* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Taiwan Geographical Environment and
Survey
Document related concepts
Transcript
Physical Geology of Taiwan By Adjunct Professor Hao-Tsu, Chu Department of Geography National Taiwan University Unless noted, the course materials are licensed under Creative Commons AttributionNonCommercial-ShareAlike 2.5 Taiwan (CC BY-NC-SA 2.5) Plate Tectonics Definition: How the Earth's surface is built of plates Key Principles: The entire outer surface of Earth is divided into rocky plates The plates are consistently in relative motion to each other Plate tectonics is responsible for most of Earth's geologic and topographical characteristics Taiwan Geographical Environment & Resources Physical Geology of Taiwan Plate Tectonics The initiator Continental drift theory by Alfred Lothar Wegener in 1912 Four major scientific advancement form the plate tectonics theory Demonstration of the ruggedness and youth of the ocean floor around 1950 Seafloor-spreading hypothesis near 1960 Confirmation of repeated reversals of the Earth magnetic field in the geologic in 1967 Precise documentation that the world's earthquake and volcanic activity is concentrated along oceanic trenches and submarine mountain ranges Taiwan Geographical Environment & Resources Physical Geology of Taiwan Plate Tectonics Provide a unified mechanism to explain Continental drift Evolution and extinction of organisms The frequencies and distribution of earthquakes and volcano eruptions The formation and location of ocean basins and continents Mountain building processes and mountain chain locations Distribution and formation of natural resources Taiwan Geographical Environment & Resources Physical Geology of Taiwan Lithosphere The plate tectonics are segments of the lithosphere. The lithosphere is the outer rigid part of the earth, including the crusts and upper mantle It floats on the asthenosphere, which is the outer plastically deforming region of Earth's mantle The lithosphere is not totally rigid, but slightly elastic Image& text courtesy of Windows to the Universe This image shows a cross section through the earth’s crust and upper mantle showing lithosphere plates (made of the crust layer and the top part of the mantle) moving over the asthenosphere (upper mantle). Taiwan Geographical Environment & Resources Physical Geology of Taiwan Two Types of Lithosphere Oceanic lithosphere Continental lithosphere About 150 km thick 50-100 km thick It develops in the ocean It makes up about 70% basins of the volume of Earth's crust It mainly consisted of mafic rocks rich in iron It comprised mostly of and magnesium granitic rock Density: 3.3g/cm3 Density: 2.7g/cm3 Taiwan Geographical Environment & Resources Physical Geology of Taiwan A – Oceanic Lithosphere B – Continental Lithosphere C – Mantle Taiwan Geographical Environment & Resources Physical Geology of Taiwan Plate Boundaries Earth's crust is fractured into about 20 lithospheric plates. The place where two plates encounter is called plate boundary Earth is dynamic and plates are kept moving very slowly relative to each other All plates move at between 2cm ~ 10cm per year Lithosphere exists as separate and distinct tectonic plates, which float on the fluid-like (visco-elastic solid) asthenosphere. The relative fluidity of the asthenosphere allows the tectonic plates to undergo motion in different directions. This map shows 15 of the largest plates. Note that the IndoAustralian Plate may be breaking apart into the Indian and Australian plates, which are shown separately on this map. Taiwan Geographical Environment & Resources Physical Geology of Taiwan Plate Boundaries It is associated with earthquakes and volcano eruptions The earthquakes of the interior area of all plates are much less frequent than ones on the plate boundaries. East African Rift: An active continental rift zone marked by a series of faults caused by volcanic action in eastern Africa Taiwan Geographical Environment & Resources Physical Geology of Taiwan 3 Types of Plate Boundaries Divergent boundaries The plates move away from each other (i.e.the Red Sea http://www.nature.nps.gov/geology/usgsnps/pltec/diverge.html) Convergent boundaries The plate move toward another (i.e. Mariana Trench) Transform boundaries The plates slide horizontally past each other (i.e. New Zealand's Alpine Fault ) Taiwan Geographical Environment & Resources Physical Geology of Taiwan Divergent boundaries 1. 2. Earth's surface layer is pulled apart and separate in the opposite directions The cracks between the plates will fill in the liquid rock (magma) and then well up from the mantle to fill the gap. Taiwan Geographical Environment & Resources Physical Geology of Taiwan Mid-Ocean Ridge The molten rock will be cooled and produce a new oceanic crust. This continuous process builds a chain of volcanoes and rift valleys called a mid-ocean ridge Taiwan Geographical Environment & Resources Physical Geology of Taiwan Mid-Ocean Ridges The mid-ocean ridge wraps around the globe for more than 65,000 km like the seam of a baseball, with an average depth to the ridge crest of 2500 m. Taiwan Geographical Environment & Resources Physical Geology of Taiwan Text courtesy of Haymon et al., NOAA-OE, WHOI. Convergent Boundaries When one plate is denser than the other; the denser lithosphere does inevitably move under the less denser. This process is called subduction Since the oceanic lithosphere may get subducted, generally the age of the ocean basins is quite young, while the older crust locates away from a ridge. Taiwan Geographical Environment & Resources Physical Geology of Taiwan Subduction Features Three key features are associated with subduction zones: Deep oceanic trenches Volcanic arc parallel to the zones Oceanic arcs (or Volcanic island arcs) Continental arcs Eearthquakes Taiwan Geographical Environment & Resources Physical Geology of Taiwan Age of Oceanic Crust In this graph, the ocean crustal age is shown by different colors. Red means the crust has been newly created on the geologic time scale; and the blue represnets the ones formed million years ago. Taiwan Geographical Environment & Resources Physical Geology of Taiwan Subduction Features Wiki mikenorton Taiwan Geographical Environment & Resources Physical Geology of Taiwan Convergent Boundaries Accretionary wedge (Accretionary prism) Sediments, the top layer of material on a tectonic plate, that accumulate and deform where oceanic and continental plates collide. These sediments are scraped off the top of the downgoing oceanic crustal plate and are added to the edge of the continental plate. Taiwan Geographical Environment & Resources Physical Geology of Taiwan Image and text courtesy of USGS Plate Collision Collisions may happen between Two continental plates A continental plate and an island arc The collision between the Indian and Eurasian plates has pushed up the Himalayas and the Tibetan Plateau Taiwan Geographical Environment & Resources Physical Geology of Taiwan Plate Driving Forces Possible driving forces for plate tectonics (coutesy of USGS) Bottom lithosphere tractions by convection currents. Trench pull (covered earlier). Ridge push (sliding off a high, crust in compression). Trench suck (rollback). Global expanding or contracting forces. Membrane forces on spinning ellipsoid (e.g. variants of polar fleeing forces). Taiwan Geographical Environment & Resources Physical Geology of Taiwan Unsolved Question on Driving Forces Ridge-push and trench-pull forces may be influenced by decreasing forces Conceptual drawing of assumed convection cells in the mantle (see text). Below a depth of about 700 km, the descending slab begins to soften and flow, losing its form. Below: Sketch showing convection cells commonly seen in boiling water or soup. This analogy, however, does not take into account the huge differences in the size and the flow rates of these cells. (Courtesy USGS) Taiwan Geographical Environment & Resources Physical Geology of Taiwan Wiki Surachit Hot Spot Volcanic regions presumed to be formed by underlying mantle that is hoteter compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. Those locations are called hot spots Postulated "hot spots" around the world Taiwan Geographical Environment & Resources Physical Geology of Taiwan Plate Velocities Plate velocities are determined by the following hypotheses: Hotspot reference frame Hotspots are fixed to one location Most hotspot chains are linear. If you know the age of two hotspots and their in-between distance, you will know the velocity of the plates when they are formed. distance time (Age) Taiwan Geographical Environment & Resources Physical Geology of Taiwan velocity Transform Boundaries It is a fault caused by tectonic plates sliding by each other, usually not smoothly, and often the reason of powerful earthquakes. They do not have obvious topographical feautures as divergent/convergent plates. Examples of some types of faults (transform boundaries). Part of them are the active producers of earthequakes globally. Taiwan Geographical Environment & Resources Physical Geology of Taiwan Aerial view of the San Andreas fault slicing through the Carrizo Plain in the Temblor Range east of the city of San Luis Obispo. (Photograph by Robert E. Wallace, USGS.) Taiwan Geographical Environment & Resources Physical Geology of Taiwan Wiki Francesco Vitali Copyrights Work License Author/Source Windows to the universe http://www.windows2universe.org/earth/interior/earths_crust.html 2011/08/02 visited Wiki USGS http://en.wikipedia.org/wiki/File:Oceanicoceanic_convergence_Fig21oceanocean.gif 2011/08/02 visited Wiki NASA http://commons.wikimedia.org/wiki/File:Subduktion_int.JPG 2011/08/02 visited Wiki USGS http://commons.wikimedia.org/wiki/File:Plates_tect2_en.svg 2011/08/02 visited Wiki USGS http://commons.wikimedia.org/wiki/File:Rift_Valley.JPG 2011/08/02 visited USGS http://pubs.usgs.gov/gip/dynamic/Vigil.html 2011/08/02 visited and revised Wiki NASA http://commons.wikimedia.org/wiki/File:Ridge_render.jpg 2011/08/02 visited Taiwan Geographical Environment & Resources Physical Geology of Taiwan Copyrights Work License Author/Source Wiki USGS http://commons.wikimedia.org/wiki/File:World_Distribution_of_Mid-Oceanic_Ridges.gif 2011/08/02 visited Wiki NOAA http://commons.wikimedia.org/wiki/File:Earth_seafloor_crust_age_1996.gif 2011/08/02 visited Wiki mikenorton http://en.wikipedia.org/wiki/Accretionary_wedge 2011/08/03 visited USGS http://earthquake.usgs.gov/learn/glossary/?term=accretionary%20wedge 2011/08/02 visited USGS http://pubs.usgs.gov/gip/dynamic/understanding.html 2011/08/02 visited Wiki Surachit http://commons.wikimedia.org/wiki/File:Oceanic_spreading.svg 2011/08/02 visited and revised Wiki Foulger http://commons.wikimedia.org/wiki/File:CourtHotspots.png 2011/08/06 visited Taiwan Geographical Environment & Resources Physical Geology of Taiwan Copyrights Work License Author/Source NASA http://rst.gsfc.nasa.gov/Sect2/Sect2_1a.html 2011/08/06 visited USGS http://pubs.usgs.gov/gip/dynamic/San_Andreas.html 2011/08/06 visited Taiwan Geographical Environment & Resources Physical Geology of Taiwan