Mountain Building Flashcards
how are mountain belts formed?
At young divergent plate boundaries where lithosphere is stretched + thinned by tensional stress
At convergent plate boundaries (due to shortening + thickening of lithosphere)
what plate boundary is associated in formation of rift valleys?
divergent
how are rift valleys created?
Mantle plume domes upward
Crustal tension causes lithosphere to thin + crack
Lithosphere blocks slide down on normal faults
Volcanism often accompanies crustal stretching
waht are fault-block mountains?
tilted edges of large crustal blocks
what are horsts?
elongated, high-standing blocks of crust bounded by faults
what are grabens
formed by downward displacement of fault-bounded blocks (tilted “half grabens” are produced on either side of a rift)
with continued spreading what do rifts become
rifts evolve into ocean basins
what are largest mountain belts associated with?
Largest mountain belts are associated w/ convergent plate boundaries (compressive stress dominant, and crustal shortening + growth of volcanoes are the main causes of uplift)
what are the 2 types of convergence?
Aleutian-type (oceanic-oceanic convergence, island arc)
Andean-type (oceanic-continental convergence, continental arc)
what is Aleutian-type convergence?
Convergence of two oceanic plates (cool, dense, old, oceanic plate subducted under warmer, more buoyant, young, oceanic plate)
Forms island arcs
what is Andean-type convergence?
Lots of compressive stress (as plates move toward one another + oceanic plate is subducted under continental plate)
Deformation, metamorphism + uplift of continental margin
Continental volcanic arc develops
Accretionary wedge of sediments are scraped off the subducting oceanic plate + plastered against the edge of the continental block
what is continental collision
Two continental lithospheric plates crash together as ocean basin is consumed by subduction
Neither will subduct (both plates too “light”)
Resulting in crustal thickening + very high mountains
Why does uplift occur at convergent boundaries?
Effects of Isostasy: height of any given point on surface of continent is partially dependent lithospheric thickness
Envision a series of wooden blocks floating in water (thin blocks float low, thick blocks stand very high)
Similar way, in regions of lithospheric thickening, Earth’s surface stands higher than in thinner lithosphere
Another consequence is that high mountains also have deep “roots”
what is isostatic adjustment?
the process of establishing a new level of gravitational equilibrium when the thickness of the “floating “ plate changes (usually due to thickening of rock or piling of other material such as ice on top, or the removal of this material)
Compression associated w/ convergence with well-developed synclines + anticlines
commonly produces extensive folding
Mountain belts produced by compression, faults tend to be ______
reverse faults
what is allochthonous terranes?
crustal blocks (microcontinents, island arcs, oceanic plateaus) w/ a distinct geologic history that have drifted from elsewhere
what are accreted terranes
Terranes become accreted terranes when they collide w/ continental margin
Owing to their inability to be subducted
what is a orogen?
deformed belt in a continental landmass linked to mountain building associated w/ plate convergence and/or collision (ancient orogens provide evidence of mountain building in the past)
what is a orogeny
refers to the events leading to , and involving, severe structural deformation associated with mountain building
what is teh Wilson Cycle
Cycle involving continental breakup, ocean basin development, and ocean basin closure is called the Wilson Cycle (named after J. Tuzo Wilson)
List the stages of the Wilson cycle
Rifting occurs + sediment accumulates on passive margins
Plate motion changes, basin closes, continents converge
Subduction of oceanic slab leads to Andean-type volcanic arc
Continental blocks eventually collide, forming a mountain belt
Mountains erode, crust thins, setting up conditions for a new cycle
