NE Asia Research Articles

Timing and processes of late Mesozoic mid-lower-crustal extension in continental NE Asia and implications for the tectonic setting of the destruction of the North China Craton: Mainly constrained by zircon U–Pb ages from metamorphic core complexes

Late Mesozoic large-scale crustal extension occurred across the northeastern section of continental Asia, and metamorphic core complexes (MCCs) are the major features in this region. This paper presents new zircon U–Pb and Ar–Ar ages of biotite and hornblende for pre- or syn- (mylonitized) and post-kinematic (unmylonitized) intrusions from these MCCs, and attempts to determine the timing of initiation, duration and termination of the mid-lower-crustal ductile extension by integrating with geochronological data from previous studies. These MCCs have similar 40Ar/39Ar biotite and hornblende ages (130 to 110Ma, mainly from 130 to 120Ma), which are interpreted as the cooling ages and represent the timing of the late-stage formation of the MCCs. Zircon U–Pb ages for syn- to post-kinematic intrusions from some MCCs suggest that the mid-lower-crustal extension probably initiated at ca. 150–145Ma with a peak occurring 145–130Ma and continued to 130–120Ma, which is older than that suggested by 40Ar/39Ar ages by 10–20Ma. The early ductile extension most likely initiated in Mongolia and northern China during the Late Jurassic (150–145Ma) at a deeper level, then propagated southwards (140–130Ma), and finally developed throughout the entire continental NE Asia (130–120Ma). Based on the timing and processes of the extension, a geodynamic model and tectonic setting of the destruction of the North China Craton (NCC) are proposed.

Interactive effects of mechanical stress, sand burial and defoliation on growth and mechanical properties in Cynanchum komarovii

In drylands, wind, sand burial and grazing are three important factors affecting growth and mechanical properties of plants, but their interactive effects have not yet been investigated. Plants of the semi-shrub Cynanchum komarovii, common in semi-arid parts of NE Asia, were subjected to brushing, burial and defoliation. We measured biomass allocation and relative increment rates of dry mass (RGR(m)), height (RGR(h)) and basal diameter (RGR(d)). We also measured the stem mechanical properties, Young's modulus (E), second moment of area (I), flexural stiffness (EI) and breaking stress (σ(b)), and scaled these traits to the whole-plant level to determine the maximum lateral force (F(lateral)) and the buckling safety factor (BSF). Brushing increased RGR(m); neither burial nor defoliation independently affected RGR(m), but together they reduced it. Among buried plants, brushing positively affected stem rigidity and strength through increasing RGR(d), E, I and EI, and at whole plant level this resulted in a larger BSF and F(lateral). However, among unburied plants this pattern was not observed. Our results thus show that effects of mechanical stress and grazing on plants can be strongly modified by burial, and these interactions should be taken into account when considering adaptive significance of plant mechanical traits in drylands.

Potential influence of selection criteria on the demographic composition of students in an Australian medical school

BackgroundPrior to 1999 students entering our MBBS course were selected on academic performance alone. We have now evaluated the impact on the demographics of subsequent cohorts of our standard entry students (those entering directly from high school) of the addition to the selection process of an aptitude test (UMAT), a highly structured interview and a rural incentive program.MethodsStudents entering from 1985 to 1998, selected on academic performance alone (N = 1402), were compared to those from 1999 to 2011, selected on the basis of a combination of academic performance, interview score, and UMAT score together with the progressive introduction of a rural special entry pathway (N = 1437).ResultsMales decreased from 57% to 45% of the cohort, students of NE or SE Asian origin decreased from 30% to 13%, students born in Oceania increased from 52% to 69%, students of rural origin from 5% to 21% and those from independent high schools from 56% to 66%. The proportion of students from high schools with relative socio-educational disadvantage remained unchanged at approximately 10%. The changes reflect in part increasing numbers of female and independent high school applicants and the increasing rural quota. However, they were also associated with higher interview scores in females vs males and lower interview scores in those of NE and SE Asian origin compared to those born in Oceania or the UK. Total UMAT scores were unrelated to gender or region of origin.ConclusionsThe revised selection processes had no impact on student representation from schools with relative socio-educational disadvantage. However, the introduction of special entry quotas for students of rural origin and a structured interview, but not an aptitude test, were associated with a change in gender balance and ethnicity of students in an Australian undergraduate MBBS course.

Pattern and kinematic polarity of late Mesozoic extension in continental NE Asia: Perspectives from metamorphic core complexes

Late Mesozoic extension in NE Asia resulted in the development of a large extensional province. Metamorphic core complexes (MCCs) are the major features in this province and have 40Ar/39Ar ages of 130–110 Ma for the mylonites and U‐Pb zircon ages of 150–110 Ma for the integral granitic intrusions. Based on this and previous studies, this paper summarizes major characteristics of these MCCs and recognizes a regional kinematic shear sense. Most MCCs in the Transbaikalia region, Sino‐Mongolia border tract, and the northwest‐central portion of the North China craton (NCC) show a top‐to‐the‐southeast (SE) shear, whereas those in the eastern and southern NCC locally underwent top‐to‐the‐northwest (NW) shear. The three largest basins (Songliao, Huabei and Ordos) in North China are located in the transitional zone between domains of opposing shear sense. We interpret the extension in the Transbaikalia, Sino‐Mongolia tract and northwestern part of the NCC to reflect late‐orogenic collapse of thickened crust following Middle‐Late Jurassic collision along the Okhotsk suture. The southeastward extension is probably controlled by crustal‐scale top‐to‐the‐SE tangential shear. The transition from contraction to extension is marked by detachment faults that nucleated as extensional crenulation cleavage (ecc, i.e., C′) in sub‐horizontal ductile shear zones late in orogenic crustal thickening. The combined effect of gravitational loading and thermal‐uplifting is considered to be the origin of the late‐or post‐orogenic collapse. The top‐to‐the‐NW extension in the NE of the NCC might reflect antithetic sub‐extensional zones or Mesozoic back‐arc extension as a far‐field effect of Cretaceous Pacific plate subduction.

RECENT CHANGE OF GLACIERS OF THE NORTHEASTERN ASIA AND PROJECTION FOR THE FUTURE

Paper presents the results of comparative analysis of the satellite images data about the glacier state in glacier systems of Byrranga, Suntar-Khayata, and Chersky ranges (2003) with the data given in the Glacier Inventory of the USSR (1945, 1967 and 1970). We studied change of glacier area since the Glacier inventory compilation, which was based mainly on areal-photo and visual services with the satellite (LANDSAT) images data. The retreated glaciers have been analyzed by groups, sorted by the same aspect and morphological type of a glacier in terms of the rate of reduction. In total glacierization of Chersky Range reduced by about 30% (1970–2003), Suntar-Khayata by 20% (1945–2003), Byrranga—by 17% (1967–2003). The method for projection of glacier systems development in 2049–60 is applied for NE Asia Mountains using the ECHAM 4,5 and some other climatic scenarios. We have considered continental glacier systems (Suntar-Khayata, Chersky, Orulgan) and temperate-marine ones (Kamchatka). The method involves construction of vertical balance profiles for baseline and projected period, hypsographic schemes of ice distribution via altitude in a glacier system. The results of the method application to the glacier systems of the NE Asia are discussed in the paper.

Cretaceous conifer woods of Korea: Occurrences and palaeobiological implications

Six different types of conifer wood were recovered from Cretaceous terrestrial deposits in six sites in Korea: Xenoxylon latiporosum (Cramer) Gothan from the Nakdong Formation (Hauterivian to Barremian), Agathoxylon togeumense Oh, Kim, Paik and Lim, sp. nov. and Agathoxylon kiiense (Ogura) Oh, Kim, Paik and Lim from the Togeum Formation (Albian), Agathoxylon byeongpungense (Kim et al.) Oh, Kim, Paik and Lim from the Donghwachi Formation (Aptian to Albian), Brachyoxylon sp. from the Dogyedong Formation (Aptian to Albian), and Taxodioxylon nihongii Nishida and H. Nishida from the two islands' deposits in Yeosu City which have not yet been classified lithostratigraphically, but can be dated as Campanian to Maastrichtian. Two palaeophytogeographic zones are known from the Lower Cretaceous of NE Asia. In addition, there is a Mixed-type flora with floristic elements from the northern and southern phytogeographic regions. The Korean Peninsula has been regarded to have hosted a Mixed-type flora during the Early Cretaceous. The fossil wood taxa described here indicate that the palaeovegetation in the southern Korean Peninsula shows a transition from a Mixed-type flora largely dominated by Tetori-type taxa in the early Early Cretaceous to a Mixed-type flora dominated by Ryoseki-type taxa in the late Early Cretaceous. The Late Cretaceous flora of the Korean Peninsula was similar to Ryoseki-type flora of the Early Cretaceous. Pinaceous fossil wood has not been recorded yet and only one poorly preserved dicotyledonous fossil wood has been reported from the southern Korean Peninsula. The Korean Peninsula and the adjacent regions thus show differences in the composition of the fossil wood flora suggesting differences in the composition of the palaeovegetation in these regions.

Late Quaternary vegetation and environments in the Verkhoyansk Mountains region (NE Asia) reconstructed from a 50-kyr fossil pollen record from Lake Billyakh

Here we present a detailed radiocarbon-dated 936 cm long pollen record from Lake Billyakh (65°17′N, 126°47′E; 340 m a.s.l.) situated in the western part of the Verkhoyansk Mountains, about 140 km south of the Arctic Circle. A set of 53 surface pollen samples representing tundra, cold deciduous forest and taiga was collected in northern and central Yakutia communities to verify the accuracy of the quantitative biome reconstruction method and to obtain a more precise attribution of the identified pollen taxa to the main regional biomes. The adjusted method is then applied to the pollen record from Lake Billyakh to gain a reconstruction of vegetation and environments since about 50.7 kyr BP. The results of the pollen analysis and pollen-based biome reconstruction suggest that herbaceous tundra and steppe communities dominated the area from 50.7 to 13.5 kyr BP. Relatively low pollen concentrations and high percentages of herbaceous pollen taxa (mainly Cyperaceae, Poaceae and Artemisia) likely indicate a reduced vegetation cover and/or lower pollen production. On the other hand, extremely low percentages of drought-tolerant taxa, such as Chenopodiaceae and Ephedra, and the constant presence of various mesophyllous herbaceous ( Thalictrum, Rosaceae, Asteraceae) and shrubby taxa ( Betula sect. Nanae/Fruticosae, Duschekia fruticosa, Salix) in the pollen assemblages prevent an interpretation of the last glacial environments around Lake Billyakh as extremely arid. The lowest pollen percentages of woody taxa and the highest values of Artemisia pollen attest that the 31–15 kyr BP period as the driest and coldest interval of the entire record. A relative high content of taxa representing shrub tundra communities and the presence of larch pollen recorded prior to 31 kyr and after 13.5 kyr BP likely indicate interstadial climate amelioration associated with the middle and latest parts of the last glacial. An increase in pollen percentages of herbaceous taxa around 12 kyr BP suggests broader distribution of drier communities in response to the colder and drier than present climate of the Younger Dryas (YD). The onset of the Holocene is marked in the pollen record by the highest values of shrub taxa, mainly B. sect. Nanae/Fruticosae. Pollen percentages of arboreal taxa increase gradually and reach maximum values after 7 kyr BP. The latter maximum mainly reflects the spread of Pinus sylvestris in central Yakutia as a response to the mid-Holocene climatic optimum. The quasi-continuous presence of larch, shrubby birch and alder pollen throughout the whole record is the most striking feature of the pollen record. Noticeable variations in larch pollen percentages point to multiple short-term warming episodes, which might be synchronous with the Dansgaard-Oeschger cycles in the North Atlantic records. The Lake Billyakh pollen record suggests that larch possibly survived during the last 50 kyr BP in locally favourable environments in the study region.

Comparison of Cretaceous granitoids of the Chaun tectonic zone to those of the Taigonos Peninsula, NE Asia: rock chemistry, composition of rock forming minerals, and conditions of formation

Abstract. The Cretaceous granitoid complexes of the Eastern Taigonos and the Prybrezhny Taigonos belts (southern part of the Taigonos Peninsula), Tanyurer pluton of the Okhotsk-Chukotka volcanic belt, and the Peekiney, Moltykan, and Telekay plutons of the Chaun tectonic zone are discussed in relation to their structural position, petrography, rock and mineral chemistry and physicochemical conditions of melt crystallization. These granitoid plutons were generated through melting of a compositionally heterogeneous crustal source, with direct contribution from mafic melts produced in the mantle wedge above active or extinct Benioff zones. Variations of the trace-element composition of granitoids are controlled to a greater extent by local compositional peculiarities of the source regions than by the geodynamic regime as such. The final crystallization of these plutons occurred at comparatively shallow depths, between 1–2 and 6–7 km, in a temperature interval of 700–770°C. The depth of emplacement of the bodies decreases with increasing distance from the areas with oceanic and transitional type crust, as does the degree of incompatible element enrichment of the mantle and crustal sources of melts. Variations in fo2 values at the late stages of crystallization of the plutons reach 3–4 orders of magnitude, exceeding the limits of the quartz-fayalite-magnetite (QFM) and nickel-nickel oxide (NNO) buffer equilibria, which likely results from local variations of the source composition.

Summary of Northeast Asia geodynamics and tectonics*

Abstract. The compilation, synthesis, description, and interpretation of regional geology and tectonics of major regions, such as Northeast Asia (Eastern Russia, Mongolia, Northern China, South Korea, and Japan) and the Circum-North Pacific (the Russian Far East, Alaska, and Canadian Cordillera), requires a complex methodology that includes: (1) definitions of key terms; (2) compilation of a regional geodynamics map that can be constructed according to modern tectonic concepts and definitions; and (3) formulation of a comprehensive tectonic model. This article presents a summary of the regional dynamics and tectonics of Northeast Asia as developed for a new summary geodynamics map of the region. This article also describes how a high-quality summary geodynamics map and companion tectonic analysis substantially aids in the understanding of the origin of major rock units, major structures, and contained mineral and fuel resources, and provides important guidelines for new research. * Prepared in memory of Leonid M. Parfenov, the leader of the geodynamics map team for the International collaborative project on NE Asia tectonics and metallogenesis.

Global crustal stress pattern based on the World Stress Map database release 2008

The World Stress Map (WSM) project is a global compilation of information on the contemporary crustal stress field from a wide range of stress indicators. The WSM database release 2008 contains 21,750 stress data records that are quality-ranked using an updated and refined quality-ranking scheme. Almost 17,000 of these data records have A–C quality and are considered to record the orientation of maximum horizontal compressional stress S H to within ±25°. As this is almost a triplication of data records compared with the first WSM database release in 1992, we reinvestigate the spatial wave-length of the stress patterns with a statistical analysis on a global 0.5° grid. The resulting smoothed global stress map displays both; the mean S H orientation that follows from the maximum smoothing radius for which the standard deviation is <25° and a countour map that displays the wave-length of the stress pattern. This smoothed global map confirms that long wave-length stress patterns (>2000 km) exist for example in North America and NE Asia. These have been used in earlier analyses to conclude that the global stress pattern is primarily controlled by plate boundary forces that are transmitted into the intraplate region. However, our analysis reveals that rather short wave-length of the stress pattern <200 km are quite frequent too, particularly in western Europe, Alaska and the Aleutians, the southern Rocky Mountains, Basin and Range province, Scandinavia, Caucasus, most of the Himalayas and Indonesia. This implies that local stress sources such as density contrasts and active fault systems in some areas have high impact in comparison to plate boundary forces and control the regional stress pattern.

Evolution of Global Economy in the First Semester of 2009

Recent figures from the more developed NE Asian exporters show global manufacturing industries falling at a shocking rate, indicating possible double-digit declines in GDP in 2009. There have been worse than expected results in South America, with Brazil likely to see a fall of 3-5% in GDP. Mexico's results could be much worse. The economic and financial situation in Eastern Europe and Central Asia is deteriorating rapidly and dangerously. News from the US and Europe has also been poor but policy efforts may just about succeed in stabilizing these economies by mid-2009.

Carbon isotope fluctuations of terrestrial organic matter for the Upper Cretaceous (Cenomanian–Santonian) in the Obira area of Hokkaido, Japan

AbstractStratigraphic fluctuations of carbon isotope values of terrestrial organic matter within the Upper Cretaceous (Cenomanian–Santonian) sequence in the Obira area of Hokkaido, Japan, record distinctive δ13C fluctuations for the Cenomanian–Turonian boundary, the Middle Turonian, the upper Turonian–lower Coniacian, and the Santonian. A biostratigraphic framework of the age-diagnostic taxa (ammonoids, bivalves and planktic foraminifers) indicates that these δ13C fluctuation events are comparable with those recorded in δ13C data of terrestrial organic matter in Japan and marine carbonates in Europe. These correlations reinforce the utility of these δ13C events in terms of global chemostratigraphy. In particular, the δ13C patterns within the overall positive interval of the Cenomanian–Turonian boundary event are highly conformable between marine and terrestrial records. The consistent nature of these different records of δ13C fluctuation patterns demonstrates that the terrestrial organic δ13C data mirror the global-scale δ13C patterns in the carbon reservoir of ocean–atmosphere–terrestrial biosphere during the Cenomanian–Turonian boundary event. In addition, global correlation of short-term marine and terrestrial organic δ13C fluctuations of the Upper Cretaceous sequence indicate that the magnitude of several terrestrial organic δ13C events appears more amplified than that of coeval marine carbonate δ13C events. This correlation is interpreted to mean that the effects of local CO2 emission into the atmosphere by release of terrestrial methane hydrate or biomass burning of terrestrial vegetation in the hinterland of the NE Asian region have been superimposed on the global δ13C trend and resulted in the terrestrial organic δ13C records of the Yezo Group.

Microevolution of eastern palaearctic Grey tits as indicated by their vocalizations (Parus [Poecile]: Paridae, Aves) I. Parus montanus: Contributions to the Fauna of the Far East, No. 2

Within the Palaearctic Region, the Willow tit (Parus montanus) displays four vicariant forms of territorial song. 1. “Alpine” form (pure single-frequency whistles, Fig. 5: 1) in the Alps and adjacent mountains to the East. 2. “Lowland” or “Normal” form (frequency change from high to low within one note, Fig. 5: 2) in the other parts of NW, Central and SE Europe. 3. In populations of N and E Europe as well as of W and E Siberia every individual bird uses - so far as known - both song types; this “Siberian” form (Figs. 1, 2) includes intergrades (Fig. 3). The comparatively type-rich Siberian repertoire is found in a vast area from N and E Europe to the Amur River and Ussuriland in Siberia. 4. In song types of S Palaearctic Asia whistled notes dominate, as in the Alpine form, but the single notes contrast by marked differences in pitch (frequency jumps); this is the “Sino-Japanese” form (Altai, China, Japan, Fig. 4). These acoustically defined groups of Eurasia comprise several morphological subspecies. Subspecies groups with the same song type are closely related. We hypothesize that the Alpine and Lowland song types developed in Pleistocene refuge areas in the southern Alps and in the Balkan Peninsula, respectively, both originating from the complex Siberian song type. According to this hypothesis, both extant Central European song types lost one note type of the Siberian song type (Lowland or Alpine, respectively). In contact zones and hybrid belts of Alpine and Lowland song, the Secondary Siberian song type occurs, which combines the Lowland and Alpine types. Marked song types, which cover vast areas, also characterize the closest relatives in the Nearctic Region, the Chickadees P. atricapillus, P. carolinensis and P. sclateri (Mexico), the most southerly representative of Chickadees in America. P. carolinensis uses Sino-Japanese song, P. atricapillus a derived form with only minor frequency jumps. The Willow tit probably evolved in the E Palaearctic Region, perhaps in the area of E China, Amur/Ussuri and NE Siberia, rich in diverse local taxa at present (songarus sector; parts of montanus sector; kamtschatkensis sector, respectively, Fig. 5). The Sino-Japanese song type was also developed here. Starting from this area, montanus settled the W Palaearctic Region, where the song types were modified as follows: loss of frequency jumps of the old Sino-Japanese form, threefold geographical splitting into areas of Alpine, Lowland and Siberian song. Also starting from NE Asia, the Nearctic Region was colonized by at least two immigration waves. The first one resulted in the present P. carolinensis, which introduced Sino-Japanese song into the Nearctic Region. Considered not closely related to P. carolinensis on genetic grounds, the present P. atricapillus may represent another immigrant from E Asia with already modified Sino-Japanese song (minor frequency jumps). In the Nearctic Region, Alpine song occurs in Alaska, where it resembles much Alpine song in Siberia and the rare Alpine form in Japan. Territorial song supports the currently rejected assumption of conspecifity of palaearctic and nearctic Willow tits under the name P. atricapillus. Despite allozyme differences, P. atricapillus and P. carolinensis behave largely as a common biological species. In accordance with its peculiar song, the allopatric P. sclateri is attributed species status. Song structure in both the montanus and atricapillus / carolinenis complexes of the Holarctic Region is highly conservative and gives even better insight into evolutionary history than morphological characters.

Seismic structure and origin of active intraplate volcanoes in Northeast Asia

Three-dimensional P-wave velocity structure beneath the Changbai and other intraplate volcanic areas in Northeast Asia is determined by inverting 1378 high-quality P-wave arrival times from 186 teleseismic events recorded by 61 broadband seismic stations. Low-velocity (low-V) anomalies are revealed beneath the Changbai, Longgan, Xianjindao volcanoes. High-velocity (high-V) anomalies are found in the mantle transition zone, where deep-focus earthquakes under Hunchun occur at depths of 500–600 km. The high-V anomaly reflects the deep subduction of the Pacific slab under NE Asia which may have contributed to the formation of the Changbai, Longgang, Xianjindao and Jingpohu intraplate volcanoes. A low-V anomaly is also revealed in the mantle transition zone, which may have a close relationship with the occurrence of deep earthquakes under the Hunchun area. Our results support the Big Mantle Wedge (BMW) model by Zhao et al. [Zhao, D., Lei, J., Tang, Y., 2004. Origin of the Changbai volcano in northeast China: evidence from seismic tomography, Chin. Sci. Bull. 49, 1401–1408; Zhao, D., Maruyama, S., Omori, S., 2007. Mantle dynamics of western Pacific and East Asia: insight from seismic tomography and mineral physics. Gondwana Res. 11, 120–131.] who proposed that the intraplate volcanoes in NE Asia are caused by the back-arc magmatism associated with the deep dehydration process of the subducting slab and convective circulation process in the BMW above the stagnant Pacific slab.

Where does the South Anyui suture go in the New Siberian islands and Laptev Sea?: Implications for the Amerasia basin origin

The South Anyui suture is a major tectonic boundary in NE Asia, believed to represent the remains of an ocean basin which separated Siberia from North America in Jurassic time. Its history also figures prominently in the Mesozoic reconstruction of the Arctic and the origin and evolution of the Amerasia basin. Three types of proposed trends of the South Anyui suture are evaluated. 1) The suture ends near the Kolyma River mouth where it meets the rotational transform. The paper, however, proves that the suture continues further westward up to Big Lyakhov Is. Consequently, a simple geometric rotational model for Amerasia basin origin must be rejected. 2) The suture trends from Big Lyakhov to the Anjou islands. The Anjou islands geology is examined, and it is concluded that the suture could not go through them. Hence, all proposed versions of the rotational hypothesis of the Amerasia basin opening are claimed to be invalid. 3) A proposed Taimyrian connection of the suture is examined, and it is concluded that this model must be rejected as well. The failure of all previously suggested models for the suture extent through the New Siberian islands and Laptev Sea means that in Early Mesozoic there was no oceanic basin that separated the New Siberian–Chukotka terrane from Siberia. Thus Siberia and North America formed a continuous continent in Jurassic time. This paper presents evidence that the South Anyui suture has instead turned back from Big Lyakhov island and followed a sinuous path designated as the Chroma Loop before connecting with the Kolyma Loop suture. On this model the South Anyui suture can be interpreted as a small segment of extensive boundary which separated the Amerasia Jurassic margin and terranes accreted to it from the Pacific. The modern boundary around the North Pacific is also quite sinuous. It was suggested that in Jurassic time it was straighter and the Amerasia ocean was originated as a common back-arc basin. Finally a new two-pole parallelogram hypothesis for the Amerasia basin opening is suggested and the approaches to its verification are outlined.

Late Mesozoic silicic magmatism of the North Chukotka area (NE Russia): Age, magma sources, and geodynamic implications

The Cretaceous Okhotsk–Chukotka volcanic belt (OCVB) is one of the largest subduction-related volcanic provinces of the Earth. It is thought to be related with the subduction of paleo-Pacific plates under the collage of terranes of NE Asia accreted during Jurassic and Early Cretaceous time. The OCVB comprises a remarkably high portion of silicic rocks, up to 80–90% in some segments. Within the Central Chukotka segment of the belt, volcanic sequences reveal a rather uniform 40Ar/ 39Ar and U–Pb isotopic age of near 89–87 Ma. But the felsic volcanic unit with coeval subsurface intrusives named the ‘Berlozhya magmatic assemblage’ (BMA) yields much older zircon U–Pb ages (146.0 ± 2.4 for rhyolitic tuff and 145.5 ± 1.8 Ma for related granodiorite). The relationship of the BMA with the active boundary between the Chukotka–Arctic Alaska microcontinent and the Anyui–Angayucham oceanic basin is suggested. BMA rocks seem to be undeformed, and their age puts constraints on the timing of main compressional events in the North Chukotka area. We present analytical data for both BMA and OCVB silicic magmatic rocks, including the first isotopic compositions of Sr, Nd, Pb, and Hf for the 1500 km long northern part of the OCVB. We infer that felsic magmas of both BMA and OCVB were produced by the melting of the continental crust, without a significant direct contribution from mantle sources. However, the crustal protolith could contain some ancient island arc complexes, which affected the chemical and isotopic composition of magmatic derivatives. The BMA exhibits a relatively uniform isotopic composition ( 87Sr/ 86Sr i = 0.7057 to 0.7070, ε Nd i = − 0.51 to − 0.12, ε Hf i = 4.41 to 4.92, 206Pb/ 204Pb i = 18.50 to 18.57, and 208Pb/ 204Pb i = 38.23 to 38.31), and its chemical diversity likely results from crystal fractionation. The protolith of OCVB rhyolites has more variable isotopic characteristics ( 87Sr/ 86Sr i = 0.7032 to 0.7082, ε Nd i = − 4.06 to − 2.84, ε Hf i = − 1.56 to 3.77, 206Pb/ 204Pb i = 18.56 to 18.81, and 208Pb/ 204Pb i = 38.21 to 38.63), and reveals at least three end-members. Each of them is distinct from the source of the Berlozhya assemblage, thus suggestive of compositional layering of the crust. Nd and Hf model ages of all studied rocks correspond to Neoproterozoic. The estimated Nd model age of the OCVB protolith is slightly older than that for the BMA, but both fall into the Neoproterozoic interval (1000 to 800 Ma).

Osteoglossomorphs of the marine Lower Eocene of Denmark – with remarks on other Eocene taxa and their importance for palaeobiogeography

Abstract The geological, faunal and palaeoecological conditions of the marine deposits from lowermost Eocene in North Jutland are briefly reviewed as background for the descriptions of six species of osteoglossiform fishes from the Stolle Klint Clay and the overlying Mo-clay (Ølst and Fur Formations respectively). Four of these primitive teleosteans are referred to new genera and species (one based on an almost complete skeleton, three others on skull material, one very incomplete), and the two most fragmentary specimens are referred to Brychaetus sp. and an indeterminate osteoglossiform. The phylogenetic relationships of these fossils are evaluated in the framework of two different models of osteoglossomorph phylogeny provided earlier by Taverne and Hilton. Despite differences in both data bases, methodologies and results given by the two models (the former based on c . 300 characters in an intuitive, qualitative phylogenetic parsimony analysis, the latter on 72 characters in a critical, rigorous, quantitative cladistic analysis) the phylogenetic positions of four of the fossil species are very similar in the two models concerning the relations to the recent forms. The other two species, rather fragmentary, but similar in many ways to the Eocene phareodonts (paraphyletic group), end up very differently in relation to extant forms in the two models. The phylogenetic systematics of all the marine, fossil osteoglossiforms (including Brychaetus, Opsithrissops and Monte Bolca forms) is evaluated as background for interpretation of their (palaeo-)biogeographic significance as marine members of a group, Osteoglossomorpha (of which the recent forms are prime examples of ‘primary division freshwater fishes', and of which the extant osteoglossiforms have a classical ‘Gondwana distribution’. There are 9 marine, Eocene taxa (plus an otolith from the Maastrichtian of USA) and none of the 9 appear more closely-related to any other marine form in either model: they might constitute 9 separate migrations from freshwater into the sea. The phylogenetic results strongly suggest instead, that the extant osteoglossiforms have independently entered freshwater from the sea on two, perhaps even three occasions. This may have happened as late as the Eocene, and phareodonts could be yet another independent invasion of freshwater in the Late Cretaceous. The mormyriforms most likely had an independent invasion into freshwater (in one model even with notopterids as a separate migration from the sea by Mid or Early Cretaceous). Because all the closest outgroups of the Osteoglossomorpha are marine, the group obviously originated in the sea, probably by the Late Jurassic, and it is not impossible that Hiodontiforms in NE Asia and North America underwent another independent freshwater invasion very early in the Cretaceous. What then is wanting? The expected Cretaceous, marine osteoglossomorphs are not found (but note the above otolith).

ORIGINAL ARTICLE: Phylogeography of the giant wood spider (Nephila pilipes, Araneae) from Asian–Australian regions

AbstractAim There are currently few population genetic studies on widely distributed SE Asian terrestrial organisms. We have studied the genetic diversification pattern of the giant wood spider, Nephila pilipes (Araneae: Tetragnathidae) to see whether fluctuations in rain forest extents generated by Quaternary climatic changes left signatures on populations of this agile terrestrial arthropod.Location The collecting localities were distributed in the following seven regions: (1) N Australia; (2) India (Calcutta, Karziranga and Sukna); (3) SE Asia (N Vietnam, Malaysia, Singapore and Bali); (4) SE China (Fujian, Guandong, Hong Kong and Hainan); (5) SW China (Guangxi and Yunnan); (6) E Asian islands (Ryukyu islands and Taiwan); and (7) the Philippine Islands.Methods A total of 374 specimens were collected from the East Asian continent and islands, SE Asia, India, and northern Australia. Mitochondrial cytochrome oxidase I gene partial sequences were used as the molecular marker to infer the phylogeographic diversification patterns.Results From the specimens collected, 67 haplotypes were identified, which could be grouped into five major clades. The dominant clade contained populations in regions ranging from Okinawa to Bali (spanning a distance of more than 4000 km), but their genetic variations were not structured and were not significantly associated with geographical distances. Three clades contained specimens collected from peripheral regions of the distribution range of N. pilipes, such as India, N Australia, and NE Asia. Members of the clade distributed in NE Asia were sympatric but those of the clades distributed in Australia and India were allopatric with those of the dominant clade.Main conclusions The results of this study indicate that, during Quaternary glacial periods, the rain forests in SE Asia might have been more or less continuous and thus generated an unstructured genetic diversification pattern of N. pilipes inhabiting this region. However, during such periods, populations in peripheral regions such as India, N Australia and NE Asia might have been isolated in refugia, thus accounting for the observed genetic divergence from populations in the SE Asian region.

Late Mesozoic volcanism in the Great Xing'an Range (NE China): Timing and implications for the dynamic setting of NE Asia

Mesozoic volcanism is widespread throughout northeastern China, but precise geochronological constraints were previously lacking. Twenty samples, including basalt and basaltic andesites, from the Great Xing'an Range were collected and subjected to 40Ar/ 39Ar dating. The ages mainly concentrate in four periods: ∼ 163–∼ 160 Ma, ∼ 147–∼ 140 Ma, ∼ 125–∼ 120 Ma and ∼ 116–∼113 Ma, show that the volcanic succession pulsed from ∼ 160 Ma in the Late Jurassic until the Early Cretaceous. This result, combined with the previous compilation of data from the adjacent areas, suggest a volcanic migration from west to east in the northeastern Asia. These volcanic rocks were formed in an extensional setting, as indicated by the occurrence of A-type granites, mafic dyke swarms, metamorphosed core complexes and basins. The timing (∼ 160–140 Ma) of mantal underplating and transition from crustal contraction to extension in this region suggests that all these geological activities occurred immediately followed the closure of Mongol–Okhotsk ocean, which supposed to be closed by ∼ 160 Ma. Based on these observations, a shears-shaped lithospheric delamination mechanism is proposed to construe the geodynamic scenario of northeastern Asia during Late Mesozoic: the collision between north China and Siberia around ∼ 160 Ma obstructed the westwards movement of the lithosphere induced by the subduction of Pacific plate, this tremendous stress caused the thickened lithospheric delaminating from west edge of the northeast China–Mongolia block at ∼ 160 Ma and extended gradually eastwards. This led to mantle upwelling and underplating, resulting volcanism migration from west to east in northeastern Asia during Late Mesozoic.

Climatic Control on Forests and Tree Species Distribution in the Forest Region of Northeast China

AbstractNorth‐east (NE) China covers considerable climatic gradients and all major forests types of NE Asia. In the present study, 10 major forest types across the forest region of NE China were sampled to investigate forest distribution in relation to climate. Canonical correspondence analysis (CCA) revealed that growing season precipitation and energy availability were primary climatic factors for the overall forest pattern of NE China, accounting for 66% of the explanatory power of CCA. Conversely, annual precipitation and winter coldness had minor effects. Generalized additive models revealed that tree species responded to climatic gradients differently and showed three types of response curve: (i) monotonous decline; (ii) monotonous increase; and (iii) a unimodal pattern. Furthermore, tree species showed remarkable differences in limiting climatic factors for their distribution. The power of climate in explaining species distribution declined significantly with decreasing species dominance, suggesting that the distribution of dominant species was primarily controlled by climate, whereas that of subordinate species was more affected by competition from other species.(Managing editor: Ya‐Qin Han)