Characteristics of Heiyingshan Late Triassic thrust nappe structure in the Beishan orogenic belt and its constraint on the evolution of the orogenic belt

Beishan orogenic belt is located in the southern margin of the Central Asian tectonic belt, where the Tarim Plate, North China Plate and Siberia Plate meet, which is the most significant area of the Phanerozoic continental crust accretion and transformation in the world, has become the key area for studying the process from subduction to final collage closure and intracontinental transformation of the Paleo−Asian Ocean, and the process of intracontinental transformation covers the complex process of intracontinental deformation, basin-mountain coupling and readjusting since Late Paleozoic, especially during the Mesozoic and Cenozoic. Previous studies on the Beishan orogenic belt mainly focus on the early subduction and collision process, but the study on the intracontinental stage, especially the Indosinian tectonic process is relatively weak. In the field geological survey of the Heiyingshan area in the northern of the Beishan orogenic belt, we found the Early Paleozoic metamorphic sandstone-volcanic rocks thrust southward onto the carboniferous andesitic volcanic tuff and Triassic acid fused tuff, metamorphic sandstone. By studying the structural characteristics of the thrust system and the zircon U−Pb ages of the upper and lower strata volcanic rocks, it is proposed that the thrust system has nappe from north to south and shows the characteristics of the ‘flyover type’ superimposed structure. The new geochronological data indicate that the thrust nappe system is the result of intracontinental compression in Beishan orogenic belt during the Late Triassic (Late Indosinian). The identification and age determination of the Heiyingshan thrust nappe structure have important significance for a further understanding of the intracontinental tectonic evolution of the Beishan orogenic belt.