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Open Access Publications from the University of California

Magmatic Architecture of Hotspot Volcanism and Large Igneous Provinces

  • Author(s): Mittal, Tushar
  • Advisor(s): Richards, Mark A
  • et al.
Abstract

Volcanoes are an important part of the Earth system - supplying volatiles (e.g., H$_2$O, CO$_2$, SO$_2$) to the atmosphere, as well as nutrients to the oceans (e.g., Fe, other trace elements), and producing subaerial and submarine topography. In particular, flood basalt events are some of the largest magmatic events in Earth history, with intrusion and eruption of millions of km$^3$ of basaltic magma over a short time period ($\sim$ 1-5 Ma). They are hypothesized to be the result of the emergence of a mantle plume head - which frequently forms the start of a hotspot track. Flood basalt eruptions are associated with significant perturbations to the Earth’s climate and biosphere, including mass extinctions. This link is generally hypothesized to be due to the emission of climatically active volatiles, such as CO$_2$ and SO$_2$. In this thesis, I utilize fluid dynamics and mechanical theory from Earth-science, astrophysical, and engineering sub-disciplines to develop intermediate-complexity models for hotspot volcanism and flood basalt eruptions.

I analyze how the mantle partial melt gets mobilized and transported in the asthenosphere before feeding the crustal magmatic system. For this, I used natural modern day occurrences of where a mantle plume interacts with a nearby mid-ocean ridge e.g., Gal {a}pagos and Iceland. My results suggest that plume-ridge interaction in general, possibly including transport of plume-derived material along ridge axes (e.g., Iceland), may involve transport in high-melt-fraction channels, as opposed to just solid-state mantle flow. With regards to the crustal magmatic system, I analyze how the loss of volatiles from a magma reservoir affects the magmatic overpressure responsible for driving ground deformation and eruptions. I developed a fully coupled poro-thermo-elastic framework to account for both the flow of volatiles as well as associated effects on the stress state of the crust and calculate an analytical solution for spherical geometry.

I utilize these ideas to understand the eruptive dynamics and magmatic architecture of continental flood basalts (CFB). I used a new volume-averaged visco-elastic mechanical model for an ellipsoidal magma reservoir coupled to a dike-shaped erodible conduit to calculate how eruptive fluxes (km$^3$/year) and volumes vary as a function of reservoir geometry and crustal properties for a single magma reservoir, as well as multiple connected reservoirs. I found that the presence of just a few large crustal magma reservoirs is inconsistent with observational constraints. Instead, I propose that CFB eruptions are fed from a number of smaller ($\sim$ 10$^2$ - 10$^{3.5}$ km$^3$) interconnected magma reservoirs present throughout the crust consistent with the paradigm of a trans-crustal magmatic system.

This work has important implications for interpreting a CFB's potential to cause environmental change.

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