共查询到20条相似文献，搜索用时 109 毫秒
1.
Carbonatite-alkalic rocks occur in the form of dykes and small volcanic plugs in the area, with major central type volcanic activity restricted to Amba Dongar. The trappean flows of Blanford and Bose are identified as plagioclasecalcite rocks. An attempt is made to explain the origin of these rocks which are extensively cut by dykes of alkaline rocks, carbonatites and dolerites. By far the dominant lavas are «fissure phonolites» (Wright, 1963) and tinguaites. The chemical analyses of these rocks show that the magma is mainly of continental sodic alkaline suite, probably turning sodi-potassic, a suggestion drawn from the occurrence of lamprophyres and pseudoleucite tinguaites, and the higher potassium contents of some rocks. Bagh sediments are mainly represented by sandstones which show mild contact effects with carbonatite, especially in the south. 相似文献
2.
Johannes Kjøde 《Physics of the Earth and Planetary Interiors》1980,21(1):38-49
Palaeomagnetic investigations have been carried out on 12 dykes of Late Precambrian age from the Varanger peninsula, north Norway. The dykes are separated into two groups, the Kongsfjord dykes and the Båtsfjord dykes. In the Kongsfjord dykes, titanomagnetite is almost entirely erased, as a result of an extreme degree of alteration. Pyrrhotite is the dominating magnetic mineral, and only three stable specimen directions can be defined. In the Båtsfjord dykes, however, the most important magnetic constituent is nearly pure magnetite, and a two-axis magnetization structure is revealed. The directions of the major component conform to a Fisherian distribution, and are assumed to represent the relative Late Precambrian field. Superimposed on this magnetization is a minor component which is assumed to be of Caledonian origin, probably Ordovician. This latter remanence is in accordance with other Middle Palaeozoic results obtained in Western Europe. The upper age limit of the Late Precambrian field is discussed, and it is proposed that the polar shift from the Late Precambrian position to the main Palaeozoic group may have occurred as late as Middle Ordovician. 相似文献
3.
Flood basalts, such as the Deccan Traps of India, represent huge, typically fissure-fed volcanic provinces. We discuss the
structural attributes and emplacement mechanics of a large, linear, tholeiitic dyke swarm exposed in the Nandurbar–Dhule area
of the Deccan province. The swarm contains 210 dykes of dolerite and basalt >1 km in length, exposed over an area of 14,500 km2. The dykes intrude an exclusively basaltic lava pile, largely composed of highly weathered and zeolitized compound pahoehoe
flows. The dykes range in length from <1 km to 79 km, and in thickness from 3 to 62 m. Almost all dykes are vertical, with
the others nearly so. They show a strong preferred orientation, with a mean strike of N88°. Because they are not emplaced
along faults or fractures, they indicate the regional minimum horizontal compressive stress (σ
3) to have been aligned ~N–S during swarm emplacement. The dykes have a negative power law length distribution but an irregular
thickness distribution; the latter is uncommon among the other dyke swarms described worldwide. Dyke length is not correlated
with dyke width. Using the aspect ratios (length/thickness) of several dykes, we calculate magmatic overpressures required
for dyke emplacement, and depths to source magma chambers that are consistent with results of previous petrological and gravity
modelling. The anomalously high source depths calculated for a few dykes may be an artifact of underestimated aspect ratios
due to incomplete along-strike exposure. However, thermal erosion is a mechanism that can also explain this. Whereas several
of the Nandurbar–Dhule dykes may be vertically injected dykes from shallow magma chambers, others, particularly the long ones,
must have been formed by lateral injection from such chambers. The larger dykes could well have fed substantial (≥1,000 km3) and quickly emplaced (a few years) flood basalt lava flows. This work highlights some interesting and significant similarities,
and contrasts, between the Nandurbar–Dhule dyke swarm and regional tholeiitic dyke swarms in Iceland, Sudan, and elsewhere.
Editorial responsibility: J. White 相似文献
4.
Houjun Mei Chunjing Tang Sunrong Li Yongming Li Xingchun Zhang Dengrong Lu Lianchang Zhang 《中国科学D辑(英文版)》1998,41(1):54-92
It is known that the lamproites occur in the southeastern Guizhou Province and in the Dahong Mountains area, Hubei Province; and many para-lamproite occurrences spread in the west half part of the South China landmass. The para-larnproite diatremes in Ningxiang County, Hunan Province, contain a few of fine grains of diamond. Parts of the kimberlite pipes and dykes in Mengyin County, Shandong Province, consist locally of basic kimberlite; and the kimberlite dykes in the Maping kimberlite area, Zhenyuan County, Guizhou Province, consist of basic kimberlite principally. Although the diamondiferous kimberlites and lamproites occur always in the cratons within continental plate, both the potassium-rich ultramafic rocks display the geochemical features of the magmatism of post-collision in orogenic belt. Both the kimberlite and lamproite magmas may originate from the local parts of the mantle transition zone, where the mantle contains the matter of ancestor slab of ancient subduction zone. And, both the K-rich ultramafic magmas generated in an active mantle plume, which came from the boundary between the core and the lower mantle. The basic kimberlite magma may be more capable of preserving the crystals of the diamond type 11. 相似文献
5.
The stress field in the vicinity of a body of fluid of simple geometry contained within a non-homogeneously stressed solid has been calculated and the result applied to the case of a magma body within a region of the crust subject to triaxial stresses. The types of faulting and minor intrusion which result are described. The theory indicates that the regional stresses in the crust together with the magma pressure control the type of faulting, the form of the minor intrusions and the occurrence of eruptions from the magma body. The stress conditions favouring caldera formation, the intrusion of radial dykes, dyke swarms and cone sheets are described. 相似文献
6.
T. Krishnamacharlu 《Bulletin of Volcanology》1971,35(4):947-956
The basaltic lava flows of the Deccan Traps in the Dadiapada area are traversed by abundant dykes trending mostly in ENE to WSW direction. The density of the dykes distribution is 2 to 3 per mile. They vary in size from a few feet to 300 feet in width and some can be traced for many miles. Some of the dolerites contain quartz in considerable amounts and it is significant to find micropegmatite texture in them indicating their tholetitic nature. 相似文献
7.
Earthquake-controlled event deposits and its tectonic significance from the Middle Permian Wandrawandian Siltstone in the Sydney Basin,Australia 总被引：3，自引：0，他引：3
DU Yuansheng G. R. Shi & GONG Yiming . Faculty of Earth Sciences China University of Geosciences Wuhan China . School of Ecology Environment Deakin University Victoria Australia 《中国科学D辑(英文版)》2005,48(9):1337-1346
Earthquake is a disaster event resulting from rapid and intensive crustal vibration caused by fault activity, volcanic eruption, or block dilapidation. Heezen and Ewing[1] and Heezen and Dyke[2] were the first to note earthquake-related mass movement and associated deposits in connection to the turbidity currents and submarine slumps triggered by the Grand Bank Earthquake in 1929. Seilacher[3] defined redeposited sedimentary beds, disturbed and modified by earth- quakes, as seismite. Since t… 相似文献
8.
Skcelov Zuzana Rapprich Vladislav Ml
och Bed&#x;ich 《Journal of Volcanology and Geothermal Research》2009,187(1-2):26-32
Basaltic rocks with low K, U and Th contents dominate the entire Volcanic Complex of the Doupovské hory Mts. Significant potassium anomaly exceeding 1.5 atomic wt.% of potassium over an area of 4 × 8 km and 2 atomic wt.% of potassium over an area of 2 × 6 km was defined by airborne gamma-ray spectrometry above the central part of the Doupovské hory Volcanic Complex. The following detailed field study, supported by field and laboratory gamma-spectrometry measurements and geochemical analyses of rock samples, resulted in discovery of a swarm of potassium-rich trachytic dykes. The existence of such highly-differentiated rocks in the volcanic complex was unknown till present. These dykes are commonly less than 1 m wide, but their potassium content varies between 4 and 8 atomic wt.%. Owing to this high-K composition and relative abundance of dykes, the dyke rocks significantly modify the regional pattern of gamma-spectrometry data. The potassium anomaly cannot be explained by the presence of Flurbühl intrusive body dominated by ijolites and essexites, as all these rocks are poor in K, with potassium typically not exceeding 1.5 wt.%. On the other hand, much more extensive intermediate trachybasaltic lavas with K content varying within the range 1.8–3 wt.% cause only minor or undetectable anomalies. 相似文献
9.
Deccan Traps are the most extensive geological formations of Deccan Peninsula with the exception of only the metamorphic and igneous complex of Archaean age. Based on their mode of emplacement, geomorphic setting and hydrogeological behaviour over an area of about 5,000 sq. km the authors have classified the Deccan Traps of western Maharashtra into 3 groups, namely, (1) The Deccan Traps of Dhulia district, characterised by numerous dolerite dykes, (2) Areally extensive trap flows of Sholapur and Osmanabad districts resulting from slow and quiescent type of flood eruption occupyng the gently undulating terrain, and (3) the traps of Kolaba, Thana and Bombay-Poona regions characterised by intertrappean sediments, dolerite dykes and volcanic ash beds, indicative of violent outbursts resulting in the Sahyadri geomorphologic unit. The groundwater possibilities in the three groups are to a great extent governed by the nature and constitution of the individual flows. The massive traps with their fracture porosities, the vesicular traps with their minutely interconnected and partly filled vesicles and the intertrappen sediments with their primary porosities play a decisive role in determining the groundwater possibilities in them. In Dhulia district the dolerite dykes to a great extent control the movement of groundwater, and success or otherwise of the well field area depends very much upon its location with reference to adjacent dykes. Areally extensive thick vesicular traps with their gentle dips towards east, in Sholapur district, have to be explored for possible artesian conditions in the downdip directions of the trappean units to be tapped. In the case of Poona, Thana and Kolaba districts, exploratory drilling based on geophysical data (to delineate the nature and extent of water bearing horizons) has to be resorted to. It is, therefore, imperative to sub-divide at this stage Taylor’s Single Unit of Deccan Trap Groundwater Province into 3 Sub-Provinces, based on geomorphological, geological and geohydrological setting in the region of western Maharashtra of the present investigation. 相似文献
10.
A new multidisciplinary study, combining geology, petrography, and geochemistry, on the rocks of the isolated hill of Mount
Calanna (Mount Etna, Italy) has provided evidence for the existence of a dyke swarm, formed by more than 200 dykes distributed
over an area of ~0.7 km2, with an intensity of intrusion up to 40%. All bodies are deeply altered, and the geological and mesostructural surveying
of 132 dykes revealed that they intruded in E–W direction, with an average dip of 60°. The faults affecting the outcrop have
in general an E–W strike and dip of ~55°: these have all normal motion and have been interpreted as coeval with the dykes.
This interpretation contrasts with the previous hypothesis that considered Mount Calanna as a thrust resulting from compressive
deformation resulting from the gravitational spreading of the volcanic edifice. Mount Calanna is here interpreted as the uppermost
portion of a vertically extensive magmatic plexus that fed the eruptive activity of one (or more) eruptive center/s sited
in the Valle del Bove area. Measurements of the apparent densities on 23 dykes and host rock samples give an average value
of 2,420 kg/m3 for the entire complex, ~15% lower than the density expected for hawaiitic magma, placing an important constraint on the
geophysical identification of similar structures. Considering that Mount Etna is not an old eroded edifice but an active and
growing volcano, the exposure of this subvolcanic structure can be regarded as exceptional. Its geometry and physical characteristics
can be thus regarded as an interesting example of the present-day shallow plumbing system of Mount Etna as well as of other
basaltic volcanoes. 相似文献
11.
Marthabreen is a 7·8 km long valley glacier in SW Spitsbergen. The glacier is partially covered by a layer of angular debris derived from rockfall in its accumulation area, pierced in places by pinnacles and ridges of glaciofluvial sediment. These concentrations of glaciofluvial sediment fall into three categories: (1) debris pinnacles; (2) longitudinal sediment dykes; (3) longitudinal ridge accumulations. Debris pinnacles are slabs of sediment (predominantly sands, gravels and cobbles) elevated to the glacier surface along thrusts. Longitudinal sediment dykes are low (<0·5 m high) ridges of debris melting out of vertical sediment dykes within the body of the glacier. They are composed of a range of facies including sands, granule gravels, pebble gravels and diamiction. These dykes are sub-parallel to the longitudinal foliation on the glacier and form during folding of the stratification. Longitudinal ridge accumulations are higher (>1 m high) ridges of sorted sand and gravels which are not associated with penetrative ice structures. Their occurrence downglacier of sediment dykes and debris pinnacles suggests that they originate as supraglacial or englacial channels or tunnels filled by sediment derived from the dykes or thrusts. The presence of large quantities of glaciofluvial sediment on the surface of Marthabreen does not imply englacial water flow at high levels within the glacier, but is related to ice deformational processes such as thrusting and folding of debris-rich stratification. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
12.
Study on the carbonate ocelli-bearing lamprophyre dykes in the Ailaoshan gold deposit zone, Yunnan Province 总被引：1，自引：0，他引：1
Three carbonate ocelli-bearing lamprophyre dykes have been found in the Laowangzhai and Beiya gold orefields in the northern
sector of the Ailaoshan gold deposit zone, Yunnan Province. Ocelli in the lamprophyre dykes are carbonates composed mainly
of dolomite and calcite. Their trace elements, REE and C isotopic compositions are characteristic of carbonatite and the main
mineral assemblages, major elements, trace elements and REE in the matrix are similar to those in the carbonate ocelli-barren
lamprophyre dykes in the orefields, which are calc-alkaline lamprophyres that derived from the fertile mantle. The results
indicate that the carbonate ocelli-bearing lamprophyre dykes in this area were produced at the time when the Himalayan lamprophyre
magma evolved to a relatively late stage of silicate-carbonate liquid immiscibility. In the process of magmatic evolution
there took place magmatic degassing with CO2 and H2O as the dominant released gases. 相似文献
13.
Karroo (Triassic-Jurassic) sediments and lavas occupy a N.N.E.-trending trough known as the Tuli Syncline 230 km in length by 45 km wide along the southern margin of Rhodesia. The structure is fault bounded, especially on the north, and comprises a sequence of gently inward dipping lava flows cut by numerous E-W and N.N.E. striking dolerite dykes. The igneous rocks have been subdivided on the basis of mineralogy and chemistry into a stratigraphic sequence of limburgites near the base, olivine basalts and upper augite-plagio-clase-phyric basalts. In addition, rare shoshonite and absarokite types occur. Twentyfour new silicate analyses are comparable to those from rocks in the neighbouring Nuanetsi Province of Rhodesia, and show strong affinities to the northern province Karroo basalts of southern Africa as defined by Cox,McDonald andHornung (1967). 相似文献
14.
15.
Giancarlo Serri 《Earth and Planetary Science Letters》1981,52(1):203-212
Ophiolites have been divided into two groups: high-Ti and low-Ti types. These can be discriminated by studying the fractionation trends of both gabbroic complexes (this work) and lavas and dykes [16], particularly in the TiO2/M.I. diagram. The first type typically shows MORB-like magmas whereas in the second the magma types have a spectrum of composition from mid-ocean ridge basalts to island arc tholeiites and boninite-like magmas often occur.High-Ti ophiolites are petrologically and geochemically similar to major oceanic and ensialic back-arc basin crusts as well as oceanic crust generated during the intermediate and late-stage opening of intraoceanic back-arc basins.Parental magmas and fractionation processes of low-Ti ophiolites fit with an hypothesis of their formation in the early stage of opening of intraoceanic back-arc basins. 相似文献
16.
The Deccan Trap basalts have long been considered to be products of fissure eruptions and the dykes intruding them have been supposed to represent the fissures of eruption. However, the question of the mode of eruption of Deccan Trap lavas seems to need more careful consideration in view of the features brought to light by detailed field work in Western Maharashtra. Detailed studies of dykes suggest that majority of the dykes could not have acted as feeders as previously supposed. When examined in detail the basalt flows have more often been found to have only a limited lateral extent and are not always quite horizontal. Thin irregular flows with ropy surfaces, dipping in different directions and piled up into a chaotic mass are frequently met with, indicating eruption from local vents of the central type. Volcanic vents are found at a number of widely separated localities. All this suggests that many lavas are products of central type of volcanicity. However, central type of volcanoes would be inadequate to account for the vast amounts of lavas, and as the known dykes are not likely to have acted as feeders, and dykes still remain to be reported from large portions of the Deccan Trap area, the question of how the lavas came to the surface largely remains unanswered. Extensive beds of volcanic breccia traceable over a few miles and upto 50 feet thick are met with. As such extensive beds are more likely to be associated with fissure cruptions the question arises whether these fissure eruptions were accompanied by considerable explosive activity. 相似文献
17.
G. Wadge 《Bulletin of Volcanology》1986,48(6):349-372
The orientations of dykes from many of the islands of the Lesser Antilles island arc have been mapped. Most of these dykes can be interpreted in terms of local or regional swarms derived from specific volcanoes of known age, with distinct preferred orientations. Dykes are known from all Cenozoic epochs except the Palaeocene, but are most common in Pliocene, Miocene and Oligocene rocks. A majority of the sampled dykes are basaltic, intrude volcaniclastic host rocks and show a preference for widths of 1–1.25 m. Locally, dyke swarms dilate their hosts by up to 9% over hundreds of metres and up to 2% over distances of kilometres. The azimuths of dykes of all ages show a general NE-SW preferred orientation with a second NW-SE mode particularly in the Miocene rocks of Martinique. The regional setting for these minor intrusions is a volcanic front above a subduction zone composed of three segments: Saba-Montserrat, Guadeloupe-Martinique, St. Lucia-Grenada. The spacing of volcanic centres along this front is interpreted in terms of rising plumes of basaltic magma spaced about 30 km apart. This magma is normally intercepted at crustal depths by dioritic plutons and andesitic/dacitic magma generated there. Plumes which intersect transverse fracture systems or which migrate along the front can avoid these crustal traps. Throughout its history the volcanic front as a whole has migrated, episodically, towards the backarc at an average velocity of about 1 km/Ma. The local direction of plate convergence is negatively correlated with the local preferred orientation of dykes. The dominant NE-SW azimuth mode corresponds closely to the direction of faulting in the sedimentary cover of the backarc and the inferred tectonic fabric of the oceanic crust on which the arc is founded. A generalised model of the regional stress field that controls dyke intrusion outside of the immediate vicinity of central volcanic vents is proposed, in which the maximum horizontal stress parallels the volcanic front except in the northern segment where subduction of the Barracuda Rise perturbs the stress field. There is also evidence of specific temporal changes in the stress field that are probably due to large scale plate kinematics. 相似文献
18.
Abstract The Archean to Paleo–Proterozoic Bundelkhand massif basement of the central Indian shield has been dissected by numerous mafic dykes of Proterozoic age. These dykes are low‐Ti tholeiites, ranging in composition from subalkaline basalt through basaltic‐andesite to dacite. They are enriched in light rare earth elements (LREE), large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE: Nb, P and Ti). Negative Sr anomaly is conspicuous. Nb/La ratios of the dykes are much lower compared with the primitive mantle, not much different from the average crustal values, but quite similar to those of continental and subduction related basaltic rocks. Bulk contamination of the mantle derived magma by crustal material is inadequate to explain the observed geochemical characteristics; instead contamination of the mantle/lithospheric source(s) via subduction of sediment is a better proposition. Thus, in addition to generating juvenile crust along the former island arcs, subduction processes appear to have influence on the development of enriched mantle/lithospheric source(s). The Bundelkhand massif basement is inferred to represent subduction related juvenile crust, that experienced lithospheric extension and rifting possibly in response to mantle plume activities. The latter probably supplied the required heat, material (fluids) and extensional environment to trigger melting in the refractory lithospheric source(s) and emplacement of the mafic dykes. Proterozoic mafic magmatic rocks from Bundelkhand, Aravalli, Singhbhum and Bastar regions of the Indian shield and those from the Garhwal region of the Lesser Himalaya display remarkably similar enriched incompatible trace elements characteristics, although limited chemical variations are observed in all these rocks. This may indicate the existence of a large magmatic province, different parts of which might have experienced similar petrogenetic processes and were probably derived from mantle/lithospheric source(s) with similar trace element characteristics. The minor, less enriched to depleted components of the Jharol Group of the Aravalli terrane and those from the Singhbhum terrane may represent protracted phases of rifting, that probably caused thinning and mobilization of the lithosphere, facilitating the eruption/emplacement of the asthenospheric melts (with N‐ to T‐types mid‐oceanic ridge basalts signatures) and deposition of deep water facies sediments in the younger developing oceanic basins. In contrast, Bundelkhand region did not experience such protracted rifting, although dyke swarms were emplaced and shallow water Bijawar Group and Vindhyan Supergroup sediments were deposited in continental rift basins. All these discrete Proterozoic terranes appear to have experienced similar petrogenetic processes, tectonomagmatic and possibly temporal evolution involving subduction processes, influencing the lithospheric source characteristics, followed by probably mantle plume induced ensialic rifting through to the development of oceanic basins in the Indian shield regions and their extension in the Lesser Himalaya. 相似文献
19.
Petrographic, geochemical and geochronological data on the volcanic sequences of the Sadah region (Yemen Arabic Republic — Y.A.R.) are presented and discussed. Two main volcanic units have been recognized in this area. The older unit (Trap Series) is characterized by alkaline and transitional basalts with minor differentiates. K/Ar age determinations on these rocks give values ranging from 30 to 22 m.y.B.P. The dominance of poorly evolved rock types indicates a fairly rapid ascent of the magmas. The feeding fissures are thought to be NNW-SSE trending fractures. This is deduced by the occurrence of many dykes cutting through the underlying basament which are comparable in both chemical composition and age range to those of the Trap Series. The younger unit (Al Harf Series) is made up of alkaline basalts whose K/Ar ages are around 10 m.y.B.P. and outcrops in a tectonic depression defined by NNW-SSE trending normal faults. The volcanism in the northern Y.A.R. extends from late Oligocene to late Miocene, and follows regional structures parallel to the present-day spreading axis of the Red Sea. 相似文献
20.
《Journal of Volcanology and Geothermal Research》2007,159(1-3):85-107
The Neoproterozoic (815.4 ± 4.3 Ma) Aries kimberlite intrudes the King Leopold Sandstone and the Carson Volcanics in the central Kimberley Basin, northern Western Australia. Aries is comprised of a N–NNE-trending series of three diatremes and associated hypabyssal kimberlite dykes and plugs. The diatremes are volumetrically dominated by massive, clast-supported, accidental lithic-rich kimberlite breccias that were intruded by hypabyssal macrocrystic phlogopite kimberlite dykes and plugs with variably uniform- to globular segregationary-textured groundmasses. Lower-diatreme facies, accidental lithic-rich breccias probably formed through fall-back of debris into the vent with a major contribution from the collapse of the vent walls. These massive breccias are overlain by a sequence of bedded volcaniclastic breccias in the upper part of the north lobe diatreme. Abundant, poorly vesicular to nonvesicular, juvenile kimberlite ash and lapilli, with morphologies that are indicative of phreatomagmatic fragmentation processes, occur in a reversely graded volcaniclastic kimberlite breccia unit at the base of this sequence. This unit and overlying bedded accidental lithic-rich breccias are interpreted to be sediment gravity-flow deposits (including possible debris flows) derived from the collapse of the crater walls and/or tephra ring deposits that surrounded the crater. Diatreme-forming eruptions may have been initiated by magma–water interactions along fracture and joint-controlled aquifers within the King Leopold Sandstone. The current level of exposure of the diatremes probably extends from the lower-diatreme facies up into the base of a bedded upper-diatreme sequence. 相似文献