Two types of Archean continental crust: Plume and plate tectonics on early Earth

2010 ◽  
Vol 310 (10) ◽  
pp. 1187-1209 ◽  
Author(s):  
M. J. Van Kranendonk
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Early Earth

scholarly journals Mafic Archean continental crust prohibited exhumation of orogenic UHP eclogite

2021 ◽  
Author(s):  
Richard Palin ◽  
James Moore ◽  
Zeming Zhang ◽  
Guangyu Huang
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Ultrahigh Pressure ◽  
Global Ocean ◽  
Secular Change ◽  
Early Earth ◽  
Low Density ◽  
Geological Record ◽  
Point Of No Return ◽  
Negatively Buoyant

Abstract The absence of ultrahigh pressure (UHP) orogenic eclogite in the geological record older than c. 0.6 Ga is problematic for evidence of subduction having begun on Earth during the Archean (4.0–2.5 Ga). Many eclogites in Phanerozoic and Proterozoic terranes occur as mafic boudins encased within low-density felsic crust, which provides positive buoyancy during subduction; however, recent geochemical proxy analysis shows that Archean continental crust was more mafic than previously thought. Here, we show via petrological modelling that secular change in the composition of upper continental crust (UCC) would make Archean continental terranes negatively buoyant in the mantle before reaching UHP conditions. Subducted or delaminated Archean continental crust passes a point of no return during metamorphism in the mantle prior to the stabilization of coesite, while Proterozoic and Phanerozoic terranes remain positively buoyant at these depths. UHP orogenic eclogite may thus readily have formed on the Archean Earth, but could not have been exhumed, weakening arguments for a Neoproterozoic onset of subduction and plate tectonics. Further, isostatic balance calculations for more mafic Archean continents indicate that the early Earth was covered by a global ocean over 1 kilometre deep.

scholarly journals Hydrated Peridotite – Basaltic Melt Interaction Part I: Planetary Felsic Crust Formation at Shallow Depth

2021 ◽  
Vol 9 ◽  
Author(s):  
Anastassia Y. Borisova ◽  
Nail R. Zagrtdenov ◽  
Michael J. Toplis ◽  
Wendy A. Bohrson ◽  
Anne Nédélec ◽  
...  
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Mafic Magma ◽  
Aqueous Fluid ◽  
Early Earth ◽  
Magma Ocean ◽  
Crust Formation ◽  
Basaltic Melt ◽  
Low Pressures ◽  
Direct Melting

Current theories suggest that the first continental crust on Earth, and possibly on other terrestrial planets, may have been produced early in their history by direct melting of hydrated peridotite. However, the conditions, mechanisms and necessary ingredients for this crustal formation remain elusive. To fill this gap, we conducted time-series experiments to investigate the reaction of serpentinite with variable proportions (from 0 to 87 wt%) of basaltic melt at temperatures of 1,250–1,300°C and pressures of 0.2–1.0 GPa (corresponding to lithostatic depths of ∼5–30 km). The experiments at 0.2 GPa reveal the formation of forsterite-rich olivine (Fo90–94) and chromite coexisting with silica-rich liquids (57–71 wt% SiO2). These melts share geochemical similarities with tonalite-trondhjemite-granodiorite rocks (TTG) identified in modern terrestrial oceanic mantle settings. By contrast, liquids formed at pressures of 1.0 GPa are poorer in silica (∼50 wt% SiO2). Our results suggest a new mechanism for the formation of the embryonic continental crust via aqueous fluid-assisted partial melting of peridotite at relatively low pressures (∼0.2 GPa). We hypothesize that such a mechanism of felsic crust formation may have been widespread on the early Earth and, possibly on Mars as well, before the onset of modern plate tectonics and just after solidification of the first ultramafic-mafic magma ocean and alteration of this primitive protocrust by seawater at depths of less than 10 km.

scholarly journals Crustal evolution and mantle dynamics through Earth history

2018 ◽  
Vol 376 (2132) ◽  
pp. 20170408 ◽  
Author(s):  
Jun Korenaga
Keyword(s):  
Continental Crust ◽  
Mantle Convection ◽  
Plate Tectonics ◽  
Indirect Evidence ◽  
Quantitative Model ◽  
Early Earth ◽  
Mantle Dynamics ◽  
Earth History ◽  
Geological Processes ◽  
Earth Dynamics

Resolving the modes of mantle convection through Earth history, i.e. when plate tectonics started and what kind of mantle dynamics reigned before, is essential to the understanding of the evolution of the whole Earth system, because plate tectonics influences almost all aspects of modern geological processes. This is a challenging problem because plate tectonics continuously rejuvenates Earth's surface on a time scale of about 100 Myr, destroying evidence for its past operation. It thus becomes essential to exploit indirect evidence preserved in the buoyant continental crust, part of which has survived over billions of years. This contribution starts with an in-depth review of existing models for continental growth. Growth models proposed so far can be categorized into three types: crust-based, mantle-based and other less direct inferences, and the first two types are particularly important as their difference reflects the extent of crustal recycling, which can be related to subduction. Then, a theoretical basis for a change in the mode of mantle convection in the Precambrian is reviewed, along with a critical appraisal of some popular notions for early Earth dynamics. By combining available geological and geochemical observations with geodynamical considerations, a tentative hypothesis is presented for the evolution of mantle dynamics and its relation to surface environment; the early onset of plate tectonics and gradual mantle hydration are responsible not only for the formation of continental crust but also for its preservation as well as its emergence above sea level. Our current understanding of various material properties and elementary processes is still too premature to build a testable, quantitative model for this hypothesis, but such modelling efforts could potentially transform the nature of the data-starved early Earth research by quantifying the extent of preservation bias.This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics’.

scholarly journals Constraining crustal silica on ancient Earth

2020 ◽  
Vol 117 (35) ◽  
pp. 21101-21107 ◽  
Author(s):  
C. Brenhin Keller ◽  
T. Mark Harrison
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Incompatible Element ◽  
Silica Content ◽  
Efficient Mechanism ◽  
Element Abundances ◽  
Terrigenous Sediments ◽  
Earth History ◽  
Crustal Composition ◽  
Earth’S Mantle

Accurately quantifying the composition of continental crust on Hadean and Archean Earth is critical to our understanding of the physiography, tectonics, and climate of our planet at the dawn of life. One longstanding paradigm involves the growth of a relatively mafic planetary crust over the first 1 to 2 billion years of Earth history, implying a lack of modern plate tectonics and a paucity of subaerial crust, and consequently lacking an efficient mechanism to regulate climate. Others have proposed a more uniformitarian view in which Archean and Hadean continents were only slightly more mafic than at present. Apart from complications in assessing early crustal composition introduced by crustal preservation and sampling biases, effects such as the secular cooling of Earth’s mantle and the biologically driven oxidation of Earth’s atmosphere have not been fully investigated. We find that the former complicates efforts to infer crustal silica from compatible or incompatible element abundances, while the latter undermines estimates of crustal silica content inferred from terrigenous sediments. Accounting for these complications, we find that the data are most parsimoniously explained by a model with nearly constant crustal silica since at least the early Archean.

scholarly journals Geoneutrinos

2012 ◽  
Vol 2012 ◽  
pp. 1-34 ◽  
Author(s):  
Ondřej Šrámek ◽  
William F. McDonough ◽  
John G. Learned
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Detection Methods ◽  
Heat Sources ◽  
Radiogenic Heat ◽  
Interdisciplinary Field ◽  
The Earth ◽  
Directional Detection ◽  
Under Construction ◽  
Current Detection

Neutrino geophysics is an emerging interdisciplinary field with the potential to map the abundances and distribution of radiogenic heat sources in the continental crust and deep Earth. To date, data from two different experiments quantify the amount of Th and U in the Earth and begin to put constraints on radiogenic power in the Earth available for driving mantle convection and plate tectonics. New improved detectors are under construction or in planning stages. Critical testing of compositional models of the Earth requires integrating geoneutrino and geological observations. Such tests will lead to significant constraints on the absolute and relative abundances of U and Th in the continents. High radioactivity in continental crust puts limits on land-based observatories' capacity to resolve mantle models with current detection methods. Multiple-site measurement in oceanic areas away from continental crust and nuclear reactors offers the best potential to extract mantle information. Geophysics would benefit from directional detection and the detectability of electron antineutrinos from potassium decay.

scholarly journals No evidence for high-pressure melting of Earth’s crust in the Archean

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Robert H. Smithies ◽  
Yongjun Lu ◽  
Tim E. Johnson ◽  
Christopher L. Kirkland ◽  
Kevin F. Cassidy ◽  
...  
Keyword(s):  
High Pressure ◽  
Continental Crust ◽  
Small Proportion ◽  
Lithospheric Mantle ◽  
Plate Tectonics ◽  
Crustal Evolution ◽  
Average Thickness ◽  
Dominant Group ◽  
Chemical Signatures ◽  
Pressure Melting

AbstractMuch of the present-day volume of Earth’s continental crust had formed by the end of the Archean Eon, 2.5 billion years ago, through the conversion of basaltic (mafic) crust into sodic granite of tonalite, trondhjemite and granodiorite (TTG) composition. Distinctive chemical signatures in a small proportion of these rocks, the so-called high-pressure TTG, are interpreted to indicate partial melting of hydrated crust at pressures above 1.5 GPa (>50 km depth), pressures typically not reached in post-Archean continental crust. These interpretations significantly influence views on early crustal evolution and the onset of plate tectonics. Here we show that high-pressure TTG did not form through melting of crust, but through fractionation of melts derived from metasomatically enriched lithospheric mantle. Although the remaining, and dominant, group of Archean TTG did form through melting of hydrated mafic crust, there is no evidence that this occurred at depths significantly greater than the ~40 km average thickness of modern continental crust.

Changing exhumation potential of (U)HP eclogite through geological time

2020 ◽  
Author(s):  
Richard Palin
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Global Network ◽  
Ultrahigh Pressure ◽  
Compositional Variation ◽  
Uhp Metamorphism ◽  
Geological Time ◽  
Geological Record ◽  
Mafic Intrusions ◽  
Archean Crust

<p>Ultrahigh-pressure (UHP) metamorphism is defined by achieving P–T conditions sufficient to transform quartz to coesite (~26–28 kbar at ~500–900 °C), which occurs at ~90-100 km depth within the Earth under lithostatic conditions. Thus, the occurrence of UHP metamorphism is often taken as being a diagnostic indicator of subduction having operated in the geological record, and hence plate tectonics. Yet, the oldest such coesite-bearing rocks belong to the Pan-African belt in northern Mali, and formed at 620 Ma, although there exist multiple lines of evidence to show that a global network of subduction had been operative on Earth for billions of years beforehand. Why, then, are these key geodynamic indicators missing from the majority of the rock record? Here, I show how secular cooling of the Earth's mantle since the Mesoarchean (c. 3.2 Ga) has affected the exhumation potential of UHP (and HP) eclogite through time due to time-dependent compositional variation of both oceanic and continental crust. Petrological modeling of density changes during metamorphism of Archean, Proterozoic, and Phanerozoic composite continental terranes shows that more mafic Archean crust reaches a point-of-no-return during transport into the mantle at shallower depths than less MgO-rich modern-day crust, regardless of whether this occurs via subduction of stagnant lid-like vertical 'drip' tectonics. Thus, while Alpine- and Himalayan-type (U)HP orogenic eclogites represented by metamorphosed mafic intrusions into continental crust may readily have formed during the Precambrian, they would have lacked the buoyancy required for exhumation and preservation in the geological record.</p>

Implementation of partial melting with a water- and composition-dependent solidus temperature adapted to TTG formation

2020 ◽  
Author(s):  
Antoine Rozel ◽  
Stephen Mojzsis ◽  
Martin Guitreau ◽  
Antonio Manjón Cabeza Córdoba ◽  
Maxim Ballmer ◽  
...  
Keyword(s):  
Partial Melting ◽  
Water Content ◽  
Continental Crust ◽  
Liquidus Temperature ◽  
Solidus Temperature ◽  
Water Concentration ◽  
Early Earth ◽  
Numerical Treatment ◽  
End Members ◽  
Basaltic Crust

<p>More and more convection codes now consider the apparition of melt when the temperature of the mantle exceeds a considered solidus temperature. How melt is treated when it appears varies a lot from one code to another. The convection code StagYY has been using an implementation in which molten eclogite is produced out of melting of mixed mantle. The melt is then teleported above ("erupted") or below ("intruded") the basaltic crust. In a recent study by Jain et al. 2019, we have shown that it is possible to also self-consistently generate continental crust (so-called TTG rocks) if the basaltic crust is entrained in the mantle and remolten. In nature, this only happens if a lot of water is present in the recycled basalt so a numerical treatment of water is necessary.</p><p>In this poster, we discuss the details of a new implementation of melting in which each cell of the convection domain is divided in several groups of different composition. Each group has a different solidus and liquidus temperature according to the composition and the water content. The solidus temperature is computed using an interpolation between composition and water concentration end members instead of using an extrapolation from the solidus temperature, as it is usually done. This ensures that TTGs form at a realistic melt fraction and provides a different view on how the continental crust of the early Earth might have formed.</p>

scholarly journals Plate tectonic regulation of global marine animal diversity

2017 ◽  
Vol 114 (22) ◽  
pp. 5653-5658 ◽  
Author(s):  
Andrew Zaffos ◽  
Seth Finnegan ◽  
Shanan E. Peters
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Marine Invertebrate ◽  
The State ◽  
Causal Mechanism ◽  
Sampling Effort ◽  
Marine Animal ◽  
Positive Correlation ◽  
Animal Diversity ◽  
Global Biodiversity

Valentine and Moores [Valentine JW, Moores EM (1970) Nature 228:657–659] hypothesized that plate tectonics regulates global biodiversity by changing the geographic arrangement of continental crust, but the data required to fully test the hypothesis were not available. Here, we use a global database of marine animal fossil occurrences and a paleogeographic reconstruction model to test the hypothesis that temporal patterns of continental fragmentation have impacted global Phanerozoic biodiversity. We find a positive correlation between global marine invertebrate genus richness and an independently derived quantitative index describing the fragmentation of continental crust during supercontinental coalescence–breakup cycles. The observed positive correlation between global biodiversity and continental fragmentation is not readily attributable to commonly cited vagaries of the fossil record, including changing quantities of marine rock or time-variable sampling effort. Because many different environmental and biotic factors may covary with changes in the geographic arrangement of continental crust, it is difficult to identify a specific causal mechanism. However, cross-correlation indicates that the state of continental fragmentation at a given time is positively correlated with the state of global biodiversity for tens of millions of years afterward. There is also evidence to suggest that continental fragmentation promotes increasing marine richness, but that coalescence alone has only a small negative or stabilizing effect. Together, these results suggest that continental fragmentation, particularly during the Mesozoic breakup of the supercontinent Pangaea, has exerted a first-order control on the long-term trajectory of Phanerozoic marine animal diversity.

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