Seismological studies on the mechanism of the large Tolbachik fissure eruption, 1975–1976

Seismological observations provided consistent information on the course and mechanism of the complicated large fissure eruption at Tolbachik volcano in Kamchatka from July 6, 1975 to December 10, 1976. Seismicity indicates that the initial magnesian basalts were rising ten days before the eruption from depths of more than 20 km. The formation of new feeding dykes was accompanied by earthquake swarms which decreased sharply one to two days before the opening of new eruptive fissures. The seismological data indicate that the main source of the different erupted basalts (2 km³) was a vast system (diameter ca. 80 km) of hydraulically connected magma chambers located in the lower crustal layers or in the crust-mantle transition layer.     

The Archean of the Baltic Shield: Geology, Geochronology, and Geodynamic settings

The Archean provinces and lithotectonic complexes of the Baltic (Fennoscandian) Shield are considered. The supracrustal complexes are classified by age: <3.2, 3.10–2.90, 2.90–2.82, 2.82–2.75, and 2.75–2.65 Ga. The data on Archean granitoid complexes and metamorphic events are mentioned briefly, whereas the recently found fragments of the Archean ophiolitic and eclogite-bearing associations are discussed in more detail. The Paleoarchean rocks and sporadic detrital grains of Paleoarchean zircons have been found in the Baltic Shield; however, the relatively large fragments of the continental crust likely began to form only in the Mesoarchean (3.2–3.1 Ga ago), when the first microcontinents, e.g., Vodlozero and Iisalmi, were created. The main body of the continental crust was formed 2.90–2.65 Ga ago. The available information on the Paleoarchean complexes of the Baltic Shield is thus far too scanty for judgment on their formation conditions. The geologic, petrologic, isotopic, and geochronological data on the Meso-and Neoarchean lithotectonic complexes testify to their formation in the geodynamic settings comparable with those known in Phanerozoic: subduction-related (ensialic and ensimatic), collisional, spreading-related, continental rifting, and the setting related to mantle plumes.     

Upward high-energy field-aligned electron beams above the polar edge of auroral oval: observations from the SKA-3 instruments onboard the Auroral Probe (Interball-2)

A new phenomenon was found at the polar edge of the auroral oval in the postmidnight-morning sectors: field-aligned (FA) high-energy upward electron beams in the energy range 20–40 keV at altitudes about 3 R_E, accompanied by bidirectional electron FA beams of keV energy. The beam intensity often reaches more than 0.5 · 10³ electrons/s · sr · keV · cm², and the beams are observed for a relatively long time (3 10²–10³ s), when the satellite at the apogee moves slowly in the ILAT-MLT frame. A qualitative scenario of the acceleration mechanism is proposed, according to which the satellite is within a region of bidirectional acceleration where a stochastic FA acceleration is accomplished by waves with fluctuating FA electric field components in both directions.