Sallares V., Charvis Philippe, Flueh E. R., Bialas J. (2005). Seismic structure of the Carnegie ridge and the nature of the Galapagos hotspot. Geophysical Journal International, 161 (3), p. 763-788. ISSN 0956-540X.
Titre du document
Seismic structure of the Carnegie ridge and the nature of the Galapagos hotspot
Sallares V., Charvis Philippe, Flueh E. R., Bialas J.
Source
Geophysical Journal International, 2005,
161 (3), p. 763-788 ISSN 0956-540X
The Galapagos volcanic province (GVP) includes several aseismic ridges resulting from the interaction between the Galapagos hotspot (GHS) and the Cocos-Nazca spreading centre (CNSC). The most prominent are the Cocos, Carnegie and Malpelo ridges. In this work, we investigate the seismic structure of the Carnegie ridge along two profiles acquired during the South American Lithospheric Transects Across Volcanic Ridges (SALIERI) 2001 experiment. Maximum crustal thickness is similar to 19 km in the central Carnegie profile, located at similar to 85 degrees W over a 19-20 Myr old oceanic crust, and only similar to 13 km in the eastern Carnegie profile, located at similar to 82 degrees W over a 11-12 Myr old oceanic crust. The crustal velocity models are subsequently compared with those obtained in a previous work along three other profiles over the Cocos and Malpelo ridges, two of which are located at the conjugate positions of the Carnegie ones. Oceanic layer 2 thickness is quite uniform along the five profiles regardless of the total crustal thickness variations, hence crustal thickening is mainly accommodated by layer 3. Lower crustal velocities are systematically lower where the crust is thicker, thus contrary to what would be expected from melting of a hotter than normal mantle. The velocity-derived crustal density models account for the gravity and depth anomalies considering uniform and normal mantle E densities (3300 kg m(-3)), which confirms that velocity models are consistent with gravity and topography data, and indicates that the ridges are isostatically compensated at the base of the crust. Finally, a two-dimensional (2-D) steady-state mantle melting model is developed and used to illustrate that the crust of the ridges does not seem to be the product of anomalous mantle temperatures, even if hydrous melting coupled with vigorous subsolidus upwelling is considered in the model. In contrast, we show that upwelling of a normal temperature but fertile mantle source that may result from recycling of oceanic crust prior to melting, accounts more easily for the estimated seismic structure as well as for isotopic, trace element and major element patterns of the GVP basalts.
