Ar-Ar doting of Coledonion ond Grenvillion rocks, Svalbard 263
NORWEGIAN JOURNAl OF GEOLOGY
Ar-Ar dating of Caledonian and Grenvillian rocks from
northeasternmost Svalbard evidence of two stages of
Caledonian tectonothermal activity in the high Arctic?
-
Åke Johan sson , Hen ri Mal uski & David G. Gee
Johansson, Å., Maluski,H. & Gee, D.G. Ar-Ar dating of Caledonian and Grenvillian rocks from northeasternmost Svalbard - evidence of two sta­
ges of Caledonian tectonothermal activity in the high Arctic ? Norsk Geologisk Tidsskrift, Vol. 81, pp. 263-281. Trondheim 200 l. ISSN 029-196X.
Ar-Ar analyses have been carried out on Caledonian and Grenvillian rocks from the northernmost Barents Shelf (approx. 80"N) on Nordaustlan­
det and Kvitøya, northeast Svalbard. Five muscovites and one biotite from Caledonian granitoids, three muscovites and one biotite from Grenvil­
lian granitoids, and two samples of hornblende from mafic rocks of uncertain age, were analysed using stepwise laser heating of single grains. T he
Grenvillian granitoids, as well as the mafic rocks, yield ages between 410 and 425 Ma, interpreted to date cooling after Caledonian regional meta­
morphism; they show no traces of a Grenvillian argon component. Thus, Caledonian metamorphism in central and eastern Nordaustlandet must
have reached above the closure temperature for argon in these minerals. In the Caledonian granitoids, two age groups may be discerned: one with
Ar-Ar ages in muscovite between 415 and 430 Ma, and another with muscovite and biotite ages around 400 Ma. The first group is related to grani­
tic and aplitic rocks having Late Ordovician to Early Silurian U-Pb monazite ages (ca. 440-460 Ma); the second group includes the large Rijpfjor­
den granite with an Early Devonian U-Pb monazite age of 412 Ma. Thus, prolonged tectonothermal activity during the Caledonian orogeny may
be discerned in northeasternmost Svalbard, possibly divisible into two stages: one stage with regional metamorphism and syn-tectonic magma­
tism occurring in the Late Ordovician to Early Silurian, and a second stage with late- or post-tectonic magmatism in the Early Devonian. For each
stage, the Ar-Ar age follows the U-Pb age with a delay of 10-20 Ma, corresponding to rapid cooling of 20-45 °C per million years from near-mag­
matic temperatures to the closure temperature of argon in these minerals.
Ake Johansson, Laboratory for Isotope Geology, Swedish Museum of Natura/ History, Box 50 007, S-104 05 Stockholm, Sweden (e-mail: ake.johans­
son@nrm.se). Henri Maluski, Laboratoire de Geochronologie, Institut des Sciences de la Terre, de l'Eau et de l'Espace de Montpellier, Universite Mont­
pellier II, Place Eugene Bataillon, F-340 95 Montpellier Cedex 05, France ( e-mail: maluski@dstu.univ-montp2.fr). David G. Gee, Department of Earth
Sciences, Uppsala University, Villavagen 16, S-752 36 Uppsala, Sweden (e-mail: gee@geofys.uu.se).
ln troducti on
The Svalbard archipelago is located in the northwestern
corner of the Barents Sea Shelf and the Eurasian Plate, in
a key area for restoring Proterozoic and Palaeozoic oro­
gens in the North Atlantic and Arctic regions. The Sval­
bard Caledonides were most likely assembled during
mid-Palaeozoic orogeny from a variety of terranes, with
different pre-orogenic evolutions (Harland 1 997). Sval­
bard's Eastern Terrane ( Fig. l) is composite and may be
subdivided into a West Ny Friesland Terrane and a Nord­
austlandet Terrane ( Gee et al. 1995; Witt-Nilsson 1 998).
Western Ny Friesland is characterized by a Caledonian
thrust pile, the Atomfjella Complex, exposed in the N-S­
trending Atomfjella Antiform, with intercalated base­
ment gneisses and granitoids, mainly of late Palaeoprote­
rozoic age, and Mesoproterozoic or younger cover rocks
(Witt-Nilsson et al. 1998, and references therein) . These
rocks were metamorphosed in amphibolite facies and
pervasively deformed during Caledonian transpression.
40Af-39Ar ages on hornblendes and muscovites from
northwestern Ny Friesland, presented by Gee & Page
( 1 994) , indicated that uplift and cooling after peak meta­
morphism took place in the Late Silurian to Early Devo­
nian, at around 420-4 1 0 Ma. Conventional U-Pb dating
of titanites from the sheared Palaeoproterozoic grani­
toids indicated a slightly younger, early Devonian ( ca.
4 1 0 Ma) lower intercept age, interpreted to be related to
metamorphic recrystallization and/or lead loss at a late
stage of the Caledonian metamorphism ( Johansson et
al. 1995), and similar lower intercept ages were also
recorded for zircon in some samples ( Larionov et al.
1 995; Johansson & Gee 1 999) .
The Nordaustlandet Terrane is characterized by a
Grenville-age basement complex, overlain by Neoprote­
rozoic to Ordovician platformal sediments and intruded
by Caledonian granitoids. Separation of Grenvillian and
Caledonian granitic magmatism has only been possible
through recent U-Pb dating (Gee et al. 1 995; Gee et al.
1 999; Johansson et al. 2000; Johansson et al., submitted,
in prep. ) . Caledonian metamorphism on Nordaustlandet
is generally in greenschist facies, except in some areas in
the central and eastern parts where the grade increases
and Caledonian migmatization influences the deeper
264 Å. Johansson et al.
structural levels (Johansson & Larionov 1999; Tebenkov
et al. 1999; Tebenkov et al., submitted) . Caledonian
deformation is generally also less pervasive than in Ny
Friesland, mainly resulting in upright to W-vergent anti­
forms and synforms.
Nordaustlandet's Early Palaeozoic successions and
faunas, underlain by characteristic Neoproterozoic tilli­
tes, carbonates and clastic formations, compose a strati­
graphy that closely correlates with the Laurentian mar­
gin of East Greenland. Even the Grenville-age basement
of late Mesoproterozoic metasediments, intruded by ca.
950 Ma granites, is present in central East Greenland
(Steiger et al. 1 993; Strachan et al. 1 995; Watt et al. 2000).
The evidence for Laurentian affinities for Nordaustlan­
det, taken together with W-vergent folding and increase
of Caledonian metamorphic grade towards the east, sug­
gests that the axial zone of the Caledonides lies further to
the east in the Barents Shelf. A major zone of Iapetus
suturing can thus be expected to separate the Nordaust­
landet Terrane from the continental margin of Baltica as
it is represented in Scandinavia, the Urals and Novaya
Zemlya.
In this paper, we present new 40Af_39Ar results on
muscovites, biotites and hornblendes from Caledonian
and Grenvillian rocks (according to U-Ph age determi­
nations) from the Nordaustlandet Terrane, as a comple­
ment to previous and on-going U-Ph studies. The aim
has been two-fold: (l) to study the Caledonian tectono­
thermal evolution of Nordaustlandet and relate it to that
of western Ny Friesland, already documented by Ar-Ar
studies, and (2) to investigate whether traces of the ear­
lier, Grenvillian, evolution have been preserved in the Ar­
Ar system in the less pervasively deformed and meta­
morphosed Nordaustlandet Terrane.
Geol ogy of Nordaustlan det
Nordaustlandet forms the eastern part of Svalbard's Eas­
tern Caledonian Terrane ( Fig. 1 ) . Caledonian and older
rocks are exposed along the north coast of Nordaustlan­
det, in an ice-free strip in central Nordaustlandet, and in
scattered outcrops in easternmost Nordaustlandet and
on the smaller islands towards the north and east, most
notably Kvitøya (Fig. l); the remaining part of Nordaust­
landet is covered by two large ice-caps (Vestfonna and
Austfonna) . Towards the south, the Caledonian base­
ment is overlain by Carboniferous and younger sedi­
mentary rocks. Detailed accounts of the Caledonian geo­
logy of Nordaustlandet are given by Flood et al. ( 1 969)
and Ohta ( 1 982), with shorter summaries in the map
description by Hjelle & Lauritzen ( 1 982) and Lauritzen
& Ohta ( 1 984) . More recent descriptions, with a focus
on structural geology and/or isotopic dating, are found
in Gee et al. ( 1 995), Gee & Tebenkov ( 1 996), Gee et al.
( 1 999) and Johansson et al. (2000); only a short sum­
mary is given below.
NORWEGIAN JOURNAL OF GEOLOGY
The oldest exposed rock unit is the Mesoproterozoic
Brennevinsfjorden Gro up, composed mainly of phyllitic
turbidites and sandstones, deposited some time between
1 1 00 Ma (age of youngest detrital zircon grains; A. Lari­
onov, unpublished Pb-Pb data) and 960 Ma (age of
unconformably overlying Kapp Hansteen Group volca­
nics; Johansson et al. 2000). The Kapp Hansteen Group
is composed of andesitic volcanic and volcaniclastic
rocks with related intrusive quartz porphyry stocks,
dated to 940-960 Ma ( Johansson et al. 2000), and intru­
ded by granites of similar age (Kontaktberget and Lapo­
niafjellet granites on the Laponiahalvøya peninsula, Gee
et al. 1 995; augen gneisses of central Nordaustlandet,
Johansson et al. 2000). Geological relations in central
Nordaustlandet suggest that their transformation to
augen gneisses occurred during Grenvillian deformation
(Tebenkov et al., submitted).
This Grenvillian basement complex is unconforma­
bly overlain by the Neoproterozoic Murchisonfjorden
Supergroup and the Vendian to mid-Ordovician Hinlo­
penstretet Supergroup. Caledonian granites are difficult
to separate from Grenvillian granitoids in the field, since
they rarely show cross-cutting relations to the Neoprote­
rozoic and younger sedimentary rocks, and the degree of
deformation is variable. U-Ph isotopic dating yields
Caledonian ages of 4 1 0 -420 Ma for the anatectic Rijp­
fjorden granite batholith in Prins Oscars Land ( Johans­
son et al., submitted) and the high-magnetic Djupkil­
sodden pluton in southern Duvefjorden ( Gee et al.
1 999) . Similar or slightly higher ages are also indicated
by U-Ph studies on the Nordkapp granite on Laponia­
halvøya, the Winsnesbreen granite in central Nordaust­
landet, and other smaller massifs and dykes of relatively
undeformed granite and aplite in the central and eastern
areas (Johansson et al., submitted, in prep. ) . Preliminary
Ph-Ph data suggest that the tectonothermal activity in
the east may have occurred slightly earlier, with migma­
tization at 440-450 Ma, and cross-cutting aplitic dykes
intruding at c. 430 Ma ( Johansson & Larionov 1 999, in
prep.).
Mafic rocks are sparse. Disregarding the Mesozoic
dolerites along Hinlopenstretet and on the northern
tip of Botniahalvøya, mafic rocks mainly occur in the
form of metagabbros and subordinate amphibolites in
the easternmost areas: eastern Orvin Land, Nord­
marka, Isispynten, Storøya, and Kræmerpynten on
Kvitøya (Hjelle et al. 1 978; Ohta 1 978). Based on their
generally little deformed nature, Ohta (1978) conside­
red the gabbros Caledonian, but their ages are not
known with certainty.
Caledonian folding along N-S-trending axes gave rise
to the present outcrop pattern of the rocks, with the
Grenvillian complex as well as the Caledonian granites
being exposed in broad antiforms in Botniahalvøya Laponiahalvøya, central Nordaustlandet, and the far
east, and the Neoproterozoic and younger formations
being preserved in the intervening synforms, most nota­
bly the Hinlopenstretet Syncline (Fig. 1 ) . A major
Ar-Ar dating of Caledonian and Grenvillian rocks, Svalbard 265
NORWEGIAN JOURNAl OF GEOlOGY
18 E
20E
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22E
24E
26E
28E
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30E
20
40
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60
80
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NORDAUSTLANDET
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Mesozoic doler i tes
g carbon iferous-Jurassic sediment s
!!!!] Caledonian grani tes
- Gab b ros of uncer tain age
� Hinlope
_ n st retet S_upergroup
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Carboniferous to Tertiary
llevonian (Old Red SandatonJy N
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Caledonian granitoids
l. Rijpfjorden granite, Vindbukta
2. Winsnesbreen granite
3. Nordkapp granite, Gryteberget
4. Red granite, Innvika
S. Aplite, Nordmarka
Grenvillian granitoids
6. Augen gneiss, Nordmarka (2 samples)
7. Augen gneiss, Innvika
Mafic rocks
8. Amphibolite, A ndn)eneset, Kvitøya
9. Gabbro, Isispynten
:•:•:•
Grenvillian Kontakt berget Grani te
� Grenvillian Laponiafjellet Gran i te
� M igmat ites and augen gneisses
� Grenvillian Kap p Hansteen Group
� volcanics and quar tz por p hyries
� Brennevi nsfjorden Group
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(Mesoproterozoic)
Fig. l. Simplified geological map ofNordaustlandet and adjacent islands, based on Flood et al. (1969), Hjelle & Lauritzen (1982), Lauritzen &
Ohta (1984) and recent SWEDARCTIC mapping, with sample locations indicated. Inset map shows the Caledonian terranes of Svalbard (from
Gee 1986). Caledonian granitoids on inset map: H = Hornemantoppen batholith, N= Newtontoppen granite, R= Rijpfjorden granite; major
Caledonian fault lines: BP= Billefjorden Fault, BBF= Breibogen-Bockfjorden Fault, RF= Raudfjorden Fault.
unconformity separates the Neoproterozoic sequence
from the underlying units in central Nordaustlandet
(Gee & Tebenkov 1 996) . Subsequently, the whole com­
plex became slightly tilted towards the south, perhaps in
connection with Tertiary uplift related to the opening of
the North Atlantic and Arctic Oceans; the late Palaeozoic
and Mesozoic cover rocks are still preserved on southern
Nordaustlandet, but have been eroded away from the
northern part.
Early K-Ar dating of rocks from Nordaustlandet,
summarized by Gayer et al. ( 1 966) and recalculated by
Ohta ( 1 994) to the decay constants recommended by
Steiger and ]iiger ( 1977), gave Caledonian ages in the 345
- 445 Ma range. From northern Ny Friesland, Gee & Page
( 1 994) presented modem stepwise heating Ar- Ar data on
horn blendes from amphibolites ( 6 samples) and musco-
vites from mica schists (2 samples). These yielded pla­
teau or "near plateau" ages in the 4 1 3 to 425 Ma range,
with one older hornblende age of 447 ± 5 Ma.
lnvesti gated rocks
Ten rock samples were used for Ar-Ar analysis: five sam­
ples of Caledonian granitic rocks, three samples of Gren­
villian granitoids transformed into augen gneisses, and
two samples of gabbro and amphibolite from eastern­
most Nordaustlandet and Kvitøya (Fig. l). Both the
Caledonian and Grenvillian granitoids are anatectic two­
mica granites, derived from crustal precursors, lacking
hornblende or other amphiboles (see Johansson et al.
266 Å. Johansson et al.
2000, for a discussion of the geochemistry and origin of
the Grenville granites) . From all eight granite samples,
muscovite was analysed, whereas biotite was analysed
from only one each of the Caledonian and Grenvillian
granitoids. From the two mafic rock samples, only horn­
blende was analysed.
Caledonian granitoids
Sample 28-1 is derived from Vindbukta dose to the nor­
thern margin of the Rijpfjorden granite massif ( Fig. 1 ) .
The Rijpfjorden granite is a generally undeformed, pink,
crustal anatectic two-mica granite containing abundant
xenoliths ( Hjelle 1 966) . It also contains abundant inheri­
ted zircons, and conventional U-Pb multigrain dating
has proved difficult; however, single-zircon Pb-evapora­
tion and ion microprobe spat analyses indicate ages of
400-430 Ma for granite emplacement, and monazite has
yielded a concordant conventional U-Pb age of 4 1 2.5 ±
0.5 Ma (Johansson et al., submitted) . Sample 28-1 itself
consists of an even- and medium-grained mosaic of
quartz, K-feldspar and plagiodase, with muscovite scat­
tered around as ca. l mm large flakes without any prefer­
red orientation. Biotite was also recovered during mine­
ral separation, and was used alongside with muscovite
for Ar-Ar analysis. However, in thin section, no fresh bia­
tite could be seen; only altered grains containing a mix­
ture of almost colourless mica and opaque material, pro­
bably iron oxides and hydroxides, were observed.
Sample 94047 is derived from the Winsnesbreen gra­
nite, a smaller massif of granite of presumed Caledonian
age occurring in the southern part of central Nordaust­
landet, apparently as a southern extension of the Rijp­
fjorden granite (Fig. 1 ) . U-Pb ion microprobe spot ana­
lyses of zircons have produced a wide array of ages, while
conventional U-Pb analyses of monazite yielded one
concordant point at 422 Ma, and two discordant points
with 207Pbf206Pb ages of 440-460 Ma ( Johansson et al.,
submitted) . The sample consists of medium-grained,
light pink to grey granite with a marked foliation defined
by the mica. In thin section, this fabric is also seen as
mm-wide lenses of quartz and K-feldspar, set in a finer
matrix of quartz, K-feldspar and plagioclase. Muscovite
occurs as flakes of varying size, up to 3 mm large, weakly
oriented after the gneissic fabric. No biotite was observed
in thin section, and opaque minerals occur in very sub­
ordinate amounts.
Sample 94048 is derived from the Nordkapp granite
on northern Laponiahalvøya, where associated pegmati­
tes cross-cut the Grenvillian Laponiafjellet augen gra­
nite. AI; with the Rijpfjorden granite, it contains abun­
dant inherited zircons, but single-zircon Pb-evaporation
dating suggests an emplacement age of 424 ± 14 Ma,
whereas discordant monazite yields a somewhat older U­
Pb upper intercept age of 440 ± 3 Ma ( Johansson et al.,
submitted) . Sample 94048 from Gryteberget is a light
grey, medium-grained, massive and leucocratic granite,
NORWEGIAN JOURNAL OF GEOlOGY
containing quartz, K-feldspar and plagioclase in a relati­
vely even-grained mosaic with grain sizes up to 2 mm.
Muscovite and biotite occur in about equal amounts as
grains less than l mm, showing no preferred orientation,
both appearing fresh and unaltered, except for the pleo­
chroic halos surrounding possible zircon grains within
the biotites. Quite often, muscovite and biotite occur
intergrown as parallel laths within the same aggregate.
The muscovite grains recovered during mineral separa­
tion were substantially larger than those observed in the
thin section, with grain sizes of several millimetres.
Sample G95:030 is from a red, undeformed sheet of
granite cutting migmatites and augen gneisses south of
Innvika in inner Duvefjorden; it is possibly related to the
nearby Caledonian Rijpfjorden granite. However, U-Pb
analysis of monazite suggests a slightly higher age: two
discordant fractions yield 207Pbf206Pb ages of 440-450
Ma, and if regressed together, an upper intercept of 438
± 5 Ma ( Johansson et al., submitted) . The sample con­
sists of a mosaic of up to 4 mm large grains of K-feld­
spar, plagioclase and quartz, with muscovite occurring as
up to 2 mm large hypidiomorphic flakes, and biotite as
smaller irregular brown flakes, sometimes intergrown
with muscovite. Neither of the micas show any preferred
orientation in thin section.
Sample G95:051 is from an aplite dyke cross-cutting
the augen gneiss in the southern part of Nordmarka, a
small ice-free area in easternmost Nordaustlandet ( Fig.
1 ) . U-Pb analysis of three discordant monazite fractions
yielded zo7pbfZ06Pb ages between 464 and 484 Ma and an
upper intercept age of 463 ± 9 Ma ( Johansson et al., in
prep. ) . Single-zircon Pb-evaporation analyses on similar
aplitie dykes from Andreeneset on Kvitøya suggest an age
of ca. 430 Ma ( Johansson & Larionov 1 999, in prep.) .
The investigated sample consists o f a medium- and
even-grained mosaic of K-feldspar, plagioclase and
quartz, lacking any fabric or foliation. Biotite occurs as
thin laths up to 2 mm long without orientation, ftlling
the interstices between the feldspar crystals, while mus­
covite occurs as a few more scattered flakes, less than l
mm, also lacking any preferred orientation.
Grenvillian granitoids
Samples G95:049 and G95:050 are both augen gneisses
from the southern part of the above-mentioned Nord­
marka area of easternmost Nordaustlandet. A geological
description of Nordmarka and the augen gneiss (porphy­
ritic granite) is found in Hjelle et al. ( 1 978). U-Pb zircon
ion microprobe dating and single-zircon Pb-evaporation
dating suggest a protolith age of ca. 950 Ma ( Johansson et
al., in prep.) , similar to the age of the Fonndalen and
Ringåsvatnet augen gneisses of central Nordaustlandet
( Johansson et al. 2000). Sample G95:049 contains quartz
and K-feldspar, with the former mineral forming elonga­
ted lenses outlining the gneissic fabric, as well as musea­
vite and biotite as elongated crystals that occur together
NORWEGIAN JOURNAL OF GEOLOGY
forming narrow hands along the foliation. Sample
G95:050 consists of quartz and partly megacrystic (cm­
sized) K-feldspar and plagioclase, but lacks strong folia­
tion or fabric. Biotite occurs as up to l mm long crystals
forming oriented aggregates outlining a weak foliation.
Muscovite occurs as up to l mm flakes in aggregates lac­
king any preferred orientation, but also as small mica
inclusions (coarser than normal sericite) following diffe­
rent crystallographic directions in the feldspar mega­
crysts. The muscovite and biotite in both samples are
fresh and unaltered, except for dark pleochroic halos sur­
rounding zircon inclusions in the biotite. A few garnet
crystals were observed in the thin section in sample
G95:049; in addition, apatite is a common accessory
phase in both samples and zircon occurs in small
amounts. From sample G95:050, both muscovite and
biotite were analysed; from G95:049 only muscovite was
analysed.
Sample G95:031 is from a similar augen gneiss, south
of Innvika, in central Nordaustlandet. It consists of up to
5 mm 'ong K-feldspar augen in a medium-grained
mosaic Jf quartz and plagioclase with a weak gneissic
fabric. Muscovite occurs as elongated small crystals for­
ming narrow hands that define the foliation. Biotite
sometimes occurs together with the muscovite, but also
forms separate irregular aggregates of anhedral brown
crystals lacking clear orientation.
Mafic rocks of uncertain age
Metagabbroic rocks occur in the eastern part of Orvin
Land, in Nordmarka, on Isispynten in easternmost
Nordaustlandet and on Storøya and Kvitøya (Kræmer­
pynten) east thereof (Hjelle et al. 1978; Ohta 1 978 ). The
large layered gabbro on Storøya (more than 7 x 1 1 km,
the size of the island) was described by Ohta ( 1 978), who
considered it Caledonian due to its well-preserved
nature, but independent isotopic evidence concerning
the age of these rocks is still lacking. For this study, a gab­
bro from Isispynten containing the most unaltered horn­
blende was selected for analysis, whereas hornblende in
gabbro samples from Storøya and Kræmerpynten on
Kvitøya was either more altered or intergrown with other
minerals, and therefore not analysed. In addition, horn­
blende from a foliated amphibolite occurring as a lens
within the migmatitic gneisses on Andreeneset on the
west tip of Kvitøya, was also analysed.
Sample 94062c from Isispynten is a medium- grained,
massive gabbro, dominated by hornblende occurring as
mm-sized pale green crystals intergrown with brown
biotite. Plagioclase and opaque minerals occur in subor­
dinate amounts. The biotite ranges from completely
fresh to relatively altered; the large amphibole crystals
show some incipient alteration along the partings. Bet­
ween the larger crystals, there are zones of fine- grained
amphibole, biotite, plagioclase, and possibly olivine,
which appear cataclastic and altered, with dark rusty
material along grain boundaries.
Ar-Ar dating of Ca l edonian and Grenvil l ian rocks, Sval bard 267
Sample 598:129 from Andreeneset on Kvitøya is a
foliated, medium-grained amphibolite, consisting of
fresh hornblende (about 50 %), plagioclase and K-feld­
spar, with minor olivine and opaque minerals.
Analytical procedures
Muscovite, biotite and hornblende were separated at the
Laboratory for Isotope Geology, Swedish Museum of
Natura! History, Stockholm, using standard mineral
separation techniques (Frantz isodynamic magnet sepa­
rator, heavy liquids, and vibrating "mica table" ) . Final
selection of grains sent for irradiation took place at the
Laboratoire de Geochronologie, Universite Montpellier
Il, where the subsequent analytical work was also done.
Irradiation took place at the McMaster reactor in
Canada, with an irradiation time of 2.5 days. As monitor,
the MMHb-1 hornblende standard was used (Alexander
et al. 1978), with an accepted age of 520.4 ± 1 . 7 Ma
(Samson & Alexander 1 987). Analysis of single mineral
grains, about 1 - 3 mm in diameter, took place using an
OptiLas Lexel 3500 continuous argon laser for stepwise
heating and a mass spectrometer of model 2 1 5-50 from
Mass Analyser Products equipped with an electron
multiplier for the mass analysis. For each heating step, lO
scans of the masses 40, 39, 38, 37 and 36 with back­
grounds in between were made. The initial intensity for
each mass at the time when the mass spectrometer was
equilibrated with the inlet section was computed using
linear regression, and used for further calculation. Every
fourth step, a blank analysis was made. The obtained
values were corrected for blank and atmospheric argon,
as well as Ca- and Cl-derived neutron-induced argon
using the masses 3 7 and 38, befare calculation of argon
isotope ratios and ages. The reported errors are l stan­
dard deviation, and include uncertainties in the J-factor
(radiation). A detailed description of the analytical
methods used is found in Monie et al. ( 1 994) .
Resu lts
The isotope ratios and ages obtained from each step are
reported in Appendix l, and resulting plateau ages, total
gas ages and isochron ages for each sample are summari­
zed in Table l. The age spectra are illustrated in Figs. 2 - 4.
For most samples, two plateau ages have been calculated,
one broad plateau with contiguous steps corresponding
to more than 90 o/o of the released 39Ar, and one more
restricted, but more well-defined, plateau, encompassing
between 40 and 70 o/o of the released 39Ar. However, the
differences between the two plateau ages, or between the
plateau ages and the total gas ages, are not significant.
The isochron ages, both normal (40Arf36Ar vs. 39Arf36Ar
using the regression calculation of York 1 969) and inver-
268 Å. Johansson el al.
ted (36Arf40Ar vs. 39Arf40Ar following Turner 1 9 7 1 , Rod­
dick 1 978, and Roddick et al. 1 980) have been calculated
using the same steps as the "broad plateau age': but may
still deviate somewhat due to outlying points. In the case
of the inverted isochrons, most analyses p lot in a duster
dose to the intercepts with the x-axis, so that an isochron
age can be determined with quite good precision.
Because of this dustering, the slopes of the isochrons
and the y-intercepts, however, become badly defined,
irrespective of MSWD value. The y-intercept ideally
should fall at the composition of atmospheric argon
( 40Arf36Ar 295.5), but in many cases shows large devia­
tions (values in brackets in the last column of Table 1 ) ,
due to the small contributions o f atmospheric argon in
the analyses. Thus, the main emphasis is put on the pla­
teau ages when interpreting the data.
The hornblendes from the mafic rocks did not pro­
duce any well-defined plateaux, due to the small
amounts of argon present and the limited number of
steps during which it was released. The "plateau ages"
reported in Tab le l and illustrated in Fig. 4 are thus more
loosely defined, based on only 1 -3 steps, and have to be
interpreted with caution.
=
Caledonian granitoids
From the Rijpjjorden granite ( sample 28- 1 ) , both musco­
vite and biotite give similar plateau ages of 399 ± 5 and
405 ± 1 1 Ma, respectively, encompassing more than 90
% of the released Ar (Table l, Fig. 2 ) . Although biotite is
supposed to have a lower closure temperature for Ar
than muscovite (Purdy & Jager 1 976; Harrison et al.
1 985; McDougall & Harrisorrt988 ; Hames & Bowring
1 995), it gives the older age; however, within the margin
of error, the ages are identical. A slight tendency for a
resetting of the biotite at a lower age may be discerned in
the first two steps; a possible cause for such a resetting
would be heating related to the intrusion of Mesozoic
dolerites in eastern Svalbard (cf. Lauritzen & Ohta 1 984) .
The Ar-Ar ages are ca. 10 M a younger than the U-Pb
monazite age of 4 1 2 Ma (Johansson et al., submitted) , an
offset that probably is related to post-magmatic cooling.
The Winsnesbreen granite (sample 94047) gives a
muscovite Ar-Ar age similar to that of the Rijpfjorden
granite, with a plateau at 406 ± 5 Ma, whereas the Nord­
kapp granite (sample 94048) yields a significantly higher
muscovite plateau age of 428 ± 12 Ma. The higher age of
the Nordkapp granite muscovite is also supported by
total gas and normal and inverse isochron ages in the
range 427 to 434 Ma, and would agree with the U-Pb
monazite age of 440 ± 3 Ma for this granite, with a simi­
lar offset for cooling of about lO Ma as seen in the Rijp­
fjorden granite. A single spot analysis in another musco­
vite grain from the same sample gave a slightly lower age
of 422.5 ± 1 .4 Ma (Appendix l); however, still within the
margin of error for the result of the step analysis.
The red granite from south of Innvika (sample
G95:030) yields a plateau age for muscovite at 420 ± 1 2
NORWEGIAN JOURNAL OF GEOLOGY
Ma, and the aplite from Nordmarka (sample G95:05 1 )
yields a 4 1 7 ± 5 Ma muscovite age. The U-Pb monazite
ages available from these rocks are uncertain because of
discordant analyses, but suggest similar or even higher
ages than for the Nordkapp granite.
Grenvillian granitoids
In none of the analysed Grenvillian granitoids are any tra­
ces of Precambrian Ar-Ar ages preserved; they all yield
relatively well-defined Caledonian plateau ages, indicating
that Caledonian metamorphism was strong enough to
reset the K-Ar system in both biotite and muscovite (i.e.
reached temperatures above about 300-350 °C) . Augen
gneiss sample G95:050 from Nordmarka yields plateau ages
of 425 ± 5 Ma for muscovite, and 422 ± 5 Ma for biotite,
respectively (Table l , Fig. 3). As with the biotite in the
Rijpfjorden granite, the biotite in the Nordmarka augen
gneiss shows a tendency for Ar loss in the first few steps,
which could be related to heating during Mesozoic burial
and/or mafic magmatism in the area (cf. Lauritzen &
Ohta 1 984) . The much higher inverse isochron age for this
biotite, 458 Ma, is an artefact of the dustering of all points
dose to the x-axis of the isochron diagram (not shown);
the corresponding negative y-intercept (40Arf36Ar ratio)
shows its lack of reliability.
Muscovite from the other augen gneiss sample from
Nordmarka (G95:049) in eastern Nordaustlandet, and
from the augen gneiss south of Innvika ( G95:03 1 ) in cen­
tral Nordaustlandet, yields slightly lower plateau ages of
4 1 5 ± 6 and 4 1 1 ± 1 1 Ma, respectively. However, within
the margin of error, these ages are identical to the ages
from sample G95:050, all being related to heating during
Caledonian regional metamorphism and magmatism.
Mafic rocks of uncertain age
As discussed above, the hornblende from the mafic rocks
did not produce any well-defined plateau ages, due to the
much smaller amounts of argon present. From amphibo­
lite sample 598:129 from Andreeneset on Kvitøya, the first
analysis of hornblende released about 80 % of the argon
in one step, corresponding to an age of 4 1 8 ± 8 Ma (Table
l , Fig. 4A) . The total gas age of that sample is slightly
lower, 4 1 1 ± 8 Ma. A second hornblende crystal from the
same sample was then analysed. This yielded an age spec­
trum with ages starting at ca. 460 Ma ( disregarding the
two first steps with less than l o/o of the gas) and decrea­
sing to ca. 350 Ma, but with three steps encompassing 57
% of the released argon yielding a plateau at 406 ± 7 Ma
(Tables l and 2, Fig. 4B) . The total gas age is 399 ± 7 Ma.
From the gabbro at Isispynten (sample 94062c) , a
spectrum with slightly increasing ages was obtained (Fig.
4C). Two possible plateaux may be discerned: one at ca.
390 Ma encompassing steps S-7, and one at ca. 4 1 7 Ma
being the average of steps 8, l O and 1 1 (the deviating and
much lower step 9 was disregarded) . The total gas age is
397 ± 7 Ma.
Ar-Ar dating of Caledonian and Grenvillion rocks, Svalbard 269
NORWEGIAN JOURNAL OF GEOLOGY
Table l Summary ofJ\r-Ar results from �st Svalbard
--
-·
Sample number,
mineral
-
--
Rock type,
location
Pla tea u age '
Rijpfjorden granite,
398.6± 4.9 Ma
3-14, 90.5
Vindbukta
401.1± 4.9 Ma
S-8,
Steps, o/o 39Ar
Caledonian
granitoids
28-1 muscovite
28-1 biotite
94047 muscovite
94048 muscovite
G95:030 muscovite
G95:051 muscovite
o/o
o/o
96.3 o/o
Rijpfjorden granite,
404.7±!I.lMa
3-18,
403.5±11.2Ma
3-11, 63.9%
405.6± S.OMa
4-15, 98.6 o/o
406.1± S.OMa
S-8,
46.1 o/o
l nverse isochron
age (MSWD)4
396.2± 4.9Ma
404.7± 5.1Ma (0.99)
403.8± 4.9Ma (8.26)
(21± 7)
402.3±!I.lMa
412.4±11.4Ma (1.33)
412.8±11.3Ma (1.69)
(36±10)
405.4± S.OMa
417.0± 5.3Ma (1.33)
414.2± 5.0Ma (1.16)
(-47±14)
427.1±11.7Ma
434.4±12.5Ma (7.09)
427.2±11.7Ma (5.72)
309± 94
40Aff36Ar
intercept
o/o
Nordkapp granite,
428.2±11.7Ma
9-19, 96.2
Gryteberget
425.5±11.7Ma
13-17,45,4%
Red granite,
420.1±!l.SMa
6-21, 98.8
o/o
421.8 ±11.6Ma (3.55)
420.2±!l.SMa (2.38)
345± 28
418.7±!l.S Ma
10-18,66.5 o/o
420.1±11.5 Ma
Innvika
Ap lite,
416.7± 5.4 Ma
4-27, 99.5
424.9± 5.9Ma (18.8)
418.1± 5.5Ma (ILO)
279± 40
416.8± 5.4Ma
10-23,66.9
o/o
o/o
416.1± 5.4Ma
Nordmarka
Augen gneiss,
425.1± 5.2Ma
11-23,93.9
o/o
424.6± 5.2Ma
429.3± 5.4Ma (1.49)
427.0± 5.2Ma (0.62)
(61±23)
o/o
419.5± 5.1Ma
426.4 ± 5.7Ma (5.34)
458.4±10.1Ma (2.61)
(-3435±
Grenvillian
granitoids
G95:050 muscovite
Normal isochron
age (M SWD)'
61.8
Vindbukta
Winsnesbreen granite
Total gas age'
Nordmarka
Augen gneiss,
422.4± S.!Ma
5-18, 92.2
Nordmarka
425.3± 5.1Ma
7-15, 59.7%
G95:049 muscovite
Augen gneiss,
415.2± S.SMa
9-26, 96.7%
414.8± 5.4Ma
418.1± 5.6Ma (1.56)
416.3± 5.4Ma (1.68)
268±56
G95:031 muscovite
Augen gneiss,
411.3±11.2Ma
9-16, 93.0%
411.2±11.2Ma
417.1±11.5 Ma (0.62)
415.5±11.3Ma (0.33)
(71±41)
410.3±11.2Ma
9-11. 56.0%
418.5± 8.5Ma
Il only, 82.6
o/<
411.4± 8.3Ma
423.7± 8.6Ma (0.74)
412.4±29.3Ma (9.64)
236±383
406.4± 6.8Ma
4-6,
56.8
o/o
398.8± 7.1Ma
420.6±11.7Ma (7.21)
401.6± 7.4Ma (3.87)
280±68
49.9% 396.9± 7.0Ma
429.3± 7.9Ma (1.63)
428.4± 5.9Ma (1.22)
(104±35)
G95:050 biotite
2268)
Nordmarka
Innvika
Mafic rocks of
uncertain age
S98:129 hornblende l Amphibolite,
Andn!eneset,Kvitøya
S98:129 hornblende 2 Amphibolite,
Andreeneset,Kvitøya
94062c hornblende
Gabbro,
391.5± 7.3Ma
5-7,
Isispynten
c. 417Ma
8,10-11,36.0
o/o
l. Two plateau ages are normally reported, the first one containing more than 90 % of the released 39Ar, the second derived from a more restricted but well-defined plateau
encompassing 40-70% of the released 39Ar. From the hornblendes in the mafic rocks,no well-defined plateaux were obtained,and the ages reported are more loosely
defined <<pseudo-plateam> ages.
2. Weighted average age of all released radiogenic argon gas.
3. Normal isochron : 40Ar f36Ar vs. 39Arf36Ar (York 1969).
4.1nverse isochron : 36Arf40Arvs. 39Arf40Ar (Turner 1971; Roddick et al. 1980).
In summary, with the possible exception of the first
steps in
598:129 hornblende 2, there are no traces of pre­
Caledonian ages. The hornblende ages of ca. 418 Ma are
comparable to the mica ages, indicating resetting of horn­
dan (Llanvirn) platform successions (Hinlopenstretet
Supergroup). Only in the uppermost unit (Valhallfonna
Formation in eastern Ny Friesland, Fortey & Bruton
does the carbonate platform facies give way
1973)
blende during Caledonian metarnorphism (if the mafic
upwards into basinal graptolitic shales. Younger strata
rocks themselves are older), or cooling after Caledonian
may be present in the hinge of the Hinlopenstretet Syne­
intrusive magmatism (if the rocks are Caledonian). The
line, beneath the waters of the Hinlopen Strait. Thus the
be related to incipient alteration of the hornblendes.
the Neoproterozoic and Palaeozoic successions of the
plateaux at ca. 390 and 405 Ma, respectively, may possibly
upright to W-vergent folding and associated thrusting of
Nordaustlandet Terrane occurred at some stage after the
Llanvirn (ca.
460
Ma, Tucker & McKerrow
1995)
and
before the intrusion of late to post-tectonic Caledonian
Discussion
granites. U-Ph and Ph-Ph zircon data indicate that most
The Neoproterozoic strata (Murchinsonfjorden Super­
Early Devonian, or perhaps the latest Silurian (accepting
of these peraluminous granites were intruded in the
417
group) deposited on the Grenville-age basement of
an age of
Nordaustlandet are overlain by Vendian to mid-Ordovi-
Tucker & McKerrow
Ma for the Silurian-Devonian boundary,
1995).
270 Å. Johansson et al.
NORWEGIAN JOURNAL OF GEOLOGY
r--.---,--r=:::::t:==:::�==:;-.----,
5oo
500
Rijpfjorden gronffe:
Rijpfjorden gran/te:
28-1 blot/te
28-1 muscovlte
450
�
±
401.1
4-----
O'
�
398.6
4-----
±
4. 9 Mo
4.9M:J
---J>
--i>
h
400
450
n
o .......
�
IT
�
Totol gas age: 402.3 ± 11.1 Mo
350
Normal isochron age : 404.7 ± 5.1 Mo
Norrrx:�lisochron age: 412.4 ± 11.4 Mo
Inverse isochron age: 412.B ± 11.3 Mo
Inverse isochron age: 403.B ± 4.9 Mo
300
300
o
60
40
20
%
39
BO
100
�--��--�----�
100
BO
60
40
20
o
39
% Ar cumu/ottve
Ar cumu/ottve
r---.---,--��====�==�.----,
500
Wlnsnesbreen gronlte:
Nordkapp gran/te:
94048 muscovffe
94047 muscovffe
450
405.6
406.1 ± 5.0M:J
<l--
±
428.2
450
5.0Mo
±
11.7 Mo
-i>
O'
O'
�
11.1Mo
'-'- 400
L
Totolgas age: 396.2 ± 4. 9Mo
350
±
404.7
403.5 ± 11.2M:J
�
400
<f-
400
425.5 ± 11.7Ma
�
�
�
350
Totol gasage: 405.4 ± 5.OMo
Totolgosage: 427.1 ± 11.7Mo
350
Normalisochron age: 417.0 ± 5. 3Mo
Normalisochron age: 434.4 ± 12.5Mo
Inverse isochron age: 427.2 ± 11.7 Mo
Inverse isochron age: 414.2 ± 5.0 Mo
300
L---�--�---��--100
60
80
40
20
o
%
450
39
300
L-----4--�-�-�-�-�-�----�
100
60
BO
40
20
o
%39 Ar cumulattve
Ar cumu/ottve
Red gran/te, lnnvfko:
Ap/lte. Nordmarka:
G95:030 muscovtte
G95:051 muscovffe
t>cf----
420.1
±
11.5Mo
416.7
450
�
±
5.4 fv1o
._....__
..
�
�
�
�
'-'- 400
350
'-'- 400
70tolgas age: 420.1 ± 11.5 Ma
Normo/ isochron age : 421.B ± 11.6 Mo
Totolgosage: 416.1 ± 5.4Ma
350
Normal isochron age: 424.9 ± 5.9 Mo
Inverse isochron age: 420.2 ± 11.5Mo
300
�----��----�---J
20
60
40
BO
100
o
%
39
Ar cumu/affve
Inverse isochron age: 41B.1 ± 5.5Mo
�0 �----�--�
o
20
40
60
BO
100
% 39 Ar cumulatlve
Fig. 2. Ar-Ar spectra on muscovite and biotite from Caledonian granitoids from northeast Svalbard. Height of boxes corresponds to l sigma
uncertainty of analyses.
Ar-Ar dating of Caledonian and Grenvillian rocks, Svalbarda 271
NORWEGIAN jOURNAl OF GEOLOGY
Tåble2 Comparison of lt-Pb monazile ages and lv-ArrnUkovitedhd biotiteages fbrCaledohiat granitoids fl&n northeast SValbard
U-Ph monazite age
Ar-Ar muscovite/biotite age 2
l
Rijpfjorden granite
4125 ±0.5 Ma (4 conc. points)
399± 5 Mal 405 ±11 Ma
Winsnesbreen granite
c. 420 Ma
406±5 Ma
Nordkapp granite
440±3 Ma (upper intercept)
Red granite, Innvika
c. 440 Ma (upper intercept)
420± 12 Ma
Aplite, Nordmarka
463±9 Ma (upper intercept)
417±5 Ma
l. Concordant analyses or upper intercept age of
(l concordant point)
428±12 Ma
discordia (Johansson et al., submitted; Johansson et al., in prep.).
2. Plateau ages (this paper).
pre-Caledonian argon component preserved. Caledo­
al. 1985; McDougall & Harrison 1988; Hames & Bowring
1995) during the Silurian and into the Early Devonian.
dence of regional heating above the Ar-Ar closure tem­
Supergroup increase from west to east across Nordaust­
°C, Purdy & Jager
landet. Hornblende Ar-Ar data are particularly impor-
In none of the Grenville-age rocks are any traces of a
nian plateau ages in micas (ca. 410-425 Ma) provide evi­
perature
(300-350
1976;
Harrison et
Temperatures at the base of the Murchisonfjorden
500
Augen gneiss, Nordmarka:
G95:050 muscovite
450
425.1 ± 5.2 Ma
<1---
l
450
----i>
422.4 ± 5.1 Ma
o
�
- 400
±
425.3
5.1
Ma
--i>
�
Total gas age:
350
424.6
Normal isochron age:
Inverse isochron age:
o
G95:050 biotite
r
l=!
300
Augen gneiss, Nordmarka:
20
427.0
39
5.2 Ma
±
±
5.2
Total gas age:
350
5.4 Ma
419.5
Namd isochron age:
Ma
lnverseisochron age:
80
60
40
%
±
429.3
±
5.1
±
426.4
458.4
±
Ma
5.7
Ma
10.1
Ma
300 �----�----L---�--�
80
100
20
60
40
o
100
%39 Ar cumulative
Ar cumulatrve
500
l
Augen gneiss, Nordmarka:
G95:049 muscov!te
450
450
415.2 ± 5.5 Ma
o
�
- 400
o
�
(])
�
-
400
350
Total gas age:
414.8
Normal iOClchron age:
Inverse isochron age:
±
418.1
41 6.3
5.4 Ma
±
±
5.6 Ma
%
39
Ar cumulative
300
o
---l>
411 .3 ± 11 .2 Ma
410.3
±
11.2 Ma
--i>
D
Total gas age:
350
5.4 Ma
300 �----�----�
80
100
60
40
o
20
G95:031 muscovite
.,...._
n<l-�--
51
Augen gneiss, lnnvika:
411.2
±
11.2 Ma
Namallsochron age:
41 7 .l
±
11 .5
Ma
InverseiOClchron age:
415.5
±
11.3
Ma
20
40
%
39
60
80
100
Ar cumulative
Fig. 3. Ar-Ar spectra on muscovite and biotite from Grenvillian granitoids (augen gneisses) from northeast Svalbard. Height of boxes corres­
ponds to I sigma uncertainty of analyses.
272 A. Johansson et al.
NORWEGIAN JOURNAL OF GEOLOGY
tant in this context and it is indeed unfortunate that this
tible with recently acquired zircon data (Johansson &
mineral is extremely scarce and, if present, usually
Larionov
altered to actinolite in Nordaustlandet. The two horn­
nian migmatization of the Grenvillian basement occur­
1999;
Johansson et al., in prep.) that Caledo­
blendes analysed here indicate that at least the eastern
red in the latest Ordovician (ca.
areas were subject to Caledonian temperatures above
Nordaustlandet.
500-550
°C (Ar-Ar closure temperature of hornblende,
McDougall & Harrison
1988).
This evidence is compa-
440-450 Ma) in eastern
In the Caledonian granitoids, two groups of Ar-Ar
ages may be discerned, one at
4 15-430 Ma, similar to the
400-405
ages in the Grenvillian rocks, and another at
Ma. In Table
l
500
450
598:129 homblende l
<!---
Step 11:418.5 :t 8 . 5
Ma
ages around
5
compare the U-Pb monazite
440
Ma (Nordkapp granite and red granite
from Innvika), the second group to granites with U-Pb
ages at
----1>
410-420 Ma (Rijpfjorden and Winsnesbreen
gra­
nite). The Ar-Ar ages thus follow the U-Pb ages with a
10-20 Ma delay in each group. Using a closure tempera­
700-750 °C for U-Ph in monazite (Parrish 1990;
Heaman & Parrish 1991; Parrish & Whitehouse 1999),
and a closure temperature of 300-350 oc for Ar-Ar in
muscovite (Purdy & Higer 1976; Harrison et al. 1985;
McDougall & Harrison 1988; Hames & Bowring 1995),
the sub-parallel cooling paths depicted in Fig. 5 (in a
ture of
�
To1al gas age:
350
411.4"' 8.3
Norrn d isochroo age:
Inverse isochroo age:
o
l
500
r450
�
�
Ma
423.7"' 8.6 Ma
412.4 "= 29.3 Ma
60
40
20
%39
100
80
Ar cumulative
S98: 129 hornblende 2
406.4:!: 6.8
million years. The
Mo
---:::!:>
463 ± 9 Ma,
4 17 ± 5 Ma, corresponding
cooling rate of ca. 10 oc per
and a Ar-Ar muscovite age of
to a much slower average
million years. However, the U-Ph monazite age for this
sample is highly uncertain, being based on three discor­
�
dant points. If the Nordmarka aplite instead has an age
-_
r--
similar to the aplite from Kvitøya, ca.
'---_
Told gas age:
o
20-45 o C per
Nordmarka, with a U-Pb monazite age of
l
Amphibolite. Andreeneset:
1L--
350
slightly curved fashion) would correspond to rapid coo­
ling rates of at average
only rock diverging from this pattern is the aplite from
o
6 400
300
and Fig.
T he first age group is related to granites having U-Ph
1
Amphibolite, Andreeneset:
o
6 400
300
2
and Ar-Ar muscovite ages for the Caledonian granitoids.
398.8 "'7.1
'-
Ma
Nam. isochroo age:
420.6 "'11.7 Ma
Inverse isochroo age :
401 .6 "'7.4 Ma
40
20
%39
60
430
Ma, it would
follow the same cooling pattern. If, on the other hand, it
'---
really crystallized at around
460 Ma, it may
have remai­
ned at elevated temperatures for a considerable time
during regional metamorphism, and then cooled along a
80
100
Ar cumulative
similar path as the other samples, still yielding the calcu­
lated cooling rate meaningless.
The rapid cooling rates of
20-45 oC per million years
are probably related to post-magmatic cooling of the
individual intrusions from magmatic or near-magmatic
temperatures to the closure temperature of the K-Ar sys­
Gabbro. lsispynten:
94062c hornblende
tem in muscovite and biotite, rather than post-meta­
450
morphic cooling of the whole bedrock packet. This
would suggest that the Caledonian granites intruded at
�- 400
�
350
relatively shallow depths in a much cooler environment,
after the peak of metamorphism.
To1al gas age:
396.9 "'7.0 Ma
Norrn.lsochroo age:
nverse isochroo age:
429.3"' 7.9
428.4 "'5.9
Ma
Ma
300 U-----�-----L--�--�
o
20
40
60
80
100
%39
Ar cumulative
The Nordaustlandet Ar-Ar ages are very similar to the
majority of the plateau ages recorded from metamorphic
muscovites and hornblendes from the upper amphibo­
lite facies Atomfjella Complex of western Ny Friesland
(413-425 Ma, Gee & Page 1994), suggesting that Caledo­
nian metamorphism was contemporaneous in the West
Ny Friesland and Nordaustlandet Terranes. One horn­
blende age from that area reaches back to 447 Ma; it sug­
Fig. 4. Ar-Ar spedra on hornblende from mafic rocks of uncertain age
from northeast Svalbard. Height of boxes corresponds to l sigma
uncertainty of analyses.
gests the possibility that, as in Nordaustlandet, the tecto­
nothermal activity may have started in the Late Ordovi­
cian. Despite this similarity, it is important to note that
Ar·Ar dating of Caledonian and Grenvillian rocks, Svalbard 273
NORWEGIAN JOURNAL OF GEOLOGY
In summary, the new Ar-Ar data would support a
tentative two-stage scenario for the Caledonian orogeny
Ordovician to Early Silurian (prior to ca.
ro
.._
E
"E
cooling ages of
z
to
410
430
Ma, with
Ma) encompassing regional
magmatism, and a second stage in the latest Silurian to
�­
Early Devonian (at
a.
<(
800
430
metamorphism and deformation as well as syn-tectonic
o
900
700
in northeasternmost Svalbard, a first stage in the Late
ro
�
1000
400
420-410 Ma,
with cooling ages of ca.
Ma) encompassing late- to post-tectonic magma­
tism forming large granitic massifs such as the Rijpfjor­
U-Pb monazite
den granite. A similar two-stage development of Caledo­
nian magmatism is seen in northwest Spitsbergen
(Balashov et al.
600
1996), with
early grey granites followed
by the late- to post-tectonic Hornemantoppen batholith.
In the East Greenland Caledonides, crustal anatexis and
granite formation have been dated to
500
420-440 Ma, using
2000;
U-Pb ion microprobe dating of zircons (Watt et al.
Kalsbeek et al.
400
2001). Whether a similar
two-stage deve­
lopment as in Svalbard can be found in East Greenland,
and whether these stages can be linked to the large-scale
Ar-Ar muscovite
300
geotectonic evolution of the North Atlantic and Arctic
Caledonides, remain to be seen.
200
Age (Ma)
500
480
460
440
420
400
380
Fig. 5. Time-temperature diagram, with U-Pb monazite ages
(Johansson et al., submitted; Johansson et al. , in prep. ) and Ar-Ar
muscovite ages (this paper) for Caledonian granitoids from northeast
Svalbard, and approximate cooling paths. Uncertain U-Ph ages indi­
cated by dotted outlines of symbols.
Acknowledgements - Some of the samples used in this study were col­
lected by our Svalbard colleagues Stefan Sandelin (Uppsala), Alexan­
der Tebenkov (St. Petersburg), and Yoshihide Ohta (Oslo), during
fieldwork financed by the Swedish Polar Research Secretariat, the
Russian Polar Marine Geological Expedition and the Norwegian
Polar Institute. T he gabbro sample from Isispynten was collected by
Captain Per Engwall of M/S Origo. Pa ula Allart (Stockholm) assisted
with the mineral separation, Ann-Marie Kahr and Dan Holtstam
(Stockholm) with hornblende identification using XRD and EDAX,
respectively, and Patrick Monie and Dirk Marheine advised on vari­
ous aspects of the analytical work in Montpellier. The paper benefit­
ted from critical reviews by Synnøve Elvevold and Elizabeth Eide.
Caledonian metamorphic grade diminishes from east to
west across Nordaustlandet towards eastern Ny Fries­
land; in the West Ny Friesland orogen, Caledonian meta­
morphism occurred at higher pressures than in the
Åke Johansson's stay in Montpellier and the associated analytical
costs were financed by the Swedish Natura! Science Research Coun­
cil. T his paper is a contribution to the Swedish Arctic research pro­
gramme
(SWEDARCT IC)
and
to
EUROPROBE's
T IMPEBAR
(T iman-Pechora-Barents Sea) programme.
Nordaustlandet Terrane.
Caledonian granite intrusion in Nordaustlandet,
eastern Ny Friesland (Chydeniusbreen granitoid suite:
Newtontoppen and Ekkoknausane granitoids, Rb-Sr age
432
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Appendix l.
Ste p
NORWEGIAN JOURNAL OF GEOLOGY
Ar-Ar data on Caledonian and Grenvillian rOc:ks from northeast Svall?ard.
40Ar*f39Ar
36Arf40Ar
X 1000
39Arf40Ar
3?Arf39Ar
% 39Ar
o/o atm. Ar
cum.
Age +/- lsd
(Ma)
J = 0.014390 ± 0.000194
Rijpfjorden granite, sample 28-1 muscovite
l
15.380
1.348
0.0391
0.151
0.2
39.83
360.7 +/- 55.2
2
18.591
0.168
0.0511
0.013
0.7
4.98
427.7 +1- 22.4
3
17.068
0.177
0.0555
0.014
1.1
5.24
396.2 +1- 34.8
4
17.397
0.084
0.0560
0.076
2.1
2.48
403.1 +/- 11.4
5
17.542
0.035
0.0564
0.033
5.9
1.04
406.1 +/- 5.8
6
17.186
0.038
0.0575
0.011
21.1
1.12
398.7 +/- 2.5
7
17.385
0.024
0.0571
0.000
48.9
0.71
402.8 +/- 1.8
8
17.213
0.057
0.0571
0.004
63.9
1.69
399.2 +/- 1.7
9
16.503
0.205
0.0569
0.011
68.0
6.05
384.4 +/- 3.8
10
17.072
0.041
0.0578
0.002
71.7
1.20
396.3 +/- 4.2
11
16.757
0.082
0.0582
0.001
77.4
2.43
389.7 +/- 3.0
12
16.872
0.100
0.0575
0.001
84.3
2.96
392.1 +/- 3.0
13
17.302
0.058
0.0568
0.068
88.9
1.72
401.1 +/- 6.3
14
17.084
0.052
0.0576
0.003
91.2
1.54
396.6 +/- 11.7
15
15.113
0.471
0.0569
0.118
92.6
13.93
355.0 +/- 12.3
16
16.287
0.253
0.0568
0.013
94.1
7.48
379.9 +/- 8.1
17
16.078
0.244
0.0577
0.159
95.7
7.22
375.5 +1- 7.8
18
17.473
0.092
0.0556
O.QlS
96.6
2.73
404.6 +/- 17.4
19
16.410
0.209
0.0571
0.042
97.7
6.19
382.4 +/- 13.8
20
13.892
0.616
0.0588
0.062
98.5
18.21
328.8 +/- 23.5
21
15.608
0.333
0.0577
0.064
100.0
9.83
365.5 +/- 10.5
Total age=
396.2 +/- 4.9
J = 0.014645 ± 0.000449
Rijpfjorden granite, sample 28-1 biotite
l
13.093
1.113
0.0512
0.001
1.9
32.90
316.5 +/- 7.4
2
15.186
0.385
0.0583
0.003
3.7
11.37
362.3 +/- 8.7
3
17.232
0.157
0.0553
0.003
8.7
4.64
406.0 +/- 4.2
4
17.187
0.055
0.0572
0.004
15.3
1.64
405.0 +/- 3.4
5
17.120
0.041
0.0577
0.006
27.4
1.21
403.6 +/- 2.7
6
17.244
0.055
0.0570
0.009
39.8
1.62
406.2 +/- 2.4
7
17.144
0.062
0.0572
0.000
51.1
1.84
404.1 +/- 7.3
8
16.954
0.131
0.0567
0.025
57.8
3.87
400.1 +/- 2.5
9
16.796
0.177
0.0564
0.049
61.0
5.22
396.8 +/- 3.7
10
16.990
0.140
0.0564
0.031
64.1
4.15
400.9 +/- 4.7
11
16.934
0.102
0.0572
0.011
67.6
3.00
399.7 +/- 3.7
12
16.535
0.176
0.0573
0.009
70.9
5.20
391.2 +/-
13
17.229
0.054
0.0571
0.005
74.0
1.61
405.9 +/- 4.8
4.7
14
16.822
0.128
0.0572
0.024
76.8
3.77
397.3 +/- 5.3
15
17.410
0.029
0.0569
0.041
79.3
0.86
409.7 +/- 5.1
16
17.459
0.032
0.0567
0.003
86.4
0.96
410.8 +/- 2.0
17
17.151
0.069
0.0571
0.006
87.6
2.03
404.3 +/- 5.6
18
17.481
0.039
0.0565
0.229
100.0
1.15
411.2 +/-
Total age=
l.S
402.3 +/- 11.1
Ar-Ar datin9 of Caledonian ond Grenvillian rocks, Svalbard 277
NORWEGIAN jOURNAl OF GEOLOGY
Ste p
40Ar*f39Ar
36Arf40Ar
39Arf40Ar
37 Arf39Ar
X 1000
o/o 39Ar
%atm.Ar
Age +/- 1sd
(Ma)
cum.
J = 0.014390 ± 0.000194
Winsnesbreen granite, sample 94047 muscovite
2
6.794
1.924
0.0634
0.336
0.02
56.87
168.3 +/- 754.6
3
16.813
0.288
0.0544
0.009
1.4
8.52
390.9 +/- 9.5
4
17.033
0.137
0.0563
0.001
4.8
4.06
395.5 +/- 5.2
5
17.676
0.055
0.0556
0.003
12.3
1.64
408.8 +/- 2.4
6
17.564
0.046
0.0561
0.005
32.0
1.38
406.5 +/- 1.8
7
17.342
0.037
0.0570
0.009
41.3
1.09
401.9 +/- 4.2
8
17.598
0.064
0.0557
0.000
51.0
1.89
407.2 +1- 2.8
9
17.011
0.147
0.0562
0.001
55.1
4.34
395.0 +/- 3.3
10
17.131
0.168
0.0554
0.001
59.0
4.95
397.5 +/- 3.8
11
17.229
0.074
0.0567
0.099
60.6
2.19
399.6 +1- 5.3
12
16.347
0.251
0.0566
0.132
61.7
7.41
381.1 +/- 10.8
416.7 +/- 6.6
13
18.058
0.002
0.0553
0.063
64.3
0.05
14
16.745
0.172
0.0566
0.015
67.0
5.08
389.5 +/- 3.7
15
17.727
0.039
0.0557
0.005
100.0
1.15
409.9 +1- 3.2
Total age=
405.4 +/- 5.0
J = 0.014645 ± 0.000449
Nordkapp granite, sample 94048 muscovite
340.9 +l-190.1
14.200
3.110
0.0057
0.864
0.05
91.89
2
13.064
1.466
0.0433
0.464
0.2
43.32
315.8 +/- 57.6
3
13.955
1.083
0.0487
0.262
0.5
32.01
335.5 +/- 25.2
4
16.380
0.698
0.0484
0.018
1.0
20.64
387.9 +/- 18.2
5
18.668
0.660
0.0431
0.017
l.S
19.50
436.0 +/- 18.4
0.043
2.0
28.65
384.7 +/- 16.8
0.020
2.7
5.99
414.1 +/- 9.3
0.011
3.8
5.64
415.2 +/- 5.4
3.76
428.5 +/- 2.0
0.72
434.7 +/- 2.9
6
16.227
0.970
0.0439
7
17.618
0.203
0.0533
8
17.670
0.191
0.0534
9
18.304
0.127
0.0525
0.001
11.2
10
18.603
0.024
0.0533
0.001
17.2
11
18.362
0.118
0.0525
0.001
22.2
3.50
429.7 +1- 2.3
12
18.798
0.051
0.0523
0.001
31.5
1.51
438.7 +/- 5.3
424.6 +1- 2.7
13
18.119
0.034
0.0546
0.000
43.1
1.00
14
18.329
0.041
0.0538
0.001
55.0
1.21
429.0 +/- 3.0
15
18.167
0.049
0.0542
0.005
63.5
1.46
425.6 +/- 2.6
16
18.096
0.066
0.0541
0.003
70.0
1.97
424.1 +/- 2.3
76.9
2.00
422.5 +/- 2.0
416.4 +/- 2.2
17
18.Q17
0.068
0.0543
0.004
18
17.727
0.106
0.0546
0.005
81.9
3.14
19
18.395
0.047
0.0536
0.009
100.0
1.39
430.4 +/- 1.4
Total age=
427.1 +/- 11.7
2.55
422.5 +1- 1.4
94048 muscovite, grain 2, one single spot analysis :
l
18.018
0.086
0.0540
0.001
278 A. Johansson et al.
Step
40Ar*J39Ar
NORWEGIAN JOURNAL OF GEOLOGY
36ArJ40Ar
39Arf40Ar
37ArJ39Ar
Ofo 39Ar
%atm. Ar
Age +/- lsd
(Ma)
cum.
xlOOO
J = 0.014645 ± 0.000449
Red granite, Innvika, sample G95:030 muscovite
18.192
1.636
0.0283
0.031
O. l
48.36
426.1 +/- 44.8
2
16.5S4
0.774
0.046S
0.122
0.2
22.88
391.6 +/- 23.1
3
17.364
0.463
0.0497
0.020
0.3
13.67
408.8 +/- 33.4
4
18.240
0.426
0.0479
0.126
0.6
12.S8
427.1 +/- 1 l.S
l
s
18.49S
0.24S
O.OSOI
0.038
1.2
7.2S
432.4 +/- 6.2
6
18.124
0.287
O.OS04
0.016
S.4
8.49
424.7 +/- 1.8
7
18.172
0.218
O.OS14
0.008
6.5
6.44
42S.7 +/- 4.S
8
18.120
0.143
O.OS28
0.004
7.8
4.24
424.6 +/- 3.S
9
18.182
0.100
O.OS33
0.000
18.3
2.96
42S.9 +/- 1.7
10
17.667
0.061
o.osss
0.001
39.4
1.79
41S.2 +/- 1.8
11
17.8S2
O.OS8
o.osso
0.022
S3.0
1.71
419.0 +/-
12
17.79S
0.096
O.OS4S
0.011
S7.9
2.84
417.8 +/- 1.9
13
17.817
0.088
O.OS46
0.001
60.0
2.S9
418.3 +/-
14
17.896
0.061
O.OS48
0.001
6 l.S
1.80
419.9 +/- 4.8
1S
18.067
0.044
O.OS46
0.000
68.2
1.30
423.5 +/- 1.4
16
17.942
0.048
O.OS49
0.000
74.0
1.43
420.9 +/- 2.5
17
18.039
o.oss
O.OS4S
0.003
77.1
1.63
422.9 +/- 2.0
18
17.96S
0.023
O.OS52
0.000
84.8
0.68
421.4 +/-
19
17.720
0.04S
O.OSS6
0.003
89.4
1.32
416.3 +/- 2.3
20
17.262
0.087
O.OS64
0.017
90.0
2.58
406.6 +1- 8.3
21
18.024
0.030
O.OS49
0.002
100.0
0.88
422.6 +/-
Total age=
l.S
3.9
l.S
2.1
420.1 +/- ll.S
J = 0.0143S6 ± 0.000208
Aplite, Nordmarka, sample G9S:OS1 muscovite
l
6.334
2.2S7
O.OS2S
0.006
0.2
66.69
1S7.0 +/- 22.4
2
1S.949
1.2SO
0.039S
0.011
0.3
36.93
372.0 +/- 10.1
3
16.998
1.008
0.0413
0.004
0.5
27.79
393.9 +/- 7.3
4
18.088
0.509
0.0469
0.001
1.3
1S.03
416.S +/- 3.8
s
18.101
0.263
O.OS09
0.008
2.2
7.77
416.8 +/- S.2
6
18.069
0.183
O.OS23
0.007
3.7
S.42
416.1 +/- 2.3
7
18.260
0.14S
O.OS24
0.011
s.s
4.30
420.0 +/- 2.3
8
17.S66
0.094
O.OSS3
0.004
8.9
2.78
40S.7 +/- 1.8
9
17.606
0.08S
O.OSS3
0.006
13.4
2.51
406.6 +/- 1.8
10
18.190
o.oso
O.OS41
0.000
21.2
1.46
418.6 +/- 1.3
11
18.123
0.06S
O.OS41
0.001
31.6
1.92
417.2 +/- 1.3
12
17.774
0.061
0.0552
0.001
40.1
1.81
410.0 +/- 1.2
13
17.993
0.039
0.0549
0.002
47.9
1.15
414.5 +/- 1.4
14
17.865
O.OS5
0.0550
0.004
S3.4
1.63
411.9 +/- I. l
15
17.948
0.057
O.OS47
0.002
57.8
1.67
413.6 +/- 1.9
16
18.439
0.021
0.0538
0.019
59.0
0.63
423.7 +/- 2.3
17
18.624
0.022
0.0533
0.008
60.9
0.65
427.S +/- 1.6
18
18.638
0.022
0.0532
0.005
62.4
0.67
427.8 +/- 2.4
19
18.175
0.101
0.0533
0.005
63.7
2.99
418.3 +/- 2.9
20
18.326
0.088
O.OS31
0.009
66.0
2.60
421.4 +/- 1.8
21
18.240
O.OS1
O.OS39
0.004
74.8
l.SO
419.6 +/- I. l
22
18.264
0.039
O.OS41
0.004
78.7
1.14
420.1 +/- 1.4
23
18.289
0.062
O.OS36
0.003
80.3
1.82
420.6 +/- 2.1
24
18.283
0.07S
O.OS34
0.001
81.6
2.23
420.5 +/- 19.2
2S
18.422
O.OS9
O.OS33
0.000
83.4
1.73
423.3 +/- 1.9
26
18.326
0.027
O.OS41
0.002
90.7
0.81
421.4 +/-
27
18.202
0.019
O.OS46
0.002
100.0
0.57
418.8 +/- 1. 2
Total age=
416.1 +/- S.4
2.1
Ar-Ar doting of Coledonian ond Grenvillian rocks, Svalbard 279
NORWEGIAN JOURNAL OF GEOLOGY
Step
39fuf40AI
37Arf39fu
o/o 39Ar
o/o atm. AI
cum.
Age +/- lsd
(Ma)
J = 0.014390 ± 0.000196
Augen gneiss, Nordmarka, sample G95:050 muscovite
l
17.870
0.581
0.0463
0.616
0.03
17.17
2
15.972
0.735
0.0490
0.140
0.06
21.71
373.2 +/- S6.7
3
17.011
0.769
0.04S4
0.062
O. l
22.72
39S.O +/- 42.1
412.9 +/- S2.S
4
19.137
0.207
0.0490
0.010
0.3
6.11
438.8 +/- 12.0
5
18.665
0.081
0.0522
0.014
0.7
2.41
429.2 +/- S.8
6
18.092
0.101
O.OS36
0.049
1.0
2.97
417.4 +/- 9.7
7
17.8S2
0.116
0.0540
0.040
1.3
3.44
412.5 +/- 9.8
420.3 +/- S.8
8
18.229
0.082
0.0535
0.008
1.6
2.42
9
18.042
0.098
0.0538
0.014
2.1
2.88
416.4 +/- S.2
10
17.995
0.029
o.osso
0.000
6.1
0.87
41S.4 +/- 1.4
11
18.362
0.028
O.OS40
0.002
10.9
0.83
423.0 +/- 1.3
12
18.331
0.027
O.OS41
0.006
1S.6
0.79
422.4 +/- 1.6
13
18.341
0.039
O.OS38
0.003
19.4
1.17
422.6 +/- 1.3
14
18.499
0.021
0.0537
0.004
29.5
0.61
42S.8 +/- 1.9
15
18.443
0.014
O.OS39
0.002
49.1
0.43
424.6 +/- 1.7
16
18.446
0.050
O.OS34
0.008
S4.2
1.47
424.7 +/- 2.1
17
18.526
0.026
0.0535
0.001
S6.9
0.77
426.3 +/- 1.9
18
18.440
0.025
0.0538
0.001
S9.5
0.73
424.6 +l-
19
18.375
0.012
O.OS42
0.000
79.1
0.34
423.2 +/- 1.8
20
18.641
0.022
0.0533
0.002
83.0
0.64
428.7 +/- 2.3
21
18.192
0.049
0.0541
0.003
83.8
1.44
419.5 +/- 3.8
22
18.5S l
0.016
O.OS36
0.002
84.9
0.48
426.9 +/- 2.6
23
18.681
0.008
0.0534
0.001
100.0
0.23
429.5 +/- 2.7
Total age=
424.6 +/- S.2
l.S
J= 0.014390 ± 0.000196
Augen gneiss, Nordmarka, sample G9S:050 biotite
l
14.040
1.08S
0.0483
0.001
o.s
32.06
332.0 +/- 13.2
2
14.752
0.2S4
0.0626
0.007
1.6
7.50
347.3 +1- 6.0
3
15.857
0.139
0.0604
o.oos
3.1
4.11
370.8 +/- S.8
4
17.3S9
0.076
O.OS63
0.001
7.8
2.26
402.3 +l- 2.2
5
17.909
O.OS2
O.OS49
0.002
1S.8
l.S3
413.7 +/- 2.0
6
17.878
0.032
O.OSS4
0.001
32.1
0.9S
413.0 +1- 1.7
7
18.231
0.030
O.OS43
0.001
37.1
0.88
420.3 +/- 2.0
8
18.448
0.012
O.OS40
0.001
4S.O
0.37
424.8 +/- 1.6
9
18.691
0.019
O.OS32
0.001
S3.2
o.ss
429.7 +/-
l.S
10
18.41S
0.019
O.OS39
0.000
64.0
0.57
424.1 +/-
l.S
11
18.483
0.021
O.OS37
0.001
72.S
0.61
42S.5 +/- 1.4
12
18.S39
0.021
0.0536
0.001
83.7
0.61
426.6 +1- 1.3
13
18.471
0.019
O.OS38
o.oos
88.1
o.ss
42S.2 +/- 2.1
14
18.331
O.OS4
O.OS36
0.021
90.2
1.60
422.4 +/- 4.2
15
18.422
0.044
O.OS3S
0.009
91.8
1.30
424.2 +/- 4.2
16
18.919
0.044
O.OS21
0.003
94.0
1.30
434.4 +/- 3.6
17
18.770
O.OS2
O.OS24
0.002
96.8
l.S4
431.3 +/- 2.7
18
18.370
0.060
0.0534
0.001
100.0
1.77
423.1 +/- 2.2
Total age=
419.5 +/- 5.1
280 Å. Johansson
NORWEGIAN JOURNAl OF GEOLOGY
et al.
37 Arf3 9Ar
36Arf40Ar
Step
% 39Ar
% atm. Ar
euro.
X 1000
J = 0.0 14356
Augen gneiss, Nordmarka, sample G95:049 muscovite
Age +1- 1sd
(Ma)
± 0.000209
1.654
3.288
0.0171
0.580
0.03
97.16
42.3 +/- 131.1
2
10.160
1.949
0.0417
0.213
O. l
57.59
245.6 +/- 32.7
3
18.277
0.616
0.0447
O.OS1
0.5
18.80
420.4 +/-
4
18.110
0.506
0.0469
0.007
1.1
14.96
416.9 +/-
4.0
5
17.340
0.455
0.0499
0.03S
1.4
13.45
401.0 +/-
9.8
5.1
9.2
6
17.051
0.524
0.049S
0.027
1.8
15.49
39S.O +/-
7
17.941
0.173
O.OS28
0.000
2.3
5.12
413.5 +/-
5.4
8
17.669
0.134
O.OS43
0.006
3.3
3.97
407.8 +/-
3.0
2.0
9
18.136
0.083
O.OS37
0.000
4.8
2.46
41 7.5 +/-
10
17.980
0.07S
O.OS43
0.003
6.8
2.22
414.3 +/-
2.1
11
18.024
0.063
O.OS44
0.002
9.9
1.86
415.2 +/-
1.4
12
18.021
0.044
0.0547
0.002
14.2
1.30
415.1 +/-
l.S
13
17.985
0.029
0.0551
0.001
20.2
0.86
414.4 +/-
l.S
14
18.093
0.030
O.OS47
0.002
29.4
0.89
416.6 +/-
1.7
15
17.817
0.036
0.055S
0.001
35.9
1.07
410.9 +/-
2.3
16
18.088
0.034
O.OS47
0.002
43.7
1.01
416.S +/-
3.3
17
17.931
o.oss
O.OS48
0.006
47.7
1.64
413.3 +/-
3.0
18
17.543
O.OS9
0.0560
0.007
S l.9
1.76
405.2 +/-
3.9
19
18.036
0.020
0.0551
0.000
SS.4
0.60
41S.4 +/-
2.8
20
18.009
0.018
O.OS52
0.000
58.2
O.S2
414.9 +/-
3.5
21
18.067
0.040
0.0546
0.000
72.1
1.18
416.1 +/-
2.3
22
17.884
0.036
0.0553
0.000
75.6
l. OS
412.3 +/-
1.9
23
18.264
0.022
O.OS43
0.000
77.8
0.64
420.1 +/-
2.0
24
18.212
0.016
O.OS46
0.000
80.0
0.49
419.0 +/-
1.8
2S
18.089
0.011
0.0550
0.000
84.5
0.33
416.5 +/-
2.4
26
18.121
0.016
0.0549
0.000
100.0
0.47
417.2 +/-
5.2
Total age =
J
Augen gneiss, lnnvika, sample G95:03 1 muscovite
=
4 1 4.8 +/-
5.4
0.0 14645 ± 0.000446
l
25.368
0.404
0.0347
2.S92
0.02
11.95
S69.9 +/- 3S3.5
2
11.366
1.767
0.0420
0.836
O. l
52.21
277.8 +1- 141.7
3
2.814
2.924
0.0482
0.852
0.2
86.41
72.9 +1- 243.3
4
17.736
0.374
0.0501
0.164
0.5
11.04
416.6 +/- 27.8
5
1 7.507
0.255
0.0528
0.000
2.9
7.S4
411.8 +/-
6.1
6
17.108
0.175
0.0554
0.001
4.8
5.17
403.4 +/-
7.9
7
18.238
0.038
0.0542
0.001
6.1
1.12
427.1 +/- 12.0
8
17.826
O.D l8
0.0558
0.002
7.0
0.52
418.5 +/- 14.3
9
17.305
0.101
0.0560
0.002
13.6
2.98
407.5 +/-
3.2
10
1 7.442
0.060
O.OS63
0.000
30.2
1.79
410.4 +/-
2.6
11
17.461
0.038
O.OS66
0.000
63.0
1.12
410.8 +/-
1.4
12
1 7.077
0.133
0.0562
0.000
68. 7
3.92
402.7 +/-
3.4
13
1 7.686
0.030
0.0560
0.000
7S.4
0.88
415.5 +/-
4.4
S.9
14
17.723
0.007
0.0563
0.000
77.9
0.20
416.3 +/-
15
17.485
0.039
0.0565
0.000
82.2
1.14
411.3 +/-
5.0
16
17.678
O.D l8
O.OS62
0.000
100.0
0.53
41S.4 +/-
2.9
Total age =
4 1 1 .2 +/- 1 1 .2
Ar-Ar dating of Caledonian and Grenvillian rocks, Svalbard 281
NORWEGIAN JOURNAL OF GEOLOGY
Step
40Ar*J39Ar
36ArJ40Ar
X 1000
39ArJ40Ar
l
74.845
10.386
-12.348
18.384
12.535
14.515
18.252
16.183
18.972
17.251
18.187
12.611
16.620
18.009
17.227
2.610
3.202
4.398
0.645
1.112
0.936
-0.013
0.326
-0.012
0.285
0.072
1.060
0.119
0.024
0.041
Ofo 39Ar
%atm.Ar
cum.
Amphibolite,Andreeneset (Kvitøya), sample
2
3
4
5
6
7
8
9
10
11
12
13
14
15
37ArJ39Ar
S98:129 hornblende l
0.0030
0.0051
0.0242
0.0440
0.0535
0.0498
0.0550
0.0558
0.0528
0.0530
0.0538
0.0544
0.0580
0.0551
0.0573
J= 0.014356 ± 0.000209
0.2
0.4
0.8
2.5
4.4
5.4
6.3
7.1
7.9
9.2
91.8
94.4
95.5
97.2
100.0
30.843
29.885
14.924
5.327
5.244
5.920
4.373
4.360
4.498
5.099
4.707
4.605
3.694
5.258
5.020
77.12
94.63
100.0
19.07
32.86
27.66
-0.39
9.64
-0.36
8.44
2.14
31.33
3.51
0.70
1.20
Total age=
Amphibolite,Andreeneset (Kvitøya), sample S98:129 hornblende
l
2
3
4
5
6
7
8
9
10
11
12
13
14
183.59
50.463
20.199
17.589
17.380
18.032
16.760
16.924
16.455
8.098
3.521
5.731
16.293
15.082
0.160
1.131
0.604
0.182
0.191
0.068
0.246
1.020
-0.045
0.113
2.705
2.387
0.391
0.562
0.0051
0.0131
0.0406
0.0538
0.0542
0.0543
0.0553
0.0412
0.0615
0.1193
0.0570
0.0513
0.0542
0.0552
0.208
0.025
4.647
5.240
4.942
5.093
4.936
4.275
4.294
3.294
3.883
4.722
5.360
5.296
2
l
2
3
4
5
6
7
8
9
10
11
12
13
14
-49.967
-21.704
14.262
15.498
16.984
16.614
17.412
18.283
15.623
17.907
18.137
13.818
19.730
20.793
0.06
0.5
6.9
47.8
57.5
63.7
70.0
74.8
79.2
80.2
81.1
81.8
91.0
100.0
4.72
33.43
17.83
5.36
5.65
2.02
7.25
30.13
-1.33
3.33
79.93
70.55
11.55
16.60
2329 +1- 1388
983.1 +/- 172.3
459.4 +1- 24.8
4.3
406.2 +1401.9 +1- 10.8
415.3 +1- 20.8
389.0 +1- 16.4
392.4 +1- 24.4
382.6 +1- 28.6
198.4 +1- 150.8
89.0 +1- 127.5
142.6 +1- 225.3
379.2 +1- 14.3
353.6 +1- 14.5
398.8 +1- 7.1
J = 0.014356 ± 0.000209
94062c hornblende
3.894
4.190
1.265
0.986
0.467
0.413
0.252
0.145
0.662
0.184
0.271
0.923
0.065
-0.038
1316.5 +/- 262.9
250.7 +1- 326.2
-352.0 +1- 274.8
422.6 +1- 37.1
298.5 +1- 35.8
341.5 +1- 73.3
419.9 +1- 67.7
376.9 +1- 106.4
434.6 +1- 99.6
399.2 +1- 67.9
6.5
418.5 +/300.2 +1- 42.9
386.0 +1- 84.7
414.9 +1- 50.5
398.7 +1- 29.0
411.4 +1- 8.3
J = 0.014356 ± 0.000209
Total age=
Gabbro, Isispynten, sample
Age +/- lsd
(Ma)
0.0030
0.0109
27.306
8.252
0.0439
7.031
0.0457
0.0507
0.0528
0.0531
0.0523
0.0514
0.0528
0.0507
0.0526
0.0497
0.0486
8.026
6.142
5.483
5.342
5.335
5.530
5.508
6.126
6.548
7.134
6.780
0.09
0.3
2.6
6.9
23.6
47.6
56.9
76.3
80.7
90.9
97.3
98.3
98.7
100.0
100.0
100.0
37.38
29.13
13.79
12.20
7.45
4.29
19.56
5.45
8.00
27.27
1.93
-1.13
Total age=
-2280 +1- 5432
-673.6 +1- 695.2
336.0 +1- 52.2
362.4 +1- 21.2
393.6 +1- 5.2
385.9 +1- 7.8
402.5 +1- 15.2
420.5 +1- 7.7
365.1 +1- 28.0
412.8 +1- 12.9
417.5 +1- 20.9
326.5 +1- 115.9
449.9 +1- 210.1
471.3 +/- 75.2
396.9 +l· 7.0