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Abstract

Large igneous provinces (LIPs) are known for their rapid production of enormous volumes of magma (up to several million cubic kilometres in less than a million years), for marked thinning of the lithosphere, often ending with a continental break-up, and for their links to global environmental catastrophes. Despite the importance of LIPs, controversy surrounds even the basic idea that they form through melting in the heads of thermal mantle plumes. The Permo-Triassic Siberian Traps--the type example and the largest continental LIP--is located on thick cratonic lithosphere and was synchronous with the largest known mass-extinction event. However, there is no evidence of pre-magmatic uplift or of a large lithospheric stretching, as predicted above a plume head. Moreover, estimates of magmatic CO(2) degassing from the Siberian Traps are considered insufficient to trigger climatic crises, leading to the hypothesis that the release of thermogenic gases from the sediment pile caused the mass extinction. Here we present petrological evidence for a large amount (15 wt%) of dense recycled oceanic crust in the head of the plume and develop a thermomechanical model that predicts no pre-magmatic uplift and requires no lithospheric extension. The model implies extensive plume melting and heterogeneous erosion of the thick cratonic lithosphere over the course of a few hundred thousand years. The model suggests that massive degassing of CO(2) and HCl, mostly from the recycled crust in the plume head, could alone trigger a mass extinction and predicts it happening before the main volcanic phase, in agreement with stratigraphic and geochronological data for the Siberian Traps and other LIPs.
LETTER
doi:10.1038/nature10385
Linking mantle plumes, large igneous provinces and
environmental catastrophes
Stephan V. Sobolev
1,2
*, Alexander V. Sobolev
3,4,5
*, Dmitry V. Kuzmin
4,6
, Nadezhda A. Krivolutskaya
5
, Alexey G. Petrunin
1,2
,
Nicholas T. Arndt
3
, Viktor A. Radko
7
& Yuri R. Vasiliev
6
Large igneous provinces (LIPs) are known for their rapid produc-
tion of enormous volumes of magma (up to several million cubic
kilometres in less than a million years)
1
, for marked thinning of the
lithosphere
2,3
, often ending with a continental break-up, and for
their links to global environmental catastrophes
4,5
. Despite the
importance of LIPs, controversy surrounds even the basic idea that
they form through melting in the heads of thermal mantle
plumes
2,3,6–10
. The Permo-Triassic Siberian Traps
11
—the type
example and the largest continental LIP
1,12
—is located on thick
cratonic lithosphere
1,12
and was synchronous with the largest
known mass-extinction event
1
. However, there is no evidence of
pre-magmatic uplift or of a large lithospheric stretching
7
, as pre-
dicted above a plume head
2,6,9
. Moreover, estimates of magmatic
CO
2
degassing from the Siberian Traps are considered insufficient
to trigger climatic crises
13–15
, leading to the hypothesis that the
release of thermogenic gases from the sediment pile caused the
mass extinction
15,16
. Here we present petrological evidence for a
large amount (15 wt%) of dense recycled oceanic crust in the head
of the plume and develop a thermomechanical model that predicts
no pre-magmatic uplift and requires no lithospheric extension.
The model implies extensive plume melting and heterogeneous
erosion of the thick cratonic lithosphere over the course of a few
hundred thousand years. The model suggests that massive degass-
ing of CO
2
and HCl, mostly from the recycled crust in the plume
head, could alone trigger a mass extinction and predicts it happen-
ing before the main volcanic phase, in agreement with stratigraphic
and geochronological data for the Siberian Traps and other LIPs
5
.
Petrological studies of Siberian Traps and associated alkaline rocks
reveal high temperatures (1,600–1,650 uC)
14,17
in their mantle sources.
Olivine compositions in samples from lower units of the Norilsk lava
section provide evidence that the mantle source of the Siberian Traps
wasunusually richin ancientrecycled oceanic crust
14
, in agreement with
earlier predictions
10
. For the main volcanic phase, however, such data
were unavailable. Here we report 2,500 new olivine analyses and host-
rock compositions for 45 basalts covering the main stages of tholeiitic
magmatism in threekey localities:theNorilsk area,thePutorana plateau
and the Maymecha–Kotuy province (Fig. 1a). Almost all olivine com-
positions possess significantly higher NiO and FeO/MnO than expected
for olivine in peridotite-derived magmas (Fig. 1b, c and Supplementary
Fig. 1), suggesting a contribution of melts from pyroxenitic sources
18
.
Alternative explanations for these observations seem less plausible (see
Methods for discussion). Our interpretation of the olivine compositions
implies that the source of the Siberian Traps contained 10–20 wt%
recycled oceanic crust (Methods). More specifically, all lavas erupted
during the first stage of magmatic activity (Gudchikhinskaya and earlier
suites of the Norilsk area) are depleted in heavy rare-earth elements
19,20
,
indicating residual garnet and derivation within or below the base
of thick lithosphere (more than 130 km depth)
14
. The source of
Gudchikhinskaya lavas was probably almost entirely pyroxenitic
14
(Fig. 1b–d). Younger magmas are not depleted in heavy rare-earth
elements, indicating their formation at shallow depths and marked
thinning of the lithosphere. Our calculation suggests that these
magmas had a near-constant proportion of pyroxenite-derived melt
of about 50% (Fig. 1d and Supplementary Table 1) and were strongly
contaminated by the continental crust
20
. Because the main Norilsk
section spans less than 1 Myr (ref. 1), it is likely that the lithosphere
was thinned in only a few hundred thousand years.
High mantle temperatures over a vast area (Fig. 1a) are consistent
with the head of a hot mantle plume
6,9,17
. On the basis of the petrological
constraints we develop a thermomechanical model of the interaction of
the plume and lithosphere (see Methods). We assume that the plume
arrived below the lithosphere at about 253 Myr ago (model time 0),
perhaps near the northern border of the Siberian Shield, where the
hottest melts (meimechites) erupted
17
. We further assume that the
plume head was hot (T
p
5 1,600 uC; 250 uC excess temperature) and
containeda high content (15 wt%) of recycled oceanic crust. In our two-
dimensional model we approximate the plume head by a half-circle of
radius 400 km located below cratonic lithosphere of variable thickness
corresponding to the margin of the Archean craton (130–250 km of
depleted lithosphere and 160–250 km of thermal lithosphere; Fig. 2b
and Supplementary Fig. 2).
The arrival of a large and hot mantle plume head at the base of the
lithosphere has been predicted
6,21
to cause about 0.8–1 km of broad
surface uplift per 100 uC of plume excess temperature. For a purely
thermal plume with an excess temperature of 250 uC, we do indeed
obtain about 2.0 km of surface uplift (Fig. 2a, red curve). However, if a
large fraction (15 wt%) of dense recycled material is present within the
plume, its buoyancy is strongly decreased, resulting in little regional
uplift (250 m) (Fig. 2a, black curve). Other processes leading to surface
subsidence, such as the plume-induced rise of the 670-km phase
boundary
22
or the crystallization and evacuation of melts, may easily
counteract such a small uplift.
The plume head erodes the lowest part of the thermal lithosphere
and rapidly spreads below the more refractory depleted lithosphere
(Fig. 2b). Its ascent leads to progressive melting of recycled eclogitic
material in the plume and to the formation of reaction pyroxenite,
which melts at depths of 130–180 km, well before the peridotite
(Fig. 2e). The early, purely pyroxenite-derived, melts yielded the lavas
of the Gudchikhinskaya and earlier suites that display the ‘garnet
signature’ (Fig. 1d).
We propose that massive intrusion of the Gudchikhinskaya suite by
dykes imposed compressive stress in the upper brittle part of the litho-
sphere, ‘locking’it to the magmatransport (Fig. 2b, e shows the moment
of ‘locking’). After that, the melt could intrude only into the lower
1
Deutsches GeoForschungsZentrum GFZ, Telegrafenberg, 14473, Potsdam, Germany.
2
O.Yu. Schmidt Institute of the Physics of the Earth, Russian Academy of Sciences, 10 ul. B. Gruzinskaya, Moscow,
123995, Russia.
3
ISTerre, CNRS, University Joseph Fourier, Maison des Ge
´
osciences, 1381 rue de la Piscine, BP 53, 38041 Grenoble Cedex 9, France.
4
Max Planck Institute for Chemistry, 27 J.-J.-Becher-
Weg, Mainz, 55128, Germany.
5
V. I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 19 ul. Kosygina, Moscow, 119991, Russia.
6
V. S. Sobolev Institute of
Geology and Mineralogy, Siberian Branch of Russian Academy of Sciences, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia.
7
Limited Liability Company ‘Norilskgeologiya’ Norilsk, PO Box 889,
663330, Russia.
*These authors contributed equally to this work.
312 | NATURE | VOL 477 | 15 SEPTEMBER 2011
Macmillan Publishers Limited. All rights reserved
©2011
55 60 65 70
FeO/MnO
Gd/Yb
Gd/Yb
75 80 85
3,000
2,500
2,000
1,500
1,000
500
0
3,500
Sm
Hr
Nd
3
Mk
Mr
2
Mr
1
Nd
2
TK
Nd
1
Km
Iv-Gd
m
Deep
Shallow
GA
GA Per.
1:1
a
cb
d
5000 1,000 km
N deep Fo>60
N shallow Fo<60
N shallow Fo>60
P shallow Fo>60
M shallow Fo>60
P deep Fo>60
P deep Fo<60
1
2
3
4
5
X
px
Mn
X
px
Ni
0
0
0.4
0.4
0.2
0.2 1 32
X
px
010.5
0.6
0.6
1.0
1.0
1.2
1.2
0.8
0.8
1.4
1.4
Figure 1
|
Petrological constraints. a, Geological map of the Siberian Traps
32
.
Dark green areas are lavas, light green areas are tuffs. The dashed black line
marks the border of the province. Red lines outline areas with different
magmatic activities: solid indicates maximal, dashed is moderate, and dotted is
minimal. The three studied regions are Norilsk (N), Putorana plateau (P) and
Maymecha–Kotuy province (M). White numbers stand for the potential
mantle temperature estimated for lavas of the corresponding areas
14,17
. b, FeO/
MnO ratios of olivine phenocrysts over normalized Gd/Yb ratios of host lavas.
The blue line marks the pressure that divides ‘deep’ lavas depleted in heavy rare-
earth elements from ‘shallow’ lavas. The green oval is the reference for the
almost pure shallow peridotitic mantle source and indicates the compositions
of olivine and lavas from the mid-ocean ridge (Knipovich Ridge, North
Atlantic) with minimum amounts of recycled ocean crust in their sources
18
. All
olivines are the averages of the three highest Fo percentages of each sample. GA,
garnet in the mantle source. c, The proportions of pyroxenite-derived melt in
the mixture of pyroxenite-derived and peridotite-derived melts calculated
independently of Mn deficiency (X
px
Mn) and Ni excess (X
px
Ni) (Methods).
d, Integrated lava section for Siberian Traps based on the Norilsk section
(Supplementary Information). X
px
is the proportion of pyroxenite-derived
melt, calculated as the average of X
px
Mn and X
px
Ni for high-forsterite olivines
and as X
px
Mn for low-forsterite olivines, because X
px
Ni for the latter yields
systematic overestimation (Fig. 1c). Small black dots show lavas of the Norilsk
section
19
. For abbreviations indicating the lava suites of the Norilsk area and
normalization for Dy/Yb ratio, see Supplementary Information. Per, peridotite-
derived melt component.
0.5 Myr
0.15 Myr
0.15 Myr
Thermal plume
Thermo-chemical plume
0.5 Myr
0.29 Myr 0.32 Myr 0.39 Myr 0.42 Myr 0.52 Myr
0
50
100
150
Depth (km)
d
e
f
d
Distance (km)
Distance (km)
Depth (km) Depth (km) H (km)
2
1
0
400
600
200
0
400
600
200
0
5000–500–1,000 1,000
5000–500–1,000 1,000
a
b
c
1,200
1,000
800
600
1,600
T(ºC)
T
p
(ºC)
1,400
1,200
1,000
800
600
1,600
1,400
0.31
0.26
0.21
0.16
0.11
0.06
0.01
0.36
0.31
0.26
0.21
0.16
0.11
0.06
0.01
0.36
C
px
C
px
Figure 2
|
Model. a, Maximum pre-magmatic surface uplift (H) atop a
spreading mantle plume with an excess temperature of 250 uC. The red curve
corresponds to the purely thermal plume, and the black curve corresponds to a
thermo-chemical plume containing 15 wt% of recycled crust. b, c, Temperature
distributions (uC) in the model cross-section at model times of 0.15 Myr (b) and
0.5 Myr (c). The solid line marks the boundary of the depleted lithosphere, and
the dashed half-circle denotes the initial shape of the starting plume.
d, Snapshots of the plume breaking through the lithosphere in the domain
shown by the white rectangle in f. Colours show concentrations of the
pyroxenitic component in the plume or in the crystallized melt.
e, f, Distribution of the pyroxenite component in the plume (C
px
)orinthe
crystallized melt in the model cross-section at model times of 0.15 Myr (e) and
0.5 Myr (f). The solid line marks the boundary of the depleted lithosphere.
LETTER RESEARCH
15 SEPTEMBER 2011 | VOL 477 | NATURE | 313
Macmillan Publishers Limited. All rights reserved
©2011
lithosphere (see Methods). The intruding melt cools and crystallizes to
dense eclogite. It also strongly heats and weakens the lithosphere, pro-
moting Raleigh–Taylor instabilities
8
. The lower part founders, and the
base of the lithosphere is mechanically eroded (Fig. 2c). Enriched in
eclogite, the lithospheric material in the boundary layer above the
plume escapes to the sides of the plume and then downwards, allowing
the plume to ascend (Fig. 2d, f). The plume breaks through the litho-
sphere in several zones, and in only 100–200 kyr reaches its minimum
depth of about 50 km (Fig. 2d and Supplementary Fig. 2). At this level,
mafic melts crystallize to a garnet-free assemblage and have a density
lower than that of the ambient mantle, thus preventing the formation of
Raleigh–Taylor instabilities. This mode of rapid lithosphere destruction
does not require regional stretching and matches observations for the
Siberian Traps
7,12
.
The extent of lithospheric destruction depends, among other factors
(Supplementary Information), on the initial density of mantle litho-
sphere, which is controlled by its composition (Fig. 3a and Supplemen-
tary Information). In the case of re-fertilized or moderately depleted
mantle lithosphere, the volume of the melt that intrudes into the crust
(melt crossing 50 km depth) reaches few per cent of the plume volume
(Fig. 3a), which leads to substantial melting of the crust and contam-
ination of basalts. Using the proportion of the magma-to-plume
volumes from a two-dimensional model for a three-dimensional
plume head with a radius of 400 km, we estimate the volume of the
magma intruded into the crust to be (6–8) 3 10
6
km
3
, which is realistic
for the Siberian Traps
1,12
.
In agreement with geochemical data, the model predicts that most
magma contains about 50% of pyroxenite-derived melt (Fig. 3b, blue
curves and symbols) and lack the ‘garnet signature’ because they are
generated at depths of less than 60 km. For the melt generated deeper
than 100 km, the model predicts a much higher proportion of pyrox-
enite melt (75–100%; Fig. 3b, red curves), again in agreement with
observations (Fig. 3b, red symbols).
Our model allows us to estimate the volume of CO
2
and HCl gases
released from the plume. For these calculations we consider separately
the recycled crust and peridotitic components by using data from melt
inclusions in olivine in Gudchikhinskaya picrites and mantle peridotite
as well as published estimates (Methods). For the composition of recycled
crust this yields HCl 5 137 p.p.m., S 5 135 p.p.m., H
2
O 5 800 p.p.m.
and CO
2
. 900 p.p.m. The model predicts that most of the CO
2
and
HCl in the recycled-crust component of the plume is extracted during
its interacti on with the lithosphere (Fig. 4a), and a major part is extracted
before the main phase of magmatism. For a three-dimensional plume
with a radius of 400 km, the mass of extracted CO
2
, which comes mostly
from the recycled component of the plume, is more than 170 3 10
12
tonnes.Thisisseveraltimeslargerthanpreviousestimates
13,15
and also
exceeds the maximum estimate of the CO
2
released from the magmatic
heating of the coals from the Tunguska basin
15
.
Our prediction of the mass of CO
2
extracted from the plume is
consistent with the amount of CO
2
released during the Permo-
Triassic mass extinction estimated from Ca isotope data
23
(Fig. 4a).
Moreover, if we use a d
13
Cvalueof212% for pyroxenite-derived melt
as measured in Koolau (Hawaii) basaltic melt for the source dominated
by the recycled crust component
24
, we can alsoexplainthe
13
C excursion
associated with the main mass-extinction event
23
(Methods). Therefore
CO
2
from the plume alone may have triggered the main extinction
event. We speculate that low-density and low-viscosity volatiles were
the first to penetrate the compressed and mechanically locked crust,
triggering the extinction (Fig. 4a, upper axis). Alternatively, a sufficient
quantity of gases may have been released before lithospheric locking,
together with the deep-sited magmas of pre-Gudchikhinskaya suites,
which could also produce metamorphic gases by magmatic heating of
the coals and carbonates. This alternative is supported by the recent
discovery of coal fly ash in Permian rocks from the Canadian High
Arctic immediately before the mass extinction, interpreted as a result
of combustion of Siberian coal and organic-rich sediments by flood
basalts
25
. In either case, according to our model, the major mass
extinction happened before the main phase of flood basalt extrusion.
In contrast, most of the CO
2
and other gases released by contact meta-
morphism of carbon-rich and sulphur-rich sediments, which have been
suggested as a trigger for the mass extinction
15,16
, would be released
during the main phase of magmatism. Precise U–Pb dating of
Siberian magmatic units and the Permo-Triassic boundary is required
to distinguish between the two hypotheses. Nonetheless, existing geo-
chronological data
26,27
and the presence of abundant pyroclastic rocks
underlying lavas of the main magmatic phase
11,19
support the idea that
the major mass extinction predated the main phase of magmatism (see
Fig. 4a, upper axis). Additional large amounts of gases released from
heated sediments
15,16
may have been the cause of
13
C excursions during
the later phases of the biotic crisis
28
.
According to our data and model, the plume also generates a sur-
prisingly large amount of HCl (about 18 3 10
12
tonnes; Fig. 4a), mostly
0.4 0.8 1.2 1.6 2.0
0
1
2
3
Deep melt
Shallow melt
ab
Re-fertilized (Δρ = 25 kg m
–3
)
0.4 0.6 1.0
0
0.2
0.4
0.6
0.8
1.0
Time (Myr)
Depleted (Δρ = 50 kg m
–3
)
V
melt
/V
plume
(%)
Fraction of volume
0.2 0.8
Fraction of pyroxenite melt
Figure 3
|
Model predictions. a, Evolution in time of a melt volume crossing
the 50-km depth and normalized to the volume of the plume. The solid and
dashed curves correspond to the models with re-fertilized lithosphere and
moderately depleted lithosphere, respectively. b, Plot of the fraction of
pyroxenitic component in basalts of the Norilsk cross-section against the
fraction of the volume of extruded magmas. The blue colour corresponds to the
‘shallow’ melts that do not retain a garnet signature; the red colour corresponds
to the deep melts that retain a garnet signature. Symbols denote data from
olivine compositions; see Fig. 1b for details. Error bars correspond to 1 standard
deviation of the mean of pyroxenite-derived melt proportions estimated
independently from Ni excess and Mn deficiency of olivine (Methods and
Supplementary Table 1). The solid and dashed curves show the modelled
average melt compositions with re-fertilized and moderately depleted
lithosphere, respectively. The grey rectangle shows the range of variation of the
melt compositions predicted by the model.
RESEARCH LETTER
314 | NATURE | VOL 477 | 15 SEPTEMBER 2011
Macmillan Publishers Limited. All rights reserved
©2011
also derived from the recycled component. This quantity of toxic HCl
must have been extremely damaging for the terrestrial species and was
also sufficient to trigger deadly instability of the stratospheric ozone
layer
29
.
By accepting our viewpoint that degassing of the plume, rather than
thermogenic gases from sediments, triggered the biotic crises, we lose
an elegant explanation of why the Siberian LIP was so much more
damaging to biota than other LIPs of comparable size (Karoo, Parana
and North Atlantic) that extruded through other types of sediment or
granitic rock
15,16
. An alternative explanation is based on the correlation
of the intensity of mass extinctions with the age of Phanerozoic LIPs
(Fig. 4b), a relationship that can be explained by the temporally dif-
ferent response of the ocean to acidification by the large amounts of
released CO
2
(refs 23, 30). In contrast to the pre-Mid-Mesozoic
‘Neritan’ ocean, the more recent ‘Cretan’ ocean was buffered against
acidification by deep-sea unlithified carbonate sediments and was thus
much more resistant to acidification
23,30
. Therefore, CO
2
degassing of a
pre-Mid-Mesozoic LIP caused much more severe ocean acidification
and mass extinction than later LIPs (Fig. 4b). The only exception is the
Deccan LIP and the contemporaneous mass extinction at 65.5 Myr
ago; however, in this case the Chicxulub impact was an additional
contributing factor
31
.
Numerical tests (Supplementary Figs 4–6) suggest that rapid litho-
spheric destruction associat ed with melting in the heads of thermoche-
mical plumes is valid for the large range of plume parameters and
lithospheric thicknesses, and therefore may apply not only to the
Siberian Traps but also to other LIPs. An absence of prominent pre-
magmatic uplift does not argue against a plume origin of LIPs, but may
instead point to a high content of recycled crust within the plume. In such
cases, other parameters being equal, the model predicts that eclogite-rich
plumes caused the most extensive delamination and thinning of the
lithosphere, thus best preparing it for a possible break-up. They also
produced the strongest volcanism and led to the most marked climatic
consequences.
Another suggestion of our model—that major mass extinctions are
triggered by degassing of plume magmas that predate the main magmatic
phase—also seems to be consistent with the observations for many LIPs
5
,
implying that gas output from plume heads may be much larger than
previously thought.
METHODS SUMMARY
We report new data on 45 representative olivine-bearing samples of Siberian flood
basalts from the Norilsk, Putorana and Maimecha–Kotui regions (Supplementary
Tables 1 and 3). The bulk rocks were crushed, melted and analysed for major and
trace elements with an electron probe microanalyser (EPMA) and by laser ablation
inductively coupled plasma mass spectrometry (LA-ICP-MS) at the Max Planck
Institute for Chemistry in Mainz, Germany. Olivine phenocrysts (about 2,500
analyses) were analysed by EPMA with a special high-precision protocol
18
at the
Max Planck Institute for Chemistry. Using this new information and published
approaches we estimated the amount of recycled oceanic crust in the sources of
basalts and their potential temperatures, and discuss possible alternative models of
the source compositions. We further estimate the amounts of H
2
O, Cl, S and CO
2
in the recycled oceanic crust and develop a model of its degassing during plume–
lithosphere interaction.
We model the thermomechanical interaction of the plume and lithosphere by
numerically solving a coupled system of momentum, mass and energy conser-
vation equations in two dimensions. We employ nonlinear temperature and
stress-dependent elasto-visco-plastic rheology, consider pressure-dependent and
temperature-dependent melting of a heterogeneous mantle and employ simple
models of melt transfer and extraction of volatiles.
Full Methods and any associated references are available in the online version of
the paper at www.nature.com/nature.
Received 17 February; accepted 26 July 2011.
1. Reichow, M. K. et al. The timing and extent of the eruption of the Siberian Traps
large igneous province: implications for the end-Permian environmental crisis.
Earth Planet. Sci. Lett. 277, 9–20 (2009).
2. White, R. & McKenzie, D. Magmatism at rift zones—the generation of volcanic
continental margins and flood basalts. J. Geophys. Res. Solid Earth Planets 94,
7685–7729 (1989).
3. Garfunkel, Z. Formation of continental flood volcanism—the perspective of setting
of melting. Lithos 100, 49–65 (2008).
4. Courtillot, V. E. & Renne, P. R. On the ages of flood basalt events. C. R. Geosci. 335,
113–140 (2003).
5. Wignall, P. B. Large igneous provinces and mass extinctions. Earth Sci. Rev. 53,
1–33 (2001).
6. Campbell, I. H. & Griffiths, R. W. Implications of mantle plume structure for the
evolution of flood basalts. Earth Planet. Sci. Lett. 99, 79–93 (1990).
522.0
a
Lithosphere
locked
b
Emeishan
Deccan
CAMP
CR
NAMP
Karoo
Parana
CP
OJP
Ethiopia
300
10
20
30
40
50
60
Siberia
Time (Myr)
250 200 150 100
50
0
<2
2–4
>4
Magma volume crossing
50 km depth (Fig. 3a)
0
1
0 2.0
0
Ref. 23
Ref. 15 Ref. 26
50
100
150
200
250
0
10
20
30
40
50
Shallow magmas
and metamorphic gas
252.8 Myr
Deep gas and
magmas
252.4
Mass
extinction
250.8
251.2
251.6
CO
2
10
12
tonnes)
HCl (×10
12
tonnes)
Time (Myr)
1.61.20.80.4
CO
2
HCl
GBT(?)
Generic extinctions (%)
‘Cretan’ ocean mode
Chicxulub
impact
‘Neritan’ ocean
Figure 4
|
Production of volatilesand its consequences for mass extinctions.
a,PlotofmodelledCO
2
(left axis) and HCl (right axis) amounts extracted from the
plume against model time (lower axis). Solid curves show the minimum estimate
and dashed curves the maximum estimate of CO
2
and HCl extracted from the
plume (Methods). The grey rectangle shows the estimated range of the released
CO
2
during the Permo-Triassic mass extinction
23
. The green area shows tim e
dependence of the nor malized volume of the magma crossing the 50-km depth,
calculated for the re-fertilized lithosph ere (Fig. 3a). On the top axis we show
geological time and a possible model for triggering the Permo-Triassic mass
extinction. GBT, gases break through. Also shown is U–Pb dating of the extinction
event
27
and U–Pb dating of main-phase Siberian basalts
26
and intrusions
15
. b,Plot
of mass extinction intensity (light blue field) with major LIPs (circles) against
geological time (modified from ref. 33), together with the timing of different ocean
modes
30
. Circle colours denote the timing of LIPs relative to ocean modes: blue,
‘Cretan’ mode; red ‘Neritan’ mode; blue and red together, transition mode. The
scale of circle sizes is in millions of cubic kilometres. CAMP, Central Atlantic
Magmatic Province; NAMP, Northern Atlantic Magmatic Provinces, OJP,
Ontong Java; CP, Caribbean Plateaux; CR, Columbian River basalts.
LETTER RESEARCH
15 SEPTEMBER 2011 | VOL 477 | NATURE | 315
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Supplementary Information is linked to the online version of the paper at
www.nature.com/nature.
Acknowledgements S.V.S. and A.V.S. are especially grateful to Vladimir Stepanovich
Sobolev, who excited their interest in the origin of the Siberian Traps. We thank
G. A. Fedorenko for providing data on the Norilsk lavas and for discussions;
N. Groschopf for help in managing the electron probe microanalyser; O. Kuzmina,
N. Svirskaya and T. Shlichkova for sample preparation; P. Cardin, N. Dobretsov,
E. Galimov, C. Herzberg, A. Hofmann, L. Kogarko, H.-C. Nataf, J. Payne, Y. Podladchikov,
I. Ryabchikov, A. Turchyn and G. Wo
¨
rner for discussions; and P. Kelemenfor comments.
S.V.S. thanks the Deutsche Forschungsgemeinschaft (DFG) SPP 1375 SAMPLE (SO
425/4) for support. The study by A.V.S. was funded by the Agence Nationale de la
Recherche, France (Chair of Excellence Grant ANR-09-CEXC-003-01) and partly
supported by a Gauss Professorship in Go
¨
ttingen University, Germany, the Russian
Foundation for Basic Research (09-05-01193a), a Russian President grant for leading
Russian scientific schools (
-3919.2010.5) and an Earth Sciences Department of
Russian Academy Grants.
Author Contributions S.V.S. and A.V.S. provided major contributions to
thermomechanical (S.V.S.) and petrological (A.V.S.) modelling, to the interpretation of
data and to the writing of the paper. N.A.K. provided geological background and
contributed to interpretation. A.G.P. contributed to the thermomechanical modelling at
an initial stage. N.T.A. contributed to interpretation and writing of the paper. D.V.K.
processed samples and performed the measurements. N.A.K., V.A.R. and Y.R.V.
provided carefully selected samples. All authors contributed intellectually to the paper.
Author Information Reprints and permissions information is available at
www.nature.com/reprints. The authors declare no competing financial interests.
Readers are welcome to comment on the online version of this article at
www.nature.com/nature. Correspondence and requests for materials should be
addressed to S.V.S. (stephan@gfz-potsdam.de) or A.V.S.
(alexander.sobolev@ujf-grenoble.fr).
RESEARCH LETTER
316 | NATURE | VOL 477 | 15 SEPTEMBER 2011
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METHODS
Samples. The samples studied and their localities are described in Supplementary
Information.
Analytical methods. Olivine grains were manually separated from crushed lavas,
then mounted and polished in epoxy. The compositions of olivine were analysed
with an EPMA on a Jeol JXA 8200 SuperProbe at the Max Planck Institute for
Chemistry (Mainz, Germany) at an accelerating voltage of 20 kV and a beam
current of 300 nA, following a special procedure which allows 20–30 p.p.m. (2s
error) precision and accuracy for Ni, Ca, Mn, Al, Ti, Cr and Co, and 0.02 mol%
accuracy for the forsterite component in olivine
18
.
Bulk rocks were crushed, melted to glass
34
and then mounted and polished in
epoxy. Major and trace elements were also determined by EPMA at the Max
Planck Institute for Chemistry. Major-element abundances in glasses were mea-
sured at an accelerating voltage of 15 kV and a beam current of 12 nA with a
reference sample of natural basaltic glass USNM111240/52 (VG2)
35
, with a relative
error of 1–2%. LA-ICP MS was used to determine trace elements in glasses of melt
inclusions and in olivines, on an ELEMENT-2, Thermo Scientific mass spectro-
meter with a UP-213 New Wave Research solid-phase laser at the Max Planck
Institute for Chemistry, with reference to the KL-2G and NIST 612 standard
samples of basaltic glass
36
.
Proportions of pyroxenite-derived melt and recycled crust. We interpret excess-
ive Ni and deficient Mn concentrations in Siberian olivine phenocrysts relative to
olivine in peridotite-derived melt as a result of the contribution of olivine free
pyroxenite lithology in their source
18,37–39
. The alternative explanations of this phe-
nomenon are discussed briefly in the next section. Relative proportions of pyroxenite
and peridotite derived melts were estimated from MnO/FeO (X
px
Mn) and
NiO 3 FeO/MgO (X
px
Ni) ratios
38
for each sample, using the average composition
of most magnesian olivines (defined by olivines with Fo within 3 mol% from a
maximum Fo).
The amount of recycled crust in the plume is linked to the proportion of
pyroxenite-derived melt by the degree of melting of the eclogite component, the
amount of eclogite-derived melt needed to producehybridpyroxenitefromperidotite,
and the degrees of melting of peridotite and pyroxenite
18,39
. We calculated the
amount of recycled crust in the Siberian plume using the approach described
previously
18
and their equation S3, and the following assumptions: a maximum
degree of melting of eclogite and pyroxenite of 60%; an average proportion of
pyroxenite-derived melt in shallow magmas of 46% (Supplementary Table 1);
and melting of peridotite at 50 km depth. The amounts of recycled crust are
10% and 20% for 10% and 25% melting of peridotite, respectively.
Alternative explanations of the unusual olivine composition. Alternative
explanations of high Ni/Mg and FeO/MnO ratios in olivine include: (1) effect of
clinopyroxene crystallization, (2) an underestimated temperature effect on olivine-
melt partition of Ni, and (3) contribution of core material to the mantle source.
None of these alternatives require a significant role of olivine-free pyroxenite in the
mantle source. In addition there are different models for the pyroxenite origin,
which may affect our estimation of proportions of pyroxenite in the Siberian plume.
These include (4) solid-state reaction of peridotite and recycled crust in the lower
mantle and (5) partial reaction between eclogite-derived melt and peridotite. Below
we briefly discuss these alternatives.
1. Crystallization of clinopyroxene together with olivine may increase both Ni/Mg
and Fe/Mn ratios in olivine. This effect could be particularly important for the low
magnesian evolved olivine.Howeverclinopyroxene crystallizationcanbe recognized
bylowCainolivine.InSupplementaryInformationweshowthatthisisanunlikely
situation for most studied olivines, which do not show a significant decrease in Ca
concentrations. In particular, early clinopyroxene crystallization cannot explain the
composition of the olivines from picrites of the Gudchikhinskaya formation and the
Ayan river, which are extremely rich in Ni and deficient in Mn. In addition, melt
inclusions in the former
14
and olivines in the latter (Supplementary Table 3) do not
indicate early clinopyroxene crystallization. We conclude that the fractionation of
clinopyroxene could not have produced the observed anomalies in the olivine
compositions.
2. An underestimated temperature effect on olivine-melt partition coefficient, if
present, may increase Ni concentration in the shallow olivine compared with
olivine in the deep source as a result of temperature difference between the sites
of generation and crystallization. This issue has been discussed previously
37,39
,
where it was shown that any temperature effect additional to the compositional
one considered in the model of Ni partitioning between melt and olivine used in
this study
40
is too small to explain the extent of Ni excess observed in Siberian
olivines.
3. The contribution of core material to increase Ni/Mg (ref. 41) and Fe/Mn
(ref. 42) ratios has been discussed previously
18
, where it was shown that this
explanation is highly unlikely because of a lack of correlation between Ni excess
and high Co concentrations in the olivines.
4. The solid-state reaction between recycled crust and per idotite in the lower
mantle may produce pyroxenite with a composition much closer to that of peridotite,
which in the upper mantle will be transformed to olivine-bearing pyroxenite
37
. If this
lithology exists, it could potentially be the source of parental melts of typical Siberian
basalts. However, olivine-bearing lithologies could not be the source of deep-sourced
lavas such as the Gudchikhinskaya formation and Ayan river picrites, whose olivine
compositions demonstrate derivation from a dominating olivine-free source. In
addition, solid-state reactions of the type envisaged in ref. 37 will be limited by slow
volume diffusion in the mantle
43
, whereas the production of reaction olivine-free
pyroxenite will be restricted only by melt percolation velocity
18,39
.
5. Incomplete reaction between eclogite-derived melt and peridotite may pro-
duce olivine-bearing lithologies
44
, which could be potential sources of the parental
melts of typical Siberian traps. However, these olivine-bearing lithologies cannot
produce Siberian deep-sourced magmas (see above).
We conclude that although we cannot fully exclude some of proposed alter-
natives, our explanation of the olivine compositions is based on solid grounds and
seems the most plausible.
Potential temperatures. The published potential temperature of 1,540 uCforthe
source of Gudchikhinskaya magmas
14
has been corrected for the effect of 40% melting
of pyroxenitic source
17
, the amount of pyroxenite in the plume (15%) and the latent
heat of melting
45
. The value obtained is about 1,600 uC. Potential temperatures for the
Maimecha–Kotuy province
17
and the Putorana plateau
46
(see Fig. 1a) were obtained
formagmasstronglyenrichedinhighlyincompatible elements. These magmas origi-
nated at low degrees of melting and thus were not corrected for the melting effect.
Amount of volatile elements. The concentrations of volatile elements in the
recycled oceanic crust in the Siberian plume were constrained using the composi-
tions of inclusions of uncontaminated melt in early olivine phenocrysts from
Gudchikhinskaya magmas. For these magmas it was shown from both olivine
and melt compositions that they probably represent the melting of a pure
pyroxenitic source
14
. Inclusions in olivine from these magmas have been shown
to represent primary melts
14
and thus their concentrations of Cl, S and H
2
Ocanbe
used to estimate the contents of these volatiles in the mantle source. For the com-
position of source eclogite, this yields the following values
14,17
:Cl5 137 p.p.m.,
S 5 135 p.p.m. and H
2
O 5 800 p.p.m., after normalization of the values to K. In
the deep mantle, these amounts of Cl, S and H
2
O could reside in chloride
47
,
sulphide, and garnet or pyroxene respectively. In contrast with Cl, S and H
2
O,
the amount of CO
2
in relatively shallow melts does not represent the primary
concentration, because of almost complete degassing at high pressures. Thus for
an assessment of CO
2
in the recycled oceanic crust we use global estimations of
3,000 p.p.m. CO
2
for the bulk 7-km-thick oceanic crust and its maximum
outgassing rate through arc volcanism of 70% (ref. 48). This gives a conservative
minimum estimate of 900 p.p.m. CO
2
in the deeply recycled oceanic crust. The
maximum estimate would be about 1,800 p.p.m. using the same initial bulk con-
centrations of CO
2
and minimal outgassing of 40% (ref. 48). In the deep mantle this
amount of CO
2
could reside in carbonates or diamond
47
. For our model we use the
minimum conservative estimate of CO
2
5 900 p.p.m.
Thermo-mechanical numerical technique. We use a fully coupled thermo-
mechanical formulation for the system of momentum, mass and energy con-
servation equations in two dimensions with nonlinear temperature and
stress-dependent elasto-visco-plastic rheology, described in detail in ref. 49 (for para-
meters and procedure for calculating density, see Supplementary Information).
Equations are solved numerically using the explicit Lagrangean FEM technique
LAPEX2D (ref. 50) based on a FLAC algorithm (prototype described in ref. 51)
combined with a particle-in-cell approach. All time-dependent fields including
full stress tensor are stored at particles.
Melting models. We use a simplified model for batch melting of four components:
peridotite, pyroxenite and two eclogites formed through the crystallization of
peridotitic and pyroxenitic melts, respectively. Melting temperatures are defined
as follows: for peridotite we use the dry batch melting model
52
; for pyroxenite we
use the following relation from experiments
18
for dry batch melting of pyroxenite:
T
Px
m
~976z12:3P{0:051P
2
z663:8X{611:4X
2
where P is pressure in kbars, T is potential temperature in uC and X is degree of
melting, 0 , X , 0.55.
For eclogite of both types (peridotite-derived or pyroxenite-derived) we use the
following relations approximating experiments
53
for dry batch melting of eclogite
at 50% melting:
T
e
m
~1173:4z5:78P
at P , 55 kbar, and
T
e
m
~{237:5z48:0P{0:3P
2
at 55 ( P , 80 kbar.
LETTER RESEARCH
Macmillan Publishers Limited. All rights reserved
©2011
The melting for each finite element is organized sequentially, beginning with the
component with the lowest melting temperature (usually eclogite), then usually
pyroxenite and finally peridotite. If the current temperature (T) in a finite element
exceeds the melting temperature (T
m
) of the component that exists in this element,
than a certain amount of melt (dC
m
) is generated that lowers the current temper-
ature to the melting temperature, dC
m
5 (T 2 T
m
)C
p
/(DS
m
T), where C
p
is heat
capacity and DS
m
is entropy of melting, set to 1,200 J kg
21
K
21
and 400 J kg
21
K
21
,
respectively, for all components.
Model for melt transfer. We assume that melt transfer within the melting domain
occurs much faster than the Raleigh–Taylor instability develops in the lithosphere.
This assumption holds if the velocity of melt transfer (V
m
) is much higher than
H/t, where H is the typical distance of melt transfer and t is typical time of
Raleigh–Taylor instability. With values of H , 50 km and t < 50,000 years (see
Supplementary Fig. 2), this assumption is valid if V
m
is much higher than 1 m yr
21
.
In reality, V
m
is at least tenfold higher in the upper mantle regions where intensive
melting occurs
54
.
If present, the entire melt is assumed to move rapidly upwards within the
domain where the local temperature is higher than the melting temperature. As
usual for melt porous flow, we also assume that it is thermally equilibrating at each
element. In practice, at every nth calculation time-step, for every element we check
the melting condition and move the entire volume of melt (if present) one element
upwards, recalculating the temperature of that element according to the local
energy conservation law.
For the melt in the uppermost elements of the melting domain, we consider two
transfer modes. First we consider a mode that mimics transfer through fractures:
in this case, a fraction or the entire melt is assumed to move to the surface; in
practice it is just taken out from the model. Second, we consider a mode of
mechanically locked lithosphere: in this case the entire melt from each uppermost
element of the melting zone is moved to, and evenly distributed between, K ele-
ments in the column just above it (usually we take K 5 4) and is assumed to
crystallize. Simultaneously, the rheology of melt-accepting lithospheric elements
is switched from ‘dry’ to ‘wet’ olivine rheology if the crystallized melt content
exceeds some critical value (we take this value as 1%). The temperature and
composition of the accepting elements are recalculated according to the local
energy and mass conservation laws.
Extraction of volatiles. We consider two endmember models for the extraction of
volatiles. In the first model we assume that CO
2
and HCl are fully extracted from
the plume if the temperature approaches that of the carbonatite solidus
55
.This
model gives an upper bound for melt mobility,assumingthat melts produced by an
infinitely low degree of melting can move out of the plume. In the second model we
assume that CO
2
and HCl are fully extracted from both peridotitic and pyroxenitic
components only if 1% melting is achieved. This model gives lower boundary for
melt mobility, assuming that only 1% carbonate–silicate melts can move out of the
plume. For both models we assume a concentration of HCl in recycled crust of
137 p.p.m. derived from melt inclusions in olivine, no HCl in the peridotitic
component and minimum conservative estimates of CO
2
content in both recycled
crust (900 p.p.m.) and plume peridotite (70 p.p.m.) (see above).
Expected mode of motion of volatiles in the lithosphere. Melt from the plume is
trapped and crystallizes in the lithosphere; it then returns to the mantle as the
lithosphere founders. The volatiles extracted by melting of the plume are released
as the melt crystallizes because host phases are not stable at the high temperatures
at the base of the lithosphere. They migrate upwards, then react and are fixed in
carbonates or chlorides in the cooler upper part of the lithosphere. Continuous
upward migration of high-temperature isotherms then decomposes these phases,
promoting further displacement of the volatile front ahead of the basalt-melting
front. According to our model, more than 70% of the mafic magmas generated in
the plume crystallized to eclogites and subsided back into the mantle as the
densified lithosphere foundered; less than 30% were intruded into the crust.
However, almost all carbonatite melts traversed the lithosphere and crust, because
the temperature of the detached blocks was significantly higher than the melting
temperature of carbonatite. It is therefore likely that a significant part of the
volatiles released from the plume finally reached the surface, promoting explosive
eruptions, which are very common in the early stage of Siberian Traps
11,19
and
other LIPs, that is, Emeishan flood basalts
56
. Note that the volatiles that were
initially stored in the minerals of the destructed portions of the lithosphere should
be also melted out and could finally reach the surface as well.
Why output of volatiles from LIPs could be drastically underestimated. The
amount of volatiles released was previously estimated using only the volume of
extruded magmas or magmas intruded into the shallow crust. In these studies were
disregarded the magmas that crystallized in the deep crust and, more importantly,
the much larger volumes of magmas that we propose were involved in the destruc-
tion of the lithosphere and never reached the crust, although most of the volatiles
extracted from them probably did (see above). Additionally, the recycled crust
component of the plume, which contains much more volatiles than the peridotitic
component, was not previously considered in the balance calculation.
Estimation of
13
C excursion. The
13
C-isotope change due to the released CO
2
(considered to be instantaneous) can be estimated from a simple mass-balance
equation
38
. According to our model, about 172 3 10
12
tonnes of CO
2
is released
from the plume—about 70% from recycled crust and the remaining 30% from
peridotite. Assuming that d
13
C 5212% for crust-derived CO
2
(ref. 24) and
d
13
C 525% for peridotite-derived CO
2
, we obtain an average isotopic composi-
tion of the plume-released carbon of d
13
C 529.9%. Assuming d
13
C 5 3.6% for
the initial carbon isotope composition and 300 3 10
12
tonnes of CO
2
(or 82 3 10
12
tonnes of C)
23
for the Late Permian CO
2
reservoir, we estimate that the magnitude
of the carbon isotope excursion was 4.9% if all plume-released gases migrated to
the surface, and 3.5% if only half of them arrived. Both numbers are well within
the range of reported values for the Permian–Triassic excursion
57
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Samples description
Studied samples are olivine phyric, olivine-plagioclase phyric or
aphyric basalts and rarely picrites from outcrops or drill core of lava
flows (most samples), and outcrops of dykes (few samples) see
Supplementary Table S1. They contain visually fresh olivine
phenocrysts, microphenocrysts or olivine-pyroxene intergrowths and
were carefully selected from lavas from Norilsk area, Putorana
plateau and Maymecha-Kotuy province.
Norilsk area.
We studied samples from most lava units of the Norilsk
section, covering most parts of the region
14,19,58,59
. Samples were
carefully located relative to the lower boundaries of the units and
were placed within the integrated lava section of Siberian traps using
this information and absolute positions of unit boundaries after
Fedorenko et al, 1996 ref(19). Abbreviations at Fig. 1D indicate the
following lava suites of the Norilsk area placed in the order of
decreasing age: Iv-Ivakinskaya, Gd-Gudchikhinskaya, Tk-
Tuklonskaya, Nd-Nadezhdinskaya, Mr-Morangovskaya, Mk-
Mukulaevskaya, Hr-Haerlakhskaya, Km-Kumginskaya, Sm-
Samoedskaya. (Gd/Yb)
n
indicates the element ratio normalized to the
primitive mantle composition
60
. We also studied olivine phyric
basaltic dykes (samples 22-12 and 22-6), cutting the upper
Mukulaevskaya suite and thus representing any of upper units from
Hr to Sm.
Putorana plateau.
Studied samples came from collection of V.
Nesterenko
61-64
and Y. Vasiliev (picrites of Ayan river)
65
. We
estimated approximate positions of studied samples in the integrated
lava section (Fig 1D) using data reported in ref(19, 61).
Maymecha-Kotuy province. Most lavas of this province are highly
alkaline
66,67
and are not discussed in this paper. Here we report olivine
compositions from only one sample, which represents the major type
of voluminous tholeiitic lavas from the Maymecha-Kotuy province
68
.
It is similar in composition to the predominant type of Norilsk and
Putorana basalts and is placed in the integrated lava section (Fig 1D)
using the data
19
.
Olivine compositions
Magmas originated from mantle peridotite or reaction pyroxenite
should crystallize magnesian olivine at low pressures
18,37
. The
minimum forsterite component is expected for olivine in equilibrium
with melt originated from the pure pyroxenitic source. Sobolev et al
(2009) ref(14) estimated the composition of such an olivine to be in
the range of Fo84-86 similar to the most magnesian composition of
actual olivine from lavas of Gudchikhinkaya formation (up to Fo
83.5, ref(14)). This suggests minimal fractionation of these lavas. The
subalkaline picrites from Ayan River on the Putorana plateau have
also high-Mg olivine (up to Fo 90, see Fig S1) and thus a low degree
of fractionation. The shallow-derived Siberian lavas (no garnet in the
source) underwent more crystal fractionation and highly magnesian
olivine is exceptionally rare in these lavas. Here we report olivine
with up to Fo79 in upper, most voluminous volcanic formations of
Norilsk area and corresponding lava suites at Maymecha-Kotuy and
Putorana regions (see Fig S1). This value is more magnesian than
previously reported in these suites. Figure S1 compares the
compositions of the most magnesian olivines reported in this paper
with compositions of olivine expected to crystallize from peridotite-
derived magmas
18,37
. For the same Fo content, all Siberian olivines
are significantly higher in Ni and lower in Mn (seen also in higher
FeO/MnO ratio) than olivine from peridotite derived magmas.
Crystallization of large amounts of early clinopyroxene could
potentially create a similar affect in coexisting olivine. This is
demonstrated by compositional trend of olivine from sample CY-315
from Tuklonskaya formation (Fig S1). This olivine has lowest Ni of
the all Siberian samples and defines the flattest trend in Fo-NiO
space. In this olivine CaO decreases rapidly and FeO/MnO increases
with decreasing Fo. Thus for this lava we cannot exclude the
possibility that the primary high-Mg melt was derived from a
peridotite- dominated source. However, the CaO contents of olivine
from other samples do not support this interpretation (see Fig S1C).
Instead, we suggest that high Ni and low Mn in Siberian olivines
imply a large fraction of non-peridotitic lithology in their source
18,37
.
We note that FeO/MnO ratio of olivine does not change significantly
during shallow fractional crystallization as indicated by the trends on
Figure S1D. This supports the use of this ratio for estimating amount
of pyroxenitic component for highly evolved low magnesian olivine.
The most magnesian olivine reported here (Fo79) comes from the
most voluminous traps lavas but it is still much less magnesian than
expected for their primary melts. This may suggest that an early stage
of their fractionation took place at deep magma chambers, perhaps at
40-50 km depth close to the level of their origin predicted by model.
Calculation of density
Apart from temperature, pressure and initial composition, the
densities of all materials are assumed to be affected by variable
content of melt, crystallized melt or melt extraction. All these effects
are linearized and are considered in Boussinesq approximation.
Density of material i is
(S1)
Where
),(
0
Tp
i
ρ
is density of pure non molten i-th material, X
pr
is
concentration of extracted peridotitic melt, X
px
is concentration of the
pyroxenitic component, X
epx
is concentration of crystallized melt
derived from the pyroxenitic component, X
epr
is concentration of
crystallized melt derived from the peridotitic component, X
mpx
is
concentration of melt derived from the pyroxenitic component, X
mpr
is
concentration of melt derived from the peridotitic component. All
concentrations are volume concentrations. Multipliers of
concentrations (“a” parameters) are constants depending on material
and pressure. The “a” parameters related to melt were assumed to be -
0.1 for all materials. Values for the “a” parameters related to
crystallized melt and pyroxenitic component in mantle materials
(mantle lithosphere, asthenosphere and plume) were estimated
calculating rock densities for different pressure and temperature from
bulk chemical compositions of pyroxenite-derived
14
and peridotite-
derived basalts
70
using a thermodynamic modeling approach
71
. For
density effect of melt extraction from peridotite (depletion) we use
data
72
. All these parameters were found to be close to 0.05 (0.045-
0.055) in the eclogite stability field. For simplicity, we assume them
to be equal to 0.05 in the eclogite stability field (here at depth > 55
km). Change of density due to gabbro-eclogite transformation
71
is
considered by linearly decreasing “a” parameters from 0.05 at depth
of 55 km to -0.05 at depth of 40 km.
With the accepted values of parameters, the buoyancy of the
thermo-chemical plume with an excess temperature of 250 °C
(Tp=1600°C) and an eclogite content of 15 % is only 10% of the
buoyancy of the purely thermal plume with the same temperature.
)1)(,(
0
mpr
mpr
impx
mp
iepr
epr
iepx
ep
x
ipx
px
ipr
pr
iii
X
a
X
a
X
a
X
a
X
a
X
a
T
P
+++++=
ρ
ρ
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Fig.S1. Compositions of representative Siberian trap olivine, compared with olivine from peridotite derived melts. A. Numbered lines and field are
compositions of olivine crystallized from peridotite derived melt with initial MgO content indicated by corresponding number
37
. Blue field outline compositions of
low magnesian olivines (Fo<60) from Siberian traps (Supplementary Table S3). Knipovich MORB K22-23-stands for olivine compositions from Knipovich ridge
MORB sample with almost zero content of pyroxenitic component in the melt
18
. C. Solid black lines indicate linear regression lines for the olivine of different
samples. Other symbols are as on Fig S1A. D. Dashed red and green lines are suggested boundaries for FeO/MnO ratios of end-member olivines crystallized from
pyroxenite and peridotite derived melts respectively. Slope of these lines constrained to be parallel to the dominant slope of trend lines. Other symbols are as on
Fig S1A,B. Error bars outlined by the blue circle are 2-standard deviations estimated from repeated analyses of olivine standard.
Model setup
The setup and boundary conditions for our
preferred model are presented in Fig. S2. We
assume that the plume head arrives at the base
of the cratonic root at model time 0. The left
model boundary is open for inwards- and
outwards flow of material, while the right
boundary and bottom are closed, to avoid
instabilities. We use a non-uniform grid to
better resolve the central part of the model.
Finite element size is 5 X 5 km in the best-
resolved part of the model. Tests show no
significant influence on model results of mesh
coarsening out of that region. Plume potential
temperature for the preferred model is
Tp=1600°C and the content of recycled oceanic
crust (eclogite) is 15 wt%. Evolution in time of
temperature and pyroxenite content are shown
in Fig. S3.
Fig. S2. Initial and boundary conditions for the preferred model. Background colors show initial
distribution of rock-types. Dark blue-upper crust, blue- lower crust, green- depleted mantle lithosphere,
yellow- asthenosphere, red- plume. White dashed line shows bottom of the thermal boundary layer,
where potential temperature, reaches asthenospheric temperature of 1350 °C. Potential temperature in
the plume head is 1600°C. Also shown is the finite element grid which is finest in the central-upper
part of the model.
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.
Fig. S3. Evolution of the potential temperature distribution Tp (left column) and of distribution of the pyroxenite component in the plume or in the
crystallized melt C_Px (right column))
Model sensitivity and preferred model
The intensity of lithospheric destruction and melt production
depend on (1) the initial thickness and degree of depletion of the
lithosphere (Fig. S4), (2) plume temperature, and volume (Fig. S5),
and (3) content of the recycled crust in the plume (Fig. S6).
Our preferred model is constrained by the petrological data,
i.e. a plume head potential temperature of 1600°C, 15 wt% of
recycled crust, and an initial thickness of depleted lithosphere of
130 km. A plume head radius of 400 km was chosen arbitrarily.
With the fixed initial thickness of the lithosphere, a lower plume
potential temperature (1500-1550°C instead of 1600°C in preferred
model), or a smaller plume (200-300 km radius instead of 400 km)
would result in much less extensive lithospheric delamination and
lower melt production (Fig. S5). A content of recycled crust
significantly higher than 15 wt% makes the plume negatively
buoyant (at plume potential temperature of 1600°C), while a lower
content results in large pre-magmatic uplift (Fig. S6).
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We prefer a model of re-fertilized mantle lithosphere because
the lithosphere of Siberian Craton experienced multiple
interactions with mantle plumes before the emplacement of
Siberian Traps, as evidenced by multiple phases of kimberlite
magmatism and synchronous flood basalts
73,74
. Choosing depleted
lithosphere with two-times larger density deficit does not
significantly change the results (Fig. 3a main text, dashed curve
and Fig. S4). However, further rise of the average degree of
depletion and density deficit, to 60 and 70 kg/m
3
, significantly
impedes lithospheric destruction (Fig. S4).
Fig. S4. Effect of thickness of the depleted lithosphere Hl (a) and degree of depletion (b) on the intensity of the lithospheric destruction. Shown are
potential temperature distributions at model time 1.0 Myr.
Fig. S5. Effect of a plume potential temperature, Tp (a) and a plume radius R (b) on the intensity of the lithospheric destruction. Shown are potential
temperature distributions at model time 1.0 Myr.
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Fig. S6. Effect of a plume composition on pre-magmatic surface topography (H) and on intensity of the lithospheric destruction. Shown is the maximum
pre-magmatic surface topography (upper panel) and temperature distributions at model times 0.5 and 1.0 Myr. Content of the recycled crust component in
plume (Xe) is 15 Wt% (a) and 7.5 Wt% (b).
_______________________________________________________________
58
Krivolutskaya, N. & Rudakova, A. Structure and Geochemical
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petrochemistry, and origin of the Siberian flood basalts, USSR.
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Sharma, M., Basu, A. R. & Nesterenko, G. V. Temporal Sr-isotopic, Nd-
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TableS1.Studiedsamplesandolivine.
Table S1 notes. Group: deep (high Gd/Ybn>1.6 =garnet signature), Sh shallow (low Gd/Ybn< 1.6 = no garnet in the
source),FomaximumamountofForsteritecontentinolivineinthesample.Region:NorNorilsk,PutPutoranaplateau,
MK MaymechaKotuy province. Unit: (Norilsk region GdGudchikhinskaya, TkTuklonskaya, NdNadezhdinskaya, Mr
Morangovskaya, MkMukulaevskaya, HrHaerlakhskaya, KmKumginskaya, SmSamoedskaya; Putorana plateau Ay
Ayanskaya, HoHonumanskaya; MaymechaKotuy province On Onkuchakskaya. Ref: references. Type: lavas or dykes.
Thick:thicknessinmeters.N1:Totalamountofolivinegrainsanalyzed.MaxFo:compositionofmostmagnesianolivine.
N2:amountof olivinegrainshavingcompositionwithin maximum 3mol%Fo.Avg Fo (3)averageof mostmagnesian
olivinegrainshavingcompositionwithinmaximum 3 mol% Fo. Xpx Ni and Xpx Mnproportionofpyroxenitederived
melt calculated from Ni excess and Mn deficiency correspondingly in average most magnesian olivine. Xpxaccepted
proportionofpyroxenitederived melt (see text).S.e.standarderror of mean. FeO/MnO correspondingrationforthe
averagemostmagnesianolivine.Gd/Ybnnormalizedtoprimitivemantle
5
ratioofbulkrock.
Sample Group Region !"#$ Ref Type Thick m N1 Max Fo N2 Avg Fo (3) Xpx Ni S.e Xpx Mn S.e Xpx S.e %&'()"' Gd/Yb n
SU-50 Deep Nor Gd S3 lava 345 128
!"#$%
75 79.71 1.32 0.01 0.99 0.00 1.15 0.17 !%#! 2.60
4270/13 Deep Nor Gd S3 lava 375 47
!&#'(
33 79.18 1.34 0.01 0.98 0.00 1.16 0.18 !%#( 2.34
!)*((
Deep Nor Gd new lava 380 52
!&#)+
7 79.12 1.38 0.03 1.02 0.01 1.20 0.18 !$#! 2.24
XS-51/130 Deep Nor Gd S3 lava 408 120
!$#$%
85 81.51 1.16 0.00 0.89 0.00 1.03 0.14 (+#) 2.27
991a Deep Put Ay new lava 1540 98
+&#&'
44 87.85 0.71 0.01 0.90 0.01 0.80 0.10 (+#+ 4.25
991b Deep Put Ay new lava 1560 103
!+#',
42 87.26 0.73 0.01 0.88 0.01 0.80 0.08 (+#$ 4.41
81-133 Deep Put Ay new lava 1580 100
!!#$+
73 86.59 0.75 0.00 0.84 0.00 0.80 0.05 (!#$ 4.50
!)*!)
Sh (Fo>60) Nor Tk new lava 580 9
("#+$
9 70.87 0.41 0.01 0.59 0.01 0.50 0.09 ("#, 1.37
SU31 Sh (Fo>60) Nor Tk S3 lava 586 75 76.66 14 74.92 0.32 0.01 0.49 0.01 0.40 0.08 )!#+ 1.28
SU33 Sh (Fo>60) Nor Tk S3 lava 587 8 73.57 8 73.02 0.34 0.01 0.52 0.01 0.43 0.09 )+#! 1.30
SU36 Sh (Fo>60) Nor Tk new lava 590 16 76.66 7 74.22 0.35 0.01 0.44 0.01 0.40 0.04 )(#+ 1.32
CY-315
Sh (Fo>60) Nor Tk new lava 592 62
((#%!
54 75.59 0.27 0.00 0.42 0.01 0.35 0.07 )(#' 1.36
530/12 Sh (Fo>60) Nor Nd S3 lava 840 17 79.41 1 79.41 0.49 0.59 0.54 0.05 ("#, 1.46
140-1
Sh (Fo>60) Nor Mr new lava 1200 34
)(#+)
2 67.74 0.61 0.04 0.55 0.08 0.58 0.03 (&#' 1.33
4002-14
Sh (Fo>60) Nor
Mk new lava
2049 36
)%#(!
1 62.78 0.64 0.48 0.56 0.08 )!#! 1.30
47-1
Sh (Fo>60) Nor
Mk new lava
2180 85
(%#(!
1 72.78 0.47 0.36 0.41 0.06 ))#" 1.22
4002-18
Sh (Fo>60) Nor
Hr new lava
2260 68
)!#++
23 66.99 0.56 0.00 0.37 0.00 0.46 0.10 ))#$ 1.21
63
Sh (Fo>60) Nor
Sm new lava
3030 89
($#&+
2 72.38 0.54 0.02 0.37 0.02 0.45 0.09 ))#% 1.19
85-63 Sh (Fo>60) Put Ay new lava 1500 57
("#+'
3 70.29 0.56 0.03 0.51 0.00 0.54 0.02 )+#, 1.14
83-50 Sh (Fo>60) Put Ho new lava 1800 39
)+#%)
2 68.83 0.57 0.03 0.44 0.01 0.50 0.06 )(#+ 1.32
1934-2 Sh (Fo>60) M-K
On new lava
1600 115
((#$$
5 75.61 0.57 0.03 0.45 0.02 0.51 0.06 )!#" 1.20
141-7 Sh (Fo<60) Nor Nd new lava 1175 48
'!#),
28 46.54 0.79 0.01 0.61 0.01 0.61 ("#! 1.22
126-3
Sh (Fo<60) Nor Mr new lava 1232 67
,%#!% )
50.77 0.80 0.02 0.58 0.03 0.58 ("#" 1.28
126-4
Sh (Fo<60) Nor Mr new lava 1258 48
,%#"+ )
50.70 1.05 0.02 0.70 0.01 0.70 ('#% 1.26
126-7
Sh (Fo<60) Nor Mr new lava 1321 36
,&#'' "%
49.06 0.91 0.01 0.56 0.01 0.56 (&#) 1.21
4002-2
Sh (Fo<60) Nor Mk new lava 1659 59 56.25
"
56.25 0.62 0.44 0.44 )(#+ 1.20
4002-5
Sh (Fo<60) Nor Mk new lava 1736 69
,(#,+ ,
56.88 0.67 0.02 0.44 0.03 0.44 )(#+ 1.23
4002-7
Sh (Fo<60) Nor Mk new lava 1818 52
,+#)& $
58.74 0.78 0.02 0.55 0.01 0.55 (&#' 1.28
4002-11
Sh (Fo<60) Nor Mk new lava 1906 73
,'#&& ""
52.17 0.93 0.02 0.55 0.01 0.55 (&#, 1.25
46-1
Sh (Fo<60) Nor Mk new lava 2080 45
'+#,& ',
48.33 1.08 0.01 0.68 0.01 0.68 ($#! 1.21
19-1
Sh (Fo<60) Nor Mk new lava 2130 12
'!#(, (
46.70 1.01 0.04 0.61 0.02 0.61 (%#& 1.22
136-13
Sh (Fo<60) Nor Mk new lava 2235 51
'+#$( $)
47.30 0.98 0.01 0.52 0.01 0.52 )+#! 1.15
4002-19
Sh (Fo<60) Nor Hr new lava 2310 60
'(#$& )&
46.16 1.14 0.01 0.63 0.00 0.63 (%#' 1.23
137-2
Sh (Fo<60) Nor Hr new lava 2430 27
,"#$$ +
50.02 1.08 0.02 0.56 0.01 0.56 (&#) 1.06
61-3
Sh (Fo<60) Nor Hr new lava 2460 12
'(#&( "%
45.85 0.92 0.02 0.48 0.01 0.48 )!#! 1.18
115-1 Sh (Fo<60) Nor Hr new lava 2650 111 59.01
"
59.01 0.71 0.34 0.34 ),#( 1.16
115-9 Sh (Fo<60) Nor Hr new lava 2800 75
,$#'' )
51.21 0.70 0.01 0.26 0.02 0.26 )'#& 1.29
62
Sh (Fo<60) Nor Km new lava 2862
6
')#,$ "
46.53 0.69 0.26 0.26 )'#& 1.30
62-1
Sh (Fo<60) Nor Km new lava 2890 37
'(#,$ "%
45.78 0.67 0.01 0.20 0.01 0.20 )%#! 1.22
119-1 Sh (Fo<60) Nor Km new lava 2900 48
,)#$" " ,)#$"
0.58 0.29 0.29 )'#) 1.21
137-11
Sh (Fo<60) Nor Km new lava 2930 18
,$#,& %
52.55 0.67 0.02 0.28 0.08 0.28 )'#' 1.22
125-4 Sh (Fo<60) Nor Sm new lava 3140 74
,!#,, "%
57.24 0.79 0.01 0.37 0.01 0.37 ))#$ 1.19
65-4
Sh (Fo<60) Nor Sm new lava 3420 83
,"#," !
49.82 0.85 0.02 0.36 0.01 0.36 ))#" 1.16
65-5
Sh (Fo<60) Nor Sm new lava 3480 48 55.36
"
55.36 0.68 0.47 0.47 )!#, 1.18
81-134 Sh (Fo<60) Put Ay new lava 1300 26 59.80
"
59.80 0.69 0.51 0.51 )+#) 1.15
22-6
Sh (Fo<60) Nor Hr-Sm new dyke - 71
(,#%(
15 73.67 0.58 0.01 0.49 0.01 0.53 0.05 )!#+ 1.19
22-12
Sh (Fo<60) Nor
Hr-Sm new
dyke - 51
(!#,%
28 76.64 0.37 0.00 0.21 0.01 0.29 0.08 )$#% 1.13
12-1 Sh (Fo<60) Nor
Hr-Sm new
dyke - 56 48.62 12 46.72 0.69 0.02 0.35 0.01 0.35 ))#& 1.26
39-3 Sh (Fo<60) Nor
Hr-Sm new
dyke - 98
,'#%"
87 52.46 0.84 0.00 0.36 0.00 0.36 ))#% 1.22
125-5 Sh (Fo<60) Nor
Hr-Sm new
dyke - 50
'!#"%
24 45.80 0.78 0.01 0.51 0.01 0.51 )+#) 1.18
120 Sh (Fo<60) Nor
Hr-Sm new
dyke - 75
)"#")
34 59.49 0.73 0.00 0.28 0.00 0.28 )'#, 1.16
WWW.NATURE.COM/NATURE | 7
SUPPLEMENTARY INFORMATION RESEARCH
SUPPLEMENTARYINFORMATION
TableS2.Modelparameters.
Parameter
Uppercrust
Lowercrust
Depleted
mantle
lithosphere
Asthenosphere
/plume
Density,[kg/m
3
]
2750
2950
3330Δρ
depl
3330
Thermalexpansion,[K
1
]
3.7·10
5
2.7·10
5
3.3·10
5
3.3·10
5
Elasticmoduli,K,G,[GPa]
55,36
63,40
122,74
122,74
Heatcapacity,[J/kg/K]
1200
1200
1200
1200
Heatconductivity,[W/K/m]
2.5
2.5
3.3
3.3
Heatproductivity,[W/m
3
]
1.3
0.2
0
0
Initialfrictionangle,[degree]
30
30
30
30
Initialcohesion,[MPa]
20
20
20
20
Diffusioncreep,log(A),[Pa
n
s
1
]


10.59
10.59
Diffusioncreepactivationenergy,[kJ/mol]


300
300
Grainsize[mm];Grainsizeexponent


1.0;2.5
1.0;2.5
Dislocationcreep,log(A),[Pa
n
s
1
]
28.0
15.4
15.2
14.7/14.3
Dislocationcreepactivationenergy,[kJ/mol]
223
356
530
515
Powerlawexponent
4.0
3.0
3.5
3.5
TableS2notes.Sourcesfordislocationcreeplaws:uppercrustquartzite
21
;lowercrust–wetplagioclase
22
;depletedmantle
lithosphere–dryperidotite
23
,asthenospherewetperidotitewith1000PpmH
2
O(asthenosphere)and2000PpmH
2
O
(plume)
23
.
TableS3.Compositionsofolivineandhostlavas.(Excelfile).
... These lavas exhibit Nd, Sr and Pb isotope signatures indicative of an SCLM component, with limited crustal contamination 38 . Assimilation of the deep SCLM is particularly important because this zone is metasomatically enriched in carbonates and is thus a major carbon reservoir [39][40][41][42] . Ridge + low LIP prod. ...
... 3 and 4a and Extended Data Fig. 4) allowed for the melting of deep, carbonate-rich domains of SCLM 40,41,43 . This is in some ways analogous to the carbon-release scenario proposed for the Siberian Traps, linked to the Permo-Triassic extinction event 42 . Thickening of such carbonate-enriched SCLM is thought to occur during supercontinent formation, followed by thermal re-equilibration resulting in warming and conversion to asthenosphere 46 . ...
... This enhanced mantle melting occurred contemporaneously with methane release from hydrothermal vents related to the same phases of magmatism 15,16,54 , which potentially supplied an isotopically lighter end member to the PETM carbon cycle 11 . Our study supports the proposal that large-scale lithospheric melting can induce global warming 42 if the tectonic setting is primed to facilitate intensive magmatic CO 2 release (Fig. 4). This highlights the critical role that solid Earth degassing plays in driving abrupt hyperthermal events such as the PETM, promoting fundamental reorganization of Earth's surface environment and biosphere. ...
Article
Full-text available
Plume magmatism and continental breakup led to the opening of the northeast Atlantic Ocean during the globally warm early Cenozoic. This warmth culminated in a transient (170 thousand year, kyr) hyperthermal event associated with a large, if poorly constrained, emission of carbon called the Palaeocene–Eocene Thermal Maximum (PETM) 56 million years ago (Ma). Methane from hydrothermal vents in the coeval North Atlantic Igneous Province (NAIP) has been proposed as the trigger, though isotopic constraints from deep sea sediments have instead implicated direct volcanic carbon dioxide (CO2) emissions. Here we calculate that background levels of volcanic outgassing from mid-ocean ridges and large igneous provinces yield only one-fifth of the carbon required to trigger the hyperthermal. However, geochemical analyses of volcanic sequences spanning the rift-to-drift phase of the NAIP indicate a sudden ~220 kyr-long intensification of magmatic activity coincident with the PETM. This was likely driven by thinning and enhanced decompression melting of the sub-continental lithospheric mantle, which critically contained a high proportion of carbon-rich metasomatic carbonates. Melting models and coupled tectonic–geochemical simulations indicate that >104 gigatons of subcrustal carbon was mobilized into the ocean and atmosphere sufficiently rapidly to explain the scale and pace of the PETM. A change in the style of rifting in the North Atlantic led to carbon fluxes from subcrustal melting that helped trigger the Palaeocene–Eocene Thermal Maximum, according to geochemical analyses of volcanic sequences as well as melting and tectonic modelling.
... Geochemical records indicate that solid-Earth degassing was unlikely the sole factor shaping global climate during this event. Foremost, the prolonged warm interval extends well beyond estimates for the timing of active carbon release (estimated <0.4 Myrs) from the Siberian Traps and adjacent coals 7,8,26,30,31 . Further, a decoupling between reconstructed temperatures and carbon outgassing rates during the initial temperature rise (based on oxygen and carbon isotopes respectively 32,33 from the Meishan section (South China)) was recently highlighted as potentially deviating from other well-characterized hyperthermal events such as the Paleocene-Eocene Thermal Maximum (PETM) even when accounting for the longer and therefore more severe climatic perturbation at the end-Permian (Fig. 2) 3 . ...
... Foremost, we calibrate the model to reproduce the most recent constraints of the modern global marine silica cycle fluxes 34 (including internal recycling of silica; Fig. 3). We adopted a stochastic approach for error propagation (Monte Carlo sampling) of standard parameters including silicate weathering, reverse weathering, extinction duration, climate sensitivity (temperature change with a doubling of pCO 2 ), and a volcanic plus associated sediment outgassing range of CO 2 input that encompasses the full range proposed from previous studies 7, 30,31 (Supplementary Tables 2 and 3). ...
Article
Full-text available
In the wake of rapid CO2 release tied to the emplacement of the Siberian Traps, elevated temperatures were maintained for over five million years during the end-Permian biotic crisis. This protracted recovery defies our current understanding of climate regulation via the silicate weathering feedback, and hints at a fundamentally altered carbon and silica cycle. Here, we propose that the development of widespread marine anoxia and Si-rich conditions, linked to the collapse of the biological silica factory, warming, and increased weathering, was capable of trapping Earth’s system within a hyperthermal by enhancing ocean-atmosphere CO2 recycling via authigenic clay formation. While solid-Earth degassing may have acted as a trigger, subsequent biotic feedbacks likely exacerbated and prolonged the environmental crisis. This refined view of the carbon-silica cycle highlights that the ecological success of siliceous organisms exerts a potentially significant influence on Earth’s climate regime. The widespread disappearance of siliceous life sustained extreme temperatures in the wake of Earth’s most severe mass extinction event.
... This event resulted in the abrupt extirpation of the primary coal-forming carbon sinks, such as the Glossopteris biome of Gondwana Vajda et al. 2020) and the tropical gigantopterid and conifer forests of east Asia . Evidence is converging on the Siberian Traps Large Igneous Province (Siberian Traps herein), a vast region of magmatic emplacement and volcanic eruption in northern Eurasia, as the ultimate cause of this extinction event (e.g., Reichow et al. 2009;Sobolev et al. 2011;Burgess et al. 2017). As a result of the Siberian Traps, a series of plausible direct kill mechanisms, or 'extinction drivers', have been proposed for the loss of marine species (see review by Dal Corso et al. 2022). ...
Article
Wildfire has been implicated as a potential driver of deforestation and continental biodiversity loss during the end-Permian extinction event (EPE;~252 Ma). However, it cannot be established whether wildfire activity was anomalous during the EPE without valid pre-and post-EPE baselines. Here, we assess the changes in wildfire activity in the high-latitude lowlands of eastern Gondwana by presenting new long-term, quantitative late Permian (Lopingian) to Early Triassic records of dispersed fossil charcoal and inertinite from sediments of the Sydney Basin, eastern Australia. We also document little-transported fossil charcoal occurrences in middle to late Permian (Guadalupian to Lopingian) permineralized peats of the Lambert Graben, East Antarctica, and Sydney and Bowen basins, eastern Australia, indicating that even vegetation of consistently moist high-latitude settings was prone to regular fire events. Our records show that wildfires were consistently prevalent through the Lopingian, but the EPE demonstrates a clear spike in activity. The relatively low charcoal and inertinite baseline for the Early Triassic is likely due in part to the lower vegetation density, which would have limited fire spread. We review the evidence for middle Permian to Lower Triassic charcoal in the geosphere, and the impacts of wildfires on sedimentation processes and the evolution of landscapes. Moreover, we assess the evidence of continental extinction drivers during the EPE within eastern Australia, and critically evaluate the role of wildfires as a cause and consequence of ecosystem collapse. The initial intensification of the fire regime during the EPE likely played a role in the initial loss of wetland carbon sinks, and contributed to increased greenhouse gas emissions and land and freshwater ecosystem changes. However, we conclude that elevated wildfire frequency was a short-lived phenomenon; recurrent wildfire events were unlikely to be the direct cause of the subsequent long-term absence of peat-forming wetland vegetation, and the associated 'coal gap' of the Early Triassic.
... If CO 2 is the main culprit (Bond and Wignall, 2014), then submarine volcanic outgassing will be just as important as subaerial eruptions. On the other hand, if the launching of other species such as SO 2 , Cl, and F into the atmosphere is the main cause of mass extinction (Self et al., 2008;Sobolev et al., 2011;Black et al., 2012Black et al., , 2014aBlack et al., , 2014bCallegaro et al., 2014;Schmidt et al., 2016), then submarine volcanism may not be as relevant, since these non-CO 2 species likely must be transported high into the atmosphere (typically stratosphere) to cause severe climate and ecosystem perturbations. This transport is much harder to do if the eruptions are underwater compared to when they are on land due to the rapid cooling of the plume and the dissolution of SO 2 by the seawater. ...
... It is known that the superplume activity that formed the Siberian traps had taken place just behind the volcanic arc at Late Permian (Sobolev et al., 2011) (Fig. 19). Another possible scenario is that the heat supply from the superplume that formed the Siberian traps caused partial melting of the oceanic slab subducted beneath the continental margin (Fig. 19). ...
Article
Full-text available
The geochemistry of the Permian–Triassic large-scale igneous rock body of northern Mongolia is a key factor in understanding the subduction-related magmatism at the margin of “Siberian continent.” Several studies have been done in the Permian–Triassic igneous body; however, its detailed magmagenesis and tectonic significance remain unclear. This paper investigates the geochemistry of the Upper Permian andesites (Bugat/Baruunburen Formation) and the Late Permian–Middle Triassic plutonic rocks (Selenge plutonic rock complex) of the Permian–Triassic igneous body, and intermediate dike intruding into them, and discusses the Late Permian–Middle Triassic magmatism of the Siberian continental margin. These rocks show a linear distribution on the variation diagram. They are therefore likely to be derived from a single magmatic source. The rocks, characterized by low K2O/Na2O, high Sr/Y, high La/Yb, and high Sr/La ratios are adakitic rocks of basaltic slab-melt origin. The samples are enriched in Cr and Ni and have a high Mg# compared with the typical slab-melt. This is likely due to an interaction between the slab-melt and the overlying mantle peridotite during its ascent. The Nb/Ta variation of the samples may point crustal contamination to the magma. The paleolatitude of the Bugat/Baruunburen Formation is calculated to be 37.1° N based on thermal remanent magnetization. Therefore, the Late Permian–Middle Triassic large-scale adakitic igneous activity had taken place in the volcanic arc along the Siberian continental margin in the mid-latitudes of the Northern Hemisphere. The geochemical characteristics of the intermediate dike are almost the same as those of the Bugat/Baruunburen Formation and the Selenge plutonic rock complex, indicating that adakitic igneous activity continued after the Early Triassic.
... Prior to the onset of Hirnantian LIP conditions, stepwise magmaticfree uplifting pulses were recorded in the Alborz Terrane, as predicted above mantle plume head models. Mantle plumes are responsible for topographic thermal domes up to 2 km in elevation, and many hundreds to a few thousand kilometres in size (Saunders et al., 2007;Sobolev et al., 2011). This process is considered to be an important mechanism for driving regional pre-and syn-eruptive surface uplift and denudation of large continental areas. ...
Article
Recent reconnaissance geological mapping, identification of unconformities and chronostratigraphic dating of Miaolingian to Ordovician strata in the eastern Alborz Mountains have led to recognition of synsedimentary uplift episodes associated with block tilting and partial erosion of the Cambrian Mila and Ordovician Simeh Kuh, Qumes and Lashkarak formations. A chronostratigraphic revision of the Miaolingian-Late Ordovician fossil content is presented, and the Steptoean Positive Carbon Isotope Excursion (SPICE) chemostratigraphic shift, marking the Miaolingian–Furongian boundary, is constrained close to the Members 2/3 contact in the Mila Formation. Upper Ordovician basaltic lava flows embedded in the Abarsaj Formation and Devonian sills and dykes intruded in the Mila and Simeh-Kuh formations were geochemically analysed and compared with the voluminous lava eru