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Geoinformatika 2015; 2(54) : 52-61 (in Russian)

DEPENDENCE OF LOW VELOCITY ZONES PARAMETERS ON MINERAL COMPOSITION
OF UKRAINIAN SHIELD ROCKS IN DIFFERENT РТ-CONDITIONS OF EXPERIMENT

E.E. Karnaukhova

Institute of Geophysics of Ukraine National Academy of Science, 32 Palladin Ave., Kyiv 03680, Ukraine,
e-mail: karnauhovaee@gmail.com

Purpose. The purpose of the article is to conduct experimental studies of low velocity zone (LVZ) parameter dependences on the mineral content of Ukrainian Shield rocks in the programmed PT-conditions.
Design/methodology/approach. To solve the problem a method of multidimensional correlation-regression analysis was used, together with the explosion seismology data. The results obtained are presented as descriptive statistics, histograms, schedules, linear pair and plural cross-correlation dependences. Originally, the regional collection of rocks was preliminarily studied in laboratory conditions at atmospheric pressure and room temperature. The petrographic analysis was carried out. The most representative samples were investigated at hydrostatic pressure up to 0,5-0,6 Gpa. After this information, was statistically processed, we selected groups of samples which were studied under the simultaneous P and T effect. In these studies, P and T were changed according to the PT-program of possible regional change of these parameters with depth. According to the conditions of the experiment, a rock sample was supposed to “plunge” gradually to the preset depth and simultaneous measurements of the Vp, VS were made and the volume decrement was measured.
Findings. The experiments show that the Vp, VS = f(PT) = f(H) dependences have complicated regularities: on the curves show velocity inversion zones with maxima and minima manifestation. Inversion zones change their width with depth (ΔH) and decrease the velocity maximally (ΔVp). Here the rocks are characterized by low Young and shear modules, high brittleness (low Poisson’s ratio), high discompaction (high dilatancy), and low thermal conductivity (λ). The inversion zones established by laboratory experiments in most cases are in good agreement with LVZ in the Earth’s crust from DSS profiles. For the most selected groups of rocks ΔVp is 0,02-0,16 km/s; ΔH is in the depths interval of 6-20 km. In all the rock groups, elastic parameters dependences on the percentage content of rock-forming minerals tend to decline depth. In LVZ the influence of the mineral composition on elastic parameters is low and considerably less than structural transformations of rocks.
Practical value/implications. The obtained experimental and statistically treated data of a broad spectrum of Ukrainian Shield rocks may be used for petrophysical crustal modeling, enabling us to predict the content and state of the Earth’s crust mineral matter.

Keywords: mineral composition, pressure, temperature, elastic waves propagation velocity, cross-correlation dependences, low velocity zones.

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