Abstract
Earth's core-mantle boundary is home to a patchwork collection of thin ultralow-velocity zones (ULVZ) on the mantle side of the boundary. Core-diffracted and reflected seismic waves indicate that ULVZ patches display a strong topographic variability. We model the circulation within the ULVZ, excited by sweeping motion in the lower mantle. Our results indicate that the ULVZ topography is strongly correlated with its viscosity. Using a gravity current model, we establish a scaling relationship between the maximum topography and ULVZ viscosity. The observed range of ULVZ topography (5-20km) in the Pacific indicates that the average viscosity of the ULVZ in this region is approximately 6.8×1019Pas, about 2 orders of magnitude weaker than the surrounding lower mantle. The inferred viscosity also indicates that the ULVZ is partially molten but not disaggregated.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 382-386 |
| Number of pages | 5 |
| Journal | Earth and Planetary Science Letters |
| Volume | 299 |
| Issue number | 3-4 |
| DOIs | |
| State | Published - Nov 1 2010 |
Bibliographical note
Funding Information:This research was supported by NSF grant EAR 0911094 . Helpful comments and suggestions from CIDER 2008 participants and Marco Via are greatly appreciated. We also acknowledge the insightful comments from John Hernlund, Yanick Ricard and two anonymous reviewers.
Keywords
- Core-mantle boundary
- Gravity current
- ULVZ
- Viscosity