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11.
Multiple origins of zircons in jadeitite 总被引：1，自引：1，他引：0
Bin Fu John W. Valley Noriko T. Kita Michael J. Spicuzza Chad Paton Tatsuki Tsujimori Michael Bröcker George E. Harlow 《Contributions to Mineralogy and Petrology》2010,159(6):769-780
Jadeitites form from hydrothermal fluids during high pressure metamorphism in subduction environments; however, the origin
of zircons in jadeitite is uncertain. We report ion microprobe analyses of δ18O and Ti in zircons, and bulk δ18O data for the jadeitite whole-rock from four terranes: Osayama serpentinite mélange, Japan; Syros mélange, Greece; the Motagua
Fault zone, Guatemala; and the Franciscan Complex, California. In the Osayama jadeitite, two texturally contrasting groups
of zircons are identified by cathodoluminescence and are distinct in δ18O: featureless or weakly zoned zircons with δ18O = 3.8 ± 0.6‰ (2 SD, VSMOW), and zircons with oscillatory or patchy zoning with higher δ18O = 5.0 ± 0.4‰. Zircons in phengite jadeitite from Guatemala and a jadeitite block from Syros have similar δ18O values to the latter from Osayama: Guatemala zircons are 4.8 ± 0.7‰, and the Syros zircons are 5.2 ± 0.5‰ in jadeitite and
5.2 ± 0.4‰ in associated omphacitite, glaucophanite and chlorite-actinolite rinds. The δ18O values for most zircons above fall within the range measured by ion microprobe in igneous zircons from oxide gabbros and
plagiogranites in modern ocean crust (5.3 ± 0.8‰) and measured in bulk by laser fluorination of zircons in equilibrium with
primitive magma compositions or the mantle (5.3 ± 0.6‰). Titanium concentrations in these zircons vary between 1 and 19 ppm,
within the range for igneous zircons worldwide. Values of δ18O (whole-rock) ≅ δ18O (jadeite) and vary from 6.3 to 10.1‰ in jadeitites in all four areas. 相似文献
12.
Quantitative research on composition, biomass and production rates of zooplankton community is crucial to understand the trophic structure in coral reef pelagic ecosystems. In the present study, micro‐ (35–100 μm) and net‐ (>100 μm) metazooplankton were investigated in a fringing coral reef at Tioman Island of Malaysia. Sampling was done during the day and night in August and October 2004, and February and June 2005. The mean biomass of total metazooplankton (i.e. micro + net) was 3.42 ± 0.64 mg C·m?3, ranging from 2.32 ± 0.75 mg C·m?3 in October to 3.26 ± 1.77 mg C·m?3 in August. The net‐zooplankton biomass exhibited a nocturnal increase from daytime at 131–264% due to the addition of both pelagic and reef‐associated zooplankton into the water column. The estimated daily production rates of the total metazooplankton community were on average 1.80 ± 0.57 mg C·m?3·day?1, but this increased to 2.51 ± 1.06 mg C·m?3·day?1 if house production of larvaceans was taken into account. Of the total production rate, the secondary and tertiary production rates were 2.20 ± 1.03 and 0.30 ± 0.06 mg C·m?3·day?1, respectively. We estimated the food requirements of zooplankton in order to examine the trophic structure of the pelagic ecosystem. The secondary production may not be satisfied by phytoplankton alone in the study area and the shortfall may be supplied by other organic sources such as detritus. 相似文献
13.
Sau Pin Kok Tomohiko Kikuchi Tatsuki Toda Norio Kurosawa 《Journal of Oceanography》2012,68(5):599-613
The diversity of protistan microplankton in Sagami Bay was revealed by 18S rRNA gene clone analysis using newly designed PCR primers. PCR amplification consisted of a first reaction targeting the V3–V5 region of the 18S rRNA gene, followed by a nested reaction targeting the V3–V4 region. In total, 629 clones consisting of 108 phylotypes were affiliated with a variety of protistan groups including dinoflagellates, diatoms, prymnesiomonada, chlorophyta, ciliophora, cercozoa, and heterokonta. The dinoflagellate group was detected most frequently and shared approximately 74?% of the total clones. Within this group, approximately half of the clones belonged to the parasitic dinoflagellate Syndiniales group I, which was first reported from Sagami Bay. The genera Woloszynskia, Gonyaulax, Neoceratium, and Karlodinium have not been reported from this bay until now. The second most frequent group was diatoms, which shared approximately 22?% of the total clones. Within this group, highly diverse Thalassiosira phylotypes were detected, and they shared approximately 70?% of the diatom clones. Therefore, highly diverse protists including some candidate groups were successfully detected, indicating that the designed primers and PCR protocol will be useful for molecular diversity analyses of protistan microplankton communities in aquatic environments. 相似文献
14.
ABSTRACTField and petrologic characteristics of two new eclogite localities within the Guatemala Suture Complex (GSC) north of the Motagua Fault are presented. The Tuncaj Hill locality exposes a coherent body of retrogressed eclogite hundreds of metres long that is associated with serpentinite of the North Motagua Unit. The Tanilar River locality exposes numerous bands and lenses of eclogite hosted in sialic gneisses of the Chuacús Complex. The Tuncaj eclogite has a two-stage prograde evolution containing the peak assemblage Grt + Omp + Ttn + Czo + Zo ± Am, formed at temperatures <720°C. In contrast, eclogites of the Tanilar unit are characterized by the paragenesis Omp + Grt + Rt ± Phg ± Qtz ± Ep giving higher peak conditions of T = 720–830°C and P = 2.1–2.7 GPa, near the stability field of coesite. Previously obtained data and our thermobaric calculations suggest distinct petrotectonic evolutions for the various types of eclogites within the suture. The lawsonite eclogites south of the Motagua Fault were probably produced in a mature Farallon subduction zone during the Early Cretaceous. The northern high-pressure (HP) blocks in serpentinite mélange and coherent amphibolite bodies with eclogite relics were generated by the Early Cretaceous subduction of the proto-Caribbean lithosphere under the Great Caribbean Arc. A continental block, the North American passive margin, reached the arc’s trench in the Campanian and was subducted to ca. 80 km depth, producing the eclogites of the Chuacús Complex. As the slab was delaminated and partially exhumed, the continental Chuacús became tectonically juxtaposed with HP blocks of the proto-Caribbean that had been accreted to the Caribbean plate forming the North Motagua Unit. The juxtaposed group migrated to mid-crustal level and was contemporaneously retrogressed under epidote-amphibolite facies conditions. 相似文献
15.
The main objectives of this study were (1) to examine what has beenrecovered and what has not yet been recovered in Nishinomiya City five years after the GreatHanshin-Awaji Earthquake, and (2) to find current service needs for the earthquake survivors,especially for the disadvantaged populations. Disadvantaged populations are minorities in society, andtheir needs and opinions are often ignored and not reflected in the services or mitigation policy,despite the fact that they are the ones who are affected most by various hazards. At the same time, becauseof their unique characteristics and positions in society, their needs differ from the majorityof the society. Six hundred eighty-six opinion cards were collected in nine grassroots workshopsessions with various disadvantaged groups in Nishinomiya City, such as the physically challenged,the visually impaired, the elderly living in public housing, junior and senior high school students,mothers with small children, and those who lost their own homes because of the earthquake. Theseopinion cards were sorted out and analyzed by using a TQM(Total Quality Management)-basedassessment method. Since the TQM-based assessment method allows bottom-up integration ofopinions from each individual, it helps us identify unique needs of the disadvantaged groupsand reflect their opinions in mitigation plan and policies. The main findings of this study include (1)the city redevelopment cannot be achieved without integrating the viewpoints of thedisadvantaged; (2) the social support was a key resource for both mental health and community development;and (3) disaster experiences and adaptation produced civic mindedness among people in a community. 相似文献
16.
Very-low-temperature record of the subduction process: A review of worldwide lawsonite eclogites 总被引：11，自引：0，他引：11
Tatsuki Tsujimori Virginia B. Sisson Juhn G. Liou George E. Harlow Sorena S. Sorensen 《Lithos》2006,92(3-4):609-624
Lawsonite eclogites preserve a record of very-low-temperature conditions in subduction zones. All occur at active margin settings, typically characterized by accretionary complexes lithologies and as tectonic blocks within serpentinite-matrix mélange. Peak lawsonite-eclogite facies mineral assemblages (garnet + omphacite + lawsonite + rutile) typically occur in prograde-zoned garnet porphyroblasts. Their matrix is commonly overprinted by higher-temperature epidote-bearing assemblages; greenschist- or amphibolite-facies conditions erase former lawsonite-eclogite relics. Various pseudomorphs after lawsonite occur, particularly in some blueschist/eclogite transitional facies rocks. Coesite-bearing lawsonite-eclogite xenoliths in kimberlitic pipes and lawsonite pseudomorphs in some relatively low-temperature ultrahigh-pressure eclogites are known. Using inclusion assemblages in garnet, lawsonite eclogites can be classified into two types: L-type, such as those from Guatemala and British Columbia, contain garnet porphyroblasts that grew only within the lawsonite stability field and E-type, such as from the Dominican Republic, record maximum temperature in the epidote-stability field.
Formation and preservation of lawsonite eclogites requires cold subduction to mantle depths and rapid exhumation. The earliest occurrences of lawsonite-eclogite facies mineral assemblages are Early Paleozoic in Spitsbergen and the New England fold belt of Australia; this suggests that since the Phanerozoic, secular cooling of Earth and subduction-zone thermal structures evolved the necessary high pressure/temperature conditions. Buoyancy of serpentinite and oblique convergence with a major strike-slip component may facilitate the exhumation of lawsonite eclogites from mantle depths. 相似文献
17.
18.
Xiaofei?Pu James?G.?BrophyEmail author Tatsuki?Tsujimori 《Contributions to Mineralogy and Petrology》2014,168(3):1060
The two most commonly invoked processes for generating silicic magmas in intra-oceanic arc environments are extended fractional crystallization of hydrous island arc basalt magma or dehydration melting of lower crustal amphibolite. Brophy (Contrib Mineral Petrol 156:337–357, 2008) has proposed on theoretical grounds that, for liquids >~65 wt% SiO2, dehydration melting should yield, among other features, a negative correlation between rare earth element (REE) abundances and increasing SiO2, while fractional crystallization should yield a positive correlation. If correct, the REE–SiO2 systematics of natural systems might be used to distinguish between the two processes. The Permian-age Asago body within the Yakuno Ophiolite, Japan, has amphibolite migmatites that contain felsic veins that are believed to have formed from dehydration melting, thus forming an appropriate location for field verification of the proposed REE–SiO2 systematics for such a process. In addition to a negative correlation between liquid SiO2 and REE abundance for liquids in excess of ~65 % SiO2, another important model feature is that, at very high SiO2 contents (75–76 %), all of the REE should have abundances less than that of the host rock. Assuming an initial source amphibolite that is slightly LREE-enriched relative to the host amphibolites, the observed REE abundances in the felsic veins fully support all theoretical predictions. 相似文献
19.
Tetsumaru Itaya Hironobu Hyodo Tatsuki Tsujimori Simon Wallis Mutsuki Aoya Tetsuo Kawakami Chitaro Gouzu 《Island Arc》2009,18(2):293-305
Laser step heating 40Ar/39Ar analysis of biotite and muscovite single crystals from a Barrovian type metamorphic belt in the eastern Tibetan plateau yielded consistent cooling ages of ca. 40 Ma in the sillimanite zone with peak metamorphic temperatures higher than 600°C and discordant ages from 46 to 197 Ma in the zones with lower peak temperatures. Chemical Th‐U‐Total Pb Isochron Method (CHIME) monazite (65 Ma) and sensitive high mass‐resolution ion microprobe (SHRIMP) apatite (67 Ma) dating give the age of peak metamorphism in the sillimanite zone. Moderate amounts of excess Ar shown by biotite grains with ages of 46 to 94 Ma at metamorphic grades up to the high‐grade part of the kyanite zone probably represent incomplete degassing during metamorphism. In contrast, the high‐grade part of the kyanite zone yields biotite ages of 130 to 197 Ma. The spatial distribution of these older ages in the kyanite zone along the sillimanite zone boundary suggests they reflect trapped excess argon that migrated from higher‐grade regions. The most likely source is muscovite that decomposed to form sillimanite. The zone with extreme amounts of excess argon preserves trapped remnants of an ‘excess argon wave’. We suggest this corresponds to the area where biotite cooled below its closure temperature in the presence of an elevated Ar wave. Extreme excess Ar is not recognized in muscovite suggesting that the entrapment of the argon wave by biotite took place when the rocks had cooled down to temperatures lower than the closure temperature of muscovite. The breakdown of phengite during ultrahigh‐pressure (UHP) metamorphism may be a key factor in accounting for the very old apparent ages seen in many UHP metamorphic regions. This is the first documentation of a regional Ar‐wave spatially associated with regional metamorphism. This study also implies that resetting of the Ar isotopic systems in micas can require temperatures up to 600°C; much higher than generally thought. 相似文献
20.
Variability in the Relative Penetration of Ultraviolet Radiation to Photosynthetically Available Radiation in Temperate Coastal Waters, Japan 总被引：1，自引：0，他引：1
Victor S. Kuwahara Tatsuki Toda Koji Hamasaki Tomohiko Kikuchi Satoru Taguchi 《Journal of Oceanography》2000,56(4):399-408
UVR and PAR wavelengths are attenuated to different extents within the water column, causing variations in spectral composition with depth. The present investigation (a) describes the variability of UVR and PAR penetration at a station in the temperate coastal waters of Sagami Bay and determines (b) the characteristics of relative UVR penetration to the euphotic zone. Examination of the seasonal irradiance profile measurements indicated eight measurements displaying two distinct attenuation coefficients (K
d) for specific UVR wavelengths and PAR. The two attenuation coefficients observed from specific wavelengths in the water column may be caused not only by chlorophyll pigments, but also by dissolved organic material in the upper layer. The 1% depth of surface UVR at 305, 320, 340, and 380 nm averaged 10.8 ± 5.7, 14.9 ± 9.5, 19.8 ± 12.1, and 30.4 ± 17.6 m, respectively. The depth of euphotic layer displayed less variability averaging 62 ± 15 m throughout the entire study. Relative UVR penetration within the euphotic zone averaged 17.8 ± 8.1, 22.9 ± 10, 30.5 ± 13.8, and 46 ± 46.9% for 305, 320, 340, and 380 nm, respectively. A large variation of the relative transmission of UVR within the euphotic zone was found although the spectral composition was relatively stable in the air throughout the study. 相似文献