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Abstract We report developing a procedure for measuring concentrations of U, Th and Pb (including all natural Pb isotopes) to establish the distribution of these elements in meteorite minerals and correctly interpret Pb-isotopic ages of meteorites. The concentrations were measured on KBSI SHRIMP IIe by peak jumping using a discrete-dynode secondary electron multiplier. The concentrations were calculated relative to BCR-2G glass and monitored by analysis of the NIST glasses SRM-615 and SRM-617 as secondary reference materials. The detection limits using the spot sizes of ca. 180 μm2, primary O2 − beam current of 10.6 nA, and with amplifier dark noise of 0.015 counts per second are ~ 0.2 parts per billion (ppb) for U (500 s integration), ~ 0.6 ppb for Pb (100 s integration for each of the major isotopes), and ~ 1.2 ppb for Th (100 s integration). Analyses of the NIST glasses confirm that the measured concentrations of U and Th are consistent with their certified values, while the Pb concentrations are about four times too low, most likely due to the compositional mismatch between the primary and secondary reference materials. The achieved level of sensitivity and concentration precision (~ 20–30%) is adequate for measuring U, Th and Pb distributions in both rock-forming and accessory minerals in chondrites, achondrites, and their components.

Abstract Background The intricate textural patterns commonly observed in metamorphosed and recrystallized zircon (ZrSiO4) underscore the crucial necessity of understanding the underlying mechanisms governing their formation to ensure accurate interpretation of the chemical and isotope data they contain. This study employed a combination of microanalytical techniques, including electron backscattered diffraction (EBSD) analysis, electron microprobe (EMP) mapping, and scanning electron microscope (SEM) imaging, to investigate the processes of formation and modification of zircon in a late Pleistocene (~ 35 ka) syenite enclosed within the Nari Tephra Formation on Ulleung Island in South Korea. Findings Under cathodoluminescence (CL), zircons within the syenite reveal dark, featureless, or oscillatory-zoned cores containing numerous inclusions of britholite. These cores are partially or entirely replaced by inward-penetrating bright-CL domains that exhibit minimal inclusion presence. Despite these changes, the external morphologies of the zircons remain largely unchanged, and the faded oscillatory zoning is preserved in the replaced regions. EMP mapping discloses amoebiform micro-domains with high Y, U, and Th concentrations within the dark-CL cores, while the bright-CL domains are relatively deficient in these trace elements. Microstructural analysis of the zircons using EBSD mapping indicates no significant misorientation between the dark-CL cores and the bright-CL rims. Deformation-related low-angle boundaries by lattice distortion are clearly observed in certain grains, cutting across the discrete SEM and EMP domains, and often aligned along submicron pore trails. Conclusions Microstructural and microchemical analyses carried out in this study establish that the zircons within the Ulleung syenite have undergone subsolidus recrystallization, a process likely influenced by the presence of fresh melts or fluids. This recrystallization process could be attributed to either coupled dissolution and reprecipitation or thermoactivated particle and defect volume diffusion due to inherent lattice strain. The subsequent deformation observed in the zircons might be a result of increased stress within the magma system after the recrystallization.

Abstract A major question in geodynamic evolution of the Earth is whether the continental keel evolved geochemically or were delaminated and replaced by a new mantle. Here we present direct evidence for the geochemical evolution of continental keel from lherzolite xenoliths preserved in the Cenozoic alkali basalts from Jeju Island, Korea. Our findings, using detailed petrography and geochemical methods, reveal distinct textures and compositional changes (represented by olivine with magnesium number 91–87, 86–61 respectively) of two stages of geochemical alteration. The first stage involved a parental kimberlite melt that penetrated during the Paleozoic, and the second was caused by alkali basalt during Cenozoic. Our findings suggest that the Archean depleted harzburgitic upper mantle partially evolved to lherzolitic through interaction with melts/fluids that originated from the deep mantle, implying no wholesale delamination of the upper mantle root of East Asian continents.

Abstract Background Monazite, a moderately common light rare earth element (LREE) and thorium phosphate mineral, has chemical, age, and isotopic characteristics that are useful in the investigation of the origin and evolution of crustal melts and fluid- rock interactions. Multiple stages of growth and partial recrystallization commonly observed in monazite inevitably require microspot chemical and isotopic analyses, for which well-characterized reference materials are essential to correct instrumental biases. In this study, we introduce new monazite reference materials COM-1 and Hongcheon for the use in the microspot analysis of oxygen isotopic composition. Findings COM-1 and Hongcheon were derived from a late Mesoproterozoic (~ 1080 Ma) pegmatite dyke in Colorado, USA, and a Late Triassic (~ 230 Ma) carbonatite-hosted REE ore in central Korea, respectively. The COM-1 monazite has much higher levels of Th (8.77 ± 0.56 wt.%), Si (0.82 ± 0.07 wt.%) and lower REE contents (total REE = 49.5 ± 1.2 wt.%) than does the Hongcheon monazite (Th, 0.23 ± 0.11 wt.%; Si,

In this article, novel geochronological (U–Pb SHRIMP) and geochemical data are presented from the lowermost sandstone unit (Par formation), basement granites of Gwalior Basin and sandstones from the Bhopal Basin, located along margins of the Archaean Bundelkhand Craton. The geochemical variation diagrams imply that sandstone units in the Gwalior and Bhopal Basins were deposited in rift-induced passive margin tectonic settings. In contrast to the magmatic features that are preserved in the zircons of granite of the Gwalior Basins, detrital zircons from sandstones of both basins are fragmentary and polymodal in size. The magmatic zircon grains from the basement granites yield a 207Pb/206Pb concordant age of 2538 ± 2 Ma. A group of detrital zircons from the sandstone of the Gwalior Basin with concentric magmatic zonation yield a weighted mean average age of 2564 ± 24 Ma. The detrital zircons from Gwalior Basin exhibit a patchy U-Th distribution overgrowing the magmatic zonation yield average age of 2044 ± 2 Ma. The detrital zircons from the Bhopal basin yield three distinct concordant ages of 2511 ± 5, 1694 ± 6, and 1355±9 Ma. The presence of ~2540 Ma concordant zircon population with concentric zonation in the sandstone of Bhopal Basin suggests their derivation from the granite of similar age. Therefore, an extension of Bundelkhand Craton granite below the Bhopal Basin is suggested. The 2500 Ma ages from the Gwalior granites are linked to global magmatic activity leading to the stabilization of extended Ur at ~2500 Ma. The 2048 and 1355 Ma ages from the Gwalior and Bhopal Basins, respectively, are concluded as the maximum depositional age (MDA) of the lowermost stratigraphic units within the basins. The MDAs are concluded to be the timings of passive margin basin formations along margins of the Bundelkhand Craton during extended Ur and Nuna or Columbia disintegration, respectively, during plume-driven tectonics.

Abstract Background It is important to quantify changes in CO2 sources and sinks with land use and land cover change. In the last several decades, carbon sources and sinks in East Asia have been altered by intensive land cover changes due to rapid economic growth and related urbanization. To understand impact of urbanization on carbon cycle in the monsoon Asia, we analyze net CO2 exchanges for various land cover types across an urbanization gradient in Korea covering high-rise high-density residential, suburban, cropland, and subtropical forest areas. Results Our analysis demonstrates that the urban residential and suburban areas are constant CO2 sources throughout the year (2.75 and 1.02 kg C m−2 year−1 at the urban and suburban sites), and the net CO2 emission indicate impacts of urban vegetation that responds to the seasonal progression of the monsoon. However, the total random uncertainties of measurement are much larger in the urban and suburban areas than at the nonurban sites, which can make it challenging to obtain accurate urban flux measurements. The cropland and forest sites are strong carbon sinks because of a double-cropping system and favorable climate conditions during the study period, respectively (− 0.73 and − 0.60 kg C m−2 year−1 at the cropland and forest sites, respectively). The urban area of high population density (15,000 persons km−2) shows a relatively weak CO2 emission rate per capita (0.7 t CO2 year−1 person−1), especially in winter because of a district heating system and smaller traffic volume. The suburban area shows larger net CO2 emissions per capita (4.9 t CO2 year−1 person−1) because of a high traffic volume, despite a smaller building fraction and population density (770 persons km−2). Conclusions We show that in situ flux observation is challenging because of its larger random uncertainty and this larger uncertainty should be carefully considered in urban studies. Our findings indicate the important role of urban vegetation in the carbon balance and its interaction with the monsoon activity in East Asia. Urban planning in the monsoon Asia must consider interaction on change in the monsoon activity and urban structure and function for sustainable city in a changing climate.

Abstract Background The 238U–230Th disequilibrium dating of the mineral zircon (ZrSiO4) provides an efficient tool for investigating the time scales of Quaternary magmatic processes. In situ mass spectrometric U–Th microanalysis of zircon requires careful calibration and correction of the measured isotope data, particularly for the instrumental fractionation of U and Th isotopes. Findings For the selection of suitable calibration materials for U–Th isotopic analysis using a laser ablation multiple collector inductively coupled plasma mass spectrometer (LA-MCICPMS), we estimated the homogeneity of four reference zircons (91500, TEMORA 2, FC1, and Plešovice) and two zircon working standards (LKZ-1 and BRZ-1) in terms of their 232Th/238U ratios, based on the Pb isotopic compositions measured by a sensitive high-resolution ion microprobe (SHRIMP). The measured LA-MCICPMS 232Th/238U ratios of the zircons were calibrated externally using the SHRIMP 208Pb/206Pb-based average value of the 91500 zircon, 232Th/238U = 0.351 ± 0.035 (error corresponds to 1 standard deviation). The molecular interference-corrected 230Th/232Th ratios of the zircons were calibrated based on the assumption that the Plešovice zircon is in 238U–230Th secular equilibrium. After the calibration and correction, the activity ratios of 230Th/232Th and 238U/232Th for all reference zircons and working standards were plotted on the equiline. Conclusions This study confirms that the 91500 zircon is relatively homogeneous in terms of U/Th ratios (relative standard deviation = ~ 10%) and does not support a recent claim that the Plešovice zircon is not in 238U–230Th radioactive equilibrium. The working standards LKZ-1 and BRZ-1 can be used to check the reliability of U–Th isotopic analyses for Quaternary zircons.

Objectives This study aimed to analyze the mineral composition of naturally- and artificially-produced caries-affected root dentin and to determine the elemental incorporation of resin-modified glass ionomer (RMGI) into the demineralized dentin. Materials and Methods Box-formed cavities were prepared on buccal and lingual root surfaces of sound human premolars (n = 15). One cavity was exposed to a microbial caries model using a strain of Streptococcus mutans. The other cavity was subjected to a chemical model under pH cycling. Premolars and molars with root surface caries were used as a natural caries model (n = 15). Outer caries lesion was removed using a carbide bur and a hand excavator under a dyeing technique and restored with RMGI (FujiII LC, GC Corp.). The weight percentages of calcium (Ca), phosphate (P), and strontium (Sr) and the widths of demineralized dentin were determined by electron probe microanalysis and compared among the groups using ANOVA and Tukey test (p < 0.05). Results There was a pattern of demineralization in all models, as visualized with scanning electron microscopy. Artificial models induced greater losses of Ca and P and larger widths of demineralized dentin than did a natural caries model (p < 0.05). Sr was diffused into the demineralized dentin layer from RMGI. Conclusions Both microbial and chemical caries models produced similar patterns of mineral composition on the caries-affected dentin. However, the artificial lesions had a relatively larger extent of demineralization than did the natural lesions. RMGI was incorporated into the superficial layer of the caries-affected dentin.

The geochemistry of major Low Tatra granitic types, namely Prašivá porphyritic Bt (biotite)-granodiorite and Ďumbier Bt-tonalite, indicate their derivation from initial hybrid magmas and represent a mixture among several magma pulses formed via melting of the heterogeneous lower crust. The high K calc-alkaline peraluminous character, along with high Ba, Sr + LREE contents correspond to the partial melting of K-rich mafic and the intermediate hydrated lower crustal source in equilibrium with amphibole or possibly garnet with variable involvement of metasedimentary and/or felsic metaigneous sources. The zircon isotopic age of 360.4 ± 2.7 Ma recorded from diatexite reflects the timing of hightemperature metamorphism of subducted continental crust, and thus corresponds in an initial anatectic process within the present Tatric Unit. The magmatic ages are in the largely overlapping sequence of 353 ± 2 Ma for the Ďumbier tonalite and 352 ± 3 Ma and 351.9 ± 2.9 Ma for Prašivá Aln (allanite bearing)-subtype and Mnz (monazite bearing)-subtypes, which indicate successive multiple emplacement of magma batches and natural evolution towards their more crustal character. Magmatism in the Low Tatra Mts. represents a post-collisional plutonic system related to the slab break-off mechanism described in the close Malá Fatra crystalline basement as well. Heat from mantle upwelling and volatiles from previous subduction forced the melting of the lower crust towards K-rich mafic or intermediate lithologies, as well as during the emplacement of long-lasting melting of felsic metasedimentary crustal sources. The crystalline core of the Low Tatra Mts. is another example of composite granite pluton in the Western Carpathians, which represents a product of the multiphase Late-Variscan post-collisional setting. [ABSTRACT FROM AUTHOR]

Glacial sedimentary facies are recognised in the Palaeoproterozoic (Orosirian) Bergslagen Group in central Sweden, described previously as post-orogenic conglomerates in the Grythyttan Field. The evidence is provided by the presence of macro boulders in a megaclastic to conglomerate rock formation or diamictite around lake Brunnsjon, south of Grythyttan. Pebble to cobble size conglomerates discordantly overlie a megaclastic rock formation, with facetted clasts resembling flatirons. The sedimentary facies assemblage resembles an ice-front resedimented sequence, previously interpreted as an alluvial fan by the writers. A glacial interpretation is supported by evidence of permafrost and related periglacial structures in coeval, 1895 ± 5 Ma (U-Pb zircon age), metavolcaniclastic rocks in the Bergslagen Group. The association of glacial sedimentary facies, permafrost and banded ironstones in the low-latitudinal Bergslagen Group suggests its similarity to better known 'Snowball Earth' deposits from Palaeoproterozoic and particularly Neoproterozoic times. [ABSTRACT FROM AUTHOR]

A number of discrete slate belts of limited size occur in the Palaeoproterozoic volcano-sedimentary Bergslagen Group of western Bergslagen in the Fennoscandian Shield of south-central Sweden. The Grythyttan Slate Belt (GSB), studied for more than a century, forms a single basin with the nearby Saxån Slate Belt (SSB). We use the lithostratigraphy of the Grythyttan Slate Formation of the Grythyttan belt, based on basin-scale sedimentary facies associations of the volcaniclastic sediments in time and space, as a method to interpret overall tectonic structure. Contrary to traditional views, we reconstruct the GSB as a single overturned limb of a km-scale anticline with horizontal axis in the hanging wall of an east-vergent thrust fault, reactivating a listric extensional fault. The fold connects the GSB to the neighboring SSB. Folding and thrusting were related to tectonic closure of a volcanic back-arc or intra-arc basin. The early folds were subsequently affected by strike-slip shearing and folding around vertical fold axes, which partitioned preferentially into the least competent lithologies (slates and marbles), significantly modifying the map appearance of the slate belt. The late shearing and folding resulted from accretion of Bergslagen onto the Fennoscandian continental margin during the late, Svecobaltic phase of the Svecofennian orogeny. The GSB forms a thin, intraformational wedge in the Bergslagen Group and represents a relatively short interlude with a conglomeratic alluvial fan and turbiditic volcaniclastics followed by more felsic volcanic rocks resembling those of the Bergslagen Group. We suggest that the GSB, and by inference the other slate belts, stem from calderas, as either terrestrial volcanic lakes or shallow submarine eruption centres. The conglomerates are pre-orogenic, not a post-orogenic molasse as traditionally conceived, and their clast fabric has resulted from sedimentary processes only. Newly determined SIMS U-Pb zircon ages constrain the age of the GSB at c. 1895 Ma. [ABSTRACT FROM AUTHOR]

This study presents sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon ages, K-Ar ages, and whole-rock chemical and isotopic (Sr-Nd) compositions of the Early Cretaceous igneous activity in western South Korea. The volcanics and plutons yield zircon U-Pb ages of ca. 110 Ma, in the Albian of the late Early Cretaceous. K-Ar biotite and plagioclase ages are slightly younger, ca. 103 Ma. The geochemical signatures of the rocks are characterized by negative Nb, Ta, and Ti anomalies, relatively low ∊Nd(T) values (between -15.91 and -9.36), and enrichment in light rare earth elements, suggesting the effects of subduction-related magmatism. Together with the Sr and Nd isotopic compositions of the intermediate to acid volcanics, geochemical characteristics reflect a lower-crustal magma source. This Albian event over the Korean Peninsula is related to Early Jurassic subduction and subsequent lithospheric delamination and/or slab rollback after the Early Cretaceous amalgamation between the North China Block (e.g., China, Korea, and Japan) and the paleo-Eurasia continent. This postorogenic event was accompanied by the initial formation of voluminous igneous activity and subsequent basin formation at about 130-110 Ma. Crustal relaxation during this stage should be related to this postorogenic event and is attributed to paleo-Pacific Plate subduction. This result provides important clues for the Cretaceous tectonic evolution of Northeast Asia in the context of plate convergence [ABSTRACT FROM AUTHOR]

In this study we report on the bioactive response of self-assembled niobium oxide microstructures when immersed in a supersaturated solution emulating mineral content in blood. The structures were formed via electrochemical anodization in an electrolyte comprised of HF and NaF. The slow oxide formation kinetics associated with the presence of NaF in the electrolyte enabled microscopic examinations during microstructure evolution as shown via scanning electron microscopy (SEM). Apparently the slow growth kinetics encourage the development of bioactive sites on the microstructures, as these structures induced mineral formations. On the other hand, microstructures grown in the absence of salt were ineffective mineral nucleators. Analysis of nucleated mineral deposits was performed using X-ray diffraction and Raman spectroscopy. Both long-range and short-range order experiments verified the nucleated mineral phase was hydroxyapatite (HAP). Further characterization of the mineral phase was observed using SEM and revealed effective nucleation sites were predominantly isolated to loci on the ordered microbodies as opposed to locations lying within the amorphous strata. [ABSTRACT FROM AUTHOR]

Explores the correlation of the early Proterozoic granulites in central Korea with the cratons in China. Structural patterns during granulite formation; Smectite-neodymium composition of leucocratic gneisses; Cycles of tectonometamorphic events of the Hwacheon granulite complex.

The early Paleozoic paleogeography of East Gondwanan terranes, including the North China Craton (NCC), is contentious, primarily reflecting the paucity of integrated geochronological, biogeographic, and tectonic data sets. Our new sensitive high-resolution ion microprobe data from 14 sandstones of the Taebaeksan Basin, Korea, indicate that its platform shelf sequences, typified by trilobite faunal assemblages diagnostic of the NCC, record the vestige of coeval arc magmatism. Detrital zircons analyzed from the sandstones yielded Eoarchean to Early Ordovician ages, which define three distinct types of distribution patterns characterized by: (1) double peaks at ca. 1.85 Ga and 2.50 Ga diagnostic of basement rocks in the NCC; (2) minor peaks at ca. 1.75, 1.6, and 1.2-1.1 Ga in addition to double peaks; and finally (3) a scattered array of late Paleoproterozoic to Neoproterozoic zircons lacking double peaks. The marked contrasts among the three types reflect significant changes in provenance, most likely linked to variations in paleo-water depths during the "Sauk" transgression. Longshore- or onshore-directed currents, associated with an increase in water depth, apparently brought outboard oceanic detritus and benthic trilobites into the relatively flat outer shelf of the Taebaeksan Basin. As a result, fine-grained sandstones received a large amount of detritus from distal sources, yielding mixed signatures in zircon age patterns and trilobite assemblages. Excluding the basal sandstone-conglomerate unit, five siliciclastic formations contain syndepositional zircon populations, and their weighted mean 206Pb/238U ages decrease upsection from 512 ± 5 Ma to 483 ± 2 Ma, indicating a sedimentary influx from contemporaneous volcanic activity. In conjunction with arc-related bulk-rock geochemistry and juvenile Nd isotopic signature, early Paleozoic detrital zircons likely represent the first-cycle detritus supplied for ~30 m.y. from the proto-Japan arc that initially formed at ca. 520 Ma. Together with the occurrence of ca. 700-500 Ma detrital Pacific Gondwana zircons in fine-grained sandstones, Paleozoic arc-sourced detritus suggests that the Korean Peninsula was paleogeographically linked to an ancient convergent margin, perhaps extending from the Terra Australis orogen. [ABSTRACT FROM AUTHOR]

Zircon oxygen-hafnium and biotite magnesium isotopic compositions of Late Cretaceous to Oligocene (88-27 Ma) granitoids from the Gyeongsang continental arc, southeastern Korea, collectively provide a new insight into shallow magma petrogenesis. Zircon crystals extracted from eight calc-alkaline or alkaline plutons commonly contain xenocrystic cores and typically show magmatic cathodoluminescence zonings and sharp Raman spectra. Most zircons have positive εHf values plotting below the mid-ocean-ridge basalt evolution path, indicating that the arc magmatism was dominated by the recycling of juvenile crustal materials. Zircon δ18O values shifted upward or downward from the mantle range attest to the O isotopic exchange of crustal protoliths with surface waters at various temperature conditions. Small (<1‰) but discernable core-to-rim decreases of d18O values are recognized selectively in magmatic zircon grains from four plutons possessing biotite δ26Mg values (-0.07‰ to +2.32‰) distinctly higher than the mantle range. Such a concomitant O-Mg isotopic variation provides compelling evidence for a series of self-induced hydrothermal alteration and assimilation processes (i.e., "crustal self-cannibalization”). This study shows that the supracrustal input to magmas in a young and juvenile orogen can be traced effectively by the combination of stable isotope records from the plutonic root. [ABSTRACT FROM AUTHOR]

From the 3000 km² Eoarchean Itsaq Gneiss Complex (IGC) of Greenland, zircon U-Pb dating of numerous meta-granitoid and orthogneiss samples is integrated with geologic observations, whole rock geochemistry and a strategic subset of zircon Hf and whole rock Nd isotopic measurements. This shows that there are multiple episodes of TTG suite formation from ~3890 to 3660 Ma, characterized by zircon initial εHf≈0 and whole rock initial εNd of > +2. These rocks mostly ha geochemical signatures of partial melting of eclogitized mafic sources, with a subset of high magnesian, low silica rocks indicating fusion by fluid fluxing of upper mantle sources. The TTG suites are accompanied by slightly older gabbros, basalts and andesites, which have geochemical signatures pointing to magmas originating from fluid fluxing of upper mantle sources. The data show the formation of juvenile crust domains in several discrete events from ~3900 to 3660 Ma, probably at convergent plate boundaries in an environment analogous, but not identical to, modern island arcs. In the Isua area, a northern ~3700 Ma terrane formed distal from a predominantly ~3800 Ma terrane. These terranes were juxtaposed between ~3680 and 3660 Ma--respectively the age of the youngest rocks unique to the northern terrane and the lithologically distinctive ultramafic-granitic Inaluk dykes common to both terranes. This shows the assembly of different domains of juvenile rocks to form a more expansive domain of "continental" crust. A rare occurrence of high-pressure granulite is dated at ~3660 Ma, demonstrating that assembly involved tectonic crustal thickening. This continental crust was then reworked in the 3660 to 3600 Ma Isukasian orogeny. In the northern part of the Isua area, 3660 to 3600 Ma granites were emplaced into ~3700 Ma tonalites. The earliest granites are nebulous, and sigmoidal schlieric inclusions within them demonstrate ductile extension. Younger granite sheets were emplaced into extensional ductile-brittle fractures. These granite-tonalite relationships are overprinted by widespread development of late Eoarchean (pre-3500 Ma Ameralik dyke) brittle-ductile extensional cataclastic textures, together demonstrating that extension was polybaric. The southern part of the Isua area largely escaped 3660 to 3600 Ma high temperature processes and has sparse granite sheets commonly focused into coeval shear zones. In the rest of the complex, deeper crustal levels during the Isukasian orogeny are widely preserved. These experienced upper amphibolite to granulite facies moderate- to low-pressure syn-kinematic metamorphism, forming complex migmatites rich in granitic-trondhjemitic neosome. The migmatites were intruded by composite ferrogabbro and granite bodies, in which syn-magmatic extensional features are locally preserved. Thus 3660 to 3600 Ma crustal recycling involved elevated crustal thermal gradients in an extensional regime. Crustal melts formed in the Isukasian orogeny have zircon initial εHf <0 and whole rock initial εHd of ≤0 showing incorporation of slightly older Eoarchean juvenile crust. A Phanerozoic example of collisional orogeny followed by crustal thinning is explored as an analog for the Isukasian orogeny. [ABSTRACT FROM AUTHOR]