Contrib Mineral Petrol
DOI 10.1007/s00410-012-0830-9
ORIGINAL PAPER
A petrologic, geochemical and Sr–Nd isotopic study on contact
metamorphism and degassing of Devonian evaporites
in the Norilsk aureoles, Siberia
Kwan-Nang Pang • Nicholas Arndt • Henrik Svensen •
Sverre Planke • Alexander Polozov • Stephane Polteau
Yoshiyuki Iizuka • Sun-Lin Chung
•
Received: 19 May 2012 / Accepted: 3 November 2012
Ó Springer-Verlag Berlin Heidelberg 2012
Abstract Devonian evaporites and associated sedimentary rocks in the Norilsk region were contact metamorphosed during emplacement of mafic sills that form part of
the end-Permian (*252 Ma) Siberian Traps. We present
mineralogical, geochemical and Sr–Nd isotopic data on
sedimentary rocks unaffected by metamorphism, and metasedimentary rocks from selected contact aureoles at
Norilsk, to examine the mechanisms responsible for
magma-evaporite interaction and its relation to the endPermian environmental crisis. The sedimentary rocks
include massive anhydrite, rock salt, dolostone, calcareous
siltstones and shale, and the meta-sedimentary rocks
Communicated by T. L. Grove.
Electronic supplementary material The online version of this
article (doi:10.1007/s00410-012-0830-9) contains supplementary
material, which is available to authorized users.
K.-N. Pang N. Arndt
Institut des Sciences de la Terre, Université Joseph Fourier,
1381 rue de la Piscine, 38401 Grenoble, France
K.-N. Pang (&) S.-L. Chung
Department of Geosciences, National Taiwan University,
P.O. Box 13-318, Taipei 10699, Taiwan
e-mail: knpang@ntu.edu.tw
H. Svensen S. Planke S. Polteau
Physics of Geological Processes (PGP), University of Oslo,
PO Box 1048, Blindern, 0316 Oslo, Norway
A. Polozov
Institute of Geology of Ore Deposits, Petrography,
Mineralogy and Geochemistry, Russian Academy of Sciences,
119017 Moscow, Russia
Y. Iizuka
Institute of Earth Science, Academia Sinica, 128 Academia Road
Section 2, Nankang Taipei 11529, Taiwan
comprise calcareous hornfels, siliceous hornfels and minor
meta-anhydrite and meta-sandstone. Contact metamorphism took place at low pressure and at maximum
temperatures corresponding to the phlogopite-diopside
stability field. Calcareous hornfels have high CaO, MgO,
CO2, SO3, low SiO2 and initial Sr isotopic ratios of
0.7079–0.7092, features indicative of calcareous siltstone
protoliths. Siliceous hornfels, in contrast, have high SiO2,
Al2O3, Na2O, low in other major element oxides and initial
Sr isotopic ratios of 0.7083–0.7152, consistent with pelitic
or shaley protoliths. Loss of CO2 in a subset of calcareous
hornfels can be explained by decarbonation reactions during metamorphism, but release of SO2 from evaporites
cannot be accounted for by a similar mechanism. Occurrences of wollastonite and a variety of hydrous minerals in
the calcareous hornfels are consistent with equilibration
with hydrous fluid, which was capable of leaching large
quantities of anhydrite in the presence of dissolved NaCl.
In this way, substantial sediment-derived sulfur could have
been mobilized, incorporated into the magmatic system
and released to the atmosphere. The release of CO2 and
SO2 from Siberian evaporites added to the variety of toxic
gases generated during metamorphism of organic matter,
coal and rock salt, contributing to the end-Permian environmental crisis.
Keywords Contact aureole Metamorphism End-Permian Evaporite Norilsk Siberian Traps
Introduction
Extensive Paleozoic evaporites, marls, organic-rich shales
and coal formations in the Tunguska Basin, East Siberia,
were intruded by sills related to the plumbing system of the
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end-Permian Siberian Traps (Naldrett et al. 1995; Kontorovich et al. 1997; Naldrett and Lightfoot 1999; Arndt
et al. 2003). The Siberian flood basaltic volcanism was
associated with the largest known environmental crisis in
the Earth’s history, causing up to 70 % of terrestrial and
95 % of marine species to become extinct (Sharma 1997;
Wignall 2001). Recent studies propose that the crisis was
triggered by emission of sediment-derived greenhouse and
toxic gases during emplacement of the sills (Retallack and
Jahren 2008; Svensen et al. 2004, 2009a; Ganino and Arndt
2009). Other authors, however, suggest that the extinction
might have predated the main phase of volcanism and
propose that its trigger was degassing of magmatic CO2
and HCl from altered oceanic crust (Sobolev et al. 2011).
While the arguments for these competing hypotheses are
still debatable, new data and observations in this context
are important in understanding the relations between flood
basaltic volcanism and mass extinctions.
In the Norilsk region, northern Siberia, available data
and observations point to extensive magma-evaporite
interaction, including (1) development of extensive contact
aureoles surrounding the intrusions related to the Siberian
Traps (Likhachev 1994; Turovtsev 2002; Naldrett 2004),
(2) occurrence of magmatic anhydrite in the intrusions
(Li et al. 2009a; Ripley et al. 2010), (3) high 87Sr/86Sr in
the intrusions (Arndt et al. 2003), (4) high 34S in sulfides in
Ni–Cu–(PGE) sulfide ore-bearing intrusions (Gorbachev
and Grinenko 1973; Grinenko 1985; Li et al. 2003) and (5)
high Cl contents of olivine-hosted melt inclusions in the
Gudchikhinsky picrites (Sobolev et al. 2009). However,
most previous studies have focused mainly on the intrusions; systematic studies of the evaporitic host rocks by
modern methods have not been carried out, except for
earlier comprehensive petrographic studies in Russian that
are not generally available (e.g., Turovtsev 2002). In particular, Turovtsev (2002) focused on metamorphism of
terrigenous and carbonate rocks but did not investigate
evaporite metamorphism in detail. Further, as noted by
Walker et al. (1994) and Naldrett (2004), good Sr isotopic
analyses of anhydrite at Norilsk are not generally available
but important to evaluate magma-evaporite interaction.
Here, we present a comparative mineralogical, geochemical and Sr–Nd isotopic study on sedimentary rocks unaffected by contact metamorphism, and meta-sedimentary
rocks from selected contact aureoles from boreholes and
outcrops in the Norilsk region.
Geological background
The Tunguska Basin is situated on the Siberian craton and
contains one of the oldest known petroleum systems in the
world (Frolov et al. 2011). The Precambrian basement
123
consists of granitoids, granitic gneisses, schists and amphibolites. The sedimentary rocks are Neoproterozoic to
Permian in age with total thicknesses ranging from 3 to
12.5 km (Kontorovich et al. 1997). The Neoproterozoic
strata are dominated by carbonates with minor shale,
sandstone and evaporites, overlain by thick (up to
*2.5 km) Cambrian marine evaporite deposits composed
of salt, anhydrite and carbonates in the southern parts of the
basin. In the Norilsk region, rock salt is generally absent in
the Cambrian succession, but is present locally within
Devonian sediments. The Ordovician to Devonian sequences are also dominated by the evaporitic facies consisting of
carbonates, marls, anhydrites with minor salt layers. The
Carboniferous to Lower Permian strata comprise terrigenous sedimentary rocks including conglomerates, sandstones, siltstones and coals, collectively referred to as the
Tunguska series. Sedimentation terminated in the Upper
Permian with the onset of flood basalt volcanism of the
Siberian Traps (Surkov et al. 1991; Ulmishek 2001).
The end-Permian (*252 Ma) Siberian Traps is the
world’s largest continental large igneous province (LIP)
covering an area of at least 4.5 9 106 km2 with a total
volume of *4 9 106 km3 in the northwestern part of the
Siberian craton and widespread sub-surface extension in
the West Siberian Basin (Sharma 1997; Czamanske et al.
2002; Reichow et al. 2002; Saunders et al. 2005). The
on-craton exposure of the province encompasses a central
region of flood basalts and basaltic pyroclastic rocks suggested to have erupted in less than one million years (Kamo
et al. 2003). The lava pile, typically [3 km-thick in the
northwest, thinner to the southeast and absent in the south,
comprises dominantly tholeiite basalt and minor picrite
with minor alkaline rocks of more diverse compositions
(from trachyte to meimechite). The intrusive facies of the
province crop out mainly at the margins of the volcanic
pile but are penetrated by boreholes throughout the basin.
Phreatomagmatic pipes with hydrothermal magnetite
mineralization, likely rooted in Cambrian evaporites, are
abundant in the southern part of the province (Von der
Flaass and Naumov 1995; Svensen et al. 2009a, b). Basaltic
pipes are known from the northern part of the province (see
Fig. 1) but have not been subjected to detailed studies.
Norilsk lies between the Yenisey-Khatanga trough and
the West Siberian Basin in northern Siberia (Fig. 1). It is
located near the northwestern boundary of the Siberian
Traps where both extrusive and intrusive facies crop out.
The extrusive facies consists of thick piles of basaltic lavas
that erupted onto the Tunguska Basin sedimentary rocks.
The intrusive facies occurs as sills within Devonian to
Permian strata and, to a lesser extent, within the Precambrian basement. Exposure of the intrusions is controlled by deep crustal faults trending in northeasterly
directions (Zen’ko and Czamanske 1994). Some intrusions
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Fig. 1 Simplified geological
map of the Norilsk region,
Siberia (after Malitch et al.
1999)
(i.e., Norilsk I, Talnakh and Kharaelakh) host large Ni–Cu–
(PGE) sulfide deposits, representing one of the largest
accumulations of magmatic sulfides in the world. One
unusual feature of the ore-bearing intrusions is the development of intense metamorphic and metasomatic aureoles,
which are in many cases as thick as, or thicker than, the
intrusions (Likhachev 1994; Naldrett 2004). Sulfur isotopic
studies of the ore sulfides indicate that ore formation
involved isotopically heavy crustal S derived from the
evaporitic country rocks (Grinenko 1985; Li et al. 2003).
The presence in the Kharaelakh intrusion of magmatic
anhydrite, a rare mineral in intra-plate magmatic rocks, has
been taken as evidence of evaporite assimilation by the
ascending magma (Li et al. 2009a; Ripley et al. 2010).
Sample descriptions
During a 2006 field campaign to the Norilsk region, diamond drill-cores stored at the Talnakh mine site were
investigated. Figure 1 shows the locations of boreholes.
The on-site work included borehole logging and sampling
at representative intervals (Fig. 2). The drill-cores intersect
Silurian to Permian strata almost unaffected by contact
metamorphism (MD56), meta-sedimentary rocks in the
Mikchangda area (MD48) and those occurring in the upper
aureole of the ore-bearing Talnakh intrusion (TG21).
Table 1 shows the lithology of the samples and the geological formations that they belong to. Additional samples
were collected from outcrops and underground mine
exposure in the Norilsk region.
Drill-core MD56 contains Devonian and Silurian
evaporitic strata with thicknesses of *600 and *400 m,
respectively. The Upper Devonian Nakokhoz and Lower
Devonian Zubov Formations represent sulfate-bearing
sequences, and the Middle Devonian Manturov Formation
consists of halite-bearing sequences (Zharkov 1984).
These sequences are overlain by a *200 m-thick
sequence of Carboniferous to Permian sandstone, siltstone, shale and coal seams intruded by minor sills. The
evaporitic strata are largely free of sills and show no
petrographic evidence of metamorphism. Most samples
appear homogeneous at the scale of hand specimen or
polished thin section; laminations or veins in some
heterogeneous samples are separated to become a subsample if possible. The rocks have variable relative
abundance between chemical sedimentary and clastic
fractions and include massive anhydrite, dolostone, rock
salt, calcareous siltstones and shale (Table 2). Anhydrite,
dolomite, calcite and halite in the rocks are fine-grained
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Fig. 2 Logs of drill-cores from which the majority of samples in this
study were taken, based on our logging and available logs. Note that
drill-cores MD56 and MD48 were reduced in size by 50 % compared
to TG21. Areas bounded by the green line denote portions of the
contact aureole illustrated in Fig. 9. asl above sea level
and granular. The clastic fraction of the rocks, if present,
is composed of fine-grained mixture of quartz and clay
minerals with or without chlorite and muscovite. Sample
MD56-36 is an organic-rich shale belonging to the
Carboniferous-Permian Tunguska series. It contains rutile
and pyrite apart from the aforementioned silicate phases.
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Table 1 Lithology and geological formations of samples in this study
Formation
Evaporites and
carbonates
Carboniferous-Permian Tunguska
Clastic rocks
Calcareous hornfels
and meta-anhydrite
Siliceous
hornfels
MD56-36
Upper Devonian Kalargon (D3kl)
MD56-34
Upper Devonian Nakokhoz (D3nk)
MD56-31
Middle Devonian Manturov (D2mt)
MD56-26
MD48-1, 2, 4, 6b
Lower Devonian Razvedochnaya (D1rz)
TG21-1 to 5, 7 to 10
Lower Devonian Zubov (D1zb)
MD56-19, 22, 23 MD48-16,
17, 23a, 24
Lower Silurian Tanymen (S1tm)
MD56-9a
Drill-core MD48 was aimed for prospecting of Ni-Cu
mineralization and intersects multiple sills and the metasedimentary rocks occurring between them in the
Mikchangda area. The cumulative thickness of the sills,
which are intercalated with meta-sedimentary rocks, is
*550 m (Fig. 2). The samples are taken from an interval
corresponding to the Devonian evaporitic strata of drillcore MD56, including the high-temperature zones between
sills (MD48-1 to MD48-6) and the lower aureole of the
sills (MD48-11 to MD48-24) (Fig. 2). Samples from the
high-temperature zones occur close to the sills and some of
them even contain parts of the sills (Fig. 3a), which are
separated to become a sub-sample if possible. The metasedimentary rocks (or portions of the rocks) display
heterogranular textures typical of contact metamorphic
rocks, including the development of porphyroblasts and
mineral clusters in a fine-grained matrix. The porphyroblasts include clinopyroxene, amphibole, phlogopite,
chlorite and anhydrite. Titanite, pyrite, calcite, Fe–Ti
oxides, Cr-spinel and Mg–Al spinel occur as accessory
minerals. The matrix contains mainly microcrystals of
similar mineralogy as the porphyroblasts and minor finegrained portions whose mineralogy cannot be identified
under optical microscope. Samples from the lower aureole
in general show low degrees of recrystallization hence
higher portion of the fine-grained matrix compared to those
from the high-temperature zones. They also show fine
laminations presumably corresponding to the original
bedding prior to metamorphism. Sample MD48-11, taken
at *5.2 m from the intrusive contact, is mineralogically
similar to samples present in the high-temperature zones
mentioned above, except in addition containing small
amount of apatite. Layers of massive, fine-grained gray
anhydrite are present in the aureole at *7.9 m and 18.6 m
from the sill contact (Table 2). Sample MD48-14 further
from the contact contains K-feldspar instead of phlogopite
as the major K-bearing phase. Sample MD48-17 contains
actinolite but is clinopyroxene-free. Sample MD48-23a,
MD48-11 to 14
taken at *69.3 m from the intrusive contact, shows no
signs of recrystallization and resembles sample MD56-22
in terms of textures. Therefore, the total thickness of the
lower Mikchangda aureole might be less than *70 m as
defined by textures and mineralogy.
Drill-core TG21 intersects the *160 m-thick Talnakh
intrusion and its contact aureole. The samples, taken along
a *230 m-thick interval from the upper aureole, are heterogranular meta-sedimentary rocks. Metamorphic nodules, in the scale of several millimeters, and mineral
clusters occur in a finer-grained matrix in these rocks.
Chlorite, muscovite and quartz are major matrix phases;
albite is concentrated in the rims of the metamorphic
nodules. Apatite, calcite, anhydrite, K-feldspar, monazite,
Fe–Ti oxides, phlogopite, pyrite and rutile occur as
accessory minerals. Sulfide and magnetite mineralization,
and veins of calcite and gypsum are noted in some places
along this drill-core.
Additional samples were collected from underground
exposure of the Kharaelakh intrusion in the Oktyabysky
mine and outcrops of the Chernogorsk intrusion. Sample
NOR-2a and NOR-3 are fine-grained siliceous hornfels
adjacent to massive sulfide ore in the Kharaelakh intrusion.
They have a mineral assemblage consisting of albite,
chlorite, muscovite and quartz with or without amphibole
and garnet. Samples NOR-5, NOR-6, NOR-7a to NOR-7e
are meta-sedimentary rocks that are texturally similar to
those from the high-temperature zones of drill-core MD48.
A major difference is the presence of wollastonite and
garnet in these samples indicative of a relatively high
metamorphic grade. Samples NOR-14a, NOR-14b and
NOR-16 are enclaves of meta-sandstone in the Chernogorsk intrusion. They contain equigranular quartz and
feldspar with minor muscovite. Samples NOR-15 and
NOR-17 are fine-grained siliceous hornfels close to the
contact of the intrusion. The texture and mineralogy of
these rocks are similar to meta-sedimentary rocks in drillcore TG21.
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Table 2 Texture and mineralogy of samples in this study
Sample
Depth (m)
Rock type
Texture
Mineral phases1
Remarks
Cc vein (as MD56-9b)
Drill-core MD56
MD56-9a
1,178.0
Calcareous siltstone
Finely laminated
Cc, Qtz, Kfs
MD56-19
815.0
Rock salt
Coarse crystalline
Hl
MD56-22
744.6
Calcareous siltstone
Fine granular
Qtz, Kfs, Cc, Anh,
MD56-23
742.7
Calcareous siltstone
Fine granular
Qtz, Kfs
MD56-26
504.5
Massive anhydrite
Fine crystalline
Anh
MD56-31
382.6
Massive anhydrite
Fine crystalline
Anh
MD56-34
323.6
Dolostone
Massive
Cc2
MD56-36
231.3
Shale
Finely laminated, deformed
Ms, Chl, Qtz, Kfs, Rt
Anh-Cls vein
Drill-core MD48
MD48-1
704.6
Calcareous hornfels
Heterogranular crystalline
Cpx, Phl, Amp, Chl,
Anh, Cc, Opa, Ttn
MD48-2
717.7
Calcareous hornfels
Heterogranular crystalline
Cpx, Phl, Chl, Ep, Anh,
Ttn, Py
MD48-4
735.0
Calcareous hornfels
Heterogranular crystalline
Cpx, Phl, Chl, Anh, Cc, Opa
MD48-6b
742.8
Calcareous hornfels
Heterogranular crystalline
MD48-11
1,257.8
Calcareous hornfels
Finely laminated
Cpx, Phl, Chl, Anh, Cc,
Opa, Ap, Spn
Cpx, Phl, Amp, Chl, Anh,
Cc, Opa, Ap
MD48-12
1,260.0
Calcareous hornfels
Fine granular, spotted
Cpx, Phl, Anh, Cc
MD48-13
1,260.5
Meta-anhydrite
Fine crystalline
Anh
MD48-14
1,262.0
Calcareous hornfels
Finely laminated
Cpx, Kfs, Cc, Ttn, Ap
MD48-16
1,271.2
Meta-anhydrite
Fine crystalline
Anh
MD48-17
1,275.2
Calcareous hornfels
Finely laminated, spotted
Amp, Chl, Kfs, Ab,
Cc, Ttn, Ap
MD48-23a
1,321.9
Calcareous hornfels
Fine granular
Qtz, Kfs, Cc, Opa, Ap
MD48-24
1,338.1
Calcareous hornfels
Fine granular
Ms, Chl, Qtz, Cc, Kfs
Anh-Cls vein
(as MD48-23b)
Drill-core TG21
TG21-1
981.0
Siliceous hornfels
Heterogranular crystalline, spotted
Qtz, Chl, Ms, Ab, Cc, Ap
TG21-2
992.6
Siliceous hornfels
Heterogranular crystalline
Qtz, Chl, Ms, Ab, Ap
TG21-3
1,005.6
Siliceous hornfels
Heterogranular crystalline, spotted
Qtz, Chl, Ms, Ab, Opa,
Mnz, Rt, Cr-Spn
TG21-4
1,010.5
Siliceous hornfels
Heterogranular crystalline, spotted
Qtz, Chl, Ms, Opa, Mnz,
Ap, Rt, Py, Cr-Spn
TG21-5
1,070.5
Siliceous hornfels
Coarsely crystalline
Qtz, Chl, Ms, Ab
TG21-7
1,143.6
Siliceous hornfels
Heterogranular crystalline
Qtz, Chl, Ms, Ab, Ap
TG21-8
1,159.1
Siliceous hornfels
Coarsely crystalline
Qtz, Chl, Ms, Ab, Ap
TG21-9
1,165.1
Siliceous hornfels
Coarsely crystalline
Qtz, Chl, Ms, Ab, Ap
TG21-10
1,197.0
Siliceous hornfels
Heterogranular crystalline
Qtz, Chl, Ms, Ap, Rt, Cr-Spn
Amp, Chl, Ms, Ab, Ap, Cp
Cc-sulfide vein
Samples from mine exposures
NOR-2a
–
Siliceous hornfels
Fine crystalline
NOR-3
–
Siliceous hornfels
Fine crystalline
Grt, Chl, Ms, Ab
NOR-5
–
Calcareous hornfels
Heterogranular crystalline
Cpx, Grt, Anh, Cc, Cp
Anh vein
NOR-6
–
Calcareous hornfels
Heterogranular crystalline
Cpx, Grt, Wo, Anh, Cc
Anh vein
NOR-7a
–
Massive anhydrite
Fine crystalline
Anh
NOR-7b
NOR-7c
–
–
Calcareous hornfels
Calcareous hornfels
Heterogranular crystalline
Coarse crystalline
Cpx, Wo, Anh, Cc, Cp
Cpx, Grt, Wo, Anh, Cc, Cp
NOR-7d
–
Calcareous hornfels
Heterogranular crystalline
Cpx, Wo, Anh, Cc, Cp
NOR-7e
–
Calcareous hornfels
Heterogranular crystalline
Cpx, Grt, Wo, Anh, Cc, Cp
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Table 2 continued
Sample
Depth (m)
Rock type
Texture
Mineral phases1
NOR-14a
–
Meta-sandstone
Nodular
Qtz, Chl, Ab
NOR-14b
–
Meta-sandstone
Nodular
Qtz, Chl, Ab
NOR-15
–
Siliceous hornfels
Finely laminated
Qtz, Chl, Ms, Ab, Opa
NOR-16
–
Meta-sandstone
Nodular
Qtz, Chl, Ab
NOR-17
–
Siliceous hornfels
Finely laminated
Qtz, Chl, Ms, Ab
Remarks
1
Ab albite, Amp amphibole, Anh anhydrite, Ap apatite, Cc calcite-dolomite, Chl chlorite, Cls celestine, Cp chalcopyrite, Cpx clinopyroxene, CrSpn chrome spinel, Ep epidote, Grt garnet, Hl halite, Kfs K-feldspar, Mnz monazite, Ms muscovite, Opa opaque Fe–Ti oxides, Phl phlogopite, Py
pyrite, Qtz quartz, Rt rutile, Spn spinel, Ttn titanite, Wo wollastonite
Analytical methods
Light element analyses
Forty-three samples (8 sedimentary rocks and 35 metasedimentary rocks) were collected for this study, forming a
representative collection of available sediment and hornfels
types. Rock powders for geochemical and Sr–Nd isotopic
analyses were prepared by crushing of rock slabs on a steel
plate and pulverization in an agate mill. Polished thin
sections were prepared for petrographic observation and
electron microprobe analysis.
Measurements of total organic carbon and total inorganic
carbon were conducted by a Carbon Analyzer LECO
(CR-412) instrument at the Department of Geosciences,
University of Oslo. Sample powders weighing 350 mg
were loaded into combustible crucible boats. Aliquots of
inorganic carbon were released by addition of HCl at
40–50 °C. All crucibles with samples were washed, dried
and combusted in pure oxygen at 1,350 °C in the LECO
instrument. Analyses for H and S were performed at OEA
Laboratories Limited, Callington, UK. Sample powders
and V2O5 were loaded into tin capsules using a Mettler
ultra-microbalance. The sample capsules were dropped
sequentially into a reaction furnace packed with pure
tungsten oxide and Cu held at 1,000 °C with He as a carrier
gas. They were then flash combusted by a pulse of oxygen
at *1,700 °C. The resultant gases were purified and
separated on a packed GC column before flowing to the
detector for quantification on a CE instruments (Thermo)
EA1110 elemental analyzer. The light element data were
expressed as total organic C (TOC), CO2 (carbonates), H2O
and SO3 for the ease of comparison with other major
element data.
Electron microprobe analysis
The samples were analyzed with a JEOL JXA-8500F
electron probe microanalyzer at Institute of Earth
Sciences, Academia Sinica, Taiwan. The analyses were
performed using wavelength-dispersive method at an
accelerating voltage of 12 kV, a beam current of 3 nA, a
beam diameter of 2 lm and a peak counting time of 10 s.
Accuracy of the analyses was monitored using mineral
standards, and precision was generally better than 1 % for
most elements.
Major and trace element analyses
Sr–Nd isotopic analyses
Major element oxides and trace element abundances were
measured using routine methods by inductively coupled
plasma-atomic emission spectrometry (ICP-AES) and
inductively coupled plasma-mass spectrometry (ICP-MS),
respectively, at the University of Grenoble, France.
Analytical procedures for the trace element analysis follow
Chauvel et al. (2010), with accuracy and precision generally better than ±5 % (relative) for most trace elements as
shown by statistics of duplicate analyses of samples and of
reference material BE-N, BHVO-2, BR-24, RGM-1 and
JSd-2 (see electronic supplementary material). Loss on
ignition (LOI) was obtained by routine methods.
Measurements of Sr–Nd isotopes were performed by a
ThermoFinnigan Neptune Multi-collector ICP-MS at
Department of Geosciences, National Taiwan University,
Taiwan. Analytical procedures are the same as in Lee et al.
(2012). Within-run isotopic fractionation was corrected for
88
Sr/86Sr = 8.375209 and 146Nd/144Nd = 0.7219. The
87
Sr/86Sr ratio of the Sr standard SRM987 was
0.71029 ± 1, and the 143Nd/144Nd ratio of the La Jolla
standard JNdi-1 was 0.512122 ± 7 through the course of
the measurements. The data were calculated as initial
87
Sr/86Sr and eNd values relative to an age of 251 Ma,
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Contrib Mineral Petrol
Fig. 3 Scans of thin sections, photomicrographs and backscattered
electron images of representative samples from the Norilsk contact
aureoles, Siberia. a Contact between dolerite and calcareous hornfels
(sample MD48-1); the grain size of the hornfels is coarsened toward
the contact as a result of contact metamorphism. b Metamorphic
nodules rich in albite in a fine-grained matrix in siliceous hornfels
(sample TG21-3). c Chlorite and clinopyroxene crystals surrounded
by anhydrite porphyroblast in calcareous hornfels (sample NOR-7c,
123
crossed polars). d Fine crystals of muscovite and albite, and fibrous
chlorite in siliceous hornfels (sample NOR-2a, crossed polars).
e Chlorite, either fibrous or crystalline, and fine clinopyroxene grains
surrounded by coarse anhydrite and phlogopite crystals in calcareous
hornfels (sample MD48-4). f Fibrous chlorite and muscovite, and fine
quartz grains in siliceous hornfels (sample TG21-10). Ab albite, Anh
anhydrite, Chl(c/f) chlorite (crystalline/fibrous), Cpx clinopyroxene,
Ms muscovite, Qtz quartz
Contrib Mineral Petrol
decay constants of 1.42 9 10-11 year-1 for 87Rb, 6.54 9
10-12 year-1 for 147Sm, and present day chondritic values
143
147
of
Nd/144Nd = 0.512638,
Sm/144Nd = 0.1967,
87
86
87
86
Sr/ Sr = 0.7045 and Rb/ Sr = 0.0827 (Faure and
Mensing 2005).
Results
Mineral compositions
Representative analyses of minerals from the Norilsk
aureoles are listed in Table 3. The full dataset, together
with mineral chemical data presented by Turovtsev (2002),
is provided as an electronic supplement. Data for clinopyroxene, phlogopite and amphibole are calculated using
the programs PYROX (Yavuz 2001), MICA ? (Yavuz
2003) and WinAmphcal (Yavuz 2007), respectively. Minerals indicative of peak metamorphic conditions of the
Mikchangda aureole include clinopyroxene and phlogopite.
Clinopyroxene has compositions between augite and
diopside with variable degrees of Tschermak substitution
(Fig. 4a). This is reflected in the highly variable Al2O3
content of clinopyroxene ranging from less than 1 to *13
wt% (see supplementary material). Within-sample difference of several weight percent is common. The Mg# of
clinopyroxene ranges from 61 to 97 with the majority
between 78 and 85. Its TiO2 content is generally low
(\1 wt%), and Cr is mostly below detection limit. Some
analyses plot outside the pyroxene quadrilateral toward the
wollastonite apex, compared to those from the sills that are
dominated by augite (Fig. 4a). Phlogopite in the aureole
has low TiO2 (\0.5 wt%) and high Mg# (73–97, with the
majority [85). It contains H2O as the dominant volatile
species (3.5–4.5 wt%) and minor F (below detection limit
to 2 wt%) (see electronic supplementary material). Other
minerals from the aureole include chlorite (clinochlorechamosite solid solution), amphibole (magnesiotaramite),
albite, orthoclase (Fig. 4b), titanite and apatite (Table 3).
The major minerals from the Talnakh aureole include
muscovite, chlorite, albite and apatite (Table 3). The
muscovite has high Al2O3 (*28 to 35 wt%) and moderate
Mg# (38–80). Biotite containing up to *7 wt% F occurs as
patches associated with apatite, chlorite, rutile and pyrite in
sample TG21-4 (Table 3). Apatite contains F as the dominant volatile species (4.1–5.4 wt%, see supplementary
material), in contrast with that in the Mikchangda aureole
containing substantial Cl apart from F (Fig. 4c).
Major, trace and light elements
Major, trace and light element data for sedimentary rocks
in the Norilsk region and meta-sedimentary rocks from the
Norilsk aureoles are given as an electronic supplementary
material. Sedimentary rocks from drill-core MD56 display
wide compositional variations indicative of the relative
abundance of a chemical sedimentary and a detrital,
silty fraction (Figs. 5, 6). In a SiO2–(CaO ? MgO)–
(Al2O3 ? Na2O ? K2O) ternary diagram (Fig. 5), these
rocks fall on a linear trend between massive anhydrite and
dolostone near the (MgO ? CaO) apex and the shale
sample near the SiO2–(Al2O3 ? Na2O ? K2O) line. The
only exception is sample MD56-19, an impure rock salt
containing *6.3 wt% SiO2 and *30 wt% Na2O. Its Na2O
content implies *56 % halite by weight. Positive trends of
Al2O3, TiO2, Na2O, Cr, La, Zr and H2O with SiO2 suggest
that these components are controlled primarily by the
detrital fraction in the rocks (Figs. 6a, b, d–g, 7a). The
negative trend of (CaO ? MgO) versus SiO2 is consistent
with control by anhydrite and carbonates (Fig. 6c). The
lack of systematic variation between TOC and SiO2 indicates that the distribution of organic carbon is mostly
random (Fig. 7b). No correlations between CO2 or SO3 and
SiO2 suggest the relative abundance between anhydrite and
carbonates is variable in the chemical sedimentary fraction
(Fig. 7c, d). The sedimentary rocks display modest fractionation between light and heavy REE (e.g., La/Yb =
5.7–27.3). In mantle-normalized trace element diagrams,
they show consistent patterns marked by negative Ba, Nb,
Ta and Ti anomalies (Fig. 8a).
Samples from drill-core MD48 consist of massive
anhydrite and calcareous hornfels. The massive anhydrite
is compositionally similar to those from the nearby drillcore MD56, except for higher absolute abundance of most
trace elements (Fig. 8b). Calcareous hornfels have SiO2
(22.9–46.8 wt%), Al2O3 (5.0–13.9 wt%), Fe2O3 (3.0–6.1
wt%), CaO (9.4–28.8 wt%), MgO (6.6–22.8 wt%), CO2
(0.2–20.5 wt%), H2O (1.7–10.0 wt%) and SO3 (0.1–20.8
wt%) as major element oxides. The calcareous hornfels
tend to follow the major element trends shown by the
sedimentary rocks (Figs. 5, 6), except H2O extending to
much higher values (Fig. 7a). Like the sedimentary rocks,
massive anhydrite and calcareous hornfels from drill-core
MD48 also show negative Ba, Nb, Ta and Ti anomalies
(Fig. 8b). In addition, these rocks exhibit marked negative
Eu anomaly. Samples taken close to the intrusive contact
have low TOC and CO2 compared to those occurring at
distances greater than *60 m from the contact (Fig. 9a).
Drill-core TG21 consists entirely of siliceous hornfels
that have SiO2 (53.3–75.2 wt%), Al2O3 (13.8–24.9 wt%),
Fe2O3 (0.8–10.6 wt%), CaO (0.2–5.3 wt%), MgO (0.1–4.0
wt%), Na2O (0.4–10.8 wt%) and K2O (below detection
limit to 4.8 wt%) as major element oxides. The siliceous
hornfels do not follow the major element trends shown
by the sedimentary rocks (Figs. 5, 6). They display
slight fractionation between light and heavy REE (e.g.,
123
Contrib Mineral Petrol
Table 3 Representative electron microprobe analyses of minerals from the Norilsk contact aureoles, Siberia
Lab ID
SiO2
TiO2
Al2O3
Cr2O3
FeO
MnO
MgO
MD48-1
ES-10
50.10
1.01
3.30
0.30
10.57
0.14
14.16
MD48-2
Cs-2
46.44
0.00
10.25
0.00
5.89
0.00
12.26
MD48-4
C48
44.84
1.18
13.14
0.03
2.12
0.00
13.32
Sample
Mikchangda aureole
Clinopyroxene
MD48-6
E97
48.84
0.41
6.36
0.13
4.30
0.16
14.74
MD48-11
Bs-7
46.50
1.18
7.91
0.11
5.64
0.26
13.03
MD48-1
C-20
38.10
0.21
20.84
bdl3
4.66
0.00
21.94
MD48-2
A16
36.52
0.08
21.02
bdl
6.56
0.00
23.26
MD48-4
A11
40.08
0.15
17.68
bdl
2.25
0.00
25.44
MD48-6
E91
39.32
0.17
16.26
bdl
2.56
0.03
25.57
MD48-11
C28
38.59
0.00
18.52
bdl
5.16
0.00
23.38
MD48-2
MD48-4
B46
C58
28.83
32.02
0.17
bdl
20.25
19.60
bdl
bdl
16.89
1.88
0.00
0.13
21.93
32.71
MD48-11
C35
40.96
0.02
10.41
bdl
4.78
0.08
29.60
MD48-17
F68
31.66
0.09
19.55
bdl
10.09
0.14
25.57
Phlogopite
Chlorite
Amphibole
MD48-1
D-37
37.80
0.59
21.76
bdl
6.41
0.00
14.68
MD48-11
C24
40.66
0.69
15.74
bdl
8.28
0.00
16.12
MD48-11
D42
41.61
0.11
15.78
bdl
7.58
0.25
16.49
MD48-17
A5
54.18
0.09
6.14
bdl
5.21
0.02
18.48
MD48-14
A2-31
65.40
bdl
17.60
bdl
0.13
bdl
bdl
MD48-17
F73
65.06
bdl
18.17
bdl
0.30
bdl
bdl
MD48-17
D42
68.88
bdl
19.88
bdl
0.02
bdl
bdl
MD48-23
C6
65.41
bdl
18.21
bdl
0.01
bdl
bdl
MD48-1
MD48-2
A-5
A11
31.49
31.33
32.02
33.41
3.95
2.68
bdl
bdl
2.36
1.12
bdl
0.01
0.16
0.14
MD48-14
A2-4
31.22
36.44
1.64
bdl
1.33
0.21
bdl
MD48-11
C40
0.86
bdl
bdl
bdl
0.43
0.05
0.16
MD48-14
A2-22
0.41
bdl
bdl
bdl
0.32
0.00
0.08
MD48-17
C27
0.24
bdl
bdl
bdl
0.49
0.21
0.35
Feldspar
Titanite
Apatite
Talnakh aureole
Muscovite
TG21-3
A2-13
44.42
0.49
29.51
bdl
7.31
0.04
3.79
TG21-4
B-19
49.34
0.34
32.63
bdl
3.59
bdl
1.07
TG21-10
RR-24
46.84
bdl
32.57
bdl
4.41
0.04
1.78
TG21-10
Map1-59
46.03
0.06
32.51
bdl
4.15
0.15
1.91
TG21-4
A-83
43.41
0.57
14.25
bdl
7.96
bdl
16.86
TG21-4
A-85
44.35
0.44
16.59
bdl
7.15
0.00
14.22
Phlogopite
Chlorite
TG21-3
A2-15
28.60
0.18
24.25
bdl
25.72
0.13
8.32
TG21-3
Mat-54
24.87
0.19
23.58
bdl
29.23
0.38
10.24
TG21-4
A-90
25.56
0.72
18.00
bdl
41.55
0.03
3.04
123
Contrib Mineral Petrol
Table 3 continued
Lab ID
SiO2
TiO2
Al2O3
Cr2O3
FeO
MnO
MgO
TG21-4
B-14
39.67
0.28
19.18
bdl
22.23
bdl
5.56
TG21-10
R-17
24.88
bdl
22.89
bdl
35.30
0.04
5.35
TG21-3
Mat-60
68.28
bdl
20.00
bdl
0.22
bdl
bdl
TG21-3
Mat-63
67.95
bdl
20.39
bdl
0.00
bdl
bdl
Sample
Feldspar
Apatite
TG21-4
A-5
0.20
bdl
bdl
bdl
0.78
0.06
0.02
TG21-4
A-87
0.35
bdl
bdl
bdl
0.72
bdl
0.03
Sample
Lab ID
CaO
Na2O
K2O
P2O5
F
Cl
H2O1
Total
Mg#2
Mikchangda aureole
Clinopyroxene
MD48-1
ES-10
20.47
0.31
0.02
–
–
–
–
100.38
70.5
MD48-2
Cs-2
25.87
0.05
0.01
–
–
–
–
100.77
78.8
MD48-4
C48
24.98
0.76
0.12
–
–
–
–
100.49
91.8
MD48-6
E97
25.37
0.04
0.13
–
–
–
–
100.48
86.0
MD48-11
Bs-7
24.91
0.15
0.06
–
–
–
–
99.73
80.5
MD48-1
C-20
0.00
0.25
9.60
–
0.23
0.03
4.15
100.01
89.3
MD48-2
A16
0.20
0.44
7.49
–
0.00
0.02
4.24
99.83
86.3
MD48-4
A11
0.02
0.82
9.24
–
1.20
0.02
3.79
100.69
95.3
MD48-6
MD48-11
E91
C28
0.00
0.08
0.36
0.97
10.38
9.56
–
–
1.13
0.08
0.05
0.07
3.72
4.20
99.54
100.60
94.7
89.0
MD48-2
B46
0.16
0.00
0.13
–
0.05
0.00
12.03
100.43
69.8
MD48-4
C58
0.82
0.08
bdl
–
0.05
0.37
12.76
100.41
96.9
MD48-11
C35
1.32
0.01
0.12
–
0.12
0.23
12.76
100.41
91.7
MD48-17
F68
0.24
0.04
0.07
–
0.06
0.01
12.39
99.91
81.9
MD48-1
D-37
13.68
2.38
1.37
–
0.42
0.05
1.88
101.02
80.3
MD48-11
C24
12.67
2.77
1.05
–
0.26
0.18
1.90
100.31
77.6
MD48-11
D42
13.04
2.88
0.64
–
0.00
0.14
2.05
100.56
79.5
MD48-17
A5
11.90
0.47
1.44
–
0.11
0.04
2.09
100.18
86.3
MD48-14
A2-31
0.76
0.09
16.75
–
–
–
–
100.73
–
MD48-17
F73
0.16
0.13
16.33
–
–
–
–
100.15
–
MD48-17
MD48-23
D42
C6
0.32
0.06
10.92
0.17
0.10
16.32
–
–
–
–
–
–
–
–
100.12
100.18
–
–
MD48-1
A-5
28.34
0.06
bdl
–
0.23
0.02
1.02
99.66
–
MD48-2
A11
28.27
0.06
0.03
–
0.00
0.04
1.11
98.19
–
MD48-14
A2-4
27.80
bdl
0.24
–
bdl
bdl
1.13
100.00
–
MD48-11
C40
53.50
0.10
0.00
39.60
0.89
3.66
0.42
99.66
–
MD48-14
A2-22
54.14
0.12
0.15
41.31
2.33
2.51
0.09
101.45
–
MD48-17
C27
54.72
0.00
0.07
42.08
3.15
0.15
0.32
101.78
–
A2-13
0.00
0.26
10.22
–
0.22
0.28
4.21
100.75
48.0
Phlogopite
Chlorite
Amphibole
Feldspar
Titanite
Apatite
Talnakh aureole
Muscovite
TG21-3
123
Contrib Mineral Petrol
Table 3 continued
Lab ID
CaO
Na2O
K2O
P2O5
F
Cl
H2O1
Total
Mg#2
TG21-4
B-19
0.37
0.07
8.58
–
bdl
0.02
4.55
100.56
34.7
TG21-10
RR-24
0.04
0.23
9.51
–
0.18
0.15
4.35
100.11
41.9
TG21-10
Map1-59
0.08
0.42
9.70
–
bdl
0.23
4.38
99.60
45.1
TG21-4
A-83
0.51
0.22
9.72
–
7.31
0.29
0.91
102.02
79.0
TG21-4
A-85
0.70
0.20
9.85
–
4.65
0.26
2.11
98.76
78.0
TG21-3
A2-15
0.14
0.14
1.39
–
bdl
0.03
11.60
100.50
36.6
TG21-3
Mat-54
0.05
0.02
0.01
–
0.02
bdl
11.27
99.87
38.4
TG21-4
A-90
0.33
0.00
0.19
–
0.00
0.00
10.60
100.03
11.5
TG21-4
TG21-10
B-14
R-17
0.25
0.09
0.08
bdl
0.67
0.19
–
–
0.04
bdl
0.10
0.05
12.06
10.94
100.12
99.73
30.8
21.3
TG21-3
Mat-60
0.54
10.99
0.07
–
–
–
–
100.10
–
TG21-3
Mat-63
0.82
10.68
0.10
–
–
–
–
99.94
–
TG21-4
A-5
54.98
0.12
0.07
41.03
5.37
0.13
–
102.76
–
TG21-4
A-87
53.61
0.29
0.09
41.38
5.12
0.12
–
101.69
–
Sample
Phlogopite
Chlorite
Feldspar
Apatite
1
H2O calculated on the basis of ideal mineral formulae
2
Mg# = molar 100 9 Mg/(Mg ? Fe2?)
3
bdl = below detection limit
Fig. 4 Compositions of
a clinopyroxene, b feldspars and
c apatite in Paleozoic
sedimentary rocks and in metasedimentary rocks from the
Norilsk contact aureoles,
Siberia. Gray fields in a and
b denote our unpublished data
from the sills, whereas in
c denotes compositions of
igneous apatite in major layered
intrusions (after Boudreau et al.
1995)
a
Wo
Drill-core MD56 (sedimentary rocks)
Drill-core MD48 (calcareous hornfels
and meta-evaporites)
Drill-core TG21 (siliceous hornfels)
Diopside
Hedenbergite
Augite
Cpx from sills
Pigeonite
Enstatite
Hedenbergite
En
Fs
b
c
Or
F
Sanidine
Anorthoclase
Apatite from
layered intrusions
Plagioclase
from sills
Albite
Oligoclase
Andesine
Ab
123
Labradorite
Bytownite
Anorthite
An
Cl
OH
Contrib Mineral Petrol
La/Yb = 3.6–8.1). In mantle-normalized trace element
diagrams, most siliceous hornfels show negative Ba, Nb,
Pb, Sr anomalies (Fig. 8c). Also, a subset of samples is
much richer in large ion lithophile elements (LILE) than
the others. Concentrations of TOC, CO2 and SO3 are low at
intervals *200 m from the intrusive contact (Fig. 9b).
Sample TG21-1 collected at *230 m from the contact has
*1 wt% TOC.
Samples from mine exposure comprise massive anhydrite, calcareous hornfels, siliceous hornfels and metasandstone. The former three rock types are geochemically
similar to their counterparts in drill-cores MD48 and TG21
(Figs. 5, 6, 7, 8d, e). Meta-sandstones have SiO2
(86.1–89.0 wt%), Al2O3 (6.8–7.6 wt%) and Na2O (3.2–3.6
wt%) as the only major element oxides. Their trace element
patterns are marked by negative Ba and Ti anomalies and
positive Pb, Zr and Hf anomalies (Fig. 8f).
Sr–Nd isotopes
Sr–Nd isotopic data for sedimentary rocks in the Norilsk
region and meta-sedimentary rocks from the Norilsk
aureoles are listed in Table 4. All samples are characterized by high initial Sr isotopic ratios ranging from 0.7079
to 0.7154 (Table 4). The lowest value of 0.7079 for massive anhydrite from drill-core MD56 is similar to that of
Devonian seawater (Veizer et al. 1999). The calcareous
hornfels have a relatively restricted range of (87Sr/86Sr)i
(0.7079–0.7092), whereas siliceous hornfels have a slightly
higher and wider range of (87Sr/86Sr)i (0.7083–0.7152). In
the Mikchangda aureole, (87Sr/86Sr)i tends to increase with
increasing distance away from the intrusive contact
(Fig. 9a). The meta-sandstone (sample NOR-14a) has
(87Sr/86Sr)i of 0.7088. The Nd isotopic compositions of the
samples are highly variable, with eNd(t) from -8.0 to ?4.3
for sedimentary rocks, -1.1 to ?9.6 for calcareous
Fig. 5 A ternary diagram
SiO2–(CaO ? MgO)–
(Al2O3 ? Na2O ? K2O) of
bulk-rock compositions for
Paleozoic sedimentary rocks
and meta-sedimentary rocks
from the Norilsk contact
aureoles, Siberia. Gray field
denotes our unpublished data
from the sills
hornfels and -4.8 to ?10.2 for siliceous hornfels
(Table 4). The meta-sandstone has eNd(t) of -6.4.
On the (87Sr/86Sr)i–eNd(t) diagram, the samples have
high initial Sr isotopic ratios compared to flood basalts and
the related intrusive rocks of the Siberian Traps (Fig. 10a).
The isotopic variations of the intrusive rocks can be
explained in terms of two end-members: shale (sample
MD56-36) and impure evaporites (see Arndt et al. 2003).
Some samples have exceptionally high eNd(t) (?8.8 to
?10.2), even higher than the highest value of ?7 reported
for the flood basalts (Sharma 1997). However, there is no
evidence that these samples formed from mafic and isotopically depleted protoliths. We thus speculate that the high
eNd(t) values are due to disturbance of the Sm–Nd isotopic
system during contact metamorphism (see Polat et al.
2008). On a (87Sr/86Sr)i–Sr diagram, the data of the intrusive rocks fall roughly on trends toward contamination by
either shale or impure evaporites, but not toward that by
pure anhydrite (Fig. 10b).
Discussion
Protoliths and metamorphic conditions
Four types of meta-sedimentary rocks are recognized in
this study, that is, calcareous hornfels, siliceous hornfels,
meta-anhydrite and meta-sandstones. The fact that they
have different mineralogical, geochemical and Sr–Nd isotopic compositions, as illustrated above, is best understood
in terms of different protoliths. The relatively low SiO2,
Al2O3, Na2O and high CaO, MgO, CO2 and SO3 in calcareous hornfels are indicative of impure evaporite protoliths, such as the calcareous siltstone in drill-core MD56.
This interpretation is supported by the fact that these rocks
are intermediate between massive anhydrite (or dolostone)
SiO2
Sills
MgO +
CaO
Drill-core MD56 (sedimentary rocks)
Drill-core MD48 (calcareous hornfels
and meta-evaporites)
Drill-core TG21 (siliceous hornfels)
Samples from mine exposure
(calcareous and siliceous hornfels,
and meta-sandstone)
Al 2O 3 +
N a 2O + K 2O
123
Contrib Mineral Petrol
30
Al 2O 3 (wt.% )
a
Drill-core MD56 (sedimentary rocks)
Drill-core MD48 (calcareous hornfels
and meta-evaporites)
Drill-core TG21 (siliceous hornfels)
Samples from mine exposure
(calcareous and siliceous hornfels)
20
10
0
TiO 2 (wt.%)
1.2
60
b
MgO + CaO (wt.%)
Fig. 6 Binary plots of bulkrock concentrations of selected
major and trace elements versus
SiO2 for Paleozoic sedimentary
rocks and meta-sedimentary
rocks from the Norilsk contact
aureoles, Siberia. a Al2O3.
b TiO2. c MgO ? CaO.
d Na2O. e Cr. f La. g Zr. Data
for meta-sandstone are not
plotted
0.8
0.4
10
2
10
1
10
0
10
-1
10
-2
40
20
0
250
d
e
200
Cr (ppm)
Na 2O (wt.%)
0
c
150
100
50
0
50
600
f
g
Zr (ppm)
La (ppm)
40
30
20
400
200
10
0
0
0
20
40
SiO 2 (wt.%)
and shale for most major elements (Figs. 7, 8) and Sr
isotopic ratios (Fig. 10). In contrast, siliceous hornfels have
high SiO2, Al2O3, Na2O and low CaO, MgO, CO2 and SO3
(Figs. 7, 8), features consistent with pelitic or shaley protoliths. The different protoliths suggested for calcareous
and siliceous hornfels are also consistent with their different mineral compositions. Meta-anhydrite has very
similar composition as and thus likely formed from massive anhydrite protoliths. The very high SiO2, Al2O3 and
Na2O in meta-sandstones are indicative of quartzo-feldspathic protoliths.
The lithostatic pressure during contact metamorphism in
the Norilsk aureoles can be deduced from depths at which
the intrusions emplaced. The trace element and isotopic
123
60
80
0
20
40
60
80
SiO 2 (wt.%)
compositions of the ore-bearing sills can be matched with
those of distinctive units in the volcanic sequence (Arndt
et al. 2003), and the vertical distance between the intrusive
and volcanic units is *1.5 km. Assuming the overburden
has an average density similar to the continental crust
(2.7 g cm-3), the pressure at which the intrusions were
emplaced was likely to be *0.4 kbar or less.
The peak temperature of metamorphism can be estimated by mineral assemblages of rocks in the aureoles. The
peak metamorphic assemblage consists of phlogopite and
clinopyroxene indicated by the samples in the high-temperature zones in the Mikchangda intrusion (Fig. 2). In the
Talnakh intrusion, the peak assemblage might have been
obscured by retrograde metamorphism resulting in an
Contrib Mineral Petrol
a
6
b
5
TO C ( w t . % )
H 2O ( w t . % )
4
4
2
3
2
1
0
c
40
d
60
SO3 (wt.%)
0
40
CO2 (wt.%)
30
20
20
10
0
0
0
20
40
60
80
SiO2 (wt.%)
0
20
40
60
80
SiO 2 (wt.%)
Fig. 7 Binary plots of bulk-rock concentrations of light elements versus SiO2 for Paleozoic sedimentary rocks and meta-sedimentary rocks from
the Norilsk contact aureoles, Siberia. a H2O. b TOC. c CO2. d SO3. Data for meta-sandstone are not plotted. Legend is the same as in Fig. 6
assemblage of quartz, chlorite, muscovite and alkali feldspars (Turovtsev 2002; this study). Aarnes et al. (2010)
modeled the mineral assemblages of an average pelite with
increasing grade of metamorphism. Their results indicate
that phlogopite is stable at temperatures \750 °C and
muscovite at temperatures \500 °C. As pointed out by
these authors and Aarnes et al. (2011), the maximum
temperature that can be attained in contact aureoles is a
function of (1) the size of the intrusion, (2) the temperature
of magma, (3) the distance away from the intrusive contact,
(4) the geothermal gradient and (5) the lithology of host
rocks. In general, the temperature of wallrocks adjacent to
the intrusive contact is roughly half of the liquidus temperature of the magma and decreases exponentially with
increasing distance from the contact. Assuming a liquidus
of *1,200 °C for the sills, their contact aureoles probably
attained maximum temperatures of \600 °C (Carlsaw and
Jaeger 1959). This is generally in line with the absence of
very high-grade metamorphic assemblages in the Norilsk
aureoles.
Mechanisms of magma-evaporite interaction
The evaporite country rocks at Norilsk might interact with
the intruding magmas in various ways: (1) wholesale or
partial melting, (2) elemental transfer via hydrous fluid
(Li et al. 2003, 2009b; Ripley et al. 2003) and (3) metamorphic devolatilization (Ganino and Arndt 2009). In this
section, these mechanisms are examined in light of our
new data.
Melting of evaporites theoretically produces sulfate-rich
melts that are readily incorporated into the magmatic system, in a way similar to crustal contamination of mantlederived magmas. The melting point of anhydrite is
*1,450 °C (http://www.mindat.org/min-234.html), which
led Li et al. (2003) and Ripley et al. (2003) to suggest that
evaporite melting probably did not take place at Norilsk
due to the lack of potential agents that may lower its
melting point. Experiments indicate that partial melting of
anhydrite-dolomite mixtures occurs at *900 to 1,000 °C
(van der Sluis 2010) and probably at lower temperatures in
the presence of impurities such as silt horizons or fragments. Our findings confirm the presence of carbonates and
siliceous impurities in Devonian evaporites at Norilsk.
Assuming the basaltic magma intruding the evaporites has
a liquidus of *1,200 °C, their assimilation through partial
melting may not be completed precluded. However, this
should occur locally along the contacts against the country
rocks, and its role in causing extensive magma-evaporite
interaction is uncertain.
123
Contrib Mineral Petrol
Sample/Primitive mantle
Sample/Primitive mantle
10
Sample/Primitive mantle
Fig. 8 Primitive mantlenormalized trace element
diagram for Paleozoic
sedimentary rocks and metasedimentary rocks from the
Norilsk contact aureoles,
Siberia. a Samples in drill-core
MD56. b Samples in drill-core
MD48. c Samples in drillcore TG21. d Calcareous
hornfels from mine exposure.
e Siliceous hornfels from mine
exposure. f Meta-sandstone
from mine exposure.
Normalizing values are after
McDonough and Sun (1995)
3
b MD48
Shale
10
Calcareous siltstone
Rock salt
Dolostone
2
10
1
10 0
a MD56
10
-1
10
2
c TG21
d Mine exposure
(calcareous hornfels)
e Mine exposure
(siliceous hornfels)
f Mine exposure
(meta-sandstone)
10 1
10
0
10
-1
10
2
10 1
10
0
10 -1
Cs Ba U Ta Ce Sr Zr Sm Ti Tb Y Lu Cs Ba U Ta Ce Sr Zr Sm Ti Tb Y Lu
Rb Th Nb La Pb Nd Hf Eu Gd Dy Er
Rb Th Nb La Pb Nd Hf Eu Gd Dy Er
Transfer of elements from evaporites to magma via
circulating hydrothermal fluid merits consideration in
shallow magmatic systems like Norilsk. In this study,
several observations from the aureoles are consistent
with the presence of hydrous fluid during contact metamorphism: (1) the abundance of hydrothermal veins of
carbonates and/or sulfates in drill-cores of aureole rocks in
this study, (2) the occurrence of wollastonite in calcareous
hornfels (Li et al. 2009b; this study) indicating equilibration with hydrous fluid (Greenwood 1967; Ferry et al.
2001), (3) the abundance of hydrous phases in the aureoles,
including chlorite, hydrogrossular, muscovite, pectolite,
phengite, phlogopite, thomsonite and xonotlite (Li et al.
2009b; this study). Dehydration of chlorite, muscovite and
clay minerals in sedimentary rocks during contact metamorphism likely result in a hydrous fluid, percolating and
reacting with evaporites in the aureoles. Experiments by
Newton and Manning (2005) demonstrated that the solubility of anhydrite increases enormously with NaCl activity
in hydrothermal solutions at *600 to 800 °C. In view of
this, the presence of salt horizons in the Tunguska sedimentary sequence is noteworthy (Matukhin 1978; Zharkov
1984; Svensen et al. 2009a). There are two observations
123
consistent with participation of the salt horizons during
metamorphism: (1) most siliceous hornfels in this study
contain high Na2O (0.42–10.8 wt%; with the majority
[3 wt%), a feature that, according to van de Kamp and
Leake (1996), is best explained by addition of Na from
salts or brines, and (2) high Cl in apatite from the aureole
(Fig. 4c) and in melt inclusions in some Siberian magmatic
rocks (Sobolev et al. 2009) points to formation of a Cl-rich
fluid and addition of Cl derived from the salt horizons,
respectively. Based on the above arguments, we suggest
that elemental transfer via a hydrous fluid, together with
the presence of dissolved salts, likely contributed to
extensive magma-evaporite interaction at Norilsk.
Devolatilization of calcareous sedimentary rocks during
metamorphism directly generates fluids of CO2 (i.e.,
decarbonation) and SO2 (i.e., desulfatation), which in theory are able to enter the magmatic system. For example,
the release of CO2 by decarbonation reactions during
progressive metamorphism of siliceous dolomites is well
known (Bowen 1940). Degassing of SO2 from anhydrite in
an analogous manner was proposed by Gorman et al.
(1984). Figure 11 is a plot of (CO2 ? SO3) versus CaO of
samples in this study illustrating devolatilization. Pure
2
Rb/86Sr
0.002
0.665
0.249
0.524
0.469
0.006
0.493
0.915
0.045
0.011
0.017
2.072
0.028
280
333
273
56.0
239
502
0.029
0.001
0.047
0.017
0.001
0.033
0.109
0.001
0.714
0.240
0.086
0.141
0.600
0.007
0.007
0.000
0.000
0.011
0.455
87
61.0
246
130
62.0
349
106
89.0
478
396
226
690
2498
764
240
2796
197
40.6
0.90
31.0
34.3
6.40
72.5
75.9
0.90
48.6
0.30
56.5
93.9
94.1
56.5
1.70
127
exposure
88.5
5.20
1.00
2.70
171
41.4
164
563
389
454
2696
2,696
1,449
1829
108
91.0
Sr (ppm)
114
16.8
19.0
94.1
56.0
56.0
0.30
0.10
3.40
120
Rb (ppm)
Sr/86Sr
0.714383
0.708416
0.708630
0.709289
0.715647
0.709484
0.709786
0.711947
0.716203
0.730868
0.710964
0.709884
0.726232
0.708734
0.708114
0.709309
0.708955
0.708585
0.709743
0.712353
0.708655
0.711775
0.718173
0.708894
0.709356
0.711174
0.708958
0.708937
0.707866
0.707872
0.708707
0.728972
87
0.000009
0.000010
0.000002
0.000009
0.000004
0.000009
0.000006
0.000009
0.000008
0.000004
0.000010
0.000008
0.000003
0.000007
0.000005
0.000008
0.000006
0.000008
0.000007
0.000010
0.000005
0.000006
0.000017
0.000010
0.000005
0.000012
0.000005
0.000003
0.000006
0.000007
0.000008
0.000007
2r
0.7111
0.7083
0.7086
0.7088
0.7083
0.7086
0.7097
0.7096
0.7087
0.7152
0.7093
0.7097
0.7115
0.7079
0.7081
0.7079
0.7084
0.7086
0.7088
0.7091
0.7087
0.7092
0.7110
0.7086
0.7089
0.7090
0.7087
0.7087
0.7079
0.7079
0.7084
0.7154
(87Sr/86Sr)1i
4.69
2.50
3.52
0.67
5.71
4.69
6.26
2.69
7.37
3.73
12.0
2.50
5.62
7.01
5.79
4.63
2.38
–
3.01
3.40
–
2.33
4.12
8.50
1.03
2.65
1.86
1.86
–
–
0.26
3.27
Sm (ppm)
22.10
9.99
15.10
2.58
34.60
22.3
25.8
12.5
35.0
17.9
43.2
11.7
35.2
27.5
26.6
24.0
9.53
–
12.2
16.1
–
9.46
18.3
28.7
4.02
13.0
8.65
8.65
–
–
1.39
22.1
Nd (ppm)
0.128
0.151
0.141
0.157
0.100
0.127
0.147
0.130
0.127
0.126
0.168
0.129
0.097
0.154
0.132
0.117
0.151
–
0.149
0.128
–
0.149
0.136
0.179
0.155
0.123
0.130
0.130
–
–
0.113
0.089
Sm/144Nd
147
0.512606
0.512524
0.512517
0.512246
0.512312
0.512279
0.512481
0.512513
0.513044
0.512574
0.512633
0.512484
0.512546
0.512530
0.512475
0.512521
0.513015
–
0.512716
0.513019
–
0.512657
0.512757
0.512684
0.512503
0.512524
0.512489
0.512489
–
–
0.512163
0.512051
Nd/144Nd
143
0.000001
0.000004
0.000002
0.000008
0.000005
0.000002
0.000002
0.000002
0.000006
0.000003
0.000003
0.000002
0.000002
0.000007
0.000004
0.000002
0.000005
–
0.000003
0.000009
–
0.000003
0.000004
0.000005
0.000009
0.000006
0.000003
0.000008
–
–
0.000006
0.000001
2r
0.5124
0.5123
0.5123
0.5120
0.5121
0.5121
0.5122
0.5123
0.5128
0.5124
0.5124
0.5123
0.5124
0.5123
0.5123
0.5123
0.5128
–
0.5125
0.5128
–
0.5124
0.5125
0.5124
0.5122
0.5123
0.5123
0.5123
–
–
0.5120
0.5119
(143Nd/144Nd)i
1.6
-0.8
-0.6
-6.4
-3.2
-4.8
-1.5
-0.3
10.2
1.0
0.8
-0.8
1.4
-0.8
-1.1
0.3
8.8
–
3.0
9.6
–
1.9
4.3
1.5
-1.3
0.1
-0.8
-0.8
–
–
-6.6
-8.0
eNd(t)
(87Sr/86Sr)i and eNd(t) values were calculated based on an age of 251 Ma, k(87Rb) = 1.42 9 10-11 year-1, k(147Sm) = 6.54 9 10-12 year-1, and present day chondritic values of
Nd/144Nd = 0.512638, 147Sm/144Nd = 0.1967, 87Sr/86Sr = 0.7045 and 87Rb/86Sr = 0.0827 (Faure and Mensing 2005)
Samples MD56-26, MD56-31 and MD48-13 were not analyzed for Nd isotopes due to low Nd contents
143
1
Drill-core MD56
MD56-9a
MD56-9b
MD56-19
MD56-22
MD56-23
MD56-23(dup)
MD56-262
MD56-31
MD56-34
MD56-36
Drill-core MD48
MD48-1
MD48-2
MD48-4
MD48-12
MD48-13
MD48-17
MD48-23a
MD48-23b
MD48-24
Drill-core TG21
TG21-1
TG21-2
TG21-3
TG21-4
TG21-7
TG21-8
TG21-10
Samples from mine
NOR-3
NOR-5
NOR-7b
NOR-14a
NOR-15
NOR-17
Sample
Table 4 Rb-Sr and Sm–Nd isotopic data for unmetamorphosed sedimentary rocks and meta-sedimentary rocks from the Norilsk contact aureoles, Siberia
Contrib Mineral Petrol
123
Contrib Mineral Petrol
a
Mikchangda
Distance away from
intrusive contact (m)
0
Sill
Cc+
Cpx Phl Kfs Chl Anh
Anhydrite
layers
20
40
60
Hornfels
(?)
Sediments
80
0
1
2
3 0
TOC
(wt.%)
Talnakh
Distance away from
intrusive contact (m)
b
200
Qtz Chl Mus Ab Ap
0
0.5
1
20
10
30 0
CO 2
(wt.%)
1.5 0
1
2
3
20
40
60
SO 3
(wt.%)
4 0
0.5
1
0.709
87
0.710
86
( Sr/ Sr) i
1.5 0.710 0.714
Hornfels
150
Sills (minor)
100
50
0
Metasomatic
hornfels
Sill
Fig. 9 Simplified column sections of the Mikchangda and Talnakh aureoles showing variations of mineralogy, TOC, CO2, SO3 and (87Sr/86Sr)i
with distance away from the intrusive contact. The color scheme of the sections is the same as in Fig. 2
evaporites composed of anhydrite, dolomite and calcite plot
in the shaded area and shale plot near the origin. Calcareous
siltstones (i.e., impure evaporites) and any metamorphic
rocks that do not undergo extensive devolatilization should
plot in arrays between the origin and the shaded area. Here,
two assumptions are relevant: (1) Ca in the protoliths is
present exclusively in anhydrite and carbonates and (2) Ca is
neither added nor removed to the aureole rocks during
metamorphism. Rocks that plot below these arrays indicate
significant devolatilization due to preferential loss of CO2
and/or SO3 relative to CaO. Figure 11 shows that a subset of
calcareous hornfels exhibits devolatilization in various
degrees. The majority of them have less than *2.5 wt%
CO2 but *4.5–21 wt% SO3. As a result, we argue that
devolatilization is mainly brought about by loss of CO2 and
sulfate minerals are largely unaffected by this process. The
decarbonation reactions likely caused the formation of
clinopyroxene and phlogopite in calcareous hornfels at the
expense of dolomite (Rice 1977; Tracy and Frost 1991):
5 CaMgðCO3 Þ2 ðdolomiteÞ þ 8SiO2 þ H2 O
¼ Ca2 Mg5 Si8 O22 ðOHÞ2 ðtremoliteÞ þ 3 CaCO3 ðcalciteÞ
þ 7 CO2
123
Ca2 Mg5 Si8 O22 ðOHÞ2 ðtremoliteÞ
þ KAlSi3 O8 ðK-feldsparÞ þ 2 CaMgðCO3 Þ2 ðdolomiteÞ
¼ 4 CaMgSi2 O6 ðdiopsideÞ
þ KMg3 AlSi3 O10 ðOHÞ2 ðphlogopiteÞ þ 4 CO2
The latter reaction occurs at *460 to 500 °C for a wide
range of mole fractions of CO2 in the fluid (Tracy and Frost
1991), temperatures that can be reached according to our
temperature estimates based on mineral assemblage.
Gas release and the end-Permian environmental crisis
As mentioned above, the release of CO2 and SO2 from the
aureoles during contact metamorphism most likely
involves hydrothermal leaching of evaporites and decarbonation of impure evaporites, respectively. Here, we
estimate the generation potentials of these gases in a LIP
context.
We estimate CO2 production potential using decarbonation reactions and the volume of the aureole rocks that
underwent partial degassing. Based on molar volume, the
aforementioned clinopyroxene- and phlogopite-forming
Contrib Mineral Petrol
15
a
Disturbance
of Nd isotopes(?)
10
Nd(t)
5
0
Evaporite
contamination
-5
Crustal
contamination
-10
-15
0.704
0.712
0.708
87
0.716
86
( Sr/ Sr) i
b
0.716
( 87S r / 86S r ) i
Crustal
contamination
0.712
Evaporite
contamination
0.708
0.704 1
10
10 2
10 3
10 4
Sr (ppm)
Fig. 10 Binary plots of Sr–Nd isotopic compositions for Paleozoic
sedimentary rocks and meta-sedimentary rocks from the Norilsk
contact aureoles, Siberia. a eNd(t) versus (87Sr/86Sr)i. b (87Sr/86Sr)i
versus Sr concentrations. The isotopic data were calculated at
t = 252 Ma. Gray fields and white diamonds denote flood basalts
and intrusive rocks, respectively, from the Siberian Traps after
Sharma et al. (1992), Lightfoot et al. (1993), Hawkesworth et al.
(1995) and Arndt et al. (2003). Legend is the same as in Fig. 6
C O 2 + S O3 ( w t . % )
60
Anh
Dol
40
80
Cc
80
80
60
60
60
40
20
Ca-poor
sulfate
40
40
20
20
20
0
0
Assimilation
40
20
Degassing
60
CaO (wt.%)
Fig. 11 A binary plot of (CO2 ? SO3) versus CaO for Paleozoic
sedimentary rocks and meta-sedimentary rocks from the Norilsk
contact aureoles, Siberia (see text for discussion). Data for samples in
drill-core TG21 are not plotted. Legend is the same as in Fig. 6
reactions produce 375–430 g CO2 per kilogram of dolomite, or 188–215 g CO2 per kilogram of impure evaporite
with 50 % dolomite. If we assume the volume of the
metamorphosed rock in the lower Mikchangda aureole to
be 0.5 km3 [5 km (length) 9 500 m (breadth) 9 200 m
(aureole thickness)], a density of 2,500 kg m-3 and 80 %
of dolomite was transformed to clinopyroxene and phlogopite, the total amount of CO2 produced is about 0.4 Gt.
With reference to estimates of CO2 released from the
Deccan volcanism (Self et al. 2006), the amount of magmatic CO2 released from the Mikchangda intrusion [5 km
(length) 9 500 m (breadth) 9 550 m (sill thickness)]
would be *0.015 Gt, much less than the above estimate of
metamorphic CO2. Scaling the above estimates to a LIP
scale is somewhat speculative, but the present day outcropping area of the intrusions is at least 1.6 9 106 km2
and they most frequently intruded Paleozoic sedimentary
rocks (Kontorovich et al. 1997). These values imply that
the total amount of metamorphic CO2 generated by
decarbonation would be in the order of several tens of
thousand Gt or above and is not trivial compared to estimates in earlier studies (Table 5).
The SO2 production potential cannot be estimated using
the above method because it was not released directly from
heating of evaporites as for CO2 (see earlier discussion). In
the Norilsk region, the source of sulfides in the Ni-Cu(PGE) deposits is generally considered to be the reduced
form of sulfates in evaporites (Li et al. 2003, 2009a, b;
Ripley et al. 2003; Arndt et al. 2003; Naldrett 2004),
providing an indirect means to estimate SO2 release. These
deposits contain *1,300 mT of ore (Naldrett 2004) suggested to have formed from immiscible sulfide melts
equilibrated with basaltic magma belonging to the intrusive
portion of the Siberian Traps. Assuming magma/sulfide
mass ratios (R factors) of 100–400 (Li et al. 2009b), the
mass of magma was *130 to 520 Gt. The maximum
concentration of S dissolved in a basaltic magma at
1,300 °C, and 1 GPa is *0.18 wt% under reducing conditions and *1.8 wt% under oxidizing conditions (Jugo
et al. 2005). If 70 % of the S was degassed, the total
amount of SO2 produced ranges from 0.03 to 1.3 Gt. This is
a minimum estimate because it only accounts for the S
dissolved in the magma and neglects any SO2 potentially
occurring as a separate fluid phase in the magmatic system.
In addition, total amount of metamorphic SO2 on a LIP
scale would be in the order of several hundreds or thousands Gt (Table 5).
Recent studies emphasize the role of volatile release in
triggering the end-Permian environmental crisis (Berner
2002; Self et al. 2006; Beerling et al. 2007; Retallack and
Jahren 2008; Svensen et al. 2009a; Li et al. 2009a; Sobolev
et al. 2011; Black et al. 2012; Tang et al. 2012). However,
diverse opinions still exist about the source of volatiles
123
Contrib Mineral Petrol
Table 5 Estimates of gas generation potential for the Siberian Traps
Method
Carbon
Sulfur
Halogens
Reference
Bulk-rock volatile data
of magmatic rocks
4400 Gt CO
7000 Gt H2S
–
Tang et al. (2012)
85000 Gt CO2
68000 Gt SO2
Melt inclusions
–
6300 to 7800 Gt S
3400 to 8,700 Gt Cl
Black et al. (2012)
Melt inclusions
170000 Gt CO2
–
18000 Gt HCl
Sobolev et al. (2011)
S-isotopes
–
20000 to 30000 Gt
SO2
–
Li et al. (2009a, b)
Bulk-rock volatile data of rock salt
10700 to 31200 Gt C
–
5200 to 15300 Gt
CH3Cl
Svensen et al.
(2009a)
7,100 to 13,600 Gt F
39000 to 114000 Gt
CO2
87 to 255 Gt CH3Br
14300 to 41900 Gt CH4
Inference from degassing rate of the
Columbia River Basalts and the volume
of the Siberian Traps
–
Inference from degassing rate of modern
basalts and the volume of the Siberian
Traps
2000 to 13000 CO2
38000 Gt SO2
2200 Gt HCl
0.0636 Gt CH3Cl
Beerling et al.
(2007)
0.0008 Gt CH3Br
–
–
Berner (2002)
* Conversion factors: 1 gigatonne (Gt) = 1000 teragram (Tg) = 1015 gram
^To compare different species of the same element (e.g., C and CO2), conversion factors of atomic/molecular masses are required
(e.g., magmatic vs. sediment-derived, mantle vs. crust).
Our results show that contact metamorphism of impure
evaporites could have generated abundant CO2 in addition
to that of organic matter and coal (Svensen et al. 2009a)
which, when emitted to the atmosphere, can be one of the
main contributor to the end-Permian global warming. We
also note that anhydrite can be mobilized by leaching
associated with magmatic-hydrothermal activity, releasing
SO2 to the magmatic system and eventually the atmosphere. The SO2 has harmful effects on respiratory systems
of organisms and it might form acid rain. These gases,
together with other greenhouse gases like CH4 or toxic
gases of halocarbons released by magmatic or sediment
degassing (Table 5), likely contributed to the end-Permian
crisis.
of these gases into the atmosphere provides a viable
explanation for the end-Permian environmental crisis and
mass extinctions.
Acknowledgments We thank Françis Coeur for assistance in sample preparation, Catherine Chauvel, Sarah Bureau and Christèle Poggi
in major and trace element analyses, and Hao-Yang Lee and ChiuHong Chu for Sr–Nd isotopic analyses. We acknowledge funding
granted to NTA from the French ANR (BEGDy project) and the
American NSF (continental geodynamics program) and to HS and
others from PGP and the Norwegian Research Council (YFF and SFF
grants). Logistic support and access to drill-cores provided by Norilsk
Nickel are gratefully acknowledged. We express special thanks to
Valery Fedorenko, former Norilsk Nickel chief geologist, for the
assistance in the field trip and sample delivery. Comments by two
anonymous reviewers and the editor Tim Grove improved the quality
of the manuscript.
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