The Amsterdam-St. Paul volcanic province,and the formation of low Al tholeiitic andesites     

Bernard M. Gunn  Norman D. Watkins  Walter E. Trzcienski  Jacques Nougier 《Lithos》1975,8(2):137-149

The island of St. Paul in the Indian Ocean is located on the axis of the southeastern branch of the Indian Ocean Rise, as is the similar volcano of Amsterdam, 80 km to the north. Both volcanoes and possibly part of the local ridge are formed of a high-alumina plagioclase tholeiite making this a distinctive volcanic province. Lavas with Al₂O₂ contents of 12 to 22% are directly related by plagioclase fractionation. Residual rocks are a distinctive low silica, low alumina, potassic andesite with andesine and even olligoclase feldspar. Parallel lines of evolution exist in the sea floor plagioclase tholeiites, which differ only in slightly lower tenor of Sr and potassium group elements, and in the Steens Mountain tholeiites of Oregon, which differ in their significantly higher Sr and K group elements  相似文献   

Comment onestimation of the transfer function by autoregressive deconvolution techniques—An application to time series analysis by Y. S. Kang,J. J. Royer,Cl. Chambon,and L. Demassieux     

A. J. Watkins  M. S. Ngadiman 《Mathematical Geosciences》1993,25(8):1071-1073

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K-Ar ages of the Brandberg and Okenyenya igneous complexes,north-western Namibia     

R. T. Watkins  I. McDougall  A. P. Le Roex 《International Journal of Earth Sciences》1994,83(2):348-356

K-Ar mineral ages from intrusive units of the Brandberg and Okenyenya igneous complexes, north-western Namibia, confirm the Early Cretaceous age of the subvolcanic centres. The two centres are contemporaneous, although the range of ages from Brandberg, 135.2 ± 1.5 to 125.4 ± 1.3 Ma, suggests a rather longer period of intrusion than is represented by the rocks of Okenyenya, 133.3 ± 1.4 to 129.2 ± 0.7 Ma. The mean K-Ar age of the Okenyenya complex is essentially equivalent to previously determined Rb-Sr ages for the Messum and Paresis complexes on the same igneous lineament, but is a little greater than that suggested recently from Rb-Sr dating of this complex (129.1–123.4Ma). K-Ar chronology for the Brandberg complex is in conflict with the order of emplacement of granite units previously inferred from field evidence. In particular, the Amis peralkaline layered intrusion yields the oldest age from the complex, 135.2 ± 1.4 Ma. The concordancy of age measurements of amphibole and biotite, having very different potassium contents, from single rock samples is compelling evidence that neither inherited radiogenic argon, nor argon loss, presents a significant problem in the dated rocks. If the K - Ar age of 135 Ma for the Amis intrusion is correct, it constrains the minimum age for the onset of Etendeka flood volcanism, associated with continental break-up, as Etendeka lavas exhibit contact metamorphism and metasomatism around the rim of the Brandberg complex.  相似文献   

Wavelet Analysis and Filtering to Identify Dominant Orientations of Permeability Anisotropy     

Loring Watkins  Roseanna M. Neupauer  Gilbert P. Compo 《Mathematical Geosciences》2009,41(6):643-659

An accurate representation of permeability anisotropy is needed to model the rate and direction of groundwater flow correctly. We develop a wavelet analysis technique that can be used to characterize principal directions of anisotropy in both stationary and non-stationary permeability fields. Wavelet analysis involves the integral transform of a field using a wavelet as a kernel. The wavelet is shifted, scaled, and rotated to analyze different locations, sizes, and orientations of the field. The wavelet variance is used to identify scales and orientations that dominate the field. If the field is non-stationary, such that different zones of the field are characterized by different dominant scales or orientations, the wavelet variance can identify all dominant scales and orientations if they are distinct. If the dominant scales and orientations of different zones are similar, the wavelet variance identifies only the dominant scale and orientation of the primary zone. In this paper, we present a combined wavelet analysis and filtering approach to identify all dominant scales and orientations in a non-stationary permeability field. We apply the method to permeability data obtained in the laboratory from the Massillon sandstone.  相似文献   

Intrusives, Extrusives and Linear Magnetic Anomalies     

N. D. Watkins  A. Richardson 《Geophysical Journal International》1971,23(1):1-13

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Secondary mineral formation associated with respiration of nontronite,NAu-1 by iron reducing bacteria     

S?Erin?O'Reilly  Janet?Watkins  Yoko?FurukawaEmail author 《Geochemical transactions》2005,6(4):67

Experimental batch and miscible-flow cultures were studied in order to determine the mechanistic pathways of microbial Fe(III) respiration in ferruginous smectite clay, NAu-1. The primary purpose was to resolve if alteration of smectite and release of Fe precedes microbial respiration. Alteration of NAu-1, represented by the morphological and mineralogical changes, occurred regardless of the extent of microbial Fe(III) reduction in all of our experimental systems, including those that contained heat-killed bacteria and those in which O₂, rather than Fe(III), was the primary terminal electron acceptor. The solid alteration products observed under transmission electron microscopy included poorly crystalline smectite with diffuse electron diffraction signals, discrete grains of Fe-free amorphous aluminosilicate with increased Al/Si ratio, Fe-rich grains, and amorphous Si globules in the immediate vicinity of bacterial cells and extracellular polymeric substances. In reducing systems, Fe was also found as siderite. The small amount of Fe partitioned to the aqueous phase was primarily in the form of dissolved Fe(III) species even in the systems in which Fe(III) was the primary terminal electron acceptor for microbial respiration. From these observations, we conclude that microbial respiration of Fe(III) in our laboratory systems proceeded through the following: (1) alteration of NAu-1 and concurrent release of Fe(III) from the octahedral sheets of NAu-1; and (2) subsequent microbial respiration of Fe(III).  相似文献   

Reply to a paper by C. G. A. Harrison: "Comments on a paper by Watkins and Richardson: 'Intrusives, Extrusives and Linear Magnetic Anomalies'"     

N. D. Watkins  A. Richardson 《Geophysical Journal International》1972,28(2):191-192

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Analysis of Brunhes Epoch Palaeomagnetic Data in Terms of Geocentric and Offset Axial Dipole Fields: Long-Term Flattening of the Dipole Field?     

N. D. Watkins  A. Richardson 《Geophysical Journal International》1975,43(2):501-516

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Age and duration of the réunion geomagnetic polarity event     

Ian McDougall  N.D. Watkins 《Earth and Planetary Science Letters》1973,19(4):443-452

Palaeomagnetic studis on oriented samples from two sequences of olivine basalt lava flows on the island of Réunion together record the Réunion normal polarity event within the Matuyama reversed polarity epoch. Detailed K?Ar dating of the lavas indicates that the Réunion event has a mean age 2.02±0.02 my with a duration estimated to lie within the range 10,000 to 50,000 yr. This could explain the rarity of detection of the event in deep sea sedimentary cores.  相似文献   

Model support for forcing of the 8.2 ka event by meltwater from the Hudson Bay ice dome     

Amy J. Wagner  Carrie Morrill  Bette L. Otto-Bliesner  Nan Rosenbloom  Kelsey R. Watkins 《Climate Dynamics》2013,41(11-12):2855-2873

Previous model experiments of the 8.2 ka event forced by the drainage of Lake Agassiz often do not produce climate anomalies as long as those inferred from proxies. In addition to the Agassiz forcing, there is new evidence for significant amounts of freshwater entering the ocean at 8.2 ka from the disintegration of the Laurentide ice sheet (LIS). We use the Community Climate System Model version 3 (CCSM3) to test the contribution of this additional meltwater flux. Similar to previous model experiments, we find that the estimated freshwater forcing from Lake Agassiz is capable of sustaining ocean and climate anomalies for only two to three decades, much shorter than the event duration of ~150 years in proxies. Using new estimates of the LIS freshwater flux (~0.13 Sv for 100 years) from the collapse of the Hudson Bay ice dome in addition to the Agassiz drainage, the CCSM3 generates climate anomalies with a magnitude and duration that match within error those from proxies. This result is insensitive to the duration of freshwater release, a major uncertainty, if the total volume remains the same. An analysis of the modeled North Atlantic freshwater budget indicates that the Agassiz drainage is rapidly transported out of the North Atlantic while the LIS contribution generates longer-lasting freshwater anomalies that are also subject to recirculation by the subtropical gyre back into the North Atlantic. Thus, the meltwater flux originating from the LIS appears to be more important than the Agassiz drainage in generating 8.2 ka climate anomalies and is one way to reconcile some model-data discrepancies.  相似文献