Chapter Mountain Building - jkaser.com 11 Mountain... · confining pressure, rock type, and ......
Transcript of Chapter Mountain Building - jkaser.com 11 Mountain... · confining pressure, rock type, and ......
Chapter
Mountain Building
11.1 Rock Deformation
Factors that influence thestrength of a rock and how it willdeform include temperature,confining pressure, rock type, and
Factors Affecting Deformation
confining pressure, rock type, andtime.
- Most crustal deformation occursalong plate margins.
•Deformation is a general term thatrefers to all changes in the originalshape and/or size of a rock body.
Factors Affecting Deformation
11.1 Rock Deformation
•Stress is the force per unit areaacting on a solid.acting on a solid.
•Strain is the change in shape orvolume of a body of rock as a resultof stress.
Factors Affecting Deformation
11.1 Rock Deformation
Temperature and Pressure
•Rocks deform permanently in twoways: brittle deformation andways: brittle deformation andductile deformation.
- Brittle deformation is the fracturingof an object once its strength isexceeded - glass, china plates andbones are examples
11.1 Rock Deformation
• Rocks deform permanently in twoways: brittle deformation and ductiledeformation.
- Ductile deformation is a type of- Ductile deformation is a type ofsolid state flow that produces achange in the size and shape of anobject without fracturing the object- modeling clay, bee’s wax, caramelcandy and most metals are examples
Factors Affecting Deformation
11.1 Rock Deformation
Rock Type•Mineral composition and texture ofa rock also greatly affect how it willa rock also greatly affect how it willdeform.• Granite and basalt usually fail bybrittle fracture• Sedimentary and metamorphicrocks are weak and deform byductile flow
Factors Affecting Deformation
11.1 Rock Deformation
Time
•Forces that are unable to deform•Forces that are unable to deformrock when first applied may causerock to flow if the force ismaintained over a long period oftime.
Types of Stress
11.1 Rock Deformation
The three types of stresses thatrocks commonly undergo arerocks commonly undergo aretensional stress, compressionalstress, and shear stress.
Types ofStress
Pulled
Squeezed or shortened
Distorted
Anticlines and Synclines
11.1 Rock Deformation
Anticlines
•Anticlines are most
Folds
•Anticlines are mostcommonly formed by theupfolding, or arching, of rocklayers.
Anticline
11.1 Rock Deformation
Synclines•Synclines are lineardownfolds in sedimentary
Folds
•Synclines are lineardownfolds in sedimentarystrata.
•Synclines are often found inassociation with anticlines.
Synclines
11.1 Rock Deformation
Monoclines•Monoclines are large step-like folds in otherwise
Folds
like folds in otherwisehorizontal sedimentarystrata.
Monoclines
Mexican Hat, Utah
Monoclines
Monocline
11.1 Rock Deformation
Normal Faults•Normal faults occur when thehanging wall block moves downrelative to the footwall block.
Faults
relative to the footwall block.•Most have steep dips of about 60o
•Result in the lengthening, orextension, of the crust
•Occur due to tensional stresses
Reverse Faults and Thrust Faults•Result from compressional stress•Reverse faults are faults in whichthe hanging wall block moves uprelative to the footwall block.
11.1 Rock Deformation
the hanging wall block moves uprelative to the footwall block.
•High-angle faults with dips greaterthan 45o
•Thrust faults are reverse faults withdips less than 45o.
Reverse FaultsReverse Faults
Thrust Faults
Folds
11.1 Rock Deformation
Strike-Slip Fault
•Strike-slip faults are faults in whichthe movement is horizontal and
•Strike-slip faults are faults in whichthe movement is horizontal andparallel to the trend, or strike, of thefault surface.
•Caused by shear stress.
Folds
11.1 Rock Deformation
Joints
•Joints are fractures along which no•Joints are fractures along which noappreciable movement hasoccurred.
•The result of large-scale regionalstresses.
Four Types of Faults
Joints
ArchesNationalNationalPark, Moab,Utah
Folded Mountains
11.2 Types of Mountains
Mountains are classified by thedominant processes that haveformed them.formed them.
•Orogenesis is the collection ofprocesses that result in the formingof mountains.
11.2 Types of Mountains
Folded Mountains
•Mountains that are formed primarilyby folding are called foldedmountains.mountains.
•A folded mountain is caused byextreme force pushing from bothsides of the plates. This greatpressure causes mountain to break,bend, and fold
Folded Mountains Mount Kidd, Alberta, Canada
11.2 Types of Mountains
Large-scale normal faults areassociated with structures calledfault-block mountains.
•Fault-block mountains are formed
Fault-Block Mountains
•Fault-block mountains are formedas large blocks of crust are upliftedand tilted along normal faults.
•Grabens (ditch or trench) areformed by the downwarddisplacement of fault-boundedblocks.
11.2 Types of Mountains
•Horsts are elongated, upliftedblocks of crust bounded by faults.
Fault-Block Mountains
•A block fault mountain is createdwhen a mountain rises from theearth. When the mountain risespressure causes the rock to crackand slide. This creates sharp anddistinctive faces on the mountain.
Fault-Block Mountains
Large-scalefolding isapparent inthis satelliteimage of theAppalachianAppalachianMountains,Pennsylvania.
The Andes from space
Himalayan Mountains from space
Domes and Basins
11.2 Types of Mountains
When upwarping produces acircular or elongated structure, thefeature is called a dome.feature is called a dome.
•Uplifted mountains are circular orelongated structures formed byuplifting of the underlying basementrock.
Domes and Basins
11.2 Types of Mountains
•A dome mountain is formed whenmelted rock is pushed up throughthe earth's crust without folding orthe earth's crust without folding orfaulting creating a dome like shapeof the mountain
•Erosion is believed to be a majorfactor in the shaping of most domeformations.
DomedMountains
Black Hills of SD
Michigan Basin
Volcanic Mountains
11.2 Types of Mountains
A volcanic mountain is formed whenmelted rock rises from the earth andbuilds up over time on the earth’sbuilds up over time on the earth’ssurface. This is how Mount St.Helens was formed.
MOUNTAIN FORMATION DATE TYPE CONTINENT
Himalayas around 75 mya folded/block AsiaUrals around 300 mya folded EuropeAppalachians around 500 mya folded N AmericaRockies around 140 mya block/fault N AmericaAlps around 25 mya folded EuropeAlps around 25 mya folded Europe
Mount Shasta
Mount St. Helens
Mount Hood
Mountain Building at ConvergentBoundaries
11.3 Mountain Formation
Most mountain building occurs atconvergent plate boundaries.convergent plate boundaries.Colliding plates provide thecompressional forces that fold,fault, and metamorphose the thicklayers of sediments deposited atthe edges of landmasses.
Mountain Building at ConvergentBoundaries
11.3 Mountain Formation
Ocean-Ocean Convergence
•Ocean-ocean convergence mainlyproduces volcanic mountains.
11.3 Mountain Formation
Ocean-Continental Convergence•The types of mountains formed byocean-continental convergence arevolcanic mountains and folded
Mountain Building at Convergent Boundaries
volcanic mountains and foldedmountains.
• An accretionary wedge is theaccumulation of differentsedimentary and metamorphicrocks with some scraps of oceancrust.
Ocean-Ocean Convergence
Ocean-Continental Convergence
11.3 Mountain Formation
Continental-Continental Convergence
•At a convergent boundary betweentwo plates carrying continental
Mountain Building at Convergent Boundaries
two plates carrying continentalcrust, a collision between thecontinental fragments will resultand form folded mountains.
• India and the Eurasian plate
Continental-Continental Convergence
Mountain Building at DivergentBoundaries
11.3 Mountain Formation
The mountains that form alongocean ridges at divergent plateboundaries are fault-block typemountains.
Mid-Atlantic Ridge
Mountain Building byContinental Accretion
Non-Boundary Mountains
11.3 Mountain Formation
Not all mountains are formed byplate boundaries. Some areplate boundaries. Some areformed by hot spots or regionalextension or stretching.
Hawaiian Islands
Continental Accretion
11.3 Mountain Formation
Accretion is a process that occurswhen crustal fragments collidewhen crustal fragments collidewith and stay connected to acontinental plate. Many of the mountains along thePacific
Continental Accretion
11.3 Mountain Formation
Terranes•Terranes are any crustal fragments•Terranes are any crustal fragmentsthat have a geologic history distinctfrom that of the adjoiningfragments.
•Terranes occur along the PacificCoast.
Accretion inWestern NorthWestern North
America
11.3 Mountain Formation
• Isostasy is the concept that Earth’scrust is floating in gravitational balanceupon the material of the mantle.
Isostatic Adjustment for Mountains
• Because of isostasy, deformed and
Principles of Isostasy
• Because of isostasy, deformed andthickened crust will undergo regionaluplift both during mountain buildingand for a long period afterward.
• Isostatic adjustment is the process ofestablishing a new level ofgravitational equilibrium.
Isostatic Adjustment
Isostatic Adjustment in Mountains