Revised Phanerozoic Paleomagnetic Apparent Polar Wander Paths for the Three Major Blocks of China and Their Significances on Tectonic Evolution

(Paleomagnetism Laboratory, Institute of Geology & Geophysics, CAS)

SUMMARY.
Paleomagnetic study of China and its constraints on Asian tectonics has been a hot spot for a long time. The Phanerozoic apparent polar wander (APW) paths for three major continental blocks of China––North China, South China and Tarim––have been recently revised based upon a significant amount of new paleomagnetic results.
The newly revised APW paths for the three major blocks of China suggest that: (1) New APW paths are in full consistence with the published ones for both the NCB and SCB during post-Permian time, whereas significant difference exists for pre-Permian time for these two blocks; (2) APW paths of the three major blocks are in obvious discrepancy from the Paleozoic to Triassic, which would not be eliminated by simple rotation, demonstrating that they are dynamically separated from each other during that period; and (3) the three major blocks become consistent since the Late Jurassic, showing that they have completely sutured and no obvious relative displacement between them, suggesting that the three major blocks may have been dynamically a composite block.
In Particular, the three major blocks of China were located at middle to low latitudes of the Southern Hemisphere, and show some affinities with East Gondwana during the period from the Cambrian to Ordovician. However, the NCB may episodically separate from East Gondwana during that period, and may have sited close to Siberia and North America during the Middle Ordovician. The NCB was unattached with the SCB during the Cambrian: the NCB was sited adjacent to eastern Antarctic-Australia integral continent of Gondwana, whereas the SCB as well as Tarim was located adjacent to western Antarctic-Australia integral continent of Gondwana. Two Carboniferous paleomagnetic poles from the eastern part of the Hexi Corridor are distinct with the coeval ones for Inner Mongolia, Outer Mongolia, South China, Tarim and stable Europe, at greater than 95% confidence, suggesting that these continental blocks could not have been connected in their present configuration during the Carboniferous. Moreover, significantly different paleolatitudes and tectonic motions between the NCB and eastern Gondwanaland during the Carboniferous indicate that the two had rifted apart by the late Visean.

Figure 1: Equal-area projection of newly revised Phanerozoic APW paths for three major continental blocks of China. 67, 109, and 34 paleopoles were used respectively to construct the APW paths of the Phanerozoic for the North China, South China, and Tarim.

Figure 2: Equal-area projection of newly revised Phanerozoic APW path for the North China block (NCB). All plotted onto the Northern Hemisphere. 

Data (Microsoft Word).

Figure 3: Equal-area projection of newly revised Phanerozoic APW path for the South China block (SCB). Solid/dash symbols represent paleopoles plotted onto the lower/upper hemisphere.

Data (Microsoft Word).

Figure 4: Equal-area projection of newly revised Phanerozoic APW path for the Tarim block. 

Data (Microsoft Word).

Figure 5: Early Cambrian paleogeographic reconstruction of the North China, South China and adjacent areas in geographic coordinates. Relative longitudes of the blocks are unconstrained. Eular rotation poles: NCB to Africa, 4.9ºN, 70.2ºE, D=-133.5º; SCB to Africa, 39.8ºS, 134.7ºE, D=51.6º.

Figure 6: Middle Ordovician paleogeographic reconstruction in geographic coordinates. The NCB may episodically separated from the Antarctic-Australia integral continent, and may have sited close to southern Siberia and North America in the Middle Ordovician.

Figure 7: Late Devonian paleogeographic reconstruction in geographic coordinates. The APW path for the Gondwanaland (circles) is drawn according to Meert & Van der Voo (1997), Grunow (1995), and Van der Voo (1993). All the poles are plotted with palaeo-south poles. The NCB is shown to Africa according to rotation pole of 0.8°N, 270.3°E with D=119.6°.

Figure 8: Early Carboniferous paleogeographic reconstruction of the NCB and adjacent areas in geographic coordinates. The different rate of movement relative to Gondwanaland suggests that the North China and South China blocks separated together from Gondwanaland after the Late Devonian. G, Greenland.

Figure 9: Late Carboniferous paleogeographic reconstruction of the NCB and adjacent areas in geographic coordinates. The different tectonic motions of the NCB and SCB during the Carboniferous apparently lead to a longitudinal juxtaposition, separated somewhat in latitude.

Figure 10: Early Triassic paleogeographic reconstruction of the NCB, SCB and adjacent areas in geographic coordinates. The NCB and SCB may have collided in the eastern part, however, a westward triangular ocean may yet remain between the two blocks during that period. Abbreviation is: KAZ, Kazakhstan.

Figure 11: Schematic map showing propagated westward collision and suturing between the NCB and SCB during period from the Late Paleozoic to the present. Reference site: 35ºN, 119ºE.

Figure 12: Schematic map showing propagated eastward collision and suturing between the NCB-MON and Siberia during period from the Late Permian to the present. Reference site: 50ºN, 75ºE.

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