Figure 6. Sketch showing an interpretive geological cross section of the axial valley floor at a magma-starved, rifted mid-ocean ridge. Moho depth and brittle ductile transition are constrained by seismic refraction (Purdy and Detrick, 1986), gravimetric (Morris and Detrick, 1991), and microseismicity (Toomey et al., 1985; 1988) data from the MARK area. Peridotite screens surrounding the gabbro intrusions may be partially serpentinized. This sketch does not show deformation features, except for a few normal faults in the dikes and lavas. Ductile and brittle shear zones due to the extension of the axial lithosphere may be expected to significantly alter this simplified picture, adding structural discontinuities to the magmatically discontinuous crust represented here. The figure and caption are from figure 4 of Cannat (1993).