Deep controls on intraplate basin inversion - Intraplate Earthquakes - page 270

Iceland plume and the initiation of the NAA, are actually directly incompatible with the
observed secondary inversion deposition patterns (Nielsen et al ., 2007 ) . These authors went
on to point out that their stress modelling argued against a plume model for the tectonic
evolution of the North Atlantic in the Paleocene. Rather, they proposed that magmatism
and other North Atlantic tectonic events around this time were the consequence of changes
to plate boundary interactions, specifically an embryonic strike-slip initiation of the North
Atlantic plate boundary between Greenland and Scandinavia.
Third, we might presume that structures formed during pre-inversion rifting must also
play a role in primary basin inversion, specifically that they should be favourably orien-
tated with respect to the build-up of the causative tectonic convergence stress field. The
importance of compressional reactivation of faults formed during extensional basin forma-
tion was noted by Buiter and Pfiffner ( 2003 ) and investigated in more detail in numerical
experiments by Hansen and Nielsen ( 2003 ) . By adjusting the degree of strain softening in
three models they found that faults produced during rifting that remain weak, and thereby
easily reversible, have the potential to influence profoundly the load-carrying capacity of
the lithosphere and hence the future deformation history. The overall structural elements
of the inverted rifts (a central inversion ridge flanked by asymmetrical marginal troughs)
remained robust features of their models, similar therefore to the model of Nielsen and
Hansen ( 2000 ) . Regarding the orientation of reactivated structures in central Europe, it may
simply be an intraplate setting fortuitous for basin inversion, with basement trends basically
formed during late Paleozoic orogenesis (e.g., Ziegler et al ., 2006 ) being amenable to the
particular plate boundary force derived stresses related to later collision with Africa.
An interesting result of the stress model presented here is that the potential energy
stresses, expressed as effective stress ( Figure 10.2 a ), are very small in the region of Europe
that tends to have been most affected by intraplate basin inversion. This is the zone running
from the North Sea and Denmark southeastwards to the Black Sea, corresponding to
the “Trans-European Suture Zone” (TESZ; e.g., Pharaoh et al ., 2006 ) between cratonic
lithosphere to the east and mostly younger accreted terranes to the west. The present-
day stress field in this area is not one dominantly reflecting the NAA (which in any case
was not yet in existence at the time of basin inversion) but has more to do with intrinsic
lithosphere structure in the TESZ (which was already in place at that time). Though pre-
existing structure and thermal refraction effects must have played a role, it is possible that
the absence of a potentially counteracting “background” potential energy stress field in
this area (i.e., similar to what is computed for the present day) may have been a factor in
allowing the plate boundary derived stress field to be highly effective in causing intraplate
deformation in this part of Europe.
10.5 Summary and conclusions
According to plate tectonics, lithospheric plates are essentially rigid with deformation
resulting from interactions along (or very near) plate boundaries. In this respect basin
inversion is an intermediate-scale manifestation of continental intraplate deformation,