Transcript Introduction to mapping metamorphic rocks

Regional geology and tectonic
history of Wyoming
Geological Field Techniques Course
Wyoming geologic history
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See the summary chart
in your guidebook
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Begin to place events in
proper context
Regional physiography
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Wyoming straddles the
Great Plains and Rocky
Mountains
Regional tectonic provinces
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Central craton
surrounded by
orogenic belts
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NuNA = nucleus of North
America
Basement rocks
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Subdivided by age
and tectonic affinity
Tectonic history of the U.S. Cordillera
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Seven major periods of tectonism
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Antler (Mississippian)
Ancestral Rockies (Mississippian – Permian)
Sonoma (Permian)
Nevadan (Jurassic)
Sevier (Cretaceous)
Laramide (Late Cretaceous - Eocene)
Cenozoic tectonics (continuing today!)
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Basin and Range extension
San Andreas fault
Volcanism
Cambrian paleogeography
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Maps from Dr. Ron Blakey’s web site
http://jan.ucc.nau.edu/~rcb7/globaltext.html
Early Paleozoic stratigraphy
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Reflects passive margin and shallow continental sea
deposition
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Sandstones, shales and carbonates
Global sea level changes exert dominant control
Uplifts of the Ancestral Rockies
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Mississippian – Permian
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Earliest motion on some
classic Rocky Mountain
ranges
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Colorado
 Front Range
 Uncompaghre
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New Mexico
 Sangre de Cristo
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West and North Texas
 Marathon
 Llano
Permian paleogeography
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Ancestral Rockies related to continent-continent
collision
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Assembly of Pangaea
Only minor deformation in Wyoming
Major transition in depositional environments begins
Permian – Jurassic is tectonically quiet
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Little deformation in Wyoming
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Sonoma and Nevadan orogenies to west
Major fall in global sea level
Early Cretaceous paleogeography
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Accretion of exotic terranes
Creation of Andean style subduction margin
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The Sevier orogeny
Sevier – Laramide stratigraphy
Sevier orogeny
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Creation of continental magmatic arc
Extensive thin-skinned deformation
Foreland basin deposition
Sevier deformation front
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Foreland fold and thrust belt
Great Valley
Sevier orogeny deformation style
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Thin-skinned
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Sedimentary “cover”
detached from
basement
Idaho – Wyoming thrust belt
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Cross sectional view
west
east
Tectonic configuration – Late Sevier
Foreland basin of the Sevier orogeny
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Western Interior Basin
Formation of foreland basins
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Thickening and loading of crust causes flexure
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Creates accommodation space to capture debris eroded from
mountains
Cretaceous foreland basin
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Sediment sources
and crustal loading
patterns revealed
by stratigraphic
thickness and facies
variations
Late Cretaceous paleogeography
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Two major tectonic changes
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Shut down of magmatic arc
Change in deformation location and style
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Laramide orogeny
Tectonic configuration - onset Laramide
Laramide basement uplifts
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A distinctly different structural
style
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In a very different place
Colorado plateau Laramide uplifts
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Capitol Reef National Park
After Billingsley, Huntoon and Breed (1987)
Black Hills Laramide uplift
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Laramide sedimentary basins
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Basement uplifts
subdivide the Sevier
foreland basin into
many smaller basins
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Intermontaine basins
Geometry of Laramide basins
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Asymmetric
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Basin axes close to
uplift margins
Facies and thickness
changes indicate
uplifts were
sediment sources
Regional structure of Wyoming
Regional structure of Wyoming
Detailed structure of basement arches
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Flexing of crustal rocks creates many smaller scale
basement-involved folds
Erslev et al. (2001)
Why the change in structural style?
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Change in plate convergence
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Direction
Rate
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Younger, hotter, more buoyant crust begins to subduct more
rapidly
Sevier to Laramide transition
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Related to change in subduction angle
Consequences of shallow subduction
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Causes reactivation of old crustal weaknesses
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Laramide uplifts resulted from inversion of Proterozoic
extensional faults
Marshak et al. (2000)
Cenozoic tectonics
30 Ma
20 Ma
10 Ma
Present
Magmatic shift
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Laramide
magmatic gap
closes and
migrates
southward
Miocene paleogeography
Basin and Range extension
Basin and Range extension
Basin and Range faulting
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Alternating mountain
ranges and basins
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Horst and graben
systems
Basin and Range faulting
Basin and Range faulting in Wyoming
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Teton National Park
Cenozoic volcanism
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Columbia River flood basalts
Yellowstone hot spot