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Abstract At subduction zones, significant volumes of sediments and other crustal material are carried on top of the downgoing plate past the trench and into the mantle. This represents the dominant process by which material from the Earth's surface is recycled to the interior. However, the fate of these recycled materials is uncertain. Subducted material may be carried with the slab into the deep mantle, or it may form diapirs that ascend into the hotter portions of the mantle wedge, where they can melt and/or be relaminated to the base of the arc crust. While this material can be a mixture (or “mélange”) of sediments, oceanic crust and mantle rocks, here we focus on the dynamics of the uppermost layer of sediments on the downgoing slab. We modified a thermodynamic model to accurately predict the equilibrium mineral assemblage, melting behavior, and density of a range of subducted sediment compositions at pressure and temperature conditions relevant to subduction zones. Using this thermodynamic model, we constructed a coupled dynamic model of sediment diapirs and identified the primary parameters that control diapir behavior: sediment thickness and composition, and the thermal state of the subduction zone. Relamination of ascending diapirs is favored by greater sediment thicknesses, more felsic compositions, and warmer thermal conditions. By contrast, diapirism is suppressed in colder arcs, or where subducted sediment layers are thin or more mafic. Applying this model to modern subduction zones suggests that multiple processes are active today, with relamination occurring in a significant subset of modern arcs.
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Generation of Archean TTGs via sluggish subduction
Abstract The trondhjemite-tonalite-granodiorite (TTG) suite of rocks prominent in Earth’s Archean continents is thought to form by melting of hydrated basalt, but the specific tectonic settings of formation are unclear. Models for TTG genesis range from melting of downgoing mafic crust during subduction into a hotter mantle to melting at the base of a thick crustal plateau; while neither uniquely defines a global tectonic regime, the former is consistent with mobile lid tectonics and the latter a stagnant lid. One major problem for a subduction model is slabs sinking too quickly and steeply in a hotter mantle to melt downgoing crust. I show, however, that grain size reduction in the lithosphere leads to relatively strong plate boundaries on the early Earth, which slow slab sinking. During this “sluggish subduction,” sinking plates can heat up enough to melt when the mantle temperature is ≳1600 °C. Crustal melting via sluggish subduction can thus explain TTG formation during the Archean due to elevated mantle temperatures and the paucity of TTG production since due to mantle cooling.
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- Award ID(s):
- 2046598
- PAR ID:
- 10595743
- Publisher / Repository:
- Geological Society of America
- Date Published:
- Journal Name:
- Geology
- Volume:
- 52
- Issue:
- 9
- ISSN:
- 0091-7613
- Page Range / eLocation ID:
- 656 to 660
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1130/G52196.1
