Accidental spills of hydrocarbons, such as Light Non-Aqueous Phase Liquids (LNAPLs), are one of the most common sources of subsurface contamination. Migration of LNAPL in a porous medium is influenced by various factors such as the number of fluids present in the unsaturated/saturated zones and the proportion of pores occupied by each fluid. The results for relationship between matric suction and degree of saturation are presented in this paper for water–air, water–LNAPL and LNAPL–air systems in a sand. A simple and reliable setup using Buchner funnel was designed to obtain these relations. It was found that the relationship between matric suction head and degree of saturation is hysteretic for all the fluid systems (water–air, water–LNAPL and LNAPL–air). Furthermore, the amount of hysteresis depended upon the fluid system, with the maximum hysteresis occurring for water–air system. The results suggest that the amount of trapped air depends upon the reversal degree of saturation from drying to wetting. 相似文献
The Malpica–Tui complex (NW Iberian Massif) consists of a Lower Continental Unit of variably deformed and recrystallized granitoids, metasediments and sparse metabasites, overridden by an upper unit with rocks of oceanic affinities. Metamorphic minerals dated by the 40Ar/39Ar method record a coherent temporal history of progressive deformation during Variscan metamorphism and exhumation. The earliest stages of deformation (D1) under high-pressure conditions are recorded in phengitic white micas from eclogite-facies rocks at 365–370 Ma. Following this eclogite-facies peak-metamorphism, the continental slab became attached to the overriding plate at deep-crustal levels at ca. 340–350 Ma (D2). Exhumation was accompanied by pervasive deformation (D3) within the continental slab at ca. 330 Ma and major deformation (D4) in the underlying para-autochthon at 315–325 Ma. Final tectonothermal evolution included late folding, localized shearing and granitic intrusions at 280–310 Ma.
Dating of high-pressure rocks by the 40Ar/39Ar method yields ages that are synchronous with published Rb–Sr and Sm–Nd ages obtained for both the Malpica–Tui complex and its correlative, the Champtoceaux complex in the French Armorican Massif. The results indicate that phengitic white mica retains its radiogenic argon despite been subjected to relatively high temperatures (500–600 °C) for a period of 20–30 My corresponding to the time-span from the static, eclogite-facies M1 peak-metamorphism through D1-M2 eclogite-facies deformation to amphibolite-facies D2-M3. Our study provides additional evidence that under certain geological conditions (i.e., strain partitioning, fluid deficiency) argon isotope mobility is limited at high temperatures, and that 40Ar/39Ar geochronology can be a reliable method for dating high pressure metamorphism. 相似文献
Natural production of the radionuclide chlorine-36 (36Cl) has provided a valuable tracer for groundwater studies. The nuclear industry, especially the testing of thermonuclear
weapons, has also produced large amounts of 36Cl that can be detected in many samples of groundwater. In order to be most useful in hydrologic studies, the natural production
prior to 1952 should be distinguished from more recent artificial sources. The object of this study was to reconstruct the
probable preanthropogenic levels of 36Cl in groundwater in the United States. Although significant local variations exist, they are superimposed on a broad regional
pattern of 36Cl/Cl ratios in the United States. Owing to the influence of atmospherically transported ocean salt, natural ratios of 36Cl/total Cl are lowest near the coast and increase to a maximum in the central Rocky Mountains of the United States.
Electronic Publication 相似文献
An evaluation of the distribution of P concentrations in streamflow, P fractions andthe microbial biomass P pool was made of bed and bank sediments along a lowlandstream in New Zealand. Agricultural intensification increased downstream. However,most P fractions decreased downstream (total P decreased from c. 400 to 250 mg kg-1) in bed sediments, while P in streamflow remained relatively constant (generally < 0.005 mg l-1) and sediment microbial P increased from 2 to 8 mg kg-1. An investigation of P release from dried and rewetted sediments showed that solution P (CaCl2-P) increased, on average > 300%, and proportional to the size of the microbial biomass P pool before drying, except in sediments with much organic carbon (OC). When supplied with a P source (1 mg l-1) and then simultaneously with a C source (glucose, 100 mg l-1), all sediment behaved similarly and biotic sorption accounted for, on average, 27 and 34% of the total sediment uptake, respectively (maximum of 58%). The quantity of P taken up was related to the initial size of the microbial biomass P pool, and the availability of P as influenced by organic P complexes and OC. The sediment microbial biomass represents a transient, but small store of P could be useful to indicate bioavailable P inputs. 相似文献
Mafic high-pressure granulite, eclogite and pyroxenite xenoliths have been collected from a Mesozoic volcaniclastic diatreme in Xinyang, near south margin of the Sino-Korean Craton (SKC). The high-pressure granulite xenoliths are mainly composed of fine-grained granoblasts of Grt+Cpx+Pl+Hbl±Kfs±Q±Ilm with relict porphyritic mineral assemblage of Grt+Cpx±Pl±Rt. P–T estimation indicates that the granoblastic assemblage crystallized at 765–890 °C and 1.25–1.59 GPa, corresponding to crustal depths of ca. 41–52 km with a geotherm of 75–80 mW/m2. Calculated seismic velocities (Vp) of high-pressure granulites range from 7.04 to 7.56 km/s and densities (D) from 3.05 to 3.30 g/cm3. These high-pressure granulite xenoliths have different petrographic and geochemical features from the Archean mafic granulites. Elevated geotherm and petrographic evidence imply that the lithosphere of this craton was thermally disturbed in the Mesozoic prior to eruption of the host diatreme. These samples have sub-alkaline basaltic compositions, equivalent to olivine– and quartz–tholeiite. REE patterns are flat to variably LREE-enriched (LaN/YbN=0.98–9.47) without Eu anomaly (Eu/Eu*=0.95–1.11). They possess 48–127 ppm Ni and 2–20 ppm Nb with Nb/U and La/Nb ratios of 13–54 and 0.93–4.75, respectively, suggesting that these high-pressure granulites may be products of mantle-derived magma underplated and contaminated at the base of the lower crust. This study also implies that up to 10 km Mesozoic lowermost crust was delaminated prior to eruption of the Cenozoic basalts on the craton. 相似文献
The relative significance of early (Finnmarkian) and late (Scandian) Caledonian deformation in N. Norway is uncertain. Early studies suggested pervasive Finnmarkian deformation whilst later results indicated a restricted Finnmarkian domain. The present work suggests it was more widespread than accepted and that inter Finnmarkian–Scandian deformation occurred. 40Ar/39Ar dating of 2–6 and 6–11 μm pelitic fractions from the lower to mid-greenschist facies Tanahorn Nappe (five samples; base Middle Allochthon) and the epizone Løkvikfjellet and Barents Sea Groups (three samples; North Varanger Region) in the north Scandinavian Caledonides show slightly discordant spectra. Most spectra from the Tanahorn Nappe preserve possible evidence of an early Caledonian event in the high temperature steps, with recoil/excess Ar effects in the low temperature steps; no pre-Caledonian relict component has been recorded. The results indicate Finnmarkian deformation continued to 460 Ma, with Scandian reactivation at 425–415 Ma. From the North Varanger Region, a strongly crenulated sample yielded plateau ages (444–442 Ma); means of combined young steps from weakly to uncrenulated samples gave 470–450 Ma, suggesting penetrative strike-slip deformation occurred in the late Finnmarkian to inter-Finnmarkian–Scandian period. No Scandian ages were recorded in the North Varanger Region. Reassessment of published data from the Laksefjord Nappe and Gaissa Thrust Belt suggests they were affected by Finnmarkian deformation. 相似文献
Whole-rock Pb isotopic signatures and U/Pb geochronology refute a Rodinian correlation of northeastern Laurentia and proto-Andean Amazonia. According to this previously proposed model, the Labrador–Scotland–Greenland Promontory (LSGP) of northeastern Laurentia collided with the proto-Andean margin of Amazonia, at the Arica Embayment, during the Grenville/Sunsás Orogeny (ca. 1.0 Ga). Links between the two margins were based upon the correlation of the LSGP with Arequipa-Antofalla Basement (AAB), a Proterozoic block along the proto-Andean margin of Amazonia adjacent to the Arica Embayment. Specifically, similarities in 1.8–1.0 Ga basement rocks in both regions suggested that the AAB was originally a piece of the LSGP. Furthermore, similarities in unique, post-collisional, but pre-rift, glacial sedimentary sequences also supported a link between the AAB and LSGP.Tests of these apparent similarities fail to support correlation of the AAB and the LSGP and, thus, eliminate a direct link between northeastern Laurentia and southwestern Amazonia in Rodinia. However, Pb isotopic compositions and U/Pb geochronology provide the basis for two new correlations, namely, (1) the ca. 1.3–1.0 Ga basement in the central and southern Appalachians may be an allochthonous block that was transferred to Laurentia from Amazonia at ca. 1.0 Ga, and (2) an allochthonous AAB may be a piece of the Kalahari Craton that was transferred to Amazonia at ca. 1.0 Ga. Based on these new correlations and a previously proposed Grenvillian connection between southern Laurentia (Llano) and Kalahari, we propose that Amazonia may have collided with a contiguous southeastern Laurentia/Kalahari margin at ca. 1.0 Ga. 相似文献
We detail the results of recent studies describing and quantifying the large-scale chemical weathering of the main types of continental silicate rocks: granites and basalts. These studies aim at establishing chemical weathering laws for these two lithologies, describing the dependence of chemical weathering on environmental parameters, such as climate and mechanical erosion. As shown within this contribution, such mathematical laws are of primary importance for numerical models calculating the evolution of the partial pressure of atmospheric CO2 and the Earth climate at geological timescales. The major results can be summarized as follow: (1) weathering of continental basaltic lithologies accounts for about 30% of the total consumption of atmospheric CO2 through weathering of continental silicate rocks. This is related to their high weatherability (about eight times greater than the granite weatherability); (2) a simple weathering law has been established for basaltic lithologies, giving the consumption of atmospheric CO2 as a function of regional continental runoff, and mean annual regional temperature; (3) no such simple weathering law can be proposed for granitic lithologies, since the effect of temperature can only be identified for regions displaying high continental runoff; (4) a general law relating mechanical erosion and chemical weathering has been validated on small and large catchments. The consequences of these major advances on the climatic evolution of the Earth are discussed. Particularly, the impacts of the onset of the Deccan trapps and the Himalayan orogeny on the global carbon cycle are reinvestigated. To cite this article: B. Dupré et al., C. R. Geoscience 335 (2003).相似文献