Structural Charateristics Of Detachment Faults In Luxi Block

Based on the field survey and well logging and seismic data,this paper researched the geometric and kinematic characteristics of normal faults and strike-slip faults,the evolution of oblique faults,and the relationships between extensional faults and strike slip faults in Luxi block Rise by structure analysis.Moreover,data on geothermal field,lithosphere structure,geochemical characteristics of igneous rocks and Tanlu fault zone's evolution were used to analyzed the mechanism of faults and basin in different global tectonic background.With large scales,long developing time and deep cutting,with big dip angle,the NW-trending and nearly EW-trending boundary décollement faults which are parallel aligning from south to north in Luxi block,control the sediment of the half-grabent that has formed since late Mesozoic.Breccia,cataclasite and fault gouge developed in the fault belt indicate that it has undergone several tectonic movement.The analysis also suggests that shallow gently dipping décollement fault mainly developed along the unconformity between the Cambrian and Archean.Although the thickness of décollement fault belt varies from each other,the attitude is consistent with the stratums'.At the décollement fault belt,there are cataclastic rocks with dynamo-metamorphic rocks and some small folds,scratches,steps,and so on.Décollement fault composed the structure style of the Luxi block.Horizontal extension amount and vertical activity rate of normal faults show that the steep naormal faults reversed negatively in late Mesozoic,and western Shangdong began to extention.In the Paleogene,the activity rates of the NW-trending faults reached peak,western Shangdong subjected to strong extension.Then,in the Neogene,faults hardly activated,and Luxi block approximately trended to be stable.Apatite,zircon fission track,and cooling history simulation of the samples in faults'footwall manifest that Mengshan,Lianhuash,and Mountain Tai began to uplift in late Cretaceous.Cenozoic can be diviede into three rapid uplifting stages.They are 65⁶0Ma,48⁴2Ma and 25²0Ma.That,at the same,is reflected by the samples in depression.Combined with the uplifting velocity of these three stages in Cenozoic,sedimentary characteristics and igneous raock features,the results show that the main active periods are late Jurassic-early Cretaceous,65⁶0Ma 48⁴2Ma.And they indicate a law that the activation of steep detachment faults strengthens gradually from south to north,east to west.The lithosphere of study area extended by the way of wide rift mode in J₃-K₁,and showed the multiple layered extensional characteristics:the crust deformed by simple shear and the lithospheric mantle deformed by pure shear.Meanwhile,the geochemical characteristics of igneous rocks indicated that the study area was located in back-arc tensional regime.Combining with the stress and deformation fields in the study area,the stress source of deformation were deduced to be the tension mainly generated by the relative motion within the plate,and formed the extensional-strike-slipping faults and sags.However,lithosphere of study area extended by the way of narrow rift mode in Cenozoic.,the crust and the lithospheric mantle deformed all by pure shear,but the later extended more intensively.Additionally,the geochemical characteristics of igneous rocks indicate that the basin involved into continental riftting,the asthenosphere upwelled and transformed the lithospheric mantle.Apparently,the tension produced by the upwelling of asthenosphere was identified as the crucial role in basin rifting,and formed the extensional or oblique extensional faults and sags.