Liupan Tectonic Uplift History Of The Southwestern Margin

Liupanshan and Liupanshan Basin is located at the northeastern margin of Tibetan Plateau, and it is an important part of Helan-Liupan-Chuandian north-southward tectonic belt. Studies on tectonic evolution of Liupanshan and Liupanshan Basin can not only help to discover geological evolution process of the western margin of Ordos Basin from Mesozoic and Cenozoic, but also can help us with the research of the uplift process of the northeastern margin of Tibetan Plateau. Research on uplift history of Liupanshan Basin can also contribute to oil and gas exploration. Although previous studies has been done on the apatite fissiontrack data analysis of the Palaeoproterozoic Longshan group gneiss and the Late Triassic granite, the results of uplift history and the local sedimentary feature has a significant inconsistent. The aim of this thesis is to focus on the inconsistent and make a further research,to discuss the uplift feature of Helan-Liupan north-south tectonic belt from Mesozoic base on previous research.The cross section located in Sanqiao Village, Guguan Town, Long County, Baoji City is our key object of study, this cross section is also located at the southwestern margin of Liupanshan. We collected three samples from the outcrop of the cross section, they are Upper Ordovician quartz diorite、Palaeoproterozoic Longshan group biotite-plagioclase gneiss and Lower Cretaceous Liupanshan group Heshangpu formation sandstone, and took apatite fission track test. Based on the result, we analyzed the uplift history of southwestern margin of Liupanshan, and discussed the uplift history feature of Helan-Liupan area from Mesozoic Jurassic by comparing the previous studies of thermal evolution history in the same area. The main conclusions are as below:1) The southwestern area of Liupanshan uplifted in Late Jurassicand Early Cretaceous, the whole Liupanshan area uplifted in Early Cretaceous; in Cenozoic, Liupanshan significantly uplifted. 2) The central age and pooled age of the samples are154Ma、108Ma and130Ma separately, combined with analysis of single practical age in the column diagram and relative plot, the results of the appetite fission track test suggests that the southwestern margin of Liupanshan uplifted in Late Jurassic, early and late stage of Early Cretaceous. According to the time-temperature model of the samples, the cooling event occurred during Late Jurassic, Early Cretaceous and since Cenozoic, especially since Oligocene. The uplift history of the model is consistent with the local sedimentary feature—the absence of Upper Jurassic Fenfanghe formation、Upper Cretaceous and Oligocene, and the gravel sediment of Lower Cretaceous.3) The uplift events of Liupanshan、Liupanshan Basin and Helanshan area are regional and roughly simultaneous. During Cenozoic, the uplift history of Helan-Liupanshan south-north tectonic belt tends to be more simultaneous.