TY - JOUR
T1 - Timescale of Short-Term Subduction Episodicity in Convection Models With Grain Damage
T2 - Applications to Archean Tectonics
AU - Foley, Bradford J.
N1 - Funding Information:
This work was supported by NSF award number EAR‐1723057. I thank Andy Smye, Jesse Reimink, and Josh Garber for discussions on Archean igneous and metamorphic petrology, and for their comments on an earlier version of this manuscript. Reviews by Ashley Bellas and Jeroen van Hunen helped to significantly improve the clarity of the manuscript. Figures in this study use the perceptually uniform color maps “lajolla“ and “roma” to prevent visual distortion of the data (Crameri et al., 2018a , 2018b ).
Publisher Copyright:
© 2020. American Geophysical Union. All Rights Reserved.
PY - 2020/12
Y1 - 2020/12
N2 - The style of subduction that prevailed on the early Earth, or even whether subduction was prevalent at all, is an important question in the evolution of Earth's crust, mantle, and surface environment. Here, two-dimensional numerical convection models, that include grain size evolution to generate weak plate boundaries, reveal a clear transition in subduction behavior with increasing internal heating rate. Sustained subduction with a coherent slab gives way to a style where slabs periodically detach and sink rapidly into the deep mantle, with increasing internal heating rate. In this latter, “drip-like” subduction regime, repeating cycles of slab growth by subduction, followed by necking and detachment of the lower portion of the slab, are seen. These cycles are termed “slab detachment cycles,” and similar behavior has been seen in regional scale subduction models of the early Earth. Fourier analysis is used to constrain the timescale of slab detachment cycles, and a simple scaling law for this timescale is developed. Applying the scaling law to the early Earth indicates that slab detachment cycles can occur on timescales of <10 Myr, even as low as <5 Myr if the lithosphere is thick and mantle temperature is >1900 K. These cycles may thus be capable of explaining repeating sequences of rocks with “arc” and “non-arc” signatures seen in some Archean cratons. The drip-like subduction regime could also have significant implications for the generation of the tonalite-trondhjemite-granodiorite (TTG) suite of rocks and exhumation of high pressure metamorphic rocks, two important features of the early Earth geologic record.
AB - The style of subduction that prevailed on the early Earth, or even whether subduction was prevalent at all, is an important question in the evolution of Earth's crust, mantle, and surface environment. Here, two-dimensional numerical convection models, that include grain size evolution to generate weak plate boundaries, reveal a clear transition in subduction behavior with increasing internal heating rate. Sustained subduction with a coherent slab gives way to a style where slabs periodically detach and sink rapidly into the deep mantle, with increasing internal heating rate. In this latter, “drip-like” subduction regime, repeating cycles of slab growth by subduction, followed by necking and detachment of the lower portion of the slab, are seen. These cycles are termed “slab detachment cycles,” and similar behavior has been seen in regional scale subduction models of the early Earth. Fourier analysis is used to constrain the timescale of slab detachment cycles, and a simple scaling law for this timescale is developed. Applying the scaling law to the early Earth indicates that slab detachment cycles can occur on timescales of <10 Myr, even as low as <5 Myr if the lithosphere is thick and mantle temperature is >1900 K. These cycles may thus be capable of explaining repeating sequences of rocks with “arc” and “non-arc” signatures seen in some Archean cratons. The drip-like subduction regime could also have significant implications for the generation of the tonalite-trondhjemite-granodiorite (TTG) suite of rocks and exhumation of high pressure metamorphic rocks, two important features of the early Earth geologic record.
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U2 - 10.1029/2020JB020478
DO - 10.1029/2020JB020478
M3 - Article
AN - SCOPUS:85098191242
VL - 125
JO - Journal of Geophysical Research
JF - Journal of Geophysical Research
SN - 0148-0227
IS - 12
M1 - e2020JB020478
ER -