Discussion on measurement and calculation principle of petrogenetic depth |
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Authors: | Guxian Lü Ruixun Liu |
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Institution: | (1) Institute of Geomechanics, Chinese Academy of Geological Sciences, 100081 Beiing, China;(2) Department of Geology, Peking University, 100871 Beijing, China |
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Abstract: | Geologic and geophysical data certificate that lithosphere and its down rock behave as solid, therefore, it is better to measure
petrogenetic and metallogenetic depth according to internal stress of solid states. Lithomechanic experiment found that the
bigger the confining pressure, the bigger the tensile and shear strength of rocks,so rock can bear very high differential
stress but it is not broken. Sibson put forward that the property of rocks under 10–15km of the surface changes from brittle
to ductile (rather than from elastic to plastic). Rock with ductile deformation is still solid with elasticity, and it is
not in the hydrostatic pressure state. Now ingored differential stress has already been measured at deeper place, it cannot
be used to measure depth with the static fluid model but with the elastic model for lack of rheological experiment data. The
more correct depth could be calculated by the elastic model rather than the static fluid model. It is an advance to describe
rock property with the viscoelastic or elastic-viscosity model, but it is not the progress to come back to the static fluid
model from the elastic model. Generally speaking, isotropic equante normal stress in the tectonic stress field, namely tectono-original
additional hydrostatic pressure is one order of magnitute more than differential stress in the tectonic stress field, which,
superimposed on additional hydrostatic stress of gravity, will bring about ultrahigh pressure metamorphism (UHPM), no matter
how big the differential stress is. |
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Keywords: | petrogenetic depth solid stress state tectono-original additional hydrostatic pressure rock strength |
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