Seismic and electromagnetic evidence of dehydration as a free water source in the reactivated crust |
| |
| Authors: | Leonid L Vanyan & Alexander O Gliko |
| |
| Institution: | Shirshov Institute of Oceanology, Russian Academy of Sciences, Krasikova;23, 117218 Moscow, Russia, Institute of Physics of the Earth, Russian Academy of Sciences, B. Gruzinskaya;10, 123810 Moscow, Russia |
| |
| Abstract: | According to recent estimates, the continental mid-crust contains 35–40 per cent amphibolites. Heating of the crust by an underlying mantle plume, for example beneath continental rifts, high plateaus, and areas of intraplate volcanic activity, releases water. Dehydration of amphibole-bearing rocks at depths of 20–40 km occurs mainly in the temperature range 650–700 °C, and this releases about 0.4 wt per cent of water.
Seismic tomography studies of the crust in the Kirgyz Tien Shan Range, where the age of the tectonic activity is less than 30 Ma, revealed a low-velocity zone in the mid-crust. The velocity of P waves was 0.4 km s?1 lower than in normal crust. MT sounding data in the region show the existence of a low-resistivity layer with an average resistivity of about 25 Ω m at the depth of the low-velocity layer. The spatial correlation of the observed anomalous layers and calculated effect of fluid phase on seismic and electric parameters of rocks suggests the presence of aqueous fluids released by the heating of the mid-crust. |
| |
| Keywords: | amphibolite dehydration electrical conductivity free water magnetotelluric sounding seismic wave velocity |
|
|
