Permo-Triassic high-pressure metamorphism in the central western Korean Peninsula,and its link to Paleo-Tethyan Ocean closure: Key issues revisited

Permo-Triassic high-pressure(HP) mafic granulites, together with the Bibong retrogressed eclogite,preserved along the central western Korean Peninsula provide important insights into the Late Permian to Triassic collisional orogeny in northeast Asia. The metamorphic pressureetemperatureetime(P-T-t)paths of these rocks, however, remain poorly constrained and even overestimated, owing to outdated geothermobarometers and inaccurate isopleth techniques. Here we evaluate the metamorphic Pe T conditions of Triassic HP mafic granulites including those in Baekdong, Sinri and Daepan and the Bibong Triassic retrogressed eclogite in the Hongseong area, and the Permo-Triassic Samgot mafic granulite in the Imjingang Belt of the central western Korean Peninsula through the application of modern phase equilibria techniques. The Baekdong and Samgot mafic granulites and the Bibong retrogressed eclogite yield a range of 12.0 -16.0 kbar and 800 -900℃, representing HP granulite facies conditions. The Sinri and Daepan granulites from the Hongseong area show relatively lower grade metamorphic conditions between HP granulite and normal granulite facies, and are characterized by sub-isothermal decompression during exhumation. The similarities in the metamorphic ages and the post-collisional igneous activity from the central western Korean Peninsula indicate that the Triassic ages represent the retrograde stage of the metamorphic Pe T paths. In contrast, the Late Permian metamorphic ages, which are older than protolith ages of the post-collisional igneous rocks, correspond to the possible prograde stage of metamorphism. The P-T-t paths presented in this paper, together with the metamorphic ages and post-orogenic igneous events reported from these areas suggest trace of the subduction, accretion and exhumation history, and indicate a tectonic linkage among the northeast Asian continents during the Paleo-Tethyan Ocean closure.     

论《孔疏》之“兴”

通过对《孔疏》标“兴”之特点与《毛诗传》《郑笺》标“兴”之特点比较分析,提出《孔疏》之标“兴”主要着眼于“兴”与作品主旨之间的关系,而没有特别注重标“兴”的位置。这些特点使得《孔疏》之“兴”开始从政治化逐渐转向文学化。     

Model updating method for substructure pseudo‐dynamic hybrid simulation

Substructure hybrid simulation has been actively investigated and applied to evaluate the seismic performance of structural systems in recent years. The method allows simulation of structures by representing critical components with physically tested specimens and the rest of the structure with numerical models. However, the number of physical specimens is limited by available experimental equipment. Hence, the benefit of the hybrid simulation diminishes when only a few components in a large system can be realistically represented. The objective of the paper is to overcome the limitation through a novel model updating method. The model updating is carried out by applying calibrated weighting factors at each time step to the alternative numerical models, which encompasses the possible variation in the experimental specimen properties. The concept is proposed and implemented in the hybrid simulation framework, UI‐SimCor. Numerical verification is carried out using two‐DOF systems. The method is also applied to an experimental testing, which proves the concept of the proposed model updating method. Copyright © 2013 John Wiley & Sons, Ltd.     

Multi-proxy Stratigraphy and Paleoceanographic Variations in Sediment from the Korea Plateau,East Sea (Japan Sea), Over the Last 500 kyr

Ocean Science Journal - High-resolution geochemical measurements were performed on core E09-08, which was taken from the top flat area of the Korea Plateau in the East Sea (Japan Sea). Based on...     

Metamorphic K-Feldspar in Low-grade Metasediments from the Ogcheon Metamorphic Belt in South Korea

Metamorphic K-feldspar was found in the low-grade pelitic rocks from the Ogcheon metamorphic belt in South Korea. It occurs as extremely fine-grained crystals (5-15 mm in width and 15-25 mm in length) closely associated with fine-grained muscovite and biotite. Their micro structural relations by X-ray mapping analyses using an electron-probe microanalyzer strongly suggest that K-feldspar has grown directly from the matrix phases as a stable phase coexisting with muscovite and biotite during the Ogcheon metamorphism. The phengite component in muscovite indicates about 4.2 kbar at 400°C, suggesting intermediate P/T type of metamorphism. Muscovite separates of two size fractions, 2-4 and 4-8 mm, give K-Ar ages of 153.4±3.3 and 156.7±3.4 Ma, respectively. The biotite separate is 156.5±3.3 Ma in age. Coarse-grained biotite crystal (ca. 0.5 mm) often occurs and it was analyzed by ⁴⁰Ar/³⁹Ar method using a laser probe step heating technique. It gives a plateau age of 158.2±0.5 Ma that is the same as the K-Ar muscovite and biotite ages. These data, including the previous works, suggest that intermediate P/T type of Ogcheon metamorphic belt exhumed in Middle Jurassic with the dextral strike-slip fault movement.     

Volatile organic sulfur compounds as biomarkers complementary to methane: Infrared absorption spectroscopy of CH3SH enables insitu measurements on Earth and Mars

As universal products of biological processes, volatile organic sulfur compounds such as methyl mercaptan (CH₃SH) may be essential in the search for signs of life on Mars and in exoplanet atmospheres. Methyl mercaptan is implicated in the origin of life at sites of low-temperature hydrothermal activity driven by serpentinization. Serpentinization may occur on Mars, in icy satellite oceans, and in other small wet bodies to a greater extent than on Earth, with important implications for life. We characterized absorption features in pure laboratory sample spectra of CH₃SH using the Carbon Isotope Laser Spectrometer (CILS), an infrared $(3.27\mathrm{\mu }\mathrm{m})$ tunable diode laser spectrometer with capabilities nearly identical to those of the Tunable Laser Spectrometer (TLS) instrument on the Mars Science Laboratory. The molecular species proves detectable by CILS and TLS at the sensitivities approaching the level of parts per trillion with pre-concentration. These measurements demonstrate the possibility for detection of methyl mercaptan, with implications for its possible use as an in situ biosignature for Earth-based and extraterrestrial exploration.     

High resolution investigation of the 7 μm region of the ethane spectrum

Building upon previous studies, we re-investigated the ethane spectrum between 1330 and 1610 cm^?1 by combining unapodized spectra obtained at room temperature with a Bruker Fourier transform spectrometer (FTS) in Brussels and at 131 K with a Bruker FTS in Pasadena. The maximum optical path differences (MOPD) of the two datasets were 450 and 323.7 cm, corresponding to spectral resolutions of 0.0020 and 0.0028 cm^?1, respectively. Of the 15,000 lines observed, over 4592 transitions were assigned to the ν₆ (at 1379 cm^?1), ν₈ (at 1472 cm^?1), ν₄+ν₁₂ (at 1481 cm^?1) and 2ν₄+ν₉ (at 1388 cm^?1) bands, and another 1044 transitions were located for the ν₄+ν₈?ν₄ hot band (at 1472 cm^?1). Our new analysis included an improved implementation of the Hamiltonian calculation needed to interpret the complex spectral structures caused by numerous interactions affecting these four modes of vibration. From these results, we created the first line-by-line database containing the molecular parameters for over 20,000 ¹²C₂H₆ transitions at 7 μm.     

Buoyant boundary layer flows- an analogy to the Ekman spiral

Abstract

Flow details inside the buoyant boundary layer in the heat-up process of a contained, stably stratified, fluid are presented. Numerical solutions were obtained for the heatup problem in a cylinder considered by Sakurai and Matsuda (1972). By plotting the scaled vertical velocity W versus the scaled temperature θ as functions of the normal distance from the sidewall, the precise shape of the buoyant layer spiral is constructed. The analogy between this spiral and the Ekman spiral in rotating fluids is apparent. As the Rayleigh number Ra increases, the magnitude of the scaled vertical velocity increases substantially, but the scaled temperature does not vary appreciably. The buoyant layer thickness is determined by measuring the zero-crossing normal distance for the vertical velocity. The buoyant layer suction increases significantly as Ra increases. The effects of vertical level and of time on the qualitative behavior of buoyant layer flows are found to be small. The buoyant layer flows decay over the heat-up time scale t _n ; t _h characterizes the time span over which the overall adjustment process in the inviscid interior region is accomplished. This work clarifies that the analogy between heat-up and spin-up, which has been known to exist in the main body of inviscid fluid, applies equally well to the boundary layer regions.     

Pushover analysis of reinforced concrete frames considering shear failure at beam-column joints

Since most current seismic capacity evaluations of reinforced concrete(RC) frame structures are implemented by either static pushover analysis(PA) or dynamic time history analysis,with diverse settings of the plastic hinges(PHs) on such main structural components as columns,beams and walls,the complex behavior of shear failure at beam-column joints(BCJs) during major earthquakes is commonly neglected.This study proposes new nonlinear PA procedures that consider shear failure at BCJs and seek to assess the actual damage to RC structures.Based on the specifications of FEMA-356,a simplified joint model composed of two nonlinear cross struts placed diagonally over the location of the plastic hinge is established,allowing a sophisticated PA to be performed.To verify the validity of this method,the analytical results for the capacity curves and the failure mechanism derived from three different full-size RC frames are compared with the experimental measurements.By considering shear failure at BCJs,the proposed nonlinear analytical procedures can be used to estimate the structural behavior of RC frames,including seismic capacity and the progressive failure sequence of joints,in a precise and effective manner.