Phanerozoic Tectonics

PALEOZOIC TECTONICS - OVERVIEW

• SUMMARY - CONTINENTAL DISPERSION DURING THE EARLY PALEOZOIC & SUBSEQUENT CONVERGENCE DURING THE LATE PALEOZOIC (A WILSON CYCLE)
• INITIALLY - DISRUPTION OF A SUPERCONTINENT (PANGEA I - FORMED IN MIDDLE PROTEROZOIC TIME) IN THE LATE PROTEROZOIC (800 MY) & DISPERSION OF THE SEVERAL RESULTANT CONTINENTS UNTIL THE MIDDLE ORDOVICIAN (475 MY)
  • development of passive continental margins at the edges of the several continents, with accumulation of thick sedimentary sequences
• CONTINENTS REASSEMBLED INTO A SECOND SUPERCONTINENT BY THE END OF LATE PALEOZOIC (275 MY) TIME
  • development of convergent continental margins at the edges of most continents during the Ordovician, culminating with continental collisions & suturing during the Late Paleozoic

PALEOZOIC TECTONICS - DETAILS

• LATE CAMBRIAN (550 TO 540 MY) - CONTINENTS ARE WELL DISPERSED & MOSTLY MOVING APART (LIKE TODAY)
  • 6 major continents
    • LAURENTIA (North America + Scotland)
    • BALTICA (Scandinavia, northern Europe, Russia [west of the Urals])
    • SIBERIA (east of the Urals + Mongolia = Northeast Asia)
    • KAZAKHSTANIA (Central Asia)
    • CHINA (including Southeast Asia)
    • GONDWANA (South America, Africa, Antarctica, Australia, India, southern Europe & Florida!)
  • continents are mostly in low latitudes (no continents at the poles)
    • CLIMATE IS VERY WARM & THICK LIMESTONES DEPOSITED IN SHALLOW SEAS
• MIDDLE ORDOVICIAN (490-475 MY) - CONTINENTS ARE STARTING TO CONVERGE
  • Gondwana (Sahara region) at the South Pole
    • GLACIATION IN the SAHARA
• MIDDLE SILURIAN (435-430 MY) - SIBERIA, BALTICA & LAURENTIA CONVERGING
  • Late Silurian - Gondwana (Chile region) at the South Pole
    • GLACIATION IN SOUTHERN SOUTH AMERICA
• DEVONIAN (~400 MY AGO) - CONVERGENCE WAS DOMINANT & LAURENTIA & BALTICA COLLIDE TO FORM LAURUSSIA
  • Gondwana nearly covers the South Pole, but doesn't result in glaciation
    • GONDWANA TOO BIG - MOISTURE CAN'T GET TO INTERIOR
• LATE CARBONIFEROUS [PENNSYLVANIAN] (~300 MY AGO) - FINAL CONSOLIDATION OF PAN-GEA II BEGINS WITH COLLISION OF LAURUSSIA & GONDWANA & OF KAZAKHSTANIA & SIBERIA
  • Gondwana moves slightly off South Pole; glaciation results
• PERMIAN (~250 MY AGO) - PANGEA II IS ESSENTIALLY FORMED (CHINA PROBABLY IS NOT ATTACHED TO IT)
  • Gondwana again completely covers South Pole; extensive evaporites

CONTINENTAL FRAMEWORK

• MOBILE BELTS VS. CRATONS
  • mobile belt = elongate zone of intense deformation & igneous activity that generally occurs at the periphery of continent
    • contain THICK (10-15 KM) SEQUENCES OF SEDIMENTS
  • craton = ancient geologically-stable central nucleus of a continents consisting of an exposed Precambrian shield surrounded by a platform of thin (<5km), essentially flat-lying Phanerozoic sedimentary strata
    • craton surfaces are GENTLY WARPED INTO BASINS, DOMES & ARCHES

NORTH AMERICAN MOBILE BELTS

• INITIALLY PASSIVE (DIVERGENT) CONTINENTAL MARGINS WITHIN PLATES DURING EARLY PART OF PALEOZOIC WITH THICK (10-15 KM) SEDIMENTARY SEQUENCES
  • marginal to Iapetus Ocean on the east
• APPALACHIAN MOBILE BELT (INCLUDING THE APPALACHIAN & OUACHITA OROGENS - EAST & GULF COASTS OF NORTH AMERICA)
  • eastern margin of Laurentia rifted during Late Proterozoic
  • island arcs developed far from North America during the Late Proterozoic = PIEDMONT
  • 3 orogenic events - Taconic, Acadian-Caledonian, & Alleghanian-Ouachita-Hercynian
    • TACONIC - Middle Ordovician collision of eastern Laurentia with an island arc (Piedmont)
    • ACADIAN-CALEDONIAN - Devonian collision of Laurentia with Baltica to form Laurussia
    • ALLEGHANIAN-OUACHITA-HERCYNIAN - Carboniferous/Permian collision of Laurussia with Gondwana
  • Clastic Wedges shed onto North American & European cratons from eroding orogenic belts
    • QUEENSTON CLASTIC WEDGE (Taconic Orogeny - North America only)
    • CATSKILL CLASTIC WEDGE /OLD RED SANDSTONE CLASTIC WEDGE (Acadian/Caledonian orogeny) - consists of redbeds & contains lots of land plant & animal material
      • development of widespread black shales (Chattanooga Shale)
    • APPALACHIAN BASIN CLASTIC WEDGE/NEW RED SANDSTONE CLASTIC WEDGE (Alleghenian/Hercynian orogeny) - lots of coal
      • coal in CYCLOTHEMS = repeated deposition of distinct sedimentary sequence of non-marine & marine strata
      • due to delta lobe switching & to Pennsylvanian glacial cycles
• CORDILLERAN MOBILE BELT
  • Late Proterozoic rifting of the western margin of Laurentia
  • island arcs developed immediately off western Laurentia during the Ordovician separated by Back-Arc Basins
  • Only 1 Paleozoic Orogeny & No Clastic Wedges
  • ANTLER OROGENY - Devonian collision of western Laurentia with an island arc (KLAMATH MOUNTAINS)

SEDIMENTARY DEPOSITIONAL SEQUENCES

• RESULT FROM LARGE-SCALE TRANSGRESSIONS & REGRESSIONS ACROSS THE CRATON
  • transgressions begin at craton margins & progress toward the craton interior until most of the continent is covered by a shallow sea
  • during regressions, the continent is again mostly exposed & widespread unconformities develop
• SEQUENCES ARE THICKEST & MOST COMPLETE (SHORTEST UNCONFORMITIES) AT THE CRATON MARGIN & THINNEST & MOST INCOMPLETE (LONGEST UNCONFORMITIES) IN THE CRATON INTERIOR
• SEQUENCES USUALLY HAVE A BASAL TRANSGRESSIVE SS, OVERLAIN BY SHALE, WHICH IN TURN IS OVERLAIN BY CHEMICAL ROCKS (LS, DOLOSTONE, & EVAPORITES)
  • examples:
    • 1) Sauk Sequence - Tapeats SS, Bright Angel Shale & Muav LS;
    • 2) Tippecanoe Sequence - St. Peter SS & Silurian carbonates/ evaporites in Great Lakes region;
    • 3) Kaskaskia Sequence - Oriskany SS, Devonian (Western Canada) & Mississippian carbonates & Devonian/ Mississippian boundary black shale (Chattanooga Shale)
    • 4) Absaroka Sequence - Cyclothems in Pennsylvanian & evaporites in W. Texas basins

MESOZOIC/CENOZOIC TECTONICS - OVERVIEW

• MESOZOIC/CENOZOIC TECTONICS DOMINATED BY DIVERGENCE AS WEGENER'S PANGEA WAS DISMEMBERED AND THE ATLANTIC & INDIAN OCEANS OPENED
• MOUNTAIN BELTS DEVELOPED IN MESOZOIC/CENOZOIC - ASSOCIATED WITH DESTRUCTION OF OCEANIC CRUST AROUND PACIFIC OCEAN & CONTINENTAL COLLISIONS AS AFRICA/INDIA COLLIDED WITH EURASIA, ELIMINATING TETHYS SEAWAY
  • Cordilleran Mountain System
    • SUBDUCTION & CONVERGENCE ALONG WEST COASTS OF N. & S. AMERICA
    • ACCRETIONARY TECTONICS CHARACTERIZES THIS SYSTEM
  • Alpine/Himalayan Mountain System
    • COLLISION OF AFRICA & INDIA WITH EURASIA

MESOZOIC/CENOZOIC TECTONICS - DETAILS

• TRIASSIC (~215 MY AGO)
  • Divergence leading to dismemberment of Wegener's Pangea initiates
    • CONTINENTAL RIFTING ALONG WESTERN EXTENSION OF TETHYS BETWEEN EAST COAST OF NORTH AMERICA & NORTHWEST AFRICA
  • Convergent continental margins off western N. & S. America & Antarctica
• JURASSIC (208-144 MY AGO)
  • 190 my - initial breakup of Pangea II begins
    • SEAFLOOR SPREADING IN CENTRAL NORTH ATLANTIC OFF EASTERN N. AMERICA & NW AFRICA
    • WEGENER'S PANGEA BREAKS INTO LAURASIA & GONDWANA (Florida left with N. America)
  • 165 my - Gondwana begins to break up
    • SEAFLOOR SPREADING OFF EASTERN AFRICA & ANTARCTICA
    • GONDWANA BREAKS INTO WESTERN GONDWANA (S. America/Africa) & EASTERN GONDWANA (Antarctica/Australia/India/Madagascar)
      • Jurassic seafloor off NW Australia = Indonesia rifted from Gondwana?
• CRETACEOUS (144-66 MY AGO)
  • 135 my - Gondwana continues to break up
    • WESTERN GONDWANA SEPARATES INTO SOUTH AMERICA & AFRICA
    • EASTERN GONDWANA SEPARATES INTO ANTARCTICA/AUSTRALIA & INDIA/ MADAGASCAR (now part of Africa)
  • 90 my - Laurasia begins to break up
    • SEAFLOOR SPREADING IN LABRADOR SEA & BAY OF BISCAY
      • Laurasia breaks into N. America, Eurasia/Greenland, & Spain
    • INDIA SEPARATES FROM MADAGASCAR & ACCELERATES TOWARD ASIA
    • NEW ZEALAND SEPARATES FROM AUSTRALIA
• CENOZOIC
  • Early Eocene (55 my ago) - Greenland separates from Eurasia & joins North America
  • Late Eocene (45 my ago) - Antarctica & Australia break up
  • NOTE: These 2 events were critical for Cenozoic climatic cooling

NORTH AMERICAN MESOZOIC/CENOZOIC TECTONICS

• EAST & GULF COAST
  • Mesozoic rifting (Late Triassic - Early Jurassic)
    • RIFT VALLEYS FILLED WITH REDBEDS, EVAPORITES & BASALTIC VOLCANICS
  • Mesozoic/Cenozoic subsidence (Middle Jurassic to present)
    • RESULTS FROM COOLING OF THINNED CONTINENTAL CRUST
    • ALLOWS FOR ACCUMULATION OF THICK (8 KM AV., 15 KM MAXIMUM) SEQUENCES OF PREDOMINANTLY SHALLOW-MARINE SEDIMENTS
      • lots of limestone ( particularly in the southeast) & lots of petroleum in the Gulf Coast sediments, some localized along salt domes
    • THE COASTAL PLAIN IS THE THIN EDGE OF THIS THICK PILE OF SEDIMENTS
• WEST COAST
  • Dominated by accretion of exotic terranes (island arcs, volcanic plateaus & microcontinents) throughout Mesozoic & most of Cenozoic
  • Sonoma Orogeny
    • LATE PERMIAN THROUGH TRIASSIC ISLAND ARC COLLISION
  • Nevadan Orogeny
    • TRIASSIC THROUGH CRETACEOUS SUBDUCTION ALONG ANDEAN TYPE SYSTEM
    • GENERATED HUGE QUANTITIES OF GRANITE NOW EXPOSED IN CALIFORNIA (Sierra Nevada Batholith), IDAHO (Idaho Batholith), BRITISH COLUMBIA (Coast Range Batholith) & BAJA CALIFORNIA (Baja California Batholith)
  • Sevier Orogeny
    • MIDDLE JURASSIC TO EARLIEST CENOZOIC (overlapped in time with Nevadan Orogeny) FORELAND THRUSTING
    • RELATED TO SUBDUCTION OF NEVADAN OROGENY
  • Laramide Orogeny
    • LATE CRETACEOUS THROUGH EOCENE
    • MOSTLY WARPING INTO DOMES & ARCHES - FINAL GASP OF SUBDUCTION
    • RELATED TO VERY FLAT SUBDUCTING PLATE (Farallon Plate)
  • Late Cenozoic tectonics is dominated by rifting
    • DEVELOPMENT OF BASIN & RANGE BY RIFTING STARTING IN LATE MIOCENE
    • UPLIFT OF THE COLORADO PLATEAU (Grand Canyon & other western national parks)
    • CHANGE IN STYLE RELATED TO NORTH AMERICA OVERRUNNING EAST PACIFIC RISE PORTION OF MOR STARTING IN EOCENE - CONTINENTAL MARGIN CHANGED FROM CONVERGENT TO LATERAL MARGIN
• CONTINENTAL INTERIOR (WESTERN ONLY - EASTERN MOSTLY EXPOSED)
  • Series of transgressions & regressions
  • Triassic & early Jurassic - widespread nonmarine (redbeds & dune sands) sediments (sealevel low)
  • middle/late Jurassic & Cretaceous - transgression by Jurassic Sundance Sea & Cretaceous Interior Seaway [Zuni Sequence](rising sealevel)
  • Eocene & Miocene - Tejas Sequence = decrease in rate of sealevel fall

Study Questions

1. When did the Late Proterozoic-Paleozoic Wilson Cycle initiate?

2. When did it change from dispersion to convergence?

3. What were the 6 major Early Paleozoic continents & their relationship to modern continents?

4. What were the positions of these continents during the Paleozoic & the effect on climate?

5. What are the general characteristics of cratons & mobile belts in terms of tectonic stability, sediment thickness & position relative to continent interior?

6. What are the general characteristics of sedimentary depositional sequences in terms of sediment thickness & unconformity distribution & their basic cause?

7. What is the basic lithologic sequence within sedimentary depositional sequences?

8. What are some important sedimentary units within the North American Sequences?

9. What are the details of the Taconic, Acadian-Caledonian & Alleghenian-Ouchita-Hercynian Orogenies?

10. What are the details of the Queenston Clastic Wedge, the Catskill Clastic Wedge-Old Red Sandstone & the Appalachian Basin-New Red Sandstone?

11. What was the time of the initiation of the Mesozoic-Cenozoic Wilson Cycle?

12. What is the cause of Alpine-Himalayan Orogenesis?

13. What is the evidence indicating the timing & location of Wegener's Pangea?

14. What are the continents that formed during this initial breakup?

15. Summarize the breakup of Gondwana & Laurentia during the Mesozoic & Cenozoic.

16. How do the general characteristics of North American Atlantic & Gulf Coast tectonics differ from those western North American tectonics?

17. What are the general causes of the Sonoma, Nevadan, Sevier & Laramide Orogenies?

18. What are the general causes of Late Cenozoic western rifting, including development of Basin & Range during Late Miocene & the uplift of Colorado Plateau?

19. What are the general characteristics of the Zuni & Tejas Sedimentary Depositional Sequences?

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