GEOL 101 1nd Edition Lecture 33 Outline of Last Lecture I. Evidence of Plate TectonicsII. Force Driving Plate TectonicsOutline of Current Lecture I. Types of StressII. FoldsIII. FaultsIV. Andean-type OrogenesisV. Continental Collision Current Lecture- Deformation: general term that refers to all the changes that happen as a result of stress and strain of a rock.- Most crustal deformation occurs along plate boundaries- There are three types of stresses that a rock may be subjected to:o Compressional  Rocks are pushed and squeezed together Results in folded rock layers and thrust faulting Produces large quantities of metamorphic rocks Occurs at convergent plate boundarieso Extensional  Rocks are stretched and pulled apart Results in normal faults Produces “basin and range” provinces  Occurs at divergent plate boundarieso Shearing Rocks are displaced in a lateral motion- Card deck analogy Results in strike-slip faultsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Occur at transform plate boundariesFolds- One product of deformation is folding- Folds result from compressional forces that warp flat-lying sedimentary strata into wave-like bends-There are two basic types of folds:- Anticlines – folded upwards like an archo Based on the law of superposition, the oldest rocks are in the middle of the fold- Synclines – folded downwards like a trough or a U-shapeo Based on the law of superposition, the youngest rocks are in the middle of the fold-Very often, anticlines and synclines occur together, in an undulating pattern- Special kinds of folds: some features are folded upwards or downwards on all sides, rather than just two sides- Domeso Circular, or slightly elongated up-warping of rockso Oldest rocks are in the coreo Ex: Black Hills, SD- Basinso Circular, or slightly elongated down-warping of rockso Youngest rocks are in the coreo Ex: Michigan BasinFaults- Another product of deformation is faulting- Faults: fractures (breaks) in the rocks along which significant displacement has occurred-Three types of faults:- Normalo Hanging wall moves down along the fault planeo Occur as a result of extension (stretching of the crust)o Prevalent at sea floor spreading centers and continental rift basinso May produce fault-block mountains o Examples: Basin and range province of the western US, Grand Tebous, WY- Reverse (thrust)o Hanging wall moves along fault plane o Occur as a result of compression (squeezing of the crust)o Prevalent at subduction zones and continent-continent collisiono Reverse faults with dip angles of less than 45° are called thrust faults o Older rocks are pushed up and over younger rockso Examples in the Himalayas, Rocky Mts, Glacier National Park- Strike-Slipo Occur as result of shearingo Displacement is horizontal (lateral), rather than verticalo Displacement may be to the right, or to the left: Right-lateral strike-slip  Left-handed strike-slipo Example: San Andreas Fault, CA Telling right-lateral vs. left-lateral:- If you were following some feature (such as a road or a fence) thatwas offset by a fault, you can tell if it is right- or left-lateral by the way you would turn to follow the feature- Right-lateral – shearing is to the right (Make right hand turn)- Left-lateral – shearing is to the left (Make left hand turn)-Anatomy of faults:- Fault plane –surface along which sliding occurs - Hanging wall – the rock surface directly above the fault planeo The fault block you would hang on- Footwall – the rock surface directly below the fault planeo The fault block you would put your foot on- Fault scarp – line or cliff created by a fault dangleMountain Building- The geologic term for mountain building events is Orogenesis, from the Greek “oro” (mountain) and “genesis” (birth)-Most orogenic events occur along convergent plate boundary- Compressive forces result in folding and faulting (mostly thrust faulting)-Two types of mountain building may occur at convergent boundaries:- Continent-continent collision (Himalayas)- Andean-type subductionAndean-Type Orogenesis1. Prior to the formation of a subduction zone:- The continental plate is said to have a “passive margin”- No mountain building is occurring yet- Thick sequences of sedimentary rocks are being deposited off of the coast- Reg East coast of North American2. During the formation of a subduction zone:- Compressional forces force the oceanic plate, so it gets pushed down underneath the continental plate- The oceanic plate is denser than the continental plate, so it gets pushed down underneath the continental plate- This initiates a subduction zone and decompressional deformation3. After the initiation of a subduction zone:- The continental margin is said to be an “active margin”- The subducting plate causes partial melting in the overriding plate, initiating volcanismo Continental volcanic arcs - EX: Cascades, Sierra Madres, Andes- The compressional forces squeeze the edge of the continent, causing the rocks to be folded and faulted-The sedimentary rocks that were deposited at the passive margin become faulted and folded- This makes up the accretionary wedge- Rocks in the accretionary wedge are highly deformed- Post-subduction zone- The subduction zone may become inactive, and the continental plate may be uplifted- The core of the volcanic arc may become expanded as is it the accretionary wedgeo Examples: Sierra Nevadas and coastal ranges in CaliforniaContinental Collision -As subduction continues, the oceanic plate gets smaller and smaller- Eventually, it may disappear entirely as two continents draw closer together-When there is no more oceanic plate to subduct, the two continents may collide- The classic modern example is India colliding with Eurasia to form the Himalayas***** The Appalachian Mountains were also formed during continental collision as Africa collided with North American during the assembly of Pangea*****- During subduction and collisional mountain building smaller blocks of crust called terranes may also collide with the continental margins - These are not full continents, but usually islands or bits of less dense oceanic crust- This process is called accretion.- This has occurred extensively along the Pacific coast of North America as