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71.
Oxidation state of the lithospheric mantle beneath Diavik diamond mine, central Slave craton, NWT, Canada 总被引:1,自引:0,他引:1
Steven Creighton Thomas Stachel Dave Eichenberg Robert W. Luth 《Contributions to Mineralogy and Petrology》2010,159(5):645-657
Oxygen fugacity (fO2) conditions were determined for 29 peridotite xenoliths from the A154-North and A154-South kimberlites of the Diavik diamond
mine using the newly developed flank method modified specifically for measuring Fe3+ in mantle-derived pyropic garnets. The results indicate that the garnet-bearing lithospheric mantle beneath the central Slave
craton is vertically layered with respect to oxidation state. The shallow (<140 km), “ultra-depleted” layer is the most oxidized
section of garnet-bearing subcratonic mantle thus far measured, up to one log unit more oxidizing relative to the FMQ buffer
[Δlog fO2 (FMQ) + 1]. The lower, more fertile layer has fO2 conditions that extend down to Δlog fO2 (FMQ) − 3.8, consistent with xenolith suites from other localities worldwide. Based on trace element concentrations in garnets,
two distinct metasomatic events affected the mantle lithosphere at Diavik. An oxidized fluid imparted sinusoidal chondrite-normalized
REE patterns on garnets throughout the entire depth range sampled. In contrast, a reducing melt metasomatic event affected
only the lower portion of the lithospheric mantle. The fO2 state of the Diavik mantle sample suggests that diamond formation occurred by reduction of carbonate by fluids arising from
beneath the lithosphere. 相似文献
72.
Yves Goddéris Jennifer Z. Williams Dave Pollard 《Geochimica et cosmochimica acta》2010,74(22):6357-6374
Anthropogenic and natural climate change affect processes in the atmosphere, biosphere, hydrosphere, and pedosphere. The impact of climate on soil evolution has not been well-explored, largely due to slow rates and the complexity of coupled processes that must be observed and simulated. The rates of mineral weathering in loess deposited 23 kyr ago and experiencing soil formation for 13 kyr are explored here using the WITCH model for weathering and the GENESIS model for climate simulation. The WITCH model, which uses rigorous kinetic parameters and laws with provision for the effect on rates of deviation from equilibrium, can successfully simulate the depletion profiles in the soil for dolomite and albite if soil CO2 is assumed to rise over the last 10 kyr up to about 30-40× the present atmospheric pressure, and if the solubility product of the Ca-smectite is assumed equal to that of an Fe(III)-rich Ca-montmorillonite. Such simulations document that dissolution behavior for silicates and carbonates are strongly coupled through pH, and for Ca-smectite and feldspars through dissolved silica. Such coupling is not incorporated in simple geometric and analytical models describing mineral dissolution, and therefore probably contributes to the long-standing observation of discrepancies among laboratory and field mineral dissolution rates. 相似文献
73.
Constanze Haug Tim Rayner Andrew Jordan Roger Hildingsson Johannes Stripple Suvi Monni Dave Huitema Eric Massey Harro van Asselt Frans Berkhout 《Climatic change》2010,101(3-4):427-445
Climate change is widely recognised as a ‘wicked’ policy problem. Agreeing and implementing governance responses is proving extremely difficult. Policy makers in many jurisdictions now emphasise their ambition to govern using the best available evidence. One obvious source of such evidence is the evaluations of the performance of existing policies. But to what extent do these evaluations provide insights into the difficult dilemmas that governors typically encounter? We address this question by reviewing the content of 262 evaluation studies of European climate policies in the light of six kinds of dilemma found in the governance literature. We are interested in what these studies say about the performance of European climate policies and in their capacity to inform evidence-based policy-making. We find that the evaluations do arrive at common findings: that climate change is framed as a problem of market and/or state failure; that voluntary measures tend to be ineffective; that market-based instruments tend to be regressive; that EU-level policies have driven climate policies in the latecomer EU Member States; and that lack of monitoring and weak enforcement are major obstacles to effective policy implementation. However, we also conclude that the evidence base these studies represent is surprisingly weak for such a high profile area. There is too little systematic climate policy evaluation work in the EU to support systematic evidence-based policy making. This reduces the scope for sound policy making in the short run and is a constraint to policy learning in the longer term. 相似文献
74.
A technique for replicating large rock outcrops has been developed so that casts of these surfaces can be archived in their present stage of preservation. Researchers can then study these casts in the laboratory under optimum lighting conditions, sometimes revealing new fossil evidence, while students and members of the public can be shown geological features that might otherwise be inaccessible to them. 相似文献
75.
76.
The use of the metaphors of general fitness and N-K spaces can assist in the understanding of the development of the physical landscape. Different modes of change can be viewed as different types of movement in, and distortions of, these phase spaces. Visualized in this manner landscape change can be viewed as both channelized, constrained and random. 相似文献
77.
A computer model of mid-ocean ridge basalt generation using trace element geochemistry has been developed. The model simulates a periodically replenished, continually cooled and fractionated magma chamber, with periodic lava extrusion. Primitive basalts from the ocean floor are used to generate likely evolution paths for the magma chamber. The steady state variant of this model has led to the isolation of several variables which critically affect the basalt composition. Although the fraction of cumulates is an important parameter, other variables such as the volume of incoming magma batches, their frequency, and the volume of the mixing cell, play a critical part especially on slow-spreading ridges. The growing magma chamber model uses random number generators to simulate the initiation and growth of a chamber. This model predicts a rapid increase in incompatible element concentrations, immediately after chamber initiation on a fast-spreading ridge. This would occur in situations such as propagating rifts and may help in the understanding of ferrobasalt generation. 相似文献
78.
79.
Cation ordering in omphacite and effect on deformation mechanism and lattice preferred orientation (LPO) 总被引:1,自引:0,他引:1
We present microstructural data and lattice preferred orientations (LPOs) of omphacites from a suite of eclogites, from the Adula/Cima Lunga nappe (Central Alps). Our work shows a surprisingly strong correlation between the measured LPO and the ordering state of cations in omphacite. Estimates of deformation temperature from metamorphic petrology, together with measured omphacite compositions and LPOs, determine the field (ordering state), on the omphacite phase diagram, into which each sample falls. LPOs dominated by L-type and S-type signatures are developed in samples that fall in the P2/n field (ordered structure) and C2/c field (disordered structure), respectively.Dislocations with b=1/2−110 or b=[001] are observed in the transmission electron microscope (TEM) in all samples. The former change from a perfect dislocation in the C2/c structure to a partial in P2/n. Any movement of a partial dislocation requires the formation or growth of a stacking fault. Furthermore, in order to pass an obstacle a partial dislocation has to constrict to a unit dislocation. The energy to form a constriction is high in omphacite due to the large separation width. Thus, the activity of the b=1/2−110 dislocation is hindered in the P2/n structure relative to the C2/c structure, which change the balance between the two and might give rise to the different LPOs. 相似文献
80.
John M. Livingston Vladimir N. Kapustin Beat Schmid Philip B. Russell Patricia K. Quinn Timothy S. Bates Philip A. Durkee Peter J. Smith Volker Freudenthaler Matthias Wiegner Dave S. Covert Santiago Gassó Dean Hegg Donald R. Collins Richard C. Flagan John H. Seinfeld Vito Vitale Claudio Tomasi 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):594-619