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Bathymetric Chart of the Sea Floor DASAR LAUTAN Physiographic Map of the Sea Floor 3-D Computer Generated Image of the East Pacific Rise 1 Relief of Sea Floor (Bentuk Dasar Laut) Major relief ocean bottom : * Continental margin * Ocean basin floor * Mid ocean ridge Continental margin: * Continental Shelf * Continental Slope * Continental Rise Ocean basin floor: * Oceanic rise * Abyssal floor * Seamount dan Guyot * Trenches (palung) Mid ocean ridge (punggung ditengah samudera): - Mid Atlantic Ridge - Mid Indian Ridge - Pacific-Atlantic Ridge - East Pacific Rise Basins are depressions of the sea floor more or less equidimensional in form and of variable extent. Canyon are relatively narrow, deep depressions with steep slopes, the bottoms of which grade continuously downward. Continental (or island) shelves are zones adjacent to a continent (or around an island) and extending from the low-water line to the depth at which there is usually a marked increase of slope to greater depth. Continental (or island) slopes are the declivities seaward from the shelf edge into greater depth. Plains are flat, gently sloping or nearly level regions of the sea floor, e.g. an abyssal plain. Ridges are long, narrow elevations of the sea floor with steep sides and irregular topography. Seamounts are isolated or comparatively isolated elevations rising 1000 m or more from the sea floor and of limited extent across the summit. Sills are the low parts of the ridges separating ocean basins from one another or from the adjacent sea floor. Trenches are long, narrow, and deep depressions of the sea floor, with relatively steep sides. 2 Asal –usul Ocean Basin (Dasar Lautan) (1) Continental Drift Pergerakan daratan gunung-gunung dalam skala yang lebih luas pergerakan benua (movement of continent) continental drift Pergerakan massa benua pada permukaan bumi (2) Sea Floor spreading Mengapa benua bergerak relatif terhadap yang benua lainnya berkembang teori ‘sea floor spreading’ Kerak (crust) dasar benua yang baru dan materi kulit (mantle) bagian atas yang kaku bertambah sepanjang rangkaian deretan gunung-gunung pada dasar lautan dan bergerak tegak lurus menjauhi punggung (ridges) gunung-gunung tersebut. (3) Mencakup proses secara menyeluruh : Plate Tectonic Ada sejumlah lempengan (plate) utama kedalam mana batuan atau lithosphere dapat di pisah-pisahkan. Interaksi antara lempengan ini saat mereka bergerak menghasilkan bentuk-bentuk struktur kerak bumi yang dapat diamati. Tectonic (Junani) pembentukan Struktur Kerak bumi. 3 4 5 Geological Periods Precambrian Cambrian Ordovician Silurian Devonian Early Carboniferous Late Carboniferous Permian Triassic Jurassic Late Jurassic Cretaceous K/T extinction Eocene Miocene Modern Future World Future Future 4.6 B 514 Ma 458 Ma 425 Ma 390 Ma 356 Ma 306 Ma 255 Ma 237 Ma 195 Ma 152 Ma 94 Ma 66 Ma 50.2 Ma 14 Ma 570 Ma solidification Gondwana, hard shell anim. separation, coldest Laurentia collides with Baltica pre-Pangea, equatorial forests western Pangea is complete deserts, reptiles, major ext. Life begins to rediversify,Pangea Dinosaurs, Pangea starts to break Pangea rifts apart, Atlantic New oceans, India end of dinosaurs India collides with Asia Modern look +50 Ma N. Atlantic widens, Med. vanish +100 Ma new subduction +250 Ma new Pangea Precambrian break-up of the supercontinent, Rodinia, which formed 1100 million years ago. The Late Precambrian was an "Ice House" World, much like the present-day. Cambrian Animals with hard-shells appeared in great numbers for the first time during the Cambrian. The continents were flooded by shallow seas. The supercontinent of Gondwana had just formed and was located near the South Pole. Ordovician During the Ordovician ancient oceans separated the barren continents of Laurentia, Baltica, Siberia and Gondwana. The end of the Ordovician was one of the coldest times in Earth history. Ice covered much of the southern region of Gondwana. Devonian By the Devonian the early Paleozoic oceans were closing, forming a "prePangea". Freshwater fish were able to migrate from the southern hemisphere continents to North America and Europe. Forests grew for the first time in the equatorial regions of Artic Canada. Silurian Laurentia collides with Baltica closing the northen branch of the Iapetus Ocean and forming the "Old Red Sandstone" continent. Coral reefs expand and land plants begin to colonize the barren continents. Early Carboniferous During the Early Carboniferous the Paleozoic oceans between Euramerica and Gondwana began to close, forming the Appalachian and Variscan mountains. An ice cap grew at the South Pole as fourlegged vertebrates evolved in the coal swamps near the Equator. 6 Late Carboniferous By the Late Carboniferous the continents that make up modern North America and Europe had collided with the southern continents of Gondwana to form the western half of Pangea. Ice covered much of the southern hemisphere and vast coal swamps formed along the equator. Permian Vast deserts covered western Pangea during the Permian as reptiles spread across the face of the supercontinent. 99% of all life perished during the extinction event that marked the end of the Paleozoic Era. Formation of the Rocky Mountains http://wrgis.wr.usgs.gov/docs/parks/province/rockymtn.html Triassic The supercontinent of Pangea, mostly assembled by the Triassic, allowed land animals to migrate from the South Pole to the North Pole. Life began to rediversify after the great Permo-Triassic extinction and warm-water faunas spread across Tethys. Jurassic By the Early Jurassic, south-central Asia had assembled. A wide Tethys ocean separated the northern continents from Gondwana. Though Pangea was intact, the first rumblings of Mountains Subduction zone Rocky continental break up could be heard. Late Jurassic The supercontinent of Pangea began to break apart in the Middle Jurassic. In the Late Jurassic the Central Atlantic Ocean was a narrow ocean separating Africa from eastern North America. Eastern Gondwana had begun to separate form Western Gondwana Cretaceous During the Cretaceous the South Atlantic Ocean opened. India separated from Madagascar and raced northward on a collision course with Eurasia. Notice that North America was connected to Europe, and that Australia was still joined to Antarctica. 7 Collision of continental crust K/T extinction The bull's eye marks the location of the Chicxulub impact site. The impact of a 10 mile wide comet caused global climate changes that killed the dinosaurs and many other forms of life. By the Late Cretaceous the oceans had widened, and India approached the southern margin of Asia. Eocene 50 - 55 million years ago India began to collide with Asia forming the Tibetan plateau and Himalayas. Australia, which was attached to Antarctica, began to move rapidly northward. 3-2 Sea-Floor Spreading • Whereas oceanic ridges indicate tension, continental mountains indicate compressional forces are squeezing the land together. Sedimentary Rocks Squeezed by Compression Miocene 20 million years ago, Antarctica was coverd by ice and the northern continents were cooling rapidly. The world has taken on a "modern" look, but notice that Florida and parts of Asia were flooded by the sea. Last Ice Age When the Earth is in its "Ice House" climate mode, there is ice at the poles. The polar ice sheet expands and contacts because of variations in the 8 Modern World We are entering a new phase of continental collision that will ultimately result in the formation of a new Pangea supercontinent in the future. Global climate is warming because we are leaving an Ice Age and because we are adding greenhouse gases to the atmosphere. Modern World If we continue present-day plate motions the Atlantic will widen, Africa will collide with Europe closingthe Mediterranean, Australia will collide with S.E. Asia, and California will slide northward up the coast to Alaska. Future +100 Future +250 9 Bukti-bukti bahwa benua pernah bersatu: (1) Umur Batuan: * fossil * Umur radioaktif batuan (2) Kehidupan purbakala dan Cuaca: rekaman fossil lingkungan masa lalu (3) Orientasi magnet benua: * perubahan posisi kutub (polar wandering) * Pembalikan arah magnet (magnetic reversal) (4) Sea Floor Spreading * Umur batuan makin semakin jauh dari MOR * Orientasi magnit batuan 10 Evidence for Continental Drift: Puzzle Figure 1-8a Tectonic Plates According to Wegner, the continents are sections of a past super continent called Pangea, which broke apart and drifted to their present locations. Evidence for Continental Drift: Fossils Now-Extinct Life Forms Preserved in the Geologic Record tell a story Source: J. C. Carton/Carto/Bruce Coleman, Inc. New York 11 Evidence for Continental Drift: Rock Record Pangaea 200 to 300 Millions of Years Before the Present Source: William E. Ferguson Sea-Floor Spreading: 3-2 Movement at ridges • Axis of the oceanic ridge is offset by transform (strike-slip) faults which produce lateral displacement. Ridges and rifts indicate movement. 3-3 Global Plate Tectonics Earth’s geomagnetic field is recorded as new crust cools. New crust. Parallel bands of crust with the same magnetism form along the ridge. Segmented Ocean Ridge Driving Mechanisms for Plate Motions 12 Geomagnetic Polarity Reversals Magnetic Anomalies When new crust materials crystallizes, some minerals align themselves with Earth’s magnetic field, as it exists at that time, imparting a permanent magnetic field, called paleomagnetism, to the rock. Periodically Earth’s magnetic field polarity (direction) reverses poles. Geologic Time 3-2 Sea-Floor Spreading Modern humans 1_14 Extinction of dinosaurs Flowering plants and grasses • Rocks forming at the ridge crest record the magnetism existing at the time they solidify. • Sea floor increases in age and is more deeply buried by sediment away from the ridge because sediments have had a longer time to collect. First mammals Earliest dinosaurs Early reptiles Primitive fish • Rates of sea-floor spreading vary from 1 to 10 cm per year for each side of the ridge and can be determined by dating magnetic anomaly stripes of the sea floor and measuring their distance from the ridge crest. • Continents are moved by the expanding sea floor. 13 3-3 Global Plate Tectonics Because Earth’s size has not changed, expansion of the crust in one area requires destruction of the crust elsewhere. • Currently, the Pacific Ocean basin is shrinking as other ocean basins expand. 3-3 Global Plate Tectonics • Destruction of sea floor occurs in subduction zones. • Subduction is the process at a trench whereby one part of the sea floor plunges below another and down into the asthenosphere. • Seismicity is the frequency, magnitude and distribution of earthquakes. Earthquakes are concentrated along oceanic ridges, transform faults, trenches and island arcs. • Tectonism refers to the deformation of Earth’s crust. 3-3 Global Plate Tectonics • Benioff Zone is an area of increasingly deeper seismic activity, inclined from the trench downward in the direction of the island arc. 3-3 Global Plate Tectonics Earth’s surface is composed of a series of lithospheric plates. Plate edges extend through the lithosphere and are defined by seismicity. • Plate edges are trenches, oceanic ridges and transform faults. • Seismicity and volcanism are concentrated along plate boundaries. South Figi Basin and Cross Section Showing Benioff Zone 14 3-3 Global Plate Tectonics Movement of plates is caused by thermal convection of the “plastic” rocks of the asthenosphere which drag along the overlying lithospheric plates. Plate Rifting (cont'd): Earths Internal Heat Engine Driving Mechanisms for Plate Motions Figure 1-10 Mid-Ocean Ridge 3-3 Global Plate Tectonics • Mantle plumes originate deep within the asthenosphere as molten rock which rises and melts through the lithospheric plate forming a large volcanic mass at a “hot spot”. Mantle Plume 15 3-3 Global Plate Tectonics The Wilson Cycle Wilson Cycle refers to the sequence of events leading to the formation, expansion, contracting and eventual elimination of ocean basins. • Stages in basin history are: – Embryonic - rift valley forms as continent begins to split. – Juvenile - sea floor basalts begin forming as continental fragments diverge. – Mature - broad ocean basin widens, trenches eventually develop and subduction begins. – Declining - subduction eliminates much of sea floor and oceanic ridge. – Terminal - last of the sea floor is eliminated and continents collide forming a continental mountain chain. 3-4 Transform Faults The San Andreas fault in southern California is a transform fault that connects the sea-floor spreading ridge of the Gulf of California with the spreading ridge off Oregon and Washington. 3-4 Transform Faults Because the San Andreas fault has an irregular trace, strike-slip motion can cause local compression or tension. • If these plate motions continue, Baja will splinter off California. Fault Geometry 16 3-4 Juvenile Ocean Basin • The Red Sea is a juvenile ocean basin that is forming as the African plate diverges from the Arabian plate. 3-4 Juvenile Ocean Basin Hot, salty groundwater is dissolving metals from the rocks and depositing them as metal sulfides in dense brine pools like the Atlantis II Deep. • New basaltic ocean crust is just beginning to form in the center of the Red Sea. Atlantis II Deep Quiz 1 • Apa beda plate teori plate tektonik dan continental drift • Apa yg di maksud dgn siklus wilson • Apa yang dimaksud dengan – Ridge – sill 17