A Mid Cretaceous origin for the Galápagos hotspot: volcanological, petrological and geochemical evidence from Costa Rican oceanic crustal segments     

F. Hauff  K. Hoernle  H.-U. Schmincke  R. Werner 《International Journal of Earth Sciences》1997,86(1):141-155

The Quepos, Nicoya and Herradura oceanic igneous terranes in Costa Rica are conspicuous features of a Mid to Late Cretaceous regional magmatic event that encompasses similar terranes in Central America, Colombia, Ecuador and the Caribbean. The Quepos terrane (66?Ma), which consists of ol-cpx phyric, tholeiitic pillow lavas overlain by highly vesicular hyaloclastites, breccias and conglomerates, is interpreted as an uplifted seamount/ocean island complex. The Nicoya (～90?Ma) and Herradura terranes consist of fault-bounded sequences of sediments, tholeiitic volcanics (pillow lavas and massive sheet flows) and plutonic rocks. The volcanic rocks were emplaced at relatively high eruption rates in moderate to deep water, possibly forming part of an oceanic plateau. Major and trace element data from Nicoya/Herradura tholeiites indicate higher melting temperatures than inferred for normal mid-ocean-ridge basalts (MORB) and/or a different source composition. Sr–Nd–Pb isotopic ratios from all three terranes are distinct from MORB but resemble those from the Galápagos hotspot. The volcanological, petrological and geochemical data from Costa Rican volcanic terranes, combined with published age data, paleomagnetic results and plate tectonic reconstructions of this region, provide strong evidence for a Mid Cretaceous (～90Ma) age for the Galápagos hotspot, making it one of the oldest known, active hotspots on Earth. Our results also support an origin of the Caribbean Plate through melting of the head of the Galápagos starting plume.  相似文献   

Dissolution rates and activation energy for dissolution of brucite (001) : A new method based on the microtopography of crystal surfaces   总被引：1，自引：0，他引：1  

Guntram Jordan  Werner Rammensee 《Geochimica et cosmochimica acta》1996,60(24):5055-5062

Scanning Force Microscopy (SFM) was used to develop a method which can provide quantitative kinetic data of crystal growth and dissolution. Based on observations of single crystal faces in monolayer resolution, morphology and temperature dependent growth and dissolution rates can be obtained. From these kinetic data activation energies can be calculated and compared with existing theories. The experimental method works by extracting grown or dissolved terrace areas and step densities from image sequences taken at different temperatures. As an example, the method is applied for dissolution on the brucite (001) surface in acidic water (pH 2.7) within the temperature range of 21 to 35°C. At these conditions the dissolution rate depends nonlinearly on the step density and gives evidence for interstep interaction. The calculated activation energy for dissolution is 60 ± 12 kJ mol⁻¹. With this high activation energy, dissolution cannot be regarded as a transport-controlled process, and is therefore surface controlled.  相似文献   

The magmatic to hydrothermal transition and its bearing on ore-forming systems   总被引：1，自引：0，他引：1  

Werner E. Halter  James D. Webster 《Chemical Geology》2004,210(1-4):1-6

The exsolution of volatile phases from silicate magmas controls physical and chemical magma properties and influences large-scale geologic phenomena and processes having major societal and economic implications including the release of climate-altering gases to the atmosphere, the explosivity of volcanic eruptions, hydrothermal alteration, and the generation of magmatic–hydrothermal mineralization. These volatile phases exsolve from a wide variety of magmas and cover a very broad spectrum of compositions.

The transition from the orthomagmatic to the hydrothermal stages has important bearing on these fundamentally important geologic phenomena, and this report summarizes the published results of a dozen scientific investigations on the magmatic–hydrothermal transition as applied to volcanic eruption and magmatic–hydrothermal mineralization. These studies involve a variety of analytical and experimental methodologies, and many focus on fluid and melt inclusions from mineralized magmatic systems. A primary goal of each study is to better understand the role of magmatic volatiles and the importance of the magmatic–hydrothermal transition on these geologic processes.  相似文献   

Richtlinien zur stratigraphischen Nomenklatur     

Jürgen Remane&#;  Thierry Adatte  Jean-Pierre Berger  Reto Burkhalter  Stephan Dall&#;Agnolo  Danielle Decrouez  Hermann Fischer  Hanspeter Funk  Heinz Furrer  Hans-Rudolf Graf  Yves Gouffon  Werner Heckendorn  Wilfried Winkler 《Eclogae Geologicae Helvetiae》2005,98(3):385-405

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Magma evolution and the formation of porphyry Cu–Au ore fluids: evidence from silicate and sulfide melt inclusions     

Werner E. Halter  Christoph A. Heinrich  Thomas Pettke 《Mineralium Deposita》2005,39(8):845-863

Silicate and sulfide melt inclusions from the andesitic Farallón Negro Volcanic Complex in NW Argentina were analyzed by laser ablation ICPMS to track the behavior of Cu and Au during magma evolution, and to identify the processes in the source of fluids responsible for porphyry-Cu-Au mineralization at the 600 Mt Bajo de la Alumbrera deposit. The combination of silicate and sulfide melt inclusion data with previously published geological and geochemical information indicates that the source of ore metals and water was a mantle-derived mafic magma that contained approximately 6 wt.% H₂O and 200 ppm Cu. This magma and a rhyodacitic magma mixed in an upper-crustal magma chamber, feeding the volcanic systems and associated subvolcanic intrusions over 2.6 million years. Generation of the ore fluid from this magma occurred towards the end of this protracted evolution and probably involved six important steps: (1) Generation of a sulfide melt upon magma mixing in some parts of the magma chamber. (2) Partitioning of Cu and Au into the sulfide melt (enrichment factor of 10,000 for Cu) leading to Cu and Au concentrations of several wt.% or ppm, respectively. (3) A change in the tectonic regime from local extension to compression at the end of protracted volcanism. (4) Intrusion of a dacitic magma stock from the upper part of the layered magma chamber. (5) Volatile exsolution and resorption of the sulfide melt from the lower and more mafic parts of the magma chamber, generating a fluid with a Cu/Au ratio equal to that of the precursor sulfide. (6) Focused fluid transport and precipitation of the two metals in the porphyry, yielding an ore body containing Au and Cu in the proportions dictated by the magmatic fluid source. The Cu/S ratio in the sulfide melt inclusions requires that approximately 4,000 ppm sulfur is extracted from the andesitic magma upon mixing. This exceeds the solubility of sulfide or sulfate in either of the silicate melts and implies an additional source for S. The extra sulfur could be added in the form of anhydrite phenocrysts present in the rhyodacitic magma. It appears, thus, that unusually sulfur-rich, not Cu-rich magmas are the key to the formation of porphyry-type ore deposits. Our observations imply that dacitic intrusions hosting the porphyry–Cu–Au mineralization are not representative of the magma from which the ore-fluid exsolved. The source of the ore fluid is the underlying more mafic magma, and unaltered andesitic dikes emplaced immediately after ore formation are more likely to represent the magma from which the fluids were generated. At Alumbrera, these andesitic dikes carry relicts of the sulfide melt as inclusions in amphibole. Sulfide inclusions in similar dykes of other, less explored magmatic complexes may be used to predict the Au/Cu ratio of potential ore-forming fluids and the expected metal ratio in any undiscovered porphyry deposit.Editorial handling: B. Lehmann  相似文献   

Luminescence dating of ice‐marginal deposits in northern Germany: evidence for repeated glaciations during the Middle Pleistocene (MIS 12 to MIS 6)          下载免费PDF全文

Julia Roskosch  Jutta Winsemann  Ulrich Polom  Christian Brandes  Sumiko Tsukamoto  Axel Weitkamp  Werner A. Bartholomäus  Dierk Henningsen  Manfred Frechen 《Boreas: An International Journal of Quaternary Research》2015,44(1):103-126

The exact number, extent and chronology of the Middle Pleistocene Elsterian and Saalian glaciations in northern Central Europe are still controversial. This study presents new luminescence data from Middle Pleistocene ice‐marginal deposits in northern Germany, giving evidence for repeated glaciations during the Middle Pleistocene (MIS 12 to MIS 6). The study area is located in the Leine valley south of the North German Lowlands. The data set includes digital elevation models, high‐resolution shear wave seismic profiles, outcrop and borehole data integrated into a 3D subsurface model to reconstruct the bedrock relief surface. For numerical age determination, we performed luminescence dating on 12 ice‐marginal and two fluvial samples. Luminescence ages of ice‐marginal deposits point to at least two ice advances during MIS 12 and MIS 10 with ages ranging from 461±34 to 421±25 ka and from 376±27 to 337±21 ka. The bedrock relief model and different generations of striations indicate that the older ice advance came from the north and the younger one from the northeast. During rapid ice‐margin retreat, subglacial overdeepenings were filled with glaciolacustrine deposits, partly rich in re‐worked Tertiary lignite and amber. During MIS 8 and MIS 6, the study area may have been affected by two ice advances. Luminescence ages of glaciolacustrine delta deposits point to a deposition during MIS 8 or early MIS 6, and late MIS 6 (250±20 to 161±10 ka). The maximum extent of both the Elsterian (MIS 12 and MIS 10) and Saalian glaciations (MIS 8? and MIS 6) approximately reached the same position in the Leine valley and was probably controlled by the formation of deep proglacial lakes in front of the ice sheets, preventing a further southward advance.  相似文献   

Scientific problems addressed by the Spektr-UV space project (world space Observatory—Ultraviolet)     

A. A. Boyarchuk  B. M. Shustov  I. S. Savanov  M. E. Sachkov  D. V. Bisikalo  L. I. Mashonkina  D. Z. Wiebe  V. I. Shematovich  Yu. A. Shchekinov  T. A. Ryabchikova  N. N. Chugai  P. B. Ivanov  N. V. Voshchinnikov  A. I. Gomez de Castro  S. A. Lamzin  N. Piskunov  T. Ayres  K. G. Strassmeier  S. Jeffrey  S. K. Zwintz  D. Shulyak  J.-C. Gérard  B. Hubert  L. Fossati  H. Lammer  K. Werner  A. G. Zhilkin  P. V. Kaigorodov  S. G. Sichevskii  S. Ustamuich  E. N. Kanev  E. Yu. Kil’pio 《Astronomy Reports》2016,60(1):1-42

The article presents a review of scientific problems and methods of ultraviolet astronomy, focusing on perspective scientific problems (directions) whose solution requires UV space observatories. These include reionization and the history of star formation in the Universe, searches for dark baryonic matter, physical and chemical processes in the interstellar medium and protoplanetary disks, the physics of accretion and outflows in astrophysical objects, from Active Galactic Nuclei to close binary stars, stellar activity (for both low-mass and high-mass stars), and processes occurring in the atmospheres of both planets in the solar system and exoplanets. Technological progress in UV astronomy achieved in recent years is also considered. The well advanced, international, Russian-led Spektr-UV (World Space Observatory—Ultraviolet) project is described in more detail. This project is directed at creating a major space observatory operational in the ultraviolet (115–310 nm). This observatory will provide an effective, and possibly the only, powerful means of observing in this spectral range over the next ten years, and will be an powerful tool for resolving many topical scientific problems.  相似文献   

Ultramafic–Mafic Assemblage of Plutonic Rocks and Hornblende Schists of Shirshov Rise,Bering Sea,and Stalemate Ridge,Northwest Pacific: Geodynamic Interpretations of Geochemical Data     

S. A. Silantyev  I. V. Kubrakova  M. V. Portnyagin  O. A. Tyutyunnik  A. V. Zhilkina  A. S. Gryaznova  K. Hoernle  R. Werner 《Petrology》2018,26(5):492-514

The paper presents data on plutonic and metamorphic rocks dredged during Cruise 249 of the German R/V Sonne to the Stalemate Ridge, Northwest Pacific Ocean and the Shirshov Rise, western Bering Sea. Dredges in the northwestern sector of the Stalemate Ridge and central portion of the Shirshov Rise show that the plutonic and metamorphic rocks obtained here are amazingly similar. Our petrologic and geochemical data led us to view the rocks as members of a mafic–ultramafic assemblage typical of cumulate portions of ophiolite complexes and backarc spreading centers. The plutonic complexes of the Shirshov Rise and Stalemate Ridge show similarities not only in the petrography and mineralogy of their protoliths but also in the character of their metamorphic transformations. Plutonic rocks from both areas display mineralogical evidence of metamorphism within a broad temperature range: from the high-temperature amphibolite facies to the greenschist facies. Relations between the index mineral assemblages indicate that the metamorphic history of plutonic complexes in the Stalemate Ridge and Shirshov Rise proceeded along a retrograde path. Hornblende schists accompanying the plutonic rocks of the Stalemate Ridge and Shirshov Rise are petrographically close to foliated amphibolites in subophiolitic metamorphic aureoles. Within the framework of geodynamic interpretations of our results, it is realistic to suggest that the examined plutonic complexes were exhumed from subduction zones of various age.  相似文献   

Science-based approach for credible accounting of mitigation in managed forests     

Giacomo Grassi  Roberto Pilli  Jo House  Sandro Federici  Werner A. Kurz 《Carbon balance and management》2018,13(1):8

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Estimation of actual evapotranspiration from an alluvial aquifer of the Kouris catchment (Cyprus) using continuous streamflow records     

Anastasia Boronina  Sergey Golubev  Werner Balderer 《水文研究》2005,19(20):4055-4068

The Kouris catchment is located in the south of the Troodos massif in Cyprus. The hydrology is driven by a Mediterranean climate, a mountainous topography, and a complex distribution of hydrogeological properties resulting from complex geology. To quantify the regional water balance further, a simple method using continuous streamflow records in the River Limnatis (Kouris catchment) was applied to calculate the actual evapotranspiration rate in the dry seasons. It was found that daily cycles of streamflow, recorded by automatic pressure logger, were caused by direct evaporation from the groundwater table and by transpiration of riparian forest. The daily amounts of ‘missing’ streamflow were calculated for the period 30 October–4 November 2001 and were extrapolated to the entire dry season and to the whole Kouris catchment. The actual evapotranspiration rate from the alluvial aquifer of the region is 2·4 ± 0·5 Mm³ for April–September 2001. The validity of the assumptions and the uncertainties in the estimates used in the method are discussed. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献