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Abstract: The Cenozoic magmatic record within the ca. 500km long eastern Pontides orogen, located within the Alpine metallogenic belt, is critical to evaluate the tectonic history and geodynamic evolution of the eastern Mediterranean region. In this paper we report for the first time late Miocene adakitic rocks from the southeastern part of the eastern Pontides belt and present results from geochemical and Sr–Nd isotopic studies as well as zircon U–Pb geochronology. The Tavdagi dacite that we investigate in this study is exposed as round or ellipsoidal shaped bodies, sills, and dikes in the southeastern part of the belt. Zircons in the dacite show euhedral crystal morphology with oscillatory zoning and high Th/U values (up to 1.69) typical of magmatic origin. Zircon LA–ICPMS analysis yielded a weighted mean 206Pb/238U age of 7.86±0.15Ma. SHRIMP analyses of zircons with typical magmatic zoning from another sample yielded a weighted mean 206Pb/238U age of 8.79±0.19Ma. Both ages are identical and constrain the timing of dacitic magmatism as late Miocene. The Miocene Tavdagi dacite shows adakitic affinity with high SiO2 (68.95–71.41wt.%), Al2O3 (14.88–16.02wt.%), Na2O (3.27–4.12wt.%), Sr (331.4–462.1ppm), Sr/Y (85–103.7), LaN/YbN (34.3–50.9) and low Y (3.2–5ppm) values. Their initial 143Nd/144Nd (0.512723–0.512736) and 87Sr/86Sr (0.70484–0.70494) ratios are, respectively, lower and higher than those of normal oceanic crust. The geological, geochemical and isotopic data suggest that the adakitic magmatism was generated by partial melting of the mafic lower crust in the southeastern part of the eastern Pontide belt during the late Miocene. Based on the results presented in this study and a synthesis of the geological and tectonic information on the region, we propose that the entire northern edge of the eastern Pontides–Lesser Caucasus–Elbruz magmatic arc was an active continental margin during the Cenozoic. We identify a migration of the Cenozoic magmatism towards north over time resulting from the roll-back of the southward subducted Tethys oceanic lithosphere. Slab break-off during Pliocene is proposed to have triggered asthenospheric upwelling and partial melting of the subduction-modified mantle wedge which generated the alkaline magmatic rocks exposed in the northern part of the magmatic arc. [Copyright &y& Elsevier]

Abstract: The timing of partial melting and the pressure–temperature (P–T) paths in the High Himalayan Crystalline Sequence (HHCS) in far-eastern Nepal has been investigated using zircon chronology, rare earth element (REE) compositions, and P–T pseudosection analysis. Zircon from migmatites formed during Himalayan thermal events displays inherited magmatic core overgrown by two generations of metamorphic rims. The new rims are distinguished on the basis of their Tertiary ages, low MREE contents, and low Th/U ratios. The inner zircon rims from Sil+Grt+Bt+Kfs+Pl+Qtz and Ky+Sil+Grt+Bt+Ms+Pl+Qtz migmatites at different structural level of the HHCS display ages of c. 33–28Ma (Early Oligocene) and c. 21–18Ma (Early Miocene): these rims are characterized by flat MREE to HREE patterns and were overgrown by partial melt through muscovite dehydration melting under the stability of garnet, which occurred at P = c. 7–10kbar and T = c. 730–780°C, and at P = c. 8–14kbar and T = c. 720–770°C, respectively. The outer zircon rims are relatively enriched in HREE with respect to the inner rims and were overgrown at c. 27–23Ma (Late Oligocene) and at c. 18–16Ma (Early Miocene) during melt crystallization accompanying breakdown of garnet at P = c. 4–7kbar and T = c. 650–725°C. Early Miocene Ms–Bt leucogranites with two successively overgrown zircon rims at c. 18.3±0.3Ma and c. 16.3±0.2Ma were intruded into Early Oligocene migmatite hosts. Microstructural observations and the corresponding P–T conditions associated with the two generations of zircon rims indicate that the Early Oligocene and Early Miocene migmatites show relatively isobaric and nearly isothermal P–T paths during exhumation, respectively. The inferences are consistent with higher average cooling rates for the Early Miocene (c. 30–40°C/My) than the Early Oligocene (c. 15–25°C/My) migmatites, inferred from peak-T conditions and FT (c. 6Ma for both migmatites) and U–Pb zircon ages. The P–T–t paths of the two migmatites indicate that burial of the Early Miocene migmatites has been coeval with exhumation of the Early Oligocene migmatites, implying the formation of large-scale thrust within the HHCS. [Copyright &y& Elsevier]

[Display omitted] • Three distinct Archean events recorded from the Central Bundelkhand Tectonic Zone. • The 3.48 Ga calc alkaline, metaluminous protocrust formed in a subduction setting. • Anatexis of 3.48 Ga protocrust formed 2.70 Ga leucogranite in collisional setting. • The 2.54 Ga old alkali granite formed in a post collision setting. Field relations, microstructures, phase petrology, elemental geochemistry, and zircon U-Pb geochronology of migmatites and (undeformed) granites (sensu lato) from the Central Bundelkhand Tectonic Zone (CBTZ) of the Bundelkhand Craton, central India are investigated to understand the age and origin of these rocks. Anatexis of felsic proto-crust produced in situ leucocratic melts with entrained residual assemblages, forming the metatexite and diatexite in the migmatite. The chemistry of biotite (X Fe = 0.65–0.72) from the leucosome of migmatite supports its crystallization in a peraluminous felsic melt more likely in a syn-collisional tectonic setting. The residual amphibole in the leucosome from migmatites belongs to metaluminous (I-type) calc-alkaline protocrust source that originated in a subduction setting. Biotites (X Fe = 0.80–0.81) and amphiboles (X Fe = 0.84–0.87) from granites exposed proximal to the CBTZ, suggest alkaline (A-type) nature of the host magma, emplaced at mid-crustal depth (3.79–4.73 ± 0.5 kbar). Whole-rock geochemistry of migmatite reveals the magnesian nature of melt formed by differential degrees of melting of heterogeneous sources (i.e., TTG and mafic crust), at 12–14 kbar. The alkali granite was likely formed by the anhydrous melting of ancient felsic crustal rocks. U-Pb geochronology of inherited magmatic zircon cores (Th/U = 0.06–0.48) from migmatite yielded an upper intercept age of 3478 ± 48 Ma interpreted as zircon crystallization age in the protolith. The zircon rims of magmatic origin (Th/U = 0.06–0.72) grown over the 3.48 Ga old zircon cores provide an upper intercept age of 2700 ± 16 Ma; interpreted as zircon crystallization age in a leucocratic melt. This is synchronous with the timing of intense deformation/collision and the melting event in the CBTZ. Zircons (Th/U = 0.26–0.92) from alkali granite yielded a weighted mean crystallization age of 2539.9 ± 6.6 Ma without any noticeable zircon inheritance. The Bundelkhand Craton probably experienced at least two phases of collision-accretion orogens, the first one initiated at ca. 2.8 Ga with arc-related magmatism and ended with ca. 2.7 Ga collision-related felsic magmatic record. The second phase began with ca. 2.58 Ga subduction-related magmatism and culminated at ca. 2.54 Ga with a minor amount of post-collisional, alkali granite magmatism. [ABSTRACT FROM AUTHOR]

The metamorphic pressure–temperature (P–T) conditions across the Main central thrust (MCT) in the Arun area have been investigated. The MCT marks the tectono-metamorphic boundary between the overlying high-grade High Himalaya crystalline sequences (HHCS) and the underlying low-grade Lesser Himalaya sequences (LHS). The metamorphic rocks regionally preserve an inverted Barrovian sequence (i.e., intermediate P/T type metamorphism) devoid of previously reported high-pressure metamorphism. The metamorphic grade increases upwards from 670–740 °C and 6.9–9.4 kbar in the MCT zone and lower HHCS to 760–835 °C and 10.0–11.1 kbar in the middle HHCS. Orthoamphibole gneisses in the middle HHCS yield prograde Barrovian-type metamorphism, such as staurolite inclusions in garnets, showing an intermediate P/T gradient. The differences in the tectonic setting and metamorphic evolution imply that the metamorphic units in the Arun area do not correspond to the other high-pressure units in eastern Himalaya. Zircon and monazite U–Pb ages from kyanite gneiss of the lower HHCS reveal the MCT activity, associated with fluid-present anatexis, at ca. 20–14 Ma. Furthermore, similar K–Ar white mica ages (ca. 13–7 Ma) in the hanging wall and footwall of the MCT could represent the timing of later deformation events in shear zones or cooling, possibly associated with exhumation accompanied by activities on younger, structurally lower thrust faults such as the lower MCT. The similar P–T conditions near the MCT in this area could result from recrystallization during syn-metamorphic thrusting, whereas the middle HHCS away from the MCT preserve the original Barrovian metamorphic sequences related to crustal thickening. This and previous studies imply that different P–T profiles near the MCT according to each transect observed in Nepal could be apparent and the cumulative result of polyphase metamorphism. [ABSTRACT FROM AUTHOR]

Caldera fault zones, identified in many modern and ancient volcanoes, have been the subject of geological and geophysical observations and of analog and numerical modeling. However, the physicochemical processes in fault zones during a caldera collapse are still poorly understood. Here, we present field observations from a caldera fault zone in the Cretaceous Jangsan Caldera, SE Korea. The fault zone is ∼30 m wide and juxtaposes an intracaldera rhyolitic volcanic complex against older dacitic rocks; it consists of a minor fault, a main fault, and a series of fault-related intrusions (rhyolite and tuffisite). The main fault dips 90°–88°NW (vertically to steeply inward) and strikes N30°–40°E. A layer of pseudotachylyte (less than ∼10 cm thick) with some injection veins occurs along the main fault. The pseudotachylyte contains rounded to sub-rounded clasts, commonly displaying fuzzy or embayed boundaries, as well as euhedral feldspar microlites (<10 μm) and flow structures similar to those typically observed in tectonic pseudotachylytes. The tuffisite not only intrudes sharply into the pseudotachylyte and dacitic wall rocks but also displays a mingling structure with the pseudotachylyte. The contact between the rhyolitic intrusion and the tuffisite is nonplanar and complex. Based on the observed field relationships, we conclude that frictional melting and magmatic intrusion were near-coeval and that intrusion outlasted frictional melting by a short period. Although volcano–tectonic pseudotachylytes have rarely been identified in calderas (e.g., in the Glencoe Caldera, Scotland), our results suggest that frictional melting may be an important fault zone process during caldera collapse. • Pseudotachylyte, rhyolitic intrusions and tuffisite are identified in a caldera fault zone of the deeply eroded and ancient Jangsan Caldera, SE Korea. • The intrusion of pyroclastic and magmatic materials occurred shortly after frictional melting and outlasted by a short period. • Frictional melting may be an important fault zone process during caldera collapse. [ABSTRACT FROM AUTHOR]

Abstract The Imjingang belt, which is located between the Nangrim and Gyeonggi Massifs, is divided into the Imjin group in the north and the Samgot unit in the south. The southeastern part of the Imjin group, which is located within South Korea, is called the Jingok unit. The Samgot unit consists of amphibolite, psammitic schist, meta-alkali granite and meta-calc-silicate rock. The amphibolite experienced prograde metamorphism from 648-550 °C/13-11 kbar to 715 °C/11 kbar and was then retrograded to ca. 579-569 °C/6.7-6.3 kbar. The psammitic schist was metamorphosed at ca. 710 °C/11 kbar and then retrograded to ca. 670-660 °C/11-10 kbar. These data indicate that the Samgot unit underwent clockwise prograde metamorphism with peak metamorphism conditions of 715-710 °C/11 kbar, which is confirmed by pseudosection analysis. The results of this and previous studies indicate that the metamorphic grade increases southward from the garnet and staurolite zones (630-500 °C/9-3 kbar) through the kyanite zone (710-665 °C/9 kbar) in the Jingok unit to the Samgot unit (715-710 °C/11 kbar) of the Imjingang belt. This metamorphic pattern indicates that the Imjingang belt underwent regional intermediate-P/T metamorphism. The SHRIMP U-Pb age dating of zircons from the amphibolite and meta-alkali granite yields intrusion ages of ca. 371-361 Ma and 373 Ma, respectively. From the psammitic schist, ages of ca. 401-370 Ma are obtained from the youngest detrital zircons and ages of ca. 251-249 Ma are obtained from the metamorphic zircons. In addition, the SHRIMP U-Pb age dating of titanite from the amphibolite yields a retrograde metamorphic age of ca. 229-214 Ma. The whole-rock chemical composition of the amphibolite plots in the back-arc basin basalt field on the tectonic discrimination diagrams. These data indicate that the Imjingang belt, including the Samgot unit, consists of Devonian sedimentary rocks that were deposited in a back-arc basin and intruded by mafic and felsic igneous rocks at ca. 373-361 Ma. Finally, the Imjingang belt underwent intermediate-P/T metamorphism during the Triassic (251–249 Ma) instead of high-P/T metamorphism, indicating that the Imjingang belt is not the extension of the Dabie-Sulu collision belt but a back-arc basin within the North China Craton that underwent intermediate-P/T metamorphism due to the closure of the back-arc basin (arc-continent collision) during the collision between the North and South China Cratons along the Hongseong-Odesan collision belt within the Gyeonggi Massif. Graphical abstract Unlabelled Image Highlights • The Samgot unit in the Imjingang belt (IB) formed in the back-arc basin during the Devonian. • The Samgot unit was intruded by 373–361 Ma igneous rocks formed in the back-arc basin. • IB underwent intermediate-P/T metamorphism instead of high-P/T metamorphism. • The metamorphism occurred at 715–710 °C /11 kbar during the Triassic (251–249 Ma). • The IB is not the extension of the Dabie-Sulu collision belt. [ABSTRACT FROM AUTHOR]

The depositional and metamorphic ages, and provenances of metasedimentary rocks from the Nam Co Complex in the Son La area, Song Ma Suture Zone, northwestern Vietnam, were investigated in order to reveal the convergent tectonic history between the Indochina and South China cratons. This complex is structurally characterized by an antiformal metamorphic core consisting of two distinct metamorphic zones: inner garnet and outer biotite zones. The U-Pb isotopic dating on detrital zircon from metasandstones of the Nam Co Complex yielded major population (> 50%) around ~850 Ma with minor population scattered between 1.2 to 3.0 Ga. The age spectra as well as the morphologies, internal structures and geochemical features of detrital zircon are accounted for by magmatic activities prevalent at the convergent plate margin during the Neoproterozoic. In contrast, the UTh- Pb isotopic compositions of monazite from a garnet-zone schist defined a common Pb mixing line with the lower intercept age of 234 ± 10 Ma (2σ) reflecting the Indosinian metamorphic event. The U-Pb age distribution pattern of detrital zircon in the Nam Co Complex is compatible with that of the South China craton rather than that of the Indochina craton. In summary, sedimentary protoliths of the Nam Co Complex were deposited in a convergent-related basin along the southwestern margin of the South China craton during the Neoproterozoic, and then was finally amalgamated to the Indochina craton via the southerly subduction of South China craton during the Indosinian orogeny. [ABSTRACT FROM AUTHOR]

The Sancheong area in the southwestern Yeongnam Massif mainly consists of Precambrian paragneisses (quartz-feldspathic and garnet gneiss), orthogneiss (porphyritic gneiss) and anorthosite and is important for an understanding the tectonic evolution of the southern part of the Korean Peninsula and Northeast Asia. The Precambrian paragneisses in the Sancheong area underwent intermediate-P/T metamorphism (quartz-feldspathic gneiss; 730 °C and 12.2 kbar). The intermediate-P/T metamorphism was overprinted by regional low-P/T metamorphism (750–820 °C and 7.0–9.0 kbar) which was followed by amphibolite-facies retrograde metamorphism. In contrast, the orthogneiss only experienced the low-P/T (750–800 °C and 8.0–8.7 kbar) metamorphism followed by the amphibolite-facies retrograde metamorphism. Zircon U–Pb dating indicates that the intermediate-P/T metamorphism likely occurred at ca. 1880–1920 Ma and that the low-P/T metamorphism occurred at ca. 1855–1859 Ma. The whole-rock geochemical data and zircon U–Pb ages indicate that the protolith of the porphyritic gneiss and the anorthosite were emplaced in a post-collisional tectonic setting during ca. 1872–1880 Ma and ca. 1860 Ma, respectively. These data suggest that the Sancheong area underwent continental collision associated with the intermediate-P/T metamorphism (ca. 1920–1880 Ma) and post-collisional igneous activity associated with the low-P/T metamorphism during the Paleoproterozoic (ca. 1856–1880 Ma). Similar Paleoproterozoic tectonic events were recently reported from the eastern Cathaysia Block, suggesting that the Yeongnam Massif may have a close affinity to the eastern Cathaysia Block. [ABSTRACT FROM AUTHOR]

The lithounits constituting the Ladakh Himalaya are exposed along the Indus and Shyok Sutures Zones of northwest Himalaya. The Shyok Suture Zone (SSZ) in northern Ladakh represents a highly tectonized zone of a back-arc basin, which is mainly composed of volcano-sedimentary formations (Shyok and Khardung Formations) intimately, associated with intrusive granitoids. In the Nubra-Shyok valley of the SSZ calc-alkaline granitoids of batholithic dimension are exposed in the Tirit region, referred herein as the Tirit granitoids, which are intrusive evidently into the Shyok volcanic (rhyolite) rocks belonging to the Shyok Formation. In this valley the northern margins of granitoids of the Ladakh batholith can also be found intrusive into the metasediments (shale/slate) and metavolcanics of the Shyok Formation. The compositions and crystallization pressures (~ 66 to 91 MPa) of amphiboles in the intrusive Tirit granitoid corroborate a calc-alkaline nature and solidification of Tirit granitoid melt at subvolcanic level equivalent to a minimum of 2.5 km to a maximum of 3.5 km thick overburden of Shyok volcanics. U–Pb SHRIMP zircons from the Tirit granitoids have yielded mean crystallization ages of 109.4 ± 1.1 Ma and 105.30 ± 0.80 Ma, which strengthen the idea of Early Cretaceous subduction beneath the Karakoram terrain. Inherited older zircon cores (278–393 Ma, 476–519–713–952 Ma and 1933 Ma) suggest a contribution from heterogeneous Palaeozoic and Proterozoic sources in the generation of the Tirit granitoids similar to those observed elsewhere in the Karakoram-Kohistan region. A mean crystallization age (105.30 ± 0.80) of zircons in the Tirit granitoid hosting xenoliths of porphyritic volcanics places a minimum eruption age of ca. 105 Ma for the Shyok volcanics. The Ladakh granitoid, Tirit granitoids and porphyritic volcanic xenolith belong to a calc-alkaline series. A mean crystallization age (67.32 ± 0.66 Ma) for zircon in the Ladakh granitoid implies that the Shyok metasediments (shale/slate) were deposited and metamorphosed prior to ca. 68 Ma. Present and earlier determined ages on Tirit granitoids revealed that the subduction-related calc-alkaline magmatism in the Nubra-Shyok valley of the SSZ prevailed between 110 and 68 Ma, and hence a minimum age of Early Cretaceous can be suggested for development of the SSZ. [ABSTRACT FROM AUTHOR]

In this study, we investigate zircons with high U and Th contents of 12,000–24,000 and 11,000–40,000 ppm, respectively, from leucocratic granite in the Weondong region of South Korea. Hydrothermally epitaxial growth textures are observed in addition to four distinct textures with different backscattered electron (BSE) intensities within single zircon crystals . We describe the internal textures of the zircon crystals and define the chemical characteristics of each textural domain. The zircon crystals show internally recrystallized and externally crystallized textures, supporting the concept of post-magmatic fluid control. After crystallization of the primary zircon by late magmatism, four types of secondary textures were developed. The type-I domain shows patchy forms within the primary domain due to the structural and chemical recrystallization of self-irradiated zircon by a fluid-dominated diffusion reaction process. The type-II domain is characterized by a pure zircon composition, mineral inclusions (mainly thorite), and micropores due to chemical recrystallization by a coupled dissolution–reprecipitation process during interaction with aqueous fluids. The type-III domain is the purest zircon, is interconnected with type-II, and formed by a second coupled dissolution–reprecipitation process. The type-IV domain is the hydrothermal recrystallization/overgrowth texture formed by the direct crystallization process from fluorine-enriched, zircon-saturated aqueous fluid. These results indicate that the zircon crystals were formed sequentially or intermittently through multi-genetic processes by post-magmatic fluids. Furthermore, we conclude that F-enriched post-magmatic fluid migrated large amounts of zirconium, resulting in the typical overgrowth texture of zircon. [ABSTRACT FROM AUTHOR]

The Odaesan Gneiss Complex (Odesan Gneiss Complex) is the eastern end of the Hongseong–Odaesan collision belt in the Korean Peninsula, which is an extension of the Dabie–Sulu collision belt between the North and South China cratons. The Odaesan Gneiss Complex mainly consists of banded and migmatitic gneisses with porphyritic granitoids and amphibolites. The garnet-bearing banded gneisses can be subdivided into garnet–biotite and garnet–orthopyroxene banded gneisses. At the beginning of the post-collision stage, the banded gneisses underwent regional ultrahigh-temperature metamorphism (902–950 °C/8.8–9.4 kbar) at ca. 247–245 Ma due to the heat supplied from underplated basic magma, which was generated by the partial melting of the lithospheric mantle caused by the heat supplied from the asthenospheric mantle. As a result of the continuous extensional force, the study area (lower crust) uplifted onto the middle crust depths, and then the study area underwent prograde granulite facies metamorphism from 660 °C and 8.7 kbar to 750–760 °C and 6.3–6.5 kbar at ca. 227 Ma, causing migmatization, which erased the ultrahigh-temperature metamorphism in most of the study area. The ultrahigh-temperature metamorphism was preserved only in the garnet–orthopyroxene banded gneisses due to their very low water contents. During migmatization, the garnet–biotite banded gneisses were retrograded into upper granulite facies due to the relatively abundant water compared with the garnet–orthopyroxene gneisses. Finally, the study area was uplifted to a shallow depth and locally underwent amphibolite facies retrograde metamorphism (575–680 °C and 3.1–4.5 kbar). In addition, Paleoproterozoic metamorphic (ca. 1930–1886 Ma) and post-collisional magmatic events (ca. 1847 Ma) are identified based on SHRIMP age dating. These ages agree well with the regional Paleoproterozoic metamorphic and post-collisional magmatic activities reported from other areas of the Gyeonggi Massif. [ABSTRACT FROM AUTHOR]

Triassic coeval mafic and intermediate magmatism occurred in the area suggested to be the southern margin of the North China Craton (NCC) in the Gyeonggi Massif (GM) of the Korean Peninsula. This study investigates aspects of the mafic and intermediate magmatism using SHRIMP zircon ages and whole-rock chemical and isotopic Sr–Nd data. The mafic and intermediate rocks intruded into a basement paragneiss in three areas (Yangpyeong, Odesan and Yangyang) within the GM at ca. 230 Ma. The paragneiss was metamorphosed in both the Paleoproterozoic and Triassic. Gabbros (hornblende gabbro and pyroxene–mica gabbro) from the study areas exhibit strong light REE (LREE) enrichment relative to chondrite (La N /Yb N = 11.1–30.6) and a high LILE/HFSE pattern, Ta–Nb–P–Ti troughs and positive Ba–K–Pb–Sr spikes on the N-MORB-normalized multi-element variation diagram. These features are typical characteristics of arc-related gabbros. The gabbros also show strongly enriched initial isotopic compositions ( 87 Sr/ 86 Sr (i) = 0.7100–0.7137; ε Nd (t) = − 13.1 to − 19.7). The coeval intermediate intrusive rocks also exhibit whole-rock chemical and isotopic features ( 87 Sr/ 86 Sr (i) = 0.7099–0.7143; ε Nd (t) = − 10.8 to − 18.6) similar to those of the gabbros. The mafic and intermediate intrusive rocks plot in the within-plate and/or post-collisional fields on tectonic discrimination diagrams. These data indicate that the mafic and intermediate magmatism in the study areas occurred during the Triassic post-collisional relaxation period via partial melting of sub-continental lithospheric mantle (SCLM) that was enriched in a subduction environment prior to (or during) the Permo-Triassic continental collision between the NCC and the South China Craton (SCC). The highly enriched mantle signatures revealed by the gabbros from the study areas are matched to the enriched features identified in Cretaceous mafic igneous rocks (ca. 130 Ma) on the southern margin of the NCC. Thus, this study suggests that the lithospheric mantle beneath the Yangpyeong, Odesan and Yangyang areas are comparable to the SCLM of the NCC southern margin. The highly enriched nature of mafic and intermediate rocks from the study areas indicates that their source is the SCLM that was metasomatized by Permian to early Triassic subduction–continental collision processes. [ABSTRACT FROM AUTHOR]

Sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb ages and whole-rock chemical compositions of Early to Middle Jurassic plutons from the central to southern Korean Peninsula are reported to investigate the effect of paleo-Pacific plate subduction preserved along the continental margin. Twenty-one plutonic rocks from the Yeongnam massif (i.e., Sunchang and Namwon plutons), the Okcheon belt (Jeongup, Boeun, and Mungyeong plutons), the northeast (Gangreung pluton), and the Gyeonggi massif (Gonam, Anheung, and Ganghwa plutons) have age ranges from ca. 189–186 Ma to 177 Ma, 177–166 Ma, and 177–173 Ma, respectively. Most plutonic rocks have chemical compositions similar to adakites, showing high SiO 2 (45.62–74.96 wt.%), low MgO (0.01–2.84 wt.%), high Na 2 O (2.65–4.83 wt.%), high Sr/Y and La/Yb, low Y and Yb, as well as low HFSEs (Nb and Ta), but initial Sr ratios (0.7048–0.7262), K 2 O (0.50–5.88 wt.%), and K 2 O/Na 2 O (0.34–2.1) were unlikely to have been formed by melting of either a thickened and/or delaminated lower continental crust, or an altered oceanic crust. These suggest that the “adakitic” plutonic rocks in this region resulted from partial melting of an enriched mantle source metasomatized by dewatering from a delaminated flat-slab. The spatial distributions of this continental adakitic plutonic belt, based on the present study, together with previously reported geochronological results, indicate that magmatic pulses gradually migrated toward the continent across the Korean Peninsula as a result of slab shallowing caused by periodic slab buckling. The similar geochronological and geochemical characteristics, petrogenesis and tectonic setting of the plutonic belt spanning the Korean Peninsula, Japan, eastern China, and eastern Russia indicate a possible link to an active subduction system that existed during the Early to Middle Jurassic, although the products of the plate subduction might differ in different locations along the East Asian continental margin. [ABSTRACT FROM AUTHOR]

The Mesoarchaean Kapisilik and Eoarchaean Isukasia terranes in the Nuuk region of southern West Greenland were tectonically juxtaposed in the Archaean. The north of the Isukasia terrane is distal from the Kapisilik terrane and has only rare growth of ∼2690 Ma metamorphic zircon and no 2980–2950 Ma metamorphic zircon. The southern part of the Isukasia terrane lies between two ∼2690 Ma shear zones, and has locally preserved high pressure granulite facies assemblages and widespread growth of 2980–2950 Ma metamorphic zircon and also sporadic growth of ∼2690 Ma metamorphic zircon. Within this southern part of the Isukasia terrane there is a folded klippe of mylonitised Mesoarchaean detrital meta-sedimentary rocks (carrying >3600 and ∼3070 Ma detrital zircons), mafic and ultramafic rocks, with ∼2970 Ma metamorphic zircon overgrowths. South of the Isukasia terrane is the Kapisilik terrane, containing ∼3070 Ma arc-related volcanic rocks, gabbro-anorthosites and meta-tonalites, intruded by 2970–2960 Ma granites. Zircons of an Ivisârtoq supracrustal belt ∼3075 Ma intermediate volcanic rock have initial ɛ Hf values of +2 to +5 thus are juvenile crustal additions. ∼3070 Ma tonalites along the northern edge of the Kapisilik terrane have whole rock positive initial ɛ Nd values and thus are also juvenile crustal additions. In contrast, igneous zircons in 2960 Ma granites intruded into juvenile ∼3075 Ma supracrustal rocks of the Kapisilik terrane have initial ɛ Hf values of −5 to −10, and must have involved the partial melting of >3600 Ma Isukasia terrane rocks. The integrated structural and zircon U-Th-Pb-Hf isotopic data show that at 2980–2950 Ma the Kapisilik terrane juvenile arc components collided with, and over-rid, the Isukasia terrane. The southern edge of the Isukasia terrane came to lie in the deep crust under the Ivisârtoq supracrustal belt and melted at 2970–2960 Ma to produce granites. These granites derived from ancient crust rose into the upper crust, where they intruded the overlying allochthonous juvenile ∼3075 Ma Ivisârtoq supracrustal belt arc assemblages. The southern edge of the Isukasia terrane is interpreted as an interior nappe of Eoarchaean basement rocks interfolded with a klippe of Mesoarchaean metasedimentary and mafic/ultramafic rocks, both of which are affected by 2980–2950 Ma metamorphism. The mixed Eoarchaean–Mesoarchaean detrital provenance suggests that the klippe could be dismembered components of an accretionary prism or forearc crust. The northern part of the Isukasia terrane is interpreted as foreland, free of 2980–2950 Ma high-grade metamorphic overprint. This shows that the Isukasia terrane is not a coherent block, but contains ancient rocks that are parautochthonous or allochthonous to each other, with contrasting later metamorphic history. At ∼2690 Ma the crustal architecture arisen from Mesoarchaean collision between an older continental block and an island arc was reworked along intra-crustal shear zones, coeval with amphibolite facies metamorphism. This reworking followed on from major terrane assembly at 2710–2700 Ma in the southern part of the Nuuk region, when the Eoarchaean Færingehavn terrane was juxtaposed with 2840–2825 Ma arc rocks. Thus the 2980–2950 Ma assembly of the Isukasia and Kapisilik terranes is distinct from the later 2710–2700 Ma terrane assembly further south in the Nuuk region. [ABSTRACT FROM AUTHOR]

Gneisses and migmatites exposed in the Yangpyeong area in the northern Gyeonggi Massif provide insight into the Paleoproterozoic and Triassic metamorphic events in South Korea. Garnet–biotite gneiss and sillimanite–garnet–biotite gneiss in the western part of the area reveal Paleoproterozoic metamorphism (1888–1871 Ma) at P–T conditions of 760–820 °C and 8–10 kbar and 710–750 °C and 5–7 kbar, respectively. These rocks were overprinted by low-P/T type metamorphism (590–650 °C, 3–4 kbar) during the Triassic (ca. 237 Ma). In contrast, a cordierite-rich migmatite near the post-collisional Triassic igneous complex in the eastern part of the area was strongly metamorphosed during the Triassic (ca. 235 Ma) at 750–790 °C and 7–8 kbar. The similar Triassic ages in the western and eastern areas suggest that low-P/T type metamorphism occurred as a second stage of regional metamorphism, which is characterized by the production of cordierite with an irregularly shaped garnet. The metamorphic grade of the Triassic metamorphism decreases spatially towards the west from granulite facies to amphibolite facies metamorphic conditions, and the Paleoproterozoic metamorphism is well preserved in the western part with low grade Triassic metamorphism. The new discovery of the Triassic metamorphic event in the Yangpyeong area, in addition to the previously reported Triassic post-collision igneous event, supports the idea that the continental collision belt between the North and South China blocks extends from the Hongseong area into the Odesan area through the Yangpyeong area in South Korea. [ABSTRACT FROM AUTHOR]

• 50 years post-discovery the Isua supracrustal belt remains the best Eoarchean archive. • Rare relicts of volcanic and sedimentary structures are unique for the Eoarchean. • The belt provides the most robust and diverse evidence for early life (3800–3700 Ma) • The belt and adjacent orthogneisses are tectonically-complex with multiple events. • The Isua area's geology is inconsistent with stagnant-lid/heat-pipe models. In the early 1970s, Vic McGregor and Stephen Moorbath demonstrated that the Isua supracrustal belt (Greenland) and its surrounding orthogneisses formed in the Eoarchean (Moorbath et al., 1972 , 1973). Fifty years later, these rocks are a key resource globally for understanding the Eoarchean Earth. This is because there is an extensive area (∼200 km2) of abundant outcrops where superimposed Neoarchean strain is modest, and Neoarchean metamorphism was only at lowest amphibolite facies; these are low tectonothermal conditions compared with other Eoarchean crustal remnants globally. Therefore, this region can provide the clearest window onto early Earth geodynamics. Within the Isua supracrustal belt there are rare areas where Eoarchean strain is also low, and these areas provide unambiguous recognition of diverse lithologies including sedimentary carbonates with the oldest proposed but contested stromatolites, pillow lavas, volcano-sedimentary lithologies and ultramafic rocks derived from layered intrusions (accepted) and slivers of mantle-derived meta-serpentinite that underwent Eoarchean ultra-high-pressure metamorphism (contested). As explored in previous papers (e.g., Polat et al., 2002), the geochemical signatures of the mafic igneous rocks, which include a boninite-like suite, indicate their magmas were derived by fluid fluxing of peridotites. Radiogenic isotopic signatures define discrete pulses of Eoarchean juvenile crustal growth, until a tectonic event at ∼3660 Ma with high pressure metamorphism that was followed by a switch to crustal recycling with the production of granites sensu stricto. Our appraisal of the integrated evidence points to complex superimposed Eoarchean events (∼3820–3600 Ma) driven by lateral lithosphere movements in convergent boundary settings, rather than a single crustal overturn such as within a model heat-pipe scenario. [ABSTRACT FROM AUTHOR]

Highlights: [•] The Paleoproterozoic magmatic and M2 metamorphism in the Northen Gyeonggi Massif occurred at ca. 1886–1864Ma. [•] The estimated peak P–T conditions of M2 metamorphic are 790–840°C and 7.2–8.9kbar. [•] These events occurred due to the collision along Jiao-Liao-Ji belt in North China Craton. [ABSTRACT FROM AUTHOR]

Highlights: [•] D1 deformation in northern Gyeonggi Massif during collision along Jiao-Liao-Ji belt. [•] The emplacement of post-collision granitoid at ca. 1867–1881Ma. [•] D2 deformation during Permo-Triassic collision between North and South China blocks. [•] Intermediate-P/T metamorphism during Permo-Triassic collision. [Copyright &y& Elsevier]

Abstract: The establishment of robust Paleozoic tectonic links between parts of the Korean Peninsula and cratonic blocks within China remains uncertain, despite their important implications for the overall tectonic evolution of East Asia. Here we provide new SHRIMP U–Pb detrital zircon geochronological constraints on correlations between sedimentary rocks of the Taebaeksan Basin (Cambrian–Ordovician) of South Korea and possible source rocks in the North and South China cratons. The detrital grain compositions and whole-rock rare earth element (REE) compositions of sandstones from the Cambrian formations in western (Sambangsan) and eastern (Myeonsan) parts of the Taebaeksan Basin suggest that the sedimentary provenance of these two formations is either a recycled orogen or a magmatic arc. The magmatic (eastern part) versus metamorphic (western part) origins inferred for the youngest populations (ca. 0.5–0.6Ga) of detrital zircon grains from the Cambrian formations collectively indicate that rapid uplift and erosion of the source rocks for the formations took place soon after the associated magmatic and metamorphic events. Thus, we propose that the paleo-sedimentary environments in which these two formations were deposited may have been retroarc basins with the detrital zircons originating from magmatic arcs. The Early Cambrian formation in the eastern Taebaeksan Basin contains populations of detrital zircon grains that show prominent age peaks at ca. 2.0Ga and ca. 1.8Ga, and a distinct lack of Meso- to Neoproterozoic ages, whereas the Middle Cambrian formation in the western Taebaeksan Basin exhibits age peaks at ca. 1.0Ga and ca. 0.7Ga. These age spectra imply that the western Taebaeksan area at the margin of the North China Block may once have been near Gondwana, whereas the eastern Taebaeksan area may have been situated at the margin of the North China Block more distant from Gondwana. [Copyright &y& Elsevier]

Abstract: One of the challenges in dating rock surfaces is the choice of the luminescence mineral. Although quartz is the preferred dosimeter in sediment dating, it is often not sufficiently sensitive when extracted from solid rocks. The intensity of signals from feldspars tends to be much less dependent on geological origin and erosion history, but the dosimetry of K-rich feldspar grains extracted from rocks is complicated because the internal dose rate is very dependent on the original feldspar grain size. The in situ grain size information is lost during the crushing process used to separate the grains for measurement. This latter problem does not apply to Na-rich feldspar because of the absence of internal radioactivity. The potential application of Na-rich feldspar as a luminescence dosimeter for the IRSL dating of rock surfaces is investigated using a variety of sediment samples from different geological settings for which independent age control is available. The blue and yellow luminescence emissions are measured for IR stimulation at 50 °C (IR50), and post-IR IR stimulation at 290 °C (pIRIR290). Thermal stability experiments imply that the corresponding signals in both emissions have comparable thermal stabilities and that all signals have similar recombination kinetics and are thermally stable over geological timescales. The IR50 doses measured using blue and yellow emissions are similar to or lower than quartz doses while pIRIR290 blue doses are higher than those from yellow emission and quartz doses. The fading rates measured for the IR50 signals are ∼3%/decade larger than those measured for the pIRIR290 signals in both yellow and blue emissions. Furthermore the average fading rates of both yellow signals are ∼3%/decade higher than the corresponding fading rates of the blue signals. However, there is no detectable correlation between fading rates and the measured D e values. The residual doses measured from the laboratory-bleached samples and a modern analogue suggest that the IR50 signals in both blue and yellow emissions bleach to the same degree, as do the corresponding pIRIR290 signals, and that there is no significant naturally-unbleachable residual dose observed using these signals. Neither anomalous fading nor incomplete bleaching explains the observed dose discrepancy between the two emissions. Eight uncorrected and fading-corrected ages are calculated for each sample based on all four signals, using the dose rate relevant to Na-rich feldspar extracts (i.e. ∼3% K). The IR50 and pIRIR290 blue ages were also calculated assuming a dose rate based on 12.5% internal K (i.e. assuming that the blue signals were mainly derived from contamination by K-rich feldspar). The latter pIRIR290 blue ages are in agreement with the expected age control, raising the possibility that this signal originates mainly from K-rich feldspar contamination in our Na-rich fractions, and thus is not so useful in the luminescence dating of rock surfaces. On the other hand, the pIRIR290 fading-corrected ages based on the yellow emission are consistent with the independent age controls; higher preheat and stimulation temperatures may result in more stable yellow signals from Na-rich feldspar extracts from rocks, and so reduce the size of the fading correction. We conclude that, because this signal avoids the dosimetry difficulties of K-rich feldspar extracts, it has considerable potential in the IRSL dating of rock surfaces. [Copyright &y& Elsevier]

Abstract: We analyzed detrital zircons in four metasandstones and two metadiamictites of the central Ogcheon Metamorphic Belt (OMB) in order to provide geochronologic constraints on the time of deposition and protolith age distributions. SHRIMP U-Pb ages of the newly analyzed zircons range from Archean to Early Paleozoic, and their age patterns permit the definition of four lithotectonic slices: upper and lower Pibanryeong units consisting primarily of quartzite and metasandstone; an upper Poeun unit of black slate containing Early Permian plant fossils; and a lower Poeun unit made up of metasandstone and metadiamictite. A quartzite of the upper Pibanryeong unit yielded two major zircon age populations at 965±11Ma and 447±5Ma, whereas two lower Pibanryeong metasandstones show major age concentrations at ∼2.5Ga, 1.0–0.9Ga, and 545–535Ma. The youngest components of these units suggest maximum ages of sedimentation as Late Ordovician and Early Cambrian, respectively. These upper and lower Pibanryeong zircon age distribution patterns are consistent with those of Ordovician and Devonian sedimentary strata, respectively from the South China Craton (SCC). On the other hand, three samples of the lower Poeun unit yielded two distinct age populations at ∼1.87Ga and 755±7Ma. In addition, a metadiamictite contains abundant Mesoproterozoic zircons with two broad peaks centered at ∼1.3 and 1.6Ga. Protolith ages and distribution patterns are profoundly different between the Pibanryeong and Poeun lithotectonic packages, suggesting the presence of a major thrust fault juxtaposing allochthons that are also characterized by large P–T contrasts. Our detrital zircon results for the Pibanryeong unit are compatible with derivation from the SCC, in apparent contrast with the Poeun occurrence of Early Permian plant fossils most likely correlative with the North China Craton (NCC). Taken together, the suturing of Paleozoic metasedimentary terranes in the OMB is a product of Permo–Triassic orogeny reflecting collision of the North and South China cratons. [Copyright &y& Elsevier]

Abstract: We report La–Ce and Sm–Nd isotopic data for leucogranites having tetrad rare earth element (REE) patterns at Imweon area in the northeastern Yeongnam Massif, South Korea. The leucogranites are strongly peraluminous (A/CNK=1.18–1.79) S-type granite generated by the partial melting of metasediments, which consist of quartz, K-feldspar, plagioclase, muscovite, biotite, garnet and sillimanite. The leucogranites have three types of chondrite-normalized REE patterns: one showing a tetrad REE pattern of M-type with a large negative Eu anomaly, another with slightly V-shaped REE pattern with a positive Eu anomaly, and third with an REE pattern of crustal type with an LREE-enriched and HREE-depleted pattern. U–Pb zircon ages and, Sm–Nd and Rb–Sr whole-rock ages from the leucogranites are 1853±15Ma −1859±14Ma (2σ), 1833±220Ma (2σ) with ε Nd(1.83Ga)=−6.6±5.5 (2σ) and 1740±71Ma (2σ) with initial 87Sr/86Sr=0.755±0.050 (2σ), respectively. These values suggest that the leucogranites were emplaced from magma formed by partial melting of the crustal material. In the ε Ce–ε Nd diagram, the present Ce and Nd isotopic compositions of the leucogranites with a tetrad REE pattern are plotted in the positive ε Nd and ε Ce field whereas those of the leucogranites without tetrad REE pattern are in the negative ε Nd and positive ε Ce field. The initial Ce isotope values of the leucogranites with a tetrad REE pattern are plotted in a range of −2.31< ε Ce(1.85Ga)<+3.3. The initial Ce isotopic values of the leucogranites without a tetrad REE pattern are extremely high, +3.3< ε Ce(1.85Ga)<+21.8. The initial ε Nd(1.85Ga) values of the leucogranites are similar in the range of −8.63< ε Nd(1.85Ga)<−4.19 regardless of the existence of a tetrad REE pattern, suggesting that Ce isotopes of the source materials should be more heterogeneous than Nd isotopes. Our La–Ce, Sm–Nd, and Rb–Sr isotopic data indicate that the tetrad REE pattern was formed by a specific geochemical reaction during granitic magma emplacement rather than by metamorphism, alteration, and weathering. [Copyright &y& Elsevier]

• New U-Th-Pb data for TTG orthogneisses from Scott and Raggatt Mountains. • Circa 2720 Ma igneous event was widespread in the SE Napier Complex. • Formation of protoliths for ca. 2720 gneisses involved medium-pressure melting. • Synmetamorphic ca. 2530 Ma tonalitic magmatism was generated at lower pressures. • Independent crustal domains in the complex may be assembled at ca. 2.5 Ga. The Napier Complex of Enderby Land and Kemp Land is a unique part of the Eastern Antarctic Shield, as it preserves history of crustal growth extending from the Eo- to Neoarchean. It is composed mainly of enderbitic and charnockitic gneisses and granulites metamorphosed at ca. 2.5 Ga, and locally at ca. 2.8 Ga, under high- to ultra-high temperature conditions. These events have been well-characterized in the central and western parts of the complex; however, the south-southwestern region has been little studied. Samples from the southern Scott and Raggatt Mountains were selected for zircon U-Pb dating by Secondary Ion Mass Spectrometry and whole-rock geochemical analysis. Tonalitic gneiss from the Raggatt Mountains and trondhjemitic gneiss from the southern Scott Mountains have protolith ages of 2711 ± 5 Ma and 2726 ± 6 Ma, respectively. In contrast, tonalitic samples from the southern Scott Mountains have protolith ages of ca. 2539 ± 5, 2533 ± 5 and 2522 ± 9 Ma. The younger generation of magmatism overlaps the timing of metamorphic zircon growth between 2540 and 2440 Ma observed in this study. The geochemistry of ca. 2720 Ma gneisses indicates that magmatism was generated by medium-pressure melting (>1.5 GPa) of basaltic crust, whereas ca. 2530 Ma magmas were generated at lower pressures (< 1.2 GPa). The ca. 2.7 Ga magmatism may be associated with continental crust formed at 2.8 Ga, or be newly formed crust that was assembled with older prior to or during a tectonometamorphic event at ca. 2.5 Ga. Tonalitic magmatism at 2.53 Ga during the first half of the 2585–2420 Ma metamorphic event may be a product of partial melting during high-grade metamorphism. Although protolith ages across the complex are still scarce, differences between regions raise the possibility that the complex contains crustal domains of different ages and origins that may not have been assembled until the ca. 2.5 Ga tectonothermal event. [ABSTRACT FROM AUTHOR]

The Variscan basement within the Western Carpathian Alpine architecture generally consists of metaluminous/peraluminous tonalite/granodiorite massifs and high-grade metamorphic complexes of metapelites, metaultramafites, and metabasites with relics of eclogites. Unfortunately, the Variscan crystalline basement of the Western Carpathians is only fragmentally exposed. Therefore, the proposed geodynamic evolutionary model for the Variscan granites of the Western Carpathians is primarily based on granite data from the Malá Fatra Mts. with additional dating from the High Tatra Mts. The oldest magmatic age of 362 ± 4 Ma in the Malá Fatra horst was recorded in diatexites from a high-grade metamorphic complex, which is related to crustal anatexis during Variscan subduction. Subsequent collisional event and break-off of the subducted slab promoted exhumation of the diatexites within the high grade metamorphic complex and intrusion of 353 ± 3 Ma old Tournaisian tonalite. Intensive heat input after slab break-off from the rising asthenosphere generated melting of the lower crust and extensive calc-alkaline, Mg-rich granitic magmatism in a short time span from 347 ± 4 to 342 ± 3 Ma. These Visean granitic rocks caused thermal overprint on the roof metamorphic rocks, including diatexites and Tournaisian tonalites at ca. 348 ± 5.6 to 342 ± 3 Ma. The Visean granite formation was controlled by the mixing of hot magmas, which is indicated by the presence of composite oligoclase/andesine plagioclase with preserved labradorite cores, alkali feldspars with Na 2 O ≥ 2 wt%, zoned apatite, the presence of antiperthite, and quartz ocelli. Elevated contents of mantle-derived elements like V, Ni, Cr, Ba, high Sr/Y ratio of ~44, steep LREE and flat HREE segments of chondrite-normalised patterns document adakite-like feature of the investigated granitic rocks which resulted from melting of a mixed lower-crustal and mantle sources and crystallisation in the presence of garnet. Unusual abundance of Fe–Ti oxides in granodiorites with magmatic cooling temperatures of 735–756 °C supports high-T input from mantle. In the High Tatra Mts., diorite xenolith shows the age of 359.2 ± 3 Ma, and its host granodiorite the age of 350.1 ± 2.6 Ma. The diorite contains acicular zircons, which points to rapid exhumation. Stubby zircon of the host granodiorite shows regular, oscillatory zoning controlled by a gradual temperature decrease. The non-comagmatic relationships between diorite and host granodiorite are indicated also by a difference in zircon Th/U ratio, which is 0.2 for the host granodiorite, but 1.0 for the diorite on average. The presented data show that slab break-off could have been a mechanism that promoted Variscan granitic magmatism in the Western Carpathians. • Variscan subduction, slab break-off, exhumation and partial melting recorded in the Western Carpathians • Famennian (365-359 Ma), Tournaisian (359-353 Ma), and Visean (348–342 Ma) granitic magmatism recognised • Visean granites with adakitic signature derived from the melting of a mixed lower-crustal and mantle sources [ABSTRACT FROM AUTHOR]

The pattern and timing of tectonic discontinuity and partial melting in the Garhwal Himalaya, resulting from the India–Asia collision, are crucial factors for understanding the evolution of the Himalayan orogen, but these parameters remain poorly constrained. Middle- to high-grade metamorphic rocks from the Main Central Thrust (MCT) zone and the High Himalaya Crystalline Sequence (HHCS) along the Bhagirathi valley in northwest India have been investigated in this study. The primary mineral assemblage of the gneisses and migmatites in the HHCS is garnet + biotite + white mica + quartz + kyanite + rutile ± ilmenite ± sillimanite. The metamorphic grade at thermal peak rapidly increases upwards across the MCT from garnet schists (515–550 °C, 8–9 kbar) in the footwall to garnet-bearing migmatite (705–735 °C, 10–13 kbar) in the hanging wall. The P–T condition decreased upwards in kyanite gneiss of the lower HHCS (690 °C, 8.3 kbar), yielding a high field pressure gradient near the MCT. The prominent metamorphic discontinuity could have been caused by the southward extrusion of the HHCS along with the MCT. The base of the HHCS experienced high-grade metamorphism at 38–25 Ma, mainly at 31.9 ± 0.5 Ma. The new data, combined with previous studies, suggest that the prominent metamorphic discontinuity is characterized by the different periods of peak metamorphism and the overprint in the hanging wall (Eocene–Oligocene metamorphism and Early Miocene overprint) and footwall (Early Miocene metamorphism and Late Miocene to Pliocene overprint) of the MCT. The second metamorphic discontinuity occurred near the migmatite zone in the lower-middle HHCS, which experienced the anatexis (690–740 °C, 7–9 kbar) at 37–25 Ma, mainly at 33.9 ± 1.2 Ma. The Bhagirathi HHCS experienced a regional Barrovian-type Eohimalayan metamorphism associated with fluid-present melting of muscovite + plagioclase + quartz + H 2 O → melt ± kyanite at 34–32 Ma without a strong Miocene overprint. The period of partial melting is significantly older than the intrusion of ca. 22 Ma Early Miocene Gangotri leucogranites at the top of the HHCS. Protracted periods of crystallization (38–22 Ma) indicate a long duration of more than ca. 15 Myr of anatexis, from initiation of migmatization to pluton formation in the Bhagirathi HHCS. The protracted fluid-present melting and subsequent rapid exhumation in the Bhagirathi HHCS could be associated with heterogeneous extrusion forming the tectonic discontinuity in the lower-middle HHCS. The metamorphic grade decreased towards the upper HHCS (620 °C, 6.5 kbar) across the Jhala Normal Fault where occurs in the right-way-up sequence. On the other hand, in the central Himalaya, the thrusting occurred between upper HHCS and lower-middle HHCS in the inverted metamorphic sequence. The Early Miocene migmatites in the footwall of the significant tectonic discontinuity are dominant, and diachronous extrusion accompanied with the fluid-absent melting reactions is the common mechanism to exhume the HHCS, unlike the heterogeneous extrusion in the northwest Himalaya. [Display omitted] • Two tectonic discontinuities inferred from spatial and temporal P-T conditions • 38–25 Ma pervasive fluid-present melting without a strong Miocene overprint • Heterogeneous and diachronous extrusions in northwest and central Himalayas [ABSTRACT FROM AUTHOR]

The paragneiss and migmatitic gneiss on Oki-Dogo Island, located in northern part of southwest Japan, have U Pb ages ranging from Mesoarchean to Paleoproterozoic. The youngest population of detrital zircons from the paragneiss and migmatitic gneiss suggests a maximum depositional age of ca. 1.96 Ga. Further, the three granitic gneiss samples give zircon U Pb ages of 1.97, 1.88, and 1.81 Ga. The bulk rock composition of the granitic gneiss samples followed a calc-alkaline trend and showed negative Nb, Ta, P, and Ti anomalies with low Sr/Y (<35), Nb/Th (<1), and Nb/Zr (<0.1) ratios, indicating that the protolith of the granitic gneiss formed in an arc-related setting. Zircons from the granitic rocks in Oki-Dogo Island have negative ε Hf (t) values with Mesoarchean to Neoarchean model ages (T DM2). The results of geochronological and geochemical analyses and those of previous studies indicate that Oki-Dogo Island underwent two arc-related magmatic events at ca. 1.97 Ga and ca. 1.88–1.81 Ga, which correspond well with those of the Yeongnam massif in South Korea. Thus, we suggest that northern part of southwest Japan (Oki-Dogo Island) was more closely related with the Yeongnam massif than with the North China Craton during the early Paleoproterozoic period. • Oki-Dogo Island mainly occupied by the Paleoproterozoic gneiss. • Oki-Dogo Island underwent Paleoproterozoic arc-related magmatism in two times. • Oki-Dogo Island possibly located around the Yeongnam Massif during Paleoproterozoic. [ABSTRACT FROM AUTHOR]

The eastern Wolhyeonri complex in the southwestern Gyeonggi Massif, South Korea, which has a close affinity with the northern margin of the South China Craton, primarily consists of Neoproterozoic igneous and sedimentary rocks that were metamorphosed by the middle Paleozoic thermal event. In this study, we present the results from thermobarometry, whole-rock chemistry, and zircon geochronology of rocks in the eastern Wolhyeonri complex near Gwangcheon. The main rock type, such as the migmatitic biotite gneisses, was deposited after ca. 722–680 Ma, and the associated foliated amphibolites exhibit a rift-related Neoproterozoic origin. The ca. 845–820 Ma arc-related metadolerite and mafic layer in the metavolcanic-sedimentary unit are also exposed. Two Neoproterozoic magmatic events support the idea that the southwestern Gyeonggi Massif developed along the northern margin of the South China Craton. These Neoproterozoic rocks experienced upper amphibolite-facies (7–10.5 kbar and 710–735 °C) to low-pressure granulite-facies metamorphism (10.5–12.0 kbar and 810–830 °C) during 424–412 Ma, were associated with ca. 418 Ma leucogranite formation, and then underwent retrograde amphibolite-facies metamorphism. Combined with the results from previous studies, the early-middle Paleozoic orogeny in the southern Gyeonggi Massif is characterized by 470–456 Ma subduction associated with a high P/T metamorphism, and the initiation of intermediate P/T metamorphism from ca. 445 Ma followed by low-pressure granulite-facies metamorphism at 432–403 Ma, and high-pressure granulite-facies metamorphism at 392–381 Ma, indicating that the tectonic setting transitioned from a continental collision to a post-collisional setting between 432 Ma and 392 Ma. These events and the absence of Paleozoic ultrahigh-pressure metamorphism strongly correlated with the Wuyi-Yunkai orogen in the South China Craton, rather than the Qinling belt in the North China Craton. Therefore, the early-middle Paleozoic orogeny in the southern Gyeonggi Massif was caused by the subduction and subsequent collision within the South China Craton. Unlabelled Image • A rift-related Neoproterozoic event occurred in the eastern Wolhyeonri complex. • The low-pressure granulite-facies metamorphism occurred at 432–403 Ma. • Gyeonggi Massif was correlated with the Wuyi-Yunkai orogen in Paleozoic orogeny. [ABSTRACT FROM AUTHOR]

The Kitomyo Schist from Kurosegawa Belt, Shikoku, has been long considered as the oldest records of subduction metamorphism in Japan, based on an early 1970s K–Ar dating of white mica. The schist consists of mafic and pelitic layers and occurs as a tectonic block within serpentinite. Reappraisal of the schist confirmed the schist is characterized by an epidote-amphibolite peak metamorphic facies. The mafic portion is characterized by zoned amphibole + epidote + chlorite + titanite ± phengite ± rutile. The presences of relict rutile surrounded by titanite and the barroisitic cores of zoned amphibole suggest a high-pressure intermediate type metamorphism at the metamorphic peak (P = ~0.8–1.5 GPa and T = ~500–570 °C). The presence of Mn-rich garnet and the lack of biotite, oligoclase and paragonite also support high-pressure intermediate type metamorphism that eliminate the possibility of a typical blueschist-facies metamorphism. New SHRIMP and LA-ICPMS zircon U–Pb geochronology on a pelitic sample show detrital grains of Mesoproterozoic and Early Paleozoic ages, suggesting a maximum deposition age for the trench-fill sediment of ~440 Ma. Also the U–Pb data confirmed ~360 Ma overgrown rims that might have formed during the subduction zone epidote-amphibolite facies metamorphism. Reappraisal revealed that the Kitomyo Schist is not the oldest high-pressure type schist in Japan and rather comparable to the Late Paleozoic Renge Metamorphic Rocks and their equivalents in the Kurosegawa Belt. The Devono–Carboniferous high-pressure metamorphic rocks in Japan might have been paired with their coeval batholiths along the 'Greater South China' margin that was extensively eroded during later tectonic processes. Unlabelled Image • The putative oldest high-pressure schist in Japan metamorphosed at ~360 Ma • This schist shows the typical Late Paleozoic metamorphic ages found in Renge belt • 360 Ma HP rocks in Japan are coeval with batholiths • Renge HP and batholiths possibly formed a metamorphic paired belt [ABSTRACT FROM AUTHOR]

Versatile and efficient regulation of the mechanical properties of the extracellular matrix is crucial not only for understanding the dynamic changes in biological systems, but also for obtaining precise and effective cellular responses in drug testing. In this study, we developed a well plate-based hydrogel photo-crosslinking system to effectively control the mechanical properties of hydrogels and perform high-throughput assays. We improved cell biocompatibility by using gelatin methacryloyl (GelMA) with a visible light photo-crosslinking method. Multiple cell-laden GelMA hydrogels were simultaneously and uniformly created using multi-arrayed 520 nm light-emitting diodes in a well plate format. The elastic modulus of the hydrogels can be widely adjusted (0.5-30 kPa) using a photo-crosslinking system capable of independently controlling the light intensity or exposure time for multiple samples. We demonstrate the feasibility of our system by observing enhanced bone differentiation of human mesenchymal stem cells (hMSCs) cultured on stiffer hydrogels. Additionally, we observed that the osteogenic fate of hMSCs, affected by the different mechanical properties of the gel, was regulated by parathyroid hormone (PTH). Notably, in response to PTH, hMSCs in a high-stiffness microenvironment upregulate osteogenic differentiation while exhibiting increased proliferation in a low-stiffness microenvironment. Overall, the developed system enables the generation of multiple cell-laden three-dimensional cell culture models with diverse mechanical properties and holds significant potential for expansion into drug testing., (© 2024 IOP Publishing Ltd.)

Background: It is important to quantify changes in CO 2 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 CO 2 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 CO 2 sources throughout the year (2.75 and 1.02 kg C m -2  year -1 at the urban and suburban sites), and the net CO 2 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 CO 2 emission rate per capita (0.7 t CO 2  year -1  person -1 ), especially in winter because of a district heating system and smaller traffic volume. The suburban area shows larger net CO 2 emissions per capita (4.9 t CO 2  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.

Objective: The purpose of this study was to evaluate the effects of different desensitizing agents on the prevention of root caries when applied to root surfaces., Materials and Methods: Thirty human roots were sectioned into quarters with a 3 × 4 mm window. A desensitizer (VX, Clinpro™ XT Varnish; SP, Seal & Protect®; or PB, Clearfil™ Protect Bond) was applied to three of the quarters in each window. Teeth were stored separately in water for one day, 30 days, or 60 days. The remaining quarter, without the application of desensitizer, served as a control. After storage in water, all specimens were subjected to pH cycling. Scanning electron microscopy was used to observe the demineralization bands created on the subsurface layer. The weight percentages of fluorine (F), silica, and calcium (Ca) were determined using electron probe microanalysis to quantify the elemental distributions in the root dentin. The concentrations of F released during a pH cycling were measured., Results: For the control group, the average lesion depth was 18.92 ± 5.42 μm, and the average Ca loss was 15.66% ± 6.80% in the superficial layer and 30.44% ± 9.61% in the subsurface layer. No Ca loss occurred in the desensitizer-treated groups. All desensitizing agents remained intact for at least 60 days. F levels were increased in the hybrid layer but not in the subhybrid area. Outward release of F diminished with time., Conclusion: The F-containing resin-based desensitizers protected exposed root surfaces from demineralization. F liberated from the desensitizers was detected only at minimal levels.

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.

In this laboratory study, the microtensile bond strengths of a conventional glass ionomer cement (GIC) and a resin modified glass ionomer cement (CRMGIC) to artificially created carious dentin and sound dentin were compared, and the ultrastructural morphology of the fractured interface was examined with a low-vacuum scanning electron microscope (SEM). The specimens were divided into 4 groups: 1) a conventional GIC (Ketac-Fil Plus Aplicap) placed on sound dentin; 2) a conventional GIC placed on artificially created carious dentin; 3) an RMGIC (Photac-Fil Aplicap) placed on sound dentin and 4) an RMGIC placed on artificially created carious dentin. Artificial carious lesions were created using a chemical demineralizing solution of 0.1 M/L lactic acid and 0.2% carbopol. GIC buildups were made on the dentin surfaces according to the manufacturer's directions. After storage in distilled water at 37 degrees C for 24 hours, the teeth were sectioned vertically into 1 x 1 x 8-mm beams for the microtensile bond strength test. The microtensile bond strength of each specimen was measured, and failure mode was determined using an optical microscope (40x). The fractured surfaces were further examined with SEM. Two-way analysis of variance showed that the mean microtensile bond strengths of a GIC and an RMGIC to carious dentin were significantly lower than those to sound dentin, and the mean microtensile bond strengths of Photac-Fil to both sound and carious dentin were significantly higher than those of Ketac-Fil Plus. Chi-square tests indicated that there was a significant difference in failure mode between the sound dentin and carious dentin groups. In sound dentin groups, cohesive failure in GIC was pre- dominant; whereas, mixed failure was predominant in carious dentin groups. SEM examination showed that the specimens determined to be cohesive failures under light microscopy in the Photac-Fil/Sound Dentin group were actually mixed failures under high magnification of SEM.

This study compared silver penetration in the adhesive interface among four versions of adhesives from the same manufacturer: OptiBond FL, OptiBond Solo Plus, OptiBond Solo Plus Dual Cure, and OptiBond Solo Plus Self-Etch, when coupled with dual-cured composite, CoreRestore 2 (Kerr). Twenty flat dentin surfaces were prepared using one of the adhesives and bonded with the composite, following the manufacturer's instructions. The surfaces were sectioned into 2-mm slabs and immersed in ammoniacal silver nitrate for 24 hours. Each specimen was exposed to a photodeveloping solution for eight hours and examined with a scanning electron microscope (SEM). The water permeable area occupied by the silver nitrate tracer was determined, and the relative weight of silver was analyzed by wavelength dispersive spectrometry (WDS). The OptiBond FL group had a significantly lower silver content than the other groups (p < 0.0001). Each group demonstrated different patterns of silver deposition within the adhesive layer and within various features of artifactual fracture from dehydration stress of the SEM. This may be indicative of weak links in the bonded interfaces. Simplified-step adhesives showed increased permeability, which can lead to disruption of coupling with composites.