Presentation on theme: "Tectonics in Wisconsin Presentation originally created by Dr. Dyanna Czeck, UW-Milwaukee (Slides #3, 4 and 5 are from NICE (Northern Interior Continental."— Presentation transcript:
Tectonics in Wisconsin Presentation originally created by Dr. Dyanna Czeck, UW-Milwaukee (Slides #3, 4 and 5 are from NICE (Northern Interior Continental Evolution) Working group presentation at ILSG 2006
tapestry.usgs.gov/ages/ precambrian.html Exposed Precambrian Rocks in the U. S. (anything older than 570 Ma)
Precambrian (Archean and Proterozoic) rocks are underlying much of North America! http://www.paccd.cc.ca.us/instadmn/physcidv/geol_dp/dndougla/home/DRDHOME.htm
The Amazing Archean (4.6-2.5 Ga): ircamera.as.arizona.edu/ MIRI/life.htm Painting by K. M. Towe of stromatolites 3.5 Ga
How to Make Continents: Earliest earth had one crust –Ultramafic composition (not much silica) Today: –Oceanic crust (mafic) –Continental crust (felsic) What makes continental crust so special? –Most felsic material (quartz rich) –Not dense, so doesn’t get subducted How to make continental crust ? nataliedee.corrupt.net/ index.php
Volcanic Processes that can form more felsic magma from ultramafic magma 1.Fractional crystallization http://www.usd.edu/esci/figures/158370.JPG
Fractional Crystallization http://www.usd.edu/esci/figures/157525.JPG Bushveld Complex, Australia
Volcanic Processes that can form more felsic magma from ultramafic magma 2. Partial Melting Bowen’s Reaction Series: minerals with low melting temperature melt first http://www.usd.edu/esci/figures/158371.JPG Low Melting Temp High Melting Temp
whyfiles.org/031volcano/ main2.html Partial Melting = incomplete melting of a more mafic rock. http://www.crazy4candy.com/images/uploads/snickersF.gif melt - felsic residue - more mafic
Earliest Microcontinents http://earth.usc.edu/~geol150/public_html/evolution/image s/prepaleozoic/earlytectonics.jpg Small Felsic Continents Big Mafic Ocean Crust Little sedimentary basins at continent’s edges Felsic continental crust slowly created by partial melting OR fractional crystallization.
http://www.bwca.cc/activities/hiking/superiorhikingtrail.html http://www.mwpersons.com/Travels/Gooseberry-falls.html Lake Superior Shoreline: Minnesota BASALT: Gooseberry Falls RHYOLITE: Palisades Head
www.photochromecollection.com/ WI/53297.html Lake Superior Shoreline: Wisconsin SANDSTONE: Apostle Islands
http://pubs.usgs.gov/info/mwni_cu/ Lake Superior Basin
www.polkcountytourism.com/gallery2/ interstatepark.html Interstate Park: St. Croix Falls, WI & Taylors Falls, MN
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