No Job Name


Neoproterozoic metamorphic evolution of the Isbjørnhamna
Group rocks from south-western Svalbardpor_186 250..264
Jaroslaw Majka,1 Jerzy Czerny,2 Stanislaw Mazur,3 Daniel K. Holm4 & Maciej Manecki2

1 Department of Earth Sciences, Uppsala University, Villavägen 16, SE-75236 Uppsala, Sweden

2 Department of Mineralogy, Petrography and Geochemistry, AGH–University of Science and Technology, 30 Mickiewicza Av., PL-30059 Kraków, Poland

3 GETECH, Kitson House, Elmete Hall, Elmete Lane, Leeds, LS8 2LJ, UK

4 Department of Geology, Kent State University, Kent, OH 44242, USA

Abstract

A metamorphosed volcano-sedimentary complex constitutes the Caledonian
basement in the south-western part of Wedel Jarlsberg Land, Svalbard. Field,
textural and previous thermochronologic data indicate a weak, localized meta-
morphic Caledonian overprint (M2). Deformed M1 isograds and variation in
pressure–temperature estimates indicate a pervasive Neoproterozoic
amphibolite-facies metamorphism that pre-dates large-scale Caledonian age
folding. Garnet–biotite and garnet–Al silicate–plagioclase (GASP) geother-
mobarometry of the Isbjørnhamna Group mica schists, and their comparison
with the K2O–FeO–MgO–Al2O3–SiO2–H2O (KFMASH) petrogenetic grid, indi-
cates a peak pressure of ca. 11 kbar, and a peak temperature of ca. 670°C
during M1 metamorphism. A cooling rate of ca. 5°C My-1 is estimated on the
basis of geothermobarometry and the available U–Th–total Pb and Ar–Ar data.

Keywords
Caledonides; geothermobarometry;

metapelites; Neoproterozoic; Spitsbergen.

Correspondence
Jaroslaw Majka, Department of Earth

Sciences, Uppsala University, Villavägen 16,

SE-75236 Uppsala, Sweden. E-mail:

jaroslaw.majka@geo.uu.se

doi:10.1111/j.1751-8369.2010.00186.x

Southern Wedel Jarlsberg Land (Fig. 1) uniquely pre-
serves a record of Neoproterozoic metamorphism on
Spitsbergen, Svalbard. In situ uranium–thorium–lead
electron microprobe (U–Th–Pb EMP) ages of metamor-
phic monazites from a Proterozoic volcano-sedimentary
complex date amphibolite-grade metamorphism at ca.
643 Mya (Majka et al. 2008). The northern extent of
this Neoproterozoic metamorphism is bounded by the
Vimsodden–Kosibapasset zone (VKZ), which is a major
strike–slip shear zone with sinistral kinematics (Fig. 2;
Mazur et al. 2009). The VKZ separates the Neoproterozoic
metamorphic complex from the remaining part of the
south-western terranes of Svalbard, which were sub-
jected to younger, early Palaeozoic metamorphism (Gee
& Tebenkov 2004; Czerny et al. 2010). The occurrence of
a Neoproterozoic metamorphic domain in south-western
Spitsbergen has important bearing on terrane concepts
for Svalbard construction in general, and specifically for
its proposed correlation with the Timanide metamorphic
belt of north-eastern Europe (Mazur et al. 2009). A better
understanding of the nature and extent of Neo-
proterozoic metamorphism and associated pervasive
deformation, compared with earlier reports (Smulikowski
1965; Czerny et al. 1993; Majka et al. 2004), is an essen-
tial prerequisite for testing between, and refining, the

tectonic models proposed for this region. In this study we:
(1) quantify the peak pressure and temperature condi-
tions for Neoproterozoic metamorphism; (2) verify the
correlation between the peak of metamorphism and the
pervasive deformational fabric; (3) define zones of pro-
gressive metamorphism and the relationship between
isograds and major tectonic structures; and (4) constrain
the cooling history of this Neoproterozoic complex. Our
study is based on extensive fieldwork supported by results
of microstructural analysis and geothermobarometric
calculations.

Geological setting

The south-western part of Spitsbergen island exposes an
elongate north–south trending metamorphic basement
exhumed within the axial zone of an Early Palaeogene
fold-and-thrust belt (e.g., Lowell 1972; Dallmann et al.
1993; Braathen et al. 1995; Bergh et al. 1997). This
elevated basement high consists of Precambrian to
Early Palaeozoic rocks, the deformation and metamor-
phism of which were originally ascribed solely to the
Caledonian orogeny (e.g., Holtedahl 1926; Ohta 1982;
Harland 1985; Harland et al. 1992). However, the occur-
rence of regionally extensive unconformities that are

Polar Research 29 2010 250–264 © 2010 the authors, journal compilation © 2010 Blackwell Publishing Ltd250

mailto:majka@geo.uu.se


associated with metamorphic and lithological contrasts
(e.g., Sandford 1956; Krasil’ščikov 1979; Birkenmajer
1975; Bjørnerud 1990) and geochronological studies
both provide evidence that the Caledonian basement
includes Proterozoic crustal domains juxtaposed by Early
Palaeozoic tectonic events (e.g., Peucat et al. 1989;
Balashov et al. 1995; Gee et al. 1995; Hellman et al. 1997;
Johansson et al. 2004; Pettersson et al. 2009). These
domains, together with their sedimentary cover, are
interpreted to be individual tectonostratigraphic terranes
assembled during the Caledonian orogeny (e.g., Harland
1972; Harland & Gayer 1972; Gee & Page 1994). Based on
important contrasts in stratigraphy, structural develop-
ment and tectonothermal evolution, the Caledonian
rocks of Svalbard have been divided into eastern, north-

western and south-western terranes (Fig. 1; Gee 1986;
Gee & Page 1994; Gee & Tebenkov 2004).

North of Isfjorden, the south-western terranes of
Svalbard include a blueschist–eclogite allochthon known
as the Vestgötabreen complex (e.g. Ohta 1979) that
yielded argon-40 (40Ar)–argon-39 (39Ar) mineral cooling
ages of ca. 460 My (Dallmeyer et al. 1990). The complex
is non-conformably overlain by Middle Ordovician
conglomerates and limestones (Armstrong et al. 1986),
succeeded by Late Ordovician to Early Silurian turbidites
(Scrutton et al. 1976). The metamorphic basement,
together with its Early Palaeozoic cover, is thrust over a
succession of diamictites of inferred Vendian age (Gee &
Tebenkov 2004). To the south of Isfjorden, the south-
western terranes consist of a Meso- to Neoproterozoic

Fig. 1 Geological sketch map of the Svalbard
Archipelago (modified from Gee & Tebenkov

2004).

Neoproterozoic metamorphism in southern SvalbardJ. Majka et al.

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metamorphic complex, which is divided into three
units: Isbjørnhamna, Eimfjellet and Deilegga groups
(Birkenmajer 1981, 1991). The latter is non-conformably
overlain by the low-grade Neoproterozoic Sofiebogen
Group, comprising a succession of conglomerates, lime-
stones and dolomites passing up into fine-grained
siliciclastic rocks (Bjørnerud 1990; Czerny et al. 1993;
Gee & Tebenkov 2004). The Sofiebogen Group is capped
by Vendian tillites of the Kapp Lyell Group, and comprises
a thick series of diamictites (Bjørnerud 1990; Dallmann
et al. 1990; Harland et al. 1993). The Cambro–Ordovician
succession is tectonically emplaced atop the Proterozoic
complexes (Dallmann et al. 1993; Mazur et al. 2009).

Wedel Jarlsberg Land, located in the southern part of
the south-western terranes (Fig. 2), consists of two Prot-
erozoic basement blocks with contrasting metamorphic
histories. The northern block comprises rocks of the
metasedimentary Deilegga and Sofiebogen groups, which
are separated by a Late Proterozoic angular unconformity
(Torellian unconformity; Birkenmajer 1975). The south-
ern block corresponds to a stratified volcano-sedimentary
polymetamorphic complex that consists of a metasedi-
mentary sequence known as the Isbjørnhamna Group

and a metavolcanic succession of the Eimfjellet Group
(Birkenmajer 1958; Czerny et al. 1993). The Isbjørn-
hamna Group is composed of garnet–mica schists,
paragneisses, calc-silicate rocks and marbles subjected
to amphibolite-grade Barrovian metamorphism, which
was followed by greenschist facies metamorphism
(Smulikowski 1965; Majka et al. 2004). The Eimfjellet
Group consists of quartzites, amphibolites and green-
schists, accompanied by minor metarhyolites and
muscovite schists. These rocks were subjected to green-
schist to lower amphibolite facies (Czerny et al. 1993).
The contact between the two crustal blocks exposed in
the south-western part of Wedel Jarlsberg Land between
the Hornsund fjord and Torellbreen glacier is represented
by the ca. 2 km wide VKZ. The deformation zone is char-
acterized by a heterogeneous array of structures formed
during ductile shear deformation. Structural features of
the VKZ indicate bulk sinistral strike-slip to oblique-slip
shear strain formed under greenschist facies conditions.

Thermochronologic data obtained from the Isbjørn-
hamna and Eimfjellet groups indicate a Neoproterozoic
age of metamorphism. 40Ar–39Ar step heating of mineral
separates yielded a 616 My age for hornblende from the

Fig. 2 Geological sketch map of the south-
western part of Wedel Jarlsberg Land (modified

from Czerny et al. 1993).

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Eimfjellet Group, and 585–575 My ages for muscovite
from the Isbjørnhamna Group (Manecki et al. 1998).
Manecki et al. (1998) interpreted these ages as represent-
ing a previously unrecognized episode of Neoproterozoic
reheating, probably connected with the opening of the
Iapetus Ocean. Corroborating evidence of a Neoprotero-
zoic tectonothermal event is provided by a metamorphic
monazite age of 643 � 9 My recently obtained from the
Isbjørnhamna Group (Majka et al. 2008). This age was
interpreted to represent the progressive phase of a
regional metamorphic event, as monazite grains enclosed
in garnet porphyroblasts yielded the same age as matrix
monazite grains. A somewhat younger Neoproterozoic
age (615 My) was obtained on zircons separated from an
anatectic pegmatite, which intrudes the Isbjørnhamna
Group (Majka et al. 2007).

Description of metamorphic units

The Isbjørnhamna Group consists of the Skoddefjellet,
Ariekammen and Revdalen formations, representing
an originally continuous sedimentary succession
(Birkenmajer 1975).

Skoddefjellet Formation

The Skoddefjellet Formation is composed of interlayered
paragneisses and mica schists. Typical prograde mineral
assemblages in these rocks are Qtz + Pl + Bt + Ms �
Grt � Chl with greater quantities of plagioclase in parag-
neisses and garnet in mica schists.

The mica schists are well foliated with common garnet
and biotite porphyroblasts. The matrix is mainly com-
posed of quartz, plagioclase (<15% vol.) and phyllo-
silicates. Biotite occurs mainly within the foliation planes,
in the pressure shadows of garnet and as a product of
garnet decomposition. Additionally, biotite forms porphy-
roblasts transverse to the foliation and enriched in small
graphite inclusions. Very rarely biotite occurs as inclu-
sions in garnet. Muscovite occurs mainly in foliation
planes, in the pressure shadows of garnet and sometimes
replacing garnet porphyroblasts. Primary chlorite occurs
in the foliation planes, whereas secondary chlorite
replaces micas in the pressure shadows of garnet and
occurs as rosettes within the matrix. The accessory phases
comprise tourmaline, apatite, zircon, monazite, epidote
group minerals, titanite, ilmenite, hematite, pyrite, pyro-
tite and chalcopyrite.

Ariekammen Formation

The Ariekammen Formation is characterized by the
occurrence of carbonate rocks. The formation mostly

consists of carbonate–mica schists, with irregular bands
of mica schists, paragneisses of the Skoddefjellet type
and minor marble intercalations. A mineral assemblage
characteristic of carbonate-mica schists comprises Cal +
Qtz + Bt + Grt + Pl + Ms � Ep, with Ca-enriched plagio-
clase and accessory minerals similar to those found in the
Skoddefjellet Formation. Additionally, some schist variet-
ies contain rare mejonite. Notably, a thin discontinuous
horizon of yellow and white marble occurs in the middle
of the formation. Porphyroblasts of garnet up to 6 cm in
diameter are abundant at the base of this horizon.

Revdalen Formation

The Revdalen Formation represents a uniform sequence
of rusty weathered mica schist composed of Qtz + Pl
+ Ms � Bt � Grt � St � Ky � Cld � Chl. Metamorphic
isograds within these rocks are defined by the local pres-
ence of chloritoid, staurolite or kyanite. The mica schists
are well foliated with numerous garnet porphyroblasts
and rare transversal biotite and staurolite porphyroblasts.
The matrix mostly consists of quartz and phyllosilicates
and minor plagioclase. Muscovite occurs in all varieties of
the Revdalen mica schists, whereas biotite is absent from
chloritoid-bearing samples, which tend to be rich in
primary chlorite. All phyllosilicate types can be found in
the pressure shadows of garnet and staurolite, and both
micas exist as inclusions in garnet. Rare kyanite occurs in
samples containing garnet and/or staurolite. The remain-
ing accessory phases comprise abundant tourmaline,
zircon, monazite, apatite, epidote (sometimes allanite),
titanite, rutile, and Fe-oxides and -sulphides. Addition-
ally, some younger Fe-oxyhydroxides and carbonates are
also present.

Description of textures

The Isbjørnhamna metapelites exhibit a penetrative
planar S1 foliation, a well-developed L1 mineral stretch-
ing lineation, particularly in the Skoddefjellet mica
schists, and locally developed S–C fabrics (most common
in the Revdalen Formation). The S1 foliation is expressed
by aligned phyllosilicates and flattened garnet and stau-
rolite porphyroblasts (Fig. 3). Deformation resulted in the
ductile flattening of garnets and the development of
asymmetric pressure shadows filled with biotite, musco-
vite, quartz and plagioclase. The flattened and slightly
rotated garnets often contain helicitic inclusions. Inclu-
sion trails in rare euhedral garnet porphyroblasts,
occurring in low strain zones, parallel the S1 foliation.
Some staurolite porphyroblasts are slightly flattened and
accompanied by pressure shadows filled with muscovite
and quartz. In many cases, however, staurolite grains are

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inclusion-free and euhedral, with only narrow asymmet-
ric mica-filled pressure shadows.

The transversal character of biotite porphyroblasts is
expressed by the orientation of their cleavage planes that
are oblique to the S1 foliation. The cleavage is underlined
by common graphitic encrustations, possibly representing
a relict S0 layering. The biotite porphyroblasts are flat-
tened and accompanied by asymmetric tails of fine-
grained biotite.

M1 metamorphism

Metamorphic isograds are well-defined within the
metapelites of the Revdalen Formation. For samples col-
lected in the north-western part of the study area, from
the western limb of a north–south trending anticline out-
cropping in the Rålstranda, the prograde M1 mineral
assemblage is defined by Grt + Cld + Ms + Chl + Qtz � Pl.
Chloritoid-bearing and biotite-absent metapelites occur

exclusively in the region of the Russepynten cape. East-
wards from that region, the mineral assemblage changes
into Grt + Bt + Ms + Qtz � Pl � Chl and farther east into
Grt + St + Ms + Bt + Qtz � Pl � Chl. By contrast, in the
east and south-eastern part of the study area (Revdalen,
Skålfjelldalen and Fugleberget), the mineral paragenesis
is defined by the occurrence of Grt + Ms + Bt + Qtz �
Pl, whereas only in a very few cases are additional
kyanite or kyanite and staurolite recorded. The rare
occurrence of Al-saturated phases is related to local
changes in bulk rock composition. In the schists from the
Rålstranda area, very fine-grained progressive allanite
and epidote were observed, whereas farther east and
south the dominant rare earth element-bearing phase is
monazite. The transition of allanite into monazite is con-
sistent with the increasing metamorphic grade within the
Revdalen Formation to the east because allanite is stable
only at upper greenschist to lower amphibolite facies
conditions; with increasing temperatures, allanite is

Fig. 3 Photomicrographs of (a) slightly rotated anhedral garnet with asymmetrically developed pressures shadows and its relationship to biotite; (b)
deformed and slightly rotated staurolite; (c) deformed large biotite; and (d) retrogressive rosette-shaped chlorite.

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replaced by monazite (e.g., Ferry 2000; Janots et al.
2007).

Retrogressive stage of M1 metamorphism

A retrogressive alteration was associated with cooling
after the peak of M1 metamorphism. In many cases,
retrogression resulted in the partial or complete replace-
ment of garnet by the assemblage of Bt + Ms + Pl + Q �
Chl or Pl + Q � Chl. Partial replacement of biotite by
chlorite may also be related to this phase of metamorphic
evolution. Additionally, the partial or even complete
replacement of monazite by apatite–allanite–epidote
coronas in some samples is a common reaction indicative
of late-metamorphic cooling (e.g., Ferry 2000; Majka &
Budzyń 2006, Janots et al. 2007, Broska & Majka 2008).
The character of the retrogressive changes and the
mineral assemblage synchronously formed suggest that
retrogression took place shortly after the peak of M1
metamorphism.

Weak Caledonian M2 overprint

The Isbjørnhamna Group belongs to Proterozoic base-
ment exposed in the core of the West Spitsbergen fold-
and-thrust belt. The main Caledonian structure in the
study area is the VKZ trending from north-west to south-
east (Czerny et al. 1993; Mazur et al. 2009). The effects
of Caledonian deformation are widespread to the north
of this zone. Contrastingly, southwards from the VKZ,
Caledonian overprint rapidly dies out in the rigid
amphibolite facies tectonic block, including the Isbjørn-
hamna Group. Only the rocks of the Eimfjellet Group,
which are adjacent to the VKZ, experienced intense Cale-
donian mylonitization (Mazur et al. 2009), whereas the
rocks of the Isbjørnhamna Group do not reveal any sig-
nificant Caledonian reworking, except in a few relatively
thin zones of altered rocks, usually parallel with VKZ.
The only visible effect of the Caledonian event is the
partial or sometimes complete chloritization of garnet,
biotite and staurolite, as well as the alteration of musco-
vite porphyroblasts to sericite. Additionally, in some cases
Caledonian alterations are expressed by the development
of sericite reaction rims on kyanite, and by sericitization
of staurolite and plagioclase. These changes probably
took place under static conditions, as indicated by the
common growth of rosette-like chlorite neoblasts
(Fig. 3).

Mineral chemistry

Selected minerals were chemically analysed using wave-
length dispersive spectrometry with the 100SX electron

microprobe (Cameca, Grennevilliers Cedex, France) at
the Inter-Institute Analytical Complex for Minerals and
Synthetic Substances, University of Warsaw. The operat-
ing conditions were set at 15 kV, 20 nA and 20 s of the
counting time using natural and synthetic standards. The
data were calculated using atomic number, absorption
and fluorescence (ZAF) corrections.

Garnets

Garnets were analysed along rim-core-rim profiles. Por-
phyroblasts of garnet were selected from different
metamorphic zones within the Revdalen and the Skod-
defjellet formations. Representative traverses are shown
in Fig. 4. A common feature of garnets from the kyanite-
free mica schists (i.e., samples 206, 214 and 125) is the
systematic increase of pyrope content from the core to
rims, and the contemporary decrease of Fe/(Fe + Mg)
and spessartine content. The rimward decrease of
Fe/(Fe + Mg) is characteristic of the increase of tempera-
ture under upper greenschist and amphibolite facies
conditions (Spear 1993). The bell-shaped spessartine
profile also suggests prograde growth zoning during a
one-stage chemical reaction (Tracy 1982). The slight
increase of spessartine content that was observed in some
garnet rims may be related to the consumption of garnet.
Notably, garnet from the staurolite-bearing mica schists
reveals a decrease of Fe/(Fe + Mg) towards the rims, but
in the rims this tendency changes and Fe/(Fe + Mg) is flat
or even slightly increased. The almandine content in this
garnet systematically increases towards the rims, but in
the rims it decreases. The opposite trend is evident for
the grossular content, which systematically decreases
towards the rims, but rapidly increases in the rims. The
variation of grossular and almandine content in garnets
co-existing with staurolite may have been caused by the
onset of staurolite crystallization (see also Janák et al.
2001): the onset of staurolite crystallization could modify
local chemical equilibrium during garnet crystallization,
decreasing the almandine content in garnet, as observed
in our samples. Contemporaneously, the observed
enrichment in Ca is probably caused by the reduction of
crystallization of plagioclase in response to the appear-
ance of a new Al-saturated phase (e.g., staurolite).
Nevertheless, the smooth shape of decreasing spessartine
content suggests prograde growth during a single meta-
morphic event.

The compositional variation in garnet from the
kyanite-bearing mica schist (i.e., sample 124) is complex.
In all cases the profiles are strongly disturbed, probably as
a result of the presence of numerous tiny inclusions and
the diffusion that occurred between them and the hosting
garnet. Nevertheless, the almandine and pyrope zoning

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suggest garnet growth during prograde metamorphism,
although the distribution of spessartine and grossular
content seem to be homogenized. If so, this homogeniza-
tion may have occurred during an early stage of
retrogression (Spear 1993), connected with a general
decrease of pressure.

Garnets from the high-Al Revdalen Formation schists
(i.e., samples 124 and 206) are characterized by relatively
lower grossular and higher almandine content, compared

with low-Al Revdalen Formation and Skoddefjellet For-
mation schists (samples 125 and 214, respectively).

Staurolite

Staurolite porphyroblasts as well as staurolite enclosed in
garnets do not reveal any chemical zonation. They are
Fe-staurolites, with Fe in the range of 1.55–1.74 atoms
per formula unit (apfu) and Mg in the range of

Fig. 4 Examples of typical profiles through garnets from samples 124 (high-Al mica schist of Revdalen Formation, zone 4, diameter = 1.7 mm), 125 (low-Al
mica schist of the Revdalen Formation; diameter = 1.5 mm), 206 (high-Al mica schist of the Revdalen Formation, zone 2, diameter = 1.3 mm), 214 (low Al
mica schist of the Skoddefjellet Formation, diameter = 1 mm), showing the differences in garnet zoning between high-Al Revdalen Formation,
low-Al Revdalen Formation and low-Al Skoddefjellet Formation mica schists, as well as within zones 2 and 4 in the Revdalen Formation.

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0.21–0.29 apfu. The Fe/(Fe + Mg) ratio is in the range
0.85–0.88 (Table 1).

Biotite

Biotite contains VIAl in the range of 0.653–0.86 apfu and
Fe/(Fe + Mg) in the range of 0.57–0.697 (Table 2). Ti
content in the biotites scatters in the range of 0.085–
0.295 apfu, which is characteristic for biotites from
mesozonal rocks of Barrovian facies series (Henry et al.
2005). Only biotites occurring in foliation planes in the
vicinity of garnets were used for further geothermobaro-
metric calculations, except sample 124, where we used
matrix biotite not in contact with garnet.

Plagioclase

Plagioclase crystals differ from each other, depending on
their position in the fabric of the mica schists. Plagioclase
grains in contact with garnet or partially replacing it have
an anorthite content in the range of 0.1–0.17. Plagioclase
grains from the matrix are characterized by a relatively

lower level of anorthite molecules of 0.09–0.12 (Table 1).
These porphyroblasts probably crystallized near the
maximum pressure conditions during the D1 deforma-
tion. Plagioclase grains characterized by the higher level
of anorthite molecules presumably formed early during
the first stage of decompression, after the pressure asso-
ciated with the peak of metamorphism, but still under
increasing temperature. The lower An plagioclases,
located in the matrix, were used for further geobaro-
metrical calculations.

Pressure–temperature estimates

Metamorphic zones

The petrography and mineral chemistry of the Isbjørn-
hamna Group described above point to regional
amphibolite facies metamorphism. The observed mineral
parageneses in the metapelites are grouped into four
metamorphic zones: zone 1, with Cld + Chl + Grt
paragenesis in high-Al mica schists, and Chl + Bt + Grt
paragenesis in low-Al mica schists; zone 2, with

Fig. 5 Sample locations with the temperatures obtained and boundaries of mineral zones within the Isbjørnhamna Group.

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Table 1 Chemical composition of plagioclases used for garnet–Al silicate–plagioclase (GASP) geobarometry (with obtained pressures) and chemical
composition of staurolites from the Isbjørnhamna Group metapelites.

Pl

Sample

St

Sample

124-1 124-2 124-3 218-1 218A-2 204-core 204-rim 206-core 206-rim

SiO2 64.853 66.114 65.742 64.918 65.944 SiO2 27.815 27.827 27.544 27.473
Al2O3 22.478 21.669 21.677 21.950 21.393 TiO2 0.428 0.596 0.509 0.638
CaO 3.114 2.095 2.306 3.325 2.513 Al2O3 53.190 54.364 53.379 53.274
FeO 0.098 0.074 0.059 0.456 0.031 MgO 1.391 1.208 1.112 0.988
BaO 0.000 0.000 0.072 na na CaO 0.006 0.024 0.000 0.000
Na2O 10.167 10.422 10.181 9.735 10.198 MnO 0.070 0.038 0.037 0.030
K2O 0.022 0.000 0.031 0.039 0.007 FeO 14.839 13.934 13.478 13.227
Total 100.733 100.374 100.068 100.423 100.086 ZnO 0.034 0.033 0.202 0.286

H2O 2.149 2.167 2.129 2.123
Si 2.839 2.891 2.886 2.853 2.894 Total 99.922 100.191 98.390 98.039
Al 1.160 1.117 1.122 1.137 1.106
Ca 0.146 0.098 0.108 0.157 0.118 Si 3.880 3.851 3.879 3.880
Fe 0.004 0.003 0.002 0.017 0.001 Ti 0.045 0.062 0.054 0.068
Ba 0.000 0.000 0.001 na na Al 8.745 8.867 8.859 8.867
Na 0.863 0.884 0.867 0.829 0.868 Mg 0.289 0.249 0.233 0.208
K 0.001 0.000 0.002 0.002 0.000 Ca 0.001 0.004 0.000 0.000
Total 5.013 4.992 4.988 4.995 4.987 Mn 0.008 0.005 0.004 0.004

Fe 1.731 1.613 1.587 1.562
Ab 85.420 90.000 88.610 83.907 88.032 Zn 0.004 0.003 0.021 0.030
An 14.460 10.000 11.090 15.891 11.968 Total 14.703 14.654 14.637 14.619
Or 0.120 0.000 0.180 0.202 0.000
Cs 0.120 0.000 0.180 — — Fe/(Fe+Mg) 0.857 0.866 0.872 0.882
P(kbar) 9.84 11.22 11.29 6.60 8.77

Derived 2s errors of ca. 0.8 kbar for geobarometry (Holdaway 2000, 2001) have been used.

Table 2 Chemical composition of garnets and biotites used for geothermometry and obtained temperatures.

Sample

Grt Bt

Py Alm Grs Sps Fe/(Fe + Mg) Fe/(Fe + Mg) Ti Temp.

103 9.685 77.446 11.045 1.824 0.889 0.578 0.235 604
104 8.337 79.280 11.623 0.759 0.905 0.579 0.190 574
106 4.887 67.799 19.082 8.233 0.933 0.613 0.194 542
111 9.490 75.572 11.779 3.158 0.888 0.614 0.085 675
119 9.312 74.120 14.692 1.876 0.888 0.640 0.182 668
123 8.521 76.359 11.180 3.940 0.900 0.634 0.231 631
124 8.830 81.673 6.581 2.916 0.902 0.594 0.222 655
125 6.010 71.476 19.426 3.088 0.922 0.655 0.282 597
126 7.536 70.953 16.620 4.891 0.904 0.618 0.143 616
203 6.679 66.571 22.196 4.554 0.909 0.517 0.173 553
204 8.033 84.134 5.774 2.059 0.913 0.583 0.158 580
206 7.402 89.433 1.945 1.220 0.924 0.576 0.203 519
208 8.672 67.678 20.397 3.252 0.886 0.627 0.169 671
211 6.166 71.925 17.383 4.526 0.921 0.657 0.178 648
214 10.195 74.263 13.343 2.199 0.879 0.623 0.232 667
216 10.090 80.443 6.284 3.183 0.889 0.572 0.192 596
217 10.376 82.923 3.292 3.409 0.889 0.627 0.209 642
218 13.610 80.204 4.727 1.458 0.855 0.582 0.185 624
219 8.218 71.436 20.230 0.116 0.897 0.572 0.137 634
220 7.867 72.259 9.391 10.484 0.902 0.637 0.234 633
221 6.559 76.095 16.880 0.466 0.921 0.626 0.148 574
222 8.337 79.280 11.623 0.759 0.905 0.579 0.190 661

Derived 2s errors of ca. 25°C for geothermometry (Holdaway 2000, 2001) have been used.

Neoproterozoic metamorphism in southern Svalbard J. Majka et al.

Polar Research 29 2010 250–264 © 2010 the authors, journal compilation © 2010 Blackwell Publishing Ltd258



Chl + Grt + St � Bt paragenesis in high-Al mica schists,
and Grt + Chl + Bt paragenesis in low-Al mica schists;
zone 3, with Grt + St + Bt + Ky � Chl assemblage in
high-Al mica schists and Grt + Bt + St � Chl in low-Al
mica schists; zone 4, with Grt + Ky + Bt in high-Al mica
schists and Grt + Bt in low-Al mica schists.

Metamorphic isograds are defined on the first occur-
rence of the AFM mineral. The boundary between zones
1 and 2 was delineated by the first appearance of stauro-
lite. The mineral assemblage for zone 2 was recognized
only in one sample of high-Al mica schists, and thus the
boundary between zones 1 and 2 is speculative. The
boundary between zones 2 and 3 is defined by the broad
appearance of biotite and staurolite and between zones 3
and 4 by the disappearance of staurolite. The observed
parageneses and metamorphic zones suggest a sequence
of index mineral reactions characteristic of continuously
increasing pressure–temperature (P–T) conditions from
upper greenschist to middle/upper amphibolite facies
conditions at moderate to high pressure. Metamorphic
zoning without a chloritoid + biotite assemblage is well
recognized in several kyanite-bearing metamorphic com-
plexes (e.g., Spear 1993; Bucher and Frey 1994).

Geothermobarometry

We used the garnet–Al silicate–plagioclase (GASP) geoba-
rometer (Holdaway 2001) to quantitatively estimate the
peak pressure conditions. The pressure was calculated
only in samples containing an Al2SiO5 polymorph
(kyanite in this case). Only five plagioclase–garnet pairs
were analysed in both samples, mainly because of strong
retrogressive changes. Those analysed, however, were
not affected by strong retrogression. The results obtained
are in the range of 9.84–11.3 kbar for sample 124, and
6.6–8.77 kbar for sample 218 (see Table 2 and Fig. 5 for
the location of samples), and are relatively consistent
with pargeneses observed in the investigated samples.

For peak temperature estimation, the garnet–biotite
geothermometer (Holdaway et al. 1997; Holdaway 2000)
was used. The temperatures were calculated for a norma-
tive pressure of 9 kbar on the basis of mineral paragenesis
and previous preliminary pressure estimates (Majka
2003; Majka et al. 2004). The lowest Fe/(Fe + Mg) values
(usually rim) were used for further geothermometrical
calculations. The calculated temperatures are scattered in
the range of 530–675°C (Fig. 5; Table 2). The general
tendency observed in the Isbjørnhamna Group is that
calculated temperatures increase from 519 to 604°C in
the Rålstranada area (samples 103, 104, 106 and 203),
and from 624 to 675°C in the upper Revdalen area
(samples 119, 123, 124, 208, 217 and 218), which
appears in the core of the Ariebreen anticline (samples

111, 211 and 214). Slightly lower temperatures (596–
634°C) were recorded for the samples collected from the
south and south-east limb of the Ariebreen anticline
(samples 216, 219 and 220). Similarly, for the samples
from the Fuglebereget–Vesletuva area (samples 125, 126,
221 and 222), temperatures in the range of 574–628°C
were obtained.

Comparison of geothermobarometrical results and
KFMASH petrogenetic grid

The K2O–FeO–MgO–Al2O3–SiO2–H2O (KFMASH) petro-
genetic grid (Spear & Cheney 1989) was used to better
constrain the P–T path based on our geothermobaromet-
ric results. Only the samples from the Revdalen
Formation, showing well-developed metamorphic zona-
tion, were used. Observed mineral prageneses of high-Al
mica schists can be represented by the KFMASH system.
The Fe/(Fe + Mg) ratios in analysed minerals decreases in
the order garnet > staurolite > biotite, similar to many
metapelites from all over the world (e.g., Thompson
1976; Spear 1993). Therefore, we decided to ignore the
minor components MnO, Na2O, TiO2 and CaO while
choosing the petrogenetic grid. The paragenetic mineral
assemblage in samples with the lowest metamorphic
grade in the Revdalen Formation, which crop out in the
Russepynten cape area, indicates that these rocks were
metamorphosed above the chloritoid and garnet isograds.
The lack of biotite in this mica schist variety does not
mean that these rocks were formed below the biotite
isograd. In accordance with the KFMASH system, the
co-existence of chloritoid, chlorite and garnet in the
paragenesis means that chloritoid-bearing mica schists
could have been formed in the temperature range of
450–520°C. Only above the temperature of ca. 520°C is
chlorite replaced by the garnet–biotite assemblage. Simi-
larly, chloritoid can be unstable, but in very specific cases
it is stable up to 550°C (Bucher & Frey 1994).

More eastwards but still in the Rålstranda and
Torbjørnsenfjellelt areas the index mineral assemblage
changes into Grt + Bt + Chl, Grt + St � Bt � Chl and
Grt + Bt + St � Chl. Such a change means an increase in
temperature above 520°C for samples without staurolite,
and a further increase in temperature above 550°C in
rocks containing staurolite. The stability of the latter
paragenesis is restricted much more by pressure than by
temperature. Generally, the maximum temperature of
staurolite stability decreases with an increase in pressure.
The obtained temperature of 580°C for sample 204 prob-
ably corresponds to a pressure of 8–9 kbar.

Further east in the upper Revdalen Valley region, stau-
rolite disappears from the paragenesis, and is replaced by
kyanite. This paragenetic mineral assemblage is stable

Neoproterozoic metamorphism in southern SvalbardJ. Majka et al.

Polar Research 29 2010 250–264 © 2010 the authors, journal compilation © 2010 Blackwell Publishing Ltd 259



above a temperature of 630°C at 11 kbar. The results from
geothermobarometry are consistent (sample 124) at ca.
646°C and a maximum pressure of ca. 11 kbar. Addition-
ally, the probable homogenization of garnet from this
sample suggests that the rock was metamorphosed under
relatively high-grade conditions.

Rocks from the north-eastern part of the study area
contain both kyanite and staurolite. This mineral assem-
blage is stable in a relatively small P–T field at
temperatures of ca. 640–680°C and pressures of ca.
9–10 kbar. The geothermobarometrical results for this
variety of the Revdalen mica schists yielded a tempera-
ture of ca. 628°C and pressures of 6.6–8.77 kbar. The
628°C temperature is fairly consistent with the stability
field of the Grt + Bt + St + Ky paragenesis, and the pres-
sure is within error of the expected pressure field.

In the remaining two samples (217 and 125), no
Al-saturated phases were observed, as expected for the
low bulk Al content in these rocks. Nevertheless, the
temperatures of 636°C for sample 217 and 597°C for
sample 125 are reasonable. Sample 217 was collected not
far away from samples 218 and 124, and a similar tem-
perature estimation therefore seems likely. Sample 125
comes from the area at the south-eastern extremity of the

Revdalen Formation, and the temperature obtained is
comparable with that calculated for sample 126 (Fig. 5).

As the transformation of kyanite into sillimanite or
andalusite is not documented in the studied rocks,
cooling possibly took place within the kyanite stability
field. Accordingly, the retrograde part of the P–T path
obtained for the Revdalen mica schists does not cross the
boundaries of sillimanite and andalusite stability fields
(Fig. 6).

Cooling rate

Using previous geochronological data (Manecki et al.
1998; Majka et al. 2008) and thermometrical results pre-
sented in this paper, it is possible to reconstruct the
cooling history of the Isbjørnhamna Group. Manecki
et al. (1998) reported 585–575 My 40Ar–39Ar cooling ages
for muscovite from the Isbjørnhamna Group and a
616 My 40Ar–39Ar cooling age for hornblende from the
overlying Eimfjellet Group. The closing temperatures for
muscovite and hornblende are ca. 350°C and ca. 550°C,
respectively. Majka et al. (2008) obtained a 643 My
U–Th–total Pb age for monazites located both in the
matrix of mica schists and enclosed in garnet porphyro-

Fig. 6 K2O–FeO–MgO–Al2O3–SiO2–H2O
(KFMASH) petrogenetic grid (modified from

Spear & Cheney 1989; Spear & Cheney unpubl.

data) with the pressure–temperature (P–T)

path marked for the Isbjørnhamna Group

rocks.

Neoproterozoic metamorphism in southern Svalbard J. Majka et al.

Polar Research 29 2010 250–264 © 2010 the authors, journal compilation © 2010 Blackwell Publishing Ltd260



blasts, constraining the growth of garnet in the
Isbjørnhamna Group at 643 Mya. From the data men-
tioned above and with three points on the age–
temperature diagram, we construct a nominal cooling
path for the Neoproterozoic metamorphic volcanic
terrane (Fig. 7). The generally smooth shape of the
cooling path suggests a cooling rate of ca. 5°C My-1. Such
a cooling rate corresponds well with those reported from
the Neoproterozoic Pan-African orogens (e.g., Möller
et al. 2000). On average, cooling rates increase through
geological time, and are an order of magnitude faster in
Phanerozoic than in Precambrian settings (Dunlap 2000).
Despite the unavoidable simplifications, the compilation
of temperature–time (T–t) paths by Willigers et al. (2002)
shows that a cooling rate around 5°C My-1 is typical of
Neoproterozoic orogens. Two possible forms of the T–t
path for the Isbjørnhamna Group are proposed (Fig. 7).
One assumes a moderate reheating at ca. 480 Mya, the
approximate time of metamorphism in the northern tec-
tonic block of Wedel Jarlberg Land (Mazur et al. 2009).
The other postulates a decrease of the cooling rate
from 575 Mya onwards. Further thermochronological
studies are necessary to differentiate between these two
possibilities.

Concluding remarks

The Revdalen Formation is a <200 m thick continuous
horizon that provides an excellent marker for investigating
lateral changes in P–T metamorphic conditions. On the
basis of the metamorphic mineral zonation and P–T

estimates, an increase of P–T conditions from west
(Rålstranda area) to east (Revdalen Valley area) is
observed. Only the slight south-eastward temperature
decrease in the Fugleberget area departs from this general
trend. Taking into account the thermometric results
from the Skoddefjellet mica schists, a similar trend in
temperature change can be extrapolated for the entire
Isbjørnhamna Group. Maximum temperatures were
obtained from the core of the Ariebreen anticline, whereas
the calculated temperatures continuously decrease toward
the limbs of this antiform and the western part of the study
area. This relationship indicates that large-scale folding of
the Isbjørnhamna Group occurred after the peak of meta-
morphism. Because the folds are crosscut by the VKZ,
displacement along this shear zone must have been even
later. Indeed, the isograds defined for the Revdalen For-
mation are oblique to the trend of the VKZ. In summary,
the peak temperature and pressure conditions of Neopro-
terozoic metamorphism are estimated at ca. 670°C and
�11 kbar. The geothermobarometric results are consistent
with previous preliminary estimates of the P–T rock-
forming conditions (Smulikowski 1965; Czerny et al.
1993; Majka et al. 2004).

The microstructural observations show that the perva-
sive fabric of the Isbjørnhamna rocks formed under
conditions close to the peak of metamorphism. As the
constructed isograds are oblique to the foliation and litho-
logical contacts, the penetrative deformation must have
slightly preceded the peak temperature. The latter was
followed by the folding of already developed foliation
before the initiation of the VKZ. Considering that the VKZ
was developed in the Early Ordovician (Mazur et al.
2009), the structural grain of the Isbjørnhamna Group
and the entire southern tectonic block of Wedel Jarlsberg
Land must have been formed in Neoproterozoic to
Cambrian times.

The T–t path of the Isbjørnhamna Group shows cooling
at a rate of ca. 5°C My-1, interpreted to be related to slow
erosion controlled exhumation, rather than rapid uplift
connected to tectonic activity. Notably, cooling continued
undisturbed at least until the Early Ordovician, the time
of postulated juxtaposition of the Neoproterozoic
complex against the northern part of Svalbard’s south-
western terrane.

Our data confirm that the southern tectonic block of
Wedel Jarlsberg Land represents a fragment of a Neopro-
terozoic orogen, with a well-preserved structural grain
and metamorphic zonation. This Neoproterozoic domain
seems to be entirely exotic compared with Svalbard’s
remaining terranes, and is only weakly overprinted by
Caledonian metamorphism. The Neoproterozoic terrane
could not have been derived from the North American
margin, as postulated for the rest of Svalbard’s crustal

Fig. 7 Hypothetical cooling paths for the Isbjørnhamna Group, based on
data published by Manecki et al. (1998), Majka et al. (2008) and this paper.

Path 1 assumes moderate reheating at ca. 480 Mya, whereas path 2 pos-

tulates a decrease in the cooling rate from 575 Mya onwards.

Neoproterozoic metamorphism in southern SvalbardJ. Majka et al.

Polar Research 29 2010 250–264 © 2010 the authors, journal compilation © 2010 Blackwell Publishing Ltd 261



fragments (Gee & Tebenkov 2004). Instead, its presence is
more in line with models suggesting large-scale strike-slip
displacements during the Early Palaeozoic assembly of
the Svalbard Archipelago (e.g., Harland & Gayer 1972;
Harland 1985; Gee & Page 1994). The most straightfor-
ward explanation for the origin of the Neoproterozoic
terrane is a derivation from the Timanide belt of north-
eastern Europe. However, such a correlation has two
important implications that require further verifica-
tion and discussion. Firstly, the Neoproterozoic orogeny
must have commenced at least before the opening
of the Iapetus Ocean, as the Svalbard Archipelago
is separated from Europe by Caledonian sutures (Gee &
Tebenkov 2004). Secondly, the linkage between south-
western Svalbard and the Timanide belt cannot be recon-
ciled with the large-scale Early Palaeozoic rotation of
Baltica that has been postulated by Hartz & Torsvik
(2002). Ongoing studies characterizing the metamorphic,
structural and magmatic histories of Neoproterozoic
circum-Arctic terranes are necessary in order to better
constrain Neoproterozoic paleogeographic reconstruc-
tions and the proposed younger tectonic evolution
models for the region (Amato et al. 2009).

Acknowledgements

This research was supported by MNiSzW grant no.
2P04D03930. JM was also supported by the Swedish
Institute, Visby Programme and Ymer-80 Foundation. We
are grateful to two anonymous reviewers for their con-
structive comments improving the manuscript, and to L.
Jeżak and P. Dzierżanowski (Warsaw University) for their
assistance with the electron microprobe analyses.

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