关键词: 腾冲火山群, 火山口排列调查法, 线性排列, 古地应力反演, 地应力方向

Abstract: The acquisition of paleostress data has always been a key and difficult problem in the field of tectonics and crustal dynamics. Previous findings show that the distribution of dykes and the alignment of volcano vents can indicate the direction of major principal stresses during the volcanic eruption period. The extension direction of underground dyke is generally parallel to the linear arrangement direction of vent and both of them give the direction of maximum horizontal principal stress in this period. This law has similar mechanical principle to hydraulic fracturing. Vent alignment survey method is a kind of geostress inversion method based on volcanic linear mode. In this paper theoretical basis of vent alignment survey method and the linear model of volcanic array are introduced. Based on the panchromatic high-resolution remote sensing image and digital elevation model(DEM)data in the Tengchong area, combining the geological exploration data about lithologic distribution of igneous rocks and the past research results of volcanic activities in the area, the research divides the volcanoes in this area, according to the age of volcanic eruption, into Holocene, late Pleistocene, early Pleistocene and Pliocene. Nakamura model was established based on the morphological characteristics and spatial distribution of the crater, and volcanic eruption period to evaluate the linear degree of the volcano in different age, and to carry out inversion of the paleostress field of the four volcanic eruption periods in Tengchong area. The reliability of the inversion results is evaluated according to Paulsen's data reliability assessment system. The data from inverting the paleostress of each show that maximum horizontal principal stress directions in the early Pleistocene period and late Pleistocene period are 39° and 37° respectively and reliability grades of inverted paleostress results in the two eras all belong to grade B; Inverted paleostress results in Holocene and Pliocene are not reliable because of the poor linearity of volcanic arrangement. The geostress direction determined by the vent alignment survey method is fairly consistent with the current geostress field obtained by the focal mechanism solution and the anelastic strain recovery(ASR method)and matches the tectonic history of Tengchong area since Neogene. The research findings demonstrate that the vent alignment survey method is an effective paleostress inversion method. The application of this method in the paleostress inversion of the Tengchong volcanic area is of important reference significance for the study of paleostress field in other volcanic areas in China.

Key words: volcanoes in Tengchong area, vent alignment survey method, linear alignment, paleostress inversion, in-situ stress orientation