EARTHSC 1121 Lecture 11: Metamorphic Rocks and Mountain Building

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Metamorphic Rocks and Mountain Building
Mountains
A result of tectonic activity
Mountain building exhumes deep crust and subjects rock to stress, resulting in economic
resources
Key processes:
oUplift
oDeformation
oMetamorphism
Metamorphic Rocks
Metamorphism occurs in the solid state
Metamorphic: changed from an original “parent”
oMeta = change
oMorph = form or shape
Parent rocks are called “protoliths
Metamorphism can occur to any protolith
Metamorphism
Protoliths undergo pronounced changes in…
oTexture
oMineralogy
Due to change in physical or chemical conditions
oBurial
oTectonic stresses
oHeating by magma
oFluid alteration
Mountain Belts
Mountains frequently occur in elongate, linear belts
Mountains are constructed by tectonic plate interactions in a process called orogenesis
Causes of Orogenesis
Mountain building is driven by plate tectonics
oConvergent plate boundaries
oContinental collisions
oRifting
Orogenesic phases may last several hundred Ma
Ancient mountains are deeply dissected by erosion
Convergent tectonic boundaries create mountains
oSubduction-related volcanic arcs grow on overriding plate
oAccretionary prisms (off-scraped sediment) grow upward
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Ex: Taiwan, gets pushed up
Limestone rocks get scraped off the surface of the Indian plate and as the
continents continued to collide, limestone got shoved upward and formed
the Himalayas
oCompression stacks thrust faults on the far side of the mountain belt
Growth of Continents
Accretion of arc island
oIsland fragments of continental lithosphere wont subduct
oAdded to the overriding plate
o“exotic terrains” – geologic history differs from surroundings
Continental Collisions
oClosure of oceans through subduction
Brings two blocks of continental crust together
oBuoyant continental crust will not subduct
Subduction is eventually halted
oCreates a broad belt of crustal thickening
Thickening due to thrust faulting and flow folding
oFold and thrust belts extend outward on either side
oThe resulting high mountains
Will eventually erode and collapse
Orogenic Belts
Mountains are born and have a finite life space
oYoung mountains are high, steep, and growing upward
oMiddle-aged mountains are dissected by erosion
oOld mountains are deeply eroded and often buried
Ancient Orogenic belts are found in continental interiors
Uplift
Construction of mountains requires substantial uplift
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Document Summary

Mountain building exhumes deep crust and subjects rock to stress, resulting in economic resources. Metamorphic: changed from an original parent : meta = change, morph = form or shape. Protoliths undergo pronounced changes in : texture, mineralogy. Due to change in physical or chemical conditions: burial, tectonic stresses, heating by magma, fluid alteration. Mountains frequently occur in elongate, linear belts. Mountains are constructed by tectonic plate interactions in a process called orogenesis. Mountain building is driven by plate tectonics: convergent plate boundaries, continental collisions, rifting. Orogenesic phases may last several hundred ma. Ancient mountains are deeply dissected by erosion. Convergent tectonic boundaries create mountains: subduction-related volcanic arcs grow on overriding plate, accretionary prisms (off-scraped sediment) grow upward. Accretion of arc island: island fragments of continental lithosphere wont subduct, added to the overriding plate, exotic terrains geologic history differs from surroundings. Continental collisions: closure of oceans through subduction. Brings two blocks of continental crust together: buoyant continental crust will not subduct.

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