High iridium concentration of alkaline rocks of Deccan and implications to K/T boundary     

P. N. Shukla  N. Bhandari  Anirban Das  A. D. Shukla  J. S. Ray 《Journal of Earth System Science》2001,110(2):103-110

We report here an unusually high concentration of iridium in some alkali basalts and alkaline rocks of Deccan region having an age of about 65Ma, similar to the age of the Cretaceous-Tertiary boundary. The alkali basalts of Anjar, in the western periphery of Deccan province, have iridium concentration as high as 178pg/g whereas the alkaline rocks and basalts associated with the Amba Dongar carbonatite complex have concentrations ranging between 8 and 80 pg/g. Some of these values are more than an order of magnitude higher than the concentration in the tholeiitic basalts of Deccan, indicating the significance of alkaline magmatism in the iridium inventory at the Cretaceous-Tertiary boundary. Despite higher concentration, their contribution to the global inventory of iridium in the Cretaceous-Tertiary boundary clays remains small. The concentration of iridium in fluorites from Amba Dongar was found to be <30 pg/g indicating that iridium is not incorporated during their formation in hydrothermal activity.  相似文献   

Comparability of Large-Scale Studies of Agricultural Chemical Contamination of Rural Private Wells   总被引：1，自引：0，他引：1  

Chittaranjan Ray  Susan C. Schock 《Ground Water Monitoring & Remediation》1996,16(2):92-102

Detection of agricultural chemicals in ground water has prompted numerous studies. Federal, state, and regional studies were conducted in the last 10 years in order to assess the occurrence of agricultural chemicals in ground water. The results of the studies present the number or percentage of samples with agricultural chemicals above the drinking water standard or health advisory levels as well as samples with detections of one or more compounds. Data comparison from one state or region to another are frequently referred to by regulatory and agency personnel involved in water quality and agriculture issues. Unless the history of pesticide use, method of chemical analyses, detection limits, statistical design of the sampling plan, well type, well depth, geology of the formation material, and typical land use around the wellhead are known, such comparisons can be misleading. Reporting the limitations or presenting a disclaimer should be a key element for a study so that "apples and oranges" are not compared.  相似文献   

Metamorphic history of the Jutogh Series in the Simla klippe,lower Himalayas     

K. Naha  S. K. Ray 《Contributions to Mineralogy and Petrology》1970,28(2):147-164

The metamorphic rocks of the Jutogh Series around Simla, structurally overlying the less metamorphosed rock groups along a thrust contact, have been involved in three phases of deformation and two episodes of metamorphism. The first metamorphism is in the albite-epidote-amphibolite facies in a major part of the area, reaching the amphibolite facies locally in the central part. This metamorphism is late-to post-kinematic with reference to the F ₁ movement, the thermal peak having been reached in a post-F ₁ pre-F ₂ static phase. The second metamorphism, syn-to post-tectonic with respect to F ₂ but preceding F ₃, is generally in the greenschist facies, and only locally in the albite-epidote-amphibolite facies in the higher structural levels. Metamorphic overprinting has caused widespread retrogression and disequilibrium assemblages. As the large scale recumbent folding and thrusting of F ₁ and F ₂ phases belong to the Tertiary Himalayan orogeny, the metamorphism in the Jutogh Series could not have been Precambrian in age.  相似文献   

Mineralogy,petrology, and chemistry of a Luna 16 basaltic fragment,sample B-1     

A.L. AlbeeA.A. Chodos  A.J. GancarzE.L. Haines  D.A. PapanastassiouL. Ray  F. TeraG.J. Wasserburg  T. Wen 《Earth and Planetary Science Letters》1972

Luna 16 sample B-1 was the largest fragment (62 mg) obtained in the sample exchange with the USSR. Petrologic, mineralogic, and chemical investigations have been made on this fragment in conjunction with Rb-Sr and⁴⁰Ar/³⁹Ar investigations by our colleagues. Sample B-1 is a fine-grained ophitic basalt but is distinguished from the Apollo samples by containing a single pyroxene, predominantly pigeonitic, an ilmenite content (7%) intermediate to that of the Apollo 11 and 12 samples, and subequal amounts of pyroxene (50%) and plagioclase (40%). Chemically it is distinguished by a high Sr content (437 ppm) and a high K/U value (4700). The K-content (1396 ppm) is higher than that of Luna 16 soil sample A-2.  相似文献   

Mapping of fault rupture of the 28 may 2004 iran earthquake (mw= 6.2) using satellite image     

M. Sharifikia  C. S. Dubey  B. K. Sharma  M. Chaudhry  P. K. Champati Ray 《Journal of the Indian Society of Remote Sensing》2006,34(4):423-430

  相似文献   

Distribution and significance of crystalline, perlitic and vesicular textures in the Ordovician Garth Tuff (Wales)   总被引：2，自引：0，他引：2  

A. N. McArthur  R. A. F. Cas  G. J. Orton 《Bulletin of Volcanology》1998,60(4):260-285

 Diverse spherulitic and granular crystalline fabrics, perlitic textures and fabrics related to the growth and migration of vesicles occur in the Garth Tuff, a largely welded Ordovician ignimbrite. Defining the distribution of such textures helps to constrain the ignimbrite's cooling and degassing history. Suites of spherulitic and perlitic textures closely reflect variation in cooling rates. Seven facies are defined based on the style and intensity of crystallisation: (1) a medium to coarsely crystalline, equigranular facies; (2) an intensely spherulitic facies; (3) a sparsely spherulitic facies; (4) a pectinate facies; (5) a microcrystalline to cryptocrystalline, equigranular facies; (6) a lithophysal facies; and (7) a transitional perlite–pectinate facies. Textural changes from facies 1 to 5 reflect progressively higher cooling rates. Facies 1 occurs in proximal settings in the ignimbrite's core. Facies 2 to 5 successively envelop facies 1, with facies 2 becoming the dominant fabric in the ignimbrite's core in medial settings. Facies 5 is typically developed in the originally glassy perlitic zones at the ignimbrite's welded margins. Crystallisation under hydrous conditions is reflected by second-boiling textures in the sporadically developed lithophysal facies. The seventh facies reflects a subtle interplay between cooling, hydration and crystallisation which locally prevented perlitic fracturing. The distribution of amygdales reflects patterns of volatile migration and entrapment. In the lower levels of the ignimbrite, amygdales occur in irregular concentrations or rare subvertical pipe-like structures. Pipe-like structures attest to fumarolic activity while the ignimbrite was in a rheomorphic state. Amygdales are widespread and evenly distributed in the upper levels of the ignimbrite. However, the top of the welding profile is characterised by a thin, poorly vesiculated, originally vitrophyric horizon that abruptly caps an intense concentration of amygdales. Ductile and brittle fabrics developed during the upward migration of gas. Microscopic drag folds occur around some amygdales. Jigsaw-fit to clast-rotated breccias originated through both late-stage pneumatic fracturing and autobrecciation. Vaporisation of water at the flow base provided a significant source of volatiles in addition to gas released during cooling and crystallisation. Secondary alteration has enhanced or modified some fabrics. Perlitic zones were susceptible to patchy chlorite–sericite–carbonate diagenetic alteration. Diagenesis and metamorphism have contributed to the infilling of vesicles. Received: 22 August 1997 / Accepted: 24 June 1998  相似文献   

Rhyolitic fallout and pyroclastic density current deposits from a phreatoplinian eruption in the eastern Aegean Sea, Greece     

S.R Allen  R.A.F Cas   《Journal of Volcanology and Geothermal Research》1998,86(1-4)

The Kos Plateau Tuff consists of pyroclastic deposits from a major Quaternary explosive rhyolitic eruption, centred about 10 km south of the island of Kos in the eastern Aegean, Greece. Five main units are present, the first two (units A and B) were the product of a phreatoplinian eruption. The eruption style then changed to `dry' explosive style as the eruption intensity increased forming a sequence of ignimbrites and initiating caldera collapse. The final waning phase returned to phreatomagmatic eruptive conditions (unit F). The phreatomagmatic units are fine grained, poorly sorted, and dominated by blocky vitric ash, thickly ash-coated lapilli and accretionary lapilli. They are non-welded and were probably deposited at temperatures below 100°C. All existing exposures occur at distances between 10 km and 40 km from the inferred source. Unit A is a widespread (>42 km from source), thin (upwind on Kos) to very thick (downwind), internally laminated, dominantly ash bed with mantling, sheet-like form. Upwind unit A and the lower and middle part of downwind unit A are ash-rich (ash-rich facies) whereas the upper part of downwind unit A includes thin beds of well sorted fine pumice lapilli (pumice-rich facies). Unit A is interpreted to be a phreatoplinian fall deposit. Although locally the bedforms were influenced by wind, surface water and topography. The nature and position of the pumice-rich facies suggests that the eruption style alternated between `wet' phreatoplinian and `dry' plinian during the final stages of unit A deposition.Unit B is exposed 10–19 km north of the inferred source on Kos, overlying unit A. It is a thick to very thick, internally stratified bed, dominated by ash-coated, medium and fine pumice lapilli in an ash matrix. Unit B shows a decrease in thickness and grain size and variations in bedforms downcurrent that allow definition of several different facies and laterally equivalent facies associations. Unit B ranges from being very thick, coarse and massive or wavy bedded in the closest outcrops to source, to being partly massive and partly diffusely stratified or cross-bedded in medial locations. Pinch and swell, clast-supported pumice layers are also present in medial locations. In the most distal sections, unit B is stratified or massive, and thinner and finer grained than elsewhere and dominated by thickly armoured lapilli. Unit B is interpreted to have been deposited from an unsteady, density stratified, pyroclastic density current which decelerated and progressively decreased its particle load with distance from source. Condensation of steam during outflow of the current promoted the early deposition of ash and resulted in the coarser pyroclasts being thickly ash-coated. The distribution, texture and stratigraphic position of unit B suggest that the pyroclastic density current was generated from collapse of the phreatoplinian column following a period of fluctuating discharge when the eruptive activity alternated between `wet' and `dry'. The pyroclastic density current was transitional in particle concentration between a dilute pyroclastic surge and a high particle concentration pyroclastic flow. Unidirectional bedforms in unit B suggest that the depositional boundary was commonly turbulent and in this respect did not resemble conventional pyroclastic flows. However, unit B is relatively thick and poorly sorted, and was deposited more than 19 km from source, implying that the current comprised a relatively high particle concentration and in this respect, did not resemble a typical pyroclastic surge.  相似文献   

The Apoteri volcanic formation — tholeiitic flows in the North Savannas Graben of Guyana and Brazil     

Jevan P. Berrangé  Ray Dearnley 《International Journal of Earth Sciences》1975,64(1):883-899

Amygdaloidal tholeiitic flows, locally pillowed, have been mapped at intervals over a distance of 280 km along the margins of the North Savannas Rift Valley in southern Guyana and Brazil. The combined chemical and petrological evidence suggests that the formation represents an originally uniform continental tholeiitic sequence that has undergone variable secondary alteration involving increasing oxidation and ingress of soda, potash and water. The lavas are both spatially and temporally related to the rift faulting; field observations and K∶Ar age determinations on eleven samples from different localities indicate that the flows were erupted during the Early to Middle Jurassic (180-150 m. y.). It is shown that this tectono-magmatic event is synchronous with the initiation of the southern North Atlantic rift and the pan-Antarctic rift which resulted in fragmentation of the continents according to the scheme ofDietz &Holden (1970).  相似文献   

Coupled surface and ground water models for investigating hydrological processes     

Ray‐Shyan Wu  Dong‐Sin Shih  Ming‐Hsu Li  Chia‐Ching Niu 《水文研究》2008,22(8):1216-1229

  相似文献   

Comments on the size of the simulation box in cosmological N-body simulations     

J. S. Bagla  Suryadeep Ray 《Monthly notices of the Royal Astronomical Society》2005,358(3):1076-1082

  相似文献