Collisional processes at the junction of the Aleutian–Kamchatka arcs: new evidence from fission track analysis and field observations

The Aleutian island arc collides with the Kuril–Kamchatka arc in the area of the Cape Kamchatka peninsula. Field studies of neotectonic structures and apatite fission track analysis provide evidence for crustal plate shortening onshore the Cape Kamchatka peninsula. Tectonic blocks show differential mean exhumation rates varying from 0.18 ± 0.04 mm yr⁻¹ in the north up to 1.2 ± 0.18 mm yr⁻¹ in the south of the peninsula. A few of the fission track length data point to an unsteady exhumation rate. The blocks are separated by major dextral fault zones splaying off from Aleutian island arc fault zones. Across the western segment of the North American–Pacific Plate boundary the strain is partitioned along the fault zones and increases from north to south. Results from this study suggest that indentation and accretion of island arc fragments has recently occurred in the southeastern part of the Cape Kamchatka peninsula.     

中亚成矿域西部早二叠世金、镍重大成矿事件

晚古生代是地球历史上一个重要时期,蕴含着潘吉亚超大陆、规模最大冰期、最严重的生物大灭绝以及巨量矿产资源形成的关键信息。地处欧亚大陆腹地的中亚成矿域是全球最大的显生宙大陆增生区,以晚古生代大规模成矿为显著特色,尤其早二叠世（270~290 Ma）在中亚成矿域西部天山及邻区巨量金、镍爆发性集中成矿作用,造就出世界第二大金成矿省,形成了超过10000 t金,造就出具有世界特色的造山带岩浆型镍矿集区,形成了包括8个大型-超大型矿床在内的东天山、额尔齐斯、北山3个重要镍矿床集中区,镍资源达250万t,是一次全球罕见的金-镍时间耦合重大成矿事件。文章基于最新研究成果,系统论述了中亚成矿域西部早二叠世金、镍大规模成矿的时空分布和基本地质特征,探讨了该重大成矿事件的区域动力学背景和可能成矿机制。研究认为,早二叠世金矿床产于天山古缝合带附近的脆/韧性构造变形带,构成独具特色的大陆变形带金成矿系统,已有成矿理论难以涵盖,含碳碎屑岩系、地块抬升导致的大规模区域变质作用、多来源的流体作用、多期构造活化富集、多种因素耦合叠加等,可能是大规模金成矿的关键条件;早二叠世镍矿床沿天山、北山、阿尔泰地区深大断裂附近的镁铁-超镁铁质岩体线性展布,是全球造山带镍成矿作用最强烈、发现矿床数量最多的地区,俯冲熔/流体的交代岩石圈地幔/软流圈发生高程度部分熔融、区域超壳深断裂为玄武质岩浆提供快速运移的通道、壳源物质加入触发硫化物熔离、硫化物与多幕脉动侵位的岩浆反应是造山带岩浆型镍大规模成矿的关键。整体上,中亚成矿域西部早二叠世金、镍重大成矿事件表现为“时间耦合、西金东镍”的时空格局,但大规模成矿的全球和区域动力学背景、金与镍富集机制及成矿响应机理还是未解之谜。     

Peri-Gondwanan Ordovician crustal fragments in the high-grade basement of the Eastern Rhodope Massif,Bulgaria: evidence from U-Pb LA-ICP-MS zircon geochronology and geochemistry

Field, geochemical, and geochronologic data of high-grade basement metamafic and evolved rocks are used to identify the nature and timing of pre-Alpine crustal growth of the Rhodope Massif. These rocks occur intrusive into clastic-carbonate metasedimentary succession. Petrography and mineral chemistry show compositions consistent with Alpine amphibolite-facies metamorphism that obliterated the original igneous textures of the protoliths. Bulk-rock geochemistry identifies low-Ti tholeiitic to calc-alkaline gabbroic-basaltic and plagiogranite precursors, with MORB-IAT supra-subduction zone signature and trace elements comparable to modern back-arc basalts. The U-Pb zircon dating revealed a mean age of 455 Ma for the magmatic crystallization of the protoliths that contain inherited Cambrian (528–534 Ma) zircons. Carboniferous, Jurassic, and Eocene metamorphic events overprinted the Ordovician protoliths. The radiometric results of the metamorphic rocks demonstrate that Ordovician oceanic crust was involved in the build-up of the Rhodope high-grade basement. Dating of Eocene-Oligocene volcanic rocks overlying or cross-cutting the metamorphic rocks supplied Neoproterozoic, Ordovician and Permo-Carboniferous xenocrystic zircons that were sampled en route to the surface from the basement. The volcanic rocks thus confirm sub-regionally present Neoproterozoic and Paleozoic igneous and metamorphic basement. We interpret the origin of the Middle-Late Ordovician oceanic magmatism in a back-arc rift-spreading center propagating along peri-Gondwanan Cadomian basement terrane related to the Rheic Ocean widening. The results highlight the presence of elements of Cadomian northern Gondwana margin in the high-grade basement and record of Rheic Ocean evolution. The eastern Rhodope Massif high-grade basement compared to adjacent terranes with Neoproterozoic and Cambro-Ordovician evolution shares analogous tectono-magmatic record providing a linkage among basement terranes incorporated in the Alpine belt of the north Aegean region.     

Transgressive Eocene clastic–carbonate sediments from the Circum‐Rhodope belt,northeastern Greece: implications for a rocky shore palaeoenvironment

Locally exposed Middle to Upper Eocene conglomerates in the western part of the Cenozoic Thrace Basin are interpreted as products of continuous marine erosion of a rocky coast (consisting of Lower Cretaceous carbonates) and subsequent redeposition of the land‐derived limestone material in a wave‐dominated nearshore setting during a prolonged transgression. Contemporaneous biological activity in the warm‐temperate marine environment contributed to the accumulation of mixed coarse‐grained clastic–carbonate sediments on the upper shoreface. The formation of a relatively thick sedimentary succession was favoured by the interplay of several controlling factors as only shoreface deposits were preserved in the rock record. The results may help to elucidate the evolution of the hydrocarbon‐bearing Thrace Basin and to assist with the regional correlation of its basal deposits. Copyright © 2014 John Wiley & Sons, Ltd.     

Thirty-Element Active Antenna Array as a Prototype of a Huge Low-Frequency Radio Telescope

An effective wide-band (10 to 60 MHz) active antenna element has been developed. The cost of one short (3 m), thin dipole with built-in amplifier and metal construction is less than 45 euro. It was shown both theoretically and experimentally that the upper limiting frequency is at least 60 MHz, the dynamic range is 90 dB/V and the share of the amplifier noise to the background antenna temperature is about 10%. The developed active dipole was tested by building a 30-element antenna array and comparing its parameters with one of the subpart of the UTR-2 radio telescope having passive dipoles of 8.6 m in length and 1.8 m in diameter. The 3C461 ionospheric scintillation spectra observed in the experiments show that the sensitivities and noise-immunities of both antennas are close. This proves the availability using of a short cheap active dipole in new generation giant radio telescopes.     

Kamenetsk—A new impact structure in the Ukrainian Shield

The Kamenetsk impact structure is a deeply eroded simple crater that formed in crystalline rocks of the Ukrainian Shield. This study presents structural, lithologic, and shock metamorphic evidence for an impact origin of the Kamenetsk structure, which was previously described as a paleovolcano. The Kamenetsk structure is an oval depression that is 1.0–1.2 km in diameter and 130 m deep. The structure is deeply eroded, and only the lower part of the sequence of lithic breccia has been preserved in the deepest part of the crater to recent time, while the predominant part of impact rocks and postimpact sediments was eroded. Manifestations of shock metamorphism of minerals, especially planar deformation features in quartz and feldspars, were determined by petrographic investigations of lithic breccia that allowed us to determine the impact origin of the Kamenetsk structure. The erosion of the crater and surrounding target to a minimal depth of 220 m preceded the deposition of the postimpact sediments. The time of the formation of the Kamenetsk structure is bracketed within a wide interval from 2.0 to 2.1 Ga, the age of the crystalline target rocks, to the Late Miocene age of the sediments overlaying the crater. The deep erosion of the structure suggests it is probably Paleozoic in age.     

Use of Groundwater Level Fluctuations near an Operating Water Supply Well to Estimate Aquifer Transmissivity

We developed a method to estimate aquifer transmissivity from the hydraulic-head data associated with the normal cyclic operation of a water supply well thus avoiding the need for interrupting the water supply associated with a traditional aquifer test. The method is based on an analytical solution that relates the aquifer's transmissivity to the standard deviation of the hydraulic-head fluctuations in one or more observation wells that are due to the periodic pumping of the production well. We analyzed the resulting analytical solution and demonstrated that when the observation wells are located near the pumping well, the solution has a simple, Dupuit like form. Numerical analysis demonstrates that the analytical solution can also be used for a quasi-periodic pumping of the supply well. Simulation of cyclic pumping in a statistically heterogeneous medium confirms that the method is suitable for analyzing the transmissivity of weakly or moderately heterogeneous aquifers. If only one observation well is available, and the shift in the phase of hydraulic-head oscillations between the pumping well and the observation well is not identifiable. Prior knowledge of aquifer's hydraulic diffusivity is required to obtain the value of the aquifer transmissivity.     

On linking coefficient of two Keplerian orbits

We define a function of the set of pairs of Keplerian ellipses so that the sign of the function will be a topological invariant of their configuration. The sign is negative if and only if the related ellipses are linked. Two modifications of the coefficient which are more reliable in the case of closed to coplanar orbits are proposed. Explicit formulae representing the linking coefficients as functions of orbital elements are deduced. Extension in the case of unbounded orbits is obtained. We suggest different ways to use these coefficients for determining intersections of pairs of osculating Keplerian orbits. If we study dynamical behaviour of geometric configuration of pairs of Keplerian orbits, we can fix the moments of their intersections. These moments correspond exactly to the vanishing of linking coefficients. This revised version was published online in July 2006 with corrections to the Cover Date.     

Precision of the ephemerides of outer planetary satellites

Ephemerides of planetary satellites are needed to address many problems. These ephemerides are used for subsequent observations. A comparison of the available ephemerides with new observations allows the accuracy of the former to be assessed. However, the precision of the ephemerides must be known a priori when solving the tasks. In this paper we formulate and solve the problem of estimating the precision of the ephemerides of outer planetary satellites derived from observations when applied up to the future moments.The methods of assessing the precision of ephemerides involve producing a set of samples of the same ephemeris inferred from observations with different samples of Monte Carlo generated random errors (RO) superimposed onto it. The statistical parameters of simulated observational errors are based on the results of the reduction of real satellite observations. We compute the deviations of the samples of the ephemeris from the standard ephemeris inferred from real observations and adopt the root-mean-square deviation of the apparent coordinates as the precision of the ephemeris. We also use alternative methods: one based on the matrix of covariances of parameter errors (RP), and another one based on bootstrap samples of observations (BS).We use three methods (RO, RP, and BS) to estimate the precision of the ephemerides of all the 107 outer planetary satellites over the 2010-2020 time interval. The precision of the ephemerides of different satellites varies from 0.05 to 4.0 arcsec. For a number of satellites new observations are of vital importance for maintaining the precision of the ephemerides at a level that would allow identification of satellites during the reduction of observations. For some satellites the precision of their ephemerides is of the order of the sizes of their orbits and such satellites can be considered to have been lost. We show that the method of bootstrap samples (BS) can give doubtful results in the cases where there are few observations, which covered a time interval that is shorter than the orbital period of the satellite.Our results suggest obtaining more precise ephemeris making new observations at the times of maximum estimated errors of the ephemeris.All the inferred estimates of the precision of ephemerides are available from the MULTI-SAT ephemeris server: www.imcce.fr/sat (IMCCE), www.sai.msu.ru/neb/nss/index.htm (SAI).