HR: 1330h
AN: T12D-0499    [PDF]
TI: Axial Seamount crustal structure inferred from gravity modeling and seismic constraints
AU: * Gilbert, L A
EM: lgilbert@ocean.washington.edu
AF: University of Washington, School of Oceanography Box 357940, Seattle, WA 98195 United States
AB: Axial seamount is a young and active volcano, located at the intersection of the intermediate spreading rate Juan de Fuca Ridge and the Cobb hot spot (46N, 130W). Similar to the adjacent mid-ocean ridge, intermittent lava flows at Axial have built a volcanic edifice. Likewise, rifting has occurred at Axial's summit caldera. The caldera walls of Axial Seamount and the axial valley walls on the Juan de Fuca Ridge are of similar vertical extent. However, Axial stands 700 m higher than the rest of the nearby Juan de Fuca Ridge. This paper presents results from a recent gravity survey and modeling of Axial Seamount's crustal structure. In general, the narrower a feature, the more a traditional slab approximation underestimates bulk density. Initial density determinations of Axial and other seamounts have been low and then refined (e.g. Hildebrand, et al., 1990). A usual practice is to assume some higher density, such as a standard density of 2670 kg/$m^{3}$ and then model features of interest, such as density excesses or deficiencies. Taking topographic effects into consideration, this paper presents a new method of modeling bulk density and application of the method to Axial. Using constraints on crustal density from seismic velocity (West et al., 2001) and new gravity data, this paper presents a model of low bulk density crust. Combining geophysical information from gravity and seismic surveys, results of gravity modeling are presented here, which place new constraints on upper crust porosity and seamount evolution.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3010 Gravity
DE: 3035 Midocean ridge processes
DE: 8015 Local crustal structure
SC: Tectonophysics [T]
MN: 2003 Fall Meeting