Precambrian and Early Paleozoic Western USA · Early Paleozoic Ł Craton and cratonic basin...
Transcript of Precambrian and Early Paleozoic Western USA · Early Paleozoic Ł Craton and cratonic basin...
1
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
2
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
3
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
4
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
5
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
6
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
7
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
8