Environmental Engineering Reference
In-Depth Information
proposed, following Li
et al
.(
2009
)andRipley
et al
.(
2003
, 2009), that S was
liberated during interaction with aqueous
fluid that circulated through the aureole.
Firm evidence that sulfur from evaporites is transferred from wall rock to magma
is found in the heavy S isotopic compositions of the sulfide ores of the Norilsk
-
Talnakh deposits (Grinenko,
1985
;Ripley
et al
.,
2003
,
2010
). Sulfur dissolved in
the magma would be degassed on eruption and additional sulfur would be released
during transfer of
fluids to the surface, in part through the vents described by Svensen
et al
.(
2009
). As discussed by Pang
et al
.(
2012
)itisdif
cult to quantify the amount
of SO
2
released by the
fluid transfer mechanism and transferred to the surface.
10.3.1 Calculation of total thermogenic CO
2
and SO
2
release
Is it possible to use these estimates of the amount of CO
2
and SO
2
released by the
mass of sedimentary rock to estimate the total amount of gas that escapes to the
atmosphere during the course of an eruption? To do this requires some knowledge
of the mass of rock that was heated to temperatures above the breakdown tempera-
tures for the minerals involved. Svensen
et al
. (2008) estimated the total volume of
aureoles surrounding intrusions in the sedimentary basin beneath the Siberian
Traps as 800 000 km
3
and proposed that a
fixed proportion (0.5 to 1.5%) of the
organic matter in the original rocks reacted with the gas. On this basis they
calculated that between 9000 and 28 000 Gt of C would be released. Applying
the same approach to the gas released by high-temperature reactions, and suppos-
ing (1) that the rocks in the aureoles comprise 25% carbonate of which 20% breaks
down and (2) that the amount of CO
2
released is 25% of the mass of carbonate,
we calculate that the aureoles yielded an additional 1% of their mass as CO
2
,
a value similar to that from the organic matter.
The proportion of SO
2
is even more dif
cult to quantify, but if we suppose
that evaporite constitutes 10% of the rocks in the aureoles and that these rocks lose
5% of their sulfur to circulating
fluids and then to the atmosphere, then the mass of
SO
2
released is about one-tenth of that of CO
2
, or about 1000 Gt in round numbers.
To conclude, the quantities of thermogenic gases may be comparable to mag-
matic outputs. Reduced gases resulting from interaction with coal or organic matter
are more toxic than the other species and are likely to have had a signi
cant impact
on the biosphere (Iacono-Marziano
et al
.,
2012
).
10.4 Discussion
Sobolev
et al
.
'
s(
2011
) thermomechanical model of interaction of thermochemical
mantle plume with lithosphere, which is also adopted in this paper, predicts
that most of the CO
2
and HCl in the recycled-crust component of the plume is
