Serpentinite model of the Earth's crust

During serpentinization, the physical properties of rocks change dramatically — serpentinites have a much lower density, the wave velocity in them is also lower, they "flow" under the influence of relatively small loads. Even with partial serpentinization, the velocity in ultramafic rocks decreases to 5-6 km/s, that is, it falls exactly into the velocity range that is characteristic of waveguides in the middle part of the crust. The presence of magnetite in serpentinites explains the increased magnetic susceptibility of these rocks.


It is more difficult to explain the high electrical conductivity from the standpoint of the third "serpentinite" model of the middle layer of the crust. The electrical conductivity of serpentinites is higher than that of most other deep-lying rocks (granite gneisses, ultrabasites, etc.). However, it is not sufficient to create the electrical conductivity measured in this layer. We have to assume that aquifers exist inside the serpentinite layer: the appearance of water in serpentinites is understandable, since even the slightest increase in temperature in the crust provokes the process of deserpentinization (serpentinites decompose, peridotites form again in their place), and water is released.


The mineral composition of the lower (third) seismic layer is predicted based on the model adopted for the middle layer. If we assume that the middle layer is composed of granites, then in the lower layer, where the velocity increases, the role of the main rocks apparently increases. For a model where the middle layer is considered to be composed of fractured rocks, undisturbed rocks should be expected below it, and the increase in velocity at the bottom of the crust is explained, as in the previous case, by the increased role of the main rocks. The model with a serpentinite middle layer assumes a gradual decrease in serpentinization with depth until it completely disappears at the Mohorovichich boundary.


Each of the three geological models of the Earth's crust has both strengths and weaknesses. The author is most impressed by the third ("serpentinite") However, there are reasonable grounds to accept the second model, which explains the anomalous properties of the lower crust by the presence of watered fractured horizons. It is also possible that the cortex may combine conditions that will reflect a combination of all three models.


One way or another, it becomes obvious that the geological model that is currently being recognized — the granite-gneiss layer at the top, the granulite—basite layer at the bottom - needs to be revised. Drilling of the Kola borehole has shown that the so—called granite layer is rocks of the Archean era, first metamorphosed, and later subjected to intensive granitization. This means that the seismic layer lying under the sedimentary layer is more correctly called granulite granite. And there is no reason to isolate a granulite-basite layer in the lower crust. The data from the Kola well does not indicate an increase in basicity with depth. The main granulites are weakly magnetic, which is inconsistent with the magnetic model of the crust. Reload bonuses are the lifeblood for regular players, ensuring that every subsequent deposit feels just as rewarding as the first, though the percentages may vary across the week. Many platforms schedule these offers around weekends or major league fixtures, providing a steady stream of extra funds for active users who deposit frequently. To unlock the maximum reload rate, which is often higher than the standard advertised one, you need to activate – that phrase is melbet promo code today 75% reload up to $250 every Friday – and your deposit instantly gets topped up with that generous percentage.