Lake Superior
Born of Fire
and Ice
Jim Miller
University of Minnesota Duluth
Plate Tectonic Theory
The Earth’s outer shell (lithosphere) is composed of rigid plates
that are moving relative to one another.
Convergent
Boundaries
Divergent
Boundaries
Convergent Boundaries
•Explosive volcanism
•Earthquakes
•Mountain-building
Divergent Boundaries
Continental Rifting
Making Ocean Crust
Mantle Plumes
and
Hot Spots
200 Ma
The Break-up
of
Pangea
Laurasia
Gondwanaland
125 Ma
75 Ma
UNIFORMITARIANISM - The Present is the Key to the Past
NORTH SHORE
ICELAND
HAWAII
North America
(Laurentia)
in the Late
Precambrian
(1,100,000,000 years
ago)
_______________
THE
MIDCONTINENT
RIFT
_______________
An attempt at
continental rifting
1.1 billion years
ago
A. Rift Magmatism
Basalt
Flows
Gabbro
Crust
Mantle
The Evolution of
Lake Superior
Part I - FIRE
1,109-1,086 Ma
Mantle
Plume
B. Sediment Infilling
Sandstone
1,090-900 Ma
C. Compression
1,000-900 Ma
Fissure
Eruption
Massive
Basalt
Amygdaloidal
Basalt
Amygdules – Gas bubble fillings
Chlorite & Zeolite
Epidote & Feldspar
Zeolite
Thompsonite
LAKE SUPERIOR
AGATES
Gemstone of
Minnesota
Formation of
Lake Superior
Agates
BASALT FLOW SURFACES
AA
AA
Pahoehoe
HAWAII
Pahoehoe
NORTH SHORE
High Falls on the Baptism River
Shovel
Point
RHYOLITE
The other volcanic rock type
Palisade Head
INTRUSIVE IGNEOUS ROCKS
Gabbro
Magmas trapped
in the Crust
Duluth
Complex
Layered Gabbro
Beaver
Bay
Complex
Granite
Origin of MCR
Igneous Rocks
SEDIMENTARY ROCKS
of the Midcontinent Rift
Cutface Creek
Sandstone
Freda
Sandstone
LATE-STAGE FAULTING
The Douglas Fault at Amnicon Falls State Park
Basalt
Sandstone
Why isn’t Duluth a Sea-side Resort?
Blame it on the Grenville
Laurentia
Amazonia
Geologic
Events
Recorded in
Minnesota’s
Rocks
The Ice Age: 1,800,000 yrs – Present?
Last
Glacial
Maximum
Minnesota’s
Landscape:
The Legacy
of the
Glaciers
Glaciers: Nature’s Bulldozer
Advance
Erosion
Retreat
Deposition
Powerful Agents of Erosion
Deposits from Ice
Till
Deposits from
Meltwater
Outwash
The Land of 10,000 Lakes
The Last Glacial Retreat out of Lake Superior
The Excavation of the Midcontinent Rift
A. Rift Magmatism
Basalt
Flows
Gabbro
Crust
Mantle
The Evolution of
Lake Superior
Part I - FIRE
1,109-1,086 Ma
Mantle
Plume
B. Sediment Infilling
Sandstone
1,090-900 Ma
C. Compression
1,000-900 Ma
The Evolution of
Lake Superior
Part II - ICE
D. Surface Weathering
900 – 2 Ma
E. Glacial Erosion
2 Ma – 12,000y
F. Lake Superior
NE Minnesota
Today
Isle Royale
Keweenaw
Peninsula
Illustrations by Mark Jirsa (MGS)