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Post Permian tectono-thermal evolution of western Dronning Maud Land, East Antarctica: an apatite fission-track approach

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New apatite fission-track (AFT) ages from Heimefrontfjella and Mannefallknausane indicate that the Mesoproterozoic basement and Permian sedimentary cover rocks were heated to c. 100°C during the Mesozoic. Heating was due to the burial by up to 2000 m of Jurassic lavas at c. 180 Ma, when the area was affected by the Bouvet/Karoo hot spot. Near the developing coastline, the lava pile was quickly eroded and in part deposited on the continental shelf as pebbly and coarse-grained volcaniclastic sandstones. The AFT data indicate that farther inland the lava pile was not eroded until c. 100 Ma, and the Palaeozoic unconformity between the Mesoproterozoic basement and Permo–Carboniferous sedimentary rocks as a reference plane remained at temperatures of c. 80°C. Formation of an up to 800 m b.s.l. deep graben in from Heimefrontfjella as well as flexural uplift and rapid denudational cooling of the not extended crust from Heimefrontfjella southwards occurred at c. 100 Ma. It is speculated that a period of major plate reorganisation and new rifting at c. 100 Ma is responsible for affecting a much wider continental margin as far inland as Heimefrontfjella and producing a total relief in excess of 3500 m.
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Antarctic Science
7
1
(4):
457-460
(7999)
0
British
Antarctic
Survey
Printed
in
the
United
Kingdom
Post Permian tectono-thermal evolution of western Dronning
Maud Land, East Antarctica: an apatite fission-track approach
JOACHIM JACOBS*
and
FRANK LISKER
Universitat Bremen, FB Geowissenschaften,
PF
330440,D-28334
Bremen, Germany
vojacobs@uni-bremen
de
Abstract:
New apatite fission-track (AFT) ages fromHeimefrontfjella andMannefallknausane indlcate that the
Mesoproterozoic basement and Permian sedimentary cover rocks were heated to
c.
100°C during the
Mesozoic. Heating was due to the burial by up to
2000
m of Jurassic lavas at
c.
180 Ma, when the area was
affected by the BouvetKaroo hot spot. Near the developing coastline, the lava pile was quickly eroded and in
part deposited on the continental shelf as pebbly and coarse-grained volcaniclastic sandstones. The AFT data
inhcate that farther inland the lava pile was not eroded until
c.
100 Ma, and the Palaeozoic unconformity
between the Mesoproterozoic basement and Permo-Carboniferous sedimentary rocks as a reference plane
remained at temperatures of
c.
80°C. Formation of an up to 800 m b. s.1. deep graben in front of Heimefrontfjella
as well as flexural upllft and rapid denudational cooling of the not extended crust from Heimefrontfjella
southwards occurred at
c.
100 Ma. It is speculated that a period
of
major plate reorganisation and new rfing
at
c.
100
Ma is responsible for affecting a much wider continental margin as far inland as Heimefrontfjella and
producing a total relief in excess of 3500 m.
Received
20
October 1988, accepted
1
September 1999
Key words:
apatite, denudation, Dronning Maud Land, East Antarctica, fission-track, rifting
Introduction
Heimefrontfjella is a
c.
130 km long mountain range between
9" and 13"W, which is situated
c.
350 km inland from the
eastern margin of the Weddell Sea in East Antarctica. The
mountain range is exposed between
c.
1200 and 2700 m a.s.1.
and lay within the area affected by the Karoo (White
&
McKenzie 1989) or Bouvet mantle plume (Storey 1995,
Fig.
1).
It was intruded by a large number of mafk dikes and
sills and was covered by anunknown thickness of continental
flood basalts at
c.
180 Ma (Spaeth
&
Schiill 1987).
A
very
irregular relief characterizes the area between Heimefrontfjella
and the continental margin, with basement cropping out only
in a few small nunataks at Mannfallknausane. Mapping of the
subice topography reveals a steep graben that extends down to
800
mb.s.1. betweenHeimefrontfjella andMannfallknausane
(cf. Hoppe &Thyssen 1988). This grabenmost probablyjoins
the Pencksokket-Jutulstraum graben farther to the north-east
(Fig. 1). This graben system was interpreted as a possible
southern continuation of the Western
Rift
System (East African
graben system) into Antarctica or a failed Gondwana rift
(Grantham
&
Hunter 199 1).
Here, we try to quantify the tectono-thermal effects that
Heimefrontfjella and Mannefallknausane underwent during
Gondwana break-up
by
using apatite fission-track analyses.
We analysed 37 apatite samples from basement and cover
rocks using the external detector method. Twenty-two of
these samples had previously been dated using the population
technique (Jacobs 1991, Schnellbach 1991). Fourteen of the
15 newly dated samples come from a vertical profile in the
northern part of Heimefrontfjella where the basement is
unconformably overlain by Permo-Carboruferous sedimentary
rocks.
Geological setting and previous fission-track work
Heimefrontfjella and Mannefallknausane are composed of
medium to high-grade metamorphc basement rocks. The
lithology, structure and geochronology are described in detail
in Arndt
et
al.
(1991), Jacobs
et al.
(1995) and Jacobs
et
al.
(1996). Crust formation and the first major metamorphsm
occurred between
c.
1300 and 1050Ma. Large areas of
Heimefrontfjella were overprinted at
c.
500 Ma during the
Pan-AfricadRoss event, as revealed by numerous K-Ar and
Ar-Ar mineral analyses (Jacobs
et
al.
1995, 1997). In the
northern part of Heimefrontfjella a pronounced Palaeozoic
peneplain is developed, which is exposed at an elevation of
c.
2100 m. There, the basement is overlain by Permo-
Carboniferous sedimentary rocks of the Beacon Supergroup.
During the Jurassic, the basement was intruded by many dykes
and sills (Rex 1972, Spaeth
&
Schiill 1987). Large quantities
of Jurassic mafk lavas are exposed in Vestfjella farther north
(cf. Peters
et
al.
1991). Such lava flows probably covered
large parts of Heimefrontfjella during the Jurassic but are
mostly eroded now and are only preserved in one small
locality at Bj~rnnutane (Fig. 2). The Jurassic sills caused
contact metamorphsm within the sandstones. However, coal
semis more than
c.
60 m away from Jurassic sills show
45
1
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452
J.
JACOBS
&
F.
LISKER
vitrinite reflectance values of
c.
0.5
Rr,
indicating that
temperatures did not exceed 70 to 80°C during the Mesozoic
and Cenozoic (Bauer
et
al.
1997). The cover sequence dips at
1-3'
to the south-east. Seismic data indcate that the crust
north-west of Heimefrontfjella was tlunned from
c.
50
km
at
Heimefrontfjella and its hmterland to
c.
35 km north-west
of
it (Heinz Miller, personal communication 1997). Thus, the
crust north-west of Heimefrontfjella represents extended
continental crust that was strongly overprinted during the
rlfting of Gondwana.
First apatite fission-track studes using the population
technique were carried out by Jacobs (1991) and Schnellbach
(199 1). Those data revealed ages between
c.
75 and
230
Ma.
Based on mean confined track length measurements the higher
ages were interpreted as representing mixed ages, whereas the
lower ages were interpreted as cooling ages. The data show
a positive correlation between age and elevation as well as age
and distance from the coast. The mixed ages around 180 Ma
were interpreted as representing partial resetting during a
thermal event at the beginning of Gondwana break-up, which
was most likely associated with the Jurassic magmatism. The
data also imply differential uplift and cooling of three different
blocks within Heimefrontfjella, with the lghest
uplift
rates
having been concentrated in the now topographically hghest
regions. Thus, the
2700
m high mountains in Sivorgfjella
(Fig.
2)
were not interpreted as reflecting a steep Palaeozoic
reliefbut Cretaceous differential uplift during the break-up of
Gondwana.
In
this
study we tly to constrain further the major Mesozoic
Fig.
1.
Gondwana reconstruction with indication of
the Bouvet/Karoo mantle plume and associated
Jurassic volcanism (after Whlte
&
McKenzie 1989,
Storey
1995, Jacobs
et
al
1996 Profile after Spaeth
&
Schull (1987) Falkland microplate (FM) after
Marshall (1 994), Ellsworth Whitmore
(EW)
and
Filchner crustal block (FCB) after
Curtis
&
Storey
(1996) Note possible continuation
of
the Western
Rift System (East African graben system) into East
Antarctica Abbreviations M
=
Madagascar,
PJ
=
Pencksokket-Jutulstraumen,
SA
=
South
America,
V
=
Vestfjella
to Cenozoic tectono-thermal events
of
the wider eastern
margin of the Weddell Sea.
Samples and method
Thrty-seven apatite samples were analysed using the external
detector method, as described by Green
et
al.
(1989). This
method yields similar results to the grain population technique
when the apatites have homogenous U-concentrations and
constant chlorine-fluorine ratios. The latter have an effect on
the track-retention temperature of individual apatite grains.
Thus, single grain dating is better suitable for apatites with
changing composition and complex cooling path. Therefore,
we have reanalysed most of the original samples from the
study of Jacobs (1991) and Schnellbach (1991) using the
external detector method. We also selected 15 new samples,
most from a vertical profile at Budsbotnen (Fig.
2),
below
and close to the pre- Permo-Carboniferous peneplain defined
by the overlying Beacon sedimentary rocks. Apatites from the
new samples were separated using standard techniques as
recommended by Gleadow (198
1).
Apatite grains were
embedded in epoxy resin, and were then ground and polished.
Internal apatite surfaces were etched for
60
seconds at
2
1°C
in
S%HNO,.
Samples were mounted with mica detectors and
irradiated
in
the graphite reflector facility ofRis0 (Denmark).
Thermal neutron fluence was monitored by using standard
glasses
CN5
(Corning Glass) and apatite standards, Fish
Canyon and Durango. Fossil and spontaneous tracks were
counted at 1000
x,
and horizontal tracklengths were measured
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POST
PERMIAN TECTONO-THERMAL EVOLUTION
453
at 1250 x
magnification
(air lens). Whilst in the study of
Jacobs (1991) track lengths were measured in a separate
sample which was etched for
an
ad&tional 20 sec
in
20%
HNO,,
in
our
study track lengths were measured in the actual
sample
on
which the age determination was carried out. Thus,
the track lengths are generally shorter than in the study of
Jacobs (199 1) and more compatible to current international
procedures when applying the external detector method. We
usedaKintecstage
withFT-stageprogramofDumitru(l993).
Ages were determined using the zeta calibration method
(Hurford
&
Green 1983, Green 1985) with a
6
=
361
h
6
for
J.
Jacobs. Errors were calculated using conventional methods
(Green 1981) andarequotedwith
h
1 oerrors. Thedistribution
of
single grain ages were then characterized using a mixture
modelling program (Sambridge
&
Compston 1994). From
this, forward modelling by MonteTrax (Gallagher 1995) was
used to constrain the low-temperature cooling hstory consistent
with all measured track length distributions and ages.
Results
and
interpretation
The AFT data are summarized in Table
I,
sample locations are
indicated in Fig. 2. Thrty-two of the analysed samples were
taken from igneous or metamorphc crystalline basement
rocks of Palaeozoic age or older,
two
samples are Permian
sandstones, and three samples are granite-gneiss dropstones
Fig.
2.
Geological overview
map
of
Heimefrontfjella
with
location
of samples.
from the base
of
the Permo-Carboniferous sequence. The
AFT ages range from 172
f
17 to 81
f
8 Ma and &splay a
trend towards higher AFT ages at higher elevations (Fig. 3).
Generally, the new determined apatite ages were similar to
those that had been determined by the population technique
(Jacobs 1991, Schnellbach 1991). All apatite ages are
signdicantly younger than their stratigraphcal ages, inhcating
that all samples have experienced
major post-Permian
thermal
annealing.
Northern Tottanjelld Swordella
In
northern Tottanfjella and Sivor@ella, 18 AFT samples
were collected between elevations of 1200 and 27 10 m. The
AFT ages range from 172
f
17 to 87
f
7 Ma (Table
I),
with
the higher ages occurring at higher elevations and farther
inland. The mean confined track lengths vary between 13.3
and 12.0 pm with corresponding standard deviations between
1.4 and 2.1 pm
(Figs
3
&
4). The
x2
values range from
0
to
99%. Although most
x2
values are low (<40%),
only
five
samples fail the %?-test. The oldest and the youngest samples,
i.e. the samples closest to the graben and the samples farthest
inland, have both the highest
x’
values and the longest mean
track lengths. A more detailed analysis of the latter samples
reveals, that they are characterized
by
one dominant age
group. Samples near the graben show one major age component
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~~
Sample
#
Eley Locality
Litholog)
n
ps
Ns
pi
N1
pd
Nd
x1
Cc
U
Age *lo MTL =lo
b
d nl
[ml [xEhcm
'1
[xEGcm
'1
[xE6cm2]
%
[PP~I
[Ma1 [Ma1 [PI [~ml
MI
I82 9417 2100
78 2 94/8 2130
58 2 9416a 2100
J8 2 9416b 2100
ST7 2 100
BB1930 1930
BBl82O I820
BB1740 1740
BB1700 1700
BE1600 1600
J72 9413 1300
572 94/2 1300
J72 94/4 1300
572 9415 1300
J7 2 94/18 1300
5
W4 112
1300
A7 1 /8 1300
9
J2700 2700
-1
u:
51703 2710
4
J1709 2620
J1058 2300
3
51500 2280
i
J9 213 1900
J1105 1750
J14215 1350
K55 1200
K44 1855
K42 1860
K53 1530
K3
0
1740
K19 1200
K24 1740
K3 2 1200
K15
W122il 900
W142/1 900
m
J1057 2420
Schivestolen
Schivestolen
Schivestolen
Schivestolen
Schivestolen
Burasbotnen
Burasbotnen
Burasbotnen
Burasbotnen
Burasbotnen
Burasbotnen
Burasbotnen
Burasbotnen
Burasbotnen
Burasbotnen
Burasbotnen
Burasbotnen
Sivorgfjella
S
ivorgfj el
1
a
Sivorgfjella
S
ivorgfj el la
Sivorgfjella
Tottanfjella
Sivorgfjella
Sivorgfjella
Sivorgfjella
Sivorgfjella
Sivorgfjella
SivorgfJella
SivorgfJella
Sivorgfjella
Tottanfella
Sivorgfjella
Sivorgfj ella
Sivorgfjella
Mannefalk.
Mannefalk.
Sandstone
Sandstone
Granite dropstone
Granite dropstone
Granite dropstone
granitic orthogneiss
granitic orthogneiss
granitic orthogneiss
granitic orthogneiss
granitic orthogneiss
Leuco-tonalite
Tonalite
Trondhj emite
Tonalite
Tonalite
Bio-Hbl-Plag gneiss
Felsic gneiss
Augen gneiss
Augen gneiss
Mafic augen gneiss
Pegmatite
Pegmatite
Pegmatite
Felsic gneiss
Felsic gneiss
Augen gneiss
Metasediment
Amphibolite
Orthogneiss
Orthogneiss
Orthogneiss
Orthogneiss
Orthogneiss
Felsic gneiss
Orthogneiss
Charnockite
Charnockite
20 0673
20 1481
20 0873
20 0921
20 02898
20 1839
20 2398
20 097
20 1178
20 1558
20 0972
20 0932
20 0977
20 0975
20 1243
20 2709
20 1496
20 0 17
11 1659
20 2
051
6
0616
20 023
8
0
191
19 0496
20 0303
20 1283
20 1273
20 0397
20 1048
20 1987
20 0434
20 0581
20 0837
20 1384
20 0428
16 1071
18 0948
450 1191
588 2 158
592 1299
224 1543
1422 4534
922 321
898 4088
435 184.1
706 2003
727 2488
499 2135
474 1792
618 2247
563 2914
896 5286
558 2796
506 2469
554 0227
511 2087
1542 2936
228 0768
485 0274
154 0314
521 056
1085 3039
1109 2398
473 0608
1324 1659
1080
3
574
778 0861
1217 1117
737 1447
763 2 48
830 081
637 1773
657 188
542 0989
797 1147
857 1.147
881 1.147
375 1.147
2225 1.147
1609 1.147
1531 1.147
827 1.147
1201 1.147
1161 1 147
1096 1147
912
1
I47
1279 1.147
1425 1.147
1320 1.147
1748 1.147
1043 1.147
742 1.147
643 1.147
2208 1.147
284 1.147
578 1.147
253 1.147
1080 1.147
963 1.147
2570 1.147
2089 1.147
724 1.147
2097 1.147
1943 1.147
1544 1.147
2339 1.147
1274 1.147
1367 1.147
1570 1.147
1055 1.147
1303 1.147
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
174
I74
174
58
14
30
20
60
32
44
25
95
40
7
69
50
60
9
1
30
27
10
32
19
99
1
14
22
70
34
0
0
17
0
39
65
1
20
92
83
0
952
0
864
0
772
0
918
0
969
0
915
0
929
0
881
0
957
0
849
0
908
0
909
0
893
0
920
0
838
0
874
0 879
0
889
0
863
0
931
0
806
0
958
0
125
0 860
0
850
0
976
0 981
0
889
0
832
0
920
0
908
0
939
0
908
0
916
0
905
0
981
0
690
13
24
14
17
49
35
45
20
22
27
23
20
27
25
32
58
31
3
23
32
8
3
3
11
6
33
26
7
18
39
9
12
16
27
9
19
21
116
141
138
123
131
118
120
108
121
128
94
107
81
89
88
106
110
153
163
143
164
172
164
103
111
87
96
134
116
100
90
94
104
102
95
124
104
11
8
13
14
11
10
11
10
11
12
9
10
8
8
8
10
10
15
16
12
19
17
28
10
10
7
8
17
12
9
9
8
9
10
8
11
9
13
11
0.23 1.54
13.43 0.15 151
13.1 0.19 1.87
12.08
0
2
2
12.69 0.17 177
11 96 0.17 1.69
12.59
0
17 1.74
13.48
0
16 1.6
13.01
0
I7 1.71
12.82 0.19 1.91
13.25
0
19 1.89
13.13 0.25 1.99
12.75 0.3 178
12.51
0
18 1.82
13 0.16 1.62
13.16 0.27 1.62
13
55
0.18 1.83
-
~
-
12.56 0.18 1.77
13.57 0.17 1.68
13.29 0.16 1.52
13.21 0.14 1.41
12.33 0.19 1.94
12 0.33 2.01
12.19 0.19 1.95
12.11 0.18 1.83
12.07 0.27 1.74
12.28 0.19 1.87
12.34 0.23 1.9
12.58 0.22 2
49
100
99
100
97
100
100
99
100
100
100
66
36
100
100
100
36
100
-
~
~
-
100
90
100
100
37
100
100
42
99
-
~
-
~
68
82
Elev.
=
elevation;
Ns
and
Ni
=
number of spontaneous and induced tracks;
Nd
=
number
of
tracks counted in glass dosimetre;
ps,
pi
=
spontaneous and induced track density; ps1pi
=
ratio between
spontaneous and induced track density;
f
=
text for discussion, Cc
=
Correlation coefficient,
n
=
number of grains analysed; nl
=
number of track lengths
Age calculations by using decay constants of Steiger
&
Jager (1977)
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POST PERMIAN TECTONO-THERMAL EVOLUTION
-
14
455
:a
1
Fig.
3.
AFT results:
a.
AFT age vs elevation and elevation vs
mean track length
(MTL).
b.
There are no ages older than the
Jurassic volcanism at
c.
180
Ma, which
is
thought to have
caused total annealing
of
pre-Jurassic fission tracks. Erosional
unroofing caused cooling during mid-Cretaceous times and is
documented in very few single grain ages younger than
c.
80
Ma.
of
c.
100 Ma, the samples farthest inland of
c.
170 Ma; by
contrast, samples from between the latter localities show a
broad mixture of ages (Fig.
5).
The concentration
of
single
grain ages around 170 and
100
Ma in some of the samples
most probably reflect discrete tectono-thermal events, the
causes of which are discussed later.
AFT ages of similar altitudes increase from north-west to
south-east, i.e. further inland (Fig.
3).
This trend is
approximately perpendicular to the general strike of the
graben and the coastline of Dronning Maud Land. The gentle
dip of the Palaeozoic sedimentary rocks towards the
SE
probably indicates that the whole Heimefrontfjella underwent
post-Permian tilting or flexural uplift on a NE-trending axis.
In Sivorgfjella, this block rotation is documented in the
distribution of the
AFT
ages, in that the AFT ages follow
SW
inclined paleo-isotherms (Fig.
5).
All
samples taken from altitudes >2000 m (J1057, J1058,
J1500.
J1703,J1709, J2700) have AFTagesbetween 172
f
17
and 143
f
12 Ma. There is a concentration of single grain
ages between 160 and 170 Ma with an increasing component
of
younger ages toward lower altitudes. Because of very low
U-concentrations, only some samples revealed satisfactory
track length information. The longest mean confined track
length (13.57k 1.68
p)
came from the oldest sample.
Successive younger samples have mean confined track lengths
that are
up
to
c.
1 Fm shorter, indicating that they spent a
longer time in the partial annealing zone
(PAZ).
Samples with ages from
c.
140 to
c.
110 Ma (JI
105,
K42,
K44) display a very broad range in single grain ages and have
mean confined track lengths of 12.2 and 12 pm with broad
track length hstributions. They have a significant component
of short tracks with lengths <10 pm. The total number
of
11
0
50 100 150 200
AFT
age [Ma
2'5
r
"
-4
=ti+=
-9-
11 12 13 14
Mean track length [pml
0
Permian sandstones
0
Basement, Kottasberge
0
Basement, Sivorgfjelld N-Tottanfjella
%
Basement, Mannefallknausane
Fig.
4.
AFT
results:
a.
AFT age vs mean track length,
b.
AFT
age
vs standard deviation,
c.
mean track length vs standard
deviation.
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456
NW
J.
JACOBS
&
F.
LISKER
SE
Fig.
5.
The regional
AFT
age distribution indicates increasing ages towards the
SE
as well as a positive correlation between age and height.
Samples farthest south-east show only one age component of
c.
170
Ma, whilst samples
in
the very north-west show one age component
of
c.
100
Ma. Samples between show a mixture
of
these two age components. Mean confined tracks length are longest for the samples
with
one
single age component and shortest for samples with multiple age components.
AFT
ages can be grouped along palaeo-
isotherms (stippled lines). Palaeo-isotherms were derived by projecting the tilted Palaeozoic peneplain
of
Kottasberge into Sivorgfjella
(i.e. tilting
of
1-3"
toward the
SE).
Note vertical exaggeration. Bold sample numbers refer to samples that were modelled (cf.Fig.
7).
fission tracks
in
the samples comprise two dxtinct populations.
An older population of tracks was partially annealed, whilst a
younger generation of tracks with longer lengths
(>
13 pm)
accumulated during and after a second cooling stage.
Nine samples have AFT ages
of
c.
100 Ma or younger
(59.2./3, 14.2./5, K15, K19, K24, K30, K32, K53,
K55).
Theirmeantracklengthsvarybetween
13.3 and 12.1 pmwith
standard deviations between 1.4 and 2
pn.
All samples
experienced some degree of annealing but there are few tracks
<10 pm, whch would indicate major annealing.
To constrain the observed pattern
of
the apatite ages and
confined track lengths quantitatively, we applied the principles
of interpretation explained by Gleadow
et
al.
(1983, 1986)
and Green
et
al.
(1989). The data show a rapid cooling of the
oldest samples from temperatures above
c.
120-85°C at
c.
170 Ma. They cooled further to below 60°C at
c.
100-90 Ma, although ths period
of
cooling is not very well
constrained in all samples. The samples with the mixed ages
(c.
140-1
10
Ma) also display both cooling events but they
spent more time in the upper part of the PAZ, and thus have
shorter mean confined track lengths. The youngest samples,
close
to
the graben structure, show the most evidence for the
cooling event at 100-90 Ma. These samples indlcate another
cooling event during the Cenozoic. Cretaceous denudational
controlled cooling can be estimated to
c.
40°C near the graben
and
c.
20°C in the farthest inland area.
Forward modelling with MonteTrax (Gallagher 1995) has
been applied
to
test the thermal history derived from the
AFT
data by using the Monte Carlo approach for Durango apatite
(Laslett
et
al.
1987) by running 200 random thermal hstories
(Fig. 7). All samples
apartfromK3Ofitthemodelwithin*
1
(r
rejectance level.
Kottasberge
The 17 samples from Kottasberge were taken from a near-
vertical profile at Burdsbotnen (ten granitoid gneiss samples)
and Schivestolen (five sandstones and dropstones samples).
The AFT ages vary between 14 1
k
8
at the top of the profile
and
8
1
f
8
Ma at the bottom (Figs 3
&
5b). All but one sample
(W14.1./2) passed the
x2
test.
The five samples above the Palaeozoic unconformity at
c.
2100 m (Schvestolen: J8.2.94/6a, J8.2.94/6b, J8.2.9417,
J8.2.94/8, ST7) have the oldest ages between 141
*
8
and
116
f
11
Ma. The two sandstone samples (J8.2.94/7,
58.2.94/8) mark the upper and lower limit of the age spectrum.
They have the broadest range
of
single grain ages which is
thought to reflect the typical broad chemical compositional
http://journals.cambridge.org Downloaded: 11 Dec 2013 IP address: 190.7.157.90
POST PERMIAN TECTONO-THERMAL EVOLUTION
457
NW
SE
Fig.
6.
Burlsbotnen-profile, showing the positive correlation between AFT age and elevation. This profile resolves the two stage thermal
history less well than the regionally distributed samples in Sivorgfjella and Tottanfjella.
0
%
relative
36
error
17"4
10
20
Precision
[l/a]
K44
*.
52
%
relative error
167
0.
.
-.
.
-.
Precision
[lla]
10
20
J14.2.15
..
%
relative error
28
-2
O.......
10
20
30
40
.
Precision
[l/a]
Fig.
7.
Radial plots for three selected samples (cf. Fig.
5)
and numerical modelling using MonteTrax (Gallagher
1995).
a.
The topographically highest sample (52700) indicates one major cooling event at
c.
180
Ma, probably dating the cooling after Jurassic
volcanism. The sample remained within the partial annealing zone
(PAZ)
until final exhumation at
c.
100
Ma.
b.
During most
of
the
Jurassic and Early Cretaceous the sample from middle elevations
(K44)
remained in the upper part
of
the
PAZ
where not many fission-
tracks could accumulate. Exhumation at
c.
100
Ma brought the sample near to the field
of
total track stability but final cooling was
probably not earlier than Early Tertiary times,
c.
The topographically lowest sample
(J14.2.15)
has
no
Jurassic record. It only entered
the
PAZ
during the mid-Cretaceous unroofing event.
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J.
JACOBS
&
F.
LISKER
458
variation of apatites in sediments. The ages for the granite
gneiss dropstone only scatter withmthe lo-error range between
138
f
13 and 123
f
14 Ma.
None of the samples shows single grain ages above
c.
200
Ma,
indicating that they were thermally overprinted
during the Jurassic and have not retained any detrital
information. All pre-Jurassic tracks were entirely annealed
during the Jurassic thermal event. However, the duration of
heating must have been short, i.e.
<
1 Ma, because
VR
values
of coal seams in the sandstones have been determined as low
as
c.
0.5
(Bauer
et
al.
1997). This indicates that temperatures
of
80-130°C persisted long enough to anneal apatite fission
tracks but the duration of heating was not long enough
significantly to mature the coal seams (cf.3urham
&
Sweeny
1989).
The AFT ages below the Palaeozoic peneplain (12 samples
from 1900 to 1300 m)varybetween 128
f
12 and81
f
8 Ma.
The range in ages of the samples at 1300 m (110
f
10
to
8 1
f
8
Ma) is most probably controlled by differing chemical
composition of the samples as
is
also apparent from the broad
spread ofthe single grain ages between
c.
180 and
50
Ma. The
mean confined track lengths of the Kottasberge samples range
from 13.6 to 12
pm
with corresponding standard deviations
between 1.5 and 2.0 pm. These shortened lengths and the
broad standard deviations as well as the broad spread in single
grain ages of samples from similar altitudes indicate significant
annealing and a longer residence time of the samples in the
partial annealing zone.
For Kottasberge we suggest a similar thermal history to that
of northern Tottanfjelld Sivorgfjella, with a late Jurassic
episode of rapid cooling and a second cooling stage in the mid-
Cretaceous. Numerical modelling of the available fission-
track data using MonteTrax confirm this intcrpretation.
Manne
fallknausane
The samples W12.2.11 and W14.2.11 taken from
Mannefallknausane at
c.
900 m altitude have
AFT
ages of
124
*
11 and 104
f
9 Ma. Both mean track lengths of 12.6
and 12.3
pmwithstandarddeviationsof2
and 1.9 pmindicale
sigluficant annealing.
Discussion
K-Ar mica data indicate that western Dronning Maud Land
cooled to below
c.
300°C for the last time at
c.
470 Ma (e.g.
Jacobs
et
al.
1995).
A
stable platform should have been
formed during the Palaeozoic, when the basement was buried
by an unknown thickness of Permian sandstones. The next
major tectono-thermal event was associated with the break-up
ofGondwana, when westernDronning MaudLandwas affected
by the Bouvet mantle plume (White
&
McKenzie 1989). The
broader geological setting, marine geophysical and
palaeomagnetic data indicate that, in this part of Gondwana,
the Jurassic-Cretaceous break-up history can be differentiated
into three distinct stages
1. At about 180 Ma dynamic upl& above the Bouvet or
Karoo mantle plume was accompanied by initial rifting,
erosional unroofing of Permian sandstones andvolcanism
(White
&
McKenzie 1989). Large quantities of lavas are
known from the Explora wedge (Hinz
&
Krause 1982),
Vestfjella (e.g. Peters
et
al.
1991), and in smaller
quantities from localities farther inland, such as
Heimefrontfjella, Seniberget and Kinvanveggen. These
volcanic rocks are part of the Karoo volcanic province
whch was synchronous with the Ferrar magmatism along
the Pacific andTransantarctic marginoftheEast Antarctic
craton at
c.
180 Ma
(e.g.
Elliot 1992, Encarnacion
et
a1
1996). Iililial updoming and volcanism was probably
associated with magmatic underplating that caused
permanent uplift of the underplated areas (e.g. White
&
McKenzie 1989, Brown
et
al.
1994).
2. Dextral
transpressional/transtensional
movements
3
between East and West Gondwana followed from
c.
170
and
140
Ma (Henriet
&
Miller 1990). TranspressionaU
transtensional movements did not allow the full
development of the continental margin until the early
Cretaceous.
A three-plate drift configuration developed when South
America split from Africa at
c.
140 Ma. This led to
a
total reorganization
of
drift configuration, the production
of
major amounts of ocean floor, and to
an
extension of
the continental margin of Dronning Maud Land up to
350 km wide.
Especially the first and last tectonic episodes are reflected in
the AFT results of Heimefrontfjella. The Palaeozoic peneplain
proves that the basement cooled to surface temperatures
during the Palaeozoic. However, neither apatites from the
basement nor apatites from the sedimentary rocks show single
grain ages greater than
200
Ma. This indicates that the area
was affected by a short-lived thermal event of at least 100-
120°C during the Mesozoic, most probably caused by the
burial of 1500 to 2000 m of Jurassic lavas (depending on the
geothermal gradient) which ledto rising isotherms. However,
as discussed earlier, very low coal maturity within the
sedimentary cover indicates that this event was short-lived
(Bauer
et
al.
1997). This observation is in agreement with the
assumptions that the Ferrar-Karoo magmatism lasted for less
than
1
Ma(e.g. Elliot 1992).
ThePalaeozoicpeneplaincooled
quickly to temperatures of
c.
80°C and remained at such
teinperaturcs until mid-Cretaceous times.
Near thc coast, the initial formation of the continental
margin probably caused steep topography which enabled fast
erosion of large parts of the continental flood basalts, but not
as far inland
as
Heimefrontfjella, where no major unroofing
IS
recorded until
c.
100
Ma. In Heimefrontfjella the Palaeozoic
peneplain rcmained at temperatures of
c.
80°C until mid-
Cretaceous time, indicating that a substantial thickness
of
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... In the west, the Precambrian basement is unconformably overlain by remnants of late Carboniferous-early Permian sedimentary rocks of the Beacon Supergroup, now exposed at an elevation of c. 2000-2350 masl [22][23][24] . This unconformity is a part of a distinct paleosurface that can be traced over large parts of western DML (wDML) 9,22,25 , and possibly also to central DML (cDML), where mountain tops form a shallowly southward-dipping enveloping surface 16 . Furthermore, the same paleosurface can be identified as the Kukri erosional surface within the Transantarctic Mountains, separating the Devonian-Triassic section of the Beacon Supergroup from the Cambrian-Ordovician basement [26][27][28] . ...
... Furthermore, the same paleosurface can be identified as the Kukri erosional surface within the Transantarctic Mountains, separating the Devonian-Triassic section of the Beacon Supergroup from the Cambrian-Ordovician basement [26][27][28] . During the rifting of Gondwana, the Beacon sediments of wDML were in turn intruded and buried by up to 2 km of c. 183 Ma basaltic lavas, related to the Karoo mantle plume 15,25,29 . Substantial pre-Jurassic erosion of the Beacon sediments is recorded in southwest DML, where only a few meters of sediments separate the basement from the basalts 22 . ...
... Low-temperature thermochronological data are available from eight studies in western and central DML [14][15][16]25,[37][38][39][40] . The data that have been published so far include 203 apatite fission-track (AFT) analyses, 71 apatite (U-Th)/He (AHe) analyses, 14 zircon fission-track analyses, 11 zircon (U-Th)/ He analyses and 22 titanite fission-track analyses. ...
Article
Full-text available
The coast-parallel Dronning Maud Land (DML) mountains represent a key nucleation site for the protracted glaciation of Antarctica. Their evolution is therefore of special interest for understanding the formation and development of the Antarctic ice sheet. Extensive glacial erosion has clearly altered the landscape over the past 34 Myr. Yet, the total erosion still remains to be properly constrained. Here, we investigate the power of low-temperature thermochronology in quantifying glacial erosion in-situ. Our data document the differential erosion along the DML escarpment, with up to c. 1.5 and 2.4 km of erosion in western and central DML, respectively. Substantial erosion at the escarpment foothills, and limited erosion at high elevations and close to drainage divides, is consistent with an escarpment retreat model. Such differential erosion suggests major alterations of the landscape during 34 Myr of glaciation and should be implemented in future ice sheet models. The topography of the Dronning Maud Land Mountains, Antarctica, has become more pronounced and rugged since preglacial times due to higher glacial erosion at low elevations and lower erosion at high elevations, according to low-temperature thermochronology
... Previously published thermochronological data from the area are interpreted to reflect long-lasting monotonic cooling of the basement since the last orogeny in Early Paleozoic times [8][9][10]. Similar datasets from western and eastern Dronning Maud Land have revealed a much more complex thermal evolution of the mountain range, e.g., [11][12][13][14], including Late Paleozoic-Early Mesozoic peneplanation and syn-rift reburial, either due to sedimentary basins or by emplacement of Jurassic continental flood basalts. This apparently contrasting long-term tectonic and morphodynamic evolution is puzzling, and has raised several questions: Was the basement in central Dronning Maud Land also exposed to the surface during the Late Paleozoic-Early Mesozoic? ...
... Weyprechtfjella; ZH-Zwieselhøgda. Lineaments after Jacobs and Lisker [11], Bauer et al. [34] and Jacobs et al. [36]. ...
... During the early stages of Gondwana fragmentation, large amounts of continental flood basalts associated with the Karoo mantle plume were emplaced at c. 183 Ma [50][51][52][53][54]. Today, these are exposed in thicknesses up to c. 5 km within the Lebombo Monocline in southeastern Africa, whereas they are only preserved in thicknesses up to c. 1 km in Vestfjella and up to c. 400 m within the southwestern Maud Belt in western Dronning Maud Land [51,[55][56][57][58][59]. Based on thermochronological data, however, it has been suggested that western Dronning Maud Land was covered by up to 2 km of Jurassic continental flood basalts, extending at least as far east as Hochlinfjellet at c. 4 • E [11,14]. Exposures of continental flood basalts have not been reported further east in central Dronning Maud Land, but Jurassic mafic dykes in Petermannkjedene and at Schirmacheroasen have been associated with the Karoo magmatism [60,61]. ...
Article
Full-text available
The lack of preserved Mesozoic–Cenozoic sediments and structures in central Dronning Maud Land has so far limited our understanding of the post-Pan-African evolution of this important part of East Antarctica. In order to investigate the thermal evolution of the basement rocks and place constraints on landscape evolution, we present new low-temperature thermochronological data from 34 samples. Apatite fission track ages range from 280–85 Ma, while single-grain (U-Th)/He ages from apatite and zircon range from 305–15 and 420–340 Ma, respectively. Our preferred thermal history models suggest late Paleozoic–early Mesozoic peneplanation and subsequent burial by 3–6 km of Beacon sediments. The samples experienced no additional burial in the Jurassic, thus the once voluminous continental flood basalts of western Dronning Maud Land did not reach central Dronning Maud Land. Mesozoic–early Cenozoic cooling of the samples was slow. Contrary to western Dronning Maud Land, central Dronning Maud Land lacks a mid-Cretaceous cooling phase. We therefore suggest that the mid-Cretaceous cooling of western Dronning Maud Land should be attributed to the proximity to the collapse of the orogenic plateau at the Panthalassic margin of Gondwana. Cooling rates accelerated considerably with the onset of glaciation at 34 Ma, due to climate deterioration and glacial denudation of up to 2 km.
... Previous thermochronological work trying to estimate the thickness of the Jurassic continental flood basalts is restricted to Heimefrontfjella in southwestern DML (Fig. 2). Based on apatite fission track (AFT) data, Jacobs and Lisker (1999) suggested that up to 2 km of Jurassic basalts were emplaced, and later mostly eroded in Heimefrontfjella. Here we apply this approach to a much larger area, covering all of western DML in an attempt to define the eastern extent of the continental flood basalts. ...
... In Heimefrontfjella and Mannefallknausane, 37 Middle Jurassic-Late Cretaceous AFT ages all postdate the continental flood basalts, and are thus interpreted to have suffered complete annealing under 1.5-2 km of basalt, corresponding to temperatures of c. 80-130°C. Since the fission tracks were completely annealed, but the coal seams were not significantly matured, Jacobs and Lisker (1999) suggested that a shortlived Jurassic thermal event might reconcile these different temperature estimates. The Jurassic reheating was then followed by rapid exhumation during mid-Cretaceous times (Jacobs et al., 1995;Jacobs and Lisker, 1999). ...
... Since the fission tracks were completely annealed, but the coal seams were not significantly matured, Jacobs and Lisker (1999) suggested that a shortlived Jurassic thermal event might reconcile these different temperature estimates. The Jurassic reheating was then followed by rapid exhumation during mid-Cretaceous times (Jacobs et al., 1995;Jacobs and Lisker, 1999). Early Cretaceous-Eocene single-grain apatite (U-Th)/He ages from four of these samples document slow cooling until Cenozoic times, before accelerated cooling interpreted as flexural isostatic rebound and differential exhumation in response to the load of the developing ice shield (Emmel et al., 2008). ...
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The Dronning Maud Land Mountains form a c. 1500 km long, coast-parallel escarpment that possibly formed by flexural uplift during Jurassic rifting between East and West Gondwana. Contemporaneous to the rifting, considerable amounts of continental flood basalts, associated with the Karoo mantle plume, were emplaced at c. 183 Ma. The basalts are still widespread in South Africa, making up elevated topography, but are only preserved as smaller remnants in western Dronning Maud Land. By investigating the paleo-thermal effect of the basalts, we aim to constrain the extent and original thickness, as well as the subsequent erosion history of the Jurassic continental flood basalts. Thus, we have applied low-temperature thermochronological methods to 40 samples from western Dronning Maud Land. This has resulted in 34 new apatite fission track ages, ranging from c. 310 to 90 Ma, 31 apatite (U–Th)/He ages spanning from c. 400 to 50 Ma and, and 9 zircon (U–Th)/He ages between c. 650 and 200 Ma. Thermal modelling of 26 samples indicates variable thickness of the Jurassic basaltic cover. The greatest basaltic thicknesses are recorded in Heimefrontfjella and H.U. Sverdrupfjella, where up to c. 2 km are estimated. Thicknesses at Kirwanveggen, Hochlinfjellet, Midbresrabben and Ahlmannryggen range from c. 100 m to 600 m. Thickness variations are attributed to the proximity to the emplacement zone, possible pre-existing topography and syn-volcanic rift flank uplift. Since the continental flood basalt emplacement, two phases of enhanced cooling have been documented: 1) A Jurassic-Cretaceous cooling phase is attributed to reactivation of the Jutulstraumen–Penckgraben rift, the initial rifting and opening of the South Atlantic and enhanced chemical weathering and deep erosion due to a Jurassic temperate–subtropical climate. 2) Late Paleogene cooling is attributed to the transition from green house to ice-house conditions and ice-sheet initiation at the Eocene-Oligocene boundary. Post-Jurassic denudation of at least 2 km is suggested.
... The excess magmatism associated with the SDR formation of the MCP is very likely associated with mantle plume activity associated with the Bouvet-Karoo mantle plume (Jacobs and Lisker, 1999;Storey et al., 2013). We assume that the MCP SDRs formed at or near sea-level for the determination of water loaded subsidence from flexural backstripping. ...
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Using the example of the conjugate Mozambique-Antarctica rifted margins, we investigate how mantle plume magmatism interacts with extensional processes during lithospheric rifting and breakup. The presence of extensive plume related magmatic additions formed during rifting masks the edges of the continental margins, making it difficult to determine a tight conjugate margin restoration and hindering the evaluation of their pre-breakup evolution. Based on rift domain mapping from seismic reflection interpretation, crustal thickness mapping using gravity inversion, lithosphere thinning from subsidence analysis, and the testing of different plate kinematic scenario, we develop a tight initial fit of the conjugate Mozambique-Antarctica margins and describe their evolution by a three stage model. These three stages consist of: i) during early rifting, the filling of accommodation space created by continental crust thinning with Karoo related magmatism resulting in a hybrid crust that maintains bulk crustal thickness producing shallow bathymetry or emergence and allowing SDR formation; ii) the decrease of magmatic budget relative to extension rates leading to bulk crustal thinning and increased bathymetries; and iii) the transition to seafloor spreading with a steady state magmatic budget resulting in normal thickness (6,5±1km) oceanic crust. This study not only adds new constraints on the regional breakup of Gondwana but also presents a new multidisciplinary methodology for restoring magma rich rifted margins formed in the presence of mantle plumes and for improving the understanding of the nature of such hybrid magma-rich crust.
... It provides, firstly, a better model of the initial basin morphology, but also helps to understand erosion processes in the Denman and Scott ice streams. Full details of the method are provided in the supporting information [Jacobs and Lisker, 1999;Lisker et al., 2007;Lisker et al., 2014;Mory and Iasky, 1996;Olierook et al., 2016;Taylor et al., 2004]. ...
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Sedimentary basins beneath the East Antarctic Ice Sheet (EAIS) have immense potential to inform models of the tectonic evolution of East Antarctica and its ice-sheet. However, even basic characteristics such as thickness and extent are often unknown. Using airborne geophysical data, we resolve the tectonic architecture of the Knox Subglacial Sedimentary Basin in western Wilkes Land. In addition, we apply an erosion restoration model to reconstruct the original basin geometry for which we resolve geometry typical of a transtensional pull-apart basin. The tectonic architecture strongly indicates formation as a consequence of the rifting of India from East Gondwana from ca. 160-130 Ma, and we suggest a spatial link with the western Mentelle Basin offshore western Australia. The erosion restoration model shows that erosion is confined within the rift margins, suggesting that rift structure has strongly influenced the evolution of the Denman and Scott ice streams.
Chapter
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Data
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The geological overview map was compiled from 15 geological maps (1 : 25,000) and is based on Jacobs et al. 1996. The topographic basemaps were adapted from unpublished 1:250,000 provisional topographic maps, Institut f. Angewandte Geodäsie, Frankfurt, 1983. Part of the contour lines are from Radarsat (Liu et al. 2001).
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Marine sedimentary rocks drilled on the southeastern margin of the South Orkney microcontinent in Antarctica (Ocean Drilling Program Leg 113 Site 696) were deposited between ∼36.5 Ma to 33.6 Ma, across the Eocene–Oligocene climate transition. The recovered rocks contain abundant grains exhibiting mechanical features diagnostic of iceberg-rafted debris. Sand provenance based on a multi-proxy approach that included petrographic analysis of over 275,000 grains, detrital zircon geochronology and apatite thermochronometry rule out local sources (Antarctic Peninsula or the South Orkney Islands) for the material. Instead the ice-transported grains show a clear provenance from the southern Weddell Sea region, extending from the Ellsworth–Whitmore Mountains of West Antarctica to the coastal region of Dronning Maud Land in East Antarctica. This study provides the first evidence for a continuity of widespread glacier calving along the coastline of the southern Weddell Sea embayment at least 2.5 million yrs before the prominent oxygen isotope event at 34–33.5 Ma that is considered to mark the onset of widespread glaciation of the Antarctic continent.
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Zircon and apatite fission-track data of samples from three tectonic blocks are used to constrain the exhumation history of the Shackleton Range. Three discrete phases of cooling attributed to regional exhumation have been identified. The major phase occurred in the late Early Jurassic, preceding the break-up of Gondwana and the effusion of the Ferrar Dolerites. The second phase of cooling is estimated to have involved the denudation of ~2 km of material during the Late Cretaceous. This phase was probably related to the reorganisation of the plate pattern between East and West Gondwana, and was associated with the termination of Weddell Sea rifting. A third exhumation stage may be linked with the uplift of the Transantarctic Mountains since the early Cenozoic.
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Wegener Canyon represents a prominent northwest-trending system of deep incisions of variable depth, extending over about 85km from the shelf break to the continental rise. On the lower continental slope the canyon has been cut to a depth of about 1200km. It has a width of 4km at the bottom and 10km between its shoulder, and measures about 25km in length. It cuts through the northeast-trending, morphologically very prominent steep slope of the Explora Escarpment. The main topographic features of the lower Wegener Canyon are three cliff-like scarps. On the gently inclined platform of the middle slope the canyon diverges into several morphologically less prominent tributaries, only one of which cuts into the upper slope and shelf. Mesozoic sediments were dredged at 8 stations on the scarps on the southwestern flank of Wegener Canyon. Volcaniclastic sandstones and mudstones, nannofossil oozes, and claystones rich in organic matter were recovered. -from Authors
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Fission track dating is a new approach to the interpretation and quantitative modelling of thermal histories of sedimentary basins for hydrocarbon resource evaluation. This technique depends on the observation that annealing of fission tracks in minerals, like the generation and maturation of hydrocarbons, is a function of temperature and time. The temperature interval over which track annealing occurs in the mineral apatite, a common detrital mineral in sedimentary rocks, is virtually identical (60 degree to 125 degree C) with that required for the maximum generation of liquid hydrocarbons. The unique advantage of the fission track method is that it can give information not only on maximum palaetemperatures, but also their variation through time. Fission track analysis has the potential of giving a new, quantitative perspective on the temperature history of rocks, which should have an important impact on techniques of petroleum exploration.
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Chapter
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