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Structure of the Northern Symmetrical Segment of the Juan de Fuca Ridge
Authors:G L Christeson  G M Purdy  K M M Rohr
Institution:(1) WHOI/MIT Joint Program in Oceanography, Woods Hole Oceanographic Institution, 02543 Woods Hole, MA, USA;(2) Department of Geology and Geophysics, Woods Hole Oceanographic Institution, 02543 Woods Hole, MA, USA;(3) Pacific Geoscience Centre, P.O. Box 6000, V8L 4B2 Sidney, British Columbia, Canada
Abstract:A seismic refraction profile was shot along the axis of the Northern Symmetrical Segment of the Juan de Fuca Ridge system. Three models of the along-axis crustal structure fit the observed data equally well. One model includes a low-velocity zone, the top of which is at a depth below the seafloor of approximately 3 km, that is continuous along-axis for at least 30 km. A second model includes a low-Q layer, the top of which is also at a depth of approximately 3 km below the seafloor and is continuous along-axis for at least 30 km. Both the low-Q layer and low-velocity zone can be explained geologically by a region of elevated temperatures. The third model is characterized by a homogeneous seismic layer 3. All models contain an ~1 km s–1 discontinuity at the seismic layer 2/3 boundary; a wide-angle reflection from this boundary is seen on all record sections. Kappel and Ryan (1986) had previously proposed that the Northern Symmetrical Segment was in a stage of volcanic inactivity, and this theory is supported by the seismic observations. Two-dimensional modelling of travel times to ocean bottom hydrophone instruments shows that the amplitude variations in the along-axis depth to intracrustal seismic layers (a few hundred meters) is on the order of the lateral changes in topographic relief. It is suggested that the crustal emplacement processes reflect the deeper style of 3-D mantle upwelling beneath the ridge.
Keywords:Mid-Ocean Ridge  Juan de Fuca Ridge  seismic refraction
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