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Tectonophysics,
303
172 (1990) 303-322
Elsevier Science Publishers
B.V., Amsterdam
- Printed
Reconstructions
in The Netherlands
of the Arctic: Mesozoic to Present *
H. RUTH JACKSON ‘* * and KARL GUNNARSSON
’ Department
of Geology, University of Oslo, Oslo (Norway)
2 National Energy Authority,
(Received
September
Reykjavik
(Iceland)
8, 1988; revised version accepted
July 11, 1989)
Abstract
Jackson,
H.R.
Gunnarsson,
K., 1990.
Reconstructions
of the Arctic:
Mesozoic
to Present.
Tectonophysics,
172:
303-322.
Plate r~ns~ct~ons
using both
opened
in three
stages:
Eurasia
Basin. The middle
Eurasian
plates
anomaly
34 time when
anomaly
caused
Beaufort-Mackenzie
geological
24/25
event occurred
crustal
shortening
the Amerasia
Basin. Crustal
and geophysi~l
data
time to the present
from anomalies
or strike-slip
Basin
opened
shortening
caused
when
are reviewed
documented
34 to 25 when
motion
interaction
in the Arctic.
by a rotation
the spreading
centre.
It is a feature
Basin the circum-Arctic
similar to the Iceland-Faeroe
sedimentary
basins
formed
Introduction
subbasins
(Fig.
1). The Cenozoic
the
the
the
plate
seafloor spreading
has been taking place in the
Eurasia Basin contemporaneous
with the seafloor
spreading in the North Atlantic and in the Norwegian-Greenland
Sea. The plate reconst~ctions
developed
for this area and time are well constrained and changes to existing models will concern details only. In contrast,
* Geological
leave
Survey of Canada
from
Survey of Canada,
~~1951/~/$03.50
translation
about
the opening
a long period
Atlantic
interaction
Contribution
Geoscience
Dartmouth,
of plates
Geological
N.S., Canada).
Q 1990 Elsevier Science Publishers
in the
and
from prior
a pole
near
to
the
in the Brooks
of the ocean but was not
spreading
in the
of rifting.
24/25 occurred
involved com-
pression and/or
strike-slip motion that is not as
well constrained
as the most recent stage. The lack
of clearly defined seafloor spreading anomalies in
the Amerasia Basin has prevented detailed reconand
has led to many
potheses
for its opening.
There
is a consensus
that
and
varied
the Eurasia
hyBasin
opened by seafloor spreading
about the Arctic
Mid-Ocean
Ridge (Pitman
and Talwani,
1972;
Herron et al., 1974; LePichon et al., 1977; Kristoffersen
and Talwani,
1977; Srivastava,
1978,
1985;
Burke,
1984;
Vink,
Vagnes, 1985; Srivastava
Smith, in press). However,
1984;
and
many
Reksnes
and
Tapscott,
suggestions
1986;
have
been made for the development
of the Amerasia
Basin. Three groups of workers support the idea
that the Amerasia
Basin was created by in-situ
seafloor spreading
but disagree on the location
and direction of the spreading. Group one advocates that the Amerasia Basin (Fig. 1) opened by
2234.
Centre,
Ocean
American
Ridge. Prior to the onset of seafloor
during
structions
motions in the Arctic were focused in the Eurasia
Basin. Since marine magnetic
anomalies
24/25
** On
of the North
in the Arctic just prior to anomaly
in the Amerasia
Basin, probably
The Arctic Ocean can be divided into
Eurasia
and the Amerasia
basins,
where
Amerasia
Basin includes
the Canada
and
Makarov
occurred
may have been accommodated
Range and in the South Anyui Suture Zone. The Alpha Ridge was formed during
Amerasia
The Arctic
spreading
The first event occurred
with some
by this rotation
and examined.
seafloor
B.V.
H.R. JACKSON
+
=
Fig. 1. General
the rotation
location
of Alaska
f2 -
v-
ACTIVE
SPREADING
CENTRE
a
%?~'OING
-$
ACTIVE
TRANSFORM
FAULT
K. GUNNARSSON
FOSSIL
SUBDUCTION
ZONE
FOSSIL
-
CENTRE
chart of the major bathymetric
away from
-
AND
TRANSFORM
FAULT
features
the Canadian
polar
margin
(Carey,
1958;
Tailleur,
1969;
Rickwood, 1970; Grantz et al., 1979, 1981; Harland et al; 1984). A second possibility is that the
basin opened
when Alaska sheared along the
Canadian polar margin (Christie, 1979; Kerr, 1980;
Jones, 1980, 1982). A third idea is that the ocean
crust in the basin may have been formed by
complex spreading patterns by the motion of two
or more small plates (Vogt et al., 1982). A fourth
theory,
that is not based on in-situ
seafloor
in the Arctic Ocean. The plate boundaries
are illustrated.
spreading, is that the oceanic crust in the Amerasia
Basin was formed in the Pacific Ocean and trapped
in its present location (Churkin and Trexler, 1980).
A fifth theory, the oldest, is that the crust was
formed by oceanization
(Beloussov, 1970; Pogrebitskkiy, 1976).
The objectives of this paper are to review and
evaluate the plate tectonic models suggested for
the evolution of the Arctic Ocean based on data
available up to 1988. This was done in three stages
(Fig. 2). In stage III (from the present to anomaly
RECONSTRUCTIONS
ANOMALY
M.Y.
F
:
F
u-
4
-
OF THE
ARCTIC:
MESOZOIC
DEVELOPMENT
OF THE ARCTIC OCEAN
KSRFA
-30
_
13
OPENS
-50
_
-
60
-
70
24
-90
OPENING
OF THE
AMERASIA
BASIN
POSITIVE
100
2
which we tested
the rotations.
The continent-ocean
-
110
-
120
-
130
L
These
accurate
definition.
transition
the Alpha
Ridge
This
r%~”
Borderland
DEVELOPMENT
OF THE
CIRCUM-ARCTIC
SEDIMENTARY
BASINS
inIt is
as continen-
a reference
for the reader.
whose
crust
includes
the
is of uncertain
Ridge which is consid-
ered to be part of the Alpha Ridge in most but not
all of the reconstructions.
The plates are rotated to
where the 2000 m contours, excluding the ridges
overlap
and the geological
in adjacent
Geophysical
data from the Eurasia
stage III, such as magnetic
anomalies,
PM10
a more
contour
on the NA plate.
quences of closing the ocean
are noted and discussed.
z5
was
along
it is considered
and the Mendeleev
and borderland,
MO
in
doing
contour
Lack of data prevented
boundary
recon-
by actually
as the 2000 m bathymetric
the polar margins.
origin
90
0
W-_
0
o>
the literature,
Chukchi
34
-
1985).
On the AA plate the 2000 m contour
-33
4
2
k!
(Sweeney,
tal crust but to provide
ARCTIC?
2
are based on poles that are suggested
drawn in not because
~O~H;FlESSION
p
Basin
structions
cluded
2
5
Amerasia
chosen
20
- 40
k
305
TO PRESENT
conseregions
Basin in
provide
strong constraints
for the plate reconstructions;
geophysical constraints
from the interaction
of the
NA and EU plates in the middle
stage are used to
predict plate motions in the Arctic; in contrast,
geological data from the sedimentary
basins adjacI
ent to the Amerasia
used to constrain
sently available.
Fig. 2. Development of the Arctic Ocean
Basin
in the first stage
the sparse geophysical
As we progressed
first stage increasing
reliance
are
data pre-
from last to the
is put on the geo-
logical controls.
24/25;
Tapscott,
Reksnes and Vagnes, 1985; Srivastava and
1986) the Eurasia Basin opened. For this
stage published
poles are used that relied on
matching
magnetic
anomalies
and the trends of
fracture
zones
in the North
Atlantic,
the
Norwegian-Greenland
Sea, Eurasia
Basin and
Labrador
Sea. During
stage II (from anomaly
25-34) compression
may have occurred between
the North American
(NA) and Eurasian
(EU)
plates (Srivastava
and Tapscott,
1986). In this
interval the matching of magnetic anomalies and
trends in the North Atlantic are used to predict
the motion of the NA and EU plates in the Arctic.
During the period before anomaly
34 (84 m.y.)
back to approximately
the beginning
of Aptian
time (118 m.y.), stage I, seafloor was created in the
Stage III Cenozoic evolution: anomaly O-24/25
Since the time of magnetic anomaly 24/25, the
Eurasia Basin has been opening along the Arctic
Mid-Ocean
Ridge, the northernmost
extension of
the spreading axis between the North American
plate and the Eurasian
plate (Kristoffersen
and
Talwani, 1977; Srivastava, 1978,1985; Vink, 1982;
Srivastava
and Tapscott,
1986). The fit of the
magnetic anomalies from 50”N to and including
the Eurasia
Basin is shown in Fig. 3.
However, when the magnetic
anomalies
from
the opposite sides of the spreading axis are superimposed there are some complications
and discrepancies
that occur on the landmasses
and in
the oceans. For example, overlap occurs between
H.R. JACKSON
306
Fig. 3. Plate-tectonic
period
between
reconstructions
anomaly
for the North
13 and 25 from Srivastava
from adjacent
plates. The dashed
Atlantic,
Norwegian-Greenland
(1985). The superimposed
seas and the Eurasia
circles and squares
and solid lines are the continent-ocean
K. GUNNARSSON
Basin, Arctic Ocean,
represent
boundaries
AND
the magnetic
of the plates.
for the
anomalies
RECONSTRUCTIONS
OF THE
the continental
ARCTIC:
MESOZOIC
shelves of Greenland
TO PRESENT
and Svalbard
(Vink, 1982; Smith, in press). It is unclear
the plates
manner
in this
area
or whether
better
nent-ocean
boundary
Srivastava
and Tapscott
with
crustal
a combination
stretching
of Greenland
with the overlap
feature
tion
in a non-rigid
the
magnetic
is oceanic.
and
magnetic
data
definition
of the conti-
northern
the problem.
and only the southern
(1986) explain
of strike-slip
the overlap
motion
Thus,
and
these plateaus
A third problem
the anomalies
13 and 24 time
of authors
(Feden
1977;
Talwani
1978); however,
of oceanic
this
refrac-
with
origin
the
(Fig. 4)
being of continental
origin.
are not impediments
to the
is that no single pole satisfies
Sea (Kristoffersen
and
Eldholm,
et al.
Sea
and Talwani,
1977;
Srivastava,
these three discrepancies
large and do not indicate
in the plates.
first order
are not
non-rigidity
Of particular
interest is the non-symmetrical
nature of a broad band of negative
magnetic
1979; Crane, 1982; Jackson et al., 1984). Limited
refraction data on the flanks of the Morris Jesup
180*
are consistent
in the No~e~an-Greenland
and the Labrador
in the Morris Jesup and Yermak
by a number
being
indicate
Plateau
plate reconstructions.
occurs in the reconstructions
for anomalies
section
anomalies
On the Yermak
will resolve
plateaus (Fig. 1). A triple junction
existed in the
area during this interval (Feden et al., 1979). The
oceanic or continental
origin of these features has
been debated
and
Rise
whether
and thinning.
A second problem
north
behaved
307
anomalies
that occur on the margins
150”
750
of the Eurasia
120’
1
/Al”?
KARA SEA
MORRIS
PLATEAU
GREENLAND
BARENTS
Fig. 4. Asymmetrical
distribution
of undefined
crust between
anomalies
24 and continental
(from Reksnes and V&es,
1985).
SEA
crust in the Eurasia
Basin, shown stippled
308
Basin
(Vogt
et al., 1979;
1985). Several origins
Reksnes
centres
prior
tinental
early
spreading
crust,
episode
whose magnetic
or oceanic
spreading
extrapolation.
resulted
con-
crust produced
in an
prior
and
deeply
buried,
burial
and heating.
Reconstructions
Basin
to anomaly
25 have been
of the Eurasia
done
pers. commun.,
that close
1988). This
region of broad negative anomalies is considered
in one of the following reconstructions.
the Lomonosov
Ridge
Ocean.
AND
Therefore,
plate
tions are based on other criteria.
24; or foundered
has been erased by deep
In some reconstructions
in the Arctic
and
of spreading
signature
for the
crust formed by
or by jumping
to anomaly
this gap (Srivastava,
Vggnes,
have been suggested
crust (Fig. 4) in this area: oceanic
asymmetric
and
H.R. JACKSON
The opening
from the relative
NA plates;
to
anomaly
sumption
show
anomaly
recent
The
reconstructions
Basin
of
on this as-
to be 600 km
of the East Siberian
indicate
strike-slip
these plates in the Arctic
(Srivastava,
pers. commun.,
two
the EU
was true
Sea from
25 to MO time (Fig. 1). In contrast,
poles
possible
locations
is
Basin
between
the same
(1986) based
the Arctic
wider in the vicinity
One approach
motion
25.
and Tapscott
reconstruc-
of the Eurasia
so, perhaps
Srivastava
K. CiUNNARSSON
motion
during
1988).
on
either
more
between
this interval
We consider
side
of
the
is considered to be part of the NA plate (Pitman
and Talwani,
1972; Vink, 1982, 1984; Jackson,
1985; Srivastava, 1985). This assumption
not only
Lomonosov
Ridge where compression
could
occurred during anomaly 25 to 34 time.
have
produces satisfactory
matches between the magnetic anomalies but also reproduces the direction
of the fracture zones (Srivastava
and Tapscott,
Lomonosov
plate
1986). The Lomonosov
sidered
to be part
(LePichon
Ridge has also been conof the Greenland
plate
et al., 1977)
plate (Sclater
and
as an independent
et al., 1977; Phillips
1981). These latter
magnetic
anomalies
details see Srivastava
The reconstruction
possibilities
and Tapscott,
do not satisfy
and the fracture zones
and Tapscott, 1986).
at anomaly
the
(for
24 (Fig. 3) forms
the basis for the reconstructions
that are developed for stages II and I. The Eurasia Basin was
closed except for a possible narrow ocean between
anomaly 24 and the Lomonosov
Ridge where the
band
of negative
magnetic
anomalies
occurred.
Ridge part of the North American
In this model, the Lomonosov
Ridge is considered to be a part of the NA plate joining northeast
of Ellesmere
basin
Island
at anomaly
(Fig. 1). Figure
5A shows the
34 time, together
with the posi-
tions of NA, EU, and Gr plates based on the fit of
magnetic
anomalies
in
the
North
Atlantic
(Srivastava and Tapscott, 1,986). Morphologically
the Lomonosov Ridge is narrow, linear and steep
sided (Ostenso
and Weld,
tion measurements
1977). Crustal
over the ridge (Mair
refracand For-
syth, 1982) suggest that it is a continental
structure. Gravity
and magnetic
data are also consistent with a continental
origin (Sweeney et al.,
1982; Weber and Sweeney, 1985). The Siberian
termination
of the ridge is not bathymetrically
Svalbard lay adjacent to northern
Greenland
at
this time. The present Barents Sea was a shallow
epicontinental
sea. The Norwegian-Greenland
Sea
continuous
with the shelf (Demenitskaya
and
Hunkins
1970); therefore, it is unlikely to be a
was closed but in the Labrador
tectonic
basin
was connected
Sea a small ocean
to the North
Atlantic.
The
present coastlines
of Greenland
and Ellesmere
Islands were separated by a gap and displaced by
left lateral motion. The Amerasia Basin, the Alpha
Ridge and Chukchi Borderland
their present-day
configuration.
(Fig.
1) were in
Stage II Late Paleocene to Late Cretaceous evolution: anomaly 25-34
For the period previous
developed linear anomaly
to anomaly 25 no well
patterns are identified
continuation.
In Fig. 5A the Lomonosov
the NA plate and the Eurasia
Ridge is attached
Basin at anomaly
is about
at anomaly
implies
150 km wider than
that
crustal
shortening
occurred
to
34
24. This
in this
basin during the Late Cretaceous
and the early
Tertiary or there was an error in the plate reconstruction.
Assuming the reconstruction
is valid
for the present, one area that could be considered
a possible location of shortening
was along the
Amundsen
Basin side of the Lomonosov
Ridge
where the region of undefined
crust occurs (Fig.
I
is required
in the Amerasia Basin perhaps adjacent to the Alpha Ridge (a).
CR -Greenland
American plate. Data from either area that supports crustal shortening is ambiguous and insufficient.
the stippled Lomonosov Ridge compression
plate, EU-Eurasian
plate, NA -North
the dashed line and crossed line is the amount of compression required in the Eurasia Basin between anomalies 34 and 24. In (B) between the simple outlined Lomonosov Ridge and
Fig. 5. The Arctic Ocean reconstructed to anomaly 34 with the Lomonosov Ridge (LR) considered part of the NA piate (A) and as an independent plate (B). In (A) the space between
_E
/
/
\
/
\
/
310
H.R. JACKSON
AND
K. GUNNARSSON
AMUNDSEN
BASIN
LOMONOSOV
RIDGE
O21
KILOMETRES
Fig. 6. Large charge (10 kg) seismic reflection
shown in Fig. 7. The numbers
associated
with the Eurasia
profile
on the profile indicate
Basin, the second
from the base of the Lomonosov
reflectors.
is considered
The first reflector
Ridge into the Eurasia
is thought
the edge of the continental
Basin. The location
to be the base of the sedimentary
is
section
crust of the ridge and the third is from the
mantle.
4). If the crustal
the Lomonosov
shortening
occurred adjacent to
Ridge, the ridge itself may have
been produced or deformed by crustal shortening.
One interpretation
of the deep penetration
seismic
line (Jackson
et al., in press)
collected
anomalies
are characteristic
The relative low-amplitude
Lomonosov
crustal
(e.g. Kaula, 1972).
anomalies
over the
Ridge are not compatible
shortening
with major
here.
over the
ridge and into the Amundsen
Basin is consistent
with this scenario. The reflection
profile shows
that the crust of the ridge terminates about 80 km
into this basin. The mantle associated with the
thinner oceanic crust dips under the seaward extension of the ridge (Fig. 6). In areas where crustal
shortening
has taken
place negative
free-air
Lomonosov
Ridge as an independent
plate
Another possibility
is that when the EU and
NA plates were interacting
in the Arctic during
anomaly 25 to 34 time, the Lomonosov
Ridge was
detached from both of them as an independent
plate. The reconstruction
is shown in Fig. 5B. The
RECONSTRUCTIONS
OF THE
Fig. 7. The available
portion
ARCTIC:
Free Air gravity
shown in Fig. 5 extends
MESOZOIC
for the Lomonosov
towards
the 0 gravity
the oceanward
311
TO PRESENT
Ridge. The dashed
contour
extent of reflector
2 which is thought
total size of the Makarov Basin was approximately
150 km larger than at anomaly 24 and in this case
compression
is required
between
the Lomonosov
and the Alpha ridges (Kovacs et al., 1982). In this
reconstruction
the poles for the EU and NA plates
are taken from Srivastava
LR was independently
Barents Sea and Kara
lines exist between
Ridge (Jackson
show basement
tening is seen
could be due to
and Tapscott
of the seismic reflection
record.
The
to be the crust of the ridge.
basement of between
be due to the normal
7.5-10 km are too large to
subsidence of oceanic crust.
Kovacs
and Vogt (1982) suggest
several
reasons
for this feature
a relict oceanic
subduction
including
possible
zone.
(1986) and
rotated adjacent
to the
Sea shelves. Few seismic
the Lomonosov
line is the position
on the pole side of the ridge. The Arrow on the seismic track indicates
and the Alpha
et al., in press) and they do not
clearly. No obvious zone of shorin the sedimentary
section. This
shortening taking place before the
sediments were deposited, or the lack of data to
identify structures or the features being masked by
later extension. Magnetic data on the Alpha Ridge
display an interesting
and perhaps significant feature. Calculations
of depths to magnetic basement
(Kovacs and Vogt, 1982) show a basement depression along the north side of the ridge. Depths to
Variable plate boundary
A third possibility
for the configuration
of
plates in the Arctic is that the compression
in the
Arctic Basin was not colinear with the zone of
extension
but took place in the region between
Alaska and Siberia. In the Late Cretaceous
to
Early Tertiary in the Bering Sea region, between
the Chukotskiy
Peninsula
and northern
Alaska
(Fig. l), crustal shortening
is observed
in the
deflection
of structural
trends (Patton and Tailleur, 1977). This shortening
could be regarded as
compatible
with the compression
predicted
by
Srivastava and Tapscott (1986) from anomaly 25
H.R. JACKSON
312
to 34 (Eocene
Harbert
to Late Cretaceous).
et al. (1987) correlate
convergence
in the
interaction
Bering
Furthermore,
periods
deformational
that the timing
events
Stage I closure reconstructions:
with
this inter-
and style of the
can be explained
The time of opening
the
by these
derived
from
A fourth possibility
of
in northeastern
the
to be considered
pre-anomaly 34
continental
Opening
is that the
variety
of data
Basin
development
and on Banks
about
131-113
spreading
obIs-
m.y. ago
occurred
118 to 79 m.y.,
that include
is
the breakup
Alaska
Seafloor
from
with
margin
occurred
1985).
interval
of the Amerasia
associated
served
(Sweeney,
in the Arctic
rocks
phase
land.
plate interactions.
No compression
K. GUNNARSSON
of strong
Sea region
of NA and EU plates during
val and indicate
AND
based
in
on
a
the age of tholeiitic
did not affect
basal@, age versus depth and age versus heat flow
the Arctic at this time, or that the poles examined
here are inaccurate. In this case there is no reason
curves. Sweeney (1985) summarizes
this information. The age-depth
relationships,
based on com-
to assume that the Arctic Basin changed size between anomaly 25 and 34, and there is no need to
parisons
plate motions
in the North
Atlantic
consider the possible locations for crustal shortening. Wilson (1985) points out, based on world-wide
plate considerations,
that many plates are converging on the present-day
Arctic and it should be
undergoing
sufficient
compression
space
to permit
and there
age of
curves
age of
between I10 and 84 m.y. The Late Cretaceous
sediment, recovered in a core (Mudie et al., 1986)
from the Alpha
be in-
interval
that
is pre-
and
Ridge, was deposited
that corresponds
suggests
sently taking place. He suggests the crustal shortening is being taken up along the globe-encircling
occurred
zone of subduction
and the continental
that separate the Gondwana
continents
Amerasia
collisions
from the
a crustai
between 125 and 74 m.y. The heat flow-age
from the Canada Basin also give a crustal
should
spreading
with other oceans, predict
that
in the time
to anomaly
33 (78 m.y.)
the development
of the ridge
prior to this time.
Basin
others. Although
by detaching
the Lomonosov
Ridge from the NA plate, it is possible to decou-
In most of the models presented here the Alpha
Ridge (Fig. 1) is considered to be an oceanic crust
ple the motions of the NA plate from the Arctic;
it is not possible to decouple the motions of the
EU plate from the Arctic.
formed
basin. This assumption
tion acquired
during
Summarizing,
at anomaly 34 (Fig. 5) the distribution of the landmasses
around the Arctic was
(Jackson et al., 1986; Mudie et al., 1986; Sweeney
and Weber, 1986). The Mendeleev
Ridge is con-
similar
to anomaly
24 time but the Labrador
Sea
was closed and there was greater separation
between Greenland
and Ellesmere Island. There is
the possibility
that 150 km of compression
curred between the Lomonosov
Ridge and
Barents
Shelf or between
Lomonosov
compression
recent
plate
octhe
the Alpha Ridge and the
Ridge, but the only good evidence for
is in the Bering Sea area. The most
reconstruction
of Srivastava
(pers.
commun., 1988) that does not require compression
in the Arctic Ocean is consistent with the limited
seismic and gravity data available. The shape of
Alaska was about what it is now with the suturing
of small terranes occurring later (Harbart
et al.,
1987). The rest of the Amerasia Basin existed in
its present day configuration.
sidered
in place
at the time
to be part
of opening
of the
is based on the informathe CESAR
experiment
of the Alpha
Ridge
in this
paper. A wide range of geological
and geophysical
data
that
Ridge
supported
the
is oceanic
conclusion
near
Canada
the
(Jackson
Alpha
et al.,
1986; Sweeney and Weber, 1986). For example,
seismic refraction data (Forsyth et al., 1986) measure
a thick
oceanic
crust
lower crustal
layer
large oceanic
plateaus.
typical
with
of that
The twenty
a high-velocity
found
in the
similar
rocks
dredged from the Alpha Ridge are highly altered
basalts (Van Wagoner and Robinson,
1985; Van
Wagoner et al., 1986). Heat flow is consistent with
an oceanic origin but greater than that expected
for continental
crust (Taylor et al., 1986). The
Alpha Ridge is considered
to be a large oceanic
feature formed at the time of seafloor spreading,
RECONSTRUCTIONS
OF THE ARCTIC:
but not along
The
313
analogue
is the
Iceland-
centre was identified
on the basis of a magnetic
low and a gravity high in the southern
Canada
Ridge system.
Basin. Unfortunately,
Makarov
to be nonexistent
struction
Basin
is considered
in the
following
Ridge
Bathymetry
continues
data
(Jackson
indicate
morphologically
sov Ridge near Ellesmere
in this region indicate
recon-
to have formed at the same
time and by the same processes
Alpha
TO PRESENT
axis (Jackson et al.,
the spreading
1986). A present-day
Faeroe
MESOZOIC
that produced
and
Johnson,
that
the Alpha
the
of the region.
this gravity
on recent
Limited
gest the basin
period of constant
Ridge
the magnetic
discussed
during
polarity
anomalies
(Sweeney.
1985). Thus,
may be due to the topog-
to the Lomono-
raphy
Island.
Refraction
son et al., 1986). The lack of evidence
that the crust is thinner
but
magnetic
anomalies
sug-
the Cretaceous
almost
data
on basement
compilations
data already
was formed
1986).
high was found
gravity
as on the Alpha
in the Canada
Ridge (Jackfor clear
Basin thwarts
similar to the Alpha Ridge (Forsyth et al., 1986);
in particular,
the distinctive
high-velocity
lower
detailed reconstructions
of the basin.
The assumption
that the crust of the Amerasia
crustal layer of 7.3 km/s
is observed in both
areas. This suggests that there is a gradual thinning of the oceanic crust of the Alpha Ridge
that
towards the Makarov Basin. Sweeney and Weber
(1986) consider the basin as enigmatic
and pre-
1983). Namely, the basin was formed by oceanization of the continental
crust (Beloussov.
1970;
sume it formed from 118 to 54 m.y. ago.
The Chukchi Borderland
is flat-topped
and as
shallow as 273 m (Johnson et al., 1979). Grantz et
Pogrebitskkiy,
was formed
present
al. (1979) believe that the feature is of continental
origin, but rifted away from the mainland,
and is
Arctic-Alaska
not
a hinderance
to tectonic
reconstructions.
the
plate
reconstructions
to be reconcilable
if
the
features
with
are
stretched
continental
crust that were displaced
seaward during the initial opening stages of the
ocean (Srivastava
and Tapscott,
(pers. commun.,
1984) indicates
produced
types
the Alpha
of evolutionary
Ridge
scenarios
eliminates
(Lawver
two
et al.,
1976) and that the oceanic crust
in the Pacific and trapped
in its
location
(Churkin
and Trexler.
1980).
plate
A
comparable
problem in the North Atlantic would
be the overlap between Galicia Bank and Flemish
Cap, which is considered
Basin is oceanic and formed in situ by the processes
1986). Karasik
that a magnetic
edge anomaly is present on the borderland.
The
magnetic edge anomaly is described as similar to
that observed on the oceanic VGring Plateau which
has been drilled and shown to be composed of
mafic volcanic material (Eldholm et al., 1987). The
paucity
of data from the Chukchi
Borderland
makes it difficult to assess its origin; however, the
limited information
suggests it is not a major
impediment
to closing the Amerasia Basin.
Aeromagnetic
data in the Canada Basin and
over the Alpha Ridge are reviewed by Vogt et al.
(1982). The anomalies in the Amerasia Basin are
chaotic and contrast
strongly with the well-lineated anomalies
observed in the Eurasia Basin.
However, there are anomalies that can be traced
for 100 km or more and an extinct spreading
The size of the Arctic-Alaska
important
Amerasia
plate (AA) is an
factor in the reconstructions
Basin (Fig. 8). The AA plate
for the
was ex-
tended across the Bering Strait for the following
reasons. Common
Paleozoic
terrains
in Alaska
and Chukotka
(Cherkin
and Trexler,
1980) suggest
that the plate boundary extends across the Bering
Strait. Paleozoic to early Mesozoic stratigraphic
sequences in the Lawrence Islands are nearly identical to those found in the western Brooks Range;
as well, distinctive
belts of Late Paleozoic
to
Mesozoic mafic volcanics and alkaline intrusives
are traceable from the Lawrence Islands onto the
Chukotka
Peninsula
(Patton
and Tailleur,
1977).
The AA plate is extended to the South Anyui fold
belt because it is the clearest example of crustal
suturing
in the region
Fujita and Newberry,
(Shilo
and Til’man,
1982). The polarity
1981;
of crustal
shortening is difficult to determine and it is possible that subduction
occurred under both margins
before the final collision (Fujita and Newberry,
1982), now dated as the Hauterivian
(131-125
m.y.). Although this date left too short an interval
for crustal compression
due to the opening of the
H.R. JACKSON
314
Fig. 8. The preferred
surrounding
basins
closure of the Arctic Ocean, rotation
whose similar
stratigraphy
EU, AA and LR. The smaller letters are the basins:
-Pechora,
Canada
Basin,
~~-Br~ks-MacKe~e
more studies
of the AA plate with some translation
and fossils have been documented.
in the region
AM-Arctic
should
clarify the problem.
The first reconstruction
of the Amerasia Basin
(Carey, 1958; Tailleur,
1969; Rickwood,
1970;
Grantz et al., 1979, 1981; Harland et al., 1984)
involves the rotation of the AA plate about a pivot
at the mouth of the MacKenzie
River (Table 1,
Fig. 9). The basin opened with a simple rotation
which requires
500 km of erustal
shortening
Margin,
basins. The position
at the
Chukotka
end of the place. As described in the
introduction,
all rotations
for this interval
are
based on matching
the 2000 m contour on the
adjacent plates excluding the portions of the contours that describe the Alpha and Mendeleev ridges
and the Chukchi
borderlands.
The Lomonosov
AND
K. GUNNARSSON
of the pole, with the location
The larger letters are the plate names,
SV-Svalbard,
of the Chukchi
WS-Wandel
Borderland
Sea, BS-Barents
of the
NA, CR,
Sea, PB
CB is also shown.
Ridge lies adjacent to the Barents-Kara
shelf and
is considered an independent
piate. This position
of the ridge was necessary to prevent serious overlap with the AA plate.
Summari~ng.
independent
observations
that
support or refute this reconstruction;
the pre-rift
position of the AA plate along
Sverdrup
Basin is compatible
Paleozoic
and Mesozoic
the edge of the
with the Late
sedimentary
transport
di-
rections for both the NA and AA plates. In addition, seismic reflection profiles along the Alaskan margin indicate that it is a rifted as opposed
to a transform
margin (Grant2 and May, 1983).
Also supporting
the rotation
A.4 plate are paleomagnetic
hypothesis
for the
studies on a lower
RECONSTRUCTIONS
TABLE
OF THE
ARCTIC:
MESOZOIC
1
em
Pole position
lat.( o )
Anomaly
long.( o )
Rotation
Refer-
angle ( o )
ence
13.97
- 107.20
EU/NA
76.23
148.80
- 13.62
1
-21.83
1
separate
plate (Fig. 5B)
13.97
- 107.20
- 13.62
1
EU/NA
76.23
148.80
- 21.83
1
LR/NA
62.28
140.37
4.0
34 to MO (Fig. 9)
GR/NA
73.97
EU/NA
19.5
LR/NA
62.3
AA/NA
69.1
- 107.20
- 13.62
1
151.92
- 25.59
1
- 65, - 45,
-25
2
73.97
EU/NA
79.5
AA/NA
66.5
- 135.0
-50
3
3
-35
3
Aa/NA
69.0
- 135.0
-25
3
- 107.20
- 13.62
1
1
34 to MO (Fig. I I)
EU/NA
79.5
151.92
- 25.59
40.0
124.0
- 15, - 10,
4
-5
34 to MO (Fig. 12)
79.5
- 107.20
- 13.62
1
151.92
- 25.59
1
AA/NA
69.1
- 135.0
-40,
-35
2
CH/NA
69.1
- 135.0
-65,
-60
2
* References: l-Srivastava
et al. (1979); 3-Jackson
and Tapscott (1986); 2-Grantz
et al. (1986); 4-Jones
(Table
1, Fig. 10) is
lessen
to retain
the virtues
of the first and
differential
combination
shortening along the Brooks Range. A
of strike-slip and rotational
transla-
AA plate
is defined
was
as before,
chosen
(1982)
motion
north
further
migrated
AA/NA
along its length,
of the first. It attempts
Lomonosov
Ridge is assumed
NA plate. This pole produced
- 135.0
73.97
reconstruction
1
- 135.0
EU,‘NA
shortening
1
68.0
GR/NA
The second
a modification
data
et al., 1987) do
by this model.
- 13.62
67.0
Anomaly
differential
which is required
zone and in
geological
(Oldow
- 25.59
AA/NA
73.97
Range
Crustal
was accom-
Suture
Unfortunately
151.92
AA/NA
GR/NA
the Brooks
Anyui
in the
1980).
of the AA plate
in the South
Range.
orogen
et al.,
- 107.20
-45
Anomaly
(Hea
in front
the Brooks
rotation
34 to MO (Fig. IO)
GR/NA
of the Brookian
Alaska
trending
the need
for
tion for the Amerasia Basin is suggested by Green
and Kaplan, (1986) and Jackson et al. (1986). The
6.0
140.37
- 135.0
-35,
Anomaly
shortening
from
and the northwestern
faults
and
not support
34: LR
GR/NA
Anomaly
Islands,
and
Yukon
modated
34: LR part of NA (Fig. 5A)
GR/NA
Anomaly
Arctic
folds
Poles of total opening
Plates
315
TO PRESENT
time.
the pole
south
In
this
of
and
case
the
to be part of the
200 km left-lateral
in the Beaufort-MacKenzie
Basin which is
compatible
with the sinistral motion indicated by
the structural studies of Oldow et al. (1987). This
reconstruction
also required less differential
compression along the Brooks Range which is more
compatible
with the mapped
the area (Oldow et al., 1987).
structural
trends
in
The third set of reconstructions
is based on the
concept that the Arctic Ocean Basin was formed
by shear
(Kerr,
1980;
Jones,
1980,
1982).
This
theory is based on the linear shape of the Canadian
margin
and
extending
its position
from Alaska
as part
of a lineament
to Norway.
The Lomono-
sov Ridge is considered
part of the NA
Dextral faulting in the Beaufort-Mackenzie
is indicated
Cretaceous
(Neocomian)
formation
on the north
slope of Alaska (Halgedahl
and Jarrard, 1986).
When the paleomagnetic
poles for the AA plate
are compared to those of the cratonic NA plate,
significant relative motion since the Neocomian
is
suggested,
which is compatible
with the counterclockwise rotation of the AA plate from the NA
plate. There were two structural lineations
in the
vicinity of the pole of opening that agreed with
this model. They are the NE-trending
Kaltag fault
system, along the continental
margin of the west-
with
but
to the
by Yorath
and Norris,
plate.
Basin
1975; Young
et
al., 1976; Jones, 1980 and Churkin and Trexler,
1980. Sinistral as well as dextral shear are postulated
for the Canadian
Arctic
margin
(Christie,
1979; Kerr, 1980). The pole of opening suggested
by Jones, (1982) that forms a small circle of the
margins has been used (Table 1, Fig. 11); consequently, to open the Amerasia
Basin to put the
AA plate in its present position, left-lateral
shear
was required.
In this set of reconstructions
the
amount
of rotation
is difficult
of the gaps or overlaps
to choose
that occurred
because
in different
N.R. JACKSON
316
Fig. 9. The rotation
the Arctic Alaska
of the Arctic-Alaska
plate,
NA the North
Ridge plate in this and the following
assumed
m contour
plate with the pole of opening
American
figures. The narrow
to be the edge of the plate but also includes
associated
with
the NA plate
differential
which
shortening
near the Beaufort-Mackenzie
plate, GR the Greenland
EZ/ the Eurasian
black line is the 2000 m bathymetric
the Chukchi
encompasses
required
plate,
Borderland
the Alpha
Ridge.
along the AA plate boundary
The principle
K. GUNNARSSON
Basin (Fig. 1). AA indicates
plate and
contour
and the Mendeleev
AND
LR is the Lomonosov
along
the AA plate which is
Ridges. The dotted
objection
line is the 2000
to this rotation
is the
which is not observed.
parts of the region. When the Amerasia Basin is
closed so that the 2000 m contour associated with
is continental
crust (Vogt et al., 1982) because
borderland
overlaps the Arctic Islands when
the Mendeleev
2000 m contour
Ridge is adjacent
to the LR plate,
of the American
portion
the
the
of the
then encroachment
of the AA pIate occurred on
Banks Island (Fig. 1). In addition,
between the
AA plate and the Lomonosov Ridge there is a gap
AA and NA plates are superimposed
(Fig. 8). This
filled by the overlapping
Alpha and Mendeleev
Ridge 2000 m contours.
This is possible if the
Mendeleev Ridge is of continental
origin and the
available
Alpha Ridge is oceanic.
The fourth reconstruction
(Table 1 and Fig. 12)
is based on the premise that the AA plate is not
continuous
across the Bering Strait (Vogt et al.,
1982; Zonenshain
and Napatov,
in press). The
hypothesis is important if the Chukchi Borderfand
portion of the AA plate now called the AL plate is
rotated to where the 2000 m contours barely overlapped. The CH plate with the Chukchi Borderland and Mendeleev Ridge attached, is rotated so
that the irregular 2000 m contour slightly overlaps
model implies that the Canadian
Arctic continental margin was not formed in one stage. The
geological
constraints
from the Canadian
polar margin are imprecise but consistent
with a
formation at the same time (Sweeney, 1985). The
with the 2000 m contour
of the NA plate. Now the
RECONSTRUCTIONS
Fig. IO. The plate
northward
317
motions
of the Amerasia
with time producing
left Iateral
Basin about
strike-slip
and NA piates which is more consistent
Alpha
and Mendeleev
ridges fit adjacent
a pole that is initially
motion
which reduces
with the shortening
to each
other with some overlap. This reconstruction
implies that the Alpha Ridge and Mendeleev Ridge
must
same
plates
also be foundered
continental
crust.
pole of opening
is chosen for both
so that
the boundary
between
them
The
new
is a
transform fault. If this assumption
is not made, it
would be necessary for compression
or extension
to have taken place between Alaska and Chukotka.
Limited geophysical
data show no evidence of
this. The Lomonosov
Ridge in Fig. 12 is attached
to the NA plate.
~u~a~~ng,
the position of the plates in preArctic Ocean times, the AA plate was adjacent to
the NA plate aligned along the edge of the present
polar shelves (Fig. 8). The preferred way to achieve
this configuration
is by rotating the AA plate with
located
the amount
observed
south of the Mackenzie
of differential
shortening
Delta and moves
between
the AA
in the Brooks Range (Fig. 1).
a component
of strike-slip motion. The size of the
Alaska portion of the AA plate was smaller than
at present. The eastern edge of the AA plate was
adjacent
the Lomonosov
Ridge
and overlap
may
have occurred in this area. The position of the GR
plate relative to the NA plate was the same as at
anomaly
34.
Conclusions
The most
acceptable
plate
reconstruction
for
the Arctic Basin based on the presently available
data set for stage III, anomalies
O-24/25,
is the
Srivastava and Tapscott (1986) plate reconstruction for the EU and NA plates that satisfies the
magnetic anomalies
in the Eurasia Basin and in
the North Atlantic.
From anomaly
25-34,
the
H.R. JACKSON
318
Fig. 11. The plate motions
Borderland
and that they separate
suggestion
of the Amerasia
and the Mendeleev
Basin using the pole of Jones (1982). The basin
Ridge as continental.
The principal
the NA and AA plates so that the Canadian
of strike-slip
motion
in the Arctic
Oc-
ean is more compatible
with the available data
than models that require compression.
The iinear
shape of the Lomonosov Ridge could be a product
of strike-slip motion prior to the opening of the
Eurasia
Basin. For the time period prior to
anomaly 34 (stage I), the rotation
from the Canadian
polar margin,
shifts northward,
is congruous
geological and geophysical
construction
is consistent
of the AA plate
with a pole that
with the available
information.
This rewith the distribution
and the development
of the circum-Arctic
sedimentary basins.
The circum-Arctic
basins include the BrooksMacKenzie,
Sverdrup, Wendel Sea basins and the
basins of Siberia and East Greenland.
A significant amount of geological data has been gathered
difficulty
AND
is closed by considering
with this model is that these blocks
Arctic Islands cannot
K. GUNNARSSON
be the sedimentary
the Chukchi
must be continental
source for the AA plate.
that indicates from the Carboniferous
to pre-mid
Cretaceous the circum-Arctic
basins received analogous sediment types in a common tectonic setting (Balkwill et al., 1983; Haakanson
and Stemmerik, 1984; Riis et al., 1986). Similarities
in the
marine faunas in these basins indicate long lasting
connections
between them (BalkwiIl et al., 1983)
and also suggest the basins were close. In contrast,
the present Arctic margins are marked by provincial faunas. Closure of the Arctic Ocean shown in
Fig. 8 illustrates
the proximity
of the circum-Arctic
basins prior to the opening of the Amerasia Basin.
In fact, the rifting period associated with and that
occurs before seafloor spreading
that separated
the AA plate from the NA plate provided
the
mechanism for the basin formation. It also implies
that during the development
of the circum-Arctic
RECONSTRUCTIONS
OF THE ARCTIC:
Fig. 12. The plate motions
2000 m contour
reconstruction
associated
for the Amerasia
information,
spreading
319
TO PRESENT
Basin where the AA plate is divided into two plates:
with the CH plate
implies that seafloor
with the available
MESOZOIC
in contrast
was initiated
and that the Chukchi
to the solid line which
at different
Borderland,
times along the Canadian
the Mendeleev
AL and CH. The dashed
is the 2000 m contour
Ridge
Arctic islands,
and the Alpha
line is the
of the AL plate.
Ridge
This
which is inconsistent
are all continental,
which is unlikely.
basins-from
Mississippian
to mid-early
Cretaceous (320 to 125 m.y.)-no
major plate reorganization occurred in the region of the Arctic.
The principal
difference
between
this Arctic
closure model and others, such as those from Steel
and Worsley (1984) or Worsley (1986) or that
shown in Fig. 10, is that the central Arctic Ocean
at closure is not left with a large continental
high
north
of Ellesmere
Island,
consisting
of the
Lomonosov, Alpha and Mendeleev Ridges and the
Chukchi Borderland,
that separate the basins of
the EU plate margins from those on the NA and
AA plates. The preferred
reconstruction
in this
paper is in better harmony with the history of the
circum-Arctic
basins than earlier reconstructions.
For example, the continuous
distribution
of very
organic-rich
source rocks in the mid-Triassic
from
the Alaska margin, the Sverdrup Basin, Svalbard
and the Barents Sea (MGrk, 1987) is consistent
with and explained by this reconstruction.
Acknowledgements
The conscientious
reading
and constructive
suggestions
of 0. Eldholm, S. Srivastava
and J.
Sweeney greatly improved this manuscript.
H.R. JACKSON
320
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