排序方式： 共有35条查询结果，搜索用时 125 毫秒
1.
STEPHAN BORRMANN REAS THOMAS VLADIMIR RUDAKOV VLADIMIR YUSHKOV BORIS LEPUCHOV TERRY DESHLER NIKOLAI VINNICHENKO VYACHESLAV KHATTATOV LEOPOLDO STEFANUTTI 《Tellus. Series B, Chemical and physical meteorology》2000,52(4):1088-1103
In‐situ aerosol measurements were performed in the northern hemispheric stratosphere up to altitudes of 21 km between 13 November 1996 and 14 January 1997, inside and outside of the polar vortex during the Airborne Polar Experiment (APE) field campaign. These are measurements of particle size distributions with a laser optical particle counter of the FSSP‐300 type operated during 9 flights on the Russian M‐55 high‐altitude research aircraft Geophysika. For specific flights, the FSSP‐300 measurements are compared with balloon‐borne data (launched from Kiruna, Sweden). It was found that the stratospheric aerosol content reached levels well below the background concentrations measured by the NASA operated ER‐2 in 1988/89 in the northern hemisphere. During the APE campaign, no PSC particle formation was observed at flight altitudes although the temperatures were below the NAT condensation point during one flight. The measured correlations between ozone and aerosol give an indication of the subsidence inside the 1996/97 polar vortex. Despite the lower aerosol content in the winter 1996/97 compared to the 1989 background, the heterogeneous reactivity of the aerosol (as calculated from the measured data with additional model input) is comparable. This is due to the dependency of the reactive uptake coefficients on the atmospheric water vapor content. Under the described assumptions the reaction rates on the background aerosol are significantly smaller than for competing gas phase chlorine activation, as can be expected for stratospheric background conditions especially inside the polar vortex. 相似文献
2.
HEAMAN LARRY M.; CREASER ROBERT A.; COOKENBOO HARRISON O.; CHACKO TOM 《Journal of Petrology》2006,47(4):821-858
The Jericho kimberlites are part of a small Jurassic kimberlitecluster in the northern Slave craton, Canada. A variety of datingtechniques were applied to constrain the nature and age of twoJericho kimberlites, JD-1 (170·2 ± 4·3Ma Rb–Sr phlogopite megacrysts, 172·8 ±0·7 Ma U–Pb eclogite rutile, 178 ± 5 MaU–Pb eclogite zircon lower intercept) and JD-3 (173 ±2 Ma Rb–Sr phlogopite megacryst; 176·6 ±3·2 Ma U–Pb perovskite), and all yielded identicalresults within analytical uncertainty. As there is no discernibledifference in the radiometric ages obtained for these two pipes,the composite Rb–Sr phlogopite megacryst date of 173·1± 1·3 Ma is interpreted as the best estimate forthe emplacement age of both Jericho pipes. The initial Sr isotopecomposition of 0·7053 ± 0·0003 derivedfrom phlogopite megacrysts overlaps the range (0·7043–0·7084)previously reported for Jericho whole-rocks. These strontiumisotope data, combined with the radiogenic initial 206Pb/204Pbratio of 18·99 ± 0·33 obtained in thisstudy, indicate that the Jericho kimberlites are isotopicallysimilar to Group 1 kimberlites as defined in southern Africa.The Jericho kimberlites are an important new source of mantlexenoliths that hold clues to the nature of the Slave cratonsubcontinental mantle. A high proportion (30%) of the Jerichomantle xenolith population consists of various eclogite typesincluding a small number (2–3%) of apatite-, diamond-,kyanite- and zircon-bearing eclogites. The most striking aspectof the Jericho zircon-bearing eclogite xenoliths is their peculiargeochemistry. Reconstructed whole-rock compositions indicatethat they were derived from protoliths with high FeO, Al2O3and Na2O contents, reflected in the high-FeO (22·6–27·5wt %) nature of garnet and the high-Na2O (8·47–9·44wt %) and high-Al2O3 (13·12–14·33 wt %)character of the clinopyroxene. These eclogite whole-rock compositionsare highly enriched in high field strength elements (HFSE) suchas Nb (133–1134 ppm), Ta (5–28 ppm), Zr (1779–4934ppm) and Hf (23–64 ppm). This HFSE enrichment is linkedto growth of large (up to 2 mm) zircon and niobian rutile crystals(up to 3 modal %) near the time of eclogite metamorphism. Thediamond-bearing eclogites on the other hand are characterizedby high-MgO (19·6–21·3 wt %) garnet andultralow-Na2O (0·44–1·50 wt %) clinopyroxene.Paleotemperature estimates indicate that both the zircon- anddiamond-bearing eclogites have similar equilibration temperaturesof 950–1020°C and 990–1030°C, respectively,corresponding to mantle depths of 150–180 km. Integrationof petrographic, whole-rock and mineral geochemistry, geochronologyand isotope tracer techniques indicates that the Jericho zircon-bearingeclogite xenoliths have had a complex history involving Paleoproterozoicmetamorphism, thermal perturbations, and two or more episodesof Precambrian mantle metasomatism. The oldest metasomatic event(Type 1) occurred near the time of Paleoproterozoic metamorphism(1·8 Ga) and is responsible for the extreme HFSE enrichmentand growth of zircon and high-niobian rutile. A second thermalperturbation and concomitant carbonatite metasomatism (Type2) is responsible for significant apatite growth in some xenolithsand profound light rare earth element enrichment. Type 2 metasomatismoccurred in the period 1·0–1·3 Ga and isrecorded by relatively consistent whole-rock eclogite modelNd ages and secondary U–Pb zircon upper intercept dates.These eclogite xenoliths were derived from a variety of protoliths,some of which could represent metasomatized pieces of oceaniccrust, possibly linked to east-dipping subduction beneath theSlave craton during construction of the 1·88–1·84Ga Great Bear continental arc. Others, including the diamond-bearingeclogites, could be cumulates from mafic or ultramafic sillcomplexes that intruded the Slave lithospheric mantle at depthsof about 150–180 km. KEY WORDS: zircon- and diamond-bearing eclogites; Jericho kimberlite, geochronology; Precambrian metasomatism, northern Slave Craton 相似文献
3.
Depositional slope systems along continental margins contain a record of sediment transfer from shallow‐water to deep‐water environments and represent an important area for natural resource exploration. However, well‐preserved outcrops of large‐scale depositional slopes with seismic‐scale exposures and tectonically intact stratigraphy are uncommon. Outcrop characterization of smaller‐scale depositional slope systems (i.e. < 700 m of undecompacted shelf‐to‐basin relief) has led to increased understanding of stratigraphic packaging of prograding slopes. Detailed stacking patterns of facies and sedimentary body architecture for larger‐scale slope systems, however, remain understudied. The Cretaceous Tres Pasos Formation of the Magallanes Basin, southern Chile, presents a unique opportunity to evaluate the stratigraphic evolution of such a slope system from an outcrop perspective. Inherited tectonic relief from a precursor oceanic basin phase created shelf‐to‐basin bathymetry comparable with continental margin systems (～1000 m). Sedimentological and architectural data from the Tres Pasos Formation at Cerro Divisadero reveal a record of continental margin‐scale depositional slope progradation and aggradation. Slope progradation is manifested as a vertical pattern exhibiting increasing amounts of sediment bypass upwards, which is interpreted as reflecting increasing gradient conditions. The well‐exposed, seismic‐scale outcrop is characterized by four 20 to 70 m thick sandstone‐rich successions, separated by mudstone‐rich intervals of comparable thickness (40 to 90 m). Sedimentary body geometry, facies distribution, internal bedding architecture, sandstone richness and degree of amalgamation were analysed in detail across a continuous 2·5 km long transect parallel to depositional dip. Deposition in the lower section (Units 1 and 2) was dominated by poorly channellized to unconfined sand‐laden flows and accumulation of mud‐rich mass transport deposits, which is interpreted as representing a base of slope to lower slope setting. Evidence for channellization and indicators of bypass of coarse‐grained turbidity currents are more common in the upper part of the > 600 m thick succession (Units 3 and 4), which is interpreted as reflecting increased gradient conditions as the system accreted basinward. 相似文献
4.
5.
6.
郯庐断裂带形成演化的年代学研究 总被引：11，自引：0，他引：11
通过对郯庐断裂带东侧张八岭蓝片岩带内白云母4 0 Ar - 3 9Ar年龄、断裂带内片麻状花岗岩中钾长石4 0 Ar- 3 9Ar年龄以及断裂带内断层泥K -Ar、ESR年龄的测定 ,并结合有关的地质和古地磁资料 ,厘定了郯庐断裂带形成和演化的过程 :(1)三叠纪 (2 44～ 2 0 9Ma)由于华北与扬子地块碰撞 ,郯庐断裂带形成为其主要左行平移时期 ;(2 )侏罗纪 (189～ 16 4Ma)时郯庐断裂东侧下扬子地块可能经历了逆时针转动 ;(3)白垩纪 (10 3～ 94Ma)开始郯庐断裂带伴随走滑平移而发生正断活动 ;(4)晚白垩—第三纪右旋平移阶段。郯庐断裂的形成与大别 -苏鲁变质带有关。 相似文献
7.
Coarse‐grained deep‐water strata of the Cerro Toro Formation in the Cordillera Manuel Señoret, southern Chile, represent the deposits of a major channel belt (4 to 8 km wide by >100 km long) that occupied the foredeep of the Magallanes basin during the Late Cretaceous. Channel belt deposits comprise a ca 400 m thick conglomeratic interval (informally named the ‘Lago Sofia Member’) encased in bathyal fine‐grained units. Facies of the Lago Sofia Member include sandy matrix conglomerate (that show evidence of traction‐dominated deposition and sedimentation from turbulent gravity flows), muddy matrix conglomerate (graded units interpreted as coarse‐grained slurry‐flow deposits) and massive sandstone beds (high‐density turbidity current deposits). Interbedded sandstone and mudstone intervals are present locally, interpreted as inner levée deposits. The channel belt was characterized by a low sinuousity planform architecture, as inferred from outcrop mapping and extensive palaeocurrent measurements. Laterally adjacent to the Lago Sofia Member are interbedded mudstone and sandstone facies derived from gravity flows that spilled over the channel belt margin. A levée interpretation for these fine‐grained units is based on several observations, which include: (i) palaeocurrent measurements that indicate flows diverged (50° to 100°) once they spilled over the confining channel margin; (ii) sandstone beds progressively thin, away from the channel belt margin; (iii) evidence that the eroded channel base was not very well indurated, including a stepped margin and injection of coarse‐grained channel material into surrounding fine‐grained units; and (iv) the presence of sedimentary features common to levées, including slumped units inferring depositional slopes dipping away from the channel margin, lenticular sandstone beds thinning distally from the channel margin, soft sediment deformation and climbing ripples. The tectonic setting and foredeep architecture influenced deposition in the axial channel belt. A significant downstream constriction of the channel belt is reflected by a transition from more tabular units to an internal architecture dominated by lenticular beds associated with a substantially increased degree of scour. Differential propagation of the fold‐thrust belt from the west is speculated to have had a major control on basin, and subsequently channel, width. The confining influence of the basin slopes that paralleled the channel belt, as well as the likelihood that numerous conduits fed into the basin along the length of the active fold‐thrust belt to the west, suggest that proximal–distal relationships observed from large channels in passive margin settings are not necessarily applicable to axial channels in elongate basins. 相似文献
8.
Early Proterozoic cordierite-garnet–orthopyroxene–K–feldsparmetasedimentary gneisses are developed in the flat—lyingcomplex (FLC) of the southern part of the Ketilidian mobilebelt (1?8–1?7GA), Greenland. These granulites containlow—pressure assemblages and are developed in both regionalmetamorphic rocks and in some thermal aureoles of contemporaneousrapakivi granite plutons. Thermobarometry shows that both theregional and contact metamorphism took place at 2–4 kband 650–800?C. The granulites were developed in an extensionaltectonic regime, and appartently record the culmination of asingle thermotectonic event. There is a close temporal associationbetween the peak of high—grade metamorphism and the emplacementof synorogenic rapakivi granites, and melts from the metasedimentarypile probably contributed largely to the granites. The low pressuresand high temperatures for regional metamorphism require geothermalgradients in excess of 60?C/km, and are consistent with thepresence of regional extensional tectonics, synorogenic magmatism,and underplating of mafic magma in this area during the Ketilidian.
*Offprint requests to T. J. Dempster. Present address: Department of Geology and Applied Geology, University of Glasgow, Glasgow G12 8QQ, UK 相似文献
9.
STEPHAN GRUBER MARKUS EGLI ISABELLE GÄRTNER‐ROER MARTIN HOELZLE 《Geografiska Annaler: Series A, Physical Geography》2012,94(2):177-182
Gruber, S., Egli, M., Gärtner‐Roer, I. and Hoelzle, M., 2012. Preface: The mountain cryosphere – a holistic view on processes and their interactions. Geografiska Annaler: Series A, Physical Geography, ??, ??–??. doi :10.1111/j.1468‐0459.2012.00468.x 相似文献
10.
STEPHAN HARRISON E. ANDERSON D. PATEL 《Geografiska Annaler: Series A, Physical Geography》2006,88(3):199-207
ABSTRACT. Geomorphological and sedimentological evidence of former glaciation in the Bizzle valley in the Cheviot Hills of northern England and southern Scotland was used to reconstruct the dimensions of a small topographically constrained glacier with an equilibrium line altitude (ELA) of 535 m. This was interpreted as having formed during Younger Dryas cooling; this is the only glacier to have been described from the area and is the most easterly site of Younger Dryas glaciation in the British Isles. Whilst glaciation at this time was extensive in the Lake District to the southwest, the restricted nature of Cheviot ice cover suggests that a steep west–east precipitation gradient existed in this region during the Younger Dryas. 相似文献