Accretion of continental crust: thermal and geochemical consequences

1981 ◽  
Vol 301 (1461) ◽  
pp. 347-357 ◽  
Keyword(s):  
Continental Crust ◽  
Numerical Models ◽  
Granulite Facies ◽  
Vapour Phase ◽  
Controlled Processes ◽  
Sialic Crust ◽  
Partial Melt ◽  
The Past ◽  
Profound Influence ◽  
Mineral Assemblages

The irreversible chemical differentiation of the Earth’s mantle to produce sialic crust over the past 3900 Ma has most probably occurred during widely separated, but short-lived, accretion episodes. These episodes involved the massive addition of juvenile sialic magma to the Earth’s surface, thickening pre-existing crust. Simple numerical simulations, based on tectonic, petrological and geochemical observations on Archaean high-grade orthogneiss terranes, have been used to explore the metamorphic and geochemical consequences of massive thickening of sialic crust during short-lived accretion episodes. The location of the main sites of magmatic addition within the crust exert a profound influence on the thermal régimes. Geochemical differentiation of the continental crust by partial-melt and vapour-phase-controlled processes, and the development of granulite facies mineral assemblages can be integrated with the simple numerical models. Finally, the survival of thick Archaean continental crust imples the contemporaneous stabilization of thick lithospheric substructures to the newly formed continental masses.

Age and isotope evidence for the evolution of continental crust

1978 ◽  
Vol 288 (1355) ◽  
pp. 401-413 ◽  
Keyword(s):  
Continental Crust ◽  
Isotopic Ratios ◽  
Geological Environment ◽  
Geological Time ◽  
Sialic Crust ◽  
Isotope Data ◽  
The Past ◽  
Isotope Evidence ◽  
Continental Growth ◽  
Infinite Reservoir

Irreversible chemical differentiation of the mantle’s essentially infinite reservoir for at least the past 3800 Ma has produced new continental, sialic crust during several relatively short ( ca . 100-300 Ma) episodes which were widely separated in time and may have been of global extent. During each episode (termed 'accretion—differentiation superevent’), juvenile sial underwent profound igneous, metamorphic and geochemical differentiation, resulting in thick ( ca . 25-40 km), stable, compositionally gradational, largely indestructible, continental crust exhibiting close grouping of isotopic ages of rock formation, as well as mantle-type initial Sr and Pb isotopic ratios for all major constituents. Isotopic evidence suggests that within most accretiondifferentiation superevents — and especially during the earlier ones - continental growth predominated over reworking of older sialic crust. Reworking of older sialic crust can occur in several types of geological environment and appears to have become more prevalent with the passage of geological time. It is usually clearly distinguishable from continental growth, by application of appropriate age and isotope data.

Progress and Prospects in Translating Nanobiotechnology in Medical Theranostics

2020 ◽  
Vol 16 (5) ◽  
pp. 685-707 ◽  
Author(s):  
Amna Batool ◽  
Farid Menaa ◽  
Bushra Uzair ◽  
Barkat Ali Khan ◽  
Bouzid Menaa
Keyword(s):  
Biological Properties ◽  
Chemical Characteristics ◽  
Intrinsic Properties ◽  
The Past ◽  
Profound Influence ◽  
Functionalized Nanomaterials ◽  
Physico Chemical ◽  
Properties Of Materials ◽  
Targeted Drug ◽  
And Performance

: The pace at which nanotheranostic technology for human disease is evolving has accelerated exponentially over the past five years. Nanotechnology is committed to utilizing the intrinsic properties of materials and structures at submicroscopic-scale measures. Indeed, there is generally a profound influence of reducing physical dimensions of particulates and devices on their physico-chemical characteristics, biological properties, and performance. The exploration of nature’s components to work effectively as nanoscaffolds or nanodevices represents a tremendous and growing interest in medicine for various applications (e.g., biosensing, tunable control and targeted drug release, tissue engineering). Several nanotheranostic approaches (i.e., diagnostic plus therapeutic using nanoscale) conferring unique features are constantly progressing and overcoming all the limitations of conventional medicines including specificity, efficacy, solubility, sensitivity, biodegradability, biocompatibility, stability, interactions at subcellular levels. : This review introduces two major aspects of nanotechnology as an innovative and challenging theranostic strategy or solution: (i) the most intriguing (bare and functionalized) nanomaterials with their respective advantages and drawbacks; (ii) the current and promising multifunctional “smart” nanodevices.

scholarly journals Anticorrelated observed and modeled trends in dissolved oceanic oxygen over the last 50 years

2012 ◽  
Vol 9 (4) ◽  
pp. 4595-4626 ◽  
Author(s):  
L. Stramma ◽  
A. Oschlies ◽  
S. Schmidtko
Keyword(s):  
Large Scale ◽  
Model Comparison ◽  
Numerical Models ◽  
Regional Patterns ◽  
The Past ◽  
Tropical Oceans ◽  
Model Configuration ◽  
Pattern Correlation ◽  
Increasing Trends ◽  
Global Mean

Abstract. Observations and model runs indicate trends in dissolved oxygen (DO) associated with current and ongoing global warming. However, a large-scale observation-to-model comparison has been missing and is presented here. This study presents a first global compilation of DO measurements covering the last 50 years. It shows declining upper-ocean DO levels in many regions, especially the tropical oceans, whereas areas with increasing trends are found in the subtropics and in some subpolar regions. For the Atlantic Ocean south of 20° N, the DO history could even be extended back to about 70 years, showing decreasing DO in the subtropical South Atlantic. The global mean DO trend between 50° S and 50° N at 300 dbar for the period 1960 to 2010 is −0.063 μmol kg−1 yr−1. Results of a numerical biogeochemical Earth system model reveal that the magnitude of the observed change is consistent with CO2-induced climate change. However, the correlation between simulated and observed patterns of past DO change is negative, indicating that the model does not correctly reproduce the processes responsible for observed regional oxygen changes in the past 50 years. A negative pattern correlation is also obtained for model configurations with particularly low and particularly high diapycnal mixing, for a configuration that assumes a CO2-induced enhancement of the C:N ratios of exported organic matter and irrespective of whether climatological or realistic winds from reanalysis products are used to force the model. Depending on the model configuration the 300 dbar DO trend between 50° S and 50° N is −0.026 to −0.046 μmol kg−1 yr−1. Although numerical models reproduce the overall sign and, to some extent, magnitude of observed ocean deoxygenation, this degree of realism does not necessarily apply to simulated regional patterns and the representation of processes involved in their generation. Further analysis of the processes that can explain the discrepancies between observed and modeled DO trends is required to better understand the climate sensitivity of oceanic oxygen fields and predict potential DO changes in the future.

scholarly journals Integration after totalitarianism: Arendt and Habermas on the postwar imperatives of memory

2018 ◽  
Vol 16 (1) ◽  
pp. 2-24 ◽  
Author(s):  
Peter J Verovšek
Keyword(s):  
Political Community ◽  
European Politics ◽  
Public Intellectuals ◽  
The European Union ◽  
Mutual Support ◽  
Collective Memories ◽  
Total War ◽  
The Past ◽  
Profound Influence ◽  
The Holocaust

Collective memories of totalitarianism and the industrialized slaughter of the Holocaust have exerted a profound influence on postwar European politics and philosophy. Two of the most prominent political theorists and public intellectuals to take up the legacy of total war are Hannah Arendt and Jürgen Habermas. However, their prescriptions seem to pull in opposite directions. While Arendt draws on remembrance to recover politics on a smaller scale by advocating for the empowerment of local councils, Habermas draws on the past to justify his search for postnational forms of political community that can overcome the bloody legacy of nationalism. My argument brings these two perspectives together by examining their mutual support for European integration as a way of preserving the lessons of totalitarianism. I argue that both Arendt and Habermas reject the technocratic tendencies of the European Union while maintaining hope that it can develop a truly postnational form of politics.

Intrusion of Magmatic Bodies Into the Continental Crust: 3-D Numerical Models

Tectonics ◽  
2018 ◽  
Vol 37 (3) ◽  
pp. 705-723 ◽  
Author(s):  
Weronika Gorczyk ◽  
Katharina Vogt
Keyword(s):  
Continental Crust ◽  
Numerical Models

Joining the Crowd: Integrating Plant Virus Proteins into the Larger World of Pathogen Effectors

2018 ◽  
Vol 56 (1) ◽  
pp. 89-110 ◽  
Author(s):  
Scott M. Leisner ◽  
James E. Schoelz
Keyword(s):  
Plant Virus ◽  
Cauliflower Mosaic Virus ◽  
Virus Protein ◽  
Host Defenses ◽  
The Past ◽  
Pathogen Effectors ◽  
Profound Influence ◽  
Bacterial Effectors ◽  
Avr Genes ◽  
Virus Proteins

The first bacterial and viral avirulence ( avr) genes were cloned in 1984. Although virus and bacterial avr genes were physically isolated in the same year, the questions associated with their characterization after discovery were very different, and these differences had a profound influence on the narrative of host-pathogen interactions for the past 30 years. Bacterial avr proteins were subsequently shown to suppress host defenses, leading to their reclassification as effectors, whereas research on viral avr proteins centered on their role in the viral infection cycle rather than their effect on host defenses. Recent studies that focus on the multifunctional nature of plant virus proteins have shown that some virus proteins are capable of suppression of the same host defenses as bacterial effectors. This is exemplified by the P6 protein of Cauliflower mosaic virus (CaMV), a multifunctional plant virus protein that facilitates several steps in the infection, including modulation of host defenses. This review highlights the modular structure and multifunctional nature of CaMV P6 and illustrates its similarities to other, well-established pathogen effectors.

8. Glaciers of the past

2018 ◽  
pp. 146-152
Author(s):  
David J. A. Evans
Keyword(s):  
Numerical Models ◽  
Ice Core ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Aerial Imagery ◽  
The Past ◽  
Glacial Landforms

To reconstruct the former extent and dynamics of ice sheets and glaciers requires a knowledge of process-form relationships that goes beyond individual landform types. Instead, glacial geomorphologists need to analyse large areas of glaciated terrain in a more holistic way, combining the whole range of glacial landforms and sediments to reconstruct glacier systems of the past, a subject now known as palaeoglaciology. ‘Glaciers of the past’ explains how the combination of aerial imagery and landform analysis is used in palaeoglaciological reconstruction. Increasingly powerful computers are making it possible to compile sophisticated numerical models that use our knowledge of glaciological processes and ice-core-derived palaeoclimate data to create three-dimensional glacier and ice sheet reconstructions.

Analysis of Global Stability, Anchor Spacing, and Support Cable Loads in Wire Mesh and Cable Net Slope Protection Systems

2005 ◽  
Vol 1913 (1) ◽  
pp. 205-213 ◽  
Author(s):  
Navaratnarajah Sasiharan ◽  
Balasingam Muhunthan ◽  
Shanzhi Shu ◽  
Thomas C. Badger
Keyword(s):  
Numerical Models ◽  
Wire Mesh ◽  
System Failures ◽  
Design Elements ◽  
The Past ◽  
Protection Systems ◽  
Vertical Support ◽  
Stability Of Slope ◽  
The Stability ◽  
Horizontal Support

Wire mesh and cable net slope protection have been in use for more than 50 years along North American highways to control rockfall on actively eroding slopes. The basic design of these systems is comparatively similar throughout North America. It consists of a top horizontal cable suspended by regularly spaced anchors, typically a perimeter or widely spaced grid of horizontal and vertical support cables, and double-twisted, hexagonal wire mesh laced to the support ropes. To date, the design of the slope protection systems has been based primarily on empirical methods, engineering judgment, and experience. Although these systems generally perform well, there is some consensus among geotechnical specialists that some elements in the system may be overdesigned or even unnecessary. In addition, system failures under a variety of loading conditions within the past few decades indicate that certain design elements may in fact be underdesigned for their desired application. Analytical and numerical models to evaluate the stability of slope protection systems are presented. The inclusion of interior horizontal support ropes in addition to the top horizontal rope does not reduce the stress within the mesh and accordingly provides no mechanical benefit. Results also show that the stresses on the vertical support rope are much smaller than the top horizontal support rope. Therefore, the vertical ropes do not need to be as strong as the top horizontal rope. Further, some useful design charts for the design of slope protection system are presented.

Peraluminous sapphirine from the Aileron district, Arunta Block, central Australia

1987 ◽  
Vol 51 (361) ◽  
pp. 409-415 ◽  
Author(s):  
R. G. Warren ◽  
B. J. Hensen
Keyword(s):  
Bulk Composition ◽  
Granulite Facies ◽  
The Other ◽  
Stable Phase ◽  
Mineral Assemblages ◽  
Central Australia

AbstractSpecimens collected from a small lens of phlogopite-rich rock in the granulite-facies terrain of the Arunta Block, central Australia, have unusual bulk compositions and mineral assemblages. One sample consists of phlogopite enclosing blue spinel (mg 96) with minute granules of corundum and sapphirine at the margins; a second of phlogopite enclosing porphyroblasts of corundum and peraluminous sapphirine. In the first the sapphirine is close to the 7 : 9 : 3 composition; in the other it is markedly peraluminous, e.g. (Mg1.628Fe0.028)Al4.714Si0.636O10, intermediate between the 7 : 9 : 3 and 3 : 5 : 1 members. The texture suggests that this sapphirine is a stable phase in equilibrium with eastonitic phlogopite and corundum. The very potassic, very magnesian bulk composition of the rocks is attributed to potassium metasomatism of a protolith consisting of magnesian chlorite and quartz.

Sign in / Sign up

Export Citation Format

Share Document