The occurrence of flowing wells in basins has been found to be closely related to the discharge area with an upward hydraulic gradient. Unfortunately, previous studies on upward gradient induced wellbore flow with equaling total inflow (Qin) in the deep and total outflow (Qout) in the shallow could not explain the occurrence of flowing wells. By representing wells using the MNW2 Package imbedded in MODFLOW 2005, we obtain the exchange of groundwater between the aquifer and the well in the discharge area of 3D unit basins and identify three scenarios: Qin = Qout, Qin > Qout > 0 and Qin > Qout = 0. The relationship of Qin > Qout well explains why flowing wells only develop in a limited part of the discharge area. Sensitivity analysis shows that well location, water table undulation, and basin length–depth ratio do not change the profile of the ratio of cumulative flow rate in a flowing well to total inflow (Qv/Qin) versus the relative elevation in the inflow segment, zin*, but could significantly change the length of the inflow segment; well depth could change both the length of the inflow segment and the profile of Qv/Qin versus zin*. Based on the numerical results in homogeneous and isotropic basins with different basin length–depth ratios in the current study, the ratio of inflow in the lower half part of a flowing well to the total inflow is found to be at least 67% and could be close to 100%, indicating that water at the outlets of flowing wells with long open sections is mainly from the deep part of the well. 相似文献
A new jadeitite jade locality has been discovered in the serpentinite-matrix subduction mélange of the Sierra del Convento
(eastern Cuba) in a context associated with tectonic blocks of garnet-epidote amphibolite, tonalitic–trondhjemitic epidote
gneiss, and blueschist. The mineral assemblages of jadeitite jade and jadeite rocks are varied and include combinations of
jadeite, omphacite, albite, paragonite, analcime, clinozoisite-epidote, apatite, phlogopite, phengite, chlorite, glaucophane,
titanite, rutile, zircon, and quartz formed during various stages in their P–T evolution. Field relationships are obscure,
but some samples made almost exclusively of jadeite show evidence of crystallization from fluid in veins. In one of these
samples studied in detail jadeite shows complex textural and chemical characteristics (including oscillatory zoning) that
denote growth in a changing chemical medium. It is proposed that interaction of an Al–Na rich fluid with ultramafic rocks
produced Al–Na–Mg–Ca fluids of varying composition. Episodic infiltration of these fluids, as a result of episodic opening
of the veins, developed oscillatory zoning by direct precipitation from fluid and after reaction of fluid with pre-existing
jadeite. The latest infiltrating fluids were richer in Mg–Ca, favouring the formation of omphacite and Mg–Ca rich jadeite
in open voids and the replacement of earlier jadeite by fine-grained omphacite + jadeite at 550–560°C. This new occurrence
of jadeite in Cuba opens important perspectives for archeological studies of pre-Columbian jade artifacts in the Caribbean
region. 相似文献
Late Pliocene–Pleistocene tectonic evolution of the Apennines is driven by progressive eastward migration of extensional downfaulting superposed onto the Late Miocene–Early Pliocene compressional thrust belt. This process has led to distinct structural domains that show decreasing transcrustal permeability from conditions of pervasive mixing between deep and surface fluids in the hinterland (west) to conditions of restricted fluid circulation and overpressuring in the foreland (east). At present, the highest rates of normal faulting and the strongest seismicity occur in the area bounded by stretched, highly permeable crust to the west and thick, poorly permeable crust to the east. In this area, the seismogenic sources of the largest earthquakes (5<Ms<7) are potentially related to mature normal faults that deeply penetrate thick brittle upper crust, and act as transient high-permeability channels during seismic activity. In this framework, it is plausible that domains of overpressuring govern progressive inception of normal faulting and fluid redistribution in the crust, leading to eastward migration of the belt of maximum seismicity with time. 相似文献
In order to attempt to further constrain the age of the early Alpine tectonic evolution of the Mulhacén Complex and to explore the influence of inherited isotopes, micas from a small number of well-characterised rocks from the Sierra de los Filábres, with a penetrative tectonic fabric related to the exhumation of eclogite-facies metamorphic rocks, were selected for 40Ar/39Ar and Rb–Sr dating.
A single phengite grain from an amphibolite yielded an 40Ar/39Ar laser step heating plateau age of 86.9±1.2 Ma (2σ; 70% 39Ar released) and an inverse isochron age of 86.2±2.4 Ma with an 36Ar/40Ar intercept within error of the atmospheric value. Induction furnace step heating of a biotite separate from a gabbro relic in an eclogite yielded a weighted mean age of 173.2±6.3 Ma (2σ; 95% 39Ar released). These ages are diagnostic of excess argon (40ArXS) incorporation, as they are older than independent age estimates for the timing of eclogite-facies metamorphism and intrusion of the gabbros. 40ArXS incorporation probably resulted from restricted fluid mobility in the magmatic rocks during their metamorphic recrystallisation.
Rb–Sr whole-rock–phengite ages of graphite-bearing mica schists from Paleozoic rocks (Secano unit) show a dramatic variation (66.1±3.2, 40.6±2.6 and 14.1±2.2 Ma). An albite chlorite mica schist from the Mesozoic series of the Nevado–Lubrín unit has a whole-rock–mica–albite age of 17.2±1.9 Ma, which is within error of an 40Ar/39Ar plateau age published previously and of the youngest Rb–Sr age of the Paleozoic series obtained in this study. The significant spread in Rb–Sr ages implies that progressive partial resetting of an older isotopic system has occurred. The microstructure of the samples with pre-Miocene Rb–Sr ages reveals incomplete recrystallisation of white mica and inhibited grain growth due to the presence of graphite particles. This interpretation agrees with previously published, disturbed and slightly dome-shaped 40Ar/39Ar age spectra that may point similarly to the presence of an older isotope component. The progressively reset Rb–Sr system is a relic of Variscan metamorphism of the Paleozoic series of the Mulhacén Complex. In contrast, the origin of the ca. 17.2 Ma old sample from the Mesozoic series precludes any isotopic inheritance, in agreement with its pervasive tectono-metamorphic recrystallisation during the Miocene.
Exhumation of the eclogite-facies Mulhacén Complex occurred in two stages with contrasting rates of about 22.5 mm/year during the early phase and 9–10 mm/year during the late phase; the latter with a cooling rate in the order of 330 °C/Ma. 相似文献