Plate Tectonics and the Archean Earth

2020 ◽  
Vol 48 (1) ◽  
pp. 291-320 ◽  
Author(s):  
Michael Brown ◽  
Tim Johnson ◽  
Nicholas J. Gardiner
Keyword(s):  
Numerical Modeling ◽  
Lower Limit ◽  
Critical Condition ◽  
Plate Tectonics ◽  
Global Network ◽  
Future Research ◽  
Secular Evolution ◽  
Geochemical Proxies ◽  
Survivorship Bias ◽  
Mantle Temperature

If we accept that a critical condition for plate tectonics is the creation and maintenance of a global network of narrow boundaries separating multiple plates, then to argue for plate tectonics during the Archean requires more than a local record of subduction. A case is made for plate tectonics back to the early Paleoproterozoic, when a cycle of breakup and collision led to formation of the supercontinent Columbia, and bimodal metamorphism is registered globally. Before this, less preserved crust and survivorship bias become greater concerns, and the geological record may yield only a lower limit on the emergence of plate tectonics. Higher mantle temperature in the Archean precluded or limited stable subduction, requiring a transition to plate tectonics from another tectonic mode. This transition is recorded by changes in geochemical proxies and interpreted based on numerical modeling. Improved understanding of the secular evolution of temperature and water in the mantle is a key target for future research. ▪  Higher mantle temperature in the Archean precluded or limited stable subduction, requiring a transition to plate tectonics from another tectonic mode. ▪  Plate tectonics can be demonstrated on Earth since the early Paleoproterozoic (since c. 2.2 Ga), but before the Proterozoic Earth's tectonic mode remains ambiguous. ▪  The Mesoarchean to early Paleoproterozoic (3.2–2.3 Ga) represents a period of transition from an early tectonic mode (stagnant or sluggish lid) to plate tectonics. ▪  The development of a global network of narrow boundaries separating multiple plates could have been kick-started by plume-induced subduction.

scholarly journals Expanding Network Analysis Tools in Psychological Networks: Minimal Spanning Trees, Participation Coefficients, and Motif Analysis Applied to a Network of 26 Psychological Attributes

Complexity ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-27 ◽  
Author(s):  
Srebrenka Letina ◽  
Tessa F. Blanken ◽  
Marie K. Deserno ◽  
Denny Borsboom
Keyword(s):  
Network Analysis ◽  
Spanning Trees ◽  
Main Idea ◽  
Global Network ◽  
Centrality Measures ◽  
Future Research ◽  
Motif Analysis ◽  
Psychological Variables ◽  
Hierarchical Arrangement ◽  
Psychological Attributes

The analysis of psychological networks in previous research has been limited to the inspection of centrality measures and the quantification of specific global network features. The main idea of this paper is that a psychological network entails more potentially useful and interesting information that can be reaped by other methods widely used in network science. Specifically, we suggest methods that provide clearer picture about hierarchical arrangement of nodes in the network, address heterogeneity of nodes in the network, and look more closely at network’s local structure. We explore the potential value of minimum spanning trees, participation coefficients, and motif analyses and demonstrate the relevant analyses using a network of 26 psychological attributes. Using these techniques, we investigate how the network of different psychological concepts is organized, which attribute is most central, and what the role of intelligence in the network is relative to other psychological variables. Applying the three methods, we arrive at several tentative conclusions. Trait Empathy is the most “central” attribute in the network. Intelligence, although peripheral, is weakly but equally related to different kinds of attributes present in the network. Analysis of triadic configurations additionally shows that the network is characterized by relatively strong open triads and an unusually frequent occurrence of negative triangles. We discuss these and other findings in the light of possible theoretical explanations, methodological limitations, and future research.

scholarly journals Biogeography and ecology: towards the integration of two disciplines

2011 ◽  
Vol 366 (1576) ◽  
pp. 2438-2448 ◽  
Author(s):  
Robert E. Ricklefs ◽  
David G. Jenkins
Keyword(s):  
Evolutionary Biology ◽  
Plate Tectonics ◽  
Large Scale ◽  
Open Systems ◽  
Ecological Factors ◽  
Future Research ◽  
Ecological Communities ◽  
History Of ◽  
Future Research Directions ◽  
Synthetic Approaches

Although ecology and biogeography had common origins in the natural history of the nineteenth century, they diverged substantially during the early twentieth century as ecology became increasingly hypothesis-driven and experimental. This mechanistic focus narrowed ecology's purview to local scales of time and space, and mostly excluded large-scale phenomena and historical explanations. In parallel, biogeography became more analytical with the acceptance of plate tectonics and the development of phylogenetic systematics, and began to pay more attention to ecological factors that influence large-scale distributions. This trend towards unification exposed problems with terms such as ‘community’ and ‘niche,’ in part because ecologists began to view ecological communities as open systems within the contexts of history and geography. The papers in this issue represent biogeographic and ecological perspectives and address the general themes of (i) the niche, (ii) comparative ecology and macroecology, (iii) community assembly, and (iv) diversity. The integration of ecology and biogeography clearly is a natural undertaking that is based on evolutionary biology, has developed its own momentum, and which promises novel, synthetic approaches to investigating ecological systems and their variation over the surface of the Earth. We offer suggestions on future research directions at the intersection of biogeography and ecology.

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>

scholarly journals Practical needs and considerations for refugees and other forcibly displaced persons with neurological disorders: Recommendations using a modified Delphi approach

2021 ◽  
Vol 5 ◽  
pp. 178
Author(s):  
Shawheen Rezaei ◽  
Foksouna Sakadi ◽  
Fu-Liong Hiew ◽  
Ildefonso Rodriguez-Leyva ◽  
Jera Kruja ◽  
...  
Keyword(s):  
Economic Status ◽  
Global Network ◽  
Future Research ◽  
Displaced Persons ◽  
Middle Income ◽  
Internally Displaced ◽  
Modified Delphi ◽  
Delphi Approach ◽  
Displaced People ◽  
Neurological Conditions

Background: There are >70 million forcibly displaced people worldwide, including refugees, internally displaced persons, and asylum seekers. While the health needs of forcibly displaced people have been characterized in the literature, more still needs to be done globally to translate this knowledge into effective policies and actions, particularly in neurology. Methods: In 2020, a global network of published experts on neurological disease and refugees was convened. Nine physician experts from nine countries (2 low, 1 lower-middle income, 5 upper-middle, 1 high income) with experience treating displaced people originating from 18 countries participated in three survey and two discussion rounds in accordance with the Delphi method. Results: A consensus list of priority interventions for treating neurological conditions in displaced people was created, agnostic to cost considerations, with the ten highest ranking tests or treatments ranked as: computerized tomography scans, magnetic resonance imaging scans, levetiracetam, acetylsalicylic acid, carbamazepine, paracetamol, sodium valproate, basic blood tests, steroids and anti-tuberculous medication. The most important contextual considerations (100% consensus) were all economic and political, including the economic status of the displaced person’s country of origin, the host country, and the stage in the asylum seeking process. The annual cost to purchase the ten priority neurological interventions for the entire displaced population was estimated to be 220 million USD for medications and 4.2 billion USD for imaging and tests. Conclusions: A need for neuroimaging and anti-seizure medications for forcibly displaced people was emphasized. These recommendations could guide future research and investment in neurological care for forcibly displaced people.

scholarly journals An integrated data compilation for the development of a marine protected area in the Weddell Sea

2019 ◽  
Author(s):  
Katharina Teschke ◽  
Hendrik Pehlke ◽  
Volker Siegel ◽  
Horst Bornemann ◽  
Rainer Knust ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Planning Process ◽  
Marine Protected Area ◽  
Weddell Sea ◽  
Global Network ◽  
Future Research ◽  
Ecological Data ◽  
Data Compilation ◽  
Final Data ◽  
Data Layer

Abstract. The Southern Ocean may contribute a considerable part to the proposed global network of Marine Protected Areas (MPAs) that should cover about 10 % of the world oceans in 2020. In the Antarctic, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is responsible for this task, and currently Germany leads a corresponding scientific evaluation of the wider Weddell Sea region. Compared to other marine regions within the Southern Ocean, the Weddell Sea is exceptionally well investigated. A tremendous amount of data and information has been produced over the last four decades. Here, we give a compilation of these data that were acquired in the context of the Weddell Sea MPA planning process. The data compilation comprises data produced by scientists/institutions from more than twenty countries and were either available within our institutes, provided by our collaborators, downloaded via data portals, or transcribed from the literature. It is the first data compilation for this area that includes abiotic data, such as bathymetry and sea ice, and ecological data from zooplankton, zoobenthos, fish, birds and marine mammals. The final data layer products based on this data compilation, including metadata description, are available from the data publisher PANGAE via the five persistent identifiers at https://doi.org/10.1594/PANGAEA.899520 (Pehlke et al., 2019a), https://doi.org/10.1594/PANGAEA.899591 (Teschke et al., 2019a), https://doi.org/10.1594/PANGAEA.899595 (Pehlke and Teschke, 2019), https://doi.org/10.1594/PANGAEA.899619 (Pehlke et al., 2019b), https://doi.org/10.1594/PANGAEA.899645 (Teschke et al., 2019b) and https://doi.org/10.1594/PANGAEA.899667 (Teschke et al., 2019c). This data compilation with the final data layer products will serve future research and monitoring well beyond the current MPA development process.

New Mechanisms for Cryogenic Solid-Gas Sublimation Refrigeration

2015 ◽  
pp. 106-154
Author(s):  
Lin Chen
Keyword(s):  
Numerical Modeling ◽  
Low Temperature ◽  
Phase Change ◽  
Future Research ◽  
Two Phase ◽  
Food Engineering ◽  
Change Mechanism ◽  
Physical Problems ◽  
Industrial Sectors ◽  
Fast Cooling

Sublimation is one phase change mechanism which usually happens under low-to-moderate temperatures and at the same time large amounts of latent heat is absorbed or released. Low temperature sublimation has been proposed in a lot of applications as one useful fast cooling/refrigeration mechanisms, such as medical cooling, food engineering, chemical synthesis, domestic cooling and many industrial sectors. In this brief chapter, the basic mechanisms of static sublimation process and sublimation two-phase flows are clarified and analyzed first, which covers the theoretical and physical problems of sublimation phase-change. Then the previous studies are classified into numerical modeling and experimental verifications. Representative refrigeration systems are also introduced and compared in this chapter, which may give useful indications for future innovations in this field. Future research focuses are also summarized and proposed in this chapter.

scholarly journals Synthesis and future research directions linking tree diversity to growth, survival, and damage in a global network of tree diversity experiments

2018 ◽  
Vol 152 ◽  
pp. 68-89 ◽  
Author(s):  
Jake J. Grossman ◽  
Margot Vanhellemont ◽  
Nadia Barsoum ◽  
Jürgen Bauhus ◽  
Helge Bruelheide ◽  
...  
Keyword(s):  
Tree Diversity ◽  
Global Network ◽  
Future Research ◽  
Research Directions ◽  
Future Research Directions

Triple oxygen isotope constraints on the origin of ocean island basalts

2020 ◽  
Author(s):  
Xiaobin Cao ◽  
Huiming Bao ◽  
Yongbo Peng
Keyword(s):  
Theoretical Calculation ◽  
Oxygen Isotope ◽  
Mantle Source ◽  
Plate Tectonics ◽  
Unique Feature ◽  
Published Data ◽  
Ocean Island ◽  
Ocean Island Basalts ◽  
Geochemical Proxies ◽  
Subducted Oceanic Crust

<p> </p><p><span>Understanding the origin of ocean island basalts (OIB) has important bearings on Earth’s deep mantle. Although it is widely accepted that subducted oceanic crust, as a consequence of plate tectonics, contributes material to OIB’s formation, its exact fraction in OIB’s mantle source remains ambiguous largely due to uncertainties associated with existing geochemical proxies. We have shown, through theoretical calculation and examining published data, that unlike many known proxies, triple oxygen isotope compositions (i.e. Δ<sup>17</sup>O) in olivine samples are not affected by crystallization and partial melting. This unique feature allows olivine Δ<sup>17</sup>O values to identify and quantify the fractions of subducted ocean sediments and hydrothermally altered oceanic crusts in OIB’s mantle source. In this work, new Δ<sup>17</sup>O measurements for OIB will be presented, and the implications will be discussed.<span>  </span></span></p><p> </p>

scholarly journals When crust comes of age: on the chemical evolution of Archaean, felsic continental crust by crustal drip tectonics

2018 ◽  
Vol 376 (2132) ◽  
pp. 20180103 ◽  
Author(s):  
O. Nebel ◽  
F. A. Capitanio ◽  
J.-F. Moyen ◽  
R. F. Weinberg ◽  
F. Clos ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Plate Tectonics ◽  
Geochemical Data ◽  
Evolutionary Stage ◽  
Secular Evolution ◽  
Lithospheric Thickness ◽  
Asthenospheric Mantle ◽  
Wide Scale ◽  
Granitoid Intrusions ◽  
Lower Crustal

The secular evolution of the Earth's crust is marked by a profound change in average crustal chemistry between 3.2 and 2.5 Ga. A key marker for this change is the transition from Archaean sodic granitoid intrusions of the tonalite–trondhjemite–granodiorite (TTG) series to potassic (K) granitic suites, akin (but not identical) to I-type granites that today are associated with subduction zones. It remains poorly constrained as to how and why this change was initiated and if it holds clues about the geodynamic transition from a pre-plate tectonic mode, often referred to as stagnant lid, to mobile plate tectonics. Here, we combine a series of proposed mechanisms for Archaean crustal geodynamics in a single model to explain the observed change in granitoid chemistry. Numeric modelling indicates that upper mantle convection drives crustal flow and subsidence, leading to profound diversity in lithospheric thickness with thin versus thick proto-plates. When convecting asthenospheric mantle interacts with lower lithosphere, scattered crustal drips are created. Under increasing P-T conditions, partial melting of hydrated meta-basalt within these drips produces felsic melts that intrude the overlying crust to form TTG. Dome structures, in which these melts can be preserved, are a positive diapiric expression of these negative drips. Transitional TTG with elevated K mark a second evolutionary stage, and are blends of subsided and remelted older TTG forming K-rich melts and new TTG melts. Ascending TTG-derived melts from asymmetric drips interact with the asthenospheric mantle to form hot, high-Mg sanukitoid. These melts are small in volume, predominantly underplated, and their heat triggered melting of lower crustal successions to form higher-K granites. Importantly, this evolution operates as a disseminated process in space and time over hundreds of millions of years (greater than 200 Ma) in all cratons. This focused ageing of the crust implies that compiled geochemical data can only broadly reflect geodynamic changes on a global or even craton-wide scale. The observed change in crustal chemistry does mark the lead up to but not the initiation of modern-style subduction. This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics’.

scholarly journals Are global hotspots of endemic richness shaped by plate tectonics?

2017 ◽  
Author(s):  
Pellissier Loïc ◽  
Christian Heine ◽  
Camille Albouy
Keyword(s):  
Plate Tectonics ◽  
Large Fraction ◽  
Spatial Models ◽  
Future Research ◽  
Deep Time ◽  
Current Location ◽  
Lithospheric Plates ◽  
Taxonomic Groups

AbstractSingular regions of the globe harbour a disproportionally large fraction of extant biodiversity. Spatial biodiversity gradients are frequently associated to extant ecological conditions using statistical models, but more rarely to paleo-environmental conditions, especially beyond the Quaternary. On one hand the role of plate tectonics in shaping the extant diversity of lineages is supported by numerous phylogenetic and fossil evidences, and on the other hand the spatial variation of biodiversity across the globe is rarely associated to geodynamic variables. In this study, we propose that plate tectonics explain the current location of hotspots of endemic richness across the globe. As an illustration, we used paleogeographies in a model, which quantifies through time and for each cell the potential dispersal across disconnected habitat patches. Rare events of dispersal across dynamic straits of unsuitable habitats allows species colonisation and that a subsequent absence of gene flow could lead to in-situ speciation. We evaluated whether this process could pinpoint the locations of hotspots of endemic richness computed from the ranges of 181,603 species across 14 taxonomic groups. The significant congruence between the regions highlighted by the model and the endemic richness provides evidences of the contribution of plate tectonics in shaping global biodiversity gradients. Places with high tectonic complexity, predominantly located at the confluence of major lithospheric plates such as the Mediterranean basin, Central America, Madagascar and South East Asia likely provided favourable circumstances for allopatric speciation and the emergence of new species across straits. While our illustration supports the role of plate tectonics, accounting for deep time geological events in spatial models of extant biodiversity is not straightforward. Future research should develop quantitative spatial models of biodiversity including the dynamic of ancient habitats.

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