Petrology and Geochemistry of Post-Collisional Early Miocene Volcanism in the Karacada? Area (Central Anatolia, Turkey)

Early Miocene (ca.?21–18 Ma) volcanism in the Karacada? area comprises three groups of volcanic rocks: (1) calcalkaline suite (andesitic to rhyolitic lavas and their pyroclastics), (2) mildly-alkaline suite (alkali basalt, hawaiite, mugearite, benmoreite and trachydacite), and (3) a single trachyandesitic flow unit. Field observations, 40Ar/39Ar ages and geochemical data show that there was a progressive temporal transition from group 1 to 3 in a post-collisional tectonic setting. The calcalkaline suite rocks with medium-K in composition resemble those of subduction-related lavas, whereas the mildly-alkaline suite rocks having a sodic tendency (Na2O/K2O=1.5–3.2) resemble those of within-plate lavas. Incompatible element and Sr-Nd isotopic characteristics of the suites suggest that the lithospheric mantle beneath the Karacada? area was heterogeneously enriched by two processes before collision: (1) enrichment by subduction-related processes, which is important in the genesis of the calcalkaline volcanism, (2) enrichment by small degree melts from the astenosphere, which dominates the mildly alkaline volcanism. Perturbation of the enriched lithosphere by either delamination following collision and uplift or removal of the subducted slab following subduction and collision (i.e., slab breakoff) is the likely mechanism for the initiation of the post-collision volcanism.     

The future of large format HgCdTe arrays for astronomy

Rockwell has developed the 256×256 NICMOS3 FPA for the Hubble Space Telescope under funding from NASA through the University of Arizona. Since 1989, dozens of science grade devices have been delivered to astronomers throughout the world for ground based infrared observations. These devices have excellent sensitivity at 77K with mean dark currents of 0.1 e-/s, noise of 25 e-, and quantum efficiency of 55–70%. Pixel yields as high as 99.9% have been achieved. Our present plans are to develop a 1024×1024 FPA with 2.5 micron cutoff and make it available to astronomers. Such large arrays are made possible by the advances in detector material size (3 in. diameter PACE-I wafers), multiplexer advances (ability to verify the design in detail and availability of advanced foundries), and novel hybridization and reliability approaches.     

Catastrophic disruptions and cratering of solar system bodies: a review and new results

Collisions of bodies of the solar system have played an important role in their evolution and current observable state, but the mechanics and outcomes of those collisions are not well understood. This contribution discusses the mechanics and outcomes of those impacts, melding the existing theory, recent experiments and observations into a new and revised scaling theory, for both catastrophic disruptions and for the largest basins remaining for impacts below that threshold. New evidence is obtained by an analysis of those largest solar system basins and craters, and from some recent experiments on disruptions. The paper will present certain problems with the quantitative estimates of former approaches (Holsapple and Housen, Memorie della Societa Astronomica Italiana57, 65–85, 1986; Housen and Holsapple, Icarus84, 226–253, 1990), discuss remaining areas of uncertainty, and will give updated estimates for these important phenomena.     

Short-Period Features of the Interplanetary Plasma and Their Evolution

The solar wind plasma exhibits many features of the solar surface passed on to the interplanetary medium as temporal variations due to the solar rotation. The yearly average values of solar wind velocity, and geomagnetic index A _p during 1965–1999 were found to exhibit long period evolution. They were found to peak around the declining phase of each solar cycle. While the solar wind velocity peaks around the second half of the declining phase, the IMF field strength increases around the first half of the declining phase of each solar cycle. The power spectrum of these parameters shows peaks around 37-day, 30-day, 27-day, 13.5-day, 9-day, and 7-day periods. The temporal evolution of the power spectrum of the solar wind plasma parameters and the geomagnetic activity index A _p are also studied in detail and presented with the help of contour graphs. These studies indicate that the strength of the quasi-periodicities in the interplanetary medium evolves with time.     

Formation of solar system as a result of evolution of protostar of second or subsequent generation

The formation of the solar system is considered from the physico-chemical point of view. The main role in the process is ascribed to heavy metals and to the surface tension that had arisen as a result of appearance of a liquid layer of fused substance in the equatorial region of the protostar. The formation of the liquid layer was caused by the transfer of fused substance droplets under the action of centrifugal forces in the direction of the protostar surface. Due to the surface tension the prevalence of the centrifugal forces over the gravitational ones was able to reach the value when the density differentiation of the substance began to take place under the effect of the centrifugal forces, and accumulation of heavy metals proceeded in outermost equatorial region of the protostar. As a result the disk has been formed and a liquid ring was separated from the protostar. Later explosions on the young Sun sent parts of the hardened ring which possessed the first cosmic velocity to different distances away from the Sun. In such a way planets, their satellites, asteroids, meteorites and comets were formed. The physical characteristics of planets, the parameters of their orbits, and the data on the structure of meteorites are consistent with ideas developed in the paper.     

Note on the stability of parallel magnetic fields

The stability characteristics of parallel magnetic fields when fluid motions are present along the lines of force is studied. The stability criterion for both symmetric (m=0) and asymmetric (m=1) modes are discussed and the results obtained by Trehan and Singh (1978) are amended in the present study. The results obtained for the cylindrical geometry are shown to play an important role forka<4, wherek is the wave number,a is the radius of the cylinder, compared to the results obtained by Geronicolas (1977) for the slab geometry.     

The Venus ionosphere at grazing incidence of solar radiation: Transport of plasma to the night ionosphere

Using a quasi-two-dimensional model of the Venus ionosphere, we calculated the ion number densities and horizontal ion bulk velocities expected for a range of solar zenith angles near the terminator (80 to 100°), and compared them with data obtained from the Pioneer Venus Orbiter retarding potential analyzer. The calculated ion bulk velocity arises entirely from the solar EUV-induced plasma pressure gradient and has a magnitude consistent with observations; ionization by suprathermal electrons is neglected in those computations. We find that while photoionization is the dominant source of ionospheric plasma for solar zenith angles less than 92°, plasma transport from the dayside is the dominant plasma source for solar zenith angles greater than 95°. We also show that the main nightside plasma peak at approximately 140 km altitude is of the F₂ type (i.e., is diffusion controlled). Its altitude and shape are thus quite insensitive to the altitude of the ion source.     

Role of satellite remote sensing for monitoring of surface water resources in an arid environment

Abstract

Water bodies up to 0.9 ha surface area, which are indistinguishable by Landsat Multispectral Scanner (MSS) due to the latter's poor spatial resolution of 80 m, can be identified and mapped reliably and reasonably within ±10% accuracy by Landsat Thematic Mapper (TM) false colour composite because of its higher spectral and spatial resolution of 30 m. Comparative study of Landsat TM and the Survey of India topographical maps revealed reductions in the water surface and drainage basin areas up to 1.8 to 2.4 and 6.0 to 8.0 times, respectively, over a period of 28 years (1958–1986) due to the biotic interference resulting in desertification in the large adjoining areas.