Environmental Engineering Reference
In-Depth Information
10.2.4 Cl contents
Concentrations of Cl in melt inclusions are minimally affected by degassing and
post-trapping processes and thus should reliably represent magmatic contents.
Chlorine is a highly incompatible element with bulk partitioning between crystal-
that the Cl/K ratio in the melt should not change during melting or crystal
fractionation and should thus represent the ratio of the mantle source.
In Gudchikhinsky and Maslovskoe melt inclusions, chlorine displays signi
cant
excesses (
Figure 10.4
) yielding Cl/K
2
O
0.40, which is several times higher
than for typical MORB and OIB (Koleszar
et al
.,
2009
). Extreme Cl excess
(Cl/K
2
O up to 1.6) has been reported in the highly evolved melt inclusions
Gudchikhinsky suite (
Figure 10.5
), Cl/K
2
O correlates with Nb/U, a proxy of crustal
contamination (Hofmann,
2002
) indicating assimilation of crustal Cl, presumably
from evaporites (Sobolev
et al
.,
2009a
). Likewise, inclusions in clinopyroxene from
the tholeiitic Maslovskoe intrusion are strongly contaminated by continental crust, as
indicated by their low Nb/U. The Cl/K
2
O of these samples is moderate to high and
the source of the Cl is probably also crustal. In contrast, inclusions in sample 4270/13
from the Gudchikhinsky suite are strongly enriched in Cl but possess no indication
of crustal contamination
¼
0.1
-
-
their trace-element ratios are in the mantle range
(
Figures 10.3
and
10.5
). This feature was interpreted to indicate a Cl-rich source in
the mantle plume that yielded the Siberian flood volcanics (Sobolev
et al
.,
2009a
).
Chlorine
-
potassium ratios of alkaline lavas from Ayan River and the Maymecha
-
Kotuy province are similar and relatively low (Cl/K
2
O
¼
0.03,
Figure 10.4
). They
do not show a signi
cant excess over typical mantle values (Koleszar
et al
.,
2009
).
10.2.5 Sulfur contents
The tholeiitic melts are undersaturated in sul
de, which yields a positive correl-
ation between sulfur and K (
Figure 10.4
) and S/Dy
<
200, which is markedly
lower than for MORB and OIB (250
300, Koleszar
et al
.,
2009
). The sulfur
content increases with the concentration of K and other strongly incompatible
elements, approaching high contents in strongly alkaline lavas of the Maymacha
-
-
Kotuy region (Black
et al
.,
2012
). These lavas do not show a correlation between
K and S and are probably sulfide-saturated (
Figure 10.4
).
10.2.6 CO
2
contents
The concentration of carbon in melt inclusions rarely represents original CO
2
contents due to the degassing of magmas and gas-bubble segregation within melt
