The character of scaling earthquake source spectra for Kamchatka in the 3.5–6.5 magnitude range

The properties of the source spectra of local shallow-focus earthquakes on Kamchatka in the range of magnitudes M _w = 3.5–6.5 are studied using 460 records of S-waves obtained at the PET station. The family of average source spectra is constructed; the spectra are used to study the relationship between M _w and the key quasi-dimensionless source parameters: stress drop Δσ and apparent stress σ_a. It is found that the parameter Δσ is almost stable, while σ_a grows steadily as the magnitude M _w increases, indicating that the similarity is violated. It is known that at sufficiently large M _w the similarity hypothesis is approximately valid: both parameters Δσ and σ_a do not show any noticeable magnitude dependence. It has been established that M _w ≈ 5.7 is the threshold value of the magnitude when the change in regimes described occurs for the conditions on Kamchatka.     

A New Solid Solution with Garnet Structure: Berzeliite–Schäferite Isomorphic Series from the Fumarole Exhalation of the Tolbachik Volcano,Kamchatka

Geology of Ore Deposits - An extended isostructural solid solution (isomorphic series) between arsenate and vanadate of the garnet supergroup — berzeliite (NaCa2)Mg2(AsO4)3 and...     

Area,length and thickness conservation: Dogma or reality?

The basic assumption of quantitative structural geology is the preservation of material during deformation. However the hypothesis of volume conservation alone does not help to predict past or future geometries and so this assumption is usually translated into bed length in 2D (or area in 3D) and thickness conservation. When subsurface data are missing, geologists may extrapolate surface data to depth using the kink-band approach. These extrapolations, preserving both thicknesses and dips, lead to geometries which are restorable but often erroneous, due to both disharmonic deformation and internal deformation of layers. First, the Bolivian Sub-Andean Zone case is presented to highlight the evolution of the concepts on which balancing is based, and the important role played by a decoupling level in enhancing disharmony. Second, analogue models are analyzed to test the validity of the balancing techniques. Chamberlin's excess area approach is shown to be on average valid. However, neither the length nor the thicknesses are preserved. We propose that in real cases, the length preservation hypothesis during shortening could also be a wrong assumption. If the data are good enough to image the decollement level, the Chamberlin excess area method could be used to compute the bed length changes.     

Geological–Geophysical Model of the Nizhne-Koshelevskoe Vapor-Dominated Geothermal Deposit,the Largest in Kamchatka

Fundamentally new data on the structure of the Nizhne-Koshelevskoe vapor-dominated geothermal deposit (South Kamchatka) were obtained. An isometric area of intensely argillized rocks saturated with a vapor–gas mixture with the shape of an irregular cup occurring up to a depth of 250–300 m was distinguished in the central part of the deposit beneath the major zone of hydrotherm discharge. This area is controlled by a heat source through a subvertical channel of increased fracture–porous permeability for a vapor–gas fluid with a thickness of 300–350 m and a depth of >5 km. The elements of the paleohydrothermal system, such as relatively rock blocks composed of propylite and secondary quartzite with epithermal ore mineralization, were distinguished at the core of the deposit. The heat was transferred by the crustal flux of reduced hydrocarbon fluid.     

Sedimentological,mineralogical and geochemical characteristics of the ooids in Cleopatra (Sedir Island,Gökova Bay,SW Turkey) and Alexandria (NW Egypt) Beach sediments: A comparison and reality of myth of the love

According to the myth, ooid-rich sediments in Cleopatra Beach (Sedir Island, Turkey) were brought by ships from Alexandria Beach (Egypt) by the Roman leader, Marcus Antonius, for his lover Cleopatra. Ooids of both beaches have been compared in terms of sedimentology, mineralogy and geochemistry to determine reality of the myth of love. Sieve analyses exhibit that sediments of Cleopatra Beach are slightly better sorted than Alexandria Beach sediments, and have relatively smaller sized ooids, interpreted to represent a relatively less agitated environment. All ooids are composed mainly of aragonite characterized by high Sr contents (>8600 mg/kg). Hierarchical Cluster Analysis, the cross-plot of δ¹⁸Oaragonite versus δ¹³C_aragonite values of ooids, and the presence of detrital grains such as gneiss and schist hint on two distinct groups of samples that correspond to the Cleopatra and Alexandria Beach ooids. These results suggest that the myth may not be realistic, and the ooids on the shore of Sedir Island were formed in-situ, e.g., during the Late Holocene.     

The Role of Hydrocarbons in the Formation of Epithermal Gold–Silver Deposits in Kamchatka,Russia

Doklady Earth Sciences - Data on the mineralogical and geochemical features of three epithermal gold deposits in Kamchatka, as well as on the compositions and physicochemical parameters of...     

The First Finding of Sapphirine in Granulites of the Angara–Kan Block: Evidence of Ultra-High–Temperature Metamorphism in the SW Siberian Craton

This work reports the first discovery of sapphirine-bearing mineral parageneses in granulites of the Angara–Kan block, information on the mineral assemblage of rocks, and the mineral composition. Based on mineral geothermometers utilizing alumina content in orthopyroxene, reconstruction of the composition of ternary feldspar, and the titanium content in zircon, it was revealed that the peak temperatures of metamorphism reached 1100°C, after which the rocks underwent cooling under sub-isobaric conditions. It is assumed that the pulse of ultra-high-temperature metamorphism correlates with processes of extension and intraplate magmatism during the age interval of 1.78–1.75 Ga.     

Petrology of mafic enclaves in the 2006–2012 eruptive products of Bezymianny Volcano,Kamchatka

This paper reports the results of the first comprehensive petrological study of mafic enclaves widespread in the products of recent (2006–2012) eruptions of Bezymianny Volcano, Kamchatka. Four types of mafic enclaves were distinguished on the basis of the composition and morphology of minerals, P–T conditions of formation of mineral assemblages, and structural and textural characteristics of the rocks. Disequilibrium assemblages of mafic enclaves indicate a complex structure of the magmatic plumbing system of the volcano, including a shallow chamber with andesite–basaltic andesite magmas and a deep reservoir filled in part with plagioclase–hornblende cumulates and fed by basic magmas with mantle harzburgite xenoliths. The mafic enclaves were formed at different levels of the magmatic plumbing system of the volcano and correspond to different degrees of mixing of interacting magmas. The most abundant enclaves were formed during magma ascent from the deep reservoir (960–1040°C, 5–9 kbar) into the shallow andesitic chamber (940–980°C). Enclaves of plagioclase–hornblende cumulates from the basic magmas feeding the deep reservoir (T > 1090°C and P > 9 kbar) are much less common.     

Tectonic Nature of the Northern Segment of the Jiao-Liao-Ji Belt: A Rift or Continental Collision Belt?

<正>Objective The tectonic characteristics and evolution of the Paleoproterozoic Jiao-Liao-Ji belt have been extensively studied in recent decades(Fig.1 a).Two main models have been proposed for the formation of this belt:a continental-or arc-continent collisional belt,and the opening and closure of an intra-continental rift.The main reasons for these ongoing debates are own to the complex composition,including metamorphosed volcano-sedimentary rocks,multiple pulses of granitic magmatism,meta-mafic intrusions,and tectonometamorphic history.In addition,earlier work focused on the geochronology and metamorphic evolution,whereas the     

Peculiarities of Subduction in the Junction of the Kuril–Kamchatka and Aleutian Island Arcs

Doklady Earth Sciences - The peculiarities of the junction between the Kuril–Kamchatka and Aleutian island arcs are studied using different techniques and experimental data. The models of...     

Minerals of the Bournonite–Seligmannite Series in Ore of the Beresitovoe Deposit,Upper Amur Region,Russia

New data are presented on segregations and compositions of bournonite-seligmannite series of minerals in gold-bearing veinlets of the Beresitovoe deposit located in the eastern part of the Mongolia–Okhotsk Orogenic Belt. It was established that these minerals represent a discrete series of stoichiometric solid compounds with As formula coefficients varying from 0.2 to 1.2. It is shown that minerals of this series are characteristic of ore deposits that undergo high-grade metamorphism, the P–T conditions of which are sufficient for melting of primary sulfides.     

A proposed GSSP for the base of the Middle Ordovician Series： the Huanghuachang section,Yichang, China

The Huanghuachang section near Yichang, southern China meets the requirements of Global Stratotype Section and Point (GSSP) for the base of the Middle Ordovician Series and the yet-to-be-named third stage of the Ordovician System (or lower stage of Middle Ordovician Series). The conodont succession at the section is complete across the Lower to Middle Ordovician series boundary and several excellent phylogenetic lineages of Baltoniodus, Trapezognathus, Periodon, and Microzarkodina are represented. The definition of the base of the Middle Ordovician is proposed to be the first appearance datum (FAD) of Baltoniodus? triangularis in the section. It is followed closely by the FAD of Microzarkodina flabellum, which is taken as a reasonable proxy for the boundary. This level approximates the boundary between the lower and upper intervals of the Azygograptus suecicus graptolite Biozone, and nearly coincides with the base of the Belonechitina henryi chitinozoan Biozone.The proposed GSSP for the base of the international Middle Ordovician Series is located in a roadside exposure at the base of Bed (SHod) 16, 10.57 m above the base of the Dawan Formation in the measured Huanghuachang section near Yichang City, southern China. The same faunal succession is also recorded from the Chenjiahe (formerly Daping) section, 5 km to the north of the Huanghuachang section. The proposed boundary horizon can be recognized and correlated globally with high precision in both relatively shallow-water carbonate facies as well as in deep-water graptolite facies.     

First finds of Eocene diatoms in the marine Paleogene reference section in the Il’pinskii Peninsula, northeastern Kamchatka

Diatom algae from the Eocene sediments of the marine Cenozoic section in the Il’pinskii Peninsula, northeastern Kamchatka, are studied. The taxonomic composition of the diatom assemblage is characterized, including rare representatives of oceanic plankton. Correlation with planktonic foraminifer associations found in the section indicates a Middle Eocene (Lutetian) age for the diatoms. These are the first records of Eocene diatoms from the northwestern Pacific rim for which such a correlation has been achieved.     

How do “numbers” construct social reality in disaster-stricken areas?: a case of the 2008 Wenchuan earthquake in Sichuan,China

This article focuses on the dynamics of using numbers to construct an image of social reality in disaster areas. Numbers are neither objective nor value-neutral but are rather generated, transmitted and shared with social signification. In other words, numbers can be thought of as simply socially constructed information. Statistics and other numbers usually work in positive ways. However, it is also possible that using numbers in the media can lead to unintended messages that could produce negative consequences. We conducted field studies in disaster-stricken areas of the 2008 Wenchuan earthquake in China and compared findings to the case of the 1995 Kobe earthquake in Japan in order to examine how numbers—in terms of the amount of donations, the timeline of reconstruction projects and casualty figures—construct social reality and cause a variety of social dysfunctions.     

Formation of the Olyutorsky–Kamchatka foldbelt: a kinematic model

The Olyutorsky–Kamchatka foldbelt formed as a result of two successive collisions of the Achaivayam–Valaginsky and Kronotsky–Commander island arcs with the Eurasian margin where the two terranes docked after a long NW transport. We model their motion history from the Middle Campanian to Present and illustrate the respective plate margin evolution with ten reconstructions. In this modeling the arcs are assumed to travel on the periphery of the large plates of Eurasia, North America, Pacific, and Kula, for which the velocities and directions of motion are known from published data. The model predicts that the Achaivayam–Valaginsky arc was the leading edge of the Kula plate from the Middle Campanian to the Middle Paleocene and then moved slowly with the Pacific plate as long as the Middle Eocene when it accreted to Eurasia. The Kronotsky arc initiated in the Middle Campanian on the margin of North America and was its part till the latest Paleocene when the terrane changed polarity to move northwestward with the Pacific plate and eventually to collide with Eurasia in the Late Miocene. The predicted paleolatitudes of the Achaivayam–Valaginsky and Kronotsky–Commander island arcs for the latest Cretaceous and Paleogene are consistent with nine (out of eleven) reliable paleomagnetic determinations for samples from the two arcs. Additional changes imposed on the initial model parameters (kinematics of the large plates, relative position of the Kula–Pacific Ridge and the Emperor seamount chain, or time of active volcanism within the arcs) worsen the fit of the final reconstructions to available geological and paleomagnetic data. Therefore, the suggested model appears to be the most consistent one at this stage of knowledge.     

Geological events of the Late Cretaceous–Early Paleogene in Western Kamchatka

The age ranges of Upper Cretaceous lithotectonic complexes of Western Kamchatka—terrigenous Kikhchik, volcanic Irunei, and terrigenous Omgon—are analyzed to reveal their almost simultaneous deposition. The pre-Cenozoic settings of these complexes are reconstructed. Based on analysis of the composition and structural features of Late Cretaceous lithotectonic complexes and on correlation of events, the Late Cretaceous paleogeography is reconstructed. It is found that the formation of the contemporary structure of the studied region would have required significant displacement of the volcanic Irunei complex from west to east and the terrigenous Omgon complex from north to south. It is concluded that the Western Kamchatka continental block (minor lithospheric plate) was independent in the Late Cretaceous.     

Lower precambrian of the Keivy Terrane,Northeastern Baltic Shield: A stratigraphic succession or a collage of tectonic sheets?

The Keivy Terrane in the northeastern Baltic Shield appreciably differs from the adjacent tectonic blocks. In the northwestern part of this terrane (the Serpovidny Range), an outlier of Paleoproterozoic supracrustal rocks called the Serpovidny structure is surrounded by Archean (?) Keivy high-alumina paraschists. As follows from structural and magnetic data, the Paleoproterozoic rocks are deformed into a tight sheath fold 8 × 2 km in size at the surface and 5 km in length along the sheath axis. Faults parallel to the boundaries of the layers and locally cutting them off at an acute angle are involved in folding as well. The outer boundaries of the Serpovidny structure are tectonic. This structure is complementary to a larger tectonic lens composed of the Keivy mica schists. It is concluded that all of the supracrustal rocks of the Serpovidny Range are in fact tectonic sheets and lenses deformed into sheath folds. The literature data show that kilometer-scale sheath folds occur throughout the Keivy paraschist belt and most likely were formed owing to thrusting of the Murmansk Craton onto the Keivy Terrane in the south-southwestern direction. Foliation and lineation related to thrusting have been established in the Archean silicic metavolcanics and peralkaline granites occupying the most part of the terrane. In contrast, the granitoids and gabbroanorthosites of the Archean basement, which form a block 90 × 20 km in the southwestern Keivy Terrane, were not affected by Paleoproterozoic deformation. In other words, a detached assembly of tectonic sheets composed of the upper and middle crustal rocks that underwent deformation at the initial stage of the Paleoproterozoic Lapland-Kola Orogeny and the Archean basement, which is free of this deformation, are distinguished. The depth of detachment is estimated at 20–25 km. The detachment of the upper and middle crust in the Keivy Terrane and its position in the structure of the Baltic Shield are consistent with a spatiotemporal succession that resulted in the formation of a Paleoproterozoic supercontinent and the Baltic Shield as its fragment. This succession began with the amalgamation and deformation of the Archean terranes in the northeast of the Baltic Shield during the Lapland-Kola Orogeny, the Keivy Terrane showing a record of the earliest reworking (1.97–1.93 Ga). The succession completed in the southern and southwestern parts of the shield (1.80 Ga) after the Svecofennian Orogeny, expressed in the accretion of island-arc terranes composed of Paleoproterozoic juvenile crust to the continent.     

The end of the Ediacara biota: Extinction,biotic replacement,or Cheshire Cat?

The Ediacaran–Cambrian transition signals a drastic change in both diversity and ecosystem construction. The Ediacara biota (consisting of various metazoan stem lineages in addition to extinct eukaryotic clades) disappears, and is replaced by more familiar Cambrian and Paleozoic metazoan groups. Although metazoans are present in the Ediacaran, their ecological contribution is dwarfed by Ediacaran-type clades of uncertain phylogenetic affinities, while Ediacaran-type morphologies are virtually non-existent in younger assemblages. Three alternative hypotheses have been advanced to explain this dramatic change at, or near, the Ediacaran–Cambrian boundary: 1) mass extinction of most Ediacaran forms; 2) biotic replacement, with early Cambrian organisms eliminating Ediacaran forms; and 3) a Cheshire Cat model, with Ediacaran forms gradually disappearing from the fossil record (but not necessarily going extinct) as a result of the elimination of unique preservational settings, primarily microbial matgrounds, that dominated the Ediacaran. To evaluate these proposed explanations for the biotic changes observed at the Ediacaran–Cambrian transition, environmental drivers leading to global mass extinction are compared to biological factors such as predation and ecosystem engineering. We explore temporal and biogeographic distributions of Ediacaran taxa combined with evaluations of functional guild ranges throughout the Ediacaran. The paucity of temporally-resolved localities with diverse Ediacaran assemblages, combined with difficulties associated with differences in taphonomic regimes before, during, and after the transition hinders this evaluation. Nonetheless, the demonstration of geographic and niche range changes offers a novel means of assessing the downfall of Ediacara-type taxa at the hands of emerging metazoans, which we hypothesize to be most likely due to the indirect ecological impact metazoans had upon the Ediacarans. Ultimately, the combination of studies on ecosystem construction, biostratigraphy, and biogeography showcases the magnitude of the transition at the Ediacaran–Cambrian boundary.