Lecture 12 continents PDF

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Summary

Continents...

Description

Tectonics and the Evolution of the Continents

• Continental Crust: A Record of 4 billion years of crustal deformation, orogeny and accretion • The North American Cordillera • The India - Eurasia collision zone

Plate Tectonics Construction, Motion, Interaction and Destruction of Tectonic Plates

Plate Boundary Types • Divergent: Continental rifts and mid ocean ridges (Plate Construction) • Convergent: Subduction zones and continental collision zones (Destruction) • Transform: Strike-slip fault systems (Conservation)

California rocks Time Before Present (Ma)

0 100

Geologic Period Type of Margin Tertiary

400

Cretaceous Jurassic Triassic Permian Carboniferous Devonian

500

Ordovician

200 300

Local Events

Californian

San Andreas Transform

Franciscan Subduction

Andean

Foothills Subduction Sonoma Orogeny Rift Events Antler Orogeny

Japanese

Cordilleran

Silurian

600 700

Cambrian

? Rift Events

Precambrian

Sequence

Miogeocline

Atlantic

???????

?

Global Events Circum-Pacific Subduction Atlantic-Indian Spreading

Hercynian orogeny Paleopacific Ocean

Panafrican orogenies of Gondwanaland

Early Paleozoic 570-350 Ma

570-350 Ma Atlantic type passive margin Sedimentary deposits at edge of continent

Early Paleozoic 570-350 Ma

Mid Paleozoic 400-350 Ma

Late Paleozoic 400-250 Ma

400-250 Ma Japanese type subduction and accretion of island arc

Early Paleozoic 570-350 Ma

Mid Paleozoic 400-350 Ma

Late Paleozoic 400-250 Ma

Early Mesozoic 250-150 Ma

Late Mesozoic 150-65 Ma

200-65 Ma Andean type subduction and volcanic arc + forarc basin

Early Paleozoic 570-350 Ma

65-20 Ma Volcanism ends, sediment deposition in forarc basin

Early Cenozoic 65-20 Ma

Early Paleozoic 570-350 Ma

20-00 Ma California type margin San Andreas Fault initiates Basin and Range extension

Late Cenozoic 20-0 Ma

Early Paleozoic 570-350 Ma

Mid Paleozoic 400-350 Ma

Late Paleozoic 400-250 Ma

Early Mesozoic 250-150 Ma

Late Mesozoic 150-65 Ma

Early Cenozoic 65-20 Ma

Late Cenozoic 20-0 Ma

Foredeep basin of arcrelated clastic sediments Accretionary Prism (scraped off subducted oceanic slab) Sierran magmatic Arc (plutonic/volcanic)

Forearc basin

Trench axis Trench slope break Blueschist metamorphism

Hydrothermal Mother Lode Gold Quartz Veins (140-110 Ma)

Franciscan Accretionary Wedge

Great Valley Sequence

Metamorphic Foothills Belt

Andean Type Strata Volcanos

Sierra Nevada Batholith

Subducting Oceanic lithosphere

Asthenosphere

Granitic Plutons

Overriding Gold in solution in Continental hot water Lithosphere in faults

California Gold Rush (1848-1855): 12 millions ounces removed in first 5 years

Subduction regimes cause thermal anomalies: Cold dense slab induces relatively cold temperatures at depth Midocean Ridge

Oceanic Plate

500 degree isotherm

High P and Low T: Q - What type of metamorphic Rock?

Subduction

Continent

Passive margin

Metamorphic rocks: Temperature (oC) à 0

200

400

600

800

Low P, high T

0

Hornfels

10 4

Greenschist

6

20 Blueschist

8 Amphibolite

Granulite

30

10

High P, low T 12

Eclogite

40

Depth (km) à

ß Pressure (kbars)

2

During subduction

After subduction ceased

Trailing edge of slab

Structure of Continents • Continents are made and deformed by plate motion (1/3 of Earth surface). • Continental crust thickness: 30–70 km • Continents are older than oceanic crust (Up to 4.0 Ga old). • Lithosphere floats (isostatically) on a viscous layer below. • Granitic-andesitic composition of crust less dense than oceanic crust

Structure of Continents

?

Cratons (Shields & Platforms) and Orogens

Tectonics From the Beginning

< 0.23 Ga 0.55–0.23 Ga 0.6 Ga

>2.5 Ga

• Ages of crustal domains reveal the growth of the continents • Some continental crust beneath the oceans

2009 GEOLOGIC TIME SCALE

C5A

C5B

5E 6

C5E

M

13.8 16.0

20.4 23.0

30

11

C9 C10 C11

12 C12

35

13

C13

15 16

C15

17

OLIGOCENE

9 10

E

130

140

150

RUPELIAN 33.9

37.2

170

BARTONIAN

C21

22

C22

23

C23

EOCENE

21

PALEOGENE

C20

40.4

M

180

190

LUTETIAN

48.6

E

24

210

YPRESIAN

C26

60 27 28

65

C27 C28

29 C29

30 C30

PALEOCENE

C25

L M

55.8

220

58.7

230

THANETIAN SELANDIAN 61.7

E

240

DANIAN 65.5

250

PERMIAN

280

93.5 99.6

112

320

APTIAN EARLY

125

BARREMIAN

340

130

VALANGINIAN BERRIASIAN

136

360

145.5

TITHONIAN

HIST.

ANOM.

M22

151 LAT E

MIDDLE

380

KIMMERIDGIAN OXFORDIAN CALLOVIAN BATHONIAN BAJOCIAN AALENIAN

156 161 165

400

172

420

183

PLIENSBACHIAN

440 190

SINEMURIAN 197

HETTANGIAN 201.6

460

204

480 LAT E

NORIAN 500 228

CARNIAN 235 MIDDLE

LADINIAN

EARLY

OLENEKIAN

ANISIAN INDUAN

520

241 245 250

251.0

WORDIAN ROADIAN KUNGURIAN

AGE (Ma)

EON

ERA

PERIOD

540

260 266 268 271 276 284

ASSELIAN GZELIAN KASIMOVIAN MOSCOVIAN

BASHKIRIAN

297 299.0 304 306 312

EDIACARAN 630

850

TONIAN

1250

1500

345 359

1750

FAMENNIAN 374

1000

2000

M

EIFELIAN EMSIAN PRAGHIAN

L M E

PRIDOLIAN LUDFORDIAN GORST IAN HOMERIAN SHEINWOODIAN T ELYCHIAN AERONIAN RHUDDANIAN

HIRNANTIAN

L

KATIAN SANDBIAN

M

DARRIWILIAN DAPINGIAN

FLOIAN E Furongian Series 3 Series 2 Terreneuvian

TREMADOCIAN STAGE 10 STAGE 9 PAIBIAN GUZHANGIAN DRUMIAN STAGE 5 STAGE 4 STAGE 3

385

1200

MESOPROTEROZOIC

398 407 411 416 419 421 423 426 428 436 439 444 446

1400

1600

STATHERIAN 1800

OROSIRIAN

2250 2300

SIDERIAN 2500

488 492 496 501 503 507 510 517 521

2500

NEOARCHEAN 2750 2800

3000

468 472 479

535 542

2050

RHYACIAN

455 461

ECTASIAN

CALYMMIAN

392

3250

3500

MESOARCHEAN 3200

PALEOARCHEAN 3600

3750

EOARCHEAN

STAGE 2 FORTUNIAN

STENIAN

PALEOPROTEROZOIC

FRASNIAN GIVETIAN

CRYOGENIAN

1000

VISEAN TOURNAISIAN

NEOPROTEROZOIC

750

318 326

BDY. AGES (Ma) 542

251 254

SAKMARIAN

LOCKHOVIAN

TOARCIAN EARLY

CAPITANIAN

SERPUKHOVIAN MISSISSIPPIAN

E

168 176

PENNSYLVANIAN

L

140

CHANGHSINGIAN WUCHIAPINGIAN

ARTINSKIAN E

300

ALBIAN

200

C24

26

89.3

RHAETIAN

55 25

CONIACIAN

M

CENOMANIAN

M12 M14 M16 M18 M20

160

PRIABONIAN

SANT ONIAN

HAUTERIVIAN

M29

C17

45

M0r M1 M3 M5

M25

C18

20

120

28.4

L

C16

19 C19

50

CHATTIAN

L 260

83.5 85.8

T URONIAN

M10

L

18

40

110

AQUITANIAN

TERTIARY

25

34 C34

BURDIGALIAN E

C6B

C7 C7A C8

100

LANGHIAN

6C C6C 7 7A 8

CHRON.

11.6

SERRAVALLIAN

C6

6A C6A 6B

90

TORTONIAN

LAT E

PRECAMBRIAN PICKS (Ma)

PROTEROZOIC

C5

5C C5C 5D C5D

20

C33

80

7.2

L

70.6

CAMPANIAN

33

AGE

65.5

32 C32

C4 C4A

MAASTRICHTIAN

AGE PERIOD EPOCH (Ma)

CARBONIFEROUS

5B

30 C30 31 C31

PICKS (Ma)

DEVONIAN

15

5.3

MESSINIAN

70

AGE

ORDOVICIAN SILURIAN

5A

CALABRIAN

GELASIAN PIACENZIAN

ZANCLEAN

PERIOD EPOCH

CAMBRIAN*

5

PLIOCENE

MAGNET IC POLARIT Y

RAPID POLARITY CHANGES

4 4A

10

QUATERNARY PLEISTOCENE

0.01 1.8 2.6 3.6

AGE (Ma)

CRETACEOUS

C3 C3A

HOLOCENE

PALEOZOIC

MESOZOIC PICKS (Ma)

JURASSIC

3 3A

AGE

TRIASSIC

C2 C2A

EPOCH

MIOCENE

5

C1

2 2A

PERIOD

NEOGENE

HIST.

ANOM.

1

CHRON.

MAGNETIC POLARITY

ARCHEAN

CENOZOIC AGE (Ma)

3850

HADEAN

*International ages have not been fully established. These are current names as reported by the International Commission on Stratigraphy. Walker, J.D., and Geissman, J.W., compilers, 2009, Geologic Time Scale: Geological Society of America, doi: 10.1130/2009.CTS004R2C. ©2009 The Geological Society of America. Sources for nomenclature and ages are primarily from Gradstein, F., Ogg, J., Smith, A., et al., 2004, A Geologic Time Scale 2004: Cambridge University Press, 589 p. Modifications to the Triassic after: Furin, S., Preto, N., Rigo, M., Roghi, G., Gianolla, P., Crowley, J.L., and Bowring, S.A., 2006, High-precision U-Pb zircon age from the Triassic of Italy: Implications for the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs: Geology, v. 34, p. 1009–1012, doi: 10.1130/G22967A.1; and Kent, D.V., and Olsen, P.E., 2008, Early Jurassic magnetostratigraphy and paleolatitudes from the Hartford continental rift basin (eastern North America): Testing for polarity bias and abrupt polar wander in association with the central Atlantic magmatic province: Journal of Geophysical Research, v. 113, B06105, doi: 10.1029/2007JB005407.

When did continents form? Quite a bit of debate . . .

Hawkesworth and Kemp, Nature (2006)

Shields (e.g., Canada)

Shields (e.g., Canada) Earth’s oldest rocks: The Acasta Gneiss from the Slave Province of NW Canada: ~4.0 Ga

Stable Platforms • Shields covered with series of horizontal sedimentary rocks • Transgressions and regressions caused by sea level changes and vertical tectonics • Sedimentary rocks are now preserved in large basins

Stable Platforms

Vertical Tectonics of Continent Interiors Isostacy

Lithospheric thinning and asthenosphere upwelling

Loading by sedimentary basins

Cooling and sedimentation of passive margins

Uplift by rising mantle plume

Uplift Formed by Removal of Ice Sheet

Continental ice loads the mantle Ice causes isostatic subsidence

Melting of ice causes isostatic uplift Return to isostatic equilibrium

Isostacy

Models of Isostacy

Uplift Caused by Rising Mantle Plume

Mountain Belts / Orogeny • Relatively narrow zones of folded, compressed rocks formed at convergent plate boundaries • Two major active belts: Cordilleran (Alaska to Andes), and AlpineHimalayan Belts • Older examples: Appalachians, Urals

Mountain Belts / Orogeny The Appalachian orogen includes accretion of • continental fragments, island arcs and • African crust throughout the Paleozoic 3 main phases from middle Ordovician through early Permian epochs

Mountain Belts / Orogeny The Appalachian orogen includes accretion of • continental fragments, island arcs and • African crust throughout the Paleozoic 3 main phases from middle Ordovician through early Permian epochs (The Taconic, CaledonianAcadian, Variscan and Appalachian Orogenies)

Cycles of Break-up and Orogenies • The Wilson cycle

The Make-up of N America • The interior shield and platform regions (craton) have only had vertical deformation since Precambrian (epeirogeny)

The North American Cordillera • The western third of North America the “Cordillera” underwent complex geologic history with multiple episodes of accretion, deformation and magmatism over the past 500 million years • The region is actively deforming today

The North American Cordillera • Physiography reveals – Sierra Nevada batholiths and Central Valley foreland basin – Cascadia active subduction zone – Rocky Mountains resulting from intra-plate orogeny – Hot Spot tectonics of Snake River plain & Yellowstone – Basin and Range extension of faltering high plateau – San Andreas transform faulting & Coast Ranges uplift – The Mendocino Triple Junction

The North American Cordillera • Rocky Mountains – Resulted from intra-plate Laramide orogeny. possibly from shallow subduction – Cenozoic (75-35 Ma) – Minor deformation today

The North American Cordillera • Hot Spot tectonics of Snake River Plain and Yellowstone • 20 Ma – active today • Which way is plate moving?

W or E?

The North American Cordillera • Hot Spot tectonics of Snake River Plain and Yellowstone • 20 Ma – active today • Which way is plate moving?

W or E? North America is moving to the west, relative to Yellowstone hot spot

The Yellowstone Caldera •

Active hot spot geothermal activity • Mega caldera eruptions • Rapid current vertical deformation (from GPS and InSAR)

http://www.mines.utah.edu/~rbsmith/RESEARCH/YellowstoneHotspot.html

The North American Cordillera • Hot Spot tectonics of Snake River Plain and Yellowstone • 20 Ma – active today • Which way is plate moving?

W or E? North America is moving to the west, relative to hot spot

The North American Cordillera • Basin and Range – Cenozoic extension of faltering high plateau – Steep E- and W-dipping normal faults (“grabens”) – Incipient continental rift? – Stable Colorado Plateau block to SE – Mid-Cenozoic – active today

Basin and Range Deformation • GPS-measured motions are relative to stable North American shield stations • Not much east of Utah • Only ~ 2mm/yr extension across Wasatch front, but earthquake hazard is significant • About 10 mm/yr of extension and right-lateral shear along Eastern California Shear Zone

Farallon Plate Subduction and SAF Transform Faulting

The North American Cordillera Sierra Nevada, California

The North American Cordillera • San Andreas Transform – Strike-slip faulting & tranpressional coast range uplift – From Mendocino triple junction to Baja California – Some motion now E of Sierra Nevada along eastern CA shear zone – Since ~28 Ma – active today – Coast range uplift since ~5 Ma

The North American Cordillera • Mendocino Triple Junction – Transition from San Andreas transform to Cascadia subduction – Moves northward as San Andreas grows – Creates slab window; mantle upwelling; volcanism and uplift

San Andreas Fault Deformation •

Motions are relative to stable North American shield stations • ~40 mm/yr between Sierras and Pacific in N Calif • ~48 mm/yr between NOAM and Pacific plate in S Calif • About 10 mm/yr along ECSZ

SCEC CMM 3.0

How Continents Grow • Magmatic addition and differentiation: magma transferred to continents at subduction zones • Continental accretion: buoyant fragments of continents attached to continents as the result of plate motions

How Continents Grow: Accretion o Terrane ” Multiple accretions of older island arcs, oceanic plateaus, oceanic crust, and marine sedimentary rocks.

How Continents Grow: Accretion o Terrane ”

How Continents Grow: Accretion o Terrane ”

India - Eurasia Collision Zone • From subduction to collision ...

The India-Eurasia Collision Zone •

The India - Eurasia collision zone spans 1000s km of distributed deformation • Collision started in Eocene, but India relentlessly presses on .. • Today, the Himalaya rise to > 8000 m elevations, the Tibetan plateau averages > 4500 m

Eurasia Mongolia Tibet S China India

Numbers are time (in Ma), showing relative position of India

India - Eurasia Collision Zone • From subduction to collision ...

The India-Eurasia Collision Zone • Collision began ~50 Ma; ~2000 km of motion since then • India is still rapidly (~45 mm/yr) converging with Eurasia • Where and how is this convergence accommodated?

Eurasia Mongolia Tien Shan Tibetan Plateau S China

Active Continental Collision or Escape Tectonics •

•

The Tibetan plateau is high, and crustal thickness is about twice (~70 km) of normal

Eurasia Mongolia

Strike-slip faulting & extension allow E extrusion of Tibet