The Wilson CycleThe Wilson CycleSupercontinent cyclisity?Supercontinent cyclisity?

The Wilson Cycle:The Wilson Cycle: named after J. Tuzo Wilson, one of thefounding fathers of platetectonics and discoverers of transform faults.

Wilson used his old reference background, in the North Atlantic realmand the Appalachian - Caledonian orogenic belts on both sides of theAtlantic ocean to formulate a hypothesis saying that the building of mountain belts have a close relationship to the opening and closure of oceans with oceanic lithosphere.

Hence he introduced the term ”the Proto-Atlantic” as a name for the postulated ocean that according to the model once opened and closedto produce the Appalachians and the Caledonides

5) Remnant stageContinental collision, suture zones, deform-ation and metamorphism, mountain buildingExtensional collapse, faulting and collapsebasins4) Terminal stageNear closure of ocean, mature arcs andback-arc, accreationary wedges, HP-LTmetamorphic complexes(Mediterranean See area)

3) Vaning stage: Intra-oceanic subductionand island arcs transition to Andean margins. (SE Asia and Western Passific)

2) Mature stage Passive margins with largeshelf-areas (Atlantic Ocean)

1) Embryonic to Young stage.Rifts to small ocean basin with sea-floor spreading. (East African rift and Red Sea)

Traditional Wilson cycle model:Orthogonal opening and closure like on the previousslide, two-dimentional models.

Modified Wilson cycle model:Wilson-cycle type tectonics with a modern approach;---one ocean opening--- another closing, cf. Indian ocean opening -- eastern Tethyan closing.

Notice that traditionalWilson-cycle tectonicsdoes not work to explainformation of the Caledonides

Supercontinent cyclisity?Supercontinent cyclisity?From Rodinia to Pangea?? Does the earth´s continental lithospheric

plates assemble and rift apart in longer term cycles?

≈ ≈ 500 myr.500 myr.cycle?cycle?

TERRANE ANALYSESTERRANE ANALYSES

Type of tectonic analyses that focusses on differencesrather than similarities between geological units.First used in the North American CordillereasDifferences in:• Stratigraphic record• Basement• Deformation/metamorphic histories• Fauna zonation and provinciality• Geophysical signature• Apparent Polar Wander Paths

SUSPECT TERRANESSUSPECT TERRANES: TECTONOSTRATIGRAPHICTERRANES THAT HAVE UNSETTLED AFFINITY/ORIGIN WITH RESPECT TO THE CONTINENT WHEREIT ENDS UP AFTER AN OROGENY

EXOTIC TERRANESEXOTIC TERRANES: TECTONOSTRATIGRAPHICTERRANES THAT HAVE OUTBOARD ORIGIN WITH RESPECT TO THE CONTINENT WHERE IT ENDS UPAFTER AN OROGENY. EXAMPLES OPHIOLITES AND ISLAND ARCCOMPLEXES, CONTINETAL FRAGMENTS WITH AN ORIGIN IN ANOTHER CONTINENT

Terranes (terreng konseptet):A terrane is defined as a regionally mapable geological unit, limitedby faults, and with a geological history/evloution/signature thatmakes it distinct from surrounding units.

4 main types of terranes (NB! written terrane and not terrain):

1) Stratigraphic terrane: characterised by a similar stratigraphic sequence including units of continental/oceanic crust

2) Fragmented/broken terranes: characterised by blocks of variable sizes, lithologies and ages engulfed in a deformed composite matrix (suture zones and melanges)

3) Composite terranes. characterised by being composed of 2 or more terranes, which from a particular point in time share the same geological evolution across previous terrane boundaries

4) Metamorphic terranes: characterised by a penetrative metamorphic textures/structures, so that possible previous tectonic distinctions have been destroyed

Linking of terranes:

Terrane linking unconformities

A B

Composite terrane C

”Stitching” plutons, the two terranes A and B were together at the time thepluton C was intruded, in this casethis happened beforethe unconformitysince the pluton is overlainby the sediments

A B

Composite terrane D

C

Terrane analysis, Terrane analysis, Canadian ApplachiansCanadian Applachians

Terrane map of the Terrane map of the North AmericanNorth AmericanCordillerasCordilleras(After Jones et al. 1982)

Notice the wide distribution of the terrane shown in red ”Wrangelia”The collage of terranes reflects theprogressive accreation of suspect andexotic elements originating further tothe south. Notice that Baia Californiawill be detached from the continent andwith time end up in Alaska region