CPT Q005 – Are sediments in trenches deformed and contorted as expected?

5. Question: Is there evidence that sediments in trenches are deformed and contorted as one should expect if subduction is genuine?

Response: There are hundreds of articles in the peer-reviewed literature that document mélange structure in subduction zone accretionary wedges. I have already described the complex and contorted structure observed both by drilling and seismic profiling of the accretionary wedge that lies within the Nankai Trough where the Philippine Plate is actively subducting beneath southwestern Japan. Similarly, I have already described the classic example of a fossil subduction zone, the Franciscan terrane along the central and northern California coast, which displays strongly contorted sediments and ocean crustal rocks that have been subducted to depths of 20-30 km, metamorphosed to blueschist grade, and then amazingly have risen up the subduction channel back to the surface. One of many other examples I could point to is in Guatemala, similar in many ways to the Franciscan, and described in the recent paper by Marroni, M., et al., “Deformation history of the eclogite- and jadeitite-bearing mélange from North Motagua Fault Zone, Guatemala: insights in the processes of a fossil subduction channel,” Geological Journal, 44, 167-190, 2008, whose abstract I reproduce as follows.

In Guatemala, along the northern side of the Motagua Valley, a mélange consisting of blocks of eclogite and jadeitite set in a metaserpentinitic and metasedimentary matrix crops out. The metasedimentary rocks display a complex deformation history that includes four tectonic phases, from D1 to D4. The D1 phase occurs only as a relic and is characterized by a mineral assemblage developed under pressure temperature (P-T) conditions of 1.00-1.25 GPa and 206-263°C. The D2 phase, characterized by isoclinal folds, schistosity and mineral/stretching lineation, developed at P-T conditions of 0.70-1.20 GPa and 279-409°C. The following D3 and D4 phases show deformations developed at shallower structural levels. Whereas the D1 phase can be interpreted as the result of underplating of slices of oceanic lithosphere during an intraoceanic subduction, the following phases have been acquired by the mélange during its progressive exhumation through different mechanisms. The deformations related to the D2 and D3 phases can be regarded as acquired by extrusion of the mélange within a subduction channel during a stage of oblique subduction. In addition, the structural evidences indicate that the coupling and mixing of different blocks occurred during the D2 phase, as a result of flow reverse and upward trajectory in the subduction channel. By contrast, the D4 phase can be interpreted as related to extension at shallow structural levels. In this framework, the exhumation-related structures in the mélange indicate that this process, probably long-lived, developed through different mechanisms, active in the subduction channel through time.

While mélange formation is expected in places like the Nankai Trough today under the slow rates of convergence assumed in UPT because the sediments are inherently soft, many of the other striking features of the fossil accretionary wedge deposits, such as large volumes of blueschist rocks returned to the surface, are not readily explained in the framework of UPT, but instead seem to require the catastrophic conditions associated with CPT.

CPT Q004 – Are sediments, volcanoes, and plateaus actually scraped off subducting plates at trenches?

4. Question: What evidence supports the idea that sediments, volcanoes, and plateaus have been scraped off subducting plates at trenches?

Response: There are thousands of papers documenting the reality of accretionary wedges at subduction zones in the standard literature. Continue reading “CPT Q004 – Are sediments, volcanoes, and plateaus actually scraped off subducting plates at trenches?”

CPT Q003 – Is not the resistance to subduction far too great to allow a plate to subduct?

3. Question: Why does not a subducting plate experience so much resistance in diving down through just the top of the mantle that it could never penetrate any significant distance? Would not the blunt front end alone prevent any movement? Would not the force needed to overcome such large resistance (if a pushing force) crush the plate or (if a pulling force) pull the plate apart?

Response: A crucially important issue here is the strength contrast between the lithosphere at the earth’s surface and the rock layer lying immediately beneath it. This zone, discovered to be very weak relative to the lithosphere above it, is known as the asthenosphere (from Greek asthenēs ‘weak’ + sphere). The British geologist Joseph Barrell in 1914, in connection with his studies of post-glacial rebound, first introduced the idea of a strong outer layer (which he named the lithosphere) overlying a much weaker layer (which named the asthenosphere).1 He realized such a weak zone in which lateral flow of rock could occur was required for isostatic compensation to take place. Seismologists, beginning notably from their analyses of the large 1960 Chilean earthquake, have identified that low seismic wave speeds characterize this region. They now refer this portion of the upper mantle as the ‘low velocity zone’. Since seismic wave speeds depend on the shear strength, or rigidity, of the rock, the strikingly lower seismic wave speeds at asthenospheric depths imply significantly lower rock strength in that region. Just how weak is the asthenosphere relative to the lithosphere? Various lines of observational evidence indicate that thicker oceanic lithosphere has an inelastic or viscous strength on the order of 1022-1023 Pa-s, while the asthenosphere has a viscosity on the order of 1018-1019 Pa-s. In other words, the lithosphere typically is at least a thousand times, and more typically ten thousand times, stronger than the asthenosphere.

Why is the asthenosphere so weak relative to the overlying lithosphere? The primary reason is its high temperature. Rock strength depends very strongly (exponentially) on temperature, and the difference in the strength due to temperature alone is huge. Indeed, since the temperature of the asthenosphere is not that far below the melting (solidus) temperature of its lowest melting point minerals, it is not that surprising that its strength is so far below that of the overlying lithosphere. Laboratory experiments show that the viscous strength h of silicate minerals2 obeys an Arrhenius law of the form h = h0 exp[(E* + pV*)(1/T 1/T0)/R], where E* is the mineral’s activation energy, V* is its activation volume, p is the pressure, T is the absolute temperature, R = 8.3145 J/mol-K is the ideal gas constant, and h0 is the reference viscosity at reference temperature T0. For the upper mantle mineral olivine, E* is about 500 kJ/mol and V* is about 4 x 10-6 m3/mol. However, yet another factor contributing to asthenospheric weakness is the likely presence of water and carbon dioxide, at 100 ppm or so levels, within the lattices of the minerals of the asthenosphere rocks.3,4 Laboratory experiments show that the presence of these volatiles leads to a further dramatic reduction in rock strength. To summarize thus far, the layer of rock that underlies the lithospheric plates is dramatically weaker than the plates themselves. Hence, lithospheric plates should be readily able to penetrate into the layer of rock beneath them. Moreover, given the extreme contrast in rock strength between the asthenosphere and lithosphere, the drag forces on the base of the plates also should be small compared to the plate strength.

A useful tool that can be brought to bear on the mechanics of subduction is numerical simulation. Many numerical simulations of these mechanics over the last 30 years, including my own, clearly demonstrate that subduction is a robust and viable physical process. To understand the basic mechanics, several points are important to grasp. First, rocks not only can and do display reversible elastic deformation when subjected to stresses (as do most solids) but also can and do undergo inelastic non-reversible changes in shape. (Inelastic deformation is a standard and important topic included in most every graduate level mechanical engineering curriculum.) In subduction not only does the slab itself bend inelastically, it can also stretch or compress inelastically in its downward journey. But not only does the slab deform inelastically, but the mantle rock into which it sinks also deforms inelastically to accommodate the downgoing slab. The numerical methods that simulate these mechanics typically guarantee perfect conservation of mass and energy while enforcing perfect consistency of forces acting on each parcel of material throughout the computational domain. These methods also usually allow the material strength to vary from cell to cell as a function of temperature and also, in many cases, the local stress conditions. These methods are highly developed and are routinely applied in a broad spectrum of engineering applications, from the mechanical designs of turbine blades to anti-tank projectiles to nuclear weapons. The methods work. Applied to the earth and to the deformation that occurs as rock rises and sinks in the mantle as a result of differences in its buoyancy, the methods show clearly that subduction can and does take place when physically realistic values for densities, temperatures, and various material parameters are applied. Simulations confirm that the large contrast in strength between the asthenosphere and the lithosphere leads to traction forces on the base of the lithosphere which are relatively small. This in turn implies that not much pushing or pulling is required to move a plate over the underlying mantle. It also means that the stresses within the horizontal portion of a plate are generally small and well below the stress levels needed to fracture the plate.

These basic conclusions apply both to the case of uniformitarian plate tectonics (UPT) and to the regime of catastrophic plate tectonics (CPT). In the case of UPT, stress weakening in the rock deformation law is either omitted or switched off, and therefore the rocks remain strong and the deformation rates remain at the levels we observe in the present. However, when stress weakening is included (as it ought to be), the potential for runaway exists and CPT can occur. In the CPT regime, the strength contrast between lithosphere and asthenosphere remains; lithosphere subducts and behaves in largely the same way as in the non-CPT case, except that velocities are dramatically higher and the time scale is dramatically shorter.

  1. [1] Barrell, J., “The strength of the Earth’s crust. I. Geologic tests of the limits of strength,” J. Geol., 22, 28–48, 1914. 

  2. [2] A relatively simple tutorial on rheological models can be found here

  3. [3] Hirth G. and Kohlstedt D.L., “Water in the oceanic upper mantle: Implications for rheology, melt extraction and the evolution of the lithosphere,” Earth Planet. Sci. Lett. 144, 93-108, 1996 

  4. [4] Rychert, C. A., Fischer, K. M., and Rondenay, S., “A sharp lithosphere-asthenosphere boundary imaged beneath eastern North America,” Nature, 436, 542-545, 2005. 

CPT Q002 – How can continental plates move laterally with roots that extend to depths of 200-250 km?

2. Question: How can continental plates move laterally given the fact that most continental plates have lithospheric roots that extend to depths of 200-250 km into the asthenosphere?

Response: First of all, lateral motion of continents is possible only because there is this weak layer—generally referred to as the asthenosphere—beneath the continental plates whose presence results in a mechanical decoupling of an individual plate from the stronger mantle below. Continue reading “CPT Q002 – How can continental plates move laterally with roots that extend to depths of 200-250 km?”

CPT – Table of Contents – 101 Questions and Answers Concerning Catastrophic Plate Tectonics

CPT Q001 – Does Flood modeling conflict with commitment to the authority and sufficiency of Scripture?

1. Question: How do your efforts to model and understand the tectonics of the Flood square with the historic orthodox Christian view of the authority and sufficiency of Scripture?

Response: I am earnestly persuaded from Scripture that not only is Christian apologetics a legitimate enterprise but it is also an urgent imperative and non-negotiable duty for every generation of those belonging to the Lord Jesus. Continue reading “CPT Q001 – Does Flood modeling conflict with commitment to the authority and sufficiency of Scripture?”

Can random molecular interactions create life? (Highlights of the Los Alamos Origins Debate: Part I)

This entry is part 2 of 6 in the series Highlights of the Los Alamos Origins Debate

Many evolutionists are persuaded that the 15 billion years they assume for the age of the cosmos is an abundance of time for random interactions of atoms and molecules to generate life. A simple arithmetic lesson reveals this to be no more than an irrational fantasy.1

This arithmetic lesson is similar to calculating the odds of winning the lottery. The number of possible lottery combinations corresponds to the total number of protein structures (of an appropriate size range) that are possible to assemble from standard building blocks. The winning tickets correspond to the tiny sets of such proteins with the correct special properties from which a living organism, say a simple bacterium, can be successfully built. The maximum number of lottery tickets a person can buy corresponds to the maximum number of protein molecules that could have ever existed in the history of the cosmos.  Continue reading “Can random molecular interactions create life? (Highlights of the Los Alamos Origins Debate: Part I)”

  1. Featured image of the DNA Double Helix Molecule originally from here (now obsolete), from Darwin’s Theory of Evolution: DNA Causes Geneticists, Other Scientists, Join Ranks of Dissenters (April 6, 2009). 

But What About the Geological / Fossil Record? (Highlights of the Los Alamos Origins Debate: Part III)

This entry is part 4 of 6 in the series Highlights of the Los Alamos Origins Debate

Just as there has been glaring scientific fraud in things biological for the past century, there has been a similar fraud in things geological. The error, in a word, is uniformitarianism. This outlook assumes and asserts the earth’s past can be correctly understood purely in terms of present day processes acting at more or less present day rates. Just as materialist biologists have erroneously assumed material processes can give rise to life in all its diversity, materialist geologists have assumed the present can fully account for the earth’s past. In so doing, they have been forced to ignore and suppress abundant contrary evidence that the planet has suffered major catastrophe on a global scale.  Continue reading “But What About the Geological / Fossil Record? (Highlights of the Los Alamos Origins Debate: Part III)”

But How Is Geological Time To Be Reckoned? (Highlights of the Los Alamos Origins Debate: Part IV)

This entry is part 5 of 6 in the series Highlights of the Los Alamos Origins Debate

With the discovery of radioactivity about a century ago, uniformitarian scientists have assumed they have a reliable and quantitative means for measuring absolute time on scales of billions of years. This is because a number of unstable isotopes exist with half-lives in the billions of year range. Confidence in these methods has been very high for several reasons. The nuclear energy levels involved in radioactive decay are so much greater than the electronic energy levels associated with ordinary temperature, pressure, and chemistry that variations in the latter can have negligible effects on the former.

Furthermore, it has been assumed that the laws of nature are time invariant and that the decay rates we measure today have been constant since the beginning of the cosmos Continue reading “But How Is Geological Time To Be Reckoned? (Highlights of the Los Alamos Origins Debate: Part IV)”