First-order analysis of deformation of a thrust sheet moving over a ramp     

Philip Berger  Arvid M. Johnson   《Tectonophysics》1980,70(3-4):T9-T24

John L. Rich introduced the revolutionary concept that many folds in the Appalachian Mountains can be explained as superficial structures formed by passive translation of thrust blocks over ramps in detachment surfaces. The amount of layer-parallel shortening can be negligible in the formation of these folds. Rich primarily was concerned with an explanation for the Powell Valley anticline, in the southern Appalachians, but the essential kinematic features of his model of folding have been verified in other folds in the Appalachians, in the Canadian Rockies, in the Idaho-Wyoming thrust belt, and in the Pyrenees. In this paper we solve the boundary-value problem for an idealized thrust block moving over a detachment surface and ramp with zero drag, and produce theoretical fold forms in the thrust block that closely resemble those in Rich's idealized model. The anticline is narrow and rounded if the translation is small, and broad and flat-topped if the translation is large. The limbs of the anticline are symmetric. We also incorporate drag along the ramp part of the detachment surface in order to derive a possible explanation for the asymmetry of dips of the two limbs of the Powell Valley anticline. We show that drag can explain the asymmetry, particularly if drag between relatively competent rocks in opposition at the ramp caused an initial anticline to form as the thrust block began to move, and then drag reduced markedly as relatively soft shales at the base of the block were thrust over competent rocks in the ramp. The existence of the initial anticline should be reflected in asymmetry of the two limbs and in a bulge at the distal edge of the broad anticline.  相似文献   

Rainfall and the 6–9 day wave-like disturbance in West-Africa during summer 1989     

A. Viltard  J. Oubuih  P. de Felice  H. Laurent 《Meteorology and Atmospheric Physics》1998,66(3-4):229-234

Summary Using ECMWF analyses and daily rain amounts of 569 stations in Western Africa for summer 1989, the study documents the composite structure of the 6–9 day oscillation and its influence on rain. Rain is modulated by vorticity as displayed in the wave composite. There are rainfall maxima coincident with cyclonic vorticity and rainfall minima coincident with anticyclonic vorticity at the 700hPa level, at 17.5°N and 7.5°N.With 6 Figures  相似文献   

Footwall mineralization during Late Miocene extension along the West Cycladic Detachment System,Lavrion, Greece     

Alexandra Berger  David A. Schneider  Bernhard Grasemann  Daniel Stockli 《地学学报》2013,25(3):181-191

The West Cycladic Detachment System (WCDS) has been mapped from the western Cycladic islands to Lavrion (mainland Greece), where several top‐to‐SSW low‐angle normal faults at different structural levels are observed. Near the detachment horizon, hydrothermal fluid flow originating from Miocene intrusions lead to high‐temperature carbonate strata‐bound Pb–Ag–Zn ore deposits. Zircon (U–Th)/He cooling ages from the mineralized footwall are 7.1 ± 0.6 to 7.9 ± 0.6 Ma. Carbon‐ and O‐isotope analyses of the carbonate host indicate high water‐to‐rock ratios during brittle deformation‐induced metasomatism, and that this interaction, unrelated to proximity of the intrusions, plays the dominant role in the mineralization. The Late Miocene geology of Lavrion is strikingly similar to Serifos island on the SE termination of the WCDS, both characterized by strong localization of detachment faulting and the interaction of brittle deformation with the injection of fluids related to granitoid intrusions.  相似文献   

Generation?2 testbed of Fresnel imager: first results on the sky     

Laurent Koechlin  Jean-Pierre Rivet  Paul Deba  Truswin Raksasataya  Thierry Gharsa  Ren?? Gili 《Experimental Astronomy》2011,30(2-3):165-182

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Observation of Plasma Instabilities in Quiescent Prominences     

M. Ryutova  T. Berger  Z. Frank  T. Tarbell  A. Title 《Solar physics》2010,267(1):75-94

We study dynamics of quiescent prominences using several data sets taken with the Solar Optical Telescope (SOT) on Hinode. We find a number of processes occurring at different stages of prominence evolution that are common for all of our chosen cases and, having universal character, can be related to fundamental plasma instabilities. We combine the observational evidence and theory to identify these instabilities. Here we discuss three examples: i) prominence cavity formation and its evolution, associated with a screw-pinch instability; ii) development of a regular series of plumes and spikes typical to the Rayleigh?–?Taylor (RT) instability; and iii) the appearance of growing ripples at the prominence/corona interface, often followed by a sudden collimated mass upflow, attributed to the Kelvin?–?Helmholtz (KH) instability. The conditions for transition from a linear (rippling mode) to nonlinear stage of the KH instability, known to have an explosive character, are specified. Given excellent Hinode data, all three aspects of prominence dynamics allow quantitative analysis.  相似文献   

Nitrogen isotopes in the recent solar wind from the analysis of Genesis targets: Evidence for large scale isotope heterogeneity in the early solar system     

Bernard Marty  Laurent Zimmermann  Rainer Wieler  Donald L. Burnett  Peter Bochsler 《Geochimica et cosmochimica acta》2010,74(1):340-19141

We have analyzed nitrogen, neon and argon abundances and isotopic ratios in target material exposed in space for 27 months to solar wind (SW) irradiation during the Genesis mission. SW ions were extracted by sequential UV (193 nm) laser ablation of gold-plated material, purified separately in a dedicated line, and analyzed by gas source static mass spectrometry. We analyzed gold-covered stainless steel pieces from the Concentrator, a device that concentrated SW ions by a factor of up to 50. Despite extensive terrestrial N contamination, we could identify a non-terrestrial, ¹⁵N-depleted nitrogen end-member that points to a 40% depletion of ¹⁵N in solar-wind N relative to inner planets and meteorites, and define a composition for the present-day Sun (¹⁵N/¹⁴N = [2.26 ± 0.67] × 10⁻³, 2σ), which is indistinguishable from that of Jupiter’s atmosphere. These results indicate that the isotopic composition of nitrogen in the outer convective zone of the Sun has not changed through time, and is representative of the protosolar nebula. Large ¹⁵N enrichments due to e.g., irradiation, low temperature isotopic exchange, or contributions from ¹⁵N-rich presolar components, are therefore required to account for inner planet values.  相似文献   

Late Pliocene to Early Quaternary extensional detachment in the La Paz–El Cabo area (Baja California Sur, Mexico): implications on the opening of the Gulf of California and the mechanics of oblique rifting     

Laurent Geoffroy  Julie Pronost 《地学学报》2010,22(1):64-69

We demonstrate that Pliocene to Early Quaternary sedimentary formations in Baja California Sur (Mexico) were deposited syn-tectonically over a major detachment associated with the exhumation of Mesozoic crust. The detachment dips to the ENE and is associated with E–W stretching. This large extensional structure strikes almost parallel to the general trend of the Gulf of California and extension is oblique to the East-Pacific seafloor-spreading direction. Crustal-scale stretching in this area was still active after the beginning of seafloor spreading c.  3.6 Ma ago. The detachment is capped by Late Pleistocene–Holocene alluvial sediments the deposition of which seems to be partly syn-tectonic and controlled by minor stretching subparallel to the present-day North American–Pacific kinematic vector. We discuss the implications of our observations on strain partitioning during opening of the California Gulf as well as on the structure of the Gulf of California margin.  相似文献   

Solving 3D boundary element problems using constrained iterative approach     

Frantz Maerten  Laurent Maerten  Michele Cooke 《Computational Geosciences》2010,14(4):551-564

Some major challenges for geophysicists and structural geologists using three-dimensional boundary element method codes (3D-BEM) are: (1) reducing the amount of memory required to solve large and dense systems and (2) incorporation of inequality constraints such as traction inequality constraints (TIC) and displacement inequality constraints (DIC). The latter serves two purposes. First, for example, inequality constraints can be used to simulate frictional slip (using TIC). Second, these constraints can prevent element interpenetration while allowing opening mode (using DIC). We have developed a method that simultaneously incorporates both types of functionality of the inequality constraints. We show that the use of an appropriate iterative solver not only avoids the allocation of significant memory for solving the system (allowing very large model computation and simplifying parallelization on multi-core processors), but also admits interesting features such as natural incorporation of TICs and DICs. Compared to other techniques of contact management (e.g., Lagrange multipliers, penalty method, or complementarity problem), this new simple methodology, which does not use any incremental trial-and-error procedures, brings more flexibility, while making the system more stable and less subject to round-off errors without any computational overhead. We provide validations and comparisons of the inequality constraints implementation using 2D analytical and numerical solutions.  相似文献   

A new perspective on the significance of the Ranotsara shear zone in Madagascar     

Guido Schreurs  Jörg Giese  Alfons Berger  Edwin Gnos 《International Journal of Earth Sciences》2010,99(8):1827-1847

The Ranotsara shear zone in Madagascar has been considered in previous studies to be a >350-km-long, intracrustal strike-slip shear zone of Precambrian/Cambrian age. Because of its oblique strike to the east and west coast of Madagascar, the Ranotsara shear zone has been correlated with shear zones in southern India and eastern Africa in Gondwana reconstructions. Our assessment using remote sensing data and field-based investigations, however, reveals that what previously has been interpreted as the Ranotsara shear zone is in fact a composite structure with a ductile deflection zone confined to its central segment and prominent NW–SE trending brittle faulting along most of its length. We therefore prefer the more neutral term “Ranotsara Zone”. Lithologies, tectonic foliations, and axial trace trajectories of major folds can be followed from south to north across most of the Ranotsara Zone and show only a marked deflection along its central segment. The ductile deflection zone is interpreted as a result of E–W indentation of the Antananarivo Block into the less rigid, predominantly metasedimentary rocks of the Southwestern Madagascar Block during a late phase of the Neoproterozoic/Cambrian East African Orogeny (c. 550–520 Ma). The Ranotsara Zone shows significant NW–SE striking brittle faulting that reactivates part of the NW–SE striking ductile structures in the flexure zone, but also extends along strike toward the NW and toward the SE. Brittle reactivation of ductile structures along the central segment of the Ranotsara Zone, confirmed by apatite-fission track results, may have led to the formation of a shallow Neogene basin underlying the Ranotsara plain. The present-day drainage pattern suggests on-going normal fault activity along the central segment. The Ranotsara Zone is not a megascale intracrustal strike-slip shear zone that crosscuts the entire basement of southern Madagascar. It can therefore not be used as a piercing point in Gondwana reconstructions.  相似文献   

An Overview of BCC Climate System Model Development and Application for Climate Change Studies          下载免费PDF全文

WU Tongwen  SONG Lianchun  LI Weiping  WANG Zaizhi  ZHANG Hu  XIN Xiaoge  ZHANG Yanwu  ZHANG Li  LI Jianglong  WU Fanghu  LIU Yiming  ZHANG Fang  SHI Xueli  CHU Min  ZHANG Jie  FANG Yongjie  WANG Fang  LU Yixiong  LIU Xiangwen  WEI Min  LIU Qianxi  ZHOU Wenyan  DONG Min  ZHAO Qigeng  JI Jinjun  Laurent LI  ZHOU Mingyu 《Acta Meteorologica Sinica》2014,28(1):34-56

This paper reviews recent progress in the development of the Beijing Climate Center Climate System Model(BCC-CSM) and its four component models(atmosphere,land surface,ocean,and sea ice).Two recent versions are described:BCC-CSM1.1 with coarse resolution(approximately 2.8125°×2.8125°) and BCC-CSM1.1(m) with moderate resolution(approximately 1.125°×1.125°).Both versions are fully coupled climate-carbon cycle models that simulate the global terrestrial and oceanic carbon cycles and include dynamic vegetation.Both models well simulate the concentration and temporal evolution of atmospheric CO_2 during the 20th century with anthropogenic CO2 emissions prescribed.Simulations using these two versions of the BCC-CSM model have been contributed to the Coupled Model Intercomparison Project phase five(CMIP5) in support of the Intergovernmental Panel on Climate Change(IPCC) Fifth Assessment Report(AR5).These simulations are available for use by both national and international communities for investigating global climate change and for future climate projections.Simulations of the 20th century climate using BCC-CSMl.l and BCC-CSMl.l(m) are presented and validated,with particular focus on the spatial pattern and seasonal evolution of precipitation and surface air temperature on global and continental scales.Simulations of climate during the last millennium and projections of climate change during the next century are also presented and discussed.Both BCC-CSMl.l and BCC-CSMl.l(m) perform well when compared with other CMIP5 models.Preliminary analyses indicate that the higher resolution in BCC-CSM1.1(m) improves the simulation of mean climate relative to BCC-CSMl.l,particularly on regional scales.  相似文献