what is the main driving force that causes earths tectonic plates to drift?
Arlo Brandon Weil
Academy of Michigan, Ann Arbor, MI
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Tabular array of Contents
INTRODUCTION "In science a phenomenon or a hypothesis can become so familiar and its utility in providing as explanation, or consistent description of a greater number of diverse facts so axiomatic, that the underlying machinery may often be left unstudied"
(Runcorn, 1980)
WHAT Drives Plate Tectonics ???? This question has been the subject area of intense debate e'er since the plate tectonic theory was starting time eccepted past the geologic community in the late 1960'southward. The major concern is whether pall convection and the activity of mantle plumes boss the driving forces of plate motion, or whether surface boundary and plate forces, such as slab pull and ridge button provide the nearly important forces. The argument is basically whether the plates are passively riding along on the acme of a drape convection cell, or whether the plates themselves the active drivers, dragging along with them the mantle beneath.
To begin understanding and evaluating the different forces involved in the plate tectonic process, we must first isolate these forces and define their physical and mechanical properties. Once nosotros have done that, nosotros must brand sure that any hypothesis or model that we devise to produce these forces is compatible with the observations and characteristics that we know and empathise about the Earth. Mainly, is the model (ane) compatible with the rigid behavior of lithospheric plates, (2) compatible with the wide diverseness of plate sizes, geometry, type, and motion; does it (3) satisfy the beingness of complex plate boundary conditions, (four) provide enough free energy to account for all the motility; is it able to (5) produce the observed tectonic stresses observed in the upper lithosphere; and does information technology (6) satisfy the long-lived steady state relative plate motions (on the order of tens of millions of years), besides as sudden dramatic changes in motility nosotros observe from modeled plate reconstructions (i.eastward., the Pacific plate circa 43 Ma).
With this basic set of plate driving force parameters and conditions developed, nosotros can try to relate our predicted forces dorsum to the causal effects of tectonics at the Earth's surface. To date, our best tool for observing the effects of plate driving forces (PDF'southward) is the existence of large-scale tectonic stresses. Tectonic stresses effect from plate driving forces. Therefore, using measured data for the Globe's lithosphere, we can begin to think quantitatively nigh the different magnitudes of the involved forces.
There are several methods one can use to quantify PDF's, namely: (1) finite element deformation modeling, using the inter-plate stress fields to constrain the driving forces, (two) empirical mathematical relationships betwixt plate boundaries, plate historic period, type, and velocity, and (3) active Net Torque analysis. Compared to the others, the last method does a better job at accounting for all the big number of agile forces too as the complex boundary atmospheric condition and plate characteristics that our PDF model must satisfy.
Using a combination of the known tectonic stresses along with a quantified force relationship, we should be able to devise an accurate account of all the active forces involved in today's plate motion. In addition, nosotros should better empathize the magnitude scale for the unlike categories of curtain and plate forces.
As stated earlier, in order to fully empathize what drives the lithospheric plates of the Earth, we must showtime identify and empathise the forces involved. A number of forces take been postulated since the dawn of the tectonic theory, including ridge push, slab pull, trench suction, collisional resistance, and basal drag (Forsyth et al., 1975; Richardson, 1992). In the past x years, many scientists have begun to assume that the boundary and body forces of the plates, rather than the frictional drag produced by mantle convection, are the most dominant grouping of forces driving plate motions. In the post-obit department, the basic physical properties of each of the primary forces believed to be involved in the total cyberspace motion of plates will be described and defined (fig.1).
Figure 1: Bones schematic of unlike Plate Driving Forces.
Ridge Push (fig. 2) has been considered in ii different manners, every bit a body force and as a purlieus force. Every bit a body force, ridge push has been attributed to the cooling and thickening of the oceanic lithosphere with age (McKenzie, 1968; McKenzie, 1969; Richards, 1992; Vigny et al., 1992). This blazon of forcefulness tin can be thought of equally created by the horizontal pressure gradient attributable to the cooling and thickening of the oceanic lithosphere, and calculated as this force integrated over the area of the oceanic portion of a given plate (Lister, 1975). In this respect, Ridge Push can be considered a body forcefulness, rather than a boundary force acting over the oceanic part of a plate (Wilson, 1993). When making such a adding still, i must have into account that oceanic lithosphere older than ninety Ma is no longer cooling significantly, and therefore not contributing to the effective ridge push button force (Ziegler, 1993). The alternative, Ridge Push button as a purlieus force, is caused past the "gravity wedging" upshot ( Bott, 1993). This effect results from warm, buoyant mantle upwelling below the ridge crest which causes a topography-induced horizontal pressure level gradient. Here the force would be acting as a boundary strength at the edge of the lithospheric plate, proportional to the length of the ridge, and not every bit a body force over the entire oceanic portion of the plate. In both of the above cases Ridge Button would be amplified, past equally much as a factor of two when hot spot activeness is centered on a spreading ridge axis (Ziegler, 1993). This is important when considering the effects of ridge push as a cumulative force interim on all the plates, and must exist taken into account in whatsoever internet strength calculations.
Figure ii: Schematic of Ridge Button forces.
The Slab Pull (fig. 3) forces are derived from the negative buoyancy of the cold subducting lithosphere and are dependent on the bending, temperature, age and volume of the subducting slab, as well every bit the length of the respective trench (Chapple and Tullis, 1977). Slab Pull is considered a boundary forcefulness, and from nearly estimates is responsible for some of the largest forces, or torques in the driving organization (Wilson, 1993). Several empirical studies accept shown a strong correlation between plate velocities and age of subducting oceanic lithosphere for plates with long subduction boundaries (Forsyth and Uyeda, 1975; Chapple and Tullis 1977). This might suggest that slab pull is the ascendant interim force. Withal, there are several plates that have petty or no portion of their boundaries subducting and it is therefore important to look for other contributing forces.
Figure iii : Schematic of Slab Pull and Collisional Resistance forces.
Related very closely to Slab Pull is Collisional Resistance (fig. three). For every subducting slab there is an associated resistive force provided by the relatively high viscosity of the warmer, more than ductile upper drapery. Together, the negative buoyancy of the sinking slab and the resistive nature of the slab entering the mantle is chosen the Net Slab Force. The sum of these two forces is exerted at the colliding margin (Ziegler, 1992) and contributes to the intra-plate stress field of the surface plates (Wilson, 1993). Alternatively, recent work has shown that the slab forces may exist largely counterbalanced within the slab itself and contribute relatively little to the deformation of the surface plates (Richards, 1992).
Trench Suction (fig. iv) forces are observed in the overriding plate at subduction zones as a net trenchward pull, often times resulting in back arc extension (Forsyth and Uyeda, 1975; Chase, 1978). Trench Suction is thought to effect from small-scale convection in the drape wedge, driven by the subducting lithosphere. This force is hard to isolate from other forces because of how little we know about mantle convection in the shallow subsurface (Ziegler, 1993). Related to Trench Suction is Slab Roll-Back. This is caused by the modest convection current on the back-side of subducting slabs. We see this phenomena today in the Hellenic Arc of Hellenic republic, and possibly in the western Pacific. This current produces a pull abroad from the trench, consequently rolling back the hinge of the subducting slab. Both trench suction forces can be thought of as a conservation of matter argument requiring an asthenospheric counter-current in the wedge-shaped region between the downward-going slab and the upper plate. Information technology is this counter-current that will result in the trenchward pull of the overriding plate (Chapple and Tullis, 1977).
Figure four: Schematic of Trench Suction forces.
Plate Tectonic Resistive forces (fig.v) are exerted on the overriding plate in a subduction zone at the contact with the descending slab. This force is thought to event in a shear stress that is distributed over the subduction thrust interface, that dips in the direction of the plate's interior (Wilson, 1993). Even so, tectonic resistive forces are considered equal and opposite in sign to the forcefulness exerted on the subducting plate, and therefore do non contribute greatly to the net driving forcefulness for plate motion (Meijer and Wortel, 1992).
The final major strength, Basal Shear Traction or Basal Drag (fig. 5) is important because of its relevance to the primal question of whether plate motions are active or passive. Basal Shear Traction is the resistance or dragging force associated with the interface between the upper mantle and the lithosphere. Today this strength is thought to be small, just until we know more nearly the coupling between the lithosphere and the mantle is better constrained, we cannot be sure how important information technology is. It is idea to take a small magnitude per unit surface area, merely when spread over the entire under-surface of large plates can result in a big cumulative resistance.
Effigy 5 : Schematic of Plate Tectonic ans Basal Shear Traction Resistive forces.
The lack of practiced correlation betwixt plate velocity and surface area has traditionally been used to argue against Basal Shear Traction (BST) as an important driving forcefulness. In recent models researchers have considered BST a passive force, either driving or resisting plate movement, but not dominating plate move (Richardson, 1992). The contribution of BST on the movement of plates depends on whether the menses pattern at the lithosphere-mantle interface is radial or unidirectional and parallel or anti-parallel with respect to the overlying plate motions (Forsyth and Uyeda, 1975; Doglioni, 1990). However, the mechanical nature of this interface and its flow design are unknown. Other researchers are advocates of elevate forces playing an important office in driving plate motion, while the plates remain passive (Vlaar et al., 1976; Jacoby et al., 1980). In this case the lateral motion of the plates would exist caused by the drapery's exertion of a drag strength on the overriding lithosphere, in a higher place warm upwellings, which would later on create a deviatoric stress authorities. Here, the Shear Traction is estimated to exist modest per unit expanse and would be proportional to the horizontal, or toroidal, component of the upper-mantle'due south flow velocity relative to the overlying plate velocity (Ziegler, 1993). But it is of import to point out that the mechanics of upper-drapery period are poorly constrained at this time.
We must now seek out information on the subsequent effects, or in geologic terms, the associated stress related to these forces. In lodge to practice this it is very important that we sympathise the regional patterns of the nowadays-24-hour interval tectonic stress field. Tectonic stresses are those stresses produced past the forces that bulldoze plate tectonics (Middleton et al., 1996). Because of their integral relationship to the present motility of plates, the magnitude and management of tectonic stress is very difficult to predict unless we can measure recent tectonic movement or seismic activity. In society to distinguish a measured tectonic stress from those stress fields that are locally derived, nosotros must await at the spatial uniformity of the in situ stress field. For tectonic stresses the stress fields are typically uniform over distances many times (ii to more than 100 times) the thickness of the elastic function of the lithosphere, while local stresses are merely a fraction of that same thickness (Zoback et al., 1989). Information technology is also found that for tectonic fields the 3 principal stresses prevarication in approximately horizontal and vertical planes, with the horizontal stress component almost always larger than the vertical component. As a issue the orientation of the principal stress axes of the measured stress tensor tin be constrained by specifying the management of just one of the horizontal principle stresses (Zoback, 1989). This is convenient for recording and measuring crustal stresses.
One time measured, tectonic stresses tin give valuable information about the forces acting on the plates and therefore the dynamics of plate tectonics. A grouping of some 30 scientists from all over the globe, headed by Mary Lou Zoback, accept created a working database of in situ stress measurements for most of the Earth'due south lithospheric plates. They collected over 7300 in situ stress measurements, of which 4400 are considered tectonic stresses. These measurements were taken from diameter-hole breakouts, hydraulic fractures, style of active faulting, volcanic alignment, seismic focal mechanisms, and transform mistake azimuths. The unabridged database then underwent a scrutinous quality rating to asses the reliability of the individual information, with any unsatisfactory data discarded (Zoback, 1989; Zoback, 1992).
The Globe Stress Map Projection (WSMP), because of its huge database, has provided significant advocacy in our efforts to determine he relative importance of different plate driving forces (fig. 6). The project has as well provided constraints on the magnitude of both broad scale and local stresses interim on the lithosphere. Subsequent analysis has shown that a majority of the data can be fairly explained by the geometry of plate boundaries and the conventional ridge push, slab pull, and subduction forces, and practise non necessarily crave a significant contribution from sublithospheric mantle flow inferred from seismic tomography (Zoback and Magee, 1991; Wilson, 1993). It appears that regionally uniform horizontal intra-plate stress orientations are consequent with either relative or accented plate motions indicating that plate-boundary and body forces must be the dominant contributors to the stress distribution within plates (Zoback, 1989; Zoback, 1992).
Figure vi : World Stress Map Project'south averaged maximum stress data (red arrows). Color contour representative of height. After Zoback et. al. (1992) .
Numerous observations advise that elevate forces and resisting forces do non strongly control the stress field of the uppermost brittle part of the lithosphere. The general state of compression in the old oceanic lithosphere (older than ~lxxx Ma) indicates that the integrated ridge push force dominates over the associated pall drag forces (Richards et al., 1992). As well, the predicted stresses related to whole mantle menses inferred from seismic tomography practise non match well with the broadest scale tectonic stress information, especially when compared to the correlation of the boundary and trunk forces with tectonic directions (Zoback, 1992).
Correlations betwixt the Globe Stress Map's tectonic stress measurements and PDF's were immediately obvious after the measurements were plotted on a map of the Globe's plate boundaries. Normal faults that showed maximum tension perpendicular to ridge crests were seen for virtually of the globe'due south spreading ridges. Old oceanic crust (>35 Ma) experiences mainly thrust or strike-sideslip faulting. This tectonic manner is consequent with an intra-plate stress field dominated by pinch associated with the internet slab and/or ridge forces. Orientations of compressional stresses which dominate the interiors of most continental cratons, nearly importantly North America and Western Europe, are like to those predicted for ridge push and slab forces (Zoback, 1992; Richards, 1992). Furthermore, stress measurements show, on a broad scale, stress fields changing in manner (i.e. compressional to tensional) over individual plates with a tendency for the maximum horizontal stress direction (Sh Max) to be parallel to the absolute plate motion. This last fact is an important ascertainment which directly relates to the relationship between plate purlieus and trunk forces and the motion of plates. Using the evidence provided by the WSMP that plate boundary and body forces appear to boss the driving mechanism of plate motion, the next step is to quantify the different magnitudes of the individual PDF's.
Before we brainstorm to tackle the problem of quantifying PDF's, we must understand the inherent difficulty in making inferences near plate driving motions from kinematics. The difficulty lies in the physical equation that states that the motion of a rigid plate is the integrated result of all summed individual torques acting on that plate. The magnitudes of these individual torques, however, are non-unique and unconstrained. The simple example below shows how different combinations of coefficients, or in this case scalar magnitudes of torque, can lead to the aforementioned event.
Instance:
xTA + yTB + zTC + wTD = 0
one + iii + -two + -2 = 0
2 + 2 + 2 + -vi = 0
Another difficulty with using belittling or numerical methods to account for the large group of PDF'due south is the complexity of the multiple plate purlieus weather and relations. Withal, it has been shown that against an absolute reference frame we tin can come upwardly with a relatively authentic solution (Forsyth and Uyeda, 1975; Carlson et al., 1983). Past solving an inverse trouble with a known absolute move reference frame, nosotros tin estimate relative magnitudes for private plate driving forces.
There are essentially three different techniques geologists and geophysists use in order to quantify the unlike plate driving forces. Deformational modeling studies using intra-plate stress fields were popular in the belatedly 1970'south and early 1980's. Some of the earlier attempts included Solomon et al. (1975), Richards et al. (1975), and Bott (1991). These studies used finite element models in an attempt to predict both global and single plate motions based on the forces driving and resisting the private plates. The results of these models worked well for individual boundaries and even for some of the private plates, but integrated over the entire globe, the model bankrupt down and did not fairly account for all of the appropriate complex boundary conditions. A second approach was based on empirical relationships between plate size, age, type, geometry, motion, and velocity (Forsyth and Uyeda, 1975; Carlson et al., 1983). From these relationships strong correlations between plate velocities and the age of oceanic lithosphere were derived. However, this method did non let for other types of forces other than those associated with the subducting slab, such as basal elevate, tectonic resistance, etc.
The third arroyo, and the method I feel to be the near important and informative, is the Internet Torque Method. This technique studies the driving mechanism of plate move by balancing the net torque interim on each plate (Forsyth and Uyeda, 1975; Chapple and Tullis, 1977). The advantage of this method is the incorporation of all Plate Driving Forces into the equation, both driving and resistive. Inherent is the of import concept that the net torque acting on a plate is ultimately responsible for a plate's movement.
The laws of rigid trunk rotation state that if there is no dispatch and/or inertia interim on that torso, and so all applied forces, or torques, must sum to zero. It follows that the net torque acting on that trunk must too be naught, past definition. This is Newton'due south second law of motility which states that the acceleration of whatever object is straight proportional to the net force acting on it, and inversely proportional to its mass. This property is central in determining the relative magnitudes of the torques acting on an individual plate (fig. 7).
Figure 7 : Schematic diagram showing the different mathematical components of a torque acting on a lithospheric plate. (R) is the radial distance from the axis of rotation, or lever arm distance, (Beta) is the co-latitude position of the plate boundary, and (alpha) is the bending between the strike of the boundary and the azimuth to the pole of the torque axis. Figure taken from Forsyth and Uyeda (1975). At that place are several bones assumptions that must be made in society for the Internet Torque Model to work. Information technology is assumed that the inertia and acceleration of the individual plates are nonexistent or negligible, and thus the platesouthward are in dynamic equilibrium. The boundary and trunk forces, for this problem, are considered the main driving forces equally opposed to agile-mantle flow. And lastly, because the plates are confined to move on the surface of the earth, their respective motions are, by definition, described every bit a rotation about an axis passing through the center of the Earth. If, as assumed, there is no acceleration, the sum of the internet torques will add to zero.
Equation 1: Basic equation showing that the product of the lever arm distance, or radial distance from center of rotation, and the applied force equals zero when summed over a plate of expanse (P) . With these assumptions we can and then determine the relative magnitudes of the forces that minimize the net torque acting on each plate. The inverse problem that determines the relative strengths of each of the different PDF's is solved with respect to an inferred absolute reference frame. Today the earth's hot spots are our best source for an accented plate movement reference frame. In this case we are assuming the mantle is fixed with respect to the Earth's axis of rotation. To solve the changed problem a matrix must be created with the known number of forces and plates and the unknown scalars for the different forces. The bones equation is then solved for each plate in three dimensions as follows:
Equation 2 : Variables are listed below. where northward is the number of forces acting on the plate, tenij is the coefficient of magnitude (scalar) of the jth force, and aij holds all the physical and geometrical constants of the plate. If there is a existent solution, the determinant must equal zero. Once the possibility of a real solution is found, the next pace is to solve for the unknowns (xij ) by a least squares method. Since we know the solution to the scaled matrix is nada, a least squares method can be used to retrieve n eigenvectors for which several eigenvalues can be found. Here is where a problem arises. As a upshot to the beingness of several solutions, or eigenvalues for each scalar (xij ) , the coefficients become non-unique. However, the degree to which the solution is non-unique tin be estimated and minimized.
The non-unique solution may at commencement glance exist perceived as a huge drawback, simply the relative magnitude of the forces involved are constitute with accurateness. In 2 of the virtually referenced torque studies, Forsyth and Uyeda (1975) and Tullis and Chapple (1973), the pulling of the slab and the collisional resistance from the drape provide the ascendant role in controlling plate motion. The remaining forces for these ii models take the same relative magnitude, and thus can not exist uniquely determined. A more than detailed assay of the least squared no net torque method tin can be found in Forsyth and Uyeda (1975) and Tullis and Chapple (1973).
Richards (1992) did a detailed Net Torque assay combined with data from the World Stress Map Project to better understand and resolve the remaining force magnitudes (fig. 8). He constitute that the ridge push strength exhibits a strong correlation with the azimuth of the absolute velocity of the plates. This correlation suggests an alternative explanation for the alignment of intra-plate stresses and absolute plate motion. The relationship between ridge push forces on intra-plate stresses is besides consistent with slab forces being an important component of the plate driving mechanism. Considering of the equal and opposite nature of the slab pull and collisional resistant forces, the sum net slab strength contributes relatively piffling to the deformation, or stress field, of the surface plates. Therefore other forces must business relationship for our observations, namely ridge push.
Figure 8: Diagram from Richards, (1992) showing Ridge Boundaries and Force Directions in the top diagram, and Ridge Torque (black arrows) vs. Absolute Velocity (light-green arrows) in the lower diagram. Discover the squeamish correlation betwixt the two vector directions.
To the question, "What drives plate tectonics?" we have presented two options: (1) mantle convection, and (2) lithospheric plate boundary and body forces. It is in the opinion of this writer that information technology is the plates themselves that are the dominant source of strength involved in the accented movement of the lithospheric plates over the surface of the Globe. The strong correlations between observed tectonic stress and absolute plate motions shown past the World Stress Map Projection point directly to the present lithospheric stress fields being dominated past the private plate purlieus and body forces (Zoback et al., 1989, Zoback, 1992). These observations, along with the Net Torque Model, permit us to begin to put a coherent story together in terms of the relative magnitudes of different PDF's. Although the slab forces (slab pull and collisional resistance) dominate the other PDF's, their equal and contrary nature allows ridge push to be the most important appreciable plate driving forcefulness.
This solution for Plate Driving Forces works for today, only what about the by? Did slab and ridge forces always dominate, and did they always boss in that order? These questions are important when considering the driving forces backside plate movement over time. Plates must rearrange themselves throughout supercontinent cycles, continuously changing the constructive and subversive nature of their boundaries. Information technology is logical to assume then that these changes in the interactions and movements of plates must besides modify the relative importance of unlike PDF'south in time and space. Information technology follows so that the forces that drive plates are depenent on the nature of boundary conditions and plate arrangement through fourth dimension.
There are still many unanswered questions related to PDF'due south. Can plate driving forces be responsible for the breakup of supercontinents? Are plate purlieus and/or plate torso forces responsible for the initiation of subduction zones and spreading ridges? Most researchers believe in these special cases, drape forces related to large convection cells must dominate the driving forces (Jacoby, 1980; Carlson et al, 1983;Wilson, 1991; Zeigler, 1991). So, in a sense, it is considering of the present status that nosotros have today'due south magnitudes and effective forces, and through time the ascendant forces will change from plate to drape and back. Afterwards all, is it not the drape itself that inevitably supplies the energy and heat that runs the system?
"Plates could not move, or even exist, if not for the Globe's heat which must be removed from its interior to the surface through drapery convection. In this sense the mantle drives the plates, for information technology is the interior of the World that is the ultimate source of energy of all motility."
(Runcorn, 1980)
References
Bott, Grand.H.P., 1993. Modeling the Plate-Driving Mechanism, Periodical of the Geological Society, 150: p 941-951.
Bott, M.H.P, 1991. Ridge Push and Associated Plate Interior Stress in Normal and Hot Spot Regions, Tectonophyics, 200: p 17-32.
Bott, M.H.P., 1991. Sublithospheric Loading and Plate-Boundary Forces. In: Whitmarsh, R.B., Bott, M.H.P., Fairhead, J.B. & Kusznir, Due north.J. (eds) Tectonic Stress in the Lithosphere. Philosophical Transactions of the Royal Society, London, p 83-93.
Carlson, R.Fifty., 1983. Plate Motions, Boundary Forces, and Horizontal Temperature Gradients:Implications for the Driving Mechanism, Tectonophysics, 99: 149-164.
Carlson, R.L, et al., 1983. The Driving Mechanism of Plate Tectonics : Relation to Age of the Lithosphere at Trenches, Geophysical Research Alphabetic character, 10: p 297-300.
Chapple, West.M., and Tullis, T.E., 1977. Evaluation of the Forces that Drive the Plates, Journal of Geophysical Research, 82: p 1967-1984.
Doglioni, C., 1990. The Global Tectonic Pattern. Periodical of Geodynamics, 12: p 21-38.
Fleitout, 50, 1991. The Sources of Lithosperica Tectonic Stresses. In: Whitmarsh, R.B., Bott, 1000.H.P., Fairhead, J.B. & Kusznir, N.J. (eds) Tectonic Stress in the Lithosphere. Philosophical Transactions of the Royal Society, London, p 73-81.
Hager, B.H., and O'Connell, R.J., 1978. Subduction Zone Dip Angles and Menses Driven past Plate Move, Tectonophysics, fifty: p 111-133.
Jacoby, Due west.R., 1980. Plate Sliding and Sinking in Mantle Convection and the Driving Mechaism, In:
Davis, P.A., Runcorn, F.R.S. (eds) Mechanisms of Continental Drift and Plate Tectonics,
Bookish Press : p 159-172.
Jurdy, D.Yard., and Stefanick, M., 1991. The Forces Driving the Plates: Constraints from Kinematics and Stress Observations. In: Whitmarsh, R.B., Bott, M.H.P., Fairhead, J.B. & Kusznir, N.J. (eds) Tectonic Stress in the Lithosphere. Philosophical Transactions of the Royal Order, London, p 127-139.
McKenzie, D.P., 1969. Speculations on the Consequences and Causes of Plate Motions, The Geophysical Journal, 18: 1-32.
McKenzie, D.P., 1968. The Influence of the Purlieus Conditions and Rotation on Convection in the World's Curtain, The Geophysical Journal, 15: 457-500
Middleton, Thousand.V., Wilcock, P.R., 1996. Mechanics in the Earth and Ecology Sciences. Cambridge
University Press, Australia : pp 496.
Pavoni, N., 1993. Blueprint of Mantle Convection and Pangaea Pause-upwardly, every bit revealed by the development of the African plate, Journal of Geological Society, 150: p 953-964.
Richardson, R.M., 1992. Ridge Forces, Accented Plate Motions, and the Intraplate Stress Field, Periodical of Geophysical Research, 97: 11,739-eleven,748.
Runcorn, S.G., 1980. Some Comments on the Machinery of Continental Migrate, In: Davis, P.A., Runcorn,
F.R.S. (eds) Mechanisms of Continental Drift and Plate Tectonics, Academic Press : p 193-198.
Vigny, C., et al., 1991. The Driving Mechanism of Plate Tectonics, Tectonophysics, 187: p 345-360.
Wilson, One thousand., 1993. Plate-moving Mechanisms: Constraints and Controversies, Journal of the Geological Lodge, 150: p 923-926.
Wilson, M., 1993. Geochemical Signatures of Oceanic and Continental Basalts: A Key to Mantle Dynamics, Journal of Geological Club, 150: p 977-990.
Wortel, M.J.R, et al., 1991. Dynamics of the Lithosphere and the Intraplate Stress Field. In: Whitmarsh, R.B., Bott, K.H.P., Fairhead, J.B. & Kusznir, North.J. (eds) Tectonic Stress in the Lithosphere. Philosophical Transactions of the Majestic Gild, London, p 111-126.
Wortel, M.J.R., and Vlaar, Northward.J., 1976. Lithospheric Crumbling, Instability and Subduction, Tectonophysics,
32: p 331-351.
Ziegler, P.A., 1992. Plate Tectonics, Plate Moving Mechanisms and Rifting, Tectonophysics, 215: p 9-34.
Ziegler, P.A., 1993. Plate-moving Mechanisms: their Relative Importance, Journal of Geological Lodge, 150: p 927-940
Zoback, M.L., 1992. First and 2d Order Patterns of Stress in the Lithosphere: The World Stress Map Project, Journal of Geophysical Inquiry, 97: p 11,703-eleven,728.
Zoback, M.50., and Magee, M., 1991. Stress Magnitudes in the Chaff: Constraints from Stress Orientation and Relative Magnitude Information. In: Whitmarsh, R.B., Bott, M.H.P., Fairhead, J.B. & Kusznir, N.J. (eds) Tectonic Stress in the Lithosphere. Philosophical Transactions of the Royal Society, London, p 181-194.
Zoback, Grand.L., et al., 1989. Global Patterns of Tectonic Stress, Nature, 341: p 291-298.
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