Sedimentary And Tectonic Evolution Of Luonan, Sanyo Cenozoic Basin

Qinling orogenic belt has worked into the intracontinental orogenic stage after the period of the Mianlue ocean closed in Middle-Triassic. Due to the control of two domains tectonic system of the Pacific Ocean and the Himalayas, its continental evolution mainly showed as follows:a significant event about uplifting, cooling and intense magmatism so on. Magmatic activity prompted the early backbone fractures of Shangdan, Luonan-luanchuan, Shanyang-fengzhen and others resurrection, and formed a series of intermountain basins which accepted detrital material from the mountains periphery along the fault rupture. Therefore, this kind of basin became a natural place to study the evolution of qinling orogenic belt within plate.This article attempts to analyse intracontinental evolution of qinling orogenic belt through the different tectonic units, thus selects Luonan and Shan Yang basin which located in the South and the North Qinling microplate respectively as the study area. Measuring stratigraphic section and research of sedimentary tectonic analyse the basins filling process; Studying basin-controlling fault, internal stratum fault and sediment apatite in low temperature thermal chronology, promotes the further understanding of information for basin tectonic deformation and source area of uplift and denudation.The research results show that Luonan basin and ShanYang basin both are downfaulted basins for late Mesozoic Yanshan movement. In the early cretaceous, the magmatic activity of Yanshan movement caused Luonan-luanchuan fracture, Shanyang-fengzhen fracture of nearly east-west direction resurrection, and formed a series of intermountain basins along the early backbone fractures in Qinling orogenic belt; After entering the new generation, the stress in collision that India plate subducted the Asia plate through the Yangtze plate had spreaded to the east qinling region. The north-south direction of compressional fault effect appeared and even the depressional faulting disappeared, which the basin basement uplifted together along with the Qinling microplate gradually and formed today’s face.Strictly controlled by fault depression effect of Luonan and Shanyang basin had experienced the evolution of at least three stages:(1) the initial chasmic stage in the early cretaceous period to the early late cretaceous. Filling coarse clastic materials, such as the clay under the Guojiacun formation;(2) the expansion filling stage in from middle late cretaceous to Paleocene. Strong depression faulting, cause the basin sedimentat quickly, and sediment is fine grained material, such as the Shanyang group;(3) the basin shrinking period since Oligocene, the influence of Himalayan movement, brought basin uplift, curbed fault depression effect, and suffered from erosion. The three phases constitute a complete sedimentary cycle of faulting depression basins.The fission track experiments result of basin clastic apatites shows, the Taowan group and the Kuanping Group during the period of104.4-68Ma, which elevating cooling rate is2.9～6.2℃/Ma, an average of4.05℃/Ma, denudation rate is0.12～0.24km/Ma, with an average of0.18km/Ma; Liu Lingqun uplift cooling rate during129.6～64Ma is1.7～-4.2℃/Ma, with an average of2.95℃/Ma, denudation rate is0.07～0.17km/Ma, with an average of0.12km/Ma, reflect uplift rate in the north qinling plate is higher than the south Qinling plate. Its thermal history simulation also demonstrates the basins evolution had experienced two tectonic events:roughly depressional faulting (the provenance grow) and lifting movement.The research of basin tectonic deformation also showed that from late cretaceous to paleocene Luonan and Shan Yang basin existed during at least two periods of tectonic deformations:(1) a large-scale left-lateral slip and normal fault movement happened, and scratch lineations indicate more for low Angle (20to50°), which reveals the information in back-arc basin of qinling orogenic belt in yanshanian period;(2) the compressive fold deformation developed near basin fracture, and inside is not obvious, which may reflected this deformations were sedimentary and structural responses of the Himalayan movement in Qinling orogenic belt.