The dependency of rock electric conductivity on frequency was studied with AC method.Under a given pressure and temperature,the influence of frequency on the electric conductivity is very small within the range of 0.1—10Hz,the electric conductivity increases slightly with increase of frequency at higher frequency range,and this phenomenon is more remarkably under lower temperature than under higher temperature.The result of determination on electric conductivity of crust-mantle rocks in Qinling Dabie mountains was firstly reported.It is shown that:(1)The major representative rocks for middle-upper crust hornblendite,chlorite-schist,sericite-quartz-schist,phyllite,biotite granodiorite and etc.show that minerals of hornblende,chlorite and sericite kind will under go dehydration with some partial melting under the temperature and pressure conditions at the depth of 10-25km leading to the increase of electric conductivity and abrupt change at phase transition point with values of 0.1 S·m-1 to 10S.m-1.That may be the main reason for the formation of high conductivity layers or bodies.(2)The representative rocks of middle lower crustsuch as gneiss,granulite and eclogite etc.,may gorm the lower crust layers of low conductivity.Meanwhile,the layers which are rich in quartz also can lead to the decrease of electric conductivity with the values of 10-1 S·m-1 to 10-3 S·m-1 due to the α to β phase transition of quartz taken place under the pressure and temperature conditions of lower crust.(3)The representative rocks for the upper mantle such as dunite and augite peridotite,are composed of relatively alkalic minerals,being mostly olivine,pyroxene,spinel and garnet,containing ofundant Fe,Mg,Ca,and also possibly fluids.At higher pressure and temperature conditions of upper mantle,the electric conductivity will be higher than that of lower crust,with the values of 0.1 S·m-1 to 1 S·m-1 。
Gao Ping,Yang Piyuan,Li Yanjun. EXPERIMENTAL STUDY ON THE ELECTRIC CONDUCTIVITY UNDER HIGH PRESURE AND HIGH TEMPERATURE FOR THE CRUST MANTLE ROCKS IN QINLING-DABIE MOUNTAIN[J]. Chinese Journal of Geology, 1998, (2): 195-203.