introduction to geology plate tectonics, structural geology Drifting Continents and Spreading...

Chapter 11

Crags, Cracks and Crumples: Crustal

Deformation and Mountain Building

Earth: Portrait of a Planet, 4th editionby Stephen Marshak

© 2011 W.W. Norton & Company

PowerPoint slides prepared by Ronald L. Parker, Fronterra Geosciences, 700 17th Street, Suite 900, Denver, CO, 80202

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Lecture 14: Mountain BuildingLecture 14: Mountain BuildingLecture 14: Mountain BuildingLecture 14: Mountain Building

Prepared by:Prepared by:

Ronald L. ParkerRonald L. Parker, , Senior GeologistSenior Geologist

Fronterra Geosciences,Fronterra Geosciences,

Denver, ColoradoDenver, Colorado

Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 11: Crustal Deformation and Mountain BuildingChapter 11: Crustal Deformation and Mountain Building


Developed where oceanic crust is descending beneath continental Developed where oceanic crust is descending beneath continental crust (e.g. Andes, Cordilleran belt of western North America)crust (e.g. Andes, Cordilleran belt of western North America)

In collision zones where continental plates have been welded together In collision zones where continental plates have been welded together

following destruction of an ocean (e.g. Urals, Himalayas/Alps)following destruction of an ocean (e.g. Urals, Himalayas/Alps)


Causes of Mountain BuildingCauses of Mountain Building

�� SteadySteady--state state subductionsubduction(e.g. Andes)(e.g. Andes)

�� Crustal thickening results Crustal thickening results from longfrom long--term addition of term addition of magma to the crust as magma to the crust as well as transfer of well as transfer of compressionalcompressional stresses stresses from the from the subductingsubductingocean plate into the ocean plate into the overlying continental overlying continental plateplate

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�� Modern instrumentation can measure mountain growth.Modern instrumentation can measure mountain growth.

�� Global positioning systems (GPS) measure rates of: Global positioning systems (GPS) measure rates of:

Modern OrogenesisModern Orogenesis

�� Horizontal compression.Horizontal compression.

�� Vertical uplift. Vertical uplift.

Fig. 11.34


AccretionaryAccretionary orogensorogens

�� Addition of fragments of Addition of fragments of crust that are buoyant crust that are buoyant and ACCRETED onto the and ACCRETED onto the side of the continent side of the continent drives further crustal drives further crustal thickeningthickening

�� FaultFault--bounded blocks of bounded blocks of unrelated crust unrelated crust aveave been been carried as on a conveyor carried as on a conveyor belt to the active margin belt to the active margin --TERRANESTERRANES


�� SubductionSubduction (convergent) boundaries create mountains. (convergent) boundaries create mountains.

�� SubductionSubduction--related volcanic arcs grow on overriding plate. related volcanic arcs grow on overriding plate.

�� AccretionaryAccretionary prisms (offprisms (off--scraped sediment) grow upward.scraped sediment) grow upward.

�� Compression shortens and uplifts overriding plate.Compression shortens and uplifts overriding plate.

�� A foldA fold--thrust belt develops landward of the thrust belt develops landward of the orogenorogen..

Accretion and mountain buildingAccretion and mountain building

Fig. 11.22a

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Continental collision mountain beltsContinental collision mountain belts

�� Two large continental Two large continental blocksblocks

�� Each too buoyant to Each too buoyant to subductsubduct

�� A SUTURE within the A SUTURE within the mountain belt may mountain belt may define the “join” define the “join” between the two ancient between the two ancient platesplates

�� The suture may be The suture may be marked by slices of marked by slices of oceanic crust oceanic crust (OPHIOLITES)(OPHIOLITES)



�� Continental collision creates a welt of crustal thickening.Continental collision creates a welt of crustal thickening.

��Thickening due to thrust faulting and flow folding.Thickening due to thrust faulting and flow folding.

��Centre of Centre of belt consists of highbelt consists of high--grade metamorphic rocks.grade metamorphic rocks.

�� FoldFold--thrust belts extend outward on either side. thrust belts extend outward on either side.

�� The resulting high mountains may eventually collapse. The resulting high mountains may eventually collapse.


Fig. 11.23a

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�� Continental collision follows ocean basin closure.Continental collision follows ocean basin closure.

�� Complete subduction of oceanic lithosphere.Complete subduction of oceanic lithosphere.

�� Brings two blocks of continental lithosphere together. Brings two blocks of continental lithosphere together.

�� Buoyant continental crust shuts down subduction.Buoyant continental crust shuts down subduction.


Fig. 11.23b



�� Surface elevation is a balance between forces; Surface elevation is a balance between forces; isostasyisostasy..

�� Gravitational attraction pulls plates into the mantle. Gravitational attraction pulls plates into the mantle.

�� Buoyancy floats lithosphere on top of the mantle.Buoyancy floats lithosphere on top of the mantle.

�� Adding or removing weight resets isostatic equilibrium. Adding or removing weight resets isostatic equilibrium.

�� Change in lithospheric thickness or density alters Change in lithospheric thickness or density alters isostasyisostasy..

Why are Mountains High?Why are Mountains High?

Fig. 4.1a

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�� ConvergentConvergent--margin horizontal compression causes:margin horizontal compression causes:

�� Horizontal shortening, and Horizontal shortening, and

�� Vertical thickening.Vertical thickening.

�� These processes can double crustal thickness.These processes can double crustal thickness.

�� A thick crustal root develops beneath mountain ranges.A thick crustal root develops beneath mountain ranges.

Why Are Mountains High?Why Are Mountains High?

Fig. 11.26b, c

The thickest block floats highest and

sinks deepest.


�� Adding igneous rock can thicken the crust.Adding igneous rock can thicken the crust.

�� Volcanic material is added to the surface.Volcanic material is added to the surface.

�� Plutons are added at midPlutons are added at mid--crustal levels.crustal levels.


Fig. 11.22a


�� Removal of lithospheric mantle can cause uplift.Removal of lithospheric mantle can cause uplift.

�� The Tibet Plateau bears evidence of delamination.The Tibet Plateau bears evidence of delamination.


Fig. 11.27

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�� The Himalayas are the maximum height possible. Why? The Himalayas are the maximum height possible. Why?

�� There is an upper limit to mountain heights. There is an upper limit to mountain heights.

�� Erosion accelerates with height.Erosion accelerates with height.

�� Weight of high mountains overwhelms rock strength.Weight of high mountains overwhelms rock strength.

��Deep, hot rocks eventually flow out from beneath mountains. Deep, hot rocks eventually flow out from beneath mountains.

��The mountains then collapse downward like soft cheese.The mountains then collapse downward like soft cheese.

�� Uplift, erosion, and collapse exhume deep crustal rocks. Uplift, erosion, and collapse exhume deep crustal rocks.

What Goes Up Must Come DownWhat Goes Up Must Come Down

Fig. 11.29


�� A A cratoncraton is crust that has not been deformed in 1 Ga. is crust that has not been deformed in 1 Ga.

�� LowLow--geothermal gradient; cool, strong, and stable crust.geothermal gradient; cool, strong, and stable crust.

�� Two Two cratoniccratonic provinces. provinces.

��ShieldsShields——Precambrian Precambrian

igneous and metamorphicigneous and metamorphic

rocks. rocks.

��PlatformsPlatforms——sshields hields

covered by layers ofcovered by layers of

PhanerozoicPhanerozoic strata. strata.

CratonsCratons

Fig. 11.30


Himalayas & Tibet PlateauHimalayas & Tibet Plateau

�� The result of the collision The result of the collision of India with Asiaof India with Asia

�� ‘Cold’ Indian crust ‘Cold’ Indian crust collided with ‘warm’ Asian collided with ‘warm’ Asian crust resulting in massive crust resulting in massive uplift and the Tibet uplift and the Tibet Plateau (the most Plateau (the most extensive upland area on extensive upland area on EarthEarth

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Early Cretaceous (120 Ma)Early Cretaceous (120 Ma)


Late Cretaceous/Palaeogene (55Ma)Late Cretaceous/Palaeogene (55Ma)

Successive positions of IndiaSuccessive positions of India

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Regional structure of the HimalayasRegional structure of the Himalayas

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Granite with inclusions of older Granite with inclusions of older maficmafic magma magma in Karakorum in Karakorum batholithbatholith


KohistanKohistan island arcisland arc


Folded Folded turbiditesturbidites of the foreof the fore--arc lying between arc lying between the the KohistanKohistan island arc and the sutureisland arc and the suture

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Folded Folded turbiditesturbidites of the foreof the fore--arc lying between arc lying between the the KohistanKohistan island arc and the sutureisland arc and the suture


OceanOcean--floor basalts (=floor basalts (=ophioliteophiolite) lying along the ) lying along the suture zone (foresuture zone (fore--arc to N) arc to N)


Pillow lavas within the Pillow lavas within the ophioliteophiolite

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OphioliteOphiolite (dark) thrust over Indian plate (dark) thrust over Indian plate limestoneslimestones


Simplified crossSimplified cross--sections through the sections through the HimalayasHimalayas


Foreland basin river depositsForeland basin river deposits

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Seismic section below southern TibetSeismic section below southern Tibet



Satellite image of the Kunlun strikeSatellite image of the Kunlun strike--slip faultslip fault

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Ground view of the Kunlun FaultGround view of the Kunlun Fault



IndiaIndia--Asia collisionAsia collision

�� ~4500 km of northward movement accounted for by ~4500 km of northward movement accounted for by thrusting and thickening of the Indian and Asian thrusting and thickening of the Indian and Asian plates plates

�� Northward movement also accommodated by sideNorthward movement also accommodated by side--ways ‘extrusion’ of Indoways ‘extrusion’ of Indo--China and other blocks of China and other blocks of crust along strikecrust along strike--slip faultsslip faults

�� Indian plate very rigid in contrast to the Asian plate Indian plate very rigid in contrast to the Asian plate which underwent widespread deformation which underwent widespread deformation ––continental plates therefore not always strong continental plates therefore not always strong

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Older Older collisionalcollisional mountain beltsmountain belts

�� Difficult to interpret as we have no ocean floor left (all Difficult to interpret as we have no ocean floor left (all subductedsubducted) therefore knowledge of plate movements ) therefore knowledge of plate movements limitedlimited

�� Some constraints from Some constraints from palaeomagnetismpalaeomagnetism and isotopic and isotopic datingdating

�� Generally deeply eroded therefore dominated by strongly Generally deeply eroded therefore dominated by strongly deformed metamorphic rocks deformed metamorphic rocks –– again can be difficult to again can be difficult to interpretinterpret

�� Build up models and test them with new discoveriesBuild up models and test them with new discoveries



�� MarshakMarshak Chapter 11.Chapter 11.

�� Journal of Structural Geology Journal of Structural Geology

�� http://www.windows2universe.org/earth/Interior_Structure/interior.htmlhttp://www.windows2universe.org/earth/Interior_Structure/interior.html

�� The Structural Geology PageThe Structural Geology Page

� http://www.structural-geology.org/

�� Visible GeologyVisible Geology

�� http:// http:// visible-geology.appspot.com/#page/home

Useful Web ResourcesUseful Web Resources

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