АНИЗОТРОПИЯ МИКРОТВЕРДОСТИ КРИСТАЛЛОВ СЕМЕЙСТВА ЛАНГАСИТА

Microhardness of single crystals La3Ga5SiO14, La3Ta0.5Ga5.5O14, Ca3TaGa3Si2O14 family of lantanum gallium silicate of trigonal symmetry class of 32 space group P321 has been researched by Knoop method. Anisotropy of microhardness determined by the ability to bring the material under the indenter, which determines the value of microhardness on different planes and in different crystallographic directions in the plane. The technique of measuring the microhardness by Knupp method for semi−automatic hardness tester Tukon 2100B for single crystals of langasite family. Anisotropy of the I group of microhardness (microhardness polar dependence on indentor position relatively crystallography directions in the plane of measurement) on the crystallography planes (112−0), (011−0), (0001) has been founded. Anisotropy of microhardness in fragile crystals of langasite family determined by the possibility of mass transfer under the indenter due to the movement of interstitial atoms and vacancies of oxygen and gallium. Measurements have shown that microhardness on all investigated planes of CTGS single crystals, as base, and the prismatic lower than the respective planes of LGS and LGT single crystals; wherein in CTGS single crystals there is no anisotropy of microhardness microhardness as I, and II type. Polar dependence of the mechanical properties of langasite and langatate single crystals should be taken into account in the surface treatment technology and manufacturing techniques of piezo− and acoustoelements. Исследована микротвердость по методу Кнуппа монокристаллов La3Ga5SiO14 (ЛГС), La3Ta0,5Ga5,5O14 (ЛГТ), Ca3TaGa3Si2O14 (КТГС) семейства лантан−галлиевого силиката тригонального класса симметрии 32 пространственной группы Р321. Анизотропия микротвердости обусловлена возможностью выноса материала под индентором, что и определяет значение микротвердости на разных плоскостях и в разных кристаллографических направлениях на плоскости. Разработана методика измерения микротвердости по методу Кнуппа на полуавтоматическом микротвердомере Tukon 2100B для монокристаллов семейства лангасита. Обнаружена анизотропия микротвердости I рода (полярная зависимость микротвердости от положения индентора относительно кристаллографических направлений в плоскости измерения) на кристаллографических плоскостях (112−0), (011−0), (0001). Анизотропия микротвердости в хрупких кристаллах семейства лангасита определяется возможностью массопереноса под индентором за счет перемещения межузельных атомов и вакансий кислорода и галлия. Показано, что микротвердость на всех исследованных плоскостях монокристаллов КТГС (как на базисных, так и на призматических) ниже, чем на соответствующих плоскостях монокристаллов ЛГС и ЛГТ. При этом в монокристаллах КТГС отсутствует анизотропия микротвердости как I, так и II рода. Полярную зависимость механических свойств монокристаллов лангасита и лангатата необходимо учитывать в технологии обработки поверхности и в технологии изготовления пьезо− и акустоэлементов.

Magmatic plumbing systems of the monogenetic volcanic fields: A case study of Tolbachinsky Dol, Kamchatka

Clusters of small-volume volcanoes that individually may be defined as monogenetic, but have interlinked and interconnected plumbing systems, are used to be categorized as monogenetic volcanic fields (MVF).We argue that such volcanic clusters should be distinguished as separate type of volcanism, intermediate between monogenetic and polygenetic. The magma plumbing system structure of the MVF (its complexity and polymagmatic character) is the key argument for the potential separation of themin a classification. To avoid confusion caused by geneticmeaning of the used words we suggest using a term “areal volcanism” or “areal volcanic fields” (AVF instead of MVF) as defining this special type of volcanic activity. Herewe provide a reviewof themain characteristic features of one of the largest Holocene AVF, which is active now – the Tolbachik field of cinder cones in the southern part of Klyuchevskaya volcano group (Kamchatka), known in the literature as Tolbachinsky Dol. This paper is focused on the research of magma plumbing system. We consider structural,morphological, geological, geochemical and petrological data on the erupted basalts and their genesis. Specially planned seismic experiments made in 2010–2015 (seismic tomography and microseismic sounding) allowedmodeling of the principal elements of the magma plumbing system of Tolbachik AVF. Analysis of the investigations made in this area shows that Tolbachik AVF has a complex, dynamic, variable magmatic feeding system, which can be visualized as a superposition of subvertical and sublateral magma conduits. The contrast composition of the erupted rocks is caused by their different, although genetically connected, magma sources and mixing processes. One of the long-lived eruptive centers of Tolbachik AVF is Plosky Tolbachik stratovolcano, which lost its independent activity and was captured by Tolbachik AVF in Holocene. The AVF formed rejuvenated volcanism using the feeding system of the stratovolcano like an “old anthill”. The magma plumbing system characteristics of Tolbachinsky Dol strongly support the idea of separation of AVF from monogenetic volcanism type in the classification

Constraints on unrest in the Tolbachik volcanic zone in Kamchatka prior the 2012–13 flank fissure eruption of Plosky Tolbachik volcano from local seismicity and GPS data

Abstract A new fissure eruption began on 27 November 2012 on the southern slope of Plosky Tolbachik volcano, which is located in central Kamchatka, Russia, and is part of the Klyuchevskoy volcano group. We analyzed the displacement of the earth surface and the seismicity during several months before the eruption onset. According to seismic and GPS data the eruption was preceded by about 4–5 months (July–November 2012) of synchronous crustal deformation and seismicity. The seismic anomaly comprises low energy level seismicity (mainly M = 1.2–2.3) under Plosky Tolbachik volcano at a depth of less than 5 km. In the 2–3 weeks immediately preceding the eruption the rate of seismicity and the amount of radiated seismic energy exceeded the long-term average values (2000–2011) by more than 40 times. The deformation anomaly was recorded by displacement of the GPS points at distances from 20 to 60 km to the north of Tolbachik. The principal axis of the compressive strain was approximately directed towards the Tolbachik eruption site. The permanent GPS network detected radial compression and tangential stretching. The compressive strain reached about 10− 7 prior to eruption onset. The comparable duration of seismic and deformation anomalies (~ 4–5 months before the eruption) is consistent with a common origin, connected to magma rising from depth, and is interpreted as indicating that they were medium-term precursors to the eruption. Data recorded during this unrest episode of the Tolbachik volcanic zone will contribute to understanding of the reawakening of volcanic activity in this region and others worldwide with similar characteristics

Magma migration at the onset of the 2012–13 Tolbachik eruption revealed by Seismic Amplitude Ratio Analysis

Abstract In contrast of the 1975–76 Tolbachik eruption, the 2012–13 Tolbachik eruption was not preceded by any striking change in seismic activity. By processing the Klyuchevskoy volcano group seismic data with the Seismic Amplitude Ratio Analysis (SARA) method, we gain insights into the dynamics of magma movement prior to this important eruption. A clear seismic migration within the seismic swarm, started 20 hours before the reported eruption onset (05:15 UTC, 26 November 2012). This migration proceeded in different phases and ended when eruptive tremor, corresponding to lava flows, was recorded (at ~ 11:00 UTC, 27 November 2012). In order to get a first order approximation of the magma location, we compare the calculated seismic intensity ratios with the theoretical ones. As expected, the observations suggest that the seismicity migrated toward the eruption location. However, we explain the pre-eruptive observed ratios by a vertical migration under the northern slope of Plosky Tolbachik volcano followed by a lateral migration toward the eruptive vents. Another migration is also captured by this technique and coincides with a seismic swarm that started 16–20 km to the south of Plosky Tolbachik at 20:31 {UTC} on November 28 and lasted for more than 2 days. This seismic swarm is very similar to the seismicity preceding the 1975–76 Tolbachik eruption and can be considered as a possible aborted eruption

Magma migration at the onset of the 2012-13 Tolbachik eruption revealed by Seismic Amplitude Ratio Analysis

In contrast of the 1975-76 Tolbachik eruption, the 2012-13 Tolbachik eruption was not preceded by any striking change in seismic activity. By processing the Klyuchevskoy volcano group seismic data with the Seismic Amplitude Ratio Analysis (SARA) method, we gain insights into the dynamics of magma movement prior to this important eruption. A clear seismic migration within the seismic swarm, started 20 hours before the reported eruption onset (05:15 UTC, 26 November 2012). This migration proceeded in different phases and ended when eruptive tremor, corresponding to lava flows, was recorded (at similar to 11:00 UTC, 27 November 2012). In order to get a first order approximation of the magma location, we compare the calculated seismic intensity ratios with the theoretical ones. As expected, the observations suggest that the seismicity migrated toward the eruption location. However, we explain the pre-eruptive observed ratios by a vertical migration under the northern slope of Plosky Tolbachik volcano followed by a lateral migration toward the eruptive vents. Another migration is also captured by this technique and coincides with a seismic swarm that started 16-20 km to the south of Plosky Tolbachik at 20:31 UTC on November 28 and lasted for more than 2 days. This seismic swarm is very similar to the seismicity preceding the 1975-76 Tolbachik eruption and can be considered as a possible aborted eruption