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Lecture 9

Lecture 9

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Environmental Science
Nick Eyles

EESA06 Lecture 9 Page 1 EESA06 Lecture 9 The Plate Tectonic Future of Planet Earth – Where are we headed? 1) Alpine-Himalayan Orogeny: The building of the next supercontinent (Pangea II) - obduction 2) Obduction processes as Indian sub-continent collides with Asia 3) Destruction of the Tethys Ocean 4) Uplift of the Himalayas and Climate Change – in Africa created humans - Orogenic belt – cooling temperatures “History Doesn’t Repeat Itself: But it Often Rhymes” - Earth History tells us of the future - On the cusp of a resource boom - Pacific is closing, Atlantic could be closing - Everything is heading in the Japan direction - Locus of next super continent = south east asia Obduction – process where continents collide together = earthquakes - India colliding into Asia creating Himalayans - Effects are felt over a very large area – China, Pakistan experience major earthquakes - Started around 20 million years ago - Mediterranean is a remnant of the ocean that laid between Africa and Europe EESA06 Lecture 9 Page 2 Obduction (Fig 2.29) - Compression zone - most common type of rock is gneiss – high grade metamorphic rock, high pressure, high temperature - Ex: Canadian shield – used to be high mountains - Granite pluton – is more acidic, high content of silica - Rhyolite – produced from high explosive volcanism, local melting no subduction - No volcanoes in Himalayans - Fold and thrust belts - Cover rocks – dominantly sedimentary rocks in high pressure o High contents of resources: oil + gas - Ophiolite – remnants of oceanic crust o Green rocks result from basalts China Seismic Zones: Epicenters of Major Earthquakes - Indenter Model - India wedge into China - Occur in linear belts, major faults Alpine-Himalayan Orogeny - Orogeny – the process of mountain building - Orogen – name given to the folded rocks that results o Ex: Western Alps, Tibetan Plateau Closure of the Tethys Ocean as Pangea breaks up - Southern Continents = Gondawana - Tethy’s Ocean – destroyed - Northern Continent = Mega Laurasia - India separated by a mid-ocean ridge (Dark Blue) EESA06 Lecture 9 Page 3 Obduction (Fig 22.9): - A Ocean-continent convergence: Subduction of the ocean floor - B Continent-continent collision: Obduction – shearing and thrusting on a huge scale - Fallen basin - large mountains depresses the weak- athenosphere (ex: Rocky mountains), shallow sea waves accumulate around deltas o Creation of tar sands = oil, gas (ex: western interior sedimentary basin, east of Rockies) o Ancient fallen basins: dinosaur remains Mount Everest - Sedimentary rocks, limestone which was once part of a sea floor – similar to Niagara Destructive Earthquakes in China: - 2008 Sichuan – creation of large urban areas, high populations A Cooling Planet After 55Ma - Blue line = average global temperature - Paloscene-Eocene Thermal Maximum (PET)– more methane, trap heat, warmer planet - How to get climate out of sediment record - North Atlantic deep water production – big change in the way planet/ocean circulation behaves - Ocean freezes – salt gets driven out, result in brine (highly saline sea water, high density) How do we know this? – studying the ocean floors - Sediment accumulates at the bottom of ocean floor, change in microfossils when there are cold saline waters - Onset of Himalayan orogeny – drawndown of CO 2 o High mountains – gravity erodes them, Everest will not grow taller o Kahumbu – conveyer belt moving sediment away from Mt. Everest - 3 million years ago – oscillation between ice age and interglacial – living in this phase right now India The Bengal Fan – Submarine fan
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