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> Forsiden > Publikationer > Geology of Greenland Survey Bulletin > Vol. 191 Geol. Greenl. Surv. Bull. > Review of Greenland Activities 2001, pp 48-56

GEOLOGY OF GREENLAND SURVEY BULLETIN 191

 
Geological correlation of magnetic susceptibility and profiles from Nordre Strømfjord, southern West Greenland

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background image
The Palaeoproterozoic Nagssugtoqidian orogen is
dominated by reworked Archaean gneisses with minor
Palaeoproterozoic intrusive and supracrustal rocks.
The Nagssugtoqidian orogen (Fig. 1) was the focus of
regional geological investigations by the Geological
Survey of Denmark and Greenland (GEUS) in 2001
(van Gool et al. 2002, this volume). In conjunction
with this project, geophysical studies in the inner part
of Nordre Strømfjord, Kuup Akua and Ussuit were
undertaken as part of the Survey's mineral resource
assessment programme in central West Greenland.
The studies include geophysical modelling of airborne
magnetic data, follow-up studies of aeromagnetic
anomalies by magnetic ground surveying, and geosta-
tistical treatment and integration of different geological,
geophysical and geochemical data. The aim is to
obtain an interpretation of the region in terms of both
regional geological features and modelling of local
features of relevance for the mineral resource assess-
ment. This paper presents an account of the field work
and some of the new data.
The work was carried out from a rubber dinghy in
the fjords and from helicopter-supported inland camps.
In situ measurements of the magnetic susceptibility of
rocks and magnetic ground profiles were carried out
during a period of 25 days in June and July 2001. In total
133 localities were visited from three camps.
The data collected will be used together with
magnetic properties and density of rock samples de-
termined in the laboratory for geophysical modelling
of the area. The petrophysical data will constrain the
geophysical and geological interpretations and thus
provide a higher degree of confidence in the models.
Magnetic susceptibility
Magnetisation is defined as the magnetic moment per
unit volume. The total magnetisation of a rock is the
vector sum of the remanent magnetic moment that
exists irrespective of any ambient external magnetic
field, and the induced magnetic moment that exists
because of the presence of the external magnetic field.
The strength and direction of the induced magnetic
moment is proportional to the strength and direction
of the external magnetic field. The proportionality
factor is termed the magnetic susceptibility (denoted
with the symbol
and assumed to be a scalar quanti-
ty). In the following sections all quantities are referred
to the SI system (Système International) in which the
magnetic susceptibility becomes dimensionless.
The magnetic susceptibility of rocks was measured
with a hand-held magnetic susceptibility meter (Fig. 2).
To obtain estimates of the remanent magnetic compo-
nent and more precise results of the magnetic suscep-
tibility it is also necessary to investigate rock samples
in the laboratory. The in situ measurements presented
in this paper were obtained during the field work; the
results of laboratory investigations currently being
carried out at the petrophysical laboratory at the Geo-
logical Survey of Finland are not yet available.
The amount and distribution of the magnetic miner-
als in a rock determine the magnetic response
measured along a profile. The content of magnetite
(Fe
3
O
4
) and its solid solution ulvöspinel (Fe
2
TiO
4
) is
the dominating factor in crustal rocks (Blakely &
Connard 1989). The magnetic susceptibility of gneiss is
normally between 0.1
x 10
­3
SI and 25
x 10
­3
SI (Telford
et al. 1998).
Data acquisition and processing
The magnetic susceptibility meter used in the field was
a Geo Instrument GMS-2 (Fig. 2). Depending on the
homogeneity of the rocks and the size of the outcrop,
ten to forty readings were taken at each locality to
ensure a proper statistical treatment of the measure-
ments. Outcrops were selected so as to provide the
most representative measurements of the rock on
unweathered, smooth surfaces. In total 3444 readings
were taken at the 133 localities. In the statistical treat-
48
Geological correlation of magnetic susceptibility and pro-
files from Nordre Strømfjord, southern West Greenland
Bo M. Nielsen and Thorkild M. Rasmussen
Geology of Greenland Survey Bulletin 191, 48­56 (2002) © GEUS, 2002
GSB191-Indhold 13/12/02 11:29 Side 48
background image
49
500 km
Inland Ice
Greenland
Iceland
Canada
Granitic intrusion (s.l.)
Supracrustal rocks
(undifferentiated)
Arfersiorfik quartz diorite
Archaean gneiss reworked
in Palaeoproterozoic
Sisimiut charnockite suite
Syntectonic granite suite
Granitic intrusion (s.l.)
Supracrustal rocks
Orthogneiss
ARCHAEAN
PROTEROZOIC
Thrust
Fault
Structural trend line
Basic dykes
UNDIFFERENTIATED
t
t
t
t
t
t
t
t
t
t
t
t
t
t
t
t
t
Sisimiut
Holsteinsborg
K a n
g e lu
s s
ua
q
r
Nordre
Isortoq
66
°
50 km
Ikertôq
thrust zone
Inland
Ice
NNO
CNO
SNO
Nor
th Atlantic
craton
Nagssugtoqidian or
ogen
Qasigiannguit
Ikamiut
Lersletten
Aasiaat
Kangaatsiaq
NSSZ
Kangerlussuaq
Attu
Ussuit
Nordre Strømfjord
Arfersiorf
ik
Jakobshavn Isfjord
68
°
51
°
Sønd
re S
trøm
fjord
In
51
°
50
°
68
°
67
°
30´
10 km
t
t
t
t
t
t t
t
Nor
dre Isor
toq
steep belt
nor
thern CNO
flat belt
southern CNO
central
Nagssugtoqidian
orogen (CNO)
southern
Nagssugtoqidian
orogen (SNO)
Ikertôq thrust
zone
Arfersiorfik
Ussuit
Kuup Akua
northern
Nagssugtoqidian
orogen (NNO)
Fig. 1. Simplified geological map of
the study region and the Nagssug-
toqidian orogen, southern West
Greenland. The geological sub-
regions (northern CNO flat belt,
Nordre Isortoq steep belt, southern
CNO) are also shown. Modified
from van Gool et al. (1996, 2002,
this volume).
NSSZ: Nordre Strømfjord shear zone;
In: Inuarullikkat.
GSB191-Indhold 13/12/02 11:29 Side 49
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ment the measurements were grouped according to
locality, rock type and geological province. In cases of
very heterogeneous rocks, the relative proportions of
the rock types present were estimated and data weight-
ed accordingly. Magnetic susceptibility measurements
were also made as a secondary task by two other field
teams in the western part of Nordre Strømfjord, at Attu,
in the Ikamiut area and at Lersletten, but these data are
not included in this presentation.
Two long magnetic profiles were made (Fig. 3) with
measurements of both the total field and the vertical
gradient using a magnetic gradiometer (Geometrics
G-858); another magnetometer (Geometrics 856) was
used as base magnetometer. The sampling distance
along the profiles was approximately 1 m. As an exam-
ple, the magnetic total field intensity from the south-
50
Fig. 2. The hand-held magnetic susceptibility meter is small and
easy to use. Measurements are taken first with the meter at the
rock surface, followed by a reference reading with the meter
held up in the air. The photograph shows the first step of the
measurements on typical gneiss lithologies in the central part of
Ussuit fjord.
51
°
50
°
67
°
30´
67
°
45´
Nordre Strømfjord
shear zone
northern CNO
flat belt
Ik
er
tôq
thrust zone
southern
CNO
nT
Nor
dr
e
Isor
toq steep belt
10 km
D
A
B
C
549
465
408
367
330
299
269
219
243
197
177
159
142
126
112
98
86
74
63
52
42
32
22
12
1
­10
­20
­32
­44
­58
­73
­88
­106
­125
­147
­172
­206
­261
Fig. 3. Magnetic total-field intensity map with shaded relief. The tectonic boundaries and subregions of the central Nagssugtoqidian
orogen stand out as distinct lineaments and zones in the magnetics. Shading is with illumination from the north-north-west. Black
triangles mark the position of the three field camps in the study area. Dotted lines mark the boundaries within the central
Nagssugtoqidian orogen. Closely spaced dots indicate boundaries mapped in the field, and wider-spaced dots extrapolations
based on the aeromagnetic data. The airborne and ground magnetic profiles are shown with dashed (A­B) and full white lines
(C­D), respectively. The part of the ground profile used for modelling is shown as the grey part of the line C to D (see also Fig. 5).
GSB191-Indhold 13/12/02 11:30 Side 50
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ernmost two kilometres of the profile undertaken from
the eastern inland camp south of Ussuit is discussed in
a later section.
Regional geology
Reworked Archaean gneisses with minor Palaeopro-
terozoic supracrustal and intrusive rocks dominate the
Nagssugtoqidian orogen. The region studied in this
paper lies in the eastern part of the central Nagssug-
toqidian orogen (CNO; Marker et al. 1995). The CNO
is bounded by the Nordre Strømfjord shear zone to the
north and the Ikertôq thrust zone to the south (Fig. 1).
The CNO can be divided into three subregions: (1)
the northern CNO flat belt; (2) the Nordre Isortoq steep
belt; and (3) the southern CNO (van Gool et al. 1996;
Connelly & Mengel 2000).
Subregion 1. The rocks of the northern CNO flat
belt are dominated by Archaean orthogneisses with a
grey to white colour and variably developed banding;
major open upright antiformal structures are charac-
teristic. The gneisses are intercalated with narrow belts
of Palaeoproterozoic supracrustal rocks, spatially asso-
ciated with the calc-alkaline Arfersiorfik intrusive suite.
The supracrustal rocks are often strongly foliated and
migmatised with several leucosome phases, and
comprise mafic amphibolite bodies and layers, ultra-
mafic bodies, pelitic schists, marble and calc-silicate
rocks, and fine- to medium-grained quartz-rich para-
gneisses with biotite and garnet.
Subregion 2. The Nordre Isortoq steep belt sepa-
rates the northern CNO flat belt and the southern CNO.
The steep belt is a zone of steeply dipping and isocli-
nally folded orthogneiss and paragneiss, and is domi-
nated by an up to five kilometres wide belt of
supracrustal rocks. The supracrustal rocks comprise
mainly pelitic and psammitic paragneisses, with lesser
amounts of mafic to ultramafic bodies and layers,
amphibolites and calc-silicate rocks. The gneisses are
very variable in appearance, and range from felsic
migmatitic gneiss types to more pelitic and mafic types.
The rocks are in granulite facies.
Subregion 3. The southern CNO consists dominantly
of homogenous orthogneisses.
The study region is cross-cut by several NE­SW-
trending faults of unknown age. The rocks to the west
of Kuup Akua and north of the northern border of the
Nordre Isortoq steep belt, including the Ussuit area,
are all in amphibolite facies. The rocks to the east of
Kuup Akua and further north are in granulite facies.
Regional aeromagnetic data
The aeromagnetic anomaly data for the study region
resulting from project Aeromag 1999 (Rasmussen &
van Gool 2000) were obtained by subtraction of the
International Geomagnetic Reference Field (IGRF) from
the measured data, and correlate well with the surface
geology of the region (Figs 1, 3).
The subdivision of the CNO and the boundary
features are clearly reflected in the aeromagnetic anom-
aly data. The Nordre Strømfjord shear zone stands out as
a sharp discontinuous ENE­WSW lineament. Magnetic
domains can also be recognised coinciding with the
three geological subregions.
Subregion 1. The northern CNO flat belt is charac-
terised by elongated and curved, short wavelength
anomalies reflecting the folded nature of this domain.
These anomalies are superimposed on a regional
magnetic field level of around zero.
Subregion 2. The Nordre Isortoq steep belt stands
out as an ENE­WSW-trending regional magnetic low
with superimposed low amplitude, elongated, short
wavelength anomalies. Based on the magnetic data
alone, it may be argued that the northern border of the
steep belt should be placed more northerly than that
depicted in Fig. 3, for which only the central part has
so far been confirmed by mapping. The low magnetic
anomaly is partly due to the presence of supracrustal
rocks. Uniform low magnetic response of supracrustal
rocks is confirmed from many other regions of the
world (Card & Poulsen 1998).
Subregion 3. The southern CNO has a high magnetic
regional level and is characterised by closely spaced
short wavelength anomalies with steep horizontal
gradients. Several fold structures can be recognised in
the magnetic anomaly patterns. A NNW­SSE-trending
low magnetic feature cross-cuts the eastern part of the
southern CNO. The anomaly is weak in the steep and
flat belt regions.
The border between the CNO and the southern
Nagssugtoqidian orogen (SNO; Fig. 1; van Gool et al.
2002, this volume) stands out as a very sharp and large
gradient, which can be correlated with the Ikertôq
thrust zone.
Magnetic susceptibilities of different
rock types
The magnetic susceptibility measurements presented
here show that the different rock types exhibit a wide
51
GSB191-Indhold 13/12/02 11:30 Side 51
background image
range of susceptibility values within the same forma-
tion, and even on the same outcrop. The measure-
ments for the main rock types of the studied area are
given in Fig. 4 and Table 1.
The susceptibility in SI units for the entire data set
ranges from 0.0 to 91.41
x 10
­3
SI. The rock types
examined include orthogneisses, paragneisses, a vari-
ety of supracrustal rocks, and intrusives related to the
Arfersiorfik quartz diorite. The highest values corre-
spond to orthogneisses, whereas some marbles and
gneisses are virtually non-magnetic.
Gneiss
The susceptibility distribution for all types of gneisses is
shown in Fig. 4A. In total, 2372 measurements were
made on 77 gneiss localities. The variability of the
gneisses in the field is reflected in very variable magnet-
ic susceptibilities ranging from 0.0 to 68.18
x 10
­3
SI,
with a geometric mean value of about 1.21
x 10
­3
SI.
The negative skewness (Table 1) of the measurements
in Fig. 4A shows an asymmetric tail extending towards
lower values. This may reflect that the generally low
measured susceptibility values have a too low mean,
perhaps due to near-surface weathering of the rocks.
In general, the metamorphic facies is reflected in
the susceptibility values, with high values for granulite
facies gneisses and lower values for amphibolite facies
gneisses. This is probably caused by the formation of
magnetite under granulite facies metamorphism (Clark
1997). Moreover, the gneiss type is clearly reflected in the
susceptibility values, with low values for paragneisses
and higher values for orthogneisses. Visible magnetite
was often observed in migmatites, which possibly indi-
cates formation of magnetite during migmatisation, and
is reflected in the high susceptibility values.
52
0.001
10
100
0
5
10
15
20
25
30
n
= 250
n
= 240
0.001
0.01
0
5
10
15
20
25
30
0.001
10
100
0
5
10
15
20
25
30
0.001
0.01
100
0
5
10
15
20
25
30
n
= 180
Schist
Gneiss
Susceptibility distribution (%)
Susceptibility distribution (%)
Amphibolite
Marble
Susceptibility distribution (%)
0.001
0.01
0.1
1
10
100
0.001
0.01
0.1
1
10
100
Ultramafic rocks
Arfersiorfik quartz diorite
Susceptibility distribution (%)
Susceptibility distribution (%)
Susceptibility distribution (%)
Magnetic susceptibility (SI 10
­3
)
Magnetic susceptibility (SI 10
­3
)
n
= 2372
0
5
10
15
20
25
30
0
5
10
15
20
25
30
100
10
10
1
1
0.1
0.1
1
1
0.1
0.1
0.01
0.01
A
D
E
n
= 192
B
F
52%
n
= 100
C
Fig. 4. Magnetic susceptibility distri-
bution in per cent for different rock
types.
GSB191-Indhold 13/12/02 11:30 Side 52
background image
Amphibolite
Measurements of magnetic susceptibility of mafic
amphibolite (Fig. 4B) were taken at eight localities,
and give a susceptibility range from 0.17
x 10
­3
SI to
7.33
x 10
­3
SI. The amphibolites are characterised by
fairly uniform distribution of the values with a geomet-
ric mean of 0.94
x 10
­3
SI. These susceptibility values
are typical for amphibolite, reflecting their mafic, para-
magnetic mineralogy (Henkel 1991; Clark 1997). The
highest values were obtained from amphibolites with-
in gneiss lithologies, and the lowest values from
amphibolites in supracrustal sequences.
Ultramafic rocks
The susceptibility distribution for ultramafic rocks is
shown in Fig. 4C. Compared to the mafic amphibo-
lites, the ultramafics have higher susceptibility values
ranging from 1.0 to 19.44
x 10
­3
SI for seven localities.
The high values reflect the high iron content of the
ultramafic rocks. Despite the high skewness (Table 1),
the high values are in accordance with general values
for ultramafic rocks (Clark 1997). Some of the highest
values were obtained on magnetite-rich reaction rims
along contacts with the neighbouring rocks. The ultra-
mafic rocks are often heavily altered, which can explain
some of the lower susceptibility values obtained.
Schist
The susceptibility values for mica schists range from
0.0 to 34.7
x 10
­3
SI (Fig. 4D) taken at eight localities.
Susceptibility values obtained for pelitic schists were
higher than for more psammitic schist types; higher
iron content of the pelitic schists in an oxidising envi-
ronment favours metamorphic formation of magnetite.
It should be noted, however, that both pelitic and
psammitic schists at several localities had a large
content of graphite. The carbon from the graphite can
53
Gneiss
2372
0.00
68.18
1.21
­0.12
Amphibolite
192
0.17
7.33
0.94
­0.02
Ultramafic rocks
240
1.00
19.44
2.75
1.92
Schist
250
0.00
34.70
0.59
0.21
Marble
100
0.00
0.30
0.05
­0.29
Arfersiorfik quartz diorite
180
0.69
6.88
0.53
­0.45
Rock type
The skewness characterises the degree of asymmetry of a distribution around its mean. The geometric mean is the mean of all the
obtained susceptibility values larger than zero for the given rock type.
Number of
measurements
Minimum
Sl x 10­3
Maximum
Sl x 10­3
Geometric mean
Sl x 10­3
Skewness
Table 1. Measurements of magnetic
susceptibility
nT
50
°
9
67
°
41
67
°
40´
0.10
0.21
0.24
3.01
3.68
50
°
3
386
354
319
285
259
238
218
186
201
173
160
149
135
123
113
101
91
80
70
61
53
47
41
38
29
20
­9
8
­23
­39
­53
­66
­81
­94
­109
­121
­132
­140
1 km
D
C
Fig. 5. Magnetic total-field intensity map
with shaded relief. The response
observed from the airborne and ground
magnetic survey profiles south of Ussuit
(see Fig. 1). The NNW­SSE-trending
white line C­D shows the location of
the ground profile. The N­S-trending
white line is the airborne magnetic
profile. The white lines also define the
zero level for the magnetic total field
intensity data shown as a black curve.
The grey circles show locations where
selected susceptibility values were
obtained in the field.
GSB191-Indhold 13/12/02 11:30 Side 53
background image
have a reducing effect, which hinders the formation of
magnetite. As was the case for the amphibolites, the
negative tail of the distribution possibly reflects weath-
ered rocks.
Marble
Marbles from five localities are very similar, all with
very low susceptibility values (Fig. 4E) due to the high
content of non-magnetic calc-silicate minerals. The
highest values for marble were obtained at one locali-
ty where the marble contained thin intercalated mafic
mica schist bands and was penetrated by pegmatite
veins. In general, the magnetic susceptibility is almost
negligible, and the marble lithologies can thus be
considered as forming non-magnetic units.
Intrusive rocks: Arfersiorfik quartz diorite
Susceptibility values were taken at six outcrops of the
Arfersiorfik quartz diorite, and fall into two groups
(Fig. 4F). The first group has high values ranging from
0.69 to 6.88
x 10
­3
SI, while the second group has
lower values between 0.01 and 1.10
x 10
­3
SI. Field
observations indicate that the quartz diorite varies in
appearance from dark to light coloured types, due to
varying amounts of mafic components, quartz content
and grain size, which may explain the variance of the
susceptibility values.
Magnetic profile data
The NNW­SSE profile measured from the eastern
inland camp south of Ussuit is perpendicular to the
southern border of the Nordre Isortoq steep belt (line
C to D in Figs 3, 5). The profile runs from the low
magnetic zone of the steep belt into a more irregular
high magnetic anomaly zone. The profile was laid out
as a straight line, with start and end points together
with every 100 m interval determined by use of the
Global Positioning System (GPS).
The central part of this ground profile crosses a small
positive anomaly. One of the aims was to compare the
details obtained from the ground measurements with a
profile from the Aeromag 1999 survey (Rasmussen &
van Gool 2000). The airborne magnetic profile was
flown at an altitude of 300 m, runs N­S and intersects
the ground profile (Fig. 5). The difference in content
of short wavelength anomalies in the two survey types
(Fig. 5) clearly illustrates the attenuation with increased
distance to the sources, which has significant implica-
tions for the amount of detail that can be acquired
from the airborne data. However, a clear correlation
with the observed surface geology is confirmed by the
ground profile.
The sharp positive anomalies observed in the
central part of the ground profile correlate with a
100­150 m wide zone containing ultramafic rocks,
whereas the lower magnetic anomalies reflect gneiss
lithologies. The locations of the lowest anomalies can
be related to calc-silicate horizons observed in the
field. Based on these observations it can be concluded
that the small positive anomaly in the aeromagnetic
data originates from the presence of ultramafic rocks.
Combined forward modelling and inversion under-
taken with tabular bodies as the principal model is
shown in Fig. 6 for both the ground and airborne
profile. The free parameters in the final inversion are
location, size, thickness and magnetic properties.
Some initial modelling with the dip angle as free para-
meter indicates that a steep northward dip of the
bodies gave the best data-fit. In the final inversion the
dip angles for all bodies were identical, except one
body for which it was necessary to deviate slightly
from the common angle in order to obtain a proper
data-fit. The relatively thin alternating bodies of rocks
with different magnetic properties, necessary in the
modelling, reflect the banded nature of the geology in
the study region.
To test the agreement of the field susceptibility
measurements with the values obtained by the model-
ling, the modelling was undertaken without any con-
straints on the magnetic properties, but with the
assumption that the direction of magnetisation was
aligned along the present direction of the geomagnetic
field. Thus the modelling does not distinguish between
a remanent magnetisation in the direction of the geo-
magnetic field and the induced magnetic component.
The magnetic susceptibility values for the bodies in the
modelling range from 0 to 92 x 10
-3
, with a mean around
30 x 10
-3
. This is one order of magnitude higher than
the geometric mean values of the measured suscepti-
bility values, but within the range obtained from the
measured values. An explanation to this discrepancy
may be that the remanent magnetic component con-
tributes considerably to magnetisation; however, this
has not been confirmed by laboratory measurements
on rock sample from the Survey's archive.
Although modelling of potential field data is known
to be highly ambiguous, the model presented above
includes features that are expected to be common to all
54
GSB191-Indhold 13/12/02 11:30 Side 54
background image
models that are realistic representations of the geology.
More detailed modelling and further study including
measurements of the magnetic properties are warranted.
Conclusions and further work
The aeromagnetic data reflect the regional geology
well. Further work will involve interpretation through
processing and modelling.
The ongoing construction of a large database of mag-
netic susceptibilities and other petrophysical parameters,
coupled with observations on rock types and structures,
will help to elucidate the correlation between the geo-
logy and magnetic responses, and is a prerequisite for
realistic geological interpretations of the aeromagnetic
surveys from the area.
The field measurements show that the magnetic
susceptibility is variable within the same rock type,
and even on individual outcrops there are consider-
able variations. Gneiss and schist lithologies in particu-
lar have very variable susceptibilities, probably reflecting
the variable nature of the lithologies, e.g. pelitic to psam-
mitic. Ultramafic rocks and amphibolites, and to a lesser
extent some intrusives of the Arfersiorfik quartz diorite
suite, show relatively high magnetic susceptibilities with-
in a narrow range. Marble is essentially a non-magnetic
rock type. All susceptibility values obtained from the
different lithologies are within the typical range for
such rock types (Clark & Emerson 1991; Shive et al.
1992; Clark 1997; Telford et al. 1998), and are in agree-
ment with values obtained in previous investigations
(Thorning 1986). The variable susceptibility values of
the rock types reflect the different nature of the rocks
and their different geological histories, e.g. metamor-
phism, hydrothermal alteration, bulk composition, etc.
More work will be necessary to analyse the suscepti-
bility values in relation to these factors. The discrep-
55
Fig. 6. A: The airborne profile data (A­B,
the dashed white line in Fig. 3) and the
resulting model from the modelling with
the projection of the ground profile (line
C­D in Figs 3, 5). B: The ground profile
data and the resulting model from the
modelling. Measured magnetic total field
intensity data are shown in black, and
the response of the models in red.
Green-coloured bodies are the magnet-
ic bodies used to model the measured
data. The grey shaded regions in the
model correspond to magnetic reference
level; i.e. zero magnetic susceptibility.
500 nT
250
0
2000
4000
6000 m
10000
20000
5000 m
25000
15000
1500 nT
1000
500
0
-500
500
1000
1500
2000 m
500 m
1000
1500
N
S
Airborne survey
profile
A
B
D
B
A
NW
SE
Ground profile
D
Projection of
ground profile
C
C
GSB191-Indhold 13/12/02 11:30 Side 55
background image
ancy between the susceptibility values obtained in the
field and those indicated by modelling will also have
to be investigated further. The ground magnetic profile
carried out during the field season illustrates well the
significant difference in resolution of the geological
details that are possible from different survey types, at
the same time confirming the correlation of geology
and airborne anomalies.
The investigations will continue in the 2002 field
season, when ground geophysical surveys will be
undertaken in connection with lineament studies and
the study of a mineralised horizon in amphibolite at the
fjord Inuarullikkat (Stendal et al. 2002, this volume).
The database of the magnetic susceptibility of rocks
will be supplemented with new measurements and
with laboratory determinations of petrophysical prop-
erties when these become available.
Acknowledgements
Jette Blomsterberg and Aaju Simonsen (both Bureau of Minerals
and Petroleum, Government of Greenland) are thanked for their
contributions to the field work. The project is part of a Ph.D.
study by B.M.N. at the University of Aarhus and is funded by
GEUS and the Danish Research Agency. The Geological Institute
of the University of Copenhagen is thanked for lending us the
magnetic gradiometer.
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56
Authors' address
Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: bmn@geus.dk
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Review of Greenland Activities 2001, pp 48-56