Yanshanian Structural Feature And Dynamics Of The Xuefengshan Intracontinental Tectonic System

The Xuefeng intracontinental tectonic system forms the basic tectonics of this area after the transformation by Yanshanian movement. However, our knowledge to the nature of intracontinental tectonic deformation, destroy and preservation of paleo-reservoir, and the mechanism of intracontinental tectonic evolution is quite incomplete. With field geological observation, geophysical data interpretation and dating data collection combined, this thesis studies Yanshanian characteristics and activity of folds and faults; and combined with tectonic setting of South China in Yanshanian, and distribution rules and causes of granite-volcanic, the dynamics of the Xuefeng intracontinental tctonic system in Yanshanian is discussed. The major conclusions are presented as follows.(1) There are two-stage Yanshanian foldings. The early-stage fold axis is NE-NNE trending while the late-stage fold axis is SN-NNE. Structural pattern west of the Xuefengshan has obvious characteristics of block-faulting-controlled effect and boundary faults of the sub-tectonic units play a significant role in structural styles. Fold morphology is controlled by multi-boundary states.(2) The southeast to northwest-dierected compression in the early Yanshanian and the east to west-directed one in the late Yanshanian result in two-stage thrusting activities, respectively. In the east of the Xuefeng uplift belt, the fault movement has the characteristics of inheritance. In the Xuefeng uplift belt, the early faulting shows low angle thrust and the late faulting shows high angle thrust. In the northwest of the Xuefeng uplift belt, the major detachment faults take on jumping propagation from SE to NW.(3) Because the Xuefeng uplift belt had experienced Caledonian, Indosinian movements, the pre-existing faults show an asymmetric fan structure. Under the SE-NW-directed shortening in Yanshanian movement, the Xuefeng uplift suffers from not only the vertical extrusion, but also the lateral extrusion, and the degree of Fault-block extrusion are inhomogeneous.(4) The study area, especially the western flank of the Xuefengshan, has relatively thick formation of pelagic sediment, Yanshanian movement, however, has a great influence on the Xuefeng intracontinental tectonic system, consequently destroying the preservation condition of oil-gas. Because of uplift of folds cut of related fractures and afterwards, long period of erosion, the paleo-oil reservior was destroyed enormously. However, some area being not destroyed still have great prospect to explore.(5) The direct dynamics of the evolution of the Xuefeng intracontinental tectonic system during Yanshanian is the stretching and thinning of the Xiang-Gan area and lateral compression caused by the mantle upwelling, which may be induced by the starting and change of direction of the Paleo-Pacific Plate subduction, or both of the two mechanisms are dominated by higher level thermo-tectonic process in the inner Earth. These mechanisms imply both the unique dynamic mechanism in the concept of the Continental Dynamics and the relationship of the plate tectonic and the Continental Dynamics. It is important manifestation of the reworking, preservation and evolution of the continent.