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41.
Michael Raith 《Contributions to Mineralogy and Petrology》1976,57(1):99-117
The compositional variations in epidotes, Ca2Al2(Fe3+, Al)-Si3O12(OH), from a prograde Mesozoic rock series in the Eastern Alps, Austria, are systematically related to metamorphic grade and the oxidation state of the rock. With increasing metamorphic grade the average composition of the zoned epidotes shifts to Fe3+-poorer compositions reflecting not only the effect of temperature and total pressure but also the concomitant decrease of the oxidation state of the rocks. Oxidized hematite-bearing assemblages are: 90 mole % Al2FeEp (greenschists) 70 mole % Al2FeEp (garnet amphibolites) 58 mole % Al2FeEp (eclogites); reduced sulfidebearing assemblages are: 42 mole % Al2FeEp (greenschists) 24 mole % Al2FeEp (garnet amphibolites) 23 mole % Al2FeEp (eclogites).A similar compositional evolution of the epidotes as in the spatial sequence of the samples can be observed within the single zoned crystals, reflecting the temporal changes of temperature, total pressure and oxygen fugacity during the prograde crystallization. The Fe3+-contents of core and rim decrease with increasing metamorphic grade and decreasing oxidation state. Generally the zoned epidotes consist of a Fe3+-rich core (90 to 63 mole % Al2FeEp) and a Fe3+-poorer rim (55 to 23 mole % Al2FeEp). Core and rim of the epidote crystals are separated by a compositional gap the extension of which is independent of the bulk rock composition, the oxidation state, and the mineralogical composition of the assemblages but becomes smaller with increasing metamorphic grade: 7253 mole % Al2FeEp (low grade greenschists, 400° C) 6355 mole % Al2FeEp (higher grade greenschists, 500° C), and 6055 mole % Al2FeEp (garnet amphibolites, 500–550° C). At the temperature conditions of the highest grade garnet amphibolites and eclogites (550° C) the compositional gap closes at a composition of 58 mole % Al2FeEp.The data presented thus confirm clearly the existence of an asymmetric miscibility gap in the monoclinic Al-Fe(III)-epidote solid solution series, which, for the first time, has been assumed by Strens (1964, 1965).A model is proposed that describes the prograde compositional evolution of the epidotes studied through the competing mechanisms of growth and diffusional Al-Fe3+ exchange and their dependence on metamorphic grade and oxidation state. 相似文献
42.
Dionisis Katsikopoulos Ángeles Fernández-González Manuel Prieto 《Geochimica et cosmochimica acta》2009,73(20):6147-455
The enthalpy of mixing of the calcite-rhodochrosite (Ca,Mn)CO3 solid solution was determined at 25 °C from calorimetric measurements of the enthalpy of precipitation of solids with different compositions. A detailed study of the broadening of powder X-ray diffraction peaks shows that most of the precipitates are compositionally homogeneous. All the experimental enthalpy of mixing (ΔHm) values are positive and fit reasonably well (R2 = 0.86) to a Guggenheim function of three terms:
43.
Raphael Di Carlo Silva dos Santos João Carlos Ribeiro Cruz Manuel de Jesus dos Santos Costa 《Geophysical Prospecting》2020,68(7):2046-2063
Recently, the interest in PS-converted waves has increased for several applications, such as sub-basalt layer imaging, impedance estimates and amplitude-versus-offset analysis. In this study, we consider the problem of separation of PP- and PS-waves from pre-stacked multicomponent seismic data in two-dimensional isotropic medium. We aim to demonstrate that the finite-offset common-reflection-surface traveltime approximation is a good alternative for separating PP- and PS-converted waves in common-offset and common shot configurations by considering a two-dimensional isotropic medium. The five parameters of the finite-offset common-reflection-surface are firstly estimated through the inversion methodology called very fast simulated annealing, which estimates all parameters simultaneously. Next, the emergence angle, one of the inverted parameters, is used to build an analytical separation function of PP and PS reflection separation based on the wave polarization equations. Once the PP- and PS-converted waves were separated, the sections are stacked to increase the signal-to-noise ratio using the special curves derived from finite-offset common-reflection-surface approximation. We applied this methodology to a synthetic dataset from simple-layered to complex-structured media. The numerical results showed that the inverted parameters of the finite offset common-reflection-surface and the separation function yield good results for separating PP- and PS-converted waves in noisy common-offset and common shot gathers. 相似文献
44.
Manuel Bollo Manent José Ramón Hernández Santana Ana Patricia Méndez Linares 《Central European Journal of Geosciences》2014,6(2):219-228
The present work evaluates the state of the environment in Mexico based on indicators of the present status of the country’s natural resource management, social and economical conditions and anthropogenic modifications. The Mexican environment is interpreted as a spatially open system having a historical character that is essentially determined by the continual interaction between nature, society and economy. The landscape approach is followed, considering as units of territorial analysis each one of the 145 biophysical environmental units included in the national physiographic regionalization. The assessment of 16 indicators for each biophysical environmental unit was made considering their regional environmental integrity problems, the degree of disarticulation of their structure and function, and the alteration of their territorial structure, all of which determine whether or not they accomplish their environmental functions and achieve environmental stability. The classification of the state of the environment included 5 categories in 8 combinations represented in the map of the state of the environment in Mexico for the year 2008. The map shows that nearly 47.10% of the country’s surface has an environmental status ranging between unstable and critical, the problematic areas being mostly concentrated in the southeast and center of the national territory. 相似文献
45.
Xiangyang Zheng Roberto Mayerle Qianguo Xing José Manuel Fernández Jaramillo 《Ocean Dynamics》2016,66(8):1037-1050
In this paper, a data assimilation scheme based on the adjoint free Four-Dimensional Variational(4DVar) method is applied to an existing storm surge model of the German North Sea. To avoid the need of an adjoint model, an ensemble-like method to explicitly represent the linear tangent equation is adopted. Results of twin experiments have shown that the method is able to recover the contaminated low dimension model parameters to their true values. The data assimilation scheme was applied to a severe storm surge event which occurred in the North Sea in December 5, 2013. By adjusting wind drag coefficient, the predictive ability of the model increased significantly. Preliminary experiments have shown that an increase in the predictive ability is attained by narrowing the data assimilation time window. 相似文献
46.
New microthermometric data combined with stable isotope geochemistry and paragenetic relationships support a previously suggested
cooling–mixing model for the iron oxide–copper–gold mineralization in the Mantoverde district. Fluid inclusions show characteristics
of a CO2-bearing aqueous NaCl ± CaCl2 salt system. The evolution of the Mantoverde hydrothermal system is characterized by (1) an early hypersaline, high to moderate
temperature fluid; (2) a moderate saline, moderate temperature fluid; and (3) a low saline, moderate to low temperature fluid.
Early magnetite formation took place at median temperatures of 435.0°C, whereas hematite formed at median temperatures of
334.4°C. The main sulfide mineralization texturally post-dates the iron oxides and occurred before late-stage calcite, which
developed at a median temperature of 244.8°C. Boiling occurs only locally and is of no relevance for the ore formation. The
microthermometric and stable isotope data are supportive for a fluid cooling and mixing model, and suggestive for a predominantly
magmatic–hydrothermal fluid component during the iron oxide and main sulfide mineralization. Thereafter, the incursion of
a nonmagmatic fluid of ultimately meteoric or seawater gains more importance. 相似文献
47.
Yves Lagabrielle Manuel Surez Jacques Malavieille Diego Morata Felipe Espinoza Ren C. Maury Bruno Scalabrino Luis Barbero Rita de la Cruz Eduardo Rossello Herv Bellon 《地学学报》2007,19(6):413-424
Recent field work and review of radiometric data obtained from Neogene lavas and plutonic rocks exposed in the Eastern Central Patagonian Cordillera (46–48ºS), which overlie subducted segments of the South Chile Ridge, suggest important Late Miocene to Pleistocene morphological changes in relation to base level variations and/or tectonic events. We present new field observations from a region south of Lago General Carrera‐Buenos Aires, between the main Cordillera and the Meseta del Lago Buenos Aires, demonstrating that normal faulting controlled valley incisions and occurred during lava emplacement at 5–4 Ma and after 3 Ma. We also show that the 12 Ma basaltic flows of the Meseta del Lago Buenos Aires (∼2000 m a.s.l.) have been subjected to deep incision, with younger lavas dated at 1.2 Ma partially filling the valleys. These incisions are thought to reflect progressive eastward tilting of the entire meseta. Our new observations, together with additional features from Central Patagonia, strongly suggest that tectonic events led to a regional widespread morphological change after 5 Ma. The coincidence in time and space between the subduction of segments of the South Chile Ridge at 6 and 3 Ma causing opening of a slab window, and strong base level variations in the studied area, suggests a cause‐and‐effect relationship. In Central Patagonia, compressional tectonics ended well before extensional events reported here. Causes of uplift and further extension are probably completely disconnected. The uplift is purely tectonic in origin and occurred prior to the subduction of the South Chile Ridge. Extension should be a consequence of this subduction. 相似文献
48.
The gravity map of the Aveiro Basin, North West Portugal was produced in 2000/2001 and some limited two dimensional (2D) interpretation was carried out. It is intended in this article to advance the interpretation and modelling of the original Aveiro basin gravity data. Thus, the data were processed and the horizontal gradient, the second vertical derivative and downward continued field computed. The corresponding maps have been processed and a new interpretation of the basin tectonic features has been proposed. This is compared with the previous geological and tectonic information obtained from former surveys and local boreholes. As the next step a more detailed modelling of the Aveiro Basin took place. Bearing the interpretation of the basin tectonic features in mind, several north–south and east–west gravity profiles were established and modelled. The proposed models were presented and discussed. As a result, a comprehensive mass distribution model for the basin was proposed. Finally, comparison was made between the new gravity model and the previously published tectonic features map. This modelling is particularly useful for groundwater protection, exploration and exploitation and also for the dimensioning of drilling operations. Bearing in mind the geomorphology of the basin the gravity method is a very economical tool for the investigation of basin structures. 相似文献
49.
50.
EVA: GPS-based extended velocity and acceleration determination 总被引:1,自引:0,他引:1
Dagoberto Salazar Manuel Hernandez-Pajares Jose Miguel Juan-Zornoza Jaume Sanz-Subirana Angela Aragon-Angel 《Journal of Geodesy》2011,85(6):329-340
In this work, a new GPS carrier phase-based velocity and acceleration determination method is presented that extends the effective
range of previous techniques. The method is named ‘EVA’, and may find applications in fields such as airborne gravimetry when
rough terrain or water bodies make difficult or impractical to set up nearby GPS reference receivers. The EVA method is similar
to methods such as Kennedy (Precise acceleration determination from carrier phase measurements. In: Proceedings of the 15th
international technical meeting of the satellite division of the Institute of Navigation. ION GPS 2002, Portland pp 962–972,
2002b) since it uses L1 carrier phase observables for velocity and acceleration determination. However, it introduces a wide network
of stations and it is independent of precise clock information because it estimates satellite clock drifts and drift rates
‘on-the-fly’, requiring only orbit data of sufficient quality. Moreover, with EVA the solution rate is only limited by data
rate, and not by the available precise satellite clocks data rate. The results obtained are more robust for long baselines
than the results obtained with the reference Kennedy method. An advantage of being independent of precise clock information
is that, beside IGS Final products, also the Rapid, Ultra-Rapid (observed) and Ultra-Rapid (predicted) products may be used.
Moreover, the EVA technique may also use the undifferenced ionosphere-free carrier phase combination (LC), overcoming baseline
limitations in cases where ionosphere gradients may be an issue and very low biases are required. During the development of
this work, some problems were found in the velocity estimation process of the Kennedy method. The sources of the problems
were identified, and an improved version of the Kennedy method was used for this research work. An experiment was performed
using a light aircraft flying over the Pyrenees, showing that both EVA and the improved Kennedy methods are able to cope with
the dynamics of mountainous flight. A RTK-derived solution was also generated, and when comparing the three methods to a known
zero-velocity reference the results yielded similar performance. The EVA and the improved-Kennedy methods outperformed the
RTK solutions, and the EVA method provided the best results in this experiment. Finally, both the improved version of the
Kennedy method and the EVA method were applied to a network in equatorial South America with baselines of more than 1,770 km,
and during local noon. Under this tough scenario, the EVA method showed a clear advantage for all components of velocity and
acceleration, yielding better and more robust results. 相似文献