Structure, age substantiation and tectonic setting of the Lower-Middle Ordovician volcanic-sedimentary and plutonic complexes of the western part of the Kyrgyz Range (Northern Tien Shan)

Among the Caledonides exposed in the western part of the Kyrgyz Range the Lower Ordovician volcanogenic-sedimentary, plutonic, and tuffaceous-terrigenous complexes were distinguished. Volcanogenic-sedimentary sequences are the Kentash Formation, composed of volcanic rocks, tuffs and subvolcanic bodies of dacitic, andesitic and basaltic composition, sandstones and tuffites with interlayers and lenses of limestone. On the basis of conodonts and U-Pb dating of zircon grains the age of this Formation is in the age interval between Late Tremadocian Stage and Early Darriwilian Stage. Differentiated volcanites are associated with ultramafic-gabbro massifs of the Kokkiya Complex of the Late Darriwilian age (U-Pb zirconology). Features of the chemical composition of rocks of the Kentash Formation and the Kokkiya Complex indicate that they formed in suprasubduction settings within the island arc with a thick heterogeneous basement. Tuffaceous-terrigenous deposits are presented by the olistostrome formation, and coarse-grained deposits of the Taldybulak and Kyzylkainar Formations. The formation of olistostrome formation is associated with the over-thrusting of Cambrian melanocratic complexes on terrigenous-carbonate and shale strata of the Upper Precambrian-Cambrian age. Deposits of the Taldybulak and Kyzylkainar Formations accumulated in the back-arc basin and on the island arc slope, made of rocks of the Kentash Formation.     

Oxygen isotope variations in granulite-grade iron formations: constraints on oxygen diffusion and retrograde isotopic exchange

The oxygen isotope ratios of various minerals were measured in a granulite-grade iron formation in the Wind River Range, Wyoming. Estimates of temperature and pressure for the terrane using well calibrated geothermometers and geobarometers are 730±50° C and 5.5±0.5 kbar. The mineral constraints on fluid compositions in the iron formation during retrogression require either very CO₂-rich fluids or no fluid at all. In the iron formation, isotopic temperature estimates from quartz-magnetite fractionations are controlled by the proximity to the enclosing granitic gneiss, and range from 500° C ( _{qz – mt}=10.0) within 2–3 meters of the orthogneiss contact to 600° C ( _{qz – mt}=8.0) farther from the contact. Temperature estimates from other isotopic thermometers are in good agreement with those derived from the quartz-magnetite fractionations.During prograde metamorphism, the isotopic composition of the iron formation was lowered by the infiltration of an external fluid. Equilibrium was achieved over tens of meters. Closed-system retrograde exchange is consistent with the nearly constant whole-rock ¹⁸O_wr value of 8.0±0.6. The greater _qz-mt values in the iron formation near the orthogneiss contact are most likely due to a lower oxygen blocking temperature related to greater exchange-ability of deformed minerals at the contact. Cooling rates required to preserve the quartz-magnetite fractionations in the central portion of the iron formation are unreasonably high (800° C/Ma). In order to preserve the 600° C isotopic temperature, the diffusion coefficient D (for -quartz) should be two orders of magnitude lower than the experimentally determined value of 2.5×10^–16 cm²/s at 833 K. There are no values for the activation energy (Q) and pre-exponential diffusion coefficient (D ₀), consistent with the experimentally determined values, that will result in reasonable cooling rates for the Wind River iron formation. The discrepancy between the diffusion coefficient inferred from the Wind River terrane and that measured experimentally is almost certainly due to the enhancement of exchange by the presence of water in the laboratory experiments. Cooling rate estimates were also determined for iron formation retrograded under water-rich conditions. Application of the experimentally determined data to these rocks results in a reasonable cooling rate estimate, supporting the conclusion that the presence of water greatly enhances oxygen diffusion.Contribution 441 from the Mineralogical Laboratory, University of Michigan     

Burovaite-Ca, (Na,K)4Ca2(Ti,Nb)8[Si4O12]4(OH,O)8·12H2O, a new labuntsovite-group mineral species and its place in low-temperature mineral formation in pegmatites of the Khibiny pluton, Kola Peninsula, Russia

This paper presents data on burovaite-Ca, the first Ti-dominant member of the labuntsovite group with a calcium D-octahedron. The idealized formula of burovaite-Ca is (K,Na)₄Ca₂(Ti,Nb)₈[Si₄O₁₂]₄(OH,O)₈ · 12H₂O. The mineral has been found in the hydrothermal zone of aegirine-microcline pegmatite located in khibinite at Mt. Khibinpakhkchorr, the Khibiny pluton, Kola Peninsula, Russia. Radiaxial intergrowths of burovaite-Ca and labuntsovite-Mn associated with lemmleynite-Ba, analcime, and apophyllite have been identified in caverns within microcline. The mean composition of the mineral is as follows, wt %: 3.72 Na₂O, 2.76 K₂O, 4.22 CaO, 0.47 SrO, 0.23 BaO, 0.01 MnO, 0.30 Fe₂O₃, 0.14 Al₂O₃, 42.02 SiO₂, 17.30 TiO₂, 15.21 Nb₂O₅, 12.60 H₂O (measured); the total is 98.98. Its empirical formula has been calculated on the basis of [(Si,Al)₁₆O₄₈]: {(Na_3.10K_1.07Ca_0.37Sr_0.04Ba_0.04)_4.62}(Ca_1.28Zn_0.01)_1.29(Ti_4.97Nb_2.56Fe_0.08Ta_0.02)_7.63(Si_15.93Al_0.07)₁₆O₄₈(OH_6.70O_0.93)_7.63 · 12H₂O. The strongest lines in the X-ray powder diffraction pattern of burovaite-Ca (I-d ?] are as follows: 70–7.08, 40–6.39, 40–4.97, 30–3.92, 40–3.57, 100–3.25, 70–3.11, 50–2.61, 70–2.49, 40–2.15, 50–2.05, 70–1.712, 70–1.577, and 70–1.444. The structure of burovaite-Ca was solved by A.A. Zolotarev, Jr. The mineral is monoclinic, space group C2/m. The unit-cell dimensions are a = 14.529(3), b = 14.203(3), c = 7.899(1), β = 117.37(1)°, V = 1447.57 ?₃. Burovaite-Ca is an isostructural Ti-dominant analogue of karupm?llerite-Ca and gjerdingenite-Ca. Two stages of mineral formation—pegmatite proper and hydrothermal—have been recognized in the host pegmatite. The hydrothermal stage included K-Ba-Na, Na-K-Ca, and Na-Sr substages. Burovaite-Ca is related to the intermediate Na-K-Ca substage. At the first substage, labuntsovite-Mn and lemmleynite-Ba were formed, and tsepinite-Na, paratsepinite-Nd, and tsepinite-Sr were formed at the final substage. Thus, the sequence of crystallization of labuntsovite-group minerals is characterized by the replacement of the potassium regime by the sodium regime of alkaline solutions in the evolved host pegmatite.     

Utilization multi attribute decision making models for spatial prioritization and environmental decision making in new towns

This study was conducted to determine some important factors of site selection for Esfahan 4th new town-Iran, with quantification of importance index for each factor and the effect of selected criteria in determination of the prioritized location for urban development. The study followed an explanatory analytical method based on field studies, analytical hierarchy process and technique for order preference by similarity to ideal solution model. This means that after defining the criteria and the significant parameters using Delphi technique and filling out the questionnaires by experts in environmental sciences and urban constructions, the rate of effectiveness of each factor and also the significant criteria in site priority and environmental decision making for new towns were determined by analytical hierarchy process model and “Expert choice” software. The results revealed that among the main defined criteria (i.e. physical, biological, economical-social, political and pollution dispersion) and sub-criteria selected by the experts for location of Esfahan 4th new town, the physical criteria with a weight of 0.453 designated nearly 45 % of the importance index to itself, standing at the first priority. Accordingly, the economical-social and pollution dispersion criteria were ranked at the second and the third place with weights of 0.307 and 0.116, respectively. The technique for order preference by similarity to ideal solution model, which is one of the methods for multi-criteria decision making, was then used to determine the best location scenario. Comparing the three proposed locations, alternative 1 was found to be more suitable as it was well-fitted to the defined criteria.     

Electrostatic radiation of plasma in the upper ionosphere in the inhomogeneous geomagnetic field

It has been indicated that the spectrum of electrostatic waves in the ionospheric plasma depends on the geophysical conditions and solar wind parameters. The wave field measurements in the frequency band 0.1–10 MHz in the topside ionosphere were used to analyze the electrostatic instabilities of the plasma electron content (the APEX satellite experiment). A change of the sign of one magnetic field component at the geomagnetic equator can result in the formation of the large-scale irregular plasma structure with a decay of the natural electrostatic oscillations and vortices in unstable plasma. The plasma particle polarization drift from the region of decay of electrostatic oscillations and vortices can cause large plasma density and temperature gradients across the geomagnetic field. New vortices can originate at these gradients. This mechanism of plasma vortex formation and decay can be important for mass and energy convection in the topside ionosphere.     

Vibrations of beams fully or partially supported on elastic foundations

Exact stiffness and consistent mass matrices for beams on elastic foundations are derived. Using these matrices it is possible to find the natural frequencies and mode shapes of vibrations, for beams fully or partially supported on elastic foundations. Several examples are given for frequencies and mode shapes of beams partially supported on elastic foundations.     

Tidal currents,bed sediments,and bedforms at the South Branch and the South Channel of the Changjiang (Yangtze) estuary,China: Implications for the ripple-dune transition

Measurements were made of tidal currents, bed sediment particle sizes, and bedform dimensions at the South Branch and the South Channel of the Changjiang estuary, China, during the dry season in 1997 and the flood season in 1998. The near bottom current speed and direction were measured by a mechanical current meter for 10 h in 1997. The near surface current speed and direction were measured by a Current Meter of Endeco/YSI Inc. 174 SSM for 14 h in 1997 and 1998. Nine bed sediment samples were taken and their particle sizes were analyzed with sieves and siphons. The bedforms were nautically detected by an echo sounder and a side scan sonar. Results show that the ebb tides had larger near-bottom and near-surface current speeds and longer durations than the flood tides, in which the former occurred during the flood season in 1998 and not in the dry season in 1997. The bed sediments were composed of coarse silts and very fine sands during the dry season but of fine sands during the flood season. Bedforms were dominated by ebb tidal currents, the height∶length ratios of dunes and lee face angles were low, and heights and lengths were larger during the flood season in 1998. The ebb and flood tidal currents, bed sediment sizes, and dune morphology were largely controlled by the seasonal runoff variations. A new tentative boundary might be proposed for natural dunes in very fine sand with the availability of additional field data in the future.     

Comparison of the compositions of crystalline aluminosilicate rocks and their minerals in a planar triangular projection

The problem of comparison of the composition of crystalline rocks with the composition of the constituent minerals of these rocks is considered. It is proposed to present the composition of rocks and the compositions of the constituent minerals in the form of a triangle on the plane. The experience of presentation of compositions in phase diagrams was taken as a basis for the construction. Analysis of the crystallochemical characteristics of clinopyroxenes and garnets has shown that three parameters are enough for depicting the compositions of these and other minerals. For this purpose, similar composition components of rocks and their minerals are summarized in molecular proportions and are plotted on the triangle DO-1/2(R₂O3)-XO₂, where DO = (MgO + CaO + FeO + MnO + NiO + ...) + 1/4(Na₂O + Al₂O₃) + 1/4(K₂O + Al₂O₃), 1/2(R₂O₃) = 1/2(Al₂O₃ + Fe₂O₃ + Cr₂O₃ + ...) - (1/4(Na₂O + Al₂O₃) + 1/4(K₂O + Al₂O₃)), and XO₂ = SiO₂ + TiO₂. The compositions of minerals are expressed as the sums of their components: Ol = Fo + Fa + Lar + Neph + ..., Px = Di + En + Wol + Ged + Gip + Jd + Eg + ..., Ga = Pyr + Gross + Alm + Spe + Ski + Knr + Mj + ..., etc. A step-by-step calculation algorithm is proposed, which permits evaluation of the contents of bi- and trivalent iron during probe microanalyses of garnets and pyroxenes. Comparison of the compositions of deep-seated rocks and their minerals shows their good consistency. The proposed schematic projection permits a visual comparison of the compositions of rocks with low contents of carbonates and water, from ultrabasic (e.g., dunites) to acid (e.g., granites) ones.