Week 12 Flashcards
Orogeny =
structural processes at convergent plate boundaries
Most continental basement = old orogenic belts
How to old orogenic belts achieve their high elevations and topographic relief?
High elevations = isostasy
Topographic relief = erosion
- loading and more subsidence
- thrust propagation
Plate tectonics
= rigid plates moving on a sphere
Doesn’t explain patterns of behaviour in continents
Thrust =
originally low angled contractional fault where one rock body moves over another via fault surface
= net shortening/thickening/strata duplication
e.g. Moine thrust zone, Scotland
Hinterland characteristics
Penetrative deformation
Thick-skinned
Increased shortening/deformation/metamorphism towards suture
Leucogranites
Foreland characteristics
Localised deformation
Syn-collisional sediments in flexural trough
- loaded = flexes = ‘forebulge’ + foreland BASIN
Thin-skinned i.e. no basement
Allochtonous =
not in original position
Autochthonous =
in place of deposition
What are allochthonous and autochthonous sediments separated by?
Décollement
How are klippen/fensters formed?
When allochthonous thrust sheets/nappes are eroded
In what direction do brittle kinematic indicators form?
Mainly in dip direction
N.B. On fault SURFACE
What controls the duplex type?
Amount of slip vs horse length
SMALL = ‘hinterland’ dipping = normal
LARGE = ‘foreland’ dipping
INTERMEDIATE = ‘antiformal’ stack
Foreland basin =
sedimentary basin between mountain chain and adjacent carton
- form along continental interior flanks of continental margin orogenic belts
Processes in the foreland basin
- STRUCTURAL THICKENING
= thrust stacks and tectonic subsidence
e.g. Zagros, Iraq - FLEXURE of foreland basin
= marine/non-marine
Types of collision boundaries
- Continental-continental collision
2. Andean type active continental margin
Types of folds formed by thrusts
Fault-bend-fold
Fault propagation fold
Detachment fold
Trishear folds
Detachment fold =
layers above deform more than substrate
Piggy-back formation
When younger horses thrust over older horses
What is the tip of a fault/fold?
Where displacement = 0
The edge of the fault plane
Where do back thrusts form?
Common at FRONT of foreland thrust belts in ‘triangle zone’
= thrusts in opposite direction to general thrusting direction
Soft vs hard linkage
Hard linkage = tear/transfer faults
Displacement along single faults decreases along its strike to 0, but overall shortening constant due to TRANSFER ZONES
Sedimentation in thrust belts
Foreland = oldest deposits = fine-grained, turbiditic
- Mountain belt not established = low sediment supply
- Later = deposition of shallow water/continental = abundant
N.B. Front of thrust belt = ?barrier to sedimentation e.g. S Pyrenees deposited laterally // to thrust belt front
Molasses =
conglomerates/sandstones deposited as alluvial fans/lacustrine deposits
e.g. post-tectonic flysch = interbreeds of marine shales/greywacke if submerged under water
Example of petroleum in thrust belts
Oligocene-Pliocene E Venezuela, Columbia
Canadian Rockies
