MAR south of the Kane fracture zone, in one of the most magmatically robust and hydro-thermally active areas presently known along the MAR. Although some subbasement reflectors are imaged, we do not see a shallow, large-amplitude, intracrustal reflector that might be associated with a crustal magma body. If a crustal magma chamber was associated with the most recent volcanic episode along this part of the MAR, our results suggest that it was extremely short-lived. © 1990 Nature Publishing Group.