IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS001 Poster presentation 1728
Effect of mineral content of granitoids of the ukrainian shield on the
change of their elastic parameters in different thermobaric conditions of
the lithosphere (by experimental data)
Mrs. Elena Karnaukhova
Physical Properties of the Earth's substance S.I.Subbotin Inst. of Geophysics of NASU IASPEI
Korchin Valery
On an example of optimal sampling of the Ukrainian Shield (USh) granitoids whose main rock-forming
minerals are quartz, plagioclase, potassium feldspar, biotite, some dependences of their elastic
parameters on the mineral content at pressures and temperatures are shown. The increasing amount of
quartz in the rock decreases the change of the elastic velocities by pressure, while the growth of the
plagioclase content of biotite increases them. The growth of the potassium feldspar content first
increases and then decreases the velocity change. For the Ukrainian Shield rocks the elastic velocity of
longitudinal polarization (Vp) values increase abruptly in the programmed PT regimes of the
experiments at depths of 0-7 km. After reaching a definite limit, they begin to decrease nearly to the
depth of 7-15 km and then increase again. Thus, on the curves of the depth distribution of velocity,
inversion zones are distinguished which change their width with depth (∆H) and diminish the velocity
maximally (∆Vp). The existence of these zones is due to the essentially opposite effect of pressures and
temperatures (corresponding with definite depths) on the rocks. To solve the problem set the method of
the multidimensional correlation-regression analysis was used together with the explosion seismology
data. It was shown that different-gradient change of the velocity with depth sometimes corresponds
with a definite change of the mineral content of the rocks the main effect being exerted by the regional
deep pressures and temperatures. Only with notable change of Vp with depth appreciable mineral
content change may be expected. E.g., if the velocity inversion zones show ∆Vp>0,3 km·s-1 the mineral
content change should also be suggested. In this case the rocks should first of all be enriched with
quartz, while the intensive velocity growth seen after the inversion zone immediately (above 16 km)
may be due to the increased plagioclase and pyroxene content of the rocks, the quartz content being
decreased. The obtained experimental data of a broad spectrum of rocks are used for petrographic
modeling of the Earth interior enabling us to forecast the content and state of the mineral matter of the
lithosphere.
Keywords: granitoid, thermobaric conditions, lithosphere