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Early Cretaceous exhumation of the Qiangtang Terrane during collision with the Lhasa Terrane,Central Tibet 总被引：1，自引：0，他引：1 
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下载免费PDF全文 The timing of the closure of the Bangong Ocean between the Lhasa and South Qiangtang Terranes in central Tibet and the resulting crustal thickening are still under debate. We integrate published apatite fission track and (U–Th)/He thermochronometer data with new zircon (U–Th)/He ages from eight samples and with structural profiles to document that the South Qiangtang Terrane experienced slow exhumation between 200 and 150 Ma, associated with the opening of the Bangong Ocean. Accelerated exhumation (around 0.2–0.3 mm/a) of the South Qiangtang Terrane was initiated at around 150 Ma. This exhumation event is interpreted to reflect collision between the Lhasa and South Qiangtang Terranes after closure of the Bangong Ocean, associated with crustal thickening via thick‐skinned folding and thrusting within the South Qiangtang Terrane. The amalgamation of the Lhasa and South Qiangtang Terranes recorded here may represent the first stage of crustal thickening in the central Tibetan Plateau. 相似文献
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High-resolution X-Band radar measurements of currents,bathymetry and sea state in highly inhomogeneous coastal areas 总被引：1，自引：1，他引：0
Katrin Hessner Konstanze Reichert Jose Carlos Nieto Borge Craig L. Stevens Murray J. Smith 《Ocean Dynamics》2014,64(7):989-998
In this paper, high-resolution wave, current and water depth fields derived by marine X-Band radar are presented for a coastal region of extreme tidal currents in the presence of inhomogeneous bathymetry at the south coast of New Zealand’s North Island. The current and water depth information for the presented location covers an area of approximately 13 km2 with a spatial resolution of 225 m and an update rate of 3 min. The sea state data provides a spatial representation of coastal effects like wave shoaling and refraction forced by bathymetry and current interaction. The near-surface current measurements about 3 km off the coast show expected tidal current pattern with maximum northwest/southeast current of 1.5–2 m/s alongshore. This is in agreement with currents from the RiCOM hydrodynamic model. The spatial resolution of the observed current field exhibits in addition small-scale current features caused by the influence of the local bathymetry. These data demonstrate the insight to be gained in complex, high-energy coastal situations through the use of high-resolution remote sensing techniques. 相似文献
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Konstanze Stübner Raymond Jonckheere Lothar Ratschbacher 《Geochimica et cosmochimica acta》2008,72(13):3184-3199
A simple atomistic Monte Carlo simulation suggests that there are up to four stages in the evolution of an etch pit in the (0 0 1)-surface of an idealised regular lattice. During the first stage, the etch pit is an inverted pyramid; its horizontal and vertical dimensions increase at a constant rate; the apparent horizontal (vh) and vertical (vd) growth rates are faster than during all subsequent stages but nevertheless less than the step retreat rate (vs) on account of surface etching (vv). The pyramid apex is truncated in the second stage; it is thereafter bounded by an expanding bottom plane and shrinking lateral walls; this is accompanied by a gradual decrease of vh; vd drops to a negative value indicating a slow decrease of the etch-pit depth; the bottom plane acquires a concave-up curvature; the outward curvature of the walls, initiated during the first stage, increases. During the third stage the etch pit consists of a single concave-up bottom plane; vh and vd decrease at declining rates; consecutive etch-pit profiles are scalable in the horizontal direction. The hypothetical fourth stage is inferred but not documented by the simulations; it sets in when vh is reduced to zero; unless this corresponds to an as yet unidentified steady-state condition, the etch pit from here on forth shrinks until it eventually disappears altogether. The sole cause for this succession is the process of stochastic rounding of confined steps and faces.The triangular footprint of recoil-track, fission-track, ion-track and dislocation etch pits in trioctahedral mica and its compliance with the monoclinic symmetries implies that the relevant periodic bond chains are O-Mg/Fe-O chains in the octahedral layer. The size distribution of etched recoil tracks is due to (1) depth variations resulting from the size distribution of the latent tracks, (2) the random truncation of the surface tracks, (3) the variable rate of etch-pit enlargement and (4) the fact that new tracks are exposed at the surface due to surface etching. The greater size of dislocation, fission-track and ion-track etch pits is due to their greater extent below the surface. The increase of the number of etched tracks with etching time due to bulk etching is non-linear because the bulk etch rate vv is not constant. The evolution of etch-pit shape with continued etching can also cause loss of tracks due to observation effects related to loss of contrast. 相似文献
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Use of nautical radar as a wave monitoring instrument 总被引：2，自引：0，他引：2
Common marine X-Band radars can be used as a sensor to survey ocean wave fields. The wave field images provided by the radars are sampled and analysed by a wave monitoring system (called WaMoS II) developed by the German research institute GKSS. This measuring system can be mounted on a ship, on offshore stations or at coastal locations. The measurement is based on the backscatter of microwaves from the ocean surface, which is visible as ‘sea clutter' on the radar screen. From this observable sea clutter, a numerical analysis is carried out. The unambiguous directional wave spectrum, the surface currents and sea state parameters such as wave periods, wave lengths, and wave directions can be derived. To provide absolute wave heights, the response of the nautical radar must be calibrated. Similar to the wave height estimations for Synthetic Aperture Radars, the so-called ‘Signal to Noise Ratio' leads to the determination of the significant wave height (HS). In this paper, WaMoS II results are compared with directional buoy data to show the capabilities of nautical microwave radars for sea state measurements. 相似文献
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Flor Vermassen David J. Wangner Laurence M. Dyke Sabine Schmidt Amalie E. Cordua Kurt H. Kjr Konstanze Haubner Camilla S. Andresen 《第四纪科学杂志》2019,34(3):258-267
Records of ice‐rafted debris (IRD) in sediments are commonly used as a proxy for iceberg production and to reconstruct past changes of glacier stability. However, the interpretation of IRD is complex as multiple processes modulate its variability. This study investigates the relationship between IRD variability and glaciological change by measuring IRD records from Upernavik Fjord and comparing these to frontal positions of Upernavik Isstrøm during the past century. Results show that the spatial variability of IRD deposition throughout the fjord is high, indicating that randomness inherent to IRD distorts the calving signal. However, we investigate whether IRD records can be combined to improve the reconstruction, as previously suggested, and show the importance of core site selection and number of cores on this approach. The outer‐fjord core compares relatively well to the observed front positions and this is reflected in the composite record: increased IRD deposition in 1937–1946, 1968–1980, and 1996–1999 occurred during periods of faster retreat. Comparison with climatic records shows that the calving episodes in the late ‘30 s/early ‘40 s and late ‘90 s are related to warm ocean and air temperatures, whereas intensified retreat and calving during the ‘70 s reflects partly an internal glacier response to the fjord geometry. 相似文献
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