Northwestern Kyushu Research Articles

Amphibolite-facies metamorphic rocks of the Mt. Tenzan area, northern Kyushu, Southwest Japan: Correlation with the Higo metamorphic rocks

The metamorphic rocks exposed in the Sefuri and Tenzan areas, northwestern Kyushu, are composed mainly of mafic rocks with trace amounts of pelitic, ultramafic and calc-silicate rocks and crystalline limestone occurring as lenses or blocks. These rocks underwent regional metamorphism prior to the Cretaceous intrusive rocks. The metamorphic rocks in the Tenzan area, south of the Sefuri area, underwent amphibolite-facies metamorphism and estimated metamorphic P-T conditions of these rocks reach up to 700 °C and 4.0 kbar. On the other hand, the metamorphic conditions in the Sefuri area have been reported to be up to 850 °C and 5.5 kbar. The metamorphic P-T-t path of northwestern Kyushu is interpreted as a clockwise trajectory. These P-T conditions and lithological features suggest that the metamorphic rocks of northwestern Kyushu can be correlated with those of the Higo metamorphic terrane, which is thought to be a candidate of the eastern extension of collision zone between the North China and the South China cratons during Late Permian to the Triassic periods.

Estimation of the Type Locality of Hynobius naevius (Temminck and Schlegel, 1838), a Salamander from Japan (Amphibia: Caudata)

A small Japanese salamander, Hynobius naevius, long considered a single species, has recently proven to include two groups (Group A=large type and Group B=small type) that are split at the species level. We compared the type series of H. naevius with specimens of the two groups to clarify which of them corresponds to true H. naevius, and to estimate the type locality of this species, which was not given in detail in its original description. Results of various morphological analyses altogether indicated that the type series belongs to Group A and that the population sample from Mt. Tara-dake, located on northwestern Kyushu, is most similar to the type series. Therefore, the type locality of the species is estimated to be in northwestern Kyushu. These results also indicate that Group B obviously represents a cryptic species whose scientific name remains to be determined.

Shallow-marine ostracode faunas around the Eocene/Oligocene boundary in the northwestern Kyushu, southwestern Japan

Middle Eocene–early Oligocene ostracode faunal changes in northwestern Kyushu of southwestern Japan are identified in this study. Ostracodes occur from shelf deposits of five formations: the middle Eocene Okinoshima, the upper Eocene Funazu, the uppermost Eocene–lowermost Oligocene Kishima, the lowermost Oligocene Itanoura, and the lower Oligocene Waita Formations. The middle Eocene–earliest Oligocene ostracodes were characterized by warm-water genera, indicating tropical, subtropical and Tethyan genera, whereas the late early Oligocene ostracodes do not include warm-water taxa, consisting of temperate realm genera. The middle Eocene–earliest Oligocene ostracodes do not include remarkable changes of species composition, in contract with equatorial Pacific radiolarians and West Coast USA molluscs. Ostracodes suggest that distinct climatic cooling did not occur in the southwestern Japan during the middle Eocene–earliest Oligocene.

有明海沿岸域のクリークにおける淡水魚類の生息の有無・生息密度とクリークの護岸形状との関係

The presence and populations of freshwater fishes and the revetment conditions in creeks were investigated at 48 sampling sites around the Sea of Ariake in northwestern Kyushu, Japan. Each creek studied in this survey was classified into one of the three following types in terms of revetment conditions: Type-1, the creeks have earthen revetments except when crossing roads; Type-2, although there are concrete revetments in the creeks, these revetments are short, and agricultural water flows over the revetments and reaches bank vegetations or earthen banks except during the agricultural off-season; Type-3, there are high concrete revetments around the creeks, and agricultural water does not flow over the revetments during any season. The amount of Hemigrammocypris rasborella present was affected by the revetment conditions, and the amount present in Type-3 was significantly lower than those in Type-1 and Type-2. The populations of H. rasborella, Rhodeus ocellatus kurumeus, and Pseudorasbora parva were affected by the revetment conditions. For H. rasborella and R. ocellatus kurumeus, the populations in Type-3 were significantly lower than those in Type-1 and Type-2. For P. parva, the population in Type-3 was significantly lower than that in Type-1.

A37 上昇マントルの累進的な融解 : 北西九州北松浦玄武岩からの制約(火山の岩石学(2),日本火山学会2006年秋季大会)

A37 上昇マントルの累進的な融解 : 北西九州北松浦玄武岩からの制約(火山の岩石学(2),日本火山学会2006年秋季大会)

長崎県島原半島に分布する下部更新統加津佐層の貝化石相

長崎県島原半島に分布する下部更新統加津佐層の貝化石相

Phylogenetic relationships of Hynobius naevius (Amphibia: Caudata) as revealed by mitochondrial 12S and 16S rRNA genes

Using mitochondrial 12S and 16S rRNA sequences, we investigated phylogenetic relationships among populations of the endemic Japanese salamander Hynobius naevius. Monophyly of this species was recovered only in the maximum parsimony tree and was unresolved in maximum likelihood and Bayesian trees. Instead the following four haplotype clades consistently emerged clearly: Clade 1 from northwestern Kyushu, Clade 2 from Chugoku and northeastern Kyushu, Clade 3 from western Shikoku and Kyushu, and Clade 4 from Chubu-Kinki and central-eastern Shikoku. Of these, Clades 1 and 2, and Clades 3 and 4, respectively, correspond to Groups A and B previously recognized from the analyses of allozyme data in this species, but monophyly of these groups was not strongly supported. Unlike the previous results, the western and eastern samples from Shikoku did not form a clade, and were grouped with Kyushu-B in Clade 3 and Chubu-Kinki in Clade 4, respectively. The reason for this conflict between mtDNA and allozyme results is unknown, but might be related to retention of ancestral mtDNA polymorphism in Shikoku populations. Nearly simultaneous divergence of as many as four lineages in wide-ranging H. naevius is inferred for the late Miocene–Pliocene history of this taxon.

P43 マグマ化学組成に対する地殻物質の混入の影響 : 北西九州北松浦玄武岩を例として(日本火山学会2005年秋季大会)

P43 マグマ化学組成に対する地殻物質の混入の影響 : 北西九州北松浦玄武岩を例として(日本火山学会2005年秋季大会)

A prospective study of the prevalence of gastroesophageal reflux disease and confounding factors

The prevalence of gastroesophageal reflux disease (GERD) has reportedly risen in recent years. Difficulties associated with endoscopic diagnosis mean it is not easy to determine its precise prevalence. A prospective study of the prevalence of endoscopy-positive GERD (EP-GERD) was conducted at Higuchi Hospital, a general hospital in Northwestern Kyushu, Japan. The study also correlated factors that might affect prevalence (age, sex, and functions of the gastroesophageal junction). From consecutive patients undergoing endoscopic examination at Higuchi Hospital between January 2000 and April 2003, 1234 patients without severe complications were examined for the possible presence of GERD. Patients were stratified by age and sex, and the prevalence in each group ascertained. EP-GERD was defined on the four-level scale of the Los Angeles classification. Endoscopic classification of gastroesophageal flap valve ([GEFV] functional anomalie; using a four-level scale), was done as proposed by Hill et al. in 1996, to assess flap-valve morphology. Six items were evaluated: (1) symptoms and primary diseases; (2) prevalence of development of EP-GERD classified by age and sex; (3) endoscopic morphology of the GEFV as an expression of the functions of the gastroesophageal junction, and its prevalence by age and sex; (4) regression analysis and Spearman's rank correlation of GEFV and EP-GERD grades; (5) prevalence of EP-GERD and GEFV stratified by age and analyzed; and (6) multiple regression analysis of EP-GERD and explanatory variables (age, sex, and GEFV). The overall prevalence of EP-GERD was 5.8% (72/1234) and this patient group was dominated by men. Aging had minimal effect on prevalence in men, but the prevalence rose among women as they aged. The age-stratified prevalence of GEFV functional anomalies was similar to the age-stratified prevalence of EP-GERD in both sexes. The correlation between EP-GERD and GEFV functional anomalies was high regardless of sex. We postulate that the mechanisms leading to the development of GEFV functional anomalies in men are different from those in women. Future evaluations of EP-GERD should also observe GEFV function.

Metrical and nonmetrical analyses of modern female crania in the northwestern Kyushu area

In the northwestern Kyushu area, at the southwestern region of the mainland of Japan, a native people of Jomon lineage lived during the Aeneolithic Yayoi period, and differed morphologically from the immigrant people of continental lineage of the northern Kyushu area. In this study, the metric and nonmetric characteristics of 204 modern female crania from northwestern Kyushu were examined in order to investigate their morphological characteristics and lineage relationships by comparing them with several modern Japanese, Ryukyuan, Hokkaido Ainu, Korean, Chinese, and northern and northwestern Kyushu Yayoi and Jomon cranial series. The craniometric characteristics of the northwestern Kyushu Japanese females were found to be similar to those of the mainland Japanese, as well as to those of Koreans, Chinese, and the northern Kyushu Yayoi, but differed somewhat from the Ryukyuan and Hokkaido Ainu conditions, and distinctly diverged from the northwestern Kyushu Yayoi and Jomon conditions. The results of multivariate analyses of nonmetric traits coincided generally with those of the craniometrical analyses; however, the northwestern Kyushu Japanese was found to be relatively close to the Ryukyuans, and markedly remote from the Hokkaido Ainu. These findings suggest that the northwestern Kyushu Japanese possess morphological traits in common with other mainland Japanese populations due to genetic influences of the continental lineage during or after the protohistoric Kofun period.

High ³He/4He ratio in xenoliths from Takashima: Evidence for plume type volcanism in southwestern Japan

Cenozoic basalts distributed along the southwestern Japan arc system have geochemical features different from typical island‐arc basalts, suggesting that the volcanism might have been triggered by a mantle plume. To identify the source materials in these volcanics, noble gas isotopic compositions of olivines separated from dunite xenoliths in alkaline basalts from Takashima, northwestern Kyushu, were measured. Most samples contain MORB‐type helium. However, some samples showed ³He/4He ratios significantly higher than the MORB value, from 9.4 up to 16.6 times the atmospheric ratio of 1.4×10−6. This finding strongly supports the contribution of a mantle plume to the volcanism of this region.

Cranial Nonmetrical Analyses of the Yayoi People in the Northwestern Kyushu Area.

Incidence data of 22 cranial nonmetric traits were investigated in the Aeneolithic Yayoi people in the northwestern Kyushu area, and compared with those in Yayoi people in the northern Kyushu area, Yayoi people in Yamaguchi and Jomon people. Smith's Mean Measures of Divergence (MMD) were obtained in 8 groups after addition of modern people in the northwestern Kyushu area and others. Based on these data, principal co-ordinate analysis and cluster analysis were performed. The following results were obtained. The characteristics of the Yayoi people in northwestern Kyushu succeeded the characteristics of Neolithic Jomon people, and differ markedly from Yayoi people of continental lineage. Among the 22 traits, the incidences of supraorbital foramen, biasterionic suture vestige, hypoglossal canal bridging, pterygospinous foramen, transverse zygomatic suture vestige and mylohyoid bridging were greatly different between the Yayoi people in northwestern Kyushu and the Yayoi people of continental lineage. In the northwestern Kyushu area, a marked difference in cranial nonmetric traits was found between Yayoi and modern people. Such a difference probably developed because of the hereditary influence of Yayoi people of continental lineage in and after the Protohistoric Kofun period.

日本海南部〜九州周辺の新生代後期テクトニクス

Late Cenozoic tectonic history around the southern part of the Japan Sea and Kyushu is reconstructed on the basis of offshore reflection seismic survey and borehole stratigraphy together with geologic information on land. Three tectonic episodes are identified in the study area as follows;(1) Paleomagnetic data suggest that western half of the Japan Sea was generated through Early to Middle Miocene rifting and clockwise rotation of southwest Japan. Seismic profiles around the southern margin of the Japan Sea show extensional grabens filled with late Early Miocene sediments. Coeval deformation in the Fukue Basin off northwestern Kyushu, which is located around rotation pivot of the rifted sliver of southwest Japan, is characterized by right-lateral leaky wrenching along a NNE-SSW structural trend.(2) Southern margin of the Japan Sea suffered extensive inversion around the end of Miocene, probably caused by resumption of subduction of the Philippine Sea Plate. ENE-WSW trending folds (San'in Folded Zone) converge into Tsushima Island at the western end of southwest Japan. Shortening of the southern part of the Japan Sea was accommodated by left-lateral movement along the Tsushima-Goto Fault on the western margin of the back-arc basin. In a sharp contrast, Goto-nada and Amakusa-nada Seas, and central Kyushu began to subside with many extensional features in the same period, which may be linked to mantle upwelling.(3) In Quaternary, study area is divided into three tectonic domains: Inner Zone of southwest Japan is characterized by simple shear deformation caused by right-lateral movements on the Median Tectonic Line (MTL). Southern part of the Japan Sea is undulated under E-W compressive stress. Central Kyushu continued to subside alternatively controlled by pull-apart basin formation on the MTL and mantle upwelling.

ABSTRACT: Sequence stratigraphy and tectonics of Tertiary coal bearing basins in northwestern Kyushu, Japan

ABSTRACT: Sequence stratigraphy and tectonics of Tertiary coal bearing basins in northwestern Kyushu, Japan

Paleogene and Plio‐Pleistocene basin formation around northwestern Kyushu, Japan

Cenozoic basin‐forming processes in northwestern Kyushu were studied on the basis of geological and geophysical data. Gravity anomaly analysis delineated four sedimentary basins in the study area: Goto‐nada, Nishisonogi, Amakusa‐nada, and Shimabara. Borehole stratigraphy and reflection seismic interpretation suggest that the Goto‐nada Basin was subdivided into the Paleogene and Plio‐Pleistocene depocenters (Goto‐nada 1 and 2). In the Paleogene, Amakusa‐nada Basin was rapidly subsiding together with the Shimabara Basin as part of a large graben. Goto‐nada 1 and Nishisonogi basins belonged to another depositional area. After stagnant subsidence stage in the early Miocene, the study area became a site of basaltic activity (since 10 Ma) and vigorous subsidence in the Plio‐Pleistocene. Goto‐nada 2 Basin is accompanied with numerous east–west active faults, and separated from the Amakusa‐nada Basin by a northeast– southwest basement high, Nomo Ridge. Plio‐Pleistocene subsidence of the Amakusa‐nada Basin is related with low‐angle normal faulting on the eastern flank of the Nomo Ridge. Shimabara Basin is a composite volcano‐tectonic depression which is studded by east–west faults. Focal mechanism on active faults suggests transtensional stress regime in the study area.

K-Ar geochronology of a Quaternary monogenetic volcano group in Ojika Jima District, Southwest Japan

An unspiked K–Ar dating method using a mass-fractionation correction procedure was applied to a Quaternary independent group of monogenetic volcanoes, Ojikajima Volcano Group, located in northwestern Kyushu in Southwest Japan, in order to clarify in detail secular variations in eruptive volume, locations of eruptive vents, and magma compositions in a single monogenetic volcano group. The major results were as follows: (a) K–Ar ages of monogenetic volcanoes distribute from 1.08 to 0.30 Ma, with voluminous peaks at approximately 1.0 and 0.6 Ma. (b) The volcanic activity commenced in the central part of the field, expanded to the whole field at approximately 0.6 Ma, and then shrank to the central area. (3) Concentrations of incompatible elements, such as Ba, K, and Nb, increase with decreasing age, whereas P, Y, and Zr concentrations remain constant. These concentrations suggest gradual decrease in the degree of partial melting from an identical mantle source with residual garnet.

Mantle-derived xenoliths with hotspot type helium in Cenozoic alkali, basalt, northwestern Kyushu, Japan

The 3He/4He ratio of mantle-derived material is not uniform and the distinct 3He/4He signatures are found in association with different tectonic environments. Helium isotopic signature of hot-spot regions such as Hawaii, Iceland, and Rbunion range from 9 to 30 Ra, where Ra is 3He/4He of the atmosphere = 1.4 x 10 -6, which indicates that the hot-spot volcanisms tap a deeper region of the mantle enriched in 3He than MORB reservoir. Cenozoic alkaline basalts from back-arc region of the Japanese island-arc system are less depleted in Ta, Nb and Ti and less enriched in K, Sr, Ba and Rb compared with samples from northeastem Japan. These geochemical features lead to Nakamura et al. (1985) to suggest that the alkali volcanisms of this area were not directly related with subduction processes but were triggered by plumes originated from greater depth. Furthermore, it was suggested that the alkali basalt magmatism may represent the final stage of a mantle diapirism which was most active in the Miocene and caused the opening of the Sea of Japan (Iwamori, 1991). We measured noble gas isotopic compositions of xenoliths in Cenozoic alkali basalt, Takashima, northwestern Kyushu to investigate possible contribution of deep mantle plume.

Mantle-derived Xenoliths with Hot-spot Type Helium in Cenozoic Alkali Basalt, Northwestern Kyushu, Japan

The 3He/4He ratio of mantle-derived material is not uniform and the distinct 3He/4He signatures are found in association with different tectonic environments. Helium isotopic signature of hot-spot regions such as Hawaii, Iceland, and Rbunion range from 9 to 30 Ra, where Ra is 3He/4He of the atmosphere = 1.4 x 10 -6, which indicates that the hot-spot volcanisms tap a deeper region of the mantle enriched in 3He than MORB reservoir. Cenozoic alkaline basalts from back-arc region of the Japanese island-arc system are less depleted in Ta, Nb and Ti and less enriched in K, Sr, Ba and Rb compared with samples from northeastem Japan. These geochemical features lead to Nakamura et al. (1985) to suggest that the alkali volcanisms of this area were not directly related with subduction processes but were triggered by plumes originated from greater depth. Furthermore, it was suggested that the alkali basalt magmatism may represent the final stage of a mantle diapirism which was most active in the Miocene and caused the opening of the Sea of Japan (Iwamori, 1991). We measured noble gas isotopic compositions of xenoliths in Cenozoic alkali basalt, Takashima, northwestern Kyushu to investigate possible contribution of deep mantle plume.

Lower crustal erosion induced by mantle diapiric upwelling: Constraints from sedimentary basin formation followed by voluminous basalt volcanism in northwest Kyushu, Japan

A sequence of geological events, beginning with basement subsidence to form a shallow-water sedimentary basin and subsequent voluminous basalt volcanism and uplift of land, has been observed in the back-arc region of northwestern Kyushu, Japan. The basin consists of a succession of marine and non-marine sediments with a total thickness of 1000–1500 m which range in age from 43 to 10 Ma. The basalt volcanism commenced at 10 Ma and continued until 1 Ma. Uplift started at around 30 Ma and continued after the cessation of the basalt volcanism. These geological phenomena may be explained by the convective coupling between the ductile lower crust and upper mantle induced by mantle diapiric upwelling. Thus, surface subsidence leading to sedimentary basin formation is attributed to lower crustal erosion by mantle diapiric upwelling. For an earth model with lower crustal and upper mantle viscosities of 10 19–10 20 Pa s, 5 km of lower crust can be eroded 10–20 Myr after the start of convective coupling between the ductile lower crust and upper mantle, compatible with the period estimated by observations. In this process, the melt due to adiabatic mantle diapiric upwelling accumulates beneath the lower crust. The accumulation of low density melt in the space originally occupied by mantle material causes crustal uplift. When the stress state became extensional, as inferred from the extension of Okinawa Trough during the middle to late Miocene [1], the melt filling the eroded lower crustal area may have reached the surface, leading to voluminous basalt volcanism.

Allozyme polymorphism and geographic variation in the small brown planthopper, Laodelphax striatellus (Homoptera: Delphacidae).

The small brown planthopper, Laodelphax striatellus, immigrates annually into Japan over the East China Sea from the Asian mainland. It is not known whether this long-distance dispersal has any effect on the genetic structure of Japanese L. striatellus populations. The dispersal of L. striatellus is suspected to be relevant to the population dynamics of infection with the parasitic bacterium Wolbachia, which causes cytoplasmic incompatibility in L. striatellus. Wolbachia infection has spread within and among Japanese L. striatellus populations due to this cytoplasmic incompatibility. In the present study, the geographic differences among II L. striatellus populations from Japan and Taiwan was investigated using allozyme polymorphism. FST values on three enzyme loci (GPI, PGM, and AK) indicated a geographically differentiated population structure. Significant differentiation was found even among populations located along the course of the long-distance dispersal. The results indicated that long-range dispersal of L. striatellus does not occur regularly over the main islands of Japan and that it does not have a large effect on the population structure of L. striatellus. This conclusion is in agreement with the geographically variable life history of L. striatellus adapted to local climates. The short-term rice stripe epidemic, which is vectored by L. striatellus, in northwestern Kyushu, Japan, during 1985 and 1986 corresponds to these results. Based on the present findings, short-distance dispersal was considered to drive the spatial spread of Wolbachia infection among L. striatellus populations.