Crustal structure across the Colorado Basin, offshore Argentina   总被引：1，自引：0，他引：1  

Dieter Franke  Soenke Neben  Bernd Schreckenberger  Albrecht Schulze  Manfred Stiller  Charlotte M. Krawczyk 《Geophysical Journal International》2006,165(3):850-864

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Making continental crust through slab melting: Constraints from niobium-tantalum fractionation in UHP metamorphic rutile   总被引：6，自引：0，他引：6  

Yilin Xiao  Weidong Sun  Jochen Hoefs  Zeming Zhang  Albrecht W. Hofmann 《Geochimica et cosmochimica acta》2006,70(18):4770-4782

The formation of the continental crust (CC) is one of the most important processes in the evolution of the silicate Earth. Exactly how the CC formed is the subject of ongoing debate that focuses on its subchondritic Nb/Ta ratio. Nb and Ta are “geochemical identical twins,” so they usually do not fractionate from each other. Here, we show that rutile grains from hydrous rutile-bearing eclogitic layers recovered from drillcores in the Dabie-Sulu ultrahigh pressure terrain have highly variable Nb/Ta values (ranging from 5.4 to 29.1, with an average of 9.8 ± 0.6), indicating major fractionation of Nb and Ta most likely occurred during blueschist to amphibole-eclogite transformation in the absence of rutile. It is suggested that the released fluids with subchondritic Nb/Ta were transported to, and retained by, hydrous rutile-bearing eclogite in colder regions, resulting in suprachondritic Nb/Ta ratios for drier eclogite in hotter regions. Further dehydration of hydrous rutile-bearing eclogites cannot transfer the fractionated Nb/Ta values to the CC due to the low solubility of Nb and Ta in fluids in the presence of rutile, while dehydration-melting results in a major component of the CC, the tonalite-trondhjemite-granodiorite (TTG) component, which is responsible for the low Nb/Ta of the CC. Consequently, residual eclogites have variable but overall suprachondritic Nb/Ta.  相似文献   

A New Age for Geosimulation     

Jochen Albrecht 《Transactions in GIS》2005,9(4):451-454

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Book Reviews     

Samuel F. Dennis Jr.  Jochen Albrecht 《Transactions in GIS》2005,9(2):265-268

Books reviewed:
MARSHA ALIBRANDI, GIS in the Classroom: Using Geographic Information Systems in Social Studies and Environmental Science
JO WOOD, Java Programming for Spatial Sciences  相似文献   

2: Hydrothermal ore deposits related to post-orogenic extensional magmatism and core complex formation: The Rhodope Massif of Bulgaria and Greece     

Peter Marchev  Majka Kaiser-Rohrmeier  Christoph Heinrich  Maria Ovtcharova  Albrecht von Quadt  Raya Raicheva 《Ore Geology Reviews》2005,27(1-4):53

The Rhodope Massif in southern Bulgaria and northern Greece hosts a range of Pb–Zn–Ag, Cu–Mo and Au–Ag deposits in high-grade metamorphic, continental sedimentary and igneous rocks. Following a protracted thrusting history as part of the Alpine–Himalayan collision, major late orogenic extension led to the formation of metamorphic core complexes, block faulting, sedimentary basin formation, acid to basic magmatism and hydrothermal activity within a relatively short period of time during the Early Tertiary. Large vein and carbonate replacement Pb–Zn deposits hosted by high-grade metamorphic rocks in the Central Rhodopean Dome (e.g., the Madan ore field) are spatially associated with low-angle detachment faults as well as local silicic dyke swarms and/or ignimbrites. Ore formation is essentially synchronous with post-extensional dome uplift and magmatism, which has a dominant crustal magma component according to Pb and Sr isotope data. Intermediate- and high-sulphidation Pb–Zn–Ag–Au deposits and minor porphyry Cu–Mo mineralization in the Eastern Rhodopes are predominantly hosted by veins in shoshonitic to high-K calc-alkaline volcanic rocks of closely similar age. Base-metal-poor, high-grade gold deposits of low sulphidation character occurring in continental sedimentary rocks of synextensional basins (e.g., Ada Tepe) show a close spatial and temporal relation to detachment faulting prior and during metamorphic core complex formation. Their formation predates local magmatism but may involve fluids from deep mantle magmas.The change in geochemical signatures of Palaeogene magmatic rocks, from predominantly silicic types in the Central Rhodopes to strongly fractionated shoshonitic (Bulgaria) to calc-alkaline and high-K calc-alkaline (Greece) magmas in the Eastern Rhodopes, coincides with the enrichment in Cu and Au relative to Pb and Zn of the associated ore deposits. This trend also correlates with a decrease in the radiogenic Pb and Sr isotope components of the magmatic rocks from west to east, reflecting a reduced crustal contamination of mantle magmas, which in turn correlates with a decreasing crustal thickness that can be observed today. Hydrogen and oxygen isotopic compositions of the related hydrothermal systems show a concomitant increase of magmatic relative to meteoric fluids, from the Pb–Zn–Ag deposits of the Central Rhodopes to the magmatic rock-hosted polymetallic gold deposits of the Eastern Rhodopes.  相似文献   

GeoReM: A New Geochemical Database for Reference Materials and Isotopic Standards   总被引：13，自引：2，他引：13  

Klaus Peter Jochum  Uwe Nohl  Kirstin Herwig  Esin Lammel  Brigitte Stoll  Albrecht W. Hofmann 《Geostandards and Geoanalytical Research》2005,29(3):333-338

We have developed a new database named GeoReM ( http://georem.mpch-mainz.gwdg.de ) for reference materials and isotopic standards of geochemical and mineralogical interest. Reference samples include rock powders originating from the USGS, GSJ, GIT-IWG, synthetic and natural reference glasses originating from NIST, USGS, MPI-DING, as well as mineral (e.g., 91500 zircon), isotopic (e.g., La Jolla, E&A, NIST SRM 981), river water and seawater reference materials. GeoReM is a relational database, which strongly follows the concept of the three EARTHCHEM databases. It contains published analytical and compilation values (major and trace element concentrations, radiogenic and stable isotope ratios), important metadata about the analytical values, such as uncertainty, uncertainty type, method and laboratory. Sample information and references are also included. Three different ways of interrogating the database are possible: (1) sample names or material types, (2) chemical criteria and (3) bibliography. Some typical applications are described. GeoReM currently (October 2005) contains more than 750 geological reference materials, 6000 individual sets of results and references to 650 publications.  相似文献   

Methods of computing global radiation     

Dr. F. H. W. Albrecht 《Pure and Applied Geophysics》1955,32(1):131-138

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Os mobilization during melt percolation: The evolution of Os isotope heterogeneities in the mantle sequence of the troodos ophiolite, Cyprus     

Anette Büchl  Gerhard E. Brügmann  Albrecht W. Hofmann 《Geochimica et cosmochimica acta》2004,68(16):3397-3408

This study focuses on the origin of the Os isotope heterogeneities and the behaviour of Os and Re during melt percolation and partial melting processes in the mantle sequence of the Troodos Ophiolite Complex. The sequence has been divided into an eastern (Unit 1) and a western part (Unit 2) (Batanova and Sobolev, 2000). Unit 1 consists mainly of spinel-lherzolites and a minor amount of dunites, which are surrounded by cpx-bearing harzburgites. Unit 2 consists of harzburgites, dunites, and contains chromitite deposits.Unit 1 (¹⁸⁷Os/¹⁸⁸Os: 0.1169 to 0.1366) and Unit 2 (¹⁸⁷Os/¹⁸⁸Os 0.1235 to 0.1546) peridotites both show large ranges in their Os isotopic composition. Most of the ¹⁸⁷Os/¹⁸⁸Os ratios of Unit 1 lherzolites and harzburgites are chondritic to subchondritic, and this can be explained by Re depletion during ancient partial melting and melt percolation events. The old Os isotope model ages (>800 Ma) of some peridotites in a young ophiolitic mantle show that ancient Os isotopic heterogeneities can survive in the Earth upper mantle. Most harzburgites and dunites of Unit 2 have suprachondritic ¹⁸⁷Os/¹⁸⁸Os ratios. This is the result of the addition of radiogenic Os during a younger major melt percolation event, which probably occurred during the formation of the Troodos crust 90 Ma ago.Osmium concentrations tend to decrease from spinel-lherzolites (4.35 ± 0.2 ng/g) to harzburgites (Unit 1: 4.06 ± 1.12 ng/g; Unit 2: 3.46 ± 1.38 ng/g) and dunites (Unit 1: 2.71 ± 0.84 ng/g; Unit 2: 1.85 ± 1.20 ng/g). Therefore, this element does not behave compatibly during melt percolation as it is observed during partial melting, but becomes dissolved and mobilized by the percolating melt. The Os contents and Re/Os ratios in the mantle peridotites can be explained if they represent mixing products of old depleted mantle with cpx- and opx-veins, which are crystallization products of the percolating melt. This mixing occurred during the melting of a continuously fluxed mantle in a supra-subduction zone environment.This study shows that Unit 1 and Unit 2 of the Troodos mantle section have a complex and different evolution. However, the Os isotopic characteristics are consistent with a model where the harzburgites and dunites of both units belong to the same melting regime producing the Troodos oceanic crust.  相似文献   

Strontium isotope systematics of hydrothermal vein minerals in deposits of West Germany   总被引：1，自引：0，他引：1  

Dr. Albrecht Baumann  Dr. Richard Hofmann 《International Journal of Earth Sciences》1988,77(3):747-762

Vein minerals in West Germany hosted by crystalline basement rocks and Paleozoic and Mesozoic sedimentary rocks are characterized by⁸⁷Sr/⁸⁶Sr ratios which indicate continental derivation of Sr incorporated into the minerals. Neither mantle-derived Sr nor prominent contribution of this element from sea water (except for the strontianites of Münsterland) can be substantiated by the data presented.Minerals in veins hosted by sedimentary rocks have acquired their Sr most plausibly from buried sedimentary rock sequences.Mineralization of veins hosted by Moldanubian crystalline rocks in the Bayerischer Wald is confined to a Permian-Triassic time span. The⁸⁷Sr/⁸⁶Sr ratios of the minerals cover a relatively narrow range reflecting the time-dependent Sr isotopic composition of the host environment.Mineralization of veins in the Schwarzwald crosscutting crystalline basement rocks and partly extending into Mesozoic caprocks obviously occurred episodically or continuously from the Late Variscan event to Tertiary time. Mineral sequences of the Schwarzwald veins incorporated Sr with time-integrated isotopic composition most likely derived predominantly from gneisses.

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Zusammenfassung Gangminerale im kristallinen Grundgebirge und in paläozoischen und mesozoischen Sedimentgesteinen Westdeutschlands zeichnen sich durch⁸⁷Sr/⁸⁶Sr-Verhältnisse aus, die eine kontinentale Herkunft des Sr anzeigt. Weder Sr vom Erdmantel noch ein wesentlicher Beitrag dieses Elementes aus Meerwasser in den Mineralen (abgesehen von den Strontianiten des Münsterlandes) kann aus den vorliegenden Daten abgeleitet werden.Gangminerale in Sedimentgesteinen haben sehr wahrscheinlich Sr aus tieferliegenden Sedimentgesteinsabfolgen eingebaut.Die Mineralisation von Gängen in Gesteinen des kristallinen Grundgebirges im Moldanubikum des Bayerischen Waldes ist auf den Zeitraum Perm-Trias beschränkt. Die⁸⁷Sr/⁸⁶Sr-Verhältnisse umfassen eine relativ enge Spanne und spiegeln die zeitabhängige Isotopenzusammensetzung der umgebenden Gesteine und der des Untergrundes wider.Gänge im Schwarzwald durchschneiden kristallines Grundgebirge und setzen sich teilweise in mesozoisches Deckgebirge fort. Die Mineralisation erfolgte episodisch oder kontinuierlich von der variszischen Orogenèse bis ins Tertiär. Die Mineralabfolgen der Schwarzwaldgänge enthalten Sr mit einer zeitintegrierten Isotopenzusammensetzung, das sehr wahrscheinlich vorwiegend aus Gneisen stammt.

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Résumé Les minéraux des filons hydrothermaux contenus dans le socle cristallin et dans les sédiments paléozoïques et mésozoïques de l'Allemagne occidentale présentent des rapports initiaux⁸⁷Sr/⁸⁶Sr qui indiquent une origine continentale du Sr. Les résultats présentés dans cette note ne permettent d'accepter ni une origine mantellique ni un apport à partir de l'eau de mer (à l'exception des strontianites du Münsterland).Les minéraux des veines contenues dans les roches sédimentaires doivent très probablement leur Sr aux séries sédimentaires profondément enfouies.La minéralisation des veines contenues dans les roches cristallines moldanubiennes du Bayerische Wald date du Permo-Trias. Les rapports initiaux embrassent un éventail relativement étroit qui traduit la composition isotopique, fonction du temps, des roches encaissantes.Les filons de la Forêt Noire, qui traversent le socle cristallin et se prolongent partiellement dans la couverture mésozoïque, se sont foïmés manifestement, par épisodes ou de manière continue, depuis l'orogenèse varisque jusqu'au Tertiaire. Leurs séquences minérales renferment du Sr de composition isotopique temporellement intégrée, qui provient principalement des gneiss.

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Zur Paläomorphologie im Jungvariszikum des Saarlandes     

Dipl.-Geol. Hans Becker  Privatdozent Dr. Gottfried Kneuper  Dipl. Geol. Albrecht Schall 《International Journal of Earth Sciences》1968,58(1):128-144

Zusammenfassung Während des Oberkarbons befand sich das Rheinische Schiefergebirge im Endstadium der Faltung und im Aufstieg. Zur gleichen Zeit entwickelte sich im Saarland ein intramontanes Becken, das die Schuttmassen des aufsteigenden Gebirges aufnahm. Es kam zur Ablagerung von limnischen Sedimenten in dem flachen Saar-Nahe-Becken. Die paläomorphologische Gestaltung des Gebietes ist aus dem Faziesbild der Sedimente ablesbar.

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During the Upper Carboniferous the Rheinisches Schiefergebirge was in the final stage of folding and in the act of uplift. At the same time an intrageosyncline developed in the Saarland, which took up the detritus of the uplifting Northern mountains. Limnic sediments deposited in the flat Saar-Nahe-Basin. The paleomorphological development of the region can be recognized.

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Résumé Pendant le Carbonifère supérieur le massif schisteux rhénan se trouvait dans la phase finale de plissement et de surrection. En même temps se formait une dépression interne recevant les masses d'érosion de la montagne bordiére septentrionale. Des sédiments limniques se déposaient dans la dépression peu profonde de la Sarre-Nahe. Les faciès des sédiments nous montrent la topographie paléomorphologique du territoire.

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Wir danken der Deutschen Forschungsgemeinschaft für die Förderung der Untersuchungen.  相似文献