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

NICE, 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

Tectonic Events in Wisconsin Granite-greenstone terrane formation (approximately Ma) Penokean Orogeny (~1900 Ma) Mazatzal Orogeny (~1600 Ma) Mid-Continent Rift (~1000 Ma) Terranes = mini continents Orogenies = mountain- building events Rifts = lithosphere pulls apart

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.

Results in: 1.Deformation (reverse faults, folds, shear zones)! 2.metamorphic rocks! 3.big mountain chain! Traces of Continental Collisions:

Traces of Archean Mini Continental Collisions: Granite- Greenstone Terranes Special rock assemblages found in Archean areas

North American Superior Province Based on Card and Ciesielski, 1986 The best granite- greenstone terrane in the world!!!!

Penokean Orogeny Sutured two Archean Terranes and a Proterozoic Terrane

report9_01.html Thomson Formation near Jay Cooke State Park and Thomson, MN

Tilted Layers of Baraboo Quartzite and Phyllite: Van Hise Rock

Magnetic Anomaly Map Midcontinent Gravity High

Ma Mid Continent Rift

Continental Rifting Caused by a Mantle Plume

Magnetic Anomaly Map Midcontinent Gravity High

Lake Superior Shoreline: Minnesota BASALT: Gooseberry Falls RHYOLITE: Palisades Head

WI/53297.html Lake Superior Shoreline: Wisconsin SANDSTONE: Apostle Islands

Lake Superior Basin

interstatepark.html Interstate Park: St. Croix Falls, WI & Taylors Falls, MN

The Grenville Orogeny was a huge collision!!!!! Resulted in: 1.Deformation (reverse faults, folds, shear zones)! 2.metamorphic rocks! 3.big mountain chain! 4.Formed a supercontinent! Diagrams from Chuck Bailey instruct.uwo.ca/earth-sci/ 200a-001/200lab1.htm Grenville Gneiss Erosion level