摘要
本文通过地质、地球物理综合研究,阐明下扬子拗陷是在海西-印支前陆盆地基底上形成的中新生代裂谷带。它有东西分段、南北差异的特点。裂谷平面组合类型有平行状、三叉状和分裂状。苏北-南黄海代表拗陷中心渐趋东移的“漂移型”裂谷盆地。从地壳细结构观点探讨了裂谷盆地的形成机理和动力演化,给出了地质、地球物理论据和力源分析结果。
Based on a comprehensive study of geophysics and geology, it is postulated that the Lower Yangtze depression is a Meso-Cenozoic rift zone formed on the basement of the Hercynian-Indosinian foreland basins through long-continued and polycyclic geological development. It has the following geophysical and geological features: 1. Meso-Cenozoic graben-horst structure or wedge-shaped faulted depressions with a gear thickness of sediments; 2. complete or partial sedimentary sequence of rift type; 3. alkaline olivine basalt magmatism; 4. alternatively positive and negative Bougner gravity anomalies with an anomaly amplitude of about ±20 mGal; 5. high heat flow (76.9 mw/m^2) and high geothermal gradient or hot spring distribution; 6. moderate-weak seismism and shallow-focus earthquakes; 7. mid-crust low-density (low-velocity) layer and anomalous mantle; 8. crustal thinning; 9. quite shallo depth of the Curie isothermal surface.The rift zone may be divided into eastern and western sectors and its northern and southern parts are different. The surface configuration patterns of the rift basins are parallel, trijunctive, and split respectively. The Guzhen-Wuhe-Xuyi (south)-Liuhe-Yizheng (-Shangahi) region is a Cenozoic transitional zone dividing the rift zone into the eastern and the western sector (Fig. 5). And the Northern Jiangsu-South Yellow Sea region represents a 'drift-type' rift basin whose deposition centers migrated gradually eastwards. Based on the data of crustal fine-structure, the formation mechanism of the Lower Yangtze rift basins can be expressed as follows: the anomalous mantle is domed and diapirically upwelled, the 'peridotitic' layer extended and thinned, the 'basaltic' layer ruptured, thus forming a passageway of molten materials, the mid-crust low-density layer dilated, and finally the upper tectonic layers are extended to form faulted depressions. The stress concentration caused by the crustal thickness inhomogeneities is one of the internal dynamic sources resulting in the spreading and bed-slipping of the crust. Morphologically there may be two types of rifts, i.e. the wedge type in northern Jiangsu and the archsplit type in southern diangsu.
出处
《地质学报》
EI
CAS
CSCD
北大核心
1990年第2期107-120,共14页
Acta Geologica Sinica
