Eoarchean formation of the Isua supracrustal belt

2020 ◽  
Author(s):  
A Alexander G Webb ◽  
Thomas Müller ◽  
Jiawei Zuo ◽  
Peter Haproff ◽  
Anthony Ramírez-Salazar
Keyword(s):  
Plate Tectonics ◽  
Multiple Scales ◽  
Early Earth ◽  
Plate Tectonic ◽  
Mantle Dynamics ◽  
Change Models ◽  
Fine Grained ◽  
Tectonic Events ◽  
Supracrustal Belt ◽  
Major Shift

<p>A major shift in Earth’s crustal generation processes at ~3.2 to 2.5 Ga has been inferred from mineralogical, geological, and geochemical records, particularly those recorded by fine-grained sediments and zircon crystals. The most common hypothesis to explain this shift is the onset of plate tectonic recycling following some form of hot stagnant lid geodynamics. However, all prior detailed geologic studies of our best-preserved Eoarchean terrane, the ~3.85 - 3.60 Ga Isua supracrustal belt of SW Greenland, interpret this site to record terrane collision within the context of plate tectonics. This represents a significant counterweight to the assumption underpinning the ~3 Ga tectonic-mode-change models, i.e., the idea that early Earth’s record is broadly representative. The Isua belt is divided into ~3.8 and ~3.7 Ga halves, and these have been interpreted as plate fragments which collided by ~3.6 Ga. Here, we examine the evidence used to support plate tectonic interpretations, focusing on 1) reanalysis of prior geochronological results and associated cross-cutting relationships which have previously been interpreted to record as many as eight tectonic events, and 2) new field observations leading to reinterpretation of basic structural relationships. Simpler interpretations of the geochronological and deformation data are viable: the belt may have experienced nearly homogeneous metamorphic conditions and strain during a single deformation event prior to intrusion of ~3.5 Ga mafic dikes. Curtain and sheath folds occur at multiple scales throughout the belt, with the entire belt potentially representing Earth’s largest a-type fold. We propose a new model: two cycles of volcanic burial and resultant melting and TTG intrusion produced first the ~3.8 Ga rocks and then the ~3.7 Ga rocks above, after which the whole belt was deformed and thinned in a shear zone, producing the multi-scale a-type folding patterns. The Eoarchean assembly of the Isua supracrustal belt is therefore most simply explained by vertical-stacking volcanic and instrusive processes followed by a single shearing event. In combination with well-preserved Paleoarchean terranes, these rocks record the waning downward advection of lithosphere inherent in volcanism-dominated heat-pipe tectonic models for early Earth. These interpretations are consistent with recent findings that early crust-mantle dynamics are remarkably similar across the solar system’s terrestrial bodies.</p>

scholarly journals A non–plate tectonic model for the Eoarchean Isua supracrustal belt

Lithosphere ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 166-179 ◽  
Author(s):  
A. Alexander G. Webb ◽  
Thomas Müller ◽  
Jiawei Zuo ◽  
Peter J. Haproff ◽  
Anthony Ramírez-Salazar
Keyword(s):  
Multiple Scales ◽  
Field Observations ◽  
Plate Tectonic ◽  
Mantle Dynamics ◽  
Tectonic Model ◽  
Tectonic Events ◽  
Tectonic Processes ◽  
Intrusive Rocks ◽  
Supracrustal Belt ◽  
Deformation Event

Abstract The ca. 3.8–3.6-b.y.-old Isua supracrustal belt of SW Greenland is Earth’s only site older than 3.2 Ga that is exclusively interpreted via plate-tectonic theory. The belt is divided into ca. 3.8 Ga and ca. 3.7 Ga halves, and these are interpreted as plate fragments that collided by ca. 3.6 Ga. However, such models are based on idiosyncratic interpretations of field observations and U-Pb zircon data, resulting in intricate, conflicting stratigraphic and structural interpretations. We reanalyzed published geochronological work and associated field constraints previously interpreted to show multiple plate-tectonic events and conducted field-based exploration of metamorphic and structural gradients previously interpreted to show heterogeneities recording plate-tectonic processes. Simpler interpretations are viable, i.e., the belt may have experienced nearly homogeneous metamorphic conditions and strain during a single deformation event prior to intrusion of ca. 3.5 Ga mafic dikes. Curtain and sheath folds occur at multiple scales throughout the belt, with the entire belt potentially representing Earth’s largest a-type fold. Integrating these findings, we present a new model in which two cycles of volcanic burial and resultant melting and tonalite-trondhjemite-granodiorite (TTG) intrusion produced first the ca. 3.8 Ga rocks and then the overlying ca. 3.7 Ga rocks, after which the whole belt was deformed and thinned in a shear zone, producing the multiscale a-type folding patterns. The Eoarchean assembly of the Isua supracrustal belt is therefore most simply explained by vertical stacking of volcanic and intrusive rocks followed by a single shearing event. In combination with well-preserved Paleoarchean terranes, these rocks record the waning downward advection of lithosphere inherent in volcanism-dominated heat-pipe tectonic models for early Earth. These interpretations are consistent with recent findings that early crust-mantle dynamics are remarkably similar across the solar system’s terrestrial bodies.

scholarly journals The inception of plate tectonics: a record of failure

2018 ◽  
Vol 376 (2132) ◽  
pp. 20170414 ◽  
Author(s):  
Craig O'Neill ◽  
Simon Turner ◽  
Tracy Rushmer
Keyword(s):  
Subduction Zones ◽  
Plate Tectonics ◽  
Initial Conditions ◽  
Numerical Models ◽  
Early History ◽  
Early Earth ◽  
Strong Nonlinearity ◽  
Plate Tectonic ◽  
Geological Record ◽  
History Of

The development of plate tectonics from a pre-plate tectonics regime requires both the initiation of subduction and the development of nascent subduction zones into long-lived contiguous features. Subduction itself has been shown to be sensitive to system parameters such as thermal state and the specific rheology. While generally it has been shown that cold-interior high-Rayleigh-number convection (such as on the Earth today) favours plates and subduction, due to the ability of the interior stresses to couple with the lid, a given system may or may not have plate tectonics depending on its initial conditions. This has led to the idea that there is a strong history dependence to tectonic evolution—and the details of tectonic transitions, including whether they even occur, may depend on the early history of a planet. However, intrinsic convective stresses are not the only dynamic drivers of early planetary evolution. Early planetary geological evolution is dominated by volcanic processes and impacting. These have rarely been considered in thermal evolution models. Recent models exploring the details of plate tectonic initiation have explored the effect of strong thermal plumes or large impacts on surface tectonism, and found that these ‘primary drivers’ can initiate subduction, and, in some cases, over-ride the initial state of the planet. The corollary of this, of course, is that, in the absence of such ongoing drivers, existing or incipient subduction systems under early Earth conditions might fail. The only detailed planetary record we have of this development comes from Earth, and is restricted by the limited geological record of its earliest history. Many recent estimates have suggested an origin of plate tectonics at approximately 3.0 Ga, inferring a monotonically increasing transition from pre-plates, through subduction initiation, to continuous subduction and a modern plate tectonic regime around that time. However, both numerical modelling and the geological record itself suggest a strong nonlinearity in the dynamics of the transition, and it has been noted that the early history of Archaean greenstone belts and trondhjemite–tonalite–granodiorite record many instances of failed subduction. Here, we explore the history of subduction failure on the early Earth, and couple these with insights from numerical models of the geodynamic regime at the time. This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics'.

Reconciling thermal regimes and tectonics of the early Earth

Geology ◽  
2019 ◽  
Vol 47 (10) ◽  
pp. 923-927 ◽  
Author(s):  
F.A. Capitanio ◽  
O. Nebel ◽  
P.A. Cawood ◽  
R.F. Weinberg ◽  
P. Chowdhury
Keyword(s):  
High Pressure ◽  
Mantle Convection ◽  
Plate Tectonics ◽  
Early Earth ◽  
Plate Tectonic ◽  
Metamorphic Belt ◽  
Thermal Regimes ◽  
Tectonic Environments

Abstract Thermomechanical models of mantle convection and melting in an inferred hotter Archean Earth show the emergence of pressure-temperature (P-T) regimes that resemble present-day plate tectonic environments yet developed within a non–plate tectonics regime. The models’ P-T gradients are compatible with those inferred from evolving tonalite-trondhjemite-granodiorite series rocks and the paired metamorphic belt record, supporting the feasibility of divergent and convergent tectonics within a mobilized, yet laterally continuous, lithospheric lid. “Hot” P-T gradients of 10–20 °C km–1 form along asymmetric lithospheric drips, then migrate to areas of deep lithospheric downwelling within ∼300–500 m.y., where they are overprinted by high-pressure warm and, later, cold geothermal signatures, up to ∼8 °C km–1. Comparisons with the crustal production and reworking record suggest that this regime emerged in the Hadean.

Modern plate tectonic cycles are inherited from Hadean mantle convection

2020 ◽  
Author(s):  
Ross N. Mitchell ◽  
Christopher J. Spencer ◽  
Uwe Kirscher ◽  
Simon A. Wilde
Keyword(s):  
Time Series ◽  
Mantle Convection ◽  
Plate Tectonics ◽  
The Other ◽  
Early Earth ◽  
Plate Tectonic ◽  
Hafnium Isotopes ◽  
Planetary Evolution ◽  
Secular Changes ◽  
Jack Hills

<p><strong>Earth’s oldest preserved crustal archive, the Jack Hills zircon of Western Australia, has been controversial to interpret in terms of the onset of plate tectonics. Here we conduct time series analysis on hafnium isotopes of the Jack Hills zircon and reveal an array of statistically significant cycles that are reminiscent of plate tectonics, i.e., subduction. At face value, such cycles may suggest early Earth conditions similar to today—the uniformitarian “day one” hypothesis. On the other hand, in the context of expected secular changes due to planetary evolution and geological observations, the cycles could instead imply that modern plate tectonic subduction inherited convective harmonics already facilitated by an early phase of stagnant-lid delamination—the “lid-to-plates” hypothesis. Either way, any model for the initiation of plate tectonics must begin in Hadean time.</strong></p>

scholarly journals Noise in the Cretaceous Quiet Zone uncovers plate tectonic chain reaction

2021 ◽  
Author(s):  
Derya Guerer ◽  
Roi Granot ◽  
Douwe van Hinsbergen
Keyword(s):  
Subduction Zone ◽  
Mantle Plume ◽  
Plate Tectonics ◽  
Convergence Rates ◽  
Plate Motion ◽  
Plate Tectonic ◽  
Chain Reaction ◽  
African Plate ◽  
Mantle Dynamics ◽  
Chain Reactions

Global plate reorganizations, intriguing but loosely defined periods of profoundly changing plate motions, may be caused by a single trigger such as a continental collision or a rising mantle plume. But whether and how such triggers propagate throughout a plate circuit remains unknown. Here, we show how a rising mantle plume set off a ‘plate tectonic chain reaction’. Plume rise has been shown to trigger formation of a subduction zone within the Neotethys Ocean between Africa and Eurasia at ~105 Ma. We provide new constraints on Africa-Eurasia convergence rates using variations in geomagnetic ‘noise’ within the Cretaceous Normal Superchron (the 126-83 Ma period without magnetic reversals) recorded in the Atlantic Quiet Zones crust. These new constraints are consistent with the timing of numerically predicted African Plate acceleration and deceleration associated with onset and arrest of the intra-Neotethyan subduction zone. The acceleration was associated with a change in Africa-Eurasia convergence direction, which in turn was accommodated by a next subduction initiation at ~85 Ma in the Alpine region that cascaded into regional tectonic events. Our concept of plate tectonic chain reactions shows how changes in plate motion, underpinned by mantle dynamics, may self-perpetuate through a plate circuit, making global plate reorganizations a key to unlock the driving mechanisms behind plate tectonics.

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’.

Precambrian tectonic evolution of Earth: an outline

2021 ◽  
Vol 124 (1) ◽  
pp. 141-162 ◽  
Author(s):  
J.F. Dewey ◽  
E.S. Kiseeva ◽  
J.A. Pearce ◽  
L.J. Robb
Keyword(s):  
Tectonic Evolution ◽  
Plate Tectonics ◽  
Global Scale ◽  
Sensu Stricto ◽  
Strike Slip ◽  
Small Scale ◽  
Data Sets ◽  
Crustal Material ◽  
Plate Tectonic ◽  
Single Plate

Abstract Space probes in our solar system have examined all bodies larger than about 400 km in diameter and shown that Earth is the only silicate planet with extant plate tectonics sensu stricto. Venus and Earth are about the same size at 12 000 km diameter, and close in density at 5 200 and 5 500 kg.m-3 respectively. Venus and Mars are stagnant lid planets; Mars may have had plate tectonics and Venus may have had alternating ca. 0.5 Ga periods of stagnant lid punctuated by short periods of plate turnover. In this paper, we contend that Earth has seen five, distinct, tectonic periods characterized by mainly different rock associations and patterns with rapid transitions between them; the Hadean to ca. 4.0 Ga, the Eo- and Palaeoarchaean to ca. 3.1 Ga, the Neoarchaean to ca. 2.5 Ga, the Proterozoic to ca. 0.8 Ga, and the Neoproterozoic and Phanerozoic. Plate tectonics sensu stricto, as we know it for present-day Earth, was operating during the Neoproterozoic and Phanerozoic, as witnessed by features such as obducted supra-subduction zone ophiolites, blueschists, jadeite, ruby, continental thin sediment sheets, continental shelf, edge, and rise assemblages, collisional sutures, and long strike-slip faults with large displacements. From rock associations and structures, nothing resembling plate tectonics operated prior to ca. 2.5 Ga. Archaean geology is almost wholly dissimilar from Proterozoic-Phanerozoic geology. Most of the Proterozoic operated in a plate tectonic milieu but, during the Archaean, Earth behaved in a non-plate tectonic way and was probably characterised by a stagnant lid with heat-loss by pluming and volcanism, together with diapiric inversion of tonalite-trondjemite-granodiorite (TTG) basement diapirs through sinking keels of greenstone supracrustals, and very minor mobilism. The Palaeoarchaean differed from the Neoarchaean in having a more blobby appearance whereas a crude linearity is typical of the Neoarchaean. The Hadean was probably a dry stagnant lid Earth with the bulk of its water delivered during the late heavy bombardment, when that thin mafic lithosphere was fragmented to sink into the asthenosphere and generate the copious TTG Ancient Grey Gneisses (AGG). During the Archaean, a stagnant unsegmented, lithospheric lid characterised Earth, although a case can be made for some form of mobilism with “block jostling”, rifting, compression and strike-slip faulting on a small scale. We conclude, following Burke and Dewey (1973), that there is no evidence for subduction on a global scale before about 2.5 Ga, although there is geochemical evidence for some form of local recycling of crustal material into the mantle during that period. After 2.5 Ga, linear/curvilinear deformation belts were developed, which “weld” cratons together and palaeomagnetism indicates that large, lateral, relative motions among continents had begun by at least 1.88 Ga. The “boring billion”, from about 1.8 to 0.8 Ga, was a period of two super-continents (Nuna, also known as Columbia, and Rodinia) characterised by substantial magmatism of intraplate type leading to the hypothesis that Earth had reverted to a single plate planet over this period; however, orogens with marginal accretionary tectonics and related magmatism and ore genesis indicate that plate tectonics was still taking place at and beyond the bounds of these supercontinents. The break-up of Rodinia heralded modern plate tectonics from about 0.8 Ga. Our conclusions are based, almost wholly, upon geological data sets, including petrology, ore geology and geochemistry, with minor input from modelling and theory.

Plume-induced subduction and plate fracturation, deep mantle overturn, and the onset of plate tectonics.

2021 ◽  
Author(s):  
Anne Davaille
Keyword(s):  
Plate Tectonics ◽  
Colloidal Dispersions ◽  
Small Scale ◽  
Dense Layer ◽  
Mantle Dynamics ◽  
Simultaneous Generation ◽  
Tensile Fractures ◽  
Back Arc ◽  
The Impact ◽  
Surface Plate

<p>Mantle dynamics can now be recovered in the laboratory, when aqueous colloidal dispersions are dryed from above, and either insulated or heated from below. As their rheology varies from viscous to visco-elasto-plastic to brittle when drying proceeds, a skin (i.e. an experimental lithosphere) develops at the surface. Submitted to buckling, small-scale convection, or an impinging hot plume, this skin can break and one-sided subduction is then observed to proceed. In the case of plume-induced subduction (PIS), the impact of the plume under the skin induces tensile fractures, plume material upwelling through them and spreading at the surface, analogous to volcanic flooding, leading to skin bending and eventually one-sided subduction along arcuate segments which retreat away from the plume. A system of accreting ridges can develop inside the back-arc basin. If PIS develops isolated in an overall stagnant lithosphere, subduction eventually either stops as the result of subducted plate necking, or when plume spreading stops. On the other hand, if the lithosphere contains other heterogeneities (damage) such as faults, accretion ridges or another PIS event, the weight of the subducting plate can induce faraway plate breaking and horizontal mobilization of the surface plate.</p><p>As the lithosphere has to accumulate damage to fracture, it takes time from the first subduction event to the organization of a network of subducting and accreting plates. But the presence of several hot plumes simultaneously accelerates the establishment of an organized pattern of plates, subduction and accretion. And when we run experiments where the mantle contains initially a denser layer at the bottom, the global overturn of this dense layer results in the simultaneous generation of plumes over the whole mantle surface, which produces a burst of PIS events and the quick establishment of a plate tectonic-like regime. <br>Such a global overturn has been proposed to explain the big peak in continental crust growth 2.7 Ga on Earth. Our experiments suggest that it could also have triggered the formation of the plates boundaries and flow organization necessary to plate tectonics.</p>

Spatially Explicit, Statistical Land-Change Models in Data-Sparse Conditions

2004 ◽  
Author(s):  
Jacqueline Geoghegan ◽  
Laura Schneider
Keyword(s):  
Satellite Imagery ◽  
Geographical Information Systems ◽  
Census Data ◽  
Spatial Scales ◽  
Global Environmental Change ◽  
Geophysical Data ◽  
Land Change ◽  
Change Models ◽  
Fine Grained ◽  
The Individual

A range of research interests beyond global environmental change science increasingly calls for advances in land-change models and, specifically, models that have fine-grained locational outputs. The rationale for such modeling about land change has been articulated elsewhere in this book (Ch. 1; Introduction to Part IV) and need not be reiterated here. It is important to note, however, that advances in question are assisted by the advances in the analytical sophistication of geographical information systems, hardware (GPS) that permits geographical coordinates to be established easily in the field, and for land-change studies, increasing temporal and spatial resolution of satellite imagery. Much of the first phase of land-change models that incorporate these systems and data has been empirical-based, time series assessments, such as Markov-chain models (e.g. Turner 1988), that let the record of land change determine future projections, or the spatial level of assessment has been large-grain (e.g. counties, states, regions). The SYPR project seeks a different approach demonstrated here: to test theories of land change in regard to their ability to explain fine-grained land change in the region at different spatial scales of assessment. Two complementary econometric modeling approaches are used here to investigate the factors that affect deforestation at the regional and household scales of analysis. Both approaches use the individual satellite pixels as the data on land-use change, from the classification of TM imagery described in Ch. 6. A regional model spans the entire study area of agricultural ejidos, and links the satellite imagery with publicly available geophysical data and socio-demographic government census data. The second model focuses exclusively on the parcels associated with the household survey data collected specifically for this project, discussed in Part III, especially Ch. 8. This latter approach uses the same geophysical data of the aggregate approach, but uses the much richer socio-demographic data derived from the linkage of individual farm plots and the satellite imagery via the sketch mapping exercise described in Chs. 8 and 9. While both models take a theoretical approach of individual maximization, they differ in a number of ways, the most important of which is the role of time in the decision-making process.

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