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3D geological and potential field modelling of the buried alkaline-carbonatite Tajno massif (East European Craton, NE Poland)

Petecki Zdzisław, Rosowiecka Olga, Krzemiński Leszek

Geological Quarterly

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2022

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Vol. 66, No. 1

art. no. 10

EN

Geological and geophysical data are used to model the 3D geometry of the Tajno alkaline massif intruded during the Early Carboniferous in NE Poland. The massif consists mainly of pyroxenite, mafic intrusive and volcanic rocks, and carbonatites containing rare earth elements (REE) and other important mineral resources. The deep structure of the massif, and its thickness, shape and internal structure, has been poorly known making it impossible to properly search for useful mineral resources. In order to better constrain the distribution, geometries and relationships between the main rock types, a 3D geological model of the Tajno massif has been developed. The input data comprise a set of geological cross-sections built on an updated subsurface geological map, and borehole, magnetic and gravity data. 3D Geomodeller software was applied to integrate geological data into a coherent and geologically feasible model of the massif using geostatistical analysis. The magnetic and gravity data were used to constrain the 3D geological modelling results. The final 3D model is thus compatible with the geological data, as well as with geophysical data. The most important conclusions obtained from the modelling are as follows: (i) a higher proportion of nepheline syenites or tuffs and pyroclastic breccia in relation to pyroxenites; and, (ii) a smaller proportion of chimney breccia relative to chimney-hosted tuffs and volcanic breccia than proposed in previous geological interpretation. These results are important for further studies on the evolution of the Tajno massif and its associated carbonatites.

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Internal structure of the buried Suwałki Anorthosite Massif (East European Craton, NE Poland) based on borehole, magnetic and gravity data combined with new petrological results

Petecki Zdzisław, Wiszniewska Janina

Geological Quarterly

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2021

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Vol. 65, No. 1

art. no. 4

EN

Advanced magnetic and gravity data analysis has been used to acquire geophysical constraints providing new insights into the geological structure of the Suwałki Anorthosite Massif (SAM). The large negative magnetic anomaly of the SAM anorthosite intrusion is a result of the negative inclination of remanent magnetization, directed antiparallel to the present Earth’s magnetic field. Several filtering processes were applied to the magnetic and gravity maps to better understand the subsurface geology of the SAM area. The geological analysis of residual magnetic and gravity anomaly maps reveals the presence of different rock units, reflecting variation in petrological composition of the crystalline basement rocks. The 2-D modelling of magnetic and gravity data delineate the location and extent of the anorthosite-norite massif. The data is consistent with a thick upper crustal body with density 2690 kg/m3, low susceptibility (0.005 SI) and natural remanent magnetization (1.95 A/m), having inclination of I = –68°, and declination of D = –177°. The rocks bordering the central anorthosite body consist of norite and gabbronorite, granodiorite, diorite and charnockite. These main crystalline basement crustal units are shown more precisely on a new geological map of the SAM.

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The Tajno ultramafic-alkaline-carbonatite massif, NE Poland : a review. Geophysics, petrology, geochronology and isotopic signature

Wiszniewska Janina, Petecki Zdzisław, Krzemińska Ewa, Grabarczyk Anna, Demaiffe Daniel

Geological Quarterly

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2020

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Vol. 64, No. 2

402--421

EN

This paper reviews all available geological data on the Tajno Massif that intruded the Paleoproterozoic crystalline basement of NE Poland (Mazowsze Domain) north of the Teisseyre-Tornquist Zone, on the East European Craton. This massif (and the nearby Ełk and Pisz intrusions) occurs beneath a thick Mesozoic-Cenozoic sedimentary cover. It has first been recognized by geophysical (magnetic and gravity) investigations, then by drilling (12 boreholes down to 1800 m). The main rock types identified (clinopyroxenites, syenites, carbonatites cut by later multiphase volcanic/subvolcanic dykes) allow characterizing this massif as a differentiated ultramafic, alkaline and carbonatite complex, quite comparable to the numerous massifs of the Late Devonian Kola Province of NW Russia. Recent geochronological data (U-Pb on zircon from an albitite and Re-Os on pyrrhotite from a carbonatite) indicate that the massif was emplaced at ~348 Ma (Early Carboniferous). All the rocks, but more specifically the carbonatites, are enriched in Sr, Ba and LREE, like many carbonatites worldwide, but depleted in high field strength elements (Ti, Nb, Ta, Zr). The initial87Sr/86Sr (0.70370 to 0.70380) and ɛNd(t) (+3.3 to +0.7) isotopic compositions of carbonatites plot in the depleted quadrant of the Nd-Sr diagram, close to the “FOcal ZOne” deep mantle domain. The Pb isotopic data (206Pb/204Pb <18.50) do not point to an HIMU (high U/Pb) source. The ranges of C and O stable isotopic compositions of the carbonatites are quite large; some data plot in (or close to) the “Primary Igneous Carbonatite” box, while others extend to much higher, typically crustal ẟ18O and ẟ13C values.

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Strefa Teisseyre’a-Tornquista : dawne koncepcje a nowe dane

Narkiewicz Marek, Petecki Zdzisław

Przegląd Geologiczny

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2019

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Vol. 67, nr 10

837--848

EN

Concepts prevailing among the Polish geoscientists during the last decades assumed that the Teisseyre-Tornquist Zone is a major tectonic discontinuity separating the pre-Ediacaran East European Craton (EEC) crust from the Paleozoic Platform composed of terranes accreted during the Caledonian and Variscan orogenic processes. The recent interpretations of the TTZ by Mazur and collaborators, basedon gravity modelling and new PolandSPAN seismic reflection data, revive earlier ideas of the EEC crust extending to the western Poland and NE Germany. These authors propose that the TTZ is in fact a Sveconorwegian (ca. 1 Ga old) collisional suture marked by a crustal keel expressed as the Pomeranian and Kuiavian gravity lows in northern and central Poland. However, the present review of seismic data available, as well as a closer evaluation of the modelling results, do not confirm the keel/suture concept. On the other hand, the idea of the TTZ as an Early Paleozoic tectonic discontinuity is supported by several lines of evidence, including a strong regional magnetic gradient and a contrast in the crustal structure. The latter is revealed by seismic velocity distribution from the refraction data, in the results of magnetotelluric profiling and in recent seismicity patterns. The interpretation of the PolandSPAN data attempting to prove the continuity of the cratonic crust and its Ediacaran-Lower Paleozoic cover across the TTZ appears questionable. At the same time the POLCRUST-01 deep seismic profile in SE Poland documents that the zone is associated with the subvertical Tomaszów Fault. The basement top displacement by ca. 0,5 km and associated change in its slope are related to the fault whose deep crustal roots are further documented by reflectivity patterns in the lower crust. The recent modelling exercise by Krzywiec and collaborators aimed at questioning the thick-skinned nature of this fault does not present compelling results, being based on a poorly constrained geological model. The general conclusion from the present review is that the recently published data either support or at least do not contradict the concept of the TTZ as a tectonic zone separating the continuous EEC crust from several allochtonous blocks - mostly proximal Early Paleozoic terranes to the south-west. Thelithospheric memory of the TTZ echoed in successive stages of its reactivation in different intra-plate tectonic regimes - transpressive Variscan, mostly extensional or transtensional Permian through Early Cretaceous, compressional Late Cretaceous and finally Neogene, related to the Carpathian orogenic compression.

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Ideal body analysis of the Pomerania Gravity Low (northern Poland)

Petecki Zdzisław

Geological Quarterly

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2019

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Vol. 63, No. 3

558--567

EN

The large negative residual Bouguer gravity anomaly in northern Poland called the Pomerania Gravity Low (PGL) was analysed using Parker's ideal body theory. A residual gravity anomaly along the profile was inverted to find bounds on the density contrast, depth, and minimum thickness of its sources. As the ideal body reaches the surface, the greatest maximum negative density contrast is -0.038 g/cm3, while the body itself has a thickness of 52 km. If 8 km is taken as a depth to the source body top, the density contrast must correspond to at least -0.092 g/cm3, with a maximum allowable thickness of 18 km. The ideal body inversions show that the depth to the body top cannot exceed 15 km. Assuming a geologically reasonable maximum density contrast as small as -0.2 g/cm3, the source body top can be no deeper than 11.5 km, and its thickness greater than or equal to 6 km, assuming it extends up to the Earth surface, or greater than or equal to 7 km, when its top is below 8 km depth. It can be hypothesized that the main source of the negative gravity anomaly is reIated to a predominance of felsic rocks in the Paleoproterozoic Dobrzyń Domain of the East European Platform basement.