All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
769.
Fabric kinematics of the ultrahigh-pressure metamorphic rocks from the main borehole of the Chinese Continental Scientific Drilling Project: Implications for continental subduction and exhumation
Tectonophysics,
475
(2)
235 – 250
2009
ISSN: 00401951Keywords:▾
Asia; China; Eurasia; Far East; Sulu Belt; Yangtze Platform; Drilling; Electron diffraction; Garnets; Housing; Kinematics; Metal vapor lamps; Mica; Olivine; Oxide minerals; Quartz; Rocks; Shear deformation; Silicate minerals; Spontaneous emission; Structural design; Structural geology; Tectonics; X ray powder diffraction; Ar dating; Continental subduction; Exhumation; Lattice-preferred orientation; Sulu terrane; amphibolite; asymmetry; borehole geophysics; Chinese Continental Scientific Drilling Project; deformation; dip-slip fault; eclogite; exhumation; gneiss; kinematics; lineation; petrofabric; preferred orientation; regional metamorphism; retrograde metamorphism; shear zone; subduction; tectonic evolution; tectonic setting; ultrahigh pressure metamorphism; ultramafic rock; Metamorphic rocks
Abstract: ▾ The 5158-m-deep main borehole of the Chinese Continental Scientific Drilling Project (CCSD-MH) penetrated granitic gneisses, paragneisses, eclogites, retrograde eclogites, amphibolites and ultramafic rocks in the Sulu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. The CCSD-MH consists of four petro-structural units separated by three SE-dipping ductile shear zones DFa (835-1280 m), DFb (2010-2280 m) and DFc (2920-3225 m), which are correspondent with the regional shear zones in the northern Sulu UHP supracrustal zone. Using the electron backscatter diffraction (EBSD) technique, we investigated the lattice-preferred orientations (LPOs) of omphacite, diopside and quartz in core samples from the CCSD-MH. Omphacite from eclogites and diopside from garnet pyroxenites display very strong LPOs, which are characterized by the maximum concentration of [001]-axes parallel to the lineation and (010)-poles normal to the foliation. Quartz in para- and granitic mylonites/gneisses from the shear zones DFa, DFb and DFc developed multiple slip systems. 40Ar/39Ar dating of biotite in para- and granitic gneisses from the CCSD-MH yields 223-202 Ma, which constrains the formation ages of the quartz high-temperature prism slip systems {m}<a> and {m}[c]. The asymmetric LPOs of omphacite, diopside, olivine and quartz with respect to the structural frame reveal three deformation phases in the Sulu terrane. In the Middle Triassic, the northward subduction of the Yangtze plate to depths > 100 km produced a top-to-the-south shear sense in LPOs of omphacite, diopside and olivine, and a nearly N-S-striking foliation and a subhorizontal N-S-trending lineation in eclogites and ultramafic rocks. In the Late Triassic, the UHP rocks were exhumed to the lower crust and quartz developed high-temperature slip systems with a top-to-the-NW shear sense, which is consistent with the regional SE-dipping foliation and SE-plunging lineation in the ductile shear zones. In the Cretaceous the UHP rocks were exhumed to the middle crust when the migmatization and granitic intrusion formed a NE-striking antiform structure. As a result, the activation of quartz low-temperature basal slip (0001)<a> is characterized by a top-to-the-SE shear sense in the south, but a top-to-the-NW shear sense in the north. © 2009 Elsevier B.V. All rights reserved.
768.
San Andreas Fault damage at SAFOD viewed with fault-guided waves
Geophysical Research Letters,
35
(8)
2008
ISSN: 00948276Keywords:▾
Seismology; Waveguides, American Geophysical Union; Bore hole; Fault zones; Finite difference (FD); Guided waves; Low velocities; Parkfield; San Andreas Fault (SAF); Surface array; Travel time, Guided electromagnetic wave propagation, fault zone; finite difference method; San Andreas Fault; seismic data; seismic wave; seismograph; three-dimensional modeling; wave velocity, California; North America; Parkfield; United States
Abstract: ▾ Highly damaged rocks within the San Andreas fault zone at Parkfield form a low-velocity waveguide for seismic waves, giving rise to fault-guided waves. Prominent fault-guided waves have been observed at the San Andreas Fault Observatory at Depth (SAFOD) site, including a surface array across the fault zone and a borehole seismograph placed in the SAFOD well at a depth of ∼2.7 km below ground. The resulting observations are modeled here using 3-D finite-difference methods. To fit the amplitude, frequency, and travel-time characteristics of the data, the models require a downward tapering, 30-40-m wide faultcore embedded in a 100-200-m wide jacket. Compared with the intact wall rocks, the core velocities are reduced by ∼40% and jacket velocities by ∼25%. Based on the depths of earthquakes generating guided waves, we estimate that the low-velocity waveguide along the fault at SAFOD extends at least to depths of ∼7 km, more than twice the depth reported in pervious studies. Copyright 2008 by the American Geophysical Union.
767.
Reply to 'Chicxulub impact predates K-T boundary: New evidence from Brazos, Texas' Comment by Schulte et al.
Earth and Planetary Science Letters,
269
(3-4)
621-629
2008
766.
Response to comment on "Determining chondritic impactor size from the marine osmium isotope record"
Science,
321
(5893)
1158b
2008
Abstract: ▾ Morgan argues that excursions in the marine Os record are of little value for estimating impactor size. This claim is based on computer simulations of the formation of the Chicxulub crater and distribution of the ejecta, which are difficult to validate. More important, by narrowly focusing on the Cretaceous-Tertiary event Morgan's comment misses the broader implications of our study.
765.
Role of crustal fluids in triggering the West Bohemia/Vogtland earthquake swarms: Just what we know (a review)
Studia Geophysica et Geodaetica,
52
(4)
455 – 478
2008
ISSN: 00393169Keywords:▾
aftershock; crustal structure; earthquake epicenter; earthquake swarm; fluid; fluid injection; pore pressure; seismic source; seismicity; trigger mechanism
Abstract: ▾ We summarise the results of seismological studies related to triggering mechanisms, driving forces and source processes of the West Bohemia/ Vogtland earthquake swarms with the aim to disclose the role of crustal fluids in the preparation, triggering and governing of the swarms. We present basic characteristics distinguishing earthquake swarms from tectonic mainshock-aftershock sequences and introduce existing earthquakes swarm models. From the statistical characteristics and time-space distribution of the foci we infer that self-organization is a peculiarity of West Bohemia/Vogtland swarms. We discuss possible causes of the foci migration in these swarms from the viewpoint of co-seismic and/or post-seismic stress changes and diffusion of the pressurized fluids, and we summarize hitherto published models of triggering the 2000-swarm. Attention is paid to the source mechanisms, particularly to their non-shear components. We consider possible causes of different source mechanisms of the 1997-and 2000-swarms and infer that pure shear processes controlled solely by the regional tectonic stress prevail in them, and that additional tensile forces may appear only at unfavourably oriented faults. On data from the fluid injection experiment at the HDR site Soultz (Alsace), we also show that earthquakes triggered by fluids can represent purely shear processes. Thus we conclude that increased pore pressure of crustal fluids in the region plays a key role in bringing the faults from the subcritical to critical state. The swarm activities are mainly driven by stress changes due to co-seismic and post-seismic slips, which considerably depend on the frictional conditions at the fault; crustal fluids keep the fault in a critical state. An open question still remains the cause of the repeatedly observed almost simultaneous occurrence of seismic activity in different focal zones in a wider area of West Bohemia/Vogtland. The analysis of the space-time relations of seismicity in the area between 1991 and 2007 revealed that during a significant part of this time span the seismicity was switching among distant focal zones. This indicates a common triggering force which might be the effect of an increase of crustal-fluid pore-pressure affecting a wider epicentral region. © Institute of Geophysics of the ASCR, v.v.i 2008.
764.
Seismicity and seismotectonics of West Saxony, Germany - New insights from recent seismicity observed with the Saxonian seismic network
Studia Geophysica et Geodaetica,
52
(4)
479 – 492
2008
ISSN: 00393169Keywords:▾
Central Europe; Eurasia; Europe; Germany; Saxony; earthquake epicenter; earthquake hypocenter; fault zone; seismicity; seismotectonics; source parameters; strike-slip fault
Abstract: ▾ A new network of permanently recording seismic stations in West Saxony has considerably improved detection threshold, location accuracy and depth determination in this seismically active region. Between 2001 and 2007 more than 900 events have been located. Seismicity mainly occurred along a band stretching north-south between Leipzig and Vogtland/NW Bohemia area with local magnitudes ranging between 0.8 and 2.8. Seismicity clearly delineates the Leipzig-Regensburg (L-R) fault zone striking N-S, and the Gera-Jachymov (G-J) fault zone striking roughly NNW-SSE. The hypocentral depths can be divided into two depth ranges, one at depths below 10 km, and a second at less than 10 km depth that only extends S-N from the Vogtland until the crossing between L-R and G-J fault zones. A small earthquake sequence that occurred near Werdau/ Zwickau in August 2006 at almost the same epicenters as an earlier sequence 1997/98 seems to confirm this finding: a relative localization of 15 events with the double-difference technique clearly reveals two distinct subclusters at about 6 and 12-14 km depth. With the improved station coverage 33 new fault plane solutions from events along the L-R fault zone north of the swarmquake area could be determined from P-polarities and P/S ratios. They do not differ significantly from solutions in the Vogtland/NW-Bohemia area and are mostly compatible with a N-S oriented fault plane. Strike slip mechanisms with or without a dip slip component dominate. © Institute of Geophysics of the ASCR, v.v.i 2008.
763.
Scientific drilling of the terrestrial Cretaceous Songliao Basin
Scientific Drilling
(6)
60-61
2008
ISSN: 18168957762.
Sedimentary cycles of the Cretaceous Quantou - Nenjiang formations and Milankovitch cycles of the south hole of the SLCORE-I in the Songliao basin
Acta Geologica Sinica (English Edition),
82
(1)
55 – 64
2008
761.
Sequence stratigraphy and inferred relative sea-level change from the onshore British Jurassic
Proceedings of the Geologists' Association,
119
(1)
19 – 34
2008
ISSN: 00167878
Publisher: Geological Society of London
Keywords:▾
Eurasia; Europe; United Kingdom; Western Europe; Ammonoidea; depositional sequence; facies; Jurassic; sea level change; sequence stratigraphy
Abstract: ▾ Sequence stratigraphy - the subdivision of successions into facies packages bounded by surfaces representing major shifts in depositional environment - has provided a systematic methodology for inference of relative sea-level change from vertical facies successions. In the present review, sequence stratigraphic work on exposures of British Jurassic successions is summarized. Resultant inferred relative sea-level curves for Early Jurassic and early Mid Jurassic successions show some strong similarities at the scale of ammonite zones between widely separated basins, implying sea-level change of at least regional extent or, alternatively, regionally co-ordinated changes in sediment supply. Also well developed are coeval stage-level influxes of sandy sediments into widely separated marine basins during the Late Pliensbachian, Late Toarcian-Aalenian and Oxfordian. Similarly, widespread synchronous shifts to more offshore facies are evident in the Early Pliensbachian, Early Toarcian, Early Callovian and Early Kimmeridgian. © 2008 Geologists' Association.
760.
Seismotectonic setting at the North Anatolian Fault Zone after the 1999 Mw=7.4 Izmit earthquake based on high-resolution aftershock locations
Advances in Geosciences,
1485-92
2008
ISSN: 16807340
Publisher: European Geosciences Union
Keywords:▾
aftershock; coseismic process; earthquake event; fault zone; faulting; Kocaeli earthquake 1999; seismotectonics; tectonic setting; triple junction, Anatolia; Duzce; Eurasia; Kocaeli [Turkey]; Turkey
Abstract: ▾ The most recent devastating earthquakes that occurred along the North Anatolian Fault Zone (NAFZ) in northwestern Turkey were the 1999 Izmit (Mw=7.4) and Düzce (Mw=7.1) events. In this study we present a catalog of Izmit aftershock hypocenters that was deduced from a network covering the entire 140 km long rupture of the mainshock. 7348 events with a location accuracy better than 5 km are analysed. Aftershocks were observed along the entire ruptured segment along a 20 km wide band of activity. Events are clustered in distinct regions and dominantly occur at 5 to 15 km depth. The eastern termination of the Izmit rupture is characterized by a sharp and steeply dipping boundary exactly where the Düzce mainshock initiated 87 days after the Izmit event. Relocation of the events using double-difference technology results in 4696 high-resolution hypocenters that allow resolving the internal structure of the seismically active areas with a resolution of 300 m (horizontal) and 400m (vertical). Below the Akyazi Plain, representing a small pull-apart structure at a triple junction of the NAFZ, we identify planes of activity that can be correlated with nodal planes of EW extensional normal faulting aftershocks. Along the easternmost Karadere-Düzce segment we identify the down-dip extension of the Karadere fault that hosted about 1 m of right-lateral coseismic slip. At the easternmost rupture we correlate a cloud-type distribution of seismic activity with the largest aftershocks in this area, a subevent of the Izmit mainshock and the Düzce mainshock that all have an almost identical focal mechanism. This part of the NAFZ is interpreted as a classical example of a seismic barrier along the fault.
759.
Raw pollen data from piston core CON01-605-3 (Vydrino)
758.
Real-time drill mud gas logging at the USDP-4 drilling, Unzen volcano, Japan
Journal of Volcanology and Geothermal Research,
175
(1-2)
28-34
2008
ISSN: 03770273Keywords:▾
Dissolution; Drilling; Drills; Gas detectors; Gases; Landforms; Mud logging; Volcanoes; Well drilling, conduit drilling; continuous gas monitoring; Drill holes; Drill strings; Fractured rocks; Gas compositions; Gas monitoring; Gas-phase; He isotopes; Mud circulation; Unzen; USDP-4, Natural gas well drilling, cooling; degassing; drilling; helium isotope; hydrothermal alteration; hydrothermal fluid; mineral alteration; real time; volcanic eruption; well logging, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano
Abstract: ▾ During the Unzen conduit drilling project USDP-4, the gas phase dissolved in the drill mud was continuously analyzed. Starting from the volcano's north flank an almost complete gas profile was achieved to the final depth of 1995.75 m in July 2004. Limitations were given due to the extremely difficult drilling conditions. The highly fractured rock formation led to loss of drill mud circulation in the shallow parts of the drill hole. Significant fluid inflow horizons did not occur above 800 m (drill string length). Starting from that depth on, invading fluids were detected with the real-time gas monitoring system. Major variations in the mud gas composition occurred only below a depth of 1000 m. Of major importance are fluid inflow zones with high 3He/4He at depths of 1555 m (7.3 RA), 1755.5 m (7.48 RA) and 1977.4 m (6.21 RA). These values indicate a significant influence of fluids with mantle signature. Furthermore, enhanced methane, radon and helium concentrations were also detected at specific depth. These detected major fluid- and gas inflow horizons may be able to explain magmatic degassing processes, related to the Unzen's eruption mechanism. This is generally true for the main fluid inflow zones and especially for the detected inflows at 1555 m, 1755.5 m and 1977.4 m. Furthermore, a correlation between lithology and gas composition was observed. Higher H2S concentrations were detected while drilling in pyrite-rich rocks. Cracks and fissures as well as lithological changes are often correlated with increasing amounts of gas. Trends with depth, from a minor to a more magmatic influenced regime were observed together with a change in hydrothermal alteration of the surrounding rock. This corresponds with the magmatic conduit zone which was penetrated at a depth of 1600 m, and supports the model of a high influence of hydrothermal fluid, accelerating cooling and mineral alteration. © 2008 Elsevier B.V. All rights reserved.
757.
Pliocaenicus seczkinae sp. nov., from lake el'gygytgyn in chukotka (Ne Russia)
Diatom Research,
23
(1)
171-184
2008
ISSN: 0269249XKeywords:▾
diatom; morphology; phytoplankton; taxonomy, Chukchi; Elgygytgyn Lake; Eurasia; Russian Federation, Pliocaenicus; Pliocaenicus costatus
Abstract: ▾ Pliocaenicus seczkinae Stachura-Suchoples, Genkal & Khursevich, sp. nov. was described from the phytoplankton samples and surface bottom deposits of Lake El'gygytgyn located in central Chukotka, NE Russia. The species is distinguished from the nominate variety of P. costatus mainly by the different structure of the valve face fultoportulae, which open externally with distinct short tubes and are flanked by two satellite pores. The tubes are located in small depressions within the radial rows of areolae. These observations have important implications for the entire genus, as up until now all known Pliocaenicus species had external fultoportulae openings lacking tubuli. Pliocaenicus seczkinae is the second known species of the genus Pliocaenicus to be found in modern populations. © 2008 Taylor & Francis Group, LLC.
756.
Raw pollen data from kasten core CON01-605-5 (Vydrino)
755.
Raw pollen data from kasten core CON01-603-5 part1 (counts)
754.
Raw pollen data from kasten core CON01-603-5 part1
753.
Rapid eclogitisation of the Dabie-Sulu UHP terrane: Constraints from Lu-Hf garnet geochronology
Earth and Planetary Science Letters,
273
(1-2)
203 – 213
2008
ISSN: 0012821XKeywords:▾
Asia; China; Dabie-Sulu Belt; Eurasia; Far East; Chemical elements; Garnets; Geochronology; Hafnium; History; Land use; Lead alloys; Lutetium; Metamorphic rocks; Mineralogy; Minerals; Mining; Neodymium; Silica; Trace elements; Zircon; Chemical compositions; Dry conditions; Eastern China; eclogite; Eclogites; eclogitisation; Genetic relationships; HF systems; High-precision; Lu-Hf geochronology; Major elements; Mineral growth; Orogenic belts; Porphyroblasts; Re-equilibration; Regional distribution; Regional scales; Short time; Sm-Nd geochronology; Subsequent cooling; Temperature conditions; U-Pb dating; U-Pb zircon; UHP metamorphism; ultrahigh-pressure; chemical composition; eclogite; garnet; geochronology; hafnium; lutetium; orogenic belt; P-T-t path; terrane; ultrahigh pressure metamorphism; Silicate minerals
Abstract: ▾ The Qinling-Dabie-Sulu orogenic belt in eastern China is one of the largest ultrahigh-pressure (UHP) terranes worldwide. Mineral Sm-Nd- and zircon U-Pb dating has been widely used to reveal the metamorphic history of this collisional orogen. However, the exact timing of the UHP metamorphic event(s) remains controversial and ages ranging from 245 Ma to 220 Ma have been suggested. We present high precision garnet-cpx Lu-Hf ages for six eclogites from the Dabie and Sulu areas. All ages fall in a narrow range between 219.6 and 224.4 Ma. Five samples define a mean age of 223.0 ± 0.9 Ma and one sample yields a slightly younger age of 219.6 ± 1.4 Ma. This very tight age range is particularly remarkable considering the large regional distribution of sample localities (on the order of 100 km at the time of UHP metamorphism) and the wide variety of garnet and eclogite chemical compositions represented. Two samples yield Sm-Nd ages that are indistinguishable from their Lu-Hf ages, albeit with larger uncertainties. The identical ages of eclogites from both the Dabie and the Sulu region emphasize their close genetic relationship and similar metamorphic histories. The Lu-Hf results appear to date a punctuated event of garnet growth. Alternatively, the Lu-Hf garnet ages may represent the onset of rapid, contemporaneous uplift and subsequent cooling. However, trace element zoning of Lu and Hf is still preserved in garnet porphyroblasts, even in those with a homogeneous major element distribution. Thus, complete re-equilibration of the Lu-Hf system during peak-temperature conditions probably did not occur. The garnet forming event can be placed toward the final stage of the UHP metamorphism, in agreement with some published U-Pb zircon ages. A possible trigger for this short-lived and widespread mineral growth episode may have been a fluid that became available at that stage of the metamorphic history. Although HREE-depleted patterns of older zircon grains may indicate the presence of an older generation of garnet, complete eclogitisation may have been inhibited during the major part of the prograde P-T path due to dry conditions during most of the UHP metamorphism. The uniform Lu-Hf (and Sm-Nd) ages of all investigated Dabie and Sulu eclogites suggest that garnet growth and thus possibly fluid availability were limited to a short time interval over a remarkably large regional scale. © 2008 Elsevier B.V. All rights reserved.
752.
PDF orientations in shocked quartz grains around the Chicxulub crater
Meteoritics and Planetary Science,
43
(4)
745-760
2008
Abstract: ▾ We measured 852 sets of planar deformation features (PDFs) in shocked quartz grains in impactite samples of the Yaxcopoil (YAX-1) core and from 4 Cretaceous/Tertiary (K/T) boundary deposits: the Monaca, the Cacarajícara, and the Peñalver formations in Cuba, and DSDP site 536, within 800 km of the Chicxulub crater, in order to investigate variations of PDF orientations in the proximity of the crater. Orientations of PDFs show a broad distribution with peaks at ω {1013}, π {1012}, and ξ {1112}, plus r, z {1011} orientations with minor c(0001), s{1121}, t{2241} plus x{5161}, and m{1010} plus a{1120} orientations. Planar deformation features with c(0001) orientation are relatively more abundant in the proximity of the Chicxulub crater than in distal sites such as North America, the Pacific Ocean, and Europe. This feature indicates that in the proximity of the crater, part of the shocked quartz grains in the K/T boundary deposits were derived from the low shock pressure zones. Moreover, the orientations of PDFs with ξ {1122} plus r, z {1011} are high in our studied sites, and frequencies of these orientations decrease with increasing distance from the crater. On the other hand, absence of c(0001) and the rare occurrence of PDFs with ξ {1122} plus r, z {1011} orientations in the sample from the YAX-1 core that was taken at the top of the impactite layer of the Chicxulub crater suggests that the sampling horizon that reflects a certain cratering stage is also an important factor for variations in shocked quartz. © The Meteoritical Society, 2008.
751.
Preliminary achievement of the Chinese Cretaceous continental scientific drilling project-SK-I
Acta Geologica Sinica (English Edition),
82
(1)
9-20
2008
ISSN: 10009515
Publisher: Science Press
Abstract: ▾ To obtain the global environmental and climatic records is going to be the aim of the international scientific drilling projects. As a paradigm of greenhouse climate in the geological history, the Cretaceous provides significant records of the global climate changes under the condition of greenhouse climate. But currently, the international scientific drilling programs on the Cretaceous have been focusing on marine sediments; in contrast, no terrestrial records have been recovered by any scientific program. Newly completed SK I and SK II drilling located at the northern part of the Songliao Basin are supposed to be an important breakthrough in this domain. After more than one year effort, the drilling project has been finished, and 2485.89 in of the cores have been obtained, with a high recovery ratio of 96.46%, and that is the longest and continuous Cretaceous terrestrial core all over the world. A number of important investigations and achievement on the cores from SK I and SK II have been carried out. One of the most significant contributions of this program is to get records with a resolution of ten thousand year by the centimeter-grade sampling and analysis, instead of the traditional records on million years of timescale, and hopefully, its research can provide an important reference to solve currently global warming. Combined with raw data and upcoming results for the core, an integrated accomplishment of the scientific can be made in ten profiles such as biostratigraphy, chemostratigraphy, magnetostratigraphy and geomicrobiology and so on. The preliminary progress has been achieved on sedimentology, organic geochemistry, cyclostratigraphy, paleolimnology, geomicrobiology and reconstruction of Pco'2. All the cores will be preserved in professional storeroom after being cut for our researches, and scientists all over the world are highly welcome. The follow-up the SK II drilling program has also been selected as one of the candidate programs of ICDP (International Continental Drilling Project).
750.
Post-impact carbonate deposition in the Chicxulub impact crater region, Yucatan Platform, Mexico
Current Science,
95
(2)
248-252
2008
Abstract: ▾ The Chicxulub crater has attracted considerable attention as one of the largest terrestrial impact structures and its association with the Cretaceous/Palaeogene boundary. Analyses of stable isotopes and magnetostratigraphic results for the Paleocene carbonate sequence in the Santa Elena borehole are used to investigate the post-impact sequence and estimate the age of basal sediments in the southern crater sector. Studies of impact ejecta and cover sediments and modelling of post-impact processes suggest erosion effects due to seawater back surge, block slumping and partial rim collapse of post-impact crater modification. Correlation of stable isotope patterns with the global pattern for marine carbonate sediments provides a stratigraphic framework for the basal Paleocene carbonates. Magnetic polarity constrains correlation of stable isotope variations with the reference Cenozoic isotopic data suggest that the first 17 m above the breccia-carbonate contact represents about 2.5 Ma. The stable isotope data suggest a gap of less than 0.1 Ma, whereas the magnetic polarity data (absence of reverse-polarity samples above impact breccia contact) suggest a gap up to 0.25 Ma.
749.
Post 2000-swarm microearthquake activity in the principal focal zone of West Bohemia/Vogtland: Space-time distribution and waveform similarity analysis
Studia Geophysica et Geodaetica,
52
(4)
493 – 512
2008
ISSN: 00393169
Publisher: Springer New York
Keywords:▾
earthquake hypocenter; earthquake swarm; microearthquake; seismic migration; seismicity; strike-slip fault; waveform analysis
Abstract: ▾ We present the pattern of seismic activity in the period between 2001 and 2007 for the Novä Kostel focal zone, which is recently the most active zone of the West-Bohemia/Vogtland earthquake swarm region. While the year 2001 was characterized by dying out of the 2000-swarm activity in the form of a few microswarms, almost no seismicity occurred in the period between 2002 and 2003. Since 2004 an elevated seismic activity occurs in the form of repeating microearthquake swarms. We used a relative location method to relate the hypocenter positions of the post-swarm activity to the geometry of the 2000-swarm cluster. We found that the activity has concentrated in several clusters, which have been repeatedly activated. Some clusters coincide with the position of the previous activity; the others have activated so far inactive deep segments at the southern edge of the Novä Kostel fault. Besides the shift of the hypocenters to the edges of the previously active area we observe a southward migration of the activity and an increase of maximum depths of earthquakes from 10 to 13 km. The waveform similarity analysis disclosed that some fault patches consist of only a single, repeatedly activated fault plane, while the others consist of multiple, differently oriented fault planes activated almost simultaneously. Most of the focal mechanisms are consistent with the geometry of hypocenters showing NNW-SSE trending steep fault planes with left-lateral strike-slip mechanisms and varying dip-slip component. © Institute of Geophysics of the ASCR, v.v.i 2008.
748.
Physical rock properties in and around a conduit zone by well-logging in the Unzen Scientific Drilling Project, Japan
Journal of Volcanology and Geothermal Research,
175
(1-2)
13-19
2008
ISSN: 03770273Keywords:▾
Acoustic logging; Acoustic wave velocity; Degassing; Drilling; Forestry; Gamma rays; Harvesting; Human computer interaction; Hydraulic structures; Levees; Lithology; Logging (forestry); Neutron logging; Oil well logging; Porosity; Rock drilling; Rocks; Scale (deposits); Spontaneous potential logging; Structural geology, Alternating layers; Conduit structure; Data support; High porosity; Log data; Low resistivity; Magma ascent; Neutron porosity; P-wave velocities; Physical Properties; Pyroclastic rocks; Rock properties; Scale formation; Scientific drilling; Spontaneous potential; Unzen volcano; Wave velocities; Well logging, Well drilling, degassing; drilling; lava; lithology; magma; permeability; rock property; volcanic eruption; wave velocity; well logging, Corrosion; Degassing; Deposits; Drilling; Hydraulic Structures; Logging; Porosity; Velocity, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano
Abstract: ▾ The objective of the Unzen Scientific Drilling Project (USDP) is not only to reveal the structure and eruption history of the Unzen volcano but also to clarify the ascent and degassing mechanisms of the magma conduit. Conduit drilling (USDP-4) was conducted in 2004, which targeted the magma conduit for the 1990-95 eruption. The total drilled length of USDP-4 was 1995.75 m. Geophysical well logging, including resistivity, gamma-ray, spontaneous potential, sonic-wave velocity, density, neutron porosity, and Fullbore Formation MicroImager (FMI), was conducted at each drilling stage. Variations in the physical properties of the rocks were revealed by the well-log data, which correlated with not only large-scale formation boundaries but also small-scale changes in lithology. Such variations were evident in the lava dike, pyroclastic rocks, and breccias over depth intervals ranging from 1 to 40 m. These data support previous models for structure of the lava conduit, in that they indicate the existence of alternating layers of high-resistivity and high P-wave velocity rocks corresponding to the lava dikes, in proximity to narrower zones exhibiting high porosity, low resistivity, and low P-wave velocity. These narrow, low-porosity zones are presumably higher in permeability than the adjacent rocks and may form preferential conduits for degassing during magma ascent. © 2008 Elsevier B.V.
747.
Phase relations and liquid lines of descent in hydrous ferrobasalt - Implications for the skaergaard intrusion and Columbia river flood basalts
Journal of Petrology,
49
(9)
1687-1727
2008
ISSN: 00223530Keywords:▾
crystallization; differentiation; experimental study; flood basalt; hydrothermal system; magma; modeling; precipitation (chemistry); redox conditions; silicate mineral, Arctic; Columbia River; Greenland; North America; Skaergaard Intrusion
Abstract: ▾ Crystallization experiments using a hydrous ferrobasalt as starting material, conducted at 200 MPa, 940-1200°C, at a wide range of water activities (0.1-1) and redox conditions (QFM - 3 to QFM + 4, where QFM is the quartz-fayalite-magnetite oxygen buffer), show that H2O influences significantly the differentiation history of ferrobasaltic magmas. A combination of our data with published experiments on dry ferrobasalt at 1 atm provides an extensive experimental database for modeling and quantifying crystallization and differentiation processes within a typical Fe-rich tholeiitic system under both dry and hydrous conditions. The addition of H2O decreases liquidus temperatures and changes significantly the proportions, temperature range and sequence of crystallizing mineral phases. The dry liquidus is at about 1170°C whereas the liquidus for H2O-saturated melts is at ∼1060°C. The main phases crystallizing from H2O-bearing ferrobasalt at the investigated conditions are olivine (OL), clinopyroxene (CPX), plagioclase (PL), magnetite (MT), hematite (HM), ilmenite (ILM) and amphibole (AM). The phase assemblage is similar to that of the dry system except for the presence of HM at extremely oxidizing conditions and AM at low temperatures (< 950°C) and H2O-saturated conditions. The important observation made in this study is that the stability of Fe-Ti-oxides, and in particular MT, as well as the simultaneous coprecipitation of MT and ILM, are almost independent of the activity of H2O (a H2O) in the system, whereas the liquidus temperatures of the silicate minerals are dramatically depressed by increasing a H2O. The stabilities of oxides are controlled mainly by the redox conditions prevailing in the system. The most pronounced effect of a H2O on the liquidus temperatures of silicates is observed for PL, which shows a considerable delay in crystallization with progressive magma differentiation. Early crystallization of Fe-Ti-oxides in H2O-bearing ferrobasaltic compositions precludes any significant Fe enrichment during differentiation. As Fe enrichment is a characteristic feature of the Skaergaard intrusion, it implies that the Skaergaard parental magma did not contain considerable amounts of water. On the other hand, our experiments indicate that the differentiation of some ferrobasaltic series from the Columbia River flood basalt province might have occurred in magmatic systems containing significant amounts of volatiles (∼0.5-3 wt % H2O). © The Author 2008. Published by Oxford University Press. All rights reserved.
746.
Permeability measurements on rock samples from Unzen Scientific Drilling Project Drill Hole 4 (USDP-4)
Journal of Volcanology and Geothermal Research,
175
(1-2)
82-90
2008
ISSN: 03770273Keywords:▾
Capillarity; Liquids; Rocks; Solids, Compressional wave velocities; Confining pressures; crack; Drill holes; drilled core; permeability; Permeability measurements; pore structure; Rock samples; Transient pulse; Unzen volcano, Rock drilling, atmospheric pressure; country rock; crack; degassing; dike; drilling; gas flow; granite; permeability; solidification; volcanic eruption; wave velocity, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano
Abstract: ▾ Permeability measurement was made on five rock samples from USDP-4 cores. Rock samples were collected from the conduit zone and its country rock. One sample (C14-1-1) is considered as a part of the feeder dyke for the 1991-1995 eruption. The transient pulse method was employed under confining pressure up to 50 MPa. Compressional wave velocity was measured along with permeability. The measured permeability ranges from 10- 19 to 10- 17 m2 at the atmospheric pressure, and is as low as that reported for tight rocks such as granite. The permeability decreases with increasing confining pressure, while the compressional wave velocity increases. Assuming that pores are parallel elliptical tubes, the pressure dependence of permeability requires aspect ratio of 10- 4-10- 2 at the atmospheric pressure. The pore aperture is estimated to be less than 1 μm. The estimated aspect ratio and pore aperture suggest that connectivity of pores is maintained by narrow cracks. The existence of cracks is supported by the pressure dependence of compressional wave velocity. Narrow cracks (< 1 μm) are observed in dyke samples, and they must have been created after solidification. Dyke samples do not provide us information of pore structures during degassing, since exsolved gas has mostly escaped and pores governing the gas permeable flow should have been lost. Both dyke and country rock samples provide us information of materials around ascending magma. Although the measured small-scale permeability cannot be directly applied to geological-scale processes, it gives constrains on studies of large-scale permeability. © 2008 Elsevier B.V. All rights reserved.
745.
Shock metamorphism of Bosumtwi impact crater rocks, shock attenuation, and uplift formation
Science,
322
(5908)
1678 – 1681
2008
ISSN: 10959203Keywords:▾
crater; deformation; numerical model; pressure; quartz; shock metamorphism; shock wave; uplift; article; calculation; Craterostigma; crystallography; priority journal; rock; scientific literature; shock wave
Abstract: ▾ Shock wave attenuation rate and formation of central uplifts are not precisely constrained for moderately sized complex impact structures. The distribution of shock metamorphism in drilled basement rocks from the 10.5-kilometer-diameter Bosumtwi crater, and results of numerical modeling of inelastic rock deformation and modification processes during uplift, constrained with petrographic data, allowed reconstruction of the pre-impact position of the drilled rocks and revealed a shock attenuation by ∼5 gigapascals in the uppermost 200 meters of the central uplift. The proportion of shocked quartz grains and the average number of planar deformation feature sets per grain provide a sensitive indication of minor changes in shock pressure. The results further imply that for moderately sized craters the rise of the central uplift is dominated by brittle failure.