Geology Reference
In-Depth Information
Fig. 12.11
Burial, temperature
history and surface heat-flow at
three boreholes where vitrinite
reflectance data are available. (
A
)
At M
70
65
60
55
bandaka with no erosion.
(
B
)AtM
'
50
bandaka for the
2 erosion stages, 8,000 m during
Paleozoic and 4,000 m during
Jurassic. (
C
) At Dekese with
4,000 m erosion during Jurassic.
(
D
) At Samba with 3,000 m
erosion and an additional heat-
source during Cretaceous. (
E
)
The heat-flow evolution with
geological time. The vitrinite
reflectance data are shown with
the modelled profiles in
Fig.
12.10
'
45
40
E
35
30
0
2000
4000
6000
8000
10000
4
0
°C
80°C
120°C
160°C
D
700
600
500
400
300
200
100
0
0
2000
4000
6000
8000
10000
4
0
°C
80°C
120°C
C
160°C
700
600
500
400
300
200
100
0
0
2000
4000
6000
8000
10000
4
0
°C
80°C
120°C
160°C
B
700
600
500
400
300
200
100
0
0
2000
4000
6000
8000
10000
4
0
°C
80°C
120°C
A
700
600
500
400
300
200
100
0
Time (Ma)
surface heat-flow increases to a maximum of 70 mW m
2
,
which affects the lithospheric thermal regime for about
200 Ma (Fig.
12.11e
) during the lower Paleozoic: therefore,
it is possible to obtain higher temperature gradient during the
Paleozoic burial stage and increase the maturation of the
Neo-Proterozoic with respect to the Paleozoic (blue curve
labelled MBK 2 stages in Fig.
12.10
). The surface heat-flow
displays two other peaks related to the erosion stages, which
do not affect the lithospheric thermal regime and the matu-
ration. The present-day temperature gradient is different for
the two scenarios at M
'
bandaka 1 (Fig.
12.2
): the
“
no ero-
sion
scenario is characterized by a higher porosity and
therefore a lower thermal conductivity than the scenario
with high erosion for a same present-day heat-flow. This
”
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