Geology of the Skallen Region, Lutzow-Holmbukta, East Antarctica (Earth Sciences)

Results of the field surveys in the Skallen region during 1969-1970 are summarized with descriptions of stratigraphy and considerations on geotectonic history of the region. Field and aerial photographs, route maps, and field descriptions are also given. Basement rocks of the Skallen region are metamorphic rocks consisting of paragneisses, brown gneisses, marble, quartzite, and metabasite, and plutonic rocks consisting of charnockitic rocks, garnet gneissose granite, and pink granites. The metamorphic rocks comprise four stratigraphic units, namely, Skallen brown gneiss formation, Skallen lower calcareous formation, Skallen siliceous formation, and Skallen upper calcareous formation, in ascending order. These formations belong to the Skallen group, the total thickness of which, including most of the intercalated plutonic rocks which are transformed in situ from the metamorphites, is over 1500 meters. All the formations are conformable to each other, except the lowermost Skallen brown gneiss formation which is tectonically separated from other formations. The fundamental geologic structure of the region is nappe and associated isoclinal folds with gently and easterly plunging axes and axial planes dipping north ; hence a part of the stratigraphic column of the present region is doubled. Some other folds or fractures were found, being overprinted by or superposing on the main nappe structure. The geotectonic history of the Skallen region is as follows from older to younger : moderately plunging recumbent anticline (nappe) -easterly and gently plunging recumbent anticline (nappe) -east-northeasterly or west-southwesterly and gently plunging open folding-east-southeasterly plunging minor folding-easterly gentle folding and northeasterly open synform-conjugate set of west-northwesterly and northeasterly fractures. The change of stress field from older N-S compressional to younger E-W compressional is estimated. A granulite facies metamorphism resulting in the formation of the metamorphites is considered to be synchronous with both or either of the recumbent anticlines, a dynamic metamorphism to take place during the earlier nappe, formation of charnockite to be synchronous with or slightly later than the subhorizontal recumbent anticline and partly to prolong until the completion of the plunging open folding, intrusion of pink granites, which indicate amphibolite facies conditions and the radiometric age of which is already obtained as about 500 m. y., to be around the stage of the gentle folding. Neither metamorphic nor plutonic effect was found in relation to the fractures

Geology of the Region around Botnneset, East Antarctica (Earth Sciences)

Geological observations of the Botnneset region, and mineral and chemical compositions of the rock samples collected from the region are presented in this article. The structural and metamorphic history of the region is summarized as follows. First episode : Development of the foldings, probably of an isoclinal type. Metabasites and paragneisses may have been formed during this episode, probably under granulite facies conditions. Second episode : Development of the foliation structure. Formation of brown gneissose granodiorite (charnockite) under earlier granulite and later amphibolite facies conditions. E-W asymmetric folding is considered to have occurred late in this episode. Third episode : Formation of pink gneissose granites and migmatization over wide areas under amphibolite facies conditions. N-S trending open folding is probably the prevailing tectonics. Fourth episode : Development of greenschist facies or a slightly lower metamorphic conditions over wide areas of the region. This is probably attributed to the effect of the late activity of the pink gneissose granites of the third episode

Traversing the Himalayan Orogen 2019 - Report of the 8th Student Himalayan exercise Tour

The Tenth Symposium on Polar Science/Ordinary sessions: [OG] Polar Geosciences, Wed. 4 Dec. / Entrance Hall (1st floor), National Institute of Polar Researc

Black Hole Formation and Explosion from Rapidly Rotating Very Massive Stars

We explore the formation process of a black hole (BH) through the pair-instability collapse of a rotating Population III very massive star in axisymmetric numerical relativity. As the initial condition, we employ a progenitor star which is obtained by evolving a rapidly rotating zero-age main sequence (ZAMS) star with mass $320M_\odot$ until it reaches a pair instability region. We find that for such rapidly rotating model, a fraction of the mass, $\sim 10M_\odot$, forms a torus surrounding the remnant BH of mass $\sim 130M_\odot$ and an outflow is driven by a hydrodynamical effect. We also perform simulations, artificially reducing the initial angular velocity of the progenitor star, and find that only a small or no torus is formed and no outflow is driven. We discuss the possible evolution scenario of the remnant torus for the rapidly rotating model by considering the viscous and recombination effects and show that if the energy of $\sim 10^{52}$ erg is injected from the torus to the envelope, the luminosity and timescale of the explosion could be of the orders of $10^{43}$ erg/s and yrs, respectively. We also point out the possibility for observing gravitational waves associated with the BH formation for the rapidly rotating model by ground-based gravitational-wave detectors.Comment: 19 pages, 16 figures, submitted to Ap

A Method for Estimating Non-Stationary Variation of Soil Rigidity During Strong Motions

This paper provides a method for estimating the non-stationary variations of rigidity and damping of soils related intimately to the non-linear earthquake responses of ground. This method uses the concept of the “Complex Envelope” to inversely estimate soil rigidity and damping from the time histories of stress and strain induced in soils. It is quite different from the conventional method, which uses graphical technique for the stress-strain orbit, in the point of quantitatively estimating the time-dependent variations of soil rigidity and damping. The validity of the method is first discussed using theoretical derivations and numerical simulations. It is then applied to the down-hole array records of strong motions obtained at Port Island during the 1995 Kobe Earthquake, Japan. The analyzed results showed that some extreme reductions of soil rigidity occurred in the superficial layers during the mainshock of the earthquake, depending strongly on strain behaviors

Self-diffusion of water–cyclohexane mixtures in supercritical conditions as studied by NMR and molecular dynamics simulation

The self-diffusion coefficients of water (Dw) and cyclohexane (Dch) in their binary mixtures were determined using the proton pulsed field gradient spin-echo method from medium to low densities in subcritical and supercritical conditions. The density (ρ), temperature (T), and water mole fraction (xw) are studied in the ranges 0.62–6.35 M (M = mol dm−3), 250–400 °C, and 0.109–0.994, respectively. A polynomial fitting function was developed for a scaled value of Ξ = ρDT−1/2 with ρ, T, and xw as variables in combination with a comprehensive molecular dynamics (MD) simulation. The NMR and MD results agree within 5% for water and 6% for cyclohexane, on average. The differences between Dw and Dch in the dependence on ρ, T, and xw are characterized by the activation energy Ea and the activation volume ΔV‡Ξ expressed by the scaled fitting function. The decrease in the ratio Dw/Dch and the increase in the Ea of water with increasing xw are related to the increase in the number of hydrogen bonds (HBs). The Dw value for a solitary water molecule at a low xw is controlled by the solvation shell, most of which is occupied by nonpolar cyclohexane molecules that provide less friction as a result of weaker interactions with water. A microscopic diffusion mechanism is discussed based on an analysis of the HB number as well as the first-peak height of the radial distribution functions that are taken as measures of the potential of the mean field controlling self-diffusion

Neutrino-driven explosions of ultra-stripped type Ic supernovae generating binary neutron stars

We study explosion characteristics of ultra-stripped supernovae (SNe), which are candidates of SNe generating binary neutron stars (NSs). As a first step, we perform stellar evolutionary simulations of bare carbon-oxygen cores of mass from 1.45 to 2.0 $M_\odot$ until the iron cores become unstable and start collapsing. We then perform axisymmetric hydrodynamics simulations with spectral neutrino transport using these stellar evolution outcomes as initial conditions. All models exhibit successful explosions driven by neutrino heating. The diagnostic explosion energy, ejecta mass, Ni mass, and NS mass are typically $\sim 10^{50}$ erg, $\sim 0.1 M_\odot$, $\sim 0.01M_\odot$, and $\approx 1.3 M_\odot$, which are compatible with observations of rapidly-evolving and luminous transient such as SN 2005ek. We also find that the ultra-stripped SN is a candidate for producing the secondary low-mass NS in the observed compact binary NSs like PSR J0737-3039.Comment: 9 pages, 8 figures, 2 tables; accepted for publication in MNRA