Transcript Cordillera_TikoffGIVEN

A very brief overview of the rest of
the U.S. Cordillera (not California
and not Cenozoic)
Basil Tikoff
University of Wisconsin-Madison
Goal: Give an overview of US Cordillera
Dickinson, 2006
Two sources for many of the figures
Animations at: http://csmres.jmu.edu/Geollab/Whitmeyer/web/publications.html
Outline
• Geography exercise (5 minutes)
• Assembly of Precambrian North
America (Laurentia)
• The Cordillera evolution
• Idaho and the Canadian Cordillera
• A retrospective (and, perhaps, a
soapbox)
Organize into groups, with no more than one person from any
particular country in any group.
Write the name of each state in each state (ask anyone for help)
Envelope: Parts of the
Precambrian
In each “geography” group, open the
envelope. We’ll go through the
evolution of North American by putting
together a jigsaw puzzle.
Archean – grey blobs
> 2.0 Ga
Archean cratons
(positions unconstrained;
Rae and Hearne in
present-day locations)
Proterozoic accretionary belts
between Archean blocks –
pink zones
Front view
Back view
1.82-1.80 Ga
Continued shortening across
Trans Hudson orogen; closure of
Great Falls Tectonic Zone and
Vulcan Zone; accretion of Medicine
Hat Block, and Wyoming Province
Like anything that is published, it isn’t necessarly correct.
In this case, it does not look like the Selway terrane exists
(the area is underlain by Archean crust, determined by
zircon xenocrysts in Cretaceous plutons).
Proterozoic terranes
(from N to S)
• Yavapai (1.70 Ga accretion)
• Mazatzal (1.63 Ga accretion)
• Granite-rhyolite province (1.55 – 1.35 Ga)
Yavapai – dark green
1.76-1.72 Ga
Accretion of Mojavia(?)
and Yavapai Province,
as a Banda Sea style
assembly of arcs
DePaolo &
Bennet, 1987
Hoffman, 1988
CD-ROM working group
Figure 2. Geologic cross section with data from CD-ROM Cheyenne belt seismic line.
Tyson A et al. Geology 2002;30:943-946
©2002 by Geological Society of America
Mazatzal – blue
Mazatzal ( = place of the deer, or so sayeth Wikipedia)
Mountains, Arizona
1.69-1.65 Ga
Accretion of Mazatzal and
Labradorian Provinces,
as juvenile crust
Granite-rhyolite –light green
Red rock is a
1500 Ma
St Francis
Mountains,
Missouri
Llano block
1.55-1.35 Ga
Accretion of GraniteRhyolite Province, Elzevir
Block & Pinware terrane,
as juvenile crust
Belt Group, from
Glacier National Park
Deposition estimated
at ~1400 Ma
Collision!
Grenville orogeny & formation
of Rodinia
This just wasn’t a collision – it was the
assembly of a supercontinent (Rodinia)
Laurentia is at the center of this collision,
which means it is highly affected
structurally and thermally (similar to
Hercynian orogeny in Europe)
1.3-0.95 Ga
Grenville orogen:
Granitoids intrude juvenile
belts as far west as Colorado
Simultaneous with collision,
there is a major rifting event
Midcontinent rift event
1.2-1.1 Ga
Midcontinent Rift system:
Keweenawan, Ft. Wayne rifts;
Intrusion of MacKenzie and
Animikie dikes
Watch animation of Rodinia assembly
Questions?
0.78-0.68 Ga
Rifting along western margin
of Laurentia;
Intrusion of Gunbarrel dikes,
Deposition of Windermere
Supergroup
Dickinson
Inyo Mtns
Thickness of latest Proterozoic &
Early Cambria strata.
Contour lines (hard to see) are 2,
6, and 8 km.
Time for animation
From:
http://csmres.jmu.edu/Geollab/Whitmeyer/web/publications.
html
Questions?
The story of the US
Cordillera is one of
subduction and terrane
accretion to the western
margin
Accreted or “suspect” terranes
Dott & Prothero
When do they attach to each other, and when (and where) do
they attach to the North American margin?
Tectonic map for Cambrian
through Late Devonian
Black material was offshore,
but was being deposited
Late Mississippian
Dott & Prothero
Antler orogeny
• Lasted ~10 m.y.
• Major feature: Roberts Mountain thrust
• During thrusting, the thrust sheets
formed a highland and deposited
material eastward into a well-developed
foredeep
• No, low metamorphism
• Overlapped by Pennsylvanian shallowwater materials
….and, there is no/little volcanic material
Sheared and folded deep water
sediments of the distal Antler
marine basin thrust over and
emplaced on top of the shallow
water deposits of the continental
margin.
Robert’s Mountain thrust. Above
the contact we see the Early
Missisppian conglomerates and
below we see a thick band of
sheared rocks.
From MIT website (C. Burchfiel)
Burchfiel & Royden, 1991
Ancestral Rockies
• Permian age
• Basins and uplifts in southern part of
western US (they do not extend, for the
most part, into the Archean Wyoming
province)
• Results from collision of Africa on SE US
…and now for the large piles of sandstone
and conglomerates
Maroon Bells
Note: Large vertical exaggeration
Blakey, 2008
Ancestral Rockies are
interpretted by Miller et al.
(1992) as a far-field effect
of a continent-continent
collision.
The diagram shows the
scale of the ongoing
Himalayan collision to the
Ancestral Rockies collision,
emphasizing the “free”
subduction boundary.
Ancestral Rockies are
equivalent to Baikal rift.
Watch Pangea assembly
Questions?
Next: The Sonoman orogeny
Dickinson, 2006
Permian-Triassic
Dott & Prothero
Sonoman orogeny
• Permian-Triassic
• Major feature: Golconda thrust
• A lot like the Antler orogeny: 1) Thrust
sheets (Havallah sequence) were thrust
on Antler orogeny and its Paleozoic
overlap sequence; and 2) Little
metamorphism
• Overlapped by Triassic shallow-water
materials (Star Peak/Luning) and cut by
Triassic pluton in eastern Sierra Nevada
region
Triassic
• Development of an Andean margin
offshore California, possibly with backarc basin (Star Peak – Luning basin)
By Late Jurassic, the
Sevier thrust front
has developed,
including a very well
developed foreland
basin
DeCelles, 2004
Q