BLOCK FAULTING ON GORDA RISE

A study made of Gorda Rise near 41° 15′N with a novel instrument shows that the rift-valley walls have a tilted steplike profile, often with perched, planar sediments. Topography indicates that the steps were formed by block faulting. Distribution of the steps and the character of their tops suggest that they originated in the central 2 or 3 kilometers of the valley floor and were subsequently moved outward, uplifted, and tilted along with their underlying blocks as the sea floor spread. Gorda Rise is considered a slowly spreading part of the oceanic-rise system. Studies of the Mid-Atlantic Ridge report features that may be similar uplifted blocks.