Analytic models for the dynamics of diffuse oceanic plate boundaries

Zatman, Stephen; Gordon, Richard G.; Richards, Mark A.

doi:10.1111/j.1365-246x.2001.00357.x

Cited by 32 publications

(46 citation statements)

References 24 publications

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“…yield‐stress) end‐member rheologies (i.e. n = 1 and n →∞; Zatman et al 2001). These models show that the pole of relative rotation between component plates is unlikely to lie outside their mutual diffuse boundary irrespective of rheology.…”

Section: Introductionmentioning

confidence: 75%

“…A key reason why the pole of rotation tends to lie in the diffuse plate boundary is geometrical (Zatman et al 2001; Fig. 1).…”

Section: Geometrical Effectsmentioning

confidence: 99%

“…If the torque components ( T x , T y and T z ) are roughly the same size, ω x and ω y will be about the same size as each other, but ω z will be approximately 2 orders of magnitude larger than the other two. Specifically, for the Newtonian case, ω z would be about a factor f = 12/ L 2 times greater than ω x , where L is the arc length in radians of the diffuse boundary (Zatman et al 2001). Observed values of L for diffuse oceanic plate boundaries range from approximately 0.25 to 0.5 rad (about 15° to 30°), giving a scale factor of approximately 50 to 200.…”

Section: Geometrical Effectsmentioning

confidence: 99%

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Dynamics of diffuse oceanic plate boundaries: insensitivity to rheology

Zatman¹,

Gordon

Mutnuri

2005

Geophysical Journal International

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S U M M A R YDiffuse plate boundaries, which are zones of deformation hundreds to thousands of kilometres wide, occur in both continental and oceanic lithosphere. Here, we build on our prior work in which we described analytic approximations to simple dynamical models that assume that the vertically averaged viscous force resisting deformation in diffuse oceanic plate boundaries (DOPBs) is described by either a linear Newtonian viscous rheology or a yield-stress (highexponent power-law) rheology.An important observation is that the poles of relative rotation of adjacent component plates tend to lie in the diffuse plate boundary that separates them. A key cause of this tendency is that a faster spin is needed to balance a component of torque through the middle of a diffuse plate boundary than to balance an equal component of torque lying 90 • from the middle of the diffuse boundary. The strength of that tendency depends on rheology, however, with the tendency being stronger for a yield-stress rheology than for a Newtonian viscous rheology. For the special case of the pole of rotation lying outside of and along the strike of the boundary, these large differences can be simply explained in terms of the distribution of boundary-perpendicular normal forces acting across the boundary. In the Newtonian case, the distribution of forces has an along-strike gradient that can balance a component of torque about the middle of the boundary, while in the yield-stress case, the distribution of forces has zero along-strike gradient and cannot balance a component of torque about the middle of the diffuse plate boundary.To expand our analysis to intermediate power laws of geophysical interest (i.e. power-law exponents of 3 to 30), as well as to investigate more thoroughly the behaviour for a highexponent power law, we numerically integrate the force distribution to obtain the torques. Results for intermediate power laws resemble the yield-stress rheology much more than they resemble the Newtonian rheology and depend only weakly on the width of the deforming zone. To quantify the probability that a pole of rotation lies in a diffuse plate boundary, we numerically integrate the expectation assuming that all orientations of torque are equally probable. For a power-law exponent of n = 10: 49 per cent of possible torque orientations produce angular velocities outside the diffuse plate boundary if the boundary is 55 • long (similar in length to the boundary between the Nubian and Somalian component plates); 21 per cent of possible torque orientations produce angular velocities outside the diffuse plate boundary if the boundary is 30 • long (similar in length to the boundary between the Indian and Capricorn component plates and to that between the Capricorn and Australian component plates); and 6 per cent of possible torque orientations produce angular velocities outside the diffuse plate boundary if the boundary is 15 • long (similar in length to the boundary between the North American and South American component plates and to that bet...

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Section: Introductionmentioning

confidence: 75%

“…A key reason why the pole of rotation tends to lie in the diffuse plate boundary is geometrical (Zatman et al 2001; Fig. 1).…”

Section: Geometrical Effectsmentioning

confidence: 99%

Section: Geometrical Effectsmentioning

confidence: 99%

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Dynamics of diffuse oceanic plate boundaries: insensitivity to rheology

Zatman¹,

Gordon

Mutnuri

2005

Geophysical Journal International

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“…Dated samples with ages of 7-2 Ma show that in eastern Iceland, La/Sm and 87 Sr/ 86 Sr ratios decreased through time but in western Iceland, they increased, suggesting that the same mantle was not tapped in the two areas (Schilling et al, 1982). Like the Easter microplate, the Iceland region is a "diffuse oceanic spreading plate boundary" containing two triple junctions (Zatman et al, 2001). Why such plate boundary configurations develop at a few places on Earth is not understood.…”

Section: Volcanic History Of the North Atlantic Regionmentioning

confidence: 97%

Genesis of the Iceland melt anomaly by plate tectonic processes

Foulger¹,

Natland²,

Anderson³

2005

Plates, Plumes and Paradigms

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Iceland is the best studied, large-volume, active volcanic region in the world. It features the largest subaerial exposure of any hotspot at a spreading ridge, and it is conventionally attributed to a thermal plume in the mantle. However, whereas the apparently large melt productivity and low-wavespeed mantle seismic anomaly are consistent with this attribution, at any more detailed level, the observations are poorly predicted by the plume hypothesis. There is no time-progressive volcanic track, the melt anomaly having been persistently centered on the Mid-Atlantic Ridge. Spatial variations in crustal structure are inconsistent with the southeastward migration that is required of a plume fixed with respect to other Indo-Atlantic hotspots. The mantle seismic anomaly weakens with depth and does not extend into the lower mantle. Estimates of excess temperature using a broad range of methods are inconsistent with a mantle potential temperature anomaly greater than a few tens of K. Much of the lava erupted in Iceland has geochemistry little different from normal mid-ocean ridge basalt, and the detailed spatial geochemical pattern bears little resemblance to what is predicted for a plume beneath central Iceland. We propose an alternative model in an attempt to explain the observations at Iceland with fewer difficulties. Our model involves only shallow plate tectonic processes and attributes the large melt volume to the remelting of subducted oceanic crust trapped in the Caledonian suture in the form of eclogite or mantle peridotite fertilized by resorbed eclogite. Delaminated continental mantle lithosphere may also be involved. Such a source can produce several times more melt than pure peridotite without the need for high temperatures. The longevity of anomalous volcanism at the Mid-Atlantic Ridge at the latitude of Iceland is attributed to its location on a Caledonian structure that runs transversely across the north Atlantic. Many aspects of the geochemistry of Icelandic lavas fit this model, which also provides an explanation for the high maximum helium isotope ratios observed there. The "depleted plume component" may be derived from abyssal olivine gabbro cumulates and the "enriched plume component" from recycled enriched material that forms part of the crustal section of subducted slabs. Such a model for the Iceland melting anomaly raises new questions concerning how much thermal energy can be generated by isentropic upwelling of eclogite at a ridge, the location of the homogenizing 595 *on June 18, 2015 specialpapers.gsapubs.org Downloaded from reservoirs required, and the mechanism by which fertile material is incorporated into the asthenosphere beneath new oceans. Most fundamentally, if validated, such a model can explain the generic observations associated with hotspots as shallow processes associated with plate tectonics, and thus raises the question of whether thermal plumes are required in general in the Earth.

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“…When compared to predictions of stress modeling, it is seen that areas of high deviatoric compression roughly correspond with regions of observed crustal contraction, whereas areas predicted to have high deviatoric extension correspond to regions where stretching seems to be occurring. Work by Zatman et al (2001Zatman et al ( , 2005 indicates that the location of such rotation poles within the diffuse boundary is favored by both geometric and rheological arguments. The predicament of the Indo-Australian Plate is not unique.…”

Section: Diffuse Plate Boundariesmentioning

confidence: 99%

Plate Tectonics

Wessel

2015

Treatise on Geophysics

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Analytic models for the dynamics of diffuse oceanic plate boundaries

Cited by 32 publications

References 24 publications

Dynamics of diffuse oceanic plate boundaries: insensitivity to rheology

Dynamics of diffuse oceanic plate boundaries: insensitivity to rheology

Genesis of the Iceland melt anomaly by plate tectonic processes

Plate Tectonics

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