Study Guide Exam 3

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South Texas College *

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Geology

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Apr 3, 2024

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Physical Geology Study Guide Exam 3 Answer the following questions: 1) Define Metamorphic Rock. Where Metamorphism generally occur? Metamorphic Rocks form by the alteration of preexisting rock because of pressure, high temperature and/or chemically active fluids Metamorphism occurs well below the surface of the earth but at shallower depths and temperatures than would cause rocks to melt. 2) Describe Metamorphism. What are the three agents of metamorphism? What types of rock can be metamorphosed? Metamorphism conditions within the earth result in the changing of the texture and mineral content of a solid rock without melting it. Any type of rock may be metamorphosed- igneous, sedimentary, or even metamorphic. 3) Define Parent Rock. Why are parent rocks important? A Parent rock is the original rock before the metamorphism takes place. In addition to heat pressure and fluid activity, the composition of the parent rock helps determine what metamorphic rock forms. 4) Describe what can be changed during the process of metamorphism. Process of Metamorphism can change both the texture and the mineral composition of the parent rock 5) What is the parent rock for marble? Describe what occurs when this metamorphosis takes place. Does the mineral content change during this process? What happens to fossils? Limestone is the Parent Rock of Marble. When limestone is metamorphosed into marble the crystal size of it changes but not the chemical composition it will recrystallize usually forming larger crystals. 6) What is the parent rock for quartzite? Describe what occurs when this metamorphosis takes place. Does the mineral content change during this process? Why is quartzite a very resistant rock? Quartz Sandstone is the parent rock of Quartzite. Both sandstone and quartzite are composed of SiO2. When sufficient heat and pressure are applied to a sandstone the grain fuses together to form a very resistant rock quartzite. 7) Describe what happens to shale as it undergoes the process of metamorphism. What rocks are formed at low grade metamorphism, medium grade metamorphism, and high-grade metamorphism? Does the mineral content change during this process? Which of these metamorphic rocks has the finest grain size and which of these metamorphic rocks has the coarsest grain size? When shale undergoes metamorphism, it creates new minerals in response to the escalated heat and pressure conditions. Slate is formed at low grade, Schrist at medium,

and Gneiss at high grade metamorphism. The content does change during the process. Slate has the finest grain size, while Gneiss has the coarset grain size. 8) Can slate be formed from any parent rock? Explain why or why not. No, It can only be made from shale or mudstone because every rock has a rock from which it was formed (parent rock). 9) What minerals are almost exclusively found in metamorphic rocks? Kyanite, Sillimanite, and some Garnett. 10) List and describe (in detail) the three basic types of metamorphism. Contact - Occurs when magma comes into direct contact with the parent rock • Changes in the parent rock are primarily due to very high temperatures but not increased pressures • Immediately next to the magma intense metamorphism results in the formation of coarse grained crystals • Moving away from the magma the results in the formation of coarse grained crystals • Moving away from the magma the resulting rock becomes progressively finer grained • A contact metamorphic zone occurs when a parent rock is intruded by molten magma Sheer - Results from the intense pressures that exist along active fault zones where rock units slide past each other • Mechanical deformation and recrystallization of the minerals result from the heat pressure and movement of fluids as rock units slide or shear past one another Regional - Affects extremely large areas and is caused by a combination of both high temperature and high pressure • Most areas that are affected by regional metamorphism are areas undergoing intense deformation due to mountain building processes 11) Describe how metamorphic rocks are classified. Describe the two types of textures. Metamorphic rocks are classified by texture and mineral composition. Textures • Foliated- rock exhibits layering or color banding • Nonfoliated - rock is nearly uniform throughout 12) Describe how and where foliation occurs. The enormous pressure that accompanies regional metamorphism causes the newly formed mineral grains to align themselves in a distinctly parallel arrangement. Only rocks that are metamorphosed under intense pressure will exhibit foliation. Metamorphic rocks that form entirely due to high temperatures will not have foliation. 13) Describe the progressive patterns of foliation that develop in metamorphosed shale. • Slaty cleavage- develops when a shale undergoes mild metamorphism

• Schistosity - Found in foliated metamorphic rocks with larger, visible crystals. Generally, the result of the parallel arrangement of platy (micas) and ellipsoidal mineral grain. • Gneissic - layering forms under intense regional metamorphism and displays color banding 14) Create a table for the Foliated Rocks that contains Parent Rock, Metamorphic Rock, Key Minerals, and Characteristics. 15) Describe why nonfoliated rocks are nonfoliated. Rocks subjected to uniform pressure from all sides or lacking minerals with distinctive growth habits will not be foliated. The chemical composition of nonfoliate rocks is more consistent than foliated rocks. 16) Create a table for the Nonfoliated Rocks that contains Parent Rock, Metamorphic Rock, Key Minerals, and Characteristics. 17) List and describe the factors that control metamorphic rock characteristics. Mineral Composition of the Parent Rock : The initial rock before metamorphism determines the minerals present, affecting their stability during changes in temperature and pressure. Temperature : Influences mineral stability; certain minerals change or recrystallize at different temperature ranges. Pressure : Alters mineral stability and rock texture. Varying pressures lead to denser rocks and may induce foliation. Fluids (Primarily Water) : Facilitate mineral and ion transfer between and within rocks, expediting metamorphic reactions and aiding in element transportation. Time : Metamorphic processes occur slowly over vast timescales, often associated with slow tectonic activities, such as mountain formation and erosion. 18) Describe the hydrothermal processes associated with metamorphism. What minerals are often associated with hydrothermal veins? •Metamorphism: Water transmits pre-existing ions between grain •Metallic: ore deposits often form this way The minerals often associated with hydrothermal veins include quartz, calcite, sulfides (like pyrite, chalcopyrite, galena, and sphalerite), barite, and fluorite. 19) Define structural geology and geologic structures. Structural geology is the study of the shapes arrangement and interrelationships of rock units and the forces that cause them. Geologic structures are dynamically produced patterns or arrangements of rock or sediment that result from and give information about forces within the earth. Produced as rock change shape and orientation in response to applied stress 20) Define stress. What are the three types of stress and at what type of plate boundary do these occur?

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Stress in geology refers to the force applied to a rock per unit area. It's categorized into three main types: Compressive Stress : Forces acting to squeeze or shorten a rock. This stress occurs at convergent plate boundaries, where tectonic plates move toward each other. Tensile Stress : Forces pulling or stretching a rock apart. This stress occurs at divergent plate boundaries, where tectonic plates move away from each other. Shear Stress : Forces causing rocks to slide past each other horizontally in opposite directions. This stress occurs at transform plate boundaries, where tectonic plates slide past each other horizontally. 21) Describe how rocks respond to stress and what is their response dependent upon? Rocks behave as elastic, ductile, or brittle materials depending on: • Amount and rate of stress application • Types of rocks • Temperature and pressure If deformed materials return to their original shape after stress removal, they are behaving elastically. However, once the stress exceeds the elastic limit of a rock, it deforms permanently • Ductile deformation involves bending plastically • Brittle deformation involves fracturing. 22) How are rock structures determined, how are they represented on a map, and what are some of the common structures? Rock structures are determined on the ground by geologists observing rock outcrops. Outcrops are placed where bedrock is exposed at the surface. Geologic maps use standardized symbols and patterns to represent rock types and geologic structures, such as tilted beds, joints, faults, and folds 23) Describe dip and strike. How are they used? Timed beds, joints, and faults are planar features whose orientation is described by their strike and dip • Strike is the compass direction of a line formed by the intersection of an inclined plane with a horizontal plane • Dip is the direction and angle from horizontal in which a plane is oriented 24) What are folds, axial plane, hinge line, and limb? Describe the two types of horizontal folds. • Folds are wavelike bends in layered rocks. Represent rock strained in a ductile manner, usually under compression • The axial plane do fold into its limbs • The hinge line (or axis) of the fold is the surface trace of an axial plane. 25) What are plunging folds? Describe the types.

Plunging folds are bends in rock layers where the fold's axis isn't horizontal but instead tilts into the Earth at an angle. These folds give insights into the geological forces that shaped the rock layers. Anticlinal plunges : where the axis points upwards. Synclinal plunges : where the axis points downwards. 26) Describe domes, basins, joints, and faults. •Domes- structures in which the beds dip away from a central point, Sometimes called doubly plunging anticlines • Basins- structures in which the beds dip toward a central point, Sometimes called doubly plunging synclines • Joints- fractures in bedrock along which no movement has occurred, Multiple parallel joints are called joint sets • Faults- fractures in bedrock along which movement has occurred, Considered "active" if movement has occurred along them within the last 11,000 years, Categorized by the type of movement as dip-slip, strike-slip, or oblique-slip. 27) Define fault plane, hanging-wall, foot-wall and upthrown side. Fault Plane- an approximately planar surface along which the actual movement takes place. Hanging-wall- The fault block that is on the uppermost side of an incline fault plane Foot-wall- The fault block that is on the lowermost side of an incline fault plane Upthrown side- The fault block that has moved up relative to the other side is termed the upthrown side 28) What are dip-slip faults? Describe the two basic varieties and thrust faults. Dip- slip faults have movement parallel to the dip of the fault plane. • Normal faults- the hanging-wall block has moved down relative to the footwall block. • Reverse faults- the hanging- wall block has moved up relative to the footwall block 29) Describe fault blocks, horsts, and grabens. Fault blocks, bounded by normal faults, that drop down or are uplifted are known as grabens and horst, respectively. • Grabens associated with divergent plates boundaries are called rifts • Thrust fault are reverse faults with dip angles less than 30% from horizontal 30) What are strike-slip faults? What is a right-lateral strike-slip fault? What is a left- lateral strike-slip fault? Which variety is the San Andreas Fault? What are oblique-slip faults? Strike-slip faults have movement that is predominantly horizontal and parallel to the strike of the fault planes

• A viewer looking across to the other side of a right-lateral strike-slip fault would observe it to be offset to the right • A viewer looking across to the other side of a left-lateral strike-slip fault would observe it to be offset to their left. • Oblique-slip fault have movement with both vertical and horizontal components 31) Define earthquake. In general, what causes earthquakes? Where do most of the earthquakes occur? An earthquake is a trembling or shaking of the ground caused by the sudden release of energy stored in the rocks beneath earth surface • Causes of the earthquake: movements of lithospheric plates cause fault in the crustal material 1. A few small or medium of the earthquakes are vocanic in origin 2. Earthquakes can also result from human caused explosions or football games • Almost 95% of the earthquakes occur at the edge of interacting plates 32) Describe the elastic rebound theory. Stresses are exerted on the rock formation in adjacent plates, as movement occurs. Sine rock have elastic properties, energy Is stored until the stresses can overcome the friction between the two plates. At the moment of energy release, the rocks along the fault suddenly move, the energy is released, and an earthquake occurs. Energy is released during earthquakes in the form of seismic waves. 33) How are earthquakes associated with the “ring of fire”? The Ring of Fire, surrounding the Pacific Ocean, hosts frequent earthquakes due to the collisions and subductions of tectonic plates, leading to intense seismic activity across the region. This area's numerous subduction zones and plate interactions create a high frequency of smaller but still notable earthquakes within the Ring of Fire. 34) Define fault and where do most of the faults occur in the world? Fault : fracture or zone of fractures within Earth's crust where there has been movement or displacement of rocks on either side of the fracture. This movement can be horizontal, vertical, or lateral. Most faults occur along tectonic plate boundaries, where the Earth's lithospheric plates interact. 35) Describe (in detail) the San Andreas fault. The San Andreas Fault, stretching 800 miles along California's coast, marks where the Pacific Plate meets the North American Plate, causing horizontal movement. Divided into segments, it varies in seismic activity. Famous for the 1906 quake, it's not all about earthquakes—many movements are not seismic. Ongoing research helps gauge risks for populated areas nearby.

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36) Define focus and epicenter. •The point of the initial movement, or energy released, along the fault is called focus. The focus is generally underground. From a few miles perhaps several hundred miles in depth •The point on the earth's surface directly above the focus is designated the epicenter. This is the surface position that receives the greatest impact from the earthquake 37) Define seismic waves, seismology, and seismograph. Seismic Waves : These are energy waves that travel through the Earth, generated by earthquakes or other sources, conveying information about the Earth's structure. Seismology : The scientific study of earthquakes, seismic waves, and the Earth's internal processes to understand its structure and seismic hazards. Seismograph : An instrument that detects and records seismic waves caused by earthquakes or other sources, producing a visual representation called a seismogram. 38) Describe the Richter Scale and the Modified Mercalli Scale. What are the strong points and weaknesses of each? Richter Scale : quantifies an earthquake's magnitude based on seismic wave amplitude, offering a numerical rating for comparison but saturating for larger events and lacking consideration for depth or local geology. Modified Mercalli Scale : assesses earthquake intensity by observing effects at specific locations, providing detailed descriptions of impact but relying on subjective human observations and lacking a standardized quantitative measurement. Richter quantifies energy release, while Mercalli details the impact on people and structures, allowing a fuller understanding of earthquakes. 39) Describe the Effects of Earthquakes including tsunamis. Earthquakes produce several types of effects, all of which can cause loss of property and human life • Ground motion is the familiar trembling and shaking o the land during an earthquake • Can topple buildings and bridges • Fire is a problem just after earthquakes because of broken gas and water mains and fallen electrical wires • Landslides can be triggered by ground shaking, particularly in larger quakes • Liquefaction occurs when water-saturated soil or sediment sloshes like a liquid during quake • Permanent displacement of the land surface can also occur, leaving fractures and scarp 40) Describe in detail the two types of body waves and the two types of surface waves. Which is the most destructive? Primary Waves (P-Waves) : Fastest, move through solids, liquids, gases, cause compression. Secondary Waves (S-Waves) : Slower, move through solids, cause shearing. Surface Waves: Love Waves (L-Waves) : Horizontal motion at the surface.

Rayleigh Waves (R-Waves) : Circular motion affecting both vertical and horizontal directions. Surface waves, particularly Rayleigh Waves (R-Waves), are considered the most destructive during earthquakes due to their slower speed and larger amplitudes, causing significant ground displacement and structural damage. 41) Describe how the size of displacement affects the size of the earthquake. The rocks on opposite sides of a fault are offset or displaced in proportion to the size of the earthquake. In a small quake, the fracturing stops within a few seconds and the displacement may be as a fraction of a inch. In the largest quakes, the fracturing may last several minutes, and the displacement may be more than 50ft. 42) Describe what is felt during an earthquake. During an earthquake , an observer experiences an initial jolt, caused by P waves, and then a second larger jolt caused by an S wave. After this double shaking, the observer experiences a rolling and swaying motion that is caused by Surface Wave. 43) Describe how scientists locate an earthquake. Plotting distance from 3 stations on a map , as circles with ratio equaling the distance from the quake, locate earthquake epicenter. 44) Describe the depth of focus for earthquakes. • Shallow focus (0-70 km deep) • Intermediate focus (70-350 km deep) • Deep focus (350-670 km deep) 45) Where in the United States do most of the earthquakes occur? What is seismic risk and what areas in the U.S. have a high risk? Earthquakes are much more common in the western states and Alaska. Largest seismic risk or hazard exist near the plate boundaries along the U.S Pacific coast (e.g San Andreas fault) and around New Mandrid, Missouri. 46) Where in the world do most of the earthquakes occur? Most Earthquakes occur in narrow geographic belts which mark tectonic plate boundaries, the most important concentrations in, circum-Pacific (about 90%) and Mediterranean- Himalayan belts. 47) Where do shallow-focus, intermediate-focus and deep-focus earthquakes occur? Shallow-focus : within 70 kilometers of the Earth's surface along plate boundaries. Intermediate-focus : between 70 to 300 kilometers deep, often in subduction zones. Deep-focus : exceeding 300 kilometers in depth, also occur in subduction zones, providing insights into tectonic plate interactions and earthquake dynamics at various depths within the Earth’s crust.

48) Describe (in detail) the relationship between earthquakes and plate tectonics. Earthquakes occur due to the movement and interactions of Earth's tectonic plates. Stress accumulates at plate boundaries, exceeding the rock strength and causing sudden movements or fractures, resulting in earthquakes. Different types of plate boundaries lead to distinct seismic activities, shaping the Earth's surface and serving as key indicators of the dynamic nature of Earth's crust. 49) Describe the famous earthquakes that we went over in class. 50) Describe how we predict earthquakes and earthquake precursors. An earth quake prediction is a precise statement, location, and size of the future quake. Thousands of lives could be saved each year if such predictions could be made accurately. Unfortunately, the field of quake prediction is still in its infancy. 51) Describe how scientists have interpreted the internal structure of the earth using seismic waves. • Seismic waves travel through the earths interior • S waves do not travel through the liquid outer core • P waves are refracted at density boundaries 52) List and describe the four layers of the Earth. Crust: The outermost layer, including the continental and oceanic crust. Mantle: Lies beneath the crust, divided into the upper and lower mantle. Outer Core: Composed of liquid iron and nickel. Inner Core : Solid iron and nickel at the Earth's center. 53) Describe the two types of crust. What is the Mohorovicic discontinuity? Continental Crust : Thicker, less dense, forming continents with an average depth of 30- 50 kilometers. Oceanic Crust : Thinner, denser, making up ocean floors, averaging 5-10 kilometers in depth. The Mohorovicic Discontinuity (Moho) marks the boundary between the Earth's crust and mantle, representing the transition from less dense crustal rocks to denser mantle rocks. It sits at an average depth of 5-10 kilometers beneath the oceanic crust and 20-70 kilometers beneath the continental crust. 54) Describe the lithosphere and the asthenosphere. Lithosphere- outermost rigid, brittle layer, composed of the entire crust and uppermost mantle, most faults and earthquakes occur in the lithosphere. Asthenosphere- lies beneath the crust extending down to approximately 70km due to its high temperature. This layer is plastic, mobile, and is essential for tectonic plate motion.

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