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
Aeromagnetic Map of Wisconsin Geon 18 Penokean amphibolite metamorph 1744 Ma amphibolite metamorphism Yavapai age terrane Geon 16 amphibolite metamorphism Granite-rhyolites invading Mazatzal age terrane NICE, 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!
The Amazing Archean ( 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
Fractional Crystallization 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 Low Melting Temp High Melting Temp
whyfiles.org/031volcano/ main2.html Partial Melting = incomplete melting of a more mafic rock. melt - felsic residue - more mafic
Earliest Microcontinents 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.