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1.
The Droimchogaidh sill, south-central Mayo, is sheeted at high-level in the Ordovician sedimentary pile of the South Mayo Trough. This association now lies raised on the eastern fringe of the Connemara-Murrisk Tertiary uplift. The sill is basin-shaped with a maximum thickness of about 100 m. It is composed of isotropic or weakly layered olivine gabbro, and subordinate, locally-developed picritic cumulates and syenitic differentiates. The chemistry of the gabbro reveals the effects of post-emplacement hydrothermal circulation, but the magma that supplied the sill was probably similar in composition to that of the analcime-olivine dolerite dikes further west. The 40Ar/30Ar dating gives an age of 55 ± 1 Ma for the sill, consistent with a younger set of ages from the Irish/British Tertiary province. 相似文献
2.
The Precambrian–Cambrian boundary is iconic, marking the first appearance of shelly fauna in the fossil record, and opening the Phanerozoic Eon. In England and Wales, the transition from predominantly Precambrian igneous rocks to Cambrian sedimentary strata is generally unconformable. An exceptional exposure of this transition can be observed in the Ercall Quarries in Shropshire, a classic locality in all senses of the word. 相似文献
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Gabbros at Purimetla occur in close association with the alkaline pluton. Petrography and petrochemistry of these gabbros
indicate their tholeiitic nature. Chemical variation of these tholeiites suggests that an initial undersaturated tholeiitic
magma yielded oversaturated fractions in the final stages of differentiation. Their regional distribution suggests that basic
magmatism preceded the emplacement of the alkaline rocks in the Prakasam alkaline province. 相似文献
6.
Howard Falcon‐Lang 《Geology Today》2011,27(1):34-38
The Isle of Portland is one of the jewels in the crown of the ‘Jurassic Coast’ of Dorset, southern England. Thomas Hardy aptly described this limestone peninsula as the ‘Gibraltar of Wessex’, and used its stone quarries as the backdrop for one of his novels (The Well‐Beloved). Quarries then, as now, work the world‐famous Portland Stone—a Jurassic oolitic limestone—from which St Paul's Cathedral and many other well‐known buildings are constructed. Rocks exposed in the numerous disused quarries scattered across the isle, together with exposures in spectacular sea‐cliffs, paint a vivid picture of life and environments, ～150 million years ago. In addition to Jurassic patch‐reefs, coastal sabhkas, fossil forests and dinosaur footprints found in the bedrock, more recent geological phenomena include two Quaternary raised beaches, solution caves filled with vertebrates, and massive coastal landslips. The aim of this article is to provide a field guide for those wishing to explore the geology of this little‐known region for themselves. 相似文献
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The Pemali tin deposit is located in a Triassic granite pluton the magmatic evolution of which is characterized by a decrease of compatible Ca, Mg, Ti, P and Zr in the sequence: medium- to coarse-grained biotite granite, megacrystic medium-grained biotite granite, two-mica granite/muscovite granite. The tin mineralization is confined to the two-mica granite and consists of disseminated cassiterite as well as greisen-bordered veins. The highly evolved muscovite granite is tin-barren and is distinguished from the two-mica granite by its low mica content and low loss-on-ignition values. The fluid inclusions in quartz and fluorite of the two-mica granite and of the greisen homogenize in the 115–410 °C temperature range; the salinities are in the range of 0.4–23 equiv wt% NaCl and the CO2 concentrations are < 2 mole%. 相似文献
8.
S. Bergstøl 《Mineralium Deposita》1972,7(3):233-246
The large jacupirangite dyke at Kodal was first found by W.C. Brögger (1933) who published one chemical analysis of the rock. Recent investigations of the dyke as a potential ore body, including diamond-drilling operations, have shown that it is about 20 m wide and 2 km long. It strikes approximately E–W and has a general dip of 80 °S, cutting through larvikite and nordmarkite of the Oslo Permian Igneous Province. The jacupirangite has an average modal composition (volume percent): apatite 24, magnetite 37, ilmenite 9, pyroxene 25, amphibole and biotite 5. The iron-titanium oxides and apatite cement the pyroxene in a typical igneous texture. The Kodal dyke and other jacupirangites in adjoining areas of the Oslo Igneous Province all show a eutectic mixture of iron-titanium oxides and apatite which is assumed to form an immiscible liquid with silicate melts of monzonitic composition. This is assumed to be a possible explanation for the formation of the jacupirangites in the Oslo region.
Zusammenfassung Der große Jacupirangit-Gang in Kodal wurde erstmals von C. W. Brögger (1933) gefunden, der eine chemische Analyse von diesem Gestein publiziert hat. Neuere Untersuchungen an diesem Gang im Hinblick auf eine potentielle Erzlagerstätte, bei denen auch Diamant-Bohrungen eingesetzt worden sind, haben ergeben, daß der Gang etwa 20 m mächtig und 2 km lang ist. Er streicht bei einem durchschnittlichen Fallen von 80 °S annähernd O–W, wobei er Larvikite und Nordmarkite der permischen Oslo-Eruptivprovinz durch-schneidet. Die durchschnittliche modale Zusammensetzung des Jacupirangites besteht (in Volumenprozent) aus: Apatit 24%, Magnetit 37%, Ilmenit 9%, Pyroxen 25%, Amphibol und Biotit 5%. Die Eisen-Titan-Oxide und der Apatit verkitten die Pyroxene unter Bildung einer typischen Eruptivstruktur. Der Kodal-Gang und die anderen Jacupirangite der angrenzenden Oslo-Eruptivprovinz lassen alle ein eutektisches Gemenge von Eisen-Titan-Oxiden und Apatit erkennen, von dem wir annehmen, daß es eine unlösliche Schmelze neben Silikatschmelzen monzonitischer Zusammensetzung bildete. Aus dieser Annahme ergibt sich eine Deutungsmöglichkeit für das Auftreten der Jacupirangite im Oslo Gebiet.相似文献
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Wilga is one of several Au-bearing volcanogenic massive sulphide deposits localized within Silurian felsic volcanics of the Lachlan Fold Belt of NE Victoria. Exploration has delineated a resource of 3.7 Mt averaging 3.4% Cu, 5.5% Zn, 0.4% Pb, 31 g/t Ag and 0.5 g/t Au within a lensoid-shaped sulphide body which strikes NE, dips NW and occurs at a depth of 50–160 m below surface. This body has maximum dimensions of 470 m strike, 350 m down-dip and 37 m true width delineated by 59 surface diamond drill holes and an exploration adit with 40 underground diamond drill holes. There are two main types of mineralization: Stratiform massive sulphides , (mainly pyrite, low-Fe sphalerite, variable chalcopyrite and minor galena with very minor silica/dolomite gangue) and Stratiform chloritic sulphides (mainly chalcopyrite, with subordinate pyrite and sphalerite, in a gangue of chlorite and minor dolomite). The deposit is layered with at least 6 distinct stratigraphic horizons/cycles of mineralization each characterized by a Cu-rich base and Pb-(Zn)-Au-As-rich top. Facies variations are locally rapid. Economically the deposit consists of 3 sub-lenses of roughly equal tonnage: a Cu-rich central lens of Chloritic Sulphides (av. 5.9% Cu, 3.6% Zn, 0.3% Pb, 32 g/t Ag and 0.2 g/t Au) between upper and lower lenses of Zn-rich Massive Sulphides (av. 1.8% Cu, 6.7% Zn, 0.5% Pb, 31 g/t Ag and 0.7 g/t Au). Gold mineralization, locally up to 7 g/t over 6 m, shows a strong spatial association with Pb, (Zn) and As in pyritic massive sulphides. 相似文献
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北京十三陵中元古界蓟县系雾迷山组原地风暴沉积的砾屑体 总被引：1，自引：1，他引：1
研究区雾迷山组的层状藻叠层白云岩中存在一种属原地风暴成因的砾屑透镜体?砾屑体的底部为略下切的侵蚀面,顶为上凸形?砾屑呈放射状或叠瓦状排列,无磨圆作用?其形成过程是:在风暴初期,风暴浪对海底沉积物冲击?掀起?破碎,而后迅速原地堆积而成?风暴衰减后,正常沉积顺应砾屑体的顶面形态? 相似文献
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M. J. C. Walker S. J. P. Bohncke G. R. Coope M. O'Connell H. Usinger C. Verbruggen 《第四纪科学杂志》1994,9(2):109-118
A synthesis of environmental changes during the Devensian (Weichselian) Lateglacial period (14-9 ka BP) is presented for an area extending from Ireland in the west to northwest Germany in the east. Following a brief reference to the problems of chronology, the principal changes in geomorphology and soils, vegetation history and climate experienced in the region during the Late-glacial are described. Reconstructions of thermal variations during the Late-glacial period are attempted independently for Ireland, England and Wales, Scotland (Highlands and Islanads), north Belgium, The Netherlands and northwest Germany. The collective palaeotemperature data, based mainly uppoln pollen data but also in Britain and The Netherlands on coleopteran data using the ‘mutual climatic range’ approach, provide an overview of regional differences along an east-west transect in northwest Europe. 相似文献
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The Warrabin Trough in SW Queensland contains up to 3000 m of Devonian sedimentary rocks, and is a structural remnant of the formerly widespread Adavale Basin. Seismic data recently obtained by the Bureau of Mineral Resources enable reinterpretation of existing poorer quality seismic data, so that the structural framework and most of the trough margin can be mapped. Sedimentary rocks in the trough are folded and are displaced by high‐angle reverse faults, which were probably active during the Late Carboniferous. LANDSAT studies provide additional information on the position of faults, which on seismic records appear to be mainly contained within the trough sequence. Differential compaction, together with slight post‐Cretaceous rejuvenation of some structures, may have given surface expression to some of these deep faults. The western margin of the trough has been drilled, but only 775 m of the Devonian sequence was penetrated. The petroleum source‐rock and maturation levels do not appear encouraging on the basis of this drilling. However, the thick sequence of arenites, lutites and carbonates, interpreted to occur in the trough, offer considerable potential for hydrocarbon source‐rocks and reservoirs. 相似文献
14.
From 1997 to 1999, a huge number of slides, often turning into extremely rapid debris-earth flows, repeatedly affected the late Quaternary volcaniclastic deposits mantling the carbonate slopes of Campania region, Italy. The Sorrento Peninsula was the epicentral district of the 1997 regional slope-instability crisis. Some hundred shallow mass movements took place during January 1997 in this area. These were the last episode of a long series of slope failure events dating back to mid-18th century. Results from geological and geomorphologic surveys are presented. Landslide mechanism and triggering factors are analysed for the most important mass movement, which occurred during the January 9-11, 1997, regional event. On January 10, 1997, at about 8:15 PM, a rainfall-induced debris slide-debris flow occurred at Pozzano (province of Naples), mainly affecting the 79 AD pyroclastic products. Following a J-path, the landslide destroyed a private house and invaded the State Road no. 145. This event resulted in four deaths, 22 persons injured and road closure for about 2 months. There was less than 200 mm of rainfall in the 72-h period prior to the landslide, although intense precipitation had occurred during a preceding 4-month period. However, the slope failure event was not preceded by an extreme short-term antecedent rainfall, as already noticed in previous landslides of this type in Campania. Finally, following a preliminary geotechnical characterization of volcaniclastic soils, a slope-stability back analysis was carried out, which adopted the classical infinite slope scheme. This analysis gave further evidence of the role played by pore pressure in reducing the overall shear strength of pyroclastic soils. 相似文献
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On 15 May 1991, a landslide occurred at Gacharage Village in the Murang'a District of Kenya; it buried a house near the toe of a cliff, killing all eight residents in their sleep. The principal determining factors of the slide were a high, mechanically unstable slope of deeply weathered volcanic soil and a high sorption capacity of the surface soil layer. The slide was triggered by rapid saturation of the soil following a heavy downpour. Based on field investigations and laboratory studies, this paper discusses the physical properties and environmental factors that affected slope stability at Murang'a. It also points out the economic and social impact of landslides in the region and suggests remedial measures. 相似文献
16.
The Cheam rock avalanche,Fraser Valley,British Columbia,Canada 总被引：1，自引：0，他引：1
The Cheam rock avalanche, which occurred about 5,000 years ago in the lower Fraser Valley, British Columbia, is the largest known catastrophic landslide in western Canada (175×106 m3). A photo-draped digital elevation model of the rock avalanche reveals two morphologically distinct areas, an eastern area of arcuate hummocky ridges separated by flat-floored depressions and a lower western area with a subdued, gently rolling surface. Debris is up to 30 m thick and consists of rubbly, clast- and matrix-supported diamicton derived from local argillaceous metasedimentary rocks. Failure was probably caused by high pore water pressures on a thrust fault that daylights in the source area. Plastic deformation of sediment beneath the rock avalanche debris suggests that liquefaction occurred due to undrained loading when the debris struck the Cheam terrace. Liquefaction also explains the morphology and travel distance of the western debris lobe. The coincidence of well-sorted sands (the Popkum Series soil) with the rock avalanche debris indicates that significant amounts of water flowed over the surface of the landslide just after it came to rest. Stó:lõ Nation oral history suggests that the debris may have buried a village, causing the first known landslide fatalities in Canada. 相似文献
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The Tasiast gold deposits are hosted within Mesoarchean rocks of the Aouéouat greenstone belt, Mauritania. The Tasiast Mine consists of two deposits hosted within distinctly different rock types, both situated within the hanging wall of the west-vergent Tasiast thrust. The Piment deposits are hosted within metasedimentary rocks including metaturbidites and banded iron formation where the main mineral association consists of magnetite-quartz-pyrrhotite ± actinolite ± garnet ± biotite. Gold is associated with silica flooding and sulphide replacement of magnetite in the turbidites and in the banded iron formation units. The West Branch deposit is hosted within meta-igneous rocks, mainly diorites and quartz diorites that lie stratigraphically below host rocks of the Piment deposits. Most of the gold mineralisation at West Branch is hosted by quartz–carbonate veins within the sheared and hydrothermally altered meta-diorites that constitute the Greenschist Zone. At Tasiast, gold mineralisation has been defined over a strike length > 10 km and to vertical depths of 740 m. All of the significant mineralised bodies defined to date dip moderately to steeply (45° to 70°) to the east and have a south–southeasterly plunge. Gold deposits on the Tasiast trend are associated with second order shear zones that are splays cutting the hanging wall block of the Tasiast thrust. An age of 2839 ± 36 Ma obtained from the hydrothermal overgrowth on zircons from a quartz vein is interpreted to represent the age of mineralisation. 相似文献
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The calcite-aragonite transition,reinvestigated 总被引：6，自引：0，他引：6
The calcite-aragonite equilibrium has been investigated between 200 and 600° C both in a carefully calibrated hydrothermal apparatus and in a piston-cylinder device of high precision. The equilibrium pressure is 5 kb at 180° C, 7 kb at 300° C, 9 kb at 400° C, and 11 kb at 480° C.The calcite-aragonite transition boundary which has been bracketed is continuously curved between 300 and 500° C and is more or less straight above and below this temperature range. It is shown that the calcite I-calcite II reaction is probably a second (and not a first) order transition.The experimental result shows that aragonite may already be formed out of calcite at a depth of 15 km if the temperature is not much higher than 100° C. The calcitearagonite and the albite-jadeite-quartz curves intersect at about 750° C and 20 kb. There is a P-T-field (up to 3.5 kb broad) where aragonite and albite coexist. 相似文献