All ICDP Publications with Abstracts
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144.
Geochemical constraints of the eclogite and granulite facies metamorphism as recognized in the Raobazhai complex from North Dabie Shan, China
Journal of Metamorphic Geology,
19
(1)
3 – 19
2001
ISSN: 02634929Keywords:▾
China; eclogite; geochemistry; granulite; metamorphism
Abstract: ▾ A combined study of major and trace elements, fluid inclusions and oxygen isotopes has been carried out on garnet pyroxenite from the Raobazhai complex in the North Dabie Terrane (NDT). Well-preserved compositional zoning with Na decreasing and Ca and Mg increasing from the core to rim of pyroxene in the garnet pyroxenite indicates eclogite facies metamorphism at the peak metamorphic stage and subsequent granulite facies metamorphism during uplift. A P-T path with substantial heating (from c. 750 to 900 °C) after the maximum pressure reveals a different uplift history compared with most other eclogites in the South Dabie Terrane (SDT). Fluid inclusion data can be correlated with the metamorphic grade: The fluid regime during the peak metamorphism (eclogite facies) was dominated by N2-bearing NaCl-rich solutions, whereas it changed into CO2-dominated fluids during the granulite facies retrograde metamorphism. At a late retrograde metamorphic stage, probably after amphibolite facies metamorphism, some external low-salinity fluids were involved. In situ UV-laser oxygen isotope analysis was undertaken on a 7 mm garnet, and impure pyroxene, amphibole and plagioclase. The nearly homogenous oxygen isotopic composition (δ18OVSMOW=c. 6.7‰) in the garnet porphyroblast indicates closed fluid system conditions during garnet growth. However, isotopic fractionations between retrograde phases (amphibole and plagioclase) and garnet show an oxygen isotopic disequilibrium, indicating retrograde fluid-rock interactions. Unusual MORB-like rare earth element (REE) patterns for whole rock of the garnet pyroxenite contrast with most ultra-high-pressure (UHP) eclogites in the Dabie-Sulu area. However, the age-corrected initial εNd(t) is - 2.9, which indicates that the protolith of the garnet pyroxenite was derived from an enriched mantle rather than from a MORB source. Combined with the present data of oxygen isotopic compositions and the characteristics N2 content in the fluid inclusions, we suggest that the protolith of the garnet pyroxenite from Raobazhai formed in an enriched mantle fragment, which has been exposed to the surface prior to the Triassic metamorphism.
143.
Elastic properties of gas hydrate-bearing sediments
Geophysics,
66
(3)
763-771
2001
ISSN: 00168033
Publisher: Society of Exploration Geophysicists
Keywords:▾
Elasticity; Hydrates; Pore size; Sediments; Velocity; Gases; Hydration; Poisson ratio; Shear flow; Shear waves, Hydrate-bearing sediments; Compressional; Effective medium theories; Elastic properties; Gas hydrate bearing sediments; Gas hydrate concentrations; Gas hydrate saturations; Sediment porosities; Shear wave velocity, Geophysics; Gas hydrates, elastic property; gas hydrate; P-wave; S-wave; sediment; seismic velocity
Abstract: ▾ Downhole-measured compressional- and shear-wave velocities acquired in the Mallik 2L-38 gas hydrate research well, northwestern Canada, reveal that the dominant effect of gas hydrate on the elastic properties of gas hydrate-bearing sediments is as a pore-filling constituent. As opposed to high elastic velocities predicted from a cementation theory, whereby a small amount of gas hydrate in the pore space significantly increases the elastic velocities, the velocity increase from gas hydrate saturation in the sediment pore space is small. Both the effective medium theory and a weighted equation predict a slight increase of velocities from gas hydrate concentration, similar to the field-observed velocities; however, the weighted equation more accurately describes the compressional- and shear-wave velocities of gas hydrate-bearing sediments. A decrease of Poisson's ratio with an increase in the gas hydrate concentration is similar to a decrease of Poisson's ratio with a decrease in the sediment porosity. Poisson's ratios greater than 0.33 for gas hydrate-bearing sediments imply the unconsolidated nature of gas hydrate-bearing sediments at this well site. The seismic characteristics of gas hydrate-bearing sediments at this site can be used to compare and evaluate other gas hydrate-bearing sediments in the Arctic.
142.
Eclogite-facies quartz veins within metabasites of the Dabie Shan (Eastern China): Pressure-temperature-time-deformation path, composition of the fluid phase and fluid flow during exhumation of high-pressure rocks
Contributions to Mineralogy and Petrology,
141
(3)
322 – 346
2001
ISSN: 00107999Keywords:▾
China; deformation; eclogite; exhumation; fluid flow; metamorphism; P-T conditions; P-T-t path
Abstract: ▾ Metabasites in the high-pressure unit of the southern Dabie Shan (eastern China) contain quartz veins with high-pressure mineral assemblages. Two veins with the parageneses quartz-paragonite-ankerite-rutile and quartz-kyanite-talc-zoisite-rutile-calcite (pseudomorph after aragonite) as well as quartz-kyanite-paragonite- garnet-omphacite were investigated in detail. Host rocks of these veins are garnet amphibolites with eclogitic relics and quartz eclogites, respectively. The oldest phase of deformation (DI) is recorded in the eclogite, which displays a schistosity with shape alignment of high-pressure minerals such as omphacite, phengite and garnet. An estimate of the metamorphic P-T conditions yields 19-21 kbar at 570-620 °C for the eclogites. Fluid inclusion studies reveal a primary, low-salinity aqueous fluid phase responsible for the formation of the quartz veins. This is in correspondence with calculations of phase equilibrium curves on minerals of the vein paragenesis, which yield P-T conditions of 19.4 kbar and 591 °C in the presence of an aqueous fluid phase. Geochronology using the U-Pb system of rutile gives evidence for a Triassic minimum age of 207-221 Ma for the vein formation, which fits in the geotectonic framework of the orogen. This rather wide age range arises from the heterogeneous nature of the initial lead isotopic composition, reflecting the heterogeneous sources of the lead and the fluid phase. Part of the fluid was probably generated by prograde dehydration reactions in the country rocks of the veins, whereas strong evidence is also given for the derivation from an older basement, which also underwent subduction. The veins may have formed by extensive hydraulic fracturing or by volume reduction during eclogitisation of the crust. Subsequent to the formation of the veins, great parts of the high-pressure rocks experienced an intensive, syn-tectonic (D2) amphibolite facies metamorphism at 8.5-10.5 kbar and 590-645 °C, indicating isothermal decompression during exhumation. In the course of this exhumation, pseudosecondary CO2 inclusions were trapped in quartz of the veins. The last recorded stage of the retrograde overprint took place under static, greenschist facies conditions (450-480 °C) in the stability field of kyanite. The shape of the metamorphic P-T path for this stage is reflected by the fluid phase, which either re-equilibrated during this event or penetrated the rock on fractures. These findings show that fluid flow during subduction-related high-pressure metamorphism and subsequent uplift is rather complex; the fluid phase may originate from different sources and may interact with country rocks in the form of a chromatographic column transforming mineral assemblages, and also changing its own character.
141.
Differences in glacial and interglacial clay mineral associations of Baikal sediments from BDP-93-2 and BDP-96 cores
Geologiya i Geofizika,
42
(1-2)
146 – 156
2001
ISSN: 00167886Abstract: ▾ By comparing the compositions of glacial and interglacial intervals of the Late Pliocene, Pleistocene, and Holocene from different parts of Lake Baikal, we demonstrate the use of the Baikal clay mineral associations as indicators of past changes of environment and climate. The methodical part of this work discusses the optimal sample preparation techniques and develops the previously suggested method for structural modeling of X-ray diffraction patterns as the most suitable for studying the Baikal sediments. The clay mineral associations in the Selenga delta area and at the Akademichesky Ridge are very similar, thus indicating a minor influence of local sediment sources on their formation. The similarities revealed by this comparison indicate uniformity of the Baikal catchment basin in terms of the processes of erosion, weathering, and supply of sediments. Despite the conditions of continuous hemipelagic sedimentation at the sites where deep drilling took place, both drill cores reveal a strong relation between the composition of clay mineral associations and paleoclimatic conditions. Intervals if glacial sediments during both the Late Pleistocene and the Late Pliocene are similar and are characterized by dramatic enrichment in well-crystallized mica (muscovite) and plagioclase, indicating intensification of physical weathering under cold climatic conditions. Interglacial intervals are enriched in fine illite, which suggests that it is a secondary mineral, the product of chemical weathering. In addition, the content of smectite layers in mixe layer illite-smectite increases during interglacials, which is also likely to imply a warmer and more humid climate. The lower interval of the BDP-96 core with the age over 4.5 Ma is characterized by an anomalous composition: high content of illite-smectite with a high concentration of smectite component, the presence of chlorite-smectite, and low contents of illite and muscovite. This specific mineral association has formed under climatic conditions much warmer than at present.
140.
Detailed diatom biostratigraphy of Baikal sediments during the brunhes chron and climatic factors of species formation
Geologiya i Geofizika,
42
(1-2)
108 – 129
2001
ISSN: 00167886Abstract: ▾ The Baikal bottom sediments (borehole BDP-96-2) are stratigraphically characterized in detail (with a 500 year resolution) within the Brunhes Chron. The sediment section 35 m thick shows a distribution of diatoms (25 species and varieties), sponge spicules, and golden-algae cysts. Thirty-one local diatom zones are recognized in the section, providing a detailed stratigraphic division of the Baikal sediments. The distribution of diatom frustules and the diatom zones are correlated with the marine isotope stratigraphy. Climate played an important role in the formation of species of plankton diatoms in the lake. More than 21 new species of diatoms appear and then disappear in the section. Diatom species extinguished when glaciations began, and new species appeared during interglaciations. This suggests that the evolution of plankton diatoms in Baikal is under climatic control.
139.
Density of basalt core from Hilo drill hole, Hawaii
Journal of Volcanology and Geothermal Research,
112
(1-4)
221 – 230
2001
ISSN: 03770273Keywords:▾
United States; Landslides; Stratigraphy; Thermal effects; Volcanic rocks; basalt; density; hyaloclastite; pillow lava; stratigraphy; Hyaloclastite; Volcanoes
Abstract: ▾ Density measurements of 1600 samples of core from 889 to 3097 m depth below sea level in the Hawaii Scientific Drilling Program hole near Hilo, Hawaii show marked differences between the basaltic rock types and help define stratigraphy in the hole. Water-saturated densities of subaerial lava flows (occurring above 1079 m depth) have the broadest range because of the large density variation within a single lava flow. Water-saturated densities commonly range from 2.0 to 3.0 with an average of 2.55 ± 0.24 g/cc. Dikes and sills range from 2.8 to 3.1 g/cc). Densities of hyaloclastite commonly range from 2.3 to 2.7, with an overall average of about 2.5 g/cc. The low-density of most hyaloclastite is due primarily to palagonitization of abundant glass and presence of secondary minerals in the interstices between fragments. Four principal zones of pillow lava, separated by hyaloclastite, occur in the drill core. The shallowest (1983-2136 m) is paradoxically the densest, averaging 3.01 ± 0.10 g/cc. The second (2234-2470 m) is decidedly the lightest, averaging 2.67 ± 0.13 g/cc. The third (2640-2790 m) and fourth (2918-bottom at 3097 m) are high, averaging 2.89 ± 0.17 and 2.97 ± 0.08 g/cc, respectively. The first pillow zone includes degassed pillows i.e. lava erupted on land that flowed into the sea. These pillows are poor in vesicles, because the subaerial, one-atmosphere vesicles were compressed when the flow descended to deeper water and higher pressure. The second (low-density, non-degassed) pillow zone is the most vesicle-rich, apparently because it was erupted subaqueously at a shallow depth. The higher densities of the third and fourth zones result from a low vesicularity of only a few percent and an olivine content averaging more than 5% for the third zone and about 10% for the fourth zone. The uppermost hyaloclastite extending about 400 m below the bottom of the subaerial basalt is poorly cemented and absorbs up to 6 wt% of water when immersed. Progressing downward the hyaloclastite absorbs less water and becomes better cemented. This change is apparently due to palagonitization of glass and addition of secondary minerals in the deeper older hyaloclastite, a process favored by the increase of temperature with depth. The cementation is largely complete at 1800 m depth where the temperature attains about 20°C. The zone of freshest, uncemented hyaloclastite represents the weakest rock in the drill hole and is a likely level for tectonic or landslide disruption. © 2001 Published by Elsevier Science B.V.
138.
Dating of deep-water sediments of Lake Baikal from the ratios of thorium and uranium isotopes in various fractions of their authigenic part
Geologiya i Geofizika,
42
(1-2)
194 – 205
2001
ISSN: 00167886Abstract: ▾ We propose a method for dating Baikal deep-water sediments from the ratios of radioactive isotopes of Th and U in various fractions of the authigenic part of the sediments. We have determined the Th-U age of six horizons of the borehole BDP-96-2 and the average parameters of gravitational consolidation of the sediments. The extrapolated Th-U ages show a good correlation with paleomagnetic data throughout the core of BDP-96-2.
137.
Crustal structure of the eastern Dabie Shan interpreted from deep reflection and shallow tomographic data
Tectonophysics,
333
(3-4)
347 – 359
2001
ISSN: 00401951Keywords:▾
China; crustal structure; deep seismic sounding; seismic tomography; ultrahigh pressure metamorphism
Abstract: ▾ A 20-km-long seismic line characterises the crustal reflection pattern of the easternmost Dabie Shan, the archetypal ultra-high-pressure (UHP) orogen of eastern China. The weak- to non-reflective upper crust (5 s two-way travel time (TWT); ∼ 15 km depth) is interpreted to comprise UHP rocks thrust over lithologically similar but non-UHP crust. The tectonic contact, although not imaged as a distinct reflector, is probably outlined by the rather abrupt change to diffuse but strong reflectivity within the mid to lower crust. Thus, the seismic pattern of the upper crust implies that mafic, oceanic crust does not constitute a significant proportion. The middle to lower crust (5-10 s TWT; ∼15-33 km depth) probably represents cratonal Yangtze basement, unaffected by the UHP metamorphism. The prominent lowermost reflectors (10-12 s TWT; ∼33-40 km depth) are interpreted to trace the Moho, excluding the presence of a crustal root inherited from the UHP orogeny. A tomographic P-wave velocity model for the uppermost crust (<700 m) traces shallowly W-dipping sedimentary rocks east and UHP gneisses west of the Cenozoic Tan Lu fault which is imaged to dip steeply eastward. The UHP rocks exhibit little lateral and vertical velocity variations (<10%), reflecting grossly homogeneous, gneissic lithology. Hundred-metre-scale velocity variations, however, may trace distinct large-scale structures, e.g. folds, known from outcrops and maps. © 2001 Elsevier Science B.V. All rights reserved.
136.
Kinematics of exhumation of high- and ultrahigh-pressure rocks in the Hong'an and Tongbai Shan of the Qinling-Dabie collisional orogen, eastern China
Memoir of the Geological Society of America,
194231 – 245
2001
ISSN: 00721069
Publisher: Geological Society of America
Keywords:▾
China; Eurasia; Tongbai Mountains; Deformation; Kinematics; Mica; Tectonics; Continental collisions; Early Cretaceous; High pressure; Kinematic indicators; Lateral extrusion; Qinling-Dabie orogen; Sinistral shear; Ultrahigh pressure rocks; collision; Cretaceous; detachment fold; fault zone; metamorphic rock; phosphate rock; recrystallization; tectonics; Metamorphic rocks
Abstract: ▾ The Hong'an region offers an unique opportunity to investigate the tectonics of the continental collision event preserved in high-pressure (P) and ultrahigh-P metamorphic rocks in the Qinling-Dabie orogen of eastern China. Here, the extensive Cretaceous tectonic and thermal overprint observed in the Dabie Shan is weak. Normal-sense shear along the north-dipping Huwan detachment zone at the northern edge of the Hong'an block occurred ca. 235 Ma. This detachment facilitated the bulk of the exhumation of the high- and ultrahigh-P rocks as a penetratively deformed slab. The high- and ultrahigh-P rocks are exposed in a warped extensional footwall within which kinematic indicators in the high- and ultrahigh-P units show approximately top-to-north shear. Deformation was accompanied by retrograde metamorphism at amphibolite to greenschist facies conditions. Locally, younger northeast-southwest subhorizontal extension is recorded in ductile to brittle fabrics and the timing of deformation is defined by white mica recrystallization ca. 195 Ma. An Early Cretaceous dextral shear zone along the southwest boundary of the Tongbai Shan was synchronous with plutonism and normal to sinistral-oblique slip along the Xiaotian-Mozitang fault, which forms the northern boundary of the Dabie Shan. Coeval dextral and sinistral shear zones along the southwestern and northern margins of these blocks would have caused eastward lateral extrusion of the Tongbai, Hong'an, and Dabie Shan, perhaps driven by collision of the Lhasa block with Eurasia.
135.
22 - Comparison of persistent organochlorine pollutant behavior in the food webs of lakes baikal and superior
In Koji Minoura, Editor
,
Lake Baikal
Page 247-261
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
247-261134.
21 - Atmospheric and riverine input of nutrients and organic matter into lake baikal
In Koji Minoura, Editor
,
Lake Baikal
Page 236-246
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
236-246133.
20 - Study of the elemental composition of suspended particles in large continental lakes (Baikal and Khubsgul)
In Koji Minoura, Editor
,
Lake Baikal
Page 229-235
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
229-235132.
15 - Mercury distribution in the bottom and stream sediments of Lake Baikal,water reservoirs of the Angara river cascade, and adjacent drainage basins
In Koji Minoura, Editor
,
Lake Baikal
Page 165-175
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
165-175131.
19 - Nonlinear stability near the temperature of maximum density and thermobaric instability in lake baikal during summer stratification
In Koji Minoura, Editor
,
Lake Baikal
Page 214-228
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
214-228130.
18 - Environmental impact on the dynamics of Lake Baikal phytoplankton taxonomic groups: Modelling attempt
In Koji Minoura, Editor
,
Lake Baikal
Page 200-213
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
200-213129.
17 - Remote sensing methods in studies of Lake Baikal environment
In Koji Minoura, Editor
,
Lake Baikal
Page 186-199
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
186-199128.
16 - Correlations between geochemical features of recent bottom and stream sediments in the Baikal geoecological polygon
In Koji Minoura, Editor
,
Lake Baikal
Page 176-185
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
176-185127.
24 - Some speculations on the possibility of changes in deep-water renewal in Lake Baikal and their consequences
In Koji Minoura, Editor
,
Lake Baikal
Page 273-280
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
273-280126.
14 - Elemental composition of short sediment cores and ferromanganese concretions from Lake Baikal
In Koji Minoura, Editor
,
Lake Baikal
Page 155-164
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
155-164125.
23 - Carbon and nitrogen isotope studies of the pelagic ecosystem and environmental fluctuations of lake baikal
In Koji Minoura, Editor
,
Lake Baikal
Page 262-272
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
262-272124.
29 - The importance of habitat stability for the prevalence of sexual reproduction
In Koji Minoura, Editor
,
Lake Baikal
Page 324-330
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
324-330123.
25 - Contamination of the ecosystems of lake baikal by persistent organochlorines
In Koji Minoura, Editor
,
Lake Baikal
Page 281-298
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
281-298122.
26 - Genetic differentiation of gammarid (Eulimnogammarus cyaneus) populations in relation to past environmental changes in lake baikal
In Koji Minoura, Editor
,
Lake Baikal
Page 299-305
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
299-305121.
27 - Myological peculiarities of the comephoridae: An endemic fish taxon in Lake Baikal (Pisces: Teleostei)
In Koji Minoura, Editor
,
Lake Baikal
Page 306-314
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
306-314120.
28 - Morphometric comparison of skulls of seals of the subgenus Pusa
In Koji Minoura, Editor
,
Lake Baikal
Page 315-323
Publisher
Elsevier Science B.V.
,
Amsterdam
2000
315-323