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351.
352.
Gerhard?LammelEmail author Thomas?Engelhardt Adrian?Leip Christian?Neusü? Andreas?R?hrl Birgit?Wehner Alfred?Wiedensohler Paul?Wieser 《Journal of Atmospheric Chemistry》2005,51(1):95-117
The change of the chemical composition of the near-ground level atmospheric aerosol was studied during two summer episodes by a Lagrangian type of experimental approach. Bulk and single-particle chemical analyses of ions and elements in the particulate phase were deployed. N(-III) and N(V) components were also measured in the gas-phase. The measurements were completed by particle size distributions.Secondary inorganic aerosols (SIA) and fine particles of ≈0.2–0.4 μm size were still elevated 50 km downwind of the city. The direct comparison of transport over the city in contrast to transport over the surrounding areas showed that SIA was formed from emission from the city within less than 3 h. Relative increases, i.e., enrichment during transport were observed for primary and secondary aerosol components. The degree of mixing on the individual particle level increased significantly during transport in the area. In particular, newly emitted carbonaceous particles became internally mixed within hours with pre-existing sulphate particles. Mostly due to secondary aerosol formation the average particle size (mass median diameter) of major constituents of the aerosol was significantly decreased while being transported over 13 h. Given recent insights which link fine particles number and mass concentrations with health risks, the results suggest that rural populations in areas which frequently are located within an urban plume might run an elevated health risk relative to populations in areas not affected by urban plumes. 相似文献
353.
Shuan-Hong Zhang Yue Zhao Alfred Kröner Xiao-Ming Liu Lie-Wen Xie Fu-Kun Chen 《International Journal of Earth Sciences》2009,98(6):1441-1467
Recent zircon dating identified several late Carboniferous to early Permian hornblende gabbro–diorite–quartz diorite–granodiorite–tonalite–granite
plutons in lithological assemblages at the northern margin of the North China Block (NCB) that were previously regarded as
Archaean to Palaeoproterozoic. Our geochronological results indicate that emplacement of these plutons was a continuous process
during the late Carboniferous to early Permian, from 324 ± 6 to 274 ± 6 Ma, and lasted for at least 50 Ma. In this paper,
the early Permian components with compositions from gabbro to granite within the intrusive complex were studied. The early
Permian plutons exhibit calc-alkaline or high-K calc-alkaline, metaluminous geochemical features and highly variable SiO2 contents. They have no significant Eu anomaly in their REE patterns, and in primitive-mantle-normalized spidergrams they
display depletion in Th, U, Nb, Ta, P and Ti, and enrichment in Ba, K, Pb and Sr. The granitoid bodies within these plutons
display I-type and adakitic geochemical signatures. The early Permian rocks exhibit low whole-rock initial 87Sr/86Sr ratios from 0.70520 to 0.70615 and have negative whole-rock ε
Nd(t) values ranging from −17.4 to −9.3 and zircon ε
Hf(t) values of −23.2 to −10.5. The gabbros exhibit higher ε
Nd(t) values from −11.1 to −9.3 and ε
Hf(t) values from −16.5 to −10.5, and one granodiorite exhibits an even lower ε
Nd(t) value of −17.4 and zircon ε
Hf(t) values of −23.2 to −15.1. Geochemical, Sr–Nd and in situ zircon Hf isotopic compositions suggest that the hornblende gabbros
were derived from a metasomatized lithospheric mantle, and the diorite and quartz diorite were generated from a gabbroic magma
by fractional crystallization, coupled with differential assimilation of ancient lower crustal material. The granodiorite
was likely derived from partial melting of ancient lower crust with involvement of some mantle components. Involvement of
both lithospheric mantle and ancient lower crust in the generation of the early Permian plutons indicates strong crust–mantle
interaction in the northern NCB. Petrological associations as well as geochemical and Sr–Nd–Hf isotopic results show that
the early Permian plutons were emplaced along an Andean-type active continental margin during southward subduction of the
Palaeo-Asian oceanic plate beneath the NCB. Integration of our results with previously published data for late Carboniferous
and late Permian to middle Triassic intrusions suggests that the continental arc on the northern margin of the NCB existed
for at least 50 Ma during the late Palaeozoic, and final amalgamation of the Mongolian arc terranes with the northern NCB
likely occurred during a period from ~270 to ~250 Ma, i.e, in the late Permian to earliest Triassic. 相似文献
354.
Dr. Alfred Becher 《Contributions to Mineralogy and Petrology》1965,11(6):586-613
Analysis of samples taken from combined profiles of the ?Buntsandstein” (Lower Triassic in Germanic facies) has furnished proof of a regional change in clay mineral composition from its depositional margin to the centre of the sedimentary basin. this alteration occuring both vertically and horizontally, and hence in geologically comparable strata. Altogether five different characteristic mineral associations were found. arranged in a “sequence” and save two explicable in terms of environmental conditions. The horizontal and vertical range of these distinctive, characteristic slay mineral associations has been alloted to provinces. Factors alien to those arising from these provincial environments like influences of distributive areas. of climate and diagenesis, have but subordinate significance or none at all. Moreover, a comparison with the work ofSchnitzer (1957) has shown that the distribution of heavy minerals and that of clay mineral assemblages are independent of each other; the latter being indicative of differences in environmental conditions. whereas study of heavy mineral suites makes possible the reconstruction of source areas. 相似文献