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1.
内蒙古大青山煤田晚古生代砾岩的沉积特征 总被引：3，自引：0，他引：3
大青山煤田晚古生代地层中有 1 4层沉积砾岩。其中,晚石炭世地层中赋存 8层,二叠世 6层。通过对这些砾岩层的野外测量、室内岩矿鉴定等综合分析研究,查明晚石炭世的砾岩几乎全是稳定的单成分砾岩,石英砂岩和燧石质砾石的含量高达 93 %以上,砾石最大扁平面均向南倾,倾角在 5° - 1 0°之间,与砾岩伴生的粗粒石英砂岩发育大型低角度双向交错层理,萨胡环境判别参数等特征表明晚石炭世砾岩为滨海环境下的产物。二叠世的砾岩则主要是复杂成分的砾岩,尤其是早二叠世晚期及晚二叠世初期形成的 2层砾岩中砾石种类达 1 5种,以中酸性火山岩和火山碎屑岩砾石为主,并含较多量的变质岩和中酸性侵入岩砾石,砾岩层各种特征表明二叠世砾岩为河流相产物。大青山煤田晚古生代沉积砾岩的形成与北部造山带的隆升密切相关,它们是前陆盆地的沉积产物。 相似文献
2.
The Pb-Zn-ores of Minas de Cartes, Sierra de Cartagena, Spain, occur in a zon along the lower boundary of a Miocene sequence and along post-Miocene faults. Pebbly mudstone beds in the Miocene are slump sediments, which by their lithological properties form preferred horizons for the spreading of the mineralization. Faulting and flexuring have caused cavernous fault breccias in the relatively competent pebbly mudstones, while dissolution of carbonate pebbles and carbonates in the matrix of these rocks has resulted in solution cavities. The brecciated cavernous pebbly mudstones form channelways for ore solutions and sites of deposition of ore streaks with marcasite, pyrite, galena, sphalerite and quartz. The mineralization is of typical cavity-filling nature and so-called “ore pebbles” are fillings of pebble-shaped voids resulting from selective dissolution of carbonate pebbles. The ores were formed by near-surface subvolcanic-hydrothermal processes in relation with Late Tertiary trachyandesitic volcanism in the region. 相似文献
3.
Earth's oldest preserved conglomerates and basaltic pillow lavas at Isua, Greenland, provide robust field evidence for deep- and shallow-water environments on our planet within the first billion years of its formation. The conglomerates represent the first Paleoarchaean archive of sub-aerial erosion and shallow water sedimentation. These ca. 3700 million year old sedimentary rocks, now metamorphosed at amphibolite grade, comprise units of rounded quartz pebbles set in a sandy to muddy matrix that unconformably overlie an ophiolite sequence. The pillow lavas of the ophiolite are variolitic and essentially vesicle-free, indicative of formation in a deep water environment. Locally, an unconformity separates the conglomerates from the deformed ophiolite-related rocks; elsewhere the contact between these units is tectonic. Such field relationship between deep and shallow water environments resemble those preserved in younger orogenic belts, where obducted oceanic crust has been tectonically emplaced across terrestrial platforms or subaerial parts of forearc and backarc basins. 相似文献
4.
Paragenesis of mineralization within fractured pebbles in Witwatersrand conglomerates 总被引：2，自引：0，他引：2
John Parnell 《Mineralium Deposita》2001,36(7):689-699
Mineralized conglomerates in the Witwatersrand goldfields consistently exhibit intense fracturing of quartz pebbles. The fractures are coated with quartz, phyllosilicates, organic matter, uraninite, gold, and base metal sulfide minerals, showing that all of these phases were at least partially epigenetic. Samples from five goldfields (Evander, West Rand, Carletonville, Klerksdorp, Welkom) across the Witwatersrand Basin show comparable paragenetic sequences of fracture-fillings. This implies that fracturing and several episodes of mineral deposition were basinwide events, rather than the result of local processes. Fluid inclusion data for the quartz indicates precipitation from these basinwide fluids at relatively low temperatures (<250 °C), which may be consistent with other evidence for mineralization following the Vredefort Event at 2025 Ma. 相似文献
5.
A. V. Solov’ev T. N. Palechek M. N. Shapiro S. A. Johnston J. I. Garver D. M. Ol’shanetskii 《Stratigraphy and Geological Correlation》2007,15(1):112-119
In the Sredinnyi Range of Kamchatka, the Baraba Formation of continental conglomerates is assumed to be of the late Campanian age based on found flora remains, but data of isotopic geochronology suggest the Eocene age of these deposits. New data on radiolarians from cherty pebbles are considered in this work along with results of fission-track dating of zircons from pebbles and matrix of the Baraba conglomerates. Fission-track dates obtained for zircons from matrix approve the Eocene age of the Baraba Formation, and new dates characterizing pebbles are not contradicting this conclusion. The Baraba Formation structural position can hardly be lower, therefore, than that of the Irunei Formation. 相似文献
6.
《International Geology Review》2012,54(1):65-72
Chert-plus-pyrite pebbles have been known for some time in a number of Witwatersrand conglomerates, but their distribution is highly variable. A wide variety of textures in chert-plus pyrite pebbles are documented here, and these textures place constraints on the origin of such pebbles. Replacement of chert pebbles by pyrite is indicated (pyrite grains and aggregates continue across many pebble boundaries), and both distributional and textural evidence favors a post-burial timing for this process. Significant mobility of sulfur after burial is indicated. Whether this replacement was diagenetic or metamorphic is not certain. 相似文献
7.
T.J. McEwen 《Journal of Structural Geology》1981,3(1):25-37
The fracture patterns produced in pitted pebble conglomerates from the Alpine Molasse and the Carboniferous of northern Spain, have been studied in relation to the stress concentrations which were produced in the conglomerates during their deformation. The stress distributions which develop around pebble contacts at different stages of their pitting history have been determined from photoelastic experiments. The development of different types of fracture, having dominantly tensile or shear components, and their distribution within the pebbles, are shown to be related to the mineralogy of the pebbles, the strength of the matrix and the amount of deformation the conglomerate has suffered. 相似文献
8.
Two types of eclogite pebbles were discovered in Middle to Upper Jurassic conglomerates from the Hefei Basin north of the Dabie ultrahigh-pressure (UHP) terrain, China. Type A eclogite pebbles are characterized by idioblastic garnet with well preserved chemical zonation. Si content in phengite is lower than 3.5 per formula unit (pfu). The maximum metamorphic pressure is lower than 2.5 GPa, and the temperature is below 600 °C. Type B eclogite pebbles contain coesite pseudomorphs in xenoblastic garnet. Si content in phengite is higher than 3.5 pfu. The maximum metamorphic pressure is 2.8–4.0 GPa at 700 °C indicating UHP metamorphism.
Types A and B eclogite pebbles are comparable with eclogites occurring in the southern portion of the Dabie UHP terrain. Based on the petrologic similarities and northeastwards directed paleocurrents, we infer that the eclogite pebbles were eroded from the Dabie UHP terrain. Sandstones containing detrital phengite with Si content higher than 3.5 pfu are also derived from UHP rocks. These petrologic and stratigraphic data place time constraints on exhumation and erosion history of the Dabie UHP terrain. 相似文献
9.
华北地台早古生代竹叶状灰岩岩石特征及成因研究进展 总被引：1，自引：0，他引：1
砾屑灰岩在华北地台寒武系-奥陶系广泛发育,竹叶状灰岩只是其中一种,且所指范围界限模糊,常与其他类型的砾屑灰岩伴生在一起。古代陆表海提供了砾屑灰岩广泛发育的环境基础。潮坪和潮下开阔海是陆表海广泛发育的基本地貌单元,也是砾屑灰岩形成的重要场所。古板块运动表明,寒武纪华北地台处于低纬度地区,符合古风暴频发的要求。风暴及潮汐流是砾屑灰岩形成的主要动力。另外,成岩过程中的压实和固结脱水也是板条状砾屑的重要成因。条带状薄层灰泥石灰岩与泥岩及泥质灰岩的频繁互层是发生破碎并形成砾屑的物质基础。华北地台砾屑灰岩具有多种成因,可以按照砾屑的颜色特征、形态及磨圆程度、砾屑灰岩的支撑结构、充填物的类型等进行区分并进行成因分析。 相似文献
10.
In south Cumbria, Permo-Triassic breccias and conglomerates (‘brockram’) are exposed only at Rougholme Point on the Cartmel peninsula. In 1973 the Institute of Geological Sciences Humphrey Head borehole penetrated 257 m of brockram before entering probable Upper Carboniferous sediments. The brockram consists of pebbles of carbonate, chert and basalt in a matrix of haematite-stained quartz sand. Carbonate and chert fragments were derived from the upper part of the Carboniferous Limestone sequence exposed today nearby. Basalt clasts were derived from lavas, which appear to have cooled in a subaqueous environment, at least in part. They were locally derived and are the only certain evidence for Carboniferous volcanic activity in south Cumbria. As volcanic fragments increase in abundance towards the base of the borehole they must have been derived from the top of the succession being eroded and are probably of Brigantian age. Carbonate fragments were dolomitized soon after incorporation in the brockram, probably by saline fluids derived from the evaporative Zechstein Sea. The dolomitization was incomplete, leaving remnant limestone cores to clasts which were subsequently dissolved. The resultant vugs were infilled by dolomite, calcite and gypsum cements, which have been partially weathered from outcropping brockram, leaving hollow pebbles. 相似文献
11.
Microfabrics of detrital quartz grains and quartz cement of four gold- and uranium-bearing conglomerates of various goldfields of the Witwatersrand Basin, South Africa, were investigated by optical and cathodoluminescence microscopy. The study revealed that the vast majority of quartz grains (<5 mm) originate from felsic magmatic source rocks. Cherts and polymineralic mineral grains, pointing to greenschist to amphibolite facies metasedimentary rocks, follow in abundance, whereas diagenetic to weakly metamorphosed quartzites are subordinate. Material from hydrothermal vein quartz is almost completely lacking, both in the sand and in the pebble fraction. No obvious relationships are discernible between the varying proportions of detrital siliciclastic components of the different reefs and their ore grades. Assuming a sedimentological control of gold distribution, this finding supports multiple sources for the detrital components, which were thoroughly mixed during transport. The post-depositional history of the sediments is characterized by a complex polyphase succession of deformation, cementation and hydrothermal alteration events. Both fragmentation and pressure solution features within detrital quartz, quartz cement and round grains of pyrite, zircon, chromite and uraninite demonstrate that these materials were present in the conglomerates during diagenesis, and, thus, are true detrital grains with abraded, rounded grain morphologies. By analogy, it is assumed that gold is also a detrital component, although most of the gold grains display characteristics of hydrothermal overprinting. During subsequent metamorphism, micro-shear zones are developed, and brittle-ductile crystal-plastic deformation and limited quartz recrystallization occur. Maximum temperatures of about 350 °C were reached on the prograde metamorphic path. Recrystallization and redistribution of detrital siliciclastic and ore minerals took place, and various hydrothermal/metamorphic minerals including chlorite, sericite, pyrophyllite and chloritoid were formed. These redistribution processes involved existing detrital minerals only and were generally isochemical because little evidence exists for the development of a secondary porosity and permeability that would allow major external inputs into the Witwatersrand conglomerates. Most of the gold grains have hydrothermal characteristics, as evidenced by their authigenic, crystalline shapes and their chemical compositions. However, these features are regarded to result from overprinting. Most likely, the gold grains experienced more drastic modifications relative to other ore components because of the ductile and mobile nature of gold. The retrograde metamorphic path is characterized by percolating radioactive fluids at T<300 °C, recorded by radiation damage indicated by cathodoluminescence alteration rims along quartz grain boundaries and microcracks. The degrees of radiation damage observed are proportional to the uranium contents of the conglomerate ores. The collective evidence of our study supports the modified placer model for the genesis of the Witwatersrand ores. This model explains most of the observations on the detrital mineral assemblage and its post-depositional modification elegantly and in a satisfactory manner. 相似文献
12.
A. V. Melnikov S. G. Agafonenko I. V. Babichev Yu. G. Piskunov V. G. Moiseenko 《Doklady Earth Sciences》2013,449(2):380-385
The Upper Selemdzha minerogenic zone, which has the potential for noble metal mineralization in the Upper Amur, has been studied. It is confined to the thick strata of Paleozoic terrigeneous-sedimentary rocks (sandstones, siltstones, clay schists, packages of their thin rhythmical interlayering, sedimentary breccias, and conglomerates) in the Tokura subzone of the Selemdzha-Kerbinsk zone in the Amur-Okhotsk area of the Mongol-Okhotsk system, overlain by Early Cretaceous volcanogenic sedimentary rocks and intruded by Early Cretaceous quartz diorites, granodiorites, and dacites. In the Malomyr and Sagur-Semertak ore clusters, there are a few known potential deposits of noble metals and ore occurrences; when studied and prospected, they can exhibit vein-veinlet noble metal mineralization with rich contents of gold and platinoids in ore columns and metasomatic deposits. 相似文献
13.
《Journal of Structural Geology》2001,23(2-3):421-429
Geometrical and mechanical characteristics of the deformation of poorly cemented conglomerates are described. Using striated pebbles for analysis of palaeostresses, it is crucial to distinguish radial striation patterns, which result from deformation of the matrix around a rigid pebble, from unidirectional striation patterns that represent shear zones crossing the conglomeratic material. Examples of palaeostress determinations from striations of the latter type are given for extensional settings (Provence) and compressional settings (Southern Apennines, Southwest Alps). Their comparison with fault analyses in brittle rocks that underlie the conglomerates validates their usefulness for palaeostress analyses and suggests that some conglomerates behave as materials containing pre-existing surfaces of mechanical anisotropy that fail by sliding on some suitable oriented surfaces. These examples show that sheared conglomerates can be used for stratigraphic dating of the deformation, for studies of syndepositional deformation and for neotectonic analysis. 相似文献
14.
L. V. Anfimov 《Lithology and Mineral Resources》2000,35(2):189-191
Using an instrumental technique, we carried out a direct comparison of quartz from the Riphean sandstones, sandy fractions
from fragments in the Riphean conglomerates and Archean crystalline rocks, which represent the basement inlier of the Russian
Platform within the Western Urals (Taratash anticlinorium). It is shown that clastic quartz in the Riphean basal complexes
was mainly related to denudation of the Lower Proterozoic platformal cover, whose rocks occur as fragments in the Riphean
conglomerates. The probable contribution of eroded crystalline rocks into the Riphean sediments was presumably very insignificant. 相似文献
15.
Unusual intraclastic limestones in Lower Triassic carbonates and their bearing on the aftermath of the end-Permian mass extinction 总被引：5，自引：0，他引：5
Flat pebble conglomerates were a common carbonate facies in Cambrian to Early Ordovician open marine settings, but they become extremely rare in these environments after this time. However, the Early Triassic witnessed an anachronistic reappearance of flat pebbles, together with other intraclast types, in a range of carbonate depositional settings. In south China, flat pebble conglomerates are encountered in storm-dominated, platform carbonates to deep basinal settings, while prefossilized bivalve intraclasts and flat pebbles are common in mid-ramp facies of northern Italy. The emplacement mechanisms of the intraclast-bearing beds appear to have been diverse and to have included basinal turbidity flows and storm-generated hyperconcentrated flows: true storm beds, deposited under combined flow conditions, are rare. The cause of the widespread early lithification implied by the Early Triassic intraclasts appears to have been twofold: suppression of bioturbation, allowing the preservation of thin beds, and rapid submarine lithification. Both features appear to be a response to the widespread development of benthic dysoxia/anoxia during and following the end-Permian mass extinction. This event appears to have temporarily recreated the conditions that pertained in Cambro-Ordovician shelf seas. Flat pebble conglomerates may, therefore, constitute a proxy indicator of stressed environmental conditions associated with global anoxic/dysoxic events. 相似文献
16.
The study of the percentages of rhyolitic pebbles in the deposits of the rivers which cross the meridional part of the eastern plain of Corsica permits us to reconstitute the ancient shoreline in Mio-Pliocene times. The Fiumorbo is the only stream at present which removes pebbles of rhyolites (5%) before penetrating on to the plain. This kind of petrographic element comes from a single outcrop over which flows a tributary: “la Finosa”. Along the limit of the metamorphic area of Corsica, the edge of the eastern plain is constituted by a detrital formation consisting of conglomerates in which, near Saint Antoine, one can recognize the ancient delta of the Fiumorbo. Rhyolites represent 50% of all pebbles in it. This percentage regularly decreases with distance to the northeast. All river deposits contain rhyolitic pebbles but only after they have crossed this conglomerate and never before.We consider this formation to be the ancient shoreline of Corsica in the Mio-Pliocene. 相似文献
17.
In the southeastern area of the Neogene-Quaternary Granada Basin, ∼E–W trending normal faults crosscut ∼80 m-thick clay-bearing conglomerates and ∼30–40 m-thick carbonate grainstones containing centimeter-thick microconglomerate and sand interbeds. Three fundamental failure modes took place during fault nucleation: (1) phyllosilicate shear banding in the conglomerates, (2) jointing, mainly in the carbonate grainstones and (3) pressure solution in the carbonate matrix and grains of the microconglomerate and sand interbeds. Within the conglomerates, normal faults developed by pronounced clay smearing and, ultimately, cataclasis. Jointing also occurred within some of the pebbles surrounding the cataclastic rocks. In contrast, in the carbonate grainstones fault growth was characterized by predominant jointing and rock fragmentation, which localized in the extensional quadrants and/or releasing jogs of the evolving slip surfaces. Brecciation and cataclasis occurred only around the well-developed slip surfaces. Based upon their inner structure, we qualitatively assign a combined barrier-conduit fluid behavior to the tens of meters-throw normal faults juxtaposing the conglomerates against the carbonate grainstones. The inner fault cores inhibit fault-orthogonal fluid flow along their entire length. Instead, fault damage zones act as fluid barriers in the conglomerates, and as composite fluid conduits in the carbonate grainstones. 相似文献
18.
Striated and pitted pebbles provide scarce structures that preserve information on the stresses that their host rocks have undergone. This information can be obtained by the measurement of a large number of microfaults with striae and solution marks within a small rock volume. For non-rotational deformation, the statistical procedures for microfault analysis provide a valid tool for determining the overprinting of successive stress ellipsoids, including their axial ratios and the orientations of the main axes. The trends of compressions obtained from striae can be compared with the determinations from the pole of pebble solution pits. However, in complex tectonics settings, the solution pits of several deformation phases are mixed and only striae analysis allows overprinted paleostresses to be accurately distinguished. The analysis of several pebbles from the same outcrop, including five from moderately complex settings, allows determination of the homogeneity of the paleostresses at outcrop scale, the detection of redeposited pebbles, and supports the results of microtectonic analysis for large areas. Solution mark distributions on pebbles depend on the burial and tectonic stresses. Conglomerates from shallow levels, such as those from Quaternary fluvial terraces, only record horizontal compressional solution marks because the minimum vertical stress needed to develop these structures are not reached by burial.In the central Betic Cordillera, striated and pitted pebbles are composed of carbonate surrounded by a matrix containing siliciclastic elements. The study of several outcrops located across a transect of the Cordillera shows a change in the recent stress field. While conglomerates near the Internal–External zone boundary show extensional stresses that may be related to the uplift of the Cordillera since Tortonian times, the outcrops located in the External Zone and up to the mountain front indicate the existence of horizontal NW–SE and NE–SW compressions related to prolate ellipsoids. These two compression directions, which affect conglomerates up to the Quaternary in the same outcrop, may be produced by a local permutation of stress axes, which in general indicates NW–SE compression related to the Eurasia–Africa plate boundary convergence, but which locally may switch to an orthogonal compression. 相似文献
19.
陕西凤县-山阳中泥盆统发育的砾岩,包括泥砾岩、砾屑钠长板岩、砾屑白云质灰岩和砾屑状矿石,不仅空间上与热水沉积体密切相关,岩石化学成分也受到热水活动影响。笔者通过对该类砾岩岩石学和岩石化学详细研究,认为其形成受控于成矿期同沉积断裂,沿同沉积断裂发育海底地形差异变化而形成海底滞流深水洼地,同沉积断裂亦会触发海底重力流,这些砾岩即是在这些洼地中形成的重力流砾岩。此外,同沉积断裂作为热水上升的通道,会提供同沉积期矿化作用的热水介质,这些砾岩中的铅锌矿床即是这些同生期热水沉积作用的产物。 通过柞山矿田西部池沟组（D2ch）分布广泛的泥砾岩岩石学和岩石化学特征研究,结合区内矿床同位素测年资料和地层地球化学资料,笔者认为柞山矿田大西沟组（D2d）中赋存的菱铁-银-多金属-（金）热水沉积矿床系列,具有二次热水沉积特点。 相似文献
20.
Fabrice Cordey Pierre Tricart Stéphane Guillot Stéphane Schwartz 《Swiss Journal of Geoscience》2012,105(1):39-48
For the first time in the Western Alps, radiolarite pebbles collected from Tertiary foreland molasse conglomerates are treated for microfossil extraction and dated. Among forty pebbles collected in the field, seven of them released diagnostic radiolarian assemblages ranging in age from Late Bajocian?CEarly Callovian to Middle Oxfordian?CEarly Tithonian. These ages overlap previous biochronological data obtained from in situ localities of the Schistes Lustrés Piemont zone of the French-Italian Alps and triple the number of diagnostic radiolarite samples known so far in this segment of the chain. The diagnostic pebbles are characterized by low grade metamorphism, showing that some eroded thrust-sheets from the oldest parts of the ocean escaped any tectonic burial during the Alpine convergence. Mixing of low and high-grade radiolarites, mafics and ultramafics pebbles implies that various ocean-derived units were exposed. This tectonic scenario involves tight refolding and severe uplift of the Eocene subduction wedge in the Early Oligocene. 相似文献