Common features of the tectonosphere deep structure in the Western Pacific Margins (Northeast Asia Region and Australia)

This paper analyses the spatial distributions of gravity sources and density contrast of geological media between the centers of mass of density heterogeneities and surfaces of some layers, which is reflected by the values of parameter μ_z, in the Northeast Asia Region and Australia. Statistical images of complex distributions of density heterogeneities are generally consistent with the shallowest tectonic structures, wave velocity, and electric anomalies. The correlation of μ_z minimums with high heat flow suggests melted magmas beneath the crust base and in the asthenosphere. In the lower crust layer, large μ_z maximums correlate with major continental megaelements, which are divided by extended linear μ_z minimums, high conductivity anomalies, and Vp/Vs maximums marking zones of lower viscosity. Deep boundaries and a thickness of lithospheric plates and asthenosphere lenses have been defined in the Northeast Asia Region. In Australia, two roughly NS-striking low-viscosity zones crossing the continent reflect the deep setting of the Lasseter (in the west) and the Tasman (in the east) lines. These zones are displayed in a wide depth range (15–120 km) and are confined to the Archean–Proterozoic and Proterozoic–Phanerozoic boundaries in the Australian lithosphere. Statistical gravity models derived without external (relatively to gravity) geological and geophysical information prove the multilayered tectonosphere structure of both continents and the similar deep structure features of their margins.     

Tectonics and metallogeny of the Khakandzha ore district in the Okhotsk–Chukotka volcanic belt

The data on the structure, geodynamics, and metallogeny of the Khakandzha ore district in northwestern Okhotsk region are analyzed and the two main factors responsible for the localization of ore deposits are defined. The magmatic factor controls the confinement of the ore district to the tectono-magmatic structure of the central type (source of ore matter), which determines the concentric zoning patterns in the distribution of ore mineralization. The tectonic factor determines the confinement of the ore districts, deposits, and ore occurrences of the region to the meridional left-lateral shear structure, which controls the magma and fluid distribution. Local extension (transtension) in this structure against the background of general lateral compression (transpression) provided tectonic environments most favorable for ore accumulation.     

Extension and Strike-Slips in the Crust of the Yellow Sea (Probabilistic Gravity Model)

Oceanology - Distributions of the density contrast and velocity of seismic waves into the crust and upper mantle in the Yellow Sea region are considered. The rheological section of the...     

Rheological gravity model of the crust and upper mantle of Transbaikalia

Based on rheological interpretation of formalized gravity models, earlier known deep-seated structures in the Earth’s crust and mantle of Transbaikalia have been detailed and new ones discovered. The structures are asymmetric and transverse relative to the Baikal rift zone. Their presence explains the peculiar features of the Baikal rift, including the one-way southeasterly direction of horizontal displacement of tectonic masses and northwestern migration of the Earth’s crust extension processes. The prolonged history (more than 250 Ma) of the Baikal rift zone and Transbaikalia mountainous country involved gravity or rotational detachments of rigid tectonic slabs from the craton and their sliding along intracrustal and subcrustal decollement zones into the above-dome area of the Transbaikalia asthenolith.     

Structure,Rheology, Petrology,and Geodynamics of the Tectonosphere of the Sea of Japan

Oceanology - The geological-structural, magmatic, seismic, and thermometric models of the Earth’s crust and upper mantle of the Sea of Japan region are considered in relation to...     

Gravity models of two-level collision of lithospheric plates in northeastern Asia

Structural forms of emplacement of crustal and mantle rigid sheets in collision zones of lithospheric plates in northeastern Asia are analyzed using formalized gravity models reflecting the rheological properties of geological media. Splitting of the lithosphere of moving plates into crustal and mantle constituents is the main feature of collision zones, which is repeated in the structural units irrespective of their location, rank, and age. Formal signs of crustal sheet thrusting over convergent plate boundaries and subduction of the lithospheric mantle beneath these boundaries have been revealed. The deep boundaries and thickness of lithospheric plates and asthenospheric lenses have been traced. A similarity in the deep structure of collision zones of second-order marginal-sea buffer plates differing in age is displayed at the boundaries with the Eurasian, North American, and Pacific plates of the first order. Collision of oceanic crustal segments with the Mesozoic continental margin in the Sikhote-Alin is characterized, as well as collision of the oceanic lithosphere with the Kamchatka composite island arc. A spatiotemporal series of deep-seated Middle Mesozoic, Late Mesosoic, and Cenozoic collision tectonic units having similar structure is displayed in the transitional zone from the Asian continent to the Pacific plate.     

A simple algorithm for generating cross sections using 3D geological and geophysical data sets (Southeastern Russia)

We developed a simple algorithm allowing automated generation of map slices and cross sections from discrete values of geological and geophysical parameters described by 3D data sets. The data input and output were handled in the standard formats of Word, DOS, and the Surfer 8 package, which make it possible to be widely used by small scientific and technical teams in the processing of geological information and the interpretation of local GISs. The practical implementation of the proposed algorithm is exemplified by the study of the density properties in the Earth’s crust and upper mantle of Transbaikalia and Sikhote-Alin.     

Gravity indicator of rheological properties of the tectonosphere of the Russian Far East

Formal indicators of the existence of spatially isolated layers characterized by the absence of sources of intense gravity anomalies in them are revealed in the tectonosphere of the eastern Baikal region, the Amur region, the Sea of Okhotsk, Kamchatka, and northeastern Russia. A stable correlation of these layers with thermal, high electrical conductivity, and lower seismic velocity anomalies implies that they are related to rheologically weakened zones of the tectonosphere, i.e., layers of lower viscosity or higher plasticity or fluidity. Minimum vertical gradients of the surface density of spherical sources of gravity anomalies, equivalent to density inhomogeneities of the compaction class, are gravitational indicators of these zones.     

The relation of seismicity to lithospheric density inhomogeneities in the Russian Far East

A well-defined relationship has been identified between the belts, zones and areas of higher seismicity in the Russian Far East on the one hand and, on the other, maxima in the gradient of surface density of spherical sources that give rise to gravity anomalies (μ _z ) equivalent to quasi-isometric density inhomogeneities in the lower crust and upper mantle. The highest epicenter density is observed in the marginal parts of maxima of the μ _z parameter, these parts being interpreted as boundaries of rigid (sialic metamorphic and oceanic mafic) tectonic blocks and plates. The overwhelming majority of crustal seismicity is spatially related to uplifts of the asthenospheric layer reflected in the minima of the μ _z parameter, and is concentrated in uplifted crustal blocks. In addition to the linear type of seismicity due to deep-seated faults, the crust shows a concentrically zonal type of epicenter location associated with plume-generated central-type features (the Olekma-Stanovoi seismic zone). It is shown that seismic fields can be ranked by the depths of earthquake source zones using 3D models, μ _z (x,y,z).