Abstract:

Abstract: There was much controversy for long over the formation age of the Huluhe Group in eastern part of Qilian orogenic belt. Choosing the metadetrital rocks in the Huluhe Group as study objects, this article uses LAICPMS zircon UPb isotope chronology to study the formation age and material source of the Huluhe Group. The results show that the detrital zircons isotope ages of the two samples from the Huluhe Group and the age of the granite intruded in it show that the sedimentary age of the Huluhe Group ranges from 447434 Ma, mainly the early Silurian. The zircon age spectrum can evidently divided into four groups: SinianEarly Paleozoic age group from 426595 Ma, the peak value is 479 Ma; Neoproterozoic age group from 738981 Ma, the peak value is 887 Ma; Mesoproterozoic age group from 10001913 Ma, the peak value is 1499 Ma; PaleoproterozoicNeoarchaean age group from 20532872 Ma, the peak value is 2448 Ma. The SinianEarly Paleozoic age group can further be divided into 426493 Ma and 527595 Ma, the peak values are 445 Ma and 559 Ma respectively. The former indicates that its material source mainly be the adjacent North Qilian orogenic belt and northern margin of the West Qinling tectonic zone, which is a sedimentary response to the orogenic erosion of a series of igneous rocks caused by the northward subduction and collision of the MiddleSouth Qilian and West Qinling microblock in the Caledonian, respectively. The latter is related to the magmation of the FanAfrican orogenic event in the North Qilian orogenic belt and northern margin of West Qinling tectonic zone. The Neoproterozoic age group can further be divided into 738799 Ma, 839862 Ma and 902981 Ma, the peak values are 768 Ma, 848 Ma and 948 Ma respectively, and 902981 Ma age datas have the largest proportion. The 738799 Ma age datas are approximately corresponding to the age of Late Neoproterozoic tectonomagmatic event in the North Qilian orogenic belt, and are related to the breakup of the supercontinent Rodinia. The 839862 Ma and 902981 Ma age datas are approximately correponding to the age of Early Neoproterozoic tectonomagmatic event in Middle Qilian and northern margin of West Qinling area, and are related to the convergence of the supercontinent Rodinia and arc magamtism. The Mesoproterozoic age group can be divided into 10001197 Ma and 12431913 Ma, the peak values are 1036 Ma and 1593 Ma respectively, and its material source may be the basement of Qilian orogenic belt and North China block. The PaleoproterozoicNeoarchaean age group reflects that the material source is the crystalline basement of North Qilian orogenic belt and northern margin of West Qinling tectonic belt, part may also be from the basement of North China block. Comprehensive analyses show that the material source is much complicated, with obvious diversity, including the Qilian orogenic belt, northern margin of West Qinling tectonic zone and the basement of North China block, among which the first two was the predominate source areas to the sediments, but Qilian orogenic belt is the main source of the Huluhe group.

Key words: detrital zircon, LA-ICP-MS zircon U-Pb age, material source, Huluhe Group, Qilian orogenic belt