Transcript The Wilson Cycle

The Wilson Cycle
Supercontinent cyclisity?
The Wilson Cycle: named after J. Tuzo Wilson, one of the
founding fathers of platetectonics and discoverers of transform faults.
Wilson used his old reference background, in the North Atlantic realm
and the Appalachian - Caledonian orogenic belts on both sides of the
Atlantic 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 closed
to produce the Appalachians and the Caledonides
5) Remnant stage
Continental collision, suture zones, deformation and metamorphism, mountain building
Extensional collapse, faulting and collapse
basins
4) Terminal stage
Near closure of ocean, mature arcs and
back-arc, accreationary wedges, HP-LT
metamorphic complexes
(Mediterranean See area)
3) Vaning stage: Intra-oceanic subduction
and island arcs transition to Andean margins.
(SE Asia and Western Passific)
2) Mature stage Passive margins with large
shelf-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 previous
slide, 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 traditional
Wilson-cycle tectonics
does not work to explain
formation of the
Caledonides
Supercontinent cyclisity?
From Rodinia to Pangea?? Does the earth´s continental lithospheric
plates assemble and rift apart in longer term cycles?
≈ 500 myr.
cycle?
TERRANE ANALYSES
Type of tectonic analyses that focusses on differences
rather than similarities between geological units.
First used in the North American Cordillereas
Differences in:
• Stratigraphic record
• Basement
• Deformation/metamorphic histories
• Fauna zonation and provinciality
• Geophysical signature
• Apparent Polar Wander Paths
SUSPECT TERRANES: TECTONOSTRATIGRAPHIC
TERRANES THAT HAVE UNSETTLED AFFINITY/
ORIGIN WITH RESPECT TO THE CONTINENT WHERE
IT ENDS UP AFTER AN OROGENY
EXOTIC TERRANES: TECTONOSTRATIGRAPHIC
TERRANES THAT HAVE OUTBOARD ORIGIN WITH
RESPECT TO THE CONTINENT WHERE IT ENDS UP
AFTER AN OROGENY. EXAMPLES OPHIOLITES AND ISLAND ARC
COMPLEXES, CONTINETAL FRAGMENTS WITH AN ORIGIN IN ANOTHER
CONTINENT
Terranes (terreng konseptet):
A terrane is defined as a regionally mapable geological unit, limited
by faults, and with a geological history/evloution/signature that
makes 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:
Composite terrane C
Terrane linking unconformities
A
”Stitching” plutons, the two terranes
A and B were together at the time the
pluton C was intruded, in this case
this happened before
the unconformity
since the pluton is overlain
by the sediments
B
Composite terrane D
A
C
B
Terrane analysis,
Canadian Applachians
Terrane map of the
North American
Cordilleras
(After Jones et al. 1982)
Notice the wide distribution of the
terrane shown in red ”Wrangelia”
The collage of terranes reflects the
progressive accreation of suspect and
exotic elements originating further to
the south. Notice that Baia California
will be detached from the continent and
with time end up in Alaska region