紫云—罗甸—南丹裂陷带的构造演化及地质意义

【作者】 韩伟；

【导师】 罗金海；

【作者基本信息】 西北大学 ， 构造地质学， 2010， 硕士

【摘要】 论文以紫云—罗甸—南丹构造带为主要研究对象,从不同时代沉积相空间变化和沉积盆地演化的角度研究大地构造问题。在沉积学研究的同时,辅助以岩浆岩的地球化学和同位素地质年代学研究,主要取得以下初步认识：1、紫云—罗甸—南丹裂陷带在研究区内主要出露中泥盆统至早—中三叠统,上三叠统及侏罗系大部分缺失,白垩系、第四系局部发育。研究区及邻区的地质建造,从下而上可划分为四个构造层：前震旦系基底构造层、震旦系—下古生界构造层、上古生界构造层和中—新生界构造层,紫云—罗甸—南丹裂陷槽就奠基在前震旦系基底构造层和震旦系—下古生界构造层之上。2、依据紫云—罗甸—南丹裂陷槽沉积建造的时间—空间的变化特点,认为其大体经历了四个阶段的沉积—构造演化：地壳拉伸变薄—陆内裂陷阶段(D1)、断陷伸展—被动陆缘裂谷阶段(D2—P2)、走滑裂陷—断裂沉陷阶段(P3—T1)、挤压聚敛—前陆盆地阶段(T2—T3)。3、NW向紫云—罗甸—南丹构造带由紫云—罗甸—南丹裂陷槽演化而来,其两侧具有显著不同的构造变形特点,NE侧以NE或近SN向构造为主,SW侧则以NWW或SEE向构造为主。根据空间组合特征及地质特征,该构造带大体可分为关岭段,紫云—罗甸段和南丹段。4、通过对紫云—罗甸—南丹构造带的构造结构特点及变形特征分析,认为研究区内各期构造变形之间有一定的继承关系,多条长期活动的区域性大断裂和同沉积断层很大程度上控制着紫云—罗甸—南丹裂陷槽沉积演化特征。由于构造活动强烈,研究区内油气潜力前景有限。5、通过对贵州罗甸县罗悃辉绿岩的地球化学与同位素地质年代学研究,确定其形成时间为255.0±0.62Ma。可能起源于与原始地幔类似的地幔岩的部分熔融作用,是在地壳伸展背景下来自深部的幔源岩浆快速向上侵位形成的。与峨眉山玄武岩高度类似,且形成时间上基本一致,认为罗甸辉绿岩是峨眉山玄武岩同质异相岩浆活动的产物,而不是紫云—罗甸—南丹裂陷槽裂陷活动的产物。更多还原

【Abstract】 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.更多还原