Local magnetic anomalies of the Ukrainian Shield as indicators of the manifestation of different-age stages of focal-channel magmatism

Abstract

A special class of local small sizes of subisometric magnetic field anomalies (AMF) of the Ukrainian Shield (USh) is considered here. Such AMF are united by the volcanogenic-intrusive-tubular origin of the sources associated with the assumed source-channel manifestations of pulsed plutonic-degassing processes of the Earth. The geological study of such anomalies indicates the enrichment of their sources with mineralization of dark, noble, non-ferrous and rare metals. Some of these AMF (Zhdanivska group, Rivnenska) in general contours coincide with local gravitational minima due to decompaction and grinding of the rocks that cause them, despite the basic-ultrabasic composition. Other anomalies, on the contrary, fully correspond to the maxima of gravity due to the enrichment of rocks with magnetite (Pischansk AMF) or ilmenite (Stremigorodsk AMF) on an industrial scale. In the section, all the studied sources of anomalies have a funnel-shaped (sometimes fungal-shaped) or stock-like shape, which indicates the focal-channel type of their genesis. A characteristic feature of some of the studied AMF are peculiarities of the magnetization vector of their sources, which has variable directions in the section and is often subhorizontal (Kalyniv group of anomalies, Rivne and Stremigorod AMF), which is unusual for the USh latitudes. This indicates a multiphase and separation in time formation of the sources of these anomalies from the Archean-Proterozoic time of formation of the surrounding USh rocks. This time may be either Proterozoic (Stremigorod AMF), or Phanerozoic (Rivnenska AMP — early Paleozoic). A number of similar in size and concentrically-zonal shape of Cenozoic AMF has been established, for example, within the TransCarpathian fault zone. The obtained results show that within the Ukrshield there is a certain number of small-sized structures associated with different-age focal-channel manifestations of pulsed intrusive and plutonic-degassing processes of the Earth, which are much more widespread than it has been supposed. This does not only extend the prospecting possibilities for new types of minerals associated with the processes of magmatism and degassing of the Earth, but also contains a new additional information in the context of the universal history of the Ukrshield formation and its ore potential