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1.
The textural relationships and structural states of optically isotropic labradorite from the Manicouagan, Quebec, impact structure have been examined by light (optical) and transmission electron (TEM) microscopy. Two distinct diaplectic glasses have been recognized based on their contrasting morphology, timing and the inferred modes of formation. The earliest isotropic bands and grain-scale isotropism (maskelynite) optically exhibit a gradational,in situ transformation from crystalline plagioclase with preservation of relict textures (twins, grain boundaries). The same transformation from crystalline to amorphous structure is observed in TEM to occur heterogeneously at scales on the order of the unit cell. The progressive transformation of optical properties reflects an increase in the volume fraction and eventual coalescence of these amorphous units. This maskelynite-type diaplectic glass is interpreted to form in the solid-state directly from crystalline material during the compressional phase of the shock wave. The other isotropic material occurs in spatially discrete tensiongashes and planar deformation features (PDFs) that overprint the maskelynite-type glass. This second type of diaplectic glass (PDF-type) is developed homogeneously within a given glass band and exhibits sharp crystal-glass boundaries, in contrast to the gradational boundaries of the maskelynite-type glass. PDF-type glass is interpreted to form by melting in tensional release zones during passage of the rarefaction wave. These observations emphasize the ability of naturally shocked rocks to preserve subtle evidence of variations in the shock process from highly transient events.  相似文献   

2.
捕虏体麻粒岩是了解下地壳形成和演化的重要样品。汉诺坝新生代玄武岩中的二辉麻粒岩捕虏体样品中富含各种硫化物相,主要类型有:①孤立产出的球状出溶硫化物;②矿物颗粒之间或颗粒内的粗晶硫化物;③次生硫化物包裹体群;④裂隙充填硫化物。电子探针分析表明,硫化物的矿物成分均为贫镍磁黄铁矿,(Ni+Co+Cu)/Fe(原子比)远小于0.2;(Fe+Cu+Co+Ni)/S(原子比)比地幔岩的磁黄铁矿小,多小于0.875,反映了一种S过饱和环境。各种产状的磁黄铁矿中Au、Ag都有一定的含量,其平均值分别为0.19%～0.22%(Au)、0.01%～0.02%(Ag),反映下地壳的麻粒岩化与金矿化的成因联系。磁黄铁矿的Ni、Co、Cu含量与S正相关,说明微量重金属元素与S具有同源的关系,由于地幔去气伴随S而进入下地壳。  相似文献   

3.
Precise determination of REE and Ba abundances in three carbonaceous (Orgueil Cl, Murchison C2 and Allende C3) and seven olivine-bronzite chondrites were carried out by mass spectrometric isotope dilution technique. Replicate analyses of standard rock and the three carbonaceous chondrites demonstrated the high quality of the analyses (accuracies for REE are ±1–2 per cent). Certain carbonaceous chondrite specimens showed small positive irregularities in Yb abundance. The Yb ‘anomaly’ (approximately + 5 per cent relative to the average of 10 ordinary chondrites) in Orgueil may relate to high temperature components. The REE pattern of Guareña (H6) exhibits comparatively extensive fractionation (about factor 2) with a negative anomaly for Eu (17 ± 1 percent) compared to the average H chondrite. This could be interpreted in terms of extensive thermal metamorphism leading to melting.Apart from absolute abundance differences, there appears to be small but recognizable fractionation among the average relative REE abundances of Cl, E, H and L chondrites. However, individual chondrites within these groups showed more or less fractionated REE patterns relative to each other. The distinction between H and L chondrites was well demonstrated in Eu-Sm correlation curves and absolute abundance differences of REE and major elements.Si-normalized atomic ratios of the REE abundances in different kinds of chondrites to those in Orgueil (Cl) chondrite were 0.58 (E), 0.75 (H), 0.81 (L), 1.07 (C2) and 1.32 (C3).  相似文献   

4.
Komatiites are mantle-derived ultramafic volcanic rocks. Komatiites have been discovered in several States of India, notably in Karnataka. Studies on the distribution of trace-elements in the komatiites of India are very few. This paper proposes a simple, accurate, precise, rapid, and non-destructive wavelength-dispersive x-ray fluorescence (WDXRF) spectrometric technique for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites, and discusses the accuracy, precision, limits of detection, x-ray spectral-line interferences, inter-element effects, speed, advantages, and limitations of the technique. The accuracy of the technique is excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Zr, Nb, Ba, Pb, and Th and very good (within 4%) for Y. The precision is also excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th. The limits of detection are: 1 ppm for Sc and V; 2 ppm for Cr, Co, and Ni; 3 ppm for Cu, Zn, Rb, and Sr; 4 ppm for Y and Zr; 6 ppm for Nb; 10 ppm for Ba; 13 ppm for Pb; and 14 ppm for Th. The time taken for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in a batch of 24 samples of komatiites, for a replication of four analyses per sample, by one operator, using a manual WDXRF spectrometer, is only 60 hours.  相似文献   

5.
Eleven surface soil samples from calcareous soils of industrial areas in Hamadan Province, western Iran were analyzed for total concentrations of Zn, Cd, Ni, Cu and Pb and were sequentially extracted into six fractions to determine the bioavailability of various heavy metal forms. Total Zn, Cd, Ni, Cu and Pb concentrations of the contaminated soils were 658 (57–5,803), 125.8 (1.18–1,361), 45.6 (30.7–64.4), 29.7 (11.7–83.5) and 2,419 (66–24,850) mg kg−1, respectively. The soils were polluted with Zn, Pb, and Cu to some extent and heavily polluted with Cd. Nickel values were not above regulatory limits. Copper existed in soil mainly in residual (RES) and organic (OM) fractions (about 42 and 33%, respectively), whereas Zn occurred essentially as RES fraction (about 69%). The considerable presence of Cd (30.8%) and Pb (39%) in the CARB fraction suggests these elements have high potential biavailability and leachability in soils from contaminated soils. The mobile and bioavailable (EXCH and CARB) fractions of Zn, Cd, Ni, Cu, and Pb in contaminated soils averaged (7.3, 40.4, 16, 12.9 and 40.8%), respectively, which suggests that the mobility and bioavailability of the five metals probably decline in the following order: Cd = Pb > Ni > Cu > Zn.  相似文献   

6.
Abstract The 6-km-thick Karmutsen metabasites, exposed over much of Vancouver Island, were thermally metamorphosed by intrusions of Jurassic granodiorite and granite. Observations of about 800 thin sections from the Campbell River and Buttle Lake area show that the metabasites provide a complete succession of mineral assemblages ranging from the zeolite to pyroxene hornfels facies around the intrusion. The most important observations are as follows. (1) The compositional change of Ca-amphiboles with increasing metamorphic grade is not straightforward. The tremolite component decreases from the prehnite–actinolite facies to the greenschist facies with a compensating tschermak component increase, but the tendency is not clear thereafter. Instead, the edenite component increases from the amphibolite facies to the pyroxene hornfels facies. (2) The most pargasitic Ca-amphibole occurs in high-Fe2+/Mg metabasite from the greenschist/amphibolite transition zone. (3) The reasons for such irregular compositional trends, even in the rather uniform MORB-like composition of the Karmutsen metabasites, are non-ideal solid solutions of Ca-amphibole at low temperature and the effective control by bulk rock composition in the amphibolite facies. (4) The data from this study support, but do not prove, a transition loop for the actinolite–hornblende compositional gap rather than a solvus. If the gap is a solvus, its shape is asymmetric, and is highly dependent on the other compositional parameters such as Fe3+/Al and Fe2+/Mg. (5) The XNaA/XA±XAb) ratios between Ca-amphibole and plagioclase are most useful as an indicator of metamorphic grade even within the amphibolite facies, and these change systematically from 0.2 to 0.5 from the greenschist to pyroxene hornfels facies. (6) The compositional trend of Ca-amphibole from the Karmutsen metabasites indicates a typical low-P/T metamorphic facies series on a Rbk–Gln–Tr–Ts diagram.  相似文献   

7.
Nitrate contamination in irrigation groundwater,Isfahan, Iran   总被引：1，自引：1，他引：0  
Groundwater is one of the major sources of water in Isfahan. Efficient management of these resources requires a good understanding of its status. This paper focuses on the hydrochemistry and also it wants to assess the nitrate concentration in irrigation groundwater of Isfahan suburb. All the groundwater samples are grouped into three categories, including Na-Cl + Ca-Cl (63 %), Na-SO4 + Ca-SO4 (23 %) and Ca-HCO3 (14 %). According to the EC and SAR, the most dominant classes are C3S1, C4S2 and C4S3. 55 % of samples indicate very high salinity and medium to very high alkalinity that is not suitable for irrigation. 84 % of the groundwater samples show nitrate contents higher than HAV (13 mg l?), while more than 25 % exceeded the maximum contamination level (44.27 mg l?) according to EPA regulations. The horizontal and vertical distribution patterns of nitrate in groundwater samples show a surficial origin for nitrate contamination. The high nitrate content can be attributed to the agricultural activities along with domestic sewage and industrial wastewaters in populated area. Based on results, using high nitrate groundwater for irrigation can minimize the requirement for inorganic fertilizers and reduce the cost of cultivation and nitrate contamination.  相似文献   

8.
《Applied Geochemistry》2006,21(3):528-545
High mean As concentrations of up to 26.6 μmol/L (1990 μg/L) occur in ground water collected from a fractured-bedrock system composed of sulfidic schist with granitic to dioritic intrusions. Sulfides in the bedrock are the primary source of the As in the ground water, but the presence of arsenopyrite in rock core retrieved from a borehole with As concentrations in the ground water barely above the detection limit of 2.0 μmol/L, shows that there are complicating factors. Chemical analyses of water from 35 bedrock wells throughout a small watershed reveal spatial clustering of wells with high As concentrations. Stiff diagrams and box plots distinguish three distinct types; calcium-bicarbonate-dominated water with low As concentrations (CaHCO3 type), sodium-bicarbonate-dominated water with moderately high As concentrations (NaHCO3 type), and calcium-bicarbonate-dominated water with very high As concentrations (High-As type). It is proposed that differences in recharge area and ground-water evolution, and possible bedrock composition difference are responsible for the chemical distinctions within the watershed. Lack of correlation of As concentrations with pH indicates that desorption of As is an insignificant control on As concentration. Correlations of As concentrations with Fe and redox parameters indicates that reductive dissolution of Fe(III) oxyhydroxides may play a role in the occurrence of high As concentrations in the NaHCO3 and High-As type water. The oxidation of sulfide minerals occurs within the ground-water system and is ultimately responsible for the existence of As in the ground water, but there is no correlation between As and SO4 concentrations, probably due to precipitation of Fe(III) oxyhydroxides and adsorption of As under oxidizing conditions.  相似文献   

9.
Analysis of 3-m sediment cores revealed that profiles of carbon (C), sulfur (S), and iron (Fe) varied with relative distance from marine and terrestrial sediment sources in Tomales Bay California. Despite relatively high sedimentation rates throughout the bay (historically 3–30 mm yr−1), sulfate reduction of deposited organic matter led to free-sulfide accumulation in sediments only at the location farthest from terrestrial runoff, the source of reactive iron. Acid-volatile sulfide concentrations in all sediments (<10 μmol g−1) were low relative to concentrations of chromiumreducible sulfide (up to 400 μmol g−1 farthest from the reactive iron source). A calculated index of iron availability, used to describe sediment resistance to build-up of free sulfide, was lowest at this location. Recent, upward shifts in reactive Fe concentration and in the relative contribution of terrestrial orgnic carbon (measured as a shift in δ13C of bulk sediment organic matter) in all cores indicated that erosion and transport of sediments from the watershed surrounding Tomales Bay increased after European settlement in the 1850s.  相似文献   

10.
Optical constituents as suspended particulate matter (SPM), chlorophyll (Chl-a), colored dissolved organic matter (CDOM), and grain sizes were obtained on a transect in the arctic fjord-type estuary Kangerlussuaq (66°) in August 2007 along with optical properties. These comprised diffuse attenuation coefficient of downwelling PAR (K d(PAR)), upwelling PAR (K u(PAR)), particle beam attenuation coefficient (c p), and irradiance reflectance R(−0, PAR). PAR is white light between 400 and 700 nm. The estuary receives melt water from the Greenland Inland Ice and stations covered a transect from the very high turbid melt water outlet to clear marine waters. Results showed a strong spatial variation with high values as for suspended matter concentrations, CDOM, diffuse attenuation coefficient K d(PAR), particle beam attenuation coefficients (c p), and reflectance R(−0, PAR) at the melt water outlet. Values of optical constituents and properties decreased with distance from the melt water outlet to a more or less constant level in central and outer part of the estuary. There was a strong correlation between inorganic suspended matter (SPMI) and diffuse attenuation coefficient K d(PAR) (r 2 = 0.92) and also for particle beam attenuation coefficient (c p; r 2 = 0.93). The obtained SPMI specific attenuation—K d*(PAR) = 0.13 m2 g−1 SPMI—and the SPMI specific particle beam attenuation—c p* = 0.72 m2 g−1—coefficients were about two times higher than average literature values. Irradiance reflectance R(−0, PAR) was comparatively high (0.09−0.20) and showed a high (r 2 = 0.80) correlation with K u(PAR). Scattering dominated relative to absorption—b(PAR)/a(PAR) = 12.3. Results strongly indicated that the high values in the optical properties were related to the very fine particle sizes (mean = 2–6 μm) of the suspended sediment. Data and results are discussed and compared to similar studies from both temperate and tropical estuaries.  相似文献   

11.
本文用电子背散射衍射技术(electron backscatter diffraction,EBSD)测试了海南文昌玄武岩中二辉橄榄岩包体中的辉石主晶与其出溶片晶的结晶学取向关系。结合电子探针成分测试,得出:单斜辉石(透辉石)主晶中出溶了两组不同方向的片晶,一组为斜方辉石(顽火辉石-易变辉石)片晶,另一组为单斜辉石(普通辉石)片晶。由于出溶片晶在EBSD测试切面上体现为以线状体,因此需要找到一种方法将线状体所代表的片晶的晶面符号推算出来。本文介绍了一种利用吴氏网进行坐标系旋转的"晶带相交法",该方法可以作图推算出溶片晶的晶面符号。根据"晶带相交法"得出,斜方辉石(顽火辉石-易变辉石)出溶片晶为(100),单斜辉石(普通辉石)出溶片晶为~(401)。根据前人的研究资料,出溶片晶~(401)可能指示最小出溶压力为9.5~12.5GPa。出溶片晶的结晶学取向涉及到主晶与出溶体的晶体结构匹配关系,并且与出溶温度-压力有关,因此出溶片晶的结晶学取向分析具有晶体化学理论意义和反映地质温压过程的实际意义。这种"晶带相交法"可以推广应用于其他矿物出溶结构的结晶学取向研究中。  相似文献   

12.
《Gondwana Research》2001,4(3):497-508
Ocellar lamprophyres are reported from Danva, in Sirohi district, Rajasthan which lies in the Pindwara-Watera sector of the South Delhi Fold Belt (SDFB). They intrude mafic metavolcanics and garnetiferous biotite schist of the Ajabgarh Group of the Delhi Supergroup. These lamprophyres are unaltered, show porphyritic and panidiomorphic textures with olivine, clinopyroxene, amphibole, biotite and spinels constituting the phenocryst phase in a ground mass of clinopyroxene, amphibole, mica and analcime. Petrochemically, these lamprophyres can be classified as analcime monchiquite (alkaline lamprophyre), though they have some affinity towards ultramafic lamprophyres and lamproites. Chemistry of the minerals suggests that the clinopyroxenes have a compositional range of diopside and salite, amphiboles are typically kaersutites, biotites are titanium rich and spinels are Al-rich ulvospinels. These minerals plot in discriminant fields of minerals from alkaline and ultramafic lamprophyres.The Danva lamprophyres are characterized by a variety of ocellar features that include (i) porphyritic ocellus with microphenocrysts of kaersutites and biotite in ground mass of analcime, (ii) zoned ocellus with concentric zones of carbonates and analcime and (iii) composite ocellus in which type (i) ocellus enclose the type (ii) ocellus. These ocellar features are interpreted to represent late stage magmatic segregation and magmatic crystallization involving two immiscible magmatic liquids.The Danva lamprophyres are in strike continuity of the Pipela lamprophyres and therefore confirm alkaline magmatism for over 20 kms in SDFB during end-Neoproterozoic tectono-thermal event. The close spatial association of the lamprophyres with Cu-Zn-Au deposits of Danva and Pipela area and the first report of monchiquite with affinity towards ultramafic lamprophyres and lamproites may be significant in gold (and possibly diamond) exploration in the SDFB.  相似文献   

13.
Dust,clouds, rain types,and climatic variations in tropical north Africa   总被引：2，自引：0，他引：2  
Dust and processes of raindrop formation in the clouds play a very important role in the climatic evolution of tropical north Africa. Sedimentologic, stratigraphic, pedologic, geomorphologic, and palynologic data converge to show that a major environmental change occurred in tropical Africa about 7000 yr B.P. In the Sudanian and Sudano-Guinean zones (wet tropical zone), from 15,000 to 7000 yr B.P., rivers deposited mostly clay, while from 7000 to 4000 yr B.P. they deposited mostly sand. During the first period, pedogenesis was vertisolic (montmorillonite dominant), associated with pollen belonging mostly to vegetation typical of hydromorphic soils, while during the second period pedogenesis was of ferruginous type (kaolinite dominant) with pollen belonging mostly to vegetation typical of well-drained soils. The great change near 7000 yr B.P. is linked chiefly to a major hydrological change that appears related to a change in the size of raindrops: from fine rains associated with considerable atmospheric dust (raindrop diameter essentially less than 2 mm) to the second period associated with thunderstorm rains (raindrop diameter mostly greater than 2 mm). The size of raindrops is related particularly to cloud thickness and dust concentration in the troposphere. Thunderstorm activity is influenced also by fluctuations of the atmospheric electricity, modulated by the sun.  相似文献   

14.
The speciation and mobility of some selected trace metals (As, Cu, Mn, Pb and Zn) in sediments with depth was investigated in the Cam River-mouth (Vietnam) by collecting sediment cores and analysing porewater and sediment composition, complemented with single (ammonium-EDTA) and sequential (BCR 3-step) extractions and mineralogical analysis (XRD). All trace metals show overall decreasing trends with depth in porewater as a result of anthropogenic input in upper sediment layers. High porewater concentrations of As, Mn and Pb in oxic and suboxic sediment layers may result in groundwater pollution. Sediment-bound Pb and Mn dominate in the reducible and the acid-soluble fraction, respectively, while Cu and Zn distribute rather evenly between four extracted fractions. The porewater metal speciation, as predicted by a geochemical model Visual MINTEQ version 3.0, indicates that the toxicity of Cu, Mn, Pb and Zn (presented by the proportions of free metal ions) decreases with depth, while the toxicity of As increases when As(III) becomes more abundant. The dissolved concentrations of trace metals are not only controlled by the precipitation/dissolution of discrete hydroxide/oxide, carbonate and phosphate minerals, but also by sorption processes on major sorbents (i.e. As on goethite, and Mn and Zn on calcite and dolomite). Sulphide minerals do not show any control even in the anoxic zone most likely because of the low concentration of sulphur.  相似文献   

15.
The formation of calcite, aragonite, dolomite, hydromagnesite, and nesquehonite in speleothems of a small cave within dolostone may be compared with the formation of these carbonate minerals in much larger environments in which evaporation exceeds precipitation (salt lakes, tropical lagoons, sebkhas etc...). In all cases the formation and diagenetic alteration is mainly governed by the Mg/Ca-ratio of the solutions, from which precipitation (or transformation) takes place.The certain occurrence of monohydrocalcite in the speleothems and in technical incrustations lead to the conclusion, that this very rare mineral precipitates from solutions which are transported as aerosols.  相似文献   

16.
In the Tampa Bay region of Florida, extreme levels of annual and seasonal rainfall are often associated with tropical cyclones and strong El Niño episodes. We used stepwise multiple regression models to describe associations between annual and seasonal rainfall levels and annual, bay-segment mean water clarity (as Secchi depth [m]), chlorophylla (μg I?1), color (pcu), and turbidity (ntu) over a 20-yr period (1985–2004) during which estimated nutrient loadings have been dominated by non-point sources. For most bay segments, variations in annual mean water clarity were associated with variations in chlorophylla concentrations, which were associated in turn with annual or seasonal rainfall. In two bay segments these associations with annual rainfall were superimposed on significant long-term declining trends in chlorophylla. Color was significantly associated with annual rainfall in all bay segments, and in one segment variations in color were the best predictors of variations in water clarity. Turbidity showed a declining trend over time in all bay segments and no association with annual rainfall, and was significantly associated with variations in water clarity in only one bay segment. While chlorophylla, color, and turbidity a affected water clarity to varying degrees, the effects of extreme rainfall events (El Niño events in 1998 and 2003, and multiple tropical cyclone events in 2004) on water clarity were relatively short-lived, persisting for periods of months rather than years. During the 20-yr period addressed in these analyses, declining temporal trends in chlorophylla and turbidity, produced in part by a long-term watershed management program that has focused on curtailing annual loadings of nitrogen and other pollutants, may have helped to prevent the bay as a whole from responding more adversely to the high rainfall periods that occurred in 1998 and 2003–2004.  相似文献   

17.
冈底斯印支期构造-岩浆-成矿的研究比较缺乏.以出露在冈底斯隆格尔-念青唐古拉复合古岛弧带的拉隆花岗闪长岩体为研究对象,通过野外地质调查、岩石学、LA-ICP-MS锆石U-Pb定年、岩石地球化学和锆石Lu-Hf同位素等方面的研究,探讨了其岩石成因和形成的构造背景.结果显示,拉隆花岗闪长岩体的LA-ICP-MS锆石U-Pb年龄为223.5±3.9 Ma~225.4±4.9 Ma,形成于晚三叠世（T3）,属印支晚期构造-岩浆活动的产物;花岗闪长岩体表现出低Ti（w（TiO2）=0.46%~0.73%）,富Si（w（SiO2）=63.24%~67.94%）、Al（w（Al2O3）=14.14%~15.85%）、Na（w（Na2O）=2.58%~3.04%）、K（w（K2O）=3.06%~4.89%）,高钾钙碱性-钾玄岩系列和弱过铝质的主量元素地球化学特征;岩体稀土总量∑REE为138.62×10-6~255.53×10-6,配分模式为轻稀土元素富集的右倾斜型,其（La/Yb）N值为8.35~17.90,具明显的负Eu异常（Eu/Eu*=0.54~0.69）,无Ce异常（Ce/Ce*=0.92~1.02）;微量元素表现出Ba、Nb、Ta、Sr、Ti、P元素亏损和Rb、K、Th、U、Zr、Hf元素富集的特征.岩体的εHf（t）为-6.4~2.5,其两阶段模式年龄tDM2为980~1 479 Ma,相当于念青唐古拉群形成的地质时代.拉隆花岗闪长岩体属A型花岗岩,为古老下地壳物质部分熔融的岩浆产物,并有少量地幔物质的加入,形成于古特提斯俯冲碰撞形成的岛弧背景下局部拉张的构造环境.   相似文献   

18.
Summary Crystallization temperatures of the oceanic carbonatites of Fuerteventura, Canary Islands, have been determined from oxygen isotope fractionations between calcite, silicate minerals (feldspar, pyroxene, biotite, and zircon) and magnetite. The measured fractionations have been interpreted in the light of late stage interactions with meteoric and/or magmatic water. Cathodoluminescence characteristics were investigated for the carbonatite minerals in order to determine the extent of alteration and to select unaltered samples. Oxygen isotope fractionations of minerals of unaltered samples yield crystallization temperatures between 450 and 960°C (average 710°C). The highest temperature is obtained from pyroxene–calcite pairs. The above range is in agreement with other carbonatite thermometric studies.This is the first study that provides oxygen isotope data coupled with a CL study on carbonatite-related zircon. The CL pictures revealed that the zircon is broken and altered in the carbonatites and in associated syenites. Regarding geological field evidences of syenite–carbonatite relationship and the close agreement of published zircon U/Pb and whole rock and biotite K/Ar and Ar–Ar age data, the most probable process is early zircon crystallization from the syenite magma and late-stage reworking during magma evolution and carbonatite segregation. The oxygen isotope fractionations between zircon and other carbonatite minerals (calcite and pyroxene) support the assumption that the zircon would correspond to the early crystallization of syenite–carbonatite magmas.  相似文献   

19.
The survey of Messenia by the University of Minnesota Messenia Expedition (UMME) was recently followed by the Pylos Regional Archaeological Project (PRAP). Despite improvements in survey methodology, problems remain, particularly with the interpretation of field data and with extrapolation, especially when this is made based on survey results alone, without excavation. In addition, the work of the archaeologists has not yet been fully integrated with that of the earth scientists. Some examples are given of the difficulties encountered in this survey, especially concerning retrodictions (predictions about the past) of ancient settlement patterns and numbers. Suggestions are made here for further survey and selective excavation, especially in eastern Messenia, where fieldwork has been far less extensive than in western Messenia. More fieldwork is needed to determine the pattern of geomorphic changes in the region, especially in relation to the varying degrees of visibility and/or preservation of the ancient sites. Meanwhile, increased recent human activity is rapidly destroying or endangering those remains that have hitherto survived, so that survey is often de facto of a rescue nature. © 2007 Wiley Periodicals, Inc.  相似文献   

20.
The Transition Movement is a translocal phenomenon circulated through transnational grassroots networks. This study explores the geographies of the Transition Movement with a theoretical framework that perceives it as both a social movement and a grassroots innovation. Participant-observation of Transition Salt Lake (TSL), located in the suburban metropolis of Salt Lake City, Utah, was conducted, as the United States remains a largely understudied country in regards to this particular movement. In this pursuit, we asked: (i) how and what this transition initiative draws from geographically extensive and intensive relations, (ii) how it combines place-specific elements and generalized models (embeddedness), and (iii) how this impacts the success of the transition initiative and how these impacts (positive or negative) are generated. Place, space, and scale played a large role in defining the nature, dynamics, possibilities, and constraints of this transition initiative. Specifically, geographically intensive and extensive relations were critical for the mobilization of complementary resources. The Transition model was found to be flexible, allowing for the initiative to adopt those elements that worked in place and to focus on locally relevant topics. TSL faced many challenges identified by previous researchers regarding finances, participation, diversity, and intragroup competition. While networking with other similar groups, TSL demonstrated that fertile environments of activism are incubatory pools for grassroots innovations and social movements, and a trade-off was found with competition for resources between local groups.  相似文献   

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