THE PLATE TECTONICS THEORY
THE DEBATE STILL OPEN
THE PLATE TECTONICS THEORY: THE DEBATE STILL OPEN - PAGE 1
Since the 1960s the Plate Tectonics Theory (short form is PTT in this document) seemed to be the key to understand all aspects of earth's history. Today it is taught as a sure truth by most faculties of earth sciences around the world. It was rooted in a collective consciousness since it answers all questions. Since 1990, I have often suggested to my geologist colleagues to examine the shortcomings of this theory by reading articles like those published by New Concepts in Global Tectonics. Just a few colleagues got into the task. They mostly refer to the majority opinion; thousands of other geoscientists around the world are adopting the PTT. But these 'others' too never did such an investigation. This web page will help in doing this investigation.
Even if you are not a geologist you will be able to understand the weak points of the PTT. I prefer to warn you: At the end of this reading you will learn that the PTT antagonists do not offer a comprehensive and global replacement theory. Sadly, this process brings us back to a time when geologists had more questions than answers.
A GIGANTIC PUZZLE
From 1857 to 1965, geographers and geologists had been suggesting that these jigsaw pieces had been disassembled in the distant past. We are especially familiar with this illustration in our textbooks.
This image is a reproduction of a reconstruction made by Bullard, Everett et Smith in 1965. Bullard and his colleagues were the first to use a projection by a mathematical method. However, they chose continental margins (submerged surface) which suited the best apparent bonding and they obliterated a large part of Central America. This same attempt on a 3D globe reveals how the southern end of South America does not join southern Africa. Moreover, not much people notice how they shrank Africa considerably to produce such an esthetic fit. This aberration was repeatedly mentioned in scientific publications. To bet on this incongruity other experts have tried different closures of the puzzle but without the expected result. Finally, this deceptive collage found its place in our textbooks.
Just to situate ourselves in a historical context, let's look at the reconstructions of what is called Pangea or its southern part, Gondwana:
Antonio Snider Pellegrini in 1858
In 1912, Alfred Wegener published a reconstitution he will call Pangäa in 1920.
Reconstruction of the Pangaea by Boris Choubert (1935).
Antonio Snider Pellegrini in 1858
Early in the 60s, the forefathers of PTT were aware of more intriguing fit relative to this puzzle. The game is to bring together Africa, the two Americas and Europe just to the Atlantic half away. Surprisingly, the oceanic gap runs from the North Pole to the South Pole with its western and eastern coasts perfectly parallel. Moreover, the oceanic ridge is centred in the middle of the large gap all the way south. How we forgot such an amazing correlation? Geodoxa presents his illustrations from a 3D sphere:
This configuration gives the clear impression that part of the continents’ crust is missing. Fortunately, the publication of the MAGNETIC ANOMALY MAP OF THE WORLD (Korhonen, J.V. et al., 2007) kept us aware of this amazing singularity.
The magnetic signals typical of the continents (the Sial) extend for several thousand km far from the continental margin. The map suggests that much of the ocean floor is a thinned and/or submerged continental crust sunken at the level of an oceanic crust (Sima). Sima gives a stronger magnetic signal because of the high content in magnesium and iron minerals. Later, we will see more about the difference between these two types crusts (Sial and Sima).
Reasonably, we can reconfigure a sort of continental drift by considering the alleged submerged continents as did James (2010). In this model the displacement of the continents is twice as small. Note that the closure is surprisingly accurate. We invite our readers to navigate back and forth in this slideshow:
James (2010) develops a detailed analysis of this map and questions several PTT paradigms regarding the ocean floor. The PTT protagonists might insist that such an oceanic crust is just sending a “very anomalous” magnetic signal alike the one of a continental crust. But keep in mind that three independent sets of data confirm the abundance of continental crust at the bottom of the oceans:
THE OCEANIC FRACTURE ZONES VS CONTINENTAL GEOLOGY
According to the PTT the oceanic fracture zones would be the footprint of ocean floor fabrication during the seafloor spreading process. In this model it is imperative to assume the following points:
The Pangea would have broken up at the end of the Triassic and at the beginning of the Jurassic time.
From this moment, the bottom of the Atlantic was made by the cooling of successive lava (gabbro, basalt ...) which are younger than the Triassic (less than 200 million years).
The continental crust of Precambrian age is much older than the Atlantic floor.
These 3 claims require that the ancient continental crust has no structural relation with the fracture zones of the ocean floor. The continents would only bear the young scars of Pangea's fragmentation and the oceanic fractures should be younger than the Triassic/Jurassic boundary. If this is the case, it would be impossible to find oceanic fractures extending with the very old lineaments of the continental Precambrian. To the disarray of the PTT, such extensions do exist!
Barosh, P.J., 1987, Neotectonic Framework of the United States, in Basement Tectonics 7: Proceedings of the Seventh International Conference on Basement Tectonics, held in Kingston, Ontario, Canada, August 1987, Page 277.
Bullard, E, Everett, J E and Smith, A G, 1965. ‘The fit of the continents around the Atlantic’, published in the Philosophical Transactions of the Royal Society of London, Series A. Vol. 258, No. 1088, pp 41-5.
Dickins J.M., Choi D.R. & Yeates A.N., 1992 ‘Past distribution of oceans and continents’, in: New Concepts in Global Tectonics, Chatterjee & Hotton, 1992, pp. 193-199 (p. 198).
du Toit, A.L. and Reed, F.R.C. , 1927, A Geological Comparison of South America with South Africa, Carnegie Institution of Washington, Washington, USA
du Toit, A.L., 1937, Our Wandering Continents; An Hypothesis of Continental Drifting, Oliver & Boyd, London, UK
Garrett, W.E. (ed.), 1990. Atlantic Ocean Floor. National Geographic, 177, 61 a. Generalized Bathymetry on World Chart, North Atlantic Area
Google Earth Global Gravity Anomaly
Source of ocean data:
Sandwell, D. T., R. D. Müller, W. H. F. Smith, E. Garcia, R. Francis, 2014, New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure, Science, Vol. 346, no. 6205, pp. 65-67, doi: 10.1126/science.1258213, 2014.
Source of land data:
EGM2008 Gravity Anomalies and DOV Data - Nikolaos K. Pavlis, Simon A. Holmes, Steve C. Kenyon, John K. Factor; Journal of Geophysical Research: Solid Earth (1978-2012) Volume 117, Issue B4, April 2012
Friedrich, J. and Leduc, G., 2004, Curvilinear patterns of oceanic fracture zones; Journal of Geodynamics 37(2):169-179, March 2004
Hildenbrand, T.G., R.W. Simpson , R.H. Godsen and M.F. Kane, 1982,
‘Digital colored residual and regional Bouguer gravity maps of the conterminous United States with cut-off wavelengths of 250 km and 1000 km’ U.S. Geol. Survey Geophysical Investigation Map, Map GP-0953-A
James, K.H., 2010. Observations on New Magnetic Map from The Commission For The Geological Map Of The World. New Concepts in Global Tectonics Newsletter, no. 57.
Kinsland, G.L., 1983, Transcontinental Transform Fault Across North America, Basement Tectonics 5: Proceedings of the Fifth International Conference on Basement Tectonics, held Cairo, Egypt in 1983, p.267.
Korhonen, J.V. et al., 2007. Carte des Anomalies Magnétiques du Monde. Commission for the Geological Map of the World. Paris
Neev, D., Hall, J.K., 2000. Whole mantle convection as the cause of the spiraling global system of lithospheric geosutures. GSI Current Research 12, 168–176.
Smith, W.H.F., Sandwell, D. T., 1997, Measured and Estimated Sea Floor Topography (map version 4.2), World Data Center-A for Marine Geology and Geophysics research publication RP-1.
SMOOT, N.C., 1993. Bathymetry: Collection, Processing, and Interpretation: NAVOCEANO Train. Man. TM 01-93, 299.
SMOOT, N.C., 1994. Plate-wide Pacific trends-orthogonal fracture intersections, EOS, Trans., AGU, 75(25), 69.
Thomas, W.A., 1977, Evolution of Appalachian- Ouachita salients and recesses from reentrants and promontories in the continental margin: American Journal of Science, v. 277, p. 1233.
Warnken, R., 2001, Global Relief Images, 2-Minute Gridded Elevation Data, NOAA/National Geophysical Data Center, Boulder, Colorado, Download at http://www.ngdc.noaa.gov/mgg/image/2minrelief.html.