Age and paragenesis of mineralisation at Coronation Hill uranium deposit,Northern Territory,Australia     

Karin Orth  Sebastien Meffre  Garry Davidson 《Mineralium Deposita》2014,49(5):595-623

Coronation Hill is a U?+?Au?+?platinum group elements deposit in the South Alligator Valley (SAV) field in northern Australia, south of the better known unconformity-style U East Alligator Rivers (EAR) field. The SAV field differs from the EAR by having a more complex basin-basement architecture. A volcanically active fault trough (Jawoyn Sub-basin) developed on older basement and then was disrupted by renewed faulting, before being buried beneath regional McArthur Basin sandstones that are also the main hanging wall to the EAR deposits. Primary mineralisation at Coronation Hill formed at 1607?±?26 Ma (rather than 600–900 Ma as previously thought), and so it is likely that the SAV was part of a single west McArthur Basin dilational event. Most ore is hosted in sub-vertical faults and breccias in the competent volcanic cover sequence. This favoured fluid mixing, acid buffering (forming illite) and oxidation of Fe²⁺ and reduced C-rich assemblages as important uranium depositional mechanisms. However, reduction of U in fractured older pyrite (Pb model age of 1833?±?67 Ma) is an important trap in diorite. Some primary ore was remobilised at 675?±?21 Ma to form coarse uraninite?+?Ni-Co pyrite networks containing radiogenic Pb. Coronation Hill is polymetallic, and in this respect resembles the ‘egress’-style U deposits in the Athabascan Basin (Canada). However, these are all cover-hosted. A hypothesis for further testing is that Coronation Hill is also egress-style, with ores formed by fluids rising through basement-hosted fault networks (U reduction by diorite pyrite and carbonaceous shale), and into veins and breccias in the overlying Jawoyn Sub-basin volcano-sedimentary succession.  相似文献   

Character and origin of variably deformed granitoids in central southern Sweden: implications from geochemistry and Nd isotopes     

Karin Appelquist  Linus Brander  ke Johansson  Ulf Bertil Andersson  David Cornell 《Geological Journal》2011,46(6):597-618

We present major and trace element data for eighteen 1.71–1.66 Ga granitoid samples, and Sm–Nd whole‐rock isotope data for eleven of these samples, in a transect across the border between the Transscandinavian Igneous Belt (TIB) and the Eastern Segment in central southern Sweden. The geochemistry of the granitoids varies from alkalic to alkali‐calcic and peraluminous in the east to predominantly calc‐alkaline and metaluminous in the west. Rocks in the west also have lower SiO₂ contents. Trace element signatures favour formation in an active continental margin setting. Nd isotope data are completely overlapping along the transect and initial ε_Nd values are mildly depleted in the range +0.3 to +2.6. The combined data suggest that the magmas were derived mainly from juvenile, pre‐existing crust, increasingly mafic and less alkaline towards the west. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Community structure in boreal lakes with recurring blooms of the nuisance flagellate Gonyostomum semen     

Karin S. L. Johansson  Cristina Trigal  Tobias Vrede  Richard K. Johnson 《Aquatic Sciences - Research Across Boundaries》2013,75(3):447-455

Blooms of the nontoxic raphidophyte Gonyostomum semen have shown a recent increase in frequency and distribution in the Fennoscandian region. Due to large cell size and several grazer-avoidance strategies, G. semen is hypothesized to be inedible for most zooplankton species and therefore may constitute a bottleneck for the transfer of energy and nutrients in pelagic food webs. Repression of other phytoplankton through increased competition and induced mortality could further exacerbate this effect. In a field study of four lakes with recurring blooms of G. semen and four lakes without blooms, we found significant differences in community structure between the two lake groups during the bloom period. Bloom-lakes had lower biovolumes of small chrysophytes and chlorophytes and zooplankton assemblages were predominated by small, potentially bacterivorous cladocerans, suggesting a limited availability of edible phytoplankton and an increased importance of microbial pathways during G. semen blooms. Low biovolumes of large cladocerans in bloom-lakes may be due to interference of G. semen with filter feeding. Moreover, high abundances of the phantom midge Chaoborus flavicans in bloom-lakes suggest that the flow of energy and nutrients is directed more towards this invertebrate predator than fish. This could have negative impacts on fish populations, especially if bloom periods are prolonged.  相似文献   

Global change revealed by palaeolimnological records from remote lakes: a review   总被引：1，自引：0，他引：1  

Jordi Catalan  Sergi Pla-Rabés  Alexander P. Wolfe  John P. Smol  Kathleen M. Rühland  N. John Anderson  Jiři Kopáček  Evžen Stuchlík  Roland Schmidt  Karin A. Koinig  Lluís Camarero  Roger J. Flower  Oliver Heiri  Christian Kamenik  Atte Korhola  Peter R. Leavitt  Roland Psenner  Ingemar Renberg 《Journal of Paleolimnology》2013,49(3):513-535

Over recent decades, palaeolimnological records from remote sites have provided convincing evidence for the onset and development of several facets of global environmental change. Remote lakes, defined here as those occurring in high latitude or high altitude regions, have the advantage of not being overprinted by local anthropogenic processes. As such, many of these sites record broad-scale environmental changes, frequently driven by regime shifts in the Earth system. Here, we review a selection of studies from North America and Europe and discuss their broader implications. The history of investigation has evolved synchronously with the scope and awareness of environmental problems. An initial focus on acid deposition switched to metal and other types of pollutants, then climate change and eventually to atmospheric deposition-fertilising effects. However, none of these topics is independent of the other, and all of them affect ecosystem function and biodiversity in profound ways. Currently, remote lake palaeolimnology is developing unique datasets for each region investigated that benchmark current trends with respect to past, purely natural variability in lake systems. Fostering conceptual and methodological bridges with other environmental disciplines will upturn contribution of remote lake palaeolimnology in solving existing and emerging questions in global change science and planetary stewardship.  相似文献   

Pattern and timing of the northwestern Barents Sea Ice Sheet deglaciation and indications of episodic Holocene deposition   总被引：1，自引：0，他引：1  

Denise Christina Rüther  Lilja Rún Bjarnadóttir  Juho Junttila  Katrine Husum  Tine Lander Rasmussen  Renata Giulia Lucchi  Karin Andreassen 《Boreas: An International Journal of Quaternary Research》2012,41(3):494-512

The origin of two acoustic sediment units has been studied based on lithological facies, chronology and benthic stable isotope values as well as on foraminifera and clay mineral assemblages in six marine sediment cores from Kveithola, a small trough west of Spitsbergenbanken on the western Barents Sea margin. We have identified four time slices with characteristic sedimentary environments. Before c. 14.2 cal. ka, rhythmically laminated muds indicate extensive sea ice cover in the area. From c. 13.9 to 14.2 cal. ka, muds rich in ice‐rafted debris were deposited during the disintegration of grounded ice on Spitsbergenbanken. From c. 10.3 to 13.1 cal. ka, sediments with heterogeneous lithologies suggest a shifting influence of suspension settling and iceberg rafting, probably derived from a decaying Barents Sea Ice Sheet in the inner‐fjord and land areas to the north of Kveithola. Holocene deposition was episodic and characterized by the deposition of calcareous sands and shell debris, indicative of strong bottom currents. We speculate that a marked erosional boundary at c. 8.2 cal. ka may have been caused by the Storegga tsunami. Whilst deposition was sparse during the Holocene, Kveithola acted as a sediment trap during the preceding deglaciation. Investigation of the deglacial sediments provides unprecedented details on the dynamics and timing of glacial retreat from Spitsbergenbanken.  相似文献   

Petrogenesis of ca 1.50 Ga granitic gneiss of the Coompana Block: filling the ‘magmatic gap’ of Mesoproterozoic Australia     

B. P. Wade  J. L. Payne  M. Hand  K. M. Barovich 《Australian Journal of Earth Sciences》2013,60(8):1089-1102

The Coompana Block is an essentially unknown basement province that separates the Gawler Craton of South Australia from the Yilgarn Craton of Western Australia. Previously unstudied granitic gneiss intersected by deep drilling in the Coompana Block represents an important period of within-plate magmatism during a time of relative magmatic quiescence in the Australian Proterozoic. Granitic gneiss intersected at ～1500 m depth in Mallabie 1 diamond drillhole is metaluminous and dominantly granodioritic in composition. The granodiorites have distinctive A-type chemistry characterised by high contents of Zr, Nb, Y, Ga, LREE with low Mg#, Sr, CaO and HREE. U – Pb LA-ICPMS dating of magmatic zircons provides an age of 1505 ± 7 Ma, interpreted as the crystallisation age of the granite protolith. ? _Nd values are high with respect to exposed crust of the Musgrave Province and Gawler Craton, and range from +1.2 to +3.3 at 1.5 Ga. The granitic gneiss is interpreted to be a fractionated melt of a mantle-derived parental melt. The tectonic environment into which the precursor granite was emplaced is not clear. One possibility is emplacement within an extensional environment. Regardless, the granitic gneiss intersected in Mallabie 1 represents magmatic activity during the ‘Australian Mesoproterozoic magmatic gap’ of ca 1.50 – 1.35 Ga, and is a possible source for ca 1.50 detrital zircons found in sedimentary rocks of Tasmania and Antarctica, and metasedimentary rocks of the eastern Musgrave Province.  相似文献   

Using Lead Isotopes to Determine Pottery Provenance in Cyprus: Clay Source Signatures and Comparison with Late Bronze Age Cypriote Pottery     

Virginie Renson  Ariane Jacobs  Jan Coenaerts  Nadine Mattielli  Karin Nys  Philippe Claeys 《Geoarchaeology》2013,28(6):517-530

This paper presents the lead isotopic composition of potential clay sources for pottery production, collected in the four major geological zones of Cyprus (Troodos Ophiolite, Circum Troodos Sedimentary Succession, Mamonia Terrane, Kyrenia Terrane) and evaluates its usefulness in Cypriote pottery provenance studies. The clay isotopic signatures from the four zones are compared to each other and to the isotopic composition of various utilitarian pottery wares from three Late Bronze Age sites, respectively located in southern Cyprus (Alassa‐Pano Mandilaris), east Cyprus (Enkomi), and southeast Cyprus (Hala Sultan Tekke). It also explores the potential of this method to better discriminate between potential raw materials used for the production of Base‐ring ware, one of the most characteristic fine pottery of Late Bronze Age Cyprus, which was widely spread in the Eastern Mediterranean (Courtois, 1981; Vaughan, 1991, 1994). Results show that three main lead isotopic fields can be distinguished among the Cypriote clay sources and the comparison of Plain sherds with the clay sources allows discrimination between local products and imports. They also clearly indicate that all the Base‐ring sherds analyzed in this study were made of the clays from the Kathikas Formation that crops out in only limited parts of southwest Cyprus.  相似文献   

Effect of intrinsic and sampling variability on wave parameters and wave statistics     

Elzbieta M. Bitner-Gregersen  Anne Karin Magnusson 《Ocean Dynamics》2014,64(11):1643-1655

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Magmatism and metamorphism at ca. 1.45 Ga in the northern Gawler Craton: The Australian record of rifting within Nuna (Columbia)     

Laura J. Morrissey  Karin M. Barovich  Martin Hand  Katherine E. Howard  Justin L. Payne 《地学前缘(英文版)》2019,10(1):175-194

U-Pb monazite and zircon geochronology and calculated metamorphic phase diagrams from drill holes in the northern Gawler Craton, southern Australia, reveal the presence of ca. 1.45 Ga magmatism and metamorphism. Magmatism and granulite facies metamorphism of this age has not previously been recognised in the Gawler Craton. The magmatic rocks have steep LREE-enriched patterns and high Ga/Al values, suggesting they are A-type granites. Calculated metamorphic forward models suggest that this event was associated with high apparent thermal gradients and reached pressures of 3.2 -5.4 kbar and temperatures of 775-815℃. The high apparent thermal gradients may reflect pluton-enhanced metamorphism, consistent with the presence of A-type granites. The recognition of ca. 1.45 Ga tectonism in the northern Gawler Craton is added to a compilation of ca. 1.50 -1.40 Ga magmatism, shear zone reactivation, rift basin development and isotope resetting throughout the South and North Australian Cratons that shows that this event was widespread in eastern Proterozoic Australia. This event is stylistically similar to ca. 1.45 Ga A-type magmatism and high thermal gradient metamorphism in Laurentia in this interval and provides further support for a connection between Australia and Laurentia during the Mesoproterozoic. The tectonic setting of the 1.50-1.40 Ga event is unclear but may record rifting within the Nuna(or Columbia) supercontinent, or a period of intracontinental extension within a long-lived convergent setting.  相似文献   

Faroe Shelf Water     

Karin Margretha H. Larsen  Bogi Hansen  Harald Svendsen 《Continental Shelf Research》2008

Faroe Shelf Water (FSW) is the water mass that occupies the shallow parts of the Faroe Shelf, surrounding the Faroe Islands (62°N, 7°W). Intensive tidal mixing induces a high degree of homogeneity and the circulation system allows a partial isolation from surrounding waters. This water mass, therefore, supports a unique ecosystem of great importance for commercial fish stocks and studies have shown a clear dependence of the ecosystem on the physical processes that maintain this system and control the exchange between the FSW and the off-shelf waters. In order to identify and quantify these processes, a large observational dataset has been analysed and related to alternative theories. From this analysis, the extent and properties of the FSW have been quantified and the degree of stratification explained in terms of the Simpson–Hunter theory. The residual clockwise circulation system, which is responsible for the partial isolation from off-shelf waters, is shown to be mainly generated by tidal rectification. The typical exchange rate of water between the FSW and the off-shelf regimes has been determined by the use of simple models based on the heat and the salt budgets but the actual exchange rate is found to vary considerably in time and space. These results support earlier suggestions that this exchange is the main limiting factor for the phytoplankton spring bloom on the Faroe Shelf and that variations in exchange rate are responsible for the large inter-annual variation in spring bloom timing and intensity. The observations indicate that the on-shelf/off-shelf exchange intensity is not symmetrically distributed around the shelf, but rather concentrated around the narrow southern tip of the Faroe Shelf, where off-shelf waters during intensive exchange events may be imported all the way to the shore.  相似文献