Depletion of the upper mantle by convergent tectonics in the Early Earth

Capitanio

Proc. Natl. Acad. Sci. U.S.A.

et al. 2022

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.

Section: Discussionsupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Accretion of the cratonic mantle lithosphere via massive regional relamination

Capitanio

Proc. Natl. Acad. Sci. U.S.A.

et al. 2022

“…Voluminous melting of the upper mantle caused the formation of both cold lithospheric and hot sub-lithospheric, highly depleted, proto-cratonic mantles with lowered density and increased viscosity (e.g. Sizova et al 2015;Capitanio et al 2020;Perchuk et al 2020Perchuk et al , 2021. Note that this scenario is in direct contrast to the scenario proposed by Korenaga (2021), in which the Hadean was characterised by a vigorous plate tectonic regime and recycling of the earlier, thinner crust.…”

Section: Evidence For Interior Processes and Tectonics The Results Of...mentioning

confidence: 99%

The Habitability of Venus

et al. 2023

Venus today is inhospitable at the surface, its average temperature of 750 K being incompatible to the existence of life as we know it. However, the potential for past surface habitability and upper atmosphere (cloud) habitability at the present day is hotly debated, as the ongoing discussion regarding a possible phosphine signature coming from the clouds shows. We review current understanding about the evolution of Venus with special attention to scenarios where the planet may have been capable of hosting microbial life. We compare the possibility of past habitability on Venus to the case of Earth by reviewing the various hypotheses put forth concerning the origin of habitable conditions and the emergence and evolution of plate tectonics on both planets. Life emerged on Earth during the Hadean when the planet was dominated by higher mantle temperatures (by about $200~^{\circ}\text{C}$ 200 ∘ C ), an uncertain tectonic regime that likely included squishy lid/plume-lid and plate tectonics, and proto continents. Despite the lack of well-preserved crust dating from the Hadean and Paleoarchean, we attempt to review current understanding of the environmental conditions during this critical period based on zircon crystals and geochemical signatures from this period, as well as studies of younger, relatively well-preserved rocks from the Paleoarchean. For these early, primitive life forms, the tectonic regime was not critical but it became an important means of nutrient recycling, with possible consequences on the global environment in the long-term, that was essential to the continuation of habitability and the evolution of life. For early Venus, the question of stable surface water is closely related to tectonics. We discuss potential transitions between stagnant lid and (episodic) tectonics with crustal recycling, as well as consequences for volatile cycling between Venus’ interior and atmosphere. In particular, we review insights into Venus’ early climate and examine critical questions about early rotation speed, reflective clouds, and silicate weathering, and summarize implications for Venus’ long-term habitability. Finally, the state of knowledge of the Venusian clouds and the proposed detection of phosphine is covered.

“…This is similar to the model of central Tian Shan (Yu et al., 2017), in which a high‐velocity lithospheric root (or broken‐off lithosphere) was discovered at the 410‐km discontinuity. Numerical simulations show that the delaminated continental root can sink to MTZ (Perchuk et al., 2021). It is believed that the downward movement of the lithospheric segment may have begun in the Late Miocene and that it sank into the MTZ in less than 10 Ma.…”

Section: Discussionmentioning

confidence: 99%

Receiver Function Mapping of the Mantle Transition Zone Beneath the Tian Shan Orogenic Belt

et al. 2022

The Tian Shan orogenic belt is located in central Asia around 2,000 km far from the collisional boundary between India and Eurasia. It is the world's largest and most active intracontinental orogenic and seismic belt (Figure 1) (Burtman, 1975). Due to its active tectonics and rich stratigraphic exposure, the Tian Shan orogenic belt is regarded as an ideal study area for understanding the evolution and processes of an intracontinental orogen. The orogenic belt is over 1,700 km long from west to east and consists of several parallel mountains and intermountain basins. It is bordered to the north by the Junngar Basin and the Kazakh Shield and to the south by the Tarim Basin (Burtman, 1975;Lei, 2011). The NW-SE trending Talas-Fergana fault and the geographic longitude of 80°E divide the Tian Shan into the western, central, and eastern Tian Shan (Lü et al., 2019). Our study area included the eastern Tian Shan as well as the surrounding areas (Figure 1).