Приближение гравитационных и магнитных аномалий ГМТ - Гравимагнитная геотомография В.И. Сегалович

Требования к методу приближения Точность приближения – Порядка 1-3%, чтобы «исчерпать» информационный ресурс съемки Соответствие реальности – Гравимагнитная модель тождественна геологическим, топографическим и другим геофизическим данным Контроль точности модели – Возможность оценивать надежность результата Приемлемая трудоемкость вычислений

Особенности метода модель привязывается к геологической карте местности, к топографии и к тектонической концепции вектор намагниченности (включая направление) и плотность масс вычисляются с учетом двусторонних ограничений использование полных, а не остаточных аномалий Буге и аномальных значений магнитного поля размер участка не менее 10*кратной глубины освещения разреза

Direct problem solution for systems of polyhedrons Analytical solution for the polyhedron with quadratic density distribution x,y,z) = 6 z xz + 4 yz + 3 x + 2 y + 1 z + 0 Laplacian form of the potential field:

Inversion problem solution for systems of polyhedrons Solution of inverse tasks: 1. linear – based on extremely over-determined ( ) systems of algebraic equations 2. nonlinear – based on various interactive procedures under the condition of minimization of linear form

The contours of geological bodies are the lines of polyhedron intersection at Z = 0.1km The basic parameters of the model: square – km 2 number of elements – 250 linear variables – 900 equations – nonlinear parameters – 10 5 Model Completeness Middle Urals in plane Note: Contours of empty polyhedrons cover outliers

Precision estimation and indeterminacy reduction: data integration, variables aggregation

Selecting tectonic conception (1) Baltic Shield Geological Map 2 km Tomography Date Geological Section (3-3). Tomography Date

Selecting tectonic conception (2) Urals. Tagil Zone EEC - East-Europe continent; TZ - Tagil zone; КC - Kazakhstan continent; CUZ - Central-Ural zone; EUZ - East-Ural zone; MUF - Main Ural fault; ATF - Axled Tagil fault; SF - Serov fault; SG - Salda granite; SM - Saranovsky massif; PС - sediment rocks (Pavda series); CS - volcanic rocks of oceanic and island arc genesis - Caban, Salatim and Krasnouralsk series, ImC-Imenovka series; SDH - Ural Super-Deep hole. ImC

Square – 200 ths. km2 Number of elements – 90 Nonlinear variables – 3300 Observations – 50 ths. Magnetic fieldSection Nature of the geophysical phenomenon. T-Anomalies of Timano-Pechora Basin

Nature of the geophysical Phenomenon. Impact Structures of Puchesh-Katunka Astrobleme

Search for mineral deposits in the noise environment. Lomonosov Diamonds Magnetic field Square km2 Model of regional sources - 12 structures Topography and quaternary cover – 28 structures Linear variables – 90 Nonlinear variables – 1250 Observations (0.1 х 0.1 km) – 26.5 ths. Dolerite bodies (plane)

GMT Applications: Baltic Shield. Pechenga GeoMap 0 km GMTMap 0.1 km GMTMap 2 km GMTMap 3 km Horizontal section Vertical section X=143 km (1-1) X=160 km (2-2)

GMT Applications: Urals Orogenic Belt GMT 3D Geological Map 1 – ophiolites; 2 – effusive rocks of volcanic arc and turbidites; 3 – oceanic basalt and gabbro; 4 – subduction prism sediments; 5 – collision granite; 6 – PR layered gabbro

GMT Applications: N-Caspian Basin (1) Approximation of the Kungur Salt Massif (a fragment) Polyhedron (top view) Polyhedron (north-side view) The tomogram includes more than 50 units – polyhedrons. They present the environment under the following conditions: - the square is about 500 thous.km2; - the model units are bound to geological and seismic boundaries; - hypothetical structural units are distinguished in the basement at more than km depth; - normal field level with 0.1 mGl error; - continuous fillup; - up to 40 km depth; - Bouger anomaly approximation with ~1.6 mGl accuracy. The top and the bottom of Phanerozoe structural units are bound to seismostratigraphic boundaries obtained by CDP method

GMT Applications: N-Caspian Basin (2) Gravity Field Bouger anomalies Residual anomalies The negative anomalies correspond to: in the north – to salt massifs; in the east and south – thick sedimentary strata of UstYurt and Precaucasus. The positive anomalies correspond to: in the north- eastern side – to the end of Ural collision belt; in the center – to the hypothetical volcanic belt buried under PZ2-3 and MZ-KZ sedimentary strata The result of GMT-reduction. The Bouger anomaly approximation error: maximum error – 4.5 mGl; mean- square error – 1.6 mGl. By the example of correlation with salt massif one can see that the result of reduction is satisfactory.

GMT Applications: N-Caspian Basin (3) Final Results Level depths 4 km Level depths 7 km Density Section in Plane Y=600 km

Magnetic Field and Tomogram of Horejver Depression GMT Applications: Timano-Pechora Basin

GMT Applications: West-Sibirian Basins Magnetic tomogram

Paleomagnetic Dating of Impact Event by External T Field Ta - Kara Tomograms Ta - Puchesh-Katunka Calculation is on slide 18

GMT Applications: Yakutia Kimberlite Pipes TaDyke and kimberlite (Z=0.05km) Section (X=-0.9km) In Ta field one can see dykes (linear zones, anomalies in the center and in the south-east) and sills (smooth anomalies), but kimberlites cannot be seen. GMT reduction takes into account these sources of main anomalies as well as the bearing sediments PR2 – O1, AR- PR basement that overlaps the J cover, quaternary deposits and relief. As a result the anomaly connected to the known by kimberlite pipe (1). The anomaly (3) is perspective for kimberlites. Anomalies sources magnetization from the results of computation is shown by the arrows. |J| - в A/m.