HR: 0800h
AN: V11A-1402    [Abstracts]
TI: Tectonic stress field of brittle deformation within 2000 m of the main borehole of Chinese Continental Scientific Drilling
AU: * Cui, J
EM: cuijunwen@ccsd.org.cn
AF: Institute of Geology, CAGS, 26 Baiwanzhuang Street, Beijing, 100037 China
AU: Li, P
EM: lipengwe@cags.net.cn
AF: Institute of Geology, CAGS, 26 Baiwanzhuang Street, Beijing, 100037 China
AU: Wang, L
EM: wangli1933@sohu.com
AF: Institute of Geodynamics, CAGS, Xueyuan Road, Beijing, 100081 China
AB: Four phases of tectonic stress fields: 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. The determination of in-situ stress from wellbore breakouts: The breakouts began to occur under the depth of 1200m in the main borehole of Chinese Continental Scientific Drilling (CCSD), 82 breakout images are collected from acoustic borehole televiewer data between 1200m and 2010 m. The averaged orientation of breakouts is 324.8­a­A3.3­a. The averaged orientation of maximum horizontal stress is 54.8­a­A3.3­a. Using parameters measured from breakouts (depth and width of breakout) and rock cohesive strength determined from triaxial rock compression and deformation test, the magnitudes of principal stress are calculated at 16 different depths of 1269m, 1500m, 2000m and so on. Overburden stress is calculated using the density logging data. According to the orientations and magnitudes of three principal stresses, the least principal stress is horizontal, and stress state (SH>Sv>Sh) determined from the analysis of wellbore breakouts of CCSD indicates the strike-slip stress regime and is coincident with the strike-slip stress field observed from earthquake focal plane mechanisms.
DE: 9320 Asia
DE: 3660 Metamorphic petrology
DE: 3902 Creep and deformation
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting