Home – Home – Jornals – Russian Geology and Geophysics 2007 number 5

Complex study and comparative analysis were carried out for two gold deposits, Vodorazdel'noe and Ondol'toi, localized among carbonate and siliceous-carbonate rocks of the Il'chir Formation in southeastern East Sayan. The Vodorazdel'noe deposit is of gold-quartz-sulfide type; it formed at 275-300

Spinel-anthophyllite rocks that may be classified as ultrabasic low-Ca spinel amphibolites have been first discovered in the Kokchetav collision zone (northern Kazakhstan). They outcrop 2 km west of Enbek-Berlyk Village among schists and quartzites and are closely associated with spinel harzburgites and garnet pyroxenites. The main hosted minerals are spinel (hercynite) and anthophyllite. The rocks bear magnetite-hornblende-spinel-anthophyllite pseudomorphs with rounded and polygonal sections, which might have been resulted from the replacement of garnet grains. The prismatic anthophyllite crystals and scarce olivine relics contain elongate parallel spinel inclusions resembling spinel-olivine syntactic intergrowths in the Enbek-Berlyk spinel harzburgites. The spinel-anthophyllite rocks are similar to the associated spinel harzburgites in CaO, MnO, SiO₂, and Al₂O₃ contents but are richer in FeO and poorer in MgO ( F = FeO/(FeO + MgO) = 57% against 35% in the harzburgites). Geological, mineralogical, and geochemical data suggest that the spinel-anthophyllite rocks formed during the isochemical contact metamorphism of garnet-bearing spinel harzburgites, which contained more FeO and less MgO than garnet-free harzburgites of the same area. Variations in FeO and MgO contents in both types of harzburgites seem to be due to different chemical compositions of the chlorite protoliths of these rocks.

The relief of a vast area of western China and southern Mongolia was analyzed by methods of specialized morphometry to reveal structural and morphological features of recent tectonism. The tectonic relief of some part of the collisional system of Inner Asia, including the eastern Tien Shan, Govi Altay, and Bei Shan, is characterized by a general decrease in heights from west to east and a complicated system of domal ridges and intermontane troughs controlled by lenticular-rhombic faulting in the upper lithosphere. Submeridional transverse linear lows play an important role in the structure of the tectonic relief. It is likely that they are due to an irregular longitudinal flow of lithosphere blocks in the process of submeridional transverse compression. The structural signature of collisional geodynamics is traced eastward to the Ordos Province in a large meander of the Huang He and northward to the Hangayn Mountains, Tuva, and southern Gorny Altai. The predominance of domal deformations in young uplifts and no signs of their block desintegration suggest a crucial role of vertical tectonic motions largely responsible for the recent tectonic style of the eastern Tien Shan and Altay.

The Bohai Gulf basin is the largest petroliferous basin in China. Its Carboniferous-Permian deposits are thick (on the average, ca. 600 m) and occur as deeply as 5000 m. Coal and carbonaceous shale of the Carboniferous Taiyuan Formation formed in inshore plain swamps. Their main hydrocarbon-generating macerals are fluorescent vitrinite, exinite, alginite, etc. Coal and carbonaceous shale of the Permian Shanxi Formation were deposited in delta-alluvial plain. Their main hydrocarbon-generating macerals are vitrinite, exinite, etc. The carbonaceous rocks of these formations are characterized by a high thermal maturity, with the vitrinite reflectance R⁰ > 2.0%. The Bohai Gulf basin has been poorly explored so far, but it is highly promising for natural gas.

The study aims at developing petroleum potential criteria for reservoirs at the Paleozoic-Mesozoic boundary in West Siberia, by the example of the Chuzik-Chizhapka regional oil and gas accumulation in the Parabel District (Tomsk Region).
Oil and gas accumulations in formations of the Paleozoic-Mesozoic boundary were discovered in the Archa, Urman, Gerasimovka, Kalinovoe, North Kalinovoe, Tambai, Ostanino, North Ostanino, and other fields within the Chuzik-Chizhapka zone. Hydrocarbons are hosted by reservoirs of different lithologies and ages, including Devonian and Carboniferous organic, dolomite, and siliceous limestones and argillaceous-siliceous rocks.
Synthetic interpretation of seismic profiling and log data was used to model the geological structure of the Chuzik-Chizhapka regional accumulation, to develop potential criteria for reservoirs of the Paleozoic basement and weathering zone, and to suggest methods for detection of complex traps in upper Paleozoic strata.

The paper summarizes twenty years of studies in crustal sensitive zones. Sensitive zones show prominent geophysical responses to stress and strain changes and high-amplitude and distant preseismic and postseismic effects. Four sensitive zones are known today in Turkmenistan, Uzbekistan, Armenia, and northeastern China, which occur at junctions of large crustal blocks. High-amplitude and distant responses are due to deformation and high strain sensitivity of geophysical parameters along block boundaries. Data from sensitive zones are used to investigate earthquake-related effects as controlled by crustal heterogeneity and nonlinearity. These effects act also outside sensitive zones and should be taken into account when interpreting precursor signals. The knowledge of sensitive zones has important implications for active deformation along block boundaries.

The study addresses the space distribution of lithospheric density contrasts in 3D and 2D surface (spherical) sources of gravity anomalies to depths of 120 km below the geoid surface and their relationship with shallow deformation and Archean, Early Paleozoic, and Late Mesozoic geodynamic environments. The lithospheric section in northeastern Transbaikalia and the Upper Amur region includes two layers of low-density gradients attendant with low seismic velocities and low electrical resistivity. The lower layer at depths of 80-120 km is attributed to an asthenospheric upwarp that extends beneath the North Asian craton from the Emuershan volcanic belt and the Songliao basin. The concentric pattern of density contrasts in the middle and lower crust beneath the Upper Amur region may be produced by the activity of the Aldan-Zeya plume, which spatially correlates with the geometry of the asthenospheric upwarp as well as with the regional seismicity field, magnetic and heat flow anomalies, and stresses caused by large earthquakes and recent vertical crustal movements. The relationship between shallow and deep structures in the crust and upper mantle bears signature of horizontal displacement (subduction) of the lower crust of the Baikal-Vitim and Amur superterranes beneath the North Asian craton.