All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
503.
Petrology and thermal structure of the Hawaiian plume from Mauna Kea volcano
Nature,
444
(7119)
605-609
2006
ISSN: 00280836
Publisher: Nature Publishing Group
Keywords:▾
Lithology; Melting; Rocks; Thermal plumes; Uncertain systems; Volcanoes, Hawaiian core; Mauna Kea magmatism; Pyroxenite/eclogite rocks; Tholeiitic lavas, Petrology, aluminum derivative; aluminum trioxide; calcium oxide; chromium trioxide; dipotassium oxide; glass; iron oxide; iron trioxide; magnesium oxide; manganese oxide; nitrogen oxide; oxacillin; oxide; phosphorus pentoxide; potassium derivative; silicon dioxide; titanium dioxide, core analysis; lava; magma; mantle plume; oceanic crust; peridotite; petrology; pyroxenite; thermal structure; tholeiite, article; calibration; crystallization; fractionation; garnet; melting point; peridotite; petrology; priority journal; pyroxenite; rock; volcano
Abstract: ▾ There is uncertainty about whether the abundant tholeiitic lavas on Hawaii are the product of melt from peridotite or pyroxenite/eclogite rocks. Using a parameterization of melting experiments on peridotite with glass analyses from the Hawaii Scientific Deep Project 2 on Mauna Kea volcano, I show here that a small population of the core samples had fractionated from a peridotite-source primary magma. Most lavas, however, differentiated from magmas that were too deficient in CaO and enriched in NiO (ref. 2) to have formed from a peridotite source. For these, experiments indicate that they were produced by the melting of garnet pyroxenite, a lithology that had formed in a second stage by reaction of peridotite with partial melts of subducted oceanic crust. Samples in the Hawaiian core are therefore consistent with previous suggestions that pyroxenite occurs in a host peridotite, and both contribute to melt production. Primary magma compositions vary down the drill core, and these reveal evidence for temperature variations within the underlying mantle plume. Mauna Kea magmatism is represented in other Hawaiian volcanoes, and provides a key for a general understanding of melt production in lithologically heterogeneous mantle. ©2006 Nature Publishing Group.
502.
Petrographic studies of "fallout" suevite from outside the Bosumtwi impact structure, Ghana
Meteoritics and Planetary Science,
41
(11)
1761 – 1774
2006
ISSN: 10869379
Publisher: University of Arkansas
Keywords:▾
Africa; Ghana; Sub-Saharan Africa; West Africa; crater; crystalline rock; ejecta; fallout; impact structure; metasedimentary rock; suevite
Abstract: ▾ Field studies and a shallow drilling program carried out in 1999 provided information about thickness and distribution of suevite to the north of the Bosumtwi crater rim. Suevite occurrence there is known from an ∼1.5 km2 area; its thickness is ≤15 m. The present suevite distribution is likely the result of differential erosion and does not reflect the initial areal extent of continuous Bosumtwi ejecta deposits. Here we discuss the petrographic characteristics of drill core samples of melt-rich suevite. Macroscopic constituents of the suevites are melt bodies and crystalline and metasedimentary rock (granite, graywacke, phyllite, shale, schist, and possibly slate) clasts up to about 40 cm in size. Shock metamorphic effects in the clasts include multiple sets of planar deformation features (PDFs), diaplectic quartz and feldspar glasses, lechatelierite, and ballen quartz, besides biotite with kink bands. Basement rock clasts in the suevite represent all stages of shock metamorphism, ranging from samples without shock effects to completely shock-melted material that is indicative of shock pressures up to ∼60 GPa. © The Meteoritical Society, 2006.
501.
Paleoenvironmental record in Lake Baikal sediments: Environmental changes in the last 160 ky
Palaeogeography, Palaeoclimatology, Palaeoecology,
237
(2-4)
240 – 254
2006
ISSN: 00310182Keywords:▾
Arctic Ocean; Atlantic Ocean; Atlantic Ocean (North); Eurasia; Lake Baikal; Russian Federation; Siberia; Bacillariophyta; climate change; environmental change; fossil record; magnetic susceptibility; paleoenvironment; reflectance; sediment analysis; X-ray diffraction
Abstract: ▾ Measurement of magnetic susceptibility (MS) and diffuse reflectance spectra (DRS) were used to construct environmental proxies in a 6.5 m section of the sediment core VER98-1-13 from the Academician Ridge, Lake Baikal. The interpretation of MS and DRS was supported by X-ray diffraction and microparticle voltammetry to identify the main Fe-bearing minerals. The record of the relative paleointensity of the Earth's magnetic field was used to construct an age model showing the core interval covers the last 160 ky. The time resolution of the record was ∼1 ky. The main environmental changes were recognized by a combination of DRS and MS records and compared to marine isotopic stages in addition to the diatom record from 120 to 60 ky BP so as to demonstrate the importance of these inorganic proxies as paleoenvironmental records. A dramatic climatic deterioration between 66 and 60 ky BP was probably preceded by a dry intermediate stage between 77 and 66 ky BP. The DRS-based proxies of Fe(II) / Fe(III) ratios in the mineral assemblage, MS and/or diatom records clearly reveal 1-2 ky long environmental extremes at 110, 103, 90, 85, 77, 61, 54, 36, 27, 23, and 19 ky BP. The majority of these extremes were contemporaneous with discharges of North Atlantic and Arctic Ocean icebergs (Heinrich events) documenting a teleconnection between the North Atlantic Ocean and East Central Siberia. These sharp changes coincided with a major transition to the colder climatic stages of the last 100 ky. © 2006.
500.
Paleoclimatic variations in West Africa from a record of late Pleistocene and Holocene lake level stands of Lake Bosumtwi, Ghana
Palaeogeography, Palaeoclimatology, Palaeoecology,
242
(3-4)
287 – 302
2006
ISSN: 00310182Keywords:▾
Africa; Ashanti; Ghana; Lake Bosumtwi; Sub-Saharan Africa; West Africa; climate variation; crater lake; highstand; Holocene; ice sheet; lacustrine deposit; lake level; Last Glacial; monsoon; paleoclimate; Pleistocene; radiocarbon dating; Younger Dryas
Abstract: ▾ A detailed investigation of geomorphological evidence of paleoshorelines and exposed stratigraphic sections of lake deposits, combined with a chronology based on radiocarbon dated charcoal and in-situ 14C dating of wave polished bedrock, provide important new constraints on lake level changes of Lake Bosumtwi, Ghana. Thick sequences of laminated silts, alternating with transgressive sands and deltaic gravels, attest to a long history of climatically controlled lake level variations. The post-glacial rise in lake level began sometime after 16.3 ka, reached stable levels first at 14.5 ± 0.6 ka and then rose again after ca. 14.3 ka. A significant lake level regression spanned the interval from 12.6 ± 0.3 to 11.6 ± 0.5 ka, synchronous with the Younger Dryas. Deep lake conditions were reestablished after ca. 11 ka, at which time the lake overtopped the crater. Overflow continued until 8.8 ± 0.5 ka, when another significant but short-lived regression occurred. Deep, but probably not overflowing conditions were again reestablished by > 7.2 ± 0.3 ka and continued until around 3.2 ± 0.1 ka, when lake level dropped precipitously. Multicentury late Holocene highstands occurred at 2.2 ± 0.1 and 1.7 ± 0.2 ka, although these were significantly lower than those registered in the late glacial and early Holocene. The timing of late glacial events is similar to those recorded elsewhere in Africa and the higher latitudes, and likely reflects the dominant control of high latitude northern hemisphere conditions on the African tropics during the times of large northern hemisphere ice sheets. Mid- to late-Holocene variations appear to be less coupled with changes across Africa and elsewhere, suggesting that regional forcing may be more important during warmer periods. © 2006.
499.
Paleoclimate and human evolution workshop
Eos,
87
(16)
161
2006
ISSN: 00963941
Publisher: Blackwell Publishing Ltd
Keywords:▾
human evolution; Neogene; paleoclimate
498.
Origin of Pleistocene-Holocene ashes of the Russian northeast based on trace and rare earth element data
Doklady Earth Sciences,
411
(2)
1351-1356
2006
ISSN: 1028334X
Publisher: Maik Nauka-Interperiodica Publishing
Keywords:▾
Pleistocene-Holocene boundary; rare earth element; trace element; volcanic ash; volcanic eruption
497.
Orbital forcing of continental climate during the Pleistocene: a complete astronomically tuned climatic record from Lake Baikal, SE Siberia
Quaternary Science Reviews,
25
(23-24)
3431 – 3457
2006
ISSN: 02773791Keywords:▾
Eurasia; Lake Baikal; Russian Federation; Siberia; Astronomy; Cell culture; Correlation methods; Glaciers; Lakes; Mathematical models; Sedimentation; age determination; biogenic mineral; climate change; Holocene; insolation; magnetic reversal; orbital forcing; paleoclimate; Pleistocene; precession; proxy climate record; sedimentation rate; silica; Astronomically tuned climatic records; Biogenic silica; Pleistocene paleomagnetic reversals; Regional climate; Climate change
Abstract: ▾ A new composite BDP-96 biogenic silica record over the entire Pleistocene was generated by splicing BDP-96-1 and BDP-96-2 drill cores from Lake Baikal, crosschecked against a similar record from a nearby BDP-98 drill core. A new astronomically tuned age model is proposed based on correlating peak biogenic silica responses with the timing of September perihelia. This target is derived from analysis of regional climate proxy responses during the Holocene, the last interglacial and around paleomagnetic reversals. By resolving virtually every precessional cycle during the Pleistocene, the new age model represents a major improvement compared with previously reported Lake Baikal timescales. The astronomically tuned ages of the Pleistocene paleomagnetic reversals are consistent with published dates. The minimal tuning approach we used (precession only) has also aligned high signal power in a narrow obliquity band, confirming the strong presence of orbital forcing. There are also strong ca 100-ka scale cycles, but these are not aligned with the orbital eccentricity. Despite the location of Lake Baikal in a continental interior that is highly sensitive to insolation forcing, the tuned biogenic silica record reveals a consistent phase difference of -32° (ca 4 ka) relative to insolation in the obliquity band. An inherent lag embedded in a continental proxy record, not driven by global ice volume, is an intriguing finding. Another new observation is that long-term changes in sedimentation rates in Lake Baikal appear to be related to the amplitude of orbital forcing; both amplitudes and sedimentation rates undergo significant changes during MIS 24-MIS 19 interval corresponding to the Middle Pleistocene Transition. With potential for linking continental and marine climato-stratigraphies, the new Baikal record serves a new benchmark correlation target in continental Eurasia, as an alternative to June 65°N insolation and ODP-correlated timescales. © 2006 Elsevier Ltd. All rights reserved.
496.
On Pliocaenicus costatus (Bacillariophyceae) in Lake El’gygytgyn, East Siberia
European Journal of Phycology,
41
(2)
169-178
2006
495.
Occurrence and palaeoenvironmental significance of aromatic hydrocarbon biomarkers in Oligocene sediments from the Mallik 5L-38 Gas Hydrate Production Research Well (Canada)
Organic Geochemistry,
37
(5)
519-538
2006
ISSN: 01466380Keywords:▾
Angiosperm-gymnosperm aromatic ratio (AGAR); Aromatic diterpenoids; Climatic conditions; Gymnosperm markers, Aromatic hydrocarbons; Composition; Environmental impact; Gas chromatography; Hydration; Mass spectrometry; Sediments, Biomarkers, aromatic hydrocarbon; biomarker; geochemistry; Oligocene; paleoenvironment; sediment; vegetation, Canada; North America, Coniferophyta; Gymnospermae; Magnoliophyta
Abstract: ▾ The aromatic hydrocarbon biomarker distributions of thirty Oligocene sediment samples with different lithology (lignite, clay and sand) from the JAPEX/JNOC/GSC et al. Mallik 5L-38 Gas Hydrate Production Research Well, Canada, were analyzed using gas chromatography-mass spectrometry (GC-MS). The compositions vary with lithology, indicating a change in palaeoenvironmental conditions at the time of deposition. Aromatic diterpenoids of the abietane type are more abundant in the lignite samples than in the clay samples and represent a gymnosperm (e.g., conifer) dominated palaeovegetation. In contrast, in the clay samples aromatic triterpenoids are generally preserved as major constituents, indicating angiosperm dominated vegetation. The sand samples contain only minor amounts of aromatic terpenoids, but show a preference for diterpenoid gymnosperm markers. To recognise gymnosperm versus angiosperm dominated palaeoenvironments a new ratio, termed the angiosperm-gymnosperm aromatic ratio (AGAR), has been developed. Thus, the terpenoid distribution in the deltaic sediments provides information on the compositional changes in the plant community at the Mallik site (lignites) and the hinterland (clays) over time. Concomitantly, the changing dominance in the plant communities allows an insight into varying climatic conditions during the late Oligocene in the area. Additionally, the aromatic biomarker composition has been used to assess the level of thermal maturity of the organic matter in the Mallik samples and indicates a prevailing immature character. © 2006 Elsevier Ltd. All rights reserved.
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.