Crustal growth history of the Korean Peninsula: Constraints from detrital zircon ages in modern river sediments

U-Pb analyses were carried out on detrital zircon grains from major river-mouth sediments draining South Korea to infer provenance characteristics and the crustal growth history of the southern Korean Peninsula, using a laser ablation inductively coupled plasma mass spectrometer（LA-ICP-MS）. The Korean Peninsula is located in the East Asian continental margin and mainly comprises three Precambrian massifs and two metamorphic belts in between them. We obtained 515 concordant to slightly discordant zircon ages ranging from ca. 3566 to ca. 48 Ma. Regardless of river-mouth location, predominance of Mesozoic（249e79 Ma） and Paleoproterozoic（2491e1691 Ma） ages with subordinate Archean ages indicates that the zircon ages reflect present exposures of plutonic/metamorphic rocks in the drainage basins of the South Korean rivers and the crustal growth of the southern Korean Peninsula was focused in these two periods. Comparison of detrital zircon-age data between the North and South Korean river sediments reveals that the Paleoproterozoic zircon age distributions of both regions are nearly identical,while the Neoproterozoice Paleozoic ages exist and the Mesozoic ages are dominant in southern Korean Peninsula. This result suggests that Precambrian terrains in Korea record the similar pre-Mesozoic magmatic history and that the influence of Mesozoic magmatism was mainly focused in South Korea.

Cluster Analysis of Tropical Cyclones Making Landfall on the Korean Peninsula

Cluster analysis has been performed on the tracks of 51 Tropical Cyclones （TCs） that made landfall on the Korean Peninsula （KP） for the period of 1951-2004. The classification technique of the landfalling tracks used in this study was the fuzzy clustering method （FCM） and the resultant silhouette coefficient suggested four clusters as an optimal cluster number. Most TCs of Cluster 2 and Cluster 3 （C-23） tended to pass through China's Mainland before landfall, but those of Cluster 1 and Cluster 4 （C-14） tended to mostly land after moving northward from the East China Sea （ECS） without passing over China's Mainland. The TC landfalling frequency of C-14 has begun to clearly increase since the late 1980s, particularly the maximum landfalling frequency in the early 2000s set a record for the 54-year analysis period. The ridge axis of the western North Pacific high （WNPH） of C-23 bends more equatorward than that of C-14, so that the monsoon trough of C-23 is located more equatorward than that of C-14. As a consequence, most TCs of C-23 tend to recurve inland of China, but over the ECS for C-14.

Characteristics of carbonatites from the northern part of the Korean Peninsula: A perspective from distribution, geology and geochemistry

The present study introduces the carbonatite in the northern part of the Korean Peninsula for the first time.Recent exploration and development of the phosphorus-bearing carbonate rocks in the area have accumulated new geological data which gave us an opportunity to study origin of the carbonate rocks.We conducted geological survey,geochemical analyses of trace elements and rare earth elements,and carbon and oxygen isotope analyses for the carbonatites from Ssangryong,Pungnyon,Yongyu and Puhung districts of the northern part of the Korean Peninsula.This research confirms that the phosphorus-bearing carbonate rocks are carbonatite originating from the mantle.The studied carbonatites are distributed at the junctions of ring and linear structures or around their margins and contain a greater amount of REEs,Y,and Sr than carbonate rocks.The carbonatites in Yongyu and Puhung area show evidence that they were formed from mantle plume generated at the lower mantle and display similar fractionation characteristics to carbonatites in Barrado Itapirapua in Brazil and Kalkfeld and Ondurakorume in Namibia.REE patterns of the carbonatites are typical of carbonatites and the carbon and oxygen isotope analyses demonstrate that the carbonatites were originated from mantle.The carbonatites from the northern part of the Korean Peninsula have a great potential for sources of REE,Y,PGE(platinum group elements),copper,and gold.

Damage of 1975 Haicheng M_s7.3 earthquake in the Korean Peninsula and its effect on Kyushu,Japan

The 1975 Haicheng Ms7.3 earthquake affected whole Korean Peninsula and even Kyushu, Japan. In this paper isoseismal map of this earthquake was drawn for these areas by sorting out and analyzing data systematically collected, furthermore, the characteristics of the earthquake damage were discussed. In the northern Korean Peninsula, the intensity is V in great majority of this area except local area with intensity VI, and the damage is basically in accordance with typical characteristics of corresponding intensity grade. In the southern Korean Peninsula, the intensity is IV in large part of the area, however, in some big cities such as Seoul etc., not only high buildings shook strongly, but also some people appeared perceptions such as feeling dizzy and so on, and electrical service was interrupted on one or two districts because of transformer tripping. These phenomena could be caused by the effect of long-period wave generated from a large earthquake on far-field.

Research in historical earthquakes in the Korean peninsula and its circumferential regions

The historical earthquake data is one of the important foundations for seismic monitoring, earthquake fore-cast and seismic safety evaluation. However, the recognition of earthquake is limited by the scientific and techno-logical level. Therefore, the earthquake can only be described using perfect earthquake catalogue after the seismo-graph is invented. Before this time, the earthquake parameters were determined according to the earthquake disas-ter on the surface and the written records in history, and the earthquake level was measured using earthquake in-tensity. ……

On Russia' s Korean Peninsula Policy

The past two years have witnessed great fluctuations ininternational oil prices,and diplomatic efforts,both above andunder the table,by major powers around this issue.The currenttension in the war-threatened Iraq has added more uncertainties to thefuture world oil situation.Will the world oil supply and demand change?What impact would this exert on big powers’ oil strategy choices,geopolitics as well as world economy?What should China do in such asituation?To find the answers to these questions,at the invitation of theeditor of the Contemporary International Relations,seven experts fromChina Institute of Contemporary International Relations gathered to have adiscussion in early February this year.Naturally,they have differentviews over many issues.Still,we hope our readers would find theirdiscussion interesting.Following is the list of participants.

THE KOREAN PENINSULA

Both North Korea and South Korea will be busily occupied with their internalaffairs in 1997. (1) Regime building will be the central task for North Korea before and af-ter Kim Jong-il takes over the country’ s leadership. After Kim Jong-il’s 3-yearmourning period expires on July 8, he may formally assume his office as generalsecretary of the Korean Worker’ s Party and president of the state sometime be-

The Korean Peninsula at Present and in the Future

In 2017,the tense situation on the Korean Peninsula has been marked by ongoing crises.However,the situation is one of conflict without complete break.There is neither dialog nor mitigation in the overall situation,nor is there strong condemnation leading to the military conflict.However,with increasingly fierce competition among countries related to the Korean Peninsula,uncertainty and complexity becomes

Paleozoic tectonic evolution of the proto-Korean Peninsula along the East Asian continental margin from detrital zircon U-Pb geochronology and Hf isotope geochemistry

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 ofεHf(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 differentεHf(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.

Phylogenetic relationship,biogeography,and conservation genetics of endangered Fraxinus chiisanensis(Oleaceae),endemic to South Korea

Endemic plants are important for understanding phylogenetic relationships,biogeographical history,and genetic variation because of their restricted distribution and their role in conserving biodiversity.Here,we investigated the phylogenetic relationships of the Korean endemic Fraxinus chiisanensis by reconstructing the molecular phylogeny of Fraxinus based on two nuclear DNA(nrITS and phantastica)and two chloroplast DNA(psbA-trnH and rp132-trnL)regions.Within our fossil-calibrated phylogenetic framework,we also inferred the biogeographical history of F.chiisanensis.To provide a scientific basis for the conservation of F.chiisanensis,we determined the levels of genetic diversity and genetic differentiation in this species.Combining information from nuclear and chloroplast DNA sequence data,our molecular phylogenetic analyses identified F.chiisanensis as a genetically distinct unit from its sister group,Fraxinus platypoda from Japan.Our molecular dating analyses using nuclear and chloroplast DNA data sets show F.chiisanensis diverged from its sister F.platypoda in the Early or Middle Miocene and differentiated in the Late Miocene on the Korean Peninsula.Our results suggest that the divergence of F.chiisanensis was associated with the submergence of the East China Sea land bridge and enhanced monsoons in East Asia.When compared to F.platypoda,F.chiisanensis exhibits low genetic diversity within populations and high genetic differentiation among populations.These results help us to understand the evolutionary history of F.chiisanensis and to develop a conservation strategy for this species.

A new species of Zanclognatha Lederer and three new records of the families Erebidae and Noctuidae(Lepidoptera,Noctuoidea)from Korea,with notes on larval feeding habits

A new species of Zanclognatha Lederer,1857 of the family Erebidae,Z.querciella sp.n.,one species of Family Erebidea,Asota egens(Walker,1854)and two species of Family Noctuidae:Meganephria retinea Gyulai and Ronkay,1999 and Amphipyra subrigua Bremer and Grey,1853,are reported for the first time from Korea.In addition,larval feeding habits with their host plants for three species are newly recognized from Korea.Illustration of adults,larvae for Zanclognatha querciella and Meganephria retinea,and the genitalia of male or female for all species are provided.

有关朝核前景的若干焦点问题评析

For over two decades the international community has been perplexed by the Korean nuclear issue.A clear-eye is needed to see that“no”is the realistic answer to these questions:Will the DPRK give up nuclear capability completely?Will the US resolve the issue with force?Can the DPRK collapse under maximum pressure?On the other hand,what could happen if Six-Party Talks resumed and the international community would“acquiesce”in a nuclear DPRK?Arguing the slippery slope that others in Northeast Asia will become nuclear is delusional:Japan and the ROK are unlikely to join the nuclear arms race.The most plausible next step is that the DPRK holds on to its hard-won nuclear capability,the international community acquiesces,and Six-Party Talks resume.It is an opportunity for China to play a leading role in resolving the nuclear issue and advancing Northeast Asian diplomacy.

Lithospheric thinning and ignition of a Cordilleran magmatic flare-up:Geochemical and O-Hf isotopic constraints from Cretaceous plutons in southern Korea

Northeast Asian continental margins contain the products of magma emplacement driven by prolonged subduction of the(paleo-)Pacific plate.As observed in many Cordilleran arcs,magmatic evolution in this area was punctuated by high-volume pulses amid background periods.The present study investigates the early evolution of the Cretaceous magmatic flare-up using new and published geochronological,geochemical,and O-Hf isotope data from plutonic rocks in the southern Korean Peninsula.After a long(~50 m.y.)magmatic hiatus and the development of the Honam Shear Zone through flat-slab subduction,the Cretaceous flare-up began with the intrusion of monzonites,granodiorites,and granites in the inboard Gyeonggi Massif and the intervening Okcheon Belt.Compared to Jurassic granitoids formed during the former flare-up,Albian(~111 Ma)monzonites found in the Eopyeong area of the Okcheon Belt have distinctly higher zirconε_(Hf)(t)(-7.5±1.3)andδ^(18)O(7.78‰±0.25‰)values and lower wholerock La/Yb and Sr/Y ratios.The voluminous coeval granodiorite and granite plutons in the Gyeonggi Massif are further reduced in Sr/Y and to a lesser extent,in La/Yb,and have higher zirconε_(Hf)(t)values(-13 to-19)than the Precambrian basement(ca.-30).These chemical and isotopic features indicate that Early Cretaceous lithospheric thinning,most likely resulting from delamination of tectonically and magmatically overthickened lithospheric keel that was metasomatized during prior subduction episodes,and consequent asthenospheric upwelling played vital roles in igniting the magmatic flare-up.The O-Hf isotopic ranges of synmagmatic zircons from the Albian plutons and their Paleoproterozoic and Jurassic inheritance attest to the involvement of lithospheric mantle and crustal basement in magma generation during this decratonization event.Arc magmatism then migrated trenchward and culminated in the Late Cretaceous,yielding widespread granitoid rocks emplaced at shallow crustal levels.The early Late Cretaceous(94-85 Ma)granites now prevalent in Seoraksan-Woraksan-Sokrisan National Parks are highly silicic and display flat chondrite-normalized rare earth element patterns with deep Eu anomalies.Synmagmatic zircons in these granites mimic their host rock's chemistry.Delamination-related rejuvenation of crustal protoliths is indicated by zirconε_(Hf)(t)values of granites(-6 to-20)that are consistently higher than the Precambrian basement value.Concomitant core-to-rim variation in zircon O-Hf isotopic compositions reflects a typical sequence of crustal assimilation and fresh input into the magma chamber.