THE EVOLUTION OF THE PAMIR: APPLICATIONS OF MULTI-GEOCHRONOLOGY TO MODERN RIVERS DRAINING THE EASTERN PAMIR

The Pamir Mountains are located south of the Tien Shan and west of the Tibetan Plateau. Tectonic processes related to multiple collisions within the Paleozoic-Mesozoic and Cenozoic has resulted in the present-day configuration of the Pamir and accretion of different terranes. The correlation of these terranes has been a subject of considerable debate and two different models of terrane correlations have been proposed by Schwab et al. (2004) and Robinson et al. (2007). The former correlates Northern and Central Pamir to Songpan-Ganze and Qiangtang terranes of Tibet, based on the geologic structures and geochemistry of magmatic belts in the Pamir-Tibet orogen. The latter, however, correlates the same tectonic divisions of the Pamir to Qaidam and Songpan-Ganze terranes of Tibet respectively, based on the data from previous studies.

Here we present new zircon U-Pb detrital geochronology data from 7 modern river samples along the Eastern Chinese Pamir near the town of Muji, Oytag and Tashkorgan. About seven hundred detrital zircons were analyzed by MC-LA-ICPMS at the Laserchron lab at the University of Arizona in order to determine crystallization ages of the source areas. Samples from the Eastern Pamir are characterized by prominent ~200-250 Ma and ~400-450 Ma age groups. Our data show that the source rocks of the sampled rivers have an affinity with the Kunlun and Songpan-Ganze arc, thus, supporting the correlation made by Schwab et al. (2004). The detrital U-Pb ages recorded in rivers draining the eastern Pamir are very distinct from detrital U-Pb ages recorded in rivers from the western Pamir where a large component of the analyzed grains show ages younger then 200 Ma (<200Ma). This suggests affinity with Gangdese arc rocks of the Lhasa terrane in Tibet (Lukens et al. 2010).