Upper mantle velocity structure beneath the Cameroon Volcanic Line region and implications for the formation of mantle hot lines
Abstract
The Cameroon Volcanic Line (CVL) is a 1800km long feature, extending SW-NE from the Gulf of Guinea into Central Africa. Volcanism along the line does not display the typical age progression exhibited by hotspot-related volcanic tracks, leading to speculation over the geodynamic source of this intraplate feature. Numerous models have been proposed to explain the linear nature of the CVL in the absence of age progression, including laterally transported material from a single or multiple plumes, reactivation of the Central African Shear Zone, edge-flow convection associated with the neighboring Congo Craton, and convection driven by lithospheric instabilities at the edge of continental lithosphere. In this study, we calculate Rayleigh wave phase velocities and upper mantle shear wave velocity structure beneath the continental portion of the CVL to investigate the geodynamic source of the CVL. Rayleigh wave phase velocities are measured at periods from 20 to 182 seconds following the two-plane wave methodology developed by Forsyth and Li (2005), and using data from the Cameroon Seismic Experiment, which consists of 32 broadband stations deployed between 2005 and 2007. These phase velocities are then inverted to build a model of shear wave velocity structure in the upper mantle beneath the CVL. We find that phase velocities beneath the CVL are reduced, while velocities beneath the Congo Craton to the south are elevated. This is observed for all periods, but the difference between regions decreases at the longest periods measured in the study. Shear wave velocity structure indicates a tabular low velocity anomaly directly beneath the CVL, extending from 50km to at least 200km depth, with a sharp vertical boundary with the faster velocities beneath the Congo Craton. These observations are most consistent with the edge convection or lithospheric instability models as the source of the continental CVL. Further study of offshore structure will aid in better characterizing the source of the CVL as a whole.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMDI33B2244A
- Keywords:
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- 7270 SEISMOLOGY Tomography;
- 8121 TECTONOPHYSICS Dynamics: convection currents;
- and mantle plumes;
- 8120 TECTONOPHYSICS Dynamics of lithosphere and mantle: general;
- 8415 VOLCANOLOGY Intra-plate processes