Introductory remarks

1980 ◽  
Vol 297 (1431) ◽  
pp. 137-138
Keyword(s):  
Mantle Convection ◽  
Plate Tectonics ◽  
Sharp Change ◽  
Indirect Approach ◽  
Sea Floor ◽  
Wave Velocities ◽  
The Earth ◽  
Magnesium Silicates ◽  
Sea Floor Spreading ◽  
Seismic Discontinuity

The substratum of the Earth, as Arthur Holmes originally described it, now generally known as the mantle , is the envelope, mainly of magnesium silicates, surrounding the fluid metallic core. It is separated from the continental and oceanic crusts which overlie it by the Mohorovicic seismic discontinuity, where there is a sharp change from earthquake wave velocities less than 7.2 km s -1 above to 7.8-8.1 km s -1 below. The thickness of the envelope is of the order of 2900 km, compared with about 4 km for ocean crust and 30 km for unthickened continental crust. Much attention has been devoted by geophysicists to the properties of the mantle, particularly in the course of the Geodynamics Project of I.U.G.G./I.U.G.S., during which important conclusions regarding sea floor spreading, plate tectonics and mantle convection have been reached. The fact that the overwhelming bulk of the mantle is not, and never will be, accessible for direct collection has perhaps resulted in less interest so far from the geochemical side. Accepting, however, that a partly indirect approach is inevitable, the time is now ripe for a thorough examination of the contribution that geochemical techniques can make.

scholarly journals A Geologist Reflects on a Long Career

2018 ◽  
Vol 46 (1) ◽  
pp. 1-20 ◽  
Author(s):  
Dan MKenzie
Keyword(s):  
Plate Tectonics ◽  
Continental Drift ◽  
Temperature Structure ◽  
Earth’S Gravity Field ◽  
Plate Motions ◽  
Sea Floor ◽  
Long Wavelength ◽  
Geological Processes ◽  
The Earth ◽  
Sea Floor Spreading

Fifty years ago Jason Morgan and I proposed what is now known as the theory of plate tectonics, which brought together the ideas of continental drift and sea floor spreading into what is probably their final form. I was twenty-five and had just finished my PhD. The success of the theory marked the beginning of a change of emphasis in the Earth sciences, which I have spent the rest of my career exploring. Previously geophysicists had principally been concerned with using ideas and techniques from physics to make measurements. But the success of plate tectonics showed that it could also be used to understand and model geological processes. This essay is concerned with a few such efforts in which I have been involved: determining the temperature structure and rheology of the oceanic and continental lithosphere, and with how mantle convection maintains the plate motions and the long-wavelength part of the Earth's gravity field. It is also concerned with how such research is supported.

PLANETARY SELF-ORGANIZATION

2020 ◽  
Vol 42 (3) ◽  
pp. 271-282
Author(s):  
OLEG IVANOV
Keyword(s):  
Dynamical System ◽  
Heat Source ◽  
Mantle Convection ◽  
Plate Tectonics ◽  
Rotation Speed ◽  
Self Organization ◽  
Heat Sources ◽  
Kinematic Parameters ◽  
The Earth ◽  
New Type

The general characteristics of planetary systems are described. Well-known heat sources of evolution are considered. A new type of heat source, variations of kinematic parameters in a dynamical system, is proposed. The inconsistency of the perovskite-post-perovskite heat model is proved. Calculations of inertia moments relative to the D boundary on the Earth are given. The 9 times difference allows us to claim that the sliding of the upper layers at the Earth's rotation speed variations emit heat by viscous friction.This heat is the basis of mantle convection and lithospheric plate tectonics.

scholarly journals Geological archive of the onset of plate tectonics

2018 ◽  
Vol 376 (2132) ◽  
pp. 20170405 ◽  
Author(s):  
Peter A. Cawood ◽  
Chris J. Hawkesworth ◽  
Sergei A. Pisarevsky ◽  
Bruno Dhuime ◽  
Fabio A. Capitanio ◽  
...  
Keyword(s):  
Plate Tectonics ◽  
Foreland Basin ◽  
Sea Floor ◽  
Palaeomagnetic Data ◽  
Peraluminous Granites ◽  
Lithospheric Plates ◽  
Crustal Reworking ◽  
Sea Floor Spreading ◽  
Back Arc ◽  
Earth Dynamics

Plate tectonics, involving a globally linked system of lateral motion of rigid surface plates, is a characteristic feature of our planet, but estimates of how long it has been the modus operandi of lithospheric formation and interactions range from the Hadean to the Neoproterozoic. In this paper, we review sedimentary, igneous and metamorphic proxies along with palaeomagnetic data to infer both the development of rigid lithospheric plates and their independent relative motion, and conclude that significant changes in Earth behaviour occurred in the mid- to late Archaean, between 3.2 Ga and 2.5 Ga. These data include: sedimentary rock associations inferred to have accumulated in passive continental margin settings, marking the onset of sea-floor spreading; the oldest foreland basin deposits associated with lithospheric convergence; a change from thin, new continental crust of mafic composition to thicker crust of intermediate composition, increased crustal reworking and the emplacement of potassic and peraluminous granites, indicating stabilization of the lithosphere; replacement of dome and keel structures in granite-greenstone terranes, which relate to vertical tectonics, by linear thrust imbricated belts; the commencement of temporally paired systems of intermediate and high dT/dP gradients, with the former interpreted to represent subduction to collisional settings and the latter representing possible hinterland back-arc settings or ocean plateau environments. Palaeomagnetic data from the Kaapvaal and Pilbara cratons for the interval 2780–2710 Ma and from the Superior, Kaapvaal and Kola-Karelia cratons for 2700–2440 Ma suggest significant relative movements. We consider these changes in the behaviour and character of the lithosphere to be consistent with a gestational transition from a non-plate tectonic mode, arguably with localized subduction, to the onset of sustained plate tectonics. This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics'.

A Discussion on volcanism and the structure of the Earth - Proposals concerning the variation of volcanic products and processes within the oceanic environment

1972 ◽  
Vol 271 (1213) ◽  
pp. 131-140 ◽  
Keyword(s):  
Structural Model ◽  
Early Stage ◽  
Volcanic Rocks ◽  
Fracture Zones ◽  
Sea Floor ◽  
Stage Of Development ◽  
Incompatible Elements ◽  
The Earth ◽  
Sea Floor Spreading ◽  
Low Pressures

An attempt is made to fit available petrochemical data on oceanic volcanic rocks into the structural model for the ocean basins presented by the plate tectonic theory. It is suggested that there are three major volcanic regimes: (i) the low-potassic olivine tholeiite association of the axial zones of the oceanic ridges where magmatic liquids are generated at low pressures high in the mantle, (ii) the alkalic (Na > K) associations along linear fractures where liquids generated at greater depth gain easy egress to the surface, (iii) those alkalic associations, rich in incompatible elements, of island groups, remote from fracture zones, where magmas created at depth proceed slowly to the surface and in consequence suffer intense fractionation. There are certain discrepancies in this pattern, notably that there is no apparent relation between rate of sea-floor spreading and degree of over-saturation of the axial zone basalts and that certain areas, such as Iceland, are characterized by excess volcanism. Explanation of these anomalies is sought by examining an oceanic area in an early stage of development—the Red Sea. It is tentatively suggested that the initial split of a contiguous continent might be brought about by the linking of profound fractures, caused by domal uplift related to rising isolated lithothermal systems, and that the present anomalies in oceanic volcanism may reflect the variation in rate of thermal convection within the original isolated lithothermal plumes.

scholarly journals 888–444 Ma Global Plate Tectonic Reconstruction With Emphasis on the Formation of Gondwana

2021 ◽  
Vol 9 ◽  
Author(s):  
Christian Vérard
Keyword(s):  
Plate Tectonics ◽  
Additional Data ◽  
Continuous Process ◽  
Tectonic Activity ◽  
Plate Tectonic ◽  
Sea Floor ◽  
Tectonic Model ◽  
The Earth ◽  
Tectonic Reconstruction ◽  
Accretion Rates

The formation of Gondwana results from a complex history, which can be linked to many orogenic sutures. The sutures have often been gathered in the literature under broad orogenies — in particular the Eastern and Western Pan-African Orogenies — although their ages may vary a lot within those wide belts. The Panalesis model is a plate tectonic model, which aims at reconstructing 100% of the Earth’s surface, and proposes a geologically, geometrically, kinematically, and geodynamically coherent solution for the evolution of the Earth from 888 to 444 Ma. Although the model confirms that the assembly of Gondwana can be considered complete after the Damara and Kuunga orogenies, it shows above all that the detachment and amalgamation of “terranes” is a roughly continuous process, which even persisted after the Early Cambrian. By using the wealth of Plate Tectonics, the Panalesis model makes it possible to derive numerous additional data and maps, such as the age of the sea-floor everywhere on the planet at every time slice, for instance. The evolution of accretion rates at mid-oceanic ridges and subduction rates at trenches are shown here, and yields results consistent with previous estimates. Understanding the variation of the global tectonic activity of our planet through time is key to link plate tectonic modeling with other disciplines of Earth sciences.

Sea-floor spreading and plate tectonics

Eos ◽  
1971 ◽  
Vol 52 (5) ◽  
pp. IUGG 130
Author(s):  
W. C. Pitman
Keyword(s):  
Plate Tectonics ◽  
Sea Floor ◽  
Sea Floor Spreading

scholarly journals About this title - Fifty Years of the Wilson Cycle Concept in Plate Tectonics

10.1144/sp470 ◽  
2019 ◽  
Vol 470 (1) ◽  
pp. NP-NP
Keyword(s):  
Mantle Convection ◽  
Plate Tectonics ◽  
Physical Processes ◽  
Mantle Dynamics ◽  
Tectonic Inheritance ◽  
The Earth ◽  
Geological Evolution ◽  
Wilson Cycle ◽  
Opening And Closing ◽  
Orogenic Belts

Fifty years ago, Tuzo Wilson published his paper asking ‘Did the Atlantic close and then re-open?’. This led to the ‘Wilson Cycle’ concept in which the repeated opening and closing of ocean basins along old orogenic belts is a key process in the assembly and breakup of supercontinents. The Wilson Cycle underlies much of what we know about the geological evolution of the Earth and its lithosphere, and will no doubt continue to be developed as we gain more understanding of the physical processes that control mantle convection, plate tectonics, and as more data become available from currently less accessible regions.This volume includes both thematic and review papers covering various aspects of the Wilson Cycle concept. Thematic sections include: (1) the Classic Wilson v. Supercontinent Cycles, (2) Mantle Dynamics in the Wilson Cycle, (3) Tectonic Inheritance in the Lithosphere, (4) Revisiting Tuzo's question on the Atlantic, (5) Opening and Closing of Oceans, and (6) Cratonic Basins and their place in the Wilson Cycle.

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