mountain building (14) Flashcards
American Cordillera and Alpine-Himalaya
Young mountain belts
Orogenesis
The processes that collectively result in the formation of mountains
Orogeny
A specific episode of orogenesis (mountain building)
Collisional mountain
A mountain in which compressive horizontal forces have shortened and thickened the crust. Most major mountain belts are of this type.
Four regions of subduction zones
Volcanic arc
Deep-ocean trench
Forearc region
Back-arc region
Volcanic arc
Built on the overlying plate
Deep-ocean trench
Subducting slabs of oceanic lithosphere bend and descend into the asthenosphere
Forearc region
Located between a trench and a volcanic arc
Back-arc region
Located on the side of the volcanic arc opposite the trench
Volcanic island arc
A chain of volcanic islands generally located a few hundred kilometers from a trench where there is active subduction of one oceanic plate beneath another
Continental volcanic arc
Mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent. Examples include the Andes and the Cascades.
Deep-ocean trench
A narrow, elongated depression of the seafloor
Forearc
A subduction zone located between a deep-ocean trench and an associated volcanic arc
Back-arc
The backside of a volcanic arc when viewed from the trench
Back-arc basin
A basin that forms on the side of a volcanic arc away from the trench
Accretionary wedge
A large wedge-shaped mass of sediment that accumulates in subduction zones. Here sediment is scraped from the subducting oceanic plate and accreted to the overriding crustal block
Forearc basin
The region located between a volcanic arc and an accretionary wedge where shallow-water marine sediments typically accumulate
Batholiths
Magma that crystallizes at depth to form massive collections of igneous plutons, most batholiths consist of intrusive igneous rocks that range in composition from granite to diorite
What does island arc-type mountain building result from?
The steady subduction of oceanic lithosphere under oceanic lithosphere
What does Andean-type mountain building result from?
Subduction beneath a continent rather than oceanic lithosphere
What is the result of active continental margins of Andean-type mountains?
Long-lasting magmatic activity and crustal thickening
What does Alpine-type mountain building result from?
Episodes of mountain building that occur where two continental masses collide
Suture
A zone along which two crustal fragments are jointed together. For example, following a continental collision, the two continental blocks are sutured together
Ophiolites
The unique structure of these pieces of oceanic lithosphere help researchers identify the collision boundary
Fold-and-thrust belt
A region within a compressional mountain system where large areas have been shortened and thickened by the processes of folding and thrust faulting, as exemplified by the Valley and Ridge province of the Appalachians
How were the Himalayas built?
50-30 million years ago
India collided with Asia
Taconic Orogeny
Caused the volcanic arc and ocean sediments located on the upper plate to be accreted to the edge of the larger continental block
Acadian Orogeny
A second episode of mountain building (about 350 million years ago) continued closing of this ancient ocean basin resulting in the collision of. a microcontinent with North America
Alleghanian Orogenty
Occurred between 250 and 300 million years ago when Africa collided with North America
Terrane
A crustal block bounded by faults, whose geologic history is distinct from the histories of adjoining crustal blocks
Microcontinents
A relatively small fragment of continental crust that may lie above sea level, such as the island of Madagascar, or that may be submerged, as exemplified by the Campbell Plateau near New Zealand
Fault-block mountains
A mountain that is formed by the displacement of rock along a fault
Basic structure of Basin and Range Province
Fault-block mountains (east west stretching)
Delamination
Upwelling and lateral spreading of hot mantle rock, which produced tensional forces that stretched and thinned the overlying crust
What does isostasy cause?
Causes mountains to rise, so they remain mountainous long after the tectonic processes that initially created them have ceased
What happens if tectonic processes raise a mountain belt “too high”?
The rock at is core will become too weak to support the load and the mountain will spread
Isostasy
The concept that Earth’s crust is “floating” in gravitational balance upon the material of the mantle
Isostatic adjustment
Compensation of the lithosphere when weight is added or removed. When weight is added, the lithosphere responds by subsiding, and when weight is removed, there is uplift
Gravitational collapse
The gradual subsidence of mountains caused by lateral spreading of weak material located deep within the mountains
