Formalized analysis of crustal seismicity in the Sikhote Alin orogen and adjacent areas

The fractal dimension of the epicentral field of earthquakes (D = 1.6) is determined for the Sikote Alin orogen and adjacent areas. According to this parameter, the region occupies the position between the Kamchatka Peninsula, Kuril Islands (1.61 and 1.69), the East China area, and the Lake Baikal region (1.55 and 1.40). Differentiation of the studied area based on the fractal dimension of the number of earthquakes and on the released energy calculated per unit square shows that the most active crustal areas are associated with the Kharpi–Kur–Priamur’e zone of the northeastern orientation, which is the northern segment of the Tan-Lu transregional fault system. Analysis of the time series of seismic events (MLH ≥ 2.4) in the Sikhote Alin and adjacent areas in the period from 1960 to 2013 shows that the “harmonic” with a 10.5-year period is most clearly displayed. This period (11–13 years) was previously distinguished by B.V. Levin and coauthors from the study of the largest number of earthquakes with M ≥ 4.4 for the period of 1971–2003.     

Geochemistry of the thermal waters of Sikhote Alin

This paper reports new geochemical data on the low temperature nitric thermal waters of Sikhote Alin. The studied alkaline waters belong to the HCO₃-Na type with significant trace element variations. The waters demonstrate an increase in temperature and TDS from the south northward of Sikhote Alin. The oxygen and hydrogen isotopic data suggest their infiltration origin. The chemical composition of these waters was formed by water-rock interaction.     

Consedimentation tectonites in the Paleozoic of Sikhote Alin

Carboniferous and Permian terrigenous sediments in the basin of the Iman, Vaka and Ulakhe rivers show features known as tectonites — lens structures in conglomerate-type rocks, elongated pebbles and so on. These features and other considerations indicate that the central and eastern parts of the main Sikhote-Alin anticlinorium was experiencing contemporaneous differential movements. Competent beds of sandstones and flints form lenses, ovals and sometimes shapeless blocks embedded in incompetent siltstones and clay shales. Competent beds range greatly in thickness; fragments indicate most ranged from 1–5 cm with some beds 1–5 m. Most of the enclosing sequences are 100–300 m thick. Disposition of fragments indicates clearly the lines of the original beds. Direction of displacement is parallel to the plane of the layer. Elongation of fragments is in the direction of transport. Latest papers show a tendency to assign these tectonites a consedimentation origin; they are believed to be products of endogenous forces acting on consolidated sediments. The term hydrotectonite is used when morphologically similar products are formed under water through the joint action of forces both tectonic and otherwise. Two such structures are illustrated and their origin considered. Effects of dewatering are also discussed. Epochs favorable to hydrotectonites are rapid sinking a geosyncline when inclination of the floor increases and when earth tremors are common, in combination with rapid sedimentation. High tectonic activity in the Sikhote Alin syncline, based on hydrotectonites, may correlate with numerous magmatic effects in the adjacent Khanda central massif.—W.D. Lowry     

Phlogopite-olivine rocks of the Taukha terrane in southeastern Sikhote Alin

The Paleocene ultraferrous Mn-rich phlogopite-olivine rocks of the Taukha terrane belong to the alkaline ultrabasic rocks of the potassic series. The olivine is represented by hortonolite, while the phlogopite is enriched in Cl. Other minerals are represented by Ti-magnetite, Mn-rich ilmenite, Zn-rich pleonaste, apatite, and zircon. There are also epigenetic serpentine, talc, carbonates, magnetite, breithauptite, nickeline, hedleyite, cobaltite, tsumoite, auricupride, cuproauride, and other minerals. The phlogopite-olivine rocks possibly represent a part of a magmatic complex previously unknown in Sikhote Alin, the rocks of which are associated with fluidolites of a large diatreme. There are grounds to suggest that they were formed by the injection of fluid-rich (mainly, H₂O, Cl, F, and S) deep magmas into the upper lithosphere. Based on these specific features, as well as the sharp K predominance over Na and the enrichment in some incompatible elements (Sn, Ta, Nb, and Zr), the phlogopite-olivine rocks are the most close to lamproites but differ in the high contents of Fe, Mn, Au, Pt, and Pd and in the olivine’s composition. The manifestation of such magmatism in the Taukha terrane records the transition from subduction to transform continental margin settings.     

Composition and provenances of mesozoic sandstones in Sikhote Alin

The composition of sandstones constituting different structural stages of the Jurassic accretionary wedge in the Samarka (upper and middle? structural levels in the Lyamfana Creek and Katen River basins, respectively) and Nadan’khada-Bikin (lower level in the Ulitka River basin) terranes of the Sikhote Alin region reflects changes in provenances and tectonic settings of the near-continental sedimentation basin in different periods of the wedge formation. In the terminal Middle Jurassic (Lyamfana Creek), the region was dominated by the subduction regime with sedimentary material transported from the eroded part of the continental-margin magmatic arc. During the Kimmeridgian-Tithonian (Katen River), erosion of granitoid batholiths of the arc exposed blocks of the crystalline basement along strike-slip faults. In the Tithonian-Berriasian period (Ulitka River), the role of these blocks increased, suggesting intensification of oblique subduction or development of transform faults during the accretion.     

Ablation spherules in the Sikhote Alin meteorite and their genesis

Practically all of the examined spherules extracted in 1948?C1949 from soil at the crater field of the 1947 Sikhote Alin meteorite shower are ablation spherules produced during this meteorite fall. The spherules can classified into two textural types: (i) fine-grained, which consist of Ni-bearing magnetite (3?C6 wt % NiO) dendrites, sometimes with minor amounts of interstitial P- and Fe-rich material, and (ii) coarse-grained, which also consist of Ni-bearing magnetite dendrites or grains, sometimes with wuestite, an interstitial material, which resembles that in type (i) or has a silicate composition. The texture, mineralogy, and chemistry (presence of P and Si) of these spherules differ from those of iron cosmic spherules (type I) that occur in the background flux of micrometeorites. The spherules are thought to were produced by the ablation of meteoritic material at elevations of about 12 km (in the region where disintegration starts) and below, at maximum temperatures of 1600?C2180°C and oxygen fugacity of 10^?14 to 10^?1 atm. Conceivably, the ablated material was enriched in silicates compared to the fallen material.     

Minerals in the Triassic carbonaceous silicites of Sikhote Alin

Over 60 minerals, including native elements, intermetallic compounds, haloids, sulfides, sulfates, arsenides, oxides and hydroxides, silicates, borosilicates, wolframates, phosphates and REE phosphates, were established in Triassic siliceous rocks of Sikhote Alin. Allothigenic and authigenic minerals in the carbonaceous silicites were formed over a long period through several stages. Judging from morphology, chemical composition, and structural position, K-feldspar (K-Fsp), illite, kaolinite, metahalloysite, monazite, xenotime, zircon, rutile, or its polymorphs are the disintegration products of sialic rocks of continental crust. Authigenic sulfides are dominated by diagenetic pyrite (fine-crystalline, microglobular, framboidal, as well as those developed after biogenic siliceous and carbonate fragments), which has been formed prior to precipitation of siliceous cement and lithification of siliceous rocks. Most of other sulfides (sphalerite, galena, chalcopyrite, pyrrhotite, argentite, pentlandite, antimonite, ulmanite, and bravoite), arsenides and sulfoarsenides (arsenopyrite, nickeline, skutterudite, cobaltite, glaucodot, and gersdorffite), wolframates (scheelite and wolframite), intermetallides (Cu₂Zn, Cu₃Zn₂, Cu₃Zn, Cu₄Zn, CuSn, Cu₄Sn, Cu₈Sn, Cu₄Zn₂Ni, Ni₂Cu₂Zn, Ni₄Cd), and native elements (Au, Pd, Ag, Cu, Fe, W, Ni, Se) were crystallized later (during catagenesis after the lithification and brecciation of siliceous beds) from metals involved in the easily mobile fractions of bitumens. Supergene mineral formation was mainly expressed in the sulfide oxidation and replacement of diagenetic pyrite by jarosite and iron hydroxides.     

Cenozoic volcanism of the eastern Sikhote Alin: Petrological studies and outlooks

Based on geological and isotope geochemical data obtained during the past decade, the eastern Sikhote Alin volcanic belt can be considered as a polygenic structure with spatially superimposed magmatic complexes of different geodynamic stages. Only Late Cretaceous intermediate and silicic volcanics enriched in LILE and depleted in HFSE can be interpreted as typical subduction complexes. Cenozoic lavas of mainly basic composition were formed after the termination of active subduction under complex dynamic conditions of the rearrangement of eastern Eurasia owing to the collision with the Indian plate. The eruption of Eocene-Oligocene-early Miocene basalts corresponded to the transform continental margin environment, rupture of an ancient subducted slab, and upwelling of hot depleted oceanic asthenosphere of the Pacific MORB-type into the Asian subcontinental lithosphere with EMII-like isotopic characteristics. The late Miocene-Pliocene magmatic activity of the eastern Sikhote Alin showed an intraplate character, but the composition of erupted magmas was strongly affected by previous tectonomagmatic events: subduction of different ages and opening of the Sea of Japan Basin. The distinct EMI isotopic signature of low-potassium plateau basalts, which is not observed in the lavas of earlier stages of volcanic belt evolution, suggests that the continental asthenosphere contributed to magma formation, and the direction of mantle flows changed owing to the formation of a new subduction zone.     

Siliceous-volcanogenic complexes of western Sikhote Alin: Their stratigraphy and origin

New age and structural data are reported for the siliceous-volcanogenic complexes developed in the lower reaches of the Ussuri River. These complexes, which were previously treated as one stratigraphic unit, are subdivided into the Snarsky tectonostratigraphic complex (end of the Middle Jurassic-Middle Aptian) and the basaltic sequence (supposedly, Campanian-Maastrichtian). The Snarsky Complex is made up of basic volcanics, cherts, siliceous-clayey rocks, as well as subordinate limestones, sandstones, and conglomerates. Its distinctive features are the large amounts of genetically diverse basalts, the abundance of volcanomictic and pyroclastic material in siliceous-clayey rocks, the absence of fragmental rocks typical of the continental convergent zone, and the facies heterogeneity of the deposits. The complex is considered to be the southwestern continuation of the Kiselevka-Manoma terrane. Its origin is presumably related to the tectonic piling of genetically heterogeneous assemblages. The basaltic sequence includes basalts, basaltic andesites, their tuffs, and tuff conglomerates. The tuff conglomerates contain numerous fragments of granites and garnet-bearing felsic volcanics. The sequence was formed on the crystalline paleocontinental basement in the Late Cretaceous.     

Geochemistry and metal potential of triassic carbonaceous silicites in Sikhote Alin

In the Triassic siliceous formation of Sikhote Alin, carbonaceous silicites occur in the late Olenekian-middle Anisian member (4–20 m) of alternating cherts and clayey cherts (“phtanite member”) near the section base. The silicites are represented by radiolarian and spicule-radiolarian cherts alternating with clayey cherts. They contain up to 8.5% C_org. In the majority of sections, the rocks underwent structural and mineral transformation at the mesocatagenetic stage. The slightly oxidized organic (primarily, marine sapropelic) matter contains quinones, methyl, methylene, and ether groups. The content of neutral bitumens in rocks shows a wide variation range. The carbon isotopic composition in phtanites and clayey phtanites (δ¹³C from ?27.3 to ?30.2‰) is identical to that in many Paleozoic-Mesozoic bitumens and oils. As compared with other Mesozoic sedimentary rocks of Sikhote Alin, the carbonaceous silicites are enriched in V, B, Mo, Ni, Cu, and Ag. Anomalously high concentrations of Ba are recorded in phtanite rock sections at the Gornaya and Khor rivers and in the vicinity of Khabarovsk. Modal value of the Au content in phtanites and clayey phtanites is three or four times higher than the clarke value in carbonaceous silicites and reaches anomalous values in some sections (e.g., Ogorodnaya River section). Carbonaceous silicites of this section are also enriched in Pt. Positive Au-C_org correlation is recorded in clayey phtanites of the Ogorodnaya River section containing more than 0.5% C_org. In organic fractions, Au and Ag are concentrated in alcohol and alcohol-benzene bitumens, asphalt acids, and asphaltenes. Migration of bitumens from high-carbonaceous clayey phtanites to the pore-fissure space of cherts and phtanites also fostered the concentration of these metals in some low-carbonaceous layers of the member.     

Tectonic evolution of the Knipovich Ridge based on the anomalous magnetic field

Calculation of the downward continuation for the anomalous magnetic field at the Knipovich Ridge showed more complicate segmentation of the spreading oceanic basement than was earlier considered. The structural pattern of the field is evidence that the area consists of no less than four segments separated by transform fracture zones with the azimuth of oceanic crust accretion about 310° and the normal position relative to the rift segments with the azimuth of 40°. The modern location of the axis of the Knipovich Ridge straightens the complicate divergent boundary between the plates in the strike-slip conditions between the spreading centers of the Mohns and Gakkel ridges. The axis is a detachment zone intersecting the oceanic basement having formed from the Late Oligocene. A new magnetoactive layer composed of magmatic products has not yet been formed in this structure.     

Basalts of the Pantalassa ocean in the Samarka terrane, Central Sikhote Alin

Basalts developed on the right bank of the Matai River belong to the Samarka terrane (Central Sikhote Alin), which is a fragment of the Jurassic accretionary prism. They associate with Carboniferous-Permian reef limestones, Permian pelagic cherts, Jurassic hemipelagic cherty-clayey deposits, and terrigenous rocks of the near-continental sedimentation area. The petrogeochemical features of the basalts provide insight into the character of the volcanism in different settings of the ancient Pantalassa ocean. In terms of chemistry, the Carboniferous-Permian basalts are similar to the within-plate ocean-island basalts related to plume mantle sources. They were presumably formed in an oceanic area with numerous islands and seamounts. The Permian basalts associated with cherts are tholeiitic in composition and were formed from depleted mantle in a spreading center located in the pelagic area. The Jurassic basalts are of plume origin and, in terms of geochemistry, occupy an intermediate position between OIB and E-MORB. They were presumably formed in a convergent zone in a geodynamic setting of rapid oblique subduction.     

Clastic heavy mineral assemblages in Permian-Mesozoic accretionary cherty and siliceous-clayey complexes of Sikhote Alin

The paper presents results of the study of assemblages of clastic heavy minerals and geochemical features of some assemblages in several Permian-Mesozoic cherty and siliceous-clayey sequences of Sikhote Alin. They are composed of pelagic and hemipelagic sediments of the Panthalassa (Paleopacific) Ocean. Four typical mineral assemblages and their environments are established. In one of the ocean segments, where sedimentary cover formed during the Late Paleozoic-Early Cretaceous, the Permian pelagic domain was characterized by the amphibole-pyroxene assemblage with heavy minerals derived from ophiolites. The Triassic-Jurassic stage was marked by development of the clinopyroxene assemblage with heavy minerals derived from intraplate alkaline volcanic complexes. Middle-Late Jurassic hemipelagic sediments host the zircon-clinopyroxene assemblage with a greater role of continental environments and the presence of volcanic products of the convergence zone. Another segment of the ocean accumulated red cherts and siliceous-clayey sediments during the Jurassic-Early Cretaceous under the influence of island-arc volcanism.     

Study of the anomalous magnetic field structure in the Ural region using parallel algorithms

The anomalous structure in the magnetic field of the Ural Region has been studied in the segment bounded by 52°?C64° N and 54°?C66° E. Analytical apparatus for upward continuation of airborne magnetic data to different heights was applied. To recalculate magnetic field, parallel algorithms and software for multiprocessor computers were used. Maps of magnetic anomalies for different ranges of wave lengths showing the distribution of magnetization in the layers of the Earth??s crust were built.     

Maestrichtian-Danian andesite series of the Eastern Sikhote Alin: Mineralogy,geochemistry, and petrogenetic aspects

In the stratigraphic sequence of volcanic rocks in the Eastern Sikhote Alin, Maestrichtian-Danian predominantly andesitic volcanics are characterized by a boundary position between the Late Cretaceous subduction, mostly acid volcanic rocks and Cenozoic post-subduction basaltoids. Data on these rocks are important for elucidating the genesis of andesitic magmas, constraining and specifying the geodynamic evolutionary stages in this territory, and revealing the conditions under which the parental melts of these rocks were derived and evolved. Results of detailed mineralogical and geochemical studies, including ICP-MS analysis for trace elements point to a hybrid character of the andesitic volcanic rocks and an important role of fractional crystallization and crustal contamination in their genesis. Although geological evidence (variations in the style of volcanism, the composition of its products, and the character of their distribution) testifies to a change in the geodynamic environment in the Eastern Sikhote Alin in the Maestrichtian-Danian, geochemically the volcanics of this age range are typical subduction-related rocks with anomalously low concentrations of Nb and high contents of K, Ba, Rb, Pb, and U. The volcanic piles contain no adakites, which are indicators of the geodynamic environment in which slab windows are formed. The inconsistency between geological and geochemical indicators of the geodynamic environment suggests certain genetic features of the transitional magmatic series. The parental magmas of the andesitic volcanics were derived from the suprasubduction mantle wedge, which had been metasomatically recycled in the course of the dehydration and melting of the subducted oceanic slab. The increasing extension provided the possibility for the parental basaltic magmas to enter upper crustal levels, where they could interact with the host rocks and form hybrid andesitic melts.