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A fold and thrust belt (FTB) is a series of mountainous foothills adjacent to an
orogenic belt An orogenic belt, or orogen, is a zone of Earth's crust affected by orogeny. An orogenic belt develops when a continental plate crumples and is uplifted to form one or more mountain ranges; this involves a series of geological processes collec ...
, which forms due to contractional
tectonics Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents k ...
. Fold and thrust belts commonly form in the forelands adjacent to major orogens as deformation propagates outwards. Fold and thrust belts usually comprise both folds and
thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...
s, commonly interrelated. They are commonly also known as thrust-and-fold belts, or simply thrust-fold belts.


Geometry

Fold and thrust belts are formed of a series of sub-parallel thrust sheets, separated by major thrust faults. As the total shortening increases in a fold and thrust belt, the belt propagates into its foreland. New thrusts develop at the front of the belt, folding the older thrusts that have become inactive. This sequential propagation of thrusts into the foreland is the most common. Thrusts that form within the belt rather than at the thrust front are known as "out-of-sequence".


Map view

In map view, fold and thrust belts are generally sinuous rather than completely linear. Where the thrust front bulges out in the direction of tectonic transport, a ''salient'' is formed. Between the bulges the areas are known as ''recesses'', ''reentrants'' or sometimes ''embayments''.


Thrust belts


Africa


Asia


Australia


Europe


North America

Much of this table is adapted from Nemcok ''et al.'', 2005Nemcok, M., Schamel, S. & Gayer, R. 2005. Thrustbelts - Structural Architecture, Thermal Regimes and Petroleum Systems. Cambridge University Press


South America


References


External links


Fold and thrust belts publications
Orogeny Geological processes {{tectonics-stub