The Great Terrane The Great Terrane Wreck of the CordilleraWreck of the Cordillera

Allen J. McGrewAllen J. McGrewApril 2005April 2005

What is a What is a TectonostratigraphiTectonostratigraphi

c Terrane?c Terrane?

Terranes can be:

• Native – showing shared traits with North American crust, indicating an origin adjacent to North America.

• Exotic – Far-traveled, not born adjacent to North America

• Superterranes – amalgamated with other terranes before accretion to the continental margin.

Evidence of origins?Evidence of origins? Stratigraphic Stratigraphic

similaritiessimilarities Faunal Faunal

affinitiesaffinities Sedimentary Sedimentary

provenanceprovenance– e.g.,detrital e.g.,detrital

zircon datingzircon dating PaleomagnetiPaleomagneti

c evidencec evidence

Paleomagnetic EvidencePaleomagnetic Evidence PaleomagnetismPaleomagnetism

– InclinationInclination– DeclinationDeclination– PolarityPolarity

Paleopoles and Paleopoles and PaleolatitudePaleolatitude

Apparent Polar Apparent Polar Wander PathsWander Paths

Comparison with Comparison with APWP for North APWP for North America allows America allows assessment of assessment of whether terrane whether terrane could have been could have been close to No. close to No. America at time of America at time of deposition of the deposition of the measured rock.measured rock.

Limitations of Paleomagnetic Limitations of Paleomagnetic AnalysisAnalysis

Paleolatitude North or South?Paleolatitude North or South? No constraint on paleolongitude.No constraint on paleolongitude. What if paleomagnetism was not What if paleomagnetism was not

acquired when we thought it was? (fold acquired when we thought it was? (fold tests)tests)

How well do we know paleohorizontal How well do we know paleohorizontal at the time magnetism was acquired?at the time magnetism was acquired?

What if paleomagnetic vectors changed What if paleomagnetic vectors changed in orientation after deposition? (e.g., in orientation after deposition? (e.g., due to flattening or deformation)due to flattening or deformation)

An Example: Paleomagnetic An Example: Paleomagnetic Reconstruction of the Alexander Reconstruction of the Alexander

Terrain Terrain (after Butler, Gehrels & Bazard, GSAB, 1997)(after Butler, Gehrels & Bazard, GSAB, 1997)

Ordovician-SilurianOrdovician-Silurian:: No dependable No dependable paleolatitude.paleolatitude.

Early DevonianEarly Devonian:: Karheen Fm Karheen Fm 1414ºº ± ± 44ºº possibly Australia or possibly Australia or pref. Balticapref. Baltica

Middle DevonianMiddle Devonian - - PennsylvanianPennsylvanian:: no no dependable dependable information.information.

Alexander Paleogeographic Alexander Paleogeographic Reconstructions (cont’d)Reconstructions (cont’d)

PermianPermian: Halleck volcanics & : Halleck volcanics & three other formations three other formations indicate paleoposition of indicate paleoposition of amalgamated Alexander-amalgamated Alexander-Wrangellia terrane at Wrangellia terrane at 2525ºº - - 3030ºº N N off the west coast of off the west coast of No. America.No. America.

TriassicTriassic - - 1010ºº - 20 - 20ºº N N at at paleolatitude of northern paleolatitude of northern Oregon (Seven Devils & Oregon (Seven Devils & Huntington Arcs).Huntington Arcs).

JurassicJurassic & & CretaceousCretaceous – no – no primary magnetizations; primary magnetizations; Alexander-Wrangellia Alexander-Wrangellia accreted to North American accreted to North American continental margin and continental margin and dispersed northward as far as dispersed northward as far as Alaska by translation on Alaska by translation on strike-slip faults.strike-slip faults.

Recognizing Amalgamation & Recognizing Amalgamation & AccretionAccretion

• “Stitching Plutons” – plutons intruded into adjacent terranes demonstrating that they had to be adjacent at the time of pluton injection.

• “Overlap Assemblages” Stratigraphic packages deposited across terrane boundaries indicating that terranes had to be adjacent at time of deposition.

A History of Terrane A History of Terrane AccretionAccretion

Mesozoic Mesozoic Paleogeography and Paleogeography and Tectonic History of Tectonic History of

Western North AmericaWestern North America

Images and text modified from a poster Images and text modified from a poster session presented to the Annual Meeting of session presented to the Annual Meeting of the Geological Society of America, Seattle, the Geological Society of America, Seattle, Nov. 2003 by Ron Blakey and Paul Nov. 2003 by Ron Blakey and Paul Umhoefer, Department of Geology, NAUUmhoefer, Department of Geology, NAU

http://jan.ucc.nau.edu/~rcb7/http://jan.ucc.nau.edu/~rcb7/mz_paleogeog_wus.htmlmz_paleogeog_wus.html

Permian Tectonics and Paleogeography Permian Tectonics and Paleogeography (290 Ma)(290 Ma)

Mc Cloud arc fragmented Mc Cloud arc fragmented during late Paleozoic truncation during late Paleozoic truncation of SW North America of SW North America

Assembly of western Pangaea Assembly of western Pangaea completed completed

Transform margin coupled Transform margin coupled McCloud arc with arcs built on McCloud arc with arcs built on Chortis and South America Chortis and South America

Havallah back arc basin (HB) Havallah back arc basin (HB) and Slide Mtn back arc and Slide Mtn back arc separated northern arc, separated northern arc, Quesnellia (Q), from Antler belt Quesnellia (Q), from Antler belt (A) and western North America(A) and western North America

Blakey and Umhoefer, 2003Blakey and Umhoefer, 2003

Triassic Tectonics and Triassic Tectonics and Paleogeography (240 Ma) Paleogeography (240 Ma)

Early to Middle Triassic Early to Middle Triassic (240 Ma) (240 Ma)

McCloud arc fragmented McCloud arc fragmented and accreted to North and accreted to North America resulting in America resulting in Sonoman orogeny Sonoman orogeny

Caborca terrane moved Caborca terrane moved SE along truncated SE along truncated continental margin continental margin

Subsequent Cordilleran Subsequent Cordilleran arc was continental to arc was continental to south and marine to south and marine to north north

Blakey and Umhoefer, 2003Blakey and Umhoefer, 2003

Early Jurassic Tectonics and Early Jurassic Tectonics and Paleogeography (180 Ma) Paleogeography (180 Ma)

Early to Middle Jurassic Early to Middle Jurassic (180 Ma) (180 Ma)

?? Fringing Cordilleran ?? Fringing Cordilleran arc accreted to arc accreted to western North America western North America including Bridge River, including Bridge River, North Cascades, North Cascades, western parts of western parts of Eastern Oregon Eastern Oregon terranes, and western terranes, and western terranes of Klamaths terranes of Klamaths and Sierra Nevada and Sierra Nevada

?? Older Mesozoic ?? Older Mesozoic back arc basins closed back arc basins closed

Blakey and Umhoefer, 2003Blakey and Umhoefer, 2003

Middle Jurassic Tectonics and Middle Jurassic Tectonics and Paleogeography (160 Ma)Paleogeography (160 Ma)

Middle to Late Jurassic (160 Middle to Late Jurassic (160 Ma) Ma)

Major arc magmatism Major arc magmatism Initial collision between Initial collision between

southern Wrangellia and southern Wrangellia and Cordilleran margin at Cordilleran margin at approximately the latitude of approximately the latitude of Klamaths and Sierras Klamaths and Sierras

Fringing arcs south of Fringing arcs south of collision zone collision zone

Ophiolites obducted in Ophiolites obducted in collision zone and in inter arc collision zone and in inter arc region between Cordilleran region between Cordilleran arc and fringing arcs arc and fringing arcs

Foreland basin in Utah and Foreland basin in Utah and thrusting in Nevada thrusting in Nevada

Rift basin in southwestern Rift basin in southwestern North America related to North America related to opening Gulf of Mexico opening Gulf of Mexico Blakey and Umhoefer, 2003Blakey and Umhoefer, 2003

Late Jurassic Tectonics and Late Jurassic Tectonics and Paleogeography (145 Ma)Paleogeography (145 Ma)

Major plate reorganization -- Major plate reorganization -- change to sinistral motion of change to sinistral motion of Farallon plate relative to North Farallon plate relative to North America causes Wrangellia to America causes Wrangellia to move southward move southward

Complex series of events at Complex series of events at SW margin of North America: SW margin of North America: Chortis and related terranes Chortis and related terranes shift SE as Atlantic and Proto-shift SE as Atlantic and Proto-Caribbean expand; transform Caribbean expand; transform fault and oblique rift systems fault and oblique rift systems developed along waning developed along waning continental arc (McCoy-continental arc (McCoy-Bisbee; Mojave-Sonoran Bisbee; Mojave-Sonoran megashear); early Franciscan megashear); early Franciscan mÈlange formed farther mÈlange formed farther outboard outboard

Nutzotin Ocean between Nutzotin Ocean between northern Wrangellia and North northern Wrangellia and North America remained open America remained open

Oblique convergence shut Oblique convergence shut down much of Cordilleran arc down much of Cordilleran arc Blakey and Umhoefer, 2003Blakey and Umhoefer, 2003

Early Cretaceous Tectonics and Early Cretaceous Tectonics and Paleogeography (125 Ma)Paleogeography (125 Ma)

Guerrero arc collided and Guerrero arc collided and subduction zone rebuilt to west.subduction zone rebuilt to west.

South-moving Wrangellia linked South-moving Wrangellia linked to North Cascades, Tyaughton-to North Cascades, Tyaughton-Methow, and adjacent terranes Methow, and adjacent terranes to form Baja BC to form Baja BC

Tectonic escape of Tectonic escape of Intermontane terrane and parts Intermontane terrane and parts of California northward Great of California northward Great Valley forearc basin and Valley forearc basin and Franciscan subduction complex Franciscan subduction complex built on reorganized Cordilleran built on reorganized Cordilleran margin; as Baja BC moved margin; as Baja BC moved southward, northern Great southward, northern Great Valley a transpressive basin Valley a transpressive basin

North Slope terrane rotated North Slope terrane rotated CCW as Canadian basin opened CCW as Canadian basin opened

Early Sevier thrust belt and Early Sevier thrust belt and foreland basin formed foreland basin formed

Blakey and Umhoefer, 2003Blakey and Umhoefer, 2003

Late Early Cretaceous Late Early Cretaceous Tectonics and Paleogeography Tectonics and Paleogeography

(105 Ma)(105 Ma) Two large volume magmatic Two large volume magmatic

belts formed (Peninsular, Sierra belts formed (Peninsular, Sierra Nevada, Idaho; Coast Plutonic Nevada, Idaho; Coast Plutonic complex built on Baja BC); complex built on Baja BC); plutonic complexes may have plutonic complexes may have been fed by volatiles from been fed by volatiles from under-thrusting of North under-thrusting of North American miogeocline American miogeocline

South-moving Baja BC South-moving Baja BC approached maximum S position approached maximum S position at latitude of southern Arizona at latitude of southern Arizona

Baja BC west of classic Great Baja BC west of classic Great Valley and Franciscan Valley and Franciscan complexes; Great Valley as complexes; Great Valley as interarc basin(?) interarc basin(?)

Rotated North Slope terrane Rotated North Slope terrane collided with Yukon-Tanana and collided with Yukon-Tanana and related terranes related terranes

Sevier orogeny continued and Sevier orogeny continued and foreland basin expanded foreland basin expanded eastward eastward

Blakey and Umhoefer, 2003Blakey and Umhoefer, 2003

Late Cretaceous Tectonics and Late Cretaceous Tectonics and Paleogeography (85 Ma)Paleogeography (85 Ma)

Plate reorganization as Kula Plate reorganization as Kula separated from Farallon Plate; separated from Farallon Plate; dextral transpression with dextral transpression with North America; Kula-Farallon North America; Kula-Farallon ridge moved northward along ridge moved northward along coast coast

Baja BC transported Baja BC transported northward with obliquely northward with obliquely converging Kula plate converging Kula plate

Major magmatic activity in two Major magmatic activity in two belts (110-85 Ma) followed by belts (110-85 Ma) followed by strong decline and null in strong decline and null in magmatic activity (80-40 Ma) magmatic activity (80-40 Ma)

Andean-style segmentation of Andean-style segmentation of Farallon arc from Central Farallon arc from Central America to Southern California America to Southern California

Sevier thrusting continued and Sevier thrusting continued and foreland basin shifted locus of foreland basin shifted locus of subsidence southward in subsidence southward in response to shallow response to shallow

Laramide ‘flat-slab’ Laramide ‘flat-slab’ subductionsubduction

Blakey and Umhoefer, 2003Blakey and Umhoefer, 2003

Cretaceous-Tertiary Tectonics Cretaceous-Tertiary Tectonics and Paleogeography (65 Ma)and Paleogeography (65 Ma)

Triple junction and Baja BC Triple junction and Baja BC moved rapidly northward moved rapidly northward

Intermontane terranes Intermontane terranes translated to north translated to north

Forearc sedimentation Forearc sedimentation (Franciscan-Great Valley) (Franciscan-Great Valley) continued along southern continued along southern margin margin

Uplift of Coast plutonic complex Uplift of Coast plutonic complex generated large deep-sea fan generated large deep-sea fan deposits (Chugach flysch) deposits (Chugach flysch)

Strong Sevier thrusting and Strong Sevier thrusting and foreland basin foreland basin

Laramide orogeny: Farallon Laramide orogeny: Farallon Plate shallow subduction Plate shallow subduction caused expansion NE of caused expansion NE of foreland uplifts and basins foreland uplifts and basins

Blakey and Umhoefer, 2003Blakey and Umhoefer, 2003

Eocene Tectonics and Eocene Tectonics and Paleogeography (50 Ma)Paleogeography (50 Ma)

Intermontane and Baja BC Intermontane and Baja BC blocks continue northward blocks continue northward translation along with north-translation along with north-migrating Kula-Farallon plate migrating Kula-Farallon plate boundary; many terranes boundary; many terranes approach their present latitude approach their present latitude with respect to North America with respect to North America

Olympic terrane accreted Olympic terrane accreted Extensive fore arc Extensive fore arc

sedimentation along most of sedimentation along most of Cordilleran margin Cordilleran margin

Rocky Mountain foreland uplift, Rocky Mountain foreland uplift, deformation, and shallow-deformation, and shallow-subduction-related subduction-related magmatism; interior magmatism; interior sedimentation mostly sedimentation mostly restricted to Rocky Mountain restricted to Rocky Mountain foreland basins foreland basins

Blakey and Umhoefer, 2003Blakey and Umhoefer, 2003