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11.
The geometry of mineral deposits can give insights into fluid flow in shear zones. Lode gold ore bodies at Renco Mine, in the Limpopo Belt, Zimbabwe, occur as siliceous breccias and mylonites within amphibolite facies shear zones that dip either gently or steeply. The two sets of ore bodies formed synchronously from hydrothermal fluids. The ore bodies are oblate, but have well‐defined long axes. Larger ore bodies are more oblate. High‐grade gold ore shoots have long axes that plunge down dip; this direction is perpendicular to the long axes of the low‐grade ore bodies. The centres of the high‐grade ore bodies align within the low‐grade ore bodies along strike in both gently and steeply dipping groups. The range of sizes and shapes of the ore bodies are interpreted as a growth sequence. Geometrical models are proposed for the gently and steeply dipping ore bodies, in which individual ore bodies grow with long axes plunging down dip, and merge to form larger, more oblate ore bodies. The models show that when three or more ore bodies coalesce, the long axis of the merged ore body is perpendicular to the component ore bodies, and that ore bodies in the deposit may have a range of shapes due to both growth of individual ore bodies, and their coalescence. The long axes of the high‐grade ore bodies are parallel to the shear directions of both the gently and steeply dipping dip slip shear zones, which were the directions of greatest permeability and fluid flow. The larger, lower grade bodies, which may have formed by coalescence, are elongate perpendicular to these directions.  相似文献   
12.
    
Tooth ablation is identified differentially among Iron Age inhabitants of the inland region of central Thailand at the archaeological sites of Ban Mai Chaimongkol and Tha Kae (ca. 2650–1450 bp ). Analysis of the subsets of adult individuals with adequately preserved anterior dentition (Ban Mai Chaimongkol n = 12; Tha Kae n = 6) documents bilateral removal of the maxillary lateral incisors and canines at Ban Mai Chaimongkol and bilateral removal of the maxillary lateral incisors at Tha Kae, affecting 17% (n = 2) and 67% (n = 4) of observable individuals, respectively. Ablation was not associated with sex, age, mortuary features, or grave goods in this sample. Possible social significances of this practice are discussed in relation to skeletal evidence of tooth ablation elsewhere in Mainland Southeast Asia and archaeological contexts specific to central Thailand.  相似文献   
13.
    
Artificial cranial modification (ACM) involves the alteration of cranial vault shape by cultural means, and is performed during infancy while the cranial bones remain soft and malleable. The direction of normal cranial growth is altered through the application of external forces. In this study, three types of ACM from north‐central Peru (posterior flattening, bilobed and circumferential) were analysed using standard craniometric techniques. The aim was to determine the effects of these forms of ACM on craniofacial morphology, and the extent to which different types of ACM could be distinguished from one another and unmodified crania on the basis of these measurements. Significant differences between artificially modified and unmodified crania, and between different types of ACM, were demonstrated in cranial vault shape for all types. Significant differences in facial morphology were found only in the bilobed group compared with the unmodified crania. Canonical variates analysis (discriminant analysis) confirmed that major differences between modification types and unmodified crania were in measurements and angles of the cranial vault. While the results show some similarities to previous studies, they add to the variability in the patterns and extent of differences documented to date. It is suggested, based on these results and visual observations, that interpopulation variation in ACM within major modification categories may explain some of the variability in results between studies, an explanation which has previously received insufficient recognition but which remains to be tested since varied methodology between studies may also be a contributory factor. While previous studies have often sought to generalise about the effects of ACM, the examination of the differences between populations even within major ACM categories may offer new insight into cultural variation in modification techniques between populations and the nature of craniofacial development. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
14.
    
Accurate reconstruction of diagenetic P‐T conditions in petroleum reservoirs from fluid inclusion data relies on valid measurements of methane concentration in aqueous inclusions. Techniques have been developed (Raman spectrometry) to provide sufficiently accurate data, assuming measured methane concentration has not been modified after aqueous inclusion entrapment. This study investigates the likelihood that organic acids derived from petroleum fluids and dissolved in formation water might suffer decarboxylation upon postentrapment heating within the fluid inclusion chamber, thereby generating excess CH4 in the inclusions. Four different experiments were conducted in fused silica capillary capsules (FSCCs), mimicking fluid inclusions. The capsules were loaded with acetic (CH3COOH) or formic (HCOOH) acid solution and were heated to 250°C for short durations (<72 h) in closed‐system conditions, with or without applying a fixed PH2. Reaction products were characterized by Raman and FT‐IR spectrometry. Results indicate that decarboxylation reactions did take place, at variable degrees of progress, and that measurable excess CH4 was produced in one experiment using acetic acid. This suggests that methane may be produced from dissolved organic acids in natural aqueous inclusions in specific situations, possibly inducing errors in the thermodynamic interpretation.  相似文献   
15.
    
This article considers the metaphors we use when studying what geographers have come to call policy mobility. Specifically, it argues that a metaphor developed by Mol and Law (1994) of fluid space offers something different to metaphors that are currently being used in the area, including diffusion, transfer and network. In particular, the metaphor of fluid space describes a distributed and highly differentiated space of policy mobility and circulation that remains connected and robust despite the lack of a strong centre. This is illustrated through a discussion of the global spread of policies that claim to act on or through some aspect of human creativity, such as the creative industries, the creative class, the creative city and so on. The article concludes that this metaphor helps us to explain why some policy types are able to move to so many places while avoiding the tendency to link this movement to a universal critique.  相似文献   
16.
    
A series of crania from the site of Huamelulpan, Oaxaca, Mexico (400 BC to AD 800), were examined. Four showed notable cultural modifications. One exhibited a healed trephination, while the other three were perforated through the frontal. The cultural context and significance of these modifications is discussed, especially in relationship to the site of Monte Albán, where trephination was more common than anywhere else in Mesoamerica. The post-mortem cranial perforations appear to be connected with the practice of ancestor veneration. © 1997 John Wiley & Sons, Ltd.  相似文献   
17.
    
Early Stone Age cut marks created during tool‐assisted carnivory potentially offer inferences into hominin butchery behaviour and access to complete or defleshed carcasses. Actualistic butchery trials of 16 goat and cow half‐carcasses were completed by an experienced butcher with replicated Oldowan tools to investigate how the geometric organisation of cut mark clusters reflects flake versus core tool use and bulk muscle versus scrap defleshing. A cluster of cut marks is defined as a series of adjacent cut mark striations that occur at an anatomical location and are bounded by unmarked cortical surface. Tool type and butchery action were predicted to differentially mark certain long bone portions and influence cluster attributes. Moulds of 613 cut mark clusters were photographed and measured using ImageJ software (National Institutes of Health, Bethesda, Maryland, USA) for cluster area, cut mark count, median cut mark length and standard deviation of cut mark length and angle. Analysis suggests the following results: (i) cluster attributes are correlated;(ii) changes in cluster geometry are related to increasing cut mark count and length but not tool type or defleshed muscle amount; (iii) large clusters occur on large animals; and (iv) long bone midshaft portions are cut‐marked during both bulk and scrap muscle defleshing. Analysis of 179 cut mark clusters on long bone shafts of sizes 1–4 mammals from three Okote member assemblages at Koobi Fora, Kenya, shows that archaeological clusters have a similar number of marks when compared with experimental clusters but are significantly smaller, have shorter median marks and include less deviation in mark length and angle. Archaeological clusters corroborate that increasing area is positively correlated with cut mark count, median mark length and standard deviation of mark length and angle. A quantitative inferential model that links cut mark cluster geometry to tool type or the amount of muscle defleshed is not supported by these data. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
18.
The effect of pore size on cementation in porous rocks   总被引:1,自引:0,他引:1  
A. Putnis  G. Mauthe 《Geofluids》2001,1(1):37-41
Halite cementation in porous sandstone from the Lower Triassic Bunter Formation in North‐West Germany has been studied using measurements of porosity and permeability, before and after salt extraction, as well as from petrographic observations. The results show that in cemented sandstones there is a clear tendency for the larger pores to be halite‐filled while the smaller pores, which are responsible for the residual porosity, are left empty. Observations on cemented ‘pin‐stripe’ aeolian sandstones, in which laminations of fine and coarser sand grains alternate on a millimetre scale, indicate that this selective cementation is not due to differences in the brine composition in the pores. The implication, which is also supported by other observations, is that fluids in small pores can maintain a higher supersaturation with respect to crystallization.  相似文献   
19.
A recent advancement in petroleum geochemistry is to model fossil oil composition using microthermometric and volumetric data acquired from individual fluid inclusion analysis. Fourier transform infrared (FT‐IR) microspectroscopy can record compositional information related to gas (CH4 and CO2) and alkane contents of petroleum inclusions. In this study, a quantitative procedure for FT‐IR microspectrometry has been developed to obtain, from individual fluid inclusions, mol percentage concentrations of methane, alkanes and carbon dioxide as constraints to thermodynamic modelling. A petroleum inclusion in a sample from the Québec City Promontory nappe area was used as standard to record a reference spectrum of methane. The analytical procedure is based on the measurement of CH4/alkane and CH4/CO2 band area ratios. CH4/alkane infrared band area ratio is obtained after spectral subtraction of the reference methane spectrum. This area ratio, affected by absolute absorption intensities of methane, methyl and methylene, provides a molar CH4/alkane ratio. Methyl/methylene ratio (CH2/CH3) ratio is obtained following procedures established in previous work. CO2/CH4 concentration ratio is estimated from relative absolute absorption intensities. Application to natural inclusions from different environments shows good correlation between FT‐IR quantification and PIT (petroleum inclusion thermodynamic) modelling.  相似文献   
20.
Cathodoluminescence (CL) images of quartz grains in the Appin Quartzite from the aureole of the Ballachulish Igneous Complex (Scotland) reveal a textural complexity that we interpret in the light of published models of the evolution of the contact aureole. Five distinct generations of quartz can be discriminated in CL. The oldest of these is a dark luminescing mottled quartz (Type 1 quartz) that occurs in the centres of pre‐existing grains, in samples collected from 210 m to 0.1 m from the contact. Dark mottled quartz is interpreted to be unrecrystallized material and has a regional metamorphic CL spectral signature. The onset of contact metamorphism resulted in grain growth visible in CL as a series of fine‐scale alternating bands of bright and dark luminescing material (Type 2 quartz), which we attribute to infiltration of repeated pulses of small amounts of H2O along grain boundaries. Close to the intrusion, a subgrain‐scale network of intragranular, bright luminescing features could have resulted from either intragranular microcrack‐controlled infiltration of H2O at high temperatures or intergranular cracking followed by grain growth (Type 3 quartz). Broad bands of bright material on grain boundaries in samples that are inferred to have undergone partial melting are interpreted as quartz crystallized from the melt phase (Type 4 quartz). The final stage in the textural development is marked by a series of aligned fractures, detected in CL by nonluminescing material (Type 5 quartz) and corresponding closely with trails of fluid inclusions. These fractures are interpreted as the pathways for late‐stage, low‐temperature, retrogressive fluids.  相似文献   
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