mountain building Flashcards
mountain building
- orogenesis (greek) oros = mountains, genesis = to come into being
- the process that collectively produce a mountain belt
- result of plate tectonics
- origin is plate boundaries
mechanism 1. horizontal compressional forces
that have shortened and thickened the crust, producing folding and thrust faulting of preexisting sedimentary rocks and crystalline crustal fragments
mechanism 2. horizontal tensional stress
- causes the upper crust to be broken along normal faults, while the lower crust deforms by ductile stretching
- as a result they form fault block mountains
types of mountains
- unwarped mountains, ex black hills
- volcanic mountains, ex White Island
- fault block mountains, ex basin and range California
- folded or compressional, ex Himalayas
features of subduction zones
- deep oceanic trench
- volcanic arch
- forarch region
- backarc region
deep oceanic trench
- where two plates converge and one is subjected beneath the other
- a region where subjecting oceanic lithosphere bends and descends into the asthenosphere
volcanic arc
- built upon overlying arch
- two types
1. volcanic island arc, oceanic- oceanic plates convergence, ex Aleutian Islands. - basin between the arc and mainland
2. continental volcanic arc, oceanic- continental plates convergence. - area on the continental behind the arc
forearc region
between the trench and the volcanic arc
backarc region
located on the side of the volcanic arc opposite of the trench
island arc type mountain building
- steady subduction of oceanic lithosphere
- periodic volcanic activity, emplacement of plutons at depth, the accumulation of sediments scraped from the subduction plate, gradually increase the volume of the arc, resulting in mountainous topography.
Andean type mountain building
- collision between continental and oceanic plates
- located along the active continental margins around Pacific Ocean
stage 1
passive margin,
- accumulation of sediments
stage 2
passive margin transforms into active margin
- beginning of subduction, compressional forces between two colliding plates deform rocks by bending and fracturing
stage 3
building a continental volcanic arc, emplacement of plutons(batholiths)
-subduction and partial melting of mantle rock generates primary magmas
stage 4
- development of an accretionary wedge
- an accretionary wedge is a chaotic accumulation of deformed sediments and scraps of oceanic crust
- prolonged subduction may thicken an accretionary wedge enough so it protrudes above sea level, forming a mountain
stage 5
- formation of a forearm basin
- the growing accretionary wedge acts as a barrier to sediment from the arc to the trench
- it forms a region called a forearc basin of relatively undeformed layers of sediment and sedimentary rock
stage 6
- subduction ends
- subduction ends and it is followed a period of uplift and erosion
- uplifting and erosion exposes batholith consisting of numerous erosion
- ex Sierra Nevada batholith - former volcanic arc
- California’s coast ranges constitutes the accretionary wedge
- great valley represents the remains of the forearm basin
cordilleran type mountain building
- terranes
- place- subduction zone along active continental margin
- process- collision and merge ( or accretion) of large crustal fragments
nature of terranes
-carry embedded oceanic plateaus, island arcs, and sea mountains
- plateaus or islands arcs may be too large and too buoyant toe subducted
- so they collide and merge ( or accrete) with continental margins
- accreted crustal blocks
once scattered throughout the eaters pacific as oceanic plateaus, islands arcs and sea mountains
alpine type mountain building
continental collisions
- two lithospheric plates, both carrying continental crust
- result in the devolvement of compressional mountains
ex collision between Australian-indian and euro asian plates created himalayas mts. Himalayas are compressional mountains
- most compressional mountains exhibit a region of intense folding and thrust faulting called a fold and thrust belt
suture zone
zone where two continents collide
continental collisions major events event 1
passive continental margin converts into an active margin
major event 2
subduction zone is born with an Andean type volcanic arc growing above it
