3 - Lithosphere.pdf

Lithosphere: The Solid Part of the Earth  Earth’s solid structure; ▪ describe the changes in the Earth’s continental LEARNING arrangements t...

Lithosphere: The Solid Part of the Earth  Earth’s solid structure; ▪ describe the changes in the Earth’s continental LEARNING arrangements through Theory OBJECTIVES on Plate Tectonics; and 2 ▪ analyze how the Earth’s activities have shaped the Earth’s physical features ▪ identify the different parts of the  The Earth’s Structure What are the different parts of the Earth’s structure? 4 The Earth’s Structure  Inner Core–solid and very dense, and hasa radius of 1390 km; magnetized and hasa temperature of about 4000-4700 ˚C. Transition Zone– about 700 km think; boundary between outer and inner core 5 The Earth’s Structure Outer Core– liquid molten metallic iron; less dense and less hot than inner core; generates at least 90% of the Earth’s  magnetic field Gutenberg Discontinuity– uneven line that separates the outer core from the inner mantle 6 Magnetic Field ▪ protects the Earth from solar wind and cosmic radiation ▪ experiences Geomagnetic Reversal in which its polarity sometimes fades to zero and then returns to full strength, with the magnetic poles reversed *Note: Magnetic field does not blink on and off 7 The Earth’s Structure Inner Mantle- about 1200 km thick; made of olivine, iron/magnesium silicates Upper Mantle- about 350  to 700 km thick; made of olivine, silicate minerals Note: Mantle contains the largest mass among the three main layers of the Earth (about 70% of the mass) 8 The Earth’s Structure Asthenosphere– contains pockets of increased heat from  radioactive decay and is susceptible to low convective currents; thick layer of plastic mantle material (can be deformed) Above asthenosphere is the elastic solid (solid and brittle) is the uppermost mantle, which is part of the lithosphere. The Earth’s 9  Structure ▪ The boundary between mantle and crust is known as Mohorovicic Discontinuity. ▪ Crust is the outermost, cold, rigid, and thin layer of the Earth. Its thickness is up to about 70 km. It can be classified as: ❖Continental – essentially granite; crystalline and high in silica, aluminum, potassium, calcium and sodium ❖Oceanic – basalt, high in silica, magnesium, and iron; denser and  thinner than continental crust 10 The Earth’s Structure ▪ The difference between the elevation of the continents and oceans is determined principally by differences in the thickness and density of the crusts – known as isostasy. ▪ Isostasy is the balance of all large portions of Earth’s lithosphere as though they were floating on the denser underlying layer, the asthenosphere - a section of the upper mantle composed of  weak, plastic rock. ▪ Crust sinks when the load is heavier, and it experiences isostatic rebound if the load is reduced. Plate Tectonics What is plate tectonics? How did it affect the surface of the Earth? History of Plate 12  Tectonics Several people in the past (including Humboldt and Bacon) noted that the bulge of South America seemed to fit into the bight of Africa. In the early 20th century, Alfred Wegener and Frank Taylor independently proposed that the fit was not accidental and that the continents are drifting on the surface of the Earth.  Wegener suggested that there was a large single continent that existed millions of years ago called Pangea. History of Plate 13 Tectonics A wide range of evidence, apart from the fit of continents across  the Atlantic, was advanced to support the theory of continental drift. Rare, identical fossils were found in rocks on different continents, now separated by thousands of kilometers of ocean. Glaciations that were known to have occurred in Carboniferous times appeared to have affected contiguous areas but only if the continents were fitted back together.  14 Plate Tectonics Likewise, mountain belts of similar age, rock types and tectonic history such as the mountains of Scandinavia, the Highlands of Scotland and the Appalachians of North America could all be fitted together within a reconstructed supercontinent. History of Plate Tectonics 15  Wegener’s theory was not taken seriously until after World War II. Detailed bathymetric surveys exposed valleys at the center of the mid-ocean mountain ranges, and interpreted as evidence for the pulling apart of the ocean basins. These are used as one of the first direct pieces of evidence of continental drift. History of Plate Tectonics 16  Henry Hess’ theory on the convection cells within the mantle also gave an explanation to the sinking of the older crusts on the trenches and the creation of new crusts in the sea floor. Henry Hess’ theory became known as the “Sea Floor Spreading”. History of Plate Tectonics 17  The changes in the direction of the magnetite as they moved from the oceanic ridges is also seen as another proof of the existence of plate tectonics. The study of earthquakes and the amount and deepness of sedimentary cover are also another pieces of evidence that plate tectonics exist. 18 What is Plate Tectonics? It states that the Earth’s lithosphere is divided into a series of rigid plates which are outlined by the major earthquake belts of the world.” Plate 19  The boundaries of the plates coincide with: ❖mid-ocean ridges ❖transform faults ❖trenches ❖growing mountain belts The following are the major lithospheric plates: ✪Pacific ✪Australian ✪Eurasian ✪African ✪North American ✪South American ✪Antarctic  20 Mid-Ocean Ridges  spreading centers where the lithosphere is created faster spreading rate, broader mountain range associated with that spreading; slower spreading rate, steeper slopes characteristic  21 Subduction of the Lithosphere  In contrast to the upwelling zones along the mid-ocean ridges are the areas of descending lithosphere known as subduction zone. When the continental crust and the oceanic crust slowly collide, the denser ocean floor will grind beneath the lighter continental crust.  The subducting slab of crust exerts a gravitational pull on the rest of the plate – an important driving force in plate motion. Subduction of the 22 Lithosphere The world’s deep ocean trenches coincide with the subduction zones and are the lowest features on Earth’s surface.  The world’s deepest trench is the Marianas or Mariana Trench with an elevation of about -11, 030 m. The deepest trench in the Atlantic Ocean is the Puerto Rico Trench (-8605 m), and the deepest trench in the Indian Ocean is the Java Trench (-7125 m). 23 Cross-Section of Marianas Plate 24 Tectonics 25 Plate Boundaries DIVERGENT PLATE TRANSFORM PLATE CONVERGENT PLATE BOUNDARIES BOUNDARIES BOUNDARIES boundaries where plates occur when one plate slides boundaries where plates move away from each horizontally past another move toward each other other plate 26 Plate Boundaries  plate intersections are not only locations susceptible to readjustment in the lithosphere some breaks weakened to the point that they become hotspots, areas of volcanic eruption due to rising plume of molten materials  History of the Continents How did the continents evolve into its contemporary appearances? History of the 28  Continents The study of past geographical environments is known as PALEOGEOGRAPHY. The goal of paleogeography is to try to reconstruct the past environment of a geographical region based on geologic and climatic evidence. The GEOLOGIC TIMESCALE is the calendar of Earth history. EONS are divided into ERAS;  ERAS are divided into PERIODS; PERIODS are divided into EPOCHS. History of the 29 Continents Using the magnetic record found within the oceanic crust and other direct evidence, it has been possible to reconstruct accurately the history of  continental drift over the past 200 million years. The reconstruction would result to the supercontinent that was created more than 200 million years ago called PANGAEA (or Pangea). Supercontinent Cycle 30 31 Some of the Supercontinents: Nuna or Columbia (1.8 to 1.35 billion years ago) 32 Some of the Supercontinents: Rodinia (1.07 – 0.75 billion years ago) 33 Some of the Supercontinents: Pannotia (0.62 – 0.55 billion years ago) 34 Some of the Supercontinents: Pangaea (0.335 – 0.173 billion years ago) 200 m.y. ago  History of the 35 Continents PANGAEA (or Pangea), the latest supercontinent, was comprised of two smaller continents, namely: Laurasia and Gondwana (or Gondwanaland). Laurasia was composed of modern- day North America, Asia (except India), and Europe. Gondwana was comprised of  modern-day Africa, Arabia, India, Madagascar, Antarctica, and Australia. The superocean that surrounded Pangea is called Panthalassa. History of the Continents 36 The Earth (600 million years ago to present times)37 Future of the Earth’s Continents 38 Earth’s Surface Relief Features and Topographic Zones What are the different relief features of the Earth? What are the topographic regions of the world?  Earth’s Surface 40 Relief Features Relief refers to the vertical elevation differences in the landscape. Topography is the study of the land surface. In particular, it lays the underlying foundation of a landscape.  The relief and topography of Earth’s landforms played a vital role in human history. Earth’s Surface Relief Features 41  Contour Lines (Isolines) connect points of equal elevation. ⮚ If the contours are close together, the slope is steep ⮚ If the contours are spread apart, the slope is gradual 42 Earth’s Surface Relief Features  Earth’s Surface Relief Features 43 Hypsometry is the measurement of land elevation. Bathymetry is the measurement of depth of water in oceans, seas, or lakes. 44 Topographic Regions of Earth 45 than 600 m; may be as low ❖ PLAINS – local relief of as 60 m at the edge of the less than 100 m (325 ft.); sea has gentle slope angles of ❖ MOUNTAINS – local relief ≤ 5˚; more than 600 m ❖ HILLS – local relief of ❖ HIGH TABLELANDS – more than 100 m but less elevation of over 1520 m with local relief of less than 300 m ❖ ❖ DEPRESSIONS – basins LOW TABLELANDS – surrounded by mountains, hills, elevation less than 1520 m or tablelands, which abruptly (5000 ft) with a local relief of delimit the basins less than 100 m 46 Crustal Formation and Deformation  Processes Geomorphic Process 48 PROCESSES processes that originate within the Earth result in an increase in surface relief EXOGENIC PROCESSES processes that originate at the Earth’s surface ENDOGENIC  result in an decrease in surface relief Endogenic 49 Processes Endogenic Processes result in gradual uplift and new landforms, with major mountain building occurring along plate boundaries. The following are the categories of uplifted crustal regions: ❖Residual mountains and stable continental cratons ❖Tectonic mountains and landforms ❖Volcanic features Endogenic Processes 50 Continental Shield – a region where a craton is  exposed at the surface. Craton – old and stable part of the lithosphere. Building 51 Continental Crust  Formation of continental crust involves the entire sequence of sea-floor spreading and formation of oceanic crust, its later subduction and remelting, and its subsequent rise as new magma.  52 53 Diastrophism Diastrophism refers to the large-scale deformation of Earth’s crust by natural processes, which leads to the formation of ocean basins, mountain systems, continents, etc. Diastrophism involves broad warping, folding, faulting and leveling 54 Crustal Deformation Processes Rocks are subjected to powerful stress by tectonic forces, gravity, and weight of overlying rocks.  The types of stress are tension, compression, and shear. 55 Crustal  DeformationProces ses Strain depends whether the rock is brittle or ductile. Folding occurs when rocks are compressed such that the layers buckle and fold; ductile deformation. Faulting occurs when rocks fracture under the accumulation of extreme stress created by compression and extensional forces; brittle deformation. 56 Crustal Deformation Processes: Folding 57 Crustal Deformation Processes  Faulting is an action in which rock is forcefully broken or fractured with an accompanying displacement of the crust. There might be uplift on one side and downthrust on the other, slide to each other, or separate away from each other (rift). 58 Philippine Geologic History by Wu, J., et. al. (2016) Case of the Philippines by Earth Observatory of SG59 Basins and Sea Floor Spreading by Lallemand, S. (2016)  Case of the 61 Philippines Case of the Philippines 62 Rocky Mountains Mountain Appalachian Andes Building 63Orogenesis is the Alps thickening of the continental crust and the mountain building episode over millions of years. Orogenesis occurs either by forcing the materials  upward or causing one plate to be subducted below the other. Types of Orogenies 64  Oceanic Plate – Oceanic Plate Continental Plate Continental Plate – Oceanic – Continental Collision Plate Collision Plate Collision Example: Example: Example: Nazca Plate and Philippine Plate Indian Plate and South American and Eurasian Eurasian Plate Plate Plate Endogenic Processes: Igneous Processes 65 Landforms resulting from igneous processes may be related to the eruptions of extrusive igneous rock material or emplacements of intrusive igneous rocks. Volcanism refers to the extrusion of rock matter from Earth’s subsurface to the exterior and the creation of surface terrain features in this way. Plutonism refers to igneous processes that occur below the  Earth’s surface including the cooling of magma to form intrusive igneous rocks and rock masses. Volcanic Eruptions 66 Although large, violent eruptions tend to be infrequent events, they can devastate the surrounding environment and completely change the nearby  terrain. Types of eruption: ❖ Explosive –pieces of molten and solid rocks are violently blast into the air. ❖Effusive – molten rocks pour less violently onto the surface as flowing streams of lava Volcanic Eruptions 67 Variations in eruptive style and in the landforms produced by volcanism result mainly from temperature and chemical differences in the magma that feeds the eruption. ❖ Silica-rich felsic magmas tend to be  relatively cool in temperature while molten and have a viscous consistency; have the potential to erupt more violently ❖ Malfic magmas are more likely to be extremely hot and less viscous, and thus flow readily in comparison to silica-rich magmas; tend to be effusive than explosive Types of Volcanic Landforms – Lava Flows 68 LAVA FLOWS are layers of erupted  rock matter that when molten poured or oozed over landscape. After they cool and solidify they retain the appearance of having flowed. Lava flows do not have to emanate directly from volcanoes, but can pour out of deep fractures in the crust, called fissures. Multiple layers of basalt flow may create constructed relatively flat topped, but elevated tablelands called basalt plateaus. Types of Volcanic Landforms - Shield 69 SHIELD VOLCANOES - formed by lava flows of low viscosity - lava that flows easily. Consequently, a volcanic mountain having a broad profile is built up over time by flow after flow of relatively fluid basaltic lava issuing from vents or fissures on the surface of the volcano.  The extremely hot and fluid basalt can flow long distances before solidifying, and the accumulation of flow layers develops broad, dome shaped volcanoes with gentle slopes. Types of Volcanic Landforms: 70 Shield Volcanoes Skjaldbreiður – Iceland Republic of Congo Nyamuragira– Democratic  Types of Volcanic Landforms: Cinder Cones CINDER CONES- smallest type of volcano; typically only about a couple of hundreds of meter high; steep conical hill of loose pyroclastic fragments It generally consists largely of gravel-sized pyroclastic fragments into the air. The pyroclastic fragments are formed by explosive eruptions or lava fountains from a single, typically cylindrical, vent. 71 Types of Volcanic Landforms: 72 Cinder Cones Mount Suribachi – Iwo Paricutin – Mexico Jima, Japan  Types of Volcanic 73 Landforms: Composite Volcanoes COMPOSITE CONES- known as stratovolcanoes, result when formative eruptions are sometimes effusive and sometimes explosive.  Composite cones are composed of a combination of lava flows and pyroclastic materials. Types of Volcanic Landforms: 74 Composite Volcano Its shape is considered by many people as the classic volcano shape. Lavas either flow through breaks in the crater wall or  issue from fissures on the flanks of the cone. Lava, solidified within the fissures, forms dikes that act as ribs which greatly strengthen the cone. Types of Volcanic Landforms: 75 Composite Cones Mt. Mayon - Mt. Apo Philippines - Philippines Types of Volcanic Landforms: 76 Composite Cones Mt. Kanlaon Philippines - Mt. Arayat -  Philippines Types of Volcanic Landforms: 77 Composite Cones Mt. Banahaw - Philippines  - Philippines Mt. Makiling Types of Volcanic Landforms: 78 Composite Cones Sakurajima - Japan Types of Volcanic Landforms: 79 Composite Cones Mt. Kilimanjaro - Tanzania Types of Volcanic Landforms: 80 Composite Cones  Pico de Orizaba Mexico Mt. Rainier/ Tahoma - USA