All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
603.
The Corinth Rift laboratory or an in situ investigation on interactions between fluids and active faults
Scientific Drilling
(1 SUPPL. 1)
35 – 38
2007
ISSN: 18163459602.
The Cretaceous Songliao Basin: Volcanogenic Succession, Sedimentary Sequence and Tectonic Evolution, NE China
Acta Geologica Sinica - English Edition,
81
(6)
1002-1011
2007
Keywords:▾
Cretaceous superposed Songliao basin, volcanic rocks, sedimentary sequence, tectonic evolution, Mongolia-Okhotsk collisional belt, Pacific and Eurasian plates, retroarc strike-slip tectonic-inverse basins
Abstract: ▾ Abstract: The Songliao basin (SB) is a superposed basin with two different kinds of basin fills. The lower one is characterized by a fault-bounded volcanogenic succession comprising of intercalated volcanic, pyroclastic and epiclastic rocks. The volcanic rocks, dating from 110 Ma to 130 Ma, are of geochemically active continental margin type. Fast northward migration of the SB block occurred during the major episodes of the volcanism inferred from their paleomagnetic information. The upper one of the basin fill is dominated by non-marine sag-style sedimentary sequence of siliciclastics and minor carbonates. The basin center shifted westwards from the early to late Cretaceous revealed by the GGT seismic velocity structure suggesting dynamic change in the basin evolution. Thus, a superposed basin model is proposed. Evolution of the SB involves three periods including (1) Alptian and pre-Aptian: a retroarc basin and range system of Andes type related to Mongolia-Okhotsk collisional belt (MOCB); (2) Albian to Companian: a sag-like strike-slip basin under transtension related to oblique subduction of the Pacific plate along the eastern margin of the Eurasian plate; (3) since Maastrichtian: a tectonic inverse basin under compression related to normal subduction of the Pacific plate under the Eurasian plate, characterized by overthrust, westward migration of the depocenter and eastward uplifting of the basin margin.
601.
The ICDP Lake Bosumtwi impact crater scientific drilling project (Ghana): Core LB-08A litho-log, related ejecta, and shock recovery experiments
Meteoritics and Planetary Science,
42
(4-5)
635 – 654
2007
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ The 1.07 Myr old Lake Bosumtwi impact crater in Ghana was drilled within the framework of the International Continental Scientific Drilling Project (ICDP). Hole LB-08A, drilled into the outer flank of the central uplift and with a total depth of 451 m, yielded 215.71 m of impact-related rocks. This paper summarizes observations of the lithological logging on core LB-08A. Between a depth of 235.6 and ∼260 m, the section consists of a melt-bearing allochthonous, polymict, and mostly clast-supported impact breccia. Down to ∼418 m, the section comprises a rather uniform unit of meta-graywacke alternating with phyllite to slate (lower greenschist facies); few (par-) autochthonous impact breccia bodies and rare impact dike breccias are present. The lowermost part of the section contains several centimeter- to decimeter-thick melt-bearing breccia dikes in country rocks identical to those occurring above. Omnipresent fracturing was mapped in a qualitative manner. Most prominent shock effects in the uplifted target rocks comprise planar fractures and deformation elements in quartz and polysynthetic twinning in carbonate minerals; the maximum shock pressure as evidenced by quartz is below 26 GPa. The allochthonous breccias occasionally contain a few vol% of melt particles. Suevites occur outside the crater rim, carrying diaplectic crystals, coesite, and ballen quartz as well as true melt glasses and a variety of lithic clasts, among those spectacular staurolite-rich mica-schists. The recorded shock level in the uplifted target rocks is lower than expected and modeled. Shock recovery experiments with analogue carbonaceous graywackes at 34 and 39.5 GPa yielded nearly complete transformation of quartz into diaplectic glass. We therefore exclude a specific shock behavior of the soft, fluid-rich target material (carbonaceous graywackes, shales, slates) in core LB-08A as the prime or only reason for the melt deficit and the generally low shock levels recorded inside the Lake Bosumtwi impact crater. © The Meteoritical Society, 2007. Printed in USA.
600.
The Lake Bosumtwi meteorite impact structure, Ghana - A magnetic image from a third observational level
Meteoritics and Planetary Science,
42
(4-5)
793 – 800
2007
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ The Bosumtwi impact structure in Ghana is the youngest and best-preserved medium-sized impact structure on Earth, and because of the vast amount of prior geophysical and geological data gathered in the area, it constitutes a great natural laboratory to try to develop new geophysical interpretation and modeling techniques. During the 2004 International Continental Scientific Drilling Program (ICDP) drilling campaign at Lake Bosumtwi, we made magnetic field observations at 162 stations around the lake. This study differs from all previous magnetic surveys at Bosumtwi, which only measured the scalar portion of the Earth's magnetic field, in that we measured the full magnetic vector at each station. Acquisition of the full magnetic vector was made possible by innovative use of a borehole deviation probe, which uses a magnetic sensor for absolute orientation reference. Estimates of the magnetic vector orientation and magnitude at each observation station were derived from a series of measurements collected at 50 cm spacing over a depth range of 25 m. In this study, we report a comparison between the scalar total field intensity derived from this new survey approach with the other two previously acquired marine and airborne magnetic data sets. The scalar total magnetic intensity (TMI) computed from the vector data set compares in close agreement with the other two data sets. Some discrepancies between the data sets can be explained by differences in the distances between the sensor and the magnetic sources for the various surveys. The highlight of this study is that we demonstrate that is possible to acquire at least partial vector data with readily available instrumentation. © The Meteoritical Society, 2007. Printed in USA.
599.
Zoned Zircon from Eclogite Lenses in Marbles from the Dabie-Sulu UHP Terrane, China: A Clear Record of Ultra-deep Subduction and Fast Exhumation
Acta Geologica Sinica - English Edition,
81
(2)
204-225
2007
Keywords:▾
zoned zircon, SHRIMP U-Pb dating, ultra-deep subduction, fast exhumation, eclogite, lenses in marble, Dabie-Sulu UHP belt
Abstract: ▾ Abstract: Eclogite lenses in marbles from the Dabie-Sulu ultrahigh-pressure (UHP) terrane are deeply subducted meta-sedimentary rocks. Zircons in these rocks have been used to constrain the ages of prograde and UHP metamorphism during subduction, and later retrograde metamorphism during exhumation. Inherited (detrital) and metamorphic zircons were distinguished on the basis of transmitted light microscopy, cathodoluminescence (CL) imaging, trace element contents and mineral inclusions. The distribution of mineral inclusions combined with CL imaging of the metamorphic zircon make it possible to relate zircon zones (domains) to different metamorphic stages. Domain 1 consists of rounded, oblong and spindly cores with dark-luminescent images, and contains quartz eclogite facies mineral inclusion assemblages, indicating formation under high-pressure (HP) metamorphic conditions of T = 571–668°C and P = 1.7-2.02 GPa. Domain 2 always surrounds domain 1 or occurs as rounded and spindly cores with white-luminescent images. It contains coesite eclogite facies mineral inclusion assemblages, indicating formation under UHP metamorphic conditions of T = 782–849°C and P > 5.5 GPa. Domain 3, with gray-luminescent images, always surrounds domain 2 and occurs as the outermost zircon rim. It is characterized by low-pressure mineral inclusion assemblages, which are related to regional amphibolite facies retrograde metamorphism of T = 600–710°C and P = 0.7-1.2 GPa. The three metamorphic zircon domains have distinct ages; sample H1 from the Dabie terrane yielded SHRIMP ages of 245 ± 4 Ma for domain 1, 235 ± 3 Ma for domain 2 and 215 ± 6 Ma for domain 3, whereas sample H2 from the Sulu terrane yielded similar ages of 244 ± 4 Ma, 233 ± 4 Ma and 214 ± 5 Ma for Domains 1, 2 and 3, respectively. The mean ages of these zones suggest that subduction to UHP depths took place over 10–11 Ma and exhumation of the rocks occurred over a period of 19–20 Ma. Thus, subduction from ∼ 55 km to > 160 km deep mantle depth took place at rates of approximately 9.5–10.5 km/Ma and exhumation from depths >160 km to the base of the crust at −30 km occurred at approximately 6.5 km/Ma. We propose a model for these rocks involving deep subduction of continental margin Iithosphere followed by ultrafast exhumation driven by buoyancy forces after break-off of the UHP slab deep within the mantle.
598.
The Lake Bosumtwi meteorite impact structure, Ghana - Where is the magnetic source?
Meteoritics and Planetary Science,
42
(4-5)
867 – 882
2007
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ The Bosumtwi impact structure (Ghana) is a young and well-preserved structure where a vast amount of information is available to constrain any geophysical model. Previous analysis of the airborne magnetic data and results of numerical simulation of impact predicted a strongly magnetic impact-melt body underneath the lake. Recent drilling through the structure did not penetrate such an expected impact-melt rock magnetic source. A new 3-D magnetic model for the structure was constructed based on a newly acquired higher-resolution marine magnetic data set, with consideration of the observed gravity data on the lake, previous seismic models, and the magnetic properties and lithology identified in the two International Continental Scientific Drilling Program (ICDP) deep boreholes. The new model contains highly magnetic bodies located in the northeast sector of the structure, not centered onto the drilling sites. As in previous models, higher magnetization than that measured in outcropping impactites had to be assigned to the unexposed source bodies. Integration of the new model with the borehole petrophysics and published geology indicates that these bodies likely correspond to an extension to the south of the Kumasi batholith, which outcrops to the northeast of the structure. The possibility that these source bodies are related to the seismically identified central uplift or to an unmapped impact-melt sheet predicted by previous models of the structure is not supported. Detailed magnetic scanning of the Kumasi batholith to the north, and the Bansu intrusion to the south, would provide a test for this interpretation. © The Meteoritical Society, 2007. Printed in USA.
597.
The pollen record from El'gygytgyn Lake: Implications for vegetation and climate histories of northern Chukotka since the late middle Pleistocene
Journal of Paleolimnology,
37
(1)
135-153
2007
ISSN: 09212728Keywords:▾
paleoclimate; paleoecology; palynology; Pleistocene; pollen; vegetation history, Chukchi; Eurasia; Lake El'gygytgyn; Russian Federation
Abstract: ▾ Three types of pollen assemblages (shrub-dominated, mixed herb- and shrub-dominated, and herb-dominated) characterize the ∼300,000 year palynological record from El'gygytgyn Lake. Despite major changes in global climatic forcings, all pollen spectra, with a few isolated exceptions, have strong to possible analogs in the modern plant communities of Northeast Siberia and Alaska. Paleoclimatic reconstructions based on squared chord-distance analog analyses indicate two periods (∼8600-10,700 14C year B.P. and OIS 5e) when summers were perhaps ∼2 to 4°C warmer than modern. January temperatures were also warmer than present, and both July and January were wetter than today. Palynological data remain inconclusive as to the establishment of forests near El'gygytgyn Lake at these times. The wettest Julys occurred during OIS 5 d. July temperatures were near modern, and Januarys were colder and drier than now. January temperatures, even into the Middle Pleistocene, generally show little variability, suggesting that the suppression of arboreal taxa during glaciations was likely caused by cool summers with low effective moisture and not by frigid winters. Because age schemes that correlate magnetic susceptibility to variations in summer insolation or ∂18O have cool plant taxa persisting in warm times (and vice versa), we propose an alternative age model based on the palynological data. © 2006 Springer Science+Business Media B.V.
596.
Ultrahigh-pressure mineral assemblages in zircons from the surface to 5158 m depth in cores of the main drill hole, Chinese Continental Scientific Drilling Project, Southwestern Sulu Belt, China
International Geology Review,
49
(5)
454 – 478
2007
ISSN: 00206814Keywords:▾
Asia; China; Eurasia; Far East; Sulu Belt; amphibolite facies; crustal structure; eclogite; exhumation; fluid inclusion; Ocean Drilling Program; orthogneiss; retrograde metamorphism; subduction; ultrahigh pressure metamorphism; ultramafic rock; zircon
Abstract: ▾ The 5158 m deep main hole of the Chinese Continental Scientific Drilling Project (CCSD-MH) at Maobei, southwestern Sulu Belt, penetrated five major lithologic units: eclogite, amphibolite ± retrograde eclogite, ultramafic rock, paragneiss, and orthogneiss. All analyzed samples are overprinted to various extents by amphibolite-facies retrograde metamorphism. Ultrahigh-pressure (UHP) index minerals are preserved as inclusions in zircons separated from 137 core samples. These index assemblages include: Coe + Phe + Grt from Grt-Ep-Bt paragneiss; Coe + Jd + Grt + Ap, Coe + Jd + Phe + Ap and Coe + Grt + Jd + Phe from Grt-Ep-Hbl paragneiss; Coe + Phe, Coe + Ky + Ap, and Coe + Ky + Ttn from orthogneiss; and Coe + Grt + Omp, Coe + Grt + Phe, Coe + Omp + Rt, and Coe + Grt + Omp + Phe from Bt-Ep amphibolite and other retrograde eclogites. The common occurrences of these UHP assemblages throughout the section indicate that the drill hole did not penetrate through the UHP tectonic slice. All of the UHP mineral assemblages, whether from retrograde ecologites or from the surrounding gneisses, record similar metamorphic conditions of 773-843°C and 3.2-4.0 GPa. Zircons separated from surface samples and cores from other shallow holes in the area also contain similar coesite-bearing UHP mineral inclusions. This widespread occurrence of UHP assemblages in the southwestern Sulu area suggests that voluminous continental materials were subducted and metamorphosed at mantle depths > 100 km, and then were rapidly exhumed to crustal levels. Copyright © 2007 by V. H. Winston & Son, Inc. All rights reserved.
595.
Upper mantle beneath the Eger Rift (Central Europe): Plume or asthenosphere upwelling?
Geophysical Journal International,
169
(2)
675 – 682
2007
ISSN: 1365246XKeywords:▾
Bohemian Massif; Central Europe; Eurasia; Europe; asthenosphere; lithosphere; P-wave; rift zone; seismic anisotropy; seismic tomography; teleseismic wave; travel time; upper mantle
Abstract: ▾ We present the first results of a high-resolution teleseismic traveltime tomography and seismic anisotropy study of the lithosphere-asthenosphere system beneath the western Bohemian Massif. The initial high-resolution tomography down to a depth of 250 km did not image any columnar low-velocity anomaly which could be interpreted as a mantle plume anticipated beneath the Eger Rift, similar to recent findings of small plumes beneath the French Massif Central and the Eifel in Germany. Alternatively, we interpret the broad low-velocity anomaly beneath the Eger Rift by an upwelling of the lithosphere-asthenosphere transition. We also map lateral variations of seismic anisotropy of the mantle lithosphere from spatial variations of P-wave delay times and the shear wave splitting. Three major domains characterised by different orientations of seismic anisotropy correspond to the major tectonic units - Saxothuringian, Moldanubian and the Teplá-Barrandian - and their fabrics fit to those found in our previous studies of mantle anisotropy on large European scales. © 2007 The Authors Journal compilation © 2007 RAS.
594.
Uppermost impact fallback layer in the Bosumtwi crater (Ghana): Mineralogy, geochemistry, and comparison with Ivory Coast tektites
Meteoritics and Planetary Science,
42
(4-5)
709 – 729
2007
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ In 2004, an International Continental Scientific Drilling Program (ICDP) drilling project at the Bosumtwi impact crater, Ghana (10.5 km in diameter, 1.07 Myr old), was performed to study the sediments that fill the lake as well as the underlying impactites. In one (LB-05) of 16 cores drilled into the lake sediments, the zone between the impact breccias and the post-impact sediments was penetrated, preserving the final, fine-grained impact fallback layer. This ∼30 cm thick layer contains in the top 10 cm. "accretionary" lapilli, microtektite-like glass spherules, and shocked quartz grains. Glass particles - mostly of splash form less than 1 mm size - make up the bulk of the grains (∼70-78% by number) in the coarser size fraction (> 125 μm) of the top of the fallback layer. About one-third of all quartz grains in the uppermost part of the layer are shocked, with planar deformation features (PDFs); almost half of these grains are highly shocked, with 3 or more sets of PDFs. K-feldspar grains also occur and some show shock deformation. The abundance of shocked quartz grains and the average shock level as indicated by the number of sets of PDFs, for both quartz and K-feldspar, decrease with depth into the layer. The well-preserved glass spherules and fragments are chemically rather homogeneous within each particle, and also show relatively small variations between the various particles. On average, the composition of the fallback spherules from core LB-5B is very similar to the composition of Ivory Coast tektites and microtektites, with the exception of CaO contents, which are about 1.5 to 2 times higher in the fallback spherules. This is a rare case in which the uppermost fallback layer and the transition to the post-impact sediments has been preserved in an impact structure; its presence indicates that the impactite sequence at Bosumtwi is complete and that Bosumtwi is a very well-preserved impact crater. © The Meteoritical Society, 2007. Printed in USA.
593.
Using drill cutting separates to estimate the strength of narrow shear zones at SAFOD
Geophysical Research Letters,
34
(11)
2007
ISSN: 00948276Keywords:▾
Drilling; Friction; Shear strength, Friction coefficient; Frictional strength; Shear zone, Tectonics, deformation; estimation method; San Andreas Fault; serpentine; shear zone; strength, California; North America; Parkfield; United States
Abstract: ▾ A technique is presented for estimating frictional strength of narrow shear zones based on hand selection of drillhole cuttings separates. Tests were conducted on cuttings from the SAFOD scientific drillhole near Parkfield, California. Since cuttings are mixed with adjacent material as they travel up the drillhole, these fault-derived separates give a better representation of the frictional properties of narrow features than measurements from the bulk material alone. Cuttings from two shear zones (one an active trace of the San Andreas fault) contain a significant weight percent of clay-rich grains that exhibit deformation-induced slickensides. In addition, cuttings from the active SAF trace contain around 1% serpentine. Coefficients of friction for clay-rich and serpentine grains were 0.3-0.5 and 0.4-0.45, respectively. These values are around 0.12 lower than the friction coefficient of the corresponding bulk cuttings, providing an improved estimate of the frictional strength of the San Andreas fault. Copyright 2007 by the American Geophysical Union.
592.
Vibration characteristic analysis and information transmission test of bottom drilling tool (in Chinese with English abstract);[松科1井南孔钻井取心技术]
Oil Drilling & Production Technology,
5
(8-12)
117-118
2007
591.
Platinum group elements provide no indication of a meteoritic component in ICDP cores from the Bosumtwi crater, Ghana
Meteoritics and Planetary Science,
42
(4-5)
731 – 741
2007
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ In an attempt to identify the type of projectile, 14 samples from the Bosumtwi crater in Ghana were analyzed for platinum group element (PGE) concentrations by nickel sulfide fire assay inductively coupled plasma-mass spectrometry (ICP-MS). The majority of the samples come from the impactite material recovered by cores LB-07A and LB-08A, which were drilled by the International Continental Scientific Drilling program (ICDP). One sample originates from the fallback material found at the contact between the impactite and the overlying lake sediment in core LB-05B. No clear signature of a meteoritic contamination was identified in the 13 impactite samples. The target rock apparently dominates the PGE contribution in the impactites. These results agree with the PGE concentrations reported for the suevites collected at the crater rim and in other parts of the Bosumtwi ICDP cores. However, based on Cr and Os isotopic signatures, a meteoritic component could be present in the sample of fallback material, supporting the reports of the existence of meteoritic material in the Ivory Coast tektites. Further analyses of the fallback material from the Bosumtwi drill cores should confirm (or not) this first result. © The Meteoritical Society, 2007. Printed in USA.
590.
Three-dimensional shear-wave splitting tomography in the Parkfield, California, region
Geophysical Research Letters,
34
(24)
2007
ISSN: 00948276Keywords:▾
Anisotropy; Compressive stress; Mathematical models; Microcracks; Shear waves; Three dimensional; Tomography; Velocity, Shear wave splitting delay; Shear-wave splitting tomography; Spatial anisotropy distribution, Seismic waves, anisotropy; fault zone; imaging method; microcrack; polarization; ray tracing; S-wave; San Andreas Fault; seismic tomography; spatial variation; wave splitting, California; North America; Parkfield; United States
Abstract: ▾ We developed a three-dimensional (3D) shear-wave splitting tomography method to image the spatial anisotropy distribution by back projecting shear wave splitting delay times along ray paths derived from a 3D shear velocity model, assuming the delay times are accumulated along the ray paths. The local strength of the anisotropy is indicated by a parameter of anisotropy percentage, K. Using the shearwave splitting delay times for 575 earthquakes measured at PASO and HRSN stations, we imaged a detailed 3D anisotropy percentage model around the San Andreas Fault Observatory at Depth (SAFOD). The anisotropy percentage model shows strong heterogeneities, consistent with the strong spatial variations in both measured delay times and fast polarization directions. The San Andreas Fault (SAF) zone is highly anisotropic down to a depth of ∼4 km and then becomes less anisotropic at greater depths. Outside the fault zone, the highly anisotropic zone extends as deep as ∼7 km, consistent with the systematic depth dependence of the average time delays. To the southwest of the SAF, the Salinian granitic block shows relatively strong anisotropic: anomalies that are presumably caused by aligned microcracks consistent with the direction of the regional maximum compressive horizontal stress. To the northeast of the fault zone, a strong anisotropic anomaly between depths ∼2 and ∼4 km corresponds to a serpentinite body sandwiched between Franciscan rocks. Copyright 2007 by the American Geophysical Union.
589.
Physical property measurements: ICDP boreholes LB-07A and LB-08A, Lake Bosumtwi impact structure, Ghana
Meteoritics and Planetary Science,
42
(4-5)
801 – 809
2007
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ Physical rock property measurements provide the primary constraints for any geological models hypothesized from geophysical observations. Previous geophysical models of the Bosumtwi impact structure hypothesized that a highly magnetic and dense impact-melt sheet might be the source of the observed magnetic anomalies. However, magnetic susceptibility and density measurements made on International Continental Scientific Drilling Program (ICDP) cores LB-07A and LB-08A from the interior of the Bosumtwi meteorite impact structure contain no evidence for that. Both density and magnetic susceptibility logs on both boreholes exhibit low-amplitude contrasts between the uppermost polymict lithic breccia and suevite, the intermediate monomict lithic breccia, and the lowermost bedrock. The depth extent of fracture-related density reduction is much greater at LB-08A than at LB-07A. A total magnetic intensity log from borehole LB-08A supports the suggestion that magnetic anomalies over Lake Bosumtwi are mainly sourced in undetected and/or covered bedrock intrusions, like the ones outcropping at the northeast and to the southwest of the lake. © The Meteoritical Society, 2007. Printed in USA.
588.
Drill core LB-08A, Bosumtwi impact structure, Ghana: Geochemistry of fallback breccia and basement samples from the central uplift
Meteoritics and Planetary Science,
42
(4-5)
689 – 708
2007
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ The 1.07 Myr old Bosumtwi impact structure in Ghana (West Africa), which measures 10.5 km in diameter and is largely filled by Lake Bosumtwi, is associated with one of four currently known tektite strewn fields. Two boreholes were drilled to acquire hard-rock samples of the deep crater moat and from the flank of the central uplift (LB-07A and LB-08A, respectively) during a recent ICDP-sponsored drilling project. Here we present results of major and trace element analysis of 112 samples from drill core LB-08A. This core, which was recovered between 235.6 and 451.33 m depth below lake level, contains polymict lithic breccia intercalated with suevite, which overlies fractured/brecciated metasediment. The basement is dominated by meta-graywacke (from fine-grained to gritty), but also includes some phyllite and slate, as well as suevite dikelets and a few units of a distinct light greenish gray, medium-grained meta-graywacke. Most of the variations of the major and trace element abundances in the different lithologies result from the initial compositional variations of the various target rock types, as well as from aqueous alteration processes, which have undeniably affected the different rocks. Suevite from core LB-08A (fallback suevite) and fallout suevite samples (from outside the northern crater rim) display some differences in major (mainly in MgO, CaO, and Na2O contents) and minor (mainly Cr and Ni) element abundances that could be related to the higher degree of alteration of fallback suevites, but also result from differences in the clast populations of the two suevite populations. For example, granite clasts are present in fallout suevite but not in fallback breccia, and calcite clasts are present in fallback breccia and not in fallout suevite. Chondrite-normalized rare earth element abundance patterns for polymict impact breccia and basement samples are very similar to each other. Siderophile element contents in the impact breccias are not significantly different from those of the metasediments, or compared to target rocks from outside the crater rim. So far, no evidence for a meteoritic component has been detected in polymict impact breccias during this study, in agreement with previous work. © The Meteoritical Society, 2007. Printed in USA.
587.
Core description and characteristics of fault zones from Hole-A of the Taiwan Chelungpu-Fault Drilling Project
Terrestrial, Atmospheric and Oceanic Sciences,
18
(2)
327-357
2007
ISSN: 10170839Keywords:▾
Chi-Chi earthquake 1999; core analysis; deformation mechanism; drilling; fault zone; lithology; normal fault; rupture; tectonic structure, Asia; Eurasia; Far East; Taichung; Taiwan
Abstract: ▾ Taiwan Chelungpu-fault Drilling Project was conducted in drill site Dakeng, Taichung City of central western Taiwan during 2004 - 2005 principally to investigate the rupture mechanism in the northern segment of the Chi-Chi earthquake of 21 September 1999, and also to examine regional stratigraphy and tectonics. Core examination (500 - 1800 m) of Hole-A gave profound results aiding in illustrating the lithologic column, deformation structure, and architectural pattern of fault zones along the borehole. Lithology column of Hole-A was identified downward as the Cholan Formation (500 - 1027 m), Chinshui Shale (1027 - 1268 m), Kueichulin Formation (1268 - 1712 m), and back to the Cholan Formation (1712 - 2003 m) again. A dramatic change is observed regarding sedimentation age and deformation structure around 1712 m. Along the core, most bedding dips 30° toward N105°. Around 1785 m, bedding dip jumps up to 70° until the bottom of borehole. Five structure groups of different orientations (dip direction/dip) are observed throughout the core. Based on the orientation and sense of shear, they are categorized as thrust (105/30), left-lateral fault (015/30 - 80), right-lateral fault (195/30 - 80), normal fault (105/5 - 10), and backthrust (285/40 - 50). Ten fault zones have been recognized between 500 and 2003 m. We interpret the fault zone located at around 1111 m as being the most likely candidate for rupture deformation during Chi-Chi earthquake. The fault zone seated around 1712 m is recognized as the Sanyi fault zone which is 600 m beneath the Chelungpu fault zone. Ten fault zones including thrust faults, strike-slip faults and backthrust are classified as the Chelungpu Fault System (<1250 m) and the Sanyi Fault System (>1500 m). According to the deformation textures within fault zones, the fault zones can be categorized as three types of deformation: distinct fracture deformation, clayey-gouge deformation, and soft-rock deformation. Fracture deformation is dominant within the Chelungpu Fault System and abother two architectures prevail in the Sanyi Fault System. The fracture deformation pattern is asymmetric, which depended the shear sense of fault zone. From the core examination of TCDP Hole-A, the lithology plays an important role in controlling the location and deformation of fault zones.
586.
Core slabbing and nannofossil analysis on the Chelungpu fault zone, Taichung, Taiwan
Terrestrial, Atmospheric and Oceanic Sciences,
18
(2)
295-325
2007
ISSN: 10170839Keywords:▾
biostratigraphy; core analysis; lithology; mudstone; nanofossil; Pliocene-Pleistocene boundary; shear zone; slab, Asia; Eurasia; Far East; Taichung; Taiwan
Abstract: ▾ The results of this nannofossil analysis supply essential information for determining the formation boundaries in the upper Pliocene to Pleistocene. These results also verify the existence of a repetition fossil zone. The TCDP well-A was sunk through the soft fine-grain muddy sandstone and mudstone dominated formations of the Pliocene and Pleistocene in the Taichung area. This study determines methods for providing core preservation in wells at fault zones and establishes a nannofossil biostratigraphy for the integrated Taiwan Chelungpu-fault Drilling Project (TCDP). Good core fabrics are useful for core description and sampling. In this present study, over 400 meters of subsurface cores were covered in resin and slabbed. Digitized images were created for all the core fabrics. More than 150 rock samples were analyzed for nannofossils to give a detailed appraisal of the biostratigraphic column of TCDP well-A. A fossil zone at a depth interval of 431 - 869 m is a NN16 - 18 biozone. This zone is within the Cholan Formation, a lithologic stratigraphy in northern and central Taiwan. The depth interval 883-1226 m is NN15, and is within the Chinshui Shale. The Chelungpu fault is composed of five major shear zones. These are all found at depth within the marine Chinshui Shale. At a depth interval of 1293.37 - 1710 m is a NN12 - 14 biozone; this interval is within the Kueichulin Formation. Interestingly, both the interval beneath 1714 m and the nannofossil zone near the well bottom are NN16 - 18 (Cholan Formation), indicating a repeat of the Cholan Formation. The lowest fossil zone is also abundant in secondary reworked fossils in its assemblages. Hence, the repetition of the younger fossil zone, NN16 - 18, at the bottom of the well verifies the subsurface position of the Sanyi Fault and indicates that TCDP well-A must have passed through it.
585.
Crustal structure due to collisional and escape tectonics in the Eastern Alps region based on profiles Alp01 and Alp02 from the ALP 2002 seismic experiment
Journal of Geophysical Research: Solid Earth,
112
(6)
2007
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
Alps; Eastern Alps; Eurasia; Europe; Pannonian Basin; crustal structure; forward modeling; Moho; ray tracing; seismic reflection; seismic refraction; seismic velocity; seismotectonics
Abstract: ▾ Alp01 and Alp02 are the longest profiles recorded during ALP 2002, a large international seismic refraction and wide-angle reflection experiment undertaken in the Eastern Alps in 2002. Alp01 crosses the Alpine orogen from north to south, thus providing a cross section mainly affected by the collision between Europe and the Adriatic microplate. Alp02 extends from the Eastern Alps to the Pannonian basin, supplying evidence on the relation between Alpine crustal structure and tectonic escape to the Pannonian basin. During this experiment, 363 single-channel recorders were deployed along these profiles with an average spacing of 3.2 km. Recordings from 20 inline shots were used in this study. Two-dimensional forward modeling using interactive ray-tracing techniques produced detailed P wave velocity models that contain many features of tectonic significance. Along Alp01, the European Moho dips generally to the south and reaches a maximum depth of 47 km below the transition from the Eastern to the Southern Alps. The Adriatic Moho continues further south at a significantly shallower depth. Moho topography and a prominent south-dipping mantle reflector in the Alpine area support the idea of southward subduction of the European lithosphere below the Adriatic microplate. The most prominent tectonic feature on the Alp02 profile is a vertical step of the Moho at the transition between the Alpine and Pannonian domains, suggesting the existence of a separate Pannonian plate fragment. The development of the Pannonian fragment is interpreted to be a consequence of crustal thinning due to tectonic escape from the Alpine collision area to the Pannonian basin. Copyright 2007 by the American Geophysical Union.
584.
Diatom stratigraphy of the last 250 ka at Lake El'gygytgyn, northeast Siberia
Journal of Paleolimnology,
37
(1)
155-162
2007
ISSN: 09212728Keywords:▾
climate conditions; core analysis; diatom; paleoclimate; periphyton; plankton; Quaternary; stratigraphy, Chukchi; Eurasia; Lake El'gygytgyn; Russian Federation, Bacillariophyta; Cyclotella ocellata
Abstract: ▾ Diatom species counts were conducted on 171 sediment samples from the 13-m-long core PG1351 from Lake El'gygytgyn, northeast Siberia. The planktonic Cyclotella ocellata-complex dominates the diatom assemblage through most of the core record, persisting through a variety of climate conditions. Periphytic diatoms, although less abundant, have greater diversity and greater down-core assemblage variation. During warm climate modes, longer summer ice-free conditions may have allowed more complex diatom communities to develop in shallow-water habitats, and enhanced circulation may have increased transport of these diatoms to deeper parts of the lake. Zones of low overall diatom abundance further support inferred intervals of low lake productivity during times of extended lake ice and snow cover. More data on the modern spatial and temporal distribution of diatom species in the Lake El'gygytgyn system will improve inferences from core records. © 2006 Springer Science+Business Media B.V.
583.
A dynamic study of frictional and viscous effects on earthquake rupture: A case study of the 1999 Chi-Chi, Taiwan, earthquake
Bulletin of the Seismological Society of America,
97
(4)
1233-1244
2007
ISSN: 00371106Keywords:▾
Approximation theory; Computer simulation; Dynamics; Friction; Mathematical models; Physical properties; Viscosity, Earthquake rupture; Fault-striking direction; Transpressive fault, Earthquakes, Chi-Chi earthquake 1999; displacement; earthquake magnitude; earthquake rupture; friction; simulation; strike-slip fault; transpression; viscosity, Asia; Eurasia; Far East; Taiwan
Abstract: ▾ Friction is commonly considered an important factor in controlling earthquake rupture. In this work, it is assumed that viscosity is also a significant factor. A strike-slip-type, two-body spring-slider model in the presence of both friction and viscosity is applied to approximate the rupture processes of an earthquake along the fault-striking direction. Results show that in addition to friction, viscosity is also an important factor in controlling rupture. The Ms 7.6 Chi-Chi earthquake which struck central Taiwan on 20 September 1999, ruptured a 100-km-long east-dipping transpressive fault (the Chelungpu fault). Measured and inferred results show that there are differences in physical properties between the northern and southern segments of the fault. Simulation results from a two-body model can explain the differences in displacement, velocity, acceleration, and predominant period between the two fault segments.
582.
Directional Coring Technology in Well Songke-1 (in Chinese with English abstract);[松科1井定向取心技术]
Petroleum Drilling Techniques,
622-26
2007
581.
Drill core LB-08A, Bosumtwi impact structure, Ghana: Petrographic and shock metamorphic studies of material from the central uplift
Meteoritics and Planetary Science,
42
(4-5)
611 – 633
2007
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ During a recent drilling project sponsored by the International Continental Scientific Drilling Progam (ICDP), two boreholes (LB-07A and LB-08A) were drilled into the crater fill of the Bosumtwi impact structure and the underlying basement, into the deep crater moat and the outer flank of the central uplift, respectively. The Bosumtwi impact structure in Ghana (West Africa), which is 10.5 km in diameter and 1.07 Myr old, is largely filled by Lake Bosumtwi. Here we present the lithostratigraphy of drill core LB-08A (recovered between 235.6 and 451.33 m depth below lake level) as well as the first mineralogical and petrographic observations of samples from this core. This drill core consists of approximately 25 m of polymict, clast-supported lithic breccia intercalated with suevite, which overlies fractured/brecciated metasediment that displays a large variation in lithology and grain size. The lithologies present in the central uplift are metasediments composed dominantly of fine-grained to gritty meta-graywacke, phyllite, and slate, as well as suevite and polymict lithic impact breccia. The suevites, principally present between 235.6 and 240.5 m and between 257.6 and 262.2 m, display a fine-grained fragmental matrix (about 39 to 45 vol%) and a variety of lithic and mineral clasts that include meta-graywacke, phyllite, slate, quartzite, carbon-rich organic shale, and calcite, as well as melt particles, fractured quartz, unshocked quartz, unshocked feldspar, quartz with planar deformation features (PDFs), diaplectic quartz glass, mica, epidote, sphene, and opaque minerals). The crater-fill suevite contains calcite clasts but no granite clasts, in contrast to suevite from outside the northern crater rim. The presence of melt particles in suevite samples from the uppermost 25 meters of the core and in suevite dikelets in the basement is an indicator of shock pressures exceeding 45 GPa. Quartz grains present in suevite and polymict lithic impact breccia abundantly display 1 to (rarely) 4 sets of PDFs per grain. The shock pressures recorded by the PDFs in quartz grains in the polymict impact breccia range from 10 to ∼30 GPa. We also observed a decrease of the abundance of shocked quartz grains in the brecciated basement with increasing depth. Meta-graywacke samples from the basement are heterogeneously shocked, with shock pressures locally ranging up to 25-30 GPa. Suevites from this borehole show a lower proportion of melt particles and diaplectic quartz glass than suevites from outside the northern crater rim (fallback impact breccia), as well as a lack of ballen quartz, which is present in the external breccias. Similar variations of melt-particle abundance and shock-metamorphic grade between impact-breccia deposits within the crater and fallout impact breccia outside the crater have been observed at the Ries impact structure, Germany. © The Meteoritical Society, 2007. Printed in USA.
580.
CONTINENT sampling positions and related projects
579.
Drilling of the chelungpu fault after the 1999 Chi-Chi, Taiwan earthquake (Mw7.6): Understanding physics of faulting
Scientific Drilling
(1 SUPPL. 1)
33-34
2007
ISSN: 18168957
Publisher: Integrated Ocean Drilling Program