U-Pb Age and Hf Isotope Systematics of Zircon from Eclogite Xenoliths in Devonian Kimberlites: Preliminary Data on the Archaean Roots in the Junction Zone between the Sarmatian and Fennoscandian Segments of the East European Platform

The results of a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb dating and a Hf isotope study of zircon crystals separated from small eclogite xenoliths found in Devonian kimberlites within the Prypyat horst, Ukraine, have been reported. The studied area is located in the junction zone between the Sarmatian and Fennoscandian segments of the East European Platform. Four laser ablation sites on two zircon grains yielded Paleoproterozoic U–Pb ages between 1954 ± 24 and 1735 ± 54 Ma. In contrast, three of four Hf sites revealed negative εHf values and Paleoarchean to Mesoarchean model ages, excluding the possibility that the eclogite xenoliths represented segments of a juvenile Paleoproterozoic subducted slab or younger mafic melts crystallized in the subcontinental lithospheric mantle. A single laser ablation Hf spot yielded a positive εHf value (+3) and a Paleoproterozoic model age. Two models for eclogite origin can be proposed. The first foresees the extension of the Archean lower-crustal or lithospheric roots beneath the Sarmatia–Fennoscandia junction zone for over 200 km from the nearest known outcrop of Archean rocks in the Ukrainian Shield. The second model is that the Central Belarus Suture Zone represents a rifted-out fragment of the Kola–Karelian craton that was accreted to Sarmatia before the actual collision of these two segments of Baltica.

Rhyolites of the Kiliya-Zmeinyi uplift on the Black Sea shelf: geochemical evidence of a non-subduction boundary between the East European Platform and the Scythian Plate

The geochemistry of rhyolites uncovered at shallow depth by a borehole on the Kiliya-Zmeinyi uplift of the Black Sea northwestern shelf northeast of Zmeinyi island, in the junction zone of the East European platform and the Scythian plate, has been studied for the first time. This zone is considered by many geologists and geophysicists as a Late Paleozoic collisional suture that had been formed due to subduction of oceanic crust of the ocean, which adjoined the East European platform from the south, under the Scythian plate; it is traced from Dobrudzha to the Caspian Sea and named North Crimean. To check the subduction nature of the boundary between the East European platform and the Scythian plate, igneous rocks’ geochemical characteristics beeng indicators of various geodynamic regimes were used. A petrogeochemical comparison of rhyolites from the borehole in Zmeinyi area with acid igneous rocks known nearby has been carried out, namely with: 1) Late Permian subalkaline granites and rhyolites Turcoaia of the Macin zone of Northern Dobruja; 2) Triassic and / or Triassic-Jurassic trachyrhyolites and rhyolites of the Tulcea zone of Northern Dobruja and the Tatarbunar complex of the Pre-Dobruja depression. Some acid rocks of various ages and genesis from the southernmost margin of the Scythian plate (southwestern Crimea on- and offshore) were taken additionally for comparison. According to the distribution of rare earth elements, the position on the discriminant geochemical diagrams and the shape of curves on the multicomponent spider diagrams, the rhyolites of the Kiliya-Zmeinyi uplift exhibit not subduction but intraplate geochemical features closest to those of granites and rhyolites Turcoaia of the Macin zone of Northern Dobruja. Considering that the latter are reputed to be Late Permian, one can assume the same age for the rhyolites from the borehole in Zmeinyi area. Taking into account section features, geophysical information and geochemical similarity of magmatism, Kiliya-Zmeinyi uplift of the northwestern shelf seems to be a continuation of the Northern Dobruja structure into the Black Sea; it was a part of the hypothetical Late Paleozoic Euxinian orogen near its northern boundary. An absence of subduction geochemical properties in the studied presumably Late Permian rhyolites indicates that the junction zone of the East European platform and the Scythian plate in the Ukrainian shelf area is not a Late Paleozoic suture, but rather represents a thrust of the Euxinian orogen.

Current ECG Aspects of Interatrial Block

Interatrial blocks like other types of block may be of first degree or partial second degree, also named transient atrial block or atrial aberrancy, and third degree or advanced. In first degree, partial interatrial block (P-IAB), the electrical impulse is conducted to the left atrium, through the Bachmann’s region, but with delay. The ECG shows a P-wave ≥ 120 ms. In third-degree, advanced interatrial block (A-IAB), the electrical impulse is blocked in the upper part of the interatrial septum (Bachmann region); the breakthrough to LA has to be performed retrogradely from the AV junction zone. This explains the p ± in leads II, III and aVF. In typical cases of A-IAB, the P-wave morphology is biphasic (±) in leads II, III and aVF, because the left atrium is activated retrogradely and, therefore, the last part of the atrial activation falls in the negative hemifield of leads II, III and aVF. Recently, some atypical cases of A-IAB have been described. The presence of A-IAB is a risk factor for atrial fibrillation, stroke, dementia, and premature death.

Electrothermal Coil Detachment Failure in Flow Diverter-Assisted Coiling of a Small Blister Aneurysm: Technical Considerations and Possible Solutions

Flow diversion stenting combined with coiling offers both immediate protection from rebleeding for ruptured aneurysms and long-term stability for wide-necked or blister aneurysms. It is particularly useful for tiny ruptured aneurysms, alleviating the concern that small coils may prolapse between the struts of conventional stents. We employed this technique in a very small, broad-based ruptured aneurysm of the internal carotid, jailing the coiling microcatheter with a Pipeline Embolization Device. However, coil detachment repeatedly failed, until we withdrew the detachment zone into the microcatheter. We suggest that if the tip of the coiling catheter is adjacent to the stent, contact between the junction zone of the coil and the high metal density of the flow diverter may prevent proper electrothermal coil detachment. Detachment can be undertaken successfully within the microcatheter, though care must be taken thereafter to fully push the detached coil tail into the aneurysm.

Integrated geological-geophysical study of the junction zone of Eurasia and Gondwana

<p>Tectonically the considered area of junction of four lithospheric plates (Nubian, Arabian, Aegean-Anatolian and Sinai) belongs to the Eastern Mediterranean, with its Cyprus-Levantine marine and Anatolian-Nubian-Arabian continental framing. The anomalousness of the region is manifested in the tectono-structural features of the mantle, lithosphere, hydrosphere and specifics of atmospheric, biospheric processes, and Hominid evolution.</p><p>The study region is distinguished by a complex junction of elements of the continental and oceanic crust. This intricate structure is caused by the simultaneous development of collision processes associated with the latitudinal zone of the Neotethys Ocean closure and manifestation of the initial stages of spreading of the Red Sea – Indian Ocean submeridional rift system. This area is characterized by presence of several geological-geophysical phenomena: (1) anomalous thickening of the mantle lithosphere in the Cyprus-Levantine zone, (2) development of the most ancient oceanic crust block with the Kiama paleomagnetic hyperzone, (3) presence of significant in size and amplitude gravitational and magnetic anomalies and lowest values of thermal flow, (4) presence of mantle diapirs, (5) high seismic activity, (5) development of a counterclockwise circular rotation of the GPS vectors, and (6) the location of the apical part of the oval structure occurring in the Earth's lower mantle. The study area is also distinguished by unique geomorphological and paleogeographic features. At present, the lowest elevations of the earth's surface relief developed here reach –430 m on the Dead Sea coast, and the deepest zones of the Mediterranean Sea almost reach the ultra-abyssal depth of –5267 m in the Calypso depression in the Ionian arc of Greece. In the epoch of the Mediterranean Sea drying out in the end of the Miocene (the Messinian crisis), the earth's surface marks (taking into account the hydro-isostatic effect) could reach 3000-4000 m below the hydrosphere level; this was probably the lowest land hypsometric minimum in the Earth geological history.</p><p>The aforementioned phenomena make it possible to conclude that this region is a giant geodynamic node formed in the northern hemisphere at the intersection of the latitudinal critical parallel (35<sup>о</sup>) in the Eurasia and Gondwana junction zone and the meridional step of the Ural-African geoid anomaly. The combined use of systematic data analysis, geodynamic constructions, structural-tectonic zonation, and cyclic analysis enabled to clarify  the history of geodynamic development and genesis of the tectono-physical formation of individual geological structures, and the region as a whole. </p><p>A special importance was paid to the satellite gravity data analysis with the subsequent modeling and transformation and identification of the heterogeneous structures in the Earth's crust, mantle lithosphere and lower mantle. Paleomagnetic mapping of the region indicates an increase of the frequency and diversity of magmatic complexes from the west to east. Obviously, this manifestation is due to the counterclockwise rotation of the Earth's crust relative to elongated axis of the discovered deep mantle structure (Eppelbaum <em>et al</em>., 2021).</p><p>Eppelbaum, L.V., Ben-Avraham, Z., Katz, Y., Cloetingh, S. and Kaban, M., 2021.<strong> </strong>Giant quasi-ring mantle structure in the African-Arabian junction: Results derived from the geological-geophysical data integration. <em>Geotectonics</em>, <strong>55</strong>, No. 1, 1-28</p>

Mapping of the West Yakut barrier reef in the junction zone of the Vilyui syneclise and Aldan anteclise using electro-facies analysis

The aim of the study was to test the method of electro-facies analysis for mapping reef structures in the conditions of the junction of the Vilyui syneclise and Aldan anteclise. The article presents the results of a study of geoelectric characteristics using the method of electro-facies analysis. The confinement of buried bioherms to fault zones has been established. Facies zones corresponding to paleographic representations of the development of the region were identified. A map of the distribution of electrofacies for the Cambrian section interval was constructed, with boundaries of the distribution of reef deposits in the aisles of the study area. A typical geoelectric section showing the geoelectric properties of a section of the West Yakut barrier reef is given. Separation of facies based on electrical exploration data is able to provide operational information on the boundaries of the studied area. With insufficient drilling data, electro-facies analysis can speed up the interpretation of electrical exploration data.