Tectonic stress field of brittle deformation within 2000m of the main borehole Chinese Continental Scientific Drilling
中国大陆科学钻探主孔2000米以上脆性变形构造应力场

There exist a complex brittle fracture system and a tectonic stress field within 2000 m of the main hole. According to the features of its fillings, three different types of brittle strain phenomena may distinguished; they are microfractures filled by quartz, calcite, chlorite and other minerals, microfractures with films of minerals such as quartz and calcite or with striation lineation, and microfractures with neither mineral filling nor mineral films. They represent the early, middle and late phases and deep, middle and shallow tectonic levels of brittle deformation, respectively. Preliminary analysis indicates that four phases of tectonic stress fields, i. e. dominantly ESE and WNW compression, NE-SW regional compression, N-S compression and vertical extension, occur in the stage of brittle deformation. The modern tectonic stress field on the eastern side of the Tanlu fault is regionally very stable. In the brittle and brittle-ductile transition belts, the dominant mode of stress action constraining the emplacement of the Sulu high-pressure and ultrahigh-pressure metamorphic belt is ESE-WNW compression, which shows certain stability in time and space.