precambrian and early paleozoic western usa · early paleozoic Ł craton and cratonic basin...

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CORDILLERAN SYSTEM CORDILLERAN SYSTEM OVERVIEWOVERVIEW

Precambrian and Early Precambrian and Early Paleozoic Western USAPaleozoic Western USA

� Proterozoic rifting and deposition

� Grand Canyon series, Wendemere, Belt Group, etc.

� Development of an oceanic crust to the west of North America

� Passive margin shelf deposition

Paleozoic Passive MarginPaleozoic Passive Margin

� Existed in Late Precambrian and Early Paleozoic

� Craton and cratonic basin deposits

� Miogeocline continental shelf deposits

� An arc formed in the Ordovician

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Paleozoic Accretion Paleozoic Accretion Confined to NevadaConfined to Nevada

� Accretion mainly occurred along transform faults

� Some blocks were flakes related to subduction

� An arc formed in the Ordovician

Antler Orogeny (300Antler Orogeny (300--375 Ma)375 Ma)

� Collision of the arc with a passive margin

� Roberts Mountain Allochton thrust over the passive margin

� A series of foreland basins formed in eastern Nevada

� Mesozoic to Mid-Tertiary

Sonoma Orogeny Sonoma Orogeny (200(200--280 Ma)280 Ma)

� Collision of arc with a passive margin

� Island arc terrains were accreted

� Golconda allochthon thrust partly over Roberts Mountain allochthon

� Late Triassic continental margin arc system developed

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Accretionary TerranesAccretionary Terranes

� Paleozoic accretion confined to Nevada

� Mainly occurred along transform faults

� Some blocks were flakes related to subduction

Sierra Nevada UpliftSierra Nevada Uplift

� Continental sedimentation patterns

� Volcanic detritus shed onto a large foreland basin

� Chinle and Morrison Fms on the Colorado plateau

Wrangellia and Other Wrangellia and Other Suspect TerranesSuspect Terranes

� Docked with North America in late Mesozoic

� Contains an upper Paleozoic arc assemblage with an equatorial fauna

� Overlain by Permian cratonic sediments� Triassic black shales, carbonates,

basalts

Nevadan OrogenyNevadan Orogeny(140(140--150 Ma)150 Ma)

� Several arcs collided

� The Cretaceous Franciscan Fm in the accretionary prism

� The Great Valley Sequence filled an elongated forearc basin

� The Sierra Nevada was the root zone of the arc

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Late Jurassic to Late Late Jurassic to Late Cretaceous Orogen Cretaceous Orogen

(80(80--130 Ma) 130 Ma)

� The fold-thrust belt behind this arc

� Eastward directed thrusts

� Prominent retro arc basins located to the east

Laramide OrogenyLaramide Orogeny(50(50--80 Ma)80 Ma)

� Magmatism and deformation shifted eastward

� Magmatism dies out in old batholithic belt

� Causing westward directed thrusts

� Thin skinned and thick-skinned foreland deformation

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Post Laramide EventsPost Laramide Events

� Cenozoic extension

� Basin and Range formation

� Metamorphic core complexes

� Cenozoic magmatism

� Widespread volcanism

Cenozoic Tectonic AspectsCenozoic Tectonic Aspects

� Crust was cool enough for brittle fractures, but with soft middle zone

� Disappearance of subduction along a portion of the margin

� San Andreas transform fault near the coast

� Basin and Range structures

� Distributed displacements to the east

Basin and Range Structures, Basin and Range Structures, Sedimentation, and Sedimentation, and

VolcanismVolcanism� Changing patterns of deformation

� Continental sedimentation patterns

� Distributed extension and strike-slip faulting

� Core complexes

MetamorphicMetamorphic--plutonic plutonic ComplexesComplexes

� Overlain by relatively undeformed supracrustal materials

� Contact is a detachment fault underlain by mylonite

� Began to rise isostatically 20 Ma

� Related to crustal extension and heating

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Core Complex FeaturesCore Complex Features

� Detachments

� Crustal softening

� Extensional tectonics

� Listric faulting

Tertiary VolcanismTertiary Volcanism

� Time-space-composition variations

� Cascades, Columbia River, Snake River, Basin and Range, Mogollon, Sierra Madre, Aleutian Arc, etc.

� Mechanism for changes

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San Andreas Transform San Andreas Transform Fault SystemFault System

� Disappearance of subduction along a portion of the margin

� Lateral displacements and basin formation

Pacific Plate MotionsPacific Plate Motions

� Pacific, Farallon and Kula plates

� Movement of the triple junction

� Collision of the spreading center with the North American craton

� Development of the San Andreas transform

Development of the Development of the Caribbean BasinCaribbean Basin

� Separation North America and Africa

� Separation of North and South America

� Development of the Antilles arc

� Development of the Middle America Arc

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