Figure F6 (continued). C, D. Block uplift of the rift mountains at the ridge-transform corner forms a transverse ridge. Initiation of the block uplift terminates the extension, driving excess cracking, and drastically reduces permeability in the Hole 735B rocks, effectively terminating most circulation of seawater and alteration. Greenschist-facies retrograde alteration continues along the faults on which the block is uplifted, accounting for the greenschist-facies alteration that predominates among dredged gabbros.