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Constraints on Dynamic Topography from Asymmetric Subsidence Across the Mid-Ocean Ridges
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|Title:||Constraints on Dynamic Topography from Asymmetric Subsidence Across the Mid-Ocean Ridges|
|Date Issued:||Aug 2016|
|Publisher:||[Honolulu] : [University of Hawaii at Manoa], [August 2016]|
|Abstract:||Stresses from mantle convection should deflect Earth’s surface vertically, with important implications for continental dynamics and sea-level change. However, dynamic topography is difficult to observe directly because it is obscured by isostatic topography. As a result, amplitudes of long wavelength dynamic topography inferred from indirect observations tend to differ significantly from model predictions. In this study we attempt to resolve this discrepancy by analyzing asymmetries in seafloor bathymetry across mid- ocean ridges, which in the absence of dynamic topography should otherwise be symmetrical. We identify dynamic deflections of the seafloor by focusing on seafloor unperturbed by volcanism on both sides the Mid- Atlantic Ridge and the East Pacific Rise. Across both ridges the magnitude of the subsidence is greater on the South American side of the ridge, consistent with patterns predicted by numerical models of long-wavelength dynamic topography. To constrain the amplitude of dynamic topography, we compare bathymetric profiles across both ridges after correcting bathymetry for several different models of dynamic topography with varying amplitudes and spatial patterns. We found that the observed asymmetry in both ridge systems is best explained if bathymetry is deflected by dynamic topography with long-wavelength amplitudes of about 300- 500 m, which is about half of the amplitudes predicted by recent mantle flow models. This reduction in amplitude implies that long-wavelength mantle flow is driven primarily by active downwelling associated with subducted slabs in the lower mantle, and less so by active upwelling. This pattern of mantle dynamics is consistent with recent thermochemical convection models of mantle flow.|
|Description:||M.S. University of Hawaii at Manoa 2016.|
Includes bibliographical references.
|Appears in Collections:||
M.S. - Geology and Geophysics|
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