Vol 472, No 1 (2017)

A cause-and-effect relation is established between historical metallogeny of gold and uranium and extraterrestrial factors (impact events, evolution of the distance between Earth and Moon, rotation geodynamics), which significantly affected the Early Precambrian tectonic evolution of our planet. It is shown by the example of the complex Witwatersrand deposit that the Precambrian polygenetic Au and U deposits of the quartz–pebble type were formed within a near-equatorial epi-Archean supercontinent and were related to extraterrestrial factors under a rotation regime of the plume vertical tectonics. The beginning of breakup of the epi-Archean supercontinent in the Paleo- and Mesoproterozoic (2.0 ± 0.3 Ga) was related to the abrupt decrease in the velocity of the Earth’s axial rotation followed by the dominant regime of subhorizontal plate tectonics and formation of rich U deposits of the nonconformity type (which are structurally related to the horizontal inertial detachments at the contacts of the consolidated crust) and Meso- and Neoproterozoic sedimentary complexes.

A geodynamic model for the formation and movement of marginal seas in the Pacific Ocean during lateral interaction between the Eurasian and Pacific lithospheric plates is proposed. In a transition strike-slip megazone, the continental and oceanic plates disintegrate into blocks, which are involved in rotation, thus causing formation of mantle plumes and tectonospheric funnels (ascending and descending lithospheric vortexes). The implications of the model are formulated. Three scenarios of the evolution of the marginal sea basins depending on the direction of motion of the Pacific plate are discussed.

Plagiogranites and conodonts from chert intercalations in basalts of the ophiolite association in the Tekturmas zone of Central Kazakhstan were subjected to the U‒Pb geochronological and stratigraphic investigations, respectively. The age of plagiogranite crystallization is estimated to be 489 ± 8 Ma corresponding to the stratigraphic interval spanning from the uppermost Upper Cambrian to the lower Tremadocian. Conodonts from cherts of the Kuzek Formation are distributed along the section interval from the uppermost part of the Darriwilian (Middle Ordovician) to the lower part of the Sandbian (Upper Ordovician), which corresponds to the period of 457‒460 Ma. It is revealed that the formation of the ophiolite section in the Tekturmas zone was a multistage process lasting from the Late Cambrian to the initial Late Ordovician.

Glass formation takes place under conditions of rapid cooling of a melt at a great temperature difference between the melt and the host rock, which must have high thermal conductivity. The most favorable conditions for glass formation exist when the melt intrudes in the form of thin apophyses. Glass has been found in granite massifs related to the volcanic–plutonic association.

Multiphase aluminofluoride segregations were registered in aegirine–amphibole granite from the Vostochnyi massif of the Katugin rare-metal deposit. Among them are fluorides (fluorite), Ca–Na–Mg fluoraluminates (weberite, cryolite, pachnolite–thomsenolite, prosopite, gearksutite, ralstonite, and others), and Ba fluoraluminates, which had not been observed previously in this massif. Four fluoraluminates with high concentrations of Ba were found in aluminofluoride segregations: usovite Ba₂CaMgAl₂F₁₄, the most abundant phase, and three potentially new minerals (BaAlF₄(OH), BaCa₂AlF₉, and BaCa₄AlF₁₃). The chemical composition of Ba phases and the results of their Raman spectroscopic study are reported.

The possibilities of using the average compositions of tonalite–trondhjemite–granodiorite association rocks (TTG), which make up a significant part of the Archaean continental crust, have been examined. The results of the TTG average compositions obtained by other researchers and the authors' data of the average compositions of TTG from the Baltic and Ukrainian shields and the entire Archaean crust are given. It is shown that the average compositions of the Archaean TTG of continental large crustal fragments (cratons or provinces) practically do not bear any information on their sources or conditions of their formation. The possibility of obtaining of such information by means of analysis of the average compositions of TTG, composing smaller fragments of the crust, exemplified by rocks of the Karelian subprovinces of the Baltic Shield has been demonstrated.

The Lu–Hf isotope systematics of zircon from the gabbro–plagiogranite association (gabbro, diorite, tonalite, and plagiogranite), which is one of the most typical associations of igneous rocks in the Urals, was studied for the first time. The isotope study yielded a unified age limit of 433 Ma, which corresponds to the time of formation of this rock association. The younger “rejuvenated” ages characterize superimposed thermal impact events, induced by the volcanic arc activity, as well as collisional and postcollisional processes. Here, the initial ¹⁷⁶Hf/¹⁷⁷Hf(t) ratio in the studied zircon from gabbro and plagiogranite corresponds in fact to a highly LILE-depleted (DM) mantle.

New results of U–Pb geochronological and geochemical studies of rocks that form two structurally different massifs in the Mamyn Terrane are presented here. It has been found that the age of amphibole–biotite granites in the Kosmataya Massif, Oktyabrskii Complex is 488 ± 5 Ma. The same age has been defined for gneissose diorite 488 ± 8 and granodiorite 488 ± 5 Ma of the Ust–Inkan Massif. The results indicate that all the studied rocks have an identical Late Cambrian–Early Ordovician age of about 488 Ma. Considering that they were formed within a single tectonic structure (Mamyn Terrane), spatially close to each other and have similar geochemical characteristics, they may be considered as a single diorite–granodiorite–granite association. The results obtained indicate that a stage of intensive felsic magmatism occurred in the Mamyn Terrane in the eastern part of the Central Asian Fold Belt. This stage of magmatic activity is also clearly expressed in other continental massifs in the eastern part of this belt, which may indicate their common geodynamic history.

Longitudinal wave velocities (V_P) in rocks were measured experimentally in dunite (olivinite) and serpentinite at a water pressure of 300 MPa and temperatures of 20–850°C. It is shown that the strong decrease in V_P in dunite (by ~3 km/s) observed within the range of 400–800°C results from penetration of water into rock along microfractures and from the formation of hydrous minerals (mostly serpentine) along the boundaries of mineral grains as a result of water–olivine interaction. It is suggested that serpentinization or the formation of similar hydrous minerals in olivine-rich mantle rocks under the influence of deep fluids may result in the formation of zones of low-velocity elastic waves in the upper mantle at great depths (~100 km).

It is shown that, in accordance with the data used when determining velocity distribution in the Earth’s core [14], so called “precursor” earthquakes cannot be produced by wave scattering to lower mantle inhomogeneities, because seismic rays linking the earthquake sources and seismic stations are located in different inner zones of the Earth and travel at different azimuths, producing a stable wave pattern on aggregate. Thus, the present work considers the fundamental problem regarding what precursor earthquakes are. Solution of this problem will guide ideas about the structure of the Earth’s core.

The results of the Russia’s first ground-based experiment for determination of the difference in the Earth’s gravitational potentials on the basis of the measurement of the gravitational effect of the time delay with the help of a high-stability transportable atomic clock are provided. The reference atomic clock was placed in Moscow oblast, and a transportable quantum clock with an instability of 3 × 10^–15 was placed in the Caucasus Mountains, with a difference in height of the clocks of 1804 m. The measured difference in the gravitational potentials between the positions of the two quantum clocks was (182.0 ± 3.1)10²m²s^-2 at a relative measurement error of no more than 1.7%.

The variable polyrhythmicity observed in natural, technical, and humanitarian spheres can be the result of mutual desynchronization of conjugate rhythmic processes. One example of desynchronization in medicine is fibrillations of heart ventricles. To bring a patient out of this state, electroshock is applied, which frequently leads to defibrillation and recovery of normal heart rhythm (resynchronization). This phenomenon has analogies in other fields of science. It is known that lunar–solar tides cause subsurface seismic noise. We give an example of detecting such noise in the Ashkhabad seismic survey area. This noise can appear and disappear, and the reason may be certain shock impacts, in particular, earthquakes. Similar results have been obtained in studying lunar seismicity, where tidal phenomena are more strongly pronounced than on Earth.

The resistance of urban soils to organic contaminants and their capability for self-purification from benzo(a)pyrene were evaluated with the use of the concept of critical loads on urban landscapes. It is based on the balance equation between the input of benzo(a)pyrene with technogenic fallout and its decomposition in soil. The last component of the balance is described by the first-order kinetics model. The benzo(a)pyrene reserves in soils and precipitation from the atmosphere were determined and then used for calculation of its critical loads on soils in various land-use zones of the Eastern okrug of Moscow with respect to the degradation rate and the exposure period. It was revealed that when the degradation intensity is 1–10% per year, it will take many tens and hundreds of years to achieve a decrease in the benzo(a)pyrene content to an ecologically safe level in all the land-use zones except for the postagrogenic one.