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We report data on 9 samples of basaltic rocks and a spinel lherzolite xenolith collected during dredging in the area of Alba Guyot (Magellan Seamounts, Pacific Ocean). The data include ⁴⁰Ar-³⁹Ar ages of five samples and mineral chemistry of rock-forming and accessory minerals and glasses, with implications for the formation conditions of Ti-amphibole in basaltic melts. The upper slope parts at Alba Guyot and its satellite Oma Vlinder at sea depths of 3600 to 2200 m, are composed of ~1400 m thick basaltic rocks that formed within the 112 to 86 Ma interval (⁴⁰Ar-³⁹Ar plateau ages). Later, in its 60 Myr history postdating the Cretaceous volcanism, the guyot was exposed to erosion, which produced a plateau-like flat top, and underwent another pulse of volcanism in the Cenozoic. Miocene (<20 Ma) eruptions of basanitic magma on the Alba Gyot plateau were associated with petit-spot volcanoes. Judging by the absence of hyaloclastic deposits around those volcanoes and the age of the lavas, the Cenozoic eruptions occurred in subaerial conditions before the guyot submerged below the sea level. The Alba volcanics have greater contents of incompatible elements than typical oceanic island basalts (OIB), apparently, because they formed by low-degree partial melting of different sources: pargasite-bearing spinel peridotite of the metasomatized oceanic lithosphere, mainly for Cretaceous basaltic rocks, and/or garnet peridotite for Miocene petit-spot basanites. Multiple eruptions at Alba Guyot for 100 Myr may have been maintained either by the Southern Pacific Superplume in the region of the South Pacific Thermal and Isotopic Anomaly (SOPITA) in the Mesozoic or by translithospheric faulting originated at the lithosphere-asthenosphere boundary (LAB) in the Cenozoic.

We present new data on the chemical composition of the late Precambrian rocks in the upper part of the regional Balaganakh stratigraphic horizon (the Nugan Formation at the Baikal segment of the Sayan-Baikal-Patom belt (SBPB) and the Bugarikhta Formation of the Balaganakh Group at the Patom segment of the SBPB) and the U-Pb (LA-ICP-MS) age of detrital zircons from the Bugarikhta Formation. It has been established that the rocks of the Nugan and Bugarikhta formations resulted from the destruction of igneous and metamorphic rocks. The contents and ratios of trace and rare-earth elements in the rocks of the Nugan and Bugarikhta formations indicate a predominance of felsic igneous rocks in the provenance and the presence of rocks of mafic and intermediate compositions at the source of the terrigenous rocks of the Nugan Formation. The U-Pb age of detrital zircons from all rocks of the upper part of the regional Balaganakh Horizon is close to the age of the rocks in the basement of the southern margin of the Siberian Platform, which suggests that this basement was the main source of clastic material in the sedimentation basins. It is argued that the "pre-glacial" (pre-Marinoan) terrigenous deposits of the Nugan and Bugarikhta formations, as well as the deposits of the Ipsit Formation at the Sayan segment of the SBPB, accumulated in the Late Riphean (ca. 720-640 Ma), probably in postrift basins that formed immediately after the separation of Siberia from Laurentia at the early stages of the opening of the Paleoasian Ocean.

Cenozoic alkali basaltoids are developed in southern Transbaikalia (Daur-Hentiyn Range). They are represented by thin flows and nappes. Unlike the volcanic fields of the South Baikal volcanic region (SBVR), the investigated fields are not related to rifting. The volcanics from the Zharnichikha River flow were studied. By composition, they are referred to as basanites. The mineral compositions of the volcanics have been determined for the first time. In geochemical parameters the basanites correspond to mafic volcanics of oceanic islands. The P - T parameters of the equilibrium crystallization of olivine and clinopyroxene phenocrysts have been determined. For the calculated parent melt, the formation temperature was 1536 ºС, and the pressure was 3.28 GPa. The obtained original data on the isotopy of Sr, Nd, and Pb showed that the isotopic composition of the magmatic melt formed from the PREMA source, with a strong subordinance of the latter. Olivine clinopyroxenites (Ol + Cpx + Grt) were the probable mantle source for the studied basanites. The generation of basaltoid melts occurred under the influence of the mantle plume, which caused Cenozoic activation.

We present results of geochemical and geochronological (U-Pb, LA-ICP-MS) studies of plagiogranites of the Mt. Zmeinaya massif in the Nora-Sukhotino terrane. The studied rocks are of calc-alkaline series and peraluminous type. They formed in collision settings at the final stage of evolution of the Nora-Sukhotino terrane. The high Sr/Y ratios and low Y and Yb contents of the plagiogranites indicate that these are adakitic rocks. The trace element composition of the rocks suggests their high-pressure (>15 kbar) genesis through the melting of metabasites. The youngest zircon population from the plagiogranite has a mean weighted concordant age of 295 ± 4 Ma, which corresponds to the early Permian. With regard to the zircon morphology, the obtained age can be considered the age of the plagiogranites.

The crustal stress field of the Baikal Rift System has been reconstructed by tectonophysical inversion of focal mechanisms from the catalog of earthquakes recorded by the regional seismological network. Cataclastic analysis of fault slip data developed at the Shmidt Institute of the Physics of the Earth (Moscow) revealed previously unknown features in the behavior of principal stresses. Namely, the maximum deviatoric stresses diverge off the rift axis while the normalized spherical and deviatoric stress tensor components reach high magnitudes in the crust of the Baikal Basin. The obtained stress pattern of the Baikal Rift System is consistent with the rift origin by a joint action of a vertical mantle flow (upwelling branch of convection) and a horizontal flow in the asthenosphere which drives the NW-SE motion of the Amur plate off Eurasia.

The Central Aldan ore district (CAOD) is unique by the abundance of gold deposits associated with Mesozoic alkaline magmatism. Four types of gold deposits are distinguished here: porphyry gold, gold-sulfide, gold-argillizite-K-feldspar-quartz, and gold-uranium. The available geochronological data on the age of igneous rocks and gold mineralization in the CAOD show that the latter formed in the period 151-120 Ma. These data also agree with the results of U-Pb dating of the El’kon gold-uranium ore-magmatic system (143-125 Ma). Analysis of our geochronological data and previously published ones shows that two stages of magmatism evolution in this region. At the early stage (151-130 Ma), most of alkali syenites, monzonites, and their analogues (sills, stocks, ring intrusions, and volcanic sequences) and ores formed. They are widespread in various deposits and massifs. In the Ryabinovyi massif, this stage is marked by the formation of most of alkaline rocks (Aldan Complex) and ores: aegirine syenites, 151.4 ± 1.9 Ma; pyroxene-K-feldspar pegmatites, 144.8 ± 1.5 Ma; and Au-Cu ores, 137.5 ± 1.7-131.1 ± 16 Ma. The crystallization of amphibole from syenite of the Lunnoe deposit (143.1 ± 2.0 Ma) and clinopyroxenite of the Inagli massif (142.4 ± 2.0 Ma) and the formation of most of the alkaline rocks of its ring framing also took place at this stage. At the Samolazovskoe deposit, this stage is marked by the formation of zircon in pseudoleucite syenite, 135.9 ± 1.9 Ma, and in different syenite porphyry phases, 141.39 ± 0.90-142.4 ± 5.0 and 134.25 ± 0.70-129.9 ± 2.6 Ma, as well as gold-skarn mineralization, 129.9 ± 2.6-134.9 ± 2.8 Ma. The same period included the formation of primary ores at the Kuranakh deposit, 136.2 ± 1.7 Ma, and the deposition of breunnerite mineralization at the Lunnoe deposit, 132.4 ± 1.6 Ma. Early intrusive phases, such as potassic picrites, shonkinites, and lamprophyres, are scarce among the products of this stage of magmatism, which is possibly due to their burial beneath large volumes of later formed alkali syenites and monzanite-syenites. The second stage (128-120 Ma) was distinguished within the Ryabinovyi massif as small intrusions and dikes of olivine lamproites, shonkinite porphyry, minettes, and syenite porphyry. We revealed explosive breccias with an age of 127 Ma at the Samolazovskoe field. Magmatism of this stage was of limited occurrence in the CAOD and did not produce alkali syenites, monzonite-syenites, and ores. At the same time, rocks with an age of 121.1 ± 1.3-115.5 ± 1.6 Ma are widespread in the large (120 km2) Dzheltula ring massif of the Tyrkanda ore district, located east of the Central Aldan region.

The Chudnoe gold-palladium deposit, located within the Central Ural uplift, is confined to the axial zone of an anticlinal structure complicated by faults. Veinlet mineralization is localized in fractured and brecciated Late Riphean-Vendian rhyolites. Native gold and palladium minerals are concentrated mainly in veinlets of Cr-containing muscovite (fuchsite) and, more seldom, at local sites of rhyolite metasomatism, almost free of sulfides. Using a representative material, we studied the composition and structure of native gold and the regularities of their spatial variations. Native gold has composition Au-Ag-Cu and contains Pd and Hg impurities. The element proportion varies significantly: The content of Au ranges from 65.8 to 92.7 wt.%, the content of Ag varies from 0.4 to 33.8 wt.%, the content of Cu reaches 12.7 wt.%, and the content of Pd is up to 2.9 wt.%. Gold formed as a homogeneous Au-Ag-Cu solid solution at temperatures above 220 °C. The presence of copper in native gold is probably due to the absence of sulfide ion from the ore-forming hydrothermal solution. With decreasing temperature, Au-Ag-Cu solid solution containing more than 1.1-2.5 wt.% Cu disintegrates into two or three phases, forming characteristic plate-lattice and tabular exsolution structures. In the case of two-phase exsolution, the final phases are Au3Cu and Au-Ag solid solution or AuCu and Au-Ag solid solution; and in the case of three-phase exsolution, these are Au3Cu, AuCu, and Au-Ag solid solution. In some cases, the exsolution was accompanied by the recrystallization of gold with the formation of grain intergrowths. The composition of native gold in the deposit varies significantly, showing a discrete character at different sites of the ore zones, which is consistent with the veinlet ore mineralization. At the final stages of mineral formation, native gold was partly replaced by secondary high-fineness gold.

A sequence of argillized rocks and hydrothermal clays of the East Pauzhetka thermal field was studied in detail by means of drilling and trenching. We have identified zones composed of unusual mineral associations; their formation conditions are considered. The structure of the base of the hydrothermal-clay mass is shown. The source rocks (brecciated andesites) of the base are altered by hydrothermal-metasomatic processes and are represented by smectite-chlorite-K-feldspar-zeolite-carbonate-siliceous aggregate with sulfides, phosphates, titanium silicates and zircon silicates, and other mineral phases, including rare metals. A conceptual geological and geochemical model for the formation of argillisites and zones with mineral associations has been plotted. It is assumed that modern mineral formation in the East Pauzhetka thermal field inherits an epithermal ore-forming system located in the influence zone of a deep-seated fluid, the derivates of which are outflowing near the surface as alkaline metal-bearing solutions of the Pauzhetka hydrothermal system.

A river seismic survey technology based on using pneumatic water sources and autonomous seismic recorders, which are installed on the shore and configured for continuous seismic recording, is developed at the Geophysical Survey of the Russian Academy of Sciences (GS RAS). In recent years, several thousand kilometers of profiles have been worked out by the CDP-2D method on the rivers of East Siberia: Lena, Nizhnyaya Tunguska, and Vitim. Previously, only 6- to 10-second seismograms were used to study the structure of the upper part of the Earth’s crust. At the same time, the deep structure of the Earth’s crust in the vast territories of East Siberia remains poorly understood due to the high cost of research. The river seismic survey data are used on a profile section worked out in the lower reaches of the Lena River to demonstrate the possibility of studying the structure of the Earth’s crust to the full depth, including the Moho discontinuity. For this purpose, the archival seismic records are reprocessed the construction of montages of seismograms of increased duration (up to 23 s). The low-amplitude oscillations of reflected waves from deep boundaries are distinguished due to multiple summation, which is much larger than in conventional seismic surveys. The equipment used in this study has a sufficient dynamic range, and a high magnification is achieved by increasing the binning area. Wind noise reduces the quality of time sections of the upper part of the Earth’s crust, but does not worsen the section at great depths, so this material should not be excluded from processing. The river seismic surveys carried out using the technology developed at the GS RAS on the rivers of East Siberia within about 2700 km contain data that make it possible to build deep sections up to the Moho discontinuity, and this work needs to be done.

We propose a technique for the extended processing of cross-well seismic data for reflection imaging. Based on the analysis of the wave field and synthetic modeling, a graph for processing cross-well data is developed to separate the reflections in the presence of the boundary of a sharp change in the velocity of elastic waves. The migration of the reflection waves from the time scale to the depth one is performed by solving a forward problem for each source-receiver pair. As a result, the position of the reflection points is calculated, after which all traces are stacked based on the binning grid. The input information for performing the migration and solving a forward problem is the velocity characteristic of the massif, which is calculated using traveltime tomography on direct body waves obtained from the same data set of cross-well survey and vertical seismic profiling. The resulted depth seismic section has a much higher resolution than that of vertical seismic profiling and ground-based shallow seismic studies. This opens up the possibility of identifying various small-sized natural or technogenic objects in the interwell space. Practical implementation was carried out at the Verkhnekamskoe potassium salt deposit.