Earth's crust: How rocks dissolve in water

Flowable canals under great mountain ranges at great depths of the earth?

Rock of the lower continental crust. The deformation caused by "flow" can be recognized by the classification and orientation of the mineral grains. Bright, large crystals of potassium feldspar (KAlSi3O8) have grown in the rock and attest to material supply through aqueous solutions. © RUB
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Even before rock becomes a hot melt at great depth, its solubility in water can be extremely high. This is what scientists of the Ruhr University Bochum found out in laboratory experiments. However, whether these aqueous solutions can form flowable canals hundreds of miles under the great mountains is still unclear.

The researchers around Professor Walter Maresch report in RUBIN Geowissenschaften, the current special issue of the science magazine RUBIN.

How aqueous solutions behave at depth

Most rocks of the earth's crust are made of silicate minerals, which are much less soluble under surface conditions than limestone, for example, in a stalactite cave. As the depth of the earth increases, pressure and temperature rise. Water collects, usually migrates upwards and flows through shallower rock formations.

Mineralogists research how the aqueous solutions are composed, and to what extent they can be dissolved in the depths of the earth and transported from one place to another, in the special research area "Earth's Rheology". Rheology describes the deformation and flow behavior of rocks in depth.

Minerals: from barely soluble to thousands of times the cave water

Since a direct examination of aqueous solutions at a depth of ten to twelve kilometers is not possible, laboratory experiments were carried out in the form of high and high pressure tests. In this way, pressure and temperature in deep layers of soil can be simulated. display

Solubility for ten mineral species is presently present: While some have been found to be sparingly soluble, the solubility of a particular feldspar variety - feldspars account for more than two-thirds of the earth's crust volume - at 600 ° C, is a thousand times higher in the cave water of the Dripstone cave of dissolved calcium carbonate.

The researchers found that solvents and dissolved rock form special structures. Also solubilities can be increased drastically by other components of the solution.

Lubricants and flowable channels

The higher the proportion of dissolved rock matter, the more fluent the rock should be in depth. But in detail, there is currently only speculation: Presumably, aqueous solutions as "lubricants" will play an important role in the rock movements of orogeny. Some scientists assume that kilometer-long "flowable" canals in the lower crust stretch over hundreds of kilometers under the mountain ranges. The heaped up mountains could therefore "laterally" dissipate by their own weight.

(idw - Ruhr-University Bochum, 24.04.2007 - DLO)