MOUNTAIN AND MOUNTAIN RANGES A. Mountain

1. MOUNTAIN AND MOUNTAIN RANGES • A. Mountain • any part of the Earth’s surface sufficiently elevated above its • surroundings to have a distinct summit and to be considered worthy of • a name • peaks must rise at least 300 m above the surrounding terrain • B. Mountain Range • 1. a series of mountains or mountain ridges that are closely related • in position, direction, age, and mode of formation • 2. a group of mountain ranges found grouped together in an elongate • zone is a mountain chain • C. Continents • Shield-large areas of exposed ancient (Precambrian) rocks • Platform-buried ancient rocks underlying each continent • Craton-shield + platform together; nucleus of a continent • 4. accretion- growth; deformed rocks along edges of cratons…

2. Teton Range in Rocky Mtns- young, note high sharp peaks Smoky Mtns, Appalachians older, smooth tops

3. DEFORMATION AND RUPTURE OF ROCKS • A. Tectonic Stress • 1. tectonic force applied to rocks • 2. three types of stress • a. compressive stress--squeezes rock and tend to shorten distances parallel to the • squeezing direction • b. tensional stress--pulls rock apart • --the opposite of compressive stress and tends to increase the distance parallel to the stress • c. shear stress--acts in parallel but opposite directions • --deforms rock by causing one part of a rock mass to slide past another • B. Strain • 1. the distortion or deformation that results from stress • 2. rocks can respond to tectonic stress in 3 different ways • a. elastic strain--directly proportional to the amount of stress: return to shape • b. non-elastic strain-- a rock undergoes plastic deformation • c. rupture-- rock breakage • C. Factors Controlling Rock Response to Stress • 1. the nature of the material • -- all rocks first react to stress with small amounts of elastic deformation • -- with continuing stress, different types of rocks may behave in different ways • 2. temperature-- the higher the temperature, greater the tendency of rocks to behave plastically • 3. pressure-- high pressure favors plastic behavior • 4. time-- stress applied over a long time, rather than suddenly, also favors plastic • behavior of rocks

4. Stress and possible deformation: A. compression causes shortening of rock layers by folding and faulting. B. tension causes lengthening and faulting. C. shear stress causes deformation along planes

5. Behavior of rocks • under stress: • If rock is brittle, • it follows B, and • fractures at certain • point. • b. If rock is ductile, • it follows A, and is • deformed. Or it can • fracture if enough • stress applied.

6. Flat lying beds= infer little deformation

7. GEOLOGIC STRUCTURES A. Definitions 1. geologic structure -- any feature produced by deformation of rocks 2. fold-- a bend in rock 3. fault--a fracture along which rock on one side has moved relative to rocks on the other side 4. joint -- a fracture without movement of rock on either side of the break B. Folds 1. anticline--a fold arching upward 2. syncline--a fold arching downward (GO to slides….)

8. Folded rocks in Calico Mtns, CA. Three folds are visible from left to right- a syncline, an anticline, and a syncline S A S

9. Rocks deformed by folding and fracturing. Notice the fault-offset of folded white layers within the brown rocks

10. These sedimentary rocks were deposited flat, lithified, then tilted into this position

11. B. Folds 1. anticline--a fold arching upward 2. syncline--a fold arching downward 3. limbs--sides of a fold 4. fold axis—a line dividing the two limbs of a fold and running along the crest of an anticline or the trough of a syncline a. plunge: when the axis is inclined or tipped at an angle b. plunging fold: a fold with a plunging axis 5. axial plane: an imaginary plane that runs through the axis and divides a fold as symmetrically as possible into two halves 6. types of folds a. monocline: has only one limb b. anticline: an arch-like structure c. syncline: a bowl shaped structure d. dome: a circular or elliptical anticlinal structure e. basin: a circular or elliptical synclinal structure

12. Monoclines: simple bend or flexure in otherwise flat lying beds. Notice the strike and dip symbols and the circled cross-indicating flat lying beds.

13. Syncline and Anticline- with axial planes, axis and limbs

14. Folds and topography-anticlines and synclines do not correspond to topographic highs and lows…. Fold relationship to topography-syncline at peak of mountain

15. Complexity associated with folding-identifying eroded anticlines and synclines by strike and dip of folded rock layers and relative ages

16. Plunging folds: a. Folds that tilt in one direction. B. Cross section view- Standard geologic symbol used to indicate plunging fold=long arrow in center of map. Arrow at end of line shows direction of plunge. c. Sheep Mountain anticline In Wyoming. Eroded.. These symbols indicate an anticline as opposed to a syncline…

17. Other complexities: • Inclined fold-axial • plane not vertical, limbs • dip at different angles • b. Overturned folds-both • fold limbs dip in same • direction, but one limb is • inverted. • c. Recumbent folds-folds • overturned so far that • they are lying on their • sides. • d. Recumbent fold in • Switzerland

18. Reading a geologic map: how • can tell if circular area is an eroded • anticline or syncline?: • In anticline, oldest exposed • rocks are in center • In syncline, youngest exposed • rocks are in center…

19. D. Joints • 1. a fracture similar to a fault except that rocks on either side of the fracture have not • moved • 2. examples of joints- • a. columnar joints in basalt • -- occurs when basalt cools and shrinks causing polygonal cracking • b. exfoliation of granite • -- sometimes called sheet jointing • -- caused by distortion of the rock at shallow depth • 3. joints become less abundant with increasing depth because both pressure and • plastic behavior of rock increase with depth and both inhibit jointing. • E. Strike and Dip • 1. strike: the direction in which tilted layers of rock are oriented • -- always given as a compass direction • 2. dip: the angle of inclination of the bedding plane • -- measured from a horizontal plane • 3. strike and dip are used to measure any type of layering or other flat surfaces • in rocks

20. Joints: fractures along which no movement has taken place. a. Erosion along parallel joints in Arches Nat Park b. Joints intersecting at right angles yield a rectang- ular pattern in Wales.

21. Concepts of Strike and Dip: • Intersection of horizontal plane • (sea level) and inclined plane (surface • of rock layer) forms a line known as • the strike. The dip is the angle of • deviation of the inclined layer from • the horizontal. Notice the strike and • dip symbol with 50 adjacent to it • indicating the angle of dip. • b. Natural example of strike and dip. • The strike of the dipping rock layer • is marked by the intersection of • the layer with the water.

22. 7. folding always results in shortening of distances in rocks, and in turn, shortening is produced by • compression, reflecting compressional tectonic stress • -- folding is less commonly formed during crustal extension • C. Faults • 1. slipis the distance that rocks on opposite sides of a fault have moved • 2. numerous closely spaced fractures collectively is referred to as a fault zone • 3. repeated movement of faults and fault zones • a. tectonic stress commonly continues to be active in the same place over • long period of time • b. once a fault forms, it is easier for movement to occur again along the same • fracture than for a new fracture to develop nearby • 4. ore deposits often concentrated in faults • --miners referred to the side of a fault that hung over their heads as thehanging wall • and the side they walked on as the footwall.

23. a. Fault terminology b. Polished fault plane and scarp, Klamath Falls, Ore. c. Fault breccia-zone of rubble along a fault in Bighorn Mtns, Wyo

24. 5. normal fault -- a fault in which the hanging wall moves down relative to the footwall; normal faults result form extensional tectonic force • 6. graben– wedge-shaped block of rock dropped downward between two normal faults • 7. reverse fault – a fault in which the hanging wall moves up relative to the footwall • 8. thrust fault– a special type of reverse fault that is nearly horizontal • 9. strike-slip fault – the fault is vertical, or nearly so, and the motion along the fault is • horizontal • -- transform faults that offset the oceanic ridge are special types of strike-slip faults • 10. horst- wedge shaped block of rocks moved upward between two normal faults

25. Types of Faults: I. Dip-slip faults a. Normal fault- hanging wall block moves down relative to footwall block. b. Reverse and c. Thrust fault- hanging wall block moves up relative to footwall block. II. Lateral faults d. Strike-slip fault: all movement is parallel to strike of the fault. e. Oblique-slip fault: combination of strike slip and dip-slip movements

26. Two small normal faults cutting through layers of volcanic ash, ORE

27. Reverse fault in sandstone layers-to the right of the hammer

28. Reverse Fault Normal fault

29. Thrust fault in Glacier Nat’l Park: Precambrian on top of Cretaceous

30. Right lateral offset of gully along San Andreas Fault in CA

31. Deformation and origin of Mountains Pluton intrudes into sedimentary rocks Erosion of softer overlying sedimentary rocks reveals plutons and forms small mountains

32. a. Block faulting-origin of horsts and grabens Humboldt Range, NEV….Horst bounded by normal faults

33. PLATE TECTONICS AND MOUNTAIN BUILDING A. Orogenic Activity 1. orogeny refers to the process of mountain building 2. an orogen or orogenic belt is a long and relatively narrow region near a tectonically active continental margin where any or all of those processes have formed mountains B. Orogenic Activity and Plate Boundaries 1. rift boundary a. mid-oceanic ridge b. continental rifting is responsible for the uplift 2. transform fault boundary a. high cliffs and escarpments form along transform faults offsetting the mid-oceanic ridge 3. convergent plate boundaries’ a. ocean-ocean convergence volcanic mountain ranges b. ocean-continental convergence volcanic mountain ranges c. continental-continental convergence folded mountain belts

34. Orogenic activity concentrated in circum-Pacific and Alpine-Himalayan orogenic belts-Plate Tectonics and Mountain Building

35. F. Geologic Structures and Plate Boundaries • each of the 3 different types of plate boundaries is characterized by different • large-scale tectonic stresses • a. spreading centers are extensional • b. transform boundaries are regions of crustal shearing • c. convergent boundaries are dominated by compression. • 2. different geologic structures are commonly associated with each type of boundary • a. divergent boundaries produce normal faults, grabens, little or no folding of rocks • b. transform plate boundaries are strike-slip faults • c. convergent continent plate boundaries commonly associated with folding have • reverse and thrust faulting • --at convergent continent-ocean or ocean-ocean boundaries subduction is • accompanied by crustal extension and normal faulting • ISLAND ARCS • A. Subduction Complex • 1. The area in front of the island arc • 2. subduction of plate highly deforms sediment and part of the oceanic crust • 3. growth of the subduction complex occurs by addition of the newest slices at the • plate boundary • 4. bottom of the complex-underthrusting forces the subduction complex upward, • forming a sedimentary basin called a forearc basin between the complex and island arc • the forearc basin fills with sediment derived form erosion of the volcanic islands and • becomes a part of the island arc

36. Origin of volcanic Island Arc: a. Subduction of oceanic plate b. Continued subduction, accretion begins, continued plutonism; beginning of deformation by thrusting and folding. c. Thrusting of back-arc basin sediments onto the adjacent continent and suturing of the island arc to continent.

37. THE BUILDING OF TWO MOUNTIAN CHAINS: THE ANDES AND THE HIMALAYAS • A. Similarities and Differences • 1.immense and great height of the peaks are similar • 2. both rise abruptly from adjacent low-lying regions • 3. igneous rocks are the most abundant rock type in the Andes • 4. highly folded and thrust-faulted sedimentary and metamorphosed sedimentary • rocks dominate Himalayan geology • 5. both chains formed at convergent plate boundaries • a. Andes at ocean-continental collision’ • b. Himalayas at a continental-continental collision • B. The Andes: Subduction at a Continental Margin • Today the Andes are a relatively narrow mountain chain consisting predominantly of • volcanic and plutonic rocks produced by subduction at a continental margin • 1. the chain also contains extensive sedimentary rocks deposited in basin that • formed by sinking of the crust on both sides of the mountains • 2. some of these rocks were deformed and metamorphosed by tectonic forces and • elevated temperature and pressure related to the emplacement of huge volumes • of magma into the crust • 3. this type of a plate margin is called an Andean margin.

38. 3 Stages to development of Andes Mtns, So America: a. Prior to 200 MYA, west coast of S America was a passive margin b. An orogeny began when W coast became an active margin- breakup of Pangaea. c. Continued deformation, volcanism and plutonism…formed Andes Mtns

39. C. The Himalayan Mountain Chain: A Collision Between Continents. • 1.formation of an Andean-type margin • 2. continent-continent collision -- India and Asia • 3. Himalayas today • a. The combination of underthrusting of India beneath Tibet and the horizontal • squashing of Tibet has produced unusually thick continental crust beneath the • Himalayas and the Tibetan Plateau • b. Frequent moderate earthquakes and occasional large and destructive ones • characterize the region. • 4. the junction between two welded continents is called a suture zone or a continental • suture • a. recognized by a lack of continuity between rock types, ages, and structures on • either side of the suture • b. rocks of the suture zone are commonly deformed and sheared by the collision • c. bits and scraps of oceanic crust and mantle occur in suture zones

40. Continent-Continent collision: formation of Himalayas as India meets Asia. Through time, subduction has been long-lived; ultimately had thrusting of sediments and Indian continent onto Asia….

41. Continental Evolution: Continental accretion through time due to multiple orogenic events suturing onto edge of continent… Multiple collisions- Either continent-continent Or continent-oceanic

42. Geologic Maps-their construction and Use Construction of geologic map from surface exposures a. Valley with outcrops, much of it covered by soil b. Data from outcrops used to infer what is present in covered areas between outcrops. Lines represent boundaries between different types of rocks. c. A geologic map (top) showing area as if soil was removed. Strike and dip measurements indicated. Orientation of rocks recorded by strike and dip used to construct the cross section across the bottom.

43. Mountain Building- SUMMARY • Mountains and Mountain Ranges are results of tectonic Stresses applied to rocks: • a. compressive stress--squeezes rock and tend to shorten distances parallel to the squeezing • direction • b. tensional stress--pulls rock apart • --the opposite of compressive stress and tends to increase the distance parallel to the stress • c. shear stress--acts in parallel but opposite directions • --deforms rock by causing one part of a rock mass to slide past another • Strain- the distortion or deformation that results from stress • rocks can respond to tectonic stress in 3 different ways • a. elastic strain--directly proportional to the amount of stress: return to shape • b. nonelastic strain-- a rock undergoes plastic deformation: changes shape • c. rupture-- rock breakage • Factors Controlling Rock Response to Stress • 1. the nature of the rock • 2. temperature-- the higher the temperature, greater the tendency of rocks to behave • plastically • 3. pressure-- high pressure favors plastic behavior • 4. Time

44. Mountain Building- SUMMARY • GEOLOGIC STRUCTURES • A. Definitions • 1. geologic structure -- any feature produced by deformation of rocks • 2. folds -- a bend in rock • - limb--sides of a fold • -fold axis—a line dividing the two limbs of a fold and running along the crest • of an anticline or the trough of a syncline • - plunge: when the axis in inclined or tipped at an angle • - plunging fold: a fold with a plunging axis • - axial plane: an imaginary plane that runs through the axis and divides a fold • as symmetrically as possible into two halves • types of folds • a. monocline: has only one limb • b. anticline: an arch-like structure • c. Syncline: a bowl shaped structure • d. dome: a circular or elliptical anticlinal structure • e. basin: a circular or elliptical synclinal structure • 3. fault --a fracture along which rock on one side has moved relative to rock on the other side • a. normal fault -- a fault in which the hanging wall moves down relative to the footwall normal faults result form extensional tectonic force • b. graben – a wedge-shaped block of rock that dropped downward between two normal faults • c. reverse fault – a fault in which the hanging wall move up relative to the footwall • d. thrust fault – a special type of reverse fault that is nearly horizontal • e. strike-slip fault – fault is vertical, or nearly so, and the motion along the fault is horizontal • -- transform faults that offset the oceanic ridge are special types of strike-slip faults

45. Mountain Building- SUMMARY • 4. joint -- a facture without movement of rock on either side of the break • 1. a fracture similar to a fault except that rocks on either side of the facture have not moved • 2. examples of joints- • columnar joints in basalt- occurs when basalt cools and shrinks causing polygonal cracking • b. exfoliation of granite • Concepts of Strike and Dip: • 1. strike: the direction in which tilted layers of rock are oriented • -- always given as a compass direction • 2. dip: the angle of inclination of the bedding plane • -- measured from a horizontal plane • 3. strike and dip are used to measure any type of layering or other flat surfaces • in rocks • Types of Faults: • I. Dip-slip faults • a. Normal fault-hanging wall block moves down relative to footwall block. • b. Reverse and c. Thrust fault-hanging wall block moves up relative to footwall block. • II. Lateral faults • d. Strike-slip fault: all movement is parallel to strike of the fault. • e. Oblique-slip fault: combination of strike slip and dip-slip movements

46. Mountain Building- SUMMARY Terms used to describe complex folds: a. plunging fold: fold that dips in one direction b. Inclined fold-axial plane not vertical, limbs dip at different angles c. Overturned folds-both fold limbs dip in same direction, but one limb is inverted. d. Recumbent folds-folds overturned so far that they are lying on their sides. PLATE TECTONICS AND MOUNTAIN BUILDING A. Orogenic Activity 1. orogeny refers to the process of mountain building 2. an orogen or orogenic belt is a long and relatively narrow region near a tectonically active continental margin where any or all of those processes have formed mountains B. Orogenic Activity and Plate Boundaries 1. rift boundary a. mid-oceanic ridge b. continental rifting is responsible for the uplift 2. transform fault boundary a. high cliffs and escarpments form along transform faults offsetting the mid-oceanic ridge 3. convergent plate boundaries’ a. ocean-ocean convergence volcanic mountain ranges b. ocean-continental convergence volcanic mountain ranges c. continental-continental convergence folded mountain belts

47. Mountain Building- SUMMARY Plate-Plate interactions, resulting mountain ranges formed: a. Island Arcs: primarily from oceanic-oceanic b. Andes type mountains: oceanic-continental plate interactions c. Himalayan mountains: continent-continent interactions End result is continental accretion…’growth’ of continents Geologic Maps- interpreting complex geology from …. Reading a geologic map: how can tell if circular area is an anticline or syncline?: a. In anticline, oldest exposed rocks are in center b. In syncline, youngest exposed rocks are in center… Horst and grabens- horst: an uplifted fault block bounded on at least two sides by faults graben: a fault-caused depression bounded on at least two sides by faults…

49. Text: Historical Geology

50. Small scale foldsin sedimentary rocks.Pen is 13.5cm long