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Abstract The Oligocene to Present Wrangell Volcanic Belt (WVB) extends for ~500 km across south‐central Alaska (USA) into Canada at a volcanic arc‐transform junction. Previously, geochemistry documented mantle wedge and slab‐edge melting in <12 MaWVBvolcanic rocks; new geochemistry shows that the same processes characterized ~18–30 MaWVBmagmatism in Alaska. New40Ar/39Ar ages demonstrate thatWVBmagmatism in Alaska initiated at ~30 Ma due to flat‐slab subduction of the Yakutat microplate and that the dextral Totschunda fault was active at this time. Our results, together with prior studies, show that AlaskanWVBmagmatism occurred chiefly due to subduction and should be considered a volcanic arc (e.g. the Wrangell Arc). TheWVBprovides a long‐term geological record of subduction, strike‐slip and magmatism. Slab‐edge upwelling, flat‐slab defocused fluid‐flux and faults acting as magma conduits are likely responsible for the exceptionally large volcanoes and high eruption rates of the Wrangell Arc.
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Timescale of Short‐Term Subduction Episodicity in Convection Models With Grain Damage: Applications to Archean Tectonics
Abstract 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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- Award ID(s):
- 1723057
- PAR ID:
- 10447739
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 125
- Issue:
- 12
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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