Around the world, all high schools teach these 3 fundamental processes of Plate Tectonics Theory (PTT):
Subduction of plates;
Mountain chains as a result of subduction.
They are valuable working paradigms. Unfortunately, we fail to acknowledge when they do not resolve geological data. Let’s see some downfalls of the seafloor spreading process.
The PTT became widely accepted because of the seafloor spreading model. We know the Earth's magnetic field has alternated between periods of normal and reverse polarity. From the 50s, the study of magnetic normal/reversal in continental igneous rocks had established the geomagnetic polarity time scale.
In 1963, Vine, Matthews, and Morley (VMM model) proposed that the magnetic linear patterns on the ocean floor represent different ages of oceanic basaltic rocks that have been pushed away to either side of a spreading center and replaced by younger basaltic lava. Their theory suggested that as the new basaltic crust is created, some minerals like magnetite become magnetized in alignment with the existing magnetic field of the earth. Rocks formed during a period of normal magnetism will have a positive magnetic anomaly like the actual earth polarity, whereas rock formed during a period of reverse magnetism will have a negative magnetic anomaly. By matching the continental geomagnetic polarity time scale with the oceanic strips, we will be able to establish their age like this map of the alleged ages of North Atlantic.
The seafloor spreading theory was widely accepted before we were able to proof if the oceanic magnetic lineaments correspond to normal/reversal ages. The geoscience community became so confident that this map of the alleged ages of the oceans was widely publicized:
In the 1970s, PPT became so widely accepted that many governments poured grants money into oceanic research. If you question geology students, they would believe that deep sea drilling had confirmed this time map above. It is not the case. Sea drilling is superficial and so limited that it does not sample the unaltered basalt fit to reveal its magnetic polarity. Iceland was expected to display evidence for the VMM model as it is the only place where an emerged midocean ridge is directly accessible. As shown by many workers, Iceland has been less than successful as a source of information supportive of the model. The submerged Reykjanes Ridge south of Iceland was also extensively studied because of its proximity. Some workers have demonstrated that the linear magnetic anomalies can be easily explained by other geophysical models than the VMM’s one. You just hypothesize an entire ocean caped with a basalt with one single polarity or a mixt of it. To your model, you add strips depleted of magnetism corresponding to the deep long fractures where magnetite was flushed out by seawater alteration. Your theoretical model will give you the same magnetic profile given by the shipborne survey with an even better statistic result than the one of VMM. In mining exploration, geophysicists know well that from one magnetic profile land survey you can generate many hypothetical models of the targeted ore deposit by proposing a wide range of geometric volumes, depths and mineral concentrations. Only drilling will reveal which models are the good one. So far, deep sea drilling remains a limited technic to reveal the true nature of the oceanic magnetic lineation.
■ Surprisingly the dredging of the oceanic floor had sampled many ancient continental rocks of all ages. The Magnetic Anomaly Map of The World (Korhonen, J.V. et al., 2007) is also puzzling. A large part of the Atlantic Ocean floor gives a magnetic signal very similar to the one of continents (Read more...).
According to the VMM model, the world ocean crust should have a Pleistocene age in the central mid-ridge and Lowe Jurassic age at the continental margin. Because of this paradigm, the old continental Precambrian crust shouldn’t have any prolongation with the younger geology of the ocean. Surprisingly, major fracture zones of the Atlantic (Romanche, Vema) have a clear continuity with the giant Precambrian lineaments (deep faults & fractures) of West Africa and South America.
There are many such continent/ocean continuities all around the world (Atlantic/Appalachian; Atlantic/Amazon; Pacific/Andes; West Pacific/Asia; Indian Ocean/Australia…) Astonished by the mysterious African prolongations, oceanographers have proposed a possible rejuvenation of these ancient structures during the opening of the new oceans in Jurassic time. Rejuvenation of Precambrian faults remains an unsolved anachronism. Indeed, exposed to time and high-pressure, deep faults will recrystallize and healed so well that any sorts of weakness have vanished. If younger stress would surge during the continental split, fracturing will occur anywhere they have to make their way, regardless of the existing Precambrian lineaments.
■ The kinematic proposed by the ocean ridge spreading request that major fracture zones should never cross each other. But in the South Pacific, we observe major fracture zones orientated Ouest-East curving toward North East crossing many other fractures zones (Read more…).