2011

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ABOUT CONFINEMENT OF ALKALINE ROCKS OF PRIAZOVSKY BLOCK OF UKRAINIAN SHIELD TO THE AREA OF DEVELOPMENT AMFOLIT-WEBSTERITOVOY MANTLE

P.I. Pigulevskiy

Dnipropetrovsk Geophysical Expedition «Dneprogeofizika», Dnepropetrovsk, Ukraine

Brief characterictics of density features and material composition of Priazovsky megablock of the Ukrainian Shield at the depth - 50 km is shown. Chosenned area developments eclogite, peridotite, ampholit-vebsterit abnormal mantle. The objective laws of their intercoupling with plutonic constitution of the southeast part of the Ukrainian Shield on depth -50 km are reviewed.

Introduction. The study of the deep tectonics, material composition, the formation conditions of the upper mantle is one of the fundamental problems of geology. To date, there are five sources of information about the upper mantle: the granulite complexes with the bodies of eclogites, xenoliths of mantle rocks from the tube explosion, deep seismic techniques DSS, EWEM and the CDP, deep electromagnetic studies by methods MTS and MEP; 3D-simulation of the gravitational field.

The results of interpretation. The seismic sections by profiles DSS and CDP, electromagnetic sounding data MTS and the MEP, 3D-simulation of the gravitational field for the study of deep tectonics of the eastern part of Ukranian Shield (Srednepridneprovsky - SPM and the Priazov - PM megablock, Fig. 1) were used [1]. The petrophysical heterogeneity in the crust and upper mantle, clarified the morphology of the Moho discontinuity (Moho) by reinterpreting results were provided.

Fig. 1. The tectonic scheme of the Ukrainian Shield: 1 – Volinsky; 2 - Dniester-Bug; 3 - Rossinsky-Tikichsky; 4 - Ingul's'ky (Kirovohradsky); 5 – Pridneprovsky; 6 – Priazovsky.

The Moho has a different structure for SPM and PM. Within the SPM it is more rugged and differentiated. Vertical depth ranging from -56 to -32 km. For PM, it is respectively from -46 ¸ to -36 km [1,2] and is characterized by plateau-like shape, which was complicated by local uplifts and depressions.

Results of generalization. Generalization of geologic materials in conjunction with the results of integrated interpretation of deep geophysical techniques and 3D-simulation of the gravitational field (Fig. 2) have allowed to predict the lithology of the upper mantle of the PM (Fig. 3), which probably represented eclogites, peridotite and rocks of dunite-harzburgite formation (anomalous mantle).

Fig. 2. The isolines of the density effective values on a section of -50 km: 1 - isolines of density, g/cm³.

The mantle eclogites occupy the largest area under PM, they characterize by close to sublatitudinal and have the form of highly elongated ellipse. The presence of eclogites in the upper mantle is confirmed by findings of eclogites and eclogitic rocks in the southwest and center of the Azov Sea [3]. All findings of eclogites and eclogitic rocks are located within the contour, which is described by isoline with the calculated spontaneous density more than 3.40 g/cm³.

Fig. 3 Expected structure of the upper mantle of the eastern part of Ukranian shield on a section of -50 km.

The Letters in circles: A - Middlepridneprovsky megablok; B - Priazovsky megablok.

The major manifestation of alkaline rocks: 1 – Malotersyansky; 2 – Starobogdanovsky; 3 – Chernigovsky; 4 – Volodarsky; 5 – Kremenevsky; 6 – Oktyabrskiy.

1 – eclogites; 2 – peridotites; 3 - anomalous mantle (feldspathic peridotite, harzburgite); 4 - crust mantle mixture (gabbro and feldspathic peridotite); 5 - gabbro; 6 - gabbro-peridotite; 7 - faults according to the gravity and electric prospecting; 8 - faults according to the seismic data; 9 - contour of spread the ampholyte-vebsteritovoy mantle.

In the range of calculated values ~ 3,35-3,40 g/cm3, distribution of concomitant mantle eclogite ampholytes and websterites is supposed. All the major manifestation of alkaline rocks (Volodarsky, Kremenevsky, Oktyabrskiy, Chernigovsky, Malotersyansky, Starobogdanovsky massifs) and subalkaline rocks of Yuzhnokalchiksky complex, lamproite pipes Mriya and Konka are confined to the areas of development amfolit and vebsterit mantle [1].

Transition mantle from the ancient - eclogite (and transition amfolit) composition to more younger - significantly peridotite is projected in the northeastern part of the PM (Fig. 3). Our results are confirmed by studies of xenoliths from kimberlite pipes at the junction between Ukranian shield and folded structures of the Donbass [2]. Changing the composition of the upper mantle, respectively, was influenced on its density, which decrease from 3,40-3,35 to 3,30-3,28 g/cm3. The values with the density 3,30-3,35 g/cm3 are attributed to mantle peridotite composition. In places where they less then < 3,20-3,25 g/cm3 is planned to develop Alpine rock dunite-harzburgite formation.

In conclusion, it should be noted that the results of integrated interpretation of deep geophysical research and 3D-simulation of the gravitational field indicate the vertical and lateral heterogeneity of upper mantle petrological PM Ukranian Shield. Distribution of the major manifestations of alkaline rocks are confined to areas of ampholyte-vebsteritovoy mantle.

Estimation of petrological composition of the upper mantle allows to highlight areas of possible development of alkali, kimberlite and lamproite magmatism and predict the development of certain types of ore minerals.

Literature

1. Pigulevskiy P.I. Prognoznyu sostav verkhney mantii vostochnoy chasti Ukrainskogo shchita Geologo-geofizicheskim dannym // Materialy XVI mezhdunarodnoy konferetsii “Struktura, svoystva, dinamika i minerageniya Vostochno-Evropeyskoy platformy». Voronezh, 20-24 sentyabrya 2010 г. Voronezh: Nauchnaya kniga, 2010. – T ІІ. – С.131-134.

2. Perspektivy korennoy almazonosti Ukrainy / Geyko YU.V., Gurskiy D.S., Lykov L.I. i dr. Kiev-Lvov: Izd-vo “Tsentr Evropy”. – 2006. – 200s.

3. Razdorozhnyu V.F., Ivanenko T.Ya., Pigulevskiy P.I. O nakhodkakh eklogitov i eklogitopodobnykh porod v predelakh Priazovskogo megabloka Ukrainskogo shchita // Naukovyu vestnik NGU Ukrainy, 2009. – №9. – S.34-37.