Robust 24 ± 6 ka Ar/Ar age of a low-potassium tholeiitic basalt in the Lassen region of NE California     

Brent D. Turrin  Michael A. Clynne 《Quaternary Research》2007,68(1):96-110

⁴⁰Ar/³⁹Ar ages on the Hat Creek Basalt (HCB) and stratigraphically related lava flows show that latest Pleistocene tholeiitic basalt with very low K₂O can be dated reliably. The HCB underlies ∼ 15 ka glacial gravel and overlies four andesite and basaltic andesite lava flows that yield ⁴⁰Ar/³⁹Ar ages of 38 ± 7 ka (Cinder Butte; 1.65% K₂O), 46 ± 7 ka (Sugarloaf Peak; 1.85% K₂O), 67 ± 4 ka (Little Potato Butte; 1.42% K₂O) and 77 ± 11 ka (Potato Butte; 1.62% K₂O). Given these firm age brackets, we then dated the HCB directly. One sample (0.19% K₂O) clearly failed the criteria for plateau-age interpretation, but the inverse isochron age of 26 ± 6 ka is seductively appealing. A second sample (0.17% K₂O) yielded concordant plateau, integrated (total fusion), and inverse isochron ages of 26 ± 18, 30 ± 20 and 24 ± 6 ka, all within the time bracket determined by stratigraphic relations; the inverse isochron age of 24 ± 6 ka is preferred. As with all isotopically determined ages, confidence in the results is significantly enhanced when additional constraints imposed by other isotopic ages within a stratigraphic context are taken into account.  相似文献   

Tectonic significance of Late Neoproterozoic granites from the Tibesti massif in southern Libya inferred from Sr and Nd isotopes and U–Pb zircon data   总被引：1，自引：0，他引：1  

Ismail B. Suayah  Jonathan S. Miller  Brent V. Miller  Tovah M. Bayer  John J.W. Rogers   《Journal of African Earth Sciences》2006,44(4-5):561

The Neoproterozoic crust of the Tibesti massif was stabilized by magmatism that included subduction-generated batholithic suites and post-orogenic granite plutons. All of the magmatism occurred in a period of about 20 million years centered around 550 Ma, and nearly all of the granites have initial ⁸⁷Sr/⁸⁶Sr ratios of about 0.706. The Wadi Yebigue pluton has U–Pb zircon ages of 563 Ma and 558 Ma on two different phases and ε_Nd at 550 Ma from −0.5 to −2.2. These isotopic data and the geologic history of the massif suggest that granites in the Tibesti massif developed during and shortly after closure of a short-lived ocean basin that developed by fragmentation of pre-existing continental crust of the Saharan region.  相似文献   

UV-Vis spectrophotometric and XAFS studies of ferric chloride complexes in hyper-saline LiCl solutions at 25-90 °C     

Weihua Liu  Barbara Etschmann  Leone Spiccia  Brent McInnes 《Chemical Geology》2006,231(4):326-349

The speciation and thermodynamic properties of ferric chloride complexes in hydrothermal solutions and hypersaline brines are still poorly understood, despite the importance of this element as a micronutrient and ore-component. Available experimental data are limited to room temperature and relatively low chloride concentrations. This paper reports results of UV-Vis spectrophotometric and synchrotron XAFS experiments of ferric chloride complexes in chloride concentrations up to 15 m and at temperatures of 25-90 °C. Qualitative interpretation of the UV-Vis spectra shows that FeCl²⁺, FeCl₂⁺, FeCl_3(aq) and FeCl₄⁻ were present in the experimental solutions. As chloride concentrations increase, higher ligand number complexes become important with FeCl₄⁻ predominating in solutions containing more than 10 m at 25 °C. The predominance fields of FeCl_3(aq) and FeCl₄⁻ expand to lower Cl concentrations with increasing T. Both XANES and UV-Vis spectra reveal a major change in the geometry of the complex between FeCl₂⁺ and FeCl_3(aq). EXAFS data confirm that the number of chloride ligands increases with increasing chloride concentration and show that Fe³⁺, FeCl²⁺ and FeCl₂⁺ share an octahedral geometry. FeCl_3(aq) could be either tetrahedral or trigonal dipyramidal, while FeCl₄⁻ is expected to be tetrahedral. EXAFS data support a tetrahedral geometry for FeCl₄⁻, especially at 90 °C, but do not allow to distinguish between a tetrahedral or trigonal dipyramidal geometry for FeCl_3(aq) because of similar Fe-Cl distances. At room temperature, EXAFS data suggest that FeCl_3(aq) may be a mixture of octahedral and tetrahedral or trigonal dipyramidal forms.The room temperature formation constants for three ferric chloride complexes (FeCl₂⁺, FeCl_3(aq) and FeCl₄⁻) determined from the UV data are generally in good agreement with previous studies. Calculations based on the properties extrapolated to 300 °C show that hematite solubility is much higher than previously estimated, and that the high orders complexes FeCl_3(aq) and FeCl₄⁻ are important at high temperatures even in solutions with low chloride concentrations. The accuracy of these properties is limited by a poor understanding of activity-composition relationships in concentrated electrolytes, and by limitations in the available experimental techniques and extrapolation algorithms; however, the inclusion of higher order complexes in numerical models of ore transport and deposition allows for a more accurate qualitative prediction of Fe behaviour in hydrothermal and hypersaline systems.  相似文献   

Ashtech轨迹接收机在外业     

谢世杰 《四川测绘》2000,23(2)

美国ＤＢＢ测量公司于 1998年 10月购进Ａｓｈｔｅｃｈ公司最新产品“轨迹”单频ＧＰＳ接收机 ,以及两台ＨＰ - 48　ＧＸ电子手薄、轨迹后处理软件、红外数据通信装置及相应附件。主要用于静态控制测量、工程测量、动态地形测量和陆地勘界测量。轨迹系统的问世促使我们重新考虑ＧＰＳ技术在测绘各领域的深入应用。目前 ,ＧＰＳ外业中通常采用两台接收机安置在坐标为已知的两个基地站上持续进行静态观测 ,另一台 (或几台 )接收机在各待定点上进行静态观测和动态观测。我们试图找到一种新的测量方法完成今后的测量任务。轨迹的设计思路是 :既…  相似文献   

福建沿海铝质A型花岗岩的地球化学及岩石成因   总被引：78，自引：7，他引：71  

邱检生  王德滋  蟹泽聪史 《地球化学》2000,29(4):313-321

以乌山、金刚山和新村三个典型岩体为例,系统研究了福建沿海铝质Ａ型花岗岩的地质和地球化学特征。研究结果表明,铝质Ａ型花岗岩常含有锰铝榴石、富锰白云母等特征的富铝矿物,化学成分上相对富铝,为一套准铝到弱过铝的岩石组成,并具有贫磷、贫钛,氧化指数较低等特征。与碱性花岗岩相比,其Ｎｂ、Ｔａ、Ｚｒ、Ｈｆ、Ｇａ、Ｙ和Ｚｎ等元素的含量及稀土总量和Ｇａ／Ａｌ比值均偏低,但轻、重稀土的分馏程度（尤其是重稀土的分馏程  相似文献   

Holocene Paleohydrology and Paleoclimate at Treeline, North-Central Russia, Inferred from Oxygen Isotope Records in Lake Sediment Cellulose     

Brent B. Wolfe  Thomas W. D. Edwards  Ramon Aravena  Steven L. Forman  Barry G. Warner  Andrei A. Velichko  Glen M. MacDonald 《Quaternary Research》2000,53(3):319

Lake-water oxygen-isotope histories for three lakes in northern Russia, derived from the cellulose oxygen-isotope stratigraphies of sediment cores, provide the basis for preliminary reconstruction of Holocene paleohydrology in two regions along the boreal treeline. Deconvolution of shifting precipitation δ¹⁸O from secondary evaporative isotopic enrichment is aided by knowledge of the distribution of isotopes in modern precipitation, the isotopic composition of paleo-waters preserved in frozen peat deposits, as well as other supporting paleoclimatic information. These data indicate that during the early Holocene, when the boreal treeline advanced to the current arctic coastline, conditions in the lower Yenisey River region were moist compared to the present, whereas greater aridity prevailed to the east near the lower Lena River. This longitudinal moisture gradient is consistent with the suggestion that oceanic forcing (increased sea-surface temperatures in the Nordic Seas and reduced sea-ice cover) was a major contributor to the development of a more maritime climate in western Eurasia, in addition to increased summer insolation. East of the Taimyr Peninsula, large tracts of the continental shelf exposed by glacial sea-level drawdown may have suppressed maritime climatic influence in what are now coastal areas. In contrast, during the late Holocene the two regions have apparently experienced coherent shifts in effective moisture. The similarity of the records may primarily reflect reduced North Atlantic influence in the Nordic Seas and southward retreat of coastline in eastern Siberia, coupled with declining summer insolation.  相似文献   

Chemostatic behaviour of major ions and contaminants in a semiarid spring and stream system near Los Alamos,NM, USA          下载免费PDF全文

Jace M. Koger  Brent D. Newman  Timothy J. Goering 《水文研究》2018,32(11):1709-1716

Recent studies have focused on the relationship between solute concentrations and discharge in streams, demonstrating that concentrations can vary little relative to changes in discharge (chemostatic behaviour). Chemostatic behaviour is dependent on catchment characteristics (e.g., lithology, geomorphology, and vegetation) and chemical characteristics of the solute (e.g., availability, reactivity, and mobility). An investigation of 3 springs and a stream near Los Alamos, NM, reveals that springs can behave in a chemostatic fashion as stream systems tend to do. Another unique finding of this study is that the anthropogenic contaminants barium and the high explosive RDX (hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine) can also behave chemostatically. The chemostatic behaviour of a contaminant has important implications for the residence time of contaminants in a system as well as having a major control on contaminant flux and mass transport. Redox (reduction–oxidation) and biogeochemically sensitive analytes (e.g., Fe, SO₄, and NO₃) display a combination of chemostatic and chemodynamic behaviour, showing the influence of temporally variable conditions on stream and spring chemistries.  相似文献   

Spatially resolved estimation of ozone-related mortality in the United States under two representative concentration pathways (RCPs) and their uncertainty     

Young-Min Kim  Ying Zhou  Yang Gao  Joshua S. Fu  Brent A. Johnson  Cheng Huang  Yang Liu 《Climatic change》2015,128(1-2):71-84

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Present and future Laurentian Great Lakes hydroclimatic conditions as simulated by regional climate models with an emphasis on Lake Michigan-Huron     

Biljana?MusicEmail author  Anne?Frigon  Brent?Lofgren  Richard?Turcotte  Jean-Fran?ois?Cyr 《Climatic change》2015,130(4):603-618

Regional climate modelling represents an appealing approach to projecting Great Lakes water supplies under a changing climate. In this study, we investigate the response of the Great Lakes Basin to increasing greenhouse gas and aerosols emissions using an ensemble of sixteen climate change simulations generated by three different Regional Climate Models (RCMs): CRCM4, HadRM3 and WRFG. Annual and monthly means of simulated hydro-meteorological variables that affect Great Lakes levels are first compared to observation-based estimates. The climate change signal is then assessed by computing differences between simulated future (2041–2070) and present (1971–1999) climates. Finally, an analysis of the annual minima and maxima of the Net Basin Supply (NBS), derived from the simulated NBS components, is conducted using Generalized Extreme Value distribution. Results reveal notable model differences in simulated water budget components throughout the year, especially for the lake evaporation component. These differences are reflected in the resulting NBS. Although uncertainties in observation-based estimates are quite large, our analysis indicates that all three RCMs tend to underestimate NBS in late summer and fall, which is related to biases in simulated runoff, lake evaporation, and over-lake precipitation. The climate change signal derived from the total ensemble mean indicates no change in future mean annual NBS. However, our analysis suggests an amplification of the NBS annual cycle and an intensification of the annual NBS minima in future climate. This emphasizes the need for an adaptive management of water to minimize potential negative implications associated with more severe and frequent NBS minima.  相似文献   

An iterative global pressure solution for the semi-analytical simulation of geological carbon sequestration   总被引：1，自引：0，他引：1  

Domenico Baù  Brent M. Cody  Ana González-Nicolás 《Computational Geosciences》2015,19(4):781-789

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