QUANTITATIVE-ANALYSIS OF ABYSSAL HILLS IN THE ATLANTIC-OCEAN - A CORRELATION BETWEEN INFERRED CRUSTAL THICKNESS AND EXTENSIONAL FAULTING

A recent cruise to the Office of Naval Research Atlantic Natural Labor atory obtained similar to 100% Hydrosweep bathymetric coverage, >200% Hawaii MR1 (HMR1) side scan coverage, gravity and magnetics over an ar ea spanning three ridge segments along axis (similar to 25 degrees 25' N to similar to 27 degrees 10'N), and crustal ages from 0 to 26-30 Ma (similar to 400 km) on the west flank of the Mid-Atlantic Ridge. This data set represents a first opportunity for an extensive regional anal ysis of abyssal hill morphology created at a slow spreading ridge. The primary purpose of this work is to investigate the relationship betwe en abyssal hill morphology and the properties of the ridge crest at wh ich they were formed. We apply the method of Goff and Jordan [1988] fo r the estimation of two-dimensional statistical properties of abyssal hill morphology from the gridded Hydrosweep bathymetry. Important abys sal hill parameters derived from this analysis include root-mean-squar e (rms) height, characteristic width, and plan view aspect ratio. The analysis is partitioned into two substudies: (1) analysis of near-axis (<7 Ma) abyssal hills for each of the three segments and (2) analysis of temporal variations (similar to 2-29 Ma) in abyssal hill morpholog y along the run of the south segment. The results of this analysis are compared and correlated with analysis of the gravity data and prelimi nary determination of faulting characteristics based on HMR1 side scan data. Principal results of this study are: (1) Abyssal hill morpholog y within the study region is strongly influenced by the inside-outside corner geometry of the mid-ocean ridge segments; abyssal hills origin ating at inside corners have larger rms height and characteristic widt h and smaller plan view aspect ratio than those originating at outside corners. (2) The residual mantle Bouguer gravity anomaly is positivel y correlated with intersegment and along-flow-line variations in rms h eight and characteristic width, and it is negatively correlated with p lan view aspect ratio. From this result, we infer that lower-relief, n arrower, and more elongated abyssal hills are produced when the crust being generated is thicker. (3) Intersegment variations in near-axis r ms height negatively correlate with average fault density as determine d from analysis of HMR1 side scan imagery.