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In the Palghat–Cauvery Shear/Suture Zone of the Southern Granulite Terrane, the Sittampundi Layered Complex occurs as a mappable unit. The Sittampundi Layered Complex consists of mafic, ultramafic and anorthositic rocks with chromitite layers and has been interpreted as an arc/ophiolite complex that formed in an Archaean suprasubduction zone arc setting. In the Sittampundi Layered Complex, reddish-black metabasites occur as layers or boudins with a rim of amphibolite within anorthosite. The peak metamorphic assemblage of the metabasites is garnet + clinopyroxene + quartz + rutile ± plagioclase ± orthopyroxene, and symplectite consisting of amphibole and plagioclase formed around the garnet during retrograde metamorphism. The protolith of metabasite may have intruded in a suprasubduction zone arc setting during the late Neoarchaean (c. 2540–2520 Ma), and then underwent high-pressure granulite-facies peak metamorphism (900–800 °C and 11–14 kbar) in the early Palaeoproterozoic (c. 2460–2440 Ma), followed by amphibolite-facies metamorphism (550–480 °C and 5.5–4.5 kbar) in the middle Palaeoproterozoic (c. 1900–1850 Ma). The results obtained in this study, together with previous studies, indicate that: (1) the high-pressure granulite-facies metamorphism in the study area indicates that subduction occurred during the Archaean–Proterozoic boundary with a higher apparent average geothermal gradient (∼20–16 °C km−1) than the modern-day Earth, and (2) the apparent average geothermal gradient of the subduction zone was ∼29–14 °C km−1 during the Archaean–Proterozoic boundary, which was still too high to enter the realm of eclogite-facies metamorphism.

The Permo-Triassic adakitic magmatism in the southern Korean Peninsula preserves important tectonomagmatic records along the East Asian continental margin. In this study, we present SHRIMP/LA–MC–ICPMS U-Pb zircon ages and Hf isotope signature with whole-rock geochemical compositions of the Middle Permian to Middle Triassic granitoid gneiss-granitoid suites and the Middle to Late Triassic plutonic rocks in the southeastern Korean Peninsula. The former yields three age groups of ca. 272–263 Ma, ca. 258–251 Ma and ca. 243–240 Ma, respectively. The latter group yields ca. 237–216 Ma ages, indicating a long term magmatism that lasted from the Middle Permian to late Triassic. The granitoid gneiss-granitoid suites have chemical compositions similar to high silica adakitic rocks, showing high SiO2 (59.55–73.97 wt.%), Na2O (3.55–5.30 wt.%), Sr/Y (30–401), and La/YbN (11–173), and low MgO (0.18–1.82 wt.%), Y (2–14 ppm) and YbN (2–7). These rocks are peraluminous with high Ba and Sr, and show relatively high K2O contents and K2O/Na2O ratios (> 0.7), with positive correlation between La/YbN vs. Sr/Y ratios and high initial Sr ratios. These features reflect different contribution of the slab-derived adakite melts that interacted with peridotitic mantle in the metasomatized mantle wedge and the Middle Paleoproterozoic lower crustal basement of the Yeongnam Massif. On the contrary, the Triassic alkaline magmatism in the Yeongnam Massif is alternatively interpreted either by a tectonic switch to the extension-dominated arc system or by a delamination of an overthickened arc. The results from this study offer important evidence for a common subduction-accretion system existed between the North and South China Cratons and microcontinents between them along margins of the East Asian continental blocks, with different plate interaction in different locations generating distinct magmatic suites.

The Jangsu-gun area in the central Southwestern South Korea consists of a well-preserved Middle Paleoproterozoic gneissic basement, as well as the Late Triassic and Early Jurassic granitic rocks. Here, we present the detailed zircon U-Pb age data and whole-rock chemical compositions, including radioactive elements (e.g., U and Th) and activity concentrations of 226Ra, 232Th and 40K for the Middle Paleoproterozoic gneisses, and Late Triassic and Early Jurassic granitic rocks of the Jangsu-gun area. The Middle Paleoproterozoic gneissic basement, and the Late Triassic and Early Jurassic granitic rocks have ages of ca. 1988 Ma and 1824 Ma, 230 Ma and 187–189 Ma, respectively. Geochemically, the Middle Paleoproterozoic orthogneiss, Late Triassic granites and Early Jurassic granitic rocks show typical arc-related metaluminous to weakly peraluminous fractionated granite features with ASI (aluminum saturation index) values of 0.92 to 1.40. The mean values of U (ppm) and Th (ppm) of the Middle Paleoproterozoic orthogneisses (6.4 and 20.5, respectively), Late Triassic granites (1.5 and 10.9), and Early Jurassic granites (3.5 and 16.5) were similar to those (5 and 15) of the granitic rocks in the Earth’s crust. The mean 226Ra (Bq/kg), 232Th (Bq/kg), and 40K (Bq/kg) activity concentrations and radioactivity concentration index (RCI) are 62, 71, 1,214 and 0.96 for the Middle Paleoproterozoic orthogneisses, 16, 39, 1,614 and 0.78 for the Late Triassic granites, and 56, 70, 1,031 and 0.88 for the Early Jurassic granitic rocks, respectively. The U, Th, 226Ra, 232Th, 40K, and RCI of the Middle Paleoproterozoic biotite paragneisses are similar to those of the Middle Paleoproterozoic orthogneisses. The trend of 226Ra, 232Th, and 40K activity concentrations, and the composition of U and Th from the Precambrian and Mesozoic rocks in the Jangsu-gun area indicates that monazite is the main accessory mineral controlling the concentration of natural radioactivity. Based on a detailed examination of the natural radioactivity in the rocks of the Jangsu-gun area, the Middle Paleoproterozoic orthogneisses and paragneisses, and Late Triassic and Early Jurassic granitic rocks show average high mean RCI values of 0.88−0.96, such that 32% of the rocks exceeded the recommended value of one in the guidelines for the RCI in South Korea. Especially, the RCI is closely related to the radon levels in the rocks. As a result, the Jangsu-gun area in South Korea is a relatively high radiological risk area, which exhibits higher indoor radon levels in the residences, compared with residences in the other areas in South Korea.

In this study, petrological, structural, geochemical, and geochronological analyses of the Statherian alkali feldspar granite and porphyritic alkali feldspar granite in the southwestern part of the Korean Peninsula were conducted to examine petrogenesis of the granitoids and their tectonic setting. Zircon U-Pb dating revealed that the two granites formed around 1.71 Ga and 1.70–1.68 Ga, respectively. The results of the geochemical analyses showed that both of the granites have a high content of K2O, Nb, Ta, and Y, as well as high FeOt/MgO and Ga/Al ratios. Both granites have alkali-calcic characteristics with a ferroan composition, indicating an A-type affinity. Zircon Lu-Hf isotopic compositions yielded negative εHf(t) values (−3.5 to −10.6), indicating a derivation from ancient crustal materials. Both granite types underwent ductile deformation and exhibited a dextral sense of shear with a minor extension component. Based on field relationships and zircon U-Pb dating, it was considered that the deformation event postdated the emplacement of the alkali feldspar granite and terminated soon after the emplacement of the porphyritic alkali feldspar granite in an extensional setting. These data indicated that there were extension-related magmatic activities accompanying ductile deformation in the southwestern part of the Korean Peninsula during 1.71–1.68 Ga. The Statherian extension-related events are well correlated with those in the midwestern part of the Korean and eastern parts of the North China Craton.

Correlation of the Paleoproterozoic rocks of the Korean Peninsula and China has been considered to be important for the tectonic evolution of Northeast Asia, yet it is still unclear. Recently considerable new data have been obtained from the Korean Peninsula and China providing a better opportunity to correlate the Paleoproterozoic rocks of the Korean Peninsula and China. Intermediate–P/T metamorphism and post–collisional magmatism have been found to have occurred during ca. 1.95–1.83 Ga not only in the Jiao–Liao–Ji belt on the eastern North China Craton but also in the Nangrim and northern Gyeonggi Massifs within the Korean Peninsula representing that these Paleoproterozoic rocks can be correlated. These events occurred as a result of the collision between the Longgang Block of the eastern North China Craton and the Nangrim Massifs of the Korean Peninsula. On the other hand, the southeastern Gyeonggi Massif underwent an arc–related magmatic and metamorphic events during ca. 1.96–1.91 Ga suggesting that the Paleoproterozoic rocks in southeastern Gyeonggi Massif cannot be correlated with those in northern Gyeonggi Massif. The Yeongnam Massif is unlikely correlated to the Nangrim and northern Gyeonggi Massifs and the eastern North China Craton because arc–related igneous activity occurred during ca. 2.00–1.85 Ga in the Sobaeksan Gneiss Complex in the central to northeastern Yeongnam Massif. The Jirisan Gneiss Complex in the southwestern Yeongnam Massif underwent intermediate–P/T metamorphism that is followed by post–collisional magmatic and low–P/T metamorphic events during ca. 1.92–1.86 Ga and these events may be correlated to those in the eastern Cathaysia Block on the South China Craton. The Paleoproterozoic correlation between the Korean Peninsula and China in this study supports a tectonic model in which the Permo–Triassic Dabie–Sulu continental collision belt in China extends into the Hongseong–Odaesan collision belt in the Gyeonggi Massif within the Korean Peninsula.

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.

Although Neoproterozoic rocks were recently found in the western margin of the Gyeonggi Massif, no Neoproterozoic rocks were believed to be present within the interior of this massif. However, in this study, Neoproterozoic rocks are recognized for the first time within the interior of the Gyeonggi Massif through the discovery of the Neoproterozoic volcano-sedimentary rocks of the Gapyeong Formation (GF). The GF is located in the Gapyeong area within the northern Gyeonggi Massif to the north of the Permo-TriassicHongseong-Odesan continental collision boundary in South Korea. The GF mainly consists of mafic granulite interlayered with metacalcsilicate, marble, biotite gneiss, and metatrachyandesite and contains a serpentinized ultramafic block and hornblende biotite gneiss slab. The ages and whole-rock geochemistry indicate that the interlayered metatrachyandesite and mafic granulite in the GF were trachyandesite and basalt that formed through bimodal volcanism in a continental rift tectonic setting at ca. 854 Ma, which matches the timing of the Rodinia supercontinent breakup. The GF can be correlated to the 900–850 Ma Neoproterozoic rifting sequences in the southern Nangrim and northern Gyeonggi Massifs in the Korean Peninsula, which can be correlated to the 930–830 Ma Neoproterozoic rifting sequence along the southern margin of the North China Craton. The GF is difficult to correlate with the ca. 890–790 Ma subduction-related Neoproterozoic rocks in the Hongseong area in the southwestern Gyeonggi Massif, which are considered equivalent to rocks in the northern margin of the South China Craton. The GF underwent upper granulite-facies metamorphism (816–882 °C, 9.0–10.9 kbar) at ca. 250 Ma during the collision between the North and South China Cratons. The serpentinite block in the GF formed in a suprasubduction zone, and the hornblende biotite gneiss slab in the GF was metamorphosed under lower granulite-facies conditions (725–767 °C, 7.0–8.4 kbar) at ca. 414 Ma, indicating that the block and slab were tectonically incorporated into the GF. A strong mylonitic texture is observed in the GF but not in the basement Paleoproterozoic gneiss except at its boundary contact with the GF. These data indicate that the GF, together with the serpentinite block and hornblende biotite gneiss slab, was tectonically transported to the present area after the Triassic metamorphism.

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 (

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.

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 eHf(t) values (−7.63 to +3.3) and a Neoarchean two-stage model age (TDM2 = 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.

The Late Triassic A-type granitoids along the continental margins of East Asia are important for deciphering the crust-mantle interactions, transformation of tectonic regime, and termination of the Indosinian Orogeny (known as the Songrim Orogeny in South Korea). The newly identified Wangdong plutons are distributed in the southwestern part of Yeongnam Massif, South Korea. U–Pb dating of zircons from the Wangdong plutons has established its date of emplacement at ca. 226–221 Ma, similar to the emplacement ages of the Daegang and Ian alkali granites. Geochemical data have shown that the Wangdong granitoid samples are magnesian to ferroan in composition and can be further classified in the range from alkalic to calc-alkalic. They have a high zircon saturation temperature (~ 850 °C), K2O/Na2O and, Ga/Al ratios, and are enriched with high field strength elements (e.g., Zr and Y), indicating an A-type granite affinity. Their classification into A2-type granites based on the A-type subdivision diagrams suggest that they formed in an extension-related tectonic setting. Moreover, the Wangdong A-type granitoids have high (La/Nb)N and (Th/Nb)N ratios with peraluminous characteristics (value of aluminum saturation index >1.0). In addition, magmatic zircons from the Wangdong granitoids have negative ɛHf(t) values (−6.6 to −15.5) with a Paleoproterozoic to Mesoproterozoic two-stage Hf model ages (from 1.99 to 1.49 Ga). This suggests that the Wangdong granitoids were derived from ancient crustal materials with compositions similar to metagraywackes. Based on geochemical, isotopic, and geochronological studies, we concluded that the lithospheric mantle delamination induced by slab roll-back of the subducted Paleo-Pacific plate is the main trigger in the production of Late Triassic magmatism in Yeongnam Massif, South Korea.

Understanding the Precambrian tectonic evolution of the Gyeonggi Massif in South Korea can provide important insights into the tectonic evolution of Korea and northeast Asia, and the geological relationship between Korea and China. The Wonju–Jechon area is located in the southeastern part of the Gyeonggi Massif and is dominated by Precambrian gneisses. The protoliths of the granitic gneiss and migmatite in this area were emplaced in a collisional and/or post-collisional tectonic setting at ca. 2.5 Ga, before the intrusion of the protolith of the two-mica granitic gneiss in an arc-related tectonic setting at 1.94–1.91 Ga. The intrusion of the two-mica granitic gneiss was contemporaneous with the first stage of metamorphism of the granitic gneiss and migmatite in this area. The protolith of the porphyritic gneiss then intruded into these granitic gneiss, migmatite, and two-mica granitic gneiss in a post-collisional tectonic setting at ca. 1.79 Ga. The final major event recorded by these rocks is the second stage regional metamorphism at ca. 285 Ma. Zircons within the Precambrian rocks in the Wonju–Jechon area have e Hf (t) values and isotopic model ages ( T DM2 ) that provide evidence of two stages of crustal growth (at ca. 3.3 and 2.7 Ga) and three periods of crustal reworking (at ca. 2.5, 1.9, and 1.8 Ga) with generation of the protoliths of the two-mica granitic and porphyritic gneisses in this area by the remelting of ancient crustal material. The tectonic evolution of the southeastern Gyeonggi Massif differs from that of the northern Gyeonggi and Nangrim Massifs, both of which record continental-collision-related magmatism and metamorphism at 1.93–1.91 Ga, post-collisional magmatism and metamorphism at ca. 1.88–1.85 Ga, and within-plate magmatism at ca. 1.84–1.83 Ga. In comparison, the tectonic evolution of the southeastern part of the Gyeonggi Massif is more similar to that of the northern Yangtze Block in the South China Craton, although more research is needed to confirm this relationship.

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.

The Neoproterozoic metasedimentary successions and igneous suites in the central Korean Peninsula provide important insights into the tectonic evolution of East Asia. Here we report detailed detrital zircon U Pb age data from the Neoproterozoic metasedimentary successions as well as geochemical data on the early Neoproterozoic rift-related plutonic rocks. Our results together with the available data from the central Korean Peninsula, lead to the following inferences. (1) Regional sedimentation in the early Neoproterozoic (ca. 1000–920 Ma) as a result of the late Paleoproterozoic to early Neoproterozoic intracratonic rifting. (2) Arc magmatism in the southern periphery of the central Korean Peninsula in the early Neoproterozoic (ca. 913–895 Ma and ca. 865–770 Ma). (3) Back-arc magmatism in the inland area of the central Korean Peninsula in the early Neoproterozoic (ca. 888–852 Ma). (4) Magmatism and sedimentation in the early Neoproterozoic (ca. 765–720 Ma) due to early Neoproterozoic back-arc and intracratonic rifting. The early-Neoproterozoic geological and tectonic events in the central Korean Peninsula correlate with those in the southeastern part of the North China Craton. The spatial and temporal similarities and discrepancies in the early Neoproterozoic geological records of the Sino-Korean continent mark the tectonic evolution within a continental inland (the southeastern part of the North China Craton) and a continental margin (the central Korean Peninsula).

The Jiao-Liao-Ji Belt (JLJB) is a Paleoproterozoic collisional belt between the Longgang Block in the northeastern North China Craton and the Nangrim Massif on the Korean Peninsula. The Jinan area, located in the northeastern JLJB, was intruded by monzogranite at 2151 ± 6 Ma and then intruded again by porphyritic granites at 1842 ± 5 Ma in a postcollisional tectonic setting. The monzogranite and an associated gabbro were metamorphosed into metamonzogranite and metabasite at 1868 ± 11 Ma ∼ 1846 ± 3 Ma. Pelitic granulites occur together with the porphyritic granites. The pelitic granulites have peak metamorphic mineral assemblages of garnet + biotite + plagioclase + K-feldspar + sillimanite + quartz + ilmenite and underwent retrograde metamorphism, as evidenced by the presence of cordierite and muscovite. Pseudosection analysis of the granulites yields peak metamorphic conditions of ∼8.5-7 kbar and 800-760°C, and conventional geothermobarometry analysis of garnet rims and adjacent minerals yields retrograde metamorphic conditions of ∼5-3.5 kbar and 740-680°C. Dating of monazite from the two granulites demonstrates that peak metamorphism occurred between 1840 ± 2 Ma and 1847 ± 4 Ma. These results, together with the findings of previous studies, indicate that in the Liaodong and Jinan areas of the JLJB, igneous and metamorphic activities occurred together at ∼1.85 Ga in a postcollisional tectonic setting, suggesting that collision between the Longgang Block and the Nangrim Massif occurred before ∼1.85 Ga.

The Jangsu-Gokseong area is located in the southwestern part of the Yeongnam Massif and mainly consists of Precambrian metagranitoids (metagranite, metaleucogranite and metagranodiorite) with minor migmatite and marble. Sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb dating shows that the metagranitoids emplaced during ca. 2.02–1.96 Ga and metamorphosed at ca. 1.89–1.87 Ga. The metagranitoids show calc-alkaline trends, enrichment in large lithophile elements and negative Nb and Ta anomalies with low Sr/Y (

The Paleoproterozoic basement of the Korean Peninsula consists of three massifs, the Nangrim, Gyeonggi and Yeongnam Massifs, from north to south. In the Muju area of the northcentral Yeongnam Massif, amphibolites intruded the Paleoproterozoic metasedimentary rocks and orthogneisses. The amphibolites can be divided into Type-I and Type-II amphibolites. The whole-rock geochemical data and zircon Lu–Hf composition of the amphibolites suggest that the Type-I and Type-II amphibolites formed in an island and continental arc tectonic setting, respectively, and both amphibolites were derived from enriched mantle sources. Zircon U–Pb dating reveals that the Type-I and Type-II amphibolites were emplaced at ca. 1.87 Ga and 1.69 Ga, respectively. The surrounding metasedimentary rock (migmatite) underwent upper amphibolite facies (720–730 °C and 7.3–7.4 kbar) metamorphism and then underwent amphibolite facies retrograde metamorphism (520–622 °C and 1.7–3.5 kbar). The zircon U–Pb dating reveals that the peak metamorphism occurred at ca. 1.87–1.86 Ga. The geothermal gradient (approximately 32 °C/km) during peak metamorphism correlates with that of the arc area, indicating that metamorphism occurred in an arc tectonic setting. These data suggest that the northcentral Yeongnam Massif underwent arc-related magmatic and metamorphic events during ca. 1.87–1.69 Ga. This finding indicates that the northcentral Yeongnam Massif does not correlate well with the Nangrim and northern Gyeonggi Massifs, which are correlated with the eastern North China Craton, because the Nangrim and Gyeonggi Massifs underwent postcollisional igneous activity during ca. 1.88–1.84 Ga.

The Imjingang belt has been considered as a suture between the North and South China Cratons without clear evidences of the Permo-Triassic collision. The lines of evidences of the Permo-Triassic collision reported by previous researchers from the Imjingang belt are found to be incorrect. Therefore, the Imjingang belt should not be referred as a suture between the North and South China Cratons. Instead of the Imjingang belt, the Hongseong-Odesan belt should be used as the collision boundary between the North and South China Cratons. The Hongseong-Odesan collision boundary can be supported by the Permo-Triassic eclogite in the Hongseong area and ca. 230 Ma post-collision igneous activities occurred regionally in the northern Gyeonggi Massif (GM). In the northern GM between the Imjingang and Hongseong-Odesan belts, no high-pressure metamorphism (e.g. eclogite, blueschist) was reported. The Paleoproterozoic tectonic evolution of the northern GM studied by Yangkhom et al. (2014) is more similar to those in the North Korea and eastern part of the North China Craton than those in the South China Craton. These data indicate that it is reasonable to consider the northern GM including the Hongcheon area, as a part of the North China Craton.

The Hongcheon area is located at the northern part of Gyeonggi Massif (NGM) in the Korean Peninsula. The metamorphic rocks of the NGM at the Hongcheon area are composed of the Paleoproterozoic Yongduri Gneiss Complex (YGC), Euiam Group (EG) and the Euiam Gneiss Complex (EGC). The quartz-feldspathic gneisses in the northeastern part of the YGC record peak metamorphic temperature–pressure condition of 790–840 °C and 7.2–8.9 kbar, whereas the granitic and garnet gneisses in the western part of the YGC record peak metamorphic temperature–pressure conditions of 690–720 °C and 6.1–6.9 kbar, and 640–660 °C and 5.0–5.4 kbar, respectively. The peak metamorphic conditions represent a regional low-P/T metamorphic event (M2) in which metamorphic temperature and pressures increased towards the east. SHRIMP zircon U–Pb age dating indicates that the M2 metamorphic stage occurred at ca. 1886–1870 Ma. The presence of relict kyanite in the gneisses within the YGC suggests that the intermediate-P/T metamorphic stage (M1) occurred in ca. 1925 Ma. Whole-rock geochemistry of the metagranitoid in the EGC indicates that they are originally post-collision granitoid. SHRIMP zircon U–Pb age dating indicates that the metagranitoid formed at ca. 1885–1869 Ma. Considering the similarity in age between the Paleoproterozoic intrusion and the M2 low-P/T metamorphism, the M2 metamorphism also occurred in a post-collision tectonic setting and the M1 intermediate-P/T metamorphism with kyanite represents collision event. Further, we suggest that the Paleoproterozoic orogeny in the Hongcheon area is closely linked to the Paleoproterozoic orogeny in North Korea and the Jiao-Liao-Ji belt in the North China Craton.

The Precambrian rocks of the Gyeonggi Massif (GM) in and around the Hongcheon area, South Korea, consist of the Yongduri Gneiss Complex (YGC), Euiam Group (EG) and Euiam Gneiss Complex (EGC). The YGC and EG are composed mainly of partially migmatised metasedimentary rocks and the EGC is Paleoproterozoic intrusive rock that intruded the EG. At least three major folding (F1, F2 & F3) accompanied with the two-stages of ductile shearing and three-stages of metamorphic events (M1, M2 & M3) occurred in the study area. The F1 folds are extremely drawn out, isoclinal, intrafolial folds and have Class 2 to Class 1C geometry. The F1 folds and regional S1 foliation in the YGC and EG are the results of E-W compression during the D1 deformation. Ductile shearing in the southern part of the EG is marked by the Palbongsan Shear Zone that indicates top-to-the SW sheared movement during syn to post-F1 folding. The F2 folds are open to tight, SW plunging and inclined folds, and have Class 1A to 1C geometry. The F2 folding and subsequent NNE thrusting along multiple ductile shear zone parallel to S2 planar fabrics, represent the D2 deformation due to N-S progressive shortening. The D3 deformation was coaxial with the D1 deformation, leading to the development of the F3 kink bands in the mylonite zones. The SHRIMP zircon ages form the EG yield M1 metamorphism age of 1917–1925 Ma. However ca. 1867–1883 Ma, M2 metamorphism previously reported from the YGC is absent or weakly preserved in the EG representing that the M2 metamorphism was not strong enough to form new zircon in the EG. The igneous zircons from the augen gneiss in the EGC yield intrusion age of ca. 1867–1881 Ma and the geochemistries of the EGC gneisses show post-collision tectonic origin. The D1 deformation observed in the YGC and EG but not in the EGC. The D1 deformation occurred during M1 metamorphism, and then the M2 metamorphism and 1867–1881 Ma igneous activities could have occurred together during post-collision tectonic stage. The M1 metamorphism and ca. 1867–1881 Ma post collision magmatism in the study area are well matched with the collision related metamorphism at ca. 1.90–1.93 Ga and post collision igneous activities at ca. 1.80–1.86 Ga along the Jiao-Liao-Ji belt in the North China Craton suggesting that M1 metamorphism could have caused by the collision along the Jiao-Liao-Ji belt. The M3 metamorphism occurred at ca. 230–260 Ma and its peak metamorphic conditions were 720–730 °C/13–14.5 kbar. The D2 deformation and the M3 intermediate-P/T metamorphism occurred during the Permo-Triassic collision event between the North China Craton and South China Craton. The study area was not a collision boundary but located in the peripheral areas of the collision belt during the Paleoproterozoic and the Permo-Triassic time. The D3 deformation occurred at a time gap between the Permo-Triassic collision and the subduction related Jurassic intrusion in the Korean Peninsula.

The rates of the aminolysis of S-phenyl substituted-acetate series (RC(=O)SC 6H4Z, with R=Me, Et, i-Pr, t-Bu and Bn) with benzylamines (XC6H4CH2NH2) are not correlated simply with the Taft’s polar ( σ * ) and/or steric effect constants (Es) of the substituents due to abnormally enhanced rate of the substrate with R=Et. Furthermore, the cross-interaction constant, ρXZ, is the largest with R=Et. These anomalous behaviors can only be explained by invoking the vicinal bond ( σ)-antibond (σ * ) charge transfer interaction between C-C α and C-S bonds. In the tetrahedral zwitterionic intermediate, T ± , formed with R=Et the vicinal σ C-C-σ * C-S delocalization is the strongest with an optimum antiperiplanar arrangement and a narrow energy gap, Δe = eσ* -eσ . Due to this charge transfer interaction, the stability of the intermediate increases (with the concomitant increase in the equilibrium constant K (= ka/k-a )) and also the leaving ability of the thiophenolate leaving group increases (and hence kb increases) so that the overall rate, kN = Kkb, is strongly enhanced. Theoretical support is provided by the natural bond orbital (NBO) analyses at the B3LYP/6-31+G* level. The anomaly exhibited by R=Et attests to the stepwise reaction mechanism in which the leaving group departure is rate limiting.

The reactions of aryl benzenesulfonates (YC6H4SO2OC6H4Z) with benzylamines (XC6H4CH2NH2) in acetonitrile at 65.0 degrees C have been studied. The reactions proceed competitively by S-O (kS-O) and C-O (kC-O) bond scission, but the former provides the major reaction pathway. On the basis of analyses of the Hammett and Brönsted coefficients together with the cross-interaction constants rho(XY), rho(YZ), and rho(XZ), stepwise mechanisms are proposed in which the S-O bond cleavage proceeds by rate-limiting formation of a trigonal-bipyramidal pentacoordinate (TBP-5C) intermediate, whereas the C-O bond scission takes place by rate-limiting expulsion of the sulfonate anion (YC6H4SO3-) from a Meisenheimer-type complex.

Nucleophilic substitution reactions of benzoic anhydrides, in which one of the rings is substituted, with anilines were investigated in methanol. The product-formation step coincides with the rate–limiting step so that the two rate constants, kXZ and kXZ, for the competitive reaction pathways can be dissected. The two cross-interaction constants, ρXY and ρXY, especially an unusually large magnitude of the latter, indicate that the reaction proceeds by a frontside SN2 attack on either one of the caronyl carbon with a strong interaction between the nucleophile (X) and the leaving group (Z). The mechanism is also supposed by the trends in the activation parameters.

The magnitude ρx(ρ nuc ) is shown to decrease with increase in the extent of bond making estimated by the kinetic isotope effect for the reaetions of Y-benzoyl chlorides with anilines, XC 6 H 4 NH 2 , in acetonitrile at 25-0°C

The base-promoted nitrile-forming elimination reactions of YCH=CHCβH=NOCH=CHZ (Y=OCH3, H or Cl and Z=H or NO2) were studied by the AM1 MO theoretical method with Cl− as a base. The reaction is found to proceed by an E1cB-like E2 mechanism in which Cβ—H bond cleavage is more advanced than N—O bond breaking. The syn-elimination has a more E1cB-like transition state (TS) than the anti elimination, which is attributed to the structurally favourable nN—o* (Cβ—H) charge-transfer interaction. An electron-withdrawing Y substituent lowers the activation barrier by stabilizing negative charge developed on Cβ in the TS. An electron-withdrawing substituent in the leaving group (Z = NO2) tends to enhance the anti relative to the syn elimination process by depressing the δ*(N—O) level, which in turn makes the nc—δ*(N—O) interaction more effective. The YCH=CH— and —CβH=N fragments are perpendicular in the TS, which is stabilized by delocalization of negative charge developed on the Cβ atom.

The intramolecular cyclizations of ω-haloenolate anions, −CαH2C(O)(CH2)n−3CωH2X with X = F, Cl and Br and n = 3–7, were investigated by the AM1 method. In most cases, cycloketone formation proceeds more favourably than cycloether formation, as predicted by the HSAB principle. The reactivity increases in the order X = F < Br < Cl for both processes, and for cycloether formation it is in the order n = 3 < 4 < 7 < 6 < 5 for all X but the relative order for n = 5 and 6 reverses in favour of n = 6 for cycloketone formation with X = Cl and Br. The softness of the acid centre, Cω, decreases for a harder X( = F) whereas it increases for a softer X( = Br). Thus the reactivity order with respect to X suggests that the softness of the base centres O and Cα belongs to the borderline class. The transition state (TS) structures indicate that the BEP principle is obeyed in all cases, and a less reactive process has a more product-like TS.

Kinetic studies have been carried out on the reactions of phenyl acetates and phenyl trimethylacetates in dimethyl sulfoxide. The rate ratios between the two acyl compounds, and the positive sign and large magnitude of the cross-interaction constants, ρXZ, between substituents X in the nucleophile and Z in the leaving group are considered to favour the rate-limiting expulsion of aryl oxide from the tetrahedral intermediate T±. The aprotic solvent used makes the proposed mechanism with a cyclic transition state more attractive especially in view of the greater charge dispersion and assistance to leaving group departure provided in such a structure.

The nucleophilic substitution reactions of (Y)-indan-2-yl (Z)-arenesulfonates with (X)-anilines in methanol at 55.0 °C are reported. Sign reversals in all three second-order cross-interaction constants, ρxy, ρyz and ρxz, are observed at non-interaction points z=–0.11 (ρxy= 0), x=–0.02 (ρyz= 0) and Y= 0.43 (ρxz= 0) respectively, which have been ascribed to an unusually large third-order cross-interaction constant, ρxyz=–0.53, for the reaction series. An SN2 transition state with a tilted, parallel stacked and displaced structure of the three benzene rings in the nucleophile (X), substrate (Y) and leaving group (Z) is proposed to rationalize the strong three-body coupling manifested by the large ρxyz value.

α-Deuterium secondary kinetic isotope effects (KIEs) have been investigated for the reactions of anilines with benzyl, methyl and ethyl benzenesulfonates involving deuteriated aniline nucleophiles and substrates. The secondary KIEs observed are normal, kH/kD > 1.0, only for the deuteriated benzyl system and are of an inverse type, kH/kD < 1.0, for the deuteriated methyl and ethyl systems as well as for all the deuteriated nucleophiles. These results suggest that the relief of steric strain by bond breaking of the leaving group prevails over the steric congestion incurred by bond formation of the nucleophile in the reactions of the benzyl compound (dissociative SN2 mechanism), in contrast to the reverse trend, i.e., the strain incurred by bond formation of the nucleophile is greater than the relief of steric congestion by bond breaking of the leaving group in the reactions of alkyl compounds (associative SN2 mechanism). The effects of substituents in the nucleophile (X) and leaving group (Z) on the secondary KIEs are in complete agreement with the transition-state variation predicted by the sign and magnitude of the cross-interaction constant, ρxz.

The solvolyses of 1-phenyl-2-propyl benzenesulphonates (PPBs) have been investigated in methanol–acetonitrile mixtures and in hexafluoropropan-2-of (HFIP). The transition state structure has been discussed using various selectivity parameters, especially with the cross-interaction constants, ρYZ and λYZ, between substituents in the substrate (Y) and in the leaving group (Z). It has been found that the solvolysis proceeds by the solvent-assisted pathway, ks, in methanol, whereas in HFIP PPBs solvolyse via the aryl-assisted pathway, kΔ. The only exception was the p-MeO substituent, which deviates positively in methanol from the log ksvs. σ plot due to participation of the aryl-assisted path and negatively in HFIP from the log kΔvs. σ(neophyl) plot due to deactivation by hydrogen bonding of the methoxy oxygen in the acidic solvent. The two distinctive high values of ρYX provided evidence for the strongly bound transition states in the two processes, ks and kΔ, with a relatively low degree of bond breaking.

Mechanisms of the hydrolysis of urea have been investigated using the MNDO and AMI methods. All geometries were fully optimized and the transition states were characterized by calculating force constants. The results showed that: (i) The unimolecular decomposition process via the direct intramolecular proton transfer is preferred to both the A1 and the bimolecular nucleophilic attack by water, in agreement with the experimental results of Shaw et al. in the low acidity medium. (ii) The diprotonated form of urea exists as an equilibrium species, which undergoes the A2 type hydrolysis more favorably than the monoprotonated form, as Moodie et al. found in the intermediate acidity medium. (iii) The A2 hydrolysis of the monoprotonated form is very similar to those of acetamide and methyl carbamate. (iv) As the number of the solvate water molecules increases, the activation barrier for the A2 process of the monoprotonated form increases while that for the unimolecular decomposition of the free base form decreases, indicating a possibility of the barrier height reversal in the bulk solvent in favor of the latter process, thus accommodating all the experimentally found trends in the urea hydrolysis. The A1 mechanisms involving six-membered ring type intermediates can be ruled out as untenable since no such equilibrium species was obtained by both the MNDO and AM1 calculations.

The mechanism of the A2 acid hydrolysis of methyl carbamate was investigated using MNDO method. The reaction was found to proceed in two steps: (1) the rate-determining nucleophilic attack of water on the carbonyl carbon of the N-protonated tautomer involving the tetrahedral TS; and (2) the fast subsequent proton abstraction by the leaving group, NH3, to form products. The mechanism is similar to that involved in the A2 hydrolysis of acetamide. Effects of substituents, R1, R2, and R3 in R1OCONR2R3, on rates can be predicted by the changes in electron densities on alkoxy oxygen and N, in complete agreement with the experimental results. We concluded that there is no need for invoking two different mechanisms for amides and carbamates since a common mechanism can easily accommodate all the experimental results.

The nucleophilic substitution reactions of phenacyl benzenesulphonates with anilines in methanol–acetonitrile have been studied. A stronger nucleophile was found to cause less bond cleavage, while a better leaving group led to less bond formation, in complete agreement with predictions by the potential energy surface model. The reactions were also found to adhere to the Bell–Evans–Polanyi principle as well as the reactivity–selectivity principle, and hence constituted a good example of a thermodynamically controlled reaction series. Cross interaction constants, ρij, for the reaction series were used to characterize the transition state structure. The α-carbonyl group was shown to provide a ‘shunt’ in the resonance in the transition state, which resulted in a remarkable decrease in the cross interaction between substituents in the nucleophile and those in the substrate. The magnitudes of ρij indicated that in the transition state bond breaking had progressed very little but bond formation was substantial. Consideration of cross interaction constants led us to conclude that the involvement of a bridged transition state is unlikely.

Kinetics of reactions between 2-phenylethyl benzenesulphonates and anilines in methanol at 65.0 °C have been studied; the mechanism is discussed on the basis of cross interaction constants, ρij. The overall reaction was found to proceed by a dissociative SN2 mechanism with a relatively small degree of aryl participation. The fraction of the phenonium ion intermediate captured by the nucleophile, aniline, in the aryl-assisted pathway has been shown to increase with a stronger nucleophile, and a four-centre transition state in an intermolecular SNi mechanism is suggested for the aryl-unassisted pathway.

Epithets and pronominals 'en' and 'y' in French have a variety of Binding properties that are unexpected on conventional approach to Binding Theory. We argue that the linguistic variety observed cross-linguistically (and perhaps, more surprinsingly, within a single language) - derives from the morphological properties of the anaphoric element - which we claim lack number features. Epithets and pronominal like 'en' and 'y' are predicates modifying null but semantically active nouns, and must theefore refer to the Speaker. These properties, we claim, explain why these elements must be employed in what we define as an Epistemic Context, and are subject to Condition C of Binding Theory