A Tectonic History of the Earth

The connection between the Earth's thermal history and convection in the mantle is exploited to elucidate the early evolution of the Earth. It appears probable that convection extending over almost all of the mantle has dominated vertical heat transport throughout the whole of the Earth's history. Only in boundary layers at the surface and at a depth of 650–700 km is conduction likely to be important. The resulting evolution appears to be consistent with geological observations on early Precambrian rocks. Various arguments are put forward in favour of two horizontal scales of convective flow in the mantle at depths less than 650 km. The large scale flow is related to the motion of major plates, and must be ordered over distances of more than 5000 km. Its evolution and energetics are discussed and there are no obvious problems in maintaining the proposed convective motions. Small scale flow with an extent of the order of 500 km appears necessary both to explain the heat flow through older parts of the Earth's surface and to reconcile the geophysical observations with the results of numerical experiments. Though the existence of the small scale flow is at present speculative, various tests of its presence are proposed.

Seismicity, structure and tectonics in the Arctic region

Earth's tectonic history revisited in the light of episodic misfits between plate network and mantle convention

Earth's tectonic history revisited in the light of episodic misfits between plate network and mantle convection

Modern-style plate tectonics are mostly driven by the excess density of oceanic lithosphere sinking deeply in subduction zones and can be sustained as long as melt is produced at mid-ocean ridges. Among the silicate planets, the mechanism of plate tectonics is unique to Earth, indicating that special circumstances are required. Given that the potential temperature of Earth’s mantle has decreased by several hundred degrees Celsius since Archean time, the density of oceanic lithosphere must have systematically increased, which has profound implications for the viability of plate tectonics through time. Two things must be done to advance our understanding of Earth’s tectonic history: (1) uncritical uniformitarianism should be avoided; and (2) the geologic record must be thoughtfully and objectively interrogated. Theoretical considerations should motivate the exploration, but geologic evidence will provide the answers. The debate needs to address the criteria for identifying tectonic style in ancient rocks, whether this evidence is likely to be preserved, and what the record indicates. The most important criteria are the temporal distribution of ophiolites, blueschists, ultrahigh-pressure terranes, eclogites, paired metamorphic belts, passive margins, subduction-related batholiths, arc igneous rocks, isotopic evidence of recycling, and paleomagnetic constraints. This list of criteria should evolve; objective redefinitions and reviews of, especially, the eclogite paired metamorphic belt and subduction-related batholith records are needed. Also, the likely effects of major tectonic changes on other Earth systems should be considered, such as true polar wander, climate change, and biosphere changes. The modern episode of plate tectonics began in Neoproterozoic time, <1.0 Ga ago, with earlier alternating episodes of proto–plate tectonics (1.8–2.0 and 2.5–2.7 Ga); unstable stagnant-lid tectonics dominated the rest of Proterozoic time and an unknown part of Archean time.

One of the major challenges faced by the geotectonic community is how to determine the paleolongitude of continents and tectonic plates as we try to reconstruct Earth&amp;#8217;s tectonic history back in time, because classic paleomagnetic record is only sensitive to paleolatitude. &amp;#160;Torsvik et al. (2014) previously used mantle structure as a reference frame for palaeolongitude constraints back in Earth history, assuming that the two equatorial and antipodal large low shear velocity provinces (LLSVPs) observed in present-day Earth&amp;#8217;s lower mantle are fixed and stable ancient structures unrelated to plate tectonic history and subduction geometry. However, such an assumption is inconsistent with true polar wander (TPW) record (Li et al., 2004, 2023), the cyclic occurrence of global mantle plume activity coupled with the supercontinent cycle (Li et al., 2008; and Zhong, 2009), and geodynamic modelling results (Zhong et al., 2007; Zhang et al., 2010; Flament et al., 2017).In a recent paper of Li et al. (2023), we utilized palaeomagnetically interpreted TPW record, particularly inertia interchange true polar wander (IITPW) events, and global mantle plume record, to develop a dynamic global mantle reference frame that not only provides a first-order mantle dynamic evolution for the past 2 billion years, but also for the first time provides a way to trace the longitudinal change of continents and tectonic plates back in time. In particular, through the recognition of newly-defined type-1 and type-2 IITPW events coupled with plume record checking, we are now able to hypothesis that: (1) in periods with type-1 IITPW, the concerned supercontinent had developed its own degree-2 mantle structure (e.g., the antipodal LLSVPs divided by concurrent circum-supercontinent subduction girdle); (2) in periods with type-2 IITPW, a young supercontinent or multiple plates during the assembly of that supercontinent were moving over a legacy degree-2 mantle structure of the immediate ancestor supercontinent prior to the maturity of its own mantle structure. In our model, Nuna (lifespan 1600&amp;#8211;1300 Ma) assembled at about the same longitude as the latest supercontinent Pangaea (lifespan 320&amp;#8211;170 Ma), with an equatorial degree-2 mantle structure starting to exist as early as ca. 1700 Ma. Rodinia (lifespan 900&amp;#8211;720 Ma) formed through introversion assembly over the legacy Nuna subduction girdle either ca. 90&amp;#9702; to the west or to the east before the subduction girdle surrounding it generated its own degree-2 mantle structure by ca. 780 Ma (but not before 800 Ma). Pangea assembled over the subduction girdle of legacy Rodinian degree-2 mantle structure, with its own degree-2 mantle structure (the one we still observe today) formed no much earlier than 270 Ma.ReferencesFlament, N., Williams, S., M&amp;#252;ller, R.D. et al., 2017. Nat. Commun.&amp;#160;8, 14164.Li, Z.-X., Liu, Y. and Ernst, R., 2023. Earth-Sci. Rev. 238, 104336.Torsvik, T.H., van der Voo, R., Doubrovine, P.V. et al., 2014. Proc. Natl. Acad. Sci. 111 (24), 8735&amp;#8211;8740.Zhang, N., Zhong, S., Leng, W., Li, Z.-X., 2010. J. Geophys. Res. Solid Earth 115(B6), B06401.

Several diatom species, including Cymbella amplificata, C. janischii and Navicula aurora, are largely restricted to Asia and western North America. These disjunctions likely represent recent long-distance dispersals or chance introductions. The two continents also support clusters of diatom species in several fossil and extant genera. One of these genera, Gomphosinica, is exclusive to the two continents but includes only one species in common. This suggests that these disjunct clusters of species arose from common precursors that underwent radiations while being separated for millennia. The divergence of these lineages likely began more than 25 Ma when island arcs of Asian (Siberian) origin docked on North America. The Asian/North American connection is not restricted to diatoms; vascular plants and dinosaur fossils also exhibit this connection. Differences between diatom floras east and west of the Rocky Mountains, as first noted by Ehrenberg, can be explained by differences in Earth history and geology. Researchers interested in diatom biogeography would do well to become familiar with the tectonic history and geology of their geographic regions of interest. Some cases of ‘invasive’ or ‘alien’ diatoms may simply be that changing conditions allowed existing but latent species to prosper and become apparent to the unaided eye.

The inception of plate tectonics on Earth and its subsequent evolution are discussed on the basis of theoretical considerations and observational constraints. The likelihood of plate tectonics in the past depends on what mechanism is responsible for the relatively constant surface heat flux that is indicated by the likely thermal history of Earth. The continuous operation of plate tectonics throughout Earth's history is possible if, for example, the strength of convective stress in the mantle is affected by the gradual subduction of surface water. Various geological indicators for the emergence of plate tectonics are evaluated from a geodynamical perspective, and they invariably involve certain implicit assumptions about mantle dynamics, which are either demonstrably wrong or yet to be explored. The history of plate tectonics is suggested to be intrinsically connected to the secular evolution of the atmosphere, through sea-level changes caused by ocean-mantle interaction.

AimExplanations of pantropical distributions are challenging for taxa that diverged during the Cenozoic, after Gondwana broke apart. The ‘boreotropics hypothesis’ suggests that pantropical birds originated in the Laurasian forests. Extant parrots (Psittaciformes) are one the most species‐rich pantropical avian clades, but their known evolutionary history does not fit a boreotropical origin. Most living parrots and the earliest diverging lineages of the Psittaciformes inhabit the remnants of Gondwana, whereas the oldest stem and crown fossils are from the remnants of Laurasia. Our study proposes a biogeographic hypothesis that focuses on the Cenozoic connections between Laurasia and Gondwana to explain extant and fossil geographical distributions.LocationGlobal.TaxonPsittaciformes.MethodsWe generated a time tree using previously derived data from 32 molecular markers for 312 parrot species and reconstructed their biogeographic history using maximum likelihood. Two scenarios were compared: one with dispersal constrained to adjacent areas, including the connections between the Northern and Southern Hemispheres, and one without this constraint.ResultsOur results indicate that the pantropical distribution of parrots was shaped by two major geological events. First, the final breakup of parts of Gondwana may have caused the first splits within crown parrots, establishing two parallel radiations: Psittacidae in the Neotropics and Psittaculidae in Australasia. Second, igneous palaeoprovinces could have connected major biogeographic realms. It seems that Atlantogea and Eurogondwana were important, as they connected South America, Africa and Europe, thus reconciling the Gondwanan crown splits and the early Laurasian fossils.Main ConclusionsOur time tree allowed more concise biogeographic correlations between parrots and their sister group, the passerines and Earth's tectonic history. The crown lineages of Psittacopasseres appear to have originated in the Southern Hemisphere remnants of Gondwana, but stem lineages appear to have been able to disperse into the Northern Hemisphere through palaeobiogeographic provinces in the Cenozoic.

Subduction Initiation

First‐order variations in sea level exhibit amplitudes of ∼200 m over periods that coincide with those of supercontinental cycles (∼300–500 Myr). Proposed mechanisms for this sea level change include processes that change the container volume of the ocean basins and the relative elevation of continents. Here we investigate how unbalanced rates of water exchange between Earth's surface and mantle interior, resulting from fluctuations in tectonic rates, can cause sea level changes. Previous modeling studies of subduction water fluxes suggest that the amount of water that reaches sub‐arc depths is well correlated with the velocity and age of the subducting plate. We use these models to calibrate a parameterization of the deep subduction water flux, which we together with a parameterization of mid‐ocean ridge outgassing, then apply to reconstructions of Earth's tectonic history. This allows us to estimate the global water fluxes between the oceans and mantle for the past 230 Myr and compute the associated sea level change. Our model suggests that a sea level drop of up to 130 m is possible over this period and that it was partly caused by the ∼150Ma rift pulse that opened the Atlantic and forced rapid subduction of old oceanic lithosphere. This indicates that deep water cycling may be one of the more important sea level changing mechanisms on supercontinental time scales and provides a more complete picture of the dynamic interplay between tectonics and sea level change.

SUMMARY Thermoremanent magnetization (TRM), the primary magnetic memory of igneous rocks, depends for its stability through geologic time on mineral carriers with high coercivities and high unblocking temperatures. The palaeomagnetic record of past magnetic field directions and intensities is the key to unraveling Earth's tectonic history. Yet we still do not fully understand how the familiar mineral magnetite, in the micrometer grain size range typically responsible for stable TRM, acquires and holds its signal. Direct indicators of magnetite remanence-carrying capacity and coercivity at high temperature T are saturation remanence relative to saturation magnetization Mrs/Ms and coercive force Hc. This study is the first to measure the variation of these hysteresis properties for magnetite, from room temperature to the Curie point, across the entire size range from 25 nm to 135 µm, covering superparamagnetic, single-domain, vortex, pseudo-single-domain and multidomain magnetic behaviour. The paper focuses on: (1) Hc(T) and Mrs(T) observations and their reproducibility; (2) mathematical relationships of Hc(T) and Mrs(T) to Ms(T), used in modelling TRM and for unbiased comparisons of thermal variations; (3) the shapes of magnetite grains and the number of domains they contain, revealed by demagnetizing factors N = Hc/Mrs and (4) the grain size dependences of Hc and Mrs at ordinary and elevated T, delineating domain structure changes and mechanisms of coercivity.

Rock magnetization carries information about rocks' properties, Earth's tectonic history, and evolution of its core magnetic field. One way to study Earth's magnetization is through the magnetic signal it generates, known as the lithospheric magnetic field. Although there exist global lithospheric magnetic field models of high spatial resolution, this path has not yet been very fruitful because of an important limitation: only part of the magnetization is visible, that is, produces an observable magnetic field signal. We refer to the remaining part of the magnetization as the hidden magnetization, and we recover it from a lithospheric magnetic field model under a few reasonable assumptions. We find that Earth's hidden magnetization at high and middle latitudes is very similar, both in intensity and shape, to Earth's visible magnetization. At low latitudes, the estimated hidden magnetization relies on a priori information and can be very different from the visible one.

Stagnant lid tectonics: Perspectives from silicate planets, dwarf planets, large moons, and large asteroids

Subduction initiation in nature and models: A review