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[Display omitted] • Alkaline magmatism prevailed for about 19 Ma between 84 and 65 Ma in the EPOB. • All samples display typical characteristics of subduction-related arc magmas. • The isotopic data indicate mixing of enriched subcontinental mantle and crustal sources. • All data are consistent with a model of southward subduction in Late Cretaceous. The Eastern Pontides Orogenic Belt (EPOB) in northeastern Turkey is a continental arc that is part of the Himalayan-Alpine orogeny. Late Cretaceous magmatism in this belt is dominated by high-K calc-alkaline, shoshonitic, and alkaline rocks that occur over an area of ~600 km (E-W) and ~200 km (N-S). We present new geochemical data (whole rock major and trace element analyses, mineral compositions, U-Pb zircon and titanite ages, zircon trace element data, and Sr-Nd-Pb isotopic analyses) for 153 samples, with compiled data for an additional 265 samples. Magmatism is diachronous across the arc. In the north, Cycle-I (92–84 Ma) commenced with tholeiitic and calc-alkaline basalts and andesites, and continued with felsic extrusive rocks. Cycle-II (84–70 Ma) includes mainly intermediate and felsic extrusive rocks. Over time,the low-K granitoids progressively give way to calc-alkaline granitoids in the north. In the south, Cycle-I (84–78 Ma) includes high-K trachyandesites, trachytes and felsic extrusive rocks. Cycle-II (78–65 Ma) comprises leucitites, trachybasalts, and other K-rich rocks. Shoshonitic granitoids in the south show ages between 80 and 65 Ma. Clinopyroxene compositions in trachyandesites and leucitites indicate initial crystallization at ~38 km depth and 1120 °C. Amphibole joins the phase assemblage at ~8 km depth and T < 950 °C. All samples have LILE and LREE enrichments and negative Nb, Ta, and Ti, and positive Pb anomalies, consistent with their subduction-related origin. Isotopic data indicate mixing between magmas from heterogeneous, enriched subcontinental mantle sources and those from a range of crustal sources. Mantle-derived and crustally-derived magmas are clearly separated by (Gd/Yb) N. Chemical zoning of the EPOB, from tholeiitic and calc-alkaline rocks to high-K calc-alkaline, shoshonitic, and alkaline rocks, from north to south, and the timing of magmatism younging southward, are consistent with a model of southward subduction in the Late Cretaceous. [ABSTRACT FROM AUTHOR]

We constrain the multistage tectonic evolution of the Palaeoproterozoic UHT metamorphic (P ​= ​0.9–1.0 ​GPa, T >1000 ​°C, t ​= ​2088–2031 ​Ma) Bakhuis Granulite Belt (BGB) in Surinam on the Guiana Shield, using large- to small-scale structures, Al-in-hornblende thermobarometry and published fluid inclusion and zircon geochronological data. The BGB forms a narrow, NE–SW striking belt between two formerly connected, ~E–W oriented granite-greenstone belts, formed between converging Amazonian and West African continental masses prior to collision and Transamazonian orogeny. Inherited detrital zircon in BGB metasediments conforms agewise to Birimian zircon of West Africa and suggests derivation from the subsequently subducted African passive margin. Ultrahigh-temperature metamorphism may have followed slab break-off and asthenospheric heat advection. Peak metamorphic structures result from layer-parallel shearing and folding, reflecting initial transtensional exhumation of the subducted African margin after slab break-off. A second HT event involves intrusion, at ca. 0.49 ​GPa, of charnockites and metagabbros at 1993–1984 ​Ma and a layered anorthosite at 1980 ​Ma, after the BGB had already cooled to < 400 ​°C. The event is related to northward subduction under the greenstone belts, along a new active margin to their south. A pronounced syntaxial bend in the new margin points northward towards the BGB and is likely the result of indentation by an anticlinorial flexural bulge of the subducting plate. Tearing of the subducting oceanic plate along this bulge explains why the charnockites are restricted to the BGB. The BGB subsequently experienced doming under an extensional detachment exposed in its southwestern border zone. Exhumation was focused in the BGB as a result of the flexural bulge in the subducting plate and localised heating of the overriding plate by charnockite magmatism. The present, straight NE–SW long-side boundaries of the BGB are superimposed mylonite zones, overprinted by pseudotachylites, previously dated at ca. 1200 Ma and 950 ​Ma, respectively. The 1200 ​Ma mylonites reflect transpressional popping-up of the BGB, caused by EW-directed intraplate principal compressive stresses from Grenvillian collision preserved under the eastern Andes. Further exhumation of the BGB involved the 950 ​Ma pseudotachylite decorated faulting, and Phanerozoic faulting along reactivated Meso- and Neoproterozoic lineaments. Image 1 • Granulite belt represents southward subducted W. African passive margin sediments. • Back-sliding and transtension of subducted margin during ≥2030 ​Ma, 9–10 ​kbar UHTM. • 1993–1984 ​Ma charnockites relate to slab tear in northward subducting plate. • Post-charnockite extensional detachment overlies dome in migmatitic granulites. • Transpressional pop-up at ~1200 ​Ma by Grenvillian intraplate stresses. [ABSTRACT FROM AUTHOR]

This article reviews the geology of the Sveconorwegian orogen in south Scandinavia and existing tectonic models for the Mesoproterozoic to Neoproterozoic Sveconorwegian orogeny. It proposes an updated geodynamic scenario of large, hot, long-duration continental collision starting at c. 1065 Ma between proto-Baltica and another plate, presumably Amazonia, in a Rodinia-forming context. An orogenic plateau formed at 1280 Ma as a back-arc Cordillera-style plateau, and then grew further stepwise after 1065 Ma, as a collisional Tibetan-style plateau. Voluminous mantle- and crustal-derived Sveconorwegian magmatism took place in the hinterland in the west of the orogen, mainly: (i) bimodal magmatism at 1280–1145 Ma, overlapping with extensional intramontane basin sedimentation, (ii) the calc-alkaline Sirdal magmatic belt at 1065–1020 Ma, (iii) the hydrous ferroan hornblende-biotite granite (HBG) suite at 985–925 Ma and (iv) the anhydrous ferroan massif-type anorthosite-mangerite-charnockite (AMC) suite at 935–915 Ma. High-alumina orthopyroxene megacrysts in anorthosite imply mafic underplating at 1040 Ma and remelting of the underplates at 930 Ma. Overlapping with magmatism, protracted low-pressure, granulite-facies metamorphism reached twice ultra-high temperature conditions of 0.6 GPa-920 °C at 1030–1005 Ma and 0.4 GPa-920 °C at 930 Ma, respectively. These features imply shallow asthenosphere under the crust. Towards the foreland in the east, metamorphism shows an increasing high-pressure signature eastwards with time, with peak P-T values of 1.15 GPa-850 °C at 1150–1120 Ma in the Bamble-Kongsberg lithotectonic units, 1.5 GPa-740 °C at c. 1050 Ma in the Idefjorden lithotectonic unit, and 1.8 GPa-870 °C at c. 990 Ma in the Eastern Segment under eclogite-facies conditions. These are attributed to retreating delamination of the dense sub-continental lithospheric mantle and growth of the orogenic plateau towards the foreland. After c. 930 Ma, convergence came to a halt, the orogenic plateau collapsed, and 16 km of overburden was removed by extension and erosion. Unlabelled Image • Review of the geology of the Sveconorwegian orogen in south Scandinavia (south Norway, south Sweden). • Review of geodynamic models for the Mesoproterozoic to Neoproterozoic Sveconorwegian orogeny. • Model of large, hot, long-duration continental collision for the Sveconorwegian orogeny. • Orogenic plateau construction is associated with retreating delamination of the continental lithospheric mantle. • The Sveconorwegian orogeny contributed to assembly of Rodinia supercontinent. [ABSTRACT FROM AUTHOR]

The Napier Complex of Enderby and Kemp Lands forms the north-western part of the East Antarctic Shield and consists predominantly of gneisses and granulites metamorphosed during a ca. 2.8 Ga high-grade and a ca. 2.5 Ga ultra-high temperature event. The western segment of the Napier Complex includes coastal outcrops, islands and nunataks around Amundsen and Casey Bays, and the Tula Mountains. This region records some of the highest metamorphic temperatures measured on Earth, affecting a variety of gneisses as old as ca. 3.8 Ga. Five samples of orthogneiss from the less-studied eastern Tula Mountains, including three granitic, one trondhjemitic and one dioritic gneiss, were dated by zircon U-Pb Secondary Ion Mass Spectrometry (SIMS). The three orthogneisses yield protolith ages of 3750 ± 35 Ma (granitic), 3733 ± 21 (trondhjemitic) Ma and 3560 ± 42 Ma (dioritic), whereas the two other granitic orthogneisses record ages of 2903 ± 14 Ma and 2788 ± 24 Ma. Zircon growth during metamorphism occurred at 2826 ± 10 Ma, and also between 2530 Ma and 2480 Ma. Samples from the Tula Mountains can be geochemically subdivided into Y-HREE-Nb-Ta depleted and undepleted groups. Eoarchean granitoids are included in both geochemical groups, as are Meso- and Neoarchean granitoids. The Y-HREE-Nb-Ta depleted granitoids can be generated by medium- to high-pressure melting of mafic crust, whereas undepleted granitoids can be generated by low-pressure melting. However, relatively high potassium contents in most samples, and the presence of xenocrystic/inherited zircon in some, reflect the likely involvement of felsic crustal sources. This diversity in granitoid composition occurs across the Napier Complex. The lack of a simple correlation between protolith age and geochemical type is an indication that magmatism during the Eoarchean (and later) involved diverse sources and processes, including re-melting and recycling of various crustal components, rather than just the formation of juvenile crust. Unlabelled Image • This study extends the known localities of Eoarchean crust in the Napier Complex to the eastern part of the Tula Mountains. • Archean gneisses from the eastern Tula Mountains shows Y-HREE depleted and undepleted geochemical characteristics. • Both geochemical types of rocks are present in Eo- and Meso- to Neoarchean granitoids. [ABSTRACT FROM AUTHOR]

[Display omitted] • Provenance tracking tectonic evolution of the proto-Korean Peninsula during the Paleozoic. • Hf isotope compositions preserve important information for the Paleozoic provenance variability. • Proximal/distal sedimentation transition and global sea level change resulted in changes in detritus sources. Detrital zircon geochronology and Hf isotope analysis can be used for inferring provenance characteristics, and to evaluate the tectonic evolution of sedimentary basins and their link with regional orogenesis. The Paleozoic sequences of the Okcheon Belt consist of the Lower Paleozoic Joseon and the Upper Paleozoic Pyeongan supergroups with Middle Paleozoic hiatus locally on top of the Neoproterozoic bimodal volcanic rocks, reflecting an intracontinental rift setting between the two basements (viz. Gyeonggi and Yeongnam massifs) at southern part of the Korean Peninsula. Our detrital zircon U-Pb ages and Lu-Hf isotope results show that all these Paleozoic strata commonly have Paleoproterozoic and Paleozoic zircon ages with rare Meso- to Neoproterozoic ages. The individual zircon populations display following features, allowing estimation of their sedimentary provenances: (i) The Paleoproterozoic zircons (ca. 1.85 Ga and 2.50 Ga) with similar ranges of ε Hf (t) values are most common in the basement rocks of the Korean Peninsula, and were sourced from both the Gyeonggi and Yeongnam massifs. (ii) The Meso- to Neoproterozoic zircons, preserved only in the Middle to Late Cambrian clastic sedimentary rocks within the carbonate sequences probably reflect proximal provenance. (iii) The youngest Paleozoic zircons of each formation, almost coincident with their deposition ages, suggest presence of syndepositional magmatism, indicating proximal magmatic sources during their deposition. (iv) The Cambrian–Ordovician zircons, from the Lower Paleozoic sequences, but rare in the successive Upper Paleozoic sequences, suggest a provenance change after the hiatus between the two sedimentary successions. (v) The Permian zircons showing different ε Hf (t) values indicate that detrital sources were varied at that time. The integrated results in our study suggest provenance variability linked to diverse tectonic environments, reflecting prolonged subduction-related crustal evolution of the proto-Korean Peninsula during the Paleozoic. [ABSTRACT FROM AUTHOR]

The Muju area, located on the north–central margin of the Yeongnam Massif, mainly consists of Precambrian orthogneisses (granitic, leucogranitic, augen and dioritic gneisses) with minor migmatite. Zircon U–Pb dating indicates that the protoliths of the orthogneisses intruded at ca. 2.00–1.97 Ga and were metamorphosed at ca. 1.87–1.86 Ga. Magmatic zircon grains within the orthogneisses have positive to negative εHf(t) values (−7.63 to +3.3) and a Neoarchean two-stage model age (T DM2 = 2.78 Ga), indicating that the protoliths of most of the orthogneisses may have been derived from Archean crustal material. The results of geochemical analysis indicate that the protoliths of the orthogneisses formed by partial melting of metagraywacke and mafic igneous rocks in an arc-related tectonic setting. The intrusion ages and geochemical data of the Paleoproterozoic orthogneisses in the study area match well with those of Paleoproterozoic (ca. 2.00–1.97 Ga) orthogneisses in the northeastern Yeongnam Massif, indicating the presence of regional Paleoproterozoic subduction zones along the northern margin of the Yeongnam Massif at ca. 2.00–1.97 Ga. Meanwhile, ca. 2.00–1.97 Ga subduction-related magmatism has not been reported from the northern Gyeonggi and Nangrim Massifs in the Korean Peninsula or the Jiao–Liao–Ji belt in the eastern North China Craton, indicating that the Yeongnam Massif may not be correlatable with the northern Gyeonggi and Nangrim Massifs or the Jiao–Liao–Ji belt. The Yeongnam Massif may be correlated with the Cathaysia Block in the South China Craton and may have been located near Laurentia and the Siberian Craton within the Columbia supercontinent. Unlabelled Image • Arc magmatism in the north-central Yeongnam Massif at ca. 2.0–1.97 Ga • The arc magmatism is linked to that in the northeastern Yeongnam Massif • The Yeongnam Massif may not be correlatable with the North China Craton. [ABSTRACT FROM AUTHOR]

The Eastern Pontides Orogenic Belt offers critical clues on the origin of Early Cenozoic continental arc magmatism in the Alpine-Himalayan system. Systematic geological, geochemical and chronological studies indicate that there are three subgroups among the Early Cenozoic intrusions in the Eastern Pontides Orogenic Belt - Late Paleocene-Early Eocene adakitic intermediate-felsic intrusions, Eocene mafic intrusions, and Eocene non-adakitic granitoid intrusions. Here we focus on the petrology and geodynamic setting of the Eocene non-adakitic granitoid intrusions that are well exposed in a belt between the Thanetian-Ypresian adakitic intrusions in the south and the Lutetian gabbroic intrusions in the north. We also present data on enclaves and surrounding Eocene volcanics. The studied intrusions can be grouped into two main categories, based on their field and petrographical characteristics: granodiorite and monzodiorite-dominated and syenite-dominated bodies. They can be further subdivided into four groups of differing K 2 O content: low-K 2 O (Çevrepınar, Kaletaş, Sarıçiçek and Üzengili), mixed (Sorkunlu, Kozluk and Tamdere), and high-K 2 O (Dölek, Meşebaşı, Çakırbağ and Arslandede) rocks are granodioritic and monzodioritic, whereas shoshonitic (Kösedağ, Meydanlı and Bademli) bodies are syenitic. Zircon U-Pb age determinations reveal that these granitoids were emplaced into crustal rocks of the Eastern Pontides Orogenic Belt between 47 and 42 Ma, in Lutetian time, simultaneously with the gabbroic intrusions in the north. Mineral compositions and P-T calculations are consistent with the interpretation that crustal melting or magma storage started at mid-crustal depth (~ 25 km), with a magma system that subsequently extended to shallow levels (< 4 km). The studied granitoids, enclaves and volcanics exhibit geochemical signatures typical of subduction-related arc magmas, however, the shoshonitic intrusions are younger than most of the other Lutetian intrusions, and indicate a temporal change in arc magmatism. The Sr-Nd-Pb isotopic data indicate that the Lutetian rocks are mixtures of three or four end-member compositions. Considering all geological, geochemical and chronological data, we conclude that the Early Cenozoic magmatism was generated by slab window processes related to ridge subduction in a south-dipping subduction zone below the Eastern Pontides Orogenic Belt. [ABSTRACT FROM AUTHOR]

The migmatized gneiss (viz. Gwangcheon gneiss) of the southern Hongseong area, central–western Korean Peninsula underwent intermediate to high granulite-facies metamorphism (ca. 9.2–12.0 kbar and 770–870 °C) during Early Silurian to Early Devonian in age. Field and petrographic evidences from the Gwangcheon migmatite provide a clear indication of partial melting. Particularly the migmatized paragneiss is juxtaposed with arc-related doleritic metagabbro, which might be related to the heat source of the migmatization. The migmatized paragneiss has similar arc-related geochemical characteristics, such as depletions in Ta–Nb, Sr, P, and Ti and enrichments in large ion lithophile elements (LILE) caused by the partial melting effect related to the doleritic metagabbro. Sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb dating of the migmatized paragneiss yielded ages of 432 ± 6 Ma, 431 ± 10 Ma, 421 ± 3 Ma, and 403 ± 3 Ma. The U–Pb ages of inherited zircons from the migmatized paragneiss yielded an age spectra from Neoarchean to Early Paleozoic, with a dominant age population at Neoproterozoic. In contrast, new-growth and recrystallized equant zircons showed dominant concordant Early Silurian to Early Devonian ages that provide critical evidence on the timing of migmatization. These age results and the tectonic signatures are similar to those reported from the Central China Orogenic Belt in China, indicating their tectonic linkage at the northeastern margin of eastern Gondwana during Early to Middle Paleozoic in age. [ABSTRACT FROM AUTHOR]

The subduction polarity of Tethyan oceanic lithosphere during Jurassic is a controversial topic in relation to the geodynamic evolution of the Alpine–Himalayan system. We present new geological, geochemical and zircon U–Pb data from four different regions of the Eastern Pontides Orogenic Belt, a key area of the Alpine–Himalayan system. We discuss the origin of the magmatism and also the existence of an ocean in the eastern Mediterranean region during the Jurassic period. Jurassic intrusions, predominantly gabbro, tonalite and minor diorite, are well exposed in the southern and axial zones of the orogenic belt. Thermobarometry indicates that high-pressure (6–10 kb) crystallization of these intrusions occurred at temperatures of 1183–1250 °C. Zircon U–Pb dating from 10 samples show ages between 195 and 165 Ma, indicating that magmatism occurred between Sinemurian and Callovian time. We characterize the intrusions from electron microprobe, zircon geochronology, and whole rock and Sr, Nd, and Pb isotopes. Our data show that the studied intrusions are broadly tholeiitic, except for two calc-alkaline bodies, and formed in an arc-related setting with minimal involvement of older crust or sediment. The most widely accepted model proposes that the ultramafic–mafic rocks exposed between the Pontide arc and the Tauride belt are remnants of a Jurassic Penrose-type and/or suprasubduction zone ophiolite. However, new zircon U–Pb age data from mafic lithologies cutting the Kop ultramafic massif do not support this model and clearly indicate that the ultramafic lithologies are Paleozoic or older in age and are not remnants of a Jurassic ocean that known as ‘’Northern Branch of Neotehtys”. [ABSTRACT FROM AUTHOR]

The Eastern Pontides Orogenic Belt represents one of the best examples of fossil convergent margins in the eastern Mediterranean region. However, the origin and geodynamic setting of the late Mesozoic–Cenozoic magmatism in this belt remain controversial due to lack of systematic geological, geochemical and chronological data. The general consensus is that the late Mesozoic–Cenozoic igneous activity is related to northward subduction of oceanic lithosphere in the late Mesozoic and following collision between Tauride and Pontide blocks in the early Cenozoic. Here we present a comprehensive study focusing on the origin and geodynamic setting of gabbro bodies exposed along a narrow zone, parallel to the southeastern coast of the eastern Black Sea basin, in the Northern Zone of the Eastern Pontides Orogenic Belt. The studied gabbro bodies are hosted within late Cretaceous basaltic, andesitic, and dacitic volcanics including pyroclastic rocks and interbedded sedimentary rocks. The gabbro bodies range in size from 0.1 km 2 to 1.5 km 2 , and outcrop patterns vary from round or elliptical to markedly elongate with sharp and discordant contact with the host rocks. Their mineral assemblage includes mainly clinopyroxene, plagioclase, minor olivine, amphibole, magnetite and rarely orthopyroxene, biotite, zircon and titanite. The occurrence of sutured grain boundaries on clinopyroxene and plagioclase, and the presence of reverse compositional zoning in clinopyroxene and olivine suggest mixing between magmas of contrasting compositions during mineral growth. Thermobarometric computations indicate that the temperature at the beginning of crystallization was ~ 1250 °C and crystallization was polybaric. Zircon and titanite U–Pb ages indicate that these small intrusions were emplaced into crustal rocks of the Eastern Pontides Orogenic Belt during Lutetian (45 ± 2 Ma). The depletion of HFSE is consistent with the involvement of an arc-related source in the petrogenesis of these rocks, and low to moderate enrichment Ce, Rb, Ba, K, Pb, Sr and Th suggests that involvement of subducted oceanic sediment was modest. The low Th content and low Th/Yb indicate that the role of sediment addition was nevertheless limited. The Nd, Sr and Pb isotopic data are consistent with the interpretation that the dominant source component in these gabbros is a depleted, peridotitic mantle, and that crustal contamination is relatively unimportant. We suggest that mafic magmas that produced the gabbroic intrusions were derived from melting of a depleted mantle source under the forearc region of the Eastern Pontides Orogenic Belt during southward subduction of two oceanic plates separated by a mid-ocean ridge, leading to the formation of a slab window. We also infer fractional crystallization and assimilation during both magma storage in the crust–mantle transition zone and transfer into the overlying arc crust. [ABSTRACT FROM AUTHOR]

Sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon ages and whole-rock chemical compositions are reported here from charnockite, anorthosite and metagranite (orthogneisses) from the Jirishan complex in the southwestern part of the Yeongnam massif, Korea. The charnockite and the Kfs-megacryst metagranite yielded zircon U–Pb ages of ca. 1871–1863 Ma. In contrast, the Neoproterozoic porphyritic metagranite and anorthosite yielded zircon U–Pb ages of ca. 908–904 Ma. The geochemical signatures of both Paleoproterozoic and Neoproterozoic rocks display enrichment in LREEs and negative Nb, Ta and Ti anomalies. The geochronological and geochemical data suggest that the Proterozoic Jirishan complex preserves the imprints of arc-related magmatism at different periods associated with the formation of the Paleoproterozoic Columbia and the Neoproterozoic Rodinia supercontinents. The ca. 1871–1863 Ma ages from the charnockites and metagranites from the Jirishan complex are coeval with similar events in the North China Craton, which also represent arc magmatism in a convergent margin setting related to the amalgamation of the Columbia supercontinent. In contrast, the Neoproterozoic porphyritic metagranite and anorthosite, together with the Neoproterozoic metagranites reported from the western Gyeonggi massif, provide a temporal link to the Neoproterozoic tonalite–granodiorite plutons recently identified in and around the South China Craton. They represent orogenic-type magmas that can be attributed to the amalgamation of the Rodinia supercontinent. However, the foliated granites in the central to southwestern Yeongnam massif are related to an arc setting associated with the Permo–Triassic Paleo-Pacific subduction. [ABSTRACT FROM AUTHOR]

Abstract: Arc magmas, metavolcanics and hydrated mantle peridotite from the Hongseong area in western Gyeonggi massif provide evidence for Paleozoic subduction tectonics in the Korean Peninsula. Zircons in a tonalitic orthogneiss from the Wolhyeonri complex dated in this study through SHRIMP U–Pb technique yield ages of ca. 437Ma and ca. 414Ma. In addition, SHRIMP U–Pb zircon dating of a garnet-bearing paragneiss in the Wolhyeonri complex records evidence for Middle Paleozoic (ca. 427Ma) thermal metamorphism. Petrological and geochemical data from the Paleozoic suite provide robust evidence for mid Paleozoic arc-related magmatism. Petrological and geochemical data from the Paleozoic suite, including the composition of chromian spinel from the serpentinite bodies enclosing high-pressure mafic and felsic blocks also suggest rifted arc/forearc tectonic setting in a supra-subduction zone environment. The serpentinite bodies preserve the imprints of forearc magmas derived through significant mantle/melt interaction during the opening and subsequent evolution of the forearc. These results indicate that the Paleozoic Hongseong area might have been located in an arc–forearc tectonic environment coeval with the plutonism and volcanism preserved in the Wolhyeonri complex. The Hongseong area thus preserves important clues to the Paleozoic subduction prior to the subsequent Triassic “Alpine-type” collision, suggesting a common tectonic linkage among Paleozoic to Triassic East Asian continents before the final assembly of the Pangaea supercontinent. [Copyright &y& Elsevier]

Abstract: High-silica adakites intrude the Kop ultramafic massif in the eastern Pontide orogenic belt of NE Turkey. These dominantly dacitic to rhyodacitic plagioclase porphyries form clusters of small intrusions. U–Pb dating of zircons from two intrusions yields ages between 52 and 59Ma. The best-constrained crystallization age is 55.83±0.04Ma, indicating that these are the oldest adakitic rocks of the eastern Pontides. The rocks show geochemical signatures typical of adakites. The absence of systematic geochemical variation within the adakite suite indicates a subordinate role for fractional crystallization and binary mixing, and suggests that individual intrusions may represent separate, small batches of magma. Modeling of partial melting suggests that the degree of melting was 5–20%, that the residues after melting likely contained garnet, clinopyroxene, and rutile, and that plagioclase was either absent or totally consumed during partial melting. The most likely source compositions had large-ion lithophile elements >10 times, and heavy rare earth elements <10 times, chondritic concentrations. Modeled bulk distribution coefficients indicate that the adakites were generated as silicic magmas, and are not derived by fractional crystallization from basaltic or andesitic parental melts. Sr, Nd, and Pb isotopic data indicate at least three isotopically distinct sources, one of which is depleted mantle. The other components include upper crust (possibly a mixture of subducted sediment and Hercynian continental basement rocks) and a component that may include both lower crust and sublithospheric mantle. These adakites are unique among the late Cretaceous and Cenozoic igneous rocks of the eastern Pontides in having a large proportion of the depleted mantle component. The prominent role of the depleted mantle in their petrogenesis suggests that the adakites may be related to a slab window in a south-directed subduction zone. [Copyright &y& Elsevier]

Abstract: The Wolhyeonri complex in the southwestern margin of the Korean Peninsula is divided into three lithotectonic units: Late Paleozoic Zone I to the west, Middle Paleozoic Zone II in the middle and Early Paleozoic Zone III to the east. Zones II and III display characteristics of continental arc magmatic sequence. Zone II is dominated by mafic metavolcanics, whereas zone III is characterized by the presence of dismembered serpentinite bodies including chaotic mélange. These zones are proposed to have been formed in a convergent margin setting associated with subduction. Here we present zircon SHRIMP U–Pb ages from the various units within the Wolhyeonri complex which reveal the Paleozoic tectonic history of the region. The Late Carboniferous ages obtained from the main shear zone between the Wolhyeonri complex and the Paleoproterozoic Gyeonggi massif are thought to mark the timing of continental arc magmatism associated with the subduction process. In contrast, Zone I with Neoproterozoic arc magmatic remnants might indicate deposition in a forearc basin. The Wolhyeonri complex also preserves strong imprints of the Triassic collisional event, including the presence of Middle Triassic high-pressure metabasites and eclogites near the eastern boundary of the Zone III. These range of radiogenic ages derived from the Wolhyeonri complex correlate well with subduction and accretion history between the North and South China cratons. Similar geochronological features have also been indentified from the Qinling, Tongbai–Xinxian, and northern Dabie areas in east-central China. The existence of Paleozoic coeval subduction in East Asia prior to the Triassic collision is broadly consistent with a regional tectonic linkage to Gondwana. [Copyright &y& Elsevier]

Abstract: This study presents sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon ages, and whole-rock chemical and isotopic (Sr-Nd) compositions of representative Triassic plutons from South Korea. The plutons from the Gyeonggi massif (Hongseong, Namyang, Yangpyeong and Odesan), the central Okcheon belt (Baeknok and Yongsan), and the Yeongnam massif (Sangju, Gimcheon, Hamyang and Macheon) yield zircon U–Pb ages of ca. 232–226Ma, 227–226Ma, and 240–228Ma, respectively. Among the Triassic plutonic suite in South Korea, those within the Gyeonggi massif are dominated by granite, syenite, monzonite, monzodiorite and gabbro. Plutons within the Okcheon belt are mainly by granite to quartz monzodiorite. The Yeongnam massif mainly incorporates granite to granodiorite and minor monzodiorite intrusions. The geochemical signatures of the Triassic plutons are characterized by Ta–Nb troughs, depletion of P and Ti, and enrichment of LILE. Most plutons except Macheon monzodioritic pluton show high initial 87Sr/86Sr ratios (0.708248–0.714678) and strongly negative εNd(T) (−20.3 to −7.7) values, suggesting contribution from middle to upper crust. In contrast, the Macheon monzodioritic pluton in the Yeongnam massif shows relatively low initial 87Sr/86Sr ratios (0.706547-0.706629) and negative εNd(T) (−4.43 to −3.62) values. The Middle Triassic syenite–monzonite–granite–gabbro series in and around the Gyeonggi massif possess high-K calc-alkaline and shoshonitic affinity suggesting a post-collisional magmatic event following the Permo–Triassic collision between the North and South China blocks. The Triassic plutons in the Yeongnam massif and the Okcheon belt, together with a Permian Yeongdeok pluton in the Gyeongsang basin, show features typical of high- to medium-K calc-alkaline magmatism with LREE and LILE enrichments. This together with a depletion of Y and HREE suggests their formation in a subduction setting. Our results provide robust evidence to consider the Gyeonggi massif as an extension of the Qinling–Dabie–Sulu belt between the North and South China blocks in central China. The Okcheon belt and Yeongnam massif in South Korea, together with the continental margin of South China, are marked by a common Permian to Triassic magmatic episode, probably related to the paleo-Pacific slab subduction. [Copyright &y& Elsevier]

Abstract: Mesozoic granitoids are prevalent throughout the Korean peninsula, but precise geochronological and petrogenetic information of these granitoids is not available. For this study, 14 granitoid samples from the Gyeonggi massif and Okcheon belt in central Korea were chosen for zircon and titanite U–Pb age determination. These granitoids can be divided into two age groups: 230–225 and 184–167Ma. Triassic granitoids are metaluminous, shoshonitic diorite, while Jurassic granitoids range from metaluminous to peraluminous high-K calc-alkaline biotite granite. Nd isotopic data for both groups suggest that the granitoids were derived from younger, lower crustal rocks instead of Precambrian basement rocks in close proximity. High alkali content within the Triassic diorite implies a post-collisional signature and cessation of Indosinian (Songrim) orogeny on the Korean peninsula. The geochemical transition in granitoids from Triassic shoshonitic to a Jurassic high-K calc-alkaline series suggests a change in tectonic environments from continent–continent collision to active continental margin. The temporal difference in Triassic high-K magmatism indicates that the extension after Indosinian orogeny most likely began earlier in the Korean peninsula than in the North China block, which might be related to differences in geodynamics rather than a diachronous continental collision. [Copyright &y& Elsevier]

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