| Over Earth history volcanic vents have played a crucial role in delivering important materials
to the surface, sculpting the composition of the Earth’s crust and atmosphere. Vents (or
diatremes) occur at the Earth’s surface and ocean floor, effectively marking the interface
between the solid Earth and ocean-atmosphere systems. Vents are capable of discharging
enormous volumes of volcanic detritus to the Earth system, and play a major role in
modulating rates of gas (e.g.CO2) and aerosol release to our atmosphere. There have been
periods during Earth history when unusually intensive venting processes are thought to have
significantly perturbed the carbon cycle and climate. There have been other periods when
vent complexes have been the locus of intense eruptions that involved diamond ascent
from Earth’s deep interior. However, there is no general consensus on the triggering
mechanism of these unusually energetic and deep-sourced eruptions; existing models
include phreatomagmatism, exsolution of magmatic volatiles, ‘Verneshot’ events
and meteorite impacts. In addition, what remains uncertain is the dynamics of gas
transfer through vents over time, and how these are controlled by the geometry,
composition and permeability of their constituent deposits. This talk will describe
the architecture and textural attributes of vent-fills over a range of compositions
(kimberlitic, alkali basaltic and lamproitic). The examples described are from particularly
well-exposed and accessible sites across southern Africa (e.g. Jwaneng and Orapa,
Botswana), northern Europe (e.g. East Fife, Scotland) and India (Majhgawan, Madhya
Pradesh), all of which offer exceptional insights into the deep plumbing systems of
alkaline volcanic complexes. These data and models have important implications for
assessing the potential amounts of gas released over the lifetime of a volcanic system –
a fundamental pursuit in determining feedbacks between volcanism and climate
during specific periods in Earth history when vent complexes were widespread. |