Home – Home – Jornals – Russian Geology and Geophysics 2008 number 11

New data on the conditions and time of formation of eclogites in the Atbashi Ridge (South Tien Shan) were obtained. The PT -conditions of crystallization of high-pressure minerals from eclogites have been established: 23-25 kbar, 510-570

With geological, mineralogical, and petrographic methods, thermometry, and microprobe analysis of fluid inclusions, the structure and formation conditions of a specific orebody (zone 12) of the Ermakovskoe F-Be deposit have been established. This orebody is similar in fluorite content to other orebodies of the deposit (28.7 and 24.6%, respectively) but has the lowest average content of Be (~0.1% BeO against 1.19%). It is shown that in contrast to high-grade apocarbonate ores, the Ermakovskoe deposit formed mainly through the filling of the cavities of host rocks (syenites and schists) rather than the rock replacement. Calcium necessary for the formation of fluorite was supplied, most likely, as complexes Na₂CaF₄ and Ca₂Cl₃F by moderately saline (11.5-12.5 wt.% NaCl equiv.) F-rich (=0.3 mole/kg) solutions. The fluorite was deposited as a result of the solution cooling from ≥430 to 250

A mathematical model is proposed to describe the dynamics of phase fronts in volcanogenic orthomagmatic fluid systems (VOFS). It has been shown that these systems require rather short geologic times to reach a quasi-stationary state. This process is accompanied by slow cooling and pressure decrease as the bubbling front within the intrusive body submerges and magmatic fluid discharge decreases. Decompression boiling zone seems to develop in near-surface VOFS part for a certain combination of such parameters as porosity, permeability, and upper boundary condition. In evolving VOFS the existence of this zone is ephemeral. However in areas of seismic tremor and in mixed hydrothermal systems this zone can be stable and can produce brines below the level of hydrotherm discharge.

The recognition of pre-Riphean metamorphosed residual crust of deep chemical weathering on the Chuya-Nechera (Chuya-Kodar) granites on the basis of found gravel-like quartz-sericite rocks (apparently, residual products of feldspar hydrolysis) is still debatable. Study of this crust in relation with deep-level hypergenesis shows that it consists of not only quartz pseudogravelstones of dispersed paleozone but also pseudoquartzite schists, pseudoquartzites of lithomarge paleozone, and physically weathered granites of clastic and fissure zones in its bottom. Inequigranular (pisolitic, fine- and thin-grained) fissured quartz differentiated with depth is the main indicator of this crust. This quartz and associated sericite are the lithified and metamorphosed direct (hydrolysate alumina), side (hydrolysate silica), and residual (large-ingrowth quartz) products of the chemical decomposition of feldspar. Some of them accumulated in situ - in lateritic crust, and others were redeposited - first, in the lower layers of the weathering profile and then, in the residual crust. The early quartz and sericite accumulations in the weathering profile date the formation of peneplain, and the late ones, marking the residual crust, date the beginning of the marginal-sea transgression onto the passive continental margin, the peneplain erosion, and the origin of the Bodaibo inner trough.

A new type of Cambrian section penetrated by the Vostok-1 stratigraphic test well in the east of the West Siberian Plate, Tomsk Region, is described in terms of paleontology. It can be considered a key section for this region. According to a complex of geological and geophysical characteristics, the section in the depth range of 2766-5010 m was divided into the Churbiga, Paidugina, Pudzhelga, Podelga, Kondes, Shedelga, and Pyzhina Formations, and their first description was made. The Cambrian section in Vostok-1 well is most similar to those of the Kotui-Igarka area of the northwestern Siberian Platform, where Cambrian deposits formed in the pre-reef zone of an open sea basin. In the lower section of the borehole the highly carbonaceous siliceous-argillaceous-carbonate Paidugina Formation was stripped, which is an analog of the Lower-Middle Cambrian Shumnaya and Kuonamka Formations of the Siberian Platform. The Paidugina Formation, which accumulated on the shelf and slope of the open sea facing the Paleo-Asian ocean, is considered oil-producing and suggests the high petroleum potential of the cis-Yenisei basin. Also, a highly promising generation-accumulation petroleum system has been revealed.

The theory of orbital climate forcing implies an approximate Earth rotation model which has never been checked against other methods. We simulate the rotating Earth in compound models as a system of equal peripheral parts that orbit a central body and investigate the orbital evolution as affected by the gravity pull from the Sun, the Moon, and the planets. The predicted nutation cycles agree well with estimates by other methods. The model of periodic convergence and divergence of peripheral bodies may be useful to explain interaction of continents.

The implications of recent seismological and resistivity data for the geometry and orientations of neotectonic faults are generally consistent with the morphotectonic model of Gorny Altai as an area of crustal failure at the junction of two relatively stable blocks. The model predicts motions under general NW compression mainly on right-lateral strike-slip faults accompanied by systems of pinnate reverse and extensional faults.
The locations and mechanisms of aftershocks that followed the 2003 Chuya earthquake (Gorny Altai) indicate long seismic activity generated by a neotectonic NW right-lateral strike-slip fault which separates the North Chuya and South Chuya ranges from the Kurai-Chuya system of intermontane basins. The plane of the northwestern termination of the active fault zone dips in the SE direction, beneath the ranges, at about 70

Magnetotelluric responses of a 3D inhomogeneous earth excited by an arbitrary EM field are nonlocal, which is essential in processing regional MTS data. Due regard for this effect requires data acquisition by a dense synchronous 2D array. We suggest to invert the nonlocal MT responses applying correlation of the surface telluric and magnetic components recorded simultaneously at all stations. The new inversion algorithm has been tested using synthetic data that reproduce the conditions of the BEAR experiment.

We report forward modeling results for transient magnetic fields excited by horizontal electric or vertical magnetic dipoles. Modeling was performed with reference to resistivity patterns typical of platform areas in East Siberia. We investigate the possibilities to resolve deep reservoirs by measuring the horizontal and vertical components of the transient magnetic field and compare the depth resolution of magnetic and inductive methods.