The magmatic architecture of continental flood basalts II : A new
conceptual model
Abstract
Continental flood basalts intruded and erupted millions of km$^3$
of magma over $\sim$ 1-5 Ma. Previous work proposed the
presence of large ($>$ 10$^5$-10$^6$
km$^3$) crustal magma reservoirs to feed these eruptions. However,
in Paper I, we illustrated that this model is inconsistent with
observations, by combining eruptive rate constraints with geochemical
and geophysical observations from the Deccan Traps and other CFBs. Here,
we use a new mechanical magma reservoir model to calculate the variation
of eruptive fluxes (km$^3$/year) and volumes for different magmatic
architectures. We find that a single magma reservoir cannot explain the
eruptive rate and duration constraints for CFBs. Using a 1D thermal
model and characteristic timescales for magma reservoirs, we conclude
that CFB eruptions were likely fed by a number of interconnected
small-medium ($\sim$ 10$^2$ - 10$^{3.5}$
km$^3$) magma reservoirs. It is unlikely that each individual magma
reservoir participated in every eruption, thus permitting the occasional
formation of large xenocrysts (e.g., megacrystic plagioclase). This
magmatic architecture permits (a) large volume eruptive episodes with
10s to 100s of years duration, and (b) relatively short time-periods
separating eruptive episodes (1000s of years) since multiple mechanisms
can trigger eruptions (via magma recharge or volatile exsolution, as
opposed to long term (10$^5$ - 10$^6$ year) accumulation of
buoyancy overpressure); (c) lack of large upper-crustal intrusive bodies
in various geophysical datasets. Our new proposed magmatic architecture
has significant implications for the tempo of CFB volatile release
(CO$_2$ and SO$_2$), potentially helping explain the pre-K-Pg
warming associated with Deccan Traps.