tectonics in wisconsin presentation originally created by dr. dyanna czeck, uw-milwaukee (slides #3,...
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 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
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/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
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
www.polkcountytourism.com/gallery2/ interstatepark.html
Interstate Park:
St. Croix Falls, WI & Taylors Falls, MN