Thrust tectonics
Thrust tectonicsorcontractional tectonicsis concerned with the structures formed by, and thetectonicprocesses associated with, the shortening and thickening of thecrustorlithosphere.It is one of the three main types of tectonic regime, the others beingextensional tectonicsandstrike-slip tectonics.These match the three types ofplate boundary,convergent(thrust),divergent(extensional) andtransform(strike-slip). There are two main types of thrust tectonics, thin-skinned and thick-skinned, depending on whether or not basement rocks are involved in the deformation. The principle geological environments where thrust tectonics is observed are zones ofcontinental collision,restraining bends on strike-slip faults and as part of detached fault systems on somepassive margins.[1]
Deformation styles
[edit]In areas ofthrusttectonics, two main processes are recognized:thin-skinned deformationandthick-skinned deformation.The distinction is important as attempts to structurally restore the deformation will give very different results depending on the assumed geometry.[2]
Thin-skinned deformation
[edit]Thin-skinned deformationrefers to shortening that only involves the sedimentary cover. This style is typical of manyfold and thrust beltsdeveloped in the foreland of a collisional zone. This is particularly the case where a good basaldecollementexists such assaltor a zone of high pore fluid pressure.[3]
Thick-skinned deformation
[edit]Thick-skinned deformationrefers to shortening that involvesbasement rocksrather than just the overlying cover. This type of geometry is typically found in thehinterlandof a collisional zone. This style may also occur in the foreland where no effective decollement surface is present or where pre-existing extensional rift structures may beinverted.[4]
Geological environments associated with thrust tectonics
[edit]Collisional zones
[edit]The most significant areas of thrust tectonics are associated withdestructive plate boundariesleading to the formation oforogenic belts.The two main types are: the collision of twocontinentaltectonic plates(for example theArabian PlateandEurasian Plate,which formed theZagros fold and thrust belt) and collisions between a continent and anisland arcsuch as that which formedTaiwan.[5]
Restraining bends on strike-slip faults
[edit]When astrike-slip faultis offset along strike such that the resulting bend in the fault hinders easy movement, e.g. a right stepping bend on a sinistral (left-lateral) fault, this will cause local shortening ortranspression.Examples include the 'Big Bend' region of theSan Andreas Fault,[6]and parts of theDead Sea Transform.[7]
Passive margins
[edit]Passive marginsare characterised by large prisms of sedimentary material deposited since the original break-up of a continent associated with formation of a newspreading centre.This wedge of material will tend to spread under gravity and, where an effectivedetachmentlayer is present such assalt,the extensional faulting that forms at the landward side will be balanced at the front of the wedge by a series oftoe-thrusts.Examples include the outboard part of theNiger delta(with an overpressuredmudstonedetachment)[8]and theAngolamargin (with asalt detachment).[9]
References
[edit]- ^Butler, R.; Bond, C. (2020). "Chapter 9 - Thrust systems and contractional tectonics". In Scarselli, N.; Adam, J.; Chiarella, D. (eds.).Principles of Geologic Analysis.Regional Geology and Tectonics. Vol. 1 (2 ed.). Elsevier. pp. 149–167.doi:10.1016/B978-0-444-64134-2.00008-0.ISBN9780444641359.
- ^Shiner, P (2004). "Thin-skinned versus thick-skinned structural models for Apulian carbonate reservoirs: constraints from the Val d'Agri Fields, S Apennines, Italy".Marine and Petroleum Geology.21(7): 805–827.Bibcode:2004MarPG..21..805S.doi:10.1016/j.marpetgeo.2003.11.020.
- ^Hatcher, R. D. (2007)."Confirmation of Thin-skinned Thrust Faulting in Foreland Fold-Thrust Belts and Its Impact on Hydrocarbon Exploration: Bally, Gordy, and Stewart, Bulletin of Canadian Petroleum Geology, 1966"(PDF).AAPG Search and Discovery Article.70034.
- ^Butler, R. W. H.; Mazzoli, S.; Corrado, S.; De Donatis, M.; Di Bucci, D.; Gambini, R.; Naso, G.; Nicolai, C.; Scrocca, D.; Shiner, P.; Zucconi, V. (2004). McClay, K. R. (ed.)."Applying thick-skinned tectonic models to the Apennine thrust belt of Italy—Limitations and implications"(PDF).Thrust tectonics and hydrocarbon systems: AAPG Memoir 82.pp. 647–67.
- ^Timothy Briggs Byrne; Char-Shine Liu (2002).Geology and Geophysics of an Arc-continent Collision, Taiwan.Special Paper 358. Geological Society of America.ISBN978-0-8137-2358-7.
- ^Rust, D. 1998. Contractional and extensional structures in the transpressive ‘Big Bend’ of the San Andreas fault, southern California. Geological Society, London, Special Publications; 135; pp. 119–126
- ^Gomez, F., Nemer, T., Tabet, C., Meghraoui, M. & Barazangi, M. 2007. Strain partitioning of active transpression within the Lebanese restraining bend of the Dead Sea Fault (Lebanon and SW Syria). Geological Society, London, Special Publications; 290; 285–303
- ^Bilotti, F. & Shaw, J.H. 2005. Deep-water Niger Delta fold and thrust belt modeled as a critical taper wedge: The influence of elevated basal fluid pressure on structural styles. AAPG Bulletin; 89; 11; 1475–1491
- ^Marton, G, & Schoenborn, G. 2008. Salt Tectonics of the Continent-Ocean Transition, Deep-Water Angola. MAPG conference abstract
