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The tectonics of the Early Earth, before the establishment of plate tectonics, are poorly constrained due to the limited outcrop extent of rocks of Archean age. Several different geodynamic mechanisms have been proposed, working either independently or in combination. The main control on the likely tectonics is the temperature of the mantle, which is expected to have been 200–250°C hotter than current values during the Archean.[1]
Heat-pipe tectonics edit
This mechanism envisages an early earth in which melt rises through an early lithosphere in relatively narrow pipe-like structures, forming thick lava flows on the surface. Each stage of eruption would be accompanied by downward advection (subsidence) of earlier flows.[2]
Lid tectonics edit
The early history of the Earth and the current state of many of the rocky planets is described in terms of lid tectonics. The "lid" is a strong outermost layer, the equivalent of the lithosphere. This may be "stagnant" where the strength of the lid is sufficient to prevent it becoming involved in the underlying convecting mantle. Plate tectonics can be regarded as a form of "mobile" lid tectonics. The effect of a single continuous stagnant lid would be to reduce the amount of heat escaping from the Earth and numerical modelling suggests that this would result in episodic mantle-overturn events that would substantially rework the lid.
Onset of plate tectonics edit
The timing of the onset of plate tectonics in its current form remains uncertain, with some workers favouring a period in the middle of the Archean, at about 3.2 Ga,[3] while others suggest that it occurred between about 1.0 to 0.5 Ga.[1] This later age is supported by the analysis of apparent polar wander paths that suggests the change to full plate tectonics occurred shortly after 0.6 Ga. The same analysis does, however, also support periods of mobile tectonics affecting just the periphery of a single supercontinent from the late Archean up to the Neoproterozoic.[4]
References edit
- ^ a b Gerya, T. (2019). "Geodynamics of the early Earth: Quest for the missing paradigm" (PDF). Geology. 47 (10): 1006–1007. doi:10.1130/focus102019.1.
- ^ Moore, William B.; Webb, A. Alexander G. (2013). "Heat-pipe Earth". Nature. 501 (7468): 501–505. Bibcode:2013Natur.501..501M. doi:10.1038/nature12473. ISSN 0028-0836. PMID 24067709.
- ^ Pease, V.; Percival, J.; Smithies, H.; Stevens, G.; van Kranendonk (2008). "When did plate tectonics begin? Evidence from the orogenic record". In Condie, K.C.; Pease, V. (eds.). When Did Plate Tectonics Begin on Planet Earth?. Special Paper. Vol. 440. Geological Society of America. doi:10.1130/2008.2440(10). ISBN 9780813724409.
- ^ Piper, J.D.A. (2018). "Dominant Lid Tectonics behaviour of continental lithosphere in Precambrian times: Palaeomagnetism confirms prolonged quasi-integrity and absence of supercontinent cycles". Geoscience Frontiers. 9: 61–89. doi:10.1016/j.gsf.2017.07.009.
External links edit
- When and how did plate tectonics begin on Earth? Earth Magazine, American Geosciences Institute, May 2017.