TEST 3 REVIEW DEFORMATION Change in 1 Location 2 Orientation 3 Shape or Volume i Due to applied stress STRESS force per unit area Stress causes deformation o Weight is a force weight mg m mass g gravity accel Pressure Object feels the same stress on all sides Compression Squeezing greater stress in 1 direction Tends to thicken material Extension Pull apart greater stress in 1 direction Tends to thin material Shear Blocks of rock sliding past one another Crust is neither thickened or thinned STRAIN Change in shape or volume from stress DEFORMATION TYPES 1 Brittle material breaks discontinuous 2 Ductile material flows without breaks continuous Dependant on 1 Temperature 2 Pressure 3 Deformation Rate 4 Composition Deformation Stages of Fractures part 1 brittle Faults Crack WITH relative movement Recognized by o Offset displacement slip o Fault scarp o Drag folds o Fault breccia gouge o Slip lineations Mylonite actually ductile but depends on T P and composition Offset really same as displacement Drag Folds Small folds accompanying faults and resulting from fault motion FAULT CLASSIFICATION 1 Dip Slip movement along fault plane dip a Normal b Reverse 2 Strike slip 3 Oblique slip most common type a Thrust 35 degrees Faults Brittle Features Caused by rapid deformation rate Fractures part 2 JOINTS Natural cracks without movement Tensional forces o Tectonic collision o Nontectonic exfoliation Systematic regulary spaced long repeating Nonsystematic random short Water bearing zones Defines state of stress in rock Vein mineral filled jFoint Folding continuous deformation ductile Anticline arch Syncline trough vs ductile Brittle deformation Rocks do not all deform similarly Ductile Deformation continuous deformation Rock does not break Favored by high T and P and in salt and shale Brittle Deformation discontinuous deformation rock breaks or fractures Favored by low T and low to moderate P Active Mountain Ranges Linear range of mountains Orogeny Mountain building event processes that collectively produce a mountain belt Most mountain building at convergent boundaries They form along current plate boundaries Ranges within plates generally mark old continental collisions As soon as mountain begins growing erosion attacks Can only grow if uplift erosion Crustal Roots Isostasy High mountains are supported by thickened lithosphere Thickening is caused by collisional orogenesis o Average continental crust 35 to 40 km thick o Beneath Orogenic belts 50 to 70 km thick This thickened crust helps buoy the mountains upward Concept of a floating crust in gravitational balance o Pushing up pulling down When weight removed crustal uplifting occurs o Process is called isostatic adjustment o Wants to be in Isostatic Equilibrium Death of a mountain range Erosion and resulting isostatic adjustment of the crust erosion uplift Residual mountains The two sides of a non vertical fault are known as the hanging wall and footwall By definition the hanging wall occurs above the fault plane and the footwall occurs below the fault Various methods to make mountains 1 Orogenesis of a volcanic island arc mountain Aleutian type Founding in shrinking ocean basins such as the Pacific Similar process of hotspot mountain 2 Orogenesis along an continental volcanic arc mountain Andean type Passive Margin Thrust faulting igneous intrusions Plutons Underplating Regional metamorphism 3 Continent Continent collisions Suture zone where two land masses are joined 4 Continental Accretion Small crustal fragments collide accrete to continental margins Accreted crustal blocks are called terranes 5 Mountain building associated with Rifts a Continental thinning i Normal faulting block rotation ii Footwall can go up iii Narrow elongate mountain ranges The Wilson Cycle Appalachians The Grenville orogeny formed a supercontinent By 600 Ma much of this orogenic belt has eroded away The Grenville organic belt rifted apart 600 Ma This formed a new ocean Eastern North America developed as a passive margin A thick pile of sediment accumulated aong this margin An east dipping subduction zone built up an island arc Taconic Orogeny collision of an island arc Acadian Orogeny collision of an microcontinent Alleghenian Orogeny continental collision NJ mountains Through our mountains are the roots of the Appalachians their current elevation is actually formed due to differential erosion waves Interior Earth s using seismic Structure rock distribution is determined from seismic waves Seismic rays are perpendicular to wave fronts Fermat s Principle A ray takes the path that minimizes the travel time Seismic rays are reflected and refracted as a discontinuity Boundary separating rocks with different densities velocities Seismic Rays Velocity increases down Wave front oblate and not spherical due to velocity changes Epicenter the point on the earth s surface vertically above the focus of an earthquake A point can be used to locate the hypocenter of an earthquake also known as the focus which is in fact a true point that point at which the slip of an earthquake begins Hypocenters are therefore always located at some depth underground For general purposes it is more common to refer to the location of an earthquake by plotting its epicenter on a map An epicenter has no physical meaning it is simply the point on the Earth s surface directly above the hypocenter Waves in the mantle P main P wave S main S wave PP Reflected P wave SS reflected S wave The Mantle and Core Mantle Distribution The 400 km Seismic Discontinuity From the P and S wave curves velocities increase in a small jump at 400 km When Olivine squeezed at P equals to depth of 400 km the atoms rearrange into denser polymorph polymorphic transition Vs and Vp increase with depth in mantle Waves reflecting off core mantle boundary PcP P wave reflection ScS S wave reflection Waves traversing liquid outer core PKP P wave through outer core PKKP P wave in core reflects off core mantle boundary Waves interact with inner core PKIKP P wave through inner core PKiKP P wave reflects core core boundary Why do we have all this good data Permanent Observatories Italian national network Temporary network of portable seismic observatories Convergent Boundary Ocean continent subduction zone processes 1 Plates locked stress deformation 2 Plates release earthquake tsunami Fossil remnant or trace of an ancient living organism that has been preserved in rock or sediment What helps preserve fossils Death in a low energy