International Journal of Geosciences, 2012, 3, 289-296
http://dx.doi.org/10.4236/ijg.2012.32030 Published Online May 2012 (http://www.SciRP.org/journal/ijg)
Early Proterozoic U-Pb Zirc on Ages from Basement Gneiss
at the Solovetsky Archipelago, White Sea, Russia
Stephan Schuth1*, Victor I. Gornyy2, Jasper Berndt3, Sergei S. Shevchenko4,
Sergei A. Sergeev4, Alexandr F. Karpuzov5, Tim Mansfeldt1
1Geographisches Institut, Bodengeographie/Bodenkunde, University of Cologne, Cologne, Germany
2Scientific Research Center for Ecological Safety, Russian Academy of Sciences, Saint-Petersburg, Russia
3Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Münster, Germany
4A. P. Karpinsky Russian Geological Research Institute (VSEGEI), Saint-Petersburg, Russia
5Federal Agency of Mineral Resources, Moscow, Russia
Email: *email@example.com, firstname.lastname@example.org, email@example.com,
Received December 5, 2011; revised January 25, 2012; accepted February 24, 2012
The central region of the Neoarchaean Belomorian Mobile Belt (BMB) is, except for the Solovetsky Archipelago,
largely covered by the White Sea. A newly discovered granitic gneiss outcrop on Solovetsky Island, Russia, enables a
first age determination of the archipelago and evaluation of the hitherto poorly constrained central BMB. Zircons sepa-
rated from the orthogneiss were analysed with SIMS-SHRIMP and LA-ICP-MS techniques. Both techniques yield a
concordant U-Pb age of ca. 2.430 Ga, coinciding with ages of granitic intrusions in the BMB ca. 50 km west of the So-
Keywords: Solovetsky Archipelago; Granitic Gneiss Outcrop; Age Determination; 2.430 Ga
The Neoarchaean to Palaeoproterozoic Belomorian Mo-
bile Belt (BMB) forms a SW-NE trending belt of mostly
metamorphic rocks, which extends from northern Finland
to the southern region of the Arkhangelsk Oblast in the
Russian Federation (see e.g. , and inset of Figure 1).
Located to the NE is the Neoarchaean Murmansk Craton
(comprising granodioritic and trondhjemitic orthognei-
sses), and the Kola Province (TTG-type orthogneisses of
Neoarchaean age). In the SW, the BMB borders the
greenstone-granite domain of the Neoarchaean Karelian
Craton (e.g. ). The central area of the BMB is, except
for the Solovetsky Archipelago, largely covered by the
White Sea, making access to rocks a difficult task. The
BMB consists of abundant TTG-type rocks (age ca. 2.9
Ga), and metavolcanic rocks of an age of ca. 1.9 Ga (e.g.
[2-4]). The latter are associated with metasediments and
a younger suite of granitic and gabbroic intrusions. More-
over, it was inferred that ca. 2.4 Ga old plutonic bodies
are present in the BMB in significant proportions .
The Archaean units of the BMB were partially re-
worked during the Palaeoproterozoic Lapland-Kola col-
lisional event ca. 1.9 Gyrs ago (e.g. [1,2], and references
therein). Rifting at the Kandalaksha-Dvina aulacogen
crossing the western White Sea in SE-NW direction from
the eastern Onega Peninsula to the Kandalaksha Bay
started possibly in the late Palaeoproterozoic . The
aulacogen is segmented into grabens and horsts by seve-
ral mostly WSW-ENE trending fault systems . The
oldest deposits in the grabens are volcanoclastic sediments,
basic flows, and tuffs with a suggested age of ca. 1.8 -
1.4 Ga . A simplified geological map is illustrated in
the inset in Figure 1. A more detailed map and descrip-
tion of the BMB and Karelia is given by .
The Solovetsky Archipelago is located in the western
White Sea, about 50 km east of the city of Kem’ in Kare-
lia and ca. 30 km NW of the Onega Peninsula (Figure 1).
The island group consists of six large and several smaller
islands with Bolshoi (Big) Solovetsky Island being the
largest. About 50 km east of the archipelago, the Kan-
dalaksha-Dvina aulacogen traverses the White Sea from
SE to NW.
The first geological map (scale 1:200,000) of the ar-
chipelago was produced by , a section showing lith-
ologies of the islands and the western coast of the White
Sea is given in Figure 1. The islands are covered by gla-
cial deposits derived most likely from the Kola Peninsula
and the north-western areas of the BMB. The last glacia-
tion of the archipelago occurred in the late Pleistocene
opyright © 2012 SciRes. IJG
S. SCHUTH ET AL.
Figure 1. Simplified tectonic and geological overview of the White Sea region and the Solovetsky Archipelago. The inset
shows the boundaries of the different provinces in NE Fennoscandia (modified after ). I. T.: Inari Terrane; K. U. T. B.:
Kolvitsa-Umba-Tersk Belt; L. G. B.: Lapland Granulite Belt; M. C.: Murmansk Craton; S. T.: Strelna Terrane; K.-D.: Kan-
dalaksha-Dvina aulacogen (solid grey line); S. I.: Solovetsky Islands. The map shows strata of the Belomorian Mobile Belt
around the city of Kem’ and the Solovetsky Islands (after ). Bolshoi (Big) Solovetsky Island is characterized by numerous
lakes of different sizes and glacial deposits. The sample location at the slope of the Sekirnaya Hill is shown by the black dot.
during the Valdai glaciation (e.g. ). A Neoarchaean
basement (labelled “Bottom Strata” in Figure 1) with an
age of ca. 2.6 - 2.2 Ga was suggested by  to be present
beneath the islands. Moreover, the archipelago is directly
located on two WSW-ENE trending zones marked by
local late Archaean granitic intrusions . In addition,
gravimetric, seismic, and geoelectrical data recorded on
Bolshoi Solovetsky by  revealed that the crust is thin-
nest (ca. 28 km) in comparison to the surrounding area,
and a mantle diapir of unkown age is situated beneath the
islands. Devonian magmatic activity in the western White
Sea region was likely initiated by an upwelling mantle
plume, as suggested by , and  on the base of tec-
tonic interpretation of satellite images. This triggered an
uplift of the area and may still support present-day weak
local positive thermal anomalies observed in lakes and
soils, and formation of an extrazonal thermophilic eco-
system on Bolshoi Solovetsky Island [12,13].
In July 2009, a group of Russian and German geolo-
gists and geophysicists discovered on this island a gneiss
outcrop which is probably related to the BMB. The out-
crop (ca. 7.5 × 5 m) is located at the lower flanks of Se-
kirnaya Hill in the north-western part of the island (Fig-
ure 1). It consists of relatively fresh granitic gneiss.
Other lithologies were not found in the outcrop. This pro-
vides an opportunity of a first age determination of the
basement of the archipelago and, in a broader context,
may help to elucidate the geological evolution of the cen-
tral region of the BMB. The orthogneiss was dated via
the U-Pb zircon dating method employed to two different
instrumental techniques (SIMS-SHRIMP and LA-ICP-
The orthogneiss sample (labelled “R1”) from Bolshoi
Solovetsky Island was sawed into smaller pieces for thin
section preparation, crushing in a jaw breaker and steel
Copyright © 2012 SciRes. IJG
S. SCHUTH ET AL. 291
mortar. From the crushed sample, a part was ground to
powder for X-ray Fluorescence (XRF) analysis employ-
ing an ARL 9800 instrument at VSEGEI. The XRF data
were further processed via CIPW norm for sample classi-
Another representative portion of the crushed material
was used for separation of accessory zircon which was
required for comparative age determination in different
laboratories using SIMS (Secondary Ion Mass-Spectro-
metry) by Sensitive High-Resolution Ion Micro Probe
(SHRIMP-II, at the Centre of Isotopic Research of VSE-
GEI, St. Petersburg, Russia) and Laser Ablation-Sector
Field-Inductively Coupled Plasma-Mass Spectrometry
technique (LA-SF-ICP-MS, at the Institute for Mineralo-
gy, University of Münster, Germany), respectively. In
addition of dating a hitherto unknown outcrop in a geolo-
gically complex region, the two involved institutions
were able to compare their respective techniques by us-
ing well-defined standards and unknown zircons. The se-
paration procedures employed in the Russian and Ger-
man laboratories are given in Table 1.
For analyses, selected zircon grains were mounted in
Pb-free epoxy resin together with the TEMORA 1, GJ-1,
and/or 91500 reference zircons. The grains were sectioned
approximately in half, polished and coated. Cathodolu-
minescence (CL) images were used to reveal the internal
structures of the zircon grains and thereby define target
areas within them. The technical methods applied in the
different institutions are given in Table 1.
2.1. SHRIMP Analyses
The results were obtained with a secondary electron mul-
tiplier operated in peak-jumping mode, as outlined by
. A primary beam of molecular oxygen was em-
ployed to bombard the zircons in order to extract secon-
dary ions. A 70 μm Kohler aperture allowed focusing of
the primary beam so that the ellipse-shaped analytical
spot had a size ca 25 × 20 μm. The sputtered secondary
ions were accelerated at 10 kV. A mass-resolution of
M/ΔM ≥ 5000 (1% valley definition) was achieved via an
80 µm wide slit of the secondary ion source combined
with a 100 µm multiplier slit; thus, all possible isobaric
interferences were resolved. Rastering for one minute
over a rectangular area of ca. 65 × 50 μm before each
analysis removed the gold coating and any possible sur-
face common-Pb contamination.
The ion species of interest were measured in a se-
quence as follows: 196(Zr2O)-204Pb-background (ca. 204
a.m.u.)-206Pb-207Pb-208Pb-238U-248ThO-254UO with in-
tegration times ranging from 2 s to 14 s. Seven cycles for
each analyzed spot were acquired. Apart from “unknown”
zircons, each fourth measurement was carried out on the
zircon Pb/U standard TEMORA 1, which has an ac-
Table 1. The table lists the different analytical techniques
used for this study.
country Germany Russia
Hand magnet, sieving,
CH2I2 heavy liquid,
table, CH2I2 heavy liquid,
Frantz magnetic separator,
Grain fraction used63 - 125 µm 100 - 150 µm
for CL images JEOL JXA 82001 CamScan MX 25003
and current Carbon, 15 kV, 15 nA Gold, 15 kV, 10 nA
technique LA-SF-ICP-MS SIMS-SHRIMP
Element 22 SHRIMP-II3
Beam type New Wave ArF
Excimer laser2 2
O, 5 nA
Energy ca. 5 Jcm−2 10 kV (2nd acceleration)
Spot size (number
35 µm (n = 92),
25 µm (n = 23) ellipse 20 × 25 µm
Analysis time per
20 ns (pulse),
10 Hz (repetition) ca. 6 min
Number of analyses115 10
Discarded results17 0
Analyses ≥ 95%
concordance 70 10
Reference zircons91500 91500
U-Pb age of 915001072 Ma ± 11 Ma
(2σ, n = 5) 1066 Ma ±7 Ma (2σ, n = 6)
U-Pb zircon age
2429.1 Ma ± 9.3 Ma
(2σ) 2433 Ma ± 13 Ma (2σ)
MSWD 5.5 0.089
1Steinmann Institute at University of Bonn; 2Institute of Mineralogy at Uni-
versity of Münster; 3A. P. Karpinsky Russian Geological Research Institute
(VSEGEI), St. Petersburg.
cepted 206Pb/238U age of 416.75 ± 0.24 Ma . The
91500 zircon standard (U = 81.2 ppm, 206Pb/238U age =
1062.4 ± 0.4 Ma; ) was applied as a U-concentration
standard. The Pb-U ratios have been normalized relative
to a value of 0.0668 for 206Pb/238U of the TEMORA 1
reference zircons. Error in TEMORA standard calibration
was 0.62%. The results were then processed with the
SQUID 1.02 (see ) and Isoplot/Ex 3.00 (see )
software, using the decay constants of . The common
Pb correction was done on the basis of measured 204Pb
and present-day Pb isotope composition, according to the
model of .
2.2. LA-ICP-MS Analyses
The U-Pb age determinations were done using a LA-SF-
ICP mass spectrometer (Element 2, ThermoFinnigan)
and a New Wave ArF Excimer Laser system at Univer-
Copyright © 2012 SciRes. IJG
S. SCHUTH ET AL.
sity of Münster, Germany. Forward power was 1330 W,
gas flow rates were about 0.7 L/min for He (employed as
carrier gas for ablated material), and 0.9 L/min and 1
L/min for the Ar auxiliary and sample gas, respectively.
The cooling gas flow rate was set to 16 L/min. Before
starting the analyses, the system has been tuned on the
standard reference material SRM 612 from the NIST
(National Institute of Standards and Technology) by
measuring 139La, 232Th, and 232Th16O to get stable signals
and a high sensitivity on 139La and 232Th peaks, as well as
low oxide rates (232Th16O/232Th ~ 0.1%) during ablation.
The repetition rate was 10 Hz at an energy of ~5 J/cm2.
The typical spot size was 35 µm, in some cases also 25
For U-Pb analyses of the zircons, the masses 204Pb,
206Pb, 207Pb, and 238U were measured. In addition, 202Hg
was analyzed to correct the interference of 204Hg on 204Pb,
which is important to apply, if necessary, for a common-
Pb correction. The common Pb proportion for the indi-
vidual spots is calculated from the 204Hg-corrected 204Pb
signal, applying the two-stage model of . When the
contribution of estimated common 206Pb to the total 206Pb
exceeded 1%, which corresponds approximately to the
analytical uncertainty of the measured Pb isotope ratios,
a common Pb correction was applied. Ten unknown sam-
ples were bracketed with three calibration standards (GJ-
1; ) to correct for instrumental mass bias. The sensi-
tivity for measured Pb and U isotopes for a 35 μm spot
was typically in the range of 4000 cps/ppm. Age calcula-
tions were done with an in-house Microsoft® Excel
spreadsheet using the intercept method (e.g. ) to cor-
rect for elemental fractionation during laser analyses.
Along with the samples, the 91500 zircon standard was
measured to monitor accuracy and precision of the ana-
lyses. A three-shot pre-ablation was applied to all spots
to remove the carbon coating and potential common Pb
contamination from the surface. Out of 111 embedded
zircons, 98 were selected for analyses after inspection of
CL images. Cracks and inclusions were avoided. In total,
115 measurements were carried out.
Sample R1 is a medium-grained foliated granitic gneiss
with abundant orthoclase and amphibole. Hand specimen
and thin section inspection yielded a composition of ca.
45 vol% of feldspar, 25 vol% of amphibole, 25 vol% of
quartz, ca. 5 vol% biotite, and accessory phases like gar-
net, apatite, zircon, and opaque phases. Results of XRF
analyses are given in Table 2, classifying the sample as
an acid alkaline rock because of its high silica and alkali
content. As illustrated in Figure 2, ternary classification
schemes after  and  indicate (syeno-)granite
Table 2. Major element composition of the gneiss sample
(XRF data). tTotal iron as Fe2O3. LOI: Loss on ignition.
SiO2 67.0 CaO 3.13
Al2O3 12.3 Na2O 2.59
TiO2 1.33 K2O 4.22
Fe2O3t 7.11 P2O5 0.37
MnO 0.10 LOI 0.43
MgO 1.31 Sum 99.9
Figure 2. Classification of the gneiss R1 after  (a), and
 (b), respectively. Proportions of albite (Ab), anorthite
(An), orthoclase (Or), alkali feldspar (A, Afsp), quartz (Q,
Qtz), and plagioclase (P) were calculated after the CIPW
norm. Both schemes suggest a granite precursor rock.
as a precursor rock for R1. Therefore, R1 is classified as
an orthogneiss (metasyenogranite). In addition, low MgO-
CaO (0.42) and high P2O5-TiO2 (0.28) ratios suggest a
magmatic origin of the precursor rock .
The zircons are largely present as short prismatic and
prismatic crystals with a length-wide ratio of ca. 1.5 to 3.
Facets of prisms and pyramids are distinct, but show
sometimes signs of chemical corrosion. Small, sporadic
mineral and gas-liquid inclusions are observed under a
binocular. In addition, the zircons of R1 often show well
developed oscillatory zoning, which is sometimes present
as sector zoning and is considered a typical feature of
magmatic zircons (e.g. , and references therein).
Some examples are shown as CL images in Figure 3.
3.2. SHRIMP Results
All ten in situ U-Pb isotopic analyses on eight typical
zircon grains, free of cracks and inclusions, gave a well-
defined concordant age. The results of the zircon analy-
ses are shown in Table 3 and Figure 4(a). During the
course of this study, the 91500 standard zircon yielded a
207Pb/206Pb age of 1066 ± 7 Ma (n = 6). The zircons are
characterized by an average Th-U ratio scattering around
0.77, and low contents of uranium (average 47 ppm), and
thorium (average 36 ppm). Concentrations of non-radio-
Copyright © 2012 SciRes. IJG
S. SCHUTH ET AL.
Copyright © 2012 SciRes. IJG
Table 3. Results of the SIMS-SHRIMP analyses. Errors are 1σ; Pbc and Pb* indicate the common and radiogenic proportions,
respectively. The error for the Temora standard calibration was 0.62% (not included in above errors but required when
comparing data from different mounts). The correction for common Pb was done by using measured 204Pb according to the
model of .
C-1.1.1 0.42 37 25 0.69 14.52421
± 46 02.1821.40.16131.62.1911.50.15762.7 9.91 3.1 0.45581.50.49
C-1.1.2 0.26 58 52 0.92 22.62397
± 26 12.2131.20.15841.32.2181.30.15601.5 9.69 2.0 0.45041.30.64
C-1.2.1 0.54 31 26 0.89 11.92395
± 38 02.2071.60.15941.62.2191.70.15462.2 9.59 2.8 0.44991.70.60
C-1.3.1 0.26 18 11 0.63 7.502497
± 38 –42.1072.00.15782.02.1122.00.15552.2 10.2 3.0 0.47312.00.67
C-1.3.2 0.11 42 38 0.92 16.92450
± 23 02.1601.40.16041.32.1621.40.15941.4 10.2 1.9 0.46231.40.71
C-1.4.1 0.03 153 116 0.78 61.02456
± 15 02.1560.960.16030.862.1560.960.16000.87 10.2 1.3 0.46370.960.74
C-1.5.1 0.00 37 25 0.70 14.52440
± 28 –12.1731.5 0.1573 1.72.1731.50.15731.7 9.98 2.3 0.46021.50.67
C-1.6.1 0.44 41 31 0.76 16.02386
± 32 12.2201.40.15951.62.2291.50.15561.9 9.61 2.4 0.44791.50.61
C-1.7.1 0.57 31 23 0.77 12.52481
± 40 –22.1141.70.16361.82.1261.70.15852.4 10.3 2.9 0.46951.70.58
C-1.8.1 0.45 26 17 0.66 10.22397
± 41 12.2071.80.16152.02.2171.80.15752.4 9.78 3.0 0.45041.80.60
genic lead are insignificant (<0.5%). Zircon cores as well
as metamorphic overgrows or rims were not found. Such
geochemical features are commonly observed for zircons
in magmatic rocks (e.g. [26,27]), but are not always a
positive proof (for further discussion, see ). For age
calculation, all analytical results were used without dis-
crimination. As a result, SHRIMP analyses of eight R1
zircons yield a concordant age of 2433 ± 13 Ma (2σ).
3.3. LA-ICP-MS Results
Analyses of the standard zircon 91500 (see Figure 5)
gave an 206Pb/238U age of 1072 ± 11 Ma (2σ, n = 5)
which is in agreement with earlier reports (e.g. :
1062.4 ± 0.4 Ma; : 1061.3 ± 4.3 Ma, and references
therein). As is evident from Figure 4(b), most zircons
analysed with LA-ICP-MS give an upper intercept age of
2429.1 ± 9.3 Ma (2σ, n = 70, degree of concordance ≥
95%). However, for the remaining results, loss of Pb by
later processes seems to have affected some of the zir-
cons because of their lower Pb-U isotope ratios. These
discordant ages (n = 28) were obtained mostly for the
rims of the analysed zircons. Of the 115 analyzed spots,
17 results were discarded because the signal intensity
was too low or dropped too fast (i.e., the chosen spot did
not offer a sufficient amount of zircon material for analy-
Figure 3. CL images of four zircons (a)-(d). Laser spots are
highlighted as dashed white circles, ages (207Pb/235U in Ma,
±2σ) and the degree of concordance is given for comparison.
Sector zoning is visible in (a) and (b); Less developed zoning
and a non-zoned core region marks the crystal in (c); The
zircon shown in (d) exhibits slight resorption at the bound-
ary beneath the left laser spot. It also yielded different ages
for core and rim, respectively.
S. SCHUTH ET AL.
Figure 4. U-Pb concordia diagrams for zircons analysed by
SIMS-SHRIMP-II (a) and LA-ICP-MS (b), respectively.
The data point ellipses correspond to 2σ uncertainty. In (b),
the arrow marks the result of the rim analysis of the zircon
shown in Figure 3(d), and the stippled line represents the
discordia line. The upper intercept gives an age of 2.429 Ga.
sis). The complete LA-ICP-MS data set is available upon
The geological complexity of the Belomorian Mobile
Belt (BMB) in NW Russia has been known for several
years (e.g. [4,30]). However, little data with respect to
lithologies and rock ages are so far available for the White
Sea region that covers large parts of the central BMB
section. We show here that a hitherto unknown gneiss
outcrop on Solovetsky Island in the western White Sea is
related to granitic intrusions in the central BMB and
yields a U-Pb zircon age of ca. 2.43 Ga. This age was
achieved independently via SHRIMP and LA-ICP-MS,
again confirming the reliability of these methods as al-
ready shown by previous studies (e.g. ).
The composition of the orthogneiss R1 (a metasy-
enogranite) and its U-Pb zircon age coincide with gran-
itic intrusions observed for the western BMB at ca. 2.4
Ga (e.g. [4,32]). This new age information strongly sug-
gests magmatic activity at 2.43 Ga in the central section
of the BMB where it was unknown so far because of
missing accessible outcrops. Moreover, the granitic
gneiss of Solovetsky Island is located on the convergence
of two SW-NE trending zones of variably sized granite
intrusions as suggested by  in a pioneering geological
study of the western BMB region around the city of
Kem’ (Figure 1). The nature, origin, and extension of
these zones of granitic intrusions especially further east
are still uncertain. To note, charnockites to the west and
SW of Kem’ yield a U-Pb zircon age of 2.4 to 2.45 Ga as
well . Taken together, the central and western region
of the BMB was affected by granitic intrusions at ca. 2.4
Ga, however, the magma compositions varied on a local
scale (e.g., charnockites, syenogranites). Potassium-Ar
ages of the granites reported by  range from 1.86 to
1.93 Ga. These age data coincide with the Lapland-Kola
collisional event at ca. 1.9 Ga that has obviously reset the
granite K-Ar age due to metamorphism (e.g. [1,2]). In-
terestingly, some zircons analysed with LA-ICP-MS
yield lower discordant U-Pb ages at their rims (Figure
3(d)). Again, this is in agreement with the time of meta-
morphic events; however, we cannot exclude multiple
episodes of Pb loss as is tentatively suggested by a few
discordant zircon ages of lower than 2.4 Ga. The influ-
ence of the mantle diapir on the U-Pb isotope composi-
tion of the zircons (Pb loss due to re-heating, or younger
zircon growth during ascent of hydrothermal fluids) is
difficult to evaluate. The lower intercept age given in
Figure 4(b) is poorly constrained at 268 Ma ± 170 Ma
because of the scarcity of zircons with a discordant U-Pb
age. However, it still coincides within analytical uncer-
tainty with the time of Devonian magmatic activity in the
western White Sea region (e.g. ). The offset of the
U-Pb age of some R1 zircons may result from ascending
hydrothermal fluids and subsequent Pb loss and/or over-
growth. In contrast,  suggested on the basis of geo-
thermal data and geophysical modelling that the last tec-
tono-magmatic activity in the central BMB took place
during early Miocene. In summary, the mantle diapir has
likely affected the central BMB region in Phanerozoic
time, but the extension and intensity of magmatic activity
still remains uncertain.
Composition and age of the rock units forming the
BMB can vary on a scale of sometimes a few meters (e.g.
[4,30,33]); hence it is possible that a complex basement
is situated beneath the cover of glacial deposits at the
Solovetsky archipelago. As the geological map given by
 is of a scale of 1:4,000,000, and the map of  lacks
detailed information about magmatic rocks, thorough
Copyright © 2012 SciRes. IJG
S. SCHUTH ET AL. 295
Figure 5. U-Pb concordia diagram for the zircon standard
91500 analysed by LA-ICP-MS in Münster, Germany. The
result is in agreement with earlier reports (e.g. : 1062.4
± 0.4 Ma; : 1061.3 ± 4.3 Ma).
geological mapping and dating of possible other rock
units of outcropping basement material at the islands
may uncover a possibly complex geology. The mantle
diapir beneath the island group likely facilitated rise of
the islands above sea level , and, in conjunction with
an extrazonal ecosystem characterized by thermophilic
vegetation close to the polar circle [12,13,34], highlights
a special geotectonic setting and possible modern tec-
tonic activation to be investigated further.
From University of Bonn, S. Jahn-Awe kindly assisted
with heavy liquid separation and zircon picking, and R.
Spiering is thanked for supervision of CL imaging. From
University of Cologne, R. Kleinschrodt is thanked for
coating of the epoxy mounts, and P. Garcia for thin se-
ction preparation. This study was funded jointly by the
DFG (German Research Foundation) by grant Ma2143-
10 to T. M. and the Russian Foundation for Basic Re-
search to V. G. by grant 09-05-91360-NNIO_g as a part
of the project “Energy Supply of Extrazonal Ecosystems”.
We thank A. Zeh and S. Daly for constructive comments
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