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Fig. 6.18. Phanerozoic APWP for (a) South China using the mean pole positions given in Table 6.9 and (b) Tarim using the mean pole positions given in Table 6.10. Each mean and its circle of 95% confidence is labeled with the mean age in millions of years.

giving data from 573 sites. Paleomagnetic data for Tarim have only become available since the first APWP for the late Paleozoic was published by Bai et al. (1987). This was followed soon afterwards by the first studies involving Western scientists (Li etal., 1988; McFadden et al., 1988b).

Over the past decade sufficient data have become available to be able to determine the APWP back to the Devonian. From the Devonian to the present time the APWP is restricted to the northern hemisphere. The data set is much smaller than that for North and South China with 28 studies giving data from 328 sites. Although there are relatively few data, they are all of high quality, having been determined using all the modern methods and analytical techniques.

The timing of the amalgamation of Eurasia involves a combined analysis of the paleomagnetic data for all the major blocks and this is considered in detail in §7.2.2. Although the results for the major blocks as outlined above appear to be restricted compared with those for Laurentia and Europe, the fact that they have been acquired over the past 15 years results in a data set of higher reliability.

6.5.4 The Gondwana Continents West Gondwana

Africa and South America are referred to as West Gondwana because it is thought that the constituent parts of these continents assembled during the Brasiliano (600-530 Ma) and Pan-African («500 Ma) orogenies. West Gondwana then merged with East Gondwana, which had remained as a unit for very much longer (see §7.2.3). A simplified outline of the major blocks of Africa and South America is shown in Fig. 6.19. The three major cratons of Africa are the Congo, Kalahari, and West Africa cratons. These cratons are surrounded by the Pan-African Orogenic Belts of age «550 Ma relating to their time of amalgamation. In the northern part of Madagascar there is a small remnant of the India craton (see Fig. 6.22).

For the purpose of analyzing paleomagnetic data, the subsequent rift history of the African continent has significance because these rifts have caused internal deformations that need to be taken into account. When Africa and South America separated in the Early Cretaceous, a failed third arm of a triple junction was formed in the region of the Benue Trough. This created an Early Cretaceous

Fig. 6.19. (a) The major cratons of Africa (shaded) and their relationship to the Early Cretaceous rift system of northwest and northeast Africa following Pindell and Dewey (1982). The Benue Trough represents the failed third arm of a triple junction that formed when Africa and South America separated in the Early Cretaceous. The resulting rift system produced internal extension within the African continent. The northern part of Madagascar includes a small former part of the India craton labeled I. (b) Simplified tectonic framework of South America showing the major cratons (shaded), together with the Phanerozoic orogenic belts along the west and southern margin. The S2o Francisco craton was formerly a westerly extension of the Congo craton and WA is a former southern part of the West Africa craton. The Arequipa Massif is a former part of North Britain when it was joined to Laurentia.

Fig. 6.19. (a) The major cratons of Africa (shaded) and their relationship to the Early Cretaceous rift system of northwest and northeast Africa following Pindell and Dewey (1982). The Benue Trough represents the failed third arm of a triple junction that formed when Africa and South America separated in the Early Cretaceous. The resulting rift system produced internal extension within the African continent. The northern part of Madagascar includes a small former part of the India craton labeled I. (b) Simplified tectonic framework of South America showing the major cratons (shaded), together with the Phanerozoic orogenic belts along the west and southern margin. The S2o Francisco craton was formerly a westerly extension of the Congo craton and WA is a former southern part of the West Africa craton. The Arequipa Massif is a former part of North Britain when it was joined to Laurentia.

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