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991.
Robert O. Rye Roelof D. Schuiling Danny M. Rye J.Ben H. Jansen 《Geochimica et cosmochimica acta》1976,40(9):1031-1049
At Naxos, Greece, a migmatite dome is surrounded by schists and marbles of decreasing metamorphic grade. Sillimanite, kyanite, biotite, chlorite, and glaucophane zones are recognized at successively greater distances from the migmatite dome. Quartz-muscovite and quartz-biotite oxygen isotope and mineralogie temperatures range from 350 to 700°C.The metamorphic complex can be divided into multiple schist-rich (including migmatites) and marblerich zones. The δ18O values of silicate minerals in migmatite and schist units and quartz segregations in the schist-rich zones decrease with increase in metamorphic grades. The calculated δ18OH2O values of the metamorphic fluids in the schist-rich zones decrease from about 15‰ in the lower grades to an average of about 8.5‰ in the migmatite.The δD values of OH-minerals (muscovite, biotite, chlorite, and glaucophane) in the schist-rich zones also decrease with increase in grade. The calculated δDH2O values for the metamorphic fluid decrease from ?5‰ in the glaucophane zone to an average of about ?70‰ in the migmatite. The δD values of water in fluid inclusions in quartz segregations in the higher grade rocks are consistent with this trend.Theδ18O values of silicate minerals and quartz segregations in marble-rich zones are usually very large and were controlled by exchange with the adjacent marbles. The δD values of the OH minerals in some marble-rich zones may reflect the value of water contained in the rocks prior to metamorphism.Detailed data on 20 marble units show systematic variations of δ18O values which depend upon metamorphic grade. Below the 540°C isograd very steep δ18O gradients at the margins and large δ18O values in the interior of the marbles indicate that oxygen isotope exchange with the adjacent schist units was usually limited to the margins of the marbles with more exchange occurring in the stratigraphic bottom than in the top margins. Above the 540°C isograd lower δ18O values occur in the interior of the marble units reflecting a greater degree of recrystallization and the occurrence of Ca-Mg-silicates.Almost all the δ13C values of the marbles are in the range of unaltered marine limestones. Nevertheless, the δ13C values of most marble units show a general correlation with δ18O values.The mole ratio of fluid inclusions in quartz segregations range from 0.01 to 2. Theδ13C values of the CO2 range from ?8.0 to 3.6‰ and indicate that at some localities CO2 in the metamorphic fluid was not in carbon isotopic equilibrium with the marbles. 相似文献
992.
Ronner Bendezú Laurence Page Richard Spikings Zoltan Pecskay Lluís Fontboté 《Mineralium Deposita》2008,43(7):777-789
We present 40Ar/39Ar data acquired by infra-red (CO2) laser step-heating of alunite crystals from the large Miocene Colquijirca district in central Peru. Combined with previously
published data, our results show that a long (at least 1.3 My) and complex period of magmatic-hydrothermal activity associated
with epithermal Au–(Ag) mineralization and base metal, Cordilleran ores took place at Colquijirca. The new data indicate that
incursion of magmatic SO2-bearing vapor into the Colquijirca epithermal system began at least as early as ∼11.9 Ma and lasted until ∼10.6 Ma. Four
alunite samples associated with high-sulfidation epithermal Au–(Ag) ore gave 40Ar/39Ar plateau ages between ∼11.9 and ∼11.1 Ma (compared to the previously documented ∼11.6 to ∼11.3 Ma). By combining individually
these new ages with crosscutting relationships, the duration of the Au–(Ag) deposition period can be estimated to at least
0.4 My. Three new 40Ar/39Ar plateau ages on alunite associated with the base-metal Cordilleran ores are consistent with previously obtained ages, all
of them between 10.83 ± 0.06 and 10.56 ± 0.06 Ma, suggesting that most of the sulfide-rich polymetallic deposits of Smelter
and Colquijirca formed during this short period. The recognition of consecutive alunite-bearing and alunite-free mineral assemblages
within both the Au–(Ag) and the base-metal Cordilleran ores may suggest that SO2-bearing magmatic vapor entered the epithermal environment as multiple discontinuous pulses, a number of which was not necessarily
associated in time with ore fluids. It is likely that a period of SO2-bearing vapor degassing longer than 11.9 to 10.6 Ma may be recognized with further more detailed work.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
993.
A synthetic approach integrating surface and subsurface data for prospecting deep aquifers: the Southeast Tunisia 总被引:2,自引:0,他引:2
The Southeast Tunisia has remarkable thermal springs that have been used for bathing since many years. Currently, studies
are being carried out to investigate the possible use of the hot water for heating buildings and for greenhouses. Springs
with discharge temperatures between 26.8 and 58°C exist in the area. The flow rates range between 7 and 66 l/s with total
dissolved solids (TDS) varying between 2,020 and 4,030 mg/l. Both geological–hydrogeological setting and the similarity in
chemical characteristics between the Zarat spring and nearby water wells suggest that the hot water from this spring may be
related to the Senonian aquifer. However, the hydrogeothermal approach shows that the depth of the reservoir that supplies
the Zarat spring is greater than that of the Senonian aquifer. In fact, geothermometry approach indicates that fluids emerging
from the Lower Cretaceous sandstones reach temperatures of approximately 78°C at depth, while the fluid temperature from the
nearby water wells is 32°C. Through the integration of various types of data we found that the thermal water of Southeast
Tunisia is of meteoric origin. This water infiltrates deeply into the Lower Cretaceous sandstones and reaches a high temperature
before rising upwards to supply the hot springs and well discharge zones. It appears that the upward movement of hot water
from the deep aquifers to shallow ones is probably due to the abundant fractures in the area. 相似文献
994.
Abdelilah Tahayt Taoufik Mourabit Alexis Rigo Kurt L. Feigl Abdelali Fadil Simon McClusky Robert Reilinger Mostafa Serroukh Abdelouahed Ouazzani-Touhami Driss Ben Sari Philippe Vernant 《Comptes Rendus Geoscience》2008,340(6):400-413
GPS velocities and seismicity across the Betic–Rif Arc structural domains (Morocco and Iberia) provide a basis to evaluate present-day seismotectonic processes between different deformation belts. The results show asymmetric movements in the complex Alboran system accommodating the convergence between the African (Nubian) and Eurasian plates. While the Betic Mountains are attached to Iberia, moving toward the southeast with respect to Africa, the Rif is divided into three blocks with distinct displacements relative to Nubia: (1) the Tangier block moving southeastward, (2) the Central Rif block moving SSW, and (3) the Oriental Rif block undergoing clockwise rotation. GPS-derived motions decrease in rate from the Rif nappes complex to the foreland. 相似文献
995.
996.
Jun Wang Daniel G. Brown Rick L. Riolo Scott E. Page Arun Agrawal 《Global Environmental Change》2013,23(5):1266-1276
There has been a decrease in grazing mobility in the Mongolian grasslands over the past decades. Sedentary grazing with substantial external inputs has increased the cost of livestock production. As a result, the livelihoods of herders have become more vulnerable to climate variability and change. Sedentary grazing is the formal institutional arrangement in Inner Mongolia, China. However, this may not be an efficient institutional arrangement for climate change adaptation. Self-organized local institutions for climate change adaptation have emerged and are under development in the study area. In this study, we did exploratory analyses of multiple local institutions for climate change adaptation in the Mongolian grasslands, using an agent-based modeling approach. Empirical studies from literature and our field work show that sedentary grazing, pasture rental markets, and reciprocal pasture-use groups are three popular institutional arrangements in the study area. First, we modeled the social–ecological performance (i.e., livelihood benefits to herders and grassland quality) of these institutions and their combinations under different climate conditions. Second, we did exploratory analyses of multiple social mechanisms for facilitating and maintaining cooperative use of pastures among herders. The modeling results show that in certain value-ranges of some model parameters with assumed values, reciprocal pasture-use groups had better performance than pasture rental markets; and the comparative advantage of cooperative use of pastures over sedentary grazing without cooperation becomes more evident with the increase in drought probability. Agent diversity and social norms were effective for facilitating the development of reciprocal pasture-use groups. Kin selection and punishments on free-riders were useful for maintaining cooperation among herders. 相似文献
997.
Postglacial relative sea‐level observations from Ireland and their role in glacial rebound modelling
Anthony J. Brooks Sarah L. Bradley Robin J. Edwards Glenn A. Milne Ben Horton Ian Shennan 《第四纪科学杂志》2008,23(2):175-192
The British Isles have been the focus of a number of recent modelling studies owing to the existence of a high‐quality sea‐level dataset for this region and the suitability of these data for constraining shallow earth viscosity structure, local to regional ice sheet histories and the magnitude/timing of global meltwater signals. Until recently, the paucity of both glaciological and relative sea‐level (RSL) data from Ireland has meant that the majority of these glacial isostatic adjustment (GIA) modelling studies of the British Isles region have tended to concentrate on reconstructing ice cover over Britain. However, the recent development of a sea‐level database for Ireland along with emergence of new glaciological data on the spatial extent, thickness and deglacial chronology of the Irish Ice Sheet means it is now possible to revisit this region of the British Isles. Here, we employ these new data to constrain the evolution of the Irish Ice Sheet. We find that in order to reconcile differences between model predictions and RSL evidence, a thick, spatially extensive ice sheet of ~600–700 m over much of north and central Ireland is required at the LGM with very rapid deglaciation after 21 k cal. yr BP. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
998.
999.
1000.
Paolo Paruolo Ben Murphy Greet Janssens-Maenhout 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(1):93-107
This paper analyzes the relation between income and emissions in the period 1970–2008, for all world countries. We consider time-series of CO2, SO2 and GWP100, and use Vector Autoregressive models that allow for nonstationarity and cointegration. At 5 % significance level, income and emissions are found to be driven by unrelated random walks with drift (respectively by a common random walk with drift) in about 70 % (respectively 25 %) of cases; in the remaining cases the variables are trend-stationary. Tests of Granger-causality show evidence of both directions of causality. For the case of unrelated stochastic trends, we almost never find income driving emissions, as predicted by a consumption-function interpretation. These causality results and the absence of a common trend challenge the main implications of the Environmental Kuznets Curve, namely that the dominant direction of causality should be from income to emissions, and that for increasing levels of income, emissions should tend to decrease. 相似文献