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91.
Twenty obsidian samples from Central and North Anatolia were dated by the fission track method. Split samples analyzed in two different laboratories give consistent results. Data presented refer to three volcanic fields and are summarized as follows: Orta-Sakaeli (Northern Anatolia) obsidians with ages from 21–23 Ma; Göllü Dagi dome complex near Çiftlik (Central anatolia) has given ages between 1.33–0.98 Ma; Acigöl caldera (Central Anatolia) shows three age groups: (1) Eruptions of precaldera (Bogazköy) obsidians with ages 0.18–0.15 Ma; (2) Formation of the large intracaldera dome Kocadag-Taskesiktepe at about 0.08 Ma (uncorrected apparent age of 0.075 Ma); and (3) Acigöl peripheral obsidian domes with plateau ages of 0.020 and 0.019 Ma, and an additional uncorrected age of 0.018 Ma form a distinct age group. This fission track parameters discriminate between the various obsidian sources of prehistoric obsidian artifacts.  相似文献   
92.
Studies oriented to restoration and conservation of historical monumental buildings have recourse to structural analysis as a way to investigate the genuine structural features of the construction, to better understand its present condition and actual causes of existing damage, to estimate its safety conditions and to determine necessary remedial measures. Based on this background, this paper discusses on the seismic vulnerability of masonry fortresses by means of an analysis methodology based on three different analytical procedures, according to an increased knowledge of the structure. As a relevant case study the Albornoz fortress, a 14th stone masonry construction located in central Italy, was selected. Initially, the strategy proposed to perform this task was aimed at testing and developing an expeditious and non-destructive procedure to evaluate both the seismic vulnerability and the main mechanical properties of the different masonry typologies. The macroscale structural behavior of the fortress was then evaluated through a nonlinear static analysis (pushover) and a more simple approach based on the kinematic theorems of the limit analysis. From this point of view, by comparing the capacity of the construction to withstand lateral loads with the expected demands resulting from seismic actions, these methods provided a highly effective means of verifying the safety of the masonry structure and its vulnerability to extensive damage and collapse.  相似文献   
93.
94.
K‐Ar ages of authigenic illite from two drill‐core gouge samples of a fault in the Palaeoproterozoic basement of Finland record two distinct faulting events. The older sample yields apparent ages from 1240 ± 26 to 1006 ± 21 Ma for four grain size fractions between 6 and <0.1 μm. The second sample is structurally younger and yields statistically distinct ages ranging from 978 ± 20 to 886 ± 18 Ma. We interpret the ages of the <0.1 m fractions, which are the youngest, as representing the actual time of faulting. XRD analysis and age modelling exclude significant age contamination of the finest dated fractions with inherited host rock components. These results provide therefore an example of meaningful isotopic dating of illite‐type clay material formed during Precambrian faulting, demonstrate and constrain fault reactivation and give evidence for brittle Sveconorwegian Mesoproterozoic shortening and Neoproterozoic extension in Fennoscandia.  相似文献   
95.
The main steps of the sedimentary evolution of the west Lombardian South Alpine foredeep between the Eocene and the Early Miocene are described. The oldest is a Bartonian carbonate decrease in hemipelagic sediments linked with an increase in terrigenous input, possibly related to a rainfall increase in the Alps. Between the Middle Eocene and the early Chattian, a volcanoclastic input is associated with an extensional tectonic regime, coeval with magma emplacement in the southern-central Alps, and with volcanogenic deposits of the European foredeep and Apennines, suggesting a regional extensional tectonic phase leading to the ascent of magma. During Late Eocene to Early Oligocene, two periods of coarse clastic sedimentation occurred, probably controlled by eustasy. The first, during Late Eocene, fed by a local South Alpine source, the second, earliest Oligocene in age, supplied by the Central Alps. In the Chattian, a strong increase in coarse supply records the massive erosion of Central Alps, coupled with a structures growth phase in the subsurface; it was followed by an Aquitanian rearrangement of the Alpine drainage systems suggested by both petrography of clastic sediments and retreat of depositional systems, while subsurface sheet-like geometry of Aquitanian turbidites marks a strong decrease in tectonic activity.  相似文献   
96.
The CO2-rich geothermal fluids produced in the Piancastagnaio geothermal field (Mt. Amiata geothermal area, Southern Tuscany, Italy) show temperatures up to 360°C and pressures of about 200 bar at depths of around 3,500 m (Giolito, Ph.D. thesis, Università degli Studi di Firenze, Italy, pp 1–147, 2005). CaCO3- and/or SiO2-dominated scales are deposited in the pipes leading to the pressure and atmospheric separators of the geothermal wells. High content of metastibnite and/or stibnite in both calcite and silica scales and Sb contents of up to 50 mg/L in the fluids indicate their mineralising potential. The red or black colours of the scales depend on the predominance of red metastibnite or black stibnite, respectively. In our condensation experiments, as well as during deposition of the scales, metastibnite is the first Sb2S3 mineral to form. In a second stage, metastibnite is transformed to stibnite. During depressurization the Hg content of geothermal fluids partitions preferentially into the gas phase, whereas Sb and As remain in the liquid phase. This separation explains the often observed areal separation of Hg and Sb mineralization. The multistage deposition of Sb in the mining district of Tuscany is due to a periodic restoration of the permeability of the ore-bearing faults by microseismic events and subsequent host rock brecciation. The still ongoing microseismic events are induced by the accumulation of high-pressure CO2-rich fluids along faults followed by mechanical failure of the faults.  相似文献   
97.
98.
The city of Benevento (Southern Italy) has been repeatedly struck by large historical earthquakes. A heterogeneous geologic structure and widespread soft soil conditions make the estimation of site effects crucial for the seismic hazard assessment of the city. From 2000 until 2004, we installed seismic stations to collect earthquake data over zones with different geological conditions. Despite the high level of urban noise, we recorded more than 150 earthquakes at twelve sites. This data set yields the first, well documented experimental evidence for weak to moderate local amplifications. We investigated site effects primarily by the classical spectral ratio technique (CSR) using a rock station placed on the Benevento hill as reference. All sites in the Calore river valley and in the eastern part of the Benevento hill show a moderate high-frequency (f > 4 Hz) amplification peak. Conversely, sites in the Sabato river valley share weak-to-moderate amplification in a wide frequency band (from 1–2 to 7–10 Hz), without evident frequency peaks. Application of no-reference-site techniques to earthquake and noise data confirms the results of the CSRs in the sites of the Calore river valley and of the eastern part of the Benevento hill, but fails in providing indications for site effects in the Sabato river valley, being the H/V ratios nearly flat. One-dimensional modeling indicates that the ground motion amplification can be essentially explained in terms of a vertically varying geologic structure. High-frequency narrow peaks are caused by the strong impedance contrast existing between near-surface soft deposits and stiff cemented conglomerates. Conversely, broad-band amplifications in the Sabato river valley are likely due to a more complex layering with weak impedance contrasts both in the shallow and deep structure of the valley.  相似文献   
99.
Analysis of some sedimentary series near Rome and comparison with other series in northern and southern Italy give evidence that Arctica islandica, considered a marker species for the beginning of the Pleistocene, appears during the Re´union paleomagnetic event (about 2 my ago). A period of erosion, called the Aullan erosional phase, is evident in the lower part of the late Villafranchian (= early Pleistocene, Olivola faunal unit).  相似文献   
100.
During the Cretaceous, the Neuquén Basin transitioned from an extensional back‐arc to a retroarc foreland basin. We present a multi‐proxy provenance study of Aptian to Santonian (125–84 Ma) continental sedimentary rocks preserved in the Neuquén Basin used to resolve changes of sediment drainage pattern in response to the change in tectonic regime. Sandstone petrology and U–Pb detrital zircon geochronology constrain the source units delivering detritus to the basin; apatite U–Pb and fission track dating further resolve provenance and determine the age and patterns of exhumation of the source rocks. Sandstone provenance records a sharp change from a mixed orogenic source during Aptian time (ca. 125 Ma), to a magmatic arc provenance in the Cenomanian (ca. 100 Ma). We interpret this provenance change as the result of the drainage pattern reorganisation from divergent to convergent caused by tectonic basin inversion. During this inversion and early stages of contraction, a transient phase of uplift and basin erosion, possibly due to continental buckling, caused the pre‐Cenomanian unconformity dividing the Lower from Upper Cretaceous strata in the Neuquén Basin. This phase was followed by the development of a retroarc foreland basin characterised by a volcanic arc sediment provenance progressively shifting to a mixed continental basement provenance during Turonian‐Santonian (90–84). According to multi‐proxy provenance data and lag times derived from apatite fission track analysis, this trend is the result of a rapidly exhuming source within the Cordillera to the west, in response to active compressional tectonics along the western margin of South America, coupled with the increasing contribution of material from the stable craton to the east; this contribution is thought to be the result of the weak uplift and exhumation of the foreland due to eastward migration of the forebulge.  相似文献   
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