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The aim of this study is to investigate the shal-
low thermal field differences for two differently aged pas-
sive continental margins by analyzing regional variations in
geothermal gradient and exploring the controlling factors for
these variations. Hence, we analyzed two previously pub-
lished 3-D conductive and lithospheric-scale thermal models
of the Southwest African and the Norwegian passive mar-
gins. These 3-D models differentiate various sedimentary,
crustal, and mantle units and integrate different geophysi-
cal data such as seismic observations and the gravity field.
We extracted the temperature–depth distributions in 1 km
intervals down to 6 km below the upper thermal boundary
condition. The geothermal gradient was then calculated for
these intervals between the upper thermal boundary condi-
tion and the respective depth levels (1, 2, 3, 4, 5, and 6 km
below the upper thermal boundary condition). According to
our results, the geothermal gradient decreases with increas-
ing depth and shows varying lateral trends and values for
these two different margins. We compare the 3-D geologi-
cal structural models and the geothermal gradient variations
for both thermal models and show how radiogenic heat pro-
duction, sediment insulating effect, and thermal lithosphere–
asthenosphere boundary (LAB) depth influence the shallow
thermal field pattern. The results indicate an ongoing process
of oceanic mantle cooling at the young Norwegian margin
compared with the old SW African passive margin that seems
to be thermally equilibrated in the present day.