The crustal structure of Carnegie Ridge inferred from gravity and seismic data

Date

2005-08-29

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Publisher

Texas A&M University

Abstract

Carnegie Ridge is a prominent bathymetric feature of the Gal??pagos Volcanic Province originated from the interaction of the Gal??pagos Hot Spot and the Cocos - Nazca Spreading Center. Our present knowledge regarding its crustal structure is limited to ridge transects along which wide-angle refraction seismic experiments have been conducted. In this study, the long-wavelength crustal structure of Carnegie Ridge between ~81?? W and 89?? W was determined by employing 2-D forward gravity modeling as the primary analytical technique. Model structures were built by assuming Airy isostasy and crustal layers of constant density. The geometry and density structure of the thickened oceanic crust beneath the ridge was constrained based on available seismic velocity models. Except for regions near the Ecuador Trench, the gravity modeling solution along the different transects examined in this study accounted adequately for the observed gravity anomaly field over the ridge. Crustal overthickening mainly accommodated in oceanic layer 3 and the asymmetry of the crustal root geometry characterize the estimated long-wavelength crustal structure. The asymmetry on eastern Carnegie Ridge is thought to be related to a ridge-related rifting whereas the origin and nature of that estimated on western Carnegie Ridge remain uncertain. Crustal volume fluxes were calculated at Carnegie Ridge and the Gal??pagos Archipelago, and at Cocos Ridge in order to explain the along-axis variations of the estimated crustal thickness. Along-axis crustal thickness variations on eastern Carnegie Ridge, and the formation of its bathymetric saddle were found to be related to the decline in the total volume output of the Gal??pagos Hot Spot. According to my results, this decay started soon after the spreading center shifted to the south of the hotspot (i.e., ~15 Ma) and continued for ~4.5 m.y. Since ~10 Ma the volume output of the GHS started to increase again, giving rise to the formation of western Carnegie Ridge and the Gal??pagos Archipelago. This increase continued until ~2 Ma, when the hotspot intensity started a new decrease that continues until the present time.

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