Geochronology of the sedimentary series from Zhuo'abulake Formation in Kaladawan area of Altun and its geological significance: LA-ICP-MS U-Pb age evidence of detrital zircons

Choosing the conglomerate from the sedimentary series of Zhuo'abulake Formation in Kaladawan area as the study object and using LA-ICP-MS zircon U-Pb isotope chronology, the authors studied the sedimentary age, material source and tectonic setting of the sedimentary series. Some results were obtained:① The age spectra of detrital zircon can be evidently divided into two groups:522~427Ma and 638~1766Ma, with other two old ages 2450Ma and 3394Ma. ② The youngest age of detrital zircons is 427±4Ma, suggesting that the formation of the conglomerate was later than 427Ma, and hence the formation age of the strata may be constrained from Late Silurian to Early Devonian (427~410Ma); Zhuo'abulake Formation should be divided into more units since it consists of materials from Late Cambrian to Early Devonian. ③ The peak value of the age spectrum is 456Ma, indicating that there existed a magmatic event during this period. The 522~432Ma age data possess the largest proportion and account for about 81% of the total data, showing that the magmatic rocks that were formed in early Paleozoic, especially from late Cambrian to Ordovician constituted the most important source of the conglomerate. The compositional ages suggest a sedimentary response to the orogenic erosion of a series of igneous rocks caused by the southward subduction and collision of Dunhuang massif in early Paleozoic period. ④ Combining the recent research on North Qilian orogenic belt and the study of the detrital zircons in Kaladawan area, the authors consider that sedimentary series of Zhuo'abulake Formation in Kaladawan area and the Tianzhu Formation and Lujiaogou Formation in North Qilian have similar ages and material sources, and they may be the products of continental collision or arc-continent collision after North Qilian-North Altun limited ocean closure.