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Crustal thickness along the western Galápagos Spreading Center and the compensation of the Galápagos hotspot swell |
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| Authors: | JPablo Canales Garrett Ito Robert S DetrickJohn Sinton |
| Institution: | a Department of Geology and Geophysics, Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, MA 02543, USA b Department of Geology, University of California, Davis, CA, USA c Department of Geology and Geophysics, School of Ocean and Earth Science Technology, University of Hawaii, Honolulu, HI, USA |
| Abstract: | Wide-angle refraction and multichannel reflection seismic data show that oceanic crust along the Galápagos Spreading Center (GSC) between 97°W and 91°25′W thickens by 2.3 km as the Galápagos plume is approached from the west. This crustal thickening can account for ∼52% of the 700 m amplitude of the Galápagos swell. After correcting for changes in crustal thickness, the residual mantle Bouguer gravity anomaly associated with the Galápagos swell shows a minimum of −25 mGal near 92°15′W, the area where the GSC is intersected by the Wolf-Darwin volcanic lineament (WDL). The remaining depth and gravity anomalies indicate an eastward reduction of mantle density, estimated to be most prominent above a compensation depth of 50-100 km. Melting calculations assuming adiabatic, passive mantle upwelling predict the observed crustal thickening to arise from a small increase in mantle potential temperature of ∼30°C. The associated thermal expansion and increase in melt depletion reduce mantle densities, but to a degree that is insufficient to explain the geophysical observations. The largest density anomalies appear at the intersection of the GSC and the WDL. Our results therefore require the existence of compositionally buoyant mantle beneath the GSC near the Galápagos plume. Possible origins of this excess buoyancy include melt retained in the mantle as well as mantle depleted by melting in the upwelling plume beneath the Galápagos Islands that is later transported to the GSC. Our estimate for the buoyancy flux of the Galápagos plume (700 kg s−1) is lower than previous estimates, while the total crustal production rate of the Galápagos plume (5.5 m3s−1) is comparable to that of the Icelandic and Hawaiian plumes. |
| Keywords: | Galapagos Rift crust hot spots swells plumes mid-ocean ridges |
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