Earth History GEOL 2110

The Cryptozoic (Precambrian) SuperEon

Part 2: The Paleoproterozoic Era

Major Concepts

• After the formation of the Archean continental landmass (Kenoraland), Minnesota lay at a passive margin where sedimentary rocks accumulated including Snowball Earth tillites and the great Lake Superior banded iron formations.

• These sedimentary rocks were deformed ~1.85 Ga by the collision of volcanic arc terrane with Kenoraland, an event called the Penokean orogeny. This event sutured several Archean terrains together to form a larger continent called Laurentia.

• Laurentia continued grow in the Paleoproterozic by adding more terrains to the south at 1.7Ga (Yavapi orogen) and 1.6Ga (Mazatzal orogen).

Today’sLecture

Kenoraland

Paleoproterozoic Rocks of

MinnesotaSedimentary rock

accumulated in the Animikie Sea

then deformed in the Penokean Orogeny

Creating the Animikie Basinby Continental Rifting

Animikie Group

Menominee Group

Huronian Supergroup

Archean

Paleoproterozoic Sedimentary Rocks of the Lake Superior Region

Huronian SupergroupSedimentary

Rocks

U-bearing Matinenda Fm Carbonates of the Espanola Fm

Gowganda FmRamsey Lake Fm Bruce Fm

TILLITES

Limestone

Tillite

PaulHoffman

MESABI-TYPE IRON FORMATIONGeologic Marker of a Major Evolutionary Event

STROMATOLITES(Fossilized Algal Mats) Evidence of Early Life

Mesabi-type Iron FormationDepositional Environment (~ 2.0 Ga) - Organically mediated deposition

at the margin of the Animikie Basin

Occurrence - Minor structural disruption in northern Minnesota

Offshore Algal Reef

Si,Fe

ONearshore

Archean Crust

ANIMIKIE SEA(sand, silt, mud)(iron oxide, chert)(pelagic mud, turbidites)

Detrital sediment

Biwabik Fe-Fm.

Virginia Fm.

Pokegama Qtzt.

glacial till S N

~ 1 km

The 1.85 Ga Sudbury ImpactThe First Major Extinction Event ??

Paleoproterozoic Iron Ranges of the Lake Superior Region

Ishpeming, MI

Hibbing, MN

Hydrothermal Fluids

Taconite Ore

Natural Ore

Surficial Waters

Magnetite Hematite Goethite/Limonite

OXIDATIONLEACHING NATURAL ORENATURAL ORETACONITE ORETACONITE ORE

Fe3O4 Fe2O3 FeO•OHFe3O4 Fe2O3 FeO•OH

Rocheleau Pit

Dunka Pit Peter Mitchell Pit

Progressive Deformationacross the Penokean

Orogen

Eveleth – Flat-lying Biwabik Fe-Fm

St. Cloud – Granite intrusions

Jay Cooke Park – Deformed Thomson Fm

Eveleth Jay Cooke

St. Cloud

Volcanic Arc

Continental Shelf

Suture –Niagara Fault

DENUDATION OF A MOUNTAIN BELT

Sioux

Flambeau

Baraboo

Rib Mtn

SIOUX QUARTZITE~1.7 Ga Mature Sandstone

Blue Mounds State Park

Pipestone National Monument

More Paleoproterzoic Mountain-building Events

Yavapai Orogeny: 1770-1730 Ma

Mazatzal Orogeny: 1650-1600 Ma

Holm et al., 2007

Summary of Paleoproterozoic Tectonic Events in the Upper Midwest

Holm et al., 2007

PALEOPROTEROZOIC ACCRETED TERRANESCreation and Growth of LAURENTIA

Next Lecture

The Final Chapter of the PrecambrianThe Meso- and NeoProterozoic