Print this pageGeometry of a Concealed Trap Below the Riwat 
Thrust
,
Himalayan Foreland, Pakistan
JADOON, ISHTIAQ A. K.
The foreland-directed Riwat thrust is one of the major faults in the
Himalayan foreland of north Pakistan. Based on seismic-reflection data, the
Riwat thrust developed as a roof thrust of a hinterland-vergent tectonic wedge
(triangle zone) underlain by evaporites. The Riwat thrust propagates up-section
from a depth of about four km at the base of the Siwalik Group. At this depth,
it merges into a hinterland-vergent blind thrust that propagates up-section as a
ramp from Eocambrian evaporites covering the basement at a depth of about six
km. Bounded between this set of conjugate faults, a tectonic wedge of Eocambrian
(evaporites) to Neogene strata is thrust towards the hinterland to form a
triangle zone.
The roof thrusts of triangle zones were widely mapped as back-thrusts.
Recognition of hinterland motion of tectonic wedges as in the Riwat thrust
triangle zone with a trap forming geometry below a foreland-directed thrust is
important for the interpretation of particular fold belts and for hydrocarbon
exploration. These structures could be predicted by the surface geology data
where hinterland vergence of a fold below a thrust
is apparent. However, seismic
reflection data apears to be critical for their recognition.