Age,Mineralogical and Geochemical Features,and Tectonic Position of Gabbroids of the Dzhigdinskii Massif,Southeastern Environ of the North Asian Craton

Complex mineralogical, geochemical, and geochronological studies of the gabbroids from the Dzhigdinskii Massif located in the western part of the Dzhugdzhur–Stanovoy Superterrane are performed. It is established that the age of the rocks from the Dzhigdinskii Massif is Middle Triassic (244 ± 5 Ma), rather than Early Archean, as was previously assumed. The age of the Dzhigdinskii Massif is close to the age of the formation of the other Triassic gabbroid massifs, such as the Amnunaktinskii (~240 Ma), Lukindinskii (~250 Ma), and Luchinskii (~248 Ma) in the southeastern environ of the North Asian Craton. One of the stages in the formation of the Selenga–Vitim volcanoplutonic belt falls in this period as well. This indicates that the Selenga–Vitim volcanoplutonic belt, along with the granitoids and volcanic rocks, is composed of ultrabasic–basic and basic massifs and that this belt is superposed on the structures of the Selenga–Stanovoy Superterrane, as well as on the western part of the Dzhugdzhur–Stanovoy Superterrane. The gabbro, gabbro–diorite, and series of gabbro and gabbro–diorite with high sodic alkalinity from the Dzhigdinskii Massif show obvious geochemical features of duality, including combination of intraplate and super-subduction origin. In this relation, we can assume that the origin of the gabbroids of the Dzhigdinskii Massif is related to the detachment of the oceanic lithosphere and its subduction into the mantle with the formation of an “asthenospheric window.”     

An iterative method for constructing equilibrium phase models of stellar systems

We present a new method for constructing equilibrium phase models for stellar systems, which we call the iterative method. It relies on constrained, or guided evolution, so that the equilibrium solution has a number of desired parameters and/or constraints. This method is very powerful, to a large extent due to its simplicity. It can be used for mass distributions with an arbitrary geometry and a large variety of kinematical constraints. We present several examples illustrating it. Applications of this method include the creation of initial conditions for N -body simulations and the modelling of galaxies from their photometric and kinematic observations.     

Stages of the lower crust formation of the Belomorian mobile belt,Kola Peninsula

Doklady Earth Sciences -     

Geology and geochronology of neoarchean anorogenic magmatism of the Keivy structure, Kola Peninsula

Anorogenic magmatic complexes were formed during protoplatformal evolution of the Keivy structure. This evolution ended with development of aluminous schists, which were derived by deep disintegration and redeposition of the rocks from the lower parts of the sequence and surrounding of the structure. The anorogenic rocks of the region are represented by the following magmatic complexes: gabbro-labradorite-latite-monzonite-granites; ophitic gabbro and gabbrodiabases; quartz syenite-alkaline granites; alkaline and nepheline syenites. The magmatic activity of this period, starting from the emplacement of gabbrolabradorite massifs and ending with alkaline and nepheline syenite bodies, was caused by ascent of mantle asthenolith, which destructed the Earth’s crust basement in this area. The anorogenic magmatism of the Keivy structure lasted for no more than few or few tens of million years. The granitoid subcomplex of the gabbro-labradorite-latite-monzonite-granite complex is dated at 2674 ± 6 Ma, which is comparable with an age of alkaline granites of the Ponoy and Beliye Tundry massifs (2673 ± 6 Ma). The considered complexes are separated in time by intrusion of amphibole-biotite plagiomicrocline granites with an age of 2667 ± 8 Ma. Gabbrolabradorites of the Shchuch’e Ozero and Tsaga massifs have close ages (2663 ± 7 and 2668 ± 10 Ma, respectively, Bayanova, 2004), but were formed earlier than granitoids (Bayanova, 2004). Formation of alkaline syenites of the Sakharijok I Massif, which finalized the Neoarchean anorogenic magmatism of the region, falls in the same interval. During Paleoproterozoic transformations, the rocks of the Keivy structure were sheared and uranium was introduced in the contact zones of the alkaline granite massifs, which caused formation of palingenetic melts and subsequent formation of pegmatites in the outer contact zones of the granite bodies.     

Main formation stages of the paleoarchean crust in the Kukhtui Inlier of the Okhotsk Massif

Based on U-Pb dating (SHRIMP-II) of euhedral zircon cores from hypersthene-plagioclase granulites of the Kukhtui Inlier (Okhotsk Massif), their igneous protholith of the basic composition is estimated to be Archean in age (3.7 Ga), which is confirmed by the Sm-Nd measurements. Subsequent tectonothermal events are established to occur 3.3–3.2, 2.8–2.7, and 1.9–1.8 Ga ago.     

First information about the geology of central antarctica based on study of mineral inclusions in ice cores of the Vostok station borehole

Study of mineral inclusions in the basal part of the central Antarctic ice sheet from the borehole at the Vostok station was carried out. Mineral inclusions were trapped during freezing of the subglacial Lake Vostok water on the base of the glacier, when it crossed a shallow coastal area. It is established that the mineral inclusions are aggregates consisting mainly of clay minerals and quartz up to 150 microns. Crystals of aragonite and sulfides detected in the inclusions may indicate the presence of modern hydrothermal activity beneath the ice. Small (up to 4.5 mm) fragments of siltstone and aleuropelite in some aggregates suggest that lithified clastic sediments are exposed on the western coast of Lake Vostok, where removal of debris material occurred at the expense of exaration. Detrital zircon and monazite, found in siltstones and aleuropelite, suggest the chronology of geological complexes of the provenance area, which is, as is assumed, located in the Gamburtsev mountains in the central Antarctic. The age of the provenance area is 0.8–1.2 to 1.6–2.0 billion years.     

3D Neural Network Inversion of Field Geoelectric Data with Calculating Posterior Estimates

Izvestiya, Physics of the Solid Earth - Abstract—The approximation neural network (ANN) method for solving the inverse geoelectric problem in the piecewise constant classes of media with the...     

Secular variation of geomagnetic field intensity during polarity transitions

Summary. The palaeointensity of the geomagnetic field during some ancient polarity transitions as well as and during the Jaramillo event was determined by the method of alternating-field remagnetization. The periods of the secular variation during these transitions were also determined.