The Mid‐Atlantic Ridge at 37 and 45° N: some geophysical and petrological constraints

Abstract

Summary. At present there is a strong conflict between, on the one hand, seismological and thermal models of the Mid‐Atlantic Ridge, which indicate that no large crustal magma chamber can exist, and on the other hand petrological models many of which stress the importance of such a chamber. We review the available geophysical and petrological information from the FAMOUS area and 45° N in an attempt to resolve this conflict and demonstrate that a model (the infinite leek) can be constructed which satisfies all the available seismological, thermal, petrographic, major element and trace‐element information from these two areas. This mode is as follows: mantle rising from depth begins to melt at about 60 km, and rises in equilibrium with its melt to about 15–25 km below the sea surface. At this level melt segregates and rises rapidly to the base of the crust. Magma injection above this takes place by a process of crack propagation, or by the development of a narrow vertical magma chamber, but no large crustal chamber is present. This model successfully explains the marked petrographic zonation of the floor of the median valley (Hekinian, Moore & Bryan). Copyright © 1978, Wiley Blackwell. All rights reserved