| Popis: |
We make a careful analysis and comparison to the colored map of horizontal gradient calculated from Bouguer gravity data of the China mainland, and obtain some new insights into tectonics. Taking roughly 105°E as the boundary in the map, the eastern part of the China mainland is characterized by low gradients (blue color) background, appearing belt-shape structure of medium and high gradient as well as linear structure of gradient difference borders. The west part has a framework of belt-shape structure with medium and high gradient (red color), inlaid by low gradient areas which contain shade-line structure. In general, structures exhibited by horizontal gradient of gravity anomalies can be classified into three major sets. The first set includes high-gradient zones along the NNE trending Da hinggan ling, Taihangshan, and Wulingshan Mountains, the Tanlu great fault zone which extends obliquely through East China, and three NNW trending great fault zones through western China. The second set presents an intersection pattern of NWW and NEE direction gradient zones in the west, as well as three NWW discontinuous shade zones with roughly equal spacing, and a single tectonic line in the east, plus NE trending low gradient lines in South China. And the third set consists of several EW tectonic zones through the whole mainland and a wide complex NS striking zone in the middle of the mainland, of which on the both sides spread NS direction shade lines which are short, discontinuous and of large intervals. These three sets of tectonic zones delineated by gravity gradient are associated with variations of topography and crustal thickness on a large scale. The inner structures and formation times as well as evolution histories of each set are likely different. They have overlapped each other to shape the current tectonic patterns of the China mainland. Each tectonic zone has varied response to the recent tectonic stress fields of large scales, leading to regional change of directions of principle stresses. The ubiquitous segmentation caused by conjunction between tectonic zones of different directions is an important issue for theoretical and applied research in structural geology. |
Plný text