Connecting mantle flow below passive margins and intraplate melt generation: an application to the Cameroon Volcanic Line.

Abstract

Mantle plumes are the prevailing explanation for intraplate volcanism, with an age progression along the plume track and a geochemical signature suggesting a core-mantle boundary origin. But these observations do not correlate with some intraplate volcanism examples, requiring alternative
mechanisms to explain these outliers.
One potential example is the Cameroon Volcanic Line (CVL), a large-scale near-linear chain, lacking an age progression with a suspected asthenospheric origin. Edge-driven convection (EDC) is a proposed mechanism and is a process which forms in regions of lithospheric thickness gradients,
such as craton-oceanic boundaries. A self-sustained convection roll may form, bringing material from depth to decompress and melt. However, previous EDC work provides disagreeing results, and shows that melt generation in this process is a complex process. This thesis aims to test a recent hypothesis that an additional ‘fertile layer’, derived from metasomatized material at the base of a craton which has undergone continental collision, could aid in magma genesis and explain why EDC-derived melt is not widespread.
The use of 2D numerical models allows for a parameter sensitivity study on rheological parameters, with an ocean spreading model used to test additional parameters and examine the dynamics of this hypothesized fertile layer, which is used as a proxy for melt generation. Results show that oceanic spreading velocity is the most influential parameter in moving fertile material into the continent-ocean transition (COT), as shear-driven upwelling forms at higher velocities.
When applying the results to the CVL, fertile material moves into the COT, while EDC occurs as well. However, due to the slow spreading rate of the Atlantic, processes such as shear-driven upwelling is not influential. As such, it is proposed that further additional factors must influence
the magmatism, and that modelling of the 3D geological complexities of the CVL is required to gain further insight.