GEOL 101 Plate Tectonics
GEOL 101 Plate Tectonics GEOL 101
Popular in Introductory Geology
verified elite notetaker
Popular in Geology
This 3 page Class Notes was uploaded by Victoria Williams on Saturday February 20, 2016. The Class Notes belongs to GEOL 101 at George Mason University taught by Mark Uhen in Fall 2016. Since its upload, it has received 19 views. For similar materials see Introductory Geology in Geology at George Mason University.
Reviews for GEOL 101 Plate Tectonics
Report this Material
What is Karma?
Karma is the currency of StudySoup.
Date Created: 02/20/16
Plate Tectonics Plate tectonics is the underlying paradigm of modern geology o Unifies much of that data about the earth that was once thought to be unconnected o The theory is relatively new, started in the 1960’s and accepted over 1970’s o The theory of plate tectonics states that the crust and the uppermost mantle are broken into a series of plates that move around the surface of the earth. Wegener 1915 noted that continental margins fit together like puzzle pieces, proposed a single supercontinent, called Pangea. South America and Africa fit together particularly well Evidence? o Fossil Faunas. Across the Southern continents when they were all together (Gondowana), fossils of many different creatures and plants were found across the continents that wouldn’t have been able to swim to get to the other continents, so they had to be connected. o More evidence? Mountain ranges line up along with specific types of rocks. There is also matching glacial evidence on South America, Africa, and Australia. A giant glacier in old Antarctica left marks on these continents that can be seen today. Continental drift: where did Wegener go wrong? o Wegener challenged the existing scientific paradigm, which was that continents were stable. o He had no believable mechanism by which the continents could move Earth’s Magnetic Field o Dip needles can measure your latitude on the earth by sensing magnetic fields and where you are placed on earth o Apparent Polar Wandering – the poles have wandered in the past, showing where the continents moved Geomagnetic Reversal o Every few million years, the magnetic poles of the earth reverse. The way it is now is ‘Normal’ and the opposite way is ‘Reversed’ o Scientists can tell when the poles switch through the colors of certain magmatic rocks. White means normal, red means reversed Oceanic Magnetic Stripes o The rocks of the ocean floor have stripes of the red and the white rock. And there is one distinct line that divides the rock, and the rock is symmetrical in color on either side. The line is called a ridge axis o When magma comes through the ridge, it rises and crystalizes, it then gains the color of the magnetic pole orientation at the time. o As the magma comes up and solidifies, the ocean floor moves. This is Sea Floor Spreading. o The Sea Floor Spreading causes the earth’s plates to move apart. All land masses are connected to the plates and they move with them. o As the plates move and grow, some parts of the plates subduct under other plates and are ‘recycled’ back into the mantle. Gravity plays a part in how these plates move, spread, and subduct. Geo Trivia o How many major plates are on the surface of the earth? Answer: 7 main plates o Plates can have only oceanic crust on it, but there is often a mix of oceanic and continental crust Two kinds of crust o Continental – Thicker, about 2570km thick, less dense, composition: granite, not recycled o Oceanic – Very thin, only about 710km thick, but more dense, composition: basalt, recycled Three kinds of plate boundaries: o Divergent – Plates move apart, mantle comes up and makes more oceanic crust. Ex. MidAtlantic Ridge, a ridge in the Atlantic that is broken up into segments that are connected by transform fault lines. Juan de Fuca plate makes new crust that is almost immediately consumed under North America. This plate will disappear soon. Continental Rifting – Mantle coming up under a continent, creating dense ocean crust that lies lower than the continent, allowing a small linear sea to form, which can then become a larger ocean. o Convergent – Plates come together Oceanic crust coming in contact with continental crust, the oceanic crust is more dense so it will always subduct under the continental crust. When the oceanic crust subducts and starts partial melting in the mantle, the melted material will come up and create volcanoes/mountains Example – West coast of South America o Transform – Plates slide past one another Not common, mostly in the ocean. Rarely on continents, but there is one in North America in California. It is called the San Andreas Fault system Hot Spots o Mantle plumes under the crust, a collection of superhot magma that begins to rise in one area o Magma will rise through the crust and release through it. This creates a volcano on either continental crust or oceanic crust. If enough magma comes through, it will form an island. o The hot spot remains in the same spot, and as the plate moves the hot spot will keep punching through and create a chain of islands (ex. Hawaii) o Hot spots can also be under continents, an example in North America is in Yellowstone Mechanisms o Ridge Push – gravity driven force that results from elevated position of the ridge o Slab pull – Reults from sinking of a cold dense slab of oceanic lithosphere under continental crust