Thermochronology of Meso-Cenozoic uplift and tectonic growth of the Longmenshan Thrust Belt

This paper is the result of geological survey engineering. Objective In order to discuss the relationship between the vertical tectonic uplift and the lateral tectonic expansion happened in Meso-Cenozoic in the Longmenshan thrust belt, this paper carries out low-temperature thermal chronology testing and analysis. Methods Through the determination and analysis of apatite and zircon fission track age, the characteristics of tectonic evolution are studied. Results The study shows that the lengths of apatite fission tracks are within the range of 11.4±2.6~12.2±2.2μm, which can effectively reflect the local tectonic uplift history; the results of thermal history simulation show that the apatite samples have experienced three critical stages, including the rapid tectonic uplift, the stable tectonic stage and the rapid tectonic uplift. Besides, the uplifting events happened in the northern area were earlier than those in the southern area. The cooling rate of each rock sample is within the range of 1.211~6.053℃/Myr. The tectonic uplift rate gradually increases from southeast to northwest, and the time of uplifting gradually becomes late in the same direction. Conclusions The tectonic deformation of Longmenshan thrust belt has had the characteristics of piggyback propagation from northwest to southeast since Meso-Cenozoic (150Ma), and it has showed these characteristics again from late Cretaceous to Eocene (70~50Ma), even Oligocene (about 20Ma). The central and western regions of the Longmenshan thrust belt are characterized by multi-stage tectonic uplift and superposition.