Mesozoic-Paleozoic Tectonic Characteristics And Its Evolution In The Kongnan Area

In this paper, making full use of the 3D seismic data, combined with drilling, well logging interpretation with the theoretical views of tectonic geometry, tectonic kinematics, tectonic dynamic as guides, the basic rules of balanced section are applied in restoring the tectonic evolutionof the study area, characteristics of fracture structure, typical structural patterns, formation mechanism and the tectonic evolution stages of the Mesozoic-Palaeozoic thrust nappe belt have been analyzed in detail.In the structural analysis of Mesozoic-Palaeozoic superimposed basin, based on the integrated interpretation of through-well seismic section and grid seismic-geologic profile, and reveals the main characteristics of structural property,structural type, structural style in the Mesozoic-Palaeozoic superimposed basin, it can be divided into the four types of structural type and thirteen ways of basic structural style about the compression, extension, shear action, inversion;It has summarized five kinds of typical tectonic styles in each part of the nappe belt; Research has pointed out the correlation between the nappe belt and structures such as Wumaying anticline and Wang Guantun buried hill. In practical terms,the thrust belt can be divided into four section, the south section mainly overthrust nappe structures,overstep propagation thrust nappe in the middle-south section,piggyback propagation thrust nappe in the middle-north section,thrusting and back imbricate thrusting alternate in the north section. The general structural characteristic in the lndosinian period is wide anticline syncline, deeply imbricated thrust thick-skinned structure and shallow decollement thin-skinned structure formed longitudinal double-layer structural deformation in Yanshanian period. The Mesozoic-palaeozoic group possess the characteristic of the lower Paleozoic high-angle and far-distance imbricate thrust from south to north with anticlines-synclines,it is base-involved pattern;The thrust-nappe structures in the upper Paleozoic-Mesozoic is from northwest to southeast, it is the cover-decollement pattern. The detachment surface exist in the bottom of the carboniferous strata and the mud shale section undering the middle ordovician Majiagou group. The Cenozoic negative inversion detachment structure and sinistral shear tense-shearing structure has reconstructive effect to the the Mesozoic-palaeozoic compressional structure.The main conclusions in the study of structure forming period and forming mechanisms are as follows:(1) The papers presented there are mainly four groups of northwest transtensional-shear distribution belt exist between transfer zone for the first time, which manifests as left lateral wrench movement during earlyHimalayan in relation to the Tanlu fault dextral strike-slip.(2) Mesozoic-Palaeozoic in theresearched region can be summarized as five structural evolution, which are stable platform period, rolling anticline and syncline period, decollement nappe period, tectonic inversion period, faulted-depression sedimentation period. Wumaying anticline and Wangguantun anticline were formed in the Indosinian period, as the results of the plate marginal orogenic and intraplate progressive deformed slightly, while the anticline was transformated in the Yanshanian-Himalayan period; XuHei buried hill and WangGuantun buried hill as part of the anticline in Indosinian,the negative inversion structure in the periods of Himalayan cut the anticline into fault buried hill.(3) The upper Paleozoic-Mesozoic thrust nappe belt formed mainly in Yanshan intro-continental orogenic period, and the thrust nappe typical tectonic style distribution characteristics are closely related to the specific structure sites where the thrust nappe is developed.(4) The pre-Mesozoic angular unconformity on Paleoanticlines and nappe is the results of Indosinian stage and Yanshanian stage several periods of denudation and truncation. Positive and negative structural basin with the unconformity as the center shows up as mirror image Superimposed relationship.