Solid Earth

4.7 Hotspot tracks and transform faults

Video: Hotspot tracks and transform faults

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Image: Bathymetric map of the Pacific (created with GeoMapApp  / CC BY  / CC BY ( Ryan et al., 2009 ).

Chapter 4.7

Hotspot tracks and transform faults

This chapter presents absolute and relative plate movements on Earth in a large global context and their interaction with each other. In addition to the absolute direction of plate movement, seamount and volcano chains show other connections in the global interaction of the plates.

Fig. 4.7.1: Absolute plate movement velocities. Modified after Meschede (2018) and  Frisch & Meschede, (2021). Data calculated after Gripp & Gordon (2002).

Fig. 4.7.1 shows the directions and velocities at which the plates are moving today, based on the hotspot reference system, i.e. the absolute plate movements. You can see, for example, that the Pacific Plate is drifting relatively quickly in a northwesterly direction at up to 10 cm per year. The African Plate, on the other hand, is significantly slower, moving for the most part at less than 2 cm per year. At first glance, looking at the spreading zone between Africa and South America, one might assume that Africa is moving east, but the absolute plate movement is west. The South American plate is of course also moving westward, but much faster than the African plate.

The difference in the absolute plate movement results in the relative plate movement, which ensures that the spreading center always remains in the middle between the two continents of Africa and South America. This is due to the fact that an equal amount of oceanic crust is grown on both sides of the spreading center. In the global plate pattern, however, the spreading center slowly moves westward.

Fig. 4.7.2: Absolute and relative plate movements at a spreading center (Meschede, unpublished, 2025)

The schematic drawing of Fig. 4.7.2 illustrates the principle for relocating a spreading center and shows that spreading centers are not stationary. Both continental plates move in the same direction, but the left one moves much faster than the right one. New oceanic crust forms at a spreading zone between the two drifting plates, with the divergence movement at the spreading center being symmetrical because the same amount of new oceanic crust forms on both sides. This movement corresponds to the relative plate movement.

The situation between Africa and South America (Fig. 4.7.3) is similar: the spreading center remains in the middle of the two plates, the South American Plate moves westward while the African Plate remains more or less stationary.

Fig. 4.7.3: Animation – Drift between South America and Africa (Meschede, unpubl., 2022).

Fig. 4.7.4a: Bathymetric map of the South Atlantic. Base map created with GeoMapApp  / CC BY  / CC BY ( Ryan et al., 2009 ).

In the South Atlantic, the relationship between absolute and relative plate movement can be clearly understood from the submarine ridges present there (Fig. 4.7.4a). The Walvis Ridge extends from a hotspot to the African coast and finally to the basaltic rocks of the Etendeka Plateau; its counterpart on the South American Plate is the Rio Grande Rise, which extends into the Paraná Plateau. The hotspot is actually located entirely on the African Plate in the area of ​​the islands of Tristan da Cunha and Gough Island, so that the hotspot track only continues to grow on the African side.

Fig. 4.7.4b: Bathymetric ap of the South Atlantic with age data from seamounts of the Walvis Ridge and Rio Grande Rise. Base map created with GeoMapApp  / CC BY  / CC BY ( Ryan et al., 2009 ), data after O’Connor et al., 2009).

The age dates of the Walvis Ridge and its twin ridge on the South American Plate indicate the evolution of the ridges (Fig. 4.7.4b). The closer you get to the Etendeka Plateau in Namibia or the Paraná Plateau in Africa, the older the rocks become. Both plateaus formed over the hotspot when Africa and South America were still connected.

The hotspot tracks are shown as colored lines. They show that the direction changes slightly between 40 and 50 million years. From around this time, the Tristan da Cunha/Gough Island hotspot was completely under the African Plate, i.e. from this point onwards no volcano could form on the South American Plate. Therefore, only the older part of the hotspot track, shown here in green color, is represented on the South American Plate.

Fig. 4.7.5: Hotspot tracks in the South Atlantic. Base map created with GeoMapApp  / CC BY  / CC BY ( Ryan et al., 2009 ), data after O’Connor et al., 2009).

There are further hotspot tracks in the Atlantic, as shown in Fig. 4.7.5, but also in the Indian Ocean and …

Fig. 4.7.6: Hotspot tracks in the Pacific. Base map created with GeoMapApp  / CC BY  / CC BY ( Ryan et al., 2009 ), data after Gripp & Gordon (2002).

… in the Pacific (Fig. 4.7.6). All volcanic chains have a characteristic kink in a similar orientation around the same time at about 45 million years.

What is the reason for these kink in the volcanic chains?

Fig. 4.7.7: Plate movements in the Cretaceous and Eocene with the evolution of the Hawai’i-Emperor seamount chain and the twin ridges of Walvis Ridge and Rio Grande Rise (modified after Frisch & Meschede, 2021).

The kinks in the volcanic chains indicate a global reorientation of the absolute plate movements. Since globally all plates are connected to each other, if there are major changes in plate movement of one plate, it affects all plates on Earth. The most likely reason for the change in direction is the collision of the Indian plate with Eurasia, which occurred about 40-50 million years ago. The Indian plate drifted north at a very high plate tectonic velocity of over 20 cm/year and was abruptly stopped by the collision in the Eocene. This then led to a change in the direction of movement of many plates (Fig. 4.7.7). Most clearly this can be seen in the Hawai’i Emperor seamount chain. Here the kink can be dated almost exactly to 43 million years ago.

The dashed yellow lines in Fig. 4.7.7 show the Hawai’i-Emperor volcanic chain and the twin ridges of Walvis Ridge and Rio Grande Rise, above the development in the Cretaceous and Paleocene and below from the Eocene onwards. Both the Pacific and the African and South American plates move in different directions after the collision. The Tristan da Cunha/Gough Island hotspot was located exactly on the ridge axis until the collision, which led to the formation of the twin ridges Walvis Ridge and Rio Grande Rise. After the collision, however, the spreading zone moved westwards and thus away from the hotspot. From this point on, the volcanic chain only formed on the African plate.

Fig. 4.7.8: Bathymetric map of the South Atlantic with absolute and relative plate movement velocities. Base map created with GeoMapApp  / CC BY  / CC BY ( Ryan et al., 2009 ), velocities calculated after Gripp & Gordon (2002).

The different orientation of volcanic chains and transform faults indicate the difference between absolute and relative plate movement directions. The South Atlantic with the Walvis Ridge and the Rio Grande Rise offers a good example of this.

In Fig. 4.7.8 the hotspot tracks are shown schematically with a blue line. Absolute and relative plate movement directions and velocities are also indicated. Here you can directly see the difference between relative plate motion, as it is shown at the spreading ridge, and absolute plate motion. The African Plate is moving westward very slightly today, while the South American Plate is drifting westward much faster. The difference between the two absolute movement velocities results in the velocity for the relative movement, shown in Fig. 4.7.8 with the green arrows. One can clearly see that the hotspot tracks and the transform faults or their extension in the fracture zones do not run parallel.

In the animation in Fig. 4.7.9, three plates are moving away from each other. The spreading velocity is the same at all three spreading centers, which meet at the triple junction in the middle. There is also a hotspot under the downward branch that repeatedly causes volcanoes to form directly at the spreading center. Moreover, the spreading ridge is offset by a transform fault.

Fig. 4.7.9: Animation: Development of a volcanic chain over a spreading zone (Meschede unpublished, 2023)

The plate movement is related to the hotspot, which always remains in the same place, as is assumed for the hotspot reference system. It can be seen that the volcanic chain develops parallel to the trace of the triple junction, which, as shown in Chapter 4.4 on the geometry of triple junctions, reflects the absolute plate movement. The transform fault remains constant in length, but it migrates away from the hotspot and forms an angle to the volcanic chain. The absolute plate motion represented by the volcanic chain is thus not parallel to the relative plate motion reflected in the orientation of the transform fault.

Fig. 4.7.10: Bathymetric map of the South Atlantic with absolute and relative plate movement velocities compared to the model of the animation in Fig. 4.7.9. Base map created with GeoMapApp  / CC BY  / CC BY ( Ryan et al., 2009 ), velocities calculated after Gripp & Gordon (2002).

In Fig. 4.7.10 the model can be seen in direct comparison with the situation in the South Atlantic. There, too, the transform faults and fracture zones are not parallel to the hotspot trace. The model clearly shows that the absolute plate movements do not have to be parallel to the relative movements.

Hotspot tracks and transform faults

Subduction  (in prep.)