8th week of notes
8th week of notes GEOL 105 ( Ken Lepper)
Popular in Physical Geology
Popular in Geology
This 17 page Class Notes was uploaded by Luis Blanco Seguerit on Saturday October 17, 2015. The Class Notes belongs to GEOL 105 ( Ken Lepper) at North Dakota State University taught by Ken Lepper in Fall 2015. Since its upload, it has received 116 views. For similar materials see Physical Geology in Geology at North Dakota State University.
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Date Created: 10/17/15
GEOL 105 Ken Lepper NoteTaker 1OI12I2015 Plate Tectonics Alfred Wegner 0 Ph D 1905 Astronomy University Professor 0 Polar Explorer Several trips to Greenland o Participated in the first scientific crossing of the glacial core of Greenland in1912 o Served in WWII wounded twice 0 Died in a blizzard in his beloved Greenland in 1930 Continental Drif An idea before its time 0 Alfred Wegener 0 First proposed his continental drift hypothesis in 1912 0 Published The Origin of Continents and Oceans in 1920 0 Continental Drift o Supercontinent called Pangaea all Earth began breaking apart About 200 million years ago Continents drifted to present positions Pangea 250 million years ago 0 Evidence used in support of continental drift hypothesis 0 Fit of the continents 0 Fossil evidence AFRICA 0 Rock Types and Structural similarities o Paleo climatic evidence maTchnaclian lumclm quot new HPEHJWTQEUGGEh m1f zmi h m The Great Debate 0 Objections to the continental drift hypothesis 0 Lack of a mechanism for moving continents Wegener incorrectly suggested that continents broke through the ocean crust much like ice breakers plow through ice 0 Strong composition to the hypothesis from all areas of the scientific community 0 Continental Drift and the scientific method 0 Wegener s Hypothesis was correct in principle but contained incorrect details 0 However a few scientist considered Wegener s ideas compelling and continued the research 0 Necessary details emerged with more research A scientific revolution unfolds During the 1940s and 19505 technological strides permitted extensive bathymetric mapping of the ocean floor Seafloor spreading hypothesis was proposed by Harry Hess in 1953 Geometric reversals o Earth s magnetic field periodically reverses polarity the North magnetic pole becomes the south magnetic pole and vice versa 0 Geomagnetic reversal are recorded in the ocean crust FebearingmaficBasalts Geomagnetic reversals o In 1963 the discovery of magnetic stripes or banding in the ocean crust near ridges was linked to the concept of seafloor spreading By Fred Vine and Drummond Matthews 0 Geomagnetic reversals or Paleomagnetism was the most convincing evidence set forth to support the concepts of continental drift and seafloor spreadinq These two hypothesis were later merge into the theory of Plate Tectonics Plate Tectonics The new paradigm Earth s major plates 0 Associated with Earth s strong rigid outer layer Known as the lithosphere Consist of uppermost mantle and overlying crust Overlies a weaker region in the upper mantle called the Asthenosphere o Asthenosphere can deform plastically 0 Seven major lithospheric plates Eurasian Pacific North American lndoAustralian South American African Antarctic Eurasia 1 Plate Africa Plate Seven major Plate Tectonics 0 Several plates include an entire continent plus a large area of sea oor 0 Plates are in motion and continually changing in shape and size on geologic time scales 0 Plates move relative to each other at a very slow but constant rate About 2 inches per year 5 cmyr All subduction zones cool dense slabs of oceanic lithosphere descend into the mantle Move away from MidOcean 0 Plate Boundaries o Interactions among individual plates occur along their boundaries 0 Types of plate boundaries review Divergent plate boundaries Convergent plate boundaries Transform boundaries Testing the plate tectonics model 0 Evidence from ocean drilling Several drilling programs beginning in the methods on 1960s 0 Some of the most convincing evidence confirming seafloor spreading has come from drilling directly into and through oceanfloor sediment Age of deepest sediment o Oldest 250270 Ma Thickest of oceanfloor sediments 0 Thin near ridges thick near troughs o Mantle Plumes aka Hot Spots 0 Cause by rising plumes of mantle material 0 Volcanoes form where the plumes reach the surface Eg Hawaiian island chain 0 Some originate at gret depth perhaps at the mantlecore boundary 0 Longlived occurrences so they can trace the motion of the plate above them Sample Test Questions Compressiona seismic waves generated by an earthquake are labeled 0 D waves 0 P waves 0 Q waves 0 S Waves Answer is B Pressure waves or P waves Which type of earthquake seismic waves cannot propagate through travel through liquids 0 Sonic Waves 0 Electromagnetic waves 0 P waves 0 Shear waves Answer is D Shear Waves GEOL 105 Ken Lepper NoteTaker 1OI14I2015 ACTIVE CONTINENTAL MARGINS DIVERGENT BOUNDARIES ORIGIN AND STRUCTURE OF THE SEAFLOOR Anatomy of an oceanic ridge 0 Broad linear swells along divergent plate boundaries are called oceanic ridges or Midocean ridges 0 Extensive faulting and Earthquakes 0 High heat flow 0 Numerous volcanic structures 0 Mostly lava realease from volcanic fissures o Oceanic ridge characteristics 0 Longest topographic feature on Earth s surface Over 43000 miles in length 20 of Earth s surface Extends through all major oceans o Widths ranges from 600 to gt2400 mi 4 O 5 I r r 1 l39 uar quot h l k 39l quot quot H ll 1 r r n W JuandeFuca l 1 Ridge 4 7 r 7 77 Itquot i j 3911 quot a EqualurltI Red Line shows Midoceanic ridges Origin of oceanic lithosphere 0 Why are oceanic ridges elevated 0 Primary reason is because newly created oceanic lithosphere is hot and occupies more volume than cooler rocks 0 As the basaltic crust travels away from the ridge crest it is cooled by sweater 0 As the lithosphere moves away it thermally contracts and becomes more dense Anatomy of an oceanic ridge 0 Oceanic ridge characteristics 0 Axis of some ridge segments exhibit deep downfaulted structures called rift valleys 0 These rift valleys can be found on the continents and islands as well Great African Rift Valley Iceland Structure of the oceanic crust 0 Five distinct layers 0 Layer 1 unconsolidated sediments 0 Layer 2 pillow lavas 0 Layer 3 numerous interconnected dikes called sheeted mafic dikes 0 Layer 4 gabbro cooled below surface 0 Layer 5 olivinel upper mantle Spreading oceanic ridge Structure of the oceanic crust 0 Pieces of oceanic crust and upper mantle that get plastered onto a continent 0 Form a sequence of rocks called an ophiolite complex 0 And give us a glimpse of an entire package ocean crust including upper the mantle 0 Monte Diablo CA Ophiolite 0 Deep Ocean Sediments I Ribbon Chart 0 Pillow Basalts o Sheeted Mafic Dikes Olivine Dammit Bruit ACTIVE CONTINENTAL MARGINS CONVERGENT BOUNDARIES MOUNTAIN BUILDING AND THE EVOLUTION OF CONTINENTS Convergent boundaries 0 3 main types 0 Oceanic crust beneath oceanic crust o Oceanic crust beneath continental crust o Continent to continent collision Convergence and subduction 0 Major features of subduction zones 0 Deepocean trench region where sub ducting oceanic lithosphere bends and descends into the Asthenosphere o Volcanic Arcs Built upon the overlying plate Island arc if oceanic lithosphere is sub ducted beneath oceanic lithosphere Island volcanic arc if oceanic lithosphere is sub ducted beneath a continental block Examples Aleutian Islands Alaska Japan and the Kurile Islands Japan and Kurile trench Volcanic island arc Ocean crust under Ocean crust In W l39li Emqu 7 Samar mum HZy ll lift Windmill island r mg m 13 22 Flaarm Han Inc Subduction and mountain building Andean type mountain building 0 Involves the convergence of an oceanic plate and a plate whose leading edge contains continental crust Exemplified by the Andes mountains 0 Sub ducting and partial melting of rock generates primary mamas o Magma is less dense than surrounding rock so it begins to buoyantly rise 0 As it rises it melts continental crust and the mixing of magma produces andesitic compositions o Anasite come the name Andean Andeantype mountain building 0 Emplacement of plutonsbatholiths Thick continental crust impedes the ascent of magma A large percentage of the magma never reaches the surface and is emplaced as plutons Uplift and erosion exposes these massive structures called batholiths ie Sierra Nevada in California and Peruvian Andes Batholiths are typically intermediate Diorites to felsic compositions Granites Andeantype plate margin Fl 5 J Entin g an a lmrm Frlame margins t 39 i 39hl EEIIEIE Fears31 Fi u rli H lu i Subduction and mountain building Sierra Nevada and Coast Ranges 0 An Andeantype orogenic belt 0 Past subduction of the Pacific Basin under the western edge of the North American plate 0 Sierra Nevada batholith is a remnant of a portion of the continental volcanic arc o Franciscan Formation of California s Coast ranges constitutes the accretionary wedge California lil r agaam radium Subduction and Mountain building Andeantype mountain building 0 Building a continental volcanic arc 0 Example Olympic and Cascade Range in the pacific NW These types of magma contain a large proportion of volatiles water vapor If they reach the surface they can result in potentially violent eruptions and voluminous pyroclastic deposits Example Mt Pinatubo on 1991 Kurile Islands NE of Japan Continental Collisions Two lithospheric plates both carrying continental crust O 0 Continental collisions result in the development of compressional mountains that are characterized by dramatically shortened and thickened crust Compressional mountains exhibit foldandthrust belts Metamorphism occurs at even greater depths in Compressional mountains The zone where the two continents collide is called the suture Himalaya Mountains 0 O O Youthful mountains and active Orogenesis India collided with European plate Similar but older collision occurred when the European continent collided with the Asian continent to produce the Ural mountains and the Eurasian plate lliarr39Ilu39ruz gul are Appalachian Mountains 0 Formed long ago and have been substantially lowered by erosion o Resulted from a collision among North America Europe and Northern Africa 0 Up to 3 orogenies separate Mt building events have occurred in the Appalachians 0 Final episode occurred about 250 million to 350 million years ago during the formation of Pangea Intense folding like we see in the Appalachian valley and Ridge Province occurs in Great Depth lsostasy and erosion lsostasy 0 Less dense crust floats on top of the denser and deformable rocks of the mantle 0 Concept of floating crust in gravitational balance is called lsostasy o If weight is added or removed from the crust isostatic adjustment will take place as the crust subsides or rebounds Erosion removes mass from the mountains and deeply buried rocks rise toward the surface Examples of Orogenic Styles Divergent Plate Boundaries o MidAtlantic Ridge 0 Great African Rift Valley 0 Iceland Convergent Ocean Ocean Edges o Aleutian Islands Alaska 0 Japan and Kurile Islands Convergent Ocean Continent Edges o Andes Mountains 0 Sierra Nevada in California and Peruvian Andes Convergent Continent Continent Edges o Himalayas Mountains 0 Appalachian Mountains 0 Southern Alps in New Zealand GEOL 105 Ken Lepper NoteTaker 1OI16I2015 Structural Geology Structural Geology is the study of the processes responsible for and results of deforming the Earth s crust Deformation Deformation any change in original form andlor size of a rock body Most crustal deformation occurs along plate margins Stress Deformation involves stress 0 Stress is the force applied over an area Type of stresses 0 Compressional o Tensional o Shear Motion similar to slippage that occur betwwen individual play cards Strain Deformation Strain response to stress a change in the shape or size of a rock body 0 Rocks subjected to stresses greater than their own strength deform by fracturing folding or warping bending Types of strain Elastic Plastic Brittle Fracture a if Brittle e din 39ll H Pm EEF E39E YE strain rate Elastic deformation the rock returns to its original size and shape when the stress is removed Plastic deformation the rock folds or flows and does not return to its original size and shape when the stress is removed Brittle deformation also called fracture failure or rupture Factors Temperature Confining pressure And Stain Rate Compressional Stress causes rock bodies to shorten horizontally and thicken vertically V a r a if Joints Joints are Fractures with no movement along the fracture surfaces Most occur in roughly parallel groups Significance Joints Chemical weathiering tends to be concentrated along joints because of the increased surface area created Many important mineral deposits are emplaced along joint systems Highly jointed rocks often represent a risk or challenge to construction projects Jointcontrolled weathering of Igneous rocks Faults Faults are fractures with movement along the fracture surfaces Classified based on their direction of movement type of stresses Dre vein along fault trace Normal Faults Hanging wall drops relative to footwall Accommodate Lengthening or extension of the crust Strong tensional forces Horsts and Graben Basing and Range NV Normal Fault Sequence of faults blocks bounded by normal faults Basin and Range NV Reverse Faults Hanging wall block moves up relative to the footwall block Accommodate Shortening of the crust Strong compressional forces Thrust Faults 0 Low angle reverse faults Glacier National Park example Chief mountain MT Strikeslip Faults Dominant displacement is horizontal and parallel to the strike of the fault In addition to strikeslip these faults are also referred to as 0 Transverse faults o Transform Faults Although Transform is generally reserved for plate boundary faults Strikeslip faults can be 0 Dextral Righthanded opposite side appears to have moved to one s ght 0 Sinistral Lefthanded opposite side appears to have moved to one s left StrikeSlip Faults a sinisth rm a by I aggmw Transform fault Large Strikeslip fault that cuts through the lithosphere Example the San Andreas Fault End of the Week
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