Precambrian Geology of the Lake Superior Region
THE MAKING OF LAURENTIA
Jim Miller
University of Minnesota Duluth
The
Geologic
Record in
Minnesota
LAURENTIA
KENORALAND
Precambrian
Geology of
Minnesota
Direct Evidence:
OUTCROP
More Direct Evidence: DRILL CORE
Image from Dale Setterholm, MGS
Location of core hole
Drill core
1st vertical derivative of aeromagnetic data
Drill hole locations provided by Minnesota Department
of Natural Resources, Division of Lands and
Minerals, Hibbing 2002
Indirect Evidence: GEOPHYSICAL DATA
Supporting Evidence:
GEOCHRONOLOGY AND GEOCHEMISTRY
Geologic Paradigms
and Principles
Siccar Point
Rock Cycle
Limestone
Qtz Sandstone
Graywacke
Shale
Quartzite
Slate Marble
Quartz + Clay+Lithics
Basalt
Rhyolite
Greenstone
Gabbro
Granite
Amphibolite
Felsic
Mafic
Schist
Migmatite
Gneiss
Terrane 1:
The
Minnesota
River Valley
Gneiss
Terrane
>3.0 Ga
THE
MINNESOTA
RIVER
VALLEY
GRANITIC GNEISS
Early Continent Formation
Terrane 2:
The Superior
Province
(GraniteGreenstone
Terrane)
2.7-2.5 Ga
GREENSTONE
Metamorphosed Basalt
Pillowed Structures indicative
of submarine eruption
SEDIMENTARY ROCKS
BANDED IRON FORMATION
GRAYWACKE
GRANITE BATHOLITHS
Partially-melted Crust
(~ 2.6 Ga)
The Superior
Province
Multiple
Accreted
Terranes
TECTONIC MODEL FOR THE SUPERIOR PROVINCE
Accretion of Island Arcs, Oceanic Plateaus, and Protocontinents
SUPERIOR PROVINCE
A major episode of continental
growth creating KENORALAND,
the core of North America
Kenoraland
Terrane 3:
The Penokean
(and Yavapi
and Mazatzal)
Orogen
1.9-1.6 Ga
Making
Laurentia
Paleoproterozoic Sedimentary Rocks of the Lake Superior Region
Animikie Group
Menominee Group
Huronian Supergroup
Archean
Huronian
Supergroup
Sedimentary
Rocks
TILLITES
U-bearing Matinenda Fm
Ramsey Lake Fm
Carbonates of the Espanola Fm
Gowganda Fm
Bruce Fm
Limestone
Tillite
Paul
Hoffman
MESABI-TYPE IRON FORMATION
Geologic Marker of a Major
Evolutionary Event
STROMATOLITES
(Fossilized Algal Mats)
A Key to the Origin of
Mesabi-type Iron Formation
Mary Ellen Mine
Shark Bay, Australia
LTV Mine
The 1.85 Ga Sudbury Impact
The First Major Extinction Event ??
SUDBURY IMPACT LAYER
Localities in the Lake Superior Region
Thunder Bay
Gunflint Lake
Mesabi Iron Range
SUDBURY
850-950 km
Michigan
<500 km
Google Earth 2008
And you think you had a
bad day!
CALCULATED ARRIVAL TIMES
FOR EFFECTS AT GUNFLINT LAKE
(480 miles from Sudbury Impact)
Meteorite.org, Pangea International, Inc
1) ~13 seconds—Fireball (thermal radiation=3rd degree burns; 50 minutes)
2) ~2-3 minutes—Earthquake (magnitude >10 at Sudbury)
3) ~5-10 minutes—Airborne ejecta arrives (~1-3 m thick , fragments < 1 cm)
4) ~40 minutes—Air blast (compression wave, wind speeds >1400 mph)
5) ~1-2 hours—Tsunami (the first of several?)
6) Post-impact environmental changes (akin to those of Chicxulub?)
www.lpl.arizona.edu/impacteffects
Collins, Melosh, and Marcus, 2005
ROVE FORMATION
Transgression
GUNFLINT IRON FORMATION
CHAOS
IMPACTITE
Transgression
Stromatolites
Regression
Transgression
From Jirsa (2009)
REGIONAL CORRELATION OF IRON-FORMATIONS
BASED ON THE SUDBURY IMPACT TIMELINE
Hibbing, MN
Ishpeming, MI
Paleoproterozoic
Iron Ranges of
the Lake Superior
Region
Rocheleau Pit
Peter Mitchell Pit
Dunka Pit
Penokean
Orogeny
1.85 Ga
Thomson Dam
Eveleth
St. Cloud
Penokean Mountains (1.85 -1.75 Ga)
DENUDATION OF A MOUNTAIN BELT
SIOUX QUARTZITE
and Related 1.7 Ga Mature Sandstones
Flambeau
Rib Mtn
Sioux
Baraboo
Growing Laurentia with
More Paleoproterzoic
Mountain-building Events
and Terrane Accretion
Yavapai Orogeny: 1770-1730 Ma
Mazatzal Orogeny: 1650-1600 Ma
Holm et al., 2007
By 1.1 Ga,
Laurentia forms the core
of a new supercontinent
Rodinia
But Wait, There’s More…