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

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 terraneNICE, 2006

Tectonic Events in Wisconsin

• Granite-greenstone terrane formation (approximately 2700-2500 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!

http

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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.JPGBushveld 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/images/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 TerranesSpecial rock assemblages found in Archean areas

North American Superior Province

Based on Card and Ciesielski, 1986

The best granite-greenstone terrane in the world!!!!

http://www.uwgb.edu/dutchs/geolwisc/geohist/wipcarch.htm

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http://www.uwgb.edu/dutchs/geolwisc/geohist/wipcpor.htm

Penokean Orogeny

Sutured two Archean Terranes and a Proterozoic Terrane

http://www.d.umn.edu/geology/main/thomson.htmlwww.isk.canoe-kayak.org/reports2001/ 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 MapMidcontinent Gravity High

http://www.winona.msus.edu/geology/MRW/mrwimages/mid-continentrift.jpg

1000 Ma

Mid Continent Rift

Continental Rifting Caused by a Mantle Plume

Magnetic Anomaly MapMidcontinent Gravity High

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

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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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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