Globular clusters as microlensing targets     

Geza Gyuk  & Gilbert P. Holder 《Monthly notices of the Royal Astronomical Society》1998,297(2):L44-L48

We investigate the possibility of using globular clusters as targets for microlensing searches. Such searches will be challenging and require more powerful telescopes than now employed, but are feasible in the near future. Although expected event rates are low, we show that the wide variety of lines of sight to globular clusters greatly enhances the ability to distinguish between halo models using microlensing observations as compared with LMC/SMC observations alone. In particular, the halo core radius and power-law exponent can be determined with good accuracy.  相似文献   

Origin of Archean lamprophyre dykes,Superior Province,Canada: rare earth element and Nd−Sr isotopic evidence   总被引：1，自引：0，他引：1  

Richard A. Stern  Gilbert N. Hanson 《Contributions to Mineralogy and Petrology》1992,111(4):515-526

Hornblende- and clinopyroxene-phyric lamprophyre dykes exposed in the Roaring River Complex, Superior Province are alkaline, nepheline-normative, basaltic compositions (>50 wt% SiO₂), that range from primitive to fractionated [Mg/(Mg + total Fe)=0.66–0.40; Ni=200–35 ppm], and which have high abundances of light rare earth elements (REE) [(Ce/Yb)_n=16–26, Ce_n=60–300; n = chondrite normalized], Sr (870–1,800 ppm), P₂O₅ (0.4–1.3 wt%), and Ba (150–900 ppm). Crystal fractionation of the lamprophyres produced coeval gabbro and clinopyroxenite cumulate bodies. A whole-rock Sm–Nd isochron for lamprophyres and gabbro-pyroxenite yields a crystallization age of 2,667±51 Ma Ma (I=0.50929±0.0004; _Nd = + 2.3 0.7). Whole-rock Sr isotope data are scattered, but suggest an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7012, similar to bulk Earth. The elevated levels of light REEs and Sr in the lamprophyres were not due to crustal contamination or mixing with contemporaneous monzodioritic magmas, but a result of partial melting of a mantle source which was enriched in these and other large-ion-lithophile elements (LILEs) shortly before melting. The lamprophyres were contemporaneous with mantle-derived, high-Mg, LILE-enriched monzodiorite to granodiorite of the Archean sanukitoid suite. Both suites have concave-downward light REE profiles, suggesting that depleted mantle was common to their source regions, but the higher light REE abundances, higher Ba/La ratios, and lower _Nd values (+1.3±0.3) of the parental monzodiorites suggest a more enriched source. The lamprophyres and high-Mg monzodiorites were derived from a mineralogically and compositionally heterogeneous, LILE-enriched mantle lithosphere that may have been part of a mantle wedge above a subducting plate in an arc environment.  相似文献   

Evolution des hydrocarbures,des peuplements bacteriens et microphytiques dans les sediments des marais maritimes de l'iie grande pollues par l'amoco cadiz: 1, evolution des hydrocarbures et des bacteries     

Gilbert Mille  Yan Yu Chen  Gérard Giusti  Henri Dou  Evelyne Vacelet  Marie-Reine Plante-Cuny 《Marine environmental research》1984,11(3):213-232

The evolution of hydrocarbons in sediments was studied from 1978 to 1980 at eight stations in the Ile Grande marshes (Brittany) polluted by the Amoco Cadiz oil spill. Generally, in 1980 (except for one heavily polluted site) the amounts of hydrocarbons were found to be far less important than in 1978 and sometimes biogenic hydrocarbons were found. In the superficial layer of the sediments biodegradation processes were generally important with the preferential degradation of n-alkanes. On the other hand, aromatic hydrocarbons seem not to have been altered after three years. Degradation of percolated hydrocarbons proceeds more slowly than in the surface layer. The number of degrading bacteria decreases when n-alkanes disappear.  相似文献   

Comparative toxicity of drilling muds: role of chromium and petroleum hydrocarbons     

P.J. Conklin  D. Drysdale  D.G. Doughtie  K.R. Rao  J.P. Kakareka  T.R. Gilbert  R.F. Shokes 《Marine environmental research》1983,10(2):105-125

Samples of used drilling muds collected during the course of a single well drilling operation exhibited different degrees of acute toxicity to sheepshead minnows and grass shrimp. For moulting grass shrimp, Palaemonetes pugio, the 96-h LC₅₀'s were 360 to 14 560 ppm (μl/litre); many of these values were considerably lower than those reported from previous drilling mud assays. However, when some of the muds used in this study were tested on sheepshead minnows, Cyprinodon variegatus, the resulting 96-h LC₅₀'s (6300 to 100 000ppm) were well within the range of previously reported values.Although a number of the drilling mud samples had relatively high amounts of chromium due to the addition of sodium chromate, there was a low correlation between chromium concentration and toxicity. In only three drilling muds could chromium content alone account for the observed toxicities. Furthermore, chemical analyses revealed the presence of No. 2 fuel oil like petroleum hydrocarbons in the mud samples. Based on the results of toxicity tests with No. 2 fuel oil and the concentrations of oil present in the muds, the toxicity of the mud samples to grass shrimp appears to be largely attributable to the petroleum hydrocarbon content.  相似文献   

Excursion to Bedmond,Bennett's end and Boxmoor: Saturday,September 16th, 1922     

C.J. Gilbert 《Proceedings of the Geologists' Association. Geologists' Association》1923,34(3):242-IN6

  相似文献   

The relationship of slaty cleavage and kindred structures to tectonics     

Gilbert Wilson 《Proceedings of the Geologists' Association. Geologists' Association》1946,57(4):263-IN7

  相似文献   

Ice-melt collapse pits and associated features in the 1991 lahar deposits of Volcán Hudson,Chile: criteria to distinguish eruption-induced glacier melt     

M. J. Branney  J. S. Gilbert 《Bulletin of Volcanology》1995,57(5):293-302

In subaerial volcaniclastic sequences structures formed by ice blocks can provide information about a volcano's history of lahar generation by glacier melt. At Volcán Hudson in Chile, catastrophic lahars were initiated by eruption-induced melting of glacier ice in August and October 1991. They transported large ice blocks 50 km down the Rio de los Huemules valley to the sea. Large current crescents with lee-side lenses were formed where ice blocks were deposited during waning stages of the flood. When stranded blocks of ice melted, they left cone-shaped and ring-shaped heaps of ice-rafted debris on the sediment surface. Several hundred ice blocks were completely buried within the aggrading lahar sediment, and when these melted circular collapse pits formed in the sediment. Collapse types included subsided coherent blocks of sediment bounded by an outward-dipping ring-fracture, trapdoor structures with horseshoe-shaped fractures, downsag pits with centroclinal dips locally up to 60°, pits with peripheral graben and crevasses, piecemeal (highly fragmented) collapse structures and funnel-shaped pits containing disaggregated sediment. A sequence of progressive collapse is inferred in which initial downsag and subsidence on an outward-dipping ring fracture produces a small diameter pit. This is followed by widening of the pit by progressive development of concentric ring fractures and downsag outside the early formed pit, and by collapse of overhanging pit walls to produce vertical to inward-dipping walls and aprons of collapse debris on the pit floor. The various structures have potential for preservation even in regions prone to high rainfall and flooding, and they can be used to indicate that former lahars contained abundant blocks of ice.  相似文献   

A revised stratigraphic framework for later Cenozoic sequences in the northeastern Mediterranean region     

Cengiz Yetiş  Gilbert Kelling  Prof. Dr. Sungu L. Gökçen  Francois Baroz 《International Journal of Earth Sciences》1995,84(4):794-812

This study describes the lithostratigraphic character of mid-Cenozoic (Oligocene-Pliocene) sequences in different parts of the northeastern Mediterranean area and offers a detailed stratigraphic correlation for this region. The sequences concerned are drawn from the Camardi area (south-central Anatolia), the Adana Basin, the Misis Mountains and the Kyrenia Range (northern Cyprus) and the submerged Florence Rise (west of Cyprus). The stratigraphic relationships identified here indicate the following: (a) Following the middle Eocene (Lutetian) regression there was uplift throughout the entire region; (b) Episodes of fluvial and lacustrine deposition in intramontane settings ensued in most of this region during the late Eocene/early Miocene interval; (c) Following a regionally extensive phase of tectonic compression, major marine transgression commenced in the late Oligocene in northern Cyprus and in the early Miocene in adjacent southern Turkey, with the exception of the Ecemi§ Fault Zone where continental deposition continued; (d) These Oligo-Miocene transgressive sequences comprise a broadly diachronous complex of both shallow and deeper marine facies, including reefal carbonates, littoral clastics, basinal shales and fan-turbidites; (e) Deeper marine Miocene facies persisted longer in the Misis area and in northern Cyprus; (f) A regional regression occurred throughout most of the area during the late Serravallian to Tortonian interval and is marked by the abrupt, locally discordant appearance of extensive shallow marine, deltaic and fluvial deposits; (g) Continued regression in the Messinian led to the formation of significant evaporite deposits in the western and southern parts of the region, but localized uplift of the Misis area is attested by the initial deformation of the Neogene rocks there and the absence of Messinian sediments from this area; (h) In the Pliocene there was extensive emergence of the northern parts of the region interrupted by brief marine incursions. The present-day drainage pattern was established at this time; (i) Marine conditions persisted longer in northern Cyprus, where emergence occurred only in the latest Pliocene.  相似文献   

Amorce de la Sédimentation Synorogénique dans les PyrénéesVarisques. Données Chronologiques; Implications Paléogéographiques     

Professeur Dr. Raymond Mirouse  Gilbert Barrouquère  Gilbert Bessière  Jean-Jacques Delvolvé  Marie-France Perret 《International Journal of Earth Sciences》1983,72(1):253-281

Conodont associations and recent macrofaunal discoveries, allow us to date the beginning of detrital deposits going with the Variscan uplift in the Pyrenean marine basins during the Lower Carboniferous. Thus, the establishing of synorogenic conditions seems to have progressed from the East to the West; there appears the picture of a kind of north-Pyrenean axis already individualized in the wide Cantabrico-Pyrenean foreland.  相似文献   

Mantle heterogeneity and crustal recycling in Archean granite-greenstone belts: Evidence from Nd isotopes and trace elements in the Rainy Lake area, Superior Province, Ontario, Canada   总被引：2，自引：0，他引：2  

Steven B. Shirey  Gilbert N. Hanson 《Geochimica et cosmochimica acta》1986,50(12):2631-2651

The 2685–2752 Ma old granite-greenstone crust in the Rainy Lake area, Ontario, consists of metaigneous and metasedimentary rocks that range in composition from tholeiite to monzogranite and include anorthosite, trachyandesite, monzodiorite and high-silica rhyodacite. Major element, rare earth and other trace element data are the basis for modelling the formation of the crust by melting of large-ionlithophile element enriched and unenriched mantle, by melting of basalt at mantle to crustal levels and by melting of monzodiorite and tonalite at crustal levels.

All metaigneous rocks lie on a ¹⁴³Nd/¹⁴⁴Nd vs. ¹⁴⁷Sm/¹⁴⁴Nd isochron with an age of 2737 ±42 Ma and an initial ¹⁴³Nd/¹⁴⁴Nd of 0.509178 ±33 (ε_Nd = +1.9). This age is consistent with U-Pb zircon ages, which suggests the Nd isotopic system has been unaffected since the crust-forming events. The positive initial ε_Nd's are further evidence for time-averaged depletion in Sm/Nd relative to CHUR for the Archean mantle. The similarity of the initial Nd isotopic composition for both mantle-derived and crustally-derived rocks suggests rapid recycling of crustal components, which were previously derived from depleted mantle sources.

Initial ¹⁴³Nd/¹⁴⁴Nd ratios on individual rocks range from ε_Nd = +3.3 to ε_Nd = −0.4. Younger granitoids have lower ε_Nd values (+1.5 to −0.1) relative to tholeiites and monzodiorites crystallized from mantle-derived melts (+3.3 to +1.0). Thus, incorporation of slightly older crust (ca. 100–200 Ma) in some of the granitoid source areas is possible. Mantle-derived rocks form an isochron of 2764 ±58 Ma that represents a minimum age for enrichment processes in the mantle sources for the Rainy Lake area. Consideration of data from the Abitibi belt suggests such enrichment processes in the mantle may have preceded crust-forming events in a wide area of the Superior Province, perhaps by as much as 50–70 Ma.  相似文献