A novel approach to estimate iron distribution within different pore domains of structured media     

Wiwat Kamolpornwijit  Scott C. Brooks  Young-Jin Kim  Timothy D. Scheibe 《Applied Geochemistry》2007,22(12):2630

The Fe content of soils and aquifer solids is usually quantified using different extraction solutions performed with homogenized samples in a well-mixed batch experiment. For structured media where preferential flow prevails over the matrix flow, however, the Fe content determined from homogenized samples may not well represent the Fe available for biogeochemical reactions. In this study ammonium oxalate extraction was performed on a core of intact saprolite where physical structure was preserved. An unsaturated flow setup was modified with the intent of allowing the extraction under two pore tensions, 15 and 0 cm of water, although a malfunctioning vacuum regulator made this more difficult than anticipated. Approximately 85% of the oxalate-extractable Fe was contained within the finer pore domain (matrix potential larger than 15 cm). Less than 15.5% of the extracted Fe mass (an upper bound) was present in domains of pore tension less than15 cm. To the extent that Fe(III) oxides play an important role in contaminant biogeochemistry and solute transport, their distribution in structured subsurface media is critical to the understanding of these processes.  相似文献   

Collision leading to multiple-stage large-scale extrusion in the Qinling orogen: Insights from the Mianlue suture   总被引：10，自引：5，他引：10  

Sanzhong Li  Timothy M. Kusky  Lu Wang  Guowei Zhang  Shaocong Lai  Xiaochun Liu  Shuwen Dong  Guochun Zhao 《Gondwana Research》2007,12(1-2):121

The geologic framework of the Phanerozoic Qinling–Dabie orogen was built up through two major suturing events of three blocks. From north to south these include the North China craton (including the north Qinling block), the Qinling–Dabie microblock, and the South China craton (including the Bikou block), separated by the Shangdan and Mianlue sutures. The Mianlue suture zone contains evidence for Mesozoic extrusion tectonics in the form of major strike–slip border faults surrounding basement blocks, a Late Paleozoic ophiolite and a ca. 240–200 Ma thrust belt that reformed by 200–150 Ma thrusts during A-type (intracontinental) subduction. The regional map pattern shows that the blocks are surrounded by complexly deformed Devonian to Early Triassic metasandstones and metapelites, forming a regional-scale block-in-matrix mélange fabric. Five distinct tectonic units have been recognized in the belt: (1) basement blocks including two types of Precambrian basement, crystalline and transitional; (2) continental margin slices including Early Paleozoic strata, and Late Paleozoic fluviodeltaic sedimentary rocks, proximal and distal fan clastics, reflecting the development of a north-facing rift margin on the edge of the South China plate; (3) out of sequence oceanic crustal slices including strongly deformed postrift, deep-water sedimentary rocks, sheeted dikes, basalts, and mafic–ultramafic cumulates of a Late Paleozoic ophiolite suite, developing independent of the rift margin in a separate basin; (4) out-of-sequence island-arc slices; (5) accretionary wedge slices. All the tectonic units were deformed during three geometrically distinct deformation episodes (D₁, D₂ and D₃ during 240–200 Ma). Units 2–4 involved southward thrusting and vertical then southward extrusion of about 20 km of horizontal displacement above the autochthonous basement during the D₁ episode. Thrust slices 20 km south of the Mianlue suture are related to this vertical extrusion due to the same rock assemblages, ages and kinematics. The D₂ and D₃ episodes folded all the units in a thick-skinned style about east–west (D₂) and west–northwest (D₃) axes in the Mianlue suture zone. An early foreland propagating sequence of accretion of Late Paleozoic rocks deposited above the Yangtze craton is not involved in D₁ deformation but is temporally equivalent to the D₂ and D₃ deformation in the Mianlue suture. Two stages of strike–slip faulting mainly occurred at the end of D₂ and D₃, respectively. During D₂ deformation, the Bikou block was obliquely indented to the ESE into the Mianlue suture, rather than being thrust over the Mianlue suture from the north as a part of the Qinling–Dabie microblock. During D₃ deformation, however, the Bikou block was bounded by the south boundary fault of the Mianlue suture, and the Yangpingguan fault on the south. These faults are coeval strike–slip faults, but of opposite senses, and accommodated minor southwestward extrusion of the Bikou block into Songpan–Ganze orogen. The other basement blocks north of the Mianlue suture were extruded eastward by about 20 km of lateral displacement, based on the offset of the Wudang dome, during the D₃ episode due to the northeastward indentation of the Hannan complex of the South China craton. Post-D₃ emplacement of granite, cutting across the strike–slip faults such as the Mianlue suture, provides a minimum age of 200 Ma for D₃ deformation. Therefore, based on insights from the evolution of the Mianlue suture, the D₂ and D₃ episodes in the Mianlue suture and its neighbors are not responsible for and associated with the two-stage extrusion of the Dabie UHP-HP terranes from the Foping dome to the present erosional surface (more than 350 km).  相似文献   

Tectonic evolution of China and adjacent crustal fragments   总被引：6，自引：6，他引：6  

Mingguo Zhai  Wenjiao Xiao  Timothy Kusky  M. Santosh   《Gondwana Research》2007,12(1-2):1

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Sila dialogues on climate change: Inuit wisdom for a cross-cultural interdisciplinarity     

Timothy B. Leduc 《Climatic change》2007,85(3-4):237-250

This research begins with the recognition that climate change researchers have become interested in Inuit ecological observations because of the importance of northern changes on the global climate system, but this research often marginalizes Inuit understandings of these climate-related changes. The direct translation of the Inuktitut term Sila in much of this research is a case study in this methodological problem. In contrast to climate research translations of Sila as weather, ethnographies of Inuit conceive of Sila as a spiritual power that is related to the weather. These diverging interpretations of Sila reflect the difficulty of conducting cross-cultural research. To mitigate this difficulty a dialogue was engaged with Inuit concerning their experience of climate change in relation to the different Inuit and Western understandings of Sila. The central goals of this paper are to clearly define Sila so as to identify implications it may have for Western approaches in conducting cross-cultural climate research, and, in the process, to begin a cross-cultural dialogue that aims at an agreed upon understanding of climate change that is respectful of different knowledges.  相似文献   

Why has the market not been created for Channel Tunnel regional passenger rail services?     

Richard Knowles  John Farringtont† 《Area》1998,30(4):359-366

Summary Development benefits from the Channel Tunnel for the British regions beyond London depend largely upon the availability of through rail services to and from Europe. This paper examines the failure of deregulation, privatization and government policy to set up the forecast market in such a way that the British regions are included in the European matrix of high-speed intercity passenger rail services.  相似文献   

Particle fabric in a small, type-2 ignimbrite flow unit (Laacher See, Germany) and implications for emplacement dynamics     

Simon R. Hughes  Timothy H. Druitt 《Bulletin of Volcanology》1998,60(2):125-136

 Ignimbrites of the 13-ka Upper Laacher See Tephra were deposited from small, highly concentrated, moderately fluidized pyroclastic flows. Their unconsolidated nature, and the prominence of accidental Devonian slate fragments, make these ignimbrites ideal for clast fabric studies. The upper flow unit of ignimbrite M14 has characteristics typical of a type-2 ignimbrite. Layer 2a and the lower part of layer 2b of the flow unit have strong, upstream-inclined a[p] fabrics (a[p] means long particle axes parallel to flow direction). Only clasts with a/b axial ratios of 2.5 or greater preserve good a[p] fabrics, whereas the a–b planes of flat fragments dip upstream irrespective of axial ratio. The a-axis fabric becomes weaker, flatter, and more girdle-like in the upper half of layer 2b. At one locality the a-axis fabric appears to rotate 40° up through the flow unit, suggesting either shear decoupling of different levels in the moving flow or unsteadiness effects in a flow depositing progressively at its base. The existence of similarly strong a[p] fabrics in layer 2a and the lower half of layer 2b appears inconsistent with the common interpretation that ignimbrite flow units are emplaced as a plug of essentially non-shearing material (layer 2b) on a thin shear layer (layer 2a), and that the entire flow freezes en masse to form the deposit. The data suggest that, if the flow froze en masse, it was shearing pervasively through at least half its thickness. Another possibility is that the flow unit aggraded progressively from the base up, and that the fabrics record the integrated history of shear directions and intensities immediately above the bed throughout the duration of deposition. Received: 13 February 1997 / Accepted: 4 April 1998  相似文献   

Amphibole zonation in metabasites as a guide to the evolution of metamorphic conditions   总被引：2，自引：0，他引：2  

Timothy J. B. Holland  Stephen W. Richardson 《Contributions to Mineralogy and Petrology》1979,70(2):143-148

In low grade metabasites the amphibole components tremolite, glaucophane, edenite and tschermakite have their activities controlled by interactions with the excess components albite, clinozoisite, chlorite, quartz and H₂O vapor. Three types of reaction are involved, (i) Those in which only components of condensed phases take part: isopleths of equilibrium constant are straight lines in the P-T plane. (ii) Dehydration reactions in which entropy change due to change in Al coordination is of the same sign as that due to dehydration: isopleths of constant K are positive at low pressure and negative at high pressure. (iii) Dehydration reactions in which entropy change due to Al coordination change is opposite in sign to that of dehydration: isopleths of constant K loop in the P-T plane with positive slopes at low and at high pressure. Zonation in naturally occurring amphiboles records the evolution of metamorphic conditions in particular rocks. In an example from the eastern Alps (Austria) early conditions calculated as 15 kb, 200 ° C evolve upgrade to 6 kb, 525 ° C implying concurrent heating and erosion. The record of evolving conditions may span some 30 Ma of geological history.  相似文献   

Antarctic saline lakes—stable isotopic ratios,chemical compositions and evolution     

Osamu Matsubaya  Hitoshi Sakai  Tetsuya Torii  Harry Burton  Knowles Kerry 《Geochimica et cosmochimica acta》1979,43(1):7-25

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Organo-sulfur compounds in sediments of the Puget Sound basin     

Timothy S. Bates  Roy Carpenter 《Geochimica et cosmochimica acta》1979,43(8):1209-1221

Sediment samples from a variety of different environments were analyzed for organo-sulfur compounds (OSC) to provide the first characterization of the amounts and types of these compounds in sediments of the greater Puget Sound basin. A gas Chromatograph equipped with a sulfur specific flame photometric detector was used to quantify individual OSC. Compositions of OSC mixtures were essentially constant throughout the study area. Dibenzothiophene (DBT), its alkylated homologs, and an unknown compound were the predominant OSC in most samples. Concentrations of total OSC and DBT ranged from 4 to 60 and 0.4 to 2 μg/g organic carbon, respectively. The flux of OSC to the sediments at a station in central Puget Sound west of Seattle was approximately 140 ng/cm²/yr. The profile of total OSC concentration with depth showed three organic sulfur compounds that are apparently created in situ in the vicinity of where hydrogen sulfide production begins. The concentrations of the aromatic OSC were relatively constant with depth. Although several anthropogenic sources of OSC were identified, there was no evidence that OSC from these sources were accumulating in the sediments. The major source of the aromatic OSC in the sediments is apparently atmospheric input from natural sources such as forest fires.  相似文献   

Restless river: International law and the behaviour of the rio grande,by J. E. Mueller. Texas Western Press,El Paso, 1975, 151 pp. $5.00. ISBN 0-87404-050-7     

Timothy O'Riordan 《地球表面变化过程与地形》1976,1(3):299-299

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