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991.
Zuzana Kratinová Matej Machek Vladimír Kusbach 《Journal of the Geological Society of India》2010,75(1):267-277
Investigations on a set of experimental models of highly viscous intrusions were carried out in order to study the internal
strain pattern during vertical ascent and emplacement of granite intrusions. The strain pattern was determined by means of
anisotropy of magnetic susceptibility (AMS) resulting from the orientation of magnetite particles in a liquid plaster medium.
The modelled intrusions show distinct fabrics reflecting the flow of a rheologically complex, non-Newtonian material. During
the vertical growth of the intrusion, constrictional vertical fabrics are transposed into flattening fabrics, and along with
the development of low-intensity fabric domains are passively transported upwards. Vertical growth takes place along subvertical
thrust shear zones that satisfactorily explain the discordant magmatic fabrics in granites along intrusion sides. The resulting
complex fabric patterns suggest that the vertical movement of material in ascending intrusions is accommodated by various
flow mechanisms operating simultaneously. 相似文献
992.
Harold Clénet Georges Ceuleneer Patrick Pinet Bénédicte Abily Yves Daydou Esther Harris Isma Amri Céline Dantas 《Lithos》2010,114(3-4):265-281
Using the HyMap instrument, we have acquired visible and near infrared hyperspectral data over the Maqsad area of the Oman ophiolite (~ 15 × 60 km). This survey allowed us to identify and map the distribution of clinopyroxene-rich cumulates (inter-layered clinopyroxenites and wehrlites) whose occurrence was previously undocumented in this area. The cumulates reach several hundred meters in thickness and crop out at distances exceeding 15 km on both sides of the Maqsad former spreading centre. They occur either in mantle harzburgites, as km-sized layered intrusions surrounded by fields of pegmatitic dykes consisting of orthopyroxene-rich pyroxenite and gabbronorites, or at the base of the crustal section where they are conformably overlain by cumulate gabbros. These ultramafic cumulates crystallized from silica- and Mg-rich melts derived from a refractory mantle source (e.g. high Cr#, low [Al2O3], low [TiO2]). These melts are close to high-Ca boninites, although, strictly speaking, not perfect equivalents of present-day, supra-subduction zone, boninites. Chemical stratigraphy reveals cycles of replenishment, mixing and fractional crystallization from primitive (high Mg#) melts, typical of open magma chambers and migration of inter-cumulus melts. The TiO2 content of clinopyroxene is always low (≤ 0.2 wt.%) but quite variable compared to the associated pegmatites that are all derived from a source ultra-depleted in high field strength elements (HFSE). This variability is not caused by fractional crystallization alone, and is best explained by hybridization between the ultra-depleted melts (parent melts of the pegmatites) and the less depleted mid-ocean ridge basalts (MORB) parent of the dunitic–troctolitic–gabbroic cumulates making up the crustal section above the Maqsad diapir.We propose that, following a period of magma-starved spreading, the Maqsad mantle diapir, impregnated with tholeiitic melts of MORB affinity, reached shallow depths beneath the ocean ridge. This diapir induced melting of the formerly accreted and hydrothermally altered lithosphere. At this stage, these boninitic-like lithospheric melts crystallized as pegmatitic dykes. As the diapir continued to rise, the amount of MORB reaching shallow depths increased, together with the surrounding temperature, leading to the formation of magma chambers where the crystallization of layered cumulates became possible. These cumulates remained rich in pyroxene and devoid of plagioclase as long as the contribution of MORB-derived melts was moderate relative to the lithospheric-derived melts. As the contribution of MORB to the refilling of the magma chamber increased, gabbroic cumulates started to crystallize. 相似文献
993.
Thomas Heymes Patrick Monié Nicolas Arnaud Arnaud Pêcher Jean-Pierre Bouillin Roberto Compagnoni 《Lithos》2010,114(3-4):451-472
This study provides new 40Ar/39Ar geochronological constraints on the age of the Alpine tectonics in the Aspromonte Massif (southern part of the Calabrian–Peloritan belt). This massif exposes the upper units of the Calabride Complex which originated from the European continental margin. The Calabride Complex was incorporated in the Alpine orogenic wedge and then integrated into the Apennines and Maghrebides fold-and-thrust belts. Throughout the Calabride Complex there is evidence for a two stage tectonic history, which remains however rather poorly dated: Alpine nappe stacking is followed by extensional reworking along the former thrust contacts or along new detachment surfaces. Our new ages suggest that exhumation of the uppermost units, which accompanied nappe stacking, probably started at 45 Ma and that the deepest units were almost completely exhumed at 33 Ma. This kinematics probably corresponds to syn-orogenic extension while the end of exhumation is clearly related to the extensional tectonics dated at 28.6 Ma along detachment structures.Our geochronological data reveal a very short lag time between accretional and extensional processes in this part of the Mediterranean Alpine orogenic belt. The direction of extension, when the units are restored to their initial position (i.e. before the opening of the Western Mediterranean basins and the bending of the arc) is NNE–SSW. Such a direction does not fit with the eastward slab-retreat model generally put forward to explain extension in the Western Mediterranean. In contrast, we provide evidence for roughly N–S middle Oligocene extension in the accretionary prism, not previously described in this part of the Mediterranean domain. 相似文献
994.
Katharina Marquardt Elena Petrishcheva Rainer Abart Emmanuel Gardés Richard Wirth Ralf Dohmen Hans-Werner Becker Wilhelm Heinrich 《Physics and Chemistry of Minerals》2010,37(10):751-760
In this study, we address volume diffusion of ytterbium in yttrium aluminum garnet (YAG) using thin-film single crystal diffusion
couples. We employ analytical transmission electron microscopy (ATEM) as a tool for combined microstructural and microchemical
analysis and compare the results to Rutherford backscattering (RBS) analysis. Given the high spatial resolution of the method,
we focus on microstructural changes of the thin-film diffusant source during the diffusion anneal. We evaluate the potential
influence of the associated changes in its transport properties on the evolution of concentration profiles in the single crystal
substrate. This approach allows us to test the reliability of determination of volume diffusion coefficients from thin-film
diffusion experiments. We found that for the chosen experimental setting, the influence of thin-film re-crystallization is
small when compared with the experimental uncertainty and good estimates for the volume diffusion coefficients of Yb in YAG
can be obtained using standard assumptions. Both Yb-concentration profiles analyzed with ATEM and with RBS give similar results.
At 1,450°C and 1 bar, we infer log D
Yb (m2/s) values of −19.37 ± 0.07 (TEM) and −19.84 ± 0.02 (RBS). Although the change in thin-film transport properties associated
with successive crystallization during the diffusion anneal does not play a major role for our experimental setup, this effect
cannot generally be ignored. 相似文献
995.
F. A. Lopes G. Michard M. Poulin A. Roué F. Prévot D. Jézéquel E. Viollier 《Aquatic Geochemistry》2010,16(4):587-610
A reactive transport model was developed to describe seasonal variations of biogeochemical and physical processes in Lake
Aydat. The model includes physical processes such as vertical mixing, sedimentation and advection related to inflows into
the lake and biogeochemical conversion processes in the water column and in the sediment surface layer. The reactions described
in the model include primary redox reactions such as primary production, aerobic and anaerobic respiration, methanogenesis
and secondary reactions established between oxidants and reducers produced by the primary reactions. After adjusting various
kinetic constants, the model reasonably reproduced the main features of seasonal variations of dissolved oxygen and nitrate
depth profiles and pH. The reactive transport model was also used to quantify the relative importance of different biogeochemical
pathways. For instance, ferrous denitrification seems to play an important role when stratification is increasing. 相似文献
996.
997.
M. Villalobos D. G. García-Payne J. L. López-Zepeda A. E. Ceniceros-Gómez M. E. Gutiérrez-Ruiz 《Aquatic Geochemistry》2010,16(2):225-250
Arsenic from natural and anthropogenic sources is a worldwide contaminant of aqueous environments, such as groundwater and
soils. The present investigation was performed on Mexican soils contaminated with residues from metallurgical processes that
have shown a natural As attenuation. Experimental aqueous arsenic extractions in these were successfully simulated for almost
half of the soil samples using a database updated for all known metal arsenate formation constants, revealing the predominance
of solubility-controlled As mobility via Pb, mixed Pb–Cu, and Ca arsenate solid formation. The relatively low total Fe/As
ratios (2–13 w/w) present in the soils studied, together with the high and equivalent contents of As, Pb, and Cu in these,
favor the precipitation process over As(V) adsorption to Fe oxides, despite a 2% average Fe content in the soils studied.
Under these conditions bicarbonate was found to be a highly unsuitable extractant due to its indirect As release from the
solid arsenates, via heavy metal carbonate precipitation processes. 相似文献
998.
Chemical compositions of tetrahedrite—Ag-rich tetrahedrite—freibergite solid solutions (Ag-rich tetrahedritess) and homogenization temperatures of fluid inclusions in quartz and carbonates of seventeen samples from nine veins in the El Zancudo deposit, Antioquia, Colombia, were investigated to reveal the origin of silver in Ag-rich tetrahedritess, to derive their crystallization temperatures and to examine the relationship between chemical compositions of Ag-rich tetrahedritess and their crystallization temperatures. The ores consist of arsenopyrite, pyrite, sphalerite, Ag-rich tetrahedritess, galena, boulangerite, andorite, owyheeite, diaphorite, jamesonite, miargyrite, bournonite, chalcopyrite, and electrum. Ag-rich tetrahedritess forms about 10 volume % of the total ores and is one of the most common and widely distributed sulfosalts in this deposit. Ag-rich tetrahedritess is rich in Ag (1.13 to 31.02 wt%) and Sb (22.93 to 29.82 wt%), and poor in As (0.06 to 2.43 wt%), consistent with the reported incompatibilities of Ag and As in Ag-rich tetrahedritess. The Zn/(Zn + Fe)-, Ag/(Ag + Cu)- and Sb/(Sb + As + Bi)-atomic ratios exhibit some variations among the veins. Ag-rich tetrahedritess with higher Ag/(Ag + Cu) ratios coexist with diaphorite, whereas those with lower ratios are not associated with this sulfosalt. Ag-rich tetrahedritess in the assemblages of Ag-rich tetrahedritess+ sphalerite and of Ag-rich tetrahedritess+ bournonite + galena shows no Zn ↔ Fe and Cu ↔ Ag variations between core and rim, respectively, negating the possibility of solid state reaction during cooling. Ag-rich tetrahedritess is thus regarded as primary phase. Homogenization temperatures of primary fluid inclusions in quartz and carbonates co-existing with Ag-rich tetrahedritess define the mineralization temperatures of 134 to 263°C. Independent crystallization temperatures of Ag-rich tetrahedrite estimated based on Zn/(Zn + Fe) and Ag/(Ag + Cu) ratios of the Ag-rich tetrahedritess associated with silver minerals such as miargyrite, andorite and diaphorite using Sack's thermochemical database lie in a range between 170 and ∼250°C. Both results are thus in good agreement. 相似文献
999.
Linking geomorphology and hydrodynamics: a case study from Península Valdés, Patagonia, Argentina 总被引:1,自引:0,他引:1
A case study is presented to assess the relevance of geomorphology in hydrogeological phenomena in an arid coastal area in the Argentinean extra-Andean Patagonia (Península Valdés) with an average rainfall of 232 mm/year and a soil moisture deficit of about 472 mm/year. Various geomorphic units were identified by interpreting Landsat 7 satellite images processed with ER Mapper software and then surveyed in the field, as well as by geological characterization. The hydrodynamic analysis was based on a survey of 89 wells, the construction of equipotential maps, and the interpretation of pumping-test results by a non-equilibrium method. The hydrochemical characterization was based on chemical tests analyzed with the Easy_Quim 6.0 application. The combination of geomorphological, geological, hydrodynamic and hydrochemical elements allowed the definition of hydromorphological units that are typical of recharge, circulation and discharge areas, the latter both for coastal and inland areas in wetlands (salt pans) with elevations to ?40 m relative to sea level. These units and the criteria used for their definition allow immediate recognition of hydrogeological phenomena in arid regions such as the extra-Andean Patagonia, with low information density but with near-optimal satellite imaging of landforms due to the lack of vegetation cover. 相似文献
1000.
Ali Salim Joodi Stanislas Sizaret Stéphane Binet Ary Bruand Patrick Alberic Michel Lepiller 《Hydrogeology Journal》2010,18(2):295-309
Darcy’s law is the equation of reference widely used to model aquifer flows. However, its use to model karstic aquifers functioning with large pores is problematic. The physics occurring within the karstic conduits requires the use of a more representative macroscopic equation. A hydrodynamic model is presented which is adapted to the karstic aquifer of the Val d’Orléans (France) using two flow equations: (1) Darcy’s law, used to describe water flow within the massive limestone, and (2) the Brinkman equation, used to model water flow within the conduits. The flow equations coupled with the transport equation allow the prediction of the karst transfer properties. The model was tested by using six dye tracer tests and compared to a model that uses Darcy’s law to describe the flow in karstic conduits. The simulations show that the conduit permeability ranges from 5?×?10?6 to 5.5?×?10?5?m2 and the limestone permeability ranges from 8?×?10?11 to 6?×?10?10?m2. The dispersivity coefficient ranges from 23 to 53 m in the conduits and from 1 to 5 m in the limestone. The results of the simulations carried out using Darcy’s law in the conduits show that the dispersion towards the fractures is underestimated. 相似文献