All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
494.
Modeling the reflection coefficients and slow wave mode conversions at the top and bottom of a gas-hydrate bearing interval
SEG Technical Program Expanded Abstracts,
25
(1)
2986-2990
2006
ISSN: 10523812
Publisher: Society of Exploration Geophysicists
Keywords:▾
Bearings (machine parts); Energy conversion; Gas hydrates; Gases; Hydration; Petroleum prospecting; Reflection; Seismic prospecting; Shear flow; Shear waves; Wave energy conversion, Compressional waves; Continental margin; Gas hydrate saturations; Gas hydrate stability zones; Numerical results; Ocean sediments; Petrophysical models; Seismic exploration, Phase interfaces
ISBN:
9781604236972
Abstract: ▾ We analyze the reflectivity properties of the interfaces defined by a contact between a shaly sandstone and the top and bottom of a gas hydrate stability zone (GHSZ), a problem of particular interest in seismic exploration in ocean sediments and continental margins. Our com putations are based on a three phase Biot-type model predicting the existence of three compressional waves and two shear waves. We use some information from the Mallik 5L-38 Gas Hydrate Research Well. The mechanical properties of the gas hydrate bearing rocks are described with appropriate petrophysical models. We present numerical results showing the influence of the gas-hydrate saturation on the amplitude vs. angle curves and the importance of wave energy conversion from fast to slow waves. © 2005 Society of Exploration Geophysicists.
493.
SHRIMP U-Pb zircon dating from eclogite lens in marble, Shuanghe area, Dabie UHP terrane: Restriction on the prograde, UHP and retrograde metamorphic ages
Acta Petrologica Sinica,
22
(7)
1761 – 1778
2006
ISSN: 10000569
Publisher: Science Press
Abstract: ▾ Laser Raman spectroscopy and cathodoluminescence (CL) images show that zircons separated from eclogite lens in impure marble from Shuanghe area, Dabie UHP metamorphic belt, are characterized by inherited (detrital), prograde, UHP and retrograde metamorphic overgrowth domains. The inherited (detrital) zircons contain Pl + Ap and Qtz + Pl in the white-luminescent core and the dark-luminescent rim, respectively. Whereas the prograde metamorphic domains (with grey-luminescent CL images) preserve quartz eclogite-facies mineral assemblage of Qtz + Grt + Omp + Phe + Dol + Ap, formed at 588 ∼ 668°C and 1.7 ∼ 1.8CPa. In contrast, the UHP metamorphic domains (with white-luminescent CL images) retain index UHP mineral assemblage of Coe + Grt + Omp + Arg + Mgs + Ap, and record UHP condition of T = 784 ∼ 849°C and P > 5.5GPa. The outmost retrograde rims (with dark-luminescent CL images) however, contain no-UHP minerals such as quartz and calcite, related to the regional amphibolite-facies retrogression with T = 550 ∼ 720°C and P = 0.8 ∼ 1.4GPa. SHRIMP U-Pb dating on these zoned zircons identify four discrete and meaningful age groups: 2701 ∼ 1753Ma (207Pb/206Pb age) is recorded in the inherited (detrital) zircons derived from Archean-Proterozoic protolith, the prograde metamorphism of quartz eclogite-facies in the prograde domains occurred at 249 ∼ 241 Ma (206Pb/238U age), the UHP metamorphic event in the UHP mineral-bearing domains was at 239 ∼ 231Ma (206Pb/238U age), and the late amphibolite-facies retrograde overprint in the outmost rims was restricted at 219 ∼ 211 Ma (206Pb/238U age). Thus, Archean-Proterozoic continental materials of the Dabie UHP terrane were subducted to 55 ∼ 60km depth at Early Triassic and occurred quartz eclogite facies metamorphism simultaneously. Then these quartz eclogite-facies metamorphic rocks continued subduction to 165 ∼ 175km deep mande depth at Middle Triassic and experienced UHP metamorphism; The peak pressures are based on the equilibrium calculation of the reaction dolomite = magnesite + aragonite. This UHP metamorphism recorded a lower geotherm step of 4.7°C km-1 which is within what was previously considered a 'forbidden' condition within earth. Finally these UHP metamorphic rocks were exhumed to mid-crustal levels (about 30km) in the Late Triassic and overprinted regional amphibolite facies metamorphism. The subduction and exhumation rate deduced from the SHRIMP data and metamorphic P-T conditions is 11 ∼ 12km Myr-1 and 7.5 ∼ 8.1km Myr-1, respectively. Fast subduction and rapid exhumation has been considered to be one of the most important factors for the preservation of prograde, UHP and retrograde metamorphic minerals in zircons. Such a fast exhumation suggests that the Dabie UHP metamorphic rocks returned towards the crustal depths as dominant part of a buoyant sliver, caused as a consequence of slab breakoff.
492.
Mobile element analysis by secondary ion mass spectrometry (SIMS) of impactite matrix samples from the Yaxcopoil-1 drill core in the Chicxulub impact structure
Meteoritics and Planetary Science,
41
(12)
1929-1945
2006
Abstract: ▾ The concentrations of the fluid mobile trace elements lithium, beryllium, boron, and barium were measured in samples of the altered matrix of several impactite breccias of the Yaxcopoil-1 drill core using secondary ion mass spectrometry (SIMS) to determine the extent of transport due to aqueous or hydrothermal processes. Three of the elements, Li, Be, and B, have higher concentrations in the upper suevite impact breccias than in the lower impact melt deposits by factors of 3.5, 2.2, and 1.5, respectively. Lithium and B are the most enriched elements up section, and appear to have had the greatest mobility. The similar fractionation of Li and B is consistent with fluid transport and alteration under low-temperature conditions of less than 150 °C based on published experimental studies. In contrast to Li, Be, and B, the concentration of Ba in the altered matrix materials decreases upward in the section, and the concentration of Ba in the matrix is an order of magnitude less than the bulk concentrations, likely due to the presence of barite. The origin of the elemental variations with depth may be related to different protolith compositions in the upper versus the lower impactite units. A different protolith in the altered matrix is suggested by the Mg-rich composition of the tower units versus the Al-rich composition of the upper units, which largely correlates with the mobile element variations. The possibility that vertical transport of mobile elements is due to a postimpact hydrothermal system is supported by published data showing that the sediments immediately overlying the impactites are enriched in mobile elements derived from a hydrothermal system. However, the mobile elements in the sediments do not have to originate from the underlying impactites. In conclusion, our data suggests that the impactites at this location did not experience extensive high-temperature hydrothermal processing, and that only limited transport of some elements, including Li, Be, and B, occurred. © The Meteoritical Society, 2006.
491.
Shock-metamorphosed zircon in terrestrial impact craters
Meteoritics and Planetary Science,
41
(3)
433-454
2006
Abstract: ▾ To ascertain the progressive stages of shock metamorphism of zircon, samples from three well-studied impact craters were analyzed by optical microscopy, scanning electron microscopy (SEM), and Raman spectroscopy in thin section and grain separates. These samples are comprised of well-preserved, rapidly quenched impactites from the Ries crater, Germany, strongly annealed impactites from the Popigai crater, Siberia, and altered, variably quenched impactites from the Chicxulub crater, Mexico. The natural samples were compared with samples of experimentally shock-metamorphosed zircon. Below 20 GPa, zircon exhibits no distinct shock features. Above 20 GPa, optically resolvable planar microstructures occur together with the high-pressure polymorph reidite, which was only retained in the Ries samples. Decomposition of zircon to ZrO2 only occurs in shock stage IV melt fragments that were rapidly quenched. This is not only a result of post-shock temperatures in excess of ∼1700 °C but could also be shock pressure-induced, which is indicated by possible relics of a high-pressure polymorph of ZrO2. However, ZrO2 was found to revert to zircon with a granular texture during devitrification of impact melts. Other granular textures represent recrystallized amorphous ZrSiO4 and reidite that reverted to zircon. This requires annealing temperatures >1100 °C. A systematic study of zircons from a continuous impactite sequence of the Chicxulub impact structure yields implications for the post-shock temperature history of suevite-like rocks until cooling below ∼600 °C. © The Meteoritical Society, 2006.
490.
Ultrahigh pressure metamorphic rocks from the Chinese Continental Scientific Drilling Project: I. Petrology and geochemistry of the main hole (0-2,050 m)
Contributions to Mineralogy and Petrology,
152
(4)
421 – 441
2006
ISSN: 00107999Keywords:▾
Asia; China; Eurasia; Far East; Sulu Belt; amphibolite facies; chemical composition; geochemistry; metamorphic rock; P-T conditions; paragenesis; petrology; supracrustal rock; ultrahigh pressure metamorphism
Abstract: ▾ The main hole (MH) of the Chinese Continental Scientific Drilling Project (CCSD) in southern Sulu has penetrated into an ultrahigh-pressure (UHP) metamorphic rock slice which consists of orthogneiss, paragneiss, eclogite, ultramafic rock and minor schist. Recovered eclogites have a UHP metamorphic mineral assemblage of garnet + omphacite + rutile ± phengite ± kyanite ± coesite ± epidote. Ultramafic rocks contain garnet + olivine + clinopyroxene + orthopyroxene ± Ti-clinohumite ± phlogopite. Gneisses and schists contain an amphibolite-facies paragenesis, but their zircons have coesite, garnet, omphacite (or jadeite) and phengite inclusions, indicating that eclogites and gneisses have been subjected to in situ UHP metamorphism. Using available geothermobarometers, P-T estimates of 3.1-4.4 GPa and 678-816°C for eclogites were obtained. If surface outcrops and neighboring shallow drill holes are considered together, we suggest that a huge supracrustal rock slab (> 50 km long × > 100 km wide × 5 km deep) was subducted to a depth > 100 km and then exhumed to the surface. The depth interval (0-2,050 m) of the CCSD-MH can be divided into six lithological units. Unit 1 consists of alternating layers of quartz-rich and rutile-rich eclogites, with thin interlayers of gneiss and schist. Eclogites of unit 1 are characterized by Nb, Ta, Sr and Ti depletions, low Mg number and general LREE enrichment. Unit 2 comprises rutile- and ilmenite-rich eclogite and minor "normal" eclogite and is characterized by high TiO2, total Fe, V, Co and Sr, and very low SiO2, alkali, Zr, Ba, Nb, Ta and total REE contents, and LREE-depleted REE patterns with slightly positive Eu anomalies. Unit 3 contains ultramafic rock and minor MgO-rich eclogite. Protoliths of UHP rocks from units 1, 2 and 3 represent a layered mafic to ultramafic intrusion at crustal depth. Units 4 and 6 consist of interlayered eclogite and paragneiss; the eclogites are characterized by Th, U, Nb, Ta and Ti depletion and K enrichment and LREE-enriched REE patterns. Paragneisses show Nb, Ta, Sr and Ti depletions and LREE-enriched REE patterns occasionally with slightly negative Eu anomalies, indicating that their protoliths represent metamorphic supracrustal series. Unit 5 consists mainly of orthogneisses, showing distinct Nb, Ta, Sr and Ti depletions, and LREE-enriched REE patterns with pronounced negative Eu anomalies, suggesting granitic protoliths. In conclusion it is proposed that the southern Sulu UHP belt consists of a series of meta-supracrustal rocks, a layered mafic-ultramafic complex and granites. © Springer-Verlag 2006.
489.
SHRIMP U-Pb zircon dating from Sulu-Dabie dolomitic marble, eastern China: Constraints on prograde, ultrahigh-pressure and retrograde metamorphic ages
Journal of Metamorphic Geology,
24
(7)
569 – 589
2006
ISSN: 15251314Keywords:▾
Asia; China; Dabie-Sulu Belt; Eurasia; Far East; cathodoluminescence; dolomite; Raman spectroscopy; retrograde metamorphism; SHRIMP dating; ultrahigh pressure metamorphism; zircon
Abstract: ▾ Laser Raman spectroscopy and cathodoluminescence (CL) images show that zircon from Sulu-Dabie dolomitic marbles is characterized by distinctive domains of inherited (detrital), prograde, ultrahigh-pressure (UHP) and retrograde metamorphic growths. The inherited zircon domains are dark-luminescent in CL images and contain mineral inclusions of Qtz + Cal + Ap. The prograde metamorphic domains are white-luminescent in CL images and preserve a quartz eclogite facies assemblage of Qtz + Dol + Grt + Omp + Phe + Ap, formed at 542-693 °C and 1.8-2.1GPa. In contrast, the UHP metamorphic domains are grey-luminescent in CL images, retain the UHP assemblage of Coe + Grt + Omp + Arg + Mgs + Ap, and record UHP conditions of 739-866 °C and > 5.5 GPa. The outermost retrograde rims have dark-luminescent CL images, and contain low- P minerals such as calcite, related to the regional amphibolite facies retrogression. Laser ablation ICP-MS trace-element data show striking difference between the inherited cores of mostly magmatic origin and zircon domains grown in response to prograde, UHP and retrograde metamorphism. SHRIMP U-Pb dating on these zoned zircon identified four discrete 206Pb/238U age groups: 1823-503 Ma is recorded in the inherited (detrital) zircon derived from various Proterozoic protoliths, the prograde domains record the quartz eclogite facies metamorphism at 254-239 Ma, the UHP growth domains occurred at 238-230 Ma, and the late amphibolite facies retrogressive overprint in the outermost rims was restricted to 218-206 Ma. Thus, Proterozoic continental materials of the Yangtze craton were subducted to 55-60km depth during the Early Triassic and recrystallized at quartz eclogite facies conditions. Then these metamorphic rocks were further subducted to depths of 165-175 km in the Middle Triassic and experienced UHP metamorphism, and finally these UHP metamorphic rocks were exhumed to mid-crustal levels (about 30km) in the Late Triassic and overprinted by regional amphibolite facies metamorphism. The subduction and exhumation rates deduced from the SHRIMP data and metamorphic P-T conditions are 9-10 km Myr-1 and 6.4km Myr-1, respectively, and these rapid subduction-exhumation rates may explain the obtained P-T-t path. Such a fast exhumation suggests that Sulu-Dabie UHP rocks that returned towards crustal depths were driven by buoyant forces, caused as a consequence of slab breakoff at mantle depth. © 2006 Blackwell Publishing Ltd.
488.
Time-lapse changes in tube and guided waves in cross-well Mallik experiment
SEG Technical Program Expanded Abstracts,
25
(1)
379-383
2006
ISSN: 10523812
Publisher: Society of Exploration Geophysicists
Keywords:▾
Geophysical prospecting; Seismic waves; Seismology, Cross-well; P-wave arrival; Reservoir monitoring; Seismic datas, Guided electromagnetic wave propagation
ISBN:
9781604236972
Abstract: ▾ We analyze cross-well seismic data from the Mallik experiment and demonstrate time-lapse changes in tube and guided waves. Although such changes are challenging to interpret, they are generally of a larger magnitude compared to any time-lapse signatures of the first P-wave arrivals reported elsewhere. This suggests better sensitivity of tube and guided waves to small production-related changes and their feasibility for reservoir monitoring. © 2005 Society of Exploration Geophysicists.
487.
Mineral and fluid inclusions in zircon of UHP metamorphic rocks from the CCSD-main drill hole: A record of metamorphism and fluid activity
Lithos,
92
(3-4)
378 – 398
2006
ISSN: 00244937Keywords:▾
Asia; China; Donghai; Eurasia; Far East; Jiangsu; cathodoluminescence; chemical composition; electron probe analysis; exhumation; fluid inclusion; lithology; magmatic differentiation; mineralization; P-T conditions; Raman spectroscopy; subduction; ultrahigh pressure metamorphism
Abstract: ▾ The Chinese Continental Scientific Drilling (CCSD) main drill hole (0-3000 m) in Donghai, southern Sulu orogen, consists of eclogite, paragneiss, orthogneiss, schist and garnet peridotite. Detailed investigations of Raman, cathodoluminescence, and microprobe analyses show that zircons from most eclogites, gneisses and schists have oscillatory zoned magmatic cores with low-pressure mineral inclusions of Qtz, Pl, Kf and Ap, and a metamorphic rim with relatively uniform luminescence and eclogite-facies mineral inclusions of Grt, Omp, Phn, Coe and Rt. The chemical compositions of the UHP metamorphic mineral inclusions in zircon are similar to those from the matrix of the host rocks. Similar UHP metamorphic P-T conditions of about 770 °C and 32 kbar were estimated from coexisting minerals in zircon and in the matrix. These observations suggest that all investigated lithologies experienced a joint in situ UHP metamorphism during continental deep subduction. In rare cases, magmatic cores of zircon contain coesite and omphacite inclusions and show patchy and irregular luminescence, implying that the cores have been largely altered possibly by fluid-mineral interaction during UHP metamorphism. Abundant H2O-CO2, H2O- or CO2-dominated fluid inclusions with low to medium salinities occur isolated or clustered in the magmatic cores of some zircons, coexisting with low-P mineral inclusions. These fluid inclusions should have been trapped during magmatic crystallization and thus as primary. Only few H2O- and/or CO2-dominated fluid inclusions were found to occur together with UHP mineral inclusions in zircons of metamorphic origin, indicating that UHP metamorphism occurred under relatively dry conditions. The diversity in fluid inclusion populations in UHP rocks from different depths suggests a closed fluid system, without large-scale fluid migration during subduction and exhumation. © 2006 Elsevier B.V. All rights reserved.
486.
[English]
Wellbore stability study for the SAFOD borehole through the San Andreas Fault
Volume 5
,
Page 2965-2976
Publisher
Society of Petroleum Engineers (SPE)
2006
SPE, Stanford U., United StatesKeywords:▾
Creep; Oil well drilling; Real time systems; Well logging, Bedding planes; Microearthquakes; San Andreas Fault (SAF); Stress gradients, Boreholes
485.
[English]
Numerical study of transmission signatures of gas hydrate-bearing microstructures
Volume 5
,
Page 2483-2487
Publisher
Society of Petroleum Engineers
2006
Freie Universitaet Berlin, Germany484.
[English]
Modeling and inversion of Sonic P and S Wave velocities at the Mallik 5L-38 gas hydrate research well
Publisher
European Association of Geoscientists and Engineers, EAGE
2006
CONICET, Universidad Nacional de la Plata, Argentina483.
[English]
Hydrates as an energy source - Risks and opportunities
Volume 3
,
Page 1456
Publisher
Society of Petroleum Engineers
2006
Canadian Geol Survey, CanadaKeywords:▾
Crystalline materials; Database systems; Energy resources; Permafrost; Pressurization; Risk assessment, Cold formation temperatures; Downhole geophysical logging; Natural gas hydrates; Natural gas resources, Gas hydrates
482.
XRF titanium, iron counting and ratio Fe/Ti for CON01-603-2 and VER98-1-14
481.
Velocity dispersion in Vibroseis VSP data
SEG Technical Program Expanded Abstracts,
25
(1)
3506-3510
2006
ISSN: 10523812
Publisher: Society of Exploration Geophysicists
Keywords:▾
Data handling; Gas hydrates; Petroleum prospecting; Porous materials; Seismic prospecting; Seismic waves; Seismology; Velocity, Cross correlations; Function of frequency; Moving window; Robust methods; Seismic data processing; Seismic frequencies; Velocity dispersion; Velocity variations, Dispersion (waves)
ISBN:
9781604236972
Abstract: ▾ Seismic waves in a porous medium experience attenuation and velocity dispersion. In conventional seismic data processing, velocity dispersion is neglected partially because of insufficient or inconclusive observations. In a medium of high attenuation (Q<30), velocity dispersion is a concern. In order to detect velocity dispersion in the exploration seismic frequency band, uncorrelated Vibroseis data were utilized. We have simulated distortion of the correlation wavelet of Vibroseis data due to velocity dispersion to investigate how dispersion distorts Vibroseis data. Different methods were investigated to develop a robust method to detect and measure velocity dispersion in uncorrelated Vibroseis data. Using the CCMW (cross-correlation with a moving window) method, small velocity variations as a function of frequency were observed in the borehole Vibroseis data from the Mallik gas hydrate research wells (Mackenzie Delta, NWT, Canada). © 2005 Society of Exploration Geophysicists.
480.
Uplift, thermal unrest and magma intrusion at Yellowstone caldera
Nature,
440
(7080)
72-75
2006
ISSN: 00280836
Publisher: Nature Publishing Group
Keywords:▾
Earthquakes; Interferometry; Radar; Satellites, Cataclysmic eruptions; Hydrothermal activity, Volcanoes, caldera; crustal deformation; igneous intrusion; uplift, analytic method; article; interferometer; priority journal; surface property; telecommunication; thermal analysis; volcano, North America; United States; Wyoming; Yellowstone Caldera
Abstract: ▾ The Yellowstone caldera, in the western United States, formed ∼640,000 years ago when an explosive eruption ejected ∼1,000 km3 of material. It is the youngest of a series of large calderas that formed during sequential cataclysmic eruptions that began ∼16 million years ago in eastern Oregon and northern Nevada. The Yellowstone caldera was largely buried by rhyolite lava flows during eruptions that occurred from ∼150,000 to ∼70,000 years ago. Since the last eruption, Yellowstone has remained restless, with high seismicity, continuing uplift/subsidence episodes with movements of ∼70 cm historically to several metres since the Pleistocene epoch, and intense hydrothermal activity. Here we present observations of a new mode of surface deformation in Yellowstone, based on radar interferometry observations from the European Space Agency ERS-2 satellite. We infer that the observed pattern of uplift and subsidence results from variations in the movement of molten basalt into and out of the Yellowstone volcanic system. © 2006 Nature Publishing Group.
479.
Ultrahigh-pressure metamorphic rocks from the Chinese Continental Scientific Drilling Project: II Oxygen isotope and fluid inclusion distributions through vertical sections
Contributions to Mineralogy and Petrology,
152
(4)
443 – 458
2006
ISSN: 00107999Keywords:▾
Asia; China; Dabie-Sulu Belt; Donghai; Eurasia; Far East; Jiangsu; fluid inclusion; isotopic composition; metamorphic rock; mineralogy; oxygen isotope; ultrahigh pressure metamorphism
Abstract: ▾ In order to reconstruct the formation and exhumation mechanisms of UHP metamorphic terrains, the Chinese Continental Scientific Drilling Program (CCSD) has been carried out in Donghai of the Dabie-Sulu ultrahigh-pressure (UHP) metamorphic belt, East China. Eclogite, gneiss, amphibolite (retrograded from eclogite), ultramafic rocks, and minor schist and quartzite have been drilled. Aiming to reveal the fluid behaviour in a vertical sequence of an UHP slab, we investigated fluid inclusion and oxygen isotope characteristics of selected drillcores from the main hole and the pilot-holes PP2 and ZK 703 of the CCSD. More than 540 laser-ablation oxygen isotope analyses on garnet, omphacite, quartz, kyanite, amphibole, phengite, rutile, epidote, amphibole, plagioclase, and biotite from various rocks in the depth range of 0-3,000 m (mainly eclogite and gneiss) show that the investigated rocks can be divided into two groups: 18O-depleted rocks (as low as δ18O = -7.4‰ for garnet) indicate interaction with cold climate meteoric waters, whereas 18O-normal rocks (with bulk δ18O > +5.6‰) have preserved the O-isotopic compositions of their protoliths. Meteoric water/rock interaction has reached depths of at least 2,700 m. Oxygen isotope equilibrium has generally been achieved. Isotopic compositions of mineral phases are homogeneous on a mm to cm scale regardless of lithology, but heterogeneous on the scale of a few metres. Oxygen isotope distributions in the vertical sections favour an "in situ" origin of the UHP metamorphic rocks. The very negative δ18O eclogites usually have higher hydroxyl-mineral contents than the normal δ18O rocks, indicating higher water content during UHP metamorphism. Fluid inclusion data suggest that rocks with depleted 18O compositions have had different fluid histories compared to those with normal δ18O values. Rocks with depleted 18O mainly have primary medium-to-high salinity inclusions in omphacite, kyanite and quartz, and abundant secondary low-salinity or pure water inclusions in quartz, indicating a high-salinity-brine-dominated fluid system during peak UHP metamorphism; no carbonic inclusions have been identified in these rocks. By contrast, primary very high-density CO2 inclusions are commonly found in the rocks with normal δ18O values. These observations suggest that fluid and oxygen isotope composition of minerals are related and reflect variable degrees of alterations of the Dabie-Sulu UHP metamorphic rocks. © Springer-Verlag 2006.
478.
Tube-wave monitoring at Mallik field: Comparing modeled and experimental time-lapse responses
SEG Technical Program Expanded Abstracts,
25
(1)
3240-3244
2006
ISSN: 10523812
Publisher: Society of Exploration Geophysicists
Keywords:▾
Geophysical prospecting; Shear waves; Tubes (components), Cross-well; Data display; First arrival; P- and S-waves; Pre-processing; Time-lapse response; Tube waves; Wave forms, Acoustics
ISBN:
9781604236972
Abstract: ▾ We apply tube-wave monitoring method to a time-lapse cross-well dataset from Mallik field. Raw waveforms are used for analysis thus avoiding any smearing of 4D response introduced by pre-processing. We perform extensive modeling that includes effects of a source borehole and confirms nature of most prominent arrivals as being tube-wave related. Modeling proves that strongest conversion of tube wave into P and S waves occurs at the sharp acoustic boundary. Data displays clear time-lapse changes in tube-wave related arrivals, while shows no change in first arrivals. Modeling suggests that to explain the data the reservoir changes have to occur at a deeper interval than previously anticipated, below the perforations. Excellent agreement between modeled and experimental data provides us with good confidence in our results. This study represents first application of tube-wave monitoring concept. © 2005 Society of Exploration Geophysicists.
477.
Transmission signatures of gashydrate bearing micro-structures: A numerical study
SEG Technical Program Expanded Abstracts,
25
(1)
1978-1982
2006
ISSN: 10523812
Publisher: Society of Exploration Geophysicists
Keywords:▾
Gases; Geophysical prospecting; Hydration; Petroleum prospecting; Seismic waves; Wave propagation, Effective velocity; Gas hydrate bearing sediments; Gas hydrate saturations; High velocity; Micro-scale; Pore space; Sediment grains; Wave propagation simulation, Gas hydrates
ISBN:
9781604236972
Abstract: ▾ This work is inspired by the observation, that gas hydrate bearing sediments have a high velocity in combination with high attenuation. We study numerically the influence of different gas hydrate locations within the pore space on transmitted p-waves. From the wave propagation simulations on the micro-scale it can be seen, that different positions of the gas hydrate in the pore space results in almost the same effective velocities and attenuation, as long as the gas hydrate had contact to the sediment grains. This changes in the case of a suspension, here the attenuation increases and the effective velocity decreases. The resulting p-wave versus gas hydrate saturation plot is in a qualitatively good agreement with experimental results obtained for the Mallik 2L-38 well. © 2005 Society of Exploration Geophysicists.
476.
The Sino-Korean-Yangtze suture, the Huwan detachment, and the Paleozoic-Tertiary exhumation of (ultra)high-pressure rocks along the Tongbai-Xinxian-Dabie Mountains
Special Paper of the Geological Society of America,
40345 – 75
2006
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
China; Dabie Mountains; Henan; Tongbai; Xinxiang; Cooling; Deformation; Fission reactions; Geochronology; Metamorphic rocks; Phosphate minerals; Silicate minerals; Structural geology; Zircon; Holocenes; Huwan detachment; Qinling-dabie-sulu orogen; Sino-korean-yangtze suture; Ultrahigh pressure; exhumation; orogeny; Paleozoic; suture zone; Tertiary; ultrahigh pressure metamorphism; Buildings
Abstract: ▾ There are three sutures in the Qinling-Dabie-Sulu orogen in the Tongbai-Xinxian (northern Hong'an)-northern Dabie area: the Silurian Sino-Korean craton-Erlangping intra-oceanic arc suture, the Silurian Erlangping arc-Qinling unit (microcontinent) suture, and the Early Triassic Qinling unit-Yangtze craton suture. We resolve the controversy regarding the age of the Sino-Korean craton-Yangtze craton collisionby recognizing that there was Paleozoic collision between the Qinling unit and the Sino-Korean craton and Mesozoic collision between the Qinling unit and the Yangtze craton. The Qinling unit constitutes a long and narrow microcontinent that extends through the Qinling-Dabie area and probably into the Sulu area. Its common characteristics are the Mesoproterozoic (ca. 1.0 Ga) Jinningian orogeny, ca. 0.8-0.7 Ga arc formation and rifting, and Late Silurian-Early Devonian (ca. 400 Ma) arc magmatism with concomitant regional contact metamorphism up to granulite-facies conditions (peak: 680-740 °C at 0.9-1.1 GPa). A common Proterozoic history links the Qinling microcontinent to the Yangtze craton. Its 400 Ma arc, forearc basin, and its separation from the Yangtze craton by the partly oceanic Huwan mélange make the Qinling microcontinent distinct. The forearc basin sits on the southern part of the 400 Ma arc and underlying Proterozoic continental basement, and detrital geochronology ties it to the Qinling microcontinent basement and its arc. The Huwan mélange is a subduction-accretion complex containing elements of the Qinling microcontinent and its arc, the Paleotethyan ocean floor, and possibly the Yangtze craton. Quartz eclogites (540-590 °C, 2.1 GPa) signify ca. 315 Ma subduction. Devonian to Permian eclogite zircon ages, 40 Ar/ 39 Ar and Rb/Sr mineral ages in the forearc and its basement, and static, Permian blueschist metamorphism in the upper-plate basement testify to subduction throughout the late Paleozoic. The ̃10-km-wide Huwan detachment bounds the high- and ultrahigh-pressure rocks of the Xinxian-Hong'an block (pressure peak at older than 240 Ma) along their northern margin. It is partly responsible for exhumation of the high- and ultrahighpressure rocks, but the entire basement core of Hong'an-Dabie orogen is also strongly deformed. The Huwan shear-zone high-strain deformation indicates passage of rocks through the lithosphere by subhorizontal N-S extension and vertical contraction, showcased by condensed Triassic isograds (420 °C and ̃0.4 GPa in the hanging wall and ̃530 °C and 2.2 GPa in the footwall). The Huwan detachment produced Triassic crustal exhumation rates of 1.9-1.4 mm/yr; synkinematic phengite grew as early as ca. 235 Ma, and the main retrograde deformation occurred at 224-195 Ma. The Tongbai-Xinxian area shows a massive 130-115 Ma cluster of cooling ages, reflecting regional cooling after granitoid injection and regional Cretaceous heating. Apatite fission-track ages cluster at 80-55 Ma and signify cooling related to transtension that coincided with rifting marked by Late Cretaceous-Eocene red bed deposition throughout eastern China. Exhumation rates of for the last 70 m.y. have been slow: ̃0.06 mm/yr. The India-Asia collision reactivated the orogen in the Eocene, particularly along the Tanlu fault zone and locally along fault zones in Tongbai-Xinxian. © 2006 Geological Society of America.
475.
Slip zone and energetics of a large earthquake from the Taiwan Chelungpu-fault Drilling Project
Nature,
444
(7118)
473-476
2006
ISSN: 00280836
Publisher: Nature Publishing Group
Keywords:▾
Drilling platforms; Earthquake effects; Energy dissipation; Interfacial energy; Project management; Surface phenomena, Near field; Rupture processes; Seismic fracture energy; Slip zone, Seismology, borehole; Chi-Chi earthquake 1999; drilling; fault gouge; fault slip; fault zone; grain size; seismometry; surface energy, article; earthquake; energy transfer; geology; particle size; priority journal; surface property; Taiwan; thickness, Asia; Eurasia; Far East; Taiwan
Abstract: ▾ Determining the seismic fracture energy during an earthquake and understanding the associated creation and development of a fault zone requires a combination of both seismological and geological field data. The actual thickness of the zone that slips during the rupture of a large earthquake is not known and is a key seismological parameter in understanding energy dissipation, rupture processes and seismic efficiency. The 1999 magnitude-7.7 earthquake in Chi-Chi, Taiwan, produced large slip (8 to 10 metres) at or near the surface, which is accessible to borehole drilling and provides a rare opportunity to sample a fault that had large slip in a recent earthquake. Here we present the retrieved cores from the Taiwan Chelungpu-fault Drilling Project and identify the main slip zone associated with the Chi-Chi earthquake. The surface fracture energy estimated from grain sizes in the gouge zone of the fault sample was directly compared to the seismic fracture energy determined from near-field seismic data. From the comparison, the contribution of gouge surface energy to the earthquake breakdown work is quantified to be 6 per cent. ©2006 Nature Publishing Group.
474.
The origin and age of biogeochemical trends in deep fracture water of the witwatersrand basin, south africa
Geomicrobiology Journal,
23
(6)
369-414
2006
ISSN: 01490451Keywords:▾
biogeochemistry; dissolved inorganic carbon; groundwater; methanogenesis; microbial community; sulfate-reducing bacterium, Africa; South Africa; Southern Africa; Sub-Saharan Africa; Witwatersrand, Methanobacteriales
Abstract: ▾ Water residing within crustal fractures encountered during mining at depths greater than 500 meters in the Witwatersrand basin of South Africa represents a mixture of paleo-meteoric water and 2.0–2.3 Ga hydrothermal fluid. The hydrothermal fluid is highly saline, contains abiogenic CH4 and hydrocarbon, occasionally N2, originally formed at ∼250–300◦C and during cooling isotopically exchangedO and Hwith minerals and accrued H2,4He and other radiogenic gases. The paleo-meteoric water ranges in age from ∼10 Ka to >1.5 Ma, is of low salinity, falls along the global meteoric water line (GMWL) and is CO2 and atmospheric noble gas-rich. The hydrothermal fluid, which should be completely sterile, has probably been mixing with paleo-meteoric water for at least the past∼100 Myr, a process which inoculates previously sterile environments at depths >2.0 to 2.5 km. Free energy flux calculations suggest that sulfate reduction is the dominant electron acceptor microbial process for the high salinity fracture water and that it is 107 times that normally required for cell maintenance in lab cultures. Flux calculations also indicate that the potential bioavailable chemical energy increases with salinity, but because the fluence of bioavailable C, N and P also increase with salinity, the environment remains energy-limited. The4He concentrations and theoretical calculations indicate that the H2 that is sustaining the subsurface microbial communities (e.g. H2-utilizing SRB and methanogens) is produced by water radiolysis at a rate of ∼1nMyr−1. Microbial CH4 mixes with abiogenicCH4 to produce the observed isotopic signatures and indicates that the rate of methanogenesis diminishes with depth from∼100 at<1 kmbls, to<0.01nMyr−1 at>3 kmbls. Microbial Fe(III) reduction is limited due to the elevated pH. The δ13C of dissolved inorganic carbon is consistent with heterotrophy rather than autotrophy dominating the deeper, more saline environments. One potential source of the organic carbon may be microfilms present on the mineral surfaces. © Taylor & Francis.
473.
The Lake Petén Itzá Scientific Drilling Project
Scientific Drilling,
1
(3)
25-29
2006
ISSN: 18168957472.
The Cretaceous-Paleogene (K-P) boundary at Brazos, Texas: Sequence stratigraphy, depositional events and the Chicxulub impact
Sedimentary Geology,
184
(1-2)
77-109
2006
Abstract: ▾ Two cores from Brazos, Texas, spanning the Cretaceous-Paleogene (K-P) boundary, are investigated by a multidisciplinary approach aiming at unraveling environmental changes and sequence stratigraphic setting. In addition, the sedimentology of the K-P event deposit and its correlation with the K-P boundary is studied. Foraminifera and nannofossil stratigraphy indicates that both cores include a latest Maastrichtian (Zone CF1-CF2) and earliest Danian (P0, Pα and P1a) shale sequence with a sandy and Chicxulub ejecta-bearing event deposit at the K-P boundary; a hiatus of unknown duration may be present by the unconformable base of the event deposit. Planktic foraminifera as well as calcareous nannofossil abundance and diversity both decline abruptly above the event deposit (K-P mass extinction), whereas benthic foraminifera show a pronounced faunal change but no mass extinction. Mineralogical and geochemical proxies suggest that-except for the sandwiched K-P event deposit-no facies change took place across the K-P boundary and no evidence for adverse an- or dysoxic sedimentary conditions following the Chicxulub impact was observed. Therefore, the interval bracketing the K-P event deposit is considered as highstand systems tract. Increased coarse detritus input and low planktic/benthic (P/B) foraminifera ratios during the earliest Paleocene (P0 and Pα) both suggest an increased coastal proximity or relative sea-level lowering, although the K-P mass extinction of planktic foraminifera might have influenced the P/B ratios as well. Consequently, the sandy shales of the early Paleocene are considered as late regressive highstand or as lowstand deposit. During P1a, shales assigned as transgressive systems tract overlie a pyrite- and glauconite-rich bioturbated transgressive surface or type-2-sequence boundary. The smectite-dominated clay assemblage, with minor illite, kaolinite and chlorite indicates semiarid-humid climates with no obvious shifts across the K-P boundary. The magnetic susceptibility signature during the Maastrichtian reveals a subtle cyclic (or rhythmic) pattern, whereas a high-amplitude cyclic pattern is present during the early Danian. The K-P event deposit shows a succession of high-energetic debris flows and turbidites derived from multiple source areas, followed by a period of decreasing current energy. Deposition was likely triggered by multiple tsunami or tempestites followed by a prolonged period of reworking and settling. The Chicxulub ejecta at the base of the K-P event deposit consists of Mg-rich smectite-as well as Fe-Mg-rich chlorite-spherules. Their mineralogical composition points to target rocks of mafic to intermediate composition, presumably situated in the northwestern sector of the Chicxulub impact structure. Besides these silicic phases, the most prominent ejecta components are limestone clasts, accretionary carbonate clasts, and microspar, suggesting that the Texas area received ejecta also from shallow, carbonate-rich lithologies at the impact site on the Yucatán carbonate platform. The excellent correlation of Chicxulub ejecta at Brazos with ejecta found in the K-P boundary layer worldwide - along with the associated mass extinction - provides no evidence that Chicxulub predated the K-P boundary and allows for unequivocal positioning of the K-P boundary at the event deposit. © 2005 Elsevier B.V. All rights reserved.
471.
The 2005 Lake Malawi Scientific Drilling Project
Scientific Drilling,
217-19
2006
470.
Temperature dependence of elastic P- and S-wave velocities in porous Mt. Unzen dacite
Journal of Volcanology and Geothermal Research,
153
(1-2 SPEC. ISS.)
136-147
2006
ISSN: 03770273Keywords:▾
Anisotropy; High temperature effects; Metamorphic rocks; Porosity; Seismology; Volcanic rocks; Volcanoes, Pulse transmission technique; Silica-rich rocks; Volcano seismic activity, Elastic waves, dacite; elasticity; high temperature; P-wave; S-wave; seismic anisotropy; seismology; volcanic rock; volcanology, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano
Abstract: ▾ Laboratory measurements of elastic properties of volcanic rocks are crucial for the modelling of volcano seismic activity. Compared to the large database reported in the literature for sedimentary, igneous and metamorphic rocks, the data set for volcanic rocks is limited and mostly restricted to basalts. Data for more silica-rich rocks are sparse. In particular, velocity data for silica-rich volcanic rocks measured at elevated temperature are lacking. We measured the elastic P- and S-wave velocities and the velocity anisotropy of porous dacitic rocks from Unzen Volcano, Japan, exhibiting an open porosity of 3.3 to 24.3 vol.%. The measurements were done at temperatures of up to 600 °C and confining pressures of 100 MPa, corresponding to depths of ∼ 3000-4000 m. Samples with even higher porosities failed at the required pressures. The measurements were carried out in a cubic multi-anvil pressure apparatus, using the pulse transmission technique. In contrast to low-porosity magmatic and metamorphic rocks, the seismic velocities of the investigated volcanic rocks increased and the velocity anisotropies decreased with increasing temperature, due to further sample compaction. There is a close relationship between velocity, density and porosity. The higher the density (and the lower the porosity) the higher are the P- and S-wave velocities. These results can contribute to a better understanding of the propagation of seismic energy through the volcanic edifice. © 2005 Elsevier B.V. All rights reserved.