All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
228.
Fluid inclusion evidence for impact-related hydrothermal fluid and hydrocarbon migration in Creataceous sediments of the ICDP-Chicxulub drill core Yax-1
Meteoritics and Planetary Science,
39
(7)
1187-1197
2004
Abstract: ▾ Fluid inclusions studies in quartz and calcite in samples from the ICDP-Chicxulub drill core Yaxcopoil-1 (Yax-1) have revealed compelling evidence for impact-induced hydrothermal alteration. Fluid circulation through the melt breccia and the underlying sedimentary rocks was not homogeneous in time and space. The formation of euhedral quartz crystals in vugs hosted by Cretaceous limestones is related to the migration of hot (>200 °C), highly saline, metal-rich, hydrocarbon-bearing brines. Hydrocarbons present in some inclusions in quàrtz are assumed to derive from cracking of pre-impact organic matter. The center of the crater is assumed to be the source of the hot quartz-forming brines. Fluid inclusions in abundant newly-formed calcite indicate lower cyrstallization temperatures (75-100 °C). Calcite crystallization is likely related to a later stage of hydrothermal alteration. Calcite precipitated from saline fluids, most probably from formation water. Carbon and oxygen isotope compositions and REE distributions in calcites and carbonate host rocks suggest that the calcite-forming fluids have achieved close equilibrium conditions with the Cretaceous limestones. The precipitation of calcite may be related to the convection of local pore fluids, possibly triggered by impact-induced conductive heating of the sediments. © Meteoritical Society, 2004. Printed in USA.
227.
First results of the CRLN seismic network in the western Corinth Rift: Evidence for old-fault reactivation; [Premiers résultats du réseau sismique (CRLN) de la partie ouest du rift de Corinthe : Évidence de la réactivation d'une ancienne faille]
Comptes Rendus - Geoscience,
336
(4-5)
343 – 351
2004
ISSN: 16310713
Publisher: Elsevier Masson SAS
Keywords:▾
Gulf of Corinth; Ionian Sea; Mediterranean Sea; earthquake; fault slip; reactivation; rift zone; seismotectonics
Abstract: ▾ The 12 stations Corinth Rift Laboratory Seismological Network (CRLNET) aims at monitoring the seismicity (Ml>1) in the CRL area and at constraining the geometry of active structures at depth. Two years of microseismicity (2000-2001) recorded by the CRLNET in the Aigion area shows: (1) background seismicity inside the Corinth rift at depth of 4.5-11 km, deepening towards the north and no activity in the upper 4 km of the crust - this seismicity is not clearly related to major faults observed at the surface -; (2) a swarm, 6 km south of the city of Aigion, associated with the Mw=4.2, 8 April 2001 earthquake. This earthquake occurred at 6 km depth, on a SW-NE oriented fault dipping 40° to the northwest and corresponds to normal faulting with a right lateral component of slip. It likely occurred on an old structure reactivated in the present stress field. © 2003 Académie des sciences. Published by Elsevier SAS. All rights reserved.
226.
Glass in the submarine section of the HSDP2 drill core, Hilo, Hawaii
Geochemistry, Geophysics, Geosystems,
5
(7)
2004
ISSN: 15252027Abstract: ▾ The Hawaii Scientific Drilling Project recovered-3 km of basalt by coring into the flank of Mauna Kea volcano at Hilo, Hawaii. Rocks recovered from deeper than-1 km were deposited below sea level and contain considerable fresh glass. We report electron microprobe analyses of 531 glasses from the submarine section of the core, providing a high-resolution record of petrogenesis over ca. 200 Kyr of shield building of a Hawaiian volcano. Nearly all the submarine glasses are tholeiitic. SiO2 contents span a significant range but are bimodally distributed, leading to the identification of low-SiO2 and high-SiO2 magma series that encompass most samples. The two groups are also generally distinguishable using other major and minor elements and certain isotopic and incompatible trace element ratios. On the basis of distributions of high-and low-SiO2 glasses, the submarine section of the core is divided into four zones. In zone 1 (1079-1950 mbsl), most samples are degassed high-SiO2 hyaloclastites and massive lavas, but there are narrow intervals of low-SiO2 hyaloclastites. Zone 2 (-1950-2233 mbsl), a zone of degassed pillows and hyaloclastites, displays a continuous decrease in silica content from bottom to top. In zone 3 (2233-2481 mbsl), nearly all samples are undegassed low-SiO2 pillows. In zone 4 (2481-3098 mbsl), samples are mostly high-SiO2 undegassed pillows and degassed hyaloclastites. This zone also contains most of the intrusive units in the core, all of which are undegassed and most of which are low-SiO 2. Phase equilibrium data suggest that parental magmas of the low-SiO2 suite could be produced by partial melting of fertile peridotite at 30-40 kbar. Although the high-SiO2 parents could have equilibrated with harzburgite at 15-20 kbar, they could have been produced neither simply by higher degrees of melting of the sources of the low-SiO 2 parents nor by mixing of known dacitic melts of pyroxenite/eclogite with the low-SiO2 parents. Our hypothesis for the relationship between these magma types is that as the low-SiO2 magmas ascended from their sources, they interacted chemically and thermally with overlying peridotites, resulting in dissolution of orthopyroxene and clinopyroxene and precipitation of olivine, thereby generating high-SiO2 magmas. There are glasses with CaO, Al2O3, and SiO2 contents slightly elevated relative to most low-SiO2 samples; we suggest that these differences reflect involvement of pyroxene-rich lithologies in the petrogenesis of the CaO-Al2O3-enriched glasses. There is also a small group of low-SiO2 glasses distinguished by elevated K2O and CaO contents; the sources of these samples may have been enriched in slab-derived fluid/melts. Low-SiO2 glasses from the top of zone 3 (2233-2280 mbsl) are more alkaline, more fractionated, and incompatible-element-enriched relative to other glasses from zone 3. This excursion at the top of zone 3, which is abruptly overlain by more silica-rich tholeiitic magmas, is reminiscent of the end of Mauna Kea shield building higher in the core. Copyright 2004 by the American Geophysical Union.
225.
Fine-scale structure of the San Andreas fault zone and location of the SAFOD target earthquakes
Geophysical Research Letters,
31
(12)
L12S02 1-4
2004
ISSN: 00948276Keywords:▾
Data acquisition; Error analysis; Geophysics; Mathematical models; Seismology; Tomography; Velocity measurement; Earthquakes; Faulting; Geophysics; Seismology; Strike-slip faults, Epicenter; Inversion codes; Tomographic analysis, Earthquakes; Location, earthquake; microstructure; San Andreas Fault; seismic hazard; seismic tomography; velocity structure, California; North America; United States, Absolute location errors; Fine-scale structures; Inversion methods; Inversion results; Potential targets; San Andreas fault; Velocity contrasts; Velocity structure
Abstract: ▾ We present results from the tomographic analysis of seismic data from the Parkfield area using three different inversion codes. The models provide a consistent view of the complex velocity structure in the vicinity of the San Andreas, including a sharp velocity contrast across the fault. We use the inversion results to assess our confidence in the absolute location accuracy of a potential target earthquake. We derive two types of accuracy estimates, one based on a consideration of the location differences from the three inversion methods, and the other based on the absolute location accuracy of "virtual earthquakes." Location differences are on the order of 100-200 m horizontally and up to 500 m vertically. Bounds on the absolute location errors based on the "virtual earthquake" relocations are ∼ 50 m horizontally and vertically. The average of our locations places the target event epicenter within about 100 m of the SAF surface trace. Copyright 2004 by the American Geophysical Union.
224.
Seismic tomography of the lithosphere with body waves
Pure and Applied Geophysics,
160
(3-4)
717-737
2003
ISSN: 00334553
Publisher: Birkhauser Verlag AG
Keywords:▾
body wave; earthquake; lithospheric structure; seismic tomography; seismic velocity; teleseismic wave
Abstract: ▾ A pair of papers in 1976 lead-authored by Kei Aki heralded the beginning of the field of seismic tomography of the lithosphere. The 1976 paper by Aki, Christofferson, and Husebye introduced a simple and approximate yet elegant technique for using body-wave arrival times from teleseismic earthquakes to infer the three-dimensional (3-D) seismic velocity heterogeneities beneath a seismic array or network (teleseismic tomography). Similarly, a 1976 paper by Aki and Lee presented a method for inferring 3-D structure beneath a seismic network using body-wave arrival times from local earthquakes (local earthquake tomography). Following these landmark papers, many dozens of papers and numerous books have been published presenting exciting applications of and/or innovative improvements to the methods of teleseismic and local earthquake tomography, many by Aki's students. This paper presents a brief review of these two types of tomography methods, discussing some of the underlying assumptions and limitations. Thereafter some of the significant methodological developments are traced over the past two and a half decades, and some of the applications of tomography that have reaped the benefits of these developments are highlighted. One focus is on the steady improvement in structural resolution and inference power brought about by the increased number and quality of seismic stations, and in particular the value of utilizing shear waves. The paper concludes by discussing exciting new scientific projects in which seismic tomography will play a major role - the San Andreas Fault Observatory at Depth (SAFOD) and USArray, the initial components of Earthscope.
223.
Summary of recent research in Long Valley Caldera, California
Journal of Volcanology and Geothermal Research,
127
(3-4)
165-173
2003
ISSN: 03770273
Publisher: Elsevier
Keywords:▾
Earthquakes; Hydrology; Pressure effects; Seismology; Thermal effects, Hydrothermal fluids, Volcanoes, borehole; caldera; geodesy; hydrothermal system; research; volcanic earthquake; volcano, California; Long Valley Caldera; United States
Abstract: ▾ Since 1978, volcanic unrest in the form of earthquakes and ground deformation has persisted in the Long Valley caldera and adjacent parts of the Sierra Nevada. The papers in this special volume focus on periods of accelerated seismicity and deformation in 1980, 1983, 1989-1990, and 1997-1998 to delineate relations between geologic, tectonic, and hydrologic processes. The results distinguish between earthquake sequences that result from relaxation of existing stress accumulation through brittle failure and those in which brittle failure is driven by active intrusion. They also indicate that in addition to a relatively shallow (7-10-km) source beneath the resurgent dome, there exists a deeper (∼15-km) source beneath the south moat. Analysis of microgravimety and deformation data indicates that the composition of the shallower source may involve a combination of silicic magma and hydrothermal fluid. Pressure and temperature fluctuations in wells have accompanied periods of crustal unrest, and additional pressure and temperature changes accompanying ongoing geothermal power production have resulted in land subsidence. The completion in 1998 of a 3000-m-deep drill hole on the resurgent dome has provided useful information on present and past periods of circulation of water at temperatures of 100-200°C within the crystalline basement rocks that underlie the post-caldera volcanics. The well is now being converted to a permanent geophysical monitoring station. © 2003 Elsevier B.V. All rights reserved.
222.
Structural properties of rift-related normal faults: The case study of the Gulf of Corinth, Greece
Journal of Geodynamics,
36
(1-2)
275 – 303
2003
ISSN: 02643707
Publisher: Elsevier Ltd
Keywords:▾
Greece; Gulf of Corinth; deformation; faulting; neotectonics; rift zone; seismicity; tectonics
Abstract: ▾ In the frame of the Corinth Rift Laboratory project, which aims to understand the relation between stress, strain and fluid flow in an extensional context, three normal faults have been studied and sampled in the south-western sector of the Gulf of Corinth. Two of these faults (the Pirgaki and Helike faults) juxtapose carbonate pre-rift sediments and syn-rift conglomerates at outcrop, and the third (the Aigion fault) has been drilled and cored at 760 m depth. The distance between the faults is around 4 km, and the offsets are approximately 1000, 700 and 170 m, respectively. The fault damage zones and cores of the analysed faults exhibit different geometry, size and textural characteristics. In general, it has been assessed that fault cores behave as near-impermeable barriers to transverse fluid flow, whereas highly fractured damage zones act mostly as conduits for nearly along-strike flow. Different types of fault rocks are exposed along the main faults; these include cataclasite, ultra-cataclasite, fault breccia and gouge, with random or foliated fabrics. Along the Pirgaki fault zone only, fault rock micro-fabrics have been related to multiple tectonic episodes. The results of our work also emphasise that the current conditions of deformation, in this sector of the Gulf of Corinth, are responsible for the development of a system of extension fractures that is only partially sealed. These fractures mainly control the permeability structure of the analysed fault zones and furnish information on the stress field acting in the area. Furthermore, their orientation and distribution indicate that they are consistent with a deformation pattern resulting from active extension. © 2003 Elsevier Ltd. All rights reserved.
221.
Paleointensity in Hawaiian scientific drilling project hole (HSDP2): Results from submarine basaltic glass
Geochemistry, Geophysics, Geosystems,
4
(2)
2003
ISSN: 15252027
Publisher: Blackwell Publishing Ltd
Abstract: ▾ Paleointensity estimates based on the high quality Thellier-Thellier data from the early Brunhes (420-780 ka) are rare (only 30 in the published literature). The Second Hawaiian Scientific Drilling Project (HSDP2) drill hole recovered submarine volcanics spanning the approximate time period of 420-550 ka. These are of particular interest for absolute paleointensity studies owing to the abundance of fresh submarine basaltic glass, which can preserve an excellent record of ancient geomagnetic field intensity. We present here new results of Thellier-Thellier paleointensity experiments that nearly double the number of reliable paleointensity data available for the early Brunhes. We also show that the magnetizations of the associated submarine basalts are dominated by viscous magnetizations and therefore do not reflect the true ancient geomagnetic field intensity at the time of extrusion. The viscous contamination is particularly severe because of a combination of low blocking temperatures in the basalts and relatively high temperatures in the deeper parts of the drill core. Our new data, when placed on the approximate timescale available for HSDP and HSDP2, are at odds with other contemporaneous paleointensity data. The discrepancy can be reconciled by adjusting the HSDP timescales to be younger by about 35 kyr. © 2003 by the American Geophysical Union.
220.
Review of ground temperatures in the Mallik field area: A constraint to the methane hydrate stability
Bulletin of the Geological Survey of Canada
(544)
45-56
2003
ISSN: 00687626Abstract: ▾ Analysis of data from 32 industrial exploration wells in the Mallik field and surrounding area in the Mackenzie Delta-Beaufort Sea region allowed construction of temperature-depth profiles using regionalheat-flowvalues, temperature at the base ofice-bearing permafrost, and model so thermal conductivity with depth. An analysis of the stability conditions for methane hydrate showed that it is stable in the Mallik field area and that the depth to the base of the methane hydrate stability zone can be as deep as 1500±100minareas of thick permafrost.The depth to the base of the methane hydrate stabilityzone, calculated in this study using reconstructed temperature-depth profiles, was found in a majority of the wells to be 50-150 m deeper than that previously determined using linear temperature profiles and a constant thermal conductivity with depth.
219.
REE inverse modeling of HSDP2 basalts: Evidence for multiple sources in the Hawaiian plume
Geochemistry, Geophysics, Geosystems,
4
(2)
2003
ISSN: 15252027Abstract: ▾ The rare earth element (REE) concentrations of lavas from the Hawaiian Scientific Drilling Project (HSDP2) can be used to provide additional constraints on phase equilibria and the nature of the Hawaiian source. Major element analyses separate Mauna Kea lavas into two distinct populations, a high-silica and a low-silica suite. The low-silica samples can be separated stratigraphically into an upper low-silica alkalic series and a low-silica tholeiitic group that occurs deeper in the section. These contrasting groups could result from different extents of source partial fusion, or lithologically distinct source regions, or some combination of both factors. Petrologic modeling is performed to calculate that primary magma compositions contain about 20% MgO, and can be formed by 8-15% melting of a depleted mantle source for low-silica alkalic and high-silica lavas, respectively. The low-silica tholeiites could be generated by higher degrees of melting of a more fertile source. REE ratios and various isotopic systems reinforce the division of the low-SiO2 samples into the upper alkalic series, characterized by high Gd/Yb, and the deeper low-silica tholeiitic group, with low Gd/Yb. REE inverse modeling of fractionation-corrected basalts is consistent with lower degrees of melting to generate the late-stage alkalic lavas, with garnet present as a residual phase. The relatively constant Gd/Yb for low-silica tholeiites suggests that garnet is not an important residual phase during partial melting, implying higher extents of melting. The low-silica tholeiites are characterized by relatively enriched isotopic signatures that are consistent with contributions from a primitive source or from recycled subduction components. High 3He/4He associated with the lowsilica lavas could derive from primitive mantle, mass transfer from the core, or from a refractory lithospheric contribution to a recycled subduction package. However, the combination of major element, REE and isotopic data suggests that the deeper low-silica suite is sampling the relatively fertile, interior part of the Hawaiian plume, whereas the high-silica lavas are extracted from the more depleted periphery; later alkalic lavas are generated from a depleted source as the volcano moves off the hot spot. © 2003 by the American Geophysical Union.
218.
Quasi-continuous depth profiles of rock magnetization from magnetic logs in the HSDP-2 borehole, Island of Hawaii
Geochemistry, Geophysics, Geosystems,
4
(4)
2003
ISSN: 15252027Abstract: ▾ A quasi-continuous magnetic log has been obtained in the Hawaii Scientific Drilling Project 2 (HSDP-2) between 600 m and 1800 m, which corresponds to a time interval of approximately 350 ka to 480 ka. A tri-axial borehole magnetometer was employed to measure the horizontal and vertical magnetic fields. Measurements were taken in downhole and uphole runs, with a good correlation between the two. In a first step the logs were corrected for the transfer function of the employed low-pass filter and then for the logging depths. To calculate rock magnetizations from magnetic components, we used a multidisk cylindrical model for the penetrated rocks. The disk thickness corresponds with 0.1 m to the logging sampling rate. Magnetic borehole logging in the HSDP-2 hole has established the following: Massive lava flows can be distinguished from those with prevailing hyaloclastites and enables us to supplement the lithology, especially in depth intervals with poor core recovery. The inclinations of rock magnetization derived from the magnetic log agree well with those measured in core samples from HSDP-2 hole. The same applies to magnitudes of magnetizations from logging, as the sum of induced and remanent magnetizations, with laboratory determinations of the remanent magnetizations of core samples. We observe a distinct discrepancy between the local present-day geocentric axial dipole (GAD) inclination of 35.6° and the mean logging inclination of 22.7°. Furthermore, a systematic inclination decrease with depth is observed. Logging and core inclinations in HSDP-2 can be brought into agreement with core inclinations in the HSDP-1 pilot hole by shifting depths of HSDP-1 100 m downward. The correlation of inclination data between the two boreholes and the known age-depth relation of HSDP-1 is used to reexamine the "age versus depth" model curve for Mauna Kea of Sharp et al. (manuscript in preparation, 2003). We identify tentatively two logged inclination minima with excursion of the geomagnetic field in Brunhes, namely, "Levantine" at 360-370 ka and "Unknown" at 400-420 ka. © 2003 by the American Geophysical Union.
217.
The 320 kyr Pb isotope evolution of Mauna Kea lavas recorded in the HSDP-2 drill core
Geochemistry, Geophysics, Geosystems,
4
(5)
2003
ISSN: 15252027Abstract: ▾ [1] We analyzed Pb isotopic compositions of 50 samples from the HSDP-2 drill hole, covering the time interval 180 to 550 kyr B.P. in the stratigraphic record of Mauna Kea. All analyses were corrected for instrumental bias using a triple-spike technique. The aims of this study are to document temporal changes in sources contributing to Mauna Kea and to investigate how these may relate to the chemical structure of the Hawaiian plume. Lead isotopic compositions of the lavas have 206Pb/204Pb ratios ranging from 18.41 to 18.63, 207Pb/204Pb from 15.47 to 15.49, and 208Pb/ 204Pb from 37.97 to 38.22. In 207Pb/204Pb- 206Pb/204Pb space, the samples display a broad linear array, while three distinct arrays are found in 208Pb/ 204Pb-206Pb/204Pb space. These arrays can clearly be distinguished by their 208Pb/204Pb ratios and are referred to as "Kea-lo8," "Kea-mid8," and "Kea-hi8." The 206Pb/204Pb isotope ratios exhibit rapid shifts by ̃0.2 over 100 m depth intervals, and jumps from one Pb isotope array to another and back in less than ̃100 m depth. Despite these rapid Pb isotope fluctuations, a particular Pb isotope array dominates over periods of several tens to hundreds of kiloyears. We interpret the Pb isotope arrays found in HSDP-2 in terms of mixing of end-members lying along the radiogenic and unradiogenic extensions of the arrays. At the radiogenic extension the three HSDP-2 arrays converge to a common end-member. The lower extensions of the arrays diverge in three directions, each with different 208Pb/ 204Pb ratios. This topology suggests that the HSDP-2 arrays were produced by mixing of at least four end-members. The origin of these end-members was investigated using Monte Carlo simulations of a Pb isotope evolution model. The simulations suggest that the common radiogenic end-member of the three Pb isotope arrays contains material with elevated m values and has a relatively young age (<1.5 Ga). Such a signature can be plausibly interpreted in terms of the presence of recycled oceanic crust in the source. The HSDP-2 Kea-lo8, Keamid8, and Kea-hi8 Pb isotope arrays dominate over different time periods and can be related to the displacement of Mauna Kea relative to the plume center over time. The Kea-lo8 array is present between ̃180 and 370 ka and samples more peripheral parts of the plume, while the Kea-mid8 and Kea-hi8 arrays occur in the deeper parts of the core (̃370 to 550 kyr ago), when Mauna Kea was closer to the plume center. Over the time intervals when each array dominates, we derive corresponding "lengths" of materials in the source by integrating the estimated upwelling velocity across the plume. These calculations suggest Pb isotope heterogeneities of at least several tens of kilometers in vertical length within the Hawaiian plume. The Pb isotope arrays may correspond to relatively small-scale heterogeneities derived from the D″ layer in the lower mantle. © 2003 by the American Geophysical Union.
216.
Temperatures at the base of the Laurentide Ice Sheet inferred from borehole temperature data
Geophysical Research Letters,
30
(18)
CRY 3-1 - 3-4
2003
ISSN: 00948276
Publisher: American Geophysical Union
Keywords:▾
Boreholes; Glaciers; Ice; Melting; Atmospheric temperature; Glacial geology; Surface properties, Melting points; Borehole temperature; Geographic difference; Ground surface temperature; Last Glacial Maximum; Laurentide ice sheets; Surface temperatures; Temperature history; Temperature profiles, Geophysics; Ice, basal temperature; Last Glacial Maximum; Laurentide Ice Sheet; paleoclimate, North America
Abstract: ▾ We use temperature profiles from 4 deep (>1600 m) boreholes across Canada to determine ground surface temperature histories (GSTH's) through and after the Last Glacial Maximum (LGM). Inversion yields the temperature history at the base of the glacier and the surface temperature evolution after the glacial retreat. The results indicate geographic differences in basal temperature history across the Ice Sheet. During the Last Glacial Maximum, temperatures at the base of the Ice Sheet were lower in eastern Canada, at the southeastern edge of the glacier, than in central Canada, southwest of the glacier center. At all sites, basal temperatures were above the melting point of ice during and after the LGM, which may explain the highly unstable character of the Ice Sheet. The GSTH's are consistent with information on the history of the Laurentide ice sheet and provide quantitative constraints on glacier flow dynamics.
215.
Long continental records from Lake Baikal
2003
214.
The Gulf of Corinth: An active half graben?
Journal of Geodynamics,
36
(1-2)
323 – 340
2003
ISSN: 02643707
Publisher: Elsevier Ltd
Keywords:▾
Greece; Gulf of Corinth; active fault; deformation; faulting; graben; neotectonics; rift zone; tectonics
Abstract: ▾ The Gulf of Corinth is often considered as a typical example of a more or less simple half graben with major border faults to the south and a flexure of the northern shore. This paper reviews new data, especially subsurface data, from both onshore and offshore, compiled or acquired through the Corinth Rift Laboratory EEC project. This data indicate that (1) the Gulf of Corinth is bordered both north and south by active faults; (2) there is a lot of them, and not only the one bordering the Peloponnese coastline are still active; and (3) distinct opening phases may be recognized on the area. During the first phase, the depocenter was located near the northern shore, whereas during the most recent phase, and only in the centre and the eastern sector, the depocenter moved towards the southern shore. Furthermore, active tectonic, in this western sector, is characterised by a general uplift of the Peloponnese that leads to the formation of new faults, i.e. the Doumena, Aigion and Helike faults and to selective reactivation of older ones such as the Pirgaki fault. We suggest that this current tectonic phase started about 150-120 000 years ago in the Aigion area and about 350 000 years ago eastward (Corinth-city) and that it represents a third opening phase during the growth of the Gulf of Corinth. © 2003 Elsevier Ltd. All rights reserved.
213.
The heat transfer in the region of the Mauna Kea (Hawaii) - constraints from borehole temperature measurements and coupled thermo-hydraulic modeling
Tectonophysics,
371
(1-4)
23 – 40
2003
ISSN: 00401951
Publisher: Elsevier B.V.
Keywords:▾
Hawaii; Mauna Kea; United States; borehole; heat flow; heat transfer; hydraulic property; temperature gradient; thermal structure
Abstract: ▾ The objectives of this paper are an understanding of the thermal and hydraulic field because of a negative temperature gradient and cold temperatures in the 1-km-deep borehole of the Hawaiian Scientific Drilling Project (HSDP), located near the coast line. The temperature pattern is attributed to a superposition of thermal and hydraulic processes. In the deeper borehole (HSDP-2, depth 3.1 km) detailed temperature monitoring was performed. Temperature measurements reveal two different thermal regimes. The upper part is characterised by cold temperatures and a negative temperature gradient similar to those observed in the shallow pilot borehole. Below 1100 m, increasing temperatures are observed. Different processes, such as topographically driven groundwater flow, ingress of salt water and conductive heat flow are investigated by numerical modeling. A pure conductive scenario fails to match the temperature measurements, implying that both borehole sections are overprinted by advective conditions. Coupled fluid and heat flow modeling with solute transport yield results that agree with observed temperatures. The results of these simulations suggest that meteoric water flow from the mountain range controls the thermal conditions in the upper part of the borehole. Below this level, the thermal regime is additionally affected by circulation of salt water from the nearby ocean. Each of these flow systems has been observed at other locations: topographically driven fresh water at locations with pronounced topography and ingress of salt water is typical for islands or coastal areas. At Hawaii, they coincide and influence each other, resulting in a salt water interface occurring at greater depth than expected. © 2003 Elsevier B.V. All rights reserved.
212.
The hydromechanical behaviour of a fracture: An in situ experimental case study
International Journal of Rock Mechanics and Mining Sciences,
40
(7-8)
1257 – 1270
2003
ISSN: 13651609
Publisher: Elsevier BV
Keywords:▾
Elasticity; Fracture; Granite; Quarrying; Water; Hydromechanical behavior; fracture flow; hydromechanics; in situ stress; rock mechanics; stress measurement; Rock mechanics
Abstract: ▾ Relationships between flow distributions and mechanical opening in a single natural fracture are investigated in situ through field experiments, at a scale of about 1 m, in a granitic quarry. Experiments have been conducted at various injection flow-rates while the normal stress applied to the fracture was controlled by hydraulic flat jacks. Variations of the collected flow-rate (monitored through contiguous flow collectors distributed along the fracture periphery) with the injection pressure are fully reproducible. They show that the fracture opens only above a threshold pressure which increases with the externally applied stress. This threshold is non-zero with no applied flat jacks pressure which raises questions on the reliability of hydraulic jacking techniques for the measurement of the normal stress on preexisting fractures. It is shown that equivalent hydraulic aperture and mechanical opening are comparable only above a critical mean fracture opening estimated to be around 15-20 μm for the tested granite. For mean fracture openings smaller than this value, the standard time scale used for stress measurements distorts the results. It is also shown that channeling effects may control flow away from the injection hole so that the hydraulic jacking stress measurement technique may overestimate the mean normal stress acting on the fracture plane by as much as 4 MPa. It is concluded that hydraulic testing techniques for normal stress measurements should not include results from the fracture opening phase. Moreover, criteria should be established for validating results from the closing phase in order to demonstrate the absence of channelling effects. Finally, it is shown that, because of the elastic response of the rock, water injection in a fracture system decreases the interstitial pressure ahead of the increasing pressure front associated with the water flow. © 2003 Elsevier Ltd. All rights reserved.
211.
The mechanics of unrest at Long Valley caldera, California. 2. Constraining the nature of the source using geodetic and micro-gravity data
Journal of Volcanology and Geothermal Research,
127
(3-4)
219-245
2003
ISSN: 03770273
Publisher: Elsevier
Keywords:▾
Deformation; Gravitational effects; Microgravity processing, Ellipsoidal sources, Geology, caldera; geodetic datum; geometry; geostatistics; GPS; gravity; modeling; uplift, California; Long Valley Caldera; United States
Abstract: ▾ We model the source of inflation of Long Valley caldera by combining geodetic and micro-gravity data. Uplift from GPS and leveling, two-color EDM measurements, and residual gravity change determinations are used to estimate the intrusion geometry, assuming a vertical prolate ellipsoidal source. The U.S. Geological Survey occupied the Long Valley gravity network six times from 1980 to 1985. We reoccupied this network twice, in the summer of 1998 (33 stations), and the summer of 1999 (37 stations). Before gravity data can be used to estimate the density of the intrusion, they must be corrected for the effect of vertical deformation (the free-air effect) and changes in the water table. We use geostatistical techniques to interpolate uplift and water table changes at the gravity stations. The inflation source (a vertical prolate ellipsoid) is located 5.9 km beneath the resurgent dome with an aspect ratio equal to 0.475, a volume change from 1982 to 1999 of 0.136 km3 and a density of around 1700 kg/m3. A bootstrap method was employed to estimate 95% confidence bounds for the parameters of the inflation model. We obtained a range of 0.105-0.187 km3 for the volume change, and 1180-2330 kg/m3 for the density. Our results do not support hydrothermal fluid intrusion as the primary cause of unrest, and confirm the intrusion of silicic magma beneath Long Valley caldera. Failure to account for the ellipsoidal nature of the source biases the estimated source depth by 2.9 km (a 33% increase), the volume change by 0.019 km3 (a 14% increase) and the density by about 1200 kg/m3 (a 40% increase). © 2003 Elsevier B.V. All rights reserved.
210.
The suevite of drill hole Yucatàn 6 in the Chicxulub impact crater
Meteoritics and Planetary Science,
38
(9)
1299-1317
2003
Abstract: ▾ The suevite breccia of the Chicxulub impact crater, Yucatàn, Mexico, is more variable and complex in terms of composition and stratigraphy than suevites observed at other craters. Detailed studies (microscope, electron microprobe, SEM, XRF) have been carried out on a noncontinuous set of samples from the drill hole Yucatàn 6 (Y6) located 50 km SW from the center of the impact structure. Three subunits can be distinguished in the suevite: the upper unit is a fine-grained carbonate-rich suevite breccia with few shocked basement clasts, mostly altered melt fragments, and formerly melted carbonate material; the middle suevite is a coarse-grained suevite with shocked basement clasts and altered silicate melt fragments; the lower suevite unit is composed of shocked basement and melt fragments and large evaporite clasts. The matrix of the suevite is not clastic but recrystallized and composed mainly of feldspar and pyroxene. The composition of the upper members of the suevite is dominated by the sedimentary cover of the Yucatàn target rock. With depth in well Y6, the amount of carbonate decreases and the proportion of evaporite and silicate basement rocks increases significantly. Even at the thin section scale, melt phases of different chemistry can be identified, showing that no widespread homogenization of the melt took place. The melt compositions also reflect the heterogeneity of the deep Yucatàn basement. Calcite with characteristic feathery texture indicates the existence of formerly pure carbonate melt. The proportion of carbonate to evaporite clasts is less than 5:1, except in the lower suevite where large evaporite clasts are present. This proportion constrains the amount of CO2 and SOx released by the impact event.
209.
Three-dimensional crustal structure of Long Valley caldera, California, and evidence for the migration of CO2 under Mammoth Mountain
Journal of Geophysical Research: Solid Earth,
108
(3)
ESE 6-1 - 6-16
2003
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Abstract: ▾ A temporary network of 69 three-component seismic stations captured a major seismic sequence in Long Valley caldera in 1997. We performed a tomographic inversion for crustal structure beneath a 28 km × 16 km area encompassing part of the resurgent dome, the south moat, and Mammoth Mountain. Resolution of crustal structure beneath the center of the study volume was good down to ∼3 km below sea level (∼5 km below the surface). Relatively high wave speeds are associated with the Bishop Tuff and lower wave speeds characterize debris in the surrounding moat. A low-Vp/Vs anomaly extending from near the surface to ∼1 km below sea level beneath Mammoth Mountain may represent a CO2 reservoir that is supplying CO2-rich springs, venting at the surface, and killing trees. We investigated temporal variations in structure beneath Mammoth Mountain by differencing our results with tomographic images obtained using data from 1989/1990. Significant changes in both Vp and Vs were consistent with the migration of CO2 into the upper 2 km or so beneath Mammoth Mountain and its depletion in peripheral volumes that correlate with surface venting areas. Repeat tomography is capable of detecting the migration of gas beneath active silicic volcanoes and may thus provide a useful volcano monitoring tool.
208.
Trace element abundances of Mauna Kea basalt from phase 2 of the Hawaii Scientific Drilling Project: Petrogenetic implications of correlations with major element content and isotopic ratios
Geochemistry, Geophysics, Geosystems,
4
(6)
2003
ISSN: 15252027Abstract: ▾ [1] The temporal geochemical variations defined by lavas erupted throughout the growth of a single volcano provide important information for understanding how the Hawaiian plume works. The Hawaii Scientific Drilling Project (HSDP) sampled the shield of Mauna Kea volcano to a depth of 3100 meters below sea level during Phase 2 of the HSDP. Incompatible element abundance ratios, such as La/Yb, Sm/ Yb, Nb/Zr, and Ti/Zr, in conjunction with SiO2 abundance and radiogenic isotopic ratios, especially He and Pb, in the reference sample suites of the Mauna Kea portion of cores from Phases 1 and 2 of the HSDP define three distinct geochemical groups. The upper 550 m of Mauna Kea lavas in the Phase 2 core include the Postshield Group with eruption ages of ̃200 ka to <370 ka. These lavas have relatively low SiO2 content, 3He/4He and 206Pb/204Pb, and they define a trend to relatively high La/Yb, Sm/Yb, and Nb/Zr. The eruption of these lavas coincides with migration of the Mauna Kea shield off the hot spot. As a result, extent of melting decreased, melt segregation occurred at greater depth, within the garnet stability field, and a geochemically distinct component associated with the periphery of the plume was sampled. Deeper in the Phase 2 core two other geochemical groups of lava are intercalated. One group has relatively low SiO2 abundance and high Nb/Zr Ti/Zr, 3He/4He and high 208Pb/204Pb at a given 206Pb/204Pb. These are distinctive geochemical characteristics of lavas erupted at Loihi seamount. Variations in incompatible element abundance ratios (e.g., Sm/Yb versus Nb/Zr and La/Yb versus Ti/Zr) define mixing trends between these low SiO2 lavas (Loihi-type) and lavas belonging to a high SiO2 group that are the dominant lava type in the shield part of the core (Kea-type). These two groups are presumed to reflect components intrinsic to the plume. Correlations of incompatible element abundance ratios, such as La/Nb, with radiogenic isotope ratios show that Hawaiian shields contain different proportions of geochemically distinctive components. The Koolau shield contains a recycled sedimentary component that is not present in the Mauna Kea shield. The anomalously high Ba/Th in Hawaiian lavas is inferred to be a source characteristic. Ba/Th is correlated with some radiogenic isotope ratios in Kilauea and Mauna Loa lavas, but there is no correlation in Mauna Kea lavas which range in Ba/Th by a factor of 2.6. Copyright 2003 by the American Geophysical Union.
207.
[English]
Crosshole waveform tomography velocity and attenuation images of arctic gas hydrates
Volume 22
,
Page 2255-2258
Publisher
Society of Exploration Geophysicists
2003
Queen's University, Kingston, ON, Canada; GeoForschungsZentrum, Potsdam, GermanyKeywords:▾
Hydration; Petroleum prospecting; Tomography; Velocity, Attenuation factors; High resolution; Hydrate bearing sediments; Large-scale research; Quantitative images; Wave forms, Gas hydrates
206.
[English]
Operation overview of the 2002 mallik gas hydrate production research well program at the Mackenzie delta in the Canadian arctic
Volume 2003-May
,
Page 563-572
Publisher
Offshore Technology Conference
2003
Japan Petroleum Exploration Co., Ltd, Brazil; Japan National Oil Corporation, Brazil; Canadian Petroleum Engineering Inc., BrazilDOI:10.4043/15124-ms
Keywords:▾
Gas hydrates; Gas industry; Gasoline; Hydration; Offshore oil well production; Offshore oil wells; Offshore technology; Oil well logging; Well testing, Gas-hydrate production; Geological Survey of Canada; Japan national oil corporations; Operational management; Petroleum exploration; Reservoir simulation model; Scientific experiments; Thermal stimulation tests, Software testing
ISBN:
9781555632502
205.
Open fissure mineralization at 2600 m depth in Long Valley Exploratory Well (California) – insight into the history of the hydrothermal system
Journal of Volcanology and Geothermal Research,
127
(3)
347-363
2003
ISSN: 0377-0273Keywords:▾
Long Valley Caldera, hydrothermal system, thermal history, fluid inclusions, quartz crystallization, open fissures
Abstract: ▾ Long Valley Exploratory Well, drilled into the Resurgent Dome at Long Valley Caldera (California) to explore the potential of geothermal power in an active magmatic system, achieved temperatures of only ca. 100°C at 2500–3000 m depth, well below the range expected atop an active magma chamber. Open fissures encountered at 2600 m depth are coated by mm-sized idiomorphic quartz crystals with first- and second-order growth discontinuities. Specific growth defects indicating rapid crystallization reflect sudden changes in SiO2 supersaturation. Fluid inclusions contain low salinity (0–5 wt% NaCl) and low CO2 (<3 mole%) aqueous fluids, with V–L homogenization temperatures of 300–350°C, indicating trapping at more than 200°C above the ambient temperatures measured within the borehole today. Fluid composition and inclusion density varies between and within the growth zones, reflecting progressive changes in the hydrothermal system during crystallization. Episodic crystallization from supersaturated fluids is interpreted to reflect sudden changes in the convection pattern, presumably induced by seismic activity, with a more recent and dramatic reorganization resulting in convective cooling. The quartz crystals are sensitive recorders of the earlier higher temperature history, unaffected by the present-day situation.
204.
Oxygen isotope geochemistry of the second HSDP core
Geochemistry, Geophysics, Geosystems,
4
(8)
2003
ISSN: 15252027Abstract: ▾ Oxygen isotope ratios were measured in olivine phenocrysts (̃1 mm diameter), olivine microphenocrysts (generally ̃100-200 mm diameter), glass, and/or matrix from 89 samples collected from depths down to 3079.7 m in the second, and main, HSDP core (HSDP-2). Olivine phenocrysts from 11 samples from Mauna Loa and 34 samples from the submarine section of Mauna Kea volcano have δ18O values that are similar to one another (5.11 ± 0.10%, 1s, for Mauna Loa; 5.01 ± 0.07%, for submarine Mauna Kea) and within the range of values typical of olivines from oceanic basalts (δ18O of ̃5.0 to 5.2%). In contrast, δ18O values of olivine phenocrysts from 20 samples taken from the subaerial section of Mauna Kea volcano (278 to 1037 mbsl) average 4.79 ± 0.13%. Microphenocrysts in both the subaerial (n = 2) and submarine (n = 24) sections of Mauna Kea are on averagẽ0.2% lower in δ18O than phenocrysts within the same stratigraphic interval; those in submarine Mauna Kea lavas have an average δ18O of 4.83 ± 0.11%. Microphenocrysts in submarine Mauna Kea lavas and phencrysts in Mauna Loa lavas are the only population of olivines considered in this study that are typically in oxygen isotope exchange equilibrium with coexisting glass or groundmass. These data confirm the previous observation that the stratigraphic boundary between Mauna Loa and Mauna Kea lavas defines a shift from "normal" to unusually low δ18O values. Significantly, they also document that the distinctive 18O-depleted character of subaerial Mauna Kea lavas is absent in phenocrysts of submarine Mauna Kea lavas. Several lines of evidence suggest that little if any of the observed variations in δ18O can be attributed to subsolidus alteration or equilibrium fractionations accompanying partial melting or crystallization. Instead, they reflect variable proportions of an 18O-depleted source component or contaminant from the lithosphere and/or volcanic edifice that is absent in or only a trace constituent of subaerial Mauna Loa lavas, a minor component of submarine Mauna Kea lavas, and a major component of subaerial Mauna Kea lavas. Relationships between the δ18O of phenocrysts, microphenocrysts, and glass or groundmass indicate that this component (when present) was added over the course of crystallization-differentiation. This process must have taken place in the lithosphere and most likely at depths of between ̃5 and 15 km. We conclude that the low-δ18O component is either a contaminant from the volcanic edifice that was sampled in increasingly greater proportions as the volcano drifted off the center of the Hawaiian plume or a partial melt of low-δ18O, hydrothermally altered perdotites in the shallow Pacific lithosphere that increasingly contributed to Mauna Kea lavas near end of the volcano's shield building stage. The first of these alternatives is favored by the difference in δ18O between subaerial and submarine Mauna Kea lavas, whereas the second is favored by systematic differences in radiogenic and trace element composition between higher and lower δ18O lavas. Copyright 2003 by the American Geophysical Union.