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Normal and sliding contact experiments on gneiss
2010-01-01
The development of reliable discrete element models to simulate the mechanics of granular media requires knowledge of the grain-to-grain contact laws of the material in question. We have conducted a series of normal and sliding contact experiments on material used in laboratory triaxial experiments to obtain such contact laws for DEM simulations of the experiments. The contact experiments employed segments of 14.72 mm-diameter spherical grains from the triaxial specimens and flat specimens of the same material. The spherical grains had a uniform diameter with a smooth surface finish. Monotonic and cyclic loading paths were applied in both the normal and sliding modes, and both sphere-sphere and sphere-flat contact behavior were examined. Force-displacement behavior and frictional loss wer...
1997-05-01
This work summarizes the project aimed at developing and qualifying a suitable combination of laboratory tests to establish a statistically reliable stress-strain behaviour of the main rock types at Posiva Oy`s detailed investigation sites for disposal of spent nuclear fuel. The work includes literature study of stress-strain behaviour of brittle rock, development and qualification of laboratory tests, suggested test procedures and interpretation methods and finally testing of Olkiluoto mica gneiss. The Olkiluoto study includes over 130 loading tests. Besides the commonly used laboratory tests, direct tensile tests, damage controlled tests and acoustic emission measurements were also carried out. (orig.) (54 refs.).
1981-03-01
Rb-Sr isotopic measurements were carried out for whole rock and small sliced rock from the Himalayan gneiss which constitutes the metamorphosed basement of the Tethyan sediments. The results of the measurements on whole rock from the Barun migmatite, the Barun gneiss and the Irkhua gneiss indicate that complete Sr isotopic redistribution occurred about 520 m.y. ago. This age is interpreted as the time of the regional metamorphism. The analytical results of the small sliced slabs of the Himalayan gneiss indicate that Sr isotopic redistribution occurred among the sliced slabs 33.3 +- 13.2 m.y. ago. This age is interpreted as the time of the metamorphism in the sillimanite-amphibolite facies. The high initial /sup 87/Sr//sup 86/Sr ratio of 0.7372 +- 0.0031 from the Barun migmatite of the Himalayan gneiss suggests the Precambrian Origin of the source rocks. The analytical results on the sliced slab of the Barun migmatite indicate that the original age of the rocks is about 800 m.y. The rock is interpreted as the remobilized Precambrian crustal rock. The high initial /sup 87/Sr//sup 86/Sr ratio of the Barun gneiss and the Irkhua gneiss of the Himalayan gneiss (0.7234 +- 0.0013) indicates also the Precambrian origin of the source rocks.
The Hurd Peak gneiss of the Long Lake shear zone, eastern Sierra Nevada, California
1993-04-01
The Hurd Peak gneiss is located within the Long Lake valley of the east-central Sierra Nevada, California. This unit is the principle orthogneiss in Hathaway's (1993) Long Lake shear zone. The rock shows porphyroclasts of plagioclase and quartz, abundant mafic enclaves, and cross-cutting field associations which suggest that the gneiss had a plutonic protolith. The gneiss varies from biotite-poor nearest the contact with the Lamarck to biotite-rich nearest Long Lake. The contact zone between the gneiss and the Lamarck pluton ranges from sharp to gradational and from migmatitic to mixed, i.e., the mixed zone being greater than 50% intermingled dikes of 10 cm or greater thickness. In places this contact is marked by a quartz-free biotite hornfels approximately 5 m thick. Based on their relative deformation, at least 3 suites of aplite dikes cross-cut the gneiss, and 5 other lithologies, including basaltic, mixed, composite, andesitic, and quartz dioritic compositions, also cross-cut the gneiss. The Rb-Sr whole rock isochron age of the Hurd Peak gneiss has been determined to be 90.2 Ma. The authors interpret this isochron to be the result of mobilization of the Rb-Sr isotopic system during intrusion of the Lamarck Granodiorite (90 Ma); this may represent a regional cooling age. The initial [sup 87]/Sr[sup 86]Sr ratio of the gneiss is 0.7098, i.e., much more evolved than the surrounding plutons which have [sup 87]Sr/[sup 86]Sr ratios near 0.706. Sr model ages indicate that the protolith of the gneiss is considerably older than 90 Ma, one such calculation suggests an age of approximately 250 Ma. Single crystals of zircon have been isolated from the gneiss for U-Pb dating, and analytical work on the zircons is presently on-going.
1988-01-01
A seven-point (three zircon and four titanite ) U-Pb discordia-line from the Ingdal granite gneiss defines upper- and lover-intercept ages of 1653 +-2 Ma and 396 +-5 Ma interpreted as the time of Ingdal granite emplacement, and the time of gneiss formation and partial Pb-loss from zircon and titanite during a regional metamorphic event, respectively. These isotopic data suggest that this part of the western gneiss region was heated and cooled very quickly at both the upper- and lower-intercept ages, and that it did not experience significant Sveconorwegian (appr. 1250-900 Ma) or Finnmarkian (appr. 530-480 Ma) isotopic disturbance. A six-point Rb-Sr whole-rock errorchron (MSWD=11) from the same body of the Ingdal granite gneiss defines a date of 1665 +-49 Ma interpreted as a less precise age of granite emplacement. Rb-Sr mineral dates from three strongly discordant, non-foliated granite pegmatites fall in the age range of 415-379 Ma. A Rb-Sr biotite date of 372 +-4 Ma from the Ingdal granite gneiss establishes a minimum age of isotopic disturbance in the region.
Convergent Radial Tracing of Viral and Solute Transport in Gneiss Saprolite
2010-01-01
Deeply weathered crystalline rock aquifer systems comprising unconsolidated saprolite and underlying fractured bedrock (saprock) underlie 40% of sub-Saharan Africa. The vulnerability of this aquifer system to contamination, particularly in rapidly urbanizing areas, remains poorly understood. In order to assess solute and viral transport in saprolite derived from Precambrian gneiss, forced-gradient tracer experiments using chloride and Escherichia coli phage X174 were conducted in southeastern Uganda. The bacteriophage tracer was largely unrecovered; adsorption to the weathered crystalline rock matrix is inferred and enabled by the low pH (5.7) of site ground water and the bacteriophage's relatively high isoelectric point (pI = 6.6). Detection of the applied X174 phage in the pumping well d...
1993-04-01
Precambrian gneisses in the San Bernardino Mountains were first identified and described in the vicinity of Baldwin Lake by Guillou (1953). Five lithologic units mappable at 1:24,000 scale are recognized: biotite [+-] muscovite quartzofeldspathic gneiss, amphibolite, pyroxene metagabbro, augen gneiss, and biotite [+-] muscovite granitic gneiss. Baldwin gneiss with this L < S tectonite fabric is unconformably overlain by latest Proterozoic, upright, greenschist/hornfels facies quartzite (Big Bear Group). North and northeast of Baldwin Lake, the gneissic fabric is rotated toward the northwest, subparallel to the Doble fault. Along this fault, Baldwin gneiss is structurally underlain by overturned Paleozoic quartzite and marble (Zabriskie Quartzite and Carrara Formation). Regional relations suggest that the Doble fault is a northeast-directed basement thrust fault of pre-Late Cretaceous age, and may be contemporaneous with late Paleozoic deformation and metamorphism of Paleozoic rocks further west in the range. Field relations suggest that Baldwin gneiss in its type area largely retains Proterozoic fabrics and mineral assemblages, despite marginal Phanerozoic reworking. Silver (1971) reported a U-Pb zircon age of ca. 1,730 Ma for Baldwin augen ( ) gneiss, from an unknown locality, and Miller and Morton (1980) reported Late Cretaceous mica K-Ar ages from a sample of augen gneiss. Preliminary Pb isotopic ratios in galena, feldspar and whole rock samples of Baldwin gneiss, and feldspars in Mesozoic plutons suggest isotopic affinity to the Mojave crustal province of Wooden and Miller (1990).
1987-01-01
The geochronologic history of the northern portion of the Western Gneiss Region, south-central Norway has been investigated by U-Pb analyses of zircon and titanite from various basement units and one supracrustal gneiss. A six-point (four zircon and two titanite) discordia line from a migmatite melt-pod and its host-gneiss (Aastfjord migmatite gneiss) defines upper- and lower-intercept ages of 1659.1 +- 1.8 Ma and 393.6 +- 3.6 Ma, respectively. The upper-intercept age is interpreted as a time of tonalite emplacement and migmatite formation in the region. A seven-point (three zircon and four titanite) discordia line from the Ingdal granite gneiss has similar upper- and lower-intercept ages (1652.9 +- 1.7 Ma and 396.1 +- 4.9 Ma, respectively) and the upper-intercept age is interpreted as the time of granite crystallization. The lower-intercept age from both the Aastfjord migmatite gneiss and the Ingdal granite gneiss is interpreted as the time of regional metamorphic resetting and is evidence for Caledonian influence in the region. Episodic, diffusional lead loss from titanite during Caledonian metamorphism probably caused the discordance pattern, but a combined mechanism of mixing and diffusional lead loss cannot be ruled out. In any case, the seventeen-point titanite and zircon discordia line clearly indicates that: The bulk of the granitoid terrane in this portion of the Western Gneiss Region was emplaced, migmatized, and cooled in a short time interval about 1657 Ma ago; a second, short-lived thermal event that exceeded the blocking temperature of titanite occurred about 395 Ma ago; and titanite and zircon in the region were not isotopically disturbed by comparable geologic events in the period from 1657 to 395 Ma, or at any time after 395 Ma.
1993-03-01
The Whatley Mill Gneiss is the most voluminous exposure of the Pine Mountain Basement massif in eastern Alabama. Its type lithology is a proto-mylonitic gneiss composed of K-spar augen, up to 5 cm in diameter, in a finer matrix of biotite, microcline, and quartz. Granulite-facies mineral assemblages in the Whatley Mill Gneiss have been completely retrograded to amphibolite- and greenschist-facies assemblages in response to deformation that produced shear zones paralleling the foliation of the gneiss. The augen gneiss and its associated mylonites are well-exposed in a creek bed in Chewacla State Park. At this location the mineralogy of the mylonites is dominated by quartz indicating that shearing was associated with influx of a silica-rich fluid. A detailed geochemical study of these rocks shows that the augen gneiss displays relatively little variation in its major and trace element compositions while the quartz-rich mylonites display wider ranges, are enriched in SiO[sub 2] and depleted in the REE and other incompatible trace elements relative to the augen gneiss. When standard composition/volume calculations are applied to the mylonites the results show (1) the bulk of all of the elements, including the REE, were immobile during shearing with the exceptions of Si and Al which were added; and, (2) volume changes calculated using the REE as immobile elements range from +70% to +350%. Though these volume changes seem excessive, they apply to meter-thick shear zones which may actually represent only a small fraction of the total volume of the augen gneiss. Consistent with previous interpretations of these shear zones, the calculated volume gains imply shearing during extension.
Late Precambrian U-Pb ages for the Brookville Gneiss, southern New Brunswick
1990-11-01
Tonalitic orthogneiss from the Brookville Gneiss in southern New Brunswick has an igneous protolith age of 605 {plus minus} 3 Ma based on U-Pb dating of zircon. Metamorphic titanite from the same sample gives a minimum age of 564 {plus minus} 6 Ma for upper amphibolite facies metamorphism of the unit. Based on U-Pb analyses of single detrital zircons, a maximum sedimentary protolith age of about 641 Ma is suggested for associated paragneiss. These ages indicate that the igneous protolith of the orthogneiss was at most 35 Ma younger than the sedimentary rocks it intruded, and that the Brookville Gneiss is younger than the Green Head Group to which it was previously considered basement. Both orthogneiss and paragneiss in the Brookville Gneiss contain Proterozoic and Archean detrital zircon grains, suggesting an old, heterogeneous continental source. Bevier, White, and Barr conclude that the Brookville Gneiss does not represent the basement to the Avalon Terrane.
Sm-Nd isotopic systematics of the ancient Gneiss complex, southern Africa
In order to shed some new light on the question of the absolute and relative ages of the Ancient Gneiss Complex and Onverwacht Group, a Sm-Nd whole-rock and mineral isochron study of the AGC was begun. At this point, ...
2010-01-01
The Early Precambrian granulite-gneiss complex of the Irkut Block (Sharyzhalgai salient of the Siberian Craton basement) with the protoliths represented by a wide range of magmatic and sedimentary rocks, has a long-term history including several magmatic and metamorphic stages. To estimate the age of sedimentation and metamorphism of the terrigenous deposits, the composition of the garnet-biotite, hyper-sthene-biotite, and cordierite-bearing gneisses has been studied; their isotopic Sm-Nd values have been revealed; and the U-Pb zircon dating has been performed using the SHRIMP II ion microprobe. The protoliths of the terrigenous sediments metamorphosed under conditions of the granulite facies correspond to a rock series from siltstones and graywackes to pelites. The Nd model ages of paragn...
Structural interpretation of a double-folded gneiss-amphibolite sequence, Bunnefjorden, Akershus
1973-01-01
Observations on rock moisture variability in gneiss and basalt under natural, arctic conditions
1992-01-01
Rock moisture, Arctic, weathering, geomorphology, Greenland
Origin of plagioclase-megacrystic, orthopyroxene amphibolites within a Precambrian banded gneiss suite, Flekkefjord area, Vest-Agder, South Norway
2001-01-01
1985-01-01
The Corbin Gneiss Complex forms the core of the Salem Church anticlinorium in the Blue Ridge of NW Georgia, and is composed of quartz monzodiorite (Corbin gneiss) and pyroxene-biotite diorite. The observed foliation and the presence of thin zones of ultramylonites and phyllonites in the rocks of the gneiss complex are the result of the ductile shearing. Subsequent to the development of the mylonitic foliation these rocks were subjected for four episodes of flexural slip folding. The first generation folds were associated with the formation of the Salem Church anticlinorium. The northeasterly striking axial planes and the southeasterly plunging fold axes of the last three systems of folds suggest that these folds were formed on the southeasterly dipping foliation planes of the Salem Church anticlinorium. The trace element study of the pyroxene-biotite diorite, the Corbin gneiss (quartz monzodiorite) including its variably sheared equivalents shows that these rocks originated from independent sources by primary petrogenetic processes, and do not show any mixing relationship. The whole rock Rb-Sr isochron of the ultramylonitic Corbin gneiss yields an age of 296 +/- 4 Ma and an initial /sup 87/Sr//sup 86/Sr ratio of 0.7208 +/- 7. The much younger age of the ultramylonite in comparison to that of the unsheared Corbin gneiss (age approx. 1 Ga) is the result of resetting of the Rb-Sr systematics of the latter due to shearing, and denotes the minimum age limit of the shearing. A two point whole rock isochron of the diorite gives an apparent age of 1.22 Ga and an initial /sup 87/Sr//sup 86/Sr ratio of 0.7036. The total crustal age of the diorite is slightly greater than the Corbin gneiss.
In order to better understand phase transformations, chemical migration, and isotopic disequilibrium in highly shocked rocks, we have performed a microprobe and an ATEM study on gneisses shocked up to 60 GPa from the ...
Ion microprobe U-Pb results for zircons from three Uivak I gneisses and one specimen of Uivak II gneiss, from the Saglek-Hebron area of Northern Labrador are reported. These results are compared with ...
An ancient depleted mantle source for Archean crust in Rajasthan, India
Data from an initial set of Banded Gneiss Complex (BGC) east of the city of Udaipur are given. In this region the BGC comprises typical grey gneiss with variably abundant granitic and mafic components. Efforts ...
U-Pb zircon and monazite ages of Middle Proterozoic rocks, northern Blue Ridge, Virginia
1993-03-01
New geologic mapping of bedrock in the northern Blue Ride of Virginia and Maryland has resulted in the identification of at least ten different Middle Proterozoic granitic gneisses. The authors new U-Pb zircon data on eleven samples indicate crystallization ages ranging from about 1,055 to 1,145 Ma. The results are grouped as follows: Group 1--biotite granite gneiss, porphyroblastic granite gneiss, pink leucogranite gneiss, white leucogranite gneiss, and garnetiferous leucogranite gneiss; Group 2--biotite granite gneiss, hornblende monzogranite gneiss, and coarse-grained granitic gneiss; and, Group 3--porphyroblastic granite gneiss. Isotopic data from multigrain fractions and single zircons from a leucocratic layered gneiss are scattered, with Pb/Pb ages ranging from 1,092 to 1,139 Ma; these results support field evidence suggesting that the protolith of the layered gneiss was a composite of porphyroblastic gneiss and younger granite(s) that was highly sheared and homogenized. The geochronology agrees with structural interpretations and limited cross-cutting relations; rocks in Groups 2 and 3 are much more strongly deformed than rocks of Group 1. The name Marshall Metagranite is retained, but restricted to biotite and coarse-grained gneisses of Group 2, which resemble gneisses in the type area. U-Pb ages of monazites from several samples have a wide spread (1,033 to 1,106 Ma). In all samples but one, monazites are younger than coexisting zircons and are coeval with the next younger intrusive event. These data suggest that several of the monazite dates are not cooling ages but represent the times of metamorphic growth during subsequent intrusive events. Because the monazite ages have not been reset to a single date, the authors conclude that the regional granulite metamorphism never exceeded about 700C after 1,106 Ma in this part of the Grenville terrane.
Petrology, petrophysics and fracture mineralogy of the drill core sample OL-KR22 and OL-KR22B
2007-06-15
This report represents the results of the studies dealing with the drill core samples OL-KR22 and OL-KR22B, drilled in the south eastern part of the Olkiluoto study site. Lithological properties, whole rock chemical compositions, mineral compositions, textures, petrophysical properties and low temperature fracture infill minerals are described. The drill holes start in the diatexitic gneiss domain and intersect down to length of 360 m rather monotonous diatexitic gneisses which are intruded by a couple of wide pegmatitic granite dykes and have several homogeneous mica gneiss and mafic gneiss subsections. Below that, down to the length of 422 m, a fluctuating section of veined gneisses with narrow mica gneiss interbeds is located. The lowermost part of the core sample is composed of rather homogeneous mica gneisses with various migmatite subsections. Detailed Petrological properties have been analysed from 12 samples. The T series is represented by six diatexitic gneiss samples and one veined gneiss sample which give an extensive overview of the whole series. Only the extremely basic and acidic types are excluded. SiO{sub 2} concentration varies from 58%, analysed from biotite rich veined gneiss, to ca. 73%, analysed from light, diatexitic gneiss. One mafic gneiss sample is included into the S-series. The sample is the most mafic example analysed from this group and contains only 43% SiO{sub 2} and ca. 10% CaO. The P series is represented by one TGG gneiss, one diatexitic gneiss and two mica gneiss samples. As typical for the P series, the content of phosphorus exceeds 0.4%, given as P{sub 25} in every of those while SiO{sub 2} concentration varies between 50% and 65%. Petrophysical properties were studied from 12 samples. The parameters measured were density, magnetic susceptibility, natural remanet magnetization, electrical resistivity, P-wave velocity and porosity. Borehole represents a relatively intensively fractured rock down to the core length of 200 metres. The density of fracturing is lower at deeper level but frequency is closely linked with the grade of hydrothermal activity. The chief fracture minerals include illite, kaolinite, unspecified mixed clay phases mainly illite, chlorite and smectite-group. The amount of iron sulphides is higher at the first 200 metres, where it often forms monomineralic coatings. The fracture plains are frequently covered by cohesive chlorite. Iron oxides and oxy-hydroxides occur in fractures at surficial zone, in core length 9.53 - 18.95 m., while graphite is present in several fractures in core length 20 - 50 m. Pervasive illitization concerns 11 % of the total core length and 36 % has calcite as major constituent in fracture fillings. (orig.)
1992-03-01
Goias Velho Group of the Greenstone Belt is represented by an Archean sequence of volcanic and sedimentary rocks. These rocks are encrusted in others of the Granite-Gneiss Complex and the contact between these two units is made through N 70 W thrust faults. Rb/Sr geochronological analysis in gneiss showed isochronic ages of about 2.670 Ma. Isochronic Rb/Sr ages gotten on Bugre Creek Gneiss show values of 1.900 Ma, perhaps related to reactivations of the Transamazonic Tectonic-Thermal Event. A dike of metamorphosed basic rock cutting the Granite-Gneiss Complex also show geochronological age of about 1.275 Ma gotten by K/Ar analysis on actinolite. This age is probably related to reactivations of the Uruacuano Cycle. Cataclastic gneiss in contact with rocks of the Greenstone Belt was analysed by K/Ar method on muscovite and showed ages of 1.470 Ma, probably related with reactivations of the N 70 W faults which form the lateral boundaries of this unit. (author). 16 refs., 4 figs., 2 tabs.
Basement involvement, Bulldog Creek area, southern Canadian Rockies
1985-01-01
Two distinct basement gneiss bodies are involved in the western Main Ranges of the Rocky Mountains adjacent to the rocky Mountain Trench near Valemount, British Columbia. Bulldog Gneiss comprises paragneisses intruded by Aphebian or older granitic orthogneiss, while the larger and more easterly Yellowjacket Gneiss (new name, age unknown) is composed mostly of granodioritic orthogneiss. Both gneiss bodies are overlain by Hadrynian metasediments ascribed to the lower Miette Group. The base-cover contacts in the Bulldog Creek area are marked by mylonite, which is suggestive of detachment. These contacts were strongly annealed during middle amphibolite facies metamorphism, however, and kinematic indicators are few and ambiguous. The gneisses were incorporated into a structural culmination by imbrication of the hanging wall of the Bear Foot Fault (new name; BFF). The culmination is, in part, due to a large overturned antiform that is cored by Yellowjacket Gneiss. This antiform constitutes the leading edge of the Bear Foot sheet, which places Yellowjacket Gneiss and lower Miette cover onto lower and middle Miette Group rocks. Kinematic indicators from BFF suggest a complex movement history, the final stage of which is easterly-directed thrusting. Thus, basement is incorporated in the eastern part of the Columbian orogen by thin-skinned thrusting and subsequent development of a leading edge antiform.
Geological mapping of investigation Trench OL-TK13 at the Olkiluoto study site, Eurajoki, SW Finland
2007-04-15
Geological mapping of investigation trench OL-TK13 was carried out by the Geological Survey of Finland at the Olkiluoto study site, Eurajoki, as a part Posiva Oy's site investigation programme for the development of an underground repository for nuclear waste. The east-west striking, ca. 250 m long trench is located in the vicinity of boreholes OL-KR23 and OL-KR27, ca. 250 m east of the ONKALO research facility. The mapping was performed from washed bedrock surface and rock types were determined macroscopically. The main rock types in OL-TK13 are diatexitic gneiss, veined gneiss, pegmatitic granite and K-feldspar porphyry. Mica gneiss and granite/granitized mica gneiss exist to a lesser extent. The diatexitic gneiss is the dominant rock type in the western part and the veined gneiss in the eastern part of the trench. The veined gneiss consists of pelitic mica gneiss paleosome and pegmatitic granite leucosome veins that are parallel to the foliation. In the diatexitic gneiss, the proportion of the leucosome veins and patches is over 50 % and the rock has an ambiguous texture. The pegmatitic granite also occurs as wider sections in the western part of the trench. The K-feldspar porphyry is characterized by potassium feldspar phenocrysts (diameter <5 cm) in matrix comprising mica gneiss and leucosome material. In the granite/granitized mica gneiss, medium-grained granite veins cut fine-grained granitized mica gneiss resulting in a breccia type appearance. The mica gneiss is mainly present as inclusions. Elongated skarn inclusions are present throughout the trench. Softening of the bedrock due to weathering and alteration (chloritisation, kaolinitisation, hematisation) is a common feature in OL-TK13. Up to 1.5 m of strongly weathered bedrock was removed during the excavation in places. All rock types, except late pegmatitic granite veins, have been subjected to a polyphase deformation. The dominant tectonic feature is foliation S2B and associated leucosome veining. Mean orientation of foliation is 116/52 deg C and the dip direction is in the western part to the E or SE and in the eastern part to the SE. This transition is due to compressional event during the D{sub 4} deformation phase. The migmatitic gneisses were folded during the D{sub 3} deformation phase resulting in small scale, tight and asymmetrical F{sub 3} folds plunging moderately to the NE. During the fracture mapping, all fractures longer than one metre and all fractures intersecting the central thread were investigated. Measurements including orientation, length, fillings, Jr-value, Ja-value and undulation were recorded for a total of 860 fractures. The mean fracture density is 3.5 fracture/m. From the orientation data, three fracture sets were identified: (1) fractures parallel to the foliation, (2) subvertical N-S trending factures and (3) fractures dipping steeply to the N. {approx}45 % of all fractures are 0.5-1.5 m in length and {approx}44 % are longer than 1.5 m. Either or both of the fracture ends are under Quaternary deposits in more than half of the fractures, one third of fractures combine to another fracture and both ends are visible in a quarter of all fractures. Three quarters of all fractures contain fillings, the most common being chlorite, hematite, kaolinite and illite. Three water-conducting fractures or fracture zones were detected. A total of fifteen deformation zone intersections have been determined OL-TK13. Seven zones were classified as Brittle joint intersections (BJI), seven as Brittle fault intersections (BFI) and one as a Semi-brittle deformation zone (SFI). Most deformation zones are parallel to the foliation. (orig.)
Core drilling of drillholes ONK-PP115 - ONK-PP120 in ONKALO at Olkiluoto 2007
2007-01-15
Posiva Oy submitted an application to the Finnish Government in May 1999 for the Decision in Principle to choose Olkiluoto in the municipality of Eurajoki as the site of the final disposal facility for spent nuclear fuel. A positive decision was made at the end of 2000 by the Government. The Finnish Parliament ratified the decision in May 2001. The decision makes it possible for Posiva to focus the confirming bedrock investigations at Olkiluoto, where an underground rock characterisation facility, ONKALO, will be constructed. As a part of the investigations Suomen Malmi Oy (Smoy) core drilled six 24.87-40.35 m long drillholes with a diameter of 56 mm in ONKALO in September-October 2007. The identification numbers of the holes are ONK-PP115 - ONK-PP120. The drillholes were drilled for installation of extensometers. The extensometers were installed for long-term monitoring of rock mechanics, rock stress and elastic parameters around the personal shaft at level -180. In addition to the drilling, Suomen Malmi Oy did core logging, drillhole deviation surveys and reporting. The deviation of the drillholes was measured with the deviation measuring instruments EMS and Maxibor. The main rock types are diatexitic gneiss and pegmatitic granite. Sections of veined gneiss, mica gneiss, quartz gneiss and mafic gneiss occur in some places. The average fracture frequency is 0.2-2.3 pcs/m. The average RQD values are 96.6-99.8 %. (orig.)
1997-12-01
This report includes both experimental and modelling parts. Also, a novel approach to the diffusion experiments is introduced, where ions of the same electric charge diffuse in opposite directions through the same rock sample. Six rock-types from Olkiluoto radioactive waste disposal investigation site were used in the experiments: granite, weathered granite, mica gneiss, weathered mica gneiss, tonalite and altered mica gneiss/migmatite. The experiments consisted of the determination of the effective diffusion coefficient and the rock capacity factor for tritium, chloride (Cl-36) and sodium (Na-22). The modelling consisted of a chemical model for small pores (< 100 nm), a model for counter ion diffusion and models for the laboratory experiments. 21 refs.
... consisting largely of granitic gneiss, surrounded by a collar of metasedimentary and metavolcanic supracrustal rocks of the Dominian Group, Witwatersrand and Ventersdorp Supergroups, ...
Extent and character of early tertiary penetrative deformation, Sonora, Northwest Mexico
Reconnaissance field work has led to the recognition of extensive Early Tertiary gneiss and schist which are distinguished by weakly developed to highly conspicous northeast to east-trending stretching lineation ...
http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=19562
The current nomenclature for the Lewisian Gneiss Complex has evolved from lithological and structural correlations made prior to any dating. Initial (flawed) geochronological studies gave some names an apparent chronological standing but, as work advanced, fitting events into a coherent regional framework became increasingly difficult. Modern dating studies have shown that the Lewisian Gneiss Complex was progressively assembled from disparate blocks of Archaean continental crust and juvenile Proterozoic arcs, which satisfy the definition of terranes. Each terrane had its own separate accretionary and metamorphic history followed by a common history once juxtaposed against other terranes. Based on a new compilation of modern geochronology allied to the many detailed structural and metamorphic studies, this paper proposes a new systematic terminology for the Lewisian Gneiss Complex that is more applicable to this new tectonic framework. Publisher: Department of Applied Geology Other identifier: PUB-RES-DAG-PDK-32976; EPR-797
http://espace.library.uq.edu.au/view/UQ:144634
The Archaean gneiss complex of the Saglek-Hebron area in northern Labrador is dominated by polyphase similar to 3.7 Ga old tonalitic-trondhjemitic-granodioritic (TTG) Uivak I Gneiss, that exhibit 3.8-3.9 Ga inheritance. These gneisses are interleaved with a heterogeneous group of supracrustal rocks known as the Nulliak supracrustal assemblage. Early Archaean ultramafic rocks occur either as tectonically-emplaced slivers of lithospheric mantle along structural contacts within the Uivak I Gneiss, or as layers of metakomatiite in Nulliak supracrustal units. The metakomatiites yield a Pb-Pb isochron age of 3845 +/- 160 Ma, reflecting a significant change from an initial Archaean mantle-like mu(1)-value of 7.9 to a range of mu(2)-values of 2.0-4.2. Members of the tectonically-emplaced lithospheric mantle suite have less well correlated Pb-206/Pb-204 and Pb-207/Pb-204 compositions. Both ultramafic suites were collected in an area identified as transitional between granulite and amphibolite facies. However, model calculations show that the data scatter exhibited by the lithospheric mantle cannot be accommodated by post-3.85 Ga U-depletion. Evidence is provided that the lithospheric mantle suite reflects variable degrees of mixing between a depleted mantle and a high-mu reservoir suggesting that the two ultramafic rock suites had different evolutionary histories. Timing of late Archaean reworking during medium- to high-grade metamorphism was determined by mineral whole-rock dating of a garnet pyroxenite from an area dominated by Kiyuktok Gneiss (reworked similar to 3.75 Ga Uivak Gneiss). Sm-Nd mineral whole-rock data for this gneiss yielded an isochron equivalent to an age of 2570 +/- 17 Ma, significantly younger than its Pb-Pb isochron age of 2735 +/- 43 Ma. The negative epsilon(Nd)(t) = - 7.9 reflects a significant crustal residence time, indicating that the Sm-Nd system of the whole rock has been reset. The internal Pb mineral isochron is interpreted to reflect the maximum age of peak metamorphism. The age discrepancy of ca. 165 Ma between the Sm-Nd and the Pb-Pb isochron ages suggests slow cooling at a minimum rate of 1.3 degrees C Ma(-1). This indicates that the Saglek-Hebron segment of the North Atlantic Craton experienced gradual uplift during late Archaean exhumation. (C) 1999 Elsevier Science B.V. All rights reserved. Publisher: Elsevier Relation: isMemberOf School of Physical Sciences Publications
This guidebook describes the characteristics and interrelationships of Archean greenstone-granite and high-grade gneiss terrains of the Superior Province. A 300-km long west to east transect between Wawa and Timmins, ...
http://hdl.handle.net/2440/41508
(c) Taylor & FrancisThe Coompana Block is an essentially unknown basement province that separates the Gawler Craton of South Australia from the Yilgarn Craton of Western Australia. Previously unstudied granitic gneiss intersected by deep drilling in the Coompana Block represents an important period of within-plate magmatism during a time of relative magmatic quiescence in the Australian Proterozoic. Granitic gneiss intersected at 1500 m depth in Mallabie 1 diamond drillhole is metaluminous and dominantly granodioritic in composition. The granodiorites have distinctive A-type chemistry characterised by high contents of Zr, Nb, Y, Ga, LREE with low Mg#, Sr, CaO and HREE. U - Pb LA-ICPMS dating of magmatic zircons provides an age of 1505 ± 7 Ma, interpreted as the crystallisation age of the granite protolith. Nd values are high with respect to exposed crust of the Musgrave Province and Gawler Craton, and range from +1.2 to +3.3 at 1.5 Ga. The granitic gneiss is interpreted to be a fractionated melt of a mantle-derived parental melt. The tectonic environment into which the precursor granite was emplaced is not clear. One possibility is emplacement within an extensional environment. Regardless, the granitic gneiss intersected in Mallabie 1 represents magmatic activity during the 'Australian Mesoproterozoic magmatic gap' of ca 1.50 - 1.35 Ga, and is a possible source for ca 1.50 detrital zircons found in sedimentary rocks of Tasmania and Antarctica, and metasedimentary rocks of the eastern Musgrave Province. Publisher: Taylor & Francis Contributor: School of Earth and Environmental Sciences : Geology and Geophysics Other identifier: Australian Journal of Earth Sciences, 2007; 54 (8):1089-1102; 0812-0099; 0020074313; 10.1080/08120090701615733 Language: en
2010-01-01
Abstract Continental crust is displaced in strike-slip fault zones through lateral and vertical movement that together drive burial and exhumation. Pressure-temperature-deformation (P-T-d) histories of orogenic crust exhumed in transcurrent zones record the mechanisms and conditions of these processes. The Skagit Gneiss Complex, a migmatitic unit of the North Cascades, Washington (USA), was metamorphosed at depths of 25-30 km in a continental arc under contraction, and is bounded on its eastern side by the long-lived transcurrent Ross Lake fault zone (RLFZ). The P-T-d conditions recorded by rocks on either side of the RLFZ vary along the length of the fault zone, but most typically the fault separates high-grade gneiss and plutons from lower-grade rocks. The Ruby Mt-Elijah Ridge area at th...
2010-01-01
We have measured ^1^8^2W/^1^8^4W for Eoarchean rocks from the Itsaq Gneiss Complex (3.8-3.7Ga pillow meta-basalts, a meta-tonalite, and meta-sediments) and Acasta Gneiss Complex (4.0-3.6Ga felsic orthogneisses) to assess possible W isotopic heterogeneity within the silicate Earth and to constrain W isotopic evolution of the mantle. The data reveal that ^1^8^2W/^1^8^4W values in the Eoarchean samples are uniform within the analytical error and indistinguishable from the modern accessible mantle signature, suggesting that the W isotopic composition of the upper mantle has not changed significantly since the Eoarchean era. The results imply either that chemical communication between the mantle and core has been insignificant in post-Hadean times, or that a lowermost mantle with a distinctive ...
2010-01-01
In the central Sor Rondane Mountains, East Antarctica, orthopyroxene felsic gneiss (OPG) was converted to hornblende-biotite felsic gneiss (HBG) by hydration that accompanied the intrusion of pegmatite. The retrograde HBG contains exsolved rutile in quartz. The composition of orthopyroxene and clinopyroxene in OPG suggests a temperature of 840degreeC (interpreted as the near-peak temperature), and the composition of hornblende and plagioclase in HBG suggests a temperature of 670-700degreeC (interpreted as the temperature during hydration). Ti concentrations in quartz were measured using an electron probe micro-analyzer, and Ti-in-quartz thermometers were applied. Measured Ti concentrations were 110ppm (equivalent to 760-820degreeC) for homogeneous quartz from OPG and 35ppm (650-700degreeC)...
http://hdl.handle.net/2440/13613
The Rathjen Gneiss is the oldest and structurally most complex of the granitic intrusives in the southern Adelaide Fold-Thrust Belt and therefore provides an important constraint on the timing of the Delamerian Orogen. Zircons in the Rathjen Gneiss show a complex growth history, reflecting inheritance, magmatic crystallisation and metamorphism. Both single zircon evaporation ('Kober' technique) and SHRIMP analysis yield best estimates of igneous crystallisation of 514 ± 5 Ma, substantially older than other known felsic intrusive ages in the southern Adelaide Fold-Thrust Belt. This age places an older limit on the start of the Delamerian metamorphism and is compatible with known stratigraphic constraints suggesting the Early Cambrian Kanmantoo Group was deposited, buried and heated in less than 20 million years. High-U overgrowths on zircons were formed during subsequent metamorphism and yield a ²⁰⁶Pb/²³⁸U age of 503 ± 7 Ma. The Delamerian Orogeny lasted no more than 35 million years. The emplacement of the Rathjen Gneiss as a pre- or early syntectonic granite is emphasised by its geochemical characteristics, which show affiliations with within-plate or anorogenic granites. In contrast, younger syntectonic granites in the southern Adelaide Fold-Thrust Belt have geochemical characteristics more typical of granites in convergent orogens. The Early Ordovician post-tectonic granites then mark a return to anorogenic compositions. The sensitivity of granite chemistry to changes in tectonic processes is remarkable and clearly reflects changes in the contribution of crust and mantle sources. Publisher: Taylor & Francis Other identifier: Australian Journal of Earth Sciences, 1999; 46 (3):377-389; 0812-0099; 0019991746; 10.1046/j.1440-0952.1999.00712.x Language: en_US
Anisotropic yielding of rocks at high temperatures and pressures
1987-12-01
Results to date are: All of the starting materials for the three year project have been collected. Included in our collection are relatively fine-grained, fresh, oriented blocks of schist, gneiss, and micaceous quartzite with well-defined foliations and lineations as well as granite blocks oriented with respect to the principal quarrying orientations, the rift, grain, and hardway. A suite of samples has also been collected from an exposed granite stock and surrounding country rocks in order to evaluate the strengths and distribution of fabrics which may be encountered while drilling. These fabrics appear to be directly related to the forceful emplacement of the pluton. The literature on the mechanics of intrusion has been reviewed with regard to strain gradients and foliation development associated with diapiric flow. This information will be used to evaluate flow of varying fabrics on yield criteria within and surrounding magma chambers. Twenty-three successful experiments have been performed on samples of gneiss cored along six different orientations at temperatures ranging from 25{degrees} to 700{degrees}C. These experiments include extension tests, unconfined compression tests, and compression tests performed at P{sub c} = 100 MPa. Theoretical yield conditions for anisotropic materials have been reviewed and the assumptions upon which they are based probed. These yield conditions will ultimately be used to fit our data on gneiss, and the other foliated rocks under investigation. Two abstracts have been published and oral presentations made at the 1987 Fall Meeting of the American Geophysical Union, based upon our previous DOE-sponsored work on tensile fracturing of quartzite and related work on semi-brittle deformation of granitic rocks. 21 refs., 12 figs., 2 tabs.
Anistotropic yielding of rocks at high temperatures and pressures
1990-10-14
The anisotropic deformation of foliated and linealed rocks has been investigated, primarily to predict the mechanical response of rocks surrounding buried magma chambers to the stress fields generated by deep drilling. The principal application in this regard has been to evaluate, the scientific feasibility of extracting geothermal energy from buried magma chambers. Our approach has been to perform triaxial extension and compression tests at temperatures and pressures representative of the borehole environment on samples cored along six selected orientations and to fit the data to an orthohombric yield criterion. We have investigated Four-Mile gneiss (a strongly layered gneiss with well defined lineation), a biotite-rich schist, and Westerly granite (using a block oriented with respect to the granite's rift, grain, and hardway). Progress has been made in three areas: the experimental determination of strength anisotropies for the three starting materials, theoretical treatment and modeling of the results, and characterization of fabrics surrounding magma bodies resulting from their diaperic emplacement into shallow portions of the Earth's crust. In addition, results have been obtained for the tensile fracture of quartzite, basal slip and anisotropy of biotite single crystals, and anisotropic flow of bedded rocksalt.
Anistotropic yielding of rocks at high temperatures and pressures. Final report
1990-10-14
The anisotropic deformation of foliated and linealed rocks has been investigated, primarily to predict the mechanical response of rocks surrounding buried magma chambers to the stress fields generated by deep drilling. The principal application in this regard has been to evaluate, the scientific feasibility of extracting geothermal energy from buried magma chambers. Our approach has been to perform triaxial extension and compression tests at temperatures and pressures representative of the borehole environment on samples cored along six selected orientations and to fit the data to an orthohombric yield criterion. We have investigated Four-Mile gneiss (a strongly layered gneiss with well defined lineation), a biotite-rich schist, and Westerly granite (using a block oriented with respect to the granite`s rift, grain, and hardway). Progress has been made in three areas: the experimental determination of strength anisotropies for the three starting materials, theoretical treatment and modeling of the results, and characterization of fabrics surrounding magma bodies resulting from their diaperic emplacement into shallow portions of the Earth`s crust. In addition, results have been obtained for the tensile fracture of quartzite, basal slip and anisotropy of biotite single crystals, and anisotropic flow of bedded rocksalt.
2010-01-01
Full Text Available.This study assesses the level of terrestrial gamma radiation and associated dose rates from the naturally occurring radionuclides 232Th, 238U and 40K in 10 soil samples collected from Thanjavur (Tamil Nadu, India) using γ-ray spectrometry. The activity profile of radionuclides has clearly showed the existence of low level activity in Thanjavur. The geometric mean activity concentrations of 232Th, 238U and 40K is 42.9±9.4 Bq.kg−1, 14.7±1.7 Bq.kg−1 and 149.5±3.1 Bq.kg−1 respectively are derived from all the soil samples studied. The activity concentration of 232Th, 238U and 40K in soil is due to the presence of metamorphic rocks like shale, hornblende-biotite gneiss and quartzofeldspathic gneiss in these areas. Gamma absorbed dose rates in air outdoors were calculated to be in the range between 32 nGy.h−1 and 59.1 nGy.h−1 with an arithmetic mean of 43.3 ±9 nGy.h−1. This value is lesser than the population weighted world-averaged of 60 nGy.h−1. Inhabitants of Thanjavur are subjected to external gamma radiation exposure (effective dose) ranging between 39.2 and 72.6 μSv.y−1 with an arithmetic mean of 53.1±11 μSv.y−1. The values of the external hazard index determined from the soil radioactivity of the study area are less than the recommended safe levels.
http://eprints.jcu.edu.au/976/1/bell_1.pdf
The New England Appalachians contain some of the first documented gneiss domes. The classic domes of SE Vermont are typical of these structures in that they appear to have formed by doming of both the gneissosity in basement gneisses and the dominant matrix schistosity in the overlying rocks, after these foliations had formed. However, the three matrix foliations (other than bedding) present in these rocks, which include the one parallel to all compositional layering, post date dome development. The domes formed as upright anticlines after deposition of the overlying Lower Palaeozoic sediments and volcanics on a PreCambrian granitic or gneissic basement. This occurred during orogenesis driven by horizontally directed compressional forces with interspersed periods of relatively coaxial gravitational collapse, rather than through early nappe development followed by folding or diapiric granite emplacement, or crustal extension and upwards bowing of a necked portion of the crust. In spite of numerous subsequent deformations, the domes are very old structures that have been little modified at the level of current crustal exposure. The dominant process during each deformation was reactivation of the compositional layering or gneissosity on at least one limb of the dome. This destroyed earlier developed crenulation cleavages that lay oblique to the compositional layering and commonly prevented new ones from developing. Consequently, a schistosity parallel to bedding in the overlying rocks, and the gneissosity below, formed and was intensified by reactivation on at least one limb of the dome during all subsequent deformations. Nappe development, which has commonly been proposed as the origin of foliation parallel to bedding in the rocks overlying gneiss domes, is not necessary and there is no evidence for such a deformation history preserved within either the bedding or matrix foliations that have been folded around the Chester and Athens domes of SE Vermont. Sub-horizontally dipping foliations that formed during collapse stages of orogenesis have mainly been the product of relatively coaxial deformation rather than the highly non-coaxial deformation that accompanies nappe development. The fold to the west of the Chester and Athens domes, which has classically been regarded as the nose of the major nappe, formed with an upright rather than shallowly dipping axial plane. Publisher: Taylor & Francis Format: application/pdf Other identifier: Bell, Tim H, Ham, Andrew P, Hayward, Nick, and Hickey, Ken A (2005) On the development of gneiss domes. Australian Journal of Earth Sciences, 52 (2). pp. 183-204. ISSN 1440-0952
http://hdl.handle.net/2440/18685
Diskette for IBM/PC in pocket on back end paper.Copies of author's previously published articles inserted.Bibliography: leaves 186-207.xvii, 246 leaves : ill., maps ; 30 cm. + 1 computer disk (3 1/2 in.)Title page, contents and abstract only. The complete thesis in print form is available from the University Library.An evaluation of spatial and temporal variation in composition of soil solutions collected from a hydro-toposequence with seasonally saturated soils ranging from Xeralfs to Aqualfs. The sub-catchment is under native eucalyptus and is formed from granite gneiss. The study shows that mineral weathering under eucalypt vegetation contributes substantially to the quantity of elements measured in soil solution with some aeolian salts. Migration of soil solutions to low lying areas promotes dryland salinity in these landscapes.Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1996? Language: en_US
Single zircon grains record two Paleoproterozoic collisional events in the North China Craton
2010-01-01
The Western Block of the North China Craton consists of the Yinshan Block in the north and the Ordos Block in the south which were amalgamated along the east-west trending Khondalite Belt at ~1.95Ga. The Western Block then collided with the Eastern Block to form the coherent basement of the North China Craton along the north-south trending Trans-North China Orogen at ~1.85Ga. The Huaian Complex, a high-grade terrrane located at the conjunction of the Khondalite Belt and Trans-North China Orogen, records metamorphic events associated with both collisions. The complex consists of lithologies from both the Khondalite Belt and Trans-North China Orogen, of which the former consist of graphite-garnet-sillimanite gneiss, garnet quartzite, felsic paragneiss, calc-silicate rock and marble, together...
2010-01-01
Landslides are very common in high-altitude Himalayan terrains. Major roads in the Himalayas are frequently blocked due to heavy landslides and remain closed for long periods of time. Permanent mitigatory solutions to these landslides are required to keep the highways open. Lanta Khola, located 71.2 km north of Gangtok (capital of the Indian state of Sikkim), is one of the oldest landslides on the North Sikkim Highway and is active since 1975. The rock types on either side of the landslide are different (augen gneiss in the east and metapelitic schist in the west), and it is believed that the Main Central Thrust passes through the slide zone. Since the slide is invariably activated in the aftermath of heavy rainfall, it is important to identify the subsurface structures that channel water...
http://hdl.handle.net/1959.14/26962
Re–Os data obtained by LAM–ICPMS techniques from sulfides within the Bardane peridotite body in the Western Gneiss Region of the Norwegian Caledonides indicate a Proterozoic, or possibly Archean, origin for the peridotite, probably as depleted residue formed through melt extraction in the mantle. Sm–Nd mineral ages from primary garnet-bearing assemblages in a megacrystic orthopyroxenite within the peridotite indicate the mantle was invaded by melts that crystallized in the garnet-stability field during the mid-Proterozoic. However, microdiamonds within this megacrystic orthopyroxenite formed well after these processes, during the Paleozoic Caledonian Orogeny. Clinopyroxenes show enriched trace element patterns and radiogenic Sr and non-radiogenic Nd isotopic ratios, indicating fertilization of the Bardane peridotite with incompatible elements, presumably including carbon. Metasomatism may have occurred while the peridotite was part of the mantle wedge above an Iapetus subduction zone or it may have occurred after the lenses were introduced into the crust. Textural and field relationships and Sm–Nd mineral results from secondary garnet-bearing assemblages indicate the microdiamonds formed during Caledonian metamorphism, probably during the Scandian Orogeny, when the peridotite body was introduced from the mantle into a subducting crustal gneiss complex and carried to mantle depths within the diamond-stability field. Texturally and mineralogically similar megacrystic orthopyroxenites on the nearby island of Otrøy lack microdiamonds, suggesting they underwent all the above processes except the metasomatic introduction of carbon.12 page(s) Publisher: Elsevier Contributor: Macquarie University. Dept. of Earth and Planetary Sciences; Macquarie University. National Key Centre for Geochemical Evolution and Metallogeny of Continents (GEMOC) Relation: Earth and planetary science letters, Vol. 203, Issue 3-4, p.805-816; 10.1016/S0012-821X(02)00919-6 Other identifier: ISSN:1385-013X; mq-rm-2002015063 Language: eng
2010-01-01
To determine how topographic relief in mountainous regions evolves through time we present a new approach that uses in situ-produced cosmogenic ^1^0Be to quantify (1) spatially averaged denudation rates of small watersheds and (2) local denudation rates of the ridge crests bounding these basins. The technique is applied to two catchments in the Black Forest, a forested mountain range with a local relief of a few hundred meters, which is typical for ranges in central Europe. Both the Acher and the Gutach catchments expose predominantly Carboniferous granite, and only minor amounts of high-grade gneiss and Triassic sandstone. The latter occurs on ridges defining the eastern boundaries of the catchments, above a regional unconformity. In the Acher and northern Gutach watersheds denudation rat...
2010-01-01
This work presents and analyzes results obtained on a research program aiming at the characterization of materials belonging to weathering profiles developed in the three most common metamorphic rocks occurring in Rio de Janeiro, Brazil-Leptinite, Kinzigite and Augen Gneiss. Initially, a comprehensive field description is presented in order to point out the main weathering patterns observed for these rocks. Samples from different weathering levels were identified and tested in order to determine their mineralogical, physical and geomechanical properties. The obtained results are discussed and an evaluation of the influence of weathering on rock properties is presented. Correlations between the physical and mechanical properties of the tested materials are also presented.
2010-01-01
Greenland is by far the dominant source of glacial runoff to the oceans but the controls on the chemical and isotopic composition of this runoff are poorly known. To better constrain glacial effects on weathering processes, we have conducted elemental and lithium isotope analyses of glacial and non-glacial rivers in gneiss catchments in West Greenland. The glacial rivers have high total suspended solids (0.5gl^-^1) and low total dissolved solids (12mScm^-^1) relative to the non-glacial rivers, and they contain a higher proportion of dissolved Ca^2^+ and K^+ because of subglacial, preferential, weathering of trace carbonates and biotite. The glacial rivers also have high SO4^2^- because of the oxidation of trace sulphides under the ice. Both glacial and non-glacial rivers have high d^7Li (r...
2010-01-01
The Samgwang mine is located in the Cheongyang gold district (Cheonan Metallogenic Province) of the Republic of Korea. It consists of eight massive, gold-bearing quartz veins that filled NE- and NW-striking fractures along fault zones in Precambrian granitic gneiss of the Gyeonggi massif. Their mineralogy and paragenesis allow two separate vein-forming episodes to be recognized, temporally separated by a major faulting event. The ore minerals occur in quartz and calcite of stage I, associated with fracturing and healing of veins. Hydrothermal wall-rock alteration minerals of stage I include Fe-rich chlorite (Fe/(Fe+Mg) ratios 0.74-0.81), muscovite, illite, K-feldspar, and minor arsenopyrite, pyrite, and carbonates. Sulfide minerals deposited along with electrum during this stage include ar...
1997-12-31
Assessment of bedrock performance for nuclear waste disposal can benefit from a more detailed understanding of the rock matrix properties along actual and potential groundwater flow pathways. The spatial variability along flow paths and the correlation of groundwater flow with rock matrix properties (type of minerals, porosity, internal surface areas) is an input parameter for the quantification of retarding properties and the chemical buffering capacity of the bedrock. In this investigation tonalite, mica gneiss and vulcanite samples from Syyry were studied. The samples were taken from a drill core located near water-conducting, open fractures. The objective of the study was to describe the porosity of different altered and weathered rock matrices next to filled fissures and open fractures. 9 refs. Nuclear Waste Disposal Research.
http://hdl.handle.net/1959.14/8350
Orogenic peridotites occur enclosed in Proterozoic gneisses at several localities in the Western Gneiss Region (WGR) of western Norway; garnet peridotites typically occur as discrete zones within larger bodies of garnet-free, chromite-bearing dunite and are commonly closely associated with pyroxenites and eclogites. The dunites of the large Almklovdalen peridotite body have extremely depleted compositions (Mg-number 92–93.6); the garnet peridotites have lower Mg-number (90.6–91.7) and higher whole-rock Ca and Al contents. Post-depletion metasomatism of both rock types is indicated by variable enrichment in the light rare earth elements, Th, Ba and Sr. The dunites can be modelled as residues after very high degrees (>60%) of melt extraction at high pressure (5–7 GPa), inconsistent with the preservation of lower degrees of melting in the garnet peridotites. The garnet peridotites are, therefore, interpreted as zones of melt percolation, which resulted in refertilization of the dunites by a silicate melt rich in Fe, Ca, Al and Na, but not Ti. Previous Re–Os dating gives Archaean model ages for the dunites, but mixed Archaean and Proterozoic ages for the garnet peridotites, suggesting that refertilization occurred in Proterozoic time. At least some Proterozoic lithosphere may represent reworked and transformed Archaean lithospheric mantle.26 page(s) Publisher: Oxford University Press Contributor: Macquarie University. National Key Centre for Geochemical Evolution and Metallogeny of Continents (GEMOC) Relation: Journal of petrology, Vol. 47, Issue 8, p.1611-1636; 10.1093/petrology/egl022 Other identifier: ISSN:1460-2415; mq-rm-2006000149 Language: eng
Craton-derived alluvium as a major sediment source in the Himalayan Foreland Basin of India
2009-01-01
Within the Himalayan Foreland Basin, the axial Yamuna River with Himalayan headwaters lies along the northern margin of the Indian Craton, giving the impression that cratonic rivers have contributed little to the basin compared with Himalayan drainages. However, the Betwa, Chambal, and other rivers, which drain northward into the Yamuna, are vigorous monsoonal rivers with large catchments. Stratigraphic and petrographic evidence shows that sediment derived largely from these rivers extends north of the axial Yamuna River. Red feldspathic sand and gravel underlie much of the southern foreland basin at shallow depth (>25 m), where its topmost strata are dated at ca. 119 ka ago, and extend at deeper levels (>500 m) to about one-third of the distance across the foreland basin. Petrographic analysis confirms a match with modern Betwa River sands, which derive their feldspar from granitic gneisses of the Bundelkhand Complex. Along the Yamuna Valley the red alluvium is overlain by gray alluvium dated at 82â35 ka ago, which also yields a cratonic signature, with large amounts of smectite derived from the Deccan Traps. Cratonic contributions are evident in alluvium as young as 9 ka ago in a section 25 km north of the Yamuna. This gray cratonic sediment was probably deposited in part by the Chambal River, which transports high-grade metamorphic minerals from the Banded Gneiss Complex of the Aravalli belt. Cratonic sediment appears to interfinger with Himalayan detritus farther north below the Ganga-Yamuna Interfluve. With its headwaters in the tectonically unstable Indus-Ganga watershed area, the Yamuna River may have occupied its present course late in the Quaternary, and if so, cratonic rivers may have provided the basin's axial drainage for prolonged periods. The penetration of Himalayan sediment to the distal foreland basin may reflect avulsion of orogenic rivers along the craton margin, in addition to dynamic transverse drainage systems from the Himalaya that pushed the axial drainage to the basin's feather edge. The wide spread of cratonic sediment would have been enhanced by slow subsidence in the distal foreland basin and focusing of rivers into a basin reentrant.
Grand Rounds: Nephrotoxicity in a Young Child Exposed to Uranium from Contaminated Well Water
2007-08-01
Full Text Available.ContextPrivate wells that tap groundwater are largely exempt from federal drinking-water regulations, and in most states well water is not subject to much of the mandatory testing required of public water systems. Families that rely on private wells are thus at risk of exposure to a variety of unmeasured contaminants.Case PresentationA family of seven—two adults and five children—residing in rural northwestern Connecticut discovered elevated concentrations of uranium in their drinking water, with levels measured at 866 and 1,160 μg/L, values well above the U.S. Environmental Protection Agency maximum contaminant level for uranium in public water supplies of 30 μg/L. The uranium was of natural origin, and the source of exposure was found to be a 500-foot well that tapped groundwater from the Brookfield Gneiss, a geologic formation known to contain uranium. Other nearby wells also had elevated uranium, arsenic, and radon levels, though concentrations varied widely. At least one 24-hr urine uranium level was elevated (> 1 μg/24 hr) in six of seven family members (range, 1.1–2.5 μg/24 hr). To assess possible renal injury, we measured urinary beta-2-microglobulin. Levels were elevated (> 120 μg/L) in five of seven family members, but after correction for creatine excretion, the beta-2-microglobulin excretion rate remained elevated (> 40 μg/mmol creatinine) only in the youngest child, a 3-year-old with a corrected level of 90 μg/mmol creatinine. Three months after cessation of well water consumption, this child’s corrected beta-2-microglobulin level had fallen to 52 μg/mmol creatinine.SignificanceThis case underscores the hazards of consuming groundwater from private wells. It documents the potential for significant residential exposure to naturally occurring uranium in well water. It highlights the special sensitivity of young children to residential environmental exposures, a reflection of the large amount of time they spend in their homes, the developmental immaturity of their kidneys and other organ systems, and the large volume of water they consume relative to body mass.
http://espace.library.uq.edu.au/view/UQ:66685
Comparison of initial Pb-isotope signatures of several early Archaean (3.65-3.82 Ga) lithologies (orthogneisses and metasediments) and minerals (feldspar and galena) documents the existence of substantial isotopic heterogeneity in the early Archaean, particularly in the Pb-207/Pb-204 ratio. The magnitude of isotopic variability at 3.82-3.65 Ga requires source separation between 4.3 and 4.1 Ga, depending on the extent of U/Pb fractionation possible in the early Earth. The isotopic heterogeneity could reflect the coexistence of enriched and depleted mantle domains or the separation of a terrestrial protocrust with a U-238/Pb-204 (mu) that was ca. 20-30% higher than coeval mantle. We prefer this latter explanation because the high-p signature is most evident in metasediments (that formed at the Earth's surface). This interpretation is strengthened by the fact that no straightforward mantle model can be constructed for these high-mu lithologies without violating bulk silicate Earth constraints. The Pb-isotope evidence for a long-lived protocrust complements similar Hf-isotope data from the Earth's oldest zircons, which also require an origin from an enriched (low Lu/Hf) environment. A model is developed in which greater than or equal to3.8-Ga tonalite and monzodiorite gneiss precursors (for one of which we provide zircon U-Pb data) are not mantle-derived but formed by remelting or differentiation of ancient (ca. 4.3 Ga) basaltic crust which had evolved with a higher U/Pb ratio than coeval mantle in the absence of the subduction process. With the initiation of terrestrial subduction at, we propose, ca. 3.75 Ga, most of the greater than or equal to3.8-Ga basaltic shell (and its differentiation products) was recycled into the mantle, because of the lack of a stabilising mantle lithosphere. We argue that the key event for preservation of all greater than or equal to3.8-Ga terrestrial crust was the intrusion of voluminous granitoids immediately after establishment of global subduction because of complementary creation of a lithospheric keel. Furthermore, we argue that preservation of !3.8-Ga material (in situ rocks and zircons) globally is restricted to cratons with a high U/Pb source character (North Atlantic, Slave, Zimbabwe, Yilgarn, and Wyoming), and that the Pb-isotope systematics of these provinces are ultimately explained by reworking of material that was derived from ca. 4.3 Ga (i.e. Hadean) basaltic crust. Publisher: Springer-Verlag Relation: isMemberOf School of Physical Sciences Publications; isMemberOf Excellence in Research Australia (ERA) - Collection
http://espace.library.uq.edu.au/view/UQ:78671
Hydrothermally altered shock-metamorphosed gneisses consisting of relic igneous biotite-K-feldspor-Na-rich alkali feldspar - plagioclase - quartz assemblages ( accessory garnet, corundum, titanite, monazite, zircon), and showing extensive replacement by montmorillonite, illite, sericite, and to a lesser extent chlorite, calcite, epidote, zoisite and pyrite, occur in the basement core uplift of the Woodleigh impact structure, Western Australia. The rocks display extensive hydrothermal clay alteration, complicating identification of pre-hydrothermal and pre-impact textures and compositions. Analysis of quartz-hosted planar deformation features (PDFs) indicates a majority of indexed sets parallel to omega{10 (1) over bar3}, a lesser abundance of sets parallel to pi{10 (1) over bar2}, and some sets parallel to the basal plane (0001) and r,z {10 (1) over bar1}, consistent with pressures about or over 20 GPa. Feldspar-hosted FDFs form reticulate vein networks displaying checkerboard-like to irregular and serrated patterns attributable to preferential replacement of shock-damaged PDFs and/or perthitic twin lamella by clay minerals. The gneisses are pervaded by clay-dominated intergranular and intragranular veins of cryptocrystalline material that display marked departures from bulk-rock chemistry and from mineral compositions. XRD analysis identifies the cryptocrystalline components as illite - montmorillonite, illite and chlorite, while laser Raman analysis identifies high-fluorescence sub-micrometre clay assemblage, feldspar, quartz and minor mica. SEM/EDS-probe and laser-ICPMS analysis indicate low-K high-Mg clay mineral compositions consistent with montmorillonite. Quartz PDF-hosted cryptocrystalline laminae display distinct enrichments in Al, Mg, Ca and K. Altered intergranular veins and feldspar-hosted cryptocrystalline components show consistent enrichment in the relatively refractory elements (Al, Cc, Mg, Fe) and depletion in relatively volatile elements (Si, K, Na). The clay alteration retards determination whether clay-dominated vein networks represent altered shock-induced pseudotachylite veins, diaplectic zones and/or shock-damaged twin lamella, and/or result from purely mineralogical and chemical differentiation affected by hydrothermal fluids, Overall enrichment of the shocked gneiss and of the cryptocrystalline components in Mg and trace ferromagnesian elements (Ni, Cc, Cr) may be attributed alternatively to introduction of siderophile element-rich fluid from the projectile, or/and contamination of hydrothermal fluids by MgO from dolomites surrounding the basement uplift. High Ni/Co and Ni/Cr and anomalous DGE (platinum group elements) may support the former model. Relation: isMemberOf School of Physical Sciences Publications; isMemberOf Excellence in Research Australia (ERA) - Collection Coverage: 2005-01-01T00:00:00Z
The greenstone belts of Zimbabwe
... the evidence from various granites and gneisses. The more extensive, main greenstone belts comprise the dominantly volcanic Bulawayan Group and dominantly sedimentary Shamvaian Group. An ...
... In this context, samples of high grade gneisses from the Kapuskasing structural zone (KSZ, Fig. 1) of eastern Ontario were studied in an attempt to define the composition of syn- and ...
http://hdl.handle.net/1959.14/26750
Many points of evidence, especially igneous microstructures and structures resulting from solid-state deformation, indicate that K-feldspar megacrysts in deformed granites of the Papoose Flat pluton are residual phenocrysts, not porphyroblasts. Evidence of an igneous origin includes features such as crystal shapes, simple twinning, zonally arranged euhedral plagioclase inclusions, oscillatory compositional zoning, and local occurrence in microgranitoid enclaves. Evidence of solid-state deformation of the megacrysts (which is consistent with their existence prior to the mylonitic deformation) includes marginal recrystallization and neocrystallization, microcline twinning, marginal replacement by myrmekite, and recrystallized/neocrystallized “tails”. Evidence of porphyroblastic growth, such as overgrown inclusion trails, is absent. This appears to be the situation in most felsic augen gneisses and mylonites.9 page(s) Publisher: Springer Contributor: Macquarie University. Dept. of Earth and Planetary Sciences Relation: Electronic geosciences, Vol. 7, Issue 1, p.31-39; 10.1007/s10069-002-0005-3 Other identifier: ISSN:1610-2924; mq-rm-2002015527 Language: eng
http://hdl.handle.net/2440/49760
Copyright © 2008 InformaMajor, trace, rare-earth elements and isotopic (Sm - Nd and Rb - Sr) data from the ca 1704 - 1685 Ma Alma, Farmcote, Rasp Ridge and Hores-Potosi felsic magmatic gneisses and the ca 1600 Ma syn-orogenic felsic intrusions of the Willyama Supergroup in the Broken Hill Block of western New South Wales are documented. The ca 1704 - 1685 Ma felsic melts were generated by anatexis of the Willyama Supergroup metasediments with variable degrees of mixing of a juvenile, mantle-derived component represented by coeval high Fe - Ti metatholeiitic rocks. This is consistent with previous interpretations for bimodal magmatism occurring in an extensional environment with an elevated geothermal gradient driven by lithospheric thinning and mafic magmatism. Interpretations involving the presence of a mafic underplate as a source for the ca 1704 - 1685 Ma felsic melts are not supported by these data. The ca 1600 Ma syn-orogenic felsic intrusions are a direct product of partial melting of the sedimentary sequences of the Willyama Supergroup as a response to the high-temperature, low-pressure amphibolite- to granulite-facies metamorphic event accompanying the Olarian Orogeny. The presence of an Archean basement for the Willyama Supergroup remains unclear, although if this basement exists it was not sampled during the period of felsic magmatic activity that took place in the Broken Hill Block between ca 1710 and 1600 Ma. Publisher: Taylor and Francis Contributor: School of Earth and Environmental Sciences Other identifier: Australian Journal of Earth Sciences, 2008; 55 (4):531-553; 0812-0099; 0020081094; 10.1080/08120090801888651; 000257070100007 Language: en
http://hdl.handle.net/2440/35110
None Available Publisher: Geological Society of India Contributor: School of Earth and Environmental Sciences Other identifier: Journal of the Geological Society of India, 2006; 68 (2):176-180; 0016-7622; 0020062077 Language: en
http://hdl.handle.net/1959.14/40541
Field observations involving landform evaluation and the physical characterization of sediments, combined with a detailed analysis of the spatial distribution of bedrock and sediment geochemical patterns, suggests a limit to the glacial transport half-distance of c. 3 km in Vestfold Hills. Four morphologically distinct glacial deposits were sampled (small debris ridges, large debris ridges, debris drapes and valley fills) on the basis of field geometry. These landforms were subsequently distinguished by grain size, mineralogy and geochemistry. Since there are no nunataks south of Vestfold Hills, all debris is derived subglacially and sedimentological differences are attributed to the physical weathering of preglacial surfaces in Vestfold Hills and fluvial winnowing during deposition. Given that thrust geometries may occur in large debris ridges, glacial transport distances were short, and fluvial sorting of sediments was an important mechanism, reconstructions of glacial histories based on the stratigraphy of deposits in Vestfold Hills should be made with caution.11 page(s) Publisher: Cambridge University Press Contributor: Macquarie University. Dept. of Physical Geography; Macquarie University. Dept. of Biological Sciences Relation: Antarctic science, Vol. 15, Issue 2, p.259-269; 10.1017/S0954102003001263 Other identifier: ISSN:0954-1020; mq-rm-2003017124 Language: eng Rights: Copyright 2003 Cambridge University Press. Reprinted from Antartic science.
http://espace.library.uq.edu.au/view/UQ:59367
None Available Publisher: Elsevier Science Relation: isMemberOf School of Physical Sciences Publications
http://espace.library.uq.edu.au/view/UQ:147099
None Available Publisher: American Geophysical Union Relation: isMemberOf School of Physical Sciences Publications
http://espace.library.uq.edu.au/view/UQ:139232
None Available Publisher: Elsevier Relation: isMemberOf School of Physical Sciences Publications
http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=117468
None Available Publisher: Department of Applied Geology Other identifier: PUB-SE-DAG-NET-44066
http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=117342
None Available Publisher: Department of Applied Geology Other identifier: PUB-RES-DAG-SA-12811
http://arrow.monash.edu.au/hdl/1959.1/82958
None Available Publisher: Elsevier B. V. Other identifier: monash:12937 Language: eng Source: 0301-9268
Xenoliths from the sub-volcanic lithosphere of Mt Taranaki, New Zealand
2010-01-01
Mount Taranaki is located 140km west of the Taupo Volcanic Zone and represents the most westerly expression of subduction-related volcanism on the North Island of New Zealand. Taranaki is a predominantly high-K arc volcano but compositions range from basaltic andesite to andesite with minor dacite and basalt. The sub-volcanic basement under Taranaki is thought to comprise calc-alkaline plutonic and metamorphic rocks of the Median Batholith, overlain by a sequence of Cretaceous and Tertiary sediments. Taranaki lavas contain abundant xenoliths that represent samples of the upper to lower crust beneath the volcano. The xenolith suite has been initially organised into six groups based on petrography, geochemistry and inferred genetic relationships: supracrustal sedimentary rocks (1), mafic hor...
Very high-pressure orogenic garnet peridotites
2007-05-29
Mantle-derived garnet peridotites are a minor component in many very high-pressure metamorphic terranes that formed during continental subduction and collision. Some of these mantle rocks contain trace...Full Text Available
Very high-pressure orogenic garnet peridotites
2007-05-29
Full Text Available.Mantle-derived garnet peridotites are a minor component in many very high-pressure metamorphic terranes that formed during continental subduction and collision. Some of these mantle rocks contain trace amounts of zircon and micrometer-sized inclusions. The constituent minerals exhibit pre- and postsubduction microstructures, including polymorphic transformation and mineral exsolution. Experimental, mineralogical, petrochemical, and geochronological characterizations using novel techniques with high spatial, temporal, and energy resolutions are resulting in unexpected discoveries of new phases, providing better constraints on deep mantle processes.
Using Three-dimensional Plant Root Architecture in Models of Shallow-slope Stability
2008-05-01
Full Text Available.BackgroundThe contribution of vegetation to shallow-slope stability is of major importance in landslide-prone regions. However, existing slope stability models use only limited plant root architectural parameters. This study aims to provide a chain of tools useful for determining the contribution of tree roots to soil reinforcement.MethodsThree-dimensional digitizing in situ was used to obtain accurate root system architecture data for mature Quercus alba in two forest stands. These data were used as input to tools developed, which analyse the spatial position of roots, topology and geometry. The contribution of roots to soil reinforcement was determined by calculating additional soil cohesion using the limit equilibrium model, and the factor of safety (FOS) using an existing slope stability model, Slip4Ex.Key ResultsExisting models may incorrectly estimate the additional soil cohesion provided by roots, as the spatial position of roots crossing the potential slip surface is usually not taken into account. However, most soil reinforcement by roots occurs close to the tree stem and is negligible at a distance >1·0 m from the tree, and therefore global values of FOS for a slope do not take into account local slippage along the slope.ConclusionsWithin a forest stand on a landslide-prone slope, soil fixation by roots can be minimal between uniform rows of trees, leading to local soil slippage. Therefore, staggered rows of trees would improve overall slope stability, as trees would arrest the downward movement of soil. The chain of tools consisting of both software (free for non-commercial use) and functions available from the first author will enable a more accurate description and use of root architectural parameters in standard slope stability analyses.
Using Three-dimensional Plant Root Architecture in Models of Shallow-slope Stability
2008-05-01
BackgroundThe contribution of vegetation to shallow-slope stability is of major importance in landslide-prone regions. However, existing slope stability models use only limited plant...Full Text Available
Thermal history of a metamorphic core complex
... several varieties of mylonitic orthogneiss as well as amphibolitic orthognesses from the non-mylonitic infrastructural core. Oligocene-age porphyritic biotite granodiorite of the Harrison ...
The origin and emergence of life under impact bombardment
2006-10-29
Full Text Available.Craters formed by asteroids and comets offer a number of possibilities as sites for prebiotic chemistry, and they invite a literal application of Darwin's ‘warm little pond’. Some of these attributes, such as prolonged circulation of heated water, are found in deep-ocean hydrothermal vent systems, previously proposed as sites for prebiotic chemistry. However, impact craters host important characteristics in a single location, which include the formation of diverse metal sulphides, clays and zeolites as secondary hydrothermal minerals (which can act as templates or catalysts for prebiotic syntheses), fracturing of rock during impact (creating a large surface area for reactions), the delivery of iron in the case of the impact of iron-containing meteorites (which might itself act as a substrate for prebiotic reactions), diverse impact energies resulting in different rates of hydrothermal cooling and thus organic syntheses, and the indiscriminate nature of impacts into every available lithology—generating large numbers of ‘experiments’ in the origin of life. Following the evolution of life, craters provide cryptoendolithic and chasmoendolithic habitats, particularly in non-sedimentary lithologies, where limited pore space would otherwise restrict colonization. In impact melt sheets, shattered, mixed rocks ultimately provided diverse geochemical gradients, which in present-day craters support the growth of microbial communities.
The origin and emergence of life under impact bombardment
2006-10-29
Craters formed by asteroids and comets offer a number of possibilities as sites for prebiotic chemistry, and they invite a literal application of Darwin's ‘warm little pond’. Some of...Full Text Available
2010-01-01
The Sebes-Lotru terrane in the South Carpathians mountain range comprises a lower, Neoproterozoic metamorphic unit (Lotru) and an upper, Ordovician metamorphic unit (Cumpana) that were juxtaposed during the Variscan orogeny. Two orthogneisses from the Lotru metamorphic unit yield U/Pb LA-ICP-MS zircon crystallization ages of 549.3+/-3.8Ma and 587.5+/-3Ma, respectively. Two orthogneisses from the Cumpana metamorphic unit yield zircon crystallization ages of 458.9+/-3.5Ma and 466.0+/-4.2Ma, respectively. High U zircons from two other orthogneisses from the Cumpana metamorphic unit have ages ranging from 400Ma to 320Ma, which are interpreted to reflect protracted zircon recrystallization during the regionally significant Variscan collisional event. Detrital zircons from a metasedimentary gnei...
Seismic response to natural gas anomalies in crystalline rocks
Continental drilling reveals gas anomalies of CH4, CO2, and He in the deep crystalline rocks, which are correlated to the seismic horizontal component reflectors. Geochemical experiments show that porosity of ...
2010-01-01
The Ollo de Sapo Fm. in the Sanabria region of NW Iberia consists of subvolcanic, volcanic and volcano-sedimentary rocks underlying and partly intercalated with Early Ordovician, platform-facies sediments. Granitic plutons of the same age, presently transformed into orthogneisses, are genetically related. The metavolcanic rocks are dacites and rhyolites with potassic and peraluminous character, and volcanic arc signature, possibly inherited from the melting of calc-alkaline crustal material. In the study area, the Ollo de Sapo Fm. is made up of two large superposed volcanic domes separated by a thin screen of contemporaneous metapelites and sandstones. The domes underwent endogenous growth with subvolcanic, phenocryst-rich magma intruding and cooling under a volcanic and volcaniclastic shi...
Physical conditions on the early Earth
2006-10-29
The formation of the Earth as a planet was a large stochastic process in which the rapid assembly of asteroidal-to-Mars-sized bodies was followed by a more extended period of growth through collisions...Full Text Available
Physical conditions on the early Earth
2006-10-29
Full Text Available.The formation of the Earth as a planet was a large stochastic process in which the rapid assembly of asteroidal-to-Mars-sized bodies was followed by a more extended period of growth through collisions of these objects, facilitated by the gravitational perturbations associated with Jupiter. The Earth's inventory of water and organic molecules may have come from diverse sources, not more than 10% roughly from comets, the rest from asteroidal precursors to chondritic bodies and possibly objects near Earth's orbit for which no representative class of meteorites exists today in laboratory collections. The final assembly of the Earth included a catastrophic impact with a Mars-sized body, ejecting mantle and crustal material to form the Moon, and also devolatilizing part of the Earth. A magma ocean and steam atmosphere (possibly with silica vapour) existed briefly in this period, but terrestrial surface waters were below the critical point within 100 million years after Earth's formation, and liquid water existed continuously on the surface within a few hundred million years. Organic material delivered by comets and asteroids would have survived, in part, this violent early period, but frequent impacts of remaining debris probably prevented the continuous habitability of the Earth for one to several hundred million years. Planetary analogues to or records of this early time when life began include Io (heat flow), Titan (organic chemistry) and Venus (remnant early granites).
Full Text Available.BackgroundNeutralizing antibodies (NAbs) against Interferon beta (IFNβ) are reported to be associated with poor clinical response to therapy in multiple sclerosis (MS) patients. We aimed to quantify the contribution of NAbs to the sub-optimal response of IFNβ treatment.MethodsWe studied the prevalence of NAbs in MS patients grouped according to their clinical response to IFNβ during the treatment period. Patients were classified as: group A, developing ≥ 1 relapse after the first 6 months of therapy; group B, exhibiting confirmed disability progression after the first 6 months of therapy, with or without superimposed relapses; group C, presenting a stable disease course during therapy. A cytopathic effect assay tested the presence of NAbs in a cohort of ambulatory MS patients treated with one of the available IFNβ formulations for at least one year. NAbs positivity was defined as NAbs titre ≥ 20 TRU.ResultsSeventeen patients (12.1%) were NAbs positive. NAbs positivity correlated with poorer clinical response (p < 0.04). As expected, the prevalence of NAbs was significantly lower in Group C (2.1%) than in Group A (17.0%) and Group B (17.0%). However, in the groups of patients with a poor clinical response (A, B), NAbs positivity was found only in a small proportion of patients.ConclusionThe majority of patients with poor clinical response are NAbs negative suggesting that NAbs explains only partially the sub-optimal response to IFNβ.
BackgroundNeutralizing antibodies (NAbs) against Interferon beta (IFNβ) are reported to be associated with poor clinical response to therapy in multiple sclerosis (MS) patients....Full Text Available
Montreal Axion - Wikipedia, the free encyclopedia
The Montreal Axion are a National Women's Hockey League team located in Montreal, Quebec, Canada. v ? d ? e · Sports teams based in the province of Quebec, ...
2010-01-01
This study assesses the level of terrestrial gamma radiation and associated dose rates from the naturally occurring radionuclides 232Th, 238U and 40K in 10 soil samples...Full Text Available
2008-12-07
Sea ice loss will indirectly alter energy transfer through the pelagic food web and ultimately impact apex predators. We quantified spring-time trends in sea ice recession around each of 46 thick-billed...Full Text Available
2008-12-07
Full Text Available.Sea ice loss will indirectly alter energy transfer through the pelagic food web and ultimately impact apex predators. We quantified spring-time trends in sea ice recession around each of 46 thick-billed murre (Uria lomvia) colonies in west Greenland across 20° of latitude and investigated the magnitude and timing of the associated spring-time primary production. A geographical information system was used to extract satellite-based observations of sea ice concentration from the Nimbus-7 scanning multichannel microwave radiometer (SMMR, 1979–1987) and the Defence Meteorological Satellite Programs Special Sensor Microwave/Imager (SSMI, 1987–2004), and satellite-based observations of chlorophyll a from the moderate resolution imaging spectroradiometer (MODIS: EOS-Terra satellite) in weekly intervals in circular buffers around each colony site (150 km in radius). Rapid recession of high Arctic seasonal ice cover created a temporally predictable primary production bloom and associated trophic cascade in water gradually exposed to solar radiation. This pattern was largely absent from lower latitudes where little to no sea ice resulted in a temporally variable primary production bloom driven by nutrient cycling and upwelling uncoupled to ice. The relationship between the rate and variability of sea ice recession and colony size of thick-billed murres shows that periodical confinement of the trophic cascade at high latitudes determines the carrying capacity for Arctic seabirds during the breeding period.
January-February 2010 GSA Bulletin highlights
The January-February GSA BULLETIN is online now ahead of print. Topics cover the globe, with studies from South America, China, South Africa, Spain, Tenerife, Dominican Republic and across the United States. The first ...
2006-09-01
Full Text Available.• Background and Aims Intraspecific genome size variability of Festuca pallens occurring on relict rocky steppes in Central Europe was studied on two ploidy levels and three geographical scales: (1) local scale of 24 populations, (2) landscape scale of three transects in river canyons or hill systems, and (3) global scale of 160 samples covering the whole distribution area.• Methods DAPI flow cytometry of homogeneously cultivated samples (≥1 year), measured randomly with two internal standards, Lycopersicon esculentum and Pisum sativum. Differences in DNA content were confirmed (1) by the double peaks of simultaneously measured samples, (2) based on measurements carried out in different seasons, and (3) by additional measurements with propidium iodide.• Key Results On a global scale, the relative DNA content ranged between 1·170-fold in diploids and 1·164-fold in tetraploids. A maximum difference of 1·088-fold between the mean relative DNA content of nearby populations was found. In 16 of 24 populations significant variability was shown (P < 0·001, 1·121-fold as maximum). For both ploidy levels, the relative genome size had the same range and geographical pattern, correlated with geographical coordinates (P < 0·01). Diploids with larger genomes occur on relict habitats (P < 0·01), and in areas of periglacial steppes (20 000 years ago; P < 0·02). In tetraploids, the relative DNA content differs among the three previously recognized geographical types (Alpine, Pannonian and Scabrifolia, P < 0·001). Tetraploids have a relative DNA content smaller than twice that of the diploids (P < 0·001). An influence of microhabitat on DNA content variation was not confirmed.• Conclusions Genome size variability occurs over all spatial scales: intrapopulation, landscape and global. Correlation between geographical coordinates and palaeovegetation type, concomitant with diploids and tetraploids, and no influence of microhabitat were found. Genome size decreases in tetraploids. Lower CVs, and thus higher accuracy, resolution and reproducibility, favour DAPI measurements for the study of intraspecific genome size variability.
2006-09-01
• Background and Aims Intraspecific genome size variability of Festuca pallens occurring on relict rocky steppes in Central Europe was studied on two ploidy...Full Text Available
Hydrogeochemistry of seasonal variation of Urmia Salt Lake, Iran
Urmia Lake has been designated as an international park by the United Nations. The lake occupies a 5700 km2 depression in northwestern Iran. Thirteen permanent rivers flow into the lake. Water level...Full Text Available
Hydrogeochemistry of seasonal variation of Urmia Salt Lake, Iran
Full Text Available.Urmia Lake has been designated as an international park by the United Nations. The lake occupies a 5700 km2 depression in northwestern Iran. Thirteen permanent rivers flow into the lake. Water level in the lake has been decreased 3.5 m in the last decade due to a shortage of precipitation and progressively dry climate. Geologically the lake basin is considered to be a graben of tectonic origin. Na, K, Ca, Li and Mg are the main cations with Cl, SO4, and HCO3 as the main anions. F & Br are the other main elements in the lake. A causeway crossing the lake is under construction, which may affect the lake's annual geochemistry. The main object of this project is mainly to consider the potential of K-mineral production along with ongoing salt production.Seven hundred and four samples were taken and partially analyzed for the main cations and anions. Surface water (0.5 m. depth) was analyzed for Na, K, Mg, Ca, Br and Li, and averaged 87.118 g/lit, 1.48 g/lit, 4.82 g/lit, 4.54 g/lit, 1.19 ppm and 12.7 ppm respectively for the western half of the lake. Sodium ranged between 84 to 91.2 g/lit, and showed higher concentrations in the south than in the north. This unexpected result may be caused by shallower depth in the south and a higher net evaporation effect. Calcium ranged between 4.2 to 5 g/lit, apparently slightly higher in the north. K is higher in the south, possibly due to rivers entering from south that may carry slightly higher K in solution.In the middle-range samples (0.5–5 m.), K averaged 1.43 g/lit and ranged from 1.40 to 1.46 g/lit. At this intermediate depth the distribution of K is clearly higher to the south of the causeway that is currently under construction. It is not clear whether this increase is the effect of the causeway or the effect of the salty Aji-Chay River to the east, and the Khoy salt domes to the north of the lake. At depth (5 m–10 m), K averaged 1.48 g/lit and ranged from 1.4 to 1.49 g/lit, differing only in the second decimal from the average of the middle and surface samples.Ignoring the small difference between the averages of the three sample depths, the distribution of K is highly homogeneous in the lake water due to the mixing process. Therefore causeway construction has not yet strongly affected K distribution, or it may be at the starting point. Magnesium concentration ranged from 4.6 to 5-g/lit, and was elevated in the south. This differs somewhat compared to calcium. Lithium, with an average of 12–13 ppm, is slightly higher in the south, and has not shown any significant variation in all three seasons. Iodine was below the detection limit in the lake.Urmia Lake, geochemically, is highly uniform both to the south and north of the causeway, in both the surface and deep brines. K and Mg, which average 1.48 and 6.6 g/lit in order, could be elements worth production in addition to the NaCl currently being produced from the lake. Br, F, Li and B in the limit of <50 ppm don't look to be in the economical range.
Holocene elephant seal distribution implies warmer-than-present climate in the Ross Sea
2006-07-05
We show that southern elephant seal (Mirounga leonina) colonies existed proximate to the Ross Ice Shelf during the Holocene, well south of their core sub-Antarctic breeding and molting...Full Text Available
Holocene elephant seal distribution implies warmer-than-present climate in the Ross Sea
2006-07-05
Full Text Available.We show that southern elephant seal (Mirounga leonina) colonies existed proximate to the Ross Ice Shelf during the Holocene, well south of their core sub-Antarctic breeding and molting grounds. We propose that this was due to warming (including a previously unrecognized period from ≈1,100 to 2,300 14C yr B.P.) that decreased coastal sea ice and allowed penetration of warmer-than-present climate conditions into the Ross Embayment. If, as proposed in the literature, the ice shelf survived this period, it would have been exposed to environments substantially warmer than present.
Heterotrophic microbial communities use ancient carbon following glacial retreat
2007-10-22
Full Text Available.
Grand Rounds: Nephrotoxicity in a Young Child Exposed to Uranium from Contaminated Well Water
2007-08-01
ContextPrivate wells that tap groundwater are largely exempt from federal drinking-water regulations, and in most states well water is not subject to much of the mandatory testing...Full Text Available
Fossil evidence of Archaean life
2006-06-29
Full Text Available.Evidence for the existence of life during the Archaean segment of Earth history (more than 2500 Myr ago) is summarized. Data are presented for 48 Archaean deposits reported to contain biogenic stromatolites, for 14 such units reported to contain 40 morphotypes of putative microfossils, and for 13 especially ancient, 3200–3500 Myr old geologic units for which available organic geochemical data are also summarized. These compilations support the view that life's existence dates from more than or equal to 3500 Myr ago.
Fossil evidence of Archaean life
2006-06-29
Evidence for the existence of life during the Archaean segment of Earth history (more than 2500 Myr ago) is summarized. Data are presented for 48 Archaean deposits reported to contain biogenic...Full Text Available
Evolutionary ecology during the rise of dioxygen in the Earth's atmosphere
2008-08-27
Full Text Available.
Enhanced diffusion of Uranium and Thorium linked to crystal plasticity in zircon
The effects of crystal-plasticity on the U-Th-Pb system in zircon is studied by quantitative microstructural and microchemical analysis of a large zircon grain collected from pyroxenite of the Lewisian...Full Text Available
Enhanced diffusion of Uranium and Thorium linked to crystal plasticity in zircon
Full Text Available.The effects of crystal-plasticity on the U-Th-Pb system in zircon is studied by quantitative microstructural and microchemical analysis of a large zircon grain collected from pyroxenite of the Lewisian Complex, Scotland. Electron backscatter diffraction (EBSD) mapping reveals a c.18° variation in crystallographic orientation that comprises both a gradual change in orientation and a series of discrete low-angle (<4°) boundaries. These microstructural data are consistent with crystal-plastic deformation of zircon associated with the formation and migration of dislocations. A heterogeneous pattern of dark cathodoluminescence, with the darkest domains coinciding with low-angle boundaries, mimics the deformation microstructure identified by EBSD. Geochemical data collected using the Sensitive High Resolution Ion MicroProbe (SHRIMP) shows a positive correlation between concentrations of the elements U, Th and Pb (ranging from 20–60 ppm, 30–110 ppm, and 14–36 ppm, respectively) and Th/U ratio (1.13 – 1.8) with the deformation microstructure. The highest measured concentrations and Th/U coincide with low-angle boundaries. This enrichment is interpreted to reflect enhanced bulk diffusion of U and Th due to the formation and migration of high-diffusivity dislocations. 207Pb/206Pb ages for individual analyses show no significant variation across the grain, and define a concordant, combined mean age of 2451 ± 14 Ma. This indicates that the grain was deformed shortly after initial crystallization, most probably during retrograde Inverian metamorphism at amphibolite facies conditions. The elevated Th over U and consistent 207Pb/206Pb ages indicates that deformation most likely occurred in the presence of a late-stage magmatic fluid that drove an increase in the Th/U during deformation. The relative enrichment of Th over U implies that Th/U ratio may not always be a robust indicator of crystallization environment. This study provides the first evidence of deformation-related modification of the U-Th system in zircon and has fundamental implications for the application and interpretation of zircon trace element data.
Full Text Available.During a five-year GPS satellite tracking study in Sabi Sand Reserve (SSR) and Kruger National Park (KNP) we monitored the daily movements of an elephant cow (Loxodonta africana) from September 2003 to August 2008. The study animal was confirmed to be part of a group of seven elephants therefore her position is representative of the matriarchal group. We found that the study animal did not use habitat randomly and confirmed strong seasonal fidelity to its summer and winter five-year home ranges. The cow's summer home range was in KNP in an area more than four times that of her SSR winter home range. She exhibited clear park habitation with up to three visits per year travelling via a well-defined northern or southern corridor. There was a positive correlation between the daily distance the elephant walked and minimum daily temperature and the elephant was significantly closer to rivers and artificial waterholes than would be expected if it were moving randomly in KNP and SSR. Transect lines established through the home ranges were surveyed to further understand the fine scale of the landscape and vegetation representative of the home ranges.
During a five-year GPS satellite tracking study in Sabi Sand Reserve (SSR) and Kruger National Park (KNP) we monitored the daily movements of an elephant cow (Loxodonta africana) from...Full Text Available
2007-01-01
Scanning electron microscopy revealed great morphological diversity in biofilms from several largely unexplored subterranean thermal Alpine springs, which contain radium 226 and radon 222. A culture-independent...Full Text Available
2007-01-01
Full Text Available.Scanning electron microscopy revealed great morphological diversity in biofilms from several largely unexplored subterranean thermal Alpine springs, which contain radium 226 and radon 222. A culture-independent molecular analysis of microbial communities on rocks and in the water of one spring, the “Franz-Josef-Quelle” in Bad Gastein, Austria, was performed. Four hundred fifteen clones were analyzed. One hundred thirty-two sequences were affiliated with 14 bacterial operational taxonomic units (OTUs) and 283 with four archaeal OTUs. Rarefaction analysis indicated a high diversity of bacterial sequences, while archaeal sequences were less diverse. The majority of the cloned archaeal 16S rRNA gene sequences belonged to the soil-freshwater-subsurface (1.1b) crenarchaeotic group; other representatives belonged to the freshwater-wastewater-soil (1.3b) group, except one clone, which was related to a group of uncultivated Euryarchaeota. These findings support recent reports that Crenarchaeota are not restricted to high-temperature environments. Most of the bacterial sequences were related to the Proteobacteria (α, β, γ, and δ), Bacteroidetes, and Planctomycetes. One OTU was allied with Nitrospina sp. (δ-Proteobacteria) and three others grouped with Nitrospira. Statistical analyses suggested high diversity based on 16S rRNA gene analyses; the rarefaction plot of archaeal clones showed a plateau. Since Crenarchaeota have been implicated recently in the nitrogen cycle, the spring environment was probed for the presence of the ammonia monooxygenase subunit A (amoA) gene. Sequences were obtained which were related to crenarchaeotic amoA genes from marine and soil habitats. The data suggested that nitrification processes are occurring in the subterranean environment and that ammonia may possibly be an energy source for the resident communities.
Cerebrospinal Fluid B Cells Correlate with Early Brain Inflammation in Multiple Sclerosis
Full Text Available.BackgroundThere is accumulating evidence from immunological, pathological and therapeutic studies that B cells are key components in the pathophysiology of multiple sclerosis (MS).Methodology/Principal FindingsIn this prospective study we have for the first time investigated the differences in the inflammatory response between relapsing and progressive MS by comparing cerebrospinal fluid (CSF) cell profiles from patients at the onset of the disease (clinically isolated syndrome, CIS), relapsing-remitting (RR) and chronic progressive (CP) MS by flow cytometry. As controls we have used patients with other neurological diseases. We have found a statistically significant accumulation of CSF mature B cells (CD19+CD138−) and plasma blasts (CD19+CD138+) in CIS and RRMS. Both B cell populations were, however, not significantly increased in CPMS. Further, this accumulation of B cells correlated with acute brain inflammation measured by magnetic resonance imaging and with inflammatory CSF parameters such as the number of CSF leukocytes, intrathecal immunoglobulin M and G synthesis and intrathecal production of matrix metalloproteinase (MMP)-9 and the B cell chemokine CxCL-13.ConclusionsOur data support an important role of CSF B cells in acute brain inflammation in CIS and RRMS.
Cerebrospinal Fluid B Cells Correlate with Early Brain Inflammation in Multiple Sclerosis
BackgroundThere is accumulating evidence from immunological, pathological and therapeutic studies that B cells are key components in the pathophysiology of multiple sclerosis (MS).Methodology/Principal...Full Text Available
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Axion - Wikipedia, the free encyclopedia
The axion is a hypothetical elementary particle postulated by Peccei-Quinn theory in 1977 to resolve the strong-CP problem in quantum chromodynamics (QCD). ...
A look inside of diamond-forming media in deep subduction zones
2007-05-29
Geologists have “known” for many years that continental crust is buoyant and cannot be subducted very deep. Microdiamonds 10–80 μm in size discovered in the 1980s within...Full Text Available
A look inside of diamond-forming media in deep subduction zones
2007-05-29
Full Text Available.Geologists have “known” for many years that continental crust is buoyant and cannot be subducted very deep. Microdiamonds 10–80 μm in size discovered in the 1980s within metamorphic rocks related to continental collisions clearly refute this statement, suggesting that material of continental crust has been subducted to a minimum depth of >150 km and incorporated into mountain chains during tectonic exhumation. Over the past decade, the rapidly moving technological advancement has made it possible to examine these diamonds in detail, and to learn that they contain nanometric multiphase inclusions of crystalline and fluid phases and are characterized by a “crustal” signature of carbon stable isotopes. Scanning and transmission electron microscopy, focused ion beam techniques, synchrotron infrared spectroscopy, and nano-secondary ion mass spectrometry studies of these diamonds provide evidence that they were crystallized from a supercritical carbon-oxygen-hydrogen fluid. These microdiamonds preserve evidence of the pathway by which carbon and water can be subducted to mantle depths and returned back to the earth's surface.
'Extreme' genes shed light on origins of photosynthesis
While most school children understand that green plants photosynthesize, absorb carbon dioxide and produce oxygen, few people consider the profound global-scale effects that photosynthesis has had on Earth. One of those ...
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