All ICDP Publications with Abstracts
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869.
Search for a meteoritic component in impact breccia from the Eyreville core, Chesapeake Bay impact structure: Considerations from platinum group element contents
Special Paper of the Geological Society of America,
458469-479
2009
Abstract: ▾ This paper documents an attempt to detect a meteoritic component in both washback (resurge) crater-fill breccia (the so-called Exmore breccia) and in suevites from the Eyreville core hole, which was drilled several kilometers from the center of the 85-km-diameter Chesapeake Bay impact structure, Virginia, USA. Determining the presence of an extraterrestrial component and, in particular, the projectile type for this structure, which is the largest impact structure currently known in the United States, is of importance because it marks one of several large impact events in the late Eocene, during which time the presence of extraterrestrial 3He and multiple impact ejecta layers provide evidence for a comet or asteroid shower. Previous work has indicated an ordinary chondritic projectile for the largest of the late Eocene craters, the Popigai impact structure in Siberia. The exact relation between the Chesapeake Bay impact event and siderophile element anomalies documented in late Eocene ejecta layers from around the world is not clear. The only clear indication for an extraterrestrial component related to this structure has been the discovery of a meteoritic osmium isotopic signature in impact melt rocks recovered from a hydrogeologic test hole located on Cape Charles near the center of the structure, and confirmation of a similar signature in suevitic rocks would have been desirable in order to place constraints on the type of projectile involved in formation of the Chesapeake Bay crater. Unfortunately, the current data show no discernible differences in the contents of the platinum group elements (PGEs) among the suevite, the Exmore breccia, and several crystalline basement rocks, all from the Eyreville core hole. Abundances of PGEs are uniformly low (e.g., <0.1 ppb Ir), and chondrite-normalized abundance patterns are nonchondritic. These data do not allow unambiguous verification of an extraterrestrial signature. Thus, the nature of the Chesapeake Bay projectile remains ambiguous. © 2009 The Geological Society of America.
868.
Radiogenic heat production in the lithosphere of Sulu ultrahigh-pressure metamorphic belt
Earth and Planetary Science Letters,
277
(3-4)
525 – 538
2009
ISSN: 0012821XKeywords:▾
Asia; China; Eurasia; Far East; Sulu Belt; Calluna vulgaris; Structural geology; Uranium alloys; CCSD; CCSD-MH; Cenozoic; Chinese Continental Scientific drillings; Eclogites; Heat productions; Large ranges; Mean values; Metamorphic belts; Pilot holes; radiogenic heat production; Rock types; Sulu UHPM belt; Surface heat flows; Thermal models; thermal structure; Ultramafic rocks; Vertical distributions; Cenozoic; Chinese Continental Scientific Drilling Project; Cretaceous; eclogite; heat flow; heat production; lithosphere; metamorphism; Moho; petrology; retrogression; thermal structure; ultrahigh pressure metamorphism; ultramafic rock; vertical distribution; Production
Abstract: ▾ The Chinese Continental Scientific Drilling (CCSD) project is located at the Sulu ultrahigh-pressure metamorphic (UHPM) belt. It offers a unique opportunity for studying the radiogenic heat production of both shallower and deeper rocks. Based on the concentrations of radiogenic elements U, Th and K on 349 samples from main hole of CCSD (CCSD MH), pilot holes and exposures, we determined radiogenic heat productions of all major rock types in the Sulu UHPM belt. Results show the mean values of orthogneiss and paragneiss are respectively 1.65 ± 0.81 and 1.24 ± 0.61 μW m- 3. Due to different composition and grade of retrogressive metamorphism, the eclogites display significant scatter in radiogenic heat production, ranging from 0.01 to 2.85 μW m- 3, with a mean of 0.44 ± 0.55 μW m- 3. The radiogenic heat production in ultramafic rocks also varies within a large range of 0.02 to 1.76 μW m- 3, and the average turns out to be 0.18 ± 0.31 μW m- 3. Based on the measurements and crustal petrologic model, the vertical distribution model of heat production in Sulu crust is established. The resulting mean heat production (0.76 μW m- 3) contributes 24 mW m- 2 to the surface heat flow. 1-D thermal model indicates that the temperature at the Moho reaches above 750 °C, and the thermal thickness of the lithosphere is ~ 75 km, in good agreement with the geophysical results. The high teat flow (~ 75 mW m- 2) together with thin lithosphere presents strong support for the extension events during the late Cretaceous and Cenozoic. © 2008 Elsevier B.V. All rights reserved.
867.
Results of recent sediment drilling activities in deep crater lakes
Pages News,
17
(3)
117-118
2009
866.
Rheological properties of dome lavas: Case study of Unzen volcano
Earth and Planetary Science Letters,
279
(3-4)
263-272
2009
ISSN: 0012821XKeywords:▾
brittle; ductile; flow banding; lava; magma; non-Newtonian rheology; Unzen; visco-elastic, Cements; Crystals; Domes; Elasticity; Non Newtonian flow; Plasticity; Rheology; Volcanic rocks; Volcanoes, Viscosity, cracking; crystal structure; deformation; fragmentation; lava dome; magma; phenocryst; rheology; stress; viscoelasticity; volcanic eruption; volcanic rock, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano
Abstract: ▾ Transitions between effusive and explosive styles of lava dome eruptions are likely accompanied by changes in lava rheology. The common presence of crystals in dome lavas produces a complex non-Newtonian rheology. Thus models of such complex rheology are essential for volcanic eruption models. Here, we have measured the rheology of natural Unzen lavas with a compressive uniaxial press operating at stresses between 1 and 70 MPa and temperatures between 940 and 1010 °C. Crystal-rich Unzen lavas are characterised by two essential rheological features which produce non-Newtonian effects. The first is an instantaneous response of the apparent viscosity to applied stress which requires that the magma be described as a visco-elastic fluid that exhibits shear-thinning. The second effect takes the form of a time-dependence of the viscosity at moderate to high stress (≥ 10 MPa). In this regime, the apparent viscosity slowly decreases as increasing fracturing of the phenocrysts and the groundmass occurs. Fragmentation of crystals and alignment of crystal fragments are observed to produce flow banding-effects which in turn lower the apparent viscosity of natural dome lavas. Ultimately, deformation may lead to complete rupture of the lava if the stress is sufficient. Cracking thus stands as an important process in natural dome lava rheology. The ubiquitous non-Newtonian rheology of dome lavas, observed experimentally here, needs to be adequately treated in order to generate appropriate eruption models. © 2008 Elsevier B.V. All rights reserved.
865.
Rock-avalanche and ocean-resurge deposits in the late Eocene Chesapeake Bay impact structure: Evidence from the ICDP-USGS Eyreville cores, Virginia, USA
Special Paper of the Geological Society of America,
458587-615
2009
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Debris; Deposits; Fluidization; Granite; Infill drilling; Quartz; Sedimentology; Sediments, Chesapeake bay impact structures; Continental scientific drillings; Fluidization structures; Sedimentary structure; Shelf sedimentation; Transient cavities; Turbidite deposits; U.s. geological surveys, Sedimentary rocks, breccia; clast; debris flow; deposition; diamicton; Eocene; fluidization; impact structure; marine sediment; matrix; research program; rock avalanche; sediment transport; sedimentation; turbidite, Chesapeake Bay; United States; Virginia
Abstract: ▾ An unusually thick section of sedimentary breccias dominated by target-sediment clasts is a distinctive feature of the late Eocene Chesapeake Bay impact structure. A cored 1766-m-deep section recovered from the central part of this marine-target structure by the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) drilling project contains 678 m of these breccias and associated sediments and an intervening 275-m-thick granite slab. Two sedimentary breccia units consist almost entirely of Cretaceous nonmarine sediments derived from the lower part of the target sediment layer. These sediments are present as coherent clasts and as autoclastic matrix between the clasts. Primary (Cretaceous) sedimentary structures are well preserved in some clasts, and liquefaction and fluidization structures produced at the site of deposition occur in the clasts and matrix. These sedimentary breccias are interpreted as one or more rock avalanches from the upper part of the transient-cavity wall. The little-deformed, unshocked granite slab probably was transported as part of an extremely large slide or avalanche. Water-saturated Cretaceous quartz sand below the slab was transported into the seafloor crater prior to, or concurrently with, the granite slab. Two sedimentary breccia units consist of polymict diamictons that contain cobbles, boulders, and blocks of Cretaceous nonmarine target sediments and less common shocked-rock and melt ejecta in an unsorted, unstratified, muddy, fossiliferous, glauconitic quartz matrix. Much of the matrix material was derived from Upper Cretaceous and Paleogene marine target sediments. These units are interpreted as the deposits of debris flows initiated by the resurge of ocean water into the seafloor crater. Interlayering of avalanche and debris-flow units indicates a partial temporal overlap of the earlier avalanche and later resurge processes. A thin unit of stratified turbidite deposits and overlying laminated fine-grained deposits at the top of the section represents the transition to normal shelf sedimentation. © 2009 The Geological Society of America.
864.
Rock-magnetic properties of the ICDP-USGS Eyreville core, Chesapeake Bay impact structure, Virginia, USA
Special Paper of the Geological Society of America,
458119-135
2009
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Core samples; Deformation; Geomagnetism; Hematite; Infill drilling; Iron ores; Lithology; Magnetic properties; Magnetite; Petrophysics; Structural geology, Brittle deformation; Chesapeake bay impact structures; Crustal magnetic anomalies; Geophysical modeling; Geophysical surveys; Physical parameters; Rock magnetic properties; Subsurface information, Structural properties, brittle deformation; cratering; geophysical survey; hematite; impact structure; magnetic anomaly; magnetic method; magnetic mineral; magnetic property; magnetite; mineralogy; physical property; pyrrhotite, Chesapeake Bay; United States
Abstract: ▾ Chesapeake is a 35-Ma-old shallow-marine, complex impact structure with a diameter of ̃85 km. The structure is completely buried beneath several hundreds of meters of postimpact sediments. Therefore, subsurface information can be obtained only from geophysical surveys and drill holes. Recently, deep drilling into the inner crater zone, at Eyreville near Cape Charles, was carried out in order to provide constraints on geophysical modeling and cratering processes in a multilayered marine target. We analyzed samples of the Eyreville core including postimpact, impactproduced, and basement-derived units in order to clarify the magneto-mineralogy, to provide physical parameters for better understanding the influence of the impact on the petrophysical and rock-magnetic properties, and to provide rock-magnetic data for magnetic modeling. Results show a complex behavior of physical properties of the lithologies in the Eyreville core due to different lithologies having been affected by shock-induced changes. Our data suggest that pyrrhotite and magnetite carry the magnetic properties in most of the core samples, whereas hematite is present in oxidized clays from the uppermost impact-generated unit (Exmore beds) and related sediment megablocks. The granitic megablock appears to be undeformed based on lack of brittle deformation in magnetite and petrophysically appears as a single block. In contrast, the impactite sequence below the megablock shows brittle deformation and magnetic fabric randomization, and the pyrrhotite in the associated schist fragments is strongly fractured. Thus, the Chesapeake Bay deep core provides an extraordinary opportunity to study the effect of impact on magnetite and pyrrhotite, the two main magnetic minerals creating crustal magnetic anomalies. © 2009 The Geological Society of America.
863.
Scientific collaboration on past speciation conditions in Lake Ohrid-SCOPSCO workshop report
Scientific Drilling
(7)
51 – 53
2009
ISSN: 18163459Keywords:▾
Deep drillings; Lake ohrid; Scientific collaborations
Abstract: ▾ In summary, the SCOPSCO workshop provided a reliable platflorm to discuss the present state of knowledge and future steps towards a deep drilling campaign. A full proposal for an ICDP drilling campaign will be submitted in 2009.
862.
Search for a meteoritic component in impact breccia from the Eyreville core, Chesapeake Bay impact structure: Considerations from platinum group element contents
Special Paper of the Geological Society of America,
458469-479
2009
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Crystalline rocks; Hydrogeology; Infill drilling; Isotopes; Meteorites; Platinum; Projectiles; Rocks, Chesapeake bay impact structures; Crystalline basement; Extraterrestrial components; Impact structures; Isotopic signatures; Platinum group elements; Platinum group elements (PGEs); Siderophile elements, Economic geology, breccia; chondrite; coastal sediment; ejecta; Eocene; impact structure; isotopic composition; meteorite; osmium; platinum group element; research program; sediment chemistry; siderophile element; suevite, Chesapeake Bay; United States
Abstract: ▾ This paper documents an attempt to detect a meteoritic component in both washback (resurge) crater-fill breccia (the so-called Exmore breccia) and in suevites from the Eyreville core hole, which was drilled several kilometers from the center of the 85-km-diameter Chesapeake Bay impact structure, Virginia, USA. Determining the presence of an extraterrestrial component and, in particular, the projectile type for this structure, which is the largest impact structure currently known in the United States, is of importance because it marks one of several large impact events in the late Eocene, during which time the presence of extraterrestrial 3He and multiple impact ejecta layers provide evidence for a comet or asteroid shower. Previous work has indicated an ordinary chondritic projectile for the largest of the late Eocene craters, the Popigai impact structure in Siberia. The exact relation between the Chesapeake Bay impact event and siderophile element anomalies documented in late Eocene ejecta layers from around the world is not clear. The only clear indication for an extraterrestrial component related to this structure has been the discovery of a meteoritic osmium isotopic signature in impact melt rocks recovered from a hydrogeologic test hole located on Cape Charles near the center of the structure, and confirmation of a similar signature in suevitic rocks would have been desirable in order to place constraints on the type of projectile involved in formation of the Chesapeake Bay crater. Unfortunately, the current data show no discernible differences in the contents of the platinum group elements (PGEs) among the suevite, the Exmore breccia, and several crystalline basement rocks, all from the Eyreville core hole. Abundances of PGEs are uniformly low (e.g., <0.1 ppb Ir), and chondrite-normalized abundance patterns are nonchondritic. These data do not allow unambiguous verification of an extraterrestrial signature. Thus, the nature of the Chesapeake Bay projectile remains ambiguous. © 2009 The Geological Society of America.
861.
Seasonally chemical weathering and CO2 consumption flux of Lake Qinghai river system in the northeastern Tibetan Plateau
Environmental Earth Sciences,
59
(2)
297 – 313
2009
ISSN: 18666299Keywords:▾
China; Himalayas; Qinghai; Qinghai Lake; Qinghai-Xizang Plateau; Atmospheric chemistry; Atmospheric thermodynamics; Carbonation; Dissolution; Geochemistry; Groundwater; Lakes; Positive ions; Rain; Sediments; Silicates; Sodium chloride; Soil mechanics; Water levels; Weathering; Anion composition; Atmospheric inputs; Carbonate weathering; Chemical weathering; Forward models; High concentration; Himalayas; Lacustrine sediments; Monsoon season; Post-monsoon; Pre-monsoon; River systems; River water; Seasonal variation; Silicate weathering; Tibetan Plateau; Total dissolved solids; Water chemistry; Water composition; carbon dioxide; chemical weathering; ionic composition; lacustrine deposit; river system; river water; seasonal variation; water chemistry; Rivers
Abstract: ▾ The major cation and anion compositions of waters from the Lake Qinghai river system (LQRS) in the northeastern Tibetan Plateau were measured. The waters were collected seasonally from five main rivers during premonsoon (late May), monsoon (late July), and post-monsoon (middle October). The LQRS waters are all very alkaline and have high concentrations of TDS (total dissolved solids) compared to rivers draining the Himalayas and the southeastern Tibetan Plateau. Seasonal variations in the water chemistry show that, except the Daotang River, the TDS concentration is high in October and low in July in the LQRS waters. The forward models were used to quantify the input of three main rivers (Buha River, Shaliu River, and Hargai River) from rain, halite, carbonates, and silicates. The results suggest that (1) atmospheric input is the first important source for the waters of the Buha River and the Shaliu River, contributing 36-57% of the total dissolved cations, (2) carbonate weathering input and atmospheric input have equal contribution to the Hargai River water, (3) carbonate weathering has higher contribution to these rivers than silicate weathering, and (4) halite is also important source for the Buha River. The Daotang River water is dominated by halite input owing to its underlying old lacustrine sediments. The water compositions of the Heima River are controlled by carbonate weathering and rainfall input in monsoon season, and groundwater input may be important in pre-monsoon and post-monsoon seasons. After being corrected the atmospheric input, average CO2 drawdown via silicate weathering in the LQRS is 35×103 mol/km2 per year, with highest in monsoon season, lower than Himalayas and periphery of Tibetan Plateau rivers but higher than some rivers draining shields. © Springer-Verlag 2009.
860.
The Eocene-Oligocene sedimentary record in the Chesapeake Bay impact structure: Implications for climate and sea-level changes on the western Atlantic margin
Special Paper of the Geological Society of America,
458839-865
2009
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Deposition; Erosion; Gamma rays; Infill drilling; Isotopes; Kaolinite; Lithology; Magnetic susceptibility; Mica; Sea level; Sedimentology; Stratigraphy, Chesapeake bay impact structures; Continental scientific drillings; Depositional environment; Highstand systems tract; Mineralogical compositions; Planktonic foraminifera; U.s. geological surveys; Warm and humid climates, Sediments, biostratigraphy; depositional environment; Eocene-Oligocene boundary; eustacy; geological survey; impact structure; lithology; paleoclimate; progradation; sea level change; sedimentary sequence; sedimentation; sequence boundary; sequence stratigraphy; systems tract, Atlantic Ocean; Atlantic Ocean (West); Chesapeake Bay; United States, Foraminifera
Abstract: ▾ A multidisciplinary investigation of the Eocene-Oligocene transition in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville core from the Chesapeake Bay impact basin was conducted in order to document environmental changes and sequence stratigraphic setting. Planktonic foraminifera and calcareous nannofossil biostratigraphy indicate that the Eyreville core includes an expanded upper Eocene (Biozones E15 to E16 and NP19/20 to NP21, respectively) and a condensed Oligocene-Miocene (NP24-NN1) sedimentary sequence. The Eocene-Oligocene contact corresponds to a =3-Ma-long hiatus. Eocene- Oligocene sedimentation is dominated by great diversity and varying amounts of detrital and authigenic minerals. Four sedimentary intervals are identified by lithology and mineral content: (1) A 30-m-thick, smectite- and illite-rich interval directly overlies the Exmore Formation, suggesting long-term reworking of impact debris within the Chesapeake Bay impact structure. (2) Subsequently, an increase in kaolinite content suggests erosion from soils developed during late Eocene warm and humid climate in agreement with data derived from other Atlantic sites. However, the kaolinite increase may also be explained by change to a predominant sediment input from outside the Chesapeake Bay impact structure caused by progradation of more proximal facies belts during the highstand systems tract of the late Eocene sequence E10.Spectral analysis based on gamma-ray and magnetic susceptibility logs suggests infl uence of 1.2 Ma low-amplitude oscillation of the obliquity period during the late Eocene. (3) During the latest Eocene (Biozones NP21 and E16), several lithological contacts (clay to clayey silt) occur concomitant with a prominent change in the mineralogical composition with illite as a major component: This lithological change starts close to the Biozone NP19/20-NP21 boundary and may correspond to sequence boundary E10-E11 as observed in other northwest Atlantic margin sections. It could result from a shift to more distal depositional environments and condensed sedimentation during maximum fl ooding, rather than refl ecting a climatic change in the hinterland. The distinct 1% increase of the oxygen isotopes may correspond to the short-term latest Eocene "precursor isotope event." (4) The abrupt increase of sediment grainsize, carbonate content, and abundance of authigenic minerals (glauconite) across the major unconformity that separates Eocene from Oligocene sediments in the Eyreville core refl ects deposition in shallower settings associated with erosion, winnowing, and reworking. Sediments within the central crater were affected by the rapid eustatic sea-level changes associated with the greenhouse-icehouse transition, as well as by an abrupt major uplift event and possibly enhanced current activity on the northwestern Atlantic margin. © 2009 The Geological Society of America.
859.
Sedimentary organic matter characteristics and hydrocarbon potential of Qingshankou Formation of SK-1 drilling from Songliao Basin
Geochimica,
38487-497
2009
858.
Seismic modeling of multidimensional heterogeneity scales of mallik gas hydrate reservoirs, Northwest territories of Canada
Journal of Geophysical Research: Solid Earth,
114
(7)
2009
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
borehole; fault propagation; finite difference method; gas hydrate; geoaccumulation; heterogeneity; natural gas; P-wave; reservoir; S-wave; seismic attenuation; seismic velocity; spatial distribution; stochasticity; three-dimensional modeling, Canada; North America
Abstract: ▾ In hydrate-bearing sediments, the velocity and attenuation of compressional and shear waves depend primarily on the spatial distribution of hydrates in the pore space of the subsurface lithologies. Recent characterizations of gas hydrate accumulations based on seismic velocity and attenuation generally assume homogeneous sedimentary layers and neglect effects from large- and small-scale heterogeneities of hydrate-bearing sediments. We present an algorithm, based on stochastic medium theory, to construct heterogeneous multivariable models that mimic heterogeneities of hydrate-bearing sediments at the level of detail provided by borehole logging data. Using this algorithm, we model some key petrophysical properties of gas hydrates within heterogeneous sediments near the Mallik well site, Northwest Territories, Canada. The modeled density, and P and S wave velocities used in combination with a modified Biot-Gassmann theory provide a first-order estimate of the in situ volume of gas hydraté near the Mallik 5L-38 borehole. Our results suggest a range of 528 to 768 × 106 m3/km2 of natural gas trapped within hydrates, nearly an order of magnitude lower than earlier estimates which did not include effects of small-scale heterogeneities. Further, the petrophysical models are combined with a 3-D finite difference modeling algorithm to study seismic attenuation due to scattering and leaky mode propagation. Simulations of a near-offset vertical seismic profile and cross-borehole numerical surveys demonstrate that attenuation of seismic energy may not be directly related to the intrinsic attenuation of hydrate-bearing sediments but, instead, may be largely attributed to scattering from small-scale heterogeneities and highly attenuate leaky mode propagation of seismic waves through larger-scale heterogeneities in sediments. Copyright 2009 by the American Geophysical Union.
857.
Silicate glasses and sulfide melts in the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure, Virginia, USA
Special Paper of the Geological Society of America,
458447-468
2009
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Copper compounds; Corundum; Electron probe microanalysis; Feldspar; Hydration; Iron; Magnetite; Melting; Mixing; Phosphate minerals; Positive ions; Pyrites; Silica; Silicates; Spheres; Structure (composition); Sulfur compounds; Textures, Chesapeake bay impact structures; Compositional range; Glass compositions; High silica glass; Hydrothermal system; Peak temperatures; Pressure and temperature; Spherical globules, Glass, chemical composition; crater; impact structure; marine sediment; silicate; suevite; sulfide, Chesapeake Bay; United States
Abstract: ▾ Optical and electron-beam petrography of melt-rich suevite and melt-rock clasts from selected samples from the Eyreville B core, Chesapeake Bay impact structure, reveal a variety of silicate glasses and coexisting sulfur-rich melts, now quenched to various sulfi de minerals (±iron). The glasses show a wide variety of textures, fl ow banding, compositions, devitrifi cation, and hydration states. Electron-microprobe analyses yield a compositional range of glasses from high SiO 2 (>90 wt%) through a range of lower SiO 2 (55-75 wt%) with no relationship to depth of sample. Some samples show spherical globules of different composition with sharp menisci, suggesting immiscibility at the time of quenching. Isotropic globules of higher interfacial tension glass (64 wt% SiO 2 ) are in sharp contact with lower-surface-tension, high-silica glass (95 wt% SiO 2 ). Immiscible glass-pair composition relationships show that the immiscibility is not stable and probably represents incomplete mixing. Devitrifi cation varies and some low-silica, high-iron glasses appear to have formed Fe-rich smectite; other glass compositions have formed rapid quench textures of corundum, orthopyroxene, clinopyroxene, magnetite, K-feldspar, plagioclase, chrome-spinel, and hercynite. Hydration (H 2 O by difference) varies from ~10 wt% to essentially anhydrous; high-SiO 2 glasses tend to contain less H2O. Petrographic relationships show decomposition of pyrite and melting of pyrrhotite through the transformation series; pyrite? pyrrhotite? troilite→ iron. Spheres (~1 to ~50 μm) of quenched immiscible sulfi de melt in silicate glass show a range of compositions and include phases such as pentlandite, chalcopyrite, Ni-As, monosulfi de solid solution, troilite, and rare Ni-Fe. Other sulfi de spheres contain small blebs of pure iron and exhibit a continuum with increasing iron content to spheres that consist of pure iron with small, remnant blebs of Fe-sulfi de. The Ni-rich sulfi de phases can be explained by melting and/or concentrating targetderived Ni without requiring an asteroid impactor source component. The presence of locally unaltered glasses in these rocks suggests that in some rock volumes, isolation from postimpact hydrothermal systems was suffi cient for glass preservation. Pressure and temperature indicators suggest that, on a thin-section scale, the suevites record rapid mixing and accumulation of particles that sustained widely different peak temperatures, from clasts that never exceeded 300 ± 50 °C, to the bulk of the glasses where melted sulfi de and unmelted monazite suggest temperatures of 1500 ± 200 °C. The presence of coesite in some glass-bearing samples suggests that pressures exceeded ~3 GPa. © 2009 Geological Society of America.
856.
Static stress drop associated with brittle slip events on exhumed faults
Journal of Geophysical Research: Solid Earth,
114
(2)
2009
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
earthquake; epidote; faulting; mylonite; quartz; seismology; shear stress; slip; strike-slip fault, California; North America; San Andreas; Sierra Nevada [California]; United States
Abstract: ▾ We estimate the static stress drop on small exhumed strike-slip faults in the Lake Edison granodiorite of the central Sierra Nevada (California). The subvertical strike-slip faults were exhumed from 4 to 15 km depth and were chosen because they are exposed in outcrop along their entire tip-to-tip lengths of 8-12 m. Slip nucleated on joints and accumulated by crystal-plastic shearing (forming quartz mylonites from early quartz vein filling in joints) and successive brittle faulting (forming epidote-bearing cataclasites). The occurrence of thin, ≤300 fim wide, pseudotachylytes along some small faults throughout the study area suggests that some, if not all, of the brittle slip on the study area faults may have been seismic. We suggest that the contribution of brittle, cataclastic slip to the total slip along the studied cataclasite-bearing small faults may be estimated by the length of epidote-filled, rhombohedral dilatational jogs (rhombochasms) distributed quasi-periodically along the length of the faults. The interpretation that slip recorded by rhombochasms occurred in single events is based on evidence that (1) epidote crystals are randomly oriented and undeformed within the rhombochasm; (2) cataclasite in principal slip zones does not include clasts of previous cataclasite, and (3) rhombochasm lengths vary systematically along the length of the faults with slip maximum occurring near the fault center, tapering to the fault tips. We thereby constrain both the rupture length and slip. On the basis of these measurements, we calculate stress drops ranging over 90-250 MPa, i.e., one to two orders of magnitude larger than typical seismological estimates for earthquakes, but similar in magnitude to seismological estimates of small (<M2) earthquakes from the San Andreas Fault Observatory at Depth (SAFOD). The slip events described in the present study occurred along small, deep-seated faults, and, given the calculated stress drops and observations that brittle faults exploited joints sealed by quartz-bearing mylonite, we conclude that these were "strong" faults. © 2009 by the American Geophysical Union.
855.
Subsurface structure, physical properties, fault-zone characteristics and stress state in scientific drill holes of Taiwan Chelungpu Fault Drilling Project
Tectonophysics,
466
(3-4)
307-321
2009
ISSN: 00401951Keywords:▾
Azimuthal variations; Black materials; Chi-Chi earthquake; Drill holes; Drill sites; Drilling-induced tensile fractures; Electrical resistivities; Fault zones; Fault-zone properties; Gamma-ray; Geophysical measurements; Horizontal stress; In-situ stress; Large displacements; Leak-off tests; Low densities; Low energies; Low permeabilities; Micro cracks; Miocene; Physical mechanisms; Plio-pleistocene; Pliocene; Poisson's ratios; S-wave anisotropy; Slip zones; Smectite; Sonic velocities; Stress state; Structural geometries; Subsurface structures; Taiwan Chelungpu Fault Drilling Project; Thrust faults; Velocity anisotropies; Wave polarizations, Anisotropy; Clay minerals; Drilling; Earthquakes; Electric resistance; Gamma rays; Lithology; Poisson ratio; Polarization; Rock drills; Seismic waves; Shear waves; Stratigraphy; Structural geology; Thermal logging; Viscosity measurement; Waves, Boreholes, borehole breakout; Chi-Chi earthquake 1999; deformation; drilling; fault geometry; fault propagation; fault zone; in situ stress; lithology; Miocene; P-wave; physical property; Pleistocene; Pliocene; S-wave; seismic anisotropy; wave velocity
Abstract: ▾ Continuous cores and a suit of geophysical measurements were collected in two scientific drill holes to understand physical mechanisms involved in the large displacements during the 1999 Chi-Chi earthquake. Physical properties obtained from wire-line logs including P- and S-wave sonic velocity, gamma ray, electrical resistivity, density and temperature, are primarily dependent on parameters such as lithology, depth and fault zones. The average dip of bedding, identified from both cores and FMI (or FMS) logs, is about 30° towards SE. Nevertheless, local azimuthal variations and increasing or decreasing bedding dips appear across fault zones. A prominent increase of structural dip to 60°-80° below 1856 m could be due to deformation associated with propagation of the Sanyi fault. A total of 12 fault zones identified in hole-A are located in the Plio-Pleistocene Cholan Formation, Pliocene Chinshui Shale and Miocene Kueichulin Formation. The shallowest fault zone occurs at 1111 m depth (FZ1111). It is a 1 m gouge zone including 12 cm of thick indurate black material. We interpreted this zone as the slip zone during Chi-Chi earthquake. FZ1111 is characterized by: 1) bedding-parallel thrust fault with 30-degree dip; 2) the lowest resistivity; 3) low density, Vp and Vs, 4) high Vp/Vs ratio and Poisson's ratio; 5) low energy and velocity anisotropy, and low permeability within the homogeneous 1 m gouge zone; 6) increasing gas (CO2 and CH4) emissions, and 7) appearance of smectite within the primary slip zone. In situ stresses at the drill site were inferred from leak-off tests, borehole breakouts and drilling-induced tensile fractures from borehole FMS/FMI logs, and shear seismic wave anisotropy from DSI logs. The dominant fast shear-wave polarization direction is in good agreement with regional maximum horizontal stress axis, particularly within the strongly anisotropic Kueichulin Formation. A conjugate set of secondary directions are parallel to microcrack orientations. A drastic change of orientation of fast shear-wave polarization across the Sanyi thrust fault at the depth of 1712 m reflects the change of stratigraphy, physical properties and structural geometry. © 2007 Elsevier B.V. All rights reserved.
854.
Supplemental materials for the ICDP-USGS Eyreville A, B, and C core holes, Chesapeake Bay impact structure: Core-box photographs, coring-run tables, and depth-conversion files
Special Paper of the Geological Society of America,
458115-118
2009
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Boreholes; CD-ROM; Infill drilling; Photography, Basic application; Chesapeake bay impact structures; Continental scientific drillings; Conversion programs; Data repositories; Digital photographs; Measurement data; U.s. geological surveys, Electronic document exchange, borehole logging; impact structure; information technology; photograph, Chesapeake Bay; United States
Abstract: ▾ During 2005-2006, the International Continental Scientific Drilling Program and the U.S. Geological Survey drilled three continuous core holes into the Chesapeake Bay impact structure to a total depth of 1766.3 m. A collection of supplemental materials that presents a record of the core recovery and measurement data for the Eyreville cores is available on CD-ROM at the end of this volume and in the GSA Data Repository. The supplemental materials on the CD-ROM include digital photographs of each core box from the three core holes, tables of the three coring-run logs, as recorded on site, and a set of depth-conversion programs. In this chapter, the contents, purposes, and basic applications of the supplemental materials are briefly described. With this information, users can quickly decide if the materials will apply to their specific research needs. © 2009 The Geological Society of America.
853.
Tectonic evolution of the Ganos segment of the North Anatolian Fault (NW Turkey)
Journal of Structural Geology,
31
(1)
11-28
2009
ISSN: 01918141Keywords:▾
Fault architecture; Fluid inclusions; Ganos fault; Seismicity; Stable isotopes; Turkey, Calcite; Carbonate minerals; Deformation; Inclusions; Isotopes; Limestone; Methane; Mineralogy; Oxide minerals; Quartz, Structural geology, deformation mechanism; fault zone; faulting; kinematics; North Anatolian Fault; paleostress; strike-slip fault; tectonic evolution, Eurasia; Turkey
Abstract: ▾ We analyzed the paleostress field, ongoing deformation, meso- to micro-scale faulting, cataclasis, fault rock alteration and veining within turbidite and limestone sequences at the Ganos Fault which represent a major branch of the North Anatolian Fault Zone in NW Turkey. Fault damage was found to occur across a several kilometers wide zone. Effects of faulting are shown by localized subsidiary brittle faults and fault rock alteration in the turbidites as well as fault breccia formation in the limestone sequence. Microseismicity along the Ganos Fault cluster at two locations, the more pronounced being located offshore at a fault bend associated with a change from a transpressional to a transtensional regime. Kinematic analysis reveals a dextral strike-slip regime with components of normal and thrust faulting. Along strike paleostress orientation at the Ganos Fault is rather uniform. Deformation mechanisms and fluid inclusion data from quartz and calcite veins suggest that fault-related quartz veins were formed at temperatures between 170 and 250 °C and pressures between 40 and 120 MPa. Fault-related calcite vein growth occurred during a temperature decrease from 170 °C to 70 °C with pressures likely below 50 MPa. Fluid inclusion and stable isotope data show that the fluids are predominantly of meteoric origin and migrated upwards into the fault. Pure CH4 inclusions in quartz also suggest a biogenic or thermogenic methane origin. © 2008 Elsevier Ltd. All rights reserved.
852.
The crust-mantle transition and the Moho beneath the Vogtland/West Bohemian region in the light of different seismic methods
Studia Geophysica et Geodaetica,
53
(3)
275 – 294
2009
ISSN: 00393169Keywords:▾
Bohemian Massif; Central Europe; Eurasia; Europe; Germany; Vogtland; coda; crust-mantle boundary; crustal structure; lower crust; Moho; ray tracing; seismic method; seismic reflection; seismic refraction; transition zone
Abstract: ▾ The structure of the crust and the crust-mantle boundary in the Vogtland/ West Bohemian region have been a target of several seismic measurements for the last 25 years, beginning with the steep-angle reflection seismic studies (DEKORP-4/KTB, MVE-90, 9HR), the refraction and wide-angle experiments (GRANU'95, CELEBRATION 2000, SUDETES 2003), and followed by passive seismic studies (receiver functions, teleseismic tomography). The steep-angle reflection studies imaged a highly reflective lower crust (4 to 6 km thick) with the Moho interpreted in a depth between 30 and 32 km and a thinner crust beneath the Eger Rift. The refraction and wide-angle reflection seismic studies (CELEBRATION 2000) revealed strong wide-angle reflections in a depth of 26-28 km interpreted as the top of the lower crust. Long coda of these reflections indicates strong reflectivity in the lower crustal layer, a phenomenon frequently observed in the Caledonian and Variscan areas. The receiver function studies detected one strong conversion from the base of the crust interpreted as the Moho discontinuity at a depth between 27 and 37 km (average at about 31 km). The discrepancies in the Moho depth determination could be partly attributed to different background of the methods and their resolution, but could not fully explain them. So that new receivers function modelling was provided. It revealed that, instead of a first-order Moho discontinuity, the observations can be explained with a lower crustal layer or a crust-mantle transition zone with a maximum thickness of 5 km. The consequent synthetic ray-tracing modelling resulted in the model with the top of the lower crust at 28 km, where highly reflective lower crustal layer can obscure the Moho reflection at a depth of 32-33 km. © Institute of Geophysics of the ASCR, v.v.i 2009.
851.
In situ LA-SF-ICP-MS U-Pb dating of metasomatic zircon growth during retrogression of UHP eclogites, Sulu deep drilling hole, China
European Journal of Mineralogy,
21
(6)
1251 – 1264
2009
ISSN: 09351221
Publisher: Gebruder Borntraeger Verlagsbuchhandlung
Keywords:▾
Binary alloys; Gasoline; Geochronology; Inductively coupled plasma mass spectrometry; Infill drilling; Metamorphic rocks; Mica; Barium concentrations; Continental scientific drillings; Eclogites; Retrogression; Thermodynamic modelling; U-Pb dating; Ultra high pressure (UHP); Ultra-high pressure metamorphisms; amphibolite; Chinese Continental Scientific Drilling Project; eclogite; exhumation; inductively coupled plasma method; mass spectrometry; petrology; ultrahigh pressure metamorphism; uranium-lead dating; zircon; Zircon
Abstract: ▾ Thermobarometry and in situ U-Pb dating of zircon in texturally and petrologically defined positions are used to assess exhumation accompanied by fluid-enhanced retrogression of ultra high pressure (UHP) eclogite core samples from the Chinese Continental Scientific Drilling (CCSD) project. Eclogites from the CCSD project show discrete retrograde zones that can be attributed to exhumation processes. The retrogression from UHP eclogite to HP eclogite, amphibolite and finally greenschist facies conditions is fluid-induced. The occurrence of significant barium concentrations in two mica generations points to an external fluid source during retrogression. This Ba and F-bearing fluid mobilized zirconium from the eclogitic host, which was preferentially precipitated as overgrowths on pre-existing grains in the retrograde zone. Thermodynamic modelling with progressive addition of H2O to the bulk composition simulates the petrological development of the fluid-influenced retrograde zone. Growth of zircon precipitated from the fluid occurred between 730°-740 °C at 3.46 GPa and 700 °C at 1.4 GPa. LA-SF-ICPMS analyses point to a local onset of metasomatic zircon growth at 233.1 ± 5.3 Ma ongoing to 207.4 ± 1.6 Ma that is spatially limited to the retrograde zone. © 2009 E. Schweizerbart'sche Verlagsbuchhandlung.
850.
A petrographic and fluid inclusion assessment of hydrothermal alteration of some impactites and crystalline rocks in the Chesapeake Bay impact structure, ICDP-USGS Eyreville B core
Special Paper of the Geological Society of America,
458543-557
2009
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Calcite; Clay alteration; Crystalline rocks; Groundwater; Infill drilling; Mineralogy; Sodium chloride; Zeolites, Chesapeake bay impact structures; Continental scientific drillings; Eastern north america; Hydrothermal activity; Hydrothermal alterations; Hydrothermal circulation; Total dissolved solids; U.S geological surveys, Nitrogen compounds, assessment method; breccia; crystalline rock; fluid inclusion; hydrothermal activity; hydrothermal alteration; hydrothermal circulation; hydrothermal deposit; hydrothermal system; impact structure; impactite; petrography; research program; secondary mineral; shock metamorphism; suevite, Chesapeake Bay; United States
Abstract: ▾ Core samples from the International Continental Scientific Drilling Program (ICDP)-U.S Geological Survey (USGS) Eyreville B core, located in the central crater of the Chesapeake Bay impact structure, were studied to determine the degree to which postimpact hydrothermal activity is recorded in secondary minerals and fluid inclusions. The Chesapeake Bay impact event occurred ̃35 Ma ago on the siliciclastic continental shelf of eastern North America, in up to several hundred meters of water. The combination of hot materials, such as impact melts and suevite breccias, with overlying crater-fill material and seawater is hypothesized to have led to postimpact hydrothermal circulation. Secondary minerals are distinguished from pre-impact minerals by textural features such as the presence or absence of shock metamorphic effects. Minerals in veins and cavities that are shown to have formed after the impact include secondary calcite, chalcedony, phillipsite, clinoptilolite-heulandite, mordenite, and montmorillonite. Some secondary calcite contains liquid-only fluid inclusions with trapping temperatures constrained to be less than or equal to ̃50 °C. Salinities of the inclusion fluids are mostly around 4.3 ± 1 wt% NaCl equivalent, or ̃43 ± 10 g/L total dissolved solids. This salinity is similar to that of the anomalously saline groundwater that currently exists within the crater-fill material, and that could be relict brine that originated just after the impact. © 2009 The Geological Society of America.
849.
Identification of the projectile component in the impact structures Rochechouart, France and Sääksjärvi, Finland: Implications for the impactor population for the earth
Geochimica et Cosmochimica Acta,
73
(16)
4891-4906
2009
Abstract: ▾ A set of 11 impact melt rock samples from the Rochechouart impact structure, France and nine impact melt rock samples from Sääksjärvi impact structure, Finland were studied for their major and trace element compositions, including the abundances of the platinum group elements. The main goal of this study was to identify the projectile type(s) responsible for the formation of these two impact structures. The results confirmed previous studies that suggested extraterrestrial contamination in both the Rochechouart and Sääksjärvi impact melt rocks. The projectile types found for Rochechouart and Sääksjärvi are quite similar, and compatible with the composition of non-magmatic iron meteorites (IA and IIIC). This interpretation is based on: identical platinum group element patterns as well as peculiar Ni/Cr, Ni/Ir and Cr/Ir ratios, which can be explained by mixing of the different components of non-magmatic iron meteorites. This result indicates that, besides ordinary chondrites, non-magmatic iron may be among the most common material impacting the Earth, as they also represent the majority of the projectiles for craters smaller that 1.5 km. The abundance of non-magmatic irons as projectiles as well as their composition (olivine, pyroxene and iron) supports the assumption that a fraction of the S-type asteroids could by related to this type of material. © 2009.
848.
Cooling rates of basaltic hyaloclastites and pillow lava glasses from the HSDP2 drill core
Geochimica et Cosmochimica Acta,
73
(4)
1052 – 1066
2009
ISSN: 00167037Keywords:▾
basalt; calorimetry; chemical composition; clastic rock; cooling; Deep Sea Drilling Project; deposition; differential thermal analysis; experimental study; fragmentation; hyaloclastite; phase transition; pillow lava; underwater environment; volatile substance
Abstract: ▾ Cooling rates have been determined for basaltic glasses from different depths of the submarine section of the drill core recovered in the 1999 phase of Hawaii Scientific Drilling Project (HSDP2). The glasses include degassed blocky hyaloclastite clasts and undegassed pillow rims. The degassed glassy clasts were generated in subaerial or shallow submarine environments, during explosive interactions between lava and seawater, before eventual deposition under water. The volatile contents of the glassy pillow rims are consistent with eruption and quenching in water several hundred metres deep. The cooling rates have been calculated from the calorimetric properties of the glass across the glass transition. The heat capacity (cp) of each sample was measured during several cycles of heating from room temperature to temperatures above their glass transition using a differential scanning calorimeter (DSC). Their compositions did not change during the thermal treatment, a prerequisite for successful cp measurements, although the glasses with higher H2O contents became more opaque and their mid-IR spectra changed. Each cp-T path exhibits the now classic features of the glass transition; glassy and liquid states separated by a hysteresis marking the transition. After experiencing the same experimental thermal history the glass transition occurs at lower temperatures in glasses with higher H2O contents. Except for one sample, the cp-T path measured on initial heating also releases energy stored during the natural quench, which is not recovered during subsequent experimental cooling. The energy stored in the HSDP2 glasses is much less than that observed in hyperquenched natural and synthetic glasses. Even so, the Tool-Narayanaswamy enthalpy relaxation geospeedometer, usually used to determine the cooling rates in volcanic glasses, is unable to deal with this energy release. For those samples that exhibit this feature an alternative method, developed for hyperquenched glasses, is applied. This uses the energy released to calculate Tf, from which the cooling rate is calculated. The degassed blocky hyaloclastite clasts exhibit cooling rates 0.1-72.2 K s-1, while the undegassed pillow rims span 0.2-46.4 K s-1. The fastest cooling rates are consistent with the cooling of lava bodies in seawater. The wide variation for both types of glass could reflect quenching at different distances from the basalt-seawater interface. However, for the degassed hyaloclastite clasts the range could indicate that the clasts were generated by different processes operating during the explosive interaction between lava and seawater in the littoral zone. In the undegassed pillow lavas, glassy rims may have been reheated, giving rise to more complex, slower, thermal histories, as a result of latent heat released during the crystallisation of pillow interiors, or flow replenishment. Both types of glass may also have experienced reheating from succeeding flows or deposits. Compared to deep-sea limu o Pele hyaloclastite fragments, whose hyperquench rates indicate simultaneous cooling and fragmentation, the shallow blocky hyaloclastite clasts may have formed during post-cooling brittle fragmentation. © 2008 Elsevier Ltd. All rights reserved.
847.
Constraints on mineralization, fluid-rock interaction, and mass transfer during faulting at 2-3 km depth from the SAFOD drill hole
Journal of Geophysical Research: Solid Earth,
114
(4)
2009
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
diagenesis; disequilibrium; dissolution; electron microscopy; faulting; fluid-structure interaction; geochemistry; lithology; mass transfer; mineralization; mudstone; observatory; precipitation (chemistry); titanium; X-ray diffraction; zircon, California; North America; San Andreas; United States
Abstract: ▾ Mineralogical and geochemical changes in mudrock cuttings from two segments of the San Andreas Fault Observatory at Depth (SAFOD) drill hole (3066-3169 and 3292-3368 m measured depth) are analyzed in this study. Bulk rock samples and hand-picked fault-related grains characterized by polished surfaces and slickensides were investigated by X-ray diffraction, electron microscopy and geochemical analysis. The elemental changes in fault-related grains along the sampled San Andreas Fault are attributed to dissolution of detrital grains (particularly feldspar and quartz) and local precipitation of illite-smectite and/or chlorite-smectite mixed layers in fractures and veins. Assuming ZrO 2 and TiO2 to be immobile elements, systematic differences in element concentrations show that most of the elements are depleted in the fault-related grains compared to the wall rock lithology. Calculated mass loss between the bulk rock and picked fault rock ranges from 17 to 58% with a greater mass transport in the shallow trace of the sampled fault that marks the upper limit the fault core. The relatively large amount of element transport at temperatures of ∼110-114°C recorded throughout the core requires extensive fluid circulation during faulting. Whereas dissolution/precipitation may be partly induced by the disequilibrium between fluids and rocks during diagenetic processes, stress-induced dissolution at grain contacts is proposed as the main mechanism for extensive mineral transformation in the fault rocks and localization of neomineralization along grain interface slip surfaces. Copyright 2009 by the American Geophysical Union.
846.
Constraints on the stress state of the San Andreas Fault with analysis based on core and cuttings from San Andreas Fault Observatory at Depth (SAFOD) drilling phases 1 and 2
Journal of Geophysical Research: Solid Earth,
114
(11)
2009
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
drilling; fault gouge; fault zone; friction; pore pressure; San Andreas Fault; stress field, Calluna vulgaris
Abstract: ▾ Analysis of field data has led different investigators to conclude that the San Andreas Fault (SAF) has either anomalously low frictional sliding strength (μ < 0.2) or strength consistent with standard laboratory tests (μ > 0.6). Arguments for the apparent weakness of the SAF generally hinge on conceptual models involving intrinsically weak gouge or elevated pore pressure within the fault zone. Some models assert that weak gouge and/or high pore pressure exist under static conditions while others consider strength loss or fluid pressure increase due to rapid coseismic fault slip. The present paper is composed of three parts. First, we develop generalized equations, based on and consistent with the Rice (1992) fault zone model to relate stress orientation and magnitude to depth-dependent coefficient of friction and pore pressure. Second, we present temperature-and pressure-dependent friction measurements from wet illite-rich fault gouge extracted from San Andreas Fault Observatory at Depth (SAFOD) phase 1 core samples and from weak minerals associated with the San Andreas Fault. Third, we reevaluate the state of stress on the San Andreas Fault in light of new constraints imposed by SAFOD borehole data. Pure talc (μ≈0.1) had the lowest strength considered and was sufficiently weak to satisfy weak fault heat flow and stress orientation constraints with hydrostatic pore pressure. Other fault gouges showed a systematic increase in strength with increasing temperature and pressure. In this case, heat flow and stress orientation constraints would require elevated pore pressure and, in some cases, fault zone pore pressure in excess of vertical stress. Copyright 2009 by the American Geophysical Union.
845.
Constraints on water chemistry by chemical weathering in the Lake Qinghai catchment, northeastern Tibetan Plateau (China): Clues from Sr and its isotopic geochemistry
Hydrogeology Journal,
17
(8)
2037 – 2048
2009
ISSN: 14312174Keywords:▾
Asia; Buha River; China; Eurasia; Far East; Qinghai; Qinghai-Xizang Plateau; catchment; chemical weathering; geochemistry; groundwater flow; hydrochemistry; hydrogeology; isotopic composition; lake water; limestone; river water; sandstone; strontium isotope; tributary; water budget; water chemistry
Abstract: ▾ Lake water, river water, and groundwater from the Lake Qinghai catchment in the northeastern Tibetan Plateau, China have been analyzed and the results demonstrate that the chemical components and 87Sr/86Sr ratios of the waters are strictly constrained by the age and rock types of the tributaries, especially for groundwater. Dissolved ions in the Lake Qinghai catchment are derived from carbonate weathering and part from silicate sources. The chemistry of Buha River water, the largest tributary within the catchment, underlain by the late Paleozoic marine limestone and sandstones, constrains carbonate-dominated compositions of the lake water, being buffered by the waters from the other tributaries and probably by groundwater. The variation of 87Sr/86Sr ratios with cation concentrations places constraint on the Sr-isotopic compositions of the main subcatchments surrounding Lake Qinghai. The relative significance of river-water sources from different tributaries (possibly groundwater as well) in controlling the Sr distribution in Lake Qinghai provides the potential to link the influence of hydrological processes to past biological and physical parameters in the lake. The potential role of groundwater input in the water budget and chemistry of the lake emphasizes the need to further understand hydrogeological processes within the Lake Qinghai system. © 2009 Springer-Verlag.