TELLURIC ELECTROMAGNETIC SOUNDING STUDY OF CRUST AND UPPER MANTLE IN THE PANXI"RIFT ZONE" AND THE LONGMENSHAN FAULTED ZONE
Li Li, Jin Guoyuan(Institute of Exploration Geophysics and Geochemistry, MGMR)
Abstract The telluric electromagnetic sounding in Panxi and Longmenshan areas and their neighbouring districts has detected an intracrustal low resistivity layer buried 11-37km below the surface with thickness of 5.5-11km and resistivity of several to tens of ohms, which is likely produced by partially molten granitic substances. This layer nearly disappears along the Panxi and Longmenshan major structural belt. The thickness of lithosphere in western Sichuan is deter- mined to be 80-143km, and the lithosphere west of the above two major stru- ctural belts obviously becomes thicker. Along the major structures there exist deep-seated high resistivity anomalies, which are apparently consistent with the gravity and magnetic anomalies. lt is thought that these deep-seated high re- sistivity anomalies are probably brought about by mantle substances which flow- ed upward in large quantities at early stage, and that they must have had intimate relationship with the most important mineralization in this area, thus deserving further investigation.