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1.
ALAN E. OLDERSHAW 《Sedimentology》1968,10(4):255-272
Electron microscopic examination of Namurian bedded cherts in North Wales (Great Britain) has revealed the existence of two dominant surface textures, granular and spongy, with a range of textures intermediate between the two. These textures can be used to differentiate between three principal lithologies within the cherts and between laminae and colour bands within the lithologies. A positive relationship is demonstrated between the presence of spongy texture and a high volume of impurities; there is a gradation, with increasing argillaceous/organic content, from granular through intermediate to spongy surfaces. It is suggested that this gradation reflects an increase in chalcedony over micro-crystalline quartz resulting from: (l) an increase in impurities; (2) an increase in the rate of precipitation of silica. The relationship between surface texture and type of lithology is considered to be consistent with the order of crystallisation for silica put forward by MILLOT (1960). 相似文献
2.
Robert H. Brewer 《Estuaries and Coasts》1978,1(2):120-122
The distribution of sessile marine invertebrates is often the consequence of the selection of a suitable substrate by motile larvae. Motile planulae larvae ofAurelia aurita (Linnaeus) are exposed to an artificial substrate in the laboratory to determine if they possess the capacity both for specific orientation and for discrimination of surface texture at time of attachment. More than 90% (P<0.001) of the planulae fasten to the underside of objects. As a result, developing scyphistomae hang with the oral surface downward as commonly encountered in the field. The effect of surface texture on planula attachment is equivocal; this may reflect an indifference to surface texture, a limited capacity to locomote across rough substrate, or a mechanism of response sensitive only to large surface irregularities. These results are compared with those obtained for the planulae ofCyanea capillata (Linnaeus). The planular effected orientation of the scyphistoma may be generally true for coastal representatives of the Semaeostomeae, and perhaps for other shallow water Scyphozoa (including the Class Cubozoa). 相似文献
3.
H. -U. Nissen 《Contributions to Mineralogy and Petrology》1967,16(4):354-360
A submicroscopic domain texture consisting of small lamellae twinned after a combination of albite and pericline laws (crosshatch), closely resembling the domain texture of optically monoclinic adularia, occurs in two orthoclases from Japan. It is concluded from the electron transmission and -diffraction data that these materials, though optically nearly monoclinic, are composed of triclinic domains and that they originally grew as sanidine crystals. 相似文献
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5.
The Diamante-Terranova Unit (DIATU), in the Calabrian Arc of southern Italy, is part of an ophiolitic sequence involved in a high pressure/low temperature event (P=8 kbar; T =400 °C) followed by re-equilibration at greenschist facies conditions (P=3 kbar; T =300 °C). The rocks contain two types of quartz–calcite veins – an earlier generation of deformed, folded and faulted veins formed during or before subduction, and a later set of planar, undeformed veins formed during exhumation of the DIATU. The earlier folded quartz–calcite veins contain regularly shaped aqueous inclusions as well as inclusions with a highly irregular dendritic texture. The later planar veins contain only regularly shaped aqueous inclusions similar to those in the earlier veins. In both vein types, all inclusions are demonstrably secondary in origin. Regularly shaped inclusions from both vein types are low salinity (0–5 wt% NaCl). Most contain liquid and vapour and homogenize to the liquid (Th 135–180 °C), whereas others contain only liquid at room temperature. Both the two-phase and monophase inclusions occur in the same fractures and are thought to record the same trapping event, with the monophase inclusions remaining metastable liquid at room temperature. No microthermometric data could be obtained from the dendritic inclusions in the earlier folded veins. Inclusions with the highly irregular dendritic texture found in the earlier veins are similar to those produced experimentally during laboratory-induced deformation of synthetic inclusions in quartz under conditions of internal underpressure, simulating either isobaric cooling or isothermal compression. The occurrence of inclusions with the dendritic texture in the earlier folded veins, and their absence from the later planar veins, suggests that the earlier veins formed before or during subduction and were folded and faulted in a compressional environment and their contained fluid inclusions were modified to produce the dendritic texture. During later uplift of the DIATU, planar veins containing regularly shaped aqueous inclusions formed and some of the fluids forming these veins were also trapped as secondary inclusions in the earlier folded veins. The results of this study provide convincing evidence that inclusions with a highly irregular dendritic morphology represent early inclusions that have survived prograde conditions in a high pressure/low temperature metamorphic environment (but have been texturally modified). The high pressure/low temperature ‘implosion’ texture is preserved over geological time, even after being overprinted by internal overpressure conditions generated during retrograde decompression. We suggest that inclusions that have survived prograde metamorphism are common in high pressure/low temperature rocks, but are often not identified as such due to their morphology which makes their recognition difficult. 相似文献
6.
交代结构构造在花岗岩的结构构造中占有重要地位,它们的出现与花岗岩形成过程的挥发组分有关。本文详述了花岗质岩石中主要造岩矿物的各种交代结构构造的特点及其在不同阶段结构变化系列。花岗岩的交代结构可分为二种成因类型。混合交代和岩浆交代类型,二者在交代结构的表现上有所不同,并可形成一系列交代结构演化系列,它们大致与变质作用经混合岩化作用发展成为岩浆结晶作用的阶段相符合,可分为下列几种主要交代结构类型:由变质作用的镶嵌结构变为混合岩化作用的交代镶嵌和镶嵌交代结构并通过片麻交代结构发展成为岩浆交代的半自形交代结构,后 相似文献
7.
鄂尔多斯盆地陇东地区三叠系延长组长8储层特征 总被引：15，自引：1，他引：15
鄂尔多斯盆地陇东地区延长组长8油层段是重要的储集层之一,包括长81和长82两个砂岩组。通过储层岩石学、储层物性、孔隙结构及储层控制因素等方面对储层特征进行分析,总结并评价储层储集性能。研究结果表明,储层岩石类型主要为中细粒长石砂岩和岩屑长石砂岩,成分成熟度低,结构成熟度中—高;岩石物性总体较差,属低孔、低渗储层,发育粒间孔隙、溶蚀孔隙、晶间孔等孔隙类型,喉道以中细喉—细喉为主。储集性变化受沉积作用和成岩作用控制,沉积作用控制了储层砂体展布,进而影响其岩石学特征的表现,压实作用、胶结作用和溶蚀作用控制了储层孔隙结构特征及储层物性,根据岩性和物性分析特征可将储集岩分为4类,优质储层的勘探应以沉积作用控制的多套砂体相互叠置的水下分流河道沉积为重点。 相似文献
8.
9.
湘南香花铺云英伟晶岩研探 总被引：5，自引：1，他引：4
湘南香花铺地区产出一类具伟晶结构的云英岩,它们发育有一系列宏观,微观地质特征,充分表明其主要为岩浆结晶作用的直接产物,在已知的岩浆岩及其蚀变岩石中,尚无与之相同或相似的岩性,因此,它们实属一类新发现的火成岩,即云英伟晶岩,本文简要论述产出于香花铺地区云英伟晶岩的地质,地球化学特征;提出了云英传晶岩的分类方案;结合有关成岩实验资料,探了这类岩石的成生机制。 相似文献
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11.
P. Czar 《Geological Journal》2005,40(4):405-424
Calcareous microflora occur commonly in the early Serpukhovian (late Mississippian) rocks from the Guadiato Area (southwestern Spain) despite the fact that this area contains mostly siliciclastic sediments. The microflora recorded in the carbonate beds is regarded as representative of both relatively deep‐water and shallow‐water facies and can be compared with the slope and shelf facies environments distinguished in the Guadiato Area. Up to 45 algal taxa have been identified in the carbonate beds, of which 26 taxa occur in the relatively deep‐water assemblages, whereas the shallow‐water assemblages are composed of up to 43 taxa. The entire algal assemblage is dominated by calcifoliids, common cyanobacteria and incertae sedis, but the shallow‐water assemblages contain more commonly dasyclads, red algae and aoujgaliids. Most of these taxa are present, but poorly known, in other Serpukhovian carbonate platforms in the western Palaeotethys. Some algae (Hortonella uttingii, Kamaenella tenuis and Koninckopora inflata), usually regarded as being restricted to the Viséan, have been found in Serpukhovian rocks in the Guadiato Area, and also in Algeria, thus their stratigraphic ranges might be extended up to the Serpukhovian. Other important taxa include: Archaeolithophyllum, Cabrieropora, Calcifolium, Falsocalcifolium, Fourstonella, Frustulata, Kulikia, Neoprincipia and ‘Windsoporella’, which are exceptionally recorded in Serpukhovian rocks, or not recorded at all, because they are typically recorded in the Pennsylvanian (cf. Clavaporella), although some of them show earlier occurrences in Viséan rocks (Claracrusta, Paraepimastopora and Sparaphralysia). Some of the algal taxa can be considered as potential regional markers for the Serpukhovian, such as Archaeolithophyllum, cf. Clavaporella, Frustulata and Girvanella (?) sp. The algal assemblages found in the Guadiato Area show the greatest similarities with those in the Béchar‐Mézarif (Algeria), Pyrenees and Montagne Noire (southern France). Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
12.
Ghislain Trullenque Karsten Kunze Renee Heilbronner Holger Stünitz Stefan M. Schmid 《Tectonophysics》2006,424(1-2):69-97
Microfabrics were analysed in calcite mylonites from the rim of the Pelvoux massif (Western Alps, France). WNW-directed emplacement of the internal Penninic units onto the Dauphinois domain produced intense deformation of an Eocene-age nummulitic limestone under lower anchizone metamorphic conditions (slightly below 300 °C). Two types of microfabrics developed primarily by dislocation creep accompanied by dynamic recrystallisation in the absence of twinning. Coaxial kinematics are inferred for samples exhibiting grain shape fabrics and textures with orthorhombic symmetry. Their texture (crystallographic preferred orientation, CPO) is characterised by two c-axis maxima, symmetrically oriented at 15° from the normal to the macroscopic foliation. Non-coaxial deformation is evident in samples with monoclinic shape fabrics and textures characterised by a single oblique c-axis maximum tilted with the sense of shear by about 15°. From the analysis of suitably oriented slip systems for the main texture components under given kinematics it is inferred that the orthorhombic textures, which developed in coaxial kinematics, favour activity of <10–11> and <02–21> slip along the f and r planes, respectively, with minor contributions of basal-<a> slip. In contrast, the monoclinic textures, which developed during simple shear, are most suited for duplex <a> slip along the basal plane. The transition between the dominating slip systems for the orthorhombic and monoclinic microfabrics is interpreted to be due to the effects of dynamic recrystallisation upon texture development. Since oblique c-axis maxima documented in the literature are most often rotated not with but against the shear sense, calcite textures alone should not be used as unequivocal shear sense indicators, but need to be complemented by microstructural criteria such as shape preferred orientations, grain size estimates and amount of twinning. 相似文献
13.
Yvonne Küster Bernd Leiss Michael Schramm 《International Journal of Earth Sciences》2010,99(3):505-526
The Kristallbrocken are a characteristic centimetre- to decimetre-sized, laminated halite fabric type occurring in the Stassfurt Formation in
the Zechstein Basin. Up to now, the nature of the Kristallbrocken, i.e. if they are relics of fine-grained, polycrystalline halite beds or clasts of ‘single crystal-layers’, as well as the
deformation mechanisms of this halite type, were not clear from the literature. Drill core material from the salt deposit
Teutschenthal at the southern rim of the Zechstein Basin now allowed investigating less intensely deformed samples for the
first time. The deformational behaviour of these Kristallbrocken ranges from brittle to ductile, which is evidenced by fractured Kristallbrocken on the one hand and weakly bent or even folded Kristallbrocken on the other hand. Local X-ray texture measurements demonstrated that the Kristallbrocken are definitely single crystals and that they can be regarded as relics of formerly larger ‘single crystal-layers’ of up to
several dm2 in size. The folded Kristallbrocken clearly display by their single grain texture characteristics that their crystal lattice is bent, which was most likely enabled
by a kind of flexural-shear folding, and did not develop after deformation from a fine-grained aggregate by recrystallisation.
Due to their monocrystallinity, their originally large size, and the solid inclusions forming the internal lamination, the
Kristallbrocken have clearly stronger rheological properties than the surrounding fine- to coarse-grained polycrystalline rock salt, and
thus also deform by fracturing. 相似文献
14.
L. G. LOVE 《Sedimentology》1967,9(4):327-352
Microscopical and chemical examination of intertidal flats of the Wash indicate that phases of iron corresponding to ferric hydroxide and iron monosulphide are involved in the early diagenetic formation of pyrite, the first being an important source of the iron. Sedimentological data are tested against analyses of total iron extractable by hydrochloric acid and concentrated nitric acid, and of the pyritic fraction of this iron; ignition data for residual organic matter are considered. The occurrence of the pyrite as isolated grains and spherules of framboidal texture is recorded, their size ranges given, and iron monosulphide recognised as the precursor of both forms. Ordering in the pyrite framboidal spherules is recorded and internal coalescence confirmed as a feature of primary growth which obscures the ordering. 相似文献
15.
Melt infiltration into quartzite took place due to generation and migration of partial melts within the high‐grade metamorphic rocks of the Big Cottonwood (BC) formation in the Little Cottonwood contact aureole (UT, USA). Melt was produced by muscovite and biotite dehydration melting reactions in the BC formation, which contains pelite and quartzite interlayered on a centimetre to decimetre scale. In the migmatite zone, melt extraction from the pelites resulted in restitic schollen surrounded by K‐feldspar‐enriched quartzite. Melt accumulation occurred in extensional or transpressional domains such as boudin necks, veins and ductile shear zones, during intrusion‐related deformation in the contact aureole. The transition between the quartzofeldspathic segregations and quartzite shows a gradual change in texture. Here, thin K‐feldspar rims surround single, round quartz grains. The textures are interpreted as melt infiltration texture. Pervasive melt infiltration into the quartzite induced widening of the quartz–quartz grain boundaries, and led to progressive isolation of quartz grains. First as clusters of grains, and with increasing infiltration as single quartz grains in the K‐feldspar‐rich matrix of the melt segregation. A 3D–μCT reconstruction showed that melt formed an interconnected network in the quartzites. Despite abundant macroscopic evidence for deformation in the migmatite zone, individual quartz grains found in quartzofeldspathic segregations have a rounded crystal shape and lack quartz crystallographic orientation, as documented with electron backscatter diffraction (EBSD). Water‐rich melts, similar to pegmatitic melts documented in this field study, were able to infiltrate the quartz network and disaggregate grain coherency of the quartzites. The proposed mechanism can serve as a model to explain abundant xenocrysts found in magmatic systems. 相似文献
16.
Renée Heilbronner 《Journal of the Geological Society of India》2010,75(1):160-170
The paper is concerned with the combined application of two methods for microstructure and texture analysis: (1) optical orientation
and misorientation imaging and (2) autocorrelation function (ACF). Using two different samples, the usefulness of the methods
and the quality of the results are discussed. One sample is a quartzite layer from the limb of a small scale fold in the Suretta
Nappe (ValAvers, Switzerland) which was deformed under upper greenschist conditions, the other is a sample of Black Hills
quartzite, experimentally sheared in dislocation creep. Using the method of computer-integrated polarization microscopy (CIP),
c-axis orientation and misorientation images were prepared and pole figures were calculated from the azimuth and inclination
images. Misorientation images were prepared and analyzed in a number of ways: (1) In as much as misorientation images constitute
texture maps, they visualize the geometry and spatial distribution of texture domains; they show if the texture domains are
spatially coherent, i.e., if the rock is domainal or not. (2) Thresholded misorientation images allow the calculation of the
volume fraction of texture domains, which is a means of estimating the texture intensification independent of the shape of
the pole figure skeleton. (3) From the ACF of thresholded misorientation images the average grain size and shape in those
domains can be derived. (4) From the shape of the domains (if they exist as spatial entities), the strain or strain partitioning
as well as the rheological contrast can be estimated. The paper seeks to demonstrate the importance of localized texture analysis.
The aim is to discuss the quality of the results that can be obtained. The samples were chosen because one is domainal the
other one is not. A full discussion of the geological implications of the results of the analysis is outside the scope of
this contribution. 相似文献
17.
G. Wrner J. Lezaun A. Beck V. Heber F. Lucassen E. Zinngrebe R. Rssling H. G. Wilke 《Journal of South American Earth Sciences》2000,13(8):717
Exposures of metamorphic basement in the Central Andes are scarce and reconstructions of the history of the Pacific margin of Gondwanaland must rely on a few isolated outcrops. We studied two areas of exposed basement in northernmost Chile (Belen) and westernmost Bolivia (Cerro Uyarani). The Belen metamorphic complex has been known for some time and consists of fault-bounded amphibolites, gneisses, schists, and minor quartzites overlain by folded Mesozoic to Cenozoic strata. The Cerro Uyarani is the only basement outcrop on the Bolivian Altiplano and has only recently been found and studied by geological reconnaissance. It consists of foliated mafic and felsic granulites, charnockites, and amphibolites. How do these basement occurrences compare and how do they relate to the other Precambrian crustal domains in the Central Andes? To answer these questions, we used geothermobarometers to reconstruct the P–T conditions of metamorphism, as well as geochemical analyses and petrological methods to study these rocks. The two basement blocks were found to have distinct geological histories and are probably separated by a major crustal domain boundary. Isotopic fingerprinting by Pb-isotopes clearly exclude Laurentian crustal components either in the protoliths or as reworked material. This signature is quite distinct from basement rocks farther south in Chile and northwestern Argentina. 相似文献
18.
假蓝宝石(Sapphirine)的矿物学特征及其在超高温变质作用研究中的应用 总被引：2，自引：1，他引：1
假蓝宝石是Mg-Al质麻粒岩中一种特殊的高温矿物,对超高温变质作用的研究有重要的意义。本文通过对全球66个超高温麻粒岩中47个含假蓝宝石麻粒岩地区的文献调研,总结了几种最常见的含假蓝宝石矿物组合产出的结构位置和变质反应关系,以及假蓝宝石的矿物化学特征。假蓝宝石的化学成分一般位于7∶9∶3端元左右,X_(Mg)大于0. 7,XFe_(3+)变化范围很宽,为0～0. 7。含假蓝宝石矿物组合的形成和演化指示了岩石经历的P-T轨迹。岩石中保留的假蓝宝石取代尖晶石、Grt/Opx+Sil取代Spr+Qz组合,以及随后的Spr+Crd±Opx后成合晶取代Grt/Opx+Sil组合的结构,一般可能指示了逆时针P-T轨迹中冷却和随后减压的部分;岩石中Grt/Opx+Sil/Ky或富Mg十字石反应形成Spr+Qz组合的结构可能指示了顺时针P-T轨迹中减压升温的部分。超高温变质岩不同的P-T轨迹暗示着它们的成因机制并不单一,前者可能是幔源基性岩浆底侵或增生作用的结果,后者可能与长期的热造山作用相关。 相似文献
19.
《International Geology Review》2012,54(3):196-212
New types of carbonaceous filamentous microstructures have been identified in silica veins at two new localities in the ～3.5 Ga North Pole area of Western Australia. Their carbon isotopic compositions were measured in situ by secondary-ion mass spectrometry. The carbonaceous filaments are ～1μm wide, 10 to 100 μm long, and are permineralized in a fine-grained (～1 μm) silica matrix. They are morphologically divided into three types (i.e., spiral, threadlike, and branched filaments). Their sizes and morphologies resemble modern and previously reported fossil bacteria. These similarities and their complex three-dimensional geometry suggest that they may represent morphologically preserved fossil bacteria. δ13C values of the carbonaceous filaments range from ?42 to ?32‰, which strongly suggest that they are composed of biologically fixed organic compounds, possibly via the reductive acetyl-CoA pathway or the Calvin cycle. This is consistent with the hypothesis that autotrophs already existed on the Archean Earth. 相似文献
20.
The Badenian (Middle Miocene) Ca-sulphate deposits of the fore-Carpathian basin – including the shelf and adjacent salt depocentre – have undergone varying degrees of diagenetic change: they are preserved mainly as primary gypsum in the peripheral part of the platform, whereas toward the centre of the basin, where great subsidence occurred during the Miocene, they have been totally transformed into anhydrite. The facies variation and sequence of Badenian anhydrites reflect different genetic patterns of two members of the Ca-sulphate formation. In the lower member (restricted to the platform), anhydrite formed mainly by synsedimentary anhydritization (via nodule formation), whereas in the upper member (distributed throughout the platform and depocentre) the various gypsum/anhydrite lithofacies display a continuum of distinctive anhydrite type-fabrics. These fabrics are based on petrographic features and show from the centre to the margin: (1) syndepositional, interstitial growth of displacive anhydrite; (2) early diagenetic, displacive to replacive (by replacement of former gypsum) anhydrite formation near the depositional surface; (3) early diagenetic, displacive to replacive anhydrite formation during shallow burial; and (4) late-diagenetic (and only partial) replacement of gypsum at deeper burial. The cross-shelf lateral relations of anhydrite lithofacies and fabrics suggest that the diagenesis developed as a diachronous process. These fabrics of the upper member reflect both palaeogeographic (linked to different parts of the basin) and burial controls. Anhydrite growth started very early in the basin centre, presumably related to high-salinity pore fluids; anhydritization prograded updip toward the shelf (landward in a generalized cross-section through the basin). The intensity of gypsum replacement by anhydrite was progressively attenuated landward by a decrease in the salinity of the pore fluids. In each part of the basin, the anhydrite fabric was also controlled by the texture and degree of lithification of the fine-grained primary gypsum lithofacies. Recrystallization of these anhydrite fabrics during late diagenesis, linked to deeper burial conditions, is insignificant, allowing reconstruction of the original anhydritization pattern. 相似文献