Earth Science Lecture 4: Plate Tectonics PDF 2024-2025

EASCI1: EARTH SCIENCE LECTURE LECTURE 4: Instructor Jaffy Bustamante- College of Science 1ST SEMESTER / A.Y 2024-2025 Plate tectonics UNIT 2: INTERNAL PR...

EASCI1: EARTH SCIENCE LECTURE LECTURE 4: Instructor Jaffy Bustamante- College of Science 1ST SEMESTER / A.Y 2024-2025 Plate tectonics UNIT 2: INTERNAL PROCESSES THAT SHAPE THE EARTH − relates deformation to the existence & movement of rigid “plates” over a weaker, more plastic layer in the earth’s upper mantle. − it is a scientific theory where it explains how the earth’s lithosphere is divided into several large TOPIC OUTLINE rigid pieces known as tectonic plates. ◘ DEFINITION OF TERMS Asthenosphere ◘ PLATE TECTONICS: UNIFYING THEORY − it is weaker compared to lithosphere − It is a semi-fluid ◘ PLATE TECTONICS: THE BEGINNING − Located in the upper mantle ◘ EVIDENCES SUPPORTING CONTINENTAL PLATE TECTONICS: UNIFYING THEORY DRIFT PLATE TECTONICS: UNIFYING THEORY ◘ WHY IT IS REJECTED Explains Earth’s topography and integrates our ◘ A SCIENTIFIC REVOLUTION: THEORY OF scientific understanding of rock formation, mountain PLATE TECTONICS building, and terrain modification (Skinner and Murck 2011) ◘ MAJOR LITHOSPHERIC PLATES − Highlights the importance of tectonic processes ◘ TECTONIC PLATES in shaping the Earth’s surface features known as topography. ◘ PLATE BOUNDARIES − The study of plate tectonics help in understanding how landforms like mountains ◘ DIVERGENT PLATE BOUNDARIES and terrains are created and how they are modified over time. ◘ CONVERGENT PLATE BOUNDARIES Explains the distribution of plants and animals in the ◘ TRANSFORM PLATE BOUNDARY geologic past, as well as the distribution of economically significant mineral deposits (Tarbuck and Lutgens ◘ MOUNTAIN BUILDING PROCESSES, 2014). FAULTS, AND FOLDS − Emphasizes the role of plate tectonics in ◘ NORMAL FAULTS understanding the historical of distribution of life and valuable minerals on Earth. ◘ FOLDING − The movement of tectonic plates over millions or billions of years has a profound impact on the ◘ PLATE MOVEMENT OVER GEOLOGIC TIME distribution of our resources from both the past and present. ◘ TESTING THE PLATE TECTONIC MODEL: EVIDENCES OF PLATE TECTONICS PLATE TECTONICS: THE BEGINNING ◘ PALEOMAGNETISM Continental Drift Theory Alfred Wegener (1912/1915) DEFINITION OF TERMS − German meteorologist and geophysicist Tectonics − Pioneered the Continental Drift Theory in the early 20th century − study of largescale movement and deformation − continents were once a single landmass, of the earth’s outer layers. Pangaea, before it was disrupted and slowly − Branch of geology that focuses on drifted to their present position (Skinner and understanding the different processes that Murck 2011). shapes the Earth’s outer layer, specifically the − The theory is revolutionary since it challenged lithosphere. the long-term belief that the positions of the continents are stagnant. Crust − Wegener’s concepts of a once unified landmass provided a very coherent − is not static but dynamic. This is because it is explanations for the similarities observed continuously affected by internal force that across continents that are now far afar. caused them to move and change in position and shape over geologic time scale. ALVERO, VHON ANDRE T. 1 Mechanism not yet explained that’s why it was rejected despite impressive observational evidence. − Wegener’s inability to provide a convincing explanation for the mechanisms that droves the continents to move. EVIDENCES SUPPORTING CONTINENTAL DRIFT (Tarbuck and Lutgens 2014; Rabago et al. 2010) Glossopteris (Africa, Australia, India, and South The four evidence supporting continental drift America; later in Antarctica) theory are: Plant that lived for about 300,000 million years ago 1. Fit of the Continents 2. Similarities of Fossils Across Seas 3. Similarities of Rock Types and Continuity of − Found in Africa, Australia, India, and South Geologic Features America, later in Antarctica 4. Ancient Climate (Paleoclimate) − The presence of identical fossils on continents that are now widely separated by ocean only FIT OF THE CONTINENTS suggest that these continents were once part of a larger land masses. Remarkable jigsaw fit between the coastlines − Tongue-shaped leaves and seeds were too large to be carried by the wind. Shorelines continually modified by erosion and − Grew in cold areas, geographic distribution deposition. (QUESTIONABLE) closer to South Pole Consider continental shelf fit instead- the remarkable jigsaw fit between coastlines refers to the uncanny way in which the edges of continents appear to interlock, almost like pieces of a puzzle. The asymmetry of coastline suggested that the land masses might have been connected at some point in the past. This fit provided a visual clue that continent could have once been joint together. SIMILARITIES OF ROCK TYPES AND CONTINUITY OF GEOLOGIC FEATURES 2.2-billion-year-old igneous rocks in Brazil that closely resemble similarly aged rocks in Africa. Mountain belts that terminate at one coastline and reappear on landmasses across the ocean. The Appalachians trends north-eastward through the eastern United States, mountains of comparable age and structure are found in the British Isles, western Africa, and Scandinavia. SIMILARITIES OF FOSSILS ACROSS SEAS The presence of these matching geological features on distant continents provide a strong evidence for Mesosaurus (South America and Africa) continental drift. − Fossil of Mesosaurus are found in South It implies that these regions are part of a single America and Africa. landmass called Pangea. − Small freshwater reptile whose fossil are limited to black shales (Permian period) − The distribution of Mesosaurus’ fossils suggest that the two continents were once connected because the animal would not be able to cross a vast ocean. Criticism: Rafting, land bridges, island steppingstones? Response: There should be seafloor remnants of land bridges ALVERO, VHON ANDRE T. 2  ANCIENT CLIMATE (PALEOCLIMATE) tidal energy is much too weak to cause continents to be displaced. Glacial period that dated to the late Paleozoic discovered in Southern Africa, South America, A SCIENTIFIC REVOLUTION: THEORY OF PLATE Australia, and India. Presently lies within 30° of the TECTONICS equator, in subtropical or tropical climates. Earth’s Sublayers: − Glacial Deposits has been discovered in India, which is a tropical region. 1. Lithosphere − This finding suggests that the positions of the 2. Asthenosphere continents before was changed over time. − These glacial deposits in regions that are now Lithosphere (Greek: Litho means Rock) warm and tropical indicated that these areas were located closer to the pole. − This layer combines the rigid crust plus the upper-most mantle. Major coal fields in the eastern United States and − Is like the Earth’s outer shell that is made out of Northern Europe. tough solid crust. − The existence of coal beds in regions that are Asthenosphere (Greek: Astheno means weak) currently arid or dessert. − Sahara desserts were examined to have found − Partially molten part of upper mantle coal deposits and coal beds. − This layer is softer and can flow a bit like a thick − This only suggests that these areas were once gooey substance. covered with vegetation. − This is where the tectonic plates sits and moves around. Lush tropical life can make this possible − Tectonic plates are able to move about on top of the softer, partially molten asthenosphere. Southern continents were once together and located near the South Pole MAJOR LITHOSPHERIC PLATES WHY IT IS REJECTED Tectonic plates Why is it rejected? Are like giant puzzle pieces that makes up the Earth surface − Wegener had no credible mechanism for continental drift. They are called lithospheric plates because they made up of hard outer layer of the earth called the QUESTION 1: Gravitational forces of the Moon and Sun lithosphere. that produce Earth’s tides were also capable of gradually moving the continents? Are also called lithospheric plates because the crust and the upper-most mantle make up a sub-layer of the − This gravitational forces could exert a gradual earth called the lithosphere. consistent pressure on the continents, potentially causing them to push over time. The plates can move about because the uppermost mantle, or the asthenosphere, is partially molten and QUESTION 2: Larger and sturdier continents broke possesses a physical property called plasticity, through thinner oceanic crust? allowing the strong, rigid plates of the crust to move over the weaker, softer asthenosphere. − Suggests that continents, being larger and more robust compared to the thinner oceanic Major 7 lithospheric plates: crust, could potentially break through or displaced the ocean floor. 1. Pacific plate − So, in essence, it proposed that continents, due 2. North America plate to their size and strength, might have the 3. South America plate capacity to push through the thinner less 4. Africa plate resistance of oceanic crust. 5. Eurasia plate 6. Australia plate 7. Antarctic plate ANSWER THAT DEBUNKED THE QUESTIONS: Continents do not break through the ocean floor, and ALVERO, VHON ANDRE T. 3  TECTONIC PLATES Tectonic plates, or lithospheric plates, are constantly moving, being created, and consumed simultaneously. The motion sometimes results in earthquakes, volcanoes, and mountain ranges at the plate boundaries. Divergent Boundaries has 3 types: Plate motion is driven by heat escaping from the mantle. 1. Continental Rifting 2. Oceanic Ridges The constant movement of heat in the mantle leads to 3. Mid- Atlantic Ridge circular convection currents. DIVERGENT BOUNDARIES: CONTINENTAL These hot convective cells are similar to the rolling boil RIFTING that occurs when water is heated on a stovetop. Continental rifting (continental plates) The flowing mantle has also been compared to a “conveyor belt,” moving the rigid plates in different − When the Earth’s continental puzzle pieces are directions. slowly pulling away from each other, creating a new form of land or valley. Fundamentally, convection occurs due to uneven − Rift valley in East Africa heating and different densities within the liquid− causing rocks to move in a circular pattern. The word TECTONICS is of Greek origin, and it means “to build.” The word “tectonism” refers to the deformation of the lithosphere. This deformation most notably includes mountain building. PLATE BOUNDARIES DIVERGENT BOUNDARIES: OCEANIC RIDGES There are three basic ways that plates interact with one Oceanic Ridges (oceanic plates) another. Each of these plate boundaries has the potential to create different geological features. − Elevated areas of the seafloor characterized by high heat flow and volcanism. 1. When plates separate from each other = Divergent − Along the crest of some ridge segments is a boundary deep canyon-like structure called rift valley. − Mechanism that operates along the oceanic 2. When plates collide with each other = Convergent ridge system to create new seafloor is boundary appropriately called seafloor spreading. − Mid-Atlantic Ridge- a long underwater 3. When plates slide alongside each other = Transform mountain range boundary DIVERGENT PLATE BOUNDARIES Divergent Plate Boundaries − Constructive margins − Two plates move apart − creates narrow fractures in the ocean crust − upwelling of hot materials from mantle − creates new seafloor (spreading center/ spreading) ALVERO, VHON ANDRE T. 4  The relative age of the sea floor can be determined by changes in magnetic polarities of the earth. These periods of normal and reversed polarity are recorded in the magnetic minerals within the newly formed sea floor at mid-ocean ridges. Scientists can see a clear pattern of normal and reversed magnetization in the rock record that shows up as “magnetic stripes” on either side of mid-ocean ridges, which gives them a relative time of how old the sea floor is and lets them compare ocean basins to each other. DIVERGENT BOUNDARIES: MID-ATLANTIC RIDGE Mid-Atlantic Ridge The world’s longest mountain chain is underwater. It is 56,000 km long and is called the Mid-Atlantic Ridge. The Mid-Atlantic Ridge is considered a slow- spreading ridge, spreading at about 1-2 centimeters per year. An example of a fast-spreading ridge is the East Pacific Rise, which spreads at about 6-8 centimeters per year. Youngest- newly formed ridge (center) Oldest- away from the newly formed ridge (farthest from the center) CONVERGENT PLATE BOUNDARIES Convergent Plate Boundaries − Destructive margins − Two plates move toward each other (colliding) and the leading edge of one is bent downward, as it slides beneath the other (subduction). − Density of the descending plate is greater than the density of the underlying asthenosphere. Convergent plate boundaries has 3 types: 1. Oceanic-continental convergence 2. Oceanic-oceanic convergence 3. Continental-continental convergence SEA-FLOOR EXPLORATION: AGE-DATING OCEANIC- CONTINENTAL CONVERGENCE Sea-floor Exploration: Age-dating Oceanic-continental convergence Seafloor spreading − Oceanic plate and continental plate − it is a process in which a new oceanic crust is − Continental block remains “floating,” while the formed at mid ocean ridges. denser oceanic slab sinks into the mantle (since − These ocean ridges are long underwater continental plate is less dense compared to mountain ranges that runs through the Earth’s oceanic plate) Oceans. ALVERO, VHON ANDRE T. 5  − Produces continental volcanic arcs, deep ocean trenches, and earthquakes. − Example of this is the Andes Mountain Range in South America (due to Naska Plate subducting in South American Plate) TRANSFORM PLATE BOUNDARY Transform plate boundary − Also called a transform fault − It will just past through and will not change something in the lithosphere. − Despite that, it can still cause friction and pressure that will build up along the boundary, OCEANIC- OCEANIC CONVERGENCE and can also result in earthquake − Plates slide horizontally past one another Oceanic-oceanic convergence (two oceanic plates) without producing or destroying lithosphere. − EXAMPLE: San Andreas Fault in California − Two oceanic slabs converge, one descends beneath the other, initiating volcanic activity. − Newly formed land consisting of an arc shaped chain of volcanic islands: island arc − EXAMPLE: Japan trench where Pacific Trench is subducting beneath the North American Plate − Philippines (Eurasian Plate and Philippine Sea Plate) CONTINENTAL-CONTINENTAL CONVERGENCE Continental-continental convergence (two continental plates) − Buoyancy of continental material inhibits it from MOUNTAIN BUILDING PROCESSES, FAULTS, AND being subducted. FOLDS − Neither plate is subducted (WALANG PUMAPAILALIM), and this leads to the Plate tectonics cause many of the physical features formation of mountain ranges. that we see on earth today like volcanoes and − Collision event folds and deforms the earthquakes, but also many other geological features accumulation of sediments and sedimentary like faults. rocks along the continental margins. − Formation of a new mountain belt Faults − EXAMPLE: Himalayan Mountain Range/ Sierra Madre − are planar rock fractures along which movement has occurred. − There were a block of rocks that move relative to each other. ALVERO, VHON ANDRE T. 6  − This movement is often cause by an immense − The hanging wall is the overlying surface of an stress generated due to the shifting of tectonic inclined fault plane. plates. − Hanging wall- downward: Footwall: upward − The energy release create faults. − This movement creates a vertical displacement − The movement along these faults can results to often forming valleys or mountain ranges/ fault earthquake. block mountains. − Some faults associated to volcanic activities as they can provide pathways for magma to rise to the surface. − Faults are crucial geological structure that helps in understanding the dynamic processes and their impact on the landscapes. Transform fault − Occurs at a transform plate boundary like the San Andreas Fault in California. − It connects two of the other plate boundaries. FOLDING − Similar in movement, a strike-slip fault occurs through shearing when two blocks move in During mountain building processes, rocks can undergo horizontal but opposite directions of each other. folding as well as faulting. Depending on the direction of offset, it can be a “right lateral offset” or a “left-lateral offset.” Sometimes rocks deform ductilely, particularly if they are subjected to heat and pressure. At elevated temperature and pressure within the crust, folds can form from compressional forces. Entire mountain ranges, like the Appalachians, have extensive fold systems. NORMAL FAULTS Faults caused by blocks of crust pulling apart under the forces of tension are called normal faults. Normal faults − occur when the earth’s crust experienced tension (it is being pulled apart) This action caused the crust to fracture, resulting to fault. PLATE MOVEMENT OVER GEOLOGIC TIME Entire mountain ranges can form through these processes and are known as fault block mountains Alfred Wegener proposed that all of the continents once (examples: Basin and Range Province, Tetons). formed a “supercontinent” called Pangaea. − In a normal fault, the hanging-wall block From the Greek language, ‘pan’ meaning ALL and moves down relative to the foot-wall block. ‘gaea’ meaning EARTH. − The footwall is the underlying surface of an inclined fault plane. ALVERO, VHON ANDRE T. 7 It was thought to have come together and formed 4. Pangaea began to break apart into 2 halves approximately 200 million years ago. approximately 200 million years ago (Early Jurassic). The northern half is called Laurasia, and the southern Evidence for a supercontinent included: half is called Gondwanaland. These two huge continents were separated by a body of water called the 1. Fossils of the same plant (Glossopteris) found in Tethys Sea. Australia, India, Antarctica, and South America. 2. Fossils of same reptile (Mesosaurus) found in Africa and South America. This animal could not have swum across the existing Atlantic Ocean. 3. Glacial deposits found in current warm climates and warm-climate plant fossils found in what is now the Arctic. 4. Nearly identical rock formations found on the east coast of U.S. and the west coast of Europe and on eastern South America and western Africa. 5. Gondwanaland split to form Africa, South America, 1. About 1,100 million years ago, a supercontinent Antarctica, Australia and India. Laurasia split to form called Rodinia existed (Pre-Cambrian). North America, Eurasia (minus India) and Greenland. 2. Rodinia broke apart, and about 400 million years ago, the oceans began to close up to form a pre-Pangea 6. Around 15 million years ago, the continents finally (early Devonian). looked like they do today. CONTINENTS IN THE FUTURE 3. Pangea formed around 250 million years ago and In 50 million years, it is possible that the Mediterranean animals could migrate from the north to the south pole could close due to the collision of Africa with Europe. (Early Triassic). Australia may eventually join Asia. ALVERO, VHON ANDRE T. 8  Hawaii (mainland)- the oldest island is the farthest form the mainland (Kauai). The youngest island is the closest to the mainland (Maui). PALEOMAGNETISM Palaeomagnetism − This studies the ancient magnetic field recorded in rocks − When certain types of rocks forms, they record the direction and strength of the Earth’s It is though that in another 250 million years, another magnetic field Pangea will form. − By analysing these records in rocks found in different continents, scientists have discovered TESTING THE PLATE TECTONIC MODEL: patterns of magnetic reversal. EVIDENCE OF PLATE TECTONICS 1. Seafloor Spreading: Deep Sea Drilling Project (DSDP) (1968-1983) − Explore and gather data on Earth’s Ocean basin. − Age and thickness increases with increasing distance from the ridge. − Ocean basins are geologically young because no seafloor with an age more than 180 million years was found. − oceanic crust is continuously being recycled through the process of plate tectonics. Geographic North/South Pole − As new seafloor is created at mid ocean ridges, − Also known as true north/south pole older seafloor is gradually pushed over − Reference point: Rotational axis subduction. − The geographic poles are located where Earth’s rotational axis intersects the surface (fixed point where intersection of northern and southern hemisphere). − Remains relatively stable, though does experience slow shift due to changes in Earth’s rotation and axial tilt. Magnetic North/South Pole − It is the point where Earth’s magnetic field lines converge in the northern and southern hemisphere. − Reference point: Magnetic field − It is the location towards which a magnetic compass middle’s point. − It is dynamic depending on the changes on 2. Mantle Plumes and Hot Spots magnetic field over time. − Mapping volcanic islands and seamounts: Geographic vs Magnetic Pole Hawaii 1. Compass − Volcanoes increase in age with increasing distance from the Big Island of Hawaii − is a navigational instrument used to determine − Cylindrically shaped upwelling of hot rock, the direction based on the earth magnetic field. called a mantle plume located beneath the − It consists of magnetized needle or a set of island of Hawaii magnets that align itself with the Earth’s magnetic field. − Surface manifestation of this activity is a hot spot 2. Magnetic poles roughly align with the geographic − As the Pacific plate moved over a hot spot, a poles. chain of volcanic structures known as a hotspot track was built 3. The geographic poles are located where Earth’s rotational axis intersects the surface. 4. Magnetic field recorded by magnetite. ALVERO, VHON ANDRE T. 9 5. Rich in iron, as it cools down grains magnetized to align themselves to prevailing magnetic lines of forces APPARENT POLAR WANDERING Apparent Polar Wandering CONVECTION AS DRIVING FORCE − The magnetic alignment of iron-rich minerals in lava flows of different ages indicated that the Lithosphere is cold, hard, and brittle, and that the position of the paleomagnetic poles had underlying asthenosphere is hotter and more mobile. changed through time. − Either the magnetic north pole had migrated, an If the asthenosphere moves, the lithosphere must move idea known as polar wandering, or that the too, vice versa. poles had remained in place and the continents had drifted beneath them. The movement of the lithosphere is directly influenced by the movement of asthenosphere. Rising magma and the formation of new oceanic crust at a spreading ridge may be pushing the plates away from each other. Sinking fragment of lithosphere may act like a heavy weight, pulling or dragging the entire plate downward Plate to be sliding downhill away from the spreading ridge ALVERO, VHON ANDRE T. 10