| The structural framework in Mesozoic-Paleozoic of the middle Yangtze region and the Formation and Evolution of the Yangtze Plate are always the key issues of the research. Recently, many scholars are on the concept of the basin-mountain coupling structural viewpoint, they mainly study the relationships of the Qinlin-Dabie orogeny and the Jiangnan uplift, intra-continental orogeny formation mechanism,process of forming and the intrabasinal tectonic deformation and displacement of multi-stages. However, for the eastern of middle Yangtze region are covered with Cenozoic, it’s difficult and partial to describe structural systems and structural units meticulously by using the outcrop geology, and it’s also the arguing point about the division of tectonic units. This paper makes the regional seismic contiguous anatomy in this2-D district and structural mapping in Mesozoic-Paleozoic, and discusses the structural space distribution and the structural formation mechanism.According to the Seismic post and in reference to the ancient geophysical data verification, It is believed that there are three diferent types and varied sizes of detachment systems from the basement to the sedimentary cover. The depth between the low-grade metamorphic rocks and lower Proterozoic Era in the middle and late Proterozoic times and the Archaean high-grade metamorphic rocks basementthe internal detachment surfaces is around25km-10km.They are mainly distributed on the southern margin of the orogenic belt,that is the northern part of the area. The depth between the upper Sinian cover and middle lower Sinian low-grade metamorphic rocks basement detachment surfaces is around15km-8km, are three cover interior sedimentary cover detachment surfaces.They mainly distribute in the middle and front zone of nappe.The size of the detachment decreases from the deep to the shallow.During the time of late Triassic to early Cretaceous, owning to the strong compression of SW-trending Dahongshan nappe region and NW-trending Jiangnan-Xuefeng overthrust region, the eastern edge of the middle Yangtze region became the transpressional slim ramp tectonic system. It points out that the area in Mesozoic-Paleozoic is dominated by compressive tectonic structures, and that it is structurally characterized by ramp interference, south-north zonation, and vertical overlap. The whole area can be identified as three major tectonic belts:Jiangna-Xuefeng decollement nappe in south; ramp (back) tectonic belts in central; Qinlin-Dabie nappe structure in north. For the influence of the internal two detachment fault system in hypo and epi metamorphic rock crystallizine basement, the two nappe regions were formed. It contributed to sedimentary cover compression and multiple detachments nappe along the base of the Silurian, the base of the Devonian, and formed a variety of compression and transpressional tectonic structural type and tectonic style. Tectonic deformation and displacement of multi-stages and magmatic activity led to the development of four types of basic structural styles:compressional tectonics, compressional strike slip tectonics, diaper and blind diaper tectonics, and extensional tectonics. Compressional shrinkage tectonics include the partial structure variable styles,such as the forward and back imbricate structures, ramp/Back thrust, Backflushing,duplex, bamboo-split and so on. The stretch structure includes rift valley, halfgraben, horst, step-fault,buried hill and such structure styles;Torsion tectonics are the left-lateral Strike-slip flower fault bilateral torsion Structure,include the positive and negative flower structures;Magmatic Intrusion mainly distributes around the later period cretaceous control faults.From orogeny belt to Intra-basin, Tectonic deformation was Gradual-Change, that is asymmetry obduction (root zone)-wedges overthrust (middle zone)-decollement nappe (front zone)-ramp belt. By applying the balanced cross-section principle, restorating the Modern Tectonic assemblages conduces to the deep understanding of the formation of structure. According to the area’s secondary Structural Units, we can summarize the following multi Tectonic Evolution for typical structure assemblages. Including the formation for typical structure assemblages in the root zone of nappe in Dahongshan Mount, in the middle zone of nappe in Dahongshan Mount,and in the front zone of nappe in Dahongshan Mount;Formation for structure assemblages in decollement nappe in Jiangnan-Xuefeng; formation for structure assemblages on ramp_strike-slip_steps-broken in ramp zone, and formation for structure assemblages on imbricate-thrust_bamboo-split_steps-broken in ramp zone.The middle Yangtze region have experienced the tectonic movement from Caledonian、Hercynian-Indosinian、early Yanshanian、late Yanshanian-early Himalayan to late Himalayan. Tectonic evlution of two region seismic profile and six typical structure assemblages and compound formation mode chart have been completed by seismic structural analysis and balanced cross-section technique.The area mainly experienced six tectonic periods、times and c episodes important structural deformation stage.It is generally believed that during the time of Sinian to early and middle Triassic, the studied area and Mid-Yangtze Region have experienced two episodes of Tectonic Cycle:convergency, accretion, displacement, subduction, intracontinental collisional orogenesis of the plates on the base of Pre-Sinian continental nucleus crystal bases. And after that, they experienced foreland slope in late Triassic, intra-continental orogeny. The area formed intra-continental orogeny in line with Tongbo-Dabie and resulted structure of wide ramp during the first episodes of the late Jurassic、north and west intra-continental orogeny and it’s decollement nappe structure system formed,the ramp became narrow during the second episodes of the late Jurassic and north and west nappe right-lateral Strike-slip compressive-torsional structure with positive flower structure during the third episodes of the late Jurassic.It’s compressive fold in late Jurassic, denadation planation and reformation of magmatic rocks in late Jurassic to early Cretaceous.Continued compressive-torsional action resulted in a series of NE-trending right-lateral Strike-slip faults segmented ramp structure system. Compression turned into extension environment in late Cretaceous-Paleaogene, negative fault inversion slipped back and became major fault of fault depression in Mesozoic and Cenozoic. It is generally believed that the front zone of Dahongshan nappe region is already in line with Tonghaikou-Yanglinwei-Hannan. Influenced by Honghu Strike-slip fault and Tonghaikou fault slipped back, the main body accepts the Early Cretaceous-Neogene sedimentary and only remains the curvilinear structural belt tectonic features. The another positive inversion of tectonic regime and regional compression uplift in Neogene evolutional stage.Tectonic movement of multi-stages and the superposition and modification of prototype basin of multi-types contribute to the complexity of structural framework of the east of Jianghan Plain.For the area have experienced multiple deformations, a lots of part are structure compound for example:early periods thrust are slipped back,early imbricate-thrust are back flushing et al,resulted complex structure and various conformation. As a result,it exists integrated large-scale anticlinal trap in the front zone of nappe in Dahongshan Mount, as advantageous potential field of gas exploration... |
PDF Full Text Request