MECHANISM FOR CRUSTAL THICKENING IN TIBET: A PALEOMAGNETIC VIEW

<正> The mid-Gretaceous paleomagnetic pole for the Lhasa Terrane (69.8°N 292.9°E, A95 = 5.1°) is in strong discordance with that for the stable Eurasia (69.5°N 167.4°E, A95 = 8.7°), which suggests that the Lhasa Terrane has moved 2400±800 km NNEward and rotated 31.4±9.2 counterclockwise with respect to the stable Eurasia. The relative motion started at the time when the Indian plate began to collide with the Eurasian plate (or maybe started a little earlier), and was accomplished through the internal deformation of the southern Eurasian continent. As far as the mechanism is concerned for the crustal thickening in the Tibetan Plateau, the paleomagnetic data are therefore in favor of the internal deformation hypothesis within the Tibetan crust, but raise further challenge to the hypothesis of longdistance underthrusting of the Tibetan Plateau by the Indian subcontinent.