Continental rift systems and anorogenic magmatism   总被引：1，自引：0，他引：1  

James W. Sears  Gregory M. St. George  J. Chris Winne 《Lithos》2005,80(1-4):147-154

Precambrian Laurentia and Mesozoic Gondwana both rifted along geometric patterns that closely approximate truncated-icosahedral tessellations of the lithosphere. These large-scale, quasi-hexagonal rift patterns manifest a least-work configuration. For both Laurentia and Gondwana, continental rifting coincided with drift stagnation, and may have been driven by lithospheric extension above an insulated and thermally expanded mantle. Anorogenic magmatism, including flood basalts, dike swarms, anorthosite massifs and granite-rhyolite provinces, originated along the Laurentian and Gondwanan rift tessellations. Long-lived volcanic regions of the Atlantic and Indian Oceans, sometimes called hotspots, originated near triple junctions of the Gondwanan tessellation as the supercontinent broke apart. We suggest that some anorogenic magmatism results from decompression melting of asthenosphere beneath opening fractures, rather than from random impingement of hypothetical deep-mantle plumes.  相似文献   

Quantum-thermodynamic treatment of intrinsic anharmonicity; Wallace’s theorem revisited   总被引：1，自引：0，他引：1  

Michel H.G. Jacobs  Bernard H.W.S. de Jong 《Physics and Chemistry of Minerals》2005,32(8-9):614-626

Wallace (in Thermodynamics of crystals, 1972) developed a theorem, rooted in rigid lattice dynamics, which incorporates intrinsic anharmonic effects in solids. The practical application of this theorem in mineral physics is computationally involved and this is the main reason for the theorem not getting the attention it deserves. Because intrinsic anharmonicity is an important issue at the extreme conditions in planetary mantles, we derived a method which removes the computational obstacles in applying this theorem. We extended the theorem to incorporate details of the phonon spectrum and tested our algorithm on forsterite (Mg₂SiO₄). Using a least squares inversion technique applied to all available experimental data, we show that it results in an accurate representation of thermodynamic properties and sound wave velocities of Mg₂SiO₄ in its complete pressure–temperature stability range. We also show that the accuracy of our results is not significantly affected by the use of a different equation of state.  相似文献   

Reviewers for 2004     

W. Edwin Sharp 《Mathematical Geology》2005,37(8):947-948

  相似文献   

Variation in nitrate and calcium as indicators of recharge pathways in Nolte Spring, PA   总被引：1，自引：0，他引：1  

L. Toran  W. B. White 《Environmental Geology》2005,48(7):854-860

This study documents variations in calcium and nitrate concentrations that suggest changes in recharge pathways in a karst spring. The nitrate concentrations increased at the end of the growing season, showing the importance of the soil zone in the recharge pathway. The increase occurred over just a few days, which may be indicative of a change in contribution of baseflow in different seasons from deep to shallow groundwater. The calcium concentrations decreased several days after storm events. A change in the carbonate equilibrium is hypothesized because chloride was not diluted during these events. The decrease in calcium could be due to outgassing and calcite precipitation in the recharge area when older, higher ionic strength matrix water mixes with stormwater in open conduits. The use of geochemical indicators to better understand recharge pathways benefited from long-term monitoring and periods of daily sampling.  相似文献   

Magmatic zircon oxygen isotopes of 1.88–1.87 Ga orogenic and 1.65–1.54 Ga anorogenic magmatism in Finland     

B. A. Elliott  W. H. Peck  O. T. Rämö  M. Vaasjoki  M. Nironen 《Mineralogy and Petrology》2005,85(3-4):223-241

Summary Oxygen isotope ratios of igneous zircon from magmatic rocks in Finland provide insights into the evolution and growth of the Precambrian crust during the Svecofennian orogeny. These data preserve magmatic δ¹⁸O values and correlate with major discontinuities in the lower crust. Oxygen isotope ratios of zircon across the 1.88–1.87 Ga Central Finland granitoid complex (CFGC) range from 5.50‰ to 6.84‰, except for three plutons in contact with the adjacent greenstone and metasedimentary belts (δ¹⁸O(Zrc) = 7.60‰–7.78‰). There is a systematic variation in δ¹⁸O(Zrc) with respect to geographic location in the CFGC, ranging from 6.60±0.23‰ (σ) in the northeast to 5.90±0.40‰ in the west-southwest. These values correlate with a change in crustal thickness and shift in geochemical composition. The oxygen isotope composition of the 1.65–1.54 Ga rapakivi granites and related rocks in southern Finland show a decreasing trend from north to south, independent of their emplacement age. The southern anorogenic granite group has an average δ¹⁸O in zircon of 6.14±0.07‰ and the northern anorogenic group has an average δ¹⁸O in zircon of 8.14±0.59‰. This difference reflects the boundary between island arc terrains accreted during the Paleoproterozoic. Deceased  相似文献   

Uncertainty in adaptive capacity     

W. Neil Adger  Katharine Vincent 《Comptes Rendus Geoscience》2005,337(4):399-410

The capacity to adapt is a critical element of the process of adaptation: it is the vector of resources that represent the asset base from which adaptation actions can be made. Adaptive capacity can in theory be identified and measured at various scales, from the individual to the nation. The assessment of uncertainty within such measures comes from the contested knowledge domain and theories surrounding the nature of the determinants of adaptive capacity and the human action of adaptation. While generic adaptive capacity at the national level, for example, is often postulated as being dependent on health, governance and political rights, and literacy, and economic well-being, the determinants of these variables at national levels are not widely understood. We outline the nature of this uncertainty for the major elements of adaptive capacity and illustrate these issues with the example of a social vulnerability index for countries in Africa. To cite this article: W.N. Adger, K. Vincent, C. R. Geoscience 337 (2005).  相似文献   

Reviewers for 2004     

W. Edwin Sharp 《Mathematical Geosciences》2005,37(8):947-948

  相似文献   

Mechanism of loading on plates due to explosive detonation     

W. L. Fourney  U. Leiste  R. Bonenberger  D. J. Goodings 《Fragblast: International Journal for Blasting and Fragmentation》2005,9(4):205-217

This paper investigates the various mechanisms and parameters that are responsible for delivering impulse to a vehicle that is unfortunate enough to detonate a buried mine. Small scale tests are used to examine the effects of air blast or ejected sand in imparting impulse to a plate that is located above the surface of the saturated soil that contains the explosive. Parameters such as confinement, stand off distance, depth of burial of the explosive, density of the soil, and saturation level of the soil are also examined.  相似文献   

The post-glacial landscape evolution of the North German Basin: morphology, neotectonics and crustal deformation     

K. Reicherter  A. Kaiser  W. Stackebrandt 《International Journal of Earth Sciences》2005,94(5-6):1083-1093

The recent evolution of the north German Basin (NGB), which is presently a low-seismic area, was partly affected by glacial loading and unloading of the ice masses. Major stresses acting within the NGB are induced by the North-Atlantic ridge push, the ongoing Alpine collision, and the post-glacial rebound of Fennoscandia. Present-day horizontal stresses within the NGB are directed generally NW–SE, but fan and bend north of 52°N towards NNE. Major basement faults are directed NW–SE, minor faults NE–SW and NNE–SSW, and are clearly detectable in geomorphological and satellite lineaments. Furthermore, the drainage pattern and the distribution of lakes in northern Germany follow exactly block boundaries and, hence, mark zones of present-day subsidence. The understanding of the post-glacial morphology and reactivation of faults requires a view into the very heterogeneous crust and upper mantle below the NGB. The re-adjustment of the individual fault blocks during post-glacial relaxation of the lithosphere leads to differential, crust-dependent uplift and, probably, to the formation of Urstrom valleys. The Urstrom valleys and terminal moraines in northern Germany appear to parallel the major tectonic lineaments and lithospheric “block” boundaries. The lithospheric memory is expressed in the post-glacial landscape evolution of the NGB.  相似文献   

The Stonyford Volcanic Complex: a Forearc Seamount in the Northern California Coast Ranges   总被引：2，自引：0，他引：2  

SHERVAIS  JOHN W.; SCHUMAN  MARCHELL M. ZOGLMAN; HANAN  BARRY B. 《Journal of Petrology》2005,46(10):2091-2128

Jurassic age volcanic rocks of the Stonyford volcanic complex(SFVC) comprise three distinct petrological groups based ontheir whole-rock geochemistry: (1) oceanic tholeiites; (2) transitionalalkali basalts and glasses; (3) high-Al, low-Ti tholeiites.Major and trace element, and Sr–Nd–Pb isotopic dataindicate that the oceanic tholeiites formed as low-degree partialmelts of normal mid-ocean ridge basalt (N-MORB)-source asthenospheresimilar in isotope composition to the East Pacific Rise today;the alkalic lavas were derived from an enriched source similarto that of E-MORB. The high-Al, low-Ti lavas resemble second-stagemelts of a depleted MORB-source asthenosphere that formed bymelting spinel lherzolite at low pressures. Trace element systematicsof the high-Al, low-Ti basalts show the influence of an enrichedcomponent, which overprints generally depleted trace elementcharacteristics. Tectonic discrimination diagrams show thatthe oceanic tholeiite and alkali suites are similar to present-daybasalts generated at mid-oceanic ridges. The high-Al, low-Tisuite resembles primitive arc basalts with an enriched, alkalibasalt-like overprint. Isotopic data show the influence of recycledcomponents in all three suites. The SFVC was constructed ona substrate of normal Coast Range ophiolite in an extensionalforearc setting. The close juxtaposition of the MORB-like olivinetholeiites with alkali and high-Al, low-Ti basalts suggestsderivation from a hybrid mantle source region that includedMORB-source asthenosphere, enriched oceanic asthenosphere, andthe depleted supra-subduction zone mantle wedge. We proposethat the SFVC formed in response to collision of a mid-oceanridge spreading center with the Coast Range ophiolite subductionzone. Formation of a slab window beneath the forearc duringcollision allowed the influx of ridge-derived magmas or themantle source of these magmas. Continued melting of the previouslydepleted mantle wedge above the now defunct subduction zoneproduced strongly depleted high-Al, low-Ti basalts that werepartially fertilized with enriched, alkali basalt-type meltsand slab-derived fluids. KEY WORDS: CRO; oceanic basalts; California  相似文献