Accretion of the cratonic mantle lithosphere via massive regional relamination

Abstract

Continental, orogenic, and oceanic lithospheric mantle embeds sizeable parcels of exotic cratonic lithospheric mantle (CLM) derived from distant, unrelated sources. This hints that CLM recycling into the mantle and its eventual upwelling and relamination at the base of younger plates contribute to the complex structure of the growing lithosphere. Here, we use numerical modeling to investigate the fate and survival of recycled CLM in the ambient mantle and test the viability of CLM relamination under Hadean to present-day mantle temperature conditions and its role in early lithosphere evolution. We show that the foundered CLM is partially mixed and homogenized in the ambient mantle; then, as thermal negative buoyancy vanishes, its long-lasting compositional buoyancy drives upwelling, relaminating unrelated growing lithospheric plates and contributing to differentiation under cratonic, orogenic, and oceanic regions. Parts of the CLM remain in the mantle as diffused depleted heterogeneities at multiple scales, which can survive for billions of years. Relamination is maximized for high depletion degrees and mantle temperatures compatible with the early Earth, leading to the upwelling and underplating of large volumes of foundered CLM, a process we name massive regional relamination (MRR). MRR explains the complex source, age, and depletion heterogeneities found in ancient cratonic lithospheric mantle, suggesting this may have been a key component of the construction of continents in the early Earth.

Supplemental Material: Modification of Archean cratons in southern Africa with foundered segments dropped into the shallow lower mantle

“…3A), the sinking rate is estimated to be ∼1.2 cm/yr. This is comparable to the minimum rate for currently sinking slabs (Peng and Liu, 2022) and numerical models of cratonic delamination (Wang et al, 2022b).…”

Secular Evolution of Continents and the Earth System

“…Furthermore, the numerical models of Perchuk et al. (2020) propose that this layering is a complex multistage process that occurs through the juxtaposition of depleted lithospheric mantle by spatially and temporally discrete processes (cf., Z. Wang et al., 2022). Importantly, the formation of these lithospheric keels likely marks the transformation of a lithosphere region undergoing intense plutonism and non‐rigid, distributed deformation to a rigid and buoyant lithosphere (cratonic core) that is a prerequisite for plate tectonics.…”

Lithospheric thickness records tectonic evolution by controlling metamorphic conditions

“…The cooler asthenosphere would widen the disparities in density between the overlying continental lithosphere and subducting oceanic lithosphere, finally prompting the global modern Wilson cycle of continental rifting, plate subduction, and collision events ( 15 , 67 ). This could be an early record of lithospheric thinning, where the continental roots sink to the asthenosphere, and, eventually, when the thermal buoyancy exceeds the chemical negative buoyancy, returns to underplate and thicken the lithosphere again ( 30 ), or it could relate to continental margin collisions that thicken lithosphere ( 47 ). Therefore, the initiation of modern Wilson cycle plate tectonic appears before the Paleoarchean, and it becomes the dominant tectonic regime after ~2.8 Ga.…”

“…Therefore, the mean thickness of global lithosphere is not carved in stone and does not necessarily remain thick once thickened by tectonic or magmatic processes. This concept is supported by recent numerical models and isotopic data showing that continents can be recycled to the deep mantle and then return to relaminate the bases of other lithospheric plate in massive regional relamination events, complicating ideas of slow lithospheric and crustal growth through time (30). Therefore, as the interaction product of multilayers of Earth, the lithosphere continues to emerge, rework, and disappear, and its thickness should markedly change and record the evolution of tectonic regimes during Earth's history.…”