Plate tectonics on early Earth? Weighing the paleomagnetic evidence

2008 ◽  
pp. 249-263 ◽  
Author(s):  
David A.D. Evans ◽  
Sergei A. Pisarevsky
Keyword(s):  
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 Venus’ light slab hinders its development of planetary-scale subduction and habitability

2022 ◽  
Author(s):  
Junxing Chen ◽  
Hehe Jiang ◽  
Ming Tang ◽  
Jihua Hao ◽  
Meng Tian ◽  
...  
Keyword(s):  
Plate Tectonics ◽  
Carbon Sink ◽  
Global Scale ◽  
Climate Feedback ◽  
Early Earth ◽  
Crustal Rocks ◽  
Planetary Scale ◽  
Habitable Planet ◽  
Missing Carbon Sink

Abstract Terrestrial planets Venus and Earth have similar sizes, masses, and bulk compositions, but only Earth developed planetary-scale plate tectonics. Plate tectonics generates weatherable fresh rocks and transfers surface carbon back to Earth’s interior, which provides a long-term climate feedback, serving as a thermostat to keep Earth a habitable planet. Yet Venus shares a few common features with early Earth, such as stagnant-lid tectonics and the possible early development of a liquid ocean. Given all these similarities with early Earth, why would Venus fail to develop global-scale plate tectonics? In this study, we explore solutions to this problem by examining Venus’ slab densities under hypothesized subduction-zone conditions. Our petrologic simulations show that eclogite facies may be reached at greater depths on Venus than on Earth, and Venus’ slab densities are consistently lower than Earth’s. We suggest that the lack of sufficient density contrast between the high-pressure metamorphosed slab and mantle rocks may have impeded self-sustaining subduction. Although plume-induced crustal downwelling exists on Venus, the dipping of Venus’ crustal rocks to mantle depth fails to transition into subduction tectonics. As a consequence, the supply of fresh silicate rocks to the surface has been limited. This missing carbon sink eventually diverged the evolution of Venus’ surface environment from that of Earth.

The long-term climate evolution and planetary habitability – Onset timing of the plate tectonics in early Earth

2020 ◽  
Author(s):  
Takashi Nakagawa
Keyword(s):  
Plate Tectonics ◽  
Planetary System ◽  
Early Earth ◽  
Volcanic Degassing ◽  
Deep Mantle ◽  
Onset Timing ◽  
Climate Evolution ◽  
Plate Subduction ◽  
Volatile Cycling

<p>The plate tectonics is an essential geophysical/geological process on the deep mantle water and carbon cycling, which may also control the long-term climate evolution because the volcanic degassing induced by the plate subduction seems to change the atmospheric condition. However, as suggested by the geological evidence on the onset timing of the plate tectonics in early Earth, which is modeled by the transition from the stagnant lid tectonics to the plate subduction, this timing may have great uncertainty. Here, two questions are addressed: 1. How can the deep mantle volatile cycling would be affected by the onset timing of the plate tectonics in the planetary system evolution?; 2. As a result of the successful scenario of the deep mantle volatile cycling explained for the observational constraints of the subduction flux of the water and carbon, how can the climate evolution be responded as a function of the history of the deep mantle volatile cycling such as the subduction flux? To address these questions, a simplified model of whole planetary system evolution based on the thermal history computation of the silicate mantle coupled with the energy balance climate evolution and deep mantle volatile is used with controlling both heat transfer and volatile cycling associated with the transition between stagnant lid and plate tectonics.</p><p> </p><p>The main result indicates that plate tectonics may be essential for the mild and stable climate that allows having liquid water over billions of years of the time scale. This is because a sufficient amount of volcanic degassing can be found for the vigorous plate tectonics rather than the stagnant lid state to get the long-term mild climate. For the stagnant lid state, the snowball limit cycle can be found. Thus, the vigorous plate motion may contribute to stabilizing the warm climate.</p><p> </p><p>To find out the constraint on the present-day surface environment, the transition timing from the stagnant lid to the vigorous plate subduction for explaining the present-day amount of volatiles and their subduction flux would range from 1 to 3 Ga. And, around 5 to 10 ocean masses of the water in the total planetary system is required so that the deep mantle melting should be continuously found to supply the volatile component to the atmosphere associated with the plate subduction, which is worked for the reducing the melting temperature of the silicate mantle. However, the subduction flux for finding the mild climate is one to two orders of magnitude larger than the expected from the geological constraint – 10<sup>12</sup> to 10<sup>13 </sup>kg/yr as well as some difficulty for explaining the global sea-level change. In the presentation, some improvements on including the big storage capacity of the volatiles in the mantle transition zone will be provided for giving a better understanding of both the deep mantle volatile cycle and climate evolution in the plate-mantle evolution system.</p>

scholarly journals A CO2 greenhouse efficiently warmed the early Earth and decreased seawater 18O/16O before the onset of plate tectonics

2021 ◽  
Vol 118 (23) ◽  
pp. e2023617118
Author(s):  
Daniel Herwartz ◽  
Andreas Pack ◽  
Thorsten J. Nagel
Keyword(s):  
Plate Tectonics ◽  
Isotope Composition ◽  
Oxygen Isotopic Composition ◽  
Early Earth ◽  
Time Interval ◽  
Hot Climate ◽  
Oxygen Isotopic ◽  
Low Degrees ◽  
Chemical Sediments

The low 18O/16O stable isotope ratios (δ18O) of ancient chemical sediments imply ∼70 °C Archean oceans if the oxygen isotopic composition of seawater (sw) was similar to modern values. Models suggesting lower δ18Osw of Archean seawater due to intense continental weathering and/or low degrees of hydrothermal alteration are inconsistent with the triple oxygen isotope composition (Δ’17O) of Precambrian cherts. We show that high CO2 sequestration fluxes into the oceanic crust, associated with extensive silicification, lowered the δ18Osw of seawater on the early Earth without affecting the Δ’17O. Hence, the controversial long-term trend of increasing δ18O in chemical sediments over Earth’s history partly reflects increasing δ18Osw due to decreasing atmospheric pCO2. We suggest that δ18Osw increased from about −5‰ at 3.2 Ga to a new steady-state value close to −2‰ at 2.6 Ga, coinciding with a profound drop in pCO2 that has been suggested for this time interval. Using the moderately low δ18Osw values, a warm but not hot climate can be inferred from the δ18O of the most pristine chemical sediments. Our results are most consistent with a model in which the “faint young Sun” was efficiently counterbalanced by a high-pCO2 greenhouse atmosphere before 3 Ga.

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.

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