High-pressure metapelites from the Song Ma suture zone provide crucial insights into the tectonometamorphic evolution of convergent plate boundaries between the South China and Indochina cratons. Two distinct metamorphic stages (M1 and M2) are identified. M1 is characterized by relict inclusions of garnet, quartz, white mica, chlorite, monazite within albite porphyroblasts, with internal fabrics (S1) ranging from straight to sigmoidal and discontinuous to the major foliations (S2) indicating pre-S2 formation. M2 assemblages include porphyroblasts of garnet, albite, quartz and white mica, chlorite, monazite in the matrix, almandine is higher than spessartine from core to rim of garnet. The P-T conditions of M1, constrained by isochemical phase diagrams and geothermobarometric data, are estimated at 15-17 kbar and 440-475 degrees C, whereas those of M2 are 11-12.5 kbar and 440-490 degrees C, suggesting blueschist facies metamorphism followed by the epidote-amphibolite facies. Monazite grains associated with M1 and M2 exhibit compositional and textural differences, indicating distinct metamorphic events. U-Th-Pb isotopic data yield ages of 244 +/- 10 Ma (M1) and 234 +/- 10 Ma (M2) by SHRIMP, and 241 +/- 5 Ma (M1) and 221 +/- 4 Ma (M2) by LA-MC-ICP-MS. These results collectively record the burial and subduction of metasedimentary protoliths during the initial stages of crustal convergence, followed by subsequent exhumation during the collisional amalgamation of the Indochina and South China cratons and closure of the Song Da Ocean.

This study investigates the sources of heavy metal contamination in surface and core sediments from the semi-enclosed Pohang Old Port (POP), South Korea, using an integrated approach combining positive matrix factorization (PMF) and Zn-Cu-Pb stable isotope analyses. Geochemical profiling showed that although heavy metals were primarily derived from anthropogenic sources, sediment grain size controlled the spatial variability of their concentrations through hydrodynamic sorting. PMF resolved four major factors: (1) urban and seafood market discharges enriched in Cd and Zn; (2) Hg-dominated inputs likely associated with riverine transport of landfill-derived sediments; (3) As, Ni, and Pb linked to atmospheric deposition and industrial runoff; and (4) Cu and Zn contamination related to antifouling paint (AFP) use in shipyards. Isotopic analysis of δ66Zn, δ65Cu, and 207Pb/206Pb-208Pb/206Pb provided complementary source constraints. Zn isotopic compositions exhibited limited variability among sediments and potential sources, restricting their discriminatory power. In contrast, Cu isotopes effectively distinguished AFP-related shipyard inputs from urban-industrial contributions, while Pb isotopic ratios indicated mixing between marine background sediments and atmospheric fallout from road dust and cement-related emissions. Isotope-based mixing models were consistent with PMF results and refined the distinction between diffuse and point sources. These findings demonstrate the value of integrating receptor modeling with isotopic fingerprinting to resolve complex multi-source contamination in estuarine sediments.

This study examines the micro-texture and geochemistry of tourmalines to understand the differences between spodumene-bearing and lepidolite-bearing pegmatites in the Boam deposit, South Korea. Detailed electron microprobe analysis and laser ablation-inductively coupled plasma-mass spectrometry analysis of tourmalines from the border, wall, and core zones reveal a systematic compositional evolution from a Mg-and Fe-rich to a Li-and Al-rich composition toward the core zone across all orebodies, indicating a common fractionation trend. However, significant differences are observed between the two pegmatite types. Tourmalines from the lepidolitebearing pegmatites exhibit higher B concentrations throughout all pegmatite zones. Additionally, core zone tourmalines from the lepidolite-bearing pegmatites contain significantly higher concentrations of high field strength elements (Nb, Ta, and Pb). They also exhibit lower Na/(Na + Ca) ratios, contrasting with the continuous increase in this ratio toward the core zone in the spodumene-bearing pegmatite, indicating different crystallization pathways. Texturally, the two pegmatite types show distinct differences, with core zone tourmalines from the lepidolite-bearing pegmatites exhibiting extensive hydrothermal alteration with fluid-origin muscovite and apatite precipitation along the fractures, contrasting with relatively unaltered tourmalines from the spodumenebearing pegmatite. These textural differences are closely linked to Zn concentration patterns, which suggests that fluid exsolution occurred after core zone tourmaline crystallization in the spodumene-bearing orebody but preceded core zone formation in lepidolite-bearing orebodies, reflecting earlier volatile saturation. The earlier fluid saturation in the lepidolite-bearing pegmatites resulted in increased hydrothermal fluid activity during core zone crystallization, accounting for the extensive alteration textures. These findings demonstrate that the lepidolite-bearing pegmatites crystallized from significantly more evolved and volatile-enriched melts compared to the spodumene-bearing pegmatite. The distinct evolutionary trends observed in these two pegmatite types suggest that they likely formed through episodic extraction from a progressively evolving parental magma.

A long-standing debate in Southeast Asian geology concerns how the Proto-Tethys Ocean closed and what role subduction played in shaping the Indochina Block during the early Paleozoic. The Tam Ky-Phuoc Son ophiolite in central Vietnam preserves key evidence of this process, but its origin and age have been uncertain. In this study, we investigated serpentinized peridotites and associated plagiogranites from this suture zone. The serpentinized peridotites contain chromian spinels with high Cr# (0.46-0.69), Mg# (0.43-0.63), and very low TiO2 (<= 0.22 wt%), indicating a mantle source modified in a supra-subduction forearc environment. LA-ICP-MS zircon UPb dating of plagiogranites gives Cambrian ages (ca. 518-502 Ma). Geochemically, the plagiogranites are depleted in Nb, Ta, Ti, but enriched in LREEs and LILEs (Ba, Th, U), consistent with fractional crystallization of mafic magma in a forearc setting. Importantly, the older samples (similar to 518 Ma) show higher HFSE contents and more radiogenic epsilon Hf(t) than the younger ones (similar to 511-504 Ma), recording a transition from incipient subduction to a fluid-enriched mature arc environment. Integrated with regional magmatism (ca. 507-460 Ma) along the Truong Son Belt (TSB), these results indicate that northward subduction of the Proto-Tethys began in Early Cambrian and ended with Ordovician collision between the TSB and Kon Tum Massif (KTM), when the forearc ophiolite was obducted. This study provides direct evidence that the Tam Ky-Phuoc Son complex represents one of the earliest forearc ophiolites linked to Proto-Tethys subduction in Southeast Asia.

Strontium isotopic signatures (87Sr/86Sr) in ocean carbonates serve as a powerful tracer for reconstructing interactions between tectonic activity, terrestrial weathering (TW), and the global carbon cycle. Quantitative estimation of terrestrial weathering flux are therefore essential for understanding how tectonically driven processes influence carbonate accumulation. In this study, a quantitative estimation of TW flux was undertaken, premised on the assumption that variations in continental carbonate accumulation rates during the Early Paleozoic stemmed from shifts in TW flux driven by local tectonic events. To address this, a novel numerical Srreservoir box-model simulation method leveraging the 87Sr/86Sr isotopic proxy in carbonates was applied. The model is based on a Sr-budget framework of restricted seawater (RSW) and was used to perform numerical simulations for various 87Sr/86SrTW values. These simulations enabled us to identify the minimum F(Sr)TW/F (Sr)SW ratios, along with the maximum F(Sr)TW and F(Sr)SW values needed to reach the observed 87Sr/86SrRSW targets. Here, this method is applied to the carbonate successions in the Cathaysia terrane during the CambroOrdovician period, marked by the break-up of the Gondwana supercontinent and the subsequent opening of the Paleo-Tethys Sea. We find notably high 87Sr/86Srcarbonate values (up to 0.7386) and rapid accumulation rates (up to 94.1 m/Ma) in studied successions. Our results suggest that the elevated 87Sr/86Srcarbonate value (0.7386) at 472.2 Ma likely arose from a sharp increase in TW flux, estimated to be 10.2 to 13.5 times higher than modern maximum flux levels (F(Sr)TW = 34 Gmol yr- 1). This intensified TW would have increased the saturation index (SI, S2) of carbonate minerals, thereby accelerating both carbonatization processes and carbonate accumulation rate. Our newly developed RSW Sr-reservoir box-model simulation demonstrates significant potential as a tool for quantitatively assessing the impact of tectonic events on geochemical fluxes.

UPb zircon dating from some Variscan granites of the Central Western Carpathians (CWC) revealed the presence of relict zircons of Ediacaran/Cambrian age. Relict zircon crystals yielding an age of ~557 Ma with ɛHf(500) values (+9.6 to −5.5) are preserved in the Variscan tonalite aged ca. 353 Ma. Variscan magmatic ages in this tonalite show a narrower range of zircon ɛHf(350) values, from +4.0 to −2.2, suggesting that the granite protolith is a recycled Ediacaran/Cambrian magmatic source. Several relict zircon crystals with Cambrian ages of 535 and 527 Ma were also found in nearby Variscan granitic massifs dated to ~353 and ~ 351 Ma, respectively. Metaluminous diorite (~359 Ma) with a significant mantle signature having zircon ɛHf(350) = +8.3 to +0.2 is devoid of inherited zircons, while in the surrounding granodiorite, the relict zircon cores are ubiquitous. Variable proportions of crustal and mantle sources in the Variscan granites are indicated by Hf zircon isotopes and also from whole-rock ɛNd(350) values ranging from +1.6 to −5.9. Several Variscan zircons were detected in a peraluminous S-type metagranite with a high content of Ordovician relict zircons (~460 Ma, Cenerian orogeny), clearly providing evidence, supported by whole-rock geochemical analyses, of low-temperature partial melting of a Central Western Carpathian (CWC) crustal rocks during the Cenerian period. The preserved Ediacaran/Cambrian relict zircon crystals indicate rapid emplacement of Variscan granites driven by slab-breakoff geodynamics from the MASH (melting, assimilation, storage, homogenization) zone to the Ordovician and Upper Devonian wedge during a collisional Variscan granitic magmatism.

The Kusandong Tuff is a prominent stratigraphic unit within the Gyeongsang Basin, the largest Cretaceous sedimentary basin on the Korean Peninsula in East Asia. Extending approximately 200 km in a north-south direction, it serves as a key marker bed within the basin. Located in the upper part of the Hayang Group, the Kusandong Tuff records the onset of subduction-related arc magmatism that followed extension-related volcanism in the Gyeongsang Basin. Overlying the Hayang Group with Kusandong Tuff, the Yucheon Group in the eastern basin reflects the development of the Gyeongsang Arc System through subduction. The Kusandong Tuff thus represents an initial phase of subduction-related volcanism prior to Yucheon deposition. Despite its significance, establishing the precise eruption age of the tuff has been challenging, with previous zircon U-Pb dating studies reporting ages ranging from approximately 97 Ma to 103-104 Ma. These discrepancies have hindered consistent stratigraphic correlations and geological interpretations. In this study, we analyzed five samples from different outcrops using three zircon U-Pb dating methods to refine the eruption age. The results confirmed that the tuff erupted during the late Albian of the Early Cretaceous, approximately 103 Ma. These findings provide a refined temporal framework for understanding the tectonic evolution, stratigraphy, and volcanic activity of the Cretaceous in northeast Asia, and enhance the stratigraphic correlation within the Gyeongsang Basin.

ABSTRACT Elevated heat flow associated with mafic magmatism in accretionary orogens has often been proposed as a driving mechanism for (ultra)high‐temperature (UHT) metamorphism and anatexis. The Sancheong–Hadong complex, located in the southern Yeongnam Massif, Korea, consists of a ca. 1.87–1.86 Ga anorthosite–mangerite–charnockite–granite (AMCG) suite hosted by granulite‐facies gneisses. We present new evidence for UHT metamorphism and near‐isobaric cooling in garnet‐orthopyroxene granulite xenoliths entrained in the Sancheong anorthosite. These xenoliths record partial melting, typified by leucosomes containing peritectic garnet and orthopyroxene. The development of garnet coronas or garnet‐quartz symplectites at the orthopyroxene‐plagioclase interface in the granulite reflects near‐isobaric cooling under a low f H2O condition. P–T pseudosection modelling of a garnet‐orthopyroxene granulite reveals peak metamorphic conditions of 900°C–930°C and ~8.0 kbar, followed by near‐isobaric cooling and melt crystallization at 800°C–830°C and ~7.4 kbar. Such a UHT condition is further supported by zircon crystallization temperatures of ~900 ± 30°C, estimated from Ti‐in‐zircon thermometry. Zircons in the granulite and leucosome are distinctly zoned into three domains (cores, inner rims and outer rims) that reflect successive recrystallization under high‐temperature conditions. U(–Th)–Pb dating of zircon and monazite from two garnet‐orthopyroxene granulites and one leucosome yields weighted mean ages of 1861 ± 5 Ma ( n = 9) and 1863 ± 12 Ma ( n = 3), respectively, coeval with the emplacement of anorthosite at 1861 ± 2 Ma. This result suggests an almost complete resetting of the U–Pb systematics during the transient UHT event at ~1860 Ma. The δ 18 O values of zircon in the granulite are uniform at 8.15 ± 0.11‰ ( n = 83). Together with the zircon ɛ Hf (t) values ranging from −7.0 to −0.3, such an elevated δ 18 O value indicates a derivation from crustal sources. Zircon rims in the leucosome yield slightly lower δ 18 O values (7.67 ± 0.10‰; n = 17) which are consistent with 7.52 ± 0.14‰ ( n = 20) estimated from monazites of the granulite. In contrast, monazite from the leucosome has an even lower δ 18 O value of 6.57 ± 0.43‰. These results suggest that δ 18 O values decrease during cooling and melt crystallization, most likely due to the influx of lower δ 18 O juvenile fluids and/or melts during AMCG emplacement. Taken together, the lower crustal xenoliths of the southern Yeongnam Massif underwent UHT metamorphism and anatexis at ~1860 Ma, accompanied by anorthosite emplacement, within the context of a prolonged melt‐bearing system during the late stage of the Paleoproterozoic hot orogenesis in the North China Craton.

On the Korean Peninsula, located in the eastern region of East Asia, the Gyeongsang Basin, a representative sedimentary basin formed during the Cretaceous Period, occupies about a fourth of South Korea. In the Gyeongsang Basin, the Kusandong Tuff (ca. 103 Ma; Kim et al., 2013), a representative marker bed, is distributed across approximately 200 km from north to south. About 2.5 m-thick tuff layer also develops in Sinsu and Changseon islands, located in the southern part of the basin. There is controversy as to whether it is the southernmost extension of the Kusandong Tuff or a separate tuff body. To resolve this, a total of 4 samples were collected from two islands, and LA-MC-ICP-MS zircon U-Pb dating was performed. As a result, all samples were slightly contaminated with common lead, and lower intercept ages of ca. 99 Ma were calculated, indicating a systematically younger than the reported ages of Kusandong Tuff (ca. 103 Ma). And zircons used in age calculations are largely divided into two domains accoring to the significant differences in brightness in cathodoluminescence (CL) images. Based on the combination of these domains, zircons show: 1) dark overall, 2) dark in the core with bright rims (known as reverse zoning), and 3) only bright oscillatory zoning with/without some inherited cores. In general, dark domains have a uranium content of ca. 3000-7000 ppm, while bright ones range from 34-541 ppm. And in the CL image, some boundary of the dark domains in the cores had melted and infiltrated by bright ones. To understand the evolutionary history of the magma that formed these zircons, trace and rare earth elements were analyzed using LA-ICP-MS. The results indicate that the dark domains of zircons were formed in relatively highly evolved and cooler magma, while the bright domains of zircons were formed in less evolved and hotter magma. To summarize the magma evolution model, crystallization of dark domains occurred first in relatively highly evolved magma, and then domains showing bright and distinct oscillatory zoning were formed with the injection of less evolved magma from deeper sources. At the same time, bright domains grew on the rims of existing dark zircons due to the injected magma. It is thought that the new magma injected into the existing magma chamber caused an increase in internal pressure, which ultimately led to the volcanic eruption. Considering the dating results, it is believed that all of these processes occurred over a short period of time, roughly limited to about 99 Ma on the geological time scale.

In this study, we conduct a micro-analysis of zircons from the Li-bearing Boam pegmatite deposit in Uljin, South Korea, with the aim of understanding the specific evolution process of the pegmatitic melt. All of the zircons observed in the pegmatite have identical textural features (T1, T2, and T3) and distributions of major/minor elements. The primary domain T1 is identified by a relatively bright ring or band within oscillatory and sector zoning in backscattered electron and cathodoluminescence images. The concentrations of UO2 and HfO2 reach 0.81 wt% and 12.88 wt%, respectively. These results indicate that the zircons are derived from highly evolved melts of magmatic origin. However, the chondrite-normalized rare earth element (REE) patterns categorize these zircons into type-A and type-B groups. This distinction can be explained by a model in which each type of zircon grows from separate melts. In type-A zircons, T1 has positive Ce anomalies and a steeply increasing REE pattern from light REEs (LREEs) to heavy REEs (HREEs), suggesting crystallization from a silicic melt with a high silicate content and a relatively low H2O content. On the other hand, type-B zircons have a negative Ce anomaly at T1, with a flat REE pattern due to slight LREE enrichment, indicating crystallization from an aqueous melt with a low silicate content and a high H2O content. T2 is recognized as a relatively pure zircon composition with a secondary texture that recrystallized after T1 crystallization. The embayment/inward-penetrating textures and mineral inclusions related to the mineral assemblage in the pegmatite means T2 has the signature of hydro- thermal alteration via F-rich fluid exsolved from these melts. This domain formed via a coupled dissolution-reprecipitation process that selectively recrystallized the primary domains with a very high U and Th content. This domain exhibits a higher LREE content compared to T1 in both types of zircon, suggesting that the hydrothermal fluid is enriched in the LREEs due to their incompatible characteristics and the selective retention of REEs due to their similar ionic radii. T3 displays a mottled/porous texture and the enrichment of non-formula elements such as Ca, Fe, and Al, indicating that this domain has undergone a typical diffusion-reaction process due to metamictization. Considering the time required for the accumulation of radiation damage, this domain is not believed to have formed during the pegmatite crystallization stage but rather to have formed via the infiltration of fluids of external origin after geological-scale time. Overall, the crystallization and subsequent alteration of these zircons serve as an indicator of the overall evolutionary history of the pegmatite. Our findings specifically suggest that the zircons in the Boam deposit have been crystallized in a melt-melt immiscibility process involving a silicic melt and an aqueous melt and subsequently recrystallized by a hydrothermal fluid exsolved from the immiscible melts.

The Pangong Metamorphic Complex (PMC) lies within the Karakoram Fault (KF) zone that separates the Ladakh batholith from the easternmost Karakoram terrain in the Ladakh Trans-Himalaya. The PMC is intruded by an extensive network of leucogranite dykes and veins. K-feldspar megacryst-bearing porphyritic granitoid pluton is exposed widely in Tangste region located to the south of the PMC. Geochemistry, zircon UPb SHRIMP geochronology and Hf isotopes of leucogranite, porphyritic granitoid, and geochemistry of associated orthogneiss (migmatized) and amphibolite (refractory residuum) have been conducted to unravel the source-to-sink melt history during the KF development. All the studied rocks are metaluminous (molar Al2O3/CaO + Na2O + K2O = 0.46-1.02), except for one peraluminous orthogneiss (A/CNK = 1.16), and dominantly magnesian and calc-alkalic to alkali-calcic. Leucogranite and porphyritic granitoid exhibit adakite-like affinity, while orthogneiss has a magmatic arc signature. The geochemical features support that melting of calc-alkaline orthogneiss and infracrustal magmatic source rocks produced leucogranite and porphyritic granitoid melts in a syntectonic environment. UPb geochronology of leucogranite inherited zircon cores yielded a range of Pb-206/U-238 ages from 73.6 +/- 0.8 Ma to 46.7 +/- 0.5 Ma with a weighted mean age of 72.1 +/- 1.9 Ma. The positive epsilon Hf values (+3.81 to +11.30) of dated inherited zircon cores suggest that the sources for leucogranite melts were juvenile crust-derived magmatic rocks (ca. 73-46 Ma) formed in a subduction zone, similar to the granitoids of the Ladakh-Kohistan and Karakoram batholiths. Leucogranite zircon rims grown over the inherited cores provide a crystallization age of 18.27 +/- 0.29 Ma, synchronous to the zircon mean crystallization age of 18.50 +/- 0.16 Ma in the porphyritic granitoid. The range of epsilon Hf (-11.81 to +0.11) of leucogranite zircon rims overlaps remarkably with epsilon Hf (-10.38 to -0.02) of porphyritic granitoid zircon, which show striking evidence of recycling of a common crustal source (calc-alkaline magmatic rocks) in the formation of leucogranite dyke and porphyritic granitoid pluton. The Miocene leucogranite dyke melts thus likely acted as "feeders" to the porphyritic granitoid plutonism during the development of the KF zone in the PMC of Ladakh Trans-Himalaya.

In the Indian peninsula, the Singhbhum, Bastar, and Dharwar cratons in the South India Block (SIB) constitute a contiguous mass of >2.5 Ga crystalline rocks. Did the cratons develop as a coherently evolved mass since their origin, or do these cratons constitute an assembly of disparately evolved cratons? Variably-deformed charnockites in the Karimnagar granulite belt and associated blastoporphyritic granitoids at the NE fringe of the Eastern Dharwar Craton (EDC) contain enclaves of mafic granulites, high-Al metapelites and anatectic quartzofeldspathic gneisses. The charnockites are demonstrably intrusive into the enclave suite. The enclave suite exhibits steeply-plunging reclined folds; the axial planes of the folds coincide with the N-striking tectonic fabrics in the Karimnagar charnockite/granitoids. The foliated charnockites display magmatic flow texture defined by trains of euhedral alkali feldspar, contain euhedral-subhedral pyroxene phenocrysts, and the quartz grains exhibit abundant chessboard microstructure. The weakly-strained euhedral laths of feldspars and pyroxenes phenocrysts share high-energy boundaries between themselves, and with quartz. Emplacement temperatures of the magmatic charnockites at similar to 900 degrees C are obtained from Al-in-Opx thermometry. Whole rock chemistry is consistent with an arc-related origin for most charnockites. In zircons within charnockites, variably zoned cores yield ages of 2680 +/- 15 Ma and 2504 +/- 12 Ma in the UPb Concordia plot. Recrystallized domains in zircon grains yielded upper intercept ages constrained between 2510 +/- 4 Ma and 2509 +/- 3 Ma, identical with the U-Th-Pb chemical ages (2502-2508 Ma) retrieved from monazites. The zircon epsilon Hf(t) values (- 4.85 to 1.31) suggest the similar to 2.5 Ga magmatic charnockites were derived from <3.0 Ga crustal sources. The late Neoarchean magmatic charnockites in the EDC margin were emplaced in a 2.7-2.5 Ga convergent tectonic setting, and the high-T magmatic charnockites formed due to delamination of a subducting (E-W shortening) oceanic crust. The subduction possibly relates to the late Neoarchean growth of the Dharwar craton involving the assembly of disparately-evolved crustal blocks, now parts of the Dharwar craton. The findings suggest that the emplacement of Karimnagar magmatic charnockites in a contractional setting is unrelated to an accretion between the Eastern Dharwar and the Bastar cratons, as suggested by earlier workers.

The Eastern Pontide Orogenic Belt (EPOB) hosts numerous plutonic bodies with different dimensions, compositions and ages ranging from Paleozoic to Late Eocene in NE Turkey. U-Pb zircon dating suggests that the Arslandede pluton crystallized at 44.50 +/- 0.29 Ma, corresponding to the Lutetian (Middle Eocene) period. Rocks of this pluton have monzonitic character, with compositions ranging from monzodiorite to granite (SiO2 = 49-71 wt%). The studied monzonitic rocks have I-type, metaluminous and shoshonitic character and are enriched in large-ion lithophile elements (LILEs). The rare earth elements (REEs) have concave up shape (LaN/ YbN = 6.64-11.57) and show negative to slightly positive Eu anomalies (EuN/Eu* = 0.37-1.24). 87Sr/86Sr(i) values of 0.704801-0.705102 and epsilon Nd(i) values of 1.01-1.34 correspond to the mantle series on isotope ratio diagrams. Positive epsilon Hf(i) values (5.01-14.91) plot between the depleted mantle and the chondritic evolution lines. The petrological features of the rocks from the Arslandede pluton show that fractional crystallization with low rates of assimilation and/or magma mixing were effective during crystallization. All data show that the magma source of the pluton derived from an enriched lithospheric mantle and emplaced into the crust after differentiation in a deep seated magma chamber contaminated by relatively small proportions of crustal rocks.

To constrain the timing of magma emplacement and eruption of volcanic rocks at Mt. Halla, Jeju Island, South Korea, a range of dating techniques (U-Pb, U-Th disequilibrium, and (U-Th)/He dating of zircon, and 40Ar/39Ar dating of groundmass) were applied to one trachyandesite sample and one trachyte sample. Trachyandesite sample CS92-7 from north of Mt. Halla yielded a homogeneous population of zircon U-Pb crystallization ages averaging 97 ± 3 ka and U-Th disequilibrium ages averaging 96.2 + 6.2/−10.6 ka. Both groundmass 40Ar/39Ar ages and zircon (U-Th)/He ages corrected for disequilibrium record the time of sample cooling, yielding ages of 105 ± 5 ka and 105.4 ± 4.0 ka, respectively. The nearly concordant crystallization and cooling ages are interpreted to document eruption of the sample shortly after its relatively rapid crystallization in the magma reservoir. The eruption age of this sample, based on the available geo- and thermochronological results, is estimated at 100.4 ± 7.6 ka. Trachyte sample SS35-23 from south of Mt. Halla yielded an overdispersed spectrum of zircon crystallization ages, suggesting protracted crystallization in the magma reservoir over a period of at least 140 ka. Weighted mean ages of 40.0 ± 5.9 ka and 39.4 ± 3.8 ka (determined from U-Pb and U-Th disequilibrium dating of the youngest coherent subpopulation, respectively), provide a maximum limit for the eruption age. The eruption age is directly constrained in this work at 32.4 ± 8.4 ka by (U-Th)/He data. The 40Ar/39Ar age of 54 ± 7 ka is distinctly different from the zircon crystallization and eruption ages, and is considered to be inaccurate due to a possible issue with sample contamination or excess argon. The combined geochronological methods applied in this study constrain the timing of zircon crystallization, magma residence, and eruption of volcanic rocks on Jeju Island, and provide essential information further improving our understanding of the chronological history of volcanic rocks on Jeju Island.

The elemental and isotopic (δ65Cu and δ66Zn) characteristics of 34 AFP samples from 5 paint manufacturers, the isotopic fractionation during the dissolution of AFPs by seawater, and the subsequent adsorption of isotopes onto coastal fine-grained sediments were investigated to identify potential indicators (metal ratios and isotopes). The δ65Cu and δ66Zn values for 34 AFPs could be divided into 2 groups regardless of the type of paint or manufacturer. Dissolution by seawater induced substantial fractionation but δ65Cu and δ66Zn approached the bulk AFP values when the leached fraction increased. The adsorption of metals onto marine sediments resulted in substantial fractionation (Δ65Cusoln-solid = 0.91 ± 0.30 ‰ and Δ66Zn = -0.14 ± 0.07 ‰), but the δ65Cu values in sediments were similar to those in bulk AFP because almost all of the Cu adsorbed to marine sediments within 12 h.

The paper presents novel geochemical and geochronological data from granites in Khammam, Eastern Dharwar Craton (EDC), India. The studied granites contain major mineral phases like quartz, alkali-feldspar, plagioclase, biotite, and muscovite in decreasing order of abundance. The accessory phases are epidote, titanite, and zircon. The samples comprise 70 --77 wt% SiO2 and 12-15 wt% Al2O3. The K2O and Na2O concentrations range from 2.57 to 5.65 wt% and 1.17 to 2.69 wt%, respectively. They are enriched in Rb, Th, and Pb and depleted in Nb, Ta, and Ti. On a chondrite-normalized plot, the samples exhibit a rightward trend with a negative Eu anomaly. Zircon saturation in silicate melts yields a temperature (TZr) of 859 - 978 degrees C. The microstructure and U - Pb isotopic analysis of zircon grains (n = 79) reveals the presence of magmatic and polymetamorphic grains with 207Pb/206Pb age clusters at 1844 Ma (number of analyses, n = 7) - 1858 Ma (n = 8), 1737 Ma (n = 5) -1768 Ma (n = 4), 1619 Ma (n = 7) - 1634 Ma (n = 6), and 1554 Ma (n = 5), respectively. The magmatic zircons exhibit epsilon(Hf) values between 3 and 18.9 with a two-stage model age of 2.03 Ga. In contrast, the metamorphic zircons exhibit epsilon(Hf) values between -5.6 and 18, yielding a two-stage model age of 1.97 Ga. The geochemical and geochronological studies indicate that the rocks are A2-type granite emplaced during the accretion of the eastern block of the North China Craton (NCC) and EDC between 1844 Ma and 1858 Ma. The zircons from 1737-1768 Ma and 1620 Ma show the time of metamorphic growth during Antarctica-Nellore Schist Belt (EDC) accretion. Finally, the U-Pb zircon ages from 1554 Ma represent Nuna's final amalgamation. The results of this study posit an association between EDC and NCC during Nuna assembly.