Development of volcanic belts together with zones of deficient gravity along the margin of shifted crustal masses     

Ting Ying H. Ma D. SC.  Chia-Lin Pan 《Bulletin of Volcanology》1959,21(1):103-107

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Physical and numerical modeling of reflections from interfaces and thin layers     

Fisher  D. Gardner  G. 《Oceanic Engineering, IEEE Journal of》1984,9(1):3-11

Basic models for understanding the reflection of seismic waves by the seafloor or the sublayering consist of isolated interfaces and isolated thin layers. An isolated interface model is used to demonstrate a reasonable agreement between physical modeling and two numerical solutions of the elastic wave equation. An isolated thin-layer model is used to show that reflections from it can be regarded as a scattered wavefield caused by three secondary sources proportional toDeltaM,-Deltamu, and,Deltarhoat each element of the layer, whereDelta, indicates the difference between the layer and the surroundings,Mis the compressional wave modulus,muis the shear wave modulus, andrhois the density. This viewpoint leads to a simple explanation of the observed variations in amplitude and phase of the reflected waves as the offset distance from source to receiver increases.  相似文献   

GIS-based hazard mapping and zonation of debris flows in Xiaojiang Basin,southwestern China   总被引：11，自引：0，他引：11  

Y.?P.?HeEmail author  H.?Xie  P.?Cui  F.?Q.?Wei  D.?L.?Zhong  J.?S.?Gardner 《Environmental Geology》2003,45(2):286-293

Debris flow sites were identified at 140 locations in the Xiaojiang Basin in Yunnan province, southwestern China. Their spatial distribution and catchment characteristics are described in detail on the basis of previous research, air photo interpretation, field investigation and mapping using Geographical Information Systems (GIS). Using a statistical approach, a quantitative model of hazards assessment and zonation was developed through synthesis analysis of basin areas, gradients, and the relative reliefs of these debris flow sites. In terms of debris flow hazard assessment, areas within the Xiaojiang Basin can be classified as severe, heavy and light hazard regions.  相似文献   

Application of the luciferase cell culture bioassay for the detection of refined petroleum products   总被引：1，自引：0，他引：1  

Ziccardi MH  Gardner IA  Mazet JA  Denison MS 《Marine pollution bulletin》2002,44(10):983-991

A luciferase cell culture-based bioassay, developed to detect 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-like activity of halo-genated and polycyclic aromatic hydrocarbons, was optimized to detect refined petroleum products and to determine their relative inducing potency. Quality control standards from 32 refined products (gasolines and diesels, jet fuels, lubricating oils, fuel oils and weathered products) and three commercial products were evaluated. Induction equivalents (I-EQs) were determined by direct comparison of the EC50 and EC20 values (based on the median and 20% TCDD maximal response, respectively) from dose-response curves for each product to those obtained with TCDD. Most petroleum products were active in the luciferase bioassay, with those products composed of fractions produced later in the distillation process (i.e. fuel oils) inducing higher levels. Additionally, weathering of products reduced their induction potency. Based on the high I-EQ estimates of many products, biological effects associated with exposure may have been previously underestimated using other diagnostic methods.  相似文献   

Development of a Continental Volcanic Field: Petrogenesis of Pre-caldera Intermediate and Silicic Rocks and Origin of the Bandelier Magmas, Jemez Mountains (New Mexico, USA)     

Rowe  M. C.; Wolff  J. A.; Gardner  J. N.; Ramos  F. C.; Teasdale  R.; Heikoop  C. E. 《Journal of Petrology》2007,48(11):2063-2091

The Miocene–Quaternary Jemez Mountains volcanic field(JMVF) is the site of the Valles caldera and associated BandelierTuff. Caldera formation was preceded by > 10 Myr of volcanismdominated by intermediate composition rocks (57–70% SiO₂)that contain components derived from the lithospheric mantleand Precambrian crust. Simple mixing between crust-dominatedsilicic melts and mantle-dominated mafic magmas, fractionalcrystallization, and assimilation accompanied by fractionalcrystallization are the principal mechanisms involved in theproduction of these intermediate lavas. A variety of isotopicallydistinct crustal sources were involved in magmatism between13 and 6 Ma, but only one type (or two very similar types) ofcrust between 6 and 2 Ma. This long history constitutes a recordof accommodation of mantle-derived magma in the crust by meltingof country rock. The post-2 Ma Bandelier Tuff and associatedrhyolites were, in contrast, generated by melting of hybridizedcrust in the form of buried, warm intrusive rocks associatedwith pre-6 Ma activity. Major shifts in the location, styleand geochemical character of magmatism in the JMVF occur withina few million years after volcanic maxima and may correspondto pooling of magma at a new location in the crust followingsolidification of earlier magma chambers that acted as trapsfor basaltic replenishment. KEY WORDS: crustal anatexis; fractional crystallization; Jemez Mountain Volcanic Field; Valles Caldera; radiogenic isotopes; trace elements  相似文献   

Reddening of dune sands—evidence from southeast India     

Rita A. M. Gardner 《地球表面变化过程与地形》1981,6(5):459-468

Thin section, SEM, and TEM analyses have indicated that the red ‘teri’ sands of southeast India have formed from weathering in situ of coastal dune sands. The data does not support a detrital origin for the red sands. C¹⁴ dates indicate that dune deposition and weathering, to a maximum depth of 10 m, leading to the formation of a hematite, koalinite and illite rich matrix has taken place rapidly over the past 25,000 years. It is postulated that garnet was a major source of hematite (ferric oxide).  相似文献   

The magmatic evolution of the Seiland province,and Caledonian plate boundaries in northern Norway     

B. Robins  P.M. Gardner 《Earth and Planetary Science Letters》1975,26(2):167-178

The synorogenic intrusive activity of the eastern part of the Seiland province evolved from tholeiitic basalt low in K and Ti, through high-K calc-alkaline magmas and possible transitional basalt, to alkaline olivine basalt and picrite; finally, highly differentiated alkaline magmas and carbonatites were emplaced. For intrusive rocks with equivalent SiO₂ contents, K₂O, K₂O + Na₂O and K₂O/Na₂O increased with time, and the degree of iron enrichment in basaltic suites dimished. The western part of the province shows no equivalent evolution, tholeiitic magmas being emplaced at the same time as calc-alkaline magmas to the east.The magmatism is believed to have stemmed from a diapiric complex established in the mantle above a Benioff zone dipping to the east beneath the deforming Andean-type margin of the Baltic plate. Tectonic shortening of the continental edge and rearward movement of the underthrust plate relative to the asthenosphere resulted in migration of the plate junction, steepening of the seismic zone, and increasing depth to the magmagenetic region.  相似文献   

Organic versus inorganic trace metal complexes in sulfidic marine waters—some speculative calculations based on available stability constants     

Leonard Robert Gardner 《Geochimica et cosmochimica acta》1974,38(8):1297-1302

A theoretical model has been developed in order to test the hypothesis that simple organic acids are the chief agents of trace metal solubility in H₂S-rich marine waters. The model utilizes stability constant given by Sillen and Martell (1964, 1971) and assumes that the free cation activity of each metal is controlled by simple solubility products. Typical values of pH, pS and Eh are employed in the calculations. The results indicate that free amino acids and hydrocarboxylic acids probably are not effective but that bisulfide and polysulfide complexes may be the chief agents of trace metal solubility. To the extent that it is present, the effect of dissolved organic matter on trace metal solubility probably resides in highly polymerized substances (e.g. humic acids).  相似文献   

The Norwegian–Barents–Svalbard (NBS) continental margin: Introducing a natural laboratory of mass wasting, hydrates, and ascent of sediment, pore water, and methane     

P. R. Vogt  J. Gardner  K. Crane 《Geo-Marine Letters》1999,19(1-2):2-21

Side-scan sonar mapping and ground-truthing of the Norwegian–Barents–Svalbard continental margin shed new light on shelf glaciation, mass wasting, hydrates, and features like the Håkon Mosby mud volcano (HMMV), reflecting upward mobility of gas, pore fluids, and sediments. Detailed HMMV examination revealed thermal gradients to 10°/m, bottom-water CH₄ and temperature anomalies, H₂S- and CH₄-based chemosynthetic ecosystems, and subbottom methane hydrate (to 25%). Seismic and chemical data suggest HMMV origins at 2–3?km depth within the 6-km-thick depocenter. The HMMV and mound fields bordering the Bjørnøyrenna slide valley and pockmarks bordering the Storegga slide may all have formed in response to sediment failure.  相似文献   

Currents and sediment transport in the Mississippi Canyon and effects of Hurricane Georges     

Cheryl Burden Ross  Wilford D. Gardner  Mary Jo Richardson  Vernon L. Asper 《Continental Shelf Research》2009,29(11-12):1384-1396

The temporal variability in currents, temperature, and particulate matter concentration were measured in the Mississippi Canyon axis where the thalweg was 300 m deep from May–July and August–November 1998 using current meters, thermographs, a light-scattering sensor, and sediment traps. Canyon sediments were sampled by coring and observed using an ROV video camera. Currents in the upper Mississippi Canyon generally oscillated up/down canyon with diurnal periodicity and were bottom-intensified. Mean current speed at 3.5 mab was approximately 8 cm s^?1 during both deployments, reaching maximum speeds of over 50 cm s^?1 under normal conditions. Based on current velocities, critical bed shear stress for resuspension of canyon-floor sediments was exceeded about 30% of the time during both deployments. In late September, Hurricane Georges passed 150 km NE of the study site, significantly intensifying current velocities, bed shear stress, resuspension, trap fluxes and temperature fluctuations. As the hurricane passed, maximum current speed reached 68 cm^?s and temperature decreased ～7 °C in less than two hours. Critical bed shear stress for sediment resuspension was exceeded approximately 50% of the time during the five days of hurricane influence. Further evidence for sediment resuspension was the five-fold (and perhaps 70–130 fold) increase in trap fluxes and compositional similarities between canyon surface sediment and material collected by traps.  相似文献