The morphological characteristics and geological implications of prime segments and axial volcanoes along the East Pacific Rise

The global mid-ocean ridge system is physically partitioned at a number of scales; at times this geomorphic segmentation correlates to geophysically, geochemically, hydrothermally, or otherwise-defined portions of the ridge. As the dominant processes acting along the divergent plate-boundaries are tectonism and magmatism, we are interested in any geomorphic indicators to these processes. Using compiled, high-resolution bathymetric data from 19 cruises between 16$\sp\circ$N and 23$\sp\circ$S along 4000 kilometers of the fast-spreading (80-160 mm/yr) East Pacific Rise (EPR), we compile an inventory of morphological characteristics for almost 200 ridge-axis discontinuities, and for 3 scales of ridge segments. This analysis has located and characterized 72 Prime Segments, 189 Axial Volcanoes and 145 Eruptive Centers along the fast-spreading plate-boundary of the East Pacific Rise. Prime Segments are axial volcanic complexes that range in length from 7-285km with an average of 67km, are offset from neighboring Prime Segments by 0.5km or more, and are comprised of an average of three elongate Axial Volcanoes. The magmatic and tectonic processes of the ridge appear to be organized at the scale of the Prime Segment--most are in the same phase of rifting or volcanism throughout, independent of their adjacent Prime Segments. Axial Volcanoes are local topographic peaks of 10 meters or more in height located along the Prime Segment, and are separated from each other by topographic lows and other minor morphological changes (strike, width, slope). They range in length from 4-78km, with an average of 24km, and contain one active and possibly other inactive Volcanic Centers. Volcanic Centers are a region within an Axial Volcano, at its peak, and are defined by the length of ridge having the same strike, slope, and axial morphology (axial high, rifted high, transitional high) seen at the peak, and are the site of the most recent extrusive volcanism along the Axial Volcano. They have an average length of 11km with very little variability, and we infer that these features may represent the fundamental unit of accretion along the EPR