Pre-Mesozoic basement of Tvarditsa Stara Planina Mountain, Central South Bulgaria: U-Pb geochronology and regional implication

The easternmost coherent tract of the pre-Mesozoic basement of the Carpatho-Balkanide belt is exposed in Tvarditsa Stara Planina Mountain. Two metamorphic units – the Lazovo and Shivachevo complexes as well as the Tvarditsa pluton were distinguished, as their ages are still not well constrained. Here, we present U-Pb (ID-TIMS) data for the Shivachevo complex and the Tvarditsa pluton, putting this information in the regional context of the late Variscan geodynamic evolution of the region.

Geodynamic Evolution of the Western Part of the Russian Arctic and Its Diamond Potential

The study of the geodynamic evolution of the Baltic Shield showed that the melts of diamondiferous kimberlites and related rocks were formed due to the pulling of “heavy” ferruginous sediments of the Early Proterozoic into subduction zones beneath the Archean cratons. Later, during the Neoproterozoic and Paleozoic stages of rifting, melts conserved in the lower crust and subcrustal lithosphere were able to penetrate into the near-surface zones of the crust and form magmatic complexes of alkaline–ultramafic and kimberlite magmatism. The authors showed that diamondiferous kimberlite and lamproite explosion pipes, as well as related carbonatite and alkaline–ultramafic intrusions, are mainly located above the subduction zones of the Svecofennian (Karelian) plates, which functioned about 2.0–1.8 Ga ago. At the same time, alkaline ultramafic intrusions and (sodium) carbonatites are located closest to the front of the subduction zone of Proterozoic plates (from 100 to 200–300 km). Then (at a distance of 200 to 400 km), there is a zone of location of calcite carbonatites and melilitites, and sometimes nondiamondiferous kimberlites. Diamondiferous kimberlite and lamproite diatremes are located farther than other similar formations approximately 300 to 600–650 km from its front. Such a regular spatial arrangement of magmatic complexes of a single series unambiguously indicates a change in depth of their origin. The farther from the surface boundary of the paleosubduction zone the magmatic bodies are located, the deeper the facies representing them.

Petrography and Geochemistry of the Leucocratic Rocks in the Ophiolites from the Pollino Massif (Southern Italy)

In the Tethyan realm, leucocratic rocks were recognized as dikes and layers outcropping in the ophiolitic rocks of the Western Alps, in Corsica, and in the Northern Apennines. Several authors have suggested that the origin of leucocratic rocks is associated with partial melting of cumulate gabbro. Major and trace elements composition and paragenesis provided information about the leucocratic rocks genetic processes. This research aims at disclosing, for the first time, the petrographical and geochemical features of Timpa delle Murge leucocratic rocks, Pollino Massif (southern Italy), in order to discuss their origin and geodynamic significance through a comparison with other Tethyan leucocratic rocks. These rocks are characterized by high amounts of silica with moderate alumina and iron-magnesium contents showing higher potassium contents than plagiogranites, due to plagioclase alteration to sericite. Plagioclase fractionation reflects negative Eu anomalies indicating its derivation from gabbroic crystal mushes. The chondrite normalized REEs patterns suggest the participation of partial melts derived from a metasomatized mantle in a subduction environment. The results reveal some similarities in composition with other Tethyan leucocratic rocks, especially those concerning Corsica and the Northern Alps. These new data provide further clues on the origin of these leucocratic rocks and the Tethyan area geodynamic evolution.

Tectonics of the Barents Sea Continental Edge

The tectonic situation of the studied region was formed as a result of a long (about 3 billion years) evolution of the Earth's crust. The problem of tectonic zoning of the region is not devoted to many published works and cartographic materials. The position of the borders between the East European and West Arctic platforms remains a debatable issue. More ambiguous, and in some cases, approaches to tectonic zoning of the region are not clear. Nevertheless, the work is based on a unified theoretical basis, reflecting the approach to solving the problems of regional tectonics from the perspective of geodynamic evolution.