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This paper compares the 1.67–1.47 Ga rapakivi granites of Finland and vicinity to the 1.70–1.68 Ga rapakivi granites of the Beijing area in China, the anorogenic 130 Ma granites of western Namibia, and the 20–15 Ma granites of the Colorado River extensional corridor in the Basin and Range Province of southern Nevada. In Finland and China, the tectonic setting was incipient, aborted rifting of Paleoproterozoic or Archean continental crust, in Namibia it was continental rifting and mantle plume activity that led to the opening of southern Atlantic at 130 Ma. The 20–15 Ma granites of southern Nevada were related to rifting that followed the Triassic–Paleogene subduction of the Farallon plate beneath the southwestern United States. In all cases, extension-related magmatism was bimodal and accompanied by swarms of diabase and rhyolite–quartz latite dikes. Rapakivi texture with plagioclase-mantled alkali feldspar megacrysts occurs in varying amounts in the granites, and the latest intrusive phases are commonly topaz-bearing granites or rhyolites that may host tin, tungsten, and beryllium mineralization. The granites are typically ferroan alkali-calcic metaluminous to slightly peraluminous rocks with A-type and within-plate geochemical and mineralogical characteristics. Isotope studies (Nd, Sr) suggest dominant crustal sources for the granites. The preferred genetic model is magmatic underplating involving dehydration melting of intermediate-felsic deep crust. Juvenile mafic magma was incorporated either via magma mingling and mixing, or by remelting of newly hybridized lower crust. In Namibia, partial melting of subcontinental lithospheric mantle was caused by the Tristan mantle plume, in the other cases the origin of the mantle magmatism is controversial. For the Fennoscandian suites, extensive long-time mantle upwelling associated with periodic, migrating melting of the subcontinental lithospheric mantle, governed by heat flow and deep crustal structures, is suggested. 相似文献
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To model ice conditions in the eastern Gulf of Finland, a high-resolution three-dimensional hydrodynamic model is coupled with the advanced sea-ice model HELMI (Haapala et al., 2005). To test the model in extreme situations, the ice pattern in the eastern Gulf of Finland was simulated for a mild ice winter (2007–2008) and for a moderate one (2003–2004). The reference runs were performed on the assumption that the ice in the model domain is fast ice if the sea depth is less than 10 m. Using this assumption, the ice thickness averaged over the Neva Bay (the easternmost part of the Gulf of Finland) is overestimated by the model for almost the entire wintertime in the mild winter and during the ice formation and melting periods in the moderate winter, as compared with the thickness reported in ice charts. 相似文献
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With improved observation methods, increased winter navigation, and increased awareness of the climate and environmental changes, research on the Baltic Sea ice conditions has become increasingly active. Sea ice has been recognized as a sensitive indicator for changes in climate. Although the inter-annual variability in the ice conditions is large, a change towards milder ice winters has been detected from the time series of the maximum annual extent of sea ice and the length of the ice season. On the basis of the ice extent, the shift towards a warmer climate took place in the latter half of the 19th century. On the other hand, data on the ice thickness, which are mostly limited to the land-fast ice zone, basically do not show clear trends during the 20th century, except that during the last 20 years the thickness of land-fast ice has decreased. Due to difficulties in measuring the pack-ice thickness, the total mass of sea ice in the Baltic Sea is, however, still poorly known. The ice extent and length of the ice season depend on the indices of the Arctic Oscillation and North Atlantic Oscillation. Sea ice dynamics, thermodynamics, structure, and properties strongly interact with each other, as well as with the atmosphere and the sea. The surface conditions over the ice-covered Baltic Sea show high spatial variability, which cannot be described by two surface types (such as ice and open water) only. The variability is strongly reflected to the radiative and turbulent surface fluxes. The Baltic Sea has served as a testbed for several developments in the theory of sea ice dynamics. Experiences with advanced models have increased our understanding on sea ice dynamics, which depends on the ice thickness distribution, and in turn redistributes the ice thickness. During the latest decade, advance has been made in studies on sea ice structure, surface albedo, penetration of solar radiation, sub-surface melting, and formation of superimposed ice and snow ice. A high vertical resolution has been found as a prerequisite to successfully model thermodynamic processes during the spring melt period. A few observations have demonstrated how the river discharge and ice melt affect the stratification of the oceanic boundary layer below the ice and the oceanic heat flux to the ice bottom. In general, process studies on ice–ocean interaction have been rare. In the future, increasingly multidisciplinary studies are needed with close links between sea ice physics, geochemistry and biology. 相似文献
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Bjoern Sundquist Ilmari Haapala Jens Morten Hansen Geir Hestmark Sigurdur Steinthorsson 《《幕》》2008,31(1):185-192
The Nordic countries of Denmark, Finland, Iceland, Norway, and Sweden have been closely connected for many centuries, not least from a geological point of view. Scientific cooperation as well as contentions have been common. The earliest known records of ＂geological＂ treatises are from the 16th century, but especially in the 18th century, when the natural sciences flourished all over Europe, Nordic scholars were in the forefront in geochemistry, mineralogy, and paleontology. This was also the century when ＂geology＂ started to be taught at the universities, and science academies were founded in Norden, adding greatly to ＂geological＂ studies. In the 19th century, like in so many other countries, national geological survey organizations and geological societies were founded. In Norden, geological research has long traditions within mineralogy and ore geology, paleontology and stratigraphy, tectonics and structural geology. During the last century, focus has turned also to Quaternary and glacial geology, igneous and metamorphic petrology, geochemistry, micropaleontology, petroleum geology, sedimentology, marine geology, geophysics, geochronology, and research related to geothermal energy and deposition of radioactive waste products. In many of these research areas, Nordic geoscientists have contributed greatly over the years to the development of the science of geology. 相似文献
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秦岭环斑结构花岗岩中暗色包体的岩浆混合成因及岩石学意义——元素和Nd、Sr同位素地球化学证据 总被引：19，自引：10，他引：19
秦岭环斑结构花岗岩中的暗色包体主要为闪长质岩浆包体,SiO2(50％-62％)低,K2O Na2O(7．01％-9．4％) 高,里特曼指数(δ)为5-9,F、过渡性元素和稀土元素富集。包体和寄主岩石的主要氧化物之间具有良好的线性关系、稀土配分曲线和微量元素配分曲线相似,以及活动性组分、高场强元素、轻稀土和同位素特征等显示,寄主岩石和包体之间发生过明显的成分交换,这些成分在二者中大体上趋于平衡。这种特征表明,环斑结构花岗岩岩浆的形成至少与两种岩浆的混合有关。包体的(87Sr／86Sr)i较低(0．70514-0．70624)、εNd(t)值较高(-0．95--3．3)和富过渡性元素的特征揭示,形成包体的原始岩浆为起源于幔源的玄武质岩浆。包体和寄主岩石的关系显示岩浆的混合方式为基性岩浆注入到已经开始结晶的酸性岩浆。这些研究为环斑结构花岗岩是起源于地壳的酸性岩浆和起源于地幔的基性岩浆形成的混合岩浆结晶的产物提供了新证据;同时,也为环斑结构的混合成因研究提供了新思路和途径。 相似文献
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Summary The dyke-like 1.63 Ga Jaala-Iitti rapakivi complex forms a 25 km long and up to 2 km wide intrusive body at the northwestern margin of the Wiborg rapakivi batholith cutting both the granites of the batholith and the surrounding 1.9 Ga Svecofennian crust. The subvolcanic-epizonal Jaala-Iitti complex consists of silicic (quartz-feldspar porphyry) and basic (diabase) rocks as well as more abundant intermediate hornblende-bearing hybrid rocks.The hybrid rocks are characterised by: 1) diabase pillows and enclaves that commonly contain quartz and feldspar xenocrysts, 2) quartz megacrysts mantled by amphibole coronas, and 3) large, (up to 10 cm) rounded alkali feldspar megacrysts mantled by shells of micrographic plagioclase-quartz intergrowths. The observed data indicate that hybridization is caused by: 1) mixing of basic and silicic magmas, 2) incorporation of megacrysts from one of the interacting magmas into the another, and 3) assimilation and disaggregation of xenoliths and xenocrysts. It is proposed that the hybridization took place mainly before eruption deep in the crust where basic mantle-derived magmas and silicic crust-derived magmas interacted.
With 5 figures 相似文献
Der Jaala-Iitti Rapakivi Komplex: Beispiel eines bimodalen Magmatismus und einer Hybridisierung im Wiborg Rapakivi Batholith, Südost-Finnland
Zusammenfassung Der gangförmige, 1.63 Mia alte Jaala-Iitti Rapakivi Komplex stellt einen 25 km langen und bis zu 2 km breiten Intrusionskörper am Nordwestrand des Wiborg Rapakivi Batholithes dar, der sowohl die Granite des Batholithes, wie auch die umgebende 1.9 Mia alte svekofennische Kruste durchschneidet. Der subvulkanische, epizonale Jaalalitti Komplex besteht aus sauren (Quarz-Feldspat-Porphyr) und basischen (Diabase) Gesteinen und aus häufig vorkommenden, intermediären, hornblendeführenden, hybriden Gesteinen.Die hybriden Gesteine sind durchfolgende Charakteristika gekennzeichnet: 1) Diabas-Pillows und Enklaven, die überwiegend aus Quarz- und FeldspatXenokristallen bestehen, 2) Quarz-Megakristalle, die einen kronenartigen Amphibolsaum zeigen, und 3) große (bis 10 cm), runde Alkalifeldspat-Megakristalle, die von mikrographisch verwachsenem Quarz-Feldspat umrandet sind. Die beobachteten Erscheinungen deuten an, daß die Hybridisierung durch 1) Mischung von basischen und sauren Magmen, 2) Inkorporation von Megakristallen von einem in das andere der beiden sich mischenden Magmen, und 3) Assimilation und Disaggregation von Xenolithen und Xenokristallen, verursacht ist. Es wird angenommen, daß die Hybridisierung tief in der Kruste, vor der Eruption entstanden ist, dort, wo basische, aus dem Mantel stammende mit sauren, aus der Kruste stammenden Magmen in Wechselwirkung getreten sind.
With 5 figures 相似文献
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I. Haapala 《Mineralogy and Petrology》1995,54(3-4):149-160
Summary Two major types of ore deposits occur with Proterozoic rapakivi granite plutons: (1) greisen-, vein-, und skarn-type Sn(-W-Be-Zn-Cu-Pb) deposits associated with specialized late-stage granites, and (2) Fe oxide-Cu (-U-Au-Ag) deposits.The Sn-polymetallic deposits are usually hydrothermal greisen- and vein-type occurrences (Rondönia and Amazonas in Brazil, southeastern Missouri, southern Finland, the Ukraine, India); skarn-type deposits occur in the Pitkdranta ore field, Russian Karelia. The deposits are closely associated with topaz-bearing microcline-albite granites which occur as autometamorphosed late intrusive phases of the 1.0 to 1.7 Ga granite plutons and show the characteristics of Phanerozoic tin granites: high Sn, Li, Rb, Ga, Nb, and F, low Ba, Sr, Ti, and Zr, and a strong negative Eu anomaly. The anomalous geochemical character is interpreted to be in part magmatic, in part metasomatic in origin.The huge Olympic Dam deposit in South Australia is a hydrothermally mineralized hematite breccia complex in a 1.59 Ga rapakivi granite pluton. The deposit contains over 2000 million tons of ore with 1.6% Cu, 0.06% U3O8, 3.5 ppm Ag, and 0.6 ppm Au. The apatite-bearing Fe and Fe-Cu deposits of southeastern Missouri are associated with volcanics of the St. Francois Mountains ring complexes. The principal ore minerals are magnetite and hematite, locally also Cu sulphides. With more than 30 Fe deposits, the St. Francois Mountains constitute a major Fe provice.
With 3 Figures 相似文献
Metallogenese der Rapakivi-Granite
Zusammenfassung Mit proterozoischen Rapakivi-Granitplutonen treten zwei Haupttypen von Erzlagerstätten auf: (1) greisen-, gang- und skarnartige Sn(-W-Be-Zn-Cu-Pb)-Lagerstätten, die mit speziellen Graniten eines Spätstadiums verbunden sind und (2) Fe-Oxid-Cu (-U-Au-Ag)-Lagerstätten.Die Sn-Polymetall-Lagerstätten sind normalerweise hydrothermale greisen- und gangartige Vorkommen (Rondônia und Amazonas in Brasilien, SE Missouri, S Finnland, Ukraine, Indien), skarnartige Lagerstätten treten im Erzrevier von Pitkäranta in Russisch-Karelien auf. Die Lagerstätten sind eng mit Topas-führenden Mikroklin-Albit-Graniten verbunden, die als autometamorphisierte spätintrusive Phasen der 1,0 bis 1,7 Ga alten Granitplutone auftreten und die charakteristischen Merkmale von phanerozoischen Zinn-Graniten zeigen: hohes Sn, Li, Rb, Ga, Nb und F, niedriges Ba, Sr, Ti und Zr und eine stark negative Eu-Anomalie. Die Ursache des anomalen geochemischen Charakters wird zum Teil als magmatisch, zum Teil als metasomatisch interpretiert.Die riesige Lagerstätte von Olympic Dam in Südaustralien ist ein Komplex aus hydrothermal mineralisierter Hämatit-Brekzie in einem 1,59 Ga alten Rapakivi-Granitpluton. Das Vorkommen enthält über 2000 Millionen Tonnen Erz mit 1,6% Cu, 0,06% U3O8, 3,5 ppm Ag und 0,6 ppm Au. Die Apatit-führenden Fe- und Fe-Cu-Lagerstätten von SE Missouri sind mit Vulkaniten der Ringkomplexe in den St. Francois Mountains assoziiert. Die wichtigsten Erzminerale sind Magnetit und Hämatit, lokal auch Cu-Sulfide. Mit mehr als 30 Fe-Lagerstätten stellen die St. Francois Mountains eine bedeutende Fe-Provinz dar.
With 3 Figures 相似文献