Five hundred million years of punctuated addition of juvenile crust during extension in the Goochland Terrane,central Appalachian Piedmont Province     

Aaron J. Martin  Irene Kadel-Harder  Brent E. Owens  Kouki Kitajima  Scott D. Samson  Sanjeet K. Verma 《International Geology Review》2020,62(5):523-548

ABSTRACT

The Goochland Terrane is an enigmatic crustal block in the Appalachian Piedmont Province of central Virginia, USA. Sparse exposures of terminal Mesoproterozoic and late Neoproterozoic igneous rocks in the central Goochland Terrane offer the opportunity to investigate both the continental affinity of the terrane during the Proterozoic Eon and the timing and mechanisms of crustal growth. We apply multiple geochemical tools to these rocks: tectonic discrimination using whole-rock major and trace element abundances; whole-rock Sm-Nd isotopes; O, U-Pb, and Lu-Hf isotope analyses of spots in zircon; and measurement of O isotopes in multi-grain quartz separates. Eruption of the Sabot Amphibolite protolith is difficult to date, but we tentatively assign an age of 552 ± 11 Ma. Goochland Terrane continental crust first separated from the mantle prior to ca. 1050–1010 Ma intrusion of the Montpelier Anorthosite and the State Farm Gneiss protolith. The granitic magma that became the State Farm Gneiss protolith could have been derived entirely from partial melting of this initial Goochland Terrane crust. In contrast, the magmas that became the Montpelier Anorthosite, Neoproterozoic granitoid, and the Sabot Amphibolite were mixtures of mantle melt and preexisting Goochland Terrane crust. This production of juvenile continental crust occurred during continental extension and, eventually, rifting. The timing and compositions of terminal Mesoproterozoic magmatism in the Goochland Terrane closely match those in the nearby Blue Ridge Province. Although the compositions of the Neoproterozoic magmas in the two regions are similar, intrusion and possibly eruption occurred about 10 M.y. later in the Goochland Terrane.  相似文献   

Severn Estuary—An appraisal of water quality     

Morlais Owens 《Marine pollution bulletin》1984,15(2):41-47

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Weathering of an Arctic oil spill over 20 years: the BIOS experiment revisited. Baffin Island Oil Spill     

Prince RC  Owens EH  Sergy GA 《Marine pollution bulletin》2002,44(11):1236-1242

A small experimental oil spill was conducted on the northern tip of Baffin Island Nunavut, Canada (72 degrees 31' N, 79 degrees 50' W) in August 1981, and the natural weathering of the oil has been followed by periodic visits. This paper reports on the chemical composition of oil collected in August 2001. The vast majority of the initial oil has gone, but small patches remain. Some samples remain essentially unaltered despite their 20 years of exposure to the elements, while others show that biodegradation and photooxidation can play important roles in removing the majority of the components of the oil. Using 17alpha(H)21beta(H)hopane as a conserved marker within the oil, we show that the most biodegraded sample has lost more than 87% of the hydrocarbons initially present, while another has lost a substantial proportion of its initial chrysene and alkylated congeners. Potential explanations for the different weathering patterns seen in samples collected from this small site are briefly discussed.  相似文献   

Depositional processes and particle characteristics on fans in the Southern Alps, New Zealand     

F.A. de Scally  I.F. Owens   《Geomorphology》2005,69(1-4):46-56

Characteristics of surface particles on four fans dominated by different depositional processes are investigated in the sedimentary ranges of the Aoraki–Mount Cook area, Southern Alps, New Zealand. Statistical testing shows that on three of the fans all indices of particle size and roundness differ significantly according to the depositional process: snow avalanches produce the largest and most angular particles, streamflows the smallest and most rounded, with debris flows in between. On the fourth fan affected by all of these depositional processes, particle size and roundness indicate that snow avalanches are presently dominant with streamflow playing a secondary role. The results also show that all indices of particle size are strongly correlated with each other and suggest that the principal (a-) or intermediate (b-) axis length may provide a satisfactory substitute for more complex indices of size. Indices of particle shape generally do not differ significantly between the fans, reflecting both the strong control exerted on particle shape by source area lithology and structure and the geologic similarity of the four basins. Changes in particle size and roundness occur with down-fan distance on the snow avalanche, debris flow, and hybrid fans but not on the streamflow fan.  相似文献   

Morphometric controls and geomorphic responses on fans in the Southern Alps,New Zealand     

Fes A. de Scally  Ian F. Owens 《地球表面变化过程与地形》2004,29(3):311-322

Morphometric variables associated with 41 debris‐?ow and 18 ?uvial fans and their basins in the Southern Alps of New Zealand are examined. The results show statistically signi?cant differences in the area, maximum elevation, relief and ruggedness (Melton's R) of the basin and the area, gradient, and apex and toe elevations of the fan between debris‐?ow and ?uvial sites. Concavity of the fan longitudinal pro?le also differs between the two fan types, although this could not be tested statistically. Most of these morphometric differences re?ect differences in processes and environmental controls on them. Discriminant analysis indicates that basin area and fan gradient best differentiate the two fan types by process. Moderately strong correlations exist, on both debris‐?ow and ?uvial fans, between basin area or Melton's R and fan area. Correlations between basin area or Melton's R and fan gradient are generally weaker. The results of this study also indicate that on debris‐?ow‐prone fans the fan gradient and basin Melton's R have lower thresholds which overlap little with upper thresholds associated with basins where only stream?ow reaches the fan. These thresholds may therefore have value in preliminary morphometric assessments of debris‐?ow hazard on fans in the Southern Alps. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

岩芯饼裂机制及其对工程地质特性影响的分析   总被引：1，自引：0，他引：1  

李树森  聂德新  任光明 《地球科学进展》2004,(Z1)

提出了岩芯饼裂主要受地应力平均值控制的观点,说明了岩饼表面圆周状对称拉裂坎以及垂直拉裂坎方向擦痕的形成原因,结合工程地质讨论了岩体的弹性模量和内聚力。  相似文献   

3D TABLE-DRIVEN MIGRATION1     

G. BLACQUIRE  H. W. J. DEBEYE  C. P. A. WAPENAAR  A. J. BERKHOUT 《Geophysical Prospecting》1989,37(8):925-958

An efficient full 3D wavefield extrapolation technique is presented. The method can be used for any type of subsurface structure and the degree of accuracy and dip-angle performance are user-defined. The extrapolation is performed in the space-frequency domain as a space-dependent spatial convolution with recursive Kirchhoff extrapolation operators. To get a high level of efficiency the operators are optimized such that they have the smallest possible size for a specified accuracy and dip-angle performance. As both accuracy and maximum dip-angle are input parameters for the operator calculation, the method offers the possibility of a trade-off between these quantities and efficiency. The operators are calculated in advance and stored in a table for a range of wavenumbers. Once they have been calculated they can be used many times. At the basis of the operator design is the well-known phase-shift operator. Although this operator is exact for homogeneous media only, it is assumed that it may be applied locally in case of inhomogeneities. Lateral velocity variations can then be handled by choosing the extrapolation operator according to the local value of the velocity. Optionally the operators can be designed such that they act as spatially variant high-cut filters. This means that the evanescent field can be suppressed in one pass with the extrapolation. The extrapolation method can be used both in prestack and post-stack applications. In this paper we use it in zero-offset migration. Tests on 2D and 3D synthetic and 2D real data show the excellent quality of the method. The full 3D result is much better then the result of two-pass migration, which has been applied to the same data. The implementation yields a code that is fully vectorizable, which makes the method very suitable for vector computers.  相似文献   

Natural Hazards By D. Chapman     

Ian Owens 《New Zealand geographer》1995,51(2):63-63

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Azimuth by the method of multiple timed observations of a gyrotheodolite without electronic registration     

Major Mark C Breach MA MSc ARICS RE 《Journal of Geodesy》1985,59(3):221-232

A method of determining azimuth by gyrotheodolite without electronic registration is described. The method requires observations of time at each instant the moving mark passes a scale division. Thus many observations of time may be achieved in a single oscillation of the moving mark. The observations when used in the appropriate observation equation may determine azimuth with a standard error of ±3″ with 2 hours of observations. This assumes knowledge of the additive constant to about 1″.3 and neglects the effects of dislevelment in the prime vertical. For practical application of the method a time recording device and microcomputer, such as the Hewlett Packard HP41CV and HP85, are recommended.  相似文献   

Numerical modelling of suspended sediment fluxes in estuarine waters     

R. A. Falconer  P. H. Owens 《Estuarine, Coastal and Shelf Science》1990,31(6)

A two-dimensional finite difference numerical model, capable of predicting depth-averaged tidal flow fields in coastal and estuarine waters, has been extended to include tide-induced non-cohesive sediment transport processes. The partial differential equations governing the conservation of mass, momentum and suspended sediment in an incompressible turbulent flow are included in a depth-integrated form in the model. For the representation of the processes of erosion and deposition of sediment from the bed an empirically based source-sink term was refined, based on the results of three mobile bed flume studies. The model has been tested by simulating tidal flows and suspended sediment fluxes in two estuaries, with particular application to the Humber estuary in the U.K. The model was calibrated and found to produce an encouraging degree of agreement between the numerical predictions and corresponding field measurements for this estuary. Furthermore, the predicted gross deposition and erosion features of the estuary were found to be in close agreement with interpretations from Eulerian tidal residual predictions.  相似文献