Thermobaric elastic-density anomalies in the Earth’s crust and their origin and the dynamic of change

Fragmentary low velocity zones were revealed by DSS at depths of 5-22 km around the Earth. Their nature remains not quite clear. Interdisciplinary interpretation of DSS data including petrophysical thermobaric modelling the lithospheric rocks composition more insight into the nature of these anomalous zones. They are considered as thermodynamical phenomena rather than a result of changing composition when rocks is transformed by pressure and temperature at the depth of their occurrence. Multimethod laboratory studies of rocks show that under PT-conditions at 5-15 km depths rocks are subjected to cataclastic and dilatational changes. A major mechanism responsible for this behaviour is the united action of developing in the environment of unevenly distributed and differently oriented tensions in the sample. In contacts between grains they reach values which exceed the strength limit of individual minerals that destructs integrity medium at a microlevel. Here the rocks are characterized by low Young and shear modules, high brittleness, high discompaction, low heat conductivity. The discompacted state of rocks at 5-20 km depths is a fundamental characteristic of the Earth’s crust and well coincide with low velocity zones in the crust from DSS profiles. It results from the counteraction of pressure and temperature at these depths.