Objective: The Changjiaoba Group, located in the Foping area of the South Qinling Belt, is one the few strata of the belt that remain less well-studied. The lack of accurate definition of composition and formation age has restricted the research on the South Qinling Belt of its tectonic affinity and evolution in-depth.
Method: This paper investigates the petrological and zircon U-Pb chronology of metamorphic sedimentary rocks from the Dizhuanggou Formation in the Changjiaoba Group.
Results: The results show that the dominant peak detrital zircon ages of the two samples taken are approximately 810-835 Ma, with the youngest age range of approximately 600-700 Ma, indicating that the maximum depositional age is Neoproterozoic. This age spectrum differs significantly from that of the most exposed Devonian Heilongtan Formation of the Changjiaoba Group, but highly similar to that of another sample from the Foping Group, which has a minimum age peak of 718 Ma and a major peak of 810 Ma. In addition, metamorphic zircons from the Dizhuanggou Formation and the Foping Group yield ages of 207 Ma and 193 Ma, respectively.
Conclusion: The distinct depositional ages in Changjiaoba Group show a complexity of its composition. Combined with the petrological and field geological features, it is believed that the Dizhuanggou Formation together with some Neoproterozoic strata of the Foping Group, formed the transitional basement of the western South Qinling Belt, which is comparable to the transitional basement of the Wudang and Yaolinghe groups east of the Ningshan Fault in the South Qinling Belt.
Significance: The identification of Neoproterozoic materials in the Changjiaoba Group provides a new basis for the division of metamorphic units in the Foping area, sorting out three units with different degrees of layering and metamorphism, which in turn facilitates the understanding of the Mesozoic orogenic process in the South Qinling Belt.
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