Mineralogy and geochemistry of metalliferous black slates in the okcheon metamorphic belt, Korea: a metamorphic analogue of black shales in the South China block     

Gi Young Jeong 《Mineralium Deposita》2006,41(5):469-481

Metalliferous black slates, which were locally exploited for their low-quality coal, are distributed in the Late Proterozoic to Paleozoic Okcheon Metamorphic Belt (OMB) of the Korean Peninsula. The mineralogy of the fine matrix is dominated by either quartz–(Ba, V)–mica–graphite or Quartz-Ba-feldspar–graphite. Polycrystalline submillimeter ellipsoids and elongate lenses aligned along foliations and veinlets are scattered through the fine matrix. Both ellipsoids and veinlets include many minor minerals containing rare elements: titanite, apatite, allanite, rutile, polycrase, barite, uraninite, xenotime, armenite, zircon, molybdenite, and sphalerite. Large graphite–apatite ellipsoids (nodules) with widths of several centimeters also occur in the highly carbonaceous black slates. Goldmanite occurs locally as porphyroblasts. The maximum rare element contents are: Ba 9.7%, V 2.04%, Mo 0.13%, U 0.11%, Cr 0.33%, Cu 254 ppm, Ni 479 ppm, Zn 607 ppm, Y 255 ppm, platinum-group element (PGE) + Au 309 ppb, and carbon 57%. The occurrence of the black slates and their elemental abundances suggests that most of the rare elements were accumulated from seawater in an oxygen-poor environment. However, the high Ba content of the OMB black slates indicates some hydrothermal input into an organic-rich basin. Although metamorphism and multiple deformations prevent a direct temporal and spatial correlation, metal abundances and a close association with graphite–apatite nodules and low-quality coal suggest that the OMB black slates are metamorphosed analogues of the Early Cambrian Ba–V deposits hosted by the black shales in the South China Block.  相似文献   

Multiple deformations along the Honam shear zone in southwestern Korea constrained by Rb–Sr dating of synkinematic fabrics: Implications for the Mesozoic tectonic evolution of northeastern Asia     

Chang-Sik Cheong  Weon-Seo Kee  Youn-Joong Jeong  Gi Young Jeong 《Lithos》2006,87(3-4):289-299

The Honam shear zone, dextrally running along the southern margin of the Ogcheon belt, Korea, has drawn much attention in reconstructing the Mesozoic tectonic framework of northeastern Asia. Here we present Rb–Sr data for the middle to southwestern part of the Honam shear zone, in an attempt to directly determine ages of deformation. In the middle part, the younger limit of deformation is constrained to be 162 ± 11 Ma by feldspar–biotite Rb–Sr dating of the deformed Sunchang granodiorite. On the other hand, an early Cretaceous deformation age is estimated for synkinematic fibers in ultramylonites from the southwestern part by two reproducible Rb–Sr errorchrons at 138 ± 4 and 139 ± 23 Ma. This deformational time scale is consistent with earlier interpretations based on field evidence, magnetic susceptibility data, and age data for Jurassic plutons within the shear zone. Our data demonstrate that the Honam shear zone is not a Permian to Triassic tectonic feature related to the Chinese continental collision.  相似文献   

The role of temperature in drought projections over North America   总被引：1，自引：0，他引：1  

Dae Il Jeong  Laxmi Sushama  M. Naveed Khaliq 《Climatic change》2014,127(2):289-303

The effects of future temperature and hence evapotranspiration increases on drought risk over North America, based on ten current (1970–1999) and ten corresponding future (2040–2069) Regional Climate Model (RCM) simulations from the North American Regional Climate Change Assessment Program, are presented in this study. The ten pairs of simulations considered in this study are based on six RCMs and four driving Atmosphere Ocean Coupled Global Climate Models. The effects of temperature and evapotranspiration on drought risks are assessed by comparing characteristics of drought events identified on the basis of Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspration Index (SPEI). The former index uses only precipitation, while the latter uses the difference (DIF) between precipitation and potential evapotranspiration (PET) as input variables. As short- and long-term droughts impact various sectors differently, multi-scale (ranging from 1- to 12-month) drought events are considered. The projected increase in mean temperature by more than 2 °C in the future period compared to the current period for most parts of North America results in large increases in PET and decreases in DIF for the future period, especially for low latitude regions of North America. These changes result in large increases in future drought risks for most parts of the USA and southern Canada. Though similar results are obtained with SPI, the projected increases in the drought characteristics such as severity and duration and the spatial extent of regions susceptible to drought risks in the future are considerably larger in the case of SPEI-based analysis. Both approaches suggest that long-term and extreme drought events are affected more by the future increases in temperature and PET than short-term and moderate drought events, particularly over the high drought risk regions of North America.  相似文献   

A case study of mesoscale convective band (MCB) development and evolution along a quasi-stationary front     

Daeun JEONG  Ki-Hong MIN  Gyuwon LEE  Kyung-Eak KIM 《大气科学进展》2014,31(4):901-915

This paper presents a case study of mesoscale convective band （MCB） development along a quasi-stationary front over the Seout metropolitan area.The MCB,which initiated on 1500 UTC 20 September 2010 and ended on 1400 UTC 21 September 2010,produced a total precipitation amount of 259.5 mm.The MCB development occurred during a period of tropopause folding in the upper level and moisture advection with a low-level jet.The analyses show that the evolution of the MCB can be classified into five periods：（1） the cell-forming period,when convection initiated; （2） the frontogenetic period,when the stationary front formed over the Korean peninsula; （3） the quasi-stationary period,when the convective band remained over Seoul for 3 h; （4） the mature period,when the cloud cover was largest and the precipitation rate was greater than 90 mm h-1; and （5） the dissipating period,when the MCB diminished and disappeared.The synoptic,thermodynamic,and dynamic analyses show that the MCB maintained its longevity by a tilted updraft,which headed towards a positive PV anomaly.Precipitation was concentrated under this area,where a tilted ascending southwesterly converged with a tilted ascending northeasterly,at the axis of cyclonic rotation.The formation of the convective cell was attributed in part by tropopause folding,which enhanced the cyclonic vorticity at the surface,and by the low-level convergence of warm moist air and upperlevel divergence.The southwesterly flow ascended in a region with high moisture content and strong relative vorticity that maintained the development of an MCB along the quasi-stationary front.  相似文献   

Aragonite undersaturation in Gwangyang Bay,South Korea: Effects of fresh water input     

Dongseon Kim  Eun-Jin Yang  Seung Ho Baek  Kyung-Hee Kim  Jin-Hyun Jeong  Young-Ok Kim 《Ocean Science Journal》2014,49(3):223-230

Dissolved inorganic carbon (DIC) and alkalinity were precisely measured for surface and bottom waters in Gwangyang Bay, Korea, during the four seasons to assess seasonal variations of aragonite saturation state (Ω_arag). Both the surface and bottom waters were undersaturated with respect to aragonite during summer but were supersaturated during the other seasons. The summertime undersaturation of the surface waters with respect to aragonite may have been a result of the dilution effect caused by higher seasonal river runoff. In the bottom waters, the average DIC concentration increased by 40.6 μmol kg^?1 from spring to summer, while the average alkalinity decreased by 74.7 μeq kg^?1. As a result, the alkalinity/DIC ratio decreased from 1.07 in spring to 1.01 in summer and pH also decreased from 7.91 to 7.48, which resulted in the summertime undersaturation of the bottom waters.  相似文献   

Decentralized and coordinate-free computation of critical points and surface networks in a discretized scalar field     

Myeong-Hun Jeong  Matt Duckham  Allison Kealy  Harvey J. Miller  Andrej Peisker 《International journal of geographical information science》2014,28(1):1-21

This article provides a decentralized and coordinate-free algorithm, called decentralized gradient field (DGraF), to identify critical points (peaks, pits, and passes) and the topological structure of the surface network connecting those critical points. Algorithms that can operate in the network without centralized control and without coordinates are important in emerging resource-constrained spatial computing environments, in particular geosensor networks. Our approach accounts for the discrepancies between finite granularity sensor data and the underlying continuous field, ignored by previous work. Empirical evaluation shows that our DGraF algorithm can improve the accuracy of critical points identification when compared with the current state-of-the-art decentralized algorithm and matches the accuracy of a centralized algorithm for peaks and pits. The DGraF algorithm is efficient, requiring O(n) overall communication complexity, where n is the number of nodes in the geosensor network. Further, empirical investigations of our algorithm across a range of simulations demonstrate improved load balance of DGraF when compared with an existing decentralized algorithm. Our investigation highlights a number of important issues for future research on the detection of holes and the monitoring of dynamic events in a field.  相似文献   

Global spectral energy distributions of the Large Magellanic Cloud with interstellar dust     

Sungeun Kim  Eunjoo Kwon  Kyoung-Sook Jeong  Kihun Kim  Chiyoung Cho  Eun Jung Chung 《Astrophysics and Space Science》2014,349(1):423-435

The effects of dust on infrared emission vary among galaxies of different morphological types. We investigated integrated spectral energy distributions (SEDs) in infrared and submillimeter/millimeter emissions from the Large Magellanic Cloud (LMC) based on observations from the Herschel Space Observatory (HSO) and near- to mid-infrared observations from the Spitzer Space Telescope (SST). We also used IRAS and WMAP observations to constrain the SEDs and present the results of radiative transfer calculations using the spectrophotometric galaxy model. We explain the observations by using dust models with different grain size distributions in the interstellar medium of the LMC, noting that the LMC has undergone processes that differ from those in the Milky Way. We determined a spectral index and a normalization factor in the range of ?3.5 to ?3.45 with grain radii in the range of 1 nm–300 nm for the silicate grain and 2 nm–1 μm for the graphite grain. The best fit to the observed SED was obtained with a spectral index of ?3.47, similar to the value derived by Piovan et al. (Mon. Not. R. Astron. Soc. 366(3):923, 2006a). The grain size distribution is described using a power law but with a break that is introduced below a _b , where a larger exponent is used. Changing the graphite grain size distribution significantly changed the SED pattern within the observational uncertainties. Based on the SED fits to the observations from submillimeter wavelengths to infrared radiation from the LMC using GRASIL (Silva et al., Astrophys. J. 509(1):103, 1998), we obtained a reasonable set of parameter values in chemical and geometric space together with the grain size distributions (Weingartner and Draine, Astrophys. J. 548(1):296, 2001) and a modified MRN model with the LMC extinction curve (Piovan et al., Mon. Not. R. Astron. Soc. 366(3):923, 2006a). For a given set of parameters including the disc scale height, synthesis of the starlight spectrum, optical depth, escape time scale, dust model, and star formation efficiency, the adopted dust-to-gas ratio for modeling the observed SEDs, ～1/300 (from the literature) yields a reasonable fit to the observed SEDs and similar results with the metallicity of the LMC as those reported in Russell and Bessell (Astrophys. J. Suppl. Ser. 70:865, 1989). The dust-to-gas ratios that are given as the metallicity caused the variation in the model fits. The difference mainly appears at the wavelengths near 100 μm.  相似文献   

A subagging regression method for estimating the qualitative and quantitative state of groundwater     

Jina Jeong  Eungyu Park  Weon Shik Han  Kue-Young Kim 《Hydrogeology Journal》2017,25(5):1491-1500

A subsample aggregating (subagging) regression (SBR) method for the analysis of groundwater data pertaining to trend-estimation-associated uncertainty is proposed. The SBR method is validated against synthetic data competitively with other conventional robust and non-robust methods. From the results, it is verified that the estimation accuracies of the SBR method are consistent and superior to those of other methods, and the uncertainties are reasonably estimated; the others have no uncertainty analysis option. To validate further, actual groundwater data are employed and analyzed comparatively with Gaussian process regression (GPR). For all cases, the trend and the associated uncertainties are reasonably estimated by both SBR and GPR regardless of Gaussian or non-Gaussian skewed data. However, it is expected that GPR has a limitation in applications to severely corrupted data by outliers owing to its non-robustness. From the implementations, it is determined that the SBR method has the potential to be further developed as an effective tool of anomaly detection or outlier identification in groundwater state data such as the groundwater level and contaminant concentration.  相似文献   

A numerical study on deblending of land simultaneous shooting acquisition data via rank-reduction filtering and signal enhancement applications     

Woodon Jeong  Constantinos Tsingas  Mohammed S. Almubarak 《Geophysical Prospecting》2020,68(6):1742-1757

We propose a workflow of deblending methodology comprised of rank-reduction filtering followed by a signal enhancing process. This methodology can be used to preserve coherent subsurface reflections and at the same time to remove incoherent and interference noise. In pseudo-deblended data, the blending noise exhibits coherent events, whereas in any other data domain (i.e. common receiver, common midpoint and common offset), it appears incoherent and is regarded as an outlier. In order to perform signal deblending, a robust implementation of rank-reduction filtering is employed to eliminate the blending noise and is referred to as a joint sparse and low-rank approximation. Deblending via rank-reduction filtering gives a reasonable result with a sufficient signal-to-noise ratio. However, for land data acquired using unconstrained simultaneous shooting, rank-reduction–based deblending applications alone do not completely attenuate the interference noise. A considerable amount of signal leakage is observed in the residual component, which can affect further data processing and analyses. In this study, we propose a deblending workflow via a rank-reduction filter followed by post-processing steps comprising a nonlinear masking filter and a local orthogonalization weight application. Although each application shows a few footprints of leaked signal energy, the proposed combined workflow restores the signal energy from the residual component achieving significantly signal-to-noise ratio enhancement. These hierarchical schemes are applied on land simultaneous shooting acquisition data sets and produced cleaner and reliable deblended data ready for further data processing.  相似文献