Erratum to: Magmato-sedimentary Carboniferous to Jurassic evolution of the western Tauern window,Eastern Alps (constraints from U-Pb zircon dating and geochemistry)     

Petra Veselá  Frank Söllner  Friedrich Finger  Axel Gerdes 《International Journal of Earth Sciences》2012,101(2):603-603

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Neotectonic basin and landscape evolution in the Eastern Cordillera of NW Argentina,Humahuaca Basin (~24°S)     

Heiko Pingel  Manfred R. Strecker  Ricardo N. Alonso  Axel K. Schmitt 《Basin Research》2013,25(5):554-573

The intermontane Quebrada de Humahuaca Basin (Humahuaca Basin) in the Eastern Cordillera of the southern Central Andes of NW Argentina (23°–24°S) records the evolution of a formerly contiguous foreland‐basin setting to an intermontane depositional environment during the late stages of Cenozoic Andean mountain building. This basin has been and continues to be subject to shortening and surface uplift, which has resulted in the establishment of an orographic barrier for easterly sourced moisture‐bearing winds along its eastern margin, followed by leeward aridification. We present new U–Pb zircon ages and palaeocurrent reconstructions suggesting that from at least 6 Ma until 4.2 Ma, the Humahuaca Basin was an integral part of a largely contiguous depositional system that became progressively decoupled from the foreland as deformation migrated eastward. The Humahuaca Basin experienced multiple cycles of severed hydrological conditions and subsequent re‐captured drainage, fluvial connectivity with the foreland and sediment evacuation. Depositional and structural relationships among faults, regional unconformities and deformed landforms reveal a general pattern of intrabasin deformation that appears to be associated with different cycles of alluviation and basin excavation in which deformation is focused on basin‐internal structures during or subsequent to phases of large‐scale sediment removal.  相似文献   

Stochastic Excitation of Gravity Waves by Overshooting Convection in Solar-Type Stars     

Boris Dintrans  Axel Brandenburg  Åke Nordlund  Robert F. Stein 《Astrophysics and Space Science》2003,284(1):237-240

The excitation of gravity waves by penetrative convective plumes isinvestigated using 2D direct simulations of compressible convection.The oscillation field is measured by a new technique based on theprojection of our simulation data onto the theoretical g-modes solutionsof the associated linear eigenvalue problem. This allows us to determineboth the excited modes and their corresponding amplitudes accurately.  相似文献   

Mach number dependence of the onset of dynamo action     

Nils Erland L. Haugen  Axel Brandenburg  Antony J. Mee 《Monthly notices of the Royal Astronomical Society》2004,353(3):947-952

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The impact of groundwater–surface water interactions on the water balance of a mesoscale lowland river catchment in northeastern Germany     

Stefan Krause  Axel Bronstert 《水文研究》2007,21(2):169-184

The glacially formed northeastern German lowlands are characterized by extensive floodplains, often interrupted by relatively steep moraine hills. The hydrological cycle of this area is governed by the tight interaction of surface water dynamics and the corresponding directly connected shallow groundwater aquifer. Runoff generation processes, as well as the extent and spatial distribution of the interaction between surface water and groundwater, are controlled by floodplain topography and by surface water dynamics. A modelling approach based on extensive experimental analyses is presented that describes the specific water balance of lowland areas, including the interactions of groundwater and surface water, as well as reflecting the important role of time‐variable shallow groundwater stages for runoff generation in floodplains. In the first part, experimental investigations of floodplain hydrological characteristics lead to a qualitative understanding of the water balance processes and to the development of a conceptual model of the water balance and groundwater dynamics of the study area. Thereby model requirements which allow for an adequate simulation of the floodplain hydrology, considering also interactions between groundwater and surface water have been characterized. Based on these analyses, the Integrated Modelling of Water Balance and Nutrient Dynamics (IWAN) approach has been developed. This consists of coupling the surface runoff generation and soil water routines of the deterministic, spatially distributed hydrological model WASIM‐ETH‐I with the three‐dimensional finite‐difference‐based numerical groundwater model MODFLOW and Processing MODFLOW. The model was applied successfully to a mesoscale subcatchment of the Havel River in northeast Germany. It was calibrated for two small catchments (1·4 and 25 km²), where the importance of the interaction processes between groundwater and surface waters and the sensitivity of several controlling parameters could be quantified. Validation results are satisfying for different years for the entire 198 km² catchment. The model approach was further successfully tested for specific events. The experimental area is a typical example of a floodplain‐dominated landscape. It was demonstrated that the lateral flow processes and the interactions between groundwater and surface water have a major importance for the water balance and periodically superimposed on the vertical runoff generation. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Measuring proper motions of isolated neutron stars with Chandra     

Christian Motch  Adriana M. Pires  Frank Haberl  Axel Schwope 《Astrophysics and Space Science》2007,308(1-4):217-224

The excellent spatial resolution of the Chandra observatory offers the unprecedented possibility to measure proper motions at X-ray wavelength with relatively high accuracy using as reference the background of extragalactic or remote galactic X-ray sources. We took advantage of this capability to constrain the proper motion of RX J0806.4-4123 and RX J0420.0-5022, two X-ray bright and radio quiet isolated neutron stars (INSs) discovered by ROSAT and lacking an optical counterpart. In this paper, we present results from a preliminary analysis from which we derive 2σ upper limits of 76 mas/yr and 138 mas/yr on the proper motions of RX J0806.4-4123 and RX J0420.0-5022 respectively. We use these values together with those of other ROSAT discovered INSs to constrain the origin, distance and evolutionary status of this particular group of objects. We find that the tangential velocities of radio quiet ROSAT neutron stars are probably consistent with those of ‘normal’ pulsars. Their distribution on the sky and, for those having accurate proper motion vectors, their possible birth places, all point to a local population, probably created in the part of the Gould Belt nearest to the earth.   相似文献   

Composition of impact melt particles and the effects of post‐impact alteration in suevitic rocks at the Yaxcopoil‐1 drill core,Chicxulub crater,Mexico     

Lutz HECHT  Axel WITTMANN  Ralf‐Thomas SCHMITT  Dieter STFFLER 《Meteoritics & planetary science》2004,39(7):1169-1186

Abstract Petrographical and chemical analysis of melt particles and alteration minerals of the about 100 m‐thick suevitic sequence at the Chicxulub Yax‐1 drill core was performed. The aim of this study is to determine the composition of the impact melt, the variation between different types of melt particles, and the effects of post‐impact hydrothermal alteration. We demonstrate that the compositional variation between melt particles of the suevitic rocks is the result of both incomplete homogenization of the target lithologies during impact and subsequent post‐impact hydrothermal alteration. Most melt particles are andesitic in composition. Clinopyroxene‐rich melt particles possess lower SiO₂ and higher CaO contents. These are interpreted by mixing of melts from the silicate basement with overlying carbonate rocks. Multi‐stage post‐impact hydrothermal alteration involved significant mass transfer of most major elements and caused further compositional heterogeneity between melt particles. Following backwash of seawater into the crater, palagonitization of glassy melt particles likely caused depletion of SiO₂, Al₂O₃, CaO, Na₂O, and enrichment of K₂O and FeO_tot during an early alteration stage. Since glass is very susceptible to fluid‐rock interaction, the state of primary crystallization of the melt particles had a significant influence on the intensity of the post‐impact hydrothermal mass transfer and was more pronounced in glassy melt particles than in well‐crystallized particles. In contrast to other occurrences of Chicxulub impactites, the Yax‐1 suevitic rocks show strong potassium metasomatism with hydrothermal K‐feldspar formation and whole rock K₂0 enrichment, especially in the lower unit of the suevitic sequence. A late stage of hydrothermal alteration is characterized by precipitation of silica, analcime, and Na‐bearing Mg‐rich smectite, among other minerals. This indicates a general evolution from a silica‐undersaturated fluid at relatively high potassium activities at an early stage toward a silica‐oversaturated fluid at relatively high sodium activities at later stages in the course of fluid rock interaction.  相似文献   

SHRIMP U-Pb dating, trace elements and the Lu-Hf isotope system of coesite-bearing zircon from amphibolite in the SW Sulu UHP terrane, eastern China   总被引：3，自引：0，他引：3  

Fulai Liu  Axel Gerdes  Huaimin Xue 《Geochimica et cosmochimica acta》2008,72(12):2973-3000

In this study, we link mineral inclusion data, trace element analyses, U-Pb age and Hf isotope composition obtained from distinct zircon domains of complex zircon to unravel the origin and multi-stage metamorphic evolution of amphibolites from the Sulu ultrahigh-pressure (UHP) terrane, eastern China. Zircon grains separated from amphibolites from the CCSD-MH drill hole (G12) and Niushan outcrop (G13) were subdivided into two main types based on cathodoluminescence (CL) and Laser Raman spectroscopy: big dusty zircons with inherited cores and UHP metamorphic rims and small clear zircons. Weakly zoned, grey-white luminescent inherited cores preserve mineral inclusions of Cpx + Pl + Ap ± Qtz indicative of a mafic igneous protolith. Dark grey luminescent overgrowth rims contain the coesite eclogite-facies mineral inclusion assemblage Coe + Grt + Omp + Phe + Ap, and formed at T = 732-839 °C and P = 3.0-4.0 GPa. In contrast, white luminescent small clear zircons preserve mineral inclusions formed during retrograde HP quartz eclogite to LP amphibolite-facies metamorphism (T = 612-698 °C and P = 0.70-1.05 GPa). Inherited zircons from both samples yield SHRIMP ²⁰⁶Pb/²³⁸U ages of 695-520 Ma with an upper intercept age of 800 ± 31 Ma. The UHP rims yield consistent Triassic ages around 236-225 and 239-225 Ma for G12 and G13 with weighted means of 229 ± 3 and 231 ± 3 Ma, respectively. Small clear zircons from both samples give ²⁰⁶Pb/²³⁸U ages around 219-210 Ma with a weighted mean of 214 ± 3 Ma, interpreted as the age of retrograde quartz eclogite-facies metamorphism. Matrix amphibole from both samples indicate Ar-Ar ages of 209 ± 0.7 and 207 ± 0.7 Ma, respectively, probably dating late amphibolite-facies retrogression. The data suggest subduction of Neoproterozoic mafic igneous rocks to UHP conditions in Middle Triassic (∼230 Ma) times and subsequent exhumation to an early HP (∼214 Ma) and a late LP stage (∼208 Ma) over a period of ∼16 and 6 Myr, respectively. Thus, early exhumation from a mantle depth of 120-100 km to about 60 km occurred at an average rate of 0.3 cm/y, while subsequent exhumation to a middle crustal level took place at approximately 0.54 cm/y. These exhumation rates are considerably slower than those obtained for UHP rocks in the Dora Maira and Kokchetav massifs (2-3 cm/y).Based on similar P-T estimates and trace element and Hf isotope compositions, Sulu amphibolites can be identified as retrograde UHP eclogites. The εHf₍₈₀₀₎ of +8 implies a significant input from the depleted mantle to the Sulu-Dabie terrane during the middle Neoproterozoic. Overgrown rims are characterized by a distinct trace element composition with low Lu/Hf and Th/U and significantly higher ¹⁷⁶Hf/¹⁷⁷Hf ratios than inherited cores, consistent with formation during/after garnet (re-)crystallization and fractionation of the Lu-Hf system during UHP metamorphism. The combined dataset suggests homogenization of the ¹⁷⁶Hf/¹⁷⁷Hf ratio within the metamorphic mineral assemblage and during protolith formation. Observed variations are explained by mixing of material from both domains during laser ablation, e.g., due to partial recrystallization of inherited cores.  相似文献   

U-Pb zircon geochronology of late Neoproterozoic–Early Cambrian granitoids in Iran: Implications for paleogeography, magmatism, and exhumation history of Iranian basement     

Jamshid Hassanzadeh  Daniel F. Stockli  Brian K. Horton  Gary J. Axen  Lisa D. Stockli  Marty Grove  Axel K. Schmitt  J. Douglas Walker 《Tectonophysics》2008,451(1-4):71-96

Eurasia has largely grown to its present enormous size through episodic addition of crustal blocks by recurring birth and demise of oceans such as Paleotethys and Neotethys. Excluding the Kopet Dagh Mountains in the northeast, crystalline basement rocks of various dimensions are exposed in all continental tectonic zones of Iran. These rocks have traditionally been viewed as continental fragments with Gondwanan affinity and summarily been assigned Precambrian or younger ages, despite the fact that evidence from isotopic dating has largely been lacking. This study presents new ion microprobe and thermal-ionization zircon U-Pb geochronological data from granitoids and orthogneisses from several locations in central Iran and the Sanandaj–Sirjan structural zones to determine crystallization ages and investigate the origin and continental affinity of these various crustal fragments. The resulting U-Pb crystallization ages for the granites and orthogneisses range from late Neoproterozoic to Early Cambrian, matching the mostly juvenile Arabian–Nubian shield and Peri-Gondwanan terranes constructed after the main phase of Pan-African orogenesis. TIMS analyses of zircons with inherited cores from western Iran suggest that the Neoproterozoic crust of Iran might not be entirely juvenile, pointing to the potential presence of inherited older Proterozoic components as is common in the eastern Arabian shield. More importantly, the new zircon U-Pb crystallization ages unequivocally demonstrate that crystalline basement underlying the Sanandaj–Sirjan zone, central Iran, and the Alborz Mountains is composed of continental fragments with Gondwanan affiliation, characterized by wide spread late Neoproterozoic subduction-related magmatism. The exposure of these late Neoproterozoic–Early Cambrian basement rocks in the Iranian regions north of the Zagros is structurally controlled and linked to both large-scale crustal extension and exhumation during Mesozoic and Tertiary time as well as Tertiary collisional tectonics associated with the closure of Neotethys.  相似文献   

When timing matters-considering changing temporal structures in runoff response surfaces     

Klaus Vormoor  Ole Rössler  Gerd Bürger  Axel Bronstert  Rolf Weingartner 《Climatic change》2017,142(1-2):213-226

Scenario-neutral response surfaces illustrate the sensitivity of a simulated natural system, represented by a specific impact variable, to systematic perturbations of climatic parameters. This type of approach has recently been developed as an alternative to top-down approaches for the assessment of climate change impacts. A major limitation of this approach is the underrepresentation of changes in the temporal structure of the climate input data (i.e., the seasonal and day-to-day variability) since this is not altered by the perturbation. This paper presents a framework that aims to examine this limitation by perturbing both observed and projected climate data time series for a future period, which both serve as input into a hydrological model (the HBV model). The resulting multiple response surfaces are compared at a common domain, the standardized runoff response surface (SRRS). We apply this approach in a case study catchment in Norway to (i) analyze possible changes in mean and extreme runoff and (ii) quantify the influence of changes in the temporal structure represented by 17 different climate input sets using linear mixed-effect models. Results suggest that climate change induced increases in mean and peak flow runoff and only small changes in low flow. They further suggest that the effect of the different temporal structures of the climate input data considerably affects low flows and floods (at least 21% influence), while it is negligible for mean runoff.  相似文献