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41.
Tourmaline-rich rocks associated with clastic metasedimentary rocks of Carboniferous age occur in the Cinco Villas massif,
western Pyrenees. Three types of tourmaline-rich rocks were distinguished: (1) Fine-grained stratiform tourmaline-rich rocks,
which are associated with carbonaceous metapelites (TR1); (2) stratabound tourmaline-rich rocks, associated with metapelites
in the contact aureole of the Aya granitoid pluton (TR2); (3) stratabound to massive tourmaline-rich rocks, associated with
psammopelites in contact with granites and pegmatites (TR3). Tourmalines belong to the schorl–dravite solid solution series
and have a wide compositional range, from nearly end-member dravite for TR1 tourmalines to schorl for TR3 tourmalines; TR2
tourmalines have intermediate compositions. The Fe/(Fe+Mg) typically varies between 0.02 and ≈0.55, increasing from TR1 to
TR3. The TR1 tourmalines commonly display a discontinuous chemical zoning with Fe-rich green cores (8–8.5% FeO) and Mg-rich
colorless rims (10–11% MgO). In contrast, crystals that exhibit fine growth lamellae appear to lack significant chemical zoning.
Oxygen and hydrogen isotope compositions also reveal major differences between TR1 and TR3 tourmalines, the former displaying
heavier δ18O values (17.7–19‰) and δD values (−35 to −42‰) than TR3 tourmalines 11 to 13‰ and −47 to −76‰, respectively. The TR2 tourmalines
show intermediate values of 11.3 to 14.6‰ for δ18O and −40 to −55‰ for δD. Linear and continuous chemical variations obtained for major and trace elements of the whole rocks
reflect mixing between clay-rich and quartz-rich end-members, indicative that some tourmaline-rich rocks contain a significant
detrital component. Chondrite normalized REE (rare earth element) patterns of tourmaline-rich rocks are similar to those of
surrounding unaltered clastic metasediments, except for some TR1 rocks which are characterized by low contents of ΣREE. Mass-balance
calculations show that tourmaline-forming processes plus metamorphism led to mass and volume changes at mesoscopic scales
(≈10% for the TR1 tourmalinites). Silicon, Fe, Mn, and REE elements were partially lost from sedimentary rocks, whereas Mg
and particularly B were added to pelitic sediments. Available data, nevertheless, do not allow an assessment of the boron
source. Formation of the TR1 tourmaline-rich rocks probably was the net result of several processes, including direct precipitation
from B-rich hydrothermal fluids or colloids, early diagenetic reactions of carbonaceous pelitic sediments with these fluids,
and subsequent recrystallization during regional metamorphism. The TR2 tourmaline-rich rocks mainly developed by metamorphic
recrystallization of TR1. Tourmaline-rich rocks and veins adjacent to pegmatites and granitic rocks (TR3) are the result of
boron metasomatism; the primary boron having been recycled from stratiform tourmalinites during regional metamorphism and
magmatism.
Received: 18 November 1996 / Accepted: 25 April 1997 相似文献
42.
Alfonso Aguilar-Perera Michelle Schrer Manuel Valds-Pizzini 《Ocean & Coastal Management》2006,49(12):961-975
In Puerto Rico, the environmental legislation for establishing marine protected areas (MPAs) is complex due to its current political position with the United States (US) as not only local but also federal US laws affect designations. Historically, during the Spanish rule, mangrove forests were protected for extractive reasons (i.e., charcoal) and the first protected area was established by 1918 as an Insular Forest. Currently, of the 37 MPAs recognized and investigated in this work, the vast majority (73%) are Natural Reserves, followed by Commonwealth Forests (13.5%). Most MPAs in Puerto Rico were implemented using a top-down approach (i.e., government) which follows US federal guidelines for protecting endangered species, critical habitats, and natural and cultural resources. The development of management plans for MPAs on the island is increasingly adopting a public participatory process. However, this latter process is new for the government of Puerto Rico that has not incorporated a policy based on an Integrated Coastal Management. 相似文献
43.
Loreto Antón Alfonso Muñoz-Martin Gerardo De Vicente 《Central European Journal of Geosciences》2010,2(2):152-164
The study of intraplate tectonics is crucial for understanding the deformation within plates, far from active plate boundaries and associated stress transmission to the plate interiors. This paper examines the tectonic evolution of the Variscan basement at the western margin of the Cenozoic Duero basin. Located east of the Vilariça Fault System in NW Iberia, this intraplate zone is a relatively flat but elevated area with an intense NNE-SSW trending fault system and associated moderate seismicity. Although the area has played an important role in the Duero basin configuration, its Alpine to present-day tectonic evolution has not been well constrained. In order to characterize the successive paleostress fields, 1428 pairs of fault-striae were measured at 56 sites and two focal mechanisms were used. Stress inversion methods have been applied to analyze paleostress regimes. Results show the existence of three dominant maximum horizontal stress (Shmax) trends: N-S, NE-SW and E-W. Relative and absolute dating of the activated faults for each Shmax shows that the clearly predominant N-S paleostress field in the zone has been active since the Oligocene up to the present day; while a NE-SW stress field is found to have been active during the Cretaceous and an older E-W paleostress field was active in the earlier Alpine cycle (Late Triassic). 相似文献
44.
The application of a powerful evolutionary optimization technique for the estimation of intrinsic formation constants describing
geologically relevant adsorption reactions at mineral surfaces is introduced. We illustrate the optimization power of a simple
Genetic Algorithm (GA) for forward (aqueous chemical speciation calculations) and inverse (calibration of Surface Complexation
Models, SCMs) modeling problems of varying degrees of complexity, including problems where conventional deterministic derivative-based
root-finding techniques such as Newton–Raphson, implemented in popular programs such as FITEQL, fail to converge or yield
poor data fits upon convergence.
Subject to sound a priori physical–chemical constraints, adequate solution encoding schemes, and simple GA operators, the
GA conducts an exhaustive probabilistic search in a broad solution space and finds a suitable solution regardless of the input
values and without requiring sophisticated GA implementations (e.g., advanced GA operators, parallel genetic programming).
The drawback of the GA approach is the large number of iterations that must be performed to obtain a satisfactory solution.
Nevertheless, for computationally demanding problems, the efficiency of the optimization can be greatly improved by combining
heuristic GA optimization with the Newton–Raphson approach to exploit the power of deterministic techniques after the evolutionary-driven
set of potential solutions has reached a suitable level of numerical viability. Despite the computational requirements of
the GA, its robustness, flexibility, and simplicity make it a very powerful, alternative tool for the calibration of SCMs,
a critical step in the generation of a reliable thermodynamic database describing adsorption equilibria. The latter is fundamental
to the forward modeling of the adsorption behavior of minerals and geologically based adsorbents in hydro-geological settings
(e.g., aquifers, pore waters, water basins) and/or in engineered reactors (e.g., mining, hazardous waste disposal industries). 相似文献
45.
Hydrological and geomorphological criteria to evaluate the dispersion risk of waste sludge generated by the Aznalcollar mine spill (SW Spain) 总被引:2,自引:0,他引:2
G. Benito Alfonso Benito-Calvo Francesc Gallart Juan Pedro Martín-Vide David Regües Ernest Bladé 《Environmental Geology》2001,40(4-5):417-428
Following the Aznalcóllar pyrite mine disaster (Seville, Spain) which caused the spilling of some 4.5?hm3 of acid water, the floodplains of the rivers Agrio and Guadiamar were rapidly cleaned of waste sludge. However, despite the efficiency of cleaning activities, there is still evidence of a fine superficial layer of sludge and some soil contamination, with the consequent risk of remobilisation of the pollutants by water erosion. There is much concern that these contaminated sediments may affect the precious ecosystems of the Doñana National Park and the Guadalquivir marshlands. This report describes the evaluation of the risk of mobilisation of the waste sludge through (1) detailed geomorphological analysis, indicating potential areas of erosion-sedimentation on the floodplains of the rivers Agrio and Guadiamar, and predicted dynamics of the waste sludge, and (2) evaluation of the potential dispersion of the waste sludge provoked by future flood events, including hydraulic calculations to model channel flow and the analysis of the texture of the sludge to obtain critical transport and sedimentation values. Findings suggest that the waste sludge is likely to be transported and deposited within the Doñana National Park during future flood events. 相似文献
46.
Heidi Kreibich Veit Blauhut Jeroen C.J.H. Aerts Laurens M. Bouwer Henny A.J. Van Lanen Alfonso Mejia 《水文科学杂志》2020,65(Z2):1-18
ABSTRACTFor the development of sustainable, efficient risk management strategies for the hydrological extremes of droughts and floods, it is essential to understand the temporal changes of impacts, and their respective causes and interactions. In particular, little is known about changes in vulnerability and their influence on drought and flood impacts. We present a fictitious dialogue between two experts, one in droughts and the other in floods, showing that the main obstacles to scientific advancement in this area are both a lack of data and a lack of commonly accepted approaches. The drought and flood experts “discuss” available data and methods and we suggest a complementary approach. This approach consists of collecting a large number of single or multiple paired-event case studies from catchments around the world, undertaking detailed analyses of changes in impacts and drivers, and carrying out a comparative analysis. The advantages of this approach are that it allows detailed context- and location-specific assessments based on the paired-event analyses, and reveals general, transferable conclusions based on the comparative analysis of various case studies. Additionally, it is quite flexible in terms of data and can accommodate differences between floods and droughts. 相似文献
47.
C.A. Alfonso P.E. Sacks D.T. Secor J. Rine V. Perez 《Journal of South American Earth Sciences》1994,7(3-4)
Surface geology and heophysical data, supplemented by regional structural interpretations, indicate that the Valle del Cauca basin and adjacent areas in west-central Colombia form a west-vergent, basement-involved fold and thrust belt. This belt is part of a Cenozoic orogen developed along the west side of the Romeral fault system. Structural analysis and geometrical constraints show that the Mesozoic ophiolitic basement and its Cenozoic sedimentary cover are involved in a “thick-skinned” west-vergent foreland style deformation. The rocks are transported and shortened by deeply rooted thrust faults and stacked in imbricate fashion. The faults have a NE---SW regional trend, are listric in shape, developed as splay faults which are interpreted as joining a common detachment at over 10 km depth. The faults carry Paleogene sedimentary strata and Cretaceous basement rocks westward over Miocene strata of the Valle del Cauca Basin. Fold axes trend parallel or sub parallel to the thrust faults. The folds are westwardly asymmetrical with parallel to kink geometry, and are interpreted to be fault-propagation folds stacked in an imbricate thrust system. Stratigraphic evidence suggests that the Valle del Cauca basin was deformed between Oligocene and upper Miocene time. The kinematic history outlined above is consistent with an oblique convergence between the Panama and South American plates during the Cenozoic.A negative residual Bouguer anomaly of 20–70 mgls in the central part of the Valle del Cauca basin indicates that a substantial volume of low density sedimentary rocks is concealed beneath the thrust sheets exposed at the land surface. The hydrocarbon potential of the Valle del Cauca should be reevaluated in light of the structural interpretations presented in this paper. 相似文献
48.
49.
The concentrations of Mg2+ and Sr2+ incorporated within calcite overgrowths precipitated from seawater and related solutions, determined at 25°C, were independent of the precipitation rate over approximately an order of magnitude. The saturation states used to produce this range of precipitation rates varied from 3 to 17 depending on the composition of the solution.The amount of Mg2+ incorporated in the overgrowths was not directly proportional to in solution over the entire range (1–20) of ratios studied. Below a ratio of 7.5, the overgrowth was enriched in MgCO3 relative to what is predicted by the constant distribution coefficient measured above a ratio of 7.5. This increased MgCO3 correlates with the relative enrichment of adsorbed Mg2+. Above a ratio of 7.5 the concentration of MgCO3 in the calcite overgrowths followed a classical thermodynamic behavior characterized by a constant distribution coefficient of 0.0123 (±0.008 std dev).The concentration of SrCO3 incorporated in the overgrowths was linearly related to the MgCO3 content of the overgrowths, and is attributed to increased solubility of SrCO3 in calcite due to the incorporation of the smaller Mg2+ ions.The kinetic data indicate that the growth mechanism involves the adsorption of the cations on the surface of the calcite prior to dehydration and final incorporation. It is suggested that dehydration of cations at the surface is the rate controlling step. 相似文献
50.
Alfonso Hernández-Laguna Elizabeth Escamilla-Roa Vicente Timón Martin T. Dove C. Ignacio Sainz-Díaz 《Physics and Chemistry of Minerals》2006,33(10):655-666
Quantum mechanical calculations based on the density functional theory (DFT) are used to study the crystal structures of dioctahedral 2:1 phyllosilicates. The isomorphous cation substitution is investigated by exploring different substitutions of octahedral Al3+ by Mg2+ or Fe3+, tetrahedral substitution of Si4+ by Al3+, and different interlayer cations (IC) (Na+, K+, Ca2+, and Mg2+). Samples with different kinds of layer charges are studied: only tetrahedrally charged, only octahedrally charged, or mixed octahedral/tetrahedral charged. The effect of the relative arrangements of these substitutions on the lattice parameters and total energy is studied. The experimental observation of segregation tendency of Fe3+ and dispersion tendency of Mg2+ in the octahedral sheet is reproduced and explained with reference to the relative energies of the octahedral cation arrangements. These energies are higher than those due to the IC/tetrahedral and IC/octahedral relative arrangements. The tetrahedral and octahedral substitutions that generate charged layers also tend to be dispersed. The octahedral cation exchange potentials change with the IC-charge/ionic radius value. 相似文献