Geobarmal Gradient in Orogenic Belt and Metamorphism Caused by Ultrahigh Pressure

The components and structures of lithosphere, inhomogeneous, are changing incessantly in different periods. Therefore, the state of load, called the pressure, in lithosphere is also incessantly changing. When the lithosphere volume remains the same, namely on the premise of isovolumes, the geobarmal gradient is: (dp/dh)_v=(∂p /∂h)_v+(∂p /∂T)_v(dT/dh)_v. If β =(dp/dh)_v/(∂p /∂h)_vis supposed, then β =1+ rg^-1 C_v(dT/dh)_v. When the geothermal degree in (dT/dh)_vis zero, then the pressure grade of lithosphere is equal to the lithostatic grade, which is the minimum value in the pressure grade of lithosphere. Suppose that the lithosphere is made only up of quartz, C_v≌C_p =0.782+5.718×10^-4 T^-1.883×10⁴T^-2 (J·g^-1·K^-1) is obtained, which is the minimum one in lithospheric rock, and then the geothermal grade value of 20 ℃/km is calculated according to the geophysical transection data of Qinling Mountain orogeny. The results show that the high pressure and ultrahigh pressure eclogites in Jiangsu Province and Huangzhen, Dabie may, on the condition of incompletely isovolumes, occur in the depths of 17-40 km with the increase in geothermal temperature, whose values of β do not correspond to the theoretic value of 3.08.