02 Orogen Types

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  • An orogenic experience?

    (or - A Tale of Two Orogens)


  • Synopsis

    mountain ranges: orogens

    mountain building = orogenesis

    mountain building event(s) = orogeny (orogenies)

    subduction-related, Andean-type mountainscollision-related, Himalayan-type mountainswhat drives plate motion?
  • Cordilleran-Andean systemconvergent boundary tectonism (i.e. subduction-related)

    Andean-type mountain ranges

  • Orogenic belts

    subduction of oceanic lithosphere gives rise to 2 different features dependent on type of overriding plate:

    oceanic island arcs

    continental linear mountain chain

    formerly known as Cordilleran-type, now called Andean-type mountain ranges



  • The awesome Andes

    subduction of Nazca Plate beneath S. American Platenow 70-120 mm yr-1Colombia to Tierra del Fuego>8,000 km longAconcagua, Torres del Paine
  • Peruvian Andes

    2 parallel mountain belts Eastern Cordillera = Palaeozoic: metamorphicsWestern Cordillera = Mesozoic-Cenozoic: sedimentary/igneousseparated to S. by Altiplano (plateau)subduction since at least late Triassic?compressional tectonics
  • Intermediate eruptions, acidic intrusions

    Precambrian basement + Palaeozoic sedimentsTrias-Jur.: calc-alkaline volcanism (cf. andesite)Cretaceous-Cenozoic: Andean Coastal Batholith intruded>1,000 granite plutons injected into volcanicsform Western Cordillera


    Pacific Ocean

    Subduction trench



  • Rising in the east

    subduction and the intrusion of batholiths:

    compressional tectonics causing crustal thickening

    Eastern Cordillera riseto E. rocks thrust eastward to form Sub-Andean fold-thrust belt

    Nazca Plate

    S. American


    Western Cordillera





    Fold-Thrust Belt

  • How exotic!

    North American Cordillera (incl. Cascades/Rockies)differentmore complex mosaic of terranesexotic, suspect or displaced terranesvolcanic arcs, oceanic plateaux, fragments of continental crust, aseismic ridges
  • Bit by bit

    too buoyant to subductaccrete (weld) onto continental marginorogen grows laterallynumerous exotic terranes accrete over time (>200My)thus an accretionary orogen
  • Hazardous

    Cascades, Wn. USAmounts Baker, Hood, Adams, Rainier, Shasta, Crater Lake, etc.subduction-related, explosive volcanismstratovolcanoesmajor volcanic hazardsash falls, lava and pyroclastic flowslahars (volcanic mud flows)
  • 8.32a.m., May 18th, 1980

    eruption of Mount St. Helenslandslidelateral blastblew 540m tons of ash (~1km3) settled over 60,000km2reduced summit by 440mkilled 61 peoplelahars flowed 40km
  • Eruption of Mount St. Helens

    The ash cloud

    Forests flattened by the lateral blast

    The dead: car caught in lahar down Toutle River

    All quiet now?

  • Alpine-Himalayan systemcontinent-continent collision (Gondwana & Eurasia)

    Himalayan-type mountain ranges

  • Closure?

    subducting plate may be bordered by continental crustcontinued subduction eventual closure of oceanocean crust subducts completely: brings continental crust to trenchcontinental crust too buoyant to subduct
  • Crash, bang, wallop

    continent-continent collisionrapid relative motion haltedcollisional mountain range formed by crustal shorteningfold-thrust beltssurface along which continents collided is known as a suturesuture may contain ophiolite slivers


  • Himalaya

    youngest collisional mountain rangeHimalaya usually taken as analogy for formation of all collisional mountains250-350 km wide x 3000 km long (from Afghanistan to Burma)older: Appalachians, Caledonides, Urals, Alps
  • The Roof of the World

    lithologic/ tectonic units parallel to mountain beltincl. oceanic crust, passive continental margin, island arc & granite batholithsevidence of complex collisional historymost of Himalayan range is part of Indian Platestill rising ~0.5-4 mm yr-1
  • Ta, ta, Tethys

    accretion of small crustal blocks to Asian margin since Palaeozoicclosure of Tethyan OceanIndia collides w. Laurasia/Eurasia ~50Ma~2000km of crustal shortening due to southward thrusting




  • Himalayan history: detail

    micro-continents of N. & S. Tibet accreted to Laurasia ~140 Ma & ~100 Ma, respectivelyGondwana breaks up, India drifts northIndia collided w. Eurasia ~50 Ma as Tethys closed

    N. Tibet

    S. Tibet

    ~200 Ma

    ~100 Ma

  • Sutures and thrusts

    Indus-Zangbo Suture (IZS, below) separates India & what is now Eurasia continued convergence formed Main Central Thrust (MCT) & Main Boundary Thrust (MBT) to S.

    Eurasian Plate

    Indian Plate

  • Indentations

    India still drifting N. at ~45 mm yr-1continued deformationIndian Plate: old, strongEurasian Plate: younger, warmer, softerindentation tectonicsmodelling using rigid block indenting plasticenemodels deformation wellincl. strike-slip faults where China/E.Asia being squeezed to E.
  • Himalayan geology: 1

  • Himalayan geology: 2

    Eurasian Plate:

    Northern Trans-Himalaya: Cretaceous-Eocene granite batholiths intruding Palaeozoic sediments

    Indian Plate:

    central Higher Himalaya: Precambrian gneiss & Mesozoic sediments intruded by Miocene granite batholiths which overthrust the







  • Himalayan geology: 3

    Lower Himalaya: Precambrian-Mesozoic metasediments which overthrustSub-Himalaya: conglomerates, etc., from erosion of mountains







  • 8.50a.m., 8th October, 2005

    Kashmir earthquake7.6 on Richter ScaleIndian-Eurasian plate boundaryhypocentre 26km depth19km NE of Muzaffarabad, Pakistani Kashmir~100,000 dead>1,000 aftershocks magnitude 4.0 & above
  • Chile: 3.34a.m., 27th February, 2010

    Nazca-South American plate boundary, convergence 80 mm yr-1focus 115km NNE of Chile's 2nd city, Concepcin, depth ~35 km700 km rupture, slip ~10m8.8 on Richter Scale (=5th strongest ever)~300 deadtsunami of 2.5m struck along 700km of coast, killed 15 peopleimmediately N of the largest quake ever recorded: magnitude 9.5 (6,000 dead, tsunami 25 m/82 ft high even 10m high 104 km away)
  • What drives plate motion?

  • Driving forces

    mantle convection cellsare they mantle-wide?or in paired cells above & below MTZ?viscous drag on base of plates driven by lateral motion of mantle?this exists but not believed to be a major driving force
  • P-uuuuuush!

    edge-force mechanismsridge-pushMORs are hot, buoyant and elevated wrt older ocean crustgravity causes elevated lithosphere to push on lithosphere away from ridge
  • Cause or consequence?

    ridge-push moves new lithosphere away from ridge axisnew asthenosphere rises up to fill gapupward movement of asthenosphere at MORs is a consequence of spreading, not the cause of it!
  • Slab pull

    slab more dense than asthenospheresinks and pulls rest of plate along behind ita more minor force is trench suction
  • It all adds up

    ridge-push + slab-pull (+ trench suction)+ shear force (drag) on base of plate from mantle convectionif shear is in same direction as plate movement, plate speeds upif shear in opposite direction, plate is slowed14.unknown
  • The End

    of my bit!

  • So you want to be a vulcanologist?