- Slides: 11
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
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 5) Remnant stage Continental collision, suture zones, deform ation and metamorphism, mountain buildin 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) 11. 3) Vaning stage: Intra-oceanic subduction 12. and island arcs transition to Andean margin 13. (SE Asia and Western Passific) 14. 2) Mature stage Passive margins with larg 15. shelf-areas (Atlantic Ocean) 16. 1) Embryonic to Young stage. 17. Rifts to small ocean basin with sea-floor 18. 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 2) sequence including units of continental/oceanic crust 2) Fragmented/broken terranes: characterised by blocks of 3) variable sizes, lithologies and ages engulfed in a deformed 4) composite matrix (suture zones and melanges) 3) Composite terranes. characterised by being composed of 2 or 4) more terranes, which from a particular point in time share the 5) same geological evolution across previous terrane boundaries 4) Metamorphic terranes: characterised by a penetrative 5) metamorphic textures/structures, so that possible previous 6) 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