RAMP FLAT THRUST GEOMETRY

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 Thrust surfaces usually have stair-case geometry.

  • FLAT

    • Sub-horizontal or gently-dipping (at the time of initiation) part of a thrust.

    • Fault segments running parallel to each other

  • RAMP

    • The moderately-dipping part (at the time of initiation) of a thrust.

    • Ramps usually climb up-section across stiffer layers.

    • Fault segments cutting across the beddings

      (Flat and ramp)

  • Hanging wall flat (HWF): The portion of the thrust where the fault is parallel to the bedding surfaces on the hanging wall side.

  • Hanging wall ramp (HWR): The portion of the thrust where the fault is oblique to the bedding surfaces on the hanging wall side.

  • Footwall flat (FWF): The portion of the thrust where the fault is parallel to the bedding surfaces on the footwall side.

  • Footwall ramp (FWR): The portion of the thrust where the fault is oblique to the bedding surfaces on the footwall side.


  • Frontal ramp: Strike of the ramp is perpendicular to the regional tectonic transport direction.

  • Lateral ramp: Strike of the ramp is parallel to the regional tectonic transport direction.

  • Oblique ramp: Strike of the ramp is oblique to the regional tectonic transport direction.


THRUST VERGENCE

  • Thrust vergence refers to the direction towards which hanging wall moves relative to footwall.

  • Thrust faults are most common in fold-thrust belts (FTBs) typical of contractional orogenic setting.

  • The un-deformed sedimentary basin in front of an FTB is called foreland and the internal part of an FTB is known as hinterland.

  • FORELAND : towards transport direction

  • HINTERLAND : away from transport direction


  • Pop-up: Portion of hangingwall block that has been uplifted by a combination of forethrust and backthrust


  • Thrust sheet: In low angle thrusts, the areal extent of the hanging wall is much greater than thickness. Such a tabular- shaped hanging wall block is called a thrust sheet.

     CHARACTERISTICS OF REVERSE FAULT

  • Thrust fault: a type of reverse fault with dip angle less than 450

  • Overthrusting : when hanging wall move relative to footwall

  • Underthrusting : when footwall move relative to hanging wall

  • Nappe:

    • thrust sheets with significant movement (>10 km) relative to footwall.

    • these are allochthonous rock units that has displaced from some distant places and rests upon an autochthonous rock unit

  • Klippe : remnant portion of nappe after erosion (Outlier)

  • Window : sometimes nappe may eroded deeply through which rocks below becomes visible known as window, (Inlier)

  • Root zone: The region in the hinterland direction where a thrust sheet passes into the subsurface is known as root zone.


  • Inlier : Older rocks are surrounded by younger rocks

  • Outlier : Younger rocks are surrounded by older rocks

     THRUST SYSTEMS

  • Thrust systems are made up of group of link thrusts that are geometrically, kinematically and mechanically related

  • DUPLEX

    • Group of thrust linking a floor-thrust (sole thrust) at the base to a roof thrust at the top

    • Base : floor thrust or sole thrust

    • Top : roof thrust

  • IMBRICATES

    • A closely related array of thrusts all of which merge into a floor thrust is called imbricate thrust system

    • No roof thrust found


  • HORSE : A rock that is surrounded by all sides from fault

  • FAULT BENT FOLD

    • Ramp related fold in thrust fault

    • Ramp and fold formed simultaneously

    • Develops as the hanging wall of a thrust is transported through a ramp

    • Forelimb is shorter and steeper than backlimb

    • Backlimb is parallel to footwall ramp

  • FAULT PROPAGATION FOLD

    • Develops at the termination of a thrust

    • Fold formed after development ramp


  • OTHER TYPES

    • Decollement and Detachment faults are low angle faults

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