Archean subduction
Archean subduction is a contentious topic involving the possible existence and nature of subduction in the Archean, a geologic eon extending from 4.0-2.5 billion years ago. Until recently there was little evidence unequivocally supporting one side over the other, and in the past many scientists either believed in shallow subduction or its complete non-existence. However, the past two decades have witnessed the potential beginning of a change in geologic understanding as new evidence is increasingly indicative of episodic, non-shallow subduction.[1]
The importance of Archean subduction
Subduction is the density-driven process by which one tectonic plate moves under another and sinks into the
The case against Archean subduction
Those who favour non-existent subduction in the Archean point to the well-established model that the Archean Earth was significantly hotter than it is today, which would have affected lithospheric
The case for Archean subduction
Those who favour Archean subduction claim that recent modelling has elucidated the following fundamental features of the Archean, which they argue can be used to describe why subduction was occurring:
1) Mantle temperatures were indeed 200 K hotter than they are today.[9]
2) The oceanic crust was approximately 21 km thick, compared to 7 km thick today.[9]
3) The depth to which the mantle was partially melted was 114 km, compared to 54 km today.[9]
4) Heat flow into the base of the tectonic plates was 1.3-2.0 times higher than it is today.[9]
Mathematical reasoning based on these constraints led to the conclusion that cooling was sufficient to provide a driving force for subduction.
While the existence of Archean subduction implies that continental crust likely formed via subduction to an extent, it does not require that subduction was the only way to form continental crust. Thus the continued debate over the origin of continental crust cannot be fully resolved by subduction arguments alone.
Conclusion and future directions
Though the subject of Archean subduction has long been controversial, the emergence of innovative modelling and geologic evidence has begun to sway some of the scientific community toward favouring the existence of non-shallow, episodic subduction. Moving forward, the rheology of early-Earth materials should be emphasized in future research as it is not well understood, and therefore subduction dynamics are poorly constrained.[1] Moreover, the paucity of Archean data requires an even better understanding of the links between the Earth's interior and its surface processes if we plan on gaining additional insight into Archean subduction.[1]
References
- ^ .
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- ^ Bibcode:2007mady.book..253J.
- ^ Davidson, JP; Arculus, RJ (2006). "The significance of Phanerozoic arc magmatism in generating continental crust". Evolution and Differentiation of Continental Crust: 135–172.
- .
- .
- ^ Leitch, AM (2004). "Archean Plate Tectonics". American Geophysical Union, Spring Meeting.
- ^ S2CID 129466505.
- ^ .
- .
- ^ Condie, KC (2011). "Did early Archean continental crust form without plate tectonics?". Geological Society of America Fall Meeting. 43 (5).