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Автор Stevenson, J. Mark
Автор Hildebrand, John A.
Автор Zumberge, Mark A.
Автор Fox, Christopher G.
Дата выпуска 1994
dc.description We use seafloor and sea surface gravity data to model density structure along the southern Juan de Fuca Ridge. We determine the average density of the shallow oceanic crust at the ridge using seafloor gravity measurements and then use these data in conjunction with sea surface gravity observations to construct density structure models. Of 63 seafloor gravity measurements obtained, 42 observations were distributed over the 3‐km left‐lateral overlapping rift zone (ORZ), located at latitude 45°03′N, and separating the Juan de Fuca ridge into the Cleft and Vance segments. A 21‐measurement seafloor gravity transect was made perpendicular to the ridge strike at latitude 44°52′N, a region of linear ridge geometry on the Cleft segment. These seafloor gravity measurements, which are sensitive to shallow crustal density variations, were augmented by roughly 800 km of sea surface gravity measurements. Using a bathymetry‐Bouguer anomaly analysis of the seafloor gravity data, we determined the average density of the shallow (roughly upper 2 km) oceanic crust at these two locations to be 2630 kg m<sup>−3</sup>±50 kg m<sup>−3</sup>. Within the uncertainties of the density determinations, there is no difference between the average shallow oceanic crustal density at the linear Cleft segment and at the Cleft‐Vance ORZ. Using the seafloor measurements, we modeled the study area's underlying density to provide constraints on its fine‐scale structure. Localized porosity of up to 17% within the upper 500 m of oceanic crust (layer 2A) provide a possible explanation for the observed gravity anomalies at the Cleft segment. Two‐dimensional density models of the crust underlying the linear Cleft segment (44°52′N) show that no deep source is required to explain the topographical asymmetry observed between the east and west sides of the ridge axis. For the Cleft‐Vance ORZ, three‐dimensional modeling suggests low‐density material between the rifts, in agreement with thickened layer 2A from seismic observations. In contrast, layer 2A variations do not explain the low density inferred at the northern end of the Cleft segment since seismic observations suggest a thin layer 2A. The magmatic activity recently observed in this region may have a distinct, deeper source.
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Копирайт Copyright 1994 by the American Geophysical Union.
Тема Volcanic and Hydrothermal Processes on the Southern Juan de Fuca Ridge
Тема GEODESY AND GRAVITY
Тема Mass balance
Тема Ocean monitoring with geodetic techniques
Тема MAGNETOSPHERIC PHYSICS
Тема Magnetospheric Physics: Gravity and isostasy
Название An ocean bottom gravity study of the southern Juan de Fuca Ridge
Тип article
DOI 10.1029/93JB02076
Electronic ISSN 2156-2202
Print ISSN 0148-0227
Журнал Journal of Geophysical Research: Solid Earth
Том 99
Первая страница 4875
Последняя страница 4888
Выпуск B3
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