Regional geology and tectonic history of Wyoming Geological

Regional geology and tectonic history of Wyoming Geological Field Techniques Course

Wyoming geologic history n See the summary chart in your guidebook n Begin to place events in proper context

Regional physiography n Wyoming straddles the Great Plains and Rocky Mountains

Regional tectonic provinces n Central craton surrounded by orogenic belts n Nu. NA = nucleus of North America

Basement rocks n Subdivided by age and tectonic affinity

Tectonic history of the U. S. Cordillera n Seven major periods of tectonism n n n n Antler (Mississippian) Ancestral Rockies (Mississippian – Permian) Sonoma (Permian) Nevadan (Jurassic) Sevier (Cretaceous) Laramide (Late Cretaceous - Eocene) Cenozoic tectonics (continuing today!) n n n Basin and Range extension San Andreas fault Volcanism

Cambrian paleogeography n Maps from Dr. Ron Blakey’s web site http: //jan. ucc. nau. edu/~rcb 7/globaltext. html

Early Paleozoic stratigraphy n Reflects passive margin and shallow continental sea deposition n n Sandstones, shales and carbonates Global sea level changes exert dominant control

Uplifts of the Ancestral Rockies n Mississippian – Permian n Earliest motion on some classic Rocky Mountain ranges n Colorado § Front Range § Uncompaghre n New Mexico § Sangre de Cristo n West and North Texas § Marathon § Llano

Permian paleogeography n Ancestral Rockies related to continent-continent collision n Assembly of Pangaea Only minor deformation in Wyoming Major transition in depositional environments begins

Permian – Jurassic is tectonically quiet n Little deformation in Wyoming n n Sonoma and Nevadan orogenies to west Major fall in global sea level

Early Cretaceous paleogeography n n Accretion of exotic terranes Creation of Andean style subduction margin n The Sevier orogeny

Sevier – Laramide stratigraphy

Sevier orogeny n n n Creation of continental magmatic arc Extensive thin-skinned deformation Foreland basin deposition

Sevier deformation front n Foreland fold and thrust belt Great Valley

Sevier orogeny deformation style n Thin-skinned n Sedimentary “cover” detached from basement

Idaho – Wyoming thrust belt n Cross sectional view west east

Tectonic configuration – Late Sevier

Foreland basin of the Sevier orogeny n Western Interior Basin

Formation of foreland basins n Thickening and loading of crust causes flexure n Creates accommodation space to capture debris eroded from mountains

Cretaceous foreland basin n Sediment sources and crustal loading patterns revealed by stratigraphic thickness and facies variations

Late Cretaceous paleogeography n Two major tectonic changes n n Shut down of magmatic arc Change in deformation location and style n Laramide orogeny

Tectonic configuration - onset Laramide

Laramide basement uplifts n A distinctly different structural style n In a very different place

Colorado plateau Laramide uplifts n Capitol Reef National Park After Billingsley, Huntoon and Breed (1987)

Black Hills Laramide uplift n

Laramide sedimentary basins n Basement uplifts subdivide the Sevier foreland basin into many smaller basins n Intermontaine basins

Geometry of Laramide basins n Asymmetric n n 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 n Flexing of crustal rocks creates many smaller scale basement-involved folds Erslev et al. (2001)

Why the change in structural style? n Change in plate convergence n n Direction Rate n Younger, hotter, more buoyant crust begins to subduct more rapidly

Sevier to Laramide transition n Related to change in subduction angle

Consequences of shallow subduction n Causes reactivation of old crustal weaknesses n Laramide uplifts resulted from inversion of Proterozoic extensional faults Marshak et al. (2000)

Cenozoic tectonics 30 Ma 20 Ma 10 Ma Present

Magmatic shift n Laramide magmatic gap closes and migrates southward

Miocene paleogeography

Basin and Range extension

Basin and Range extension

Basin and Range faulting n Alternating mountain ranges and basins n Horst and graben systems

Basin and Range faulting

Basin and Range faulting in Wyoming n Teton National Park

Cenozoic volcanism n n Columbia River flood basalts Yellowstone hot spot