青藏高原构造结构特点:新重力异常成果的启示

The feature of tectonics in the Tibet Plateau from new regional gravity signals

截至2007年1:1000000区域重力工作已基本覆盖青藏高原全区,这些全新的重力成果揭示了很多有意义的现象.通过多方法处理分析研究不同深度层次的重力场特征及正反演计算构建地壳模型,认为:重力异常形态显示青藏高原独成体系,与相邻块体具有多样化的接触关系.已发现蛇绿岩的结合带、弧盆系和岩浆岩带是幅值不等、规模不一的重力高和重力低,表明青藏高原是具有多条结合带的拼合体;班公湖—怒江结合带是高原内最主要的重力高异常带,长达千余公里,将不同深度层次的重力场分成截然不同的南北两大区块,为它是冈瓦纳大陆北界提供了依据;局部重力异常指示青藏高原构造形迹自南而北以东西走向为主,东部则为北西—南北走向,具有与大地构造相似的分区特征;85°E和92°E附近存在较大尺度的南北和北东走向的重力异常特征线,揭示出青藏高原腹地的深部结构具有东中西三分现象,与表壳的东西走向格局形成对比.

As of 2007, 1 ：1000000 regional gravity investigations have been completed in Qinghai- Tibet Plateau. We obtain useful information by analyzing the gravity anomaly in different depth levels of the plateau, based on various data processing results to build a structure model. Our results show that the gravity feature in Tibet is unique, with diverse contact relations with adjacent blocks. The gravity minimum and maximum can be related to the arc-basin and magmatic belts, and suture zones where amphibolites were found. This feature above shows that Tibet is pieced together with many sutures. The gravity field is divided into two parts of the southern andnorthern within the plateau in different depth by the Bouguer gravity anomaly of Bangong- Nujiang suture zone, which is the most important gravity maximum anomalies over 1000 km long. This information provides evidence that Bangong-Nujiang suture is the northern boundary of Gondwana. Local gravity anomaly exhibits similar feature of geotectonic division. Majority of structural trend is EW-striking from south to north, whereas in the eastern plateau it strikes NW-SN. There are two gravity anomaly lines near the 85°E and 92°E longitude. It suggests that the deep structure of plateau is divided into three parts from east to west, in contrast to the EW- striking surficial structure.