6. Plate Boundary Analysis
6.1 Tensile and compressive forces in Pacific Basin
The Heezen-Tharp 1977 (H-Z 1977) oceanographic map is used as the basis for the following discussions. As the Mercator type projection distorts the land areas by displaying the spherical globe layout on an equal grid flat map (Fig 24) some misinterpretation regarding tectonic processes is very possible. Although care has been exercised in taking this into account some observations will be open to debate.
This Google downloaded map has been reproduced by the USGS & the National Geographic Society and is used as the major reference in the following sections. Examination of the ‘Transform Faults’ as noted on the H-Z 1977 map as being simply the displacement of parts of a ridge either side of the main ridge line by lateral movements of the plates after separation may not be completely true in every case. The initial northward pivoting split of Laurasia from Pangea and the subsequent break up into the North American and Eurasian Plates from the larger Laurasian plate would have initially only stretched and rifted the mantle between them and not necessarily the complete Mid-Atlantic ridge. This point is open to debate as is the question regarding the formation of the oceanic crust along the line of separation.
The following sequence of events is envisaged at this stage
The continental mass of Pangea would have been shifted northward by the combined circumferential and centripetal forces.
The ductile mantle would have stretched under the applied tensile stress forces.
The stretching would have thinned the mantle and the pulling action would be noted by the elongated stress lines some of which may have developed into the now referred to ‘Fracture Zones’. The length and width of these ‘Fracture Lines or Zones’ would have been subject to varied mantle composition and the latitude related rotational velocity-based stress forces.
Finally, fracturing at right angles to the stress forces would have occurred with the subsequent creation of separate plates. At this point magma would intrude into the ever - widening ridge giving rise to the mirror imaged parallel lines of paleo-magnetic reversal cycles either side of it. ‘Fracture Zone’ stretching would cease.
The displaced ‘Transform Fault’ along the Mid-Atlantic Ridge starting at Greenland and continuing through to a line drawn between North Africa (Morocco) and the top western point of Brazil in South America, may well have occurred during the initial breakaway stage of the North American plate prior to the later separation between the South American plate and the central and southern part of the African plate. If this is the case, the above-mentioned visually noted (H-Z map) misalignment of the ridge compared with the Mid-Atlantic ridge between South America and central and southern Africa may not be a Transform Fault.
Once further separation had taken place, between the northern part of the African plate and the Eurasian part of Laurasia, ingress of water from the Panthalassa and Tethys Oceans allowed the beginning of the formation of the new Atlantic, Indian and Pacific Ocean boundaries (at this stage, at c.150 Ma, the North Atlantic was yet to open).
An attempt has been made to display the above sequence in the illustration Fig 30.
Fig 26
Fig 27
The above argument does not preclude that the now separated plates with their different size characteristics would move relative to each other to re-align themselves with the stress loads and in so doing give rise to the transform faults that traverse the intruded magma flows (Fig 25). This separation will continue until the crustal plates are moved to the lighter (Pacific Basin) side of the Earth. The intrusion of magma onto the separating ocean floor boundaries which is generally credited with the force capable of moving continents apart causing ‘sea floor spreading is now seen as being an inevitable passive consequence of the mantle having being been split by the circumferential stresses. This process is referred to as ‘Sea Floor Stretching’ in this paper.
Following on from the initial break-up of Pangea, the separated continental blocks, presently postulated as being driven by the differential circumferential stresses and centripetal forces, will be pushed over the oceanic crust towards the lighter side of the planet. If these movements away from the now central part of the African plate are approached from a convection current circulatory system, it would be difficult to reconcile all the following moving towards the Pacific Basin, i.e.: (1) Pangea moving north in the Permian, (2) what is now the Eurasian plate moving north-east and rotating, (3) the South and North American plates moving west and (4) the Indian and Australian plates moving north-east. The same difficulty would apply in reconciling these plate movements with (a) the apparent north-westward movement of the Pacific Plate over the Hawaiian hot spot in forming the Hawaiian-Emperor volcanic seamount chain (b) the convergent boundary along the Aleutian Trench (c) the divergent boundary of the east-west circumferential Pacific/Antarctic ocean ridge and those extending south-east and south-west from India. Fig 25 shows the present plate movements and their different type boundaries. It is extremely difficult to offer a rational explanation to cover the various circulatory convection motions particularly as they would have to consider the different Earth circumference measurements with latitude.
If, however the various movements within the Pacific Basin are considered using the centripetal and differential circumferential stress forces associated with the rotation of the Earth, the following explanations may well be considered viable:
The Eurasian continental plate despite the impediment to its westward motion by its engagement with the Indo-Australian plate at the Himalayan interface, is being subjected to a Euler pivotal action over the Pacific oceanic crust in a westward direction.
The North American plate including the Transform fault area shows an overall trend for an eastward pivotal movement over the Pacific Basin as noted by the convergent boundary at the Juan de Fuca and the Cocos plate areas.
The inward and downward pivoting motion of both the Eurasian and North American plates, coupled with the centripetal force causing the total land mass to move southwards to occupy a larger area at a lower latitude, could well have contributed to an east-west compression trench split between them in the Aleutian area.
To the above, a S-N compression component is applied by the north-north-west movement of the Indo-Australia plate on the eastern side of the Pacific Basin. This additional compressive force may be responsible for the totally crumpled distorted Pacific Basin area between the Eurasian plate and the Emperor Seamount-Hawaiian mountain island chains extending south to the Kermadec trench.
This compressive force could also be the main reason for the propagation of the vertical S-N aligned Palau, Mariana and the Izu-Bonnin trenches, on the eastern side of the basin in the folded crust bordering the Eurasian plate. The ovoid shape of the Philippine Basin (Fig 27) may well be due to the S-N compressive force in association with the E-W elongation in the bulged equatorial belt by the centripetal forces. In this case the circumferential tensile forces will act in opposition to the centripetal forces at the Eurasian plate side and synergistically at the Pacific Basin side.
It is also possible that the East-West circumferentially aligned Pacific-Antarctic, south-east and south-west aligned divergent boundaries from India are a result of the centripetal forces pushing the major continents northward whilst at the same time centralising the southern Antarctic plate to find the largest area around the South Pole. This scenario would give a plausible explanation for the situation as shown in Fig 23 and detailed in Section 8 above. It is difficult to explain the disposition of the boundaries at the Polar region by convection current considerations.
The above scenarios are in keeping with the projected behaviour as outlined in Fig 17B in which the heavier side, split under tension, is opposite the lighter side in compression 180 degrees away on the other side of the planet.
The examination of the sea floor area around Southern Japan suggests that the splitting of the Nankai Trench under compression via the northern movement of Australia has produced compression type folds between Japan and the main Eurasian plate. This scenario may also be applied to the Philippine plate. However, the above points may be based on an incorrect interpretation of the enlarged portion of the H-Z 1977 map (Fig 25).