Granite intruding into Granodiorite: An example from the Damara Belt,South West Africa     

Dr. Christoph Hoffmann 《International Journal of Earth Sciences》1977,66(1):465-477

Until now (Smith, 1965) it was thought that in the central Damara Belt, South West Africa, the Red Granite and the Salem Granodiorite are two magmatic bodies separated by (essentially) marbles. Three places were discovered, where the marbles are missing; in all three places the Red Granite intrudes the Salem Granodiorite. Experimental melting done with samples from two of these localities allows to appraise the likely conditions during the intrusion of the Red Granite (680° C, 4 kb H₂O-pressure).The White Granites — until now thought to be late or post kinematic — are a geologically heterogeneous group, at least in one place such an intrusion precedes that of the Red Granite.

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Zusammenfassung Bis jetzt dachte man (Smith, 1965) daß im Zentralbereich des Damara-Orogens, Südwest Afrika, der Rote Granit und der Salem Granodiorit zwei magmatische Körper wären, die überall von (im wesentlichen) Marmoren getrennt seien. Es wurden drei Gegenden entdeckt, an denen die Marmore fehlen; an allen drei Stellen intrudiert der Rote Granit in den Salem Granodiorit. Schmelz-Experimente mit Proben von zwei dieser Lokalitäten erlauben die Bedingungen abzuschätzen, die während der Intrusion des Roten Granites geherrscht haben (680° C, 4 kb H₂O-Druck).Die Weißen Granite — von denen man bis jetzt glaubte, sie seien spät-oder nachkinematisch — sind eine geologisch heterogene Gruppe. Mindestens an einer Stelle geht eine Intrusion der Weißen Granite derjenigen der Roten Granite voraus.

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Résumé Jusqu'à présent (Smith, 1965) on a pensé que dans la zone centrale de l'orogène de Damara (Sud-Ouest Africain) le Granite Rouge et la Granodiorite de Salem étaient deux plutonites séparées partout par des couches de marbres. On a découvert trois endroits où les marbres n'existent pas et où le Granite Rouge forme des intrusions recoupant la Granodiorite de Salem.Des essais de fusibilité sur des échantillons provenant de deux de ces localité permettent d'estimer les conditions d'intrusion du Granite Rouge (680° C avec des pressions H₂O de 4–5 kb).Les Granites blancs (acceptés jusqu'à présent comme tardi orogéniques) forment géologiquement une groupe hétérogène. En un endroit au moins, une intrusion de Granite blanc est recoupée par une intrusion du Granite Rouge, plus jeune.

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(SMITH, 1965), , , - , , . 3 , , . , , , (680° C, 4 ). , , -, , . , - , .

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Paleomagnetic study of Jurassic and Cretaceous rocks from the Mixteca terrane (Mexico)     

Harald Bhnel 《Journal of South American Earth Sciences》1999,12(6):121

Three sites from Cretaceous limestone and Jurassic sandstone in northern Oaxaca, Mexico, were studied paleomagnetically. Thermal demagnetization isolated site-mean remanence directions which differ significantly from the recent geomagnetic field. The paleopole for the Albian–Cenomanian Morelos formation is indistinguishable from the corresponding reference pole for stable North America, indicating tectonic stability of the Mixteca terrane since the Cretaceous. Rock magnetic properties and a positive reversal test for the Bajocian Tecomazuchil sandstone suggest that the remanence could be of primary origin, although no fold test could be applied. The Tecomazuchil paleopole is rotated 10°±5° clockwise and displaced 24°±5° towards the study area, with respect to the reference pole for stable North America. Similar values were found for the Toarcien–Aalenian Rosario Formation, with 35°±6° clockwise rotation and 33°±6° latitudinal translation. These data support a post-Bajocian southward translation of the Mixteca terrane by around 25°, which was completed in mid-Cretaceous time.  相似文献   

Editorial     

Harald Lejenäs  Henning Rodhe 《Tellus. Series B, Chemical and physical meteorology》2009,61(3):499-499

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Evidence for enhanced hydration on the northern flank of Olympus Mons, Mars     

Giancarlo Bellucci  Joern Helbert  Francesca Altieri  Dennis Reiss  Jean-Pierre Bibring  Stephan van Gasselt  Harald Hoffmann  Yves Langevin  Gerhard Neukum  Franois Poulet 《Icarus》2007,192(2):361-377

In this paper we report about a small region on the northern scarp of Olympus Mons showing an increase of the 3 μm hydration band in the OMEGA spectra, together with low superficial temperatures. Although water ice clouds can occurs on the flank of big martian volcanoes, radiative transfer modeling indicates that atmospheric water ice alone cannot justify the shape of the observed band. A fit of the 1.9–3 μm absorption features is obtained by hypothesizing that the study region consists of a mixture of dust and water ice covered by an optically thin (τ=0.08 at 3 μm) layer of dust. Thermal modeling also suggests that water ice in this region may be stable during most of the martian year due to the saturation of the atmosphere. If water ice is responsible for the observed spectral behavior, it might consist of a number of ice or snow patches possibly deposited in small depressions.  相似文献   

The SAURON project – IX. A kinematic classification for early-type galaxies     

Eric Emsellem  Michele Cappellari  Davor Krajnovi&#;  Glenn van de Ven  R. Bacon  M. Bureau  Roger L. Davies  P. T. de Zeeuw  Jesús Falcón-Barroso  Harald Kuntschner  Richard McDermid  Reynier F. Peletier  Marc Sarzi 《Monthly notices of the Royal Astronomical Society》2007,379(2):401-417

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Sulfur cycling at the Mid-Atlantic Ridge: A multiple sulfur isotope approach     

Marc Peters  Harald Strauss  James Farquhar  Charlotte Ockert  Benjamin Eickmann  Cristiane L. Jost 《Chemical Geology》2010,269(3-4):180-196

The role of sulfur in two hydrothermal vent systems, the Logatchev hydrothermal field at 14°45′N/44°58′W and several different vent sites along the southern Mid-Atlantic Ridge (SMAR) between 4°48′S and 9°33′S and between 12°22′W and 13°12′W, is examined by utilizing multiple sulfur isotope and sulfur concentration data. Isotope compositions for sulfide minerals and vent H₂S from different SMAR sites range from + 1.5 to + 8.9‰ in δ³⁴S and from + 0.001 to + 0.051‰ in Δ³³S. These data indicate mixing of mantle sulfur with sulfur from seawater sulfate. Combined δ³⁴S and Δ³³S systematics reveal that vent sulfide from SMAR is characterized by a sulfur contribution from seawater sulfate between 25 and 33%. This higher contribution, compared with EPR sulfide, indicates increased seawater sulfate reduction at MAR, because of a deeper seated magma chamber and longer fluid upflow path length, and points to fundamental differences with respect to subsurface structures and fluid evolution at slow and fast spreading mid-ocean ridges.Additionally, isotope data uncover non-equilibrium isotopic exchange between dissolved sulfide and sulfate in an anhydrite bearing zone below the vent systems at fluid temperatures between 335 and 400 °C. δ³⁴S values between + 0.2 to + 8.8‰ for dissolved and precipitated sulfide from Logatchev point to the same mixing process between mantle sulfur and sulfur from seawater sulfate as at SMAR. δ³⁴S values between ? 24.5 and + 6.5‰ and Δ³³S values between + 0.001 and + 0.125‰ for sulfide-bearing sediments and mafic/ultramafic host rocks from drill cores taken in the region of Logatchev indicate a clear contribution of biogenic sulfides formed via bacterial sulfate reduction. Basalts and basaltic glass from SMAR sites with Δ³³S = ? 0.008‰ reveal lower Δ³³S lower values than suggested on the basis of previously published isotopic measurements of terrestrial materials.We conclude that the combined use of both δ³⁴S and Δ³³S provides a more detailed picture of the sulfur cycling in hydrothermal systems at the Mid-Atlantic Ridge and uncovers systematic differences to hydrothermal sites at different mid-ocean ridge sites. Multiple sulfur isotope measurements allow identification of incomplete isotope exchange in addition to isotope mixing as a second important factor influencing the isotopic composition of dissolved sulfide during fluid upflow. Furthermore, based on Δ³³S we are able to clearly distinguish biogenic from hydrothermal sulfides in sediments even when δ³⁴S were identical.  相似文献   

SHRIMP zircon dating and Nd isotopic systematics of Palaeoproterozoic migmatitic orthogneisses in the Epupa Metamorphic Complex of northwestern Namibia     

A. Kröner  Y. Rojas-Agramonte  E. Hegner  K.-H. Hoffmann  M.T.D. Wingate 《Precambrian Research》2010

The Epupa Metamorphic Complex constitutes the southwestern margin of the Congo Craton and is exposed in a hilly to mountainous terrain of northwestern Namibia, bordering the Kunene River and extending into southern Angola. It consists predominantly of granitoid gneisses which are migmatized over large areas. This migmatization locally led to anatexis and produced crustal-melt granites such as the Otjitanda Granite. We have undertaken reconnaissance geochemical studies and single zircon U–Pb SHRIMP and Pb–Pb evaporation dating of rocks of the Epupa Complex. The granitoid gneisses, migmatites and anatectic melts are similar in composition and constitute a suite of metaluminous to peraluminous, calc-alkaline granitoids, predominantly with volcanic arc geochemical signatures. The zircon protolith ages for the orthogneisses range from 1861 ± 3 to 1758 ± 3 Ma. Anatexis in the migmatitic Epupa gneisses was dated from a melt patch at 1762 ± 4 Ma, and the anatectic Otjitanda Granite has a zircon age of 1757 ± 4 Ma. Migmatization and anatexis therefore occurred almost immediately after granitoid emplacement and date a widespread high-temperature Palaeoproterozoic event at ∼1760 Ma which has not been recorded elswhere in northern Namibia. The Nd isotopic systematics of all dated samples are surprisingly similar and suggest formation of the protolith from a source region that probably separated from the depleted mantle about 2.4–2.0 Ga ago. A major Archaean component in the source area is unlikely.  相似文献   

A parallel global-implicit 2-D solver for reactive transport problems in porous media based on a reduction scheme and its application to the MoMaS benchmark problem     

Joachim Hoffmann  Serge Kr?utle  Peter Knabner 《Computational Geosciences》2010,14(3):421-433

In this article, an approach for the efficient numerical solution of multi-species reactive transport problems in porous media is described. The objective of this approach is to reformulate the given system of partial and ordinary differential equations (PDEs, ODEs) and algebraic equations (AEs), describing local equilibrium, in such a way that the couplings and nonlinearities are concentrated in a rather small number of equations, leading to the decoupling of some linear partial differential equations from the nonlinear system. Thus, the system is handled in the spirit of a global implicit approach (one step method) avoiding operator splitting techniques, solved by Newton’s method as the basic algorithmic ingredient. The reduction of the problem size helps to limit the large computational costs of numerical simulations of such problems. If the model contains equilibrium precipitation-dissolution reactions of minerals, then these are considered as complementarity conditions and rewritten as semismooth equations, and the whole nonlinear system is solved by the semismooth Newton method.  相似文献   

The Pleistocene evolution of the East Antarctic Ice Sheet in the Prydz bay region: stable isotopic evidence from ODP Site 1167     

Kevin M. Theissen  Robert B. Dunbar  Alan K. Cooper  David A. Mucciarone  Dirk Hoffmann 《Global and Planetary Change》2003,39(3-4):227-256

Ocean Drilling Program Leg 188, Prydz Bay, East Antarctica is part of a larger initiative to explore the Cenozoic history of the Antarctic Ice Sheet through direct drilling and sampling of the continental margins. In this paper, we present stable isotopic results from Ocean Drilling Program (ODP) Site 1167 located on the Prydz Channel Trough Mouth Fan (TMF), the first Antarctic TMF to be drilled. The foraminifer-based δ¹⁸O record is interpreted along with sedimentary and downhole logging evidence to reconstruct the Quaternary glacial history of Prydz Bay and the adjacent Lambert Glacier Amery Ice Shelf System (LGAISS). We report an electron spin resonance age date of 36.9±3.3 ka at 0.45 m below sea floor and correlate suspected glacial–interglacial cycles with the global isotopic stratigraphy to improve the chronology for Site 1167. The δ¹⁸O record based on planktonic (Neogloboquadrina pachyderma (s.)) and limited benthic results (Globocassidulina crassa), indicates a trend of ice sheet expansion that was interrupted by a period of reduced ice volume and possibly warmer conditions during the early–mid-Pleistocene (0.9–1.38 Ma). An increase in δ¹⁸O values after 900 ka appears to coincide with the mid-Pleistocene climate transition and the expansion of the northern hemisphere ice sheet. The δ¹⁸O record in the upper 50 m of the stratigraphic section indicates as few as three glacial–interglacial cycles, tentatively assigned as marine isotopic stages (MIS) 16–21, are preserved since the Brunhes/Matuyama paleomagnetic reversal (780 ka). This suggests that there is a large unconformity near the top of the section and/or that there may have been few extreme advances of the ice sheet since the mid-Pleistocene climate transition resulting in lowered sedimentation rates on the Prydz Channel TMF. The stable isotopic record from Site 1167 is one of the few available from the area south of the Antarctic Polar Front that has been linked with the global isotopic stratigraphy. Our results suggest the potential for the recovery of useful stable isotopic records in other TMFs.  相似文献   

Efficient block preconditioners for the coupled equations of pressure and deformation in highly discontinuous media     

Joachim Berdal Haga  Harald Osnes  Hans Petter Langtangen 《国际地质力学数值与分析法杂志》2011,35(13):1466-1482

Large‐scale simulations of flow in deformable porous media require efficient iterative methods for solving the involved systems of linear algebraic equations. Construction of efficient iterative methods is particularly challenging in problems with large jumps in material properties, which is often the case in geological applications, such as basin evolution at regional scales. The success of iterative methods for this type of problems depends strongly on finding effective preconditioners. This paper investigates how the block‐structured matrix system arising from single‐phase flow in elastic porous media should be preconditioned, in particular for highly discontinuous permeability and significant jumps in elastic properties. The most promising preconditioner combines algebraic multigrid with a Schur complement‐based exact block decomposition. The paper compares numerous block preconditioners with the aim of providing guidelines on how to formulate efficient preconditioners. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献