Emplacement of regularly spaced volcanic centers in the East African Rift: Melt production or melt extraction?

Regents Of The University Of Idaho, Moscow ID

Investigators

Abstract

Volcanoes and volcanic activity present significant natural hazards, but they are poorly understood. The principal goal of this project is to constrain the proccess that regulate the timing, location, and volumes of volcanism at the Earth's surface, specifically within continental rifts, but more broadly in any region undergoing tectonic extension. Observations at continental rifts, such as the East African Rift, find changes in the style of volcanism from widely, irregularly spaced volcanic centers in areas with small amounts of extension to surprisingly regularly spaced, uniform volcanoes in significantly extended regions. We propose that the changes in volcanic style may be controlled by a balance between the location of faults and fractures near the surface and the variability of magma production beneath the crust, in the Earth's mantle. To determine the role of these two processes and how those roles may change with extension, will will use both numerical simulations and analogue laboratory models to develop mathematical tools that will inform our understanding of the drivers of volcanic activity in these areas. As continental rifts evolve, volcanic centers within rift valleys often develop a characteristic spacing, or wavelength, such as observed in the Red Sea Rift and within the Afar depression, the Main Ethiopian Rift (MER), and the Kenya (Gregory) Rift of the East African Rift System (EARS). The surprisingly regular spacing of the volcanic centers within the EARS is attributed to lithosphere thickness, pre-existing fault systems, and mantle processes. However, little quantitative assessment of these hypotheses has been undertaken and few studies attempt to include the visco-elastic-plastic rheology of the lithosphere. The primary goal of this work is to use data from coupled numerical and laboratory experiments along with observations from the East African Rift System (EARS) to quantitatively assess the contribution of both melt production and melt extraction processes on the distribution of volcanic activity along the three main branches of the actively spreading EARS. We will perform two groups of coupled laboratory and numerical experiments; the first will simulate Rayleigh-Taylor type instabilities within the partially molten mantle (melt production), and the second will simulate the importance of pre-existing fractures and volcano loading on surface volcanism (melt extraction). Numerically, we will use a 3D marker-in-cell, finite difference code to initially match the laboratory experiments and then expand the parameter range beyond that possible in the laboratory. Both sets of experiments will vary rift opening rate, lithospheric thickness, pre-exiting fractures, and volcanic loading. Finally, we will develop predictive scaling laws that relate volcano spacing and volume to the above parameters. These scaling laws will permit the use of surface observations to estimate the relative importance of melt production below the lithosphere versus melt extraction through the lithosphere in both the EARS and other continental rifts.