Geochemical and Sr–Nd isotopic constraints on the petrogenesis of the Goesan monzodiorite pluton in the central Okcheon belt,Korea

The Permian–Triassic high pressure metamorphism and potassic magmatism in central Korea attest to the extension of the Dabie‐Sulu collision belt in central‐eastern China towards the Korean Peninsula and possibly the Japanese Islands. We present major and trace element and Sr–Nd isotope data for a ca. 230 Ma monzodiorite pluton emplaced in the Goesan area, central Okcheon belt, Korea. This pluton shows geochemical features comparable with those of the coeval monzonite–syenite–gabbro–mangerite suite documented recently in the Gyeonggi massif. The metaluminous and alkali–calcic signatures of the Goesan intrusives correspond to the Caledonian‐type post‐orogenic granitoids. The K₂O/Na₂O ratios of all analyzed samples are greater than 1, and are not correlative with their SiO₂ contents. The enrichment of both large‐ion‐lithophile elements and highly compatible elements in the Goesan pluton is probably indicative of metasomatized mantle origin. The elemental fractionation in the source region must have occurred in the distant past, possibly the Paleoproterozoic, to generate significantly negative ε_Nd(t) values (< –16). Chondrite‐normalized rare earth element patterns as well as Rb/Sr and Ba/Rb ranges suggest that the source consists of amphibole‐bearing rocks. Progressive decreases in negative Eu anomaly and Ba, Sr, Ni, Cr and V contents with increasing SiO₂ contents reflect an important role of plagioclase, biotite and hornblende for the fractionation process. Zr is undersaturated in the potassic, metaluminous melt. The initial Sr–Nd isotopic compositions of the samples are correlated with their SiO₂ contents, substantiating a role of crustal assimilation during the magmatic differentiation. The Sr–Nd elemental and isotopic modeling suggests that the Goesan pluton was initially slightly heterogeneous in its isotopic composition, and underwent concurrent assimilation and fractional crystallization. The occurrence of the Goesan pluton provides further evidence corroborating the amalgamation of allochthonous terranes within the Okcheon belt during the Permian–Triassic collisional orogeny.     

Optical dating of hydromagmatic volcanoes on the southwestern coast of Jeju Island, Korea

Jeju Island, the largest Quaternary volcanic island in Korea, has formed mostly since the early Pleistocene, but its latest chronology of volcanism and sedimentation is still poorly constrained. Here we report optically stimulated luminescence (OSL) ages for two hydromagmatic volcanoes on the southwestern coast of Jeju Island, i.e., the Songaksan and Suwolbong tuff rings. The basaltic tuffs of these volcanoes contain abundant quartz sands from underlying marine sedimentary sequences. Two samples collected from the middle part of the Songaksan Tuff yielded highly reproducible quartz single-aliquot regenerative-dose (SAR) OSL ages of 7.0±0.3 ka, providing the first direct age estimate of Holocene volcanism in Jeju Island. The quartz OSL age estimate of 5.1±0.3 ka for the younger reworked basaltic tuff (the Hamori Formation) is comparable with previous radiocarbon and U-series disequilibrium dating of fossil mollusk shells. Two samples from the Suwolbong Tuff show quartz OSL age estimates of 18.3±0.7 and 18.6±0.9 ka, which are identical within error ranges and younger than the quartz OSL age estimate of 23.2±1.0 ka for the underlying Gosan Formation. This study confirms that volcanism and attendant sedimentation were active in Jeju Island until very recently.     

Paleomagnetic records and mineral-magnetic properties of deep-sea sediments in the NW pacific: Paleoenvironmental implication

The paleomagnetic records and mineral-magnetic properties of unconsolidated core sediment from the east Mariana Basin of the western Pacific have been analyzed to trace the time-dependent variations in sedimentary environments. Progressive alternating field demagnetization effectively extracts a stable remanent magnetization showing both normal and reverse polarities. Comparison of successive polarity changes, recorded in the sediment core, with reference magnetic polarity time-scale, reveals that the recovered sediment column was deposited since the late Pliocene. From the sediment age model, calculated sedimentation rate during the late Pliocene was 9.8 times higher than that during the Pleistocene. Considering the oceanic environments and geologic setting in the study area, the anomalous high sediment flux during the late Pliocene was probably caused by enhanced current flows, such as North Equatorial Current, associated with atmospheric circulation as well as by debris flows from adjacent sea mounts. In addition, the systematic variation of mineral-magnetic properties indicates periodical fluxes of coarse and magnetically stable particles, on the fine-grained dominant sedimentary environments. Such influxes, however, would not be related to syn-volcanic activities, because the summits of seamounts were totally blanketed by biogenic Pliocene-Pleistocene sediments. It is, hence, reasonable to interpret that paleomagnetic and mineral-magnetic data probably reflect drastic paleoenvironmental changes at the boundary between the Pliocene and Pleistocene, where strong current and atmospheric circulations decreased.     

Geochemical characterization of the organic matter, pore water constituents and shallow methane gas in the eastern part of the Ulleung Basin, East Sea (Japan Sea)

Abstract Geochemical analyses of sediments, pore water and headspace gas of the piston cores taken from the eastern part of Ulleung Basin of the East Sea (Japan Sea) were carried out to assess the origin of the sedimentary organic matter and interstitial fluid. Several tephra layers within the core are identified as the Ulleung‐Oki (10.1 ka), the Aira‐Tanzawa (23 ka) and the Ulleung‐Yamato (30.9 ka) tephras. With the exception of these volcanic layers, the cores consist predominantly of muddy sediments that contain >0.5% total organic carbon. Atomic C/N ratios and δ¹³C_org values suggest that the organic matter originated from marine algae rather than from land vascular plants, whereas Rock‐Eval pyrolysis suggests that the organic matter is thermally immature and comes from a land vascular plant (Type III). These conflicting results seem to be caused by the heavy oxidization of the marine organic matter. Sulphate concentration profiles of pore waters show strongly linear depletion (r² > 0.97) with sediment depth. The estimated sulphate–methane interface (SMI) depth using the sulphate concentration gradient was nearly 3.5 m below seafloor (mbsf) in the southern part of the study area, and deeper than 6 mbsf in the northern part of the area. The difference in SMI depths is likely associated with the amount of the methane flux. The methane concentration below the SMI in the two southern cores increases rapidly, implying the occurrence of methanogenesis and anaerobic methane oxidation (AMO). In contrast, the two northern cores have a low methane concentration below the SMI. values measured from all cores were in the range of −83.5 to −69.5‰, which suggests that the methane derives from a methanogenic microbe. values become decreased toward SMI, but increased below SMI; therefore, has eventually the minimum value near the SMI. The values are also decreased when the methane concentration is increased. These phenomena support the typical occurrence of AMO in the study area.     

Groundwater nitrate contamination and risk assessment in an agricultural area,South Korea

The nitrate of groundwater in the Gimpo agricultural area, South Korea, was characterized by means of nitrate concentration, nitrogen-isotope analysis, and the risk assessment of nitrogen. The groundwaters belonging to Ca–(Cl + NO₃) and Na–(Cl + NO₃) types displayed a higher average NO₃ ⁻ concentration (79.4 mg/L), exceeding the Korean drinking water standard (<44.3 mg/L NO₃ ⁻). The relationship between δ¹⁸O–NO₃ ⁻ values and δ¹⁵N–NO₃ ⁻ values revealed that nearly all groundwater samples with δ¹⁵N–NO₃ ⁻ of +7.57 to +13.5‰ were affected by nitrate from manure/sewage as well as microbial nitrification and negligible denitrification. The risk assessment of nitrate for groundwater in the study area was carried out using the risk-based corrective action model since it was recognized that there is a necessity of a quantitative assessment of health hazard, as well as a simple estimation of nitrate concentration. All the groundwaters of higher nitrate concentration than the Korean drinking water standard (<44.3 mg/L NO₃ ⁻) belonged to the domain of the hazard index <1, indicating no health hazard by nitrate in groundwater in the study area. Further, the human exposure to the nitrate-contaminated soil was below the critical limit of non-carcinogenic risk.     

Zircon U–Pb geochronology and Hf isotope geochemistry of magmatic and metamorphic rocks from the Hida Belt,southwest Japan

Zircon U–Pb and Hf isotope data integrated in this study for magmatic and metamorphic rocks from the Hida Belt,southwest Japan,lead to a new understanding of the evolution of the Cordilleran arc system along the ancestral margins of present-day Northeast Asia.Ion microprobe data for magmatic zircon domains from eight mafic to intermediate orthogneisses in the Tateyama and Tsunogawa areas yielded weighted mean ~(206)Pb/~(238)U ages spanning the entire Permian period(302–254 Ma).Under cathodoluminescence,primary magmatic growth zones in the zircon crystals were observed to be partially or completely replaced by inward-penetrating,irregularly curved featureless or weakly zoned secondary domains that mostly yielded U–Pb ages of 250–240 Ma and relatively high Th/U ratios( 0.2).These secondary domains are considered to have been formed by solid-state recrystallization during thermal overprints associated with intrusions of Hida granitoids.Available whole-rock geochemical and Sr–Nd isotope data as well as zircon age spectra corroborate that the Hida Belt comprises the Paleozoic–Mesozoic Cordilleran arc system built upon the margin of the North China Craton,together with the Yeongnam Massif in southern Korea.The arc magmatism along this system was commenced in the Carboniferous and culminated in the Permian–Triassic transition period.Highly positive εHf(t) values( +12) of late Carboniferous to early Permian detrital zircons in the Hida paragneisses indicate that there was significant input from the depleted asthenospheric mantle and/or its crustal derivatives in the early stage of arc magmatism.On the other hand,near-chondritic εHf(t) values(+5 to-2) of magmatic zircons from late Permian Hida orthogneisses suggest a lithospheric mantle origin.Hf isotopic differences between magmatic zircon cores and the secondary rims observed in some orthogneiss samples clearly indicate that the zircons were chemically open to fluids or melts during thermal overprints.Resumed highly positive zircon εHf(t) values(+9) shared by Early Jurassic granitoids in the Hida Belt and Yeongnam Massif may reflect reworking of the Paleozoic arc crust.     

Enabling maps/location searches on mobile devices: constructing a POI database via focused crawling and information extraction

With the popularity of mobile devices and smartphones, we have witnessed rapid growth in mobile applications and services, especially in location-based services (LBS). According to a mobile marketing survey, maps/location searches are among the most utilized services on smartphones. Points of interest (POIs), such as stores, shops, gas stations, parking lots, and bus stops, are particularly important for maps/location searches. Existing map services such as Google Maps and Wikimapia are constructed manually either professionally or with crowd sourcing. However, manual annotation is costly and limited in current POI search services. With the abundance of information on the Web, many store POIs can be extracted from the Web. In this paper, we focus on automatically constructing a POI database to enable store POI map searches. We propose techniques that are required to construct a POI database, including focused crawling, information extraction, and information retrieval techniques. We first crawl Yellow Page web sites to obtain vocabularies of store names. These vocabularies are then investigated with search engines to obtain sentences containing these store names from search snippets in order to train a store name recognition model. To extract POIs scattered across the Web, we propose a query-based crawler to find address-bearing pages that might be used to extract addresses and store names. We crawled 1.25 million distinct POI pairs scattered across the Web and implemented a POI search service via Apache Lucent’s search platform, called Solr. The experimental results demonstrate that the proposed geographical information retrieval model outperforms Wikimapia and a commercial app called ‘What’s the Number?’     

A massif‐type (~1.86 Ga) anorthosite complex in the Yeongnam Massif,Korea: late‐orogenic emplacement associated with the mantle delamination in the North China Craton

To unravel the petrogenesis of a massif‐type anorthosite in terms of the crust‐mantle geodynamics, we dated zircons separated from six samples from the Sancheong‐Hadong (SH) complex, Korea, using a sensitive high‐resolution ion microprobe. The weighted mean ²⁰⁷Pb/²⁰⁶Pb age of two anorthosites is 1862 ± 2 Ma, whereas the ages of the hornblende gabbro and granitic gneiss are 1873 ± 4 Ma and 1875 ± 5 Ma respectively. Zircon rims from mafic granulite and migmatitic gneiss yielded ages of 1860 ± 5 Ma and 1858 ± 4 Ma, respectively, implying that the granulite facies metamorphism and anatexis are associated with anorthosite emplacement. Our results, together with available Re–Os data, are compatible with the ~1.9–1.86 Ga collisional orogeny prevalent in the North China Craton and the Korean Peninsula, and suggest that orogenesis was accompanied by mantle delamination beneath the craton. It is thus likely that the SH anorthositic rocks are a product of late‐orogenic magmatism during the post‐collisional extension‐dominated phase of orogeny.