Structural Features And Structural Evolution Of The North Margin Of Qaidam Basin During Cenozoic Era

Qaidam Basin is in the joint part of the ancient Asia tectonic domain and the Tethyan-Himalayan tectonic domain, it is a component of the Xiyu Plate. The basin is a NWW trending Mesozoic-Cenozoic fault-depression Basin with a stripe shape. A series of large faults separated it from adjacent tectonic units. The northeast boundary with South Qilian fold system is Saishiteng Mountain-Zongwulong Mountain fault; the northwest boundary with Tarim Basin is the Altyn Tagh strike-slip fault; in the southeast and southwest, E'la Mountain Fault and North Kunlun Mountain Fault separate it from West Qinling Mountain Orogenic Belt and East Kunlun Mountain Orogenic Belt. The structural features and structural evolution of the Qaidam Basin is always the concern of structural geologists. However, in the predecessors'study of the basin, seismic profiles are mostly used in the oil and gas exploration, while the usage of seismic profiles in the analysis of structural deformation is limited.Based on the interpretation of seismic profiles, this paper aimed at the determination of the Cenozoic structural features of the north margin of Qaidam Basin, and by integrating the reconstructed structural evolution of representative cross-section and predecessors'research, the paper discussed the process of structural deformation of Qaidam Basin in Cenozoic Era.In order to accomplish the objects above, this paper contains the following components: First, analyze 2-d cross sections comprehensively; then, according to the theory of growth fault related folds, plus drilling cores, logging data and core data, the author completed the comprehensive geological interpretation of seismic sections in order to study the Cenozoic structural features of the north margin of Qaidam Basin. On the basis of displacement-length theory and the study of growth-strata, the author analyzed the evolution of major fault-related folds, and then selected representative section for the reconstruction of structural evolution history, according to the reconstructed evolution history, the paper discussed the process of structural evolution of Qaidam Basin in Cenozoic Era.This paper selected 3 representative main survey lines and 1 contact survey line from the 2-D sections to fine geological interpretation, then, combined with the latest achievement of basin structure, the theory of growth fault related folds and the technique of equilibrium section recovery both home and abroad, the paper analyzed the main structural styles and structure combination in the north margin of Qaidam Basin, established the geometric and kinematical model of faults. By the reconstruction of structural evolution history of representative cross-sections, the paper summarized the process of structural evolution of the north margin of Qaidam Basin in Cenozoic Era, and got the following understanding:The Cenozoic structures in the north margin of Qaidam Basin are mainly NW trending, indicating the study area was mainly affected by the Cenozoic NE-SW trending compression.In the north margin of Qaidam Basin, the structures developed in Cenozoic are mostly fault-propagation folds and fault-bend folds, from northeast to southwest, that is, from the piedmont of Qilian Mountain to the inner basin, the formation time of these fault related folds are gradually later, indicating the compression in Cenozoic expanded to the southwest over time.Based on the combination the reconstructed structural evolution history of representative cross-section and other related data, the process of structural evolution of north margin of Qaidam Basin during Cenozoic Era is as following: from Paleocene to Eocene, compression mainly occurred in northeast anticline zone in the piedmont of Qilian Mountain in the northern margin of the Qaidam Basin; in Oligocene, the front of compression entered the central anticline zone, and the compression cluster also moved toward southwest; in Miocene, the front of compression continued to move toward Southwest, closing to the southwest border of the central anticline zone, and the compression cluster also entered the central anticline zone; from Pliocene to present, the front of compression exceeded the southwest border of the central anticline zone.