The paper presents geological and geochemical characteristics of Cretaceous guyots of Marcus-Necker intraplate rise in the Pacific Ocean. Comparison of guyots located in different parts of the extended system revealed significant differences in their geochemical characteristics, which suggest lateral and (or) vertical mantle heterogeneity in the region. The studied volcanic rocks belong to the alkaline series. In some cases, they exhibit low values of Na2O/K2O. This volcanism is not typical for most of intraplate ocean rises. No consistency is observed between volcanic rock composition of guyots, their age and (or) geographic position. A complex pattern of magnetic anomaly lineations and irregular location of seamounts of different age cause difficulties in applying hot spot model to explain the formation of this intraplate magmatic province. The location of seamounts in the structure of the rise system and the entire system in the structure of the Pacific Ocean does not contradict the formation of fault zones, which initiate melting of upper mantle geochemically inhomogeneous substrate and lead to the formation of intraplate rises. Deep fluid flows may cause a large-scale melting of the upper mantle.

О короткой экспедиции по центральным Курильским островам, проведенной в рамках проекта Российского Научного Фонда (РНФ) «Геохимия и баланс летучих в зонах субдукции на примере Курильских островов».

The origin of diamonds in the lava and ash of the recent Tolbachik eruption of 2012–2013 (Kamchatka) is enigmatic. The mineralogy of the host rocks provides no evidence for the existence of the high pressure that is necessary for diamond formation. The analysis of carbon isotope systematics showed a similarity between the diamonds and dispersed carbon from the Tolbachik lava, which could serve as a primary material for diamond synthesis. There are grounds to believe that the formation of Tolbachik diamonds was related to fluid dynamics. Based on the obtained results, it was suggested that Tolbachik microdiamonds were formed as a result of cavitation during the rapid movement of volcanic fluid. The possibility of cavitation-induced diamond formation was previously theoretically substantiated by us and confirmed experimentally. During cavitation, ultrahigh pressure is generated locally (in collapsing bubbles), while the external pressure is not critical for diamond synthesis. The conditions of the occurrence of cavitation are rather common in geologic processes. Therefore, microdiamonds of such an origin may be much more abundant in nature than was supposed previously.

Resuspended ash is common in the areas of active volcanism and can be dangerous for ecosystems, human being and animals, different means of transport including local aviation. According to KVERT scientists data, a formation of resuspended ash plumes on Kamchatka occurs in the area of Sheveluch volcano annually, mainly from August to mid-October within two days. For example, these plumes observed on August, 3, 2011, September, 15–16 and October, 3–4, 2015, September, 28–29 and October, 2–4, 2016. Dense ash plumes rising 3 km above the surface to a.s.l. and 16–22 km in width drifted 600 km to the south-east from the volcano. Analysis of various satellite data in the VolSatView information system revealed typical features of Sheveluch resuspended ash plumes. The largest concentration of ash particles is observed in ash plumes at a distance of 60–70 km from the volcano; its width on the land for over 100 km reaches 16–22 km and is 1–2 km thick from the earth’s surface; a wide ash-rich plume is retained in the atmosphere from 3–5 hours to several days.