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Paper No. 388-19
Presentation Time: 9:00 AM-6:30 PM
AN ANALYSIS OF VARIATION IN ABYSSAL HILL GEOMORPHOLOGY IN THE SOUTH ATLANTIC OCEAN
Abyssal hills, formed on oceanic crust by mid-ocean ridge volcanic and faulting processes, are the most abundant topographic feature on the seafloor. Numerous studies have shown that abyssal hill scaling parameters correlate with mid-ocean ridge spreading rate and variations in magma supply; these correlations have been attributed primarily to the response of oceanic crust to faulting and diking. However, other studies correlate timescales of eustatic sea level fluctuations, attributed to global climate cycles, with peaks in abyssal hill spectra. These studies assert that sea-level influence on volcanic output at mid-ocean ridges is controlling the primary morphology of abyssal hills, contrary to the conclusions of the prior studies. Multibeam bathymetry data acquired on the CREST expedition (Crustal Reflectivity Experiment Southern Transect) provides the unique opportunity to analyze a 1500 km (0-70 Ma) continuous transect of the South American plate oceanic crust. Employing the stochastic parameter estimation methodology of Goff and Jordan (1988), we examine the relationship between the morphology of abyssal hills, properties of the South Atlantic oceanic crust, and climate factors, such as orbital eccentricity. In particular, the role of the climate-controlled volcanic construct hypothesis is applied within the framework of the more traditional understanding of abyssal hill formation. The CREST data suggests anomalously low abyssal hill rms heights in this spreading corridor—a mean of ~100 m compared to ~200 m calculated for the Southern Mid-Atlantic Ridge (Goff et al., 1997)—as well as observed characteristic widths (2-11 km), translating to abyssal hill formation time scales of 103-551 Myrs at spreading rates of 13-32 mm/yr. Such large and variable timescales cannot be correlated to orbital frequencies. Although globally there is an inverse relationship between abyssal hill rms height and spreading rate, results in our study area demonstrate a more complex relationship between these parameters, suggesting strong local variability in tectonic and/or volcanic influences on abyssal hill formation. This study provides a deeper exploration of contemporary abyssal hill formation hypotheses, as well as a more comprehensive understanding of the relationship between variables influencing their morphology.