The forces driving plate motions and compression of the crust in fold belts

Tuzo Wilson introduces the concept of transform faults, which has the effect of transforming Earth Science forever. Resistance to the new ideas is finally overcome in the late 1960s, as the theory of moving plates is established. Two scientists play a major role in quantifying the embryonic theory that is eventually dubbed ‘plate tectonics’. Dan McKenzie applies Euler’s theorem, used previously by Teddy Bullard to reconstruct the continents around the Atlantic, to the problem of plate rotations on a sphere and uses it to unravel the entire history of the Indian Ocean. Jason Morgan also wraps plate tectonics around a sphere. Tuzo Wilson introduces the idea of a fixed hotspot beneath Hawaii, an idea taken up by Jason Morgan to create an absolute reference frame for plate motions.

Download Full-text

Feedbacks between a non-Newtonian upper mantle, mantle viscosity structure and mantle dynamics

Geophysical Journal International ◽

10.1093/gji/ggaa495 ◽

2020 ◽

Vol 224 (2) ◽

pp. 961-972

Author(s):

A G Semple ◽

A Lenardic

Keyword(s):

Upper Mantle ◽

Lower Mantle ◽

Mantle Convection ◽

Mantle Flow ◽

Mantle Dynamics ◽

Plate Motions ◽

Low Viscosity ◽

Mantle Viscosity ◽

Flow Feature ◽

Mantle Rheology

SUMMARY Previous studies have shown that a low viscosity upper mantle can impact the wavelength of mantle flow and the balance of plate driving to resisting forces. Those studies assumed that mantle viscosity is independent of mantle flow. We explore the potential that mantle flow is not only influenced by viscosity but can also feedback and alter mantle viscosity structure owing to a non-Newtonian upper-mantle rheology. Our results indicate that the average viscosity of the upper mantle, and viscosity variations within it, are affected by the depth to which a non-Newtonian rheology holds. Changes in the wavelength of mantle flow, that occur when upper-mantle viscosity drops below a critical value, alter flow velocities which, in turn, alter mantle viscosity. Those changes also affect flow profiles in the mantle and the degree to which mantle flow drives the motion of a plate analogue above it. Enhanced upper-mantle flow, due to an increasing degree of non-Newtonian behaviour, decreases the ratio of upper- to lower-mantle viscosity. Whole layer mantle convection is maintained but upper- and lower-mantle flow take on different dynamic forms: fast and concentrated upper-mantle flow; slow and diffuse lower-mantle flow. Collectively, mantle viscosity, mantle flow wavelengths, upper- to lower-mantle velocities and the degree to which the mantle can drive plate motions become connected to one another through coupled feedback loops. Under this view of mantle dynamics, depth-variable mantle viscosity is an emergent flow feature that both affects and is affected by the configuration of mantle and plate flow.

Download Full-text

The mid-Paleozoic deformation in the Hazen fold belt, Ellesmere Island, Arctic Canada

Canadian Journal of Earth Sciences ◽

10.1139/e90-146 ◽

1990 ◽

Vol 27 (10) ◽

pp. 1359-1370 ◽

Cited By ~ 12

Author(s):

Eva M. Klaper

Keyword(s):

Large Scale ◽

Ellesmere Island ◽

Small Scale ◽

Northwestern Part ◽

Fold Belt ◽

Southeastern Part ◽

Lower Paleozoic ◽

Slip Mechanism ◽

Fold Belts ◽

Surface Geology

The mid-Paleozoic deformation of lower Paleozoic subgreenschist-facies sediments of the Hazen fold belt in northern Ellesmere Island is represented predominantly by chevron-style folding. Folded multilayers display cleavage fans suggesting synchronous fold and cleavage formation. Bedding-parallel slip indicates a flexural slip mechanism of folding. The geometry of several large-scale anticlinoria has been interpreted as being due to formation of these structures over detachments and thrust ramps.The constant fold geometry, the parallel orientation of faults and large- and small-scale folds, and the axial-plane foliation are related to a single phase of folding with a migrating deformation front in the Hazen fold belt during the mid-Paleozoic orogeny. The minimum amount of shortening in the Hazen and Central Ellesmere fold belts has been estimated from surface geology to increase from 40–50% of the original bed length in the external southeastern part to 50–60% in the more internal northwestern part of the belts.The convergent, thin-skinned nature of the Hazen and Central Ellesmere fold belts indicates that the postulated transpressive plate motions during the accretion of Pearya did not affect the study area.

Download Full-text

Present tectonic-plate motions from lunar ranging

Tectonophysics ◽

10.1016/0040-1951(75)90127-4 ◽

1975 ◽

Vol 29 (1-4) ◽

pp. 1-7 ◽

Cited By ~ 7

Author(s):

P.L. Bender ◽

E.C. Silverberg

Keyword(s):

Tectonic Plate ◽

Plate Motions

Download Full-text

Fold Belts: Shall We Expect a Shift in Petroleum Exploration Priorities? (Russian)

10.2118/176609-ru ◽

2015 ◽

Author(s):

K. O. Sobornov ◽

A. P. Afanasenkov ◽

V. N. Danilov ◽

V. A. Zhemchugova ◽

Yu. A. Volozh

Keyword(s):

Petroleum Exploration ◽

Fold Belts

Download Full-text

Studying oceanic plate motions with magnetic data

Eos ◽

10.1029/94eo00658 ◽

1994 ◽

Vol 75 (5) ◽

pp. 49 ◽

Cited By ~ 1

Author(s):

Gary D. Acton ◽

Katerina E. Petronotis

Keyword(s):

Magnetic Data ◽

Oceanic Plate ◽

Plate Motions

Download Full-text

Geophysical perspective on the structural interference zone along the Neoproterozoic Brasília and Ribeira fold belts in West Gondwana

Brazilian Journal of Geology ◽

10.1590/2317-4889201720160144 ◽

2017 ◽

Vol 47 (1) ◽

pp. 3-19

Author(s):

João Gabriel Motta ◽

Norberto Morales ◽

Walter Malagutti Filho

Keyword(s):

Bouguer Anomaly ◽

Shear Zones ◽

Magnetic Data ◽

Gravity Modeling ◽

West Gondwana ◽

Fold And Thrust Belt ◽

Fold Belts ◽

Thrust Sheets ◽

Anomaly Map ◽

Bouguer Anomaly Map

ABSTRACT: The Brasília and Ribeira fold belts have been established in south-southwestern São Francisco Craton during the Brasiliano-Pan African orogeny (0.9-0.5 Ga - Tonian to Cambrian), and played an important role in West Gondwana continent assembly. The region is given by a complex regional fold and thrust belt superposed by shearing during the orogeny late times, with superposing stress fields forming a structural interference zone. These thrust sheets encompasses assemblies from lower- to upper-crust from different major tectonic blocks (Paranapanema, São Francisco), and newly created metamorphic rocks. Re-evaluation of ground gravity datasets in a geologically constrained approach including seismology (CRUST1 model) and magnetic data (EMAG2 model) unveiled details on the deep- crust settings, and the overall geometry of the structural interference zone. The Simple Bouguer Anomaly map shows heterogeneous density distribution in the area, highlighting the presence of high-density, high metamorphic grade rocks along the Alterosa suture zone in the Socorro-Guaxupé Nappe, lying amid a series of metasedimentary thrust scales in a regional nappe system with important verticalization along regional shear zones. Forward gravity modeling favors interpretations of structural interference up North into Guaxupé Nappe. Comparison to geotectonic models shows similarities with modern accretionary belts, renewing the discussion.

Download Full-text