Quaternary drainage network reorganization in the Colombian Eastern Cordillera plateau     

Lucía Struth  Emanuele Giachetta  Sean D. Willett  Lewis A. Owen  Eliseo Tesón 《地球表面变化过程与地形》2020,45(8):1789-1804

Dramatic drainage reorganization from initial longitudinal to transversal domains has occurred in the Eastern Cordillera of Colombia. We perform a regional analysis of drainage basin geometry and transformed river profiles based on the integral form of the slope-area scaling, to investigate the dynamic state of drainage networks and to predict the degree of drainage reorganization in this region. We propose a new model of drainage rearrangement for the Eastern Cordillera, based on the analyses of knickpoint distribution, normalized river profiles, landforms characteristic of river capture, erosion rates and palaeodrainage data. We establish that the oldest longitudinal basin captured by the Magdalena River network was the Suárez Basin at ≈409 ka, inferring the timing of abandonment of a river terrace using in situ produced cosmogenic beryllium-10 (¹⁰Be) depth profiles and providing a first estimation of incision rate of 0.07 mm/yr. We integrate published geochronologic data and interpret the last capture of the Sabana de Bogotá, providing a minimum age of the basin opening to the Magdalena drainage at ≈38 ka. Our results suggest that the Magdalena basin Increased its drainage area by integrating the closed basins from the western flank of the Eastern Cordillera. Our study also suggests that the Magdalena basin is an aggressor compared to the basins located in the eastern flank of the orogen and provides a framework for examining drainage reorganization within the Eastern Cordillera and in similar orogenic settings. The results improve our understanding of headward integration of closed basins across orogenic plateaux. © 2020 John Wiley & Sons, Ltd.  相似文献   

Y2K and Other Stories     

Sergei A. Gourevitch  Dale Kyle 《GPS Solutions》1999,3(1):2-4

GPS technology will face not one but two critical rollover dates over the next eight months. One is the millennium (Y2K) rollover. The other is the GPS week 1024 rollover also known as the GPS End of the Week (EOW). Each rollover dat has the potential to cause severe problems in GPS receivers and related software. This article expolres the reasons why these dates are a problem and describes choices that must be made as to their solution. The paper also describes some verification methods that may be used to test GPS receivers and software. ? 1999 John Wiley & Sons, Inc.  相似文献   

High-frequency observations of southern pulsars     

Simon Johnston  Aris Karastergiou  Kyle Willett 《Monthly notices of the Royal Astronomical Society》2006,369(4):1916-1928

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Active sonar detection in shallow water using the Page test   总被引：1，自引：0，他引：1  

Abraham  D.A. Willett  P.K. 《Oceanic Engineering, IEEE Journal of》2002,27(1):35-46

The use of active sonar in shallow water results in received echoes that may be considerably spread in time compared to the resolution of the transmitted waveform. The duration and structure of the spreading and the time of occurrence of the received echo are unknown without accurate knowledge of the environment and a priori information on the location and reflection properties of the target. A sequential detector based on the Page test is proposed for the detection of time-spread active sonar echoes. The detector also provides estimates of the starting and stopping times of the received echo. This signal segmentation is crucial to allow further processing such as more accurate range and bearing localization, depth localization, or classification. The detector is designed to exploit the time spreading of the received echo and is tuned as a function of range to the expected signal-to-noise ratio (SNR) as determined by the transmitted signal power, transmission loss, approximate target strength, and the estimated noise background level. The theoretical false alarm and detection performance of the proposed detector, the standard Page test, and the conventional thresholded matched filter detector are compared as a function of range, echo duration, SNR, and the mismatch between the actual and assumed SNR. The proposed detector and the standard Page test are seen to perform better than the conventional thresholded matched filter detector as soon as the received echo is minimally spread in time. The use of the proposed detector and the standard Page test in active sonar is illustrated with reverberation data containing target-like echoes from geological features, where it was seen that the proposed detector was able to suppress reverberation generated false alarms that were detected by the standard Page test  相似文献   

Development of heterogeneities in the subcontinental Mantle: Evidence from the Ferrar Group,Antarctica     

Philip R. Kyle 《Contributions to Mineralogy and Petrology》1980,73(1):89-104

Tholeiitic lava flows (Kirkpatrick Basalts) and dolerite sills and dikes (Ferrar Dolerites) of the Jurassic Ferrar Group from Antarctica and dolerite sills from Tasmania, Australia are characterised by initial strontium isotope ratios ranging from 0.7089 to 0.7153. The mean and standard deviation of 85 analyses is 0.7115±0.0012. Some of the scatter in the initial ⁸⁷Sr/⁸⁶Sr ratios can be attributed to sample inhomogeneity, analytical uncertainties and sample alteration. The published major element data show well-defined trends that are consistent with an evolution by fractional crystallization. Recognition of a parental magma is difficult due to the fractionated nature of the rocks. Trace element analyses, particularly the rare earth elements (REE) support a differentiation model. Compared to mid-ocean ridge basalts, Ferrar Group rocks are enriched in light REE. Kirkpatrick Basalts from the central Transantarctic Mountains show significant correlations between initial ⁸⁷Sr/⁸⁶Sr ratios and major elements only for SiO₂ and CaO. The general lack of strong correlation is the basis for rejecting the possibility of wholesale contamination by sialic material as a possible cause of the high ⁸⁷Sr/⁸⁶Sr ratios. Selective contamination of the basaltic magmas is a possibility and cannot be completely discounted. It would probably involve a fluid phase in order to transport and mix the light REE, Rb, ⁸⁷Sr, and other elements. By analogy with selective contamination of ocean ridge basalts by sea water it is difficult to envisage a similar process acting on magma emplaced in a non-marine environment. Because of the elevated values of the initial ⁸⁷Sr/⁸⁶Sr ratios, their similar average value over 2,500 km and the large volume of magma involved (4× 10⁵ km³) a mantle origin for the high Sr ratios is preferred. Models to account for the enrichment of Rb and light REE in the Antarctic mantle during or prior to the Jurassic include:

1. addition of continental material from a Palezoic Mesozoic subduction zone;
2. metasomatism of volatile elements from the lower mantle; and
3. evolution of a mantle with a high Rb/Sr ratio.

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Ukinrek Maars, Alaska, I. April 1977 eruption sequence, petrology and tectonic setting     

Juergen Kienle  Philip R. Kyle  Stephen Self  Roman J. Motyka  Volker Lorenz 《Journal of Volcanology and Geothermal Research》1980,7(1-2)

During ten days of phreatomagmatic activity in early April 1977, two maars formed 13 km behind the Aleutian arc near Peulik volcano on the Alaska Peninsula. They have been named “Ukinrek Maars”, meaning “two holes in the ground” in Yupik Eskimo. The western maar formed at the northwestern end of a low ridge within the first three days and is up to 170 m in diameter and 35 m in depth. The eastern maar formed during the next seven days 600 m east of West Maar at a lower elevation in a shallow saddle on the same ridge and is more circular, up to 300 m in diameter and 70 m in depth. The maars formed in terrain that was heavily glaciated in Pleistocene times. The groundwater contained in the underlying till and silicic volcanics from nearby Peulik volcano controlled the dominantly phreatomagmatic course of the eruption.During the eruptions, steam and ash clouds reached maximum heights of about 6 km and a thin blanket of fine ash was deposited north and east of the vents up to a distance of at least 160 km. Magma started to pool on the floor of East Maar after four days of intense phreatomagmatic activity.The new melt is a weakly undersaturated alkali olivine basalt (Ne = 1.2%) showing some transitional character toward high-alumina basalts. The chemistry, an anomaly in the tholeitic basalt-andesite-dominated Aleutian arc, suggests that the new melt is primitive, generated at a depth of 80 km or greater by a low degree of partial melting of garnet peridotite mantle with little subsequent fractionization during transport.The Pacific plate subduction zone lies at a depth of 150 km beneath the maars. Their position appears to be tectonically controlled by a major regional fault, the Bruin Bay fault, and its intersection with cross-arc structural features. We favor a model for the emplacement of the Ukinrek Maars that does not link the Ukinrek conduit to the plumbing system of nearby Peulik volcano. The Ukinrek eruptions probably represent a genetically distinct magma pulse originating at asthenospheric depths beneath the continental lithosphere.  相似文献   

Geochemical constraints on the late-stage evolution of basaltic magma as revealed by composite dikes within the Kangâmiut dike swarm, West Greenland     

Kyle R. Mayborn  Charles E. Lesher  James N. Connelly 《Lithos》2008,104(1-4):428-438

The Kangâmiut dike swarm in West Greenland contains numerous composite dikes with mafic margins and andesitic centers. Internal chilled margins show that the andesitic centers intruded into the middle of the mafic dikes. Major element systematics indicate that the fractionation of olivine, clinopyroxene, plagioclase and Fe–Ti oxides drove the evolution of the Kangâmiut parental magma during its transition from mafic to andesitic compositions. Incompatible trace elements show a marked relative decrease in middle and heavy rare-earth elements (REE) between the mafic margins and the andesitic centers. The decrease in the REE is not explicable by olivine, clinopyroxene, plagioclase and Fe–Ti oxide fractionation or by the fractionation of the accessory phases apatite, zircon or garnet. Rb–Sr and Sm–Nd isotopes from margin and center pairs from these composite dikes are nearly identical indicating that crustal contamination had little to no affect on their evolution. Trace element modeling utilizing the mixing of evolved Kangâmiut magmas and low degree melts derived from partial melting of garnet lherzolite produce excellent fits with the trace element patterns for the andesitic centers. These models suggest that the late-stage evolution of the Kangâmiut dikes included input of mantle melts produced during the end stages of rifting.  相似文献   

High resolution X-ray computed tomography studies of Grasberg porphyry Cu-Au ores,Papua, Indonesia     

J. Richard Kyle  Alison S. Mote  Richard A. Ketcham 《Mineralium Deposita》2008,43(5):519-532

High-resolution X-ray computed tomography (HRXCT) provides unique information of the geological and metallurgical significance for gold and related ore minerals in the supergiant Grasberg porphyry Cu–Au deposit. Digital radiographs have proved to be an effective means of screening samples for the presence of gold for HRXCT studies. Digital radiograph effectiveness is limited by the thickness of samples (typically to ≤2 cm), as well as the associated minerals. Thus, preselecting samples for gold studies using HRXCT is most effective using digital radiographs combined with assay information. Differentiating between metallic mineral grains with relatively small differences in density, e.g., bornite (5.1 g/cm³) from chalcopyrite (4.2 g/cm³), is relatively straightforward for isolated monominerallic grains or composites in a similar lower-density matrix, but difficulties are encountered with the interpretation of typical intergrown ore minerals. X-ray beam-hardening artifacts lead to inconsistency in attenuation determination, both within and among slice images, complicating quantitative processing. However, differentiation of chalcopyrite and bornite has been successful in smaller-diameter (≤22-mm) cores of Grasberg ores. Small-diameter (≤10 mm) cores of the Grasberg stockwork Cu–Au ore were analyzed using HRXCT methods scanned at the minimum spacing currently available (7.5 μm), and data reduction protocols using the Blob3D program were modified to improve the quantification of grain sizes and shapes. Grains as small as 6.5 μm have been identified. All of these grains are in direct contact with chalcopyrite, providing support for gold distribution in porphyry copper systems being a result of exsolution from copper sulfides. HRXCT scanning (±digital radiography) precisely defines the in situ location of mineral grains of interest within a sample, which then can be studied in conventional petrographic sections, and other types of analytical studies conducted, e.g., gold trace element geochemistry.  相似文献   

Denitrification in intact sediment cores from a constructed wetland: Examining the isotope pairing technique     

Kyle S. Herrman  Jeffrey R. White   《Applied Geochemistry》2008,23(8):2105-2112

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Coupled numerical–analytical approach to landscape evolution modeling          下载免费PDF全文

Sean D. Willett  Frédéric Herman  Jean Braun 《地球表面变化过程与地形》2014,39(4):522-545

The Earth's topography is shaped by surface processes that operate on various scales. In particular, river processes control landscape dynamics over large length scales, whereas hillslope processes control the dynamics over smaller length scales. This scale separation challenges numerical treatments of landscape evolution that use space discretization. Large grid spacing cannot account for the dynamics of water divides that control drainage area competition, and erosion rate and slope distribution. Small grid spacing that properly accounts for divide dynamics is computationally inefficient when studying large domains. Here we propose a new approach for landscape evolution modeling that couples irregular grid‐based numerical solutions for the large‐scale fluvial dynamics and continuum‐based analytical solutions for the small‐scale fluvial and hillslope dynamics. The new approach is implemented in the landscape evolution model DAC (divide and capture). The geometrical and topological characteristics of DAC's landscapes show compatibility with those of natural landscapes. A comparative study shows that, even with large grid spacing, DAC predictions fit well an analytical solution for divide migration in the presence of horizontal advection of topography. In addition, DAC is used to study some outstanding problems in landscape evolution. (i) The time to steady‐state is investigated and simulations show that steady‐state requires much more time to achieve than predicted by fixed area calculations, due to divides migration and persistent reorganization of low‐order streams. (ii) Large‐scale stream captures in a strike‐slip environment are studied and show a distinct pattern of erosion rates that can be used to identify recent capture events. (iii) Three tectono‐climatic mechanisms that can lead to asymmetric mountains are studied. Each of the mechanisms produces a distinct morphology and erosion rate distribution. Application to the Southern Alps of New Zealand suggests that tectonic advection, precipitation gradients and non‐uniform tectonic uplift act together to shape the first‐order topography of this mountain range. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献