We first analyzed the characteristics of the Bouguer gravity anomalies in the northeastern margin of the Tibetan Plateau. We then did multi-scale anomaly separation and transversely structural analyses based on the gravity anomalies respectively by using the preferential filtering and the normalized vertical derivative of the total horizontal derivative. From the characteristics of the separated multi-scale anomalies, we obtained the following conclusions: 1) There is a remarkable gravity anomaly gradient belt roughly along 106 degrees E in the northeastern margin of the Tibetan Plateau, that is the north section of the Helan Shan-Liupan Shan-Sichuan-Yunnan tectonic belt. The characteristics of the Bouguer anomalies are quite different on both side of this gradient belt, indicating the difference of density structures and tectonic features. 2) To the north of Dingbian in the Ordos block, a high gravity anomaly belt trends from NE to nearly S-N, which implies there is a density or structural interface around the transition zone. Both sides of the interface have different material compositions and tectonic features. Comparisons of the large-scale and small-scale gravity anomalies indicate that these differences are mainly caused by the deep structure of the upper mantle. 3) The tectonic boundaries in the deep northeastern margin of the Tibetan Plateau are quite different from the geological outcrops on the Earth' s surface, reflecting the tectonic complexity and diversity in the deep and shallow structures. 4) Because of the collision between the Indian plate and the Eurasian plate, and the subsequent continuous northward extrusion effects of the Indian plate, the materials of the middle-lower crust in the northeastern margin of the Tibetan Plateau squeeze into the Qinling orogenic belt which is relatively weak, under the interaction of huge northward push force and barrier of the Ordos rigid block. Based on the characteristics of the multi-scale gravity anomalies and their transverse structures, we deduced five deep fault zones in the studied area, i. e., Qinling North Margin fault, Haiyuan-Liupan Shan fault, Xiang Shan-Tianjing Shan fault, Yantong Shan fault and Longshou Shan fault. And we also analyzed the possible distribution of these five fault zones in the deep crust.
