The Ziyun - Luodian - Nandan Rift Zone Of Tectonic Evolution And Geological Significance

This paper studied the tectonics of the Ziyun-Luodian-Nandan belt in terms of the spatial variation of sedimentary facies of different times and evolution of the sedimentary basins, on which the tectonics have been discussed. Combining the sedimentary study and geochemistry and the isotope geochronology study of magmatic rocks, we mainly obtain the following initial understandings:1. In the research area, Ziyun-Luodian-Nandan belt, the main strata are D2-T1-2, and most strata of T3 and J are missing, the strata of K and Q are locally developed. We divided four structural layers form bottom up, according to the construction of the strata in this area: pre-Sinian basement, Sinian-Lower Paleozoic, Upper Paleozoic, and Mesozoic-Cenozoic.2. According to the sedimentary characteristics of temporal and spatial variation, we considered that the Ziyun-Luodian-Nandan belt mainly experienced four stages on sedimentary and tectonic evolution:crust stretched thinning-intracontinental rift stage (D1), faulting extension-passive margin rift stage (D2-P2), strike-slip rift-faulting subsidence stage (P3-T1), and convergent extrusion-foreland basin stage.3. The Ziyun-Luodian-Nandan belt developed from the Ziyun-Luodian-Nandan trough, of which deformation features are significantly different in the two sides of the belt. The structures in NE side are NE or near NS; as NWW or SEE in the SW side.The belt is distributed NW-SE in the plane that can be divided into three parts. That is Guanling segment, Ziyun-Luodian segment and Nandan segment.4. By analyzing the structural features and the deformation of the Ziyun-Luodian-Nandan belt, we maintain that there are some certain inheritance relationships between the deformations of different stages. The active regional faults and syndepositional faults in this area greatly controlled the sedimentary evolution of the Ziyun-Luodian-Nandan aulacogen. The study area has limited prospects for oil and gas because of the strong tectonic activity.5. The results of geochemistry and isotope geology study on diabase from Luodian in Guizhou province prove its formation age is 255.0±0.62 Ma. It may generate from partial melting material, which is similar to mantle rocks. The formation mechanism is mantle magma upward emplacement in the background of crustal extension. Based on the knowlege that the elevation of Luodian diabase is similar to Emeishan basalt and the formation ages are consistent, we considered that they are products of homogeneous-phase magmatism, not the production of the tectonic activity of Ziyun-Luodian-Nandan aulacogen.