The Voznovo Formation: The reflection of the early Oligocene stage in the geological history of East Sikhote-Alin

New data were obtained on the Voznovo Formation, one of the key Tertiary stratigraphic units in East Sikhote-Alin. The analysis of macro- and microflora in this unit showed that the decision to assign it to the Miocene (Resolutions…, 1994) was invalid. The early Oligocene age of the formation is justified. It is shown that the sediments constituting the formation were deposited in a barrier lake. The analysis of the Voznovo taphoflora reveals its mountainous ecotype, which indicates the ancient age of the Sikhote-Alin mountainous system. The Voznovo Formation is correlated with other coeval stratigraphic units of the region.     

Cenozoic Magmatism of the North-Eastern Eurasian Margin: The Role of Lithosphere Versus Asthenosphere

Sikhote-Alin and Sakhalin are located in the Russian Far Eastflank of the northernmost part of the Sea of Japan. Magmatismin this region preceded, was concurrent with, and continuedafter the extension and sea-floor spreading (25–18 Ma)that formed the Sea of Japan. Among the Sikhote-Alin and Sakhalinvolcanic suites, Eocene–Oligocene (55–24 Ma) lavasare characterized by greater large ion lithophile element andrare earth element enrichments compared with Early–Mid-Miocene(23–15 Ma) tholeiites, and also show a depletion in highfield strength elements (HFSE). The geochemical characteristicsof the Eocene–Oligocene and Early–Mid-Miocene basaltsare consistent with migration of the locus of magma generationbeneath the Sikhote-Alin and Sakhalin areas from subduction-modifiedlithospheric mantle into mid-ocean ridge basalt (MORB)-sourceasthenosphere as spreading in the Sea of Japan progressed. Mid-Miocene–Pliocene(14–5 Ma) lavas, erupted following the opening of theSea of Japan, include alkaline and sub-alkaline basalts withwide ranges in trace-element abundances, varying between twodistinct end-members: (1) volumetrically minor alkaline basaltswith Zr–Nb and Sr–Nb–Pb isotope compositionssimilar to asthenosphere-derived, intra-plate–hotspotbasalts from eastern China; (2) more abundant, lithosphere-derived,low-alkali tholeiites depleted in HFSE. The similarity of isotopicsignatures coupled with systematically different rare earthelement (REE) abundances in the Mid-Miocene–Pliocene andChinese basalts are best modeled by similar extents of meltingof spinel lherzolite and garnet lherzolite, respectively. TheMid-Miocene–Pliocene alkali basalts were generated bysmall degrees of partial melting of hot asthenosphere beneatha thin lithospheric lid; the thin lithospheric mantle beneaththe Sikhote-Alin and Sakhalin region resulted from heating andextension associated with the opening of the Sea of Japan. KEY WORDS: north-eastern Eurasian margin; Sikhote-Alin–Sakhalin; Japan Sea opening; subcontinental lithosphere; asthenosphere     

锡霍特-阿林成矿带金属矿床成矿作用的演化

锡霍特-阿林构造带由兴凯地块、老爷岭-格罗杰科岛弧和东锡霍特-阿林造山带3个构造单元组成.其金属矿床成矿作用可分为3期：里菲纪末期至志留纪末,在兴凯区形成了喷流-沉积为主的铁（锰）矿、铅锌矿及岩浆热液型锡矿;二叠纪中期,在老爷岭-格罗杰科岛弧地区形成了浅成低温热液型金（银）矿和变质热液型金矿;侏罗纪至古近纪末,在东锡霍特-阿林构造带中形成了夕卡岩型钨床、浅成低温热液型金（银）矿、夕卡岩型及脉状硼矿和铅锌矿、脉状金矿等矿床.     

Peridotite xenoliths in alkali basalts from the Sikhote-Alin, southeastern Siberia, Russia: trace-element signatures of mantle beneath a convergent continental margin

Abundant spinel peridotite xenoliths occur in late Cenozoic alkali basaltic rocks in the Sikhote-Alin region at the Pacific margin of the Asian continent. Major- and trace-element compositions of representative peridotite xenolith are documented for four occurrences located in different structural units of the continental margin. In each locality, the majority of xenoliths have distinctive microstructures, modal and chemical compositions that are typical for a given xenolith suite. Significant textural and compositional differences between the four xenolith suites suggest that the upper mantle beneath the Sikhote-Alin consists of distinct domains with contrasting composition. The inferred large-scale mantle heterogeneities may be due to juxtaposition of lithospheric blocks of different provenance during accretion of the Sikhote-Alin to the Asian continent.

Trace-element patterns of the xenoliths and their minerals obtained ICP-MS technique provide evidence of depletion and enrichment events and indicate contrasting behaviour of REE, HFSE and other incompatible trace elements. The HFSE behave non-concordantly, in particular, some xenoliths have highly fractionated Zr/Hf, Ti/Zr, Nb/Ta, La/Nb and U/Th ratios relative to their values in the primitive mantle. The fractionated compositions may be related to the interaction of evolved subduction-related fluids and melts with lithospheric mantle at the Mesozoic-early Cenozoic active continental margin or to metasomatism during later continental rifting.     

Provincial division of the Asian part of the Siberian-Canadian paleofloristic region in the Late Cretaceous

The following provinces are recognized in the Late Cretaceous within the Asian part of the Siberian-Canadian paleofloristic region: Chulym-Yenisei, Lena-Vilyui, North Siberian, Verkhoyansk, Mountain Okhotsk-Chukotka, Anadyr’, Amur, Sikhote-Alin, and Sakhalin-Japanese. It is proposed to consider the Central Asian (Turan) Province as belonging to the Euro-Sinian paleofloristic region. In the Cenomanian, the province also included the area of the southern Chulym-Yenisei Depression. In the maritime and northern provinces, a considerable occurrence of Mesozoic relics compared to the southern and continental ones is recorded. Similarity and distinctions between the floras of different provinces varied during the Late Cretaceous. Climatic conditions played a considerable role in species diversity and degree of differentiation or unification of the floras.     

Geoelectric section of the tectonosphere in the junction zone between the Sea of Japan depression and its continental framing

New data on the deep geoelectric structure of the tectonosphere in the junction zone between the Sea of Japan and continental structures are presented. The geolelectric section was modeled using unique data on the monitoring of the electric field variations in the JASC submarine trans-Japan communication cable and segments of land cables in the Primorye region. The monitoring was accompanied by recording of the geomagnetic field at the VLA, KHB, MMB observatories and PPI stationary site. In addition, magnetotelluric data from 80 field MTS sites in the territory of the Hankai Massif and Sikhote-Alin fold belt were used.     

Composition and genesis of the intrusive rock association of the Magloi magmatic area,the Central Amur region

New geochemical and isotopic-geochronological data are reported on the intrusive association from one of the largest and relatively poorly studied Cretaceous (Aptian-Cenomanian) magmatic zones of the Sikhote-Alin accretionary fold system. The new results and previously published studies were interpreted using concepts of a blocked (terrane) structure of the region and the different geodynamic nature of the magmatic complexes. It was shown that the “transitional” geochemical and geodynamic characteristics of the studied intrusive rocks can be explained in terms of magmatism along the transform continental margin. Additional complicating factors are the composition of the terrane rocks and the change in the geodynamic setting during the formation of the considered magmatic area (114-90 Ma).     

Rheological model of the crust beneath southern Sikhote-Alin: Evidence from gravity data

The analysis of the spatial distributions of the density gradients characteristic of spherical sources of gravity anomalies provided grounds for the assessment of the rheological properties of the crust beneath the southern Sikhote-Alin mountainous system, which includes two layers with elevated rigidity and two layers of lowered viscosity. The direct proportional correlation between the rigidity and the density of the modeled mediums is confirmed by solving the direct linear problem of the gravitational potential. The rigid medium is characteristic of the lower crystalline layer of the Amur Plate, the top of which gently dips toward the Sea of Japan coast, and clinoform slabs of the oceanic crust, which underlie the Taukhe and Kema terranes and thrust over the lower layer of the continental crust. The viscous medium corresponds to the subcrustal zone of partial melting beneath the East Sikhote-Alin volcanic belt and to the accretionary complexes of the Samarka and Zhuravlevka terranes, which are involved into shear deformations. The Late Paleozoic and Early Mesozoic geodynamic history of the Sikhote-Alin crust was characterized by the interaction between the continental and oceanic rigid crustal wedges, which determined the directed accretion of the terrigenous turbiditic and island-arc sequences of the marginal sea to the Amur Plate.     

Deep roots of seismotectonics of the Far East: The Amur River and Primorye zones

The role of the lateral structure of the lithospheric mantle in the seismotectonics and seismicity of the southern part of the Russian Far East has been investigated. The positions of the epicenters of all the major earthquakes in Sakhalin (M ≥ 6.0), as well as in the Amur region and the Primorye zones (M ≥ 5.0), are defined by the boundaries of the Anyui block of highly ferruginous mantle, which lies at the base of the Sikhote-Alin area. Three cycles of large earthquakes are recognized in the region: the end of the 19th-beginning of the 20th century, the mid-20th century, and end of the 20th-beginning of the 21st century. In the seismic zone of the Amur region (hereafter, the Amur seismic zone), the epicenters of the large earthquakes in each cycle migrate from the SW to NE along the Tan-Lu fault megasystem at a rate of 30–60 km/yr. The specific features of the seismicity of the region are explained by the repeated arrival of strain waves from the west. The waves propagate in the upper part of the mantle and provoke the activation of the deep structure of the region. The detailed analysis of the earthquakes in the Sikhote-Alin area (M ≥ 4.0) in 1973–2009 confirmed the clockwise tectonic rotation of the mantle block. The characteristics of the Primorye zone of deep-focus seismicity at the Russia-China boundary are stated. Since 1973, 13 earthquakes with M ≥ 6.0 have been recorded in the zone at a depth of 300–500 km. This number of earthquakes is at least twice as many as the number of large deep-focus earthquakes elsewhere in the Sea of Japan-Sea of Okhotsk transition zone. The unique genesis of the Primorye seismic zone is related to the additional compression in the seismofocal area due to the creeping of the Anyui mantle block onto the subduction zone during its rotation. The geodynamic implications of the seismotectonic analysis are examined, and the necessity of division of the Amur plate into three geodynamically independent lithospheric blocks is substantiated.     

Lermontovskoe Tungsten Skarn Deposit: the Oldest Mineralization in the Sikhote-Alin Orogen, Far East Russia

Abstract. Lermontovskoe tungsten skarn deposit in central Sikhote-Alin is concluded to have formed at 132 Ma in the Early Cretaceous, based on K-Ar age data for muscovite concentrates from high-grade scheelite ore and greisenized granite. Late Paleozoic limestone in Jurassic - early Early Cretaceous accretionary complexes was replaced during hydrothermal activity related to the Lermontovskoe granodiorite stock of reduced type. The ores, characterized by Mo-poor scheelite and Fe^3+- poor mineral assemblages, indicate that this deposit is a reduced-type tungsten skarn (Sato, 1980, 1982), in accordance with the reduced nature of the granodiorite stock.
The Lermontovskoe deposit, the oldest mineralization so far known in the Sikhote-Alin orogen, formed in the initial stage of Early Cretaceous felsic magmatism. The magmatism began shortly after the accretionary tectonics ceased, suggesting an abrupt change of subduction system. Style of the Early Cretaceous magmatism and mineralization is significantly different between central Sikhote-Alin and Northeast Japan; reduced-type and oxidized-type, respectively. The different styles may reflect different tectonic environments; compressional and extensional, respectively. These two areas, which were closer together before the opening of the Japan Sea in the Miocene, may have been juxtaposed under a transpressional tectonic regime after the magmatism.     

Density Structure of the Lithosphere of the Sikhote-Alin Orogenic Belt

Doklady Earth Sciences - For the first time, a detailed density 3D model of the lithosphere of the Sikhote-Alin orogenic belt to a depth of 130 km has been created. Two extended submeridional...     

Mesozoic subduction of the paleo-pacific plate along the eastern margin of the Xing-Meng orogenic belt北大核心CSCD

The eastern pari of the Xing-Meng Orogenic Belt( XMOB )consists of the Lesser Xing'an-Zhangguangcai Range Orogenic belt, the Bureya-Jiamusi-khanka Block and the Sikhote-Alin accretionary belt. This area is located between the Paleo-Asian oceanic and Paleo-Pacific tectonic regimes. Recent researches imply that the Paleo-Pacific subduction might have begun since early Permian and influenced the both sides of the Mudanjiang Fault during Triassic, which generated a N-S trending magmatic belt and accretionary complexes, such as the Heilongjiang Complex. In Late Jurassic to Early Cretaceous, some tectono st rati graph ic terranes were produced in Sikhote-Alin, which were then dismembered and migrated northwards in late Early Cretaceous by sinistral strike-slip faults. The continental margin parallel transportion weakened subduction-related magmatism in NE China which was under an extensional setting. However, in Lite Cretaceous, the Paleo-Pacific subduction was re-Activated in the eastern XMOB, which contributed to the magmatism in Sikhote-Alin.     

Fudzin-Iman lateral fault

The fault is 200 km in length, trending N 5°W., cutting the N 30° E-trending structure of the Sikhote-Alin Mountains. Correlation of northwesterly-dipping Paleozoic and Mesozoic sequences on either side of the fault show that the fault is vertical, with a left-lateral displacement of about 40 km. The youngest beds displaced are Senonian, dating the movement as Upper Senonian (a post-geosynclinal stage of the Sikhote-Alin development). — P. B. Ives     

Igneous Rocks,Fluidolites, and Rodingites of Paleocene Explosive Structures of the Taukha Terrane (Sikhote-Alin)

Geology of Ore Deposits - The Taukha terrane of the Sikhote-Alin hosts outcrops of rocks with unusual structural and textural features, the compositions of which vary from ultrabasic to...     

Age of tin ore from the Solnechnoe quartz-tourmaline-cassiterite deposit, the Khabarovsk krai, Russia from the results of Rb-Sr dating of quartz and adularia

The age of the main productive phase of ore formation at the large Solnechnoe tin deposit has been estimated for the first time based on the study of the Rb-Sr isotopic system of hydrothermal quartz and adularia from ore veins and metasomatic rocks. The Rb-Sr isochron age (84 ± 1 Ma) of mineralization coincides with the age of intrusive rocks pertaining to the third phase of the Silinka Complex, which control tin mineralization. The ⁸⁷Sr/⁸⁶Sr ratios of ore-forming solution and granitic rocks of the final intrusive phase are close to each other, indicating that the granitic melt was most likely one of the main sources of metals. The long and multistage formation history of the deposit could have been caused by complex geodynamic evolution of the Sikhote-Alin accretionary fold region in the Cretaceous.     

Geoelectric section of the crust and upper mantle of the northern Sikhote-Alin from magnetotelluric sounding data

Magnetotelluric soundings (MTS) were conducted in a broad frequency range of 10 kHz to 0.001 Hz at a total of fifty-seven sounding sites of the profile spaced 5 km apart and intersecting the northern Sikhote-Alin across the strike. The analysis of the obtained magnetotelluric parameters has been made which shows three-dimensional geoelectric nonuniformities in the lower crust and upper mantle. The MTS curve interpretation was carried out in the framework of a three-dimensional model. As a result of the inverse problem solution, the geoelectric section has been constructed down to 150 km depth. The section distinguishes the crust with a resistivity higher than 1000 Ohm m and variable thickness between 30 and 40 km which is consistent with deep seismic sounding (DSS) data. The crust is subdivided into four blocks by deep faults, and each block is characterized by a set of parameters. The data support the existence of the Vostochny deep fault in the study area, whereas, on the contrary, the deep roots for the Central Sikhote-Alin fault have not been established. The upper mantle structure is nonuniform; three low-resistivity zones are identified that coincide with the boundaries of crustal blocks. In the revealed zones, an increase in the resistivity is noted from the continent to the Tatar Strait coast. A high-resistivity layer of 300–400 Ohm m was observed in the coastal area, which was steeply dipping from the crustal base down to 120 km depth and extended beneath the continent. Based on a set of geological and geophysical data, the ancient subducting plate is suggested in this area, and the evolutionary model of the region is proposed starting from the Late Cretaceous. The most probable mechanism of conductivity within the upper mantle is determined from petrological and petrophysical data. The low resistivity values are linked to dry peridotite mantle melting.     

The Nature of Platinoid Minerals from Gold Placers of Southern Sikhote-Alin (Primorye)

Doklady Earth Sciences - Gold placers of two streams that drain Permian dislocated terrigenous deposits overlying Cambrian metagabbroids and metadiorites in southern Sikhote-Alin have been studied....     

Rare Earth Elements as a Causal Factor of Geophagy among Herbivorous Animals

Doklady Earth Sciences - Extensive geological and hydrobiogeochemical studies were conducted for the first time in two Sikhote-Alin (Primorskii krai) areas, where geophagy among wild ungulates has...     

Geologic factors of distribution of mineral deposits in eastern U.S.S.R.

The Pacific Mobile belt is differentiated into an outer (continental) zone of predominantly Mesozoic folding (Verkhoyansk -Chukotka, Mongolo-Okhotsk, and Sikhote-Alin folded provinces) and an inner oceanic zone of Cenozoic folding, adjacent to mobile provinces of the "island arc" type (Sakhalin, the Kuriles, Kamchatka). These zones are separated by the East-Asian volcanic belt associated with a fault system which cuts off the older Mesozoic Verkhoyansk-Chukotka and Sikhote- Alin structures. Two important mineralization epochs are evident - Sino-Cambrian and late Mesozoic- Cenozoic. The Mesozoic-Cenozoic mineralization epoch exhibits a definite tendency for “rejuvenation” of the mineralization processes, going away from the continent and toward the Pacific trough, from late Jurassic in the eastern Trans-Baykal region and parts of the northeast to Neogene in the province of the Okhotsk geosynclines. An outstanding feature of endogeneous mineralization in this region is the linear arrangement of the ore zones determined by a system of major magma-controlling and other faults.—C. E. Sears     

First Data on Au–Sb Mineralization of the Ariadnoe Ultramafic Intrusion,Primor’e

Doklady Earth Sciences - A new promising source of mineral deposits is found in the southern part of the Far East of Russia: the Ti-bearing intrusions of ultramafic rocks of the Sikhote-Alin...