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Neoproterozoic rift-related rocks of the North China Craton (NCC), including the Korean Peninsula, provide crucial information for global supercontinent reconstruction during the Rodinia breakup and Gondwana assembly. Here, we report not only zircon and baddeleyite U-Pb ages but also zircon Hf isotopic and bulk rock compositions of amphibolites in the Ogcheon Metamorphic Belt (OMB), Korea. Zircon occurs as either primary phase or secondary one replacing igneous baddeleyite. Primary zircons analyzed from three amphibolites yielded the weighted mean 206Pb/238U ages of 755 ± 5 Ma (n = 19), 772 ± 3 Ma (n = 9), and 779 ± 13 Ma (n = 12), respectively; this result is corroborated by the baddeleyite age of ∼760–745 Ma. Secondary zircons define discordia lines with lower intercepts corresponding to the Jurassic or Cretaceous age of granites emplaced adjacent to the amphibolite. In conjunction with the occurrence of coeval (ca. 762–745 Ma) metatrachytes, our result suggests that late Tonian bimodal magmatism has lasted for ∼30 m.yr. in the OMB. Moreover, positive ε Hf (t) values (4.9–21.4) of zircon in amphibolites indicate a depleted mantle source of mafic magma, whereas trace element compositions attest to an intraplate setting for the crystallization. A compilation of Nb-Th and Zr–Zr/Y data suggests that the intraplate setting is also pertinent to ca. 950–750 Ma mafic rocks from the Gyeonggi Marginal Belt, Korea, as well as the NCC. Such a tectonomagmatic correlation is corroborated by detrital zircon age spectra of metasedimentary rocks in the OMB equivalent to those of early Tonian rocks in the NCC. In marked contrast to tectonic scenarios conjecturing a linkage between the OMB and the Nanhua rift, South China Craton (SCC), we conclude that the Ogcheon Belt provides rare geologic-geochronologic evidence for late Tonian breakup of the Rodinia supercontinent at the eastern NCC margin. [Display omitted] • Three amphibolites in the Ogcheon Belt, Korea, precisely dated at ca. 780–750 Ma. • Late Tonian bimodal magmatism in an intraplate rift-related setting • Prolonged intraplate magmatism at ca. 950–750 Ma in the Gyeonggi Marginal Belt. • The Korean Peninsula linked to the North China Craton during the Rodinia breakup. [ABSTRACT FROM AUTHOR]

This contribution provides an overview on geology, geochronology, and tectonics of Precambrian basement massifs and adjoining Gyeonggi Marginal Belt (GMB), Korea. The three massifs (Gyeonggi, Yeongnam, and Nangrim) record tectonothermal events represented by ∼2.0-1.85 Ga arc-related magmatism and collisional orogenesis, culminating at ∼1.88-1.85 Ga. The oldest (∼2.51 Ga) migmatitic gneisses limitedly occur in the Nangrim and Gyeonggi massifs, suggesting the North China Craton (NCC) affinity of both massifs. The Yeongnam Massif is characterized by the occurrence of ∼1.87-1.86 Ga anorthosite-mangerite-charnockite-granite suite. This anorthositic suite is a late-orogenic product linked to the amalgamation of 'Paleoproterozoic Korean arc' with the North China Craton, forming the Columbia/Nuna supercontinent. The majority of Hf and Nd model ages of basement gneisses are in the range of ∼3.5-2.5 Ga, attesting to the crustal evolution since the Paleoarchean. P-T paths of the Paleoproterozoic basement gneisses are apparently variable, and the Gyeonggi and Yeongnam massifs are characterized by the kyanite-sillimanite and andalusite-sillimanite facies types, respectively. The GMB comprises three fold-and-thrust sub-belts (Imjingang Belt, Taean-Hongseong Complex, and Ogcheon Metamorphic Belt) which are correlative with each other in terms of tectonostratigraphy and detrital zircon geochronology. Two (meta)sedimentary units are diagnostic of this belt: (1) the Neoproterozoic Sangwon Supergroup sharing the provenance with younger rocks in the Ogcheon Belt; and (2) the Devonian turbiditic sequences present in all the three sub-belts. The latter are most distinctive in their detrital zircon age distribution characterized by two major populations at ∼1000-950 Ma and 450-430 Ma. This age pattern as well as the turbiditic lithology is critical for the correlation between the GMB and the Qinling Belt. Taken together, we suggest that the South China Craton-like GMB units are built upon the NCC-like basement (Gyeonggi Massif); this feature is the key to the Qinling-Gyeonggi microcontinent model which accounts for the assembly of a variety of tectonic slivers in the GMB. [ABSTRACT FROM AUTHOR]

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]

Elevated heat flow in association with mafic magmatism in an orogenic belt commonly leads to high-temperature, low-pressure (HTLP) metamorphism and the production of granulite-facies assemblages. We studied such a HTLP complex in the vicinity of the Sancheong–Hadong anorthosite-mangerite-charnockite-granite (AMCG) suite, Yeongnam Massif, Korea, in order to constrain the P–T conditions, timing, and duration of metamorphism. This complex primarily consists of massif-type anorthositic-gabbroic bodies emplaced at ∼1.87–1.86 Ga and a series of country rocks comprising orthopyroxene-bearing gneisses as well as anatectic granites and migmatites. Migmatitic gneisses were studied in detail because melt-related features are abundant and well preserved; for example, inclusion-rich peritectic phases such as cordierite or K-feldspar are characteristic for the prograde melt-forming stage, whereas biotite-quartz symplectites mantling garnet or orthopyroxene represent the cooling stage consuming melt. Pseudosection P–T analyses of migmatitic gneisses suggest peak metamorphic conditions of 810–840 °C and 5.9–6.2 kbar, followed by near-isobaric cooling and melt crystallization at  ∼780 °C and  ∼5.5 kbar. SHRIMP (sensitive high-resolution ion microprobe) U–Th–Pb ages of zircon and monazite from six migmatitic gneisses are in the range of 1870–1854 Ma. The oldest age, recorded only in high Y monazite, suggests that prograde metamorphism commenced at ∼1870 Ma. In contrast, melt crystallization had culminated by 1860–1855 Ma producing widespread leucosomes and anatectic granites. Our results suggest that high thermal gradient (∼40 °C km −1 ) attending the granulite-facies metamorphism is attributable to coeval, pulse-like emplacement of anorthositic-gabbroic magmas. Moreover, the HTLP metamorphism lasted over a period of ∼15 Ma, indicating a long-lived process corresponding to the late stage of Paleoproterozoic (∼1.95–1.85 Ga) hot orogenesis in the North China Craton. [ABSTRACT FROM AUTHOR]