Field Work Field Work

Research Programmes - COMPLETED PROJECTS

 

Cameroon Broadband Seismic Experiment

Principle Investigators: Andy Nyblade, Penn State University, Rigobert Tibi and Doug Wiens, Washington University, St. Louis
Collaborators: Charles Tabod, Dept. of Physics, University of Yaounde, Cameroon, Joseph Nnange, Institut De Rescherches Geologiques et Mineres, Yaounde, Cameroon
Sponsor: U.S. National Science Foundation (EAR-Geophysics Division)

In this project, we are critically evaluating models for the origin of volcanic lines without age progression by imaging the seismic structure of the upper mantle beneath the Cameroon Volcanic Line (CVL).  Volcanic lines without age progression cannot be explained by the conventional plume model, and there is no consensus about their origin.  One family of models proposes that hot lines can be explained by added complexities within the plume framework.  These models include lateral transport of plume material, recurrent volcanism due to relict plume material in the mantle along an old plume track, and multiple plume models.  Several investigators have proposed lithospheric tensional cracks to explain simultaneous volcanism along linear features.  Another interesting proposal suggests that hot lines may mark the upwelling limb of small scale convection cells. 

The CVL, a 1500-km long line of Cenozoic volcanic constructs, provides an excellent opportunity to investigate the mantle structure of a hot line.  The CVL is one of the most prominent volcanic lines lacking a discernable age progression, and it is relatively active, with Holocene volcanism along nearly its entire length.  About one-half of the length of the CVL occurs on land, allowing extensive study of upper mantle structure without the expense of seafloor instrumentation. 

To image the seismic structure of the upper mantle beneath the CVL, we carried out beginning in early 2005 a 21-month passive-source broadband seismic experiment in Cameroon.  For the first nine months of the experiment, the seismic network consisted of eight stations.  It was densified to 30 stations.  The broadband seismic data are being analyzed using a number of proven modeling techniques, including body and surface wave tomography, receiver functions, and shear wave splitting.  The results are enabling us to test candidate models for the origin of the CVL and are providing important constraints on the distribution of hot mantle material and the dynamics of the mantle beneath hot lines in general.