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Uplift
Kinds of Uplift Terms modified by Uplift Selected AbstractsAmphibolite and blueschist,greenschist facies metamorphism, Blue Mountain inlier, eastern JamaicaGEOLOGICAL JOURNAL, Issue 5 2008Richard N. Abbott Jr Abstract Cretaceous (possibly older) metamorphic rock occurs mainly in the Blue Mountain inlier in eastern Jamaica. Fault-bounded blocks reveal two styles of metamorphism, Westphalia Schist (upper amphibolite facies) and Mt. Hibernia Schist (blueschist (BS),greenschist (GS) facies). Both Westphalia Schist and Mt. Hibernia Schist preserve detailed records of retrograde P,T paths. The paths are independent, but consistent with different parts of the type-Sanbagawa metamorphic facies series in Japan. For each path, phase relationships and estimated P,T conditions support a two-stage P,T history involving residence at depth, followed by rapid uplift and cooling. Conditions of residence vary depending on the level in a tectonic block. For the critical mineral reaction (isograd) in Westphalia Schist, conditions were P ,7.5,kbars, T ,600°C (upper amphibolite facies). Retrograde conditions in Hibernia Schist were P,=,2.6,3.0,kbars, T,=,219,237°C for a(H2O),=,0.8,1.0 (GS facies). Mt. Hibernia Schist may represent a volume of rock that was separated and uplifted at an early time from an otherwise protracted P,T path of the sort that produced the Westphalia Schist. Reset K,Ar ages for hornblende and biotite indicate only that retrograde metamorphism of Westphalia Schist took place prior to 76.5,Ma (pre-Campanian). Uplift may have commenced with an Albian,Aptian (,112,Ma) orogenic event. Copyright © 2008 John Wiley & Sons, Ltd. [source] Uplift at lithospheric swells,I: seismic and gravity constraints on the crust and uppermost mantle structure of the Cape Verde mid-plate swellGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010D. J. Wilson SUMMARY Wide-angle seismic data have been used to determine the velocity and density structure of the crust and uppermost mantle beneath the Cape Verdes mid-plate swell. Seismic modelling reveals a ,standard' oceanic crust, ,8 km in thickness, with no direct evidence for low-density bodies at the base of the crust. Gravity anomaly modelling within the constraints and resolution provided by the seismic model, does not preclude, however, a layer of crustal underplate up to 3 km thick beneath the swell crest. The modelling shows that while the seismically constrained crustal structure accounts for the short-wavelength free-air gravity anomaly, it fails to fully explain the long-wavelength anomaly. The main discrepancy is over the swell crest where the gravity anomaly, after correcting for crustal structure, is higher by about 30 mGal than it is over its flanks. The higher gravity can be explained if the top 100 km of the mantle beneath the swell crest is less dense than its surroundings by 30 kg m,3. The lack of evidence for low densities and velocities in the uppermost mantle, and high densities and velocities in the lower crust, suggests that neither a depleted swell root or crustal underplate are the origin of the observed shallower-than-predicted bathymetry and that, instead, the swell is most likely supported by dynamic uplift associated with an anomalously low density asthenospheric mantle. [source] Modeling of a Deep-Seated Geothermal System Near Tianjin, ChinaGROUND WATER, Issue 3 2001Zhou Xun A geothermal field is located in deep-seated basement aquifers in the northeastern part of the North China Plain near Tianjin, China. Carbonate rocks of Ordovician and Middle and Upper Proterozoic age on the Cangxian Uplift are capable of yielding 960 to 4200 m3/d of 57°C to 96°C water to wells from a depth of more than 1000 m. A three-dimensional nonisothermal numerical model was used to simulate and predict the spatial and temporal evolution of pressure and temperature in the geothermal system. The density of the geothermal water, which appears in the governing equations, can be expressed as a linear function of pressure, temperature, and total dissolved solids. A term describing the exchange of heat between water and rock is incorporated in the governing heat transport equation. Conductive heat flow from surrounding formations can be considered among the boundary conditions. Recent data of geothermal water production from the system were used for a first calibration of the numerical model. The calibrated model was used to predict the future changes in pressure and temperature of the geothermal water caused by two pumping schemes. The modeling results indicate that both pressure and temperature have a tendency to decrease with time and pumping. The current withdrawal rates and a pumping period of five months followed by a shut-off period of seven months are helpful in minimizing the degradation of the geothermal resource potential in the area. [source] Cooling and inferred exhumation history of the Ryoke metamorphic belt in the Yanai district, south-west Japan: Constraints from Rb,Sr and fission-track ages of gneissose granitoid and numerical modelingISLAND ARC, Issue 2 2001Takamoto Okudaira Abstract The Ryoke metamorphic belt in south-west Japan consists mainly of I-type granitoids and associated low-pressure/high-temperature metamorphic rocks. In the Yanai district, it has been divided into three structural units: northern, central and southern units. In this study, we measured the Rb,Sr whole-rock,mineral isochron ages and fission-track ages of the gneissose granodiorite in the central structural unit. Four Rb,Sr ages fall in a range of ca 89,87 Ma. The fission-track ages of zircon and apatite are 68.9 ± 2.6 Ma and 57.4 ± 2.5 Ma (1, error), respectively. Combining the newly obtained ages with previously reported (Th,)U,Pb ages from the same unit, thermochronologic study revealed two distinctive cooling stages; 1) a rapid cooling (> 40°C/Myr) for a period (~7 Myr) soon after the peak metamorphism (~ 95 Ma) and 2) the subsequent slow cooling stage (~ 5°C/Myr) after ca 88 Ma. The first rapid cooling stage corresponds to thermal relaxation of the intruded granodiorite magma and its associated metamorphic rocks, and to the uplift by a displacement along low-angle faults which initiated soon after the intrusion of the magma. Uplift by the later stage deformation having formed large-scale upright folds resulted in progress of the exhumation during the first stage. The average exhumation velocity of the stage is , 2 mm/yr. During the second stage, the rocks were not accompanied by ductile deformation and were exhumed with the rate of 0.1,0.2 mm/yr. The difference in the exhumation velocity between the first and second cooling stages resulted from the difference in the thickness of the crust and in the activity of ductile deformation between the early and later stages of the orogenesis. [source] Dependence of reaction kinetics on H2O activity as inferred from rates of intergranular diffusion of aluminiumJOURNAL OF METAMORPHIC GEOLOGY, Issue 7 2010W. D. CARLSON Abstract Quantitative constraints on the accelerative effects of H2O on the kinetics of metamorphic reactions arise from a comparison of rates of intergranular diffusion of Al in natural systems that are fluid-saturated, hydrous but fluid-undersaturated, and nearly anhydrous. Widths of symplectitic reaction coronas around partially resorbed garnet crystals in the contact aureole of the Makhavinekh Lake Pluton, northern Labrador, combined with time,temperature histories from conductive thermal models, yield intergranular diffusivities for Al from ,700,900 °C under nearly anhydrous conditions. Those rates, when extrapolated down temperature, are approximately three orders of magnitude slower than rates derived from re-analysis of garnet resorption coronas formed under hydrous but fluid-undersaturated conditions near 575 °C in rocks of the Llano Uplift of central Texas, which are in turn approximately four orders of magnitude slower than rates at comparable temperatures derived from numerical simulations of prograde garnet growth in fluid-saturated conditions in rocks from the Picuris Range of north-central New Mexico. Thus, even at constant temperature, rates of intergranular diffusion of Al , and corresponding length scales and timescales of metamorphic reaction and equilibration , may vary by as much as seven orders of magnitude across the range of H2O activities found in nature. [source] Complex behavioural pattern as an aid to identify the producer of Zoophycos from the Middle Permian of OmanLETHAIA, Issue 2 2009DIRK KNAUST The trace fossil Zoophycos is abundant in transgressive, shallow marine carbonates in the Middle Permian (Wordian) Khuff Formation of the Huqf-Haushi Uplift of Interior Oman. It often occurs as part of a complex (compound) trace fossil that comprises two integrated elements: (i) irregular galleries with straight to gently curved tunnels and interconnected shafts, and (ii) simple planar to complex spreiten structures with a marginal tube (Zoophycos). The galleries are characterized by irregularly winding, dichotomous branching, large variation in shape and size and circular to elliptical vertical cross-sections. Zoophycos consists of spreiten with a marginal tube, either originating as a simple lobe from the convex segment of a curved tunnel, or forming more complex, subcircular, spreiten systems parallel to bedding. The spreiten were formed by simple strip mining, where the animal defecated without producing faecal pellets. U-shaped marginal tubes indicate that the burrows were well aerated. The complex trace fossil points to combined dwelling and deposit-feeding behaviour, with irregular galleries in the firm substrate and Zoophycos spreiten in the softground below it. It can be assumed that the animal used the open tunnel system mainly for dwelling (domichnion) and possibly suspension feeding, but occasionally changed to deposit feeding while creating the spreiten (fodinichnion). The integration of the irregular galleries (tunnels and interconnected shafts) with the marginal tubes of Zoophycos suggests the same producer for this compound trace fossil. Many modern polychaetes produce very similar galleries within firm and soft substrates, and polychaetes are therefore interpreted as the most likely producers. Similarities between Permian and Triassic Zoophycos suggest comparable trace making behaviour before and after the end-Permian mass extinction. [source] Erosional vs. accretionary shelf margins: the influence of margin type on deepwater sedimentation: an example from the Porcupine Basin, offshore western IrelandBASIN RESEARCH, Issue 5 2009M. C. Ryan ABSTRACT A 1000 km2 three-dimensional (3D) seismic data survey that extends out from the western margin of the Porcupine Basin, offshore western Ireland reveals the internal geometry and depositional history of a large Palaeogene (Palaeocene,Early Eocene) shelf-margin. Two wells intersect the margin thereby constraining the depositional environments. The 34/19-1 well (landward end) intersects slope, shelf, marginal marine to coastal plain facies. The 35/21-1 well (basinward end) intersects seismically imaged shelf-margin clinoforms where base of slope back up to coastal plain deposits (source-to-sink) are represented. The basin-fill stratal architecture of the Palaeogene succession reveals sediment deposition under two end member, basin physiographic styles: (1) an erosional margin style and (2) an accretionary or progradational margin style. Uplift of the western margin of the basin is suggested as the major cause of the initially oversteepened shelf-slope erosional profile. Key characteristics of an erosional margin include sediment bypass of the shelf, canyon formation, and the development of significant onlapping submarine fan deposits on the lower slope. Failure on the slope is also revealed by several mass,transport complexes (MTCs) that carve out major erosive features across the slope. Three-dimensional seismic analysis illustrates variations in size, geometry and depositional trend and transport mechanisms of the MTCs. Confined, thick chaotic seismic facies, erosional basal scours and syn-depositional thrusting (pressure ridges) at terminus as opposed to thin, high-amplitude discontinuous facies with an unconfined lobate terminus are interpreted to indicate slump- and slide-dominated vs. debris flow-dominated MTCs, respectively. The erosional margin was transformed into an accretionary margin when the gradient of the shelf-slope to basin-floor profile was sufficiently lowered through the infilling and healing of the topographic lows by the onlapping submarine-fan deposits. This shallowing of the basin allowed nearshore systems to prograde across the deepwater systems. The accretionary margin was characterised by a thick sediment prism composed of clinoforms both at the shoreface/delta (tens of metres) and shelf-margin (hundreds of metres) scales. Shelf-margin clinoforms, the focus of this study, are the fundamental regressive to transgressive building blocks (duration 10,100 kyr) of the stratigraphic succession and can be observed on a larger scale (,1 Myr) through the migration and trajectory patterns of the shelf-edge. Trajectory pathways in the accretionary margin are accretionary in a descending or ascending manner. The descending style was characterised by a shelf-slope break that migrated seawards and obliquely downwards as a result of a relative sea-level fall. The descending trajectory geometry is lobate along strike suggestive of a point source progradation. Internally, the descending trajectory consists of downward stepping, steeply dipping shelf-margin clinoforms that display extensive slumping and deposition of sediment on the lower slope indicative of rapid deposition. Furthermore, basin-floor fans and associated ,feeder' channels extend basinwards beyond toe of slope. The ascending trajectory reflects a shelf-slope break that is interpreted to have migrated seawards during steady or rising relative sea level. The ascending trajectory geometry is associated with significant lateral sediment dispersal along the shelf-edge, reflecting distributary systems that were less ,fixed' or a greater reworking and longshore drift of sediment. Accretion involving the ascending shelf-edge trajectory characteristically lacked significant basin-floor deposits. Variable ascending trajectories are recognised in this study, as read from the angle at which the shelf-slope break migrates. Horizontal to high angle ascending trajectories correspond to dominantly progradational and dominantly aggradational shelf-edge trajectories, respectively. The sequence stratigraphic analysis of the Porcupine deltaic complex reveals a long-term relative sea-level rise. [source] Uplift, exhumation and precipitation: tectonic and climatic control of Late Cenozoic landscape evolution in the northern Sierras Pampeanas, ArgentinaBASIN RESEARCH, Issue 4 2003Edward R. Sobel Deciphering the evolution of mountain belts requires information on the temporal history of both topographic growth and erosion. The exhumation rate of a mountain range undergoing shortening is related to the erodability of the uplifting range as well as the efficiency of erosion, which partly depends on the available precipitation. Young, rapidly deposited sediments have low thermal conductivity and are readily eroded, in contrast to underlying resistant basement rocks that have a higher thermal conductivity. Apatite fission-track thermochronology can quantify cooling; thermal models constrain the relationship between this cooling and exhumation. By utilizing geological relations for a datum, we can examine the evolution of rock uplift, surface uplift and exhumation. In the northern Sierras Pampeanas of Argentina, a young sedimentary basin that overlay resistant crystalline basement prior to rapid exhumation provides an ideal setting to examine the effect of contrasting thermal and erosional regimes. There, tectonically active reverse-fault-bounded blocks partly preserve a basement peneplain at elevations in excess of 4500 m. Prior to exhumation, the two study areas were covered by 1000 and 1600 m of recently deposited sediments; this sequence begins with shallow marine deposits immediately overlying the regional erosion surface. Apatite fission-track data were obtained from vertical transects in the Calchaquíes and Aconquija ranges. At Cumbres Calchaquíes, erosion leading to the development of the peneplain commenced in the Cretaceous, probably as a result of rift-shoulder uplift. In contrast, Sierra Aconquija cooled rapidly between 5.5 and 4.5 Myr. At the onset of this rapid exhumation, the sediment was quickly removed, causing fast cooling, but relatively slow rates of surface uplift. Syntectonic conglomerates were produced when faulting exposed resistant bedrock; this change in rock erodability led to enhanced surface uplift rates, but decreased exhumation rates. The creation of an orographic barrier after the range had attained sufficient elevation further decreased exhumation rates and increased surface uplift rates. Differences in the magnitude of exhumation at the two transects are related to both differences in the thickness of the sedimentary basin prior to exhumation and differences in the effective precipitation due to an orographic barrier in the foreland and hence differences in the magnitude of headward erosion. [source] Comparison of the Surface and Underground Natural Gas Occurrences in the Tazhong Uplift of the Tarim BasinACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2010TIAN Jun Abstract: The oil, gas and water volumes revealed by the productivity of exploratory wells do not reflect the actual underground situations. Under the geologic conditions, a certain amount of dissolved natural gas is stored in oil or water. Based on the production test data of exploratory wells in the Tazhong uplift of the Tarim basin, this paper discusses in detail the differences in occurrence and distribution featrues between the surface and underground natural gases; presents a restoration of the surface gas occurrence to actual underground geologic conditions according to the dissolubility of natural gas under different temperature, pressure and medium conditions; and classifies the natural gas into three states, i.e. the oversaturated, saturated and undersaturated, according to its relative content underground. Through a comparative analysis of the differences in surface and underground occurrences of natural gas, it discusses the hydrocarbon reservoir formation mechanism and distribution rules, thereby providing guidances as new methods and technologies for the prediction of potential natural gas reservoir distribution in the study area. [source] Origin of the Silurian Crude Oils and Reservoir Formation Characteristics in the Tazhong UpliftACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2010YANG Haijun Abstract: The Silurian stratum in the Tazhong uplift is an important horizon for exploration because it preserves some features of the hydrocarbons produced from multi-stage tectonic evolution. For this reason, the study of the origin of the Silurian oils and their formation characteristics constitutes a major part in revealing the mechanisms for the composite hydrocarbon accumulation zone in the Tazhong area. Geochemical investigations indicate that the physical properties of the Silurian oils in Tazhong vary with belts and blocks, i.e., heavy oils are distributed in the TZ47,15 well-block in the North Slope while normal and light oils in the No. I fault belt and the TZ16 well-block, which means that the oil properties are controlled by structural patterns. Most biomarkers in the Silurian oils are similar to that of the Mid-Upper Ordovician source rocks, suggesting a good genetic relationship. However, the compound specific isotope of n -alkanes in the oils and the chemical components of the hydrocarbons in fluid inclusions indicate that these oils are mixed oils derived from both the Mid-Upper Ordovician and the Cambrian,Lower Ordovician source rocks. Most Silurian oils have a record of secondary alterations like earlier biodegradation, including the occurrence of "UCM" humps in the total ion current (TIC) chromatogram of saturated and aromatic hydrocarbons and 25-norhopane in saturated hydrocarbons of the crude oils, and regular changes in the abundances of light and heavy components from the structural low to the structural high. The fact that the Silurian oils are enriched in chain alkanes, e.g., n -alkanes and 25-norhopane, suggests that they were mixed oils of the earlier degraded oils with the later normal oils. It is suggested that the Silurian oils experienced at least three episodes of petroleum charging according to the composition and distribution as well as the maturity of reservoir crude oils and the oils in fluid inclusions. The migration and accumulation models of these oils in the TZ47,15 well-blocks, the No. I fault belt and the TZ16 well-block are different from but related to each other. The investigation of the origin of the mixed oils and the hydrocarbon migration and accumulation mechanisms in different charging periods is of great significance to petroleum exploration in this area. [source] Control of Fades and Potential on Jurassic Hydrocarbon Accumulation and Prediction of Favorable Targets in the Hinterland Region of the Junggar BasinACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2010CHEN Dongxia Abstract: Exploration practices show that the Jurassic System in the hinterland region of the Junggar Basin has a low degree of exploration but huge potential, however the oil/gas accumulation rule is very complicated, and it is difficult to predict hydrocarbon-bearing properties. The research indicates that the oil and gas is controlled by structure fades belt and sedimentary system distribution macroscopically, and hydrocarbon-bearing properties of sand bodies are controlled by lithofacies and petrophysical facies microscopically. Controlled by ancient and current tectonic frameworks, most of the discovered oil and gas are distributed in the delta front sedimentary system of a palaeo-tectonic belt and an ancient slope belt. Subaqueous branch channels and estuary dams mainly with medium and fine sandstone are the main reservoirs and oil production layers, and sand bodies of high porosity and high permeability have good hydrocarbon-bearing properties; the facies controlling effect shows a reservoir controlling geologic model of relatively high porosity and permeability. The hydrocarbon distribution is also controlled by relatively low potential energy at the high points of local structure macroscopically, while most of the successful wells are distributed at the high points of local structure, and the hydrocarbon-bearing property is good at the place of relatively low potential energy; the hydrocarbon distribution is in close connection with faults, and the reservoirs near the fault in the region of relatively low pressure have good oil and gas shows; the distribution of lithologic reservoirs at the depression slope is controlled by the distribution of sand bodies at positions of relatively high porosity and permeability. The formation of the reservoir of the Jurassic in the Junggar Basin shows characteristics of favorable facies and low-potential coupling control, and among the currently discovered reservoirs and industrial hydrocarbon production wells, more than 90% are developed within the scope of facies-potential index FPI>0.5, while the FPI and oil saturation of the discovered reservoir and unascertained traps have relatively good linear correlation. By establishing the relation model between hydrocarbon-bearing properties of traps and FPI, totally 43 favorable targets are predicted in four main target series of strata and mainly distributed in the Badaowan Formation and the Sangonghe Formation, and the most favorable targets include the north and east of the Shinan Sag, the middle and south of the Mobei Uplift, Cai-35 well area of the Cainan Oilfield, and North-74 well area of the Zhangbei fault-fold zone. [source] Tectono-thermal Evolution in the Bachu Uplift, Tarim Basin, ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2010QIU Nansheng Abstract: The thermal evolution of source rocks in the Paleozoic has long been a problem to petroleum exploration in the Bachu uplift, Tarim basin, since the thermal history in the Paleozoic could not be rebuilt objectively due to lack of effective thermal indicators in the Lower Paleozoic successions. The apatite and zircon (U-Th)/He thermochronometry can be used as a new kind of technique to study the thermal history and tectonic uplift of sedimentary basins. Based on the measured apatite and zircon (U-Th)/He ages, apatite fission track data and equivalence vitrinite reflectance (%EVRo), the tectonothermal histories in 5 wells of the Bachu uplift were modeled. The modeling results show that there was relatively high gradient at the Early Paleozoic in the Bachu uplift and it decreased gradually during the entire Paleozoic: 33,35°C/km in the Cambrian-Ordovician, 32,33°C/km in the Silurian-Devonian, 30,32°C/km at the end of Carboniferous and 27.5,31°C/km at the end of Permian. Therefore, the thermal history can be modeled by combining multiple thermal indicators of AFT, (U-Th)/He ages and EVRo data. Especially, this provides a new method to rebuild the thermal history for the Low Paleozoic carbonate successions in the Tarim Basin. [source] Thermochemical Sulfate Reduction in the Tazhong District, Tarim Basin, Northeast China: Evidence from Formation Water and Natural Gas GeochemistryACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2010Caifu XIANG Abstract: Systematic analyses of the formation water and natural gas geochemistry in the Central Uplift of the Tarim Basin (CUTB) show that gas invasion at the late stage is accompanied by an increase of the contents of H2S and CO2 in natural gas, by the forming of the high total dissolved solids formation water, by an increase of the content of HCO,3, relative to Cl,, by an increase of the 2nd family ions (Ca2+, Mg2+, Sr2+ and Ba2+) and by a decrease of the content of SO2,4, relative to Cl,. The above phenomena can be explained only by way of thermochemical sulfate reduction (TSR). TSR often occurs in the transition zone of oil and water and is often described in the following reaction formula: ,CH+CaSO4+H- 2O,H2S+CO2+CaCO3. (1) Dissolved SO2,4 in the formation water is consumed in the above reaction, when H2S and CO2 are generated, resulting in a decrease of SO2,4 in the formation water and an increase of both H2S and CO2 in the natural gas. If formation water exists, the generated CO2 will go on reacting with the carbonate to form bicarbonate, which can be dissolved in the formation water, thus resulting in the enrichment of Ca2+ and HCO,3. The above reaction can be described by the following equation: CO2+H2O+CaCO3,Ca2++2HCO,3. The stratigraphic temperatures of the Cambrian and lower Ordovician in CUTB exceeded 120°C, which is the minimum for TSR to occur. At the same time, dolomitization, which might be a direct result of TSR, has been found in both the Cambrian and the lower Ordovician. The above evidence indicates that TSR is in an active reaction, providing a novel way to reevaluate the exploration potentials of natural gas in this district. [source] Temporal-Spatial Structure of Intraplate Uplift in the Qinghai-Tibet PlateauACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2010Dewei LI Abstract: The intraplate uplift of the Qinghai-Tibet Plateau took place on the basis of breakup and assembly of the Precambrian supercontinent, and southward ocean-continent transition of the Proto-, Paleo-, Meso- and Neo-Tethys during the Caledonian, Indosinian, Yanshanian and Early Himalayan movements. The intraplate tectonic evolution of the Qinghai-Tibet Plateau underwent the early stage of intraplate orogeny characterized by migrational tectonic uplift, horizontal movement and geological processes during 180,7 Ma, and the late stage of isostatic mountain building characterized by pulsative rapid uplift, vertical movement and geographical processes since 3.6 Ma. The spatial-temporal evolution of the intraplate orogeny within the Qinghai-Tibet Plateau shows a regular transition from the northern part through the central part to the southern part during 180,120 Ma, 65,35 Ma, and 25,7 Ma respectively, with extensive intraplate faulting, folding, block movement, magmatism and metallogenesis. Simultaneous intraplate orogeny and basin formation resulted from crustal rheological stratification and basin-orogen coupling that was induced by lateral viscous flow in the lower crust. This continental dynamic process was controlled by lateral flow of hot and soft materials within the lower crust because of slab dehydration and melted mantle upwelling above the subducted plates during the southward Tethyan ocean-continent transition processes or asthenosphere diapirism. Intraplate orogeny and basin formation were irrelevant to plate collision. The Qinghai-Tibet Plateau as a whole was actually formed by the isostatic mountain building processes since 3.6 Ma that were characterized by crust-scale vertical movement, and integral rapid uplift of the plateau, accompanied by isostatic subsidence of peripheral basins and depressions, and great changes in topography and environment. A series of pulsative mountain building events, associated with gravity equilibrium and isostatic adjustment of crustal materials, at 3.6 Ma, 2.5 Ma, 1.8,1.2 Ma, 0.9,0.8 Ma and 0.15,0.12 Ma led to the formation of a composite orogenic belt by unifying the originally relatively independent Himalayas, Gangdisê, Tanghla, Longmenshan, Kunlun, Altyn Tagh, and Qilian mountains, and the formation of the complete Qinghai-Tibet Plateau with a unified mountain root after Miocene uplift of the plateau as a whole. [source] Paleoproterozoic, High-Metamorphic, Metasedimentary Units of Siberian CratonACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2009Lena URMANTSEVA Abstract: Sensitive, high-resolution ion microprobe zircon U,Pb ages of Paleoproterozoic, high-grade, metasedimentary rocks from the south-western part of the Siberian Craton are reported. Early Precambrian, high-grade complexes, including garnet,biotite, hypersthene,biotite, and cordierite-bearing gneisses compose the Irkut terrane of the Sharyzhalgay Uplift. Protoliths of studied gneisses correspond to terrigenous sediments, ranging from greywacke to shale. The paragneiss model Nd ages of 2.4,3.1 Ga indicate Archean-to-Paleoproterozoic source provinces. Zircons from gneisses show core-rim textures in cathodoluminescence (CL) image. Round or irregular shaped cores indicate detrital origin. Structureless rims with low Th/U are metamorphic in origin. The three age groups of detrital cores are: ,2.7, ,2.3, and 1.95,2 Ga. The ages of metamorphic rims range from 1.86 to 1.85 Ga; therefore, the sediments were deposited between 1.95 and 1.86 Ga and derived from Archean and Paleoproterozoic source rocks. It should be noted that Paleoproterozoic metasedimentary rocks of the Irkut Block are not unique. High-grade metaterrigenous sediments, with model Nd ages ranging from 2.3 to 2.5 Ga, are widely distributed within the Aldan and Anabar Shields of the Siberian Craton. The same situation is observed in the North China Craton, where metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 to 2.1 Ga (Wan et al., 2006). All of these sedimentary units were subjected to Late Paleoproterozoic metamorphism. In the Siberian Craton, the Paleoproterozoic sedimentary deposits are possibly marked passive margins of the Early Precambrian crustal blocks, and their high-grade metamorphism was related to the consolidation of the Siberian Craton. [source] North-south Differentiation of the Hydrocarbon Accumulation Pattern of Carbonate Reservoirs in the Yingmaili Low Uplift, Tarim Basin, Northwest ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2008Lü Xiuxiang Abstract: By analyzing the characteristics of development, structural evolution and reservoir beds of the residual carbonate strata, this study shows that the residual carbonate strata in the Yingmaili low uplift are favorable oil and gas accumulation series in the Tabei (northern Tarim uplift) uplift. There are different patterns of hydrocarbon accumulation on the northern and southern slopes of the Yingmaili low uplift. The north-south differentiation of oil reservoirs were caused by different lithologies of the residual carbonate strata and the key constraints on the development of the reservoir beds. The Mesozoic terrestrial organic matter in the Kuqa depression and the Palaeozoic marine organic matter in the Manjiaer sag of the Northern depression are the major hydrocarbon source rocks for the northern slope and southern slope respectively. The hydrocarbon accumulation on the northern and southern slopes is controlled by differences in maturity and thermal evolution history of these two kinds of organic matter. On the southern slope, the oil accumulation formed in the early stage was destroyed completely, and the period from the late Hercynian to the Himalayian is the most important time for hydrocarbon accumulation. However, the time of hydrocarbon accumulation on the northern slope began 5 Ma B.P. Carbonate inner buried anticlines reservoirs are present on the southern slope, while weathered crust and paleo-buried hill karst carbonate reservoirs are present on the northern slope. The northern and southern slopes had different controlling factors of hydrocarbon accumulation respectively. Fracture growth in the reservoir beds is the most important controlling factor on the southern slope; while hydrocarbon accumulation on the northern slope is controlled by weathered crust and cap rock. [source] Tectonic Constraints on the Transformation of Paleozoic Framework of Uplift and Depression in the Ordos AreaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 6 2006WANG Qingfei Abstract: During the Paleozoic, the Ordos area in the western North China Plate was located at the intersecting position of microplates and controlled by their interaction. The structural framework in the Ordos area, which underwent transformations in the Ordovician, the Carboniferous and the Permian respectively, was dominated by the alternation of uplift and depression. The transformations of structural framework are utilized as the clues to investigate the microplates' interacting type and its response in the Ordos area. According to the regional structural evolution, the Ordos area is simplified into an isopachous, isotropic and elastic shell model, and under proposed various boundary conditions, three series of numerical simulations corresponding to the three structural transformations are carried out to determine the detailed tectonic constraints. Numerical simulations reveal that the structure of the uplift and depression, which is similar to the actual pattern, develops only under one special boundary condition in each of the three series, indicating that the structural framework responds to the unique tectonic background. The simulation results show that in the Early Paleozoic, the L-shaped paleouplift formed nearby the southwestern corner of the Ordos area because the intensity of the compressions in the southern and western boundaries resulting from the ocean-continent collisions was similar. In the Late Paleozoic, it evolved into continent-continent (or arc-continent) interaction in the southern and northern boundaries; in the preliminary stage of the interaction, since the interface between the North China Plate and the plates on the south and north was narrow, the relative acting force was little and the regional western boundary immobile, and the structural framework in the basin was characterized by the N-S trending slender-waist,shaped uplift; as the interface between the plates expanded gradually, the extrusive force in the southern and northern boundaries of the North China Plate increased, resulting in the paleogeographic divisions showing E-W trending, and, the western boundary of the basin was extruded westward due to the intense compression inducing the local NE trending of paleogeographic division in the central area. The simulation results further reflect that the symmetry of the uplift-depression pattern is restricted by that of the boundary conditions, suggesting that the Paleozoic structural transformations of the Ordos area under boundary constraints accord with the universal physical symmetrical principle. [source] Basic Types and Structural Characteristics of Uplifts: An Overview of Sedimentary Basins in ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2009Dengfa HE Abstract: The uplift is a positive structural unit of the crust It is an important window for continental dynamics owing to its abundant structural phenomena, such as fault, fold, unconformity and denudation of strata. Meanwhile, it is the very place to store important minerals like oil, natural gas, coal and uranium. Giant and large-scale oil and gas fields in China, such as the Daqing Oilfield, Lunnan-Tahe Oilfield, Penglai 19,3 Oilfield, Puguang Gas Field and Jingbian Gas Field, are developed mainly on uplifts. Therefore, it is the main target both for oil and gas exploration and for geological study. The uplift can be either a basement uplift, or one developed only in the sedimentary cover. Extension, compression and wrench or their combined forces may give rise to uplifts. The development process of uplifting, such as formation, development, dwindling and destruction, can be taken as the uplifting cycle. The uplifts on the giant Precambrian cratons are large in scale with less extensive structural deformation. The uplifts on the medium- and small-sized cratons or neo-cratons are formed in various shapes with strong structural deformation and complicated geological structure. Owing to changes in the geodynamic environment, uplift experiences a multi-stage or multi-cycle development process. Its geological structure is characterized in superposition of multi-structural layers. Based on the basement properties, mechanical stratigraphy and development sequence, uplifts can be divided into three basic types , the succession, superposition and destruction ones. The succession type is subdivided into the maintaining type and the lasting type. The superposition type can be subdivided into the composite anticlinal type, the buried-hill draped type, the faulted uplift type and the migration type according to the different scales and superimposed styles of uplifts in different cycles. The destruction type is subdivided into the tilting type and the negative inverted type. The development history of uplifts and their controlling effects on sedimentation and fluids are quite different from one another, although the uplifts with different structural types store important minerals. Uplifts and their slopes are the main areas for oil and gas accumulation. They usually become the composite oil and gas accumulation zones (belts) with multiple productive formations and various types of oil and gas reservoirs. [source] Index of sources of stress in nursing students: a confirmatory factor analysisJOURNAL OF ADVANCED NURSING, Issue 5 2009Chris Gibbons Abstract Title.,Index of sources of stress in nursing students: a confirmatory factor analysis. Aim., This paper is a report of a study to test the proposed factor structure of the Index of Sources of Stress in Nursing Students. Background., Research across many countries has identified a number of sources of distress in nursing students but little attempt has been made to understand and measure sources of eustress or those stressors likely to enhance performance and well-being. The Index of Sources of Stress in Nursing Students was developed to do this. Exploratory factor analysis suggested a three-factor structure, the factors being labelled: learning and teaching; placement-related and course organization. It is important, however, to subject the instrument to confirmatory factor analysis as a further test of construct validity. Method., A convenience sample of final year nursing students (n = 176) was surveyed in one university in Northern Ireland in 2007. The Index of Sources of Stress in Nursing Students, which measures sources of stress likely to contribute to distress and eustress, was completed electronically. The lisrel programme was used to carry out the confirmatory factor analysis and test the factor structure suggested in the exploratory analysis. Findings., The proposed factor structure for the items measuring ,Uplifts' proved to be a good fit to the data and the proposed factor structure for the items measuring ,Hassles' showed adequate fit. Conclusion., In nursing programmes adopting the academic model and combining university-based learning with placement experience, this instrument can be used to help identify the sources of stress or course demands that students rate as distressing and those that help them to achieve. The validity of the ISSN could be further evaluated in other education settings. [source] What Happened in the Trans-North China Orogen in the Period 2560-1850 Ma?ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 6 2006Guochun ZHAO Abstract: The Trans-North China Orogen (TNCO) was a Paleoproterozic continent-continent collisional belt along which the Eastern and Western Blocks amalgamated to form a coherent North China Craton (NCC). Recent geological, structural, geochemical and isotopic data show that the orogen was a continental margin or Japan-type arc along the western margin of the Eastern Block, which was separated from the Western Block by an old ocean, with eastward-directed subduction of the oceanic lithosphere beneath the western margin of the Eastern Block. At 2550-2520 Ma, the deep subduction caused partial melting of the medium-lower crust, producing copious granitoid magma that was intruded into the upper levels of the crust to form granitoid plutons in the low- to medium-grade granite-greenstone terranes. At 2530-2520 Ma, subduction of the oceanic lithosphere caused partial melting of the mantle wedge, which led to underplating of mafic magma in the lower crust and widespread mafic and minor felsic volcanism in the arc, forming part of the greenstone assemblages. Extension driven by widespread mafic to felsic volcanism led to the development of back-arc and/or intra-arc basins in the orogen. At 2520-2475 Ma, the subduction caused further partial melting of the lower crust to form large amounts of tonalitic-trondhjemitic-granodioritic (TTG) magmatism. At this time following further extension of back-arc basins, episodic granitoid magmatism occurred, resulting in the emplacement of 2360 Ma, ,2250 Ma 2110,21760 Ma and ,2050 Ma granites in the orogen. Contemporary volcano-sedimentary rocks developed in the back-arc or intra-arc basins. At 2150-1920 Ma, the orogen underwent several extensional events, possibly due to subduction of an oceanic ridge, leading to emplacement of mafic dykes that were subsequently metamorphosed to amphibolites and medium- to high-pressure mafic granulites. At 1880-1820 Ma, the ocean between the Eastern and Western Blocks was completely consumed by subduction, and the closing of the ocean led to the continent-arc-continent collision, which caused large-scale thrusting and isoclinal folds and transported some of the rocks into the lower crustal levels or upper mantle to form granulites or eclogites. Peak metamorphism was followed by exhumation/uplift, resulting in widespread development of asymmetric folds and symplectic textures in the rocks. [source] Climatic influence on the inter-annual variability of late-Holocene minerogenic sediment supply in a boreal forest catchmentEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2010Gunilla Petterson Abstract Processes controlling sediment yield vary over a range of timescales, although most process-based observations are extremely short. Lake sediments, however, can be used to extend the observational timescale and are particularly useful when annually laminated (varved) sediment is present. The sediment record at Kassjön (N. Sweden) consists of ,6400 varves, each 0·5,1 mm thick. Image analysis was used to determine grey-scale variation and varve thickness from which annual minerogenic accumulation rate (MinAR) (mg cm,2 year,1) was inferred for the period 4486 BC , AD 1900. MinAR varies on annual to centennial scales and mainly reflects channel bank erosion by the inflow streams. The mineral input reflects the intensity of the spring run-off, which is dependent on the amount of snow accumulated during the winter, and hence MinAR is a long-term record of variability in past winter climate; other factors will be a variable response to catchment uplift, vegetation succession and pedogenesis. A major shift from low to high MinAR occurred ,250 BC, and peaks occurred around AD 250, 600, 1000, 1350 and 1650. Wavelet power spectrum analysis (confirmed by Fourier analyses) indicated significantly different periodicities throughout the period 4000 BC , AD 1700, including 275 years for the period 4000 BC , 2900 BC, 567 years for the period 2901 BC , 1201 BC, and 350 and 725 years for the period 1200 BC , AD 1700. The long-term, centennial scale variability (,350 years) may reflect solar forcing (cf the 385-year peak in tree-ring calibrated 14C activity) but interestingly, there is no obvious link to high frequency forcing, such as the North Atlantic Oscillation. The high resolution component of the record highlights the relevance of varved lake sediment records for understanding erosion dynamics in undisturbed forested catchments and their link to long-term climate dynamics and future climate change. Copyright © 2010 John Wiley & Sons, Ltd. [source] Quantitative analysis of InSAR digital elevation models for identification of areas with different tectonic activities in southern ItalyEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2009Claudio Martino Abstract This work presents the results of a quantitative analysis of an interferometric SAR (InSAR) digital elevation model (DEM), obtained by the Shuttle Radar Topography Mission (SRTM). The analysis aims to identify additional parameters to recognize areas in southern Italy with different tectonic activities and behaviours. The axial zone of the Campania-Lucania Apennine and the Sila Massif in Calabria, Italy, characterized by quite different evolutionary histories, have been chosen as test areas sufficiently wide to validate observations on a sub-regional scale at least. Geomorphological information on the shape of palaeosurfaces has been used to estimate uplift and/or erosion amounts and rates. Palaeosurfaces are identified on the DEM as regions with an altitude higher than 1000 m a.s.l. and sub-planar land surfaces dipping less than 6°. Information about the shape of palaeosurfaces during the first stage of uplift and before the tectonic-induced block fragmentation has been extracted. A fragmentation index has been computed for these erosional surfaces. The first stage of this landscape evolution has been studied in terms of the geometric characteristics of fragmented blocks. The last erosional stage has been recognized in terms of both geometric characteristics and fragmentation index of the sub-horizontal land surfaces. Altitude and age of the palaeosurfaces, referred to ancient base-levels of the erosion, have been used to estimate the erosional rate. Copyright © 2008 John Wiley and Sons, Ltd. [source] Morphometric indices as indicators of tectonic, fluvial and karst processes in calcareous drainage basins, South Menorca Island, SpainEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2007Francesca S. Segura Abstract This study proposes using morphometric indices to discriminate the processes that shape calcareous drainage basins. To illustrate this, a DEM of the southern part of Menorca Island (Migjorn) was created and basin slope, drainage density, hypsometric curve and integral, and the area occupied by open and closed dolines were extracted from it. These indices show an important dependence on tectonics, which govern the morphology of these drainage basins and encourage the predominance of karst and/or fluvial processes in the different sectors. The morphometric indices are clearly influenced by the geological Migjorn structure, a carbonate Upper Miocene reef platform gently folded as an asymmetrical anticline. The hypsometric integral and curve discriminate the influence of tectonics and structure whilst the drainage density and the proportion of open dolines are associated with basins with more pronounced fluvial processes. A cluster analysis based on these indices discriminated three sectors where different forms and processes are found. In the western and eastern sectors, rounded basins without major fractures predominate. The basins slope at less than 5°, and karst processes outweigh fluvial processes. The central sector, however, has steeper slopes, a clearly defined drainage system, and a predominance of fluvial over karst processes. Greater uplift in this sector has facilitated the formation of elongated basins that follow the main fracture lines. Copyright © 2007 John Wiley & Sons, Ltd. [source] Regional analysis of bedrock stream long profiles: evaluation of Hack's SL form, and formulation and assessment of an alternative (the DS form)EARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2007Geoff Goldrick Abstract The equilibrium form of the fluvial long profile has been used to elucidate a wide range of aspects of landscape history including tectonic activity in tectonic collision zones, and in continental margin and other intraplate settings, as well as other base-level changes such as due to sealevel fluctuations. The Hack SL form of the long profile, which describes a straight line on a log,normal plot of elevation (normal) versus distance (logarithmic), is the equilibrium long profile form that has been most widely used in such studies; slope,area analysis has also been used in recent years. We show that the SL form is a special case of a more general form of the equilibrium long profile (here called the DS form) that can be derived from the power relationship between stream discharge and downstream distance, and the dependence of stream incision on stream power. The DS form provides a better fit than the SL form to river long profiles in an intraplate setting in southeastern Australia experiencing low rates of denudation and mild surface uplift. We conclude that, if an a priori form of the long profile is to be used for investigations of regional landscape history, the DS form is preferable. In particular, the DS form in principle enables equilibrium steepening due to an increase in channel substrate lithological resistance (parallel shift in the DS plot) to be distinguished from disequilibrium steepening due to long profile rejuvenation (disordered outliers on the DS plot). Slope,area analysis and the slope,distance (DS) approach outlined here are complementary approaches, reflecting the close relationship between downstream distance and downstream catchment area. Copyright © 2006 John Wiley & Sons, Ltd. [source] Long-term landscape evolution: linking tectonics and surface processesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2007Paul Bishop Abstract Research in landscape evolution over millions to tens of millions of years slowed considerably in the mid-20th century, when Davisian and other approaches to geomorphology were replaced by functional, morphometric and ultimately process-based approaches. Hack's scheme of dynamic equilibrium in landscape evolution was perhaps the major theoretical contribution to long-term landscape evolution between the 1950s and about 1990, but it essentially ,looked back' to Davis for its springboard to a viewpoint contrary to that of Davis, as did less widely known schemes, such as Crickmay's hypothesis of unequal activity. Since about 1990, the field of long-term landscape evolution has blossomed again, stimulated by the plate tectonics revolution and its re-forging of the link between tectonics and topography, and by the development of numerical models that explore the links between tectonic processes and surface processes. This numerical modelling of landscape evolution has been built around formulation of bedrock river processes and slope processes, and has mostly focused on high-elevation passive continental margins and convergent zones; these models now routinely include flexural and denudational isostasy. Major breakthroughs in analytical and geochronological techniques have been of profound relevance to all of the above. Low-temperature thermochronology, and in particular apatite fission track analysis and (U,Th)/He analysis in apatite, have enabled rates of rock uplift and denudational exhumation from relatively shallow crustal depths (up to about 4 km) to be determined directly from, in effect, rock hand specimens. In a few situations, (U,Th)/He analysis has been used to determine the antiquity of major, long-wavelength topography. Cosmogenic isotope analysis has enabled the determination of the ,ages' of bedrock and sedimentary surfaces, and/or the rates of denudation of these surfaces. These latter advances represent in some ways a ,holy grail' in geomorphology in that they enable determination of ,dates and rates' of geomorphological processes directly from rock surfaces. The increasing availability of analytical techniques such as cosmogenic isotope analysis should mean that much larger data sets become possible and lead to more sophisticated analyses, such as probability density functions (PDFs) of cosmogenic ages and even of cosmogenic isotope concentrations (CICs). PDFs of isotope concentrations must be a function of catchment area geomorphology (including tectonics) and it is at least theoretically possible to infer aspects of source area geomorphology and geomorphological processes from PDFs of CICs in sediments (,detrital CICs'). Thus it may be possible to use PDFs of detrital CICs in basin sediments as a tool to infer aspects of the sediments' source area geomorphology and tectonics, complementing the standard sedimentological textural and compositional approaches to such issues. One of the most stimulating of recent conceptual advances has followed the considerations of the relationships between tectonics, climate and surface processes and especially the recognition of the importance of denudational isostasy in driving rock uplift (i.e. in driving tectonics and crustal processes). Attention has been focused very directly on surface processes and on the ways in which they may ,drive' rock uplift and thus even influence sub-surface crustal conditions, such as pressure and temperature. Consequently, the broader geoscience communities are looking to geomorphologists to provide more detailed information on rates and processes of bedrock channel incision, as well as on catchment responses to such bedrock channel processes. More sophisticated numerical models of processes in bedrock channels and on their flanking hillslopes are required. In current numerical models of long-term evolution of hillslopes and interfluves, for example, the simple dependency on slope of both the fluvial and hillslope components of these models means that a Davisian-type of landscape evolution characterized by slope lowering is inevitably ,confirmed' by the models. In numerical modelling, the next advances will require better parameterized algorithms for hillslope processes, and more sophisticated formulations of bedrock channel incision processes, incorporating, for example, the effects of sediment shielding of the bed. Such increasing sophistication must be matched by careful assessment and testing of model outputs using pre-established criteria and tests. Confirmation by these more sophisticated Davisian-type numerical models of slope lowering under conditions of tectonic stability (no active rock uplift), and of constant slope angle and steady-state landscape under conditions of ongoing rock uplift, will indicate that the Davis and Hack models are not mutually exclusive. A Hack-type model (or a variant of it, incorporating slope adjustment to rock strength rather than to regolith strength) will apply to active settings where there is sufficient stream power and/or sediment flux for channels to incise at the rate of rock uplift. Post-orogenic settings of decreased (or zero) active rock uplift would be characterized by a Davisian scheme of declining slope angles and non-steady-state (or transient) landscapes. Such post-orogenic landscapes deserve much more attention than they have received of late, not least because the intriguing questions they pose about the preservation of ancient landscapes were hinted at in passing in the 1960s and have recently re-surfaced. As we begin to ask again some of the grand questions that lay at the heart of geomorphology in its earliest days, large-scale geomorphology is on the threshold of another ,golden' era to match that of the first half of the 20th century, when cyclical approaches underpinned virtually all geomorphological work. Copyright © 2007 John Wiley & Sons, Ltd. [source] Experimental study of dynamic damage of an arch damEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2007Haibo Wang Abstract Seismic responses of a 292-m high arch dam were studied by experiment on a shaking table. The model system included the arch dam with contraction joints, a part of a reservoir, and a partial foundation with a topographic feature near the dam. Potential rock wedges on the abutments and the mechanical properties including uplift on the kinematic planes were carefully simulated. A damping boundary consisting of a viscous liquid was introduced to simulate the effect of dynamic energy emission to far field, which made the dynamic interaction between the dam and the foundation be adequately represented in the model test of an arch dam system. Dynamic responses of the arch dam system under a sequence of seismic loadings in increasing strength were examined. Eleven cracks or overstresses on the model dam due to the earthquake excitations were observed, and consequently, its natural frequency dropped by about 14%, but the model dam was stable under the hydrostatic load of the impounded water after the test. Copyright © 2006 John Wiley & Sons, Ltd. [source] Shaking table tests on seismic response of steel braced frames with column upliftEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2006Mitsumasa Midorikawa Abstract Previous studies have suggested that rocking vibration accompanied by uplift motion might reduce the seismic damage to buildings subjected to severe earthquake motions. This paper reports on the use of shaking table tests and numerical analyses to evaluate and compare the seismic response of base-plate-yielding rocking systems with columns allowed to uplift with that of fixed-base systems. The study is performed using half-scale three-storey, 1 × 2 bay braced steel frames with a total height of 5.3 m. Base plates that yield due to column tension were installed at the base of each column. Two types of base plates with different thicknesses are investigated. The earthquake ground motion used for the tests and analyses is the record of the 1940 El Centro NS component with the time scale shortened by a factor of 1/,2. The maximum input acceleration is scaled to examine the structural response at various earthquake intensities. The column base shears in the rocking frames with column uplift are reduced by up to 52% as compared to the fixed-base frames. Conversely, the maximum roof displacements of the fixed and rocking frames are about the same. It is also noted that the effect of the vertical impact on the column associated with touchdown of the base plate is small because the difference in tensile and compressive forces is primarily due to the self-limiting tensile force in the column caused by yielding of the base plate. Copyright © 2006 John Wiley & Sons, Ltd. [source] Uplift-restraining Friction Pendulum seismic isolation systemEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 5 2006Panayiotis C. Roussis Abstract This paper extends the scope of seismic isolation by introducing an innovative uplift-restraining Friction Pendulum system. Termed the XY-FP isolator, the new isolation device consists of two orthogonal opposing concave beams interconnected through a sliding mechanism that permits tension to develop in the bearing, thereby preventing uplift. Owing to its distinct configuration, the XY-FP isolator possesses unique properties for a seismic isolator, including uplift restraint, decoupling of the bi-directional motion along two orthogonal directions, and capability of providing independent stiffness and energy dissipation along the principal horizontal directions of the bearing. The study concentrates on introducing the concept and establishing the underlying principles of operation of the new XY-FP isolator, formulating the mathematical model for the XY-FP isolator, and presenting its mechanical behaviour through a displacement-control testing program on a single XY-FP isolator. Copyright © 2005 John Wiley & Sons, Ltd. [source] Large displacement behaviour of a structural model with foundation uplift under impulsive and earthquake excitationsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2003Giuseppe Oliveto Abstract This paper considers the dynamical behaviour of a structural model with foundation uplift. The equations of motion of the system considered are derived for large displacements thus allowing for the eventual overturning of the system. The transition conditions between successive phases of motion, derived in terms of the specific Lagrangian co-ordinates used in the formulation of the equations of motion, present innovative aspects which resolve some previously inexplicable behaviour in the structural response reported in the literature. The dynamical behaviour of the model is considered under impulsive and long-duration ground motions. The minimum horizontal acceleration impulses for the uplift and the overturning of the system are evaluated in analytical form. The sensitivity of the model to uplifting and to overturning under impulsive excitations is established as a function of few significant structural parameters. Numerical applications have been performed changing either the structural parameters or the loading parameter, in order to analyse several dynamical behaviours and also to validate the analytical results. For earthquake ground motions the results, reported in the form of response spectra, show that linearized models generally underestimate, sometimes significantly, the structural response. Copyright © 2003 John Wiley & Sons, Ltd. [source] The profound influence of the Late Pliocene Panamanian uplift on the exchange, diversification, and distribution of New World birdsECOGRAPHY, Issue 2 2010Brian Tilston Smith Separated throughout most of the Cenozoic era, North and South America were joined during the mid-Pliocene when the uplift of Panama formed a land bridge between these two continents. The fossil record indicates that this connection allowed an unprecedented degree of inter-continental exchange to occur between unique, previously isolated biotic assemblages, a phenomenon now recognized as the "Great American Biotic Interchange". However, a relatively poor avian fossil record has prevented our understanding the role of the land bridge in shaping New World avian communities. To address the question of avian participation in the GABI, we compiled 64 avian phylogenetic studies and applied a relaxed molecular clock to estimate the timing of trans-isthmus diversification events. Here, we show that a significant pulse of avian interchange occurred in concert with the isthmus uplift. The avian exchange was temporally consistent with the well understood mammalian interchange, despite the presumed greater vagility of birds. Birds inhabiting a variety of habitats and elevational zones responded to the newly available corridor. Within the tropics, exchange was equal in both directions although between extratropical and tropical regions it was not. Avian lineages with Nearctic origins have repeatedly invaded the tropics and radiated throughout South America; whereas, lineages with South American tropical origins remain largely restricted to the confines of the Neotropical region. This previously unrecognized pattern of asymmetric niche conservatism may represent an important and underappreciated contributor to the latitude diversity gradient. [source] | ||||||||||||||||||||||||||||||||||||||||