phanerozoic history of north america tectonic context of na: part 4

Phanerozoic Phanerozoic History of North History of North

AmericaAmericaTectonic Context of NA: Part Tectonic Context of NA: Part

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Last TopicsLast Topics

CM of Eastern CM of Eastern North AmericaNorth America

CM of the CM of the Southern Southern North America North America

ENACM-Tectonic ENACM-Tectonic RegimesRegimes

SNACM – Tectonic SNACM – Tectonic RegimesRegimes

Western North AmericaWestern North America The western The western

margin of the margin of the North American North American continent extends continent extends from the southern from the southern California to California to central part of central part of Alaska and from Alaska and from the Pacific Coast to the Pacific Coast to the craton below the craton below the Great Plains. the Great Plains.

Tectonostructural Tectonostructural FeatureFeature

Western Western North North America America Continental Continental Margin Margin consists of a consists of a series of series of margin margin parallel parallel tectonic tectonic belts. belts.

Tectonostructural Tectonostructural FeatureFeature

The most The most landward of these landward of these belts is composed belts is composed of deformed of deformed Proterozoic Proterozoic North America. North America.

Seaward, the Seaward, the belts consist of a belts consist of a set of terranes, set of terranes, each of them each of them being being differentiated differentiated mainly by the age mainly by the age of attachment to of attachment to North America. North America.

Generally, Generally, younger terranes younger terranes are to be found are to be found seaward.seaward.

Belt FeaturesBelt Features The total width of the belts is highly The total width of the belts is highly

variable. Some belts seem to be continuous variable. Some belts seem to be continuous along the strike and extremely short on along the strike and extremely short on strike. strike.

Some of them consist of a single terrane Some of them consist of a single terrane but in some others several discrete but in some others several discrete segments have been identified along the segments have been identified along the strike. strike.

These terranes have undergone These terranes have undergone synattachment and postattachment synattachment and postattachment deformations. deformations.

Moreover, the structural arrangement Moreover, the structural arrangement varies significantly on strike. varies significantly on strike.

Belt FeaturesBelt Features In California and British Columbia it includes the In California and British Columbia it includes the

surfaces that accommodate the maximum rate of slip surfaces that accommodate the maximum rate of slip between the plates (San Andreas and Queen Charlotte between the plates (San Andreas and Queen Charlotte faults respectively).faults respectively).

Sucession of the Tectonic Sucession of the Tectonic RegimesRegimes

Pacific Basin LithospherePacific Basin Lithosphere

An oceanic basin has probably existed An oceanic basin has probably existed along the western margin of North along the western margin of North America throughout the Phanerozoic. America throughout the Phanerozoic.

Its evolution can be viewed in three Its evolution can be viewed in three phases phases (i) end-Proterozoic breakup of Rodinia and (i) end-Proterozoic breakup of Rodinia and

sea-floor spreading; sea-floor spreading; (ii) Cambrian-Jurassic intrabasinal tectonic (ii) Cambrian-Jurassic intrabasinal tectonic

phase from which no plate survives;phase from which no plate survives; (iii) a Cretaceous-Cenozoic phase for (iii) a Cretaceous-Cenozoic phase for

which plates exists for which their position which plates exists for which their position and kinematics can be reasonably well and kinematics can be reasonably well restored.restored.

Phase 1: End ProterozoicPhase 1: End Proterozoic Breakup of Breakup of RodiniaRodinia caused the caused the

development of the development of the Proto-PacificProto-Pacific oceanic basin and the growth of the oceanic basin and the growth of the Paleozoic oceanic lithosphere against Paleozoic oceanic lithosphere against the newly generated passive margin of the newly generated passive margin of the western North America. the western North America.

By By PermianPermian times, the sea floor times, the sea floor spreading produced a huge ocean and spreading produced a huge ocean and the Proto-Pacific was only a part of it. the Proto-Pacific was only a part of it. The name of the huge ocean that The name of the huge ocean that surrounded the Pangea supercontinent surrounded the Pangea supercontinent is is PanthalassaPanthalassa. .

Phase 2:Cambrian-Phase 2:Cambrian-JurassicJurassic

Plate boundaries have been created Plate boundaries have been created within the Proto-Pacific lithosphere, within the Proto-Pacific lithosphere, dividing it into plates. dividing it into plates.

Moreover, convergent motions relative Moreover, convergent motions relative to the Proto-Pacific plates developed at to the Proto-Pacific plates developed at various times and places along the various times and places along the western margin of North America. western margin of North America.

The convergence may not have occurred The convergence may not have occurred completelycompletely along the western along the western continental margin until the Middle continental margin until the Middle Cretaceous times. Cretaceous times.

Phase 2: CharacteristicsPhase 2: Characteristics

In this phase, the continent started to In this phase, the continent started to expand basinward (westward) by expand basinward (westward) by accretion. All the events are recorded in accretion. All the events are recorded in the rock and structural features of the the rock and structural features of the terranes and by continental arcs. terranes and by continental arcs.

Glimpses of the pre-Cretaceous plate Glimpses of the pre-Cretaceous plate tectonics within the Proto-Pacific Ocean tectonics within the Proto-Pacific Ocean come the tectonostratigraphic records of come the tectonostratigraphic records of certain terranes transferred from the certain terranes transferred from the Proto-Pacific plates to North America at Proto-Pacific plates to North America at active and collisional margins. active and collisional margins.

Phase 2: ExamplesPhase 2: Examples

Oceanic SpreadingOceanic Spreading is documented by is documented by the age of crystallization of the ophiolites the age of crystallization of the ophiolites and oceanic basalt in the terranes.and oceanic basalt in the terranes.

Ex: Ex: Trinity Terrane of the Klamath Mts.Trinity Terrane of the Klamath Mts. (California) includes Lower Cambrian ophiolites (California) includes Lower Cambrian ophiolites that can document the early magmatism at the that can document the early magmatism at the western edge of the newly formed North America.western edge of the newly formed North America.

Middle and and Late Paleozoic ophiolites of Middle and and Late Paleozoic ophiolites of Sierra NevadaSierra Nevada (Feather River & Keweah (Feather River & Keweah ultramafic rocks) indicate Paleozoic spreading in ultramafic rocks) indicate Paleozoic spreading in the Proto-Pacific Ocean. the Proto-Pacific Ocean.

Phase 2: Record Nature Phase 2: Record Nature

For these events, we can infer the For these events, we can infer the nature of the events but the real nature of the events but the real position and orientation of the plate position and orientation of the plate boundaries at which they developed boundaries at which they developed remain utterly unknown.remain utterly unknown.

Phase 3: Cretaceous Phase 3: Cretaceous CenozoicCenozoic

There is a huge amount of data for the There is a huge amount of data for the Cretaceous-Cenozoic tectonics (magnetic Cretaceous-Cenozoic tectonics (magnetic anomalies, fracture zones, hotspot anomalies, fracture zones, hotspot tracks, paleomagnetic data, structure tracks, paleomagnetic data, structure and fossil provinciality). and fossil provinciality).

These data indicate the presence of three These data indicate the presence of three major oceanic plates: major oceanic plates: PacificPacific, , FarallonFarallon and and KulaKula with divergent boundaries with divergent boundaries among themselves that migrated towards among themselves that migrated towards and intersected the convergent and intersected the convergent boundaries of the North America plate at boundaries of the North America plate at various times and places. various times and places.

Farallon PlateFarallon Plate

Collisional MarginsCollisional Margins The first collision is dated Late Devonian The first collision is dated Late Devonian

and the last one in the Middle and the last one in the Middle Cretaceous times. Cretaceous times.

Therefore, by the end of the Cretaceous Therefore, by the end of the Cretaceous the whole western margin of North the whole western margin of North America was an active one. America was an active one.

The main criterion to document an The main criterion to document an active margin is the existence of a active margin is the existence of a continental magmatic arc. Collisional continental magmatic arc. Collisional margins have no continental arc, margins have no continental arc, although arc magmatic rocks can be although arc magmatic rocks can be thrust on them during collision. thrust on them during collision.

Devonian Collision - Devonian Collision - AntlerAntler

The main effect of The main effect of the Antler Orogeny the Antler Orogeny ((Uppermost Uppermost Devonian-Devonian-MississippianMississippian) was ) was the destruction of the destruction of the Cordilleran the Cordilleran passive margin that passive margin that has been formed has been formed with the block up of with the block up of Rodinia. Rodinia.

Devonian Collision - Devonian Collision - AntlerAntler

Mississippian Pennsylvanian

Active MarginsActive Margins

At such margins there is a At such margins there is a subduction of the pacific plates subduction of the pacific plates below the North American continent. below the North American continent. Such margins have been classed as Such margins have been classed as Andean, employing western South Andean, employing western South America as the global example. America as the global example.

Active MarginsActive Margins

Active MarginsActive Margins

Associated MagmatismAssociated Magmatism

Sevier OrogenySevier Orogeny

Laramide OrogenyLaramide Orogeny