bluuebunny/crossref_metadata_2025 huggingface dataset:
First‐order Wiener‐Hermite expansion in the electromagnetic scattering by conducting rough surfaces
Authors: Eftimiu Cornel
Published: February 2008

The application of the Wiener‐Hermite expansion to the scattering of electromagnetic waves by rough conducting surfaces is examined. In this work the expansion is carried out only up to terms of first order in the Wiener‐Hermite functionals for the surface current, the average far field, and the coherent and incoherent responses. Nevertheless, the expressions obtained for these quantities contain contributions from all orders of multiple scattering and can be viewed as partial sums of selected terms in the perturbation theory expansion. The results following from this approach are compared to those calculated by using second‐order perturbation theory and also by recasting the latter in Padé approximant form.
On the concepts of a perfectly conducting material and of a perfectly conducting and infinitely thin screen
Authors: Bouchitté G. , Petit R.
Published: February 2008

The concepts of a perfectly conducting material and of a perfectly conducting and infinitely thin screen are revisited from a theoretical point of view. When both the resistivity and the thickness of a conducting film tend to zero, the properties of the infinitely thin resulting film depend on how the two vanishing parameters are linked during the limiting process.
Guided electromagnetic waves in chiral media
Authors: Eftimiu Cornel , Pearson L. Wilson
Published: February 2008

The eigenvalue problem for the determination of propagating modes in a waveguide filled with a lossless dielectric, homogeneous, isotropic, chiral medium is formulated. The approach is illustrated by considering in detail the case of a circular waveguide.
Radial propagation and steepest descent path integral representations of the planar microstrip dyadic Green's function
Authors: Barkeshli S. , Pathak P. H.
Published: February 2008

A radial propagation integral representation of the microstrip electric dyadic surface Green's function is developed. This representation is very efficient for a numerical evaluation of the field when the source and observation points are laterally rather than vertically separated with respect to the plane of the substrate. Furthermore, when the integration contour is deformed to the steepest descent path, the Green's function exhibits an even faster convergence. In contrast, the conventional Sommerfeld integral representation of the microstrip Green's function converges very poorly for this case. Numerical examples are presented which indicate that the representations obtained here are surprisingly efficient even for relatively small lateral separation of the source and field points. This work is especially useful in the moment method analysis of microstrip antenna arrays where the mutual coupling effects are important.
Vehicle charging and associated HF wave phenomena during electron beam emissions
Authors: Ernstmeyer J. , Donatelli D. E.
Published: February 2008

We present data obtained during tests of the Beam‐Emitting Rocket Test (BERT) payload in the Johnson Space Center's Chamber A. During the tests an electron gun on the main payload emitted beams of 0.5, 1, and 2 keV, which stepped through currents of 0.1–20 mA. Simultaneously, an instrumented nose cone, separate from the main payload, measured electric field fluctuations from DC to 5.5 MHz. Abrupt changes in HF wave activity and vehicle potential occurred during 0.5‐ and 1.0‐keV gun operations. Whenever beam current exceeded a threshold level, wave emissions above the chamber electron gyrofrequency, ƒce, were dramatically enhanced and emissions below ƒce were disrupted. At the same time the potential on the electrically isolated BERT payload, which steadily increased with beam current, suddenly ceased to increase and often decreased. The threshold current, Ic, is proportional to the three‐halves power of beam energy, ε, as in beam plasma discharge. However, other facts indicate we are observing a different phenomenon. We propose that the Ic ∝ ε3/2 relation arises from the space charge limitation of current flow from the payload to the chamber wall. The sudden change in the payload potential/beam current relationship results when the beam is partially reflected toward BERT by a virtual cathode which forms at the threshold current. The appearance of HF waves can be attributed to electron density enhancement in this virtual cathode or beam stagnation region. A simple one‐dimensional, analytical model is presented to explain the Ic ∝ ε3/2 proportionality and the generation of HF waves.
The sensitivity of synthetic aperture radiometers for remote sensing applications from space
Authors: Le Vine David M.
Published: February 2008

Aperture synthesis offers a means of realizing the full potential of microwave remote sensing from space by helping to overcome the limitations set by antenna size. The result is a potentially lighter, more adaptable structure for applications in space. However, because the physical collecting area is reduced, the signal‐to‐noise ratio is also reduced and may adversely affect the radiometric sensitivity. Sensitivity is an especially critical issue for measurements from low Earth orbit because the motion of the platform (about 7 km/s) limits the integration time available for forming an image. The purpose of this paper is to develop expressions for the sensitivity of remote sensing systems which use aperture synthesis. The objective is to develop basic equations general enough to be used to obtain the sensitivity of the several variations of aperture synthesis which have been proposed for sensors in space. The conventional microwave imager (a scanning total power radiometer) is treated as a special case, and the paper concludes with a comparison of three synthetic aperture configurations with the conventional imager.
On the theory of electromagnetic scattering from a raindrop splash
Authors: Wetzel L. B.
Published: February 2008

Electromagnetic scattering from a raindrop splash on a water surface is examined in terms of the splash structures that have been disclosed by high‐speed photography. Of the three basic scattering features, the “crown,” the “stalk,” and the “ring wave,” the first two are modeled as dielectric cylinders, while the third is treated by a perturbation approximation. Cross‐section predictions based on heuristic application of these models are found to be in good agreement with laboratory measurements of individual splash‐scattering events. A statistical model in which surface slope and stalk height distributions are taken into account is proposed for extending these results to natural rain on a real water surface. Unfortunately, there is at present insufficient experimental data to allow a reasonable test of the theory. Nevertheless, a few qualitative conclusions can be drawn from the formalism: the major scattering feature is the stalk, and while the vertically polarized returns will have only a weak dependence on rain rate, the horizontally polarized returns will depend strongly on both the rain rate and the shape of the stalk (or drop) size distribution curves.
Permo‐Triassic reconstruction of western Pangea and the evolution of the Gulf of Mexico/Caribbean region
Authors: Pindell James , Dewey John F.
Published: February 2008

A Permo‐Triassic reconstruction of western Pangea (North America, South America, Africa) is proposed that is characterized by (1) definition of the North Atlantic fit by matching of marginal offsets (fracture zones) along the opposing margins, (2) a South Atlantic fit that is tighter than the BuIlard fit and that is achieved by treating Africa as two plates astride the Benue Trough and related structures during the Cretaceous, (3) complete closure of the Proto‐Atlantic Ocean between North and South America, accomplished by placing the Yucatan block between the Ouachita Mountains and Venezuela, (4) a proposed Hercynian suture zone that separates zones of foreland thrusting from zones of arc‐related magmatic activity; to the northwest of this suture lie the Chortis block and Mexico and most of North America, and to the southeast lie South America, the Yucatan Block, Florida and Africa, and (5) satisfaction of paleomagmatic data from North America, South America, and Africa. Beginning with the proposed reconstruction, the relative motion history of South America with respect of North America is defined by using the finite difference method. Within the framework provided by the proposed relative motion history, an evolutionary model for the development of the Gulf of Mexico and Caribbean region is outlined in a series of 13 plate boundary reconstructions at time intervals from the Jurassic to the present. The model includes (1) formation of the Gulf of Mexico by 140 Ma, (2) Pacific provenance of the Caribbean plate through the North America‐South America gap during Cretaceous time, (3) Paleocene‐Early Eocene back arc spreading origin for the Yucatan Basin, whereby Cuba is the frontal arc and the Nicaragua Rise‐Jamaica‐Southern Hispaniola is the remnant arc, and (4) 1200 km of post‐Eocene cumulative offset along both the Northern and Southern Caribbean Plate Boundary Zones, allowing large‐scale eastward migration of the Caribbean plate with respect to the North and South American Plates.
The Limpopo Mobile Belt: A result of continental collision
Authors: Light M. P. R.
Published: February 2008

The 600‐km‐long Limpopo Mobile Belt is discussed within the frame of a Proterozoic supercontinent model [Piper, 1976]. Evidence is presented that the Rhodesian and Kaapvaal cratons may have been separated by distances of more than 1000 km of oceanic crust. From about 3350 Ma ago the Kaapvaal Craton appears to have been driven intermittently N, NW, and then WNW against the Rhodesian Craton forming the NE‐SW trending collision zone, the Limpopo Mobile Belt, and all the major fold and fracture patterns found. This movement would be similar to the oblique movement of the Pacific plate into the Aleutian trench. When collision ceased around 2500 Ma ago, it is likely that the Great Dyke and other complexes intruded along release fractures formed at right angles to the compression.
Evolution of the Pannonian Basin System: 2. Subsidence and thermal history
Authors: Royden Leigh , Horváth F. , Nagymarosy A. , Stegena L.
Published: February 2008

Analysis of sedimentation and thermal data indicates that, for most parts of the Pannonian basin, observed heat flow, thermal gradients, rates of thermal subsidence and vitrinite reflectance are about twice those predicted by assuming a uniform extension model for basin formation in late Miocene time. A modified extension model, whereby large amounts of heat are added to the uppermost mantle during extension (roughly equivalent to replacing the entire sub‐crustal lithosphere by asthenosphere), produced results in good agreement with observation and could also account for periods of uplift observed during extension. Crustal extension beneath most parts of the basin is estimated to have been about 80% to 170% (β = 1.8 to 2.7), although in the deepest parts of the basin (deeper than 4 km) crustal extension could have been much greater. Analysis of extension within the Danube and Zala basins indicates that the late Miocene extension in these basins involved the entire lithosphere, but subsidence and heat flow data are not well enough constrained to determine if extra heating is required during extension. On the basis of tectonic and structural data, the Vienna basin has been interpreted as the result of thin‐skinned extensional tectonics above a shallow detachment surface within the upper crust (Royden et al. [this issue]). Analysis of thermal and subsidence data from the northern Vienna basin suggests that little or no heating occurred during basin extension. These data are consistent with a thin‐skinned extensional origin for the Vienna basin, and are in better agreement with this interpretation than with the assumption of a uniformly extended lithosphere beneath the basin. This study emphasizes the need for good thermal, subsidence and structural data in making reconstructions of extensional and thermal histories of sedimentary basins. When such data are available, it is found that a simple uniform extension model does not explain very well the evolution of some sedimentary basins, such as the Vienna and Pannonian basins. In the first instance, the basin is thought to be the result of upper crustal extension only, due to its special tectonic setting, in the second instance, the extra heating during extension is due to some unknown processes in the lower lithosphere that may be a general feature of lithospheric extension. Thus, lithospheric extension (and associated heating) may be distributed in a variety of ways; not all extensional sedimentary basins form in the same way. Application of a uniform subsidence model to basins for which good thermal, subsidence and structural data are not available (or not properly analysed) can lead to reconstructions of thermal histories in error by a factor of 2 or more.
accreted terranes in the northern part of the Philippine Archipelago
Authors: Karig Daniel E.
Published: February 2008

The Philippine Archipelago consists of a complex array of ophiolites, continental fragments and island arc elements that can be identified as accreted terranes, similar to those increasingly recognized as components of orogenic zones. The northern Philippines, including Luzon, Mindoro and nearby smaller islands, can be divided into at least six of these tectonic elements. From west to east across central Luzon there are the Neogene accretionary prism of the West Luzon Arc, the Eocene Zambales ophiolite, the Cretaceous Angat ophiolite, and a late Cretaceous‐early Paleogene volcanic arc built on an older metamorphic basement. This arc terrane is repeated by offset along the Philippine Fault. To the south, the western Luzon terranes are juxtaposed against the metamorphic basement block of Mindoro, which itself is colliding with the North Palawan microcontinental fragment. The ophiolites appear to have originated in back arc basins rather than in oceanic plateaus, and the metamorphic belts have protoliths indicating deformation along active margins, perhaps deep within accretionary prisms. The Philippine terranes are interpreted as fragments that originated within the complex Pacific‐Eurasian plate boundary rather than as intra‐Pacific basin units. These terranes have been assembling at least since the Oligocene by strike‐slip and convergent displacements. Strike‐slip displacement, either along transcurrent faults or as a component of convergence played a very important, if not dominant, role in this assembly. Most terranes identified in the northern Philippine appear to be plate fragments, with attached crust and upper mantle. Their characteristics contrast with those usually interpreted for terranes in the North American Cordillera, where near‐orthogonal convergence and shallow dipping terrane sutures are favored.
Archaean plate tectonics revisited 2. Paleo‐sea level changes, continental area, oceanic heat loss and the area‐age distribution of the ocean basins
Authors: Abbott Dallas H.
Published: February 2008

In a previous paper, we derived plate tectonic models for continental accretion from the early Archaean (3800 m.y. B.P.) until the present. The models are dependent upon the number of continental masses, the seafloor creation rate and the continental surface area. The models can be tested by examining their predictions for three key geological indicators: sea level changes, stable isotopic evolution (e.g., continental surface area), and oceanic heat loss. Models of paleo‐sea level changes produced by the accretion of the continents reproduce the following features of earth history: (1) greater continental emergence (lower sea level) during the Archaean than the Proterozoic; (2) maximum continental emergence about 3000 m.y. B.P.; and (3) maximum continental submergence (high sea level) from 30 to 125 m.y. B.P. The high sea level stand between 380–525 m.y. B.P. is only weakly reproduced, probably due to the simplified nature of the model. Changes in the number of continental masses can result in tectonic erosion or accretion of the continents, with resulting changes in sea level. The two major transgressions in the Phanerozoic, although still requiring some increase in the total terrestrial heat loss, can be sucessfully explained by a combination of increases in continental surface area and in seafloor creation rate. Changes in the total heat loss of the ocean basins predicted by our plate tectonic models closely parallel the changes in terrestrial heat production predicted by Wasserburg et al. (1964). This result is consistent with thermal history models which assume whole mantle convection. The history of changes in continental surface area predicted by our best continental accretion models lies within the ranges of estimated continental surface area derived from independent geochemical models of isotope evolution.
A balanced section across the Pyrenean Orogenic Belt
Authors: Williams Graham D. , Fischer Michael W.
Published: February 2008

Evolutionary models that have been proposed for the Pyrenean orogenic belt involve gravitational gliding of major thrust sheets to both the north and south of an uplifted central Axial Zone. It has been suggested by previous workers that uplift is a result of Alpine compression, or long lived strike slip movement on the North Pyrenean Fault. We critically assess these models and propose a new model based on the generation of a thin‐skinned, linked thrust system, due to Alpine collision of Iberia and Europe. Pyrenean Alpine tectonics is dominated by southward thrusting on a major sole fault dipping north at approximately 6° within Hercynian basement. Northerly directed thrusts of the North Pyrenean Zone and Northern Folded Foreland are backthrusts from this sole fault. A total orogenic shortening of 106 km in the central Pyrenees was achieved between the Palaeocene and Oligocene at a time‐averaged rate of 0.62 cm yr−1. A thin‐ skinned model requires that the North Pyrenean Fault is truncated by both northward and southward moving thrusts and occurs in the footwall of the sole fault some 60km north of its present surface trace.
Evidence for mid‐Cretaceous wrench‐faulting in the Methow Basin, Washington: Tectonostratigraphic setting of the Virginian Ridge Formation
Authors: Trexler James H. , Bourgeois Joanne
Published: February 2008

The Cretaceous Methow Basin of north‐central Washington is the southernmost of a series of Mesozoic successor basins in the Canadian Cordillera. The Albian‐Campanian sedimentary sequence there documents a restricted, asymmetric basin, filled by a west‐derived, laterally amalgamated fan‐delta system (the Virginian Ridge Formation), and an east‐derived, stable fluvial‐deltaic system (the Winthrop Formation), followed by a locally derived volcanic sequence (the Midnight Peak Formation). This study focuses on the depositional and tectonic setting of the Albian‐Cenomanian Virginian Ridge Formation. The mid‐Cretaceous Methow Basin is interpreted as a wrench‐fault basin generated in response to transpressive dextral offset and uplift of a highland to the west. Stratigraphy and sedimentology of the Albian‐Cenomanian Methow sequence indicates that (1) the basin was asymmetric normal to its axis, in that the western margin was a mobile zone generating considerable relief while the eastern margin was passive, stable, and of relatively low relief; (2) the basin was asymmetric along its axis, documenting transpression and dextral offset along the western margin; (3) the relatively short and steep fan‐delta system deposited along the western margin was laterally amalgamated and possibly time‐transgressive to the north. This basin and similar, coeval successor basins to the north may record extensive transtensile‐transpressive mobility along the Cordillera in middle to Late Cretaceous time.
Geological manifestations of ridge collision: Evidence from the Golfo de Penas‐Taitao Basin, southern Chile
Authors: Forsythe Randall , Nelson Eric
Published: February 2008

Recent geological and geophysical studies in the southern Andes adjacent to the intersection of the Chile Rise with the Peru‐Chile Trench (ANT‐NAZ‐SAM triple junction) have revealed a number of features and a Neogene geologic history that are unique along the Pacific margin of South America. This history includes (1) development of a Tertiary‐Quaternary marine basin with up to 3 km of sediment infill (Golfo de Penas‐Taitao basin, GTB), (2) disruption of the region by a series of faults with both normal and strike slip movements, and (3) localization of silicic, near‐trench volcanism and epizonal plutonism and related hydrothermal activity. The northern portion of the GTB began to subside in the Late Miocene (possibly earlier), and has subsequently been deformed, uplifted, and exposed. Gravity and seismic reflection data suggest that the basin continues offshore where it is still actively subsiding today (Golfo de Penas). Subsidence and uplift have thus occurred diachronously in the region, although it is unclear when subsidence began in the Golfo de Penas. Tectonic disruption of the region is likely related to the Liquiñe‐Ofqui fault (LOF), a major, NS‐trending, crustal shear zone that curves westward and terminates in the Golfo de Penas. The LOF has both down‐to‐the‐west and right lateral offset and separates the main Andean Cordillera on the east from a large crustal block (the Chiloe block) on the west. We hypothesize that the GTB has developed as a pull‐apart basin in response to northward movement of the Chiloe block along the LOF. We propose a dynamic model whereby a stress gradient that decreases longitudinally away from the Chile Rise/Peru‐Chile Trench intersection is set up because the youngest, most buoyant, oceanic lithosphere is being subducted at the triple junction. The Chile Rise is viewed as a type of indenter which is acting to drive the Chiloe block northward in front of the northward‐migrating triple junction. This model explains the unique set of geologic features found in the region, and suggests that ridge‐trench interactions may be an important factor in orogenesis at active continental margins.
Structural history of continental volcanic arc rocks, eastern Sierra Nevada, California: A case for extensional tectonics
Authors: Tobisch Othmar T. , Saleeby Jason B. , Fiske Richard S.
Published: February 2008

Mesozoic metavolcanic rocks forming part of the continental volcanic arc along the eastern Sierra Nevada near Mt. Goddard and in the Ritter Range show a complex history related to extensional tectonics. The rocks comprise a thick section of tuffs, breccias, lava flows, sills, and ash‐flow tuffs deposited in a subaerial to subaqueous environment, with some subvolcanic sill‐like plutons. Pb/U ages of the rocks in the Mt, Goddard area range from ca. 130–160 Ma, while rocks in the Ritter Range have a somewhat wider age range as reported previously. Repetition of the section occurs by faulting, and with the exception of parts of the mid‐Cretaceous Minarets Caldera, all the volcanic rocks show a regional slaty cleavage which was subsequently crenulated and/or folded locally. The first cleavage has well‐developed stretching lineations, and does not appear to have been associated with significant folding. Finite strain measurements show considerable variation both in magnitude and symmetry. The Mt. Goddard rocks, however, tend to show slightly higher overall strain magnitude and greater constrictional component than the Ritter Range for rocks of comparable age. Calculations based on the strain data suggest the Mt. Goddard section has been thinned by about 50% normal to bedding, much as that documented previously for rocks in the Ritter Range. Deformation within this part of the continental arc was originally thought to have formed by regional compression during the late Jurassic (Nevadan) orogeny. However, our study indicates that (1) parts of the deformed volcanic section are younger than late Jurassic, (2) Nevadan‐age breaks in deposition are not present, (3) large‐scale folds expected during a regional compression event are not common, and (4) the beds were tilted to a high dip prior to internal deformation. An extensional model is proposed in which beds were rotated to high tilts early in the deformation as a result of listric normal faulting. This normal faulting is thought to have occurred above a regional tumescence related to voluminous magmatism at depth, with preservation of the steeply tilted Goddard and Ritter sections being facilitated by their downward transport along the margins of rising plutons. Flattening and steeply plunging constrictional fabrics superimposed on the tilted sections are related to strain induced by high‐level inflation of magma chambers and downward return flow of the keellike pendants. The main tectonic fabric shown by the continental volcanic arc rocks in the eastern Sierra Nevada is largely of Cretaceous age, rather than Jurassic (Nevadan) as originally supposed. In addition, the deformation, both rotation of beds and subsequent tectonite fabric, appears to be genetically related to the dynamic evolution of the magmatic arc, and not the result of an externally imposed tectonic event.
Late Caledonide Extension in western Norway: A response to extreme crustal thickening
Authors: Norton M. G.
Published: February 2008

Imbrication of the north‐west margin of the Baltic Shield during the mid‐Silurian continental collision caused continental “subduction” as recorded by the eclogites of the Western Gneiss Region of western Norway (Griffin et al., 1986). During early Devonian times bouyancy forces resulting from the extreme crustal thickening initiated a period of extension which led to the development of a major westerly dipping extensional fault affecting the whole thickness of the imbricated margin. As the footwall of this fault was uplifted the erosional products were deposited on the hanging wall to form a series of basins containing thick sequences of coarse clastic continental sediments. Similarities between this extensional regime and that of the Basin and Range province of the western United States are discussed.
The origin of the Bir Zreir rhomb‐shaped graben, eastern Sinai
Authors: Eyal Y. , Eyal M. , Bartov Y. , Steinitz G. , Folkman Y.
Published: February 2008

The Bir Zreir Graben, a rhomb‐shaped depression located in eastern Sinai is well exposed in three dimensions. A nearly horizontal nonconformity between Precambrian crystalline basement and overlying Phanerozoic sediments, contacts of basement plutons and a system of early Miocene basaltic dikes permit very precise mapping of the local structures and the determination of vertical and horizontal displacements along faults. Applying the standard “pull‐apart model” to the Bir Zreir rhomb‐shaped graben predicts greater vertical separations, 3 to 6 times larger, than those observed. An alternative model, based on a rotational movement of the Bir Zreir block, agrees more closely with field evidence. It is concluded that the shape and size of the graben was determined by the original fault pattern, and that its final shape was changed relatively little by later movements. The rotation of the Bir Zreir block resulted from a combination of sinistral displacement along N‐S faults, a change of their trend to NNE, and a regional E‐W extension. The model proposed here does not require the presence of large, deep gaps along the diagonal faults as in “pull‐aparts”.
Structural evolution in thrust belts and relative plate motion: The Upper Pennine Piemont Zone of the internal Alps, southwest Switzerland and northwest Italy
Authors: Baird A. W. , Dewey J. F.
Published: February 2008

The earliest (Ll) extension lineation of the polyphase deformation sequence in the Combin and Zermatt‐Saas Fee Units of the Piemont Zone of the upper Pennine nappes trends roughly NW‐SE and the geochronological and stratigraphical constraints indicate that the nappe transport and the associated stretching lineation occurred between about 100 and 70 Ma. This accords in a general way with the relative motion of the African Plate to the European Plate during the late Cretaceous as determined from reconstructions of the opening of the Atlantic Ocean and suggests that late Cretaceous thrusting in the Swiss Alps was driven fairly directly by the Africa/Europe plate motion.
Collision, rotation, and back‐arc spreading in the region of the Okhotsk and Japan Seas
Authors: Kimura Gaku , Tamaki Kensaku
Published: February 2008

The India‐Eurasia collision caused extensive deformation in the Eurasia Continent since late Eocene time. We propose that back‐arc spreading in the Okhotsk and Japan Seas was related to the movement of microplates relevant to the India‐Eurasia collision. The Kuril Basin of the Okhotsk Sea and the basins of the Japan Sea were formed as back‐arc basins simultaneously. Their late Oligocene to middle Miocene age is constrained by sediment stratigraphy, basement depth, and heat flow data. The movements of two microplates, the Okhotsk and Amuria Plates, are significant for the tectonics of the Okhotsk and Japan Seas. Simultaneous retreat of both microplates from trench hinge lines caused back‐arc spreading in the Kuril Basin and the Japan Sea. The Amuria Plate moved north‐northeastward due to the India‐Eurasia collision. This caused pull‐apart opening of the Baikal Rift along a transform boundary between the Siberia and Amuria Plates and a collision along the Stanovoy Range at its northern margin. This movement triggered a clockwise rotation of the Okhotsk Plate with a component of dextral collision between the Okhotsk and Amuria Plates, which is well observed along the central zone of the Sakhalin‐Hokkaido islands between the two back‐arc plates. The clockwise rotation of the Okhotsk Plate is suggested by the southwestward fan‐shaped opening of the Kuril Basin. The Kuril Basin narrows to the northeast and terminates south of the Kamchatka Peninsula, where a relative rotation pole between the Okhotsk and Kuril forearc plates is located. The Kamchatka Peninsula was a zone of collision on the other side of the clockwise rotating Okhotsk Plate during the opening of the Kuril Basin. The Sredinny Range in the Kamchatka Peninsula is one of the results of the collision between the Okhotsk Plate and the forearc plate of the Kuril Arc. The bending of the Japanese islands occurred in association with the back‐arc spreading of the Yamato Basin of the Japan Sea.
Variscan strain pattern in the Paleozoic series at the Lizard Front, southwest England
Authors: Le Gall Bernard , Darboux Jean René
Published: February 2008

A structural analysis of the Devonian sedimentary Gramscatho formations, South Cornwall, allows us to specify the Variscan strain pattern at the Lizard front. This deformation is consistent with a NNW verging tangential shear which first induces a synmetamorphic folding phase (F1S1) and whose noncoaxial character is emphasized, on different scales, by the existence of a positive deformation gradient toward narrow shear zones, the development of syncleavage noncylindrical folds whose axes tend to be reoriented, in the S1slaty cleavage plane, toward a pervasive stretching lineation (L1) which trends N160°E and by the existence of NNW verging sheath folds. This folding phase evolves finally to tangential structures which induce, over the parautochthonous Gramscatho formations, subhorizontal shear planes bearing strong slickenside lineations trending parallel to L1, lineations which thus represent, on a regional scale, the “tectonic transport” trend of allachthonous units migrating northwards. The existence of such allochthonous units in the South Cornubian area is now well established by the discovery, at the Lizard front, of a Paleozoic (Carboniferous ?) limestone lens wedged under the Lizard hornblendeschist. The structural evolution of the South Cornubian domain is consistent with the “scheme” of a continental platform progressively implicated in a tangential deformation propagating northward. This compression leads, in the internal southern zones, to an earlier (Mid‐Upper Devonian) crustal tangential tectonic which later (Carboniferous) reaches the external domain of England, and it expresses in the Devono‐Carboniferous cover by a tegumentary tectonic. This northward verging tangential pattern is now testified by SWAT (South West Approaches Traverses) profile interpretation.
Seismotectonics of the Lower Cheliff Basin: Structural background of the El Asnam (Algeria) Earthquake
Authors: Meghraoui Mustapha , Cisternas Armando , Philip Hervé
Published: February 2008

The 1980 El Asnam earthquake should be understood within its tectonic environment. A seismotectonic map of the lower Cheliff basin (scale: 1/500,000) has been synthesized from known geologic, tectonic and seismological work on the region, and from satellite photos. The data set was integrated by a computer in order to handle different scales and projections. Several important tectonic features divide the region into 5 domains. Active faults and recent folds are consistent with a NNW‐SSE direction of compression. The Cheliff basin is limited to the south by the Relizane fault. The basin is also crossed by three broken folds, the eastern one being the one associated with the El Asnam fault. Historical and instrumental seisinicity seems to be located at both ends of Relizane fault. It is suggested that the sites corresponding to folds and reverse faulting crossing the basin are relevant to seismic risk. A simple tectonic model is proposed.
A plate‐tectonic model for Late Jurassic Ophiolite Genesis, Nevadan orogeny and forearc initiation, northern California
Authors: Ingersoll Raymond V. , Schweickert Richard A.
Published: February 2008

Recently published age and structural data allow the reconciliation of previously conflicting models for Late Jurassic genesis of the Josephine, Smartville and Coast Range ophiolites, and the Nevadan orogeny in the Klamath Mountains and Sierra Nevada. The resulting model is consistent with the mode of initiation, location and geometry of the Great Valley forearc basin, and with the lack of a significant forearc basin west of the Klamath Mountains. The Coast Range ophiolite formed by backarc spreading west of an east‐facing intraoceanic arc. Soon thereafter, a remnant arc was calved off the west side of this arc, and the Smartville ophiolite formed by backarc (interarc) spreading. During this time, the Sierran phase of the Nevadan orogeny began as the intraoceanic arc encountered the west‐facing continental‐margin arc of North America. An east‐west‐trending calcalkaline dike swarm in the Sierra Nevada foothills may mark the trajectory of the colliding arcs at the initiation of the collision. Simultaneously, a new subduction zone was initiated west of the collision (suture) zone, and this new trench propagated southward, thus trapping the Coast Range ophiolite in the new forearc area south of the Klamath area. Intense deformation in the Sierran region resulted from this collision, and both magmatic arcs became inactive as the last remnant of intervening oceanic crust was subducted. Continued westward relative movement of the North American arc was permitted north of the Sierra Nevada owing to the lack of a colliding intraoceanic arc. The result was the westward rifting of the continental‐margin arc by intraarc spreading, which formed the Josephine ophiolite in the Klamath area. The Klamath phase of the Nevadan orogeny resulted from contraction of the west‐facing intraoceanic arc and Josephine backarc basin beneath the continental margin. Basal sediments of the Great Valley forearc basin were derived primarily from the sutured arc/ophiolite terranes, and were deposited on top of the Coast Range ophiolite, the southern edge of the Klamaths, and the western side of the Sierra Nevada. A new (late Mesozoic) magmatic arc was superposed across the previously accreted terranes, and formed the primary sediment source for the Cretaceous forearc basin.
The stacking of thrust slices in collision zones and its thermal consequences
Authors: Davy Ph. , Gillet Ph.
Published: February 2008

The thermal consequences of stacking‐up thrust slices in collision zones are investigated using simple one dimensional thermal models. The metamorphic evolution (geotherms and (P,T, time) paths) of a given tectonic unit belonging to a crustal stacking wedge made of more than two units is governed by three effects: cooling and pressure decrease associated with erosion, cooling by the lowest units (screen effect), heating by the upper units (cover effect). It is shown that the efficiency of these effects are dependent on the tectonic evolution of the collision zone. The metamorphic evolutions are very sensitive to the following tectonic parameters: the number of thrusted units involved in thickening, the time delay between each thrust and finally the mode of stacking of the different units (over and understacking). It appears that, for a given depth of burial, the temperature increase during uplift is less important in a crust thickened by three or four units than in the case of two units. The screen effect during understacking is more efficient for a short time delay (∼ 10 Ma) between each thrust.Overstacking leads to higher temperatures before uplift when compared to understacking. It is also shown that the thermal perturbation induced in an intermediate unit of the pile is more efficiently recorded when its thickness is rather small (∼ 10 km). It is shown that, for an erosion‐controlled uplift, the shape of the (P,T,t) path depends on the position of the rocks within a given unit and on the unit position within the pile. Finally, the general metamorphic evolutions during crustal thickening (HP‐LT metamorphism and subsequent overprint) are discussed in terms of the previously mentioned parameters. In the case of the Western Alps, it appears that the more or less efficient greenschist overprint of the units involved in thickening can be explained by different time intervals between the thrust events.
Paleoplate tectonics between Cathaysia and Angaraland in inner Mongolia of China
Authors: Wang Quan , Liu Xueya
Published: February 2008

On the basis of recent investigations in southern Inner Mongolia the authors consider that there are two Proterozoic rifts of E–W trend in the northern margin of the North China Platform. The Zhaertay Group and Baiyun'ebo Group of closed lagoon facies or neritic facies were deposited respectively in the two rifts. The lead isotopic dating of carbonaceous limestone from the middle sequence of Baiyun'ebo Group yields an age of 1500 Ma. Along the rifts a series of alkaline volcanics and intrusions is scattered in the Yinshan Mountains and Yanshan Mountains. To the north of the rifts, four ophiolite belts and at least five accreted terranes of various ages have been recognized in the Paleozoic orogenic zone. The presence of the ophiolite suites and these accreted suspect terranes in Inner Mongolia indicates that probably there was an open ocean between Siberia and North China in Paleozoic times, when repeated subduction of the oceanic crust had occurred along both continental margins. The suture line between Cathaysia and Angaraland extends from Linxi to Solon Obo. In the late Permian, epicontinental mountain systems of the two converging continents collided with each other. From the analysis of the tectonic evolution of Inner Mongolia and adjacent areas we conclude that the evolution of the southern margin of the Siberian Platform is approximately the same as the history of activity of the trench‐arc‐basin system in the eastern Asian epicontinental areas during Mesozoic and Cenozoic times but the northern margin of the North China Platform is similar in evolution to the Cordilleran system in western North America.
Tectonic inferences from oxygen isotopes in volcano‐plutonic complexes of the India‐Asia COllision Zone, NW India
Authors: Srimal Neptune , Basu Asish R. , Kyser T. Kurt
Published: February 2008

The India‐Asia collision zone in Ladakh, NW India, is characterized by two major granitic batholiths. The northern, Karakoram granitic complex and the southern, Ladakh granitic complex are separated by thrust‐bound belts of ophiolites, flysch, and calc‐alkaline volcanics (Khardung Volcanics) of Late Paleozoic to Tertiary age. Oxygen isotope analyses of whole rock and coexisting mineral separates indicate that (a) The Ladakh granitic complex belongs to an I type suite with δ18O = +5.6‰ to +6.1‰ and (b) The Karakoram granitic complex comprises two contrasting suites of granitoids, an older, predominantly I type with δ18O = +6.2‰ to + 7.7‰ and a younger S type with δ18O = +9.5‰ to +10.7‰. The Khardung volcanics show wide variation in δ18O values, ranging from +0.75‰ to +10.7‰ indicating isotopic exchange with a meteoric‐hydrothermal convective system. We suggest that the older I type suite of the Karakoram batholith represents Jurassic to Early Cretaceous arc magmatism along the Bangong‐Nujiang‐North Saltoro suture. This implies a continental collision between the Lhasa‐Shyok‐Kohistan block and the Asian plate prior to the Tertiary collision between India and Asia. India‐Asia collision resulted in the rejuvenation of the North Saltoro suture with the emplacement of the younger anatectic granite of the Karakoram batholith.
Injection of Indian crust into Tibetan lower crust: A two‐dimensional finite element model study
Authors: Zhao Wu‐Ling , Morgan W. Jason
Published: February 2008

We propose a model in which the stronger Indian crust injects into the weaker lower crust of Tibet. If the viscosity of the Tibetan lower crust is below a critical value, the continuous advancing of the Indian crust beneath Tibet would produce negligible variation in stresses on the bottom of the stronger brittle Tibetan upper crust and would result in a spatially uniform uplift and a virtually undisturbed Tibetan Plateau surface. This process is analogous to that of a piston rising in a hydraulic jack as additional fluid is forced into the chamber. We find that if the viscosity of the Tibetan lower crust is assumed to be constant throughout, the computed critical viscosity is 6 × 1018 Pa s for the present‐day lower crustal thickness of 58 km. In addition to uniform viscosity, two hypothetical depth‐dependent viscosities are also tested which give rise to essentially the same distribution of stress along the bottom of brittle upper crust. Our model also interprets the 4‐km elevation contrast between the Tibetan Plateau and the Tarim block. A 1∶160 viscosity contrast between the Tibetan and Tarim lower crust is required in order to maintain the current thickening rate of the Tibetan crust (1.2 mm/yr) while keeping the thickness of the Tarim crust unchanged.
Control of Red Sea rift geometry by Precambrian structures
Authors: Dixon Timothy H. , Stern Robert J. , Hussein Ishmael M.
Published: February 2008

The location and geometry of a rift are controlled by some combination of the extensional stress field and preexisting lithospheric structures, unless the lithosphere is perfectly homogeneous. However, the nature and location of these structures may be difficult to identify because of subsidence and sedimentation associated with later rift stages. Two regional north trending Precambrian structures in northeast Africa have been identified that may have influenced the late Cretaceous and Tertiary evolution of the Red Sea. A large (300 km north‐south, 50 km east‐west) structure in northeastern Sudan (the Onib‐Hamisana zone) may be either a late Precambrian suture zone or a zone of transcurrent faulting. Highly deformed island arc and oceanic assemblages as well as associated ultramafic rocks occur throughout the zone. In one locality the arc assemblages are juxtaposed against possible continental margin metasedimentary rocks. To the southeast, on the Sudan‐Ethiopia border, a zone of similar size and orientation occurs and has been termed the Baraka suture zone. Offsets in the trend of the Red Sea coastline and axial trough coincide with both the location and spacing of the Onib‐Hamisana and Baraka zones. That part of the Red Sea immediately adjacent to the Baraka zone also coincides with a seismically active area. We present a model relating these preexisting lithospheric structures, which act as weak zones or stress guides, to the subsequent evolution and geometry of the rift. The rift propagation direction (northwest) is assumed to be perpendicular to regional extensional stress until the rift tip intersects a north trending stress guide at some arbitrary point. Rift propagation then proceeds northward until the zone ends or becomes poorly defined, whereupon northwest propagation resumes. In the resulting plate configuration, the guiding weak zones are observed only on the southwest plate.
Structural evolution of underthrusted sediments, Kodiak Islands, Alaska
Authors: Fisher Donald , Byrne Tim
Published: February 2008

The late Cretaceous to early Tertiary sediments of the Kodiak accretionary complex preserve the earliest deformation associated with underthrusting along a thickly sedimented convergent margin. Because of the thick trench fill, this early deformation resulted in the formation of two distinct structural terranes: (1) coherent terranes of layered turbidites and (2) melange terranes. The earliest deformation (D1) in the coherent terranes is marked by normal faults, mineralized layer‐perpendicular veins in sandstones, and microfaults in shales. These features suggest that σ1 was vertical and that σ3 was horizontal and NW trending during D1. We interpret D1 structures as hydrofractures that formed in flat‐lying sediments with high fluid pressures caused by rapid tectonic loading. In contrast, the melanges appear to record a more protracted and complex history that culminated in structures similar to the D1 structures above. We have recognized three successive, transitional stages in the melanges: (I) breakup of sand beds along cataclastic shear zones with dispersal of sand inclusions within a relatively ductile shale matrix, resulting in the blocks‐in‐matrix character of the melange, (II) development of ductile shear bands that crosscut the melange fabric at a low angle, and (III) hydrofracturing with the formation of calcite and quartz‐filled veins in sandstone inclusions and microfaults in the shales. The sequence of microstructures associated with stages I–III records increased cohesion of the sediments during deformation dominated by layer‐parallel shear. Intense mineralization and microfaulting during stage III suggest that the melanges are zones of concentrated fluid flow with a fracture dominated permeability. Stage III structures are texturally indistinguishable and contemporaneous with the less pervasive D1 structures in the coherent terranes. Based on these observations, we believe that the melanges are major shear zones that formed at the top of the subducting pile and immediately below a major decollement. The coherent terranes represent the structurally and stratigraphically lowest sediments, and they bypassed the stage I and II deformations of the melanges because they were the greatest distance from the decollement when they were deformed. Moreover, both the melange and coherent terranes appear to have bypassed the shallow zone of intense horizontal shortening that dominates the toe of the overriding accretionary prism.