Week Ten Notes-Geology G-104
Week Ten Notes-Geology G-104 GEOL-104 20584
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This 2 page Class Notes was uploaded by Ashley Hughes on Wednesday March 25, 2015. The Class Notes belongs to GEOL-104 20584 at Indiana University taught by Laura Wasylenki in Spring2015. Since its upload, it has received 135 views. For similar materials see Evolution of the Earth in Geology at Indiana University.
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Date Created: 03/25/15
32415 G104 gtkFor what kinds of rocks can I directly determine the age of formation by radiometric dating 0 O O O O Basalt Sandstone Granite Fossiliferous limestone All of the above gt I have a sandstone with a lot of pink potassium feldspar clasts and a lot of orange potassium feldspar clasts I measured the K40Ar40 ratio in each batch of grains and I got two different ages What could this mean 0 0 Answer doesn t make sense I messed up the analysis somehow The older age is the age when the minerals formed and the younger age is the age of deposition The two batches of grains came from different source rocks that both were eroded to make these grains When the rock cooled different amounts of radioactive K40 got trapped in the two kinds of feldspar so it s not possible to date this rock correctly Continental drift theory evidence O O O O Glacial till match I Chemical weathering Deserts I Sand dunes Salt deposits I Dried bodies of water Fossils match types Mountains matchline up Most thought the above was inconceivable O Believed the continents used to have land joining them together but then it sank New evidence in 1950s 0 O O Crystals of magnetic minerals like magnetite can move around in a magma Get stuck lined up with the earth s field when magma solidifies An old rock with magnetite in it tells us its latitude and direction to the pole when it formed O O Rocks with same ages of different continents give different paths for the magnetic pole Continents must have moved 0 1940s global bathymetry maps O 0000 GOOD Mapped out tall mountains and deep trenches all over the sea oor I Sonar waves Every ocean basin has a mountain ridge with high heat ow Marine sediment is thick near continents thin or absent at ridges Ocean crust is mafic basalt gabbro No granite no metamorphics Magnetism on ocean oor covered in basalt I Striped I Black points North white points South Mirror image magnetic reversal stripes on sea oor Lots of heat ow in the center of the mountain chain Small shallow earthquakes at the ridge Zero age in the center where the mountain is and increasing age to either side