bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of an accretionary complex along the north arm of the Island of Sulawesi, Indonesia
Authors: Djajadihardja Yusuf Surachman , Taira Asahiko , Tokuyama Hidekazu , Aoike Kan , Reichert Christian , Block Martin , Schluter Hans U. , Neben Sonke
Published: February 2004

Abstract  Seismic reflections across the accretionary prism of the North Sulawesi provide excellent images of the various structural domains landward of the frontal thrust. The structural domain in the accretionary prism area of the North Sulawesi Trench can be divided into four zones: (i) trench area; (ii) Zone A; (iii) Zone B; and (iv) Zone C. Zone A is an active imbrication zone where a decollement is well imaged. Zone B is dominated by out‐of‐sequence thrusts and small slope basins. Zone C is structurally high in the forearc basin, overlain by a thick sedimentary sequence. The subducted and accreted sedimentary packages are separated by the decollement. Topography of the oceanic basement is rough, both in the basin and beneath the wedge. The accretionary prism along the North Sulawesi Trench grew because of the collision between eastern Sulawesi and the Bangai–Sula microcontinent along the Sorong Fault in the middle Miocene. This collision produced a large rotation of the north arm of Sulawesi Island. Rotation and northward movement of the north arm of Sulawesi may have resulted in southward subduction and development of the accretionary wedge along North Sulawesi. Lateral variations are wider in the western areas relative to the eastern areas. This is due to greater convergence rates in the western area: 5 km/My for the west and 1.5 km/My for the east. An accretionary prism model indicates that the initiation of growth of the accretionary prism in the North Sulawesi Trench occurred approximately 5 Ma. A comparison between the North Sulawesi accretionary prism and the Nankai accretionary prism of Japan reveals similar internal structures, suggesting similar mechanical processes and structural evolution.
Similarities between strike‐slip faults at different scales and a simple age determining method for active faults
Authors: Kim Young‐Seog , Sanderson David J.
Published: February 2004

Abstract  Several differently scaled strike‐slip faults were examined. The faults shared many geometric features, such as secondary fractures and linkage structures (damage zones). Differences in fault style were not related to specific scale ranges. However, it was recognized that differences in style may occur in different tectonic settings (e.g. dilational/contractional relays or wall/linkage/tip zones), different locations along the master fault or different fault evolution stages. Fractal dimensions were compared for two faults (Gozo and San Andreas), which supports the idea of self‐similarity. Fractal dimensions for traces of faults and fractures of damage zones were higher (D ∼1.35) than for the main fault traces (D ∼1.005) because of increased complexity due to secondary faults and fractures. Based on the statistical analysis of another fault evolution study, single event movements in earthquake faults typically have a maximum earthquake slip : rupture length ratio of approximately 10−4, although this has only been established for large earthquake faults because of limited data. Most geological faults have a much higher maximum cumulative displacement : fault length ratio; that is, approximately 10−2 to 10−1 (e.g. Gozo, ∼10−2; San Andreas, ∼10−1). The final cumulative displacement on a fault is produced by accumulation of slip along ruptures. Hence, using the available information from earthquake faults, such as earthquake slip, recurrence interval, maximum cumulative displacement and fault length, the approximate age of active faults can be estimated. The lower limit of estimated active fault age is expressed with maximum cumulative displacement, earthquake slip and recurrence interval as T ≅ (dmax /u) · I(M).
Petrochemical evidence for off‐ridge magmatism in a back‐arc setting from the Yakuno ophiolite, Japan
Authors: Ichiyama Yuji , Ishiwatari Akira
Published: February 2004

Abstract  The Permian ophiolite emplaced in the Yakuno area, Kyoto Prefecture, consists of metavolcanic sequences, metagabbro and a troctolitic intrusion. The metavolcanics are associated with thick mudstone through a contact that shows the flowage of lava over unconsolidated mud layers on the sea floor. The metavolcanics and metagabbro have rare earth element (REE) patterns that are similar to enriched (E)‐ and transitional (T)‐types ([La/Yb]N = 0.77–11.2) of mid‐oceanic ridge basalts (MORB), whereas their Nb/La ratios (0.40–1.20) are as low as those of back‐arc basin basalts (BABB). Cr‐spinels in the metavolcanic rocks have Cr♯ of 40–73 and an Fe3+♯ of 9–24, numbers which are comparable to the values of BABB. These lines of evidence suggest that the Yakuno ophiolite originated more likely from an early stage back‐arc basin rather than from an oceanic plateau, as has been suggested by some researchers. The troctolitic body that intrudes as a 0.5‐km long lens in the metagabbro is composed of troctolite, olivine gabbro and microgabbro. The troctolite is marked by an olivine–plagioclase crystallization sequence, different from the commonly observed olivine–clinopyroxene sequence in other mafic/ultramafic cumulates of the Yakuno ophiolite. The microgabbro, with a composition close to that of the parental magma of the troctolite, is depleted in light REE ([La/Yb]N = 0.18–0.55) so that it has an REE pattern that mimics normal (N)‐type MORB. The interstitial clinopyroxene of the troctolite has highly variable TiO2 contents (0.2–1.4 wt%), which is interpreted to result from postcumulus crystallization of heterogeneous intercumulus melts. The troctolitic intrusion may represent a late stage intrusion that formed in an off‐ridge environment during sea floor spreading of the back‐arc basin. The geochemical variation observed in the Yakuno ophiolite, ranging from N‐ to E‐MORB affinities, reflects the changes in both mantle source compositions and processes involved in magma generation during the evolution of the back‐arc basin.
Missing ophiolitic rocks along the Mae Yuam Fault as the Gondwana–Tethys divide in north‐west Thailand
Authors: Hisada Ken‐ichiro , Sugiyama Masaaki , Ueno Katsumi , Charusiri Punya , Arai Shoji
Published: February 2004

Abstract  Thailand comprises two continental blocks: Sibumasu and Indochina. The clastic rocks of the Triassic Mae Sariang Group are distributed in the Mae Hong Son–Mae Sariang area, north‐west Thailand, which corresponds to the central part of Sibumasu. The clastic rocks yield abundant detrital chromian spinels, indicating a source of ultramafic/mafic rocks. The chemistry of the detrital chromian spinels suggests that they were derived from three different rock types: ocean‐floor peridotite, chromitite and intraplate basalt, and that ophiolitic rocks were exposed in the area, where there are no outcrops of them at present. Exposition of an ophiolitic complex denotes a suture zone or other tectonic boundary. The discovery of chromian spinels suggests that the Gondwana–Tethys divide is located along the Mae Yuam Fault zone. Both paleontological and tectonic aspects support this conclusion.
Strain geometries in the Sanbagawa Metamorphic Belt inferred from deformation structures in metabasite
Authors: Shimizu Ichiko , Yoshida Shizuo
Published: February 2004

Abstract  Ductile deformation in the Sanbagawa Metamorphic Belt has been considered to be characterized by uniaxial elongation parallel to the east–west‐trending lineation, based on strain analysis of radiolarian fossils in metachert. However, only limited data were available to test this idea in strongly recrystallized schists. Strain measurements on deformed pillow structures in central Shikoku show uniaxial flattening, whereas pressure shadows around pyrite in the Kanto Mountains indicate constrictional strain. In addition, in the low‐grade part of the Sanbagawa Metamorphic Belt belonging to the Northern Chichibu Belt in the Kanto Mountains, deformed amygdules in pillow lava show flattening strain, which is consistent with the results of strain measurements using radiolarian fossils in the same area. These observations, together with the results of other strain analyses reported so far, indicate that the strain field is not uniform and that the east–west‐trending shearing and stretching were not pervasive in the Sanbagawa Metamorphic Belt.
Paleomagnetism of a pyroclastic flow deposit and its correlative widespread tephra in central Japan: Possible tectonic rotation since the late Pleistocene
Authors: Itoh Yasuto , Kimura Haruo
Published: February 2004

Abstract  The late Pleistocene Kamitakara Pyroclastic Flow Deposit (KPFD) and its correlative Kasamori (Ks22) Tephra in central Japan are found to preserve stable thermoremanent magnetization (TRM) and detrital remanent magnetization (DRM), respectively. Untilted site‐mean declinations of the KPFD are characterized by a fairly large scatter with easterly deflection, while those of the Ks22 show significantly smaller deflections. Because northerly paleomagnetic directions consistently characterize shallow marine sediments intercalating the Ks22 layer, the directional discordance is not attributed to different acquisition timing between TRM and DRM, but is probably due to a recent tectonic rotation  in  central  Japan.  Large scatter in TRM  declinations of the KPFD implies that a number of right‐lateral active faults around the depositional area of the pyroclastic flow raised differential rotation of crustal blocks in central Japan, even during the late Pleistocene.
Petrogenesis of orthopyroxene‐ and amphibole‐bearing andesites, Mustique, Grenadine Islands, Lesser Antilles Arc: Isotope, trace element and physical constraints
Authors: Smith Terence Edward , Thirlwall Matthew , Holm Paul Eric , Harris Michael John
Published: February 2004

Abstract  On the island of Mustique, fresh and propylitized olivine–plagioclase–clinopyroxene basalt, plagioclase–clinopyroxene–orthopyroxene and plagioclase–clinopyroxene–amphibole andesite lavas and minor intrusions are interbedded with Oligocene pyroclastic and epiclastic rocks. Chemical data show that two isotopically identical, but chemically different, suites of lava are present: (i) the OPXS (87Sr/86Sr 0.70403–0.70454; 143Nd/144Nd 0.512952–0.512986; δ18Ocpx 5.49 and 5.61), comprising basalts and orthopyroxene‐bearing andesites; and (ii) the AMPHS (87Sr/86Sr 0.70401–0.70457; 143Nd/144Nd 0.512981–0.513037; δ18Ocpx 5.54), made up of basalts and amphibole‐bearing andesites. The OPXS has higher contents of TiO2, P2O5, light rare earth elements, Sm, Pb, Th, U, Zr, Y and Nb, and higher La/Yb ratios than the AMPHS. The isotopic data suggest that both suites formed from melts derived from the same subduction‐modified depleted mantle source as the volcanic rocks of nearby St Vincent and Bequia, and the northern islands of the Lesser Antilles Arc. The immobile trace element contents, and La/Yb ratios, of the OPXS are indicative of ∼10% partial melting of the source, whereas those of the AMPHS are indicative of ∼25% partial melting. The within‐suite chemical variation of the OPXS is consistent with ∼45% fractional crystallization of its intratelluric mineral assemblages, and that of the AMPHS is consistent with the removal of ∼65% of its intratelluric assemblages. Experimental evidence suggests that both suites of basalt crystallized at pressures <8 kbar from melts containing 1–2 wt% water. After extensive fractional crystallization, the andesites crystallized at pressures between approximately 5 and 2 kbar. The OPXS magmas appear to have lost more of their water content than the AMPHS magmas. Thus, the OPXS andesites formed from melts with an estimated water content of 2–3 wt%, whereas the AMPHS andesites formed from melts containing at least 4.5 wt% water.
Geochemistry of the oldest MORB and OIB in the Isua Supracrustal Belt, southern West Greenland: Implications for the composition and temperature of early Archean upper mantle
Authors: Komiya Tsuyoshi , Maruyama Shigenori , Hirata Takafumi , Yurimoto Hisayoshi , Nohda Susumu
Published: February 2004

Abstract  Recent geological investigations of the Isua Supracrustal Belt (3.8 Ga), southern West Greenland, have suggested that it is the oldest accretionary complex on earth, defined by an oceanic plate‐type stratigraphy and a duplex structure. Plate history from mid‐oceanic ridge through plume magmatism to subduction zone has been postulated from analysis of the reconstructed oceanic plate stratigraphy in the accretionary complex. Comparison between field occurrence of greenstones in modern and ancient accretionary complexes reveals that two types of tholeiitic basalt from different tectonic settings, mid‐oceanic ridge basalt (MORB) and oceanic island basalt (OIB), occur. This work presents major, trace and rare earth element (REE) compositions of greenstones derived from Isua MORB and OIB, and of extremely rare relict igneous clinopyroxene in Isua MORB. The Isua clinopyroxenes (Cpx) have compositional variations equivalent to those of Cpx in modern MORB; in particular, low TiO2 and Na2O contents. The Isua Cpx show slightly light (L)REE‐depleted REE patterns, and the calculated REE pattern of the host magma is in agreement with that of Isua MORB. Analyses of 49 least‐altered greenstones carefully selected from approximately 1200 samples indicate that Isua MORB are enriched in Al2O3, and depleted in TiO2, FeO*, Y and Zr at the given MgO content, compared with Isua OIB. In addition, Isua MORB show an LREE‐depleted pattern, whereas Isua OIB forms a flat REE pattern. Such differences suggest that the Early Archean mantle had already become heterogeneous, depending on the tectonic environment. Isua MORB are enriched in FeO compared with modern MORB. Comparison of Isua MORB with recent melting experiments shows that the source mantle had 85–87 in Mg♯ and was enriched in FeO. Potential mantle temperature is estimated to be approximately 1480°C, indicating that the Early Archean mantle was hotter by at most approximately 150°C than the modern mantle.
Long‐term changes in distribution and chemistry of middle Miocene to Quaternary volcanism in the Chokai‐Kurikoma area across the Northeast Japan Arc
Authors: Kondo Hirofumi , Tanaka Kazuhiro , Mizuochi Yukihiro , Ninomiya Atusi
Published: February 2004

Abstract  To understand the characteristics of long‐term spatial and temporal variation in volcanism within a volcanic arc undergoing constant subduction since the cessation of back‐arc opening, a detailed investigation of middle Miocene to Quaternary volcanism was carried out within the Chokai‐Kurikoma area of the Northeast Japan Arc. This study involved a survey of available literature, with new K–Ar and fission track dating, and chemical analyses. Since 14 Ma, volcanism has occurred within the Chokai‐Kurikoma area in specific areas with a ‘branch‐like’ pattern, showing an east–west trend. This is in marked contrast to the widespread distribution of volcanism with a north–south trend in the 20–14 Ma period. The east–west‐ trending ‘branches’ are characterized by regular intervals (50–100 km) of magmatism along the arc. These branches since 14 Ma are remarkably discrepant to the general northwest–southeast or north‐northeast–south‐southwest direction of the crustal structures that have controlled Neogene to Quaternary tectonic movements in northeast Japan. In addition, evidence indicating clustering and focusing of volcanism into smaller regions since 14 Ma was verified. Comparison of the distribution and chemistry of volcanic rocks for three principal volcanic stages (11–8, 6–3 and 2–0 Ma) revealed that widely but sparsely distributed volcanic rocks had almost the same level of alkali and incompatible element concentrations throughout the area (with the exception of Zr) in the 11–8 Ma stage. However, through the 6–3 Ma stage to the 2–0 Ma stage, the concentration level in the back‐arc cluster increased, while that in the volcanic front cluster remained almost constant. Therefore, the degree of partial melting has decreased, most likely with a simultaneous increase in the depth of magma segregation within the back‐arc zone, whereas within the volcanic front zone, the conditions of magma generation have changed little over the three stages. In conclusion, the evolution of the thermal structure within the mantle wedge across the arc since 14 Ma has reduced the extent of ascending mantle diapirs into smaller fields. This has resulted in the tendency for the distribution of volcanism to become localized and concentrated into more specific areas in the form of clusters from the late Miocene to Quaternary.
High‐resolution shallow seismic and ground penetrating radar investigations revealing the evolution of the Uemachi Fault system, Osaka, Japan
Authors: Rashed Mohamed , Nakagawa Koichi
Published: February 2004

Abstract  Ground penetrating radar (GPR) and high‐resolution shallow reflection seismic surveying were carried out to investigate the subsurface geology in and around the Uemachi Fault zone in the Yamato River area, Osaka, Japan. Shallow drilling in the area showed a major displacement event during the middle Pleistocene. The main Uemachi Fault plane could be clearly imaged on the seismic section, except for the most shallow 200 m. Several shallow normal fault planes with less displacement could be detected on both sides of the fault plane. GPR profiles confirmed the presence of several shallow normal faults within the area near the fault zone. These shallow faults could be followed in all of the GPR profiles crossing the fault zone. The integration of seismic section, GPR profiles and drilling data led to a conceptual model that explains the evolution of the Uemachi Fault system. The proposed model suggests the occurrence of several cycles of small vertical displacement along the deep part of the fault plane caused by the regional east–west compressional stress. The ductile nature of the shallow sedimentary cover and the absence of confining pressure in the shallow part allow for a considerable amount of plastic bending before failing in the shallow sedimentary layers. This bending generates stretching force within the shallow sedimentary cover, which in time, along with gravitational force, gives rise to the formation of the swarm of normal faults within the shallow layers near the fault zone. Some of the detected faults extend to a depth of less than 3 m below the ground surface, suggesting that the last tectonic activity along the fault plane may have occurred recently.
Rock magnetism and paleomagnetic stratigraphy of forearc sediments of the Japan Trench, ODP Sites 1150 and 1151
Authors: Kanamatsu Toshiya , Niitsuma Nobuaki
Published: February 2004

Abstract  Magnetic measurements were carried out to investigate rock magnetic properties and paleomagnetic directions of late and middle Miocene sediments recovered from the land side of the Japan Trench during the Ocean Drilling Program Leg 186. Because the low coercive component in natural remanent magnetization (NRM) normalized by anhysteretic remanent magnetization shows that the drilling‐induced magnetization is severe in the sections obtained by the advanced hydraulic piston coring method, careful analyses of demagnetization of NRM using the ‘demagnetization plane’ were carried out to decompose the direction and intensity. Magnetostratigraphic correlation down to the upper Miocene, supplemented by biostratigraphic data, revealed that the sedimentation rates are characterized by drastic changes, with the early Pliocene having the highest rate. This high sedimentation rate is related to the subsidence of the southern deep‐sea terrace of the Japan Trench.
Middle Miocene to Pleistocene radiolarian biostratigraphy in the Northwest Pacific Ocean, ODP Leg 186
Authors: Kamikuri Shin‐ichi , Nishi Hiroshi , Motoyama Isao , Saito Saneatsu
Published: February 2004

Abstract  The Upper Cenozoic sedimentary sequences drilled at Sites 1150 and 1151, Ocean Drilling Program Leg 186, enabled establishment of radiolarian zonation and calibration of the age of bioevents in the forearc area of the northern Japan Islands. The sequences were divided into nine zones from the Pleistocene Botryostrobus aquilonaris Zone to the Upper Miocene Lipmanella redondoensis Zone at Site 1150, and 11 zones from the Pleistocene Stylatractus universus Zone to the Middle Miocene Dendrospyris? sakaii Zone at Site 1151. These zones correlate successfully with the studied sequences of many of deep‐sea cores in the Northwest Pacific Ocean and with some sections of onshore Japan. Of 67 important radiolarian bioevents recognized during the study, 29 Pleistocene to Upper Miocene events were directly tied to the geomagnetic polarity time scale through the well‐defined paleomagnetic polarity records, and 21 Upper Miocene events were calibrated based on the diatom biostratigraphy. Of these events, 24 geographically widespread events were selected to test synchroneity and usefulness as time‐horizons within the mid‐to‐high latitude of the Northwest Pacific, involving eight other offshore and onshore sections. Examination showed that most of the zonal boundary events are synchronous within the considered region, and that many diachronous events, most of which are eliminated from the zonal scheme, are unreliable events linked to rare and sporadic occurrences of the species. Radiolarian biostratigraphy of the studied cores clearly indicates three major hiatuses in the Middle Pleistocene, Late Miocene and late Middle Miocene. The latter two hiatuses can be correlated to two global oceanic hiatuses, NH6 and NH3, respectively.
Modeling seismic reflections from thin‐bed dolomite layers in diatomite formation
Authors: Sun Yue‐Feng
Published: February 2004

Abstract  The origin of dolomite and its diagenesis are still not fully understood. The timing and occurrence of dolomite beds remain key problems. Many thin‐bed layers of dolomite in marine sediments were discovered at drill sites in the forearc basin west of the Japan Trench during the Ocean Drilling Program Leg 186. The thickness of the dolomite layers ranges from 0.5 to 2 m, estimated from the well log. These thin‐bed dolomite layers were able to be identified on seismic data, through quantitative analysis and comparison of the data with synthetic seismograms. Amplitude‐preserved seismic data processing with broadband high‐resolution enhancement helps to estimate the reflectivity series dominated by the large impedance contrast between the dolomite layers and the host sediments. In this report, the first geophysical evidence of large‐scale dolomitization is provided. The occurrence of thin dolomitic layers embedded in diatomaceous sediments is on a basin scale rather than being an isolated event, which constrains the type of dolomitization and the timing of layered dolomitization. It was found that thin‐bed dolomite layers occur where there is an abrupt change in sedimentation rate. Layered dolomitization starts when sedimentation rate changes (from high to low or vice versa). Two dolomite layers coincide with the Miocene–Pliocene and Pliocene–Pleistocene age boundaries. Formation of dolomite beds could be a timing signal of a dramatic change in paleoceanographic and paleoclimatic environments.
Constraints on the state of in situ effective stress and the mechanical behavior of ODP Leg 186 claystones in the Japan Trench forearc
Authors: Ask Maria Vera Susanna , Kopf Achim
Published: February 2004

Abstract   The Japan Trench forearc offshore Honshu Island in northeast Japan, where the 130‐m.y.‐old Pacific oceanic plate is presently subducted, was drilled during the Ocean Drilling Program Leg 186. Results from mechanical and sedimentological studies of claystones recovered from Sites 1150 and 1151 in the overlying erosional forearc wedge are reported in the present study. Although many physical properties are similar in the seismic (Site 1150) and aseismic portion (Site 1151) of the shallow forearc, Site 1150 displayed a higher abundance of open fractures, two prominent fault zones and enigmatic pore fluid signatures in the claystones. The abundance of weak mineral phases, together with high smectite contents (from X‐ray diffraction), control the low friction coefficients of 0.33–0.39 of the claystones in ring‐shear experiments. Results from triaxial testing proposed overall low magnitudes of in situ effective vertical stress, with somewhat lower values at Site 1150 than at Site 1151. Similarly, samples from Site 1150 displayed slightly higher pore fluid pressures than those at Site 1151. The high sediment porosities, which are in part also a result of intact diatom tests (from scanning electron microscope), together with the anomalous fluid signatures and elevated pore fluid pressures, could very likely result from upward migration and influx of deep‐seated waters. Dewatering reactions at depth result in enhanced pore fluid pressure transients along out‐of‐sequence thrusts and consequently lower effective stress. At depths greater than that of Leg 186 drilling, elevated pressure–temperature conditions trigger mineral transformation and cementation, which result in increasing friction, unstable sliding and seismic rupture. Such earthquakes could have repeatedly disaggregated the consolidated claystone fabrics at the seismic site, and could be responsible for differences in yield strength and cementation when compared to the aseismic Site 1151.
Evidence for fluid flow in the Japan Trench forearc using isotope geochemistry (Cl, Sr, B): Results from ODP Site 1150
Authors: Deyhle Annette , Kopf Achim , Frape Shaun , Hesse Reinhard
Published: February 2004

Abstract  Interstitial pore waters from Ocean Drilling Program Site 1150, where ∼1200 m of sub‐sea‐floor sediment from the upper Japan Trench forearc were recovered, were analyzed for element concentrations and Cl, Sr and B isotopes. Although chlorinity showed profound down‐hole freshening to values as low as ∼310 mm (0.55 × seawater) in the deeper part of the claystone‐dominated succession, both Sr and B concentrations showed an overall increase. Sr reached concentrations of up to >250 µm (∼3.00 × seawater), whereas B‐enrichment was even stronger (3920 µm; i.e. 9.30 × seawater). The strong variations in concentration correspond to fractionation reactions in the deep, tectonically deformed part of the forearc. The heavily fractured portion of Site 1150 (from ∼700 m to the total depth of the hole) has two shear zones that very likely act as conduits that expel deep‐seated fluids to the sea floor. These fluids not only showed the strongest freshening of Cl, but were also characterized by low δ37Cl measurements (down to −1.1‰), the heaviest δ11B measurements (∼40–46‰) and the least radiogenic 87Sr/ 86Sr measurements. The profound isotope anomalies together with the excursions in element concentrations suggest that diagenetic processes operate at that depth. These include clay mineral diagenesis, alteration of tephra from the Japan and Izu Arcs, and possibly transformation of biogenic silica from abundant diatoms. Given the strong enrichment of some mobile elements (e.g. Sr, B, Li), enhanced fluid flow through permeable penetrative faults through the forearc (like the shear zones at Site 1150) could be an efficient mechanism for back‐flux of those elements from the deep forearc into the hydrosphere.
Cross‐section through the frontal Japan Trench subduction zone: Geochemical evidence for fluid flow and fluid–rock interaction from DSDP and ODP pore waters and sediments
Authors: Deyhle Annette , Kopf Achim , Pawlig Sabine
Published: February 2004

Abstract  Fluids and sediments from Deep Sea Drilling Project/Ocean Drilling Program Legs (56, 57, 87 and 186) along a transect extending from the subducting plate, across the midslope and upper slope of the Japan Trench forearc were analyzed for B and B isotopes in order to assess their composition and fluid–sediment interaction. At the reference Site 436 on the subducting plate, changes in B contents and B isotopes are controlled by the lithology and diagenesis only. The midslope Sites 440 and 584 showed stronger variations in the B geochemistry, which can be related to diagenesis and tectonic dewatering along faults. The strongest changes in the B geochemistry were observed on the upper slope Sites 1150 and 1151, where profound down‐hole freshening (chlorinities as low as ∼310 mmol) coincides with a B enrichment (up to 9.3 × seawater concentration). The B isotope pore fluid profile of Site 1150 displayed a bimodal variation with depth, first increasing to values more positive than seawater, then shifting to lower signatures typical for deep‐seated fluids, whereas Site 1151 showed a constant B decrease with depth. Sites 1150 and 1151 sediments showed B increases with depth to values as high as ∼164 p.p.m. and isotopic compositions ranging from ∼+4 to −9‰. A linear decrease in Bsolid/Bfluid ratio, suggests that B geochemistry of the upper slope sites is controlled by fluid–rock interaction and deep‐seated fluid flow, whereas constant Bsolid/Bfluid ratios were observed at the reference site on the incoming plate. This fluid overprint is probably caused by normal faults in the sediment cover which might be interconnected to deep thrusts in the underlying Cretaceous accreted wedge. This suggests that the erosive Japan Trench margin is characterized by back‐flux of deep‐seated, B‐enriched fluids into the ocean, which is facilitated by extensional normal faulting as a result of tectonic erosion and subsidence.
Middle Miocene to Pleistocene magneto‐biostratigraphy of ODP Sites 1150 and 1151, northwest Pacific: Sedimentation rate and updated regional geological timescale
Authors: Motoyama Isao , Niitsuma Nobuaki , Maruyama Toshiaki , Hayashi Hiroki , Kamikuri Shin‐ichi , Shiono Masamichi , Kanamatsu Toshiya , Aoki Kaori , Morishita Chikako , Hagino Kyoko , Nishi Hiroshi , Oda Motoyoshi
Published: February 2004

Abstract  Shipboard and shore‐based investigation on siliceous and calcareous microfossil biostratigraphy, magneto‐stratigraphy and tephrostratigraphy identified numerous datum events from the sedimentary sequences of Sites 1150 and 1151 drilled on the forearc basin of northern Japan by the Ocean Drilling Program Leg 186. Some 83 datum events were selected to construct new age–depth models for the sites. Based on the reliable magneto‐stratigraphy from the Pleistocene to the Upper Miocene, which were correlated to the standard geomagnetic polarity timescale, and on excellent records of diatom and radiolarian biostratigraphy throughout the sequences, the shipboard age model was revised. Major revisions referred to stratigraphic position of the Miocene–Pliocene boundary that has been shifted more than 200 m downward in each sequence. The age–depth relations of the forearc sites represent drastic changes in the sedimentation rate—extremely high (40 cm/k.y. on average) in the Early Pliocene and low (less than 2 cm/k.y. on average) in the Middle Miocene—and several hiatuses exist throughout the sequence. The drastic changes can be related mostly to changes in diatom sedimentation and the tectonics of the Japanese Island Arc. Local ages for some foraminiferal, calcareous nannofossil and radiolarian bioevents are estimated from the age–depth models at each site. These newly calibrated bioevents and biozones as well as established diatom biostratigraphy are incorporated into the updated magneto‐biochronologic timescale, which will contribute to an improvement in biochronologic accuracy of Neogene sediments in northern Japan and adjacent areas.
Japan Trench and tectonics of the Japanese Island Arcs
Authors: Niitsuma Nobuaki
Published: February 2004

Abstract  Seven chronostratigraphic stages were established based on the correlation of magneto‐biostratigraphic marker horizons within the Deep Sea Drilling Project and Ocean Drilling Program cores from the forearc of the Japan Trench. Because the stages are coeval with changes in the rate of sedimentation, lithofacies, magnetic intensity and composition of fossil assemblages, they probably reflect the tectonic situation in the Japan Trench forearc and also in the arc–trench system. The stages correlate to the tectonic events of the Japanese Island Arcs; for example, evolution of the Boso triple junction, initiation of Philippine Sea Plate subduction and the Japan Sea opening.
Faunal analysis of Neogene planktonic foraminifera from forearc sediments of the Japan Trench, ODP Site 1151, Leg 186
Authors: Hayashi Hiroki
Published: February 2004

Abstract  The present paper describes the general outline of Neogene paleoceanographic changes in the northwestern Pacific by means of planktonic foraminiferal assemblages. Planktonic foraminiferal fossils occur commonly in the upper Miocene to lower Pleistocene sediments of Hole 1151A, Ocean Drilling Program Leg 186 in the forearc basin off northeast Japan, with the exception of 11 barren intervals. These barren intervals are explained as a result of dissolution under organic decomposing processes. Three assemblages of planktonic foraminifers were identified by Q‐mode cluster analysis. The succession of the assemblages can be divided into four paleoceanographic stages: (i) warm‐temperate Tortonian; (ii) cold‐temperate Messinian to lower Pliocene; (iii) warm climatic optimum in the middle part of the Pliocene; and (iv) strong glacial–interglacial oscillation of the upper Pliocene to the lower Pleistocene. Three short warming events—namely, the late Miocene climatic optimum 3, the Miocene–Pliocene boundary and the middle Pliocene events—and a short cooling event of the late Miocene could be determined in the studied section of Site 1151.
Effect of interface layer on fatigue crack growth in an aluminium laminate
Authors: HE J. W. , LI N. , JIA M. , WEN S. P. , JIA P. R.
Published: February 2004

In order to study the effect of an interface layer on fatigue crack growth, a thin pure Al layer was sandwiched between two LY12 plates using explosive bonding. Experiment shows that as a fatigue crack approaches the interface a remote plastic zone appears in the soft Al layer. Energy dissipation in the interface leads to significant deceleration of crack growth rate. FEM analysis shows that crack arrest is associated with load and distance between the crack tip and the interface. The size of the plastic zone can be calculated and used to predict the reduction in crack growth rate. The predictions agree well with the experimental results.
Fracture behaviour of maraging steel tensile specimens and pressurized cylindrical vessels
Authors: CHRISTOPHER T. , SANKARNARAYANASAMY K. , RAO B. N.
Published: February 2004

A three‐parameter fracture criterion is applied for the development of a failure assessment diagram to maraging steels and its validity verified by considering the maraging steel fracture data of surface crack tension specimens (SCT) and pressure vessels having axial surface cracks. Fracture‐strength/failure‐pressure estimates based on this criterion are found to be in reasonably good agreement with test results.
Synchrotron diffraction measurement of residual stresses in friction stir welded 5383‐H321 aluminium butt joints and their modification by fatigue cycling
Authors: JAMES M. N. , HUGHES D. J. , HATTINGH D. G. , BRADLEY G. R. , MILLS G. , WEBSTER P. J.
Published: February 2004

This paper presents two‐dimensional information on the residual stresses in 8 mm 5383‐H321 aluminium plates joined by double pass (DP) friction stir welding (FSW). It considers the inherent variability in residual stress magnitudes along 0.5 m lengths of weld pass, and their modification under a sequence of applied fatigue loads. This represents one of a planned series of experiments aimed at illuminating the effects of fatigue cycling on residual stress fields. In this particular case, the magnitudes of the bending fatigue loads (R= 0.1) were chosen to correlate with the measured proof strengths of the weld metal (approximately 160 MPa) and the parent plate (approximately 260–270 MPa). In four‐point bend S–N tests at R= 0.1 on 40 mm wide FS welded specimens of this alloy and plate thickness, these peak stress levels correspond to lives of around 105 cycles and 107 cycles, respectively. Results from the work indicate that significant variability exists among welded plates in peak compressive stress magnitudes (a range of perhaps −50 MPa to −140 MPa), although peak tensile stresses were relatively low and more consistent (from around 0 to 30 MPa). Fatigue loading accentuates the peak‐to‐valley stress change and causes an overall translation of the stresses to become more positive. Peak tensile stresses increase several‐fold during fatigue cycling.
A new testing method to obtain mode II fatigue crack growth characteristics of hard materials
Authors: OTSUKA A. , FUJII Y. , MAEDA K.
Published: February 2004

Flaking type failure in rolling‐contact processes is usually attributed to fatigue‐induced subsurface shearing stress caused by the contact loading. Assuming such crack growth is due to mode II loading and that mode I growth is suppressed due to the compressive stress field arising from the contact stress, we developed a new testing apparatus for mode II fatigue crack growth. Although the apparatus is, as a former apparatus was, based on the principle that the static KI mode and the compressive stress parallel to the pre‐crack are superimposed on the mode II loading system, we employ direct loading in the new apparatus. Instead of the simple four‐point‐shear‐loading system used in the former apparatus, a new device for the application of a compressive stress parallel to the pre‐crack has been developed. Due to these alterations, mode II cyclic loading tests for hard steels have become possible for arbitrary stress ratios, including fully reversed loading (R=−1); which is the case of rolling‐contact fatigue. The test results obtained using the newly developed apparatus on specimens made from bearing steel SUJ2 and also a 0.75% carbon steel, are shown.
Theoretical and experimental determination of magnetic stress intensity factors of a crack in a double cantilever beam specimen
Authors: YOSHIMURA K. , SHINDO Y. , HORIGUCHI K. , NARITA F.
Published: February 2004

This paper presents the results of an experimental and theoretical investigation of the magnetic fracture behaviour of double cantilever beam (DCB) specimens. DCB tests were conducted on ferritic stainless steel SUS430 in the bore of a superconducting magnet at room temperature. A simple experimental technique using strain gauges was used to determine the stress intensity factor. The experiments show the predicted increase in the stress intensity factor with increasing magnetic field. The theoretical analysis is based on a beam‐plate theory for magnetoelastic interactions in a soft ferromagnetic material. Numerical calculations are carried out, and the stress intensity factor is obtained for several values of magnetic field. A comparison of the stress intensity factor is made between theory and experiment, and the agreement is good for the magnetic field considered.
Damage mode analysis of MCrAlY overlay coatings subjected to isothermal stepwise tensile testing by usingin situvideo imaging and acoustic emission monitoring
Authors: VOUGIOUKLAKIS I. , HÄHNER P. , DE HAAN F. , KOSTOPOULOS V. , PETEVES S.
Published: February 2004

The mechanical performance of gas turbine material systems consisting of a Ni‐base superalloy substrate with three different MCrAlY overlay coatings with various Al contents was assessed, close to service temperature spectrum, by means of stepwise tensile tests. Furthermore, acoustic emission (AE) activity was monitored during the tensile testing. Tensile tests were performed for all three types of coated systems at four different temperatures (300, 500, 700 and 900 °C). The AE data were analysed by means of a standardized k‐means algorithm with respect to nine parameters (such as amplitude, number of counts, duration, rise time, energy, etc.). In conjunction within situvideo imaging of the specimen surface and postmortem microstructural analysis of the samples, the classification of AE data has provided a means for damage identification and performance assessment of the substrate‐coating material systems.
Basic studies of ductile failure processes and implications for fracture prediction
Authors: ZUO J. , SUTTON M. A. , DENG X.
Published: February 2004

Fracture of ductile materials has frequently been observed to result from the nucleation, growth and coalescence of microscopic voids. Experimental and analytical studies have shown that both the stress constraint factor and the effective plastic strain play a significant role in the ductile failure process. Experimental results also suggest that these two parameters are not independent of each other at failure initiation. In this study, a methodology for characterizing the effect of stress constraint Am (which is defined to be the ratio of the mean stress and the effective stress Am=σm/σe) on ductile failure is proposed. This methodology is based on experimental evidence that shows the effective plastic strain at failure initiation has a one‐to‐one relationship with stress constraint. Numerical analyses based on plane strain and three‐dimensional unit‐cell models have been carried out to investigate failure initiation of the unit cell under different constraint conditions. Results from the numerical studies indicate (a) for each void volume fraction, there exists a local failure locus in terms of mesoscopic quantities, σm and σe, that adequately predict incipient local micro‐void link‐up, (b) the results are fully consistent with a failure criterion that maximizes mesoscopic effective stress for a constant level of stress constraint Am, (c) for high to moderate constraint Am, the link‐up envelope values for σm and σe are consistent with limit load conditions where the critical principal stress σ1c corresponds to the maximum principal stress in the loading history and (d) for low constraint, the link‐up envelope values for σm and σe correspond to link‐up conditions having high levels of plastic strain and a principal stress σ1 that is lower than the maximum value for this loading history. Thus, the results suggest that a two‐parameter ductile fracture criterion is plausible, such as critical crack opening displacement (COD) and stress constraint Am, for predicting the process of stable tearing in materials undergoing ductile void growth during the fracture process.
Overload analysis and Je‐based fatigue life prediction of spot‐welded auto seat belt anchors
Authors: LEE HYUNGIL , CHOI JINYONG
Published: February 2004

We demonstrate the validity of Je, which comprehensively describes the effects of specimen geometry and loading type, in predicting the fatigue life of auto seat belt anchor panel. We first simplify the heat‐affected zone model to reduce the number of finite elements. We then establish finite‐element models reflecting the actual overload behaviour of three types of seat belt anchor specimens. Using elaborate finite‐element models, we obtain the effective crack‐driving parameter Je composed of its ductility‐dependent modal components. It is confirmed that the Je concept successfully predicts the fatigue life of multi‐spot‐welded panel structures represented by auto seat belt anchors here.
Estimation of fracture toughness of steel using chevron notched round bar specimens
Authors: RAY K. K. , PODDAR G. P.
Published: February 2004

A generalized methodology has been outlined in this paper for estimating the minimum normalized stress intensity factor (Y*min) of chevron notched round bar specimens, subjected to three‐point bend loading. Using such specimens, a series of fracture toughness tests have been carried out for the first time on two steels. The major inferences drawn from this investigation are: (i) reproducible fracture toughness values can be achieved using chevron notched rod specimens of identical configuration and (ii) the estimated magnitudes of fracture toughness obtained by using chevron notched rod specimens are in good agreement with those achieved by using chevron notched rectangular bar specimens of the same material.
Distinct subcellular targeting of fluorescent nicotinic α3β4 and serotoninergic 5‐HT3A receptors in hippocampal neurons
Authors: Grailhe Régis , De Carvalho Lia Prado , Paas Yoav , Le Poupon Chantal , Soudant Martine , Bregestovski Piotr , Changeux Jean‐Pierre , Corringer Pierre‐Jean
Published: February 2004

The nicotinic acetylcholine receptors (nAChRs) and the 5‐HT3 serotonin receptor subtype belong to a superfamily of neurotransmitter‐gated ion channels involved in fast synaptic communication throughout the nervous system. Their trafficking to the neuron plasmalemma, as well as their targeting to specific subcellular compartments, is critical for understanding their physiological role. In order to investigate the cellular distribution of these receptors, we tagged the N‐termini of α3β4‐nAChR subunits and the 5‐HT3AR subunit with cyan and yellow fluorescent proteins (CFP, YFP). The fusion subunits were coexpressed in human embryonic kidney (HEK‐293) cells, where they assemble into functional receptor channels, as well as in primary cultures of hippocampal neurons. Fluorescence microscopy of living cells revealed that the heteropentameric α3CFP‐β4 and YFP‐α3β4 receptors are mainly distributed in the endoplasmic reticulum, while the homopentameric YFP‐5‐HT3A receptor was localized both to the plasma membrane and within intracellular compartments. Moreover, the YFP‐5‐HT3A receptor was found to be targeted to the micropodia in HEK‐293 cells and to the dendritic spines in hippocampal neurons, where it could be accessed by extracellularly applied specific fluorescent probes. The efficient targeting of the YFP‐5‐HT3A to the cytoplasmic membrane is in line with the large serotonin‐elicited currents (nA range) measured by whole‐cell voltage‐clamp recordings in transfected HEK‐293 cells. In contrast, α3β4‐nAChRs expressed in the same cells yielded weaker ACh‐evoked responses. Taken together, the fluorescent and electrophysiological studies presented here demonstrate the predominant intracellular location of α3β4‐nACh receptors and the predominant expression of the 5‐HT3AR in dendritic surface loci.
Resetting the brain clock: time course and localization of mPER1 and mPER2 protein expression in suprachiasmatic nuclei during phase shifts
Authors: Yan Lily , Silver Rae
Published: February 2004

The mechanism whereby brief light pulses reset the mammalian circadian clock involves acute Per gene induction. In a previous study we investigated light‐induced expression of mPer1 and mPer2 mRNA in the suprachiasmatic nuclei (SCN), with the aim of understanding the relationship between gene expression and behavioural phase shifts. In the present study, we examine the protein products of mPer1 and mPer2 genes in the core and shell region of SCN for 34 h following a phase‐shifting light pulse, in order to further explore the molecular mechanism of photic entrainment. The results indicate that, during the delay zone of the phase response curve, while endogenous levels of mPER1 and mPER2 protein are falling, a light pulse produces an increase in the expression of both proteins. In contrast, during the advance zone of the phase response curve, while levels of endogenous mPER1 and mPER2 proteins are rising, a light pulse results in a further increase in mPER1 but not mPER2 protein. The regional distribution of mPER1 and mPER2 protein in the SCN follows the same pattern as their respective mRNAs, with mPER1 expression in the shell region of SCN correlated with phase advances and mPER2 in the shell region correlated with phase delays.