Triassic result includes so much more data than any of the other mean poles listed in Table 6.7. There are data from 90 studies representing 1332 separate sites, most of which are of Paleozoic age. This is only about one-third of the data available from either North America or Europe, but the remoteness and difficulty of access to the region has clearly restricted the acquisition of paleomagnetic data, and this is likely to be the case for some time.
The APWP for Siberia for the Phanerozoic represents the longest of these paths for any of the world's major cratons. It extends back from the present pole through an angle of nearly 135° to its Early Cambrian position. Note that the paleomagnetic pole crosses the equator during Siluro-Devonian times and by the Early Cambrian is located at 43°S (Fig. 6.16). Unlike the data for North America and Europe, the data for Siberia in the late Paleozoic suffer from poor age control. That is, most results are stated to be broadly Permian or Carboniferous and for this reason it has not been possible to subdivide the data for these two epochs in any finer detail.
North China, South China, and Tarim
The North and South China blocks consist of Precambrian basement but are not really stable cratons because the Phanerozoic cover rocks in most parts have been deformed by subsequent orogenies. North China is often shown as including Korea and in that case has been referred to as Sino-Korea. Faunal and other similarities suggest a close affinity between Korea and North China certainly in Mesozoic times and probably also during the Paleozoic. However, paleomagnetic data from Korea suggest that there has been relative rotation of Korea with respect to North China in pre-Cretaceous times (Van der Voo, 1993). Therefore, most analyses of paleomagnetic data usually regard Korea as a separate entity from North China. The eastern boundary of North China block is represented by the Tanlu fault running north-south and to the south the boundary with the South China block is the Qilian-Qinling-Dabie Shan (mountains). There appears to be no clear suture between the North China block and Tarim and consequently many geologists have considered them to have formed a single block since the late Precambrian. However, paleomagnetic data suggest that the two blocks could not have attained their present configuration until at least the Mesozoic (McFadden et al., 1988b; Li, 1990). The collision between Tarim and Junggar occurred along the Tianshan Mountains and is inferred to have occurred sometime during the Permian. A full discussion of the paleomagnetic data from these three major blocks of China in relation to the timing of their amalgamation with Eurasia is given in §7.2.2.
Only limited paleomagnetic studies were carried out in China pre-1980 and then mostly on Mesozoic and Cenozoic rocks (McElhinny, 1973a). Many Western scientists visited China in the early 1980s and this resulted in an increased interest in paleomagnetic studies in China. The first publication resulting from this work was that of McElhinny et al. (1981), who reported new results for the Permo-Triassic of the North and South China blocks. In the 1980s cryogenic magnetometers and the methods of principal component analysis became widely used in western laboratories. As a result the database for China is overall of a much higher standard than for most other parts of the world and it is mainly the early studies from pre-1980 that have quality index Q < 3.
The first APWPs for North and South China were given by Lin et al. (1985). Zhao and Coe (1987), Enkin et al. (1992) and Zhao et al. (1990, 1996) discussed the significance of data acquired for the timing of the collision and suturing of these blocks to each other and to Asia.
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