Morphological and structural data from the whole Tharsis province suggest that a number of shallow grabens radially oriented about the Tharsis bulge on Mars are underlain by dykes, which define giant radiating swarms similar to, e.g. the Mackenzie dyke swarm of the Canadian shield. Mechanisms for graben formation are proposed, and the depth, width, and height of the associated dykes are estimated. Structural mapping leads to define successive stages of dyke emplacement, and provide stress-trajectory maps that indicate a steady source of the regional stress during the whole history of the Tharsis province. A new tectonic model of Tharsis is presented, based on an analogy with dyke swarms on the Earth that form inside hot spots. This model successfully matches the following features: (1) the geometry of the South Tharsis Ridge Belt, which may have been a consequence of the compressional stress field at the boundary between the uplifted and non-uplifted areas in the upper part of the lithosphere at the onset of hot spot activity; (2) extensive lava flooding, interpreted as a consequence of the high thermal anomaly at the onset of plume (hot spot) activity; (3) wrinkle ridge geometry in the Tharsis hemisphere, the formation of which is interpreted as a consequence of buoyant subsidence of the brittle crust in response to the lava load; (4) Valles Marineris limited stretching by preliminary passive rifting, and uplift, viewed as a necessary consequence of adiabatic mantle decompression induced by stretching. The geometrical analysis of dyke swarms suggests the existence of a large, Tharsis-independent extensional state of stress during all the period of tectonic activity, in which the minimum compressive stress is roughly N---S oriented. Although magmatism must have loaded the lithosphere significantly after the plume activity ceased and be responsible for additional surface deformations, there is no requirement for further loading stress to explain surficial features. Comparison with succession of magmatic and tectonic events related to hot spots on the Earth suggests that the total time required to produce all the surface deformation observed in the Tharsis province over the last 3.8 Ga does probably not exceed 10 or 15 Ma. 相似文献
The Vredefort dome in the Kaapvaal Craton was formed as a result of the impact of a large meteorite at 2.02 Ga. The central
core of Archaean granitic basement rocks is surrounded by a collar of uplifted and overturned strata of the Witwatersrand
Supergroup, exposing a substantial depth section of the Archaean crust. Orthogneisses of the core show little variation in
whole-rock δ18O value, with the majority being between 8 and 10‰, with a mean of 9.2‰ (n = 35). Quartz and feldspar have per mil differences that are consistent with O-isotope equilibrium at high temperatures,
suggesting minimal interaction with fluids during subsequent cooling. These data refute previous suggestions that the Outer
Granite Gneiss (OGG) and Inlandsee Leucogranofels (ILG) of the core represent middle and lower crust, respectively. Granulite-facies
greenstone remnants from the ILG have δ18O values that are on average 1.5‰ higher than the ILG host rocks and are unlikely, therefore, to represent the residuum from
the partial melting event that formed the host rock. Witwatersrand Supergroup sedimentary rocks of the collar, which were
metamorphosed at greenschist-to amphibolite-facies conditions, generally have lower δ18O values than the core rocks with a mean value for metapelites of 7.7‰ (n = 45). Overall, through an ∼20 km thick section of crust, there is a general increase in whole-rock δ18O value with increasing depth. This is the reverse of what is normal in the crust, largely because the collar rocks have δ18O values that are unusually low in comparison with metamorphosed sedimentary rocks worldwide. The collar rocks have δD values ranging from −35 to −115‰ (average −62‰, n = 29), which are consistent with interaction with water of meteoric origin, having a δD of about −25 to −45‰. We suggest that fluid movement through the collar rocks was enhanced by impact-induced secondary permeability
in the dome structure.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
The Kelçyra area is emplaced in a foreland fold-and-thrust belt (FFTB), characterized by a westward thrusting with the Triassic evaporites as the major décollement level. Several secondary features related with this evolution, like backthrusting, folding, duplex structures, evaporite diapirism are present. During the FFTB evolution, the study area has been subjected to several fracturing events with associated stages of fluid migration. During the pre-deformational stage, complex textures such as crack-and-seal features most likely reflect expulsion of overpressured fluids. These fluids were dominantly host-rock buffered. Within the post-deformational stage, a meteoric fluid caused cementation and development of a karst network during a period of emergence after the thrust emplacement. Subsequently, Mg calcite reprecipitated in the more stable carbonate phase calcite and dolomite, which filled part of the karts network. The latter is finally dedolomitized and locally partially dissolved by a second meteoric fluid flow, which greatly increased the secondary porosity. 相似文献
We present a gridded data set of Sea Surface Salinity (SSS) for the tropical Pacific (120°E–70°W; 30°N–30°S), with a grid resolution of 1° longitude, 1° latitude and 1 month, from 1950 to 2008. The product, together with its associated error field, is derived from an objective analysis of about 10 million validated SSS records, with most of the data originating from Voluntary Observing Ships, TAO/TRITON moorings and Argo profilers (during the most recent period). We expect this product to benefit studies in oceanography, meteorology and paleoceanography. As examples of applications, we analyse: (a) the seasonal and ENSO (El Niño Southern Oscillation) modes of observed SSS variability, (b) the ability of 23 coupled models used in the Intergovernmental Panel for Climate Change 4th Assessment Report (IPCC AR4) to simulate the mean SSS and these two time varying modes, and (c) the usefulness of the SSS product and of its associated error field in calibrating and validating the paleo-salinity time series. We anticipate improvements and regular updates to our product, as more SSS data become available from in situ networks and from the ongoing and near-future satellite-derived observations by SMOS (Soil Moisture and Ocean Salinity) and Aquarius. 相似文献
This article provides an analysis of the EU Emissions Trading Scheme (ETS) and the harmonized benchmark-based allocation procedures by comparing two energy-intensive sectors with activities in three Member States. These sectors include the cement industry (CEI) and the pulp and paper industry (PPI) in the UK, Sweden, and France. Our results show that the new procedures are better suited for the more homogeneous CEI, in which the outcome of stricter allocation of emissions allowances is consistent between Member States. For the more heterogeneous PPI – in terms of its product portfolios, technical infrastructures, and fuel mixes – the allocation procedures lead to diverse outcomes. It is the lack of product benchmark curves, and the alternative use of benchmark values that are biased towards a fossil fuel-mix and are based on specific energy use rather than emission intensity, which leads to allocations to the PPI that do not represent the average performance of the top 10% of GHG-efficient installations. Another matter is that grandfathering is still present via the historically based production volumes. How to deal with structural change and provisions regarding capacity reductions and partial cessation is an issue that is highly relevant for the PPI but less so for the CEI.
Policy relevance
After an unprecedented amount of consultation with industrial associations and other stakeholders, a harmonized benchmark-based allocation methodology was introduced in the third trading period of the EU ETS. Establishing a reliable and robust benchmark methodology for free allocation that shields against high direct carbon costs, is perceived as fair and politically acceptable, and still incentivizes firms to take action, is a significant challenge. This article contributes to a deeper understanding of the challenges in effectively applying harmonized rules in industrial sectors that are heterogeneous. This is essential for the debate on structural reformation of the EU ETS, and for sharing experiences with other emerging emissions trading systems in the world that also consider benchmark methodologies. 相似文献
Aviation constitutes about 2.5% of all energy-related CO2 emissions and in addition there are non-CO2 effects. In 2016, the ICAO decided to implement a Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) and in 2017 the EU decided on faster emission reductions in its Emissions Trading System (EU ETS), which since 2012 includes the aviation sector. The effects of these policies on the expected development of air travel emissions from 2017 to 2030 have been analyzed. For the sample country Sweden, the analysis shows that when emissions reductions in other sectors are attributed to the aviation sector as a result of the EU ETS and CORSIA, carbon emissions are expected to reduce by ?0.8% per year (however if non-CO2 emissions are included in the analysis, then emissions will increase). This is much less than what is needed to achieve the 2°C target. Our analysis of potential national aviation policy instruments shows that there are legally feasible options that could mitigate emissions in addition to the EU ETS and CORSIA. Distance-based air passenger taxes are common among EU Member States and through increased ticket prices these taxes can reduce demand for air travel and thus reduce emissions. Tax on jet fuel is an option for domestic aviation and for international aviation if bilateral agreements are concluded. A quota obligation for biofuels is a third option.Key policy insights
Existing international climate policies for aviation will not deliver any major emission reductions.
Policymakers who want to significantly push the aviation sector to contribute to meeting the 2°C target need to work towards putting in place tougher international policy instruments in the long term, and simultaneously implement temporary national policy instruments in the near-term.
Distance-based air passenger taxes, carbon taxes on jet fuel and quota obligations for biofuels are available national policy options; if they are gradually increased, and harmonized with other countries, they can help to significantly reduce emissions.