PLATE TECTONICS PARADIGMS

Miguel Doblas¹, Nasrrddine Youbi², Mohammed Ben Abbou³, Mohamed Khalil Bensalah² & El Hachimi Hind²

¹ Instituto de Geociencias (CSIC-UCM), Universidad Complutense de Madrid, Ciudad Universitaria, 28040 Madrid, Spain (e-mail : doblas@mncn.csic.es), ²Department of Geology, School of Sciences-Semlalia, Cadi Ayyad University, Prince Moulay Abdellah Avenue, PO Box 2390, 40000 Marrakech, Morocco, ³Department of Geology, School of Sciences Dhar El Mehraz, Sidi Mohamed Ben Abdellah University, PO Box 1796, 30003 Fès, Morocco. 

A recent Article in Nature Geoscience concerning the 2009 magmatic-induced seismic events in Saudi Arabia¹ triggered a comment in the News & Views section by Ebinger & Belachew² highlighting the concept of “active passive margins” as a supposedly ground-breaking hypothesis: “Passive margins were thought to be tectonically inactive. Documentation of a volcanic dyke intrusion along the eastern flank of the Red Sea rift proves this plate tectonic tenet wrong….thus redefining passive margins”.

The contribution by Ebinger & Belachew² is somewhat surprising as we already knew for decades this plate tectonics paradigm to be wrong. In this sense, the extensional-detachment tectonics model³ constituted a milestone with major implications concerning the asymmetric opening of oceanic basins and the differential “passivity/activity” of Atlantic-type margins. In particular, the distinctive characteristics of the Red Sea margins were already explained within this simple-shear scenario⁴. The peculiarities of passive margins were also defined in the eighties⁵ in terms of contrasted tectonic upper/lower blocks, magma-poor/-rich margins, etc. Since then, countless papers have demonstrated that the “passive margin” mobilistic dogma is the exception rather than the rule^6,7,8.

Our own investigations of the eastern central Atlantic margin from the Triassic/Jurassic to the present revealed a “less-passive Atlantic-type margin”^7,9 characterized by Cenozoic alkaline magmatism and active rifting  pervading a 4000 km-long N-NE-oriented “sublithospheric hot channel” stretching from Cape Verde up to central Europe (a hypothesis corroborated by others^10,11). We further speculated that this eastern margin might be regarded as a prospective mid-oceanic ridge and that its evolution resulted from long-lived Triassic/Jurassic to Cenozoic plume tectonics⁷. Similar “not so passive” margins have also been described in ancient oceans of the Earth such as  the Permian-Triassic Neo-Tethys displaying widespread volcanism in its western margin¹² (Oman, India and western Australia).

 Why are plate tectonics paradigms so difficult to modify?  It seems that even if geosciences are quickly evolving, scientists are often reluctant to accept changes in the more traditional dogmas. We are probably witnessing the same type of resistance that the mobilistic theory had to endure 50 years ago by the supporters of the fixist doctrine. Ironically, as “history is doomed to repeat itself”, new verticalist-oriented tenets are now undergoing a similar struggle to gain recognition by earth scientists: i.e., mantle insulation¹³, superswells, mantle avalanches, hot upwellings , cold downwellings, plume-tectonics, antipodal-tectonics, anti-plate tectonics, top-down tectonics, etc.  This fixist attitude might result from the so-called “decline of the generalist“¹⁴ triggering increasingly specialized researches and thus “a tunnel vision of the trees hiding the broad picture of the forest”.

 References

1.     Pallister, J.S. et al. Nature Geosci. 3, 705-712 (2010).

2.     Ebinger, C. & Belachew, M. Nature Geosci. 3, 670 (2010).

3.     Wernicke, B. Nature, 291, 645-648 (1981).

4.     Wernicke, B. Can. J. Earth Sci., 22, 108-125 (1985).

5.     Lister, G.S., Etheridge, M.A. & Symonds, P.A. Geology, 14, 246-250 (1986).

6.     Tankard, A.J. & Balkwill, H.R. (eds)  Extensional tectonics and stratigraphy of the north Atlantic margins (American Association of Petroleum Geologists, Memoir 46, 1989).

7.     Oyarzun, R., Doblas, M., López-Ruiz, J. & Cebriá, J.M. Geology, 25, 727-730 (1997).

8.     Doglioni, C., Carminati, E & Bonatti, E. Tectonics, 22, doi: 10.1029/ 2002TC001459 (2003).

9.     Doblas, M., López-Ruiz, J. & Cebriá, J.M. in Cenozoic Volcanism in the Mediterranean Area (eds Beccaluva, L., Bianchini, G. & Wilson, M.) 303-319 (Geological Society of America Special Paper 418, 2007).

10.  Lustrino, M., & Wilson, M. Earth Sci. Rev., 81, 1-65 (2007).

11.  Piromallo, C., Gasperini, D., Macera, P. & Faccenna, C. Earth Planet. Sci. Lett., 268, 15-27 (2008).

12.  Veevers, J.J. Earth Sci. Rev., 68, 1-132 (2004).

13.  Doblas, M. Geology, 30, 839-842 (2002).

14.  Seitz, F. Nature, 403, 483 (2000)