Crustal Deformation - METU GEOE 231 PDF

METU GEOE 231 Crustal Deformation 1 Deformation METU GEOE 231 Deformation is a general term that refers to all changes in the shape or position of a rock body in response to stress Geologic structures are the deformed featu...

METU GEOE 231 Crustal Deformation 1 Deformation METU GEOE 231 Deformation is a general term that refers to all changes in the shape or position of a rock body in response to stress Geologic structures are the deformed features that result from forces generated by the interactions of tectonic plates Includes folds, faults, and joints Factors that influence the deformation  Stress  Temperature  Rock type  Time 2 Deformation METU GEOE 231 F deformation Deformation is the change in shape, position and/or volume of a rock in response to applied forces. It is determined by comparing the deformed and undeformed states. 3  METU GEOE 231 Deformation  Deformed rocks are manifestation of the dynamic nature of the Earth  Many ancient rocks are fractured or highly contorted, clearly indicating that the forces within the Earth caused deformation during the past.  This deformation is not restricted to the past, however, seismic activity and continuing deformation at plate boundaries indicate that deforming forces remain active....  Mountain formation 4  METU GEOE 231 What Causes Rock to Deform? Stress: The Force That Deforms Rocks Stress (force per unit area) is the force that deforms rocks  When stresses acting on a rock exceed its strength, the rock will deform by flowing, folding, fracturing, or faulting  The magnitude is a function of the amount of force applied to a given area 5  METU GEOE 231 What Causes Rock to Deform? Stress: The Force That Deforms Rocks  Stress applied uniformly in all directions is confining pressure  Stress applied unequally in different directions is called differential stress 6 What Causes Rock to Deform? METU GEOE 231 Stress: The Force That Deforms Rocks Types of stress Compressional stress squeezes a rock and shortens a rock body Tensional stress pulls apart a rock unit and lengthens it Shear stress forces act parallel to one another but in opposite directions 7 What Causes Rock to Deform? METU GEOE 231 Strain: A Change in Shape Caused by Stress  Strain is the change in shape of a rock caused by differential stress  Strained bodies lose their original configuration during deformation 8  METU GEOE 231 Deformed Trilobite 9  METU GEOE 231 How Do Rocks Deform? Elastic, Brittle, and Ductile Deformation  Elastic deformation: The rock returns to nearly its original size and shape when the stress is removed  Once the elastic limit (strength) of a rock is surpassed, it either bends (ductile or plastic deformation) or breaks (brittle deformation) Rocks  at or near surface  brittle  At depth with high P & T  plastic 10 Stress vs Strain METU GEOE 231 Hooke’s Law 11 Rocks Exhibiting Ductile Deformation METU GEOE 231 12 Rocks Exhibiting Brittle Deformation METU GEOE 231 13 Factors That Affect Rock Deformation METU GEOE 231 Temperature: Higher temperature rocks deform by ductile deformation whereas cooler rocks deform by brittle deformation Confining pressure: Confining pressure squeezes rocks, making them stronger and harder to break 14 Factors That Affect Rock Deformation METU GEOE 231  Rock type: Crystalline igneous rocks generally experience brittle deformation, whereas sedimentary and metamorphic rocks with zones of weakness generally experience ductile deformation  Time: Forces applied over a long period of time generally result in ductile deformation 15 Ductile Versus Brittle Deformation METU GEOE 231 Most rocks exhibit brittle behavior in the upper 10 kilometers of the crust Joints are cracks in the rocks resulting from the rock being stretched and pulled apart Faults are fractures in the rocks where rocks on one side of the fault are displaced relative to the rocks on the other side of the fault Folds are evidence that rocks can bend (ductile deformation) without breaking  Usually the result of deformation in high-temperature and pressure environments 16 Ductile Versus Brittle Deformation METU GEOE 231 17 Strike and Dip METU GEOE 231 TO describe the orientation of deformed rock layers (or plannar geologic features e.g., fault, fracture etc.) principle of original horizontality inclined beds (tilting) 18  METU GEOE 231 https://www.facebook.com/Geo.sy.111/photos /a.1828841247172265/4926249990764693/ 19 Strike and Dip METU GEOE 231 Sedimentary rocks that are inclined or bent indicate that the layers were deformed following deposition Strike:  The compass direction of the line produced by the intersection of an inclined rock layer (or fault) with a horizontal plane  Generally expressed as an angle relative to north Dip:  The angle of inclination of the surface of a rock unit (or fault) measured from a horizontal plane.  Includes both an inclination and a direction toward which the rock is inclined. 20 Strike and Dip of Rock Layers METU GEOE 231 21 Mapping Geologic Structures METU GEOE 231 22 Ductile Deformation: Folds METU GEOE 231  Rocks bent into a series of wave like ondulations (up- and down-arched features)  Most folds result from compressional forces which shorten and thicken the crust 23  Folding and Faulting Classification METU GEOE 231 24 Types of Folds METU GEOE 231  Anticline – upfolded, or arched, rock layers: each limb dip away from each other; oldest rock is exposed at the core  Syncline – downfolded rock layers: each limb dips toward eachother; youngest rock is exposed at the core  Monocline – simple bend or flexure in otherwise horizontal or uniformly dipping rock layer. Anticlines and synclines can be:  Symmetrical - limbs are mirror images: axial plane is vertical; each limbs dip at the same angle  Asymmetrical - limbs are not mirror images: axial plane is inclined; limbs dip at different angles  Overturned - one limb is tilted beyond the vertical: both limbs dip in the same direction, one limb has been rotated 90 degres from its original position so that it is now upside down  Recumbent – axial plane is horizontal  Plunging – the axis (or hinge) of the fold penetrates the ground. 25 Parts of Folds METU GEOE 231 Fold axis Flank 26 Parts of Folds: METU GEOE 231 Plunging & non-plunging folds Crest/crest line Through/Through line Hinge/hinge line 27 A series of anticlines METU GEOE 231 and synclines 28 Types of Folds METU GEOE 231 29 Types of Folds METU GEOE 231 https://www.quora.com/What‐is‐an‐asymmetrical‐fold 30 Overturned Fold METU GEOE 231 31  METU GEOE 231 Monocline 32 Plunging Fold METU GEOE 231 https://www3.nd.edu/~cneal/PlanetEarth/Lab‐Structural/Folds.html 33 Plunging Fold METU GEOE 231 https://tr.pinterest.com/pin/175851560424999679 34  Plunging folds METU GEOE 231 http://pages.geo.wvu.edu/~kammer/g100/StructuralGeology.pdf 35 METU GEOE 231 36  METU GEOE 231 https://www.facebook.com/Geo.sy.111/photos /a.1828841247172265/4894641407258885 37 METU GEOE 231 38 METU GEOE 231 39  METU GEOE 231 http://www.stacey.peak-media.co.uk/bude-walk/bude.htm 40 METU GEOE 231 41 METU GEOE 231 42 METU GEOE 231 43 METU GEOE 231 44 METU GEOE 231 45 METU GEOE 231 46 Other Types of Folds METU GEOE 231 Dome  Circular, or sub-circular  Up-warped displacement of rocks  Oldest rocks in the center Basin  Circular, or sub-circular  Down-warped displacement of rocks  Youngest rocks in center 47 METU GEOE 231 48 Dome & Basin METU GEOE 231 49  METU GEOE 231 The bedrock geology of the Michigan Basin The Black Hills of South Dakota are a large dome 50  Folds are classified on the basis of several METU GEOE 231 geometric factors: – 1. Tightness of folding – Open – Tight – Isoclinal https://www.researchgate.net/publication/259330495_A_Critical_Revi ew_of_Landslide_Failure_Mechanisms/figures?lo=1 51  METU GEOE 231 Folds are classified on the basis of several geometric factors: Orientation of axial plane: Upright Inclined Recumbent https://www.geologypage.com/2015/12/geological‐folds.html 52  METU GEOE 231 A series of anticlines and synclines 53  METU GEOE 231 Stratigraphic Younging https://www.files.ethz.ch/structuralgeology/JPB/files/English/8folds.pdf Antiform or Synform https://www.nps.gov/articles/tectonic‐folding.htm 54 Stratigraphic Younging METU GEOE 231 55  Fracturing and Faulting METU GEOE 231 Classification 56 Brittle Deformation: Fractures METU GEOE 231 Fractures are surfaces along which rocks has lost cohesion Types of fractures Joints: fractures along which no movement has occurred or movement is perpendicular to the fracture walls: That is fractures may open-up, BUT the rocks on opposite side of fracture show no movement parallel to the fracture  Commonest structures in rocks  Brittle deformation by fracturing on all near-surface rocks  From in response to C, T or S stresses  They are related to large-scale structures like folds and faults (crest of anticlines) Columnar joints: cooling of magma in dykes, sills and thick lava flows Sheet joints: pressure release mechanism 57 Faults METU GEOE 231 Faults are fractures (breaks) in rocks along which appreciable displacement has taken place: blocks on opposite sides of fracture move parallel to the fracture surface (fault plane) Types of faults 1. Dip-slip fault 2. Strike-slip fault 3. Oblique-slip fault 58  Faults METU GEOE 231 Types of faults 1. Dip-slip fault 2. Strike-slip fault 3. Oblique-slip fault 59 Types of Faults: Concept of Hanging METU GEOE 231 wall and Footwall Along a Fault Dip-slip fault  Movement along the inclination (dip) of fault plane  Parts of a dip-slip fault  Hanging wall – the rock above the fault surface  Footwall – the rock below the fault surface 60 Types of Faults METU GEOE 231 Dip-slip fault Normal fault  Hanging wall block moves down  Associated with fault-block mountains  Prevalent at spreading centers  Caused by tensional forces 61 A Normal Fault METU GEOE 231 62 Fault Block Mountains Produced METU GEOE 231 by Normal Faulting https://eodev.com/gorev/6452445 https://www.everythingselectric.com/geology‐1/ 63 Fault Block Mountains Produced METU GEOE 231 by Normal Faulting 64 Fault block mountains produced by normal faulting METU GEOE 231 https://slideplayer.com/slide/14062204/ https://twitter.com/mithuna_mithuna/status/1195344186486272000/photo/1 65 A Normal Fault METU GEOE 231 66 A Normal Fault METU GEOE 231 67 Kuşadası Fault METU GEOE 231 68 Types of Faults METU GEOE 231 Dip-slip fault Reverse and thrust faults  Hanging wall block moves up  Caused by strong compressional stresses  Reverse fault - dips greater than 45º  Thrust fault - dips less than 45º 69 A Reverse Fault METU GEOE 231 70  METU GEOE 231 A thrust fault A reverse fault 71 Types of Faults METU GEOE 231 Strike-slip faults Dominant displacement is horizontal and parallel to the trend, or strike  Transform fault  Large strike-slip fault that cuts through the lithosphere  Often associated with plate boundaries 72  A strike-slip Fault METU GEOE 231 (Sinistral = Left Lateral) 73  A strike-slip Fault METU GEOE 231 (Dextral = Right Lateral) 74 A Strike-slip Fault METU GEOE 231 https://www.wikizero.com/en/Fault_(geology) Satellite image of a fault in the Taklamakan Desert, Southwest Xinjiang in Northwest China 75 A Strike-slip Fault METU GEOE 231 76 Types of Faults METU GEOE 231 Oblique-slip faults: Oblique-slip normal fault with sinistral component 77 Types of Faults METU GEOE 231 Oblique-slip faults: Oblique-slip reverse fault with sinistral component 78  Faulting METU GEOE 231 https://www.researchgate.net/publication/324601471_Conceptual_representation_of_fluid_flow_c onditions_associated_with_faults_in_sedimentary_basins/figures?lo=1 79 Faulting METU GEOE 231 80 METU GEOE 231 81 Mountain Belts METU GEOE 231 Orogenesis refers to processes that collectively produce a mountain belt Mountain building at convergent boundaries Most mountain building occurs at convergent plate boundaries Aleutian-type mountain building Where two oceanic plates converge and one is subducted beneath the other Mountain building at convergent boundaries Aleutian-type mountain building Volcanic island arcs forms * Found in closing/shrinking ocean basins, such as the Pacific * e.g., Mariana, Tonga, Aleutian, and Japan arcs 82 Formation of a Volcanic Island Arc METU GEOE 231 Aleutian‐type mountain building 83 Mountain Belts METU GEOE 231 Mountain building at convergent boundaries Andean-type mountain building: Oceanic-continental crust convergence Types related to the overriding plate Sequences: Passive margins: no subduction or collision * Prior to the formation of a subduction zone * e.g., East Coast of North America i. Subduction zone forms ii. Deformation process begins iii. Continental volcanic arc forms (volcanic chain on the continental crust) iv. Accretionary wedge forms Examples of inactive Andean-type orogenic belts include Sierra Nevada Range and California's Coast Ranges 84 Orogenesis along an Andean‐type subduction zone METU GEOE 231 Passive Margin 85  METU GEOE 231 Orogenesis along an Andean‐type subduction zone Subduction at the continental margin  Development of Continental Volcanic Arc  Accretionary Wedge Advanced stage of subduction and Volcanic Arc formation 86 Orogenesis: Continent‐Continent METU GEOE 231 Convergence Mountain building at convergent boundaries Continental collisions Where two plates with continental crust converge e.g., India and Eurasian plate collision Himalayan Mountains and the Tibetan Plateau Plate relationships prior to the collision of India with Eurasia 87  METU GEOE 231 Orogenesis: Continent‐Continent Convergence Position of India in relation to Eurasia at various times 88  METU GEOE 231 Orogenesis: Continent-Continent Convergence Formation of the Himalayas 89  METU GEOE 231 Mountain Belts Mountain building at convergent boundaries Continental accretion  Third mechanism of mountain building  Small crustal fragments collide with and accrete to continental margins  Accreted crustal blocks are called terranes  Occurred along the Pacific Coast 90  METU GEOE 231 Distribution of modern day oceanic plateaus and other submerged crustal fragments 91  METU GEOE 231 Accreted terranes along the western margin of North America 92  METU GEOE 231 Mountain Belts Buoyancy and the principle of isostasy  Evidence for crustal uplift includes wave-cut platforms high above sea level  Reasons for crustal uplift  Not so easy to determine  Isostasy  Concept of a floating crust in gravitational balance  When weight is removed from the crust, crustal uplifting occurs  Process is called isostatic adjustment 93 The Principle of Isostasy – METU GEOE 231 fundamental concept in the Geology  idea that the lighter crust must be floating on the denser underlying mantle. The physical properties of the lithosphere (the rocky shell that forms Earth's exterior) are affected by the way the mantle and crust respond to these perturbations.  crust is floating on the mantle, like a raft floating in the water, rather than resting on the mantle like a raft sitting on the ground.  Theory holds that the mantle is able to convect because of its plasticity, and this property also allows for another very important Earth process known as isostasy. 94 Erosion and resulting isostatic METU GEOE 231 adjustment of the crust  Through the process of mountain building for a period, mass (more weight) is added to a part of the crust, and  Thickened crust has pushed down into the mantle.  The crust slowly sinks deeper into the mantle and the mantle material that was there is pushed aside 95 Erosion and resulting isostatic METU GEOE 231 adjustment of the crust  Over the following tens of millions of years, the mountain chain is eroded  weight is removed by erosion  and the crust rebounds and the mantle rock flows back (mantle flow). 96 Erosion and resulting isostatic METU GEOE 231 adjustment of the crust The crust rebounds and the mantle rock flows back (mantle flow).  understanding the interactions and feedbacks shared between erosion and tectonics.  Isostatic uplift is both a cause and an effect of erosion. 97  Isostatic Uplift METU GEOE 231  understanding the interactions and feedbacks shared between erosion and tectonics.  is both a cause and an effect of erosion  When deformation occurs in the form of crustal thickening an isostatic response is induced causing the thickened crust to sink, and surrounding thinner crust to uplift  The resulting surface uplift leads to enhanced elevations, which in turn induces erosion.  Alternatively, when a large amount of material is eroded away from the Earth's surface uplift occurs in order to maintain isostatic equilibrium.  Because of isostasy, high erosion rates over significant horizontal areas can effectively suck up material from the lower crust and/or upper mantle.  This process is known as isostatic rebound and is analogous to Earth's response following the removal of large glacial ice sheets. https://en.wikipedia.org/wiki/Erosion_and_tectonics 98