Geological Survey of Japan

This paper reports the results from a second characterisation of the 91500 zircon, including data from electron probe microanalysis, laser ablation inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS), secondary ion mass spectrometry (SIMS) and laser fluorination analyses. The focus of this initiative was to establish the suitability of this large single zircon crystal for calibrating in situ analyses of the rare earth elements and oxygen isotopes, as well as to provide working values for key geochemical systems. In addition to extensive testing of the chemical and structural homogeneity of this sample, the occurrence of banding in 91500 in both backscattered electron and cathodoluminescence images is described in detail. Blind intercomparison data reported by both LA‐ICP‐MS and SIMS laboratories indicate that only small systematic differences exist between the data sets provided by these two techniques. Furthermore, the use of NIST SRM 610 glass as the calibrant for SIMS analyses was found to introduce little or no systematic error into the results for zircon. Based on both laser fluorination and SIMS data, zircon 91500 seems to be very well suited for calibrating in situ oxygen isotopic analyses.

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) scanner on NASA's Earth Observing System (EOS)-AM1 satellite (launch scheduled for 1998) will collect five bands of thermal infrared (TIR) data with a noise equivalent temperature difference (NE/spl Delta/T) of /spl les/0.3 K to estimate surface temperatures and emissivity spectra, especially over land, where emissivities are not known in advance. Temperature/emissivity separation (TES) is difficult because there are five measurements but six unknowns. Various approaches have been used to constrain the extra degree of freedom. ASTER's TES algorithm hybridizes three established algorithms, first estimating the normalized emissivities and then calculating emissivity band ratios. An empirical relationship predicts the minimum emissivity from the spectral contrast of the ratioed values, permitting recovery of the emissivity spectrum. TES uses an iterative approach to remove reflected sky irradiance. Based on numerical simulation, TES should be able to recover temperatures within about /spl plusmn/1.5 K and emissivities within about /spl plusmn/0.015. Validation using airborne simulator images taken over playas and ponds in central Nevada demonstrates that, with proper atmospheric compensation, it is possible to meet the theoretical expectations. The main sources of uncertainty in the output temperature and emissivity images are the empirical relationship between emissivity values and spectral contrast, compensation for reflected sky irradiance, and ASTER's precision, calibration, and atmospheric compensation.

The two largest earthquakes of the past 40 years ruptured a 1600-kilometer-long portion of the fault boundary between the Indo-Australian and southeastern Eurasian plates on 26 December 2004 [seismic moment magnitude (Mw) = 9.1 to 9.3] and 28 March 2005 (Mw = 8.6). The first event generated a tsunami that caused more than 283,000 deaths. Fault slip of up to 15 meters occurred near Banda Aceh, Sumatra, but to the north, along the Nicobar and Andaman Islands, rapid slip was much smaller. Tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer.

There are many examples of spatially associated porphyry and epithermal ore deposits; a genetic connection has been suggested for some and argued against for others. Nowhere is this spatial association better demonstrated than in the Mankayan district of northern Luzon, Philippines, where the Lepanto high-sulfidation epithermal Cu-Au deposit is superadjacent to the Far Southeast porphyry Cu-Au orebody; together they contain >3.8 million tons (Mt) Cu and >550 t Au.Quartz diorite porphyry dikes intruded Miocene basement rocks of metavolcanic and volcaniclastic rocks to a 300-m elevation. These intrusions postdate the Pliocene volcanic breccia and dacite porphyry that host much of the epithermal ore. K silicate alteration, consisting of biotite-magnetite and minor K feldspar, is centered on the quartz diorite porphyry. K-Ar ages of the biotite are 1.41 + or - 0.05 Ma (n = 6). Vitreous, anhedral quartz veins are associated with this early alteration and contain vapor-rich and hypersaline liquid inclusions with maximum homogenization temperatures of 450 degrees to 550 degrees C (and 50-55 wt % NaCl equiv salinities). Lithostatic pressure estimates indicate a paleosurface at a > or = 1,500-m elevation. Advanced argillic alteration formed over the top of the porphyry and consists of quartz-alunite, dated at 1.42 + or - 0.08 Ma (n = 5), synchronous with K silicate alteration. The lower limit of extensive quartz-alunite alteration is at a [asymp] 600-m elevation. Similar alteration and a core of leached, silicic alteration extend northwestward >4 km along the basement dacite contact, localized by the Lepanto fault. Chemical and S isotope zoning of alunite along strike indicates progressively lower temperatures away from the porphyry, from 350 degrees to 200 degrees C. K silicate alteration is overprinted by alteration consisting of chlorite plus hematite and/or sericite-illite, with a marginal zone containing pyrophyllite and an outer zone of propylitic alteration. The chlorite-sericite alteration is cut by veins of euhedral quartz that locally fill reopened anhedral quartz veins. The euhedral quartz veins contain anhydrite-white mica-pyrite + or - chalcopyrite + or - bornite and have halos of sericite; illite separated from these halos has ages of 1.30 + or - 0.07 Ma (n = 10). Fluid inclusions provide evidence for boiling on inception of this fracturing event (T h = 350 degrees C, 5 wt % NaCl equiv) and indicate a depth of 1,500 to 2,000 m below the paleowater table. This brittle-fracture event was followed by cooling and dilution of the hydrothermal fluid.The elevation of the enargite Au epithermal ore and its host of silicic alteration increases as the unconformity between the basement and dacite breccia rises from a 700- to 1,200-m elevation with increasing distance from the porphyry. Published data on enargite-hosted fluid inclusions (T h = 295 degrees -200 degrees C, 4-2 wt % NaCl equiv) indicate that the temperature and salinity both decrease with increasing distance from the porphyry. Epithermal ore consists of stage 1 euhedral pyrite-enargite-luzonite, and subsequent stage 2 Au is accompanied by tetrahedrite-chalcopyrite-sphalerite plus telluride and selenide minerals. Anhydrite and barite gangue minerals are followed by late vug-fulling quartz and minerals. The quartz-alunite alteration halo passes outward to kandite (kaolinite-nacrite-diclcite) alteration, then to chlorite or montmorillonite, depending on the host rock (basement or dacite, respectively).The dated minerals were also analyzed for their delta 18 O and delta D compositions, and their associated hydrothermal water values were calculated. Water in isotopic equilibrium with biotite averaged +6.3 and -45 per mil, respectively, typical of hypersaline liquid exsolved from felsic magma. The acidic water that deposited the alunite formed when magmatic vapor (+7ppm delta 18 O and -25ppm delta D) was absorbed by local meteoric water (-10ppm delta 18 O and -70ppm delta D) in a proportion of [asymp] 9:1 magmatic to meteoric. Lateral flow to the northwest and progressive mixing with ground water diluted the magmatic component to 1:1 at a distance of 4 km from the porphyry. At the depth of the porphyry, deposit, the later water isotopically stable with sericite was dominantly magmatic (+5.7ppm delta 18 O and -43ppm delta D) in the core. The marginal sericitie alteration (+1.5ppm delta 18 O and -51ppm delta D water values) indicates a maximum 20 to 30 percent component of local meteoric water. Pyrophyllite in both the porphyry and epithermal deposits formed from water with an isotopic composition similar to that which formed the sericitic alteration. The late euhedral quartz veining and sericitic alteration appear to have been associated with the majority of Cu and Au deposition. In addition, mineralogic, paragenetic, isotopic, and fluid inclusion evidence suggests that this water precipitated the enargite and Au within the epithermal deposit.Our results reinforce guidelines for exploration of such deposits. Advanced argillic (quartz-alunite) and K silicate alteration at Lepanto-Far Southeast are coupled in origin and result from vapor and hypersaline liquid separation. Thus, exploration programs for buried porphyry deposits should document carefully the geologic, morphologic, and temporal characteristics of exposed areas of advanced argillic alteration and its origin. Sericitic alteration at Far Southeast is associated with porphyry Cu and Au ore and appears to represent the roots of the main-stage Cu-Au mineralization in the epithermal deposit, hosted by silicic and quartz-alunite alteration that has a lower limit near the top of porphyry Cu-Au ore. In some cases, the sericitic overprint of a porphyry system, particularly where it is related to Cu and Au enrichment, may indicate a potential for nearby epithermal mineralization. Similarly, sericite and/or pyrophyllite underlying or overprinting a zone of hypogene advanced argillic (quartz-alunite) alteration indicates that mineralizing fluid may have ascended to epithermal depths. Epithermal ore at Lepanto-Far Southeast reflects a paleohydrologic regime dominated by lateral fluid flow, with a marked control by intersection of the Lepanto fault and a lithologic unconformity. Recognizing evidence for lateral flow is critical, as paleohydrology controlled the distribution of alteration and mineralization in many high-sulfidation epithermal deposits.

Recent diving with the JAMSTEC Shinkai 6500 manned submersible in the Mariana fore arc southeast of Guam has discovered that MORB‐like tholeiitic basalts crop out over large areas. These “fore‐arc basalts” (FAB) underlie boninites and overlie diabasic and gabbroic rocks. Potential origins include eruption at a spreading center before subduction began or eruption during near‐trench spreading after subduction began. FAB trace element patterns are similar to those of MORB and most Izu‐Bonin‐Mariana (IBM) back‐arc lavas. However, Ti/V and Yb/V ratios are lower in FAB reflecting a stronger prior depletion of their mantle source compared to the source of basalts from mid‐ocean ridges and back‐arc basins. Some FAB also have higher concentrations of fluid‐soluble elements than do spreading center lavas. Thus, the most likely origin of FAB is that they were the first lavas to erupt when the Pacific Plate began sinking beneath the Philippine Plate at about 51 Ma. The magmas were generated by mantle decompression during near‐trench spreading with little or no mass transfer from the subducting plate. Boninites were generated later when the residual, highly depleted mantle melted at shallow levels after fluxing by a water‐rich fluid derived from the sinking Pacific Plate. This magmatic stratigraphy of FAB overlain by transitional lavas and boninites is similar to that found in many ophiolites, suggesting that ophiolitic assemblages might commonly originate from near‐trench volcanism caused by subduction initiation. Indeed, the widely dispersed Jurassic and Cretaceous Tethyan ophiolites could represent two such significant subduction initiation events.

Tsunami generation by an earthquake is generally modeled by water surface displacement identical to the vertical deformation of ocean bottom due to faulting. The effect of horizontal deformation is usually neglected. However, when the tsunami source is on a steep slope and the horizontal displacement is large relative to the vertical displacement, the effect becomes significant. We show this for two recent earthquakes which generated much larger tsunamis than expected from seismic waves. In the case of the 1994 June 2 Java, Indonesia, earthquake, the focal mechanism was a very shallow dipping thrust and the source was near a very steep trench slope. In the case of the 1994 Nov. 14 Mindoro, Philippines, earthquake, strike‐slip faulting extended from ocean to land perpendicular to the coast line. In both cases, we found that the horizontal motion of slope had an important contribution to the tsunami generation.

[Editor’s note: This article stems partly from the lively discussion held during the Forum “Mineral Deposit Models, Their Use and Misuse,” held at the Denver SEG meeting in 1993. See SEG Newsletter No. 14, pages 12-13 for that discussion. In the spirit of encouraging the development of appropriate models of prospects during exploration, the authors provide general patterns and ranges of characteristics for epithermal deposits in which gold is the main economic metal. —HH]

Research Article| May 01, 2013 Time and Space Distribution of Coseismic Slip of the 2011 Tohoku Earthquake as Inferred from Tsunami Waveform Data Kenji Satake; Kenji Satake Earthquake Research Institute, University of Tokyo, 1‐1‐1 Yayoi, Bunkyo‐ku, Tokyo 113‐0032, Japansatake@eri.u-toko.ac.jp Search for other works by this author on: GSW Google Scholar Yushiro Fujii; Yushiro Fujii International Institute of Seismology and Earthquake Engineering, Building Research Institute, 1 Tachihara, Tsukuba, Ibaraki 305‐0802, Japanfujii@kenken.go.jp Search for other works by this author on: GSW Google Scholar Tomoya Harada; Tomoya Harada Earthquake Research Institute, University of Tokyo, 1‐1‐1 Yayoi, Bunkyo‐ku, Tokyo 113‐0032 Japanharatomo@eri.u-toko.ac.jp Search for other works by this author on: GSW Google Scholar Yuichi Namegaya Yuichi Namegaya Active Fault and Earthquake Research Center, Geological Survey of Japan, AIST, 1‐1‐1 Higashi, Tsukuba, Ibaraki 305‐8567, Japanyuichi.namegaya@aist.go.jp Search for other works by this author on: GSW Google Scholar Author and Article Information Kenji Satake Earthquake Research Institute, University of Tokyo, 1‐1‐1 Yayoi, Bunkyo‐ku, Tokyo 113‐0032, Japansatake@eri.u-toko.ac.jp Yushiro Fujii International Institute of Seismology and Earthquake Engineering, Building Research Institute, 1 Tachihara, Tsukuba, Ibaraki 305‐0802, Japanfujii@kenken.go.jp Tomoya Harada Earthquake Research Institute, University of Tokyo, 1‐1‐1 Yayoi, Bunkyo‐ku, Tokyo 113‐0032 Japanharatomo@eri.u-toko.ac.jp Yuichi Namegaya Active Fault and Earthquake Research Center, Geological Survey of Japan, AIST, 1‐1‐1 Higashi, Tsukuba, Ibaraki 305‐8567, Japanyuichi.namegaya@aist.go.jp Publisher: Seismological Society of America First Online: 14 Jul 2017 Online ISSN: 1943-3573 Print ISSN: 0037-1106 Bulletin of the Seismological Society of America (2013) 103 (2B): 1473–1492. https://doi.org/10.1785/0120120122 Article history First Online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Kenji Satake, Yushiro Fujii, Tomoya Harada, Yuichi Namegaya; Time and Space Distribution of Coseismic Slip of the 2011 Tohoku Earthquake as Inferred from Tsunami Waveform Data. Bulletin of the Seismological Society of America 2013;; 103 (2B): 1473–1492. doi: https://doi.org/10.1785/0120120122 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Abstract A multiple time window inversion of 53 high‐sampling tsunami waveforms on ocean‐bottom pressure, Global Positioning System, coastal wave, and tide gauges shows a temporal and spatial slip distribution during the 2011 Tohoku earthquake. The fault rupture started near the hypocenter and propagated into both deep and shallow parts of the plate interface. A very large slip (approximately 25 m) in the deep part off Miyagi at a location similar to the previous 869 Jogan earthquake model was responsible for the initial rise of tsunami waveforms and the recorded tsunami inundation in the Sendai and Ishinomaki plains. A huge slip, up to 69 m, occurred in the shallow part near the trench axis 3 min after the rupture initiation. This delayed shallow rupture extended for 400 km with more than a 10‐m slip, at a location similar to the 1896 Sanriku tsunami earthquake, and was responsible for the peak amplitudes of the tsunami waveforms and the maximum tsunami heights measured on the northern Sanriku coast, 100 km north of the largest slip. The average slip on the entire fault was 9.5 m, and the total seismic moment was 4.2×1022 N·m (Mw 9.0). The large horizontal displacement of seafloor slope was responsible for 20%–40% of tsunami amplitudes. The 2011 deep slip alone could reproduce the distribution of the 869 tsunami deposits, indicating that the 869 Jogan earthquake source could be similar to the 2011 earthquake, at least in the deep‐plate interface. The large tsunami at the Fukushima nuclear power station is due to either the combination of a deep and shallow slip or a triggering of a shallow slip by a deep slip, which was not accounted for in the previous tsunami‐hazard assessments.Online Material: Table of estimated slip for all subfaults at 0.5 min invervals. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

In 5 recent years (2000–2004), the Changjiang (Yangtze) River has discharged past Datong (600 km from the river mouth) an average of ∼250 million tons (mt) of sediment per year, a decrease of more than 40% since the 1950s and 1960s, whereas water discharge at Datong has increased slightly. Water and sediment discharge data from the upper, middle, and lower reaches of the river suggest that the reduction of the Changjiang sediment load has occurred in two phases between 1950 and 2002: following the closure of the Danjiangkou Reservoir on the Hanjiang tributary in 1968 and following the installation of numerous dams and water‐soil conservation works in the Jialingjijang catchment after 1985. As the Three Gorges Dam (TGD) started operating in 2003, the Changjiang entered a third phase of sediment reduction with annual sediment loads at Datong less than 200 mt/yr. Upon completion of the Three Gorges Dam (TGD) in 2009, the sediment load at Datong will decrease to ∼210 mt/yr for the first 20 years, then will recover to ∼230 mt/yr during 2030–2060, and will reach ∼310 mt/yr during 2060–2110. From the sediment budget and sediment erosion data for the Changjiang subaqueous delta, it can be assumed that the delta will be eroded extensively during the first five decades after TGD operation and then will approach a balance during the next five decades as sediment discharging from TGD again increases.

Analytical data for minor and trace elements published or communicated to us, on seventeen GSJ (Geological Survey of Japan) reference samples, “Igneous rock series” received up to April 1994 are compiled. The data were evaluated statistically in consideration of analytical methods. Based on the selected available data, 1994 recommended and proposed values for 65 minor and trace elements are presented.

Abstract Granitoids can be classified into either a magnetite-bearing magnetite series or a magnetite-free ilmenite series, a classification also applicable to their effusive equivalents. Magnetite series granitoids are associated with major sulfide mineralization, whereas ilmenite series granitoids are related to cassiterite and wolframite mineralization. The magnetite series has a magnetite content more than 0.1 vol percent; a magnetic susceptibility higher than 1 × 10‒4emu/g; a bulk Fe2O3/FeO ratio higher than 0.5; a positive δ34S value and a low δ18O value; depletion in lithophile elements; accessory magnetite, (0.1–2 vol %), ilmenite, hematite, pyrite, and chalcopyrite; biotite with high Fe2O3/FeO and low refractive index; and intrusive sequences in which Fe/(Fe + Mg) for amphiboles and biotites decreases with increasing SiO2 content of host rocks. The ilmenite series has a magnetite and ilmenite content less than 0.1 vol percent; a magnetic susceptibility less than 1 × 10‒4emu/g; a bulk Fe2O3/FeO ratio lower than 0.5; a negative δ34S value and a high δ18O value; enrichment in lithophile elements; accessory ilmenite, pyrrhotite, graphite, (monazite, garnet), and muscovite; biotite with low Fe2O3/FeO and high refractive index; and intrusive sequences in which Fe/(Fe + Mg) for amphiboles and biotites increases with increasing SiO2 content of host rocks. The two series of granitoids are considered to have resulted from the prevalence of different oxygen fugacities during evolution of the granitic magmas, in which dissociation of water in the hydrous magmas is a main oxidizing agent for magnetite series magmas and incorporation of crustal carbon is the most essential reducing media for ilmenite series magmas. The magnetite series can be correlated with I-type granitoids; the ilmenite series is composed of both I-type and S-type granitoids. The distribution of magnetite series-ilmenite series granitoids varies in time and space in the circum-Pacific orogenic belt. In the continental margin of eastern Asia, magnetite series granitoids are typically younger than ilmenite series granitoids; which may also be true in the continental margin of western America. However, the spatial distribution of the two granitoid types differs on each side of the Pacific Ocean. In eastern Asia, the volcano-plutonic belt facing the marginal sea is generally composed of the magnetite series, implying that the magnetite series rocks tend to occur along the coast in the continent. In western America, however, ilmenite series granitoids are distributed along the coast. In island arcs such as Japan, ilmenite series granitoids are found on the oceanic side and magnetite series granitoids become predominant toward the back-arc basin. These petrogenetic provinces strongly affect metallogenic provinces of volcano-plutonic affinity. Where both series occur together in one geotectonic unit, the magnetite series granitoids are characterized by sulfide mineralization and the ilmenite series granitoids by sulfide- free mineralization. In solely magnetite series or ilmenite series terrains, the metallogenic zoning is unclear, but the mineralization seems to be controlled to some degree by the temperature and pressure of the granitic magmas, as well as by their oxygen fugacity. Nearly 100 percent of the sulfur, base metal sulfides, and gold-silver, and a large part of molybdenum, including that from porphyry-type and Kuroko-type deposits, is related to magnetite series magmatism; whereas cassiterite, wolframite, beryl, and fluorite are largely associated with ilmenite series magmatism. Scheelite mineralization, including a porphyry type, appears to be related to magnetite series magmatism. Magnetite series magmatism is capable of supplying abundant sulfur and ore metals that tend to combine with sulfur (and chlorine); these magmas may originally be enriched in these components, which are expelled into the aqueous phase during fractionation and crystallization throughout a long journey to the surface in a tensional tectonic setting. Some of the ore components may have been brought to the site of magma generation by subduction. Differences in metal ratios such as Cu/Pb may be attributed to differing compositions of the source materials as well as different transport media (S, Cl) for each component. Ilmenite series magmas may have originated in much shallower levels than magnetite series magmas under a compressional tectonic setting. Thus, magnetite-free magmatism may be strongly affected by crustal materials which contain carbon, even if the magmatism is triggered by injection of mafic magmas from much deeper levels. Sulfur in this magma would have been crystallized in granitoids as rock-forming minerals, thus forming no significant sulfide deposits. Most of the ore metals such as tin appear to have been concentrated in granitoids by recycling of crustal materials and were transported to ore deposits as fluorides. Recognition of the two series of granitoids is an important first step in mineral exploration.

Radon concentration in ground water increased for several months before the 1995 southern Hyogo Prefecture (Kobe) earthquake on 17 January 1995. From late October 1994, the beginning of the observation, to the end of December 1994, radon concentration increased about fourfold. On 8 January, 9 days before the earthquake, the radon concentration reached a peak of more than 10 times that at the beginning of the observation, before starting to decrease. These radon changes are likely to be precursory phenomena of the disastrous earthquake.

Articulating a comprehensive plate-tectonic theory requires understanding how new subduction zones form (subduction initiation). Because subduction initiation is a tectonomagmatic singularity with few active examples, reconstructing subduction initiation is challenging. The lithosphere of many intra-oceanic forearcs preserves a high-fidelity magmatic and stratigraphic record of subduction initiation. We have heretofore been remarkably ignorant of this record, because the "naked forearcs" that expose subduction initiation crustal sections are distant from continents and lie in the deep trenches, and it is difficult and expensive to study and sample this record via dredging, diving, and drilling. Studies of the Izu-Bonin-Mariana convergent margin indicate that subduction initiation there was accompanied by seafloor spreading in what ultimately became the forearc of the new convergent margin. Izu-Bonin-Mariana subduction initiation encompassed ∼7 m.y. for the complete transition from initial seafloor spreading and eruption of voluminous mid-ocean-ridge basalts (forearc basalts) to normal arc volcanism, perhaps consistent with how long it might take for slowly subsiding lithosphere to sink ∼100 km deep and for mantle motions to evolve from upwelling beneath the infant arc to downwelling beneath the magmatic front. Many ophiolites have chemical features that indicate formation above a convergent plate margin, and most of those formed in forearcs, where they were well positioned to be tectonically emplaced on land when buoyant crust jammed the associated subduction zone. We propose a strategy to better understand forearcs and thus subduction initiation by studying ophiolites, which preserve the magmatic stratigraphy, as seen in the Izu-Bonin-Mariana forearc; we call these "subduction initiation rule" ophiolites. This understanding opens the door for on-land geologists to contribute fundamentally to understanding subduction initiation.

Microbial communities from a subseafloor sediment core from the southwestern Sea of Okhotsk were evaluated by performing both cultivation-dependent and cultivation-independent (molecular) analyses. The core, which extended 58.1 m below the seafloor, was composed of pelagic clays with several volcanic ash layers containing fine pumice grains. Direct cell counting and quantitative PCR analysis of archaeal and bacterial 16S rRNA gene fragments indicated that the bacterial populations in the ash layers were approximately 2 to 10 times larger than those in the clays. Partial sequences of 1,210 rRNA gene clones revealed that there were qualitative differences in the microbial communities from the two different types of layers. Two phylogenetically distinct archaeal assemblages in the Crenarchaeota, the miscellaneous crenarchaeotic group and the deep-sea archaeal group, were the most predominant archaeal 16S rRNA gene components in the ash layers and the pelagic clays, respectively. Clones of 16S rRNA gene sequences from members of the gamma subclass of the class Proteobacteria dominated the ash layers, whereas sequences from members of the candidate division OP9 and the green nonsulfur bacteria dominated the pelagic clay environments. Molecular (16S rRNA gene sequence) analysis of 181 isolated colonies revealed that there was regional proliferation of viable heterotrophic mesophiles in the volcanic ash layers, along with some gram-positive bacteria and actinobacteria. The porous ash layers, which ranged in age from tens of thousands of years to hundreds of thousands of years, thus appear to be discrete microbial habitats within the coastal subseafloor clay sediment, which are capable of harboring microbial communities that are very distinct from the communities in the more abundant pelagic clays.

Abstract The R aman spectra of carbonaceous material ( CM ) from 19 metasediment samples collected from six widely separated areas of S outhwest J apan and metamorphosed at temperatures from 165 to 655°C show systematic changes with metamorphic temperature that can be classified into four types: low‐grade CM ( c. 150–280° C ), medium‐grade CM ( c. 280–400°C), high‐grade CM ( c. 400–650°C), and well‐crystallized graphite (> c. 650°C). The Raman spectra of low‐grade CM exhibit features typical of amorphous carbon, in which several disordered bands (D‐band) appear in the first‐order region. In the R aman spectra of medium‐grade CM , the graphite band ( G ‐band) can be recognized and several abrupt changes occur in the trends for several band parameters. The observed changes indicate that CM starts to transform from amorphous carbon to crystallized graphite at around 280°C, and this transformation continues until 400°C. The G ‐band becomes the most prominent peak at high‐grade CM suggesting that the CM structure is close to that of well‐crystallized graphite. In the highest temperature sample of 655°C, the R aman spectra of CM show a strong G ‐band with almost no recognizable D ‐band, implying the CM grain is well‐crystallized graphite. In the R aman spectra of low‐ to medium‐grade CM , comparisons of several band parameters with the known metamorphic temperature show inverse correlations between metamorphic temperature and the full width at half maximum ( FWHM ) of the D 1‐ and D 2‐bands. These correlations are calibrated as new R aman CM geothermometers, applicable in the range of c. 150–400°C. Details of the methodology for peak decomposition of R aman spectra from the low to medium temperature range are also discussed with the aim of establishing a robust and user‐friendly geothermometer.

Research Article| November 01, 2001 Oceanic anoxia at the Precambrian-Cambrian boundary Hiroto Kimura; Hiroto Kimura 1Geological Institute, University of Tokyo, Tokyo 113-0033, Japan Search for other works by this author on: GSW Google Scholar Yoshio Watanabe Yoshio Watanabe 2Geological Survey of Japan, Tsukuba 305-8567, Japan Search for other works by this author on: GSW Google Scholar Geology (2001) 29 (11): 995–998. https://doi.org/10.1130/0091-7613(2001)029<0995:OAATPC>2.0.CO;2 Article history received: 22 Jan 2001 rev-recd: 07 Jun 2001 accepted: 09 Jun 2001 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Hiroto Kimura, Yoshio Watanabe; Oceanic anoxia at the Precambrian-Cambrian boundary. Geology 2001;; 29 (11): 995–998. doi: https://doi.org/10.1130/0091-7613(2001)029<0995:OAATPC>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Precambrian-Cambrian (PC-C) boundary separates fossils representing two discrete evolutionary phases: the Neoproterozoic soft-bodied Ediacarian biotas and Cambrian small shelly faunas. The biological discontinuity is suspected to have been a result of mass extinction; however, recent discoveries of the Ediacarian biotas in Cambrian sediments have led to an understanding that the faunal change was gradual through the PC-C transition. Th/U ratios, which are high in oxidizing conditions and low in reducing conditions, show a considerable positive correlation with δ13C values at all studied sites of the PC-C boundary. This correlation indicates that reported δ13C variation across the PC-C boundary from numerous localities corresponds to redox variation in the depositional environment. The negative δ13C anomaly that occurs worldwide at the PC-C boundary, therefore, corresponds to the widespread development of an oxygen-deficient shallow marine environment. This finding suggests that widespread oceanic oxygen deficiency, which has been interpreted to reflect Phanerozoic mass extinction events, also occurred immediately before the Cambrian explosion. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Microbial life inhabits deeply buried marine sediments, but the extent of this vast ecosystem remains poorly constrained. Here we provide evidence for the existence of microbial communities in ~40° to 60°C sediment associated with lignite coal beds at ~1.5 to 2.5 km below the seafloor in the Pacific Ocean off Japan. Microbial methanogenesis was indicated by the isotopic compositions of methane and carbon dioxide, biomarkers, cultivation data, and gas compositions. Concentrations of indigenous microbial cells below 1.5 km ranged from <10 to ~10(4) cells cm(-3). Peak concentrations occurred in lignite layers, where communities differed markedly from shallower subseafloor communities and instead resembled organotrophic communities in forest soils. This suggests that terrigenous sediments retain indigenous community members tens of millions of years after burial in the seabed.

Abstract As part of a comprehensive, nationwide evaluation of geothermal resources for Japan, the first of the Curie point depth maps, covering the island of Kyushu, has been prepared. The map was created by inverting gridded, regional aeromagnetic data. Two satisfactory algorithms were developed to invert the gridded data based upon a distribution of point dipoles. The first algorithm estimates x 0 , y 0 , and z 0 , the coordinates of the centroid of the distribution, by computing a least-squares fit to the radial frequency of the Fourier transform; the second algorithm estimates centroid depth only by computing a least-squares fit to the squared amplitude of the frequency estimates. The average depth to the top, z t of the collection of point dipoles, was estimated by a variation of the second algorithm. The depth to the bottom of the dipoles, inferred Curie point depth, is z b = 2z 0 - z t . The depth estimates are hand contoured to produce the final map. The Curie point depth map is then compared to regional geology and heat flow data, and to a limited set of gravity data. Good correlations are found between the Curie point depths and the heat flow and regional geology. A spatial correlation observed between gravity and Curie point depths is considered a secondary, structural effect. Locations of the currently operating geothermal power plants correspond to the shallowest Curie point depths. Based on these comparisons, we conclude that the methods provide geologically reasonable results which are usable in a nationwide geothermal assessment program.

A constant stress fracture experiment of Oshima granite was carried out at the confining pressure of 40 MPa. Hypocentres of 2064 acoustic emissions were located during the experiment. Using the ‘correlation integral’, we found that the spatial distribution of hypocentres of acoustic emission is a fractal, and that the fractal dimension decreases with the evolution of rock fracturing. The spatial distribution of earthquake's hypocentres reveals fractals ranging from regional to worldwide distribution. If we extrapolate from laboratory measurements, it is possible to predict the occurrence of large earthquakes by the decrease in the fractal dimension.

The 1700 Cascadia earthquake attained moment magnitude 9 according to new estimates based on effects of its tsunami in Japan, computed coseismic seafloor deformation for hypothetical ruptures in Cascadia, and tsunami modeling in the Pacific Ocean. Reports of damage and flooding show that the 1700 Cascadia tsunami reached 1–5 m heights at seven shoreline sites in Japan. Three sets of estimated heights express uncertainty about location and depth of reported flooding, landward decline in tsunami heights from shorelines, and post‐1700 land‐level changes. We compare each set with tsunami heights computed from six Cascadia sources. Each source is vertical seafloor displacement calculated with a three‐dimensional elastic dislocation model. For three sources the rupture extends the 1100 km length of the subduction zone and differs in width and shallow dip; for the other sources, ruptures of ordinary width extend 360–670 km. To compute tsunami waveforms, we use a linear long‐wave approximation with a finite difference method, and we employ modern bathymetry with nearshore grid spacing as small as 0.4 km. The various combinations of Japanese tsunami heights and Cascadia sources give seismic moment of 1–9 × 10 22 N m, equivalent to moment magnitude 8.7–9.2. This range excludes several unquantified uncertainties. The most likely earthquake, of moment magnitude 9.0, has 19 m of coseismic slip on an offshore, full‐slip zone 1100 km long with linearly decreasing slip on a downdip partial‐slip zone. The shorter rupture models require up to 40 m offshore slip and predict land‐level changes inconsistent with coastal paleoseismological evidence.