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Lecture 9

Planet Earth-Lecture 9.docx

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Environmental Science

Lecture 9  Final exam: focus on plate tectonics and last two lectures (10 and 11). Chapters 1-4, 11, 19, 20.  Future planet Earth  Supercontinent cycle: can use to predict future  Pangea 2  Alpine-Himalayan Orogeny: Indian Sub-continent collides with Asia after 25 Ma destroying the Tethys ocean.  Uplift of the Himalayas and climate change after 2 Ma.  Orogeny: mountain building  Alps, Himalayas have long kms belt which record closure of an ocean called the teths (teths ocean). Mediterranean is a reminant, a dying ocean createdqueezing of teths ocean between India and Africa as they move North  Climate (100, 000 year cycles) in Canada? Interglacial (short compared to ice age). Around 10,000 years ago. Before that, ice was here. Ice thirty thousand years ago and Ice age 100,000 years ago.  Long ice ages (100,000) and short interglacials.  Present interglacial should’ve stopped a long time ago but is extended by our activities.  Ice ages and interglacials result of uplift of Himalayas. Uplift changed global climate. Resulted in global cooling.  Changes in climate in Africa near the rift are controlled by the uplift of Himalayas and global climatic change that it made (species origination).  Peak of Pangea: Teths Sea (around it with a big continent)  As Pangea breaks up, the teths ocean gets squeezed (northern movement of Africa and India). Thrusts, subduction, obduction- cause long Himalayan belt-mountains made up of reminant of teths ocean  Mediterranean sea (reminant of teths ocean): will be part of the alpine block and will be a continuous range from alps to Himalayas down to Indonesian arc (Building of next supercontinent). India embedded in Eurasia.  How to view the future? View the process backwards. 250 million years in the future.  Closure of the Tethys ocean as pangea breaks up: 200 mill  East Gondwana (Australia): Proximity to Tokyo in 70 million years. Moving up. Collide with Southeast Asia  Pangea 2: obduction o Indian crust and asia grows in size  Obduction not have that subduction has? No under thrusting. Subduction recycles oceanic crust. Volcanoes with subduction. Slabs pulled down (max: 700 km). Obduction: no melting, some thrusting, no volcanoes, two plates colliding.  Volcanoes absent in area undergoing subduction.  North America: by obduction: not just destroying but also creating crust  Subduction zone (ocean): colliding oceanic plate against oceanic crust.  Indonesian island arc, Japan island arc created by subduction of oceanic crust. Production of volcanoes  Volcanism produces island arcs that are regarded as continenetal crust.  Island arcs: rocks dominated by andesites (have silica) and are less dense than continental crust. Buoyant, less dense but cannot be subducted themselves. Over millions of years, island arcs will collide with other platelets and aggregate bigger continents.  First continent of the world probably looked like an island arc that exists today.  Grabon: area of extending crust where blocks are growing down forming valleys. Valleys with step sides. Grave in Italian. Valleys are grounded by faults. Which ones? Normal faults. Allowing central blocks of grabbon to subside. Horsts (bounding blocks on either side of grabbon): rift shoulders, high standing, can look into the grabbon basin.  Compression plus extension Asian plate stretched  Indenter: India: pushing away China, Southern Asia. As they are escaping from collision zone, there is extension  Asthenosphere: base floor. Soft rocks in which plates are moving. Continenetal crust dominate by gneiss. Across the two plates: there is a suture.  Ophiolites: ancient oceanic crust dominated by basalt but what is distinct about the basalt? Pillow basalt (round masses that tell us that basalt was erupted underwater of the floor of the ancient water-typically occur along sutures). Fold and thrust belts on either sides of suture (good examples are Appalachians and Rocky mountains). Thrusts shoved over gneiss (important for oil and gas). Antecline: rocks are closed-important in terms of oil and gas because it creates a trap, hydrocarbons migrating from depth become trapped in folded rocks.  Some melting going on in granite plutons (aka batholiths).  (NO UNDERTHRUSTING, NO VOLCANOES)  Professor Augusto Gansser: wander through Himalayas. In 1920-30s. Dress up as a Buddhist monk. Made a profound discovery: ophiolites in the Himalayas, ancient marine rocks and fossils, pioneer in understanding origin of Himalayas. Existence of teths ocean before India collided, recognization. Swiss geologist. Book: geology of Himalayas  Arabian plate into Europe (like India). Turkey trying to move away.  China: massive earthquakes due to India’s push.  China is cursed by Himalayas  Tangshan earthquake in 1976  China: country driven by major faults.  Obduction: there is some subduction.  India is pushing underneath Asian continental crust. Tibetan plateau (uplifted crust). Mount Everest  Thrust fault. Locked. What do they produce? Seismic gaps. No activity. But gaps get filled. Gap filling earthquakes Tibetan plateau: highest elevation anywhere in the world  Albido: ability of surface to reflect light. Snow cover will change it. If high plateau surface and has snow fall, it will reflect light and heat. Heat will go back into the planet.  Mount Everest: not getting much higher than a few mm a year. Why? Erosion! Losing huge volumes of rock by frost activity. When water seeps through and freezes. Freezing causes breakage of rocks. The rate of uplift and rate of erosion about the same.  Alpine Himalayan orogeny: deformed rocks from the closure of the Tethys ocean. From Southern Spain through Alphs to Indonesia.  African crust pushed right up into Europe.  Mattterhorn: made up of African rocks  Far field stresses: communicated through the plate by active orogeny.  Durdle Door: rocks have ammonites: kings of the Tethys ocean. Buoyancy chambers with rims. Can adjust their depth at which they propel themselves at jetting out water.  Matterhorn: African rock. What’s at the base of mountain? Detachment zone: major fault where rocks are moved over older rocks below. Actual mountain form is young. The rocks are much older. So mountain is not thrusted but rocks are. In response to glaciations, rocks are carved by glacials.  Folded Tethys ocean rocks in the Alps:  Mount Everest: sedimentary rocks on top. Yellow band made up of limestone seen along Niagara escarpment.  Rocks in Southern Ontario: not subjected to compressional force
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