Part 3: The Meso- and Neoproterozoic Eras

• After the formation of the Paleoproterzoic continent of
Laurentia, new marginal terranes continued to be added to the “south” in the Mesoproterzoic.
• The most significant of these terranes was the Grenville which was a mobile belt formed by the collision of
Amazonia and Laurentia between 1.2 and 0.9 Ga
• A major starting plume event at 1.1 Ga impacted the lithosphere under what would become Lake Superior.
This brought on the development of the Midcontinent
Rift – an aborted attempt at continental rifting.
• Toward the end of the Proterozoic Eon (~1.0 Ga), one of the largest supercontinents in earth history formed,
Rodinia, which had Laurentia at its core.

PALEOPROTEROZOIC ACCRETED TERRANES
Creation and Growth of LAURENTIA

_______________
THE
MIDCONTINENT
RIFT
_______________
An attempt at continental rifting
1.1 billion years ago

A. Rift Magmatism
Gabbro
Crust
Mantle
Mantle
Plume
Basalt
Flows
1,109-1,086 Ma
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 Zeolite
Epidote & Feldspar Thompsonite

LAKE SUPERIOR
AGATES
Gemstone of
Minnesota

Formation of
Lake Superior
Agates

BASALT FLOW SURFACES
AA
Pahoehoe
HAWAII
Pahoehoe
NORTH SHORE
Aa

High Falls on the Baptism River
RHYOLITE
The other volcanic rock type
Palisade Head Rhyolite
Palisade Head

INTRUSIVE IGNEOUS ROCKS
Subvolcanic emplacement of magmas
Duluth
Complex
Layered Gabbro
Beaver
Bay
Complex
Gabbro
Granite

Origin of MCR
Igneous Rocks

SEDIMENTARY ROCKS of the Midcontinent
Rift
Cutface Creek
Sandstone Freda
Sandstone

The Douglas Fault at Amnicon Falls State Park
Sandstone
Basalt

Why isn’t Duluth a Sea-side
Resort?
Blame it on Grenville & Rodinia

1200 – 750 Ma
Li et al., 2008

Li et al., 2008

Deconstruction of Rodinia by a
Superplume
750 Ma
Li et al., 2008

Early Evolution of Life
Chapter 9
Midterm I returned – PROMISE!