Abstract:

The Wudalianchi National Park is located in Heilongjiang province, northeastern China, where the volcanoes are the best examples of the intra-continental monogenetic volcanoes in the world. There are also numerous faults developed in the volcanic strata. If the relationship between the fault system and the distribution of volcanoes in the area could be well analyzed and interpreted, it would be of great importance for understanding the evolution of volcanic activities of this kind. Research work shown in this article is done to study the correlativity between distribution of the intra-continental monogenetic volcanoes in Wudalianchiare and the local fractures. From ground surface observation and remote sensing image interpretation, together with the study on regional structure, falults and fault zone outcroping, volcanoes erupting sequence (such as the fact that some volcanoes erupted regularly in turns, progressively from SW to NE), regional profiles and paying attention to the fact that volcanoes in different spreading directions are of different scales, we come to the conclusion that the 7 faults discovered in the area actually belong to three faults groups. The strikes of these three groups are NE, NW and nearly E-W, respectively. Regional electromagnetic data and previous research on deep structure in northeastern China also give support to the view. Fractures of these three strikes appeared in granites temporally formed before the volcanic activies in time. Seismic data, stress state in geological history, as well as study on river terraces, all demonstrate that there were no active fractures taking place during volcanic eruption period in the area. Cusequently, the fractures should exist prior to the volcanic activities in Wudalianchi area. At the times of volcanic eruptions, the faults provided pathways for the underground magmas to migrate upward towards surface, and finally led to forming this kind of volcano distribution seen nowadays on ground surface in Wudalianchi area. It means fhat three groups of volcanoes are distributed along the NE trending faults, two groups along the NW trending faults, and the other two groups nearly E-W trending.

Key words: distribution of monogenetic volcanoes, faults, Wudalianchi National Park, northeastern China