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281.
282.
Maria Rosaria Renna Riccardo Tribuzio Massimo Tiepolo 《Contributions to Mineralogy and Petrology》2007,154(5):493-517
The post-Variscan complex of Porto consists of metaluminous to slightly peraluminous A-type biotite granites mingled with
gabbro-dioritic rocks, and late dykes with basaltic to trachyandesitic composition. U-Pb zircon dating by LA-ICP-MS on two
mafic intrusive samples constrains the time of the gabbro–granite crystallisation at 281 ± 3 Ma and 283 ± 2 Ma. Hornblende 40Ar-39Ar ages from a late trachyandesite dyke date the dyking event at 280 ± 2 Ma, which is within error the U-Pb zircon ages of
the intrusives. Biotite granites show variable major and trace element compositions and similar initial εNd (−0.3 to +0.9). Whole rock chemistry variations and trace element compositions of plagioclase and allanite indicate that
the granites are genetically linked, essentially through fractional crystallisation of feldspars and minor allanite. On the
basis of whole-rock chemistry e.g. initial εNd +4.9 to +1.7 and trace element clinopyroxene compositions, we have ascertained that the mafic intrusives and basic dykes
formed from isotopically depleted mantle source-derived melts with similar trace element signature. These basic melts experienced
slightly different evolutionary histories, controlled by fractional crystallisation and crustal contamination, mainly by the
acid magma that gave rise to the associated biotite granites, but also by the enclosing older Variscan granitoids. U-Pb zircon
data suggest that the Porto complex was affected by hydrothermal fluid circulation at 259 ± 9 Ma. 相似文献
283.
After the major 1991–1993 eruption, Mt. Etna resumed flank activity in July 2001 through a complex system of eruptive fissures
cutting the NE and the S flanks of the volcano and feeding effusive activity, fire fountains, Strombolian and minor phreatomagmatic
explosions. Throughout the eruption, magmas with different petrography and composition were erupted. The vents higher than
2,600 m a.s.l. (hereafter Upper vents, UV) erupted porphyritic, plagioclase-rich trachybasalt, typical of present-day summit
and flank activity. Differently, the vents located at 2,550 and 2,100 m a.s.l. (hereafter Lower vents, LV) produced slightly
more primitive trachybasalt dominated by large clinopyroxene, olivine and uncommon minerals for Etna such as amphibole, apatite
and orthopyroxene and containing siliceous and cognate xenoliths. Petrologic investigations carried out on samples collected
throughout the eruption provided insights into one of the most intriguing aspects of the 2001 activity, namely the coeval
occurrence of distinct magmas. We interpret this evidence as the result of a complex plumbing system. It consists in two separate
magma storage systems: a shallow one feeding the activity of the UV and a deeper and more complex storage related to the activity
of LV. In this deep storage zone, which is thermally and compositionally zoned, the favourable conditions allow the crystallization
of amphibole and the occurrence of cognate xenoliths representing wall cumulates. Throughout 2001 eruption, UV and LV magmas
remain clearly distinct and ascended following different paths, ruling out the occurrence of mixing processes between them.
Furthermore, integrating the 2001 eruption in the framework of summit activity occurring since 1995, we propose that the 2001
magma feeding the vents lower than 2,600 m a.s.l. is a precursor of a refilling event, which reached its peak during the 2002–2003
Etna flank eruption. 相似文献
284.
机载激光雷达数据的误差分析及校正 总被引:2,自引:2,他引:2
数据质量分析是遥感机理/应用研究(尤其是定量遥感)首要和关键的一步,直接影响遥感反演的精度和遥感应用的效果。激光雷达(Light Detection and Ranging,LiDAR)是一种新兴的主动遥感技术,对数据后处理算法的研究还有待进一步加强,尤其对激光雷达数据的质量分析显得十分迫切。采用了一种基于扫描航带间重叠区数据分析的方法对LiDAR数据质量进行评价,分析误差来源,计算误差的大小,并分别对数据的随机和系统误差进行校正。以机载激光雷达数据为例来进行验证,实验结果表明,这种方法能有效地减少数据误差,达到提高数据质量的目的。 相似文献
285.
286.
Massimo Civita Adriano Fiorucci Roberta Miè 《Geostandards and Geoanalytical Research》2001,25(2-3):431-439
Aluminium was determined in surface and ground waters in the Alba region of NW Italy to provide information on natural and anthropogenic sources of contamination. Determinations were made by a spectrophotometric method based on the aluminium-pyrocatechol complex. The total aluminium content of waters was determined as well as the toxic form of monomeric aluminium, obtained from samples that had been passed through 0.20 μm cellulose filters to remove colloidal and particulate material. Results were correlated with mortality data associated with Alzheimer's disease. There appeared to be a correlation between mortality data and areas having the highest aluminium content of water. 相似文献
287.
Giuseppe Capaldi Massimo Cortini Raimondo Pece 《Journal of Volcanology and Geothermal Research》1985,26(3-4)
Hemond and Condomines (1985) claim that our results on zero age volcanic materials of Vesuvius and Etna are incorrect, that no disequilibrium exists in those materials and that the validity of the 230Th-238U dating method is thus confirmed. We show that other researchers obtained similar results in zero age rocks. The validity of the 230Th-238U dating method is simply ruled out by a comparison of the ages obtained by this method with those obtained on the same samples by different methods. 相似文献
288.
A conceptual and numerical model for groundwater management: a case study on a coastal aquifer in southern Tuscany, Italy 总被引:5,自引:3,他引:2
Piero Barazzuoli Monica Nocchi Roberto Rigati Massimo Salleolini 《Hydrogeology Journal》2008,16(8):1557-1576
Ongoing hydrogeological research aims to develop a correct management model for the Plio-Pleistocene multi-aquifer system of the Albegna River coastal plain (southern Tuscany, Italy); overexploitation of this aquifer for irrigation and tourism has caused seawater intrusion. The conceptual model is based on field and laboratory data collected during the 1995–2003 period. Meteoric infiltration and flows from the adjoining carbonate aquifer recharge the aquifer. Natural outflow occurs through a diffuse flow into the sea and river; artificial outflow occurs through intensive extraction of groundwater from wells. Water exchanges in the aquifer occur naturally (leakage, closing of aquitard) and artificially (multiscreened wells). The aquifer was represented by a three-dimensional finite element model using the FEFLOW numerical code. The model was calibrated for steady-state and transient conditions by matching computed and measured piezometric levels (February 1995–February 1996). The model helped establish that seawater intrusion is essentially due to withdrawals near the coast during the irrigation season and that it occurs above all in the Osa-Albegna sector, as well as along the river that at times feeds the aquifer. The effects of hypothetical aquifer exploitation were assessed in terms of water budget and hydraulic head evolution. 相似文献
289.
Tectono‐sedimentary evolution of the northern Iranian Plateau: insights from middle–late Miocene foreland‐basin deposits 下载免费PDF全文
Paolo Ballato Francesca Cifelli Ghasem Heidarzadeh Mohammad R. Ghassemi Andrew D. Wickert Jamshid Hassanzadeh Guillaume Dupont‐Nivet Philipp Balling Masafumi Sudo Gerold Zeilinger Axel K. Schmitt Massimo Mattei Manfred R. Strecker 《Basin Research》2017,29(4):417-446
Sedimentary basins in the interior of orogenic plateaus can provide unique insights into the early history of plateau evolution and related geodynamic processes. The northern sectors of the Iranian Plateau of the Arabia–Eurasia collision zone offer the unique possibility to study middle–late Miocene terrestrial clastic and volcaniclastic sediments that allow assessing the nascent stages of collisional plateau formation. In particular, these sedimentary archives allow investigating several debated and poorly understood issues associated with the long‐term evolution of the Iranian Plateau, including the regional spatio‐temporal characteristics of sedimentation and deformation and the mechanisms of plateau growth. We document that middle–late Miocene crustal shortening and thickening processes led to the growth of a basement‐cored range (Takab Range Complex) in the interior of the plateau. This triggered the development of a foreland‐basin (Great Pari Basin) to the east between 16.5 and 10.7 Ma. By 10.7 Ma, a fast progradation of conglomerates over the foreland strata occurred, most likely during a decrease in flexural subsidence triggered by rock uplift along an intraforeland basement‐cored range (Mahneshan Range Complex). This was in turn followed by the final incorporation of the foreland deposits into the orogenic system and ensuing compartmentalization of the formerly contiguous foreland into several intermontane basins. Overall, our data suggest that shortening and thickening processes led to the outward and vertical growth of the northern sectors of the Iranian Plateau starting from the middle Miocene. This implies that mantle‐flow processes may have had a limited contribution toward building the Iranian Plateau in NW Iran. 相似文献
290.