Contractional tectonic regimes Flashcards
What four factors make up contractional tectonic regime shortening?
Volume loss, pure shear (horizontal shortning with vertical thickening, buckling, movement on contractional faults with folding related to the movement
Define thrust fault
Dip-slip fault where the upper block, above the fault plane, moves up and over the lower block
Where is most shortening in contractional orogenic belts localised?
On thrust faults
Describe thin-skinned tectonics
Deformation in the foreland where thrust systems are restricted to the cover rocks, the basement is not involved
Describe thick-skinned tectonics
Deformation in the higher metamorphic grade hinterland where the thrust systems are thicker and the basement is involved
Describe wrinkle ridges
Local contraction features
Formed during basin-localised flexure
What are lobate scarps indicative of?
Global contraction due to net cooling of the planetary interior
The surface expression of antiforms formed by the tips of reverse faults that break the surface
Define thrust
A predominantly low-angle fault or shear zonewith a predominantl reerse dip-slip sense of movement
Describe a thrust in rocks that young upwards
The thrust beings older rocks over younger rocks
Define a thrust nappe or thrust sheet
The hanging wall of a low-angle, large displacement thrust that is wide compared to its thickness
When is a thrust nappe discontinuously exposed?
When it has been eroded through
What structures are formed by the erosion of a nappe?
The erosional remnant of a nappe is a klippe and the erosional hole exposing the unts benearth the thrust is a tectonic window
Are the thrust sheet and footwall allo/autochthonous?
The thrust sheet is allochthonous because it is transported and the footwall is autochtonous because it is close to its orginal location
Describe the positions of flats and ramps in the series of steps as a low-angle thrust fault passes up through the stratigraphy
The flat is where the fault runs parallel to the layering and the ramp is where it cross-cuts and truncates the layering
For each hanging wall ramp there must be a corresponding footwall ramp
See diagram in book
Define frontal ramps
Ramps that form perpendicular to the main thrust transport direction
Define oblique ramps
Ramps that are oblqiue to the transport direction and are oblique-slip reverse faults
Define lateral ramps
Parallel to the movement direction and are strike-slip faults
They transfer slip from one frontal ramp to another, therefore they are transfer faults or tear faults when sub-vertical and cutting through the hanging wall
Define an imbricate fan in relation of thrusts
Where individual thrust sheets overlap, they are a set of listric faults with the same sense of slip
The merge down on a sole or floor thrust or up onto a roof thrust, a duplex is formed when they are bound by both
Define a decollement or basal detachment
The major floor thrust at the base of a stack of thrust nappes and/or imbricate system
Describe a leading imbricate fan
Where the maximum slip is on the frontal fault
Describe a trailing imbricate fan
Where the maximum slip is on the most internal fault
Describe a horse
An internal block of an imbricate fan that is bound completely by faults
In which direction do thrust duplexes form and how do they form?
The form sequentially and usually towards the foreland
A horse is formed in the footwall, it gets displaced forwards, becomes inactive and then a new horse is formed in the footwall
In which direction do the ramps binding the horses dip?
Towards the hinterland
