An explicit representation of steady state response of a beam on an elastic foundation to moving harmonic line loads

A closed‐form deflection response of a beam rest is presented in this paper using the integral transform method. The theory of linear partial differential equations is used to represent the deflection of beam subjected to a moving harmonic line load in integration form. The solution is finally carried out using the inverse Fourier transform. To evaluate the integration analytically, poles of the integrand are identified with the help of algebraic equation theory. Residue theorem is then utilized to represent the integration as a contour integral in the complex plane. Closed‐form deflections and numerical results are provided for different combinations of load frequency and velocity. Copyright © 2002 John Wiley & Sons, Ltd.     

Metamorphic evolution of exhumed middle to lower crustal rocks in the Mojave Extensional Belt, southern California, USA

The Waterman Metamorphic Complex of the central Mojave Desert was exposed as a consequence of early Miocene detachment-dominated extension. However, it has evidence consistent with a more extensive geological history that involves collision of a crustal fragment(s), tectonic thickening by overthrusting and two periods of extension. The metamorphic complex contains granitoid intrusives and felsic mylonitic gneisses as well as polymetamorphic rocks that include marble, calc-silicate, quartzite. mafic granulite, pyribolite, amphibolite, migmatite and biotite schist. The latter group of rocks was affected by an initial series of high-grade metamorphic events (M1 and M2) and a localized lower grade overprint (M3). The initial metamorphism (M1) can be separated into two stages along its high-grade P–T path: M1a, a granulite facies metamorphism at 800–850° C and 7.5–9 kbar and Mlb, an upper amphibolite facies overprint at 750–800° C and 10–12 kbar. M1a developed mineral assemblages and textures consistent with granulite facies conditions at a reduced activity of H₂O and is associated with intense ductile deformation (D1) and minor local partial melting. M1b overprinted the granulite assemblages with a series of hydrous phases under conditions of increasing pressure and H₂O activity and is accompanied by little or no deformation. M2 developed at lower pressures and temperatures (650–750° C, 4.5–5.5 kbar) and is distinguished by a second local overprint of hydrous phases that reflects an input of aqueous fluids probably associated with the intrusion of a series of granitic dykes and veins. Effects of M3 are confined to the Mitchel detachment zone, an anastomosing early Miocene detachment fault, and are characterized by local ductile/brittle deformation (D2) of the pre-existing high-grade rocks and granitoid intrusives and by the production of mylonites and mylonitic gneisses under greenschist facies conditions (300–350° C, 3–5 kbar). The initial overprint (M1a) represents metamorphism, devolatilization and minor partial melting of supracrustal rocks under granulite facies conditions as a consequence of tectonic and, possibly, magmatic thickening. The increasing pressure transition of M1a to M1b reflects a period of continued compressional tectonism, thrusting and influx of H₂O, in part, locally related to crystallization of partial melts. The near isothermal decompression between M1b and M2 probably represents a pre-112-Ma extensional episode that may have been the result of a decompressional readjustment of a thickened crust. Following the initial extensional event, the metamorphic complex remained at depths of 10–17 km for at least 90 Ma until it was uplifted following Miocene extension. M3 develops locally in response to this second extensional period resulting from the early Miocene detachment faulting.     

PROPAGATION OF 30—60 DAY LOW FREQUENCY OSCILLATIONS AND THEIR INFLUENCE UPON THE SUBTROPICAL WESTERLIES JET STREAM DURING NORTHERN HEMISPHERE WINTER

Based on daily ECMWF gridpoint data of two winters during 1981—1983 including an ENSOyear,propagation of low frequency oscillations(LFO)during Northern Hemisphere winters andtheir influences upon 30—60 day oscillations of the subtropical jet stream are studied with the sta-tistical methods as complex empirical orthogonal function(CEOF)and so on.Results show that inthe winter of a normal year(1981—1982),30—60 day oscillations in the subtropical zone aremainly in the northern and southern flanks of exit region of jet stream.In the ENSO year(1982—1983),they are mainly in the vicinity of entrance and exit regions of jet stream.Intraseasonalchanges of subtropical jet stream manifested themselves as latitudinal fluctuation or longitudinalprogression or regression of about 40 day period.There are marked differences between propagat-ing passages of low frequency modes responsible for changes of subtropical jet stream in the normalyear(1981—1982)and in the ENSO year(1982—1983).Changes of oscillation amplitude showobvious phases.In general,the one in late winter is stronger than that in early winter,strongestone occurs in February.     

Timing and tectonic setting of Grenvillian metamorphism—constraints from a transect along Georgian Bay,Ontario*

Systematic mapping of a transect along the well-exposed shores of Georgian Bay, Ontario, combined with the preliminary results of structural analysis, geochronology and metamorphic petrology, places some constraints on the geological setting of high-grade metamorphism in this part of the Central Gneiss Belt. Correlations within and between map units (gneiss associations) have allowed us to recognize five tectonic units that differ in various aspects of their lithology, metamorphic and plutonic history, and structural style. The lowest unit, which forms the footwall to a regional decollement, locally preserves relic pre-Grenvillian granulite facies assemblages reworked under amphibolite facies conditions during the Grenvillian orogeny. Tectonic units above the decollement apparently lack the early granulite facies metamorphism; out-of-sequence thrusting in the south produced a duplex-like structure. Two distinct stages of Grenvillian metamorphism are apparent. The earlier stage (c. 1160–1120 Ma) produced granulite facies assemblages in the Parry Sound domain and upper amphibolite facies assemblages in the Parry Island thrust sheet. The later stage (c. 1040–1020 Ma) involved widespread, dominantly upper amphibolite facies metamorphism within and beneath the duplex. Deformation and metamorphism recently reported from south and east of the Parry Sound domain at c. 1100–1040 Ma have not yet been documented along the Georgian Bay transect. The data suggest that early convergence was followed by a period of crustal thickening in the orogenic core south-east of the transect area, with further advance to the north-west during and after the waning stages of this deformation.     

Relationship between footwall composition,crustal contamination,and fluid–rock interaction in the Platreef,Bushveld Complex,South Africa

In the northern limb of the 2.06-Ga Bushveld Complex, the Platreef is a platinum group elements (PGE)-, Cu-, and Ni-mineralized zone of pyroxenite that developed at the intrusion margin. From north to south, the footwall rocks of the Platreef change from Archaean granite to dolomite, hornfels, and quartzite. Where the footwall is granite, the Sr-isotope system is more strongly perturbed than where the footwall is Sr-poor dolomite, in which samples show an approximate isochron relationship. The Nd-isotope system for samples of pyroxenite and hanging wall norite shows an approximate isochron relationship with an implied age of 2.17 ± 0.2 Ga and initial Nd-isotope ratio of 0.5095. Assuming an age of 2.06 Ga, the ɛNd values range from −6.2 to −9.6 (ave. −7.8, n = 17) and on average are slightly more negative than the Main Zone of the Bushveld. These data are consistent with local contamination of an already contaminated magma of Main Zone composition. The similarity in isotope composition between the Platreef pyroxenites and the hanging wall norites suggests a common origin. Where the country rock is dolomite, the Platreef has generally higher plagioclase and pyroxene δ ¹⁸O values, and this indicates assimilation of the immediate footwall. Throughout the Platreef, there is considerable petrographic evidence for sub-solidus interaction with fluids, and the Δ _{plagioclase–pyroxene} values range from −2 to +6, which indicates interaction at both high and low temperatures. Whole-rock and mineral δD values suggest that the Platreef interacted with both magmatic and meteoric water, and the lack of disturbance to the Sr-isotope system suggests that fluid–rock interaction took place soon after emplacement. Where the footwall is granite, less negative δD values suggest a greater involvement of meteoric water. Consistently higher values of Δ _{plagioclase–pyroxene} in the Platreef pyroxenites and hanging wall norites in contact with dolomite suggest prolonged interaction with CO₂-rich fluid derived from decarbonation of the footwall rocks. The overprint of post crystallization fluid–rock interaction is the probable cause of the previously documented lack of correlation between PGE and sulfide content on the small scale. The Platreef in contact with dolomite is the focus of the highest PGE grades, and this suggests that dolomite contamination played a role in PGE concentration and deposition, but the exact link remains obscure. It is a possibility that the CO₂ produced by decarbonation of assimilated dolomite enhanced the process of PGE scavenging by sulfide precipitation.     

Fracture analysis in the south-western Corinth rift (Greece) and implications on fault hydraulic behavior

This paper reviews the data concerning the fracture network and the hydraulic characteristics of faults in an active zone of the Gulf of Corinth. Pressure gap measured through fault planes shows that in this area the active normal faults (Aigion, Helike) act, at least temporarily and locally, as transversal seal. The analysis of the carbonate cements in the fractures on both the hangingwall and the footwall of the faults also suggests that they have acted as local seals during the whole fault zone evolution. However, the pressure and the characteristics of the water samples measured in the wells indicate that meteoric water circulates from the highest part of the relief to the coast, which means it goes through the fault zones. Field quantitative analysis and core studies from the AIG-10 well have been performed to define both regional and fault-related fracture networks. Then laboratory thin section observations have been done to recognize the different fault rocks characterizing the fault zone components. These two kinds of approach give information on the permeability characteristics of the fault zone. To synthesize the data, a schematic conceptual 3D fluid flow modeling has been performed taking into account fault zone permeability architecture, sedimentation, fluid flow, fault vertical offset and meteoric water influx, as well as compaction water flow. This modeling allows us to fit all the data with a model where the fault segments act as a seal whereas the relays between these segments allow for the regional flow from the Peloponnese topographic highs to the coast.     

伊敏五牧场区煤质特征及变质规律

伊敏五牧场区存在着从褐煤到贫煤完整的变质系列,其主要煤变质类型为接触变质.在本区煤系地层底部有一酸性侵入岩体,该侵入岩体是引起本区煤变质的直接热源,它提供了褐煤向烟煤转化的热动力.本区出现的隐爆角砾岩也是受热不均匀或热叠加造成煤类复杂多变的原因.区内构造十分发育,构造条件是煤变质的又一主要因素.研究该区煤变质规律对伊敏煤田及海拉尔褐煤盆地烟煤预测具有指导作用.     

松潘—甘孜造山带中丹巴地区变质岩的流体包裹体研究

对丹巴地区动热变质岩石英中的流体包裹体研究表明，第一类型包裹体为高密度CO2包裹体，与深层滑脱作用密切相关，其温度、压力可代表变质峰期的温压条件。第二类型包裹体为CO2－H2O包裹体，H2O含量增加，与变质峰期后的抬升作用有关。第三类型包裹体为NaCl－H2O包裹体，以H2O为主，与抬升作用引起的退变质作用有关。其形成温度依次降低，说明它们是在变质作用的不同阶段捕获的。     

瞬变电磁场的奇点展开法

在分析电磁系统自然谐振现象的基础上,简述了瞬变电磁场奇点展开法的物理基础、基本理论、极点提取方法,并考查了奇点展开法在地球物理中的应用可能性。