Paleomagnetic study of Mesozoic continental sediments along the northern Tien Shan (China) and heterogeneous strain in central Asia
Résumé
A paleomagnetic study of rocks from the northern foot of the Tien Shan and the southern border of the Dzungar Basin, east of Urumqi (44.2°N, 86.0°E), spanning ages from middle Jurassic to early Tertiary was carried out to constrain the tectonic evolution in central Asia since Mesozoic time. Five middle Jurassic sites reveal a remagnetized direction close to the present Earth field in geographic coordinates: D = 6.6°,/ = 72.6° (0.95 = 7.4°). Thirteen out of 17 upper Jurassic and lower Cretaceous sites yield a characteristic direction (stratigraphic coordinates) of D = 12.7°, I = 48.6° (0.95 = 5.5°). Nine of 16 upper Cretaceous and lower Tertiary sites provide a characteristic direction of D = 12.5°,/ = 51.3° (0.95 = 6.9°). The latter two directions pass fold and reversal tests. The pole positions are close to each other and to the Besse and Courtillot [1989, 1990] Eurasian apparent polar wander path. for ages ranging from 130 to 70 Ma. However, the difference in paleolatitudes amounts to about 5.9° ± 3.7°, which
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