Provenance of metasedimentary rocks from the Beishan orogenic collage, southern Altaids: Constraints from detrital zircon U-Pb and Hf isotopic data

摘要

The origin and tectonic settings of metasedimentary sequences in the Central Asian Orogenic Belt have been a matter of debate regarding their contributions with some proposals of being microcontinents or accreted material, largely due to a lack of high resolution geochronological data. This paper reports detrital zircon U-Pb age and Hf isotopic data for the previously mapped Precambrian metasedimentary rocks from the Beishan orogenic collage, southern Altaids. Our data show that Precambrian ages dominate all the analyzed samples, but two samples yield Paleozoic zircons which suggest that they were not deposited in the Precambrian. The late Paleoproterozoic-early Mesoproterozoic group (~. 2000-1300. Ma) is the largest age population among the six samples analyzed. This age population (~. 2000-1300. Ma) corresponds to the assembly and subsequent break-up of the Columbia supercontinent. Only one sample (11SYS01) yields Neoproterozoic ages (with two peaks at 930 and 785. Ma), which shows a possible affinity with the Tarim Craton. Hence, the age spectra presented here are generally different from that of the Tarim Craton and the metasedimentary rocks from the Central Tienshan. Our data show that the Tarim Craton is not the main source area for the metasedimentary rocks from the Beishan orogenic collage, but instead multiple source areas may have contributed to the Beishan collage. Combining our new results with published data, we favor an allochthonous origin for the metasedimentary sequences which may be associated with major thrust tectonics. Therefore, a long-lived arc accretionary model is proposed for the tectonic evolution of the Beishan orogenic collage.