航磁异常的构造解释和华北-塔南-扬子超陆块演化

在现代地球磁场中，总体感磁效应与岩石的磁化率无关。典型地区大比例尺构造组构填图结果与岩石磁组构的对照分析，证明磁线理和构造线理具有一致的矢量特征。强烈韧性剪切导致岩石中区域一致的矿物定向和磁化率各向异性，是干扰现代地球磁场、产生特定航磁异常分布格局的主要因素。对五种基本的区域尺度构造 航磁异常样式的成因进行了分析，证明华北地区的航磁异常的分布样式与结晶基底的基本构造格架基本一致。并据此对塔里木、扬子地体基底岩石的构造性质进行了解释，提出存在前寒武纪华北－ 塔南－ 扬子超陆块。结合显生宙构造演化的地质证据，划分出新太古代克拉通化、古元古代左行韧性剪切改造和活动带发育、中－ 新元古代裂解和活动大陆边缘、古生代原地改造和中生代再裂解五个演化历史阶段

Tectonic implication of aeromagnetic anomaly and evolution of Huabei - South Tarim Yangtze Superlandmass

Data coming from rock magnetism testing have been used to study on the origin of aeromagnetic anomaly patterns and its tectonic application. It has been found that the induced magnetization of the exposed metamorphic basement in the earth magnetic field has no relation with individual rock magnetic susceptibilities. Results from a detailed mapping in comparing with AMS (anisotropy of magnetic susceptibility) testing show that orientations of magnetic lineation ( k 1) in the rocks are all similar to the elongated mineral orientations measured in the same outcrop. It has been demonstrated that a regional consistent mineral and AMS orientation as a result of previous large scale ductile shearing is the principal factor to interfere the earth magnetic field and to have a special aeromagnetic anomaly pattern. Origins of five major tectonic aeromagnetic anomaly patterns in regional scale are discussed. The aeromagnetic anomaly appearance in an apparent susceptibility and a vertical derivative treated map in North China (Huabei) Shield show a pattern that mostly suited to the tectonic frame formed in the crystal basement. Based on contrasting and analysis aeromagnetic anomaly in the central and west China, the tectonic character of basement rocks underneath the Tarim and Sichuan Mesozoic basins are interpreted. These allow to suggest that a superlandmass of Huabei South Tarim Yangtze was presented since the end of Archean. The suggested Huabei South Tarim Yangtze Superlandmass is also supported by evidence of geological evolution of Proterozoic and Phanerozoic time with five developing stages, including a cratonization at the end of Archean, large scale sinistral ductile shearing and mobile belts developing in the Paleoproterozoic, splitting and mobile continental margin in the Meso to Neo proterozoic, reforming in situ in the Paleozoic, and re splitting in the Mesozoic.