Evolution of the Dok Do seamounts,Ulleung Basin,East Sea: constraints based on the reconstruction of virtual geomagnetic poles using paleomagnetic data     

Chang Hwan Kim  Chan Hong Park  Eui Young Jeong  Jong Sun Hwang  Young Tak Ko 《Geo-Marine Letters》2009,29(3):161-169

In the Ulleung Basin, East Sea, the Dok Do seamount group comprises Dok Do (Dok Island), consisting of very small islets/rocks and a large submerged volcanic edifice, and two voluminous tablemounts, Simheungtaek and Isabu. We attempted to reconstruct the evolution of these seamounts, using virtual geomagnetic poles (VGPs) determined by the least-squares and the seminorm magnetization methods, with 1,500 m upward continued magnetic anomalies. The VGPs of Dok Do with normal dipole anomaly, and of Simheungtaek with normal dipole anomaly are located near the present magnetic pole. The VGP of Isabu with normal dipole anomaly is located at low latitude, presumably due to overprints of reversals in the Tertiary, and the distortion of magnetization and structures associated with volcanism after its formation. In contrast to the tablemounts, magnetic anomalies over Dok Do are a combination of both normal polarity and reversed polarity dipoles in the northern hemisphere, indicating that Dok Do has had at least two major eruptions, one during normal and another during reversed polarity intervals. From these results, and information on the ages of the seamounts (either published radiometric ages of subaerial volcanic rocks, or ages reconstructed in terms of reported elastic thickness incorporated into an existing cooling plate model), we tentatively propose that (1) Isabu formed first, during a normal polarity interval after the opening of the East Sea had ceased; (2) this was followed by an initial and subsequent large eruption of Dok Do during a normal polarity and a reversed polarity interval after about 5 Ma; and (3) the formation of Simheungtaek occurred in between that of Isabu and Dok Do in a normal polarity interval. The pattern of normal/reversed magnetization is not inconsistent with the geomagnetic polarity timescale for at least the last 5 Ma. Nevertheless, precise ages of formation would need verification by additional geophysical/geochemical constraints. Evaluating various possible models explaining the successive formation of the Dok Do seamounts, we currently favor fracturing and volcanism related to compression-induced weakening of the extensional field from the late Miocene to Pliocene after the opening of the East Sea.  相似文献   

Eclogite and garnet pyroxenite from Stor Jougdan,Seve Nappe Complex,Sweden: implications for UHP metamorphism of allochthons in the Scandinavian Caledonides          下载免费PDF全文

I. Klonowska  M. Janák  J. Majka  N. Froitzheim  K. Kośmińska 《Journal of Metamorphic Geology》2016,34(2):103-119

Ultrahigh‐pressure metamorphism (UHPM) has recently been discovered in far‐travelled allochthons of the Scandinavian Caledonides, including finding of diamond in the Seve Nappe Complex. This UHPM of Late Ordovician age is older and less recognized than that in the Western Gneiss Region of southwestern Norway, which was related to terminal collision between Baltica and Laurentia. Here we report new evidence of UHPM in the Lower Seve Nappe, recorded by eclogite and garnet pyroxenite from the area of Stor Jougdan in northern Jämtland, central Sweden. Peak‐metamorphic assemblage of eclogite, garnet + omphacite + phengite + rutile + coesite? yields P–T conditions of 2.8–4.0 GPa and 750–900 °C, constrained by conventional geothermobarometry and thermodynamic modelling in the NCKFMTASH system. The prograde metamorphic evolution of the eclogite is inferred from inclusions of zoisite and amphibole in garnet, which are stable at lower pressure, whereas the retrograde evolution is recorded by formation of diopsidic clinopyroxene + plagioclase symplectites after omphacite, growth of amphibole replacing these symplectites, and of titanite around rutile. In garnet pyroxenite the peak‐metamorphic assemblage consists of garnet + orthopyroxene + clinopyroxene + olivine. P–T conditions of 2.3–3.8 GPa and 810–960 °C have been derived based on the conventional geothermobarometry and thermodynamic modelling in the CFMASH and CFMAS systems. Retrograde evolution has been recognized from replacement of pyroxene and garnet by amphibole. The results show that eclogite was metamorphosed during deep subduction of continental crust, most probably derived from the continental margin of Baltica, whereas the origin and tectonic setting of the garnet pyroxenite is ambiguous. The studied pyroxenite/peridotite of Baltican subcontinental affinity could have been metamorphosed as a part of the subducting plate and exhumed due to the downward extraction of a forearc lithospheric block.  相似文献   

Asian Dust effects on Total Suspended Particulate (TSP) compositions at Gosan in Jeju Island, Korea   总被引：2，自引：0，他引：2  

Chang-Hee Kang  Won-Hyung Kim  Hee-Jung Ko  Sang-Bum Hong   《Atmospheric Research》2009,94(2):345-355

The compositions of TSP between AD and NAD storm periods were compared to study their long-term variations and chemical characteristics. TSP samples were collected at Gosan site in Jeju Island of Korea from February to May of 1992–2004. The major ionic and elemental species of TSP aerosols were analyzed. During AD periods, the concentrations of crust components (nss-Ca²⁺, Al, Fe, Ca, Mg, Ba, Sr, Ti) increased remarkably, and the concentrations of anthropogenic components (nss-SO₄²⁻, NO₃⁻, S, Zn, Pb, Cr, Ni, Cd), with the exception of NH₄⁺, increased weakly. The concentration ratios of all major components between AD and NAD periods showed ranges from 1.2 to 8.5, except for NH₄⁺. The slope of the linear regression indicated that the contribution of CO₃²⁻ may have comprised up to 17% of the total anions. Our results suggested that the AD storm greatly influenced TSP compositions. Linear regression analyses indicated that NH₄⁺ was not correlated with NO₃⁻, but highly correlated with nss-SO₄²⁻ during both periods. The nss-SO₄²⁻ was also correlated with NH₄⁺, K⁺, nss-Mg²⁺, and nss-Ca²⁺ during both periods. Interestingly, NO₃⁻ was associated with nss-Ca²⁺ and nss-Mg²⁺ during AD periods. Of the metal elements, Fe, Ca, Mg, Ti, Mn, Ba, Sr, V, and Co were highly correlated with Al during both periods, signifying that these metals were mostly originated from soils.  相似文献   

Climate change impacts on dryland cropping systems in the Central Great Plains,USA     

Jonghan Ko  Lajpat R. Ahuja  S. A. Saseendran  Timothy R. Green  Liwang Ma  David C. Nielsen  Charles L. Walthall 《Climatic change》2012,111(2):445-472

Agricultural systems models are essential tools to assess potential climate change (CC) impacts on crop production and help guide policy decisions. In this study, impacts of projected CC on dryland crop rotations of wheat-fallow (WF), wheat-corn-fallow (WCF), and wheat-corn-millet (WCM) in the U.S. Central Great Plains (Akron, Colorado) were simulated using the CERES V4.0 crop modules in RZWQM2. The CC scenarios for CO₂, temperature and precipitation were based on a synthesis of Intergovernmental Panel on Climate Change (IPCC 2007) projections for Colorado. The CC for years 2025, 2050, 2075, and 2100 (CC projection years) were super-imposed on measured baseline climate data for 15–17 years collected during the long-term WF and WCF (1992–2008), and WCM (1994–2008) experiments at the location to provide inter-annual variability. For all the CC projection years, a decline in simulated wheat yield and an increase in actual transpiration were observed, but compared to the baseline these changes were not significant (p > 0.05) in all cases but one. However, corn and proso millet yields in all rotations and projection years declined significantly (p < 0.05), which resulted in decreased transpiration. Overall, the projected negative effects of rising temperatures on crop production dominated over any positive impacts of atmospheric CO₂ increases in these dryland cropping systems. Simulated adaptation via changes in planting dates did not mitigate the yield losses of the crops significantly. However, the no-tillage maintained higher wheat yields than the conventional tillage in the WF rotation to year 2075. Possible effects of historical CO₂ increases during the past century (from 300 to 380 ppm) on crop yields were also simulated using 96 years of measured climate data (1912–2008) at the location. On average the CO₂ increase enhanced wheat yields by about 30%, and millet yields by about 17%, with no significant changes in corn yields.  相似文献   

Quantification of the saturation degree of nonaqueous phase liquid in the vadose zone using hydrocarbon partitioning tracers   总被引：1，自引：1，他引：0  

Giho Park  Sanghyun Jee  Seokoh Ko 《Environmental Earth Sciences》2009,59(3):511-518

Partitioning tracer tests, as an alternative to the core sampling method, were conducted to quantify the degree of saturation of water and nonaqueous phase liquids (NAPL) in the vadose zone. Hydrocarbon gases, which have less effect on global warming than conventional tracers, were used as partitioning tracers. Column tests using CH₄, C₃H₅, and C₄H₁₀ as non-partitioning and partitioning tracers were performed to determine the retardation factor and partition coefficient of the tracer into water and NAPL. The retardation factors of these tracers were estimated to be in the range of 1.0–7.0 based on breakthrough curves of the tracers. The partition coefficient of C₃H₅ to water and diesel phase was calculated to be 0.57 and 8.45, respectively. For a heavier tracer, C₄H₁₀, the partition coefficient to the water and diesel phases was 1.2 and 40.5, respectively. The average value of water and diesel saturation estimated from column tests agreed well with known values in unsaturated soil. A residence time longer than 7.5 h within soil pores was found to provide local equilibrium partitioning of the tracer to the diesel phase. The concentration of tracer had no effect on the partitioning process.  相似文献   

Geology,stratigraphy and palaeoenvironmental evolution of the Stephanorhinus kirchbergensis-bearing Quaternary palaeolake(s) of Gorzów Wielkopolski (NW Poland,Central Europe)     

Artur Sobczyk  Ryszard K. Borówka  Janusz Badura  Renata Stachowicz-Rybka  Julita Tomkowiak  Anna Hrynowiecka  Joanna Sławińska  Michał Tomczak  Mateusz Pitura  Mariusz Lamentowicz  Piotr Kołaczek  Monika Karpińska-Kołaczek  Dariusz Tarnawski  Marcin Kadej  Piotr Moska  Marek Krąpiec  Krzysztof Stachowicz  Bartosz Bieniek  Krzysztof Siedlik  Małgorzata Bąk  Jan van der Made  Adam Kotowski  Krzysztof Stefaniak 《第四纪科学杂志》2020,35(4):539-558

The sedimentary succession exposed in the Gorzów Wielkopolski area includes Eemian Interglacial (MIS 5e) or Early Weichselian (MIS 5d–e) deposits. The sedimentary sequence has been the object of intense interdisciplinary study, which has resulted in the identification of at least two palaeolake horizons. Both yielded fossil remains of large mammals, alongside pollen and plant macrofossils. All these proxies have been used to reconstruct the environmental conditions prevailing at the time of deposition, as well as to define the geological context and the biochronological position of the fauna. Optically stimulated luminescence dating of the glaciofluvial layers of the GS3 succession to 123.6 ± 10.1 (below the lower palaeolake) and 72.0 ± 5.2 ka (above the upper palaeolake) indicate that the site formed during the Middle–Late Pleistocene (MIS 6 – MIS 5). Radiocarbon-dating of the lacustrine organic matter revealed a tight cluster of Middle Pleniglacial Period (MIS 3) ages in the range of ~41–32 ka cal bp (Hengelo – Denekamp Interstadials). Holocene organic layers have also been found, with ¹⁴C ages within a range of 4330–4280 cal bp (Neolithic). Pollen and plant macrofossil records, together with sedimentological and geochemical data, confirm the dating to the Eemian Interglacial.  相似文献   

Blueschist facies metamorphism in Nordenskiöld Land of west‐central Svalbard     

Karolina Kośmińska  Jarosław Majka  Stanisław Mazur  Michael Krumbholz  Iwona Klonowska  Maciej Manecki  Jerzy Czerny  Maciej Dwornik 《地学学报》2014,26(5):377-386

Recent fieldwork in Nordenskiöld Land, Svalbard's Southwestern Basement Province, has established the presence of high‐pressure (HP) lithologies. They are strongly retrogressed blueschists consisting mainly of garnet and Ca‐amphibole with remnants of ferroglaucophane and phengite. The pressure–temperature (P–T) conditions were estimated using phase equilibrium modelling in the NCKFMMnASHTO system. P–T estimates based on the garnet, phengite and ferroglaucophane compositional isopleths and modelled paragenetic assemblage indicate peak metamorphism at 470–490 °C and 14–18 kbar. These data fall close to the 7–8 °C km^?1 geotherm, which is similar to that from Motalafjella, the only previously known occurrence of blueschists in Svalbard's Caledonides. The newly discovered blueschists could have formed during the early stage of the Caledonian Orogeny and may represent a vestige of missing marginal basins of the western Iapetus developed at the onset of subduction. The likely counterpart to Svalbard's blueschists is the ophiolitic sequence in the Pearya Terrane of northern Ellesmere Island.  相似文献   

Preparation of low water-sorption lightweight aggregates from harbor sediment added with waste glass     

Wei YL  Lin CY  Ko KW  Wang HP 《Marine pollution bulletin》2011,63(5-12):135-140

A harbor sediment is successfully recycled at 1150 °C as low water-absorption lightweight aggregate via addition of waste glass powder. Sodium content in the waste glass is responsible for the formation of low-viscosity viscous phases during firing process to encapsulate the gases generated for bloating pellet samples. Water sorption capacity of the lightweight products can be considerably reduced from 5.6% to 1.5% with the addition of waste glass powder. Low water-absorption property of lightweight products is beneficial for preparing lightweight concrete because the water required for curing the cement would not be seized by lightweight aggregate filler, thus preventing the failure of long-term concrete strength.  相似文献   

Comparison of the geophysical excitations of polar motion from the period: 1980.0–2009.0     

Jolanta Nastula  Małgorzata Paśnicka  Barbara Kołaczek 《Acta Geophysica》2011,59(3):561-577

In this study we compared contributions to polar motion excitation determined separately from each of three kinds of geophysical data: atmospheric pressure, equivalent water height estimated from hydrological models, and harmonic coefficients of the Earth gravity field obtained from Gravity Recovery and Climate Experiment (GRACE). Hydrological excitation function (Hydrological Angular Momentum — HAM) has been estimated from models of global hydrology, based on the observed distribution of surfacewater, snow, ice, and soil moisture. In our considerationwe used several global models of land hydrosphere and models ofAtmospheric Angular Momentum (AAM) and Oceanic Angular Momentum (OAM). All of themwere compared with observed Geodetic Angular Momentum (GAM). The spectra of the following excitation functions of polar motion: GAM, AAM+OAM, AAM+OAM+HAM, GAM-AAM-OAM residual geodetic excitation function, and HAM were computed too. The time variable spectra of geodetic, gravimetric, and the sum of atmospheric, oceanic, and hydrological excitation functions are also presented. Phasor diagrams of the seasonal components of polar motion excitation functions of all HAM excitation functions as well as of two GRACE solutions: Center for Space Research (CSR), Centre National d’Etudes Spatiales/Groupe de Recherche en Geodesie Spatiale (CNES/GRGS) were determined and discussed.  相似文献   

A high-resolution numerical modeling study of the subtidal circulation in the northern South China Sea     

Chapman  D.C. Dong-Shan Ko Preller  R.H. 《Oceanic Engineering, IEEE Journal of》2004,29(4):1087-1104

A high-resolution, regional, numerical-model-based, real-time ocean prediction system for the northern South China Sea, called the Northern South China Sea Nowcast/Forecast System (NSCSNFS), has been used to investigate subtidal mesoscale flows during the time period of the Asian Seas International Acoustic Experiment (ASIAEX) field programs. The dynamics are dominated by three influences; 1) surface wind stress, 2) intrusions of the Kuroshio through Luzon Strait, and 3) the large-scale cyclonic gyre that occupies much of the northern South China Sea. Each component primarily drives currents in the upper ocean, so deep currents are rather weak. Wind stress is especially effective at forcing currents over the shallow China shelf. The Kuroshio intrusion tends to flow westward until it meets the northern edge of the large-scale cyclonic gyre. Together, these currents produce an intense, narrow jet directed northwest toward the continental slope, often in the region of the ASIAEX field programs. Upon reaching the slope, the current splits with part flowing northeastward along the slope and part flowing southwestward, producing large horizontal and vertical shears and making this region dynamically very complicated and difficult to simulate. The Kuroshio intrusion tends to be stronger (weaker) when the northeasterly winds are strong (weak) and the large-scale gyre is farther south (north), consistent with conclusions from previous model studies. At the northern boundary, the model produces a persistent northward flow through Taiwan Strait into the East China Sea. Data assimilation in the NSCSNFS model is shown to dampen the system, extracting energy and causing the entire system to spin down.  相似文献