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MesozoicMesozoic--Cenozoic Cenozoic Plate TectonicsPlate Tectonics

Reference:Reference:Condie (1978) GSA Memoir 152, Ch. 2Condie (1978) GSA Memoir 152, Ch. 2

Early to Middle JurassicEarly to Middle Jurassic

• Volcano-Plutonic terranes along Pacific margin

• Andean type in the south

• Island arcs in the north

• Several “suspect” terranes separated by ophiolites form the cratonic rocks

•Sonoran Megashear•Opening of Atlantic•Opening of Gulf of Mexico•Batholithic belt•NW movement of N. America

Late Jurassic to Late Late Jurassic to Late CretaceousCretaceous

• Well-developed volcano-plutonic belt

• Accreted subduction assemblages (Franciscan)

• Associated fore-arc deposits (Great Valley)

• Foreland east-verging thrust belts (Sevier Orogeny)

• Cordilleran metamorphic core complexes

Inferred Farallon and N.A. plate motions

Late Cretaceous to Late Late Cretaceous to Late EoceneEocene

• Andean type orogen

• Well-define volcano-plutonic belt

• Laramide “igneous gap”

• Thick-skinned deformation in Rocky Mts.

• Contemporaneous deformation throughout the cordillera

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Late Eocene to Late Eocene to Early MioceneEarly Miocene

• Widespread erosion

• Ignimbrite “flare-up”

• Young hot oceanic lithosphere subducted

• Metamorphic core complexes

• Ridge system Subducted

• Initiation of Caribbean Plate

Early Miocene to the PresentEarly Miocene to the Present

• Initiation of extensional faulting in Basin and Range

• Bimodal basaltic volcanism• Growth of plate-bounding transform faults

(San Andreas system)• Outpouring of flood basalts• Snake River Plain hot spot

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Effect of Effect of Subducted SlabSubducted Slab• Young hot

oceanic crust• Softens

liithosphere• Causes general

uplift• Source for

basaltic magmas

Crustal Crustal ThicknessThickness

• Reflects moho• Thin crust in

B&R• Thick crust

under batholiths

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