Alpine metamorphism of low-grade schists from the Slavonian Mountains (Croatia): new P-T and geochronological constraints     

Dražen Balen  Hans-Joachim Massonne  Iva Lihter 《International Geology Review》2018,60(3):288-304

Low-grade schists from the Slavonian Mountains (Tisia Mega-Unit, Mt Papuk, Croatia), previously assigned to Precambrian to Lower Palaeozoic metamorphism, have been subjected to geochemical investigations, P-T modelling, and in situ age dating of monazite. The studied fine-grained metasediments consist of chlorite (5–15 vol.%), K white-mica (40–55 vol.%), quartz (20–35 vol.%), feldspar (albite 15–20 vol.%), opaques (<2 vol.%), and accessory minerals. According to their whole-rock geochemistry, the detritus of the former sediments came from upper crustal felsic rocks as they occur, for instance, at Mt Papuk. The schists show a complex microtectonic fabric, including well-developed schistosity systems. P-T pseudosections in the system MnNCKFMASHTO, constructed for typical schists of the study area, resulted in peak P-T conditions of 445–465 °C and 4.6–6.0 kbar for a sample from Kutjevo (eastern part of the study area) and 450–460 °C and 5.2–6.0 for a Vranovo sample (western part). Electron microprobe (EMP) dating of monazite in the schists gave a weighted average age of 109.0 ± 13.1 Ma (2σ) eventually with three subgroups of ages at 225 ± 63 (two analyses), 114 ± 24 and 83 ± 22 Ma. We conclude that the metamorphism of the studied schists at depths of c. 20 km is due to an Alpine collisional event.  相似文献   

Site effects of the Roio basin, L��Aquila     

E. Bertrand  A.-M. Duval  J. R��gnier  R. M. Azzara  F. Bergamashi  P. Bordoni  F. Cara  G. Cultrera  G. Di Giulio  G. Milana  J. Salichon 《Bulletin of Earthquake Engineering》2011,9(3):809-823

During the microzonation studies of the April 6th, 2009 L??Aquila earthquake, we observed local seismic amplifications in the Roio area??a plane separated from L??Aquila city center by mount Luco. Six portable, digital instruments were deployed across the plain from 15 April to mid-May 2009. This array recorded 152 aftershocks. We analyzed the ground motion from these events to determine relative site amplification within the plain and on surrounding ridges. Horizontal over vertical spectral ratio on noise data (HVSRN), aftershock recordings (HVEQ) and standard spectral ratio (SSR) showed amplifications at 1.3 and 4.0?Hz on quaternary deposits. Seismic amplifications in the frequency range of 4 and 6?Hz were also observed on a carbonate ridge of Colle di Roio, on the northwestern border of the plateau. A small amplification was noticed near the top of mount Luco, another rocky site. Large discrepancies in the amplification levels between methods have been observed for these sites, but the HVSRN, HVEQ and SSR gave similar results at the stations located in the Roio plain. On the rocky sites, the SSR was more reliable than the HVSRN at estimating the transfer function of the site, even if the resonance frequency seemed to be well detected by the latter method.  相似文献   

Seismic response of L��Aquila downtown from comparison between 2D synthetics spectral ratios of SH, P-SV and Rayleigh waves and observations of the 2009 earthquake sequence     

Paola Bordoni  John Haines  Giuliano Milana  Sandro Marcucci  Fabrizio Cara  Giuseppe Di Giulio 《Bulletin of Earthquake Engineering》2011,9(3):761-781

This is the first part of a study on the seismic response of the L’Aquila city using 2D simulation and experimental data. We have studied two velocity-depth models with the aim of outlining the behavior of a velocity reversal in the top layer, which is associated with the stiff Brecce de L’Aquila unit (BrA). In this setting, the SMTH model is topped by a layer with about 2:1 impedance contrast with the underlying layer while the NORV model has no velocity reversal. We have simulated the propagation of SH and P-SV wavefields in the range 0–10 Hz for incidence 0°–90°. Earthquake spectral ratios of the horizontal and vertical components at six sites in L’Aquila downtown are compared to corresponding synthetics spectral ratios. The vertical component of P-SV synthetics enables us to investigate a remarkable amplification effect seen in the vertical component of the recorded strong motion. Sites AQ04 and AQ05 are best matched by synthetics from the NORV model while FAQ5 and AQ06 have a better match with synthetics spectral ratios from the SMTH model. All simulations show this behavior systematically, with horizontal and near-horizontal incident waves predicting the overall pattern of matches more clearly than vertical and near-vertical incidence. The model inferences are in agreement with new geological data reporting lateral passages in the top layer from the stiff BrA to softer sediments. Matches are good in terms of frequency of the first amplification peak and of spectral amplitude: the horizontal components have spectral ratio peaks predominantly at 0.5 Hz in the simulations and at 0.7 Hz in the data, both with amplitudes of 4, while the vertical component spectral ratios reach values of 6 at frequencies of about 1 Hz in both data and simulations. The vertical component spectral ratios are very well matched using Rayleigh waves with incidence at 90°. The NORV model without the velocity reversal predicts spectral ratio peaks for the horizontal components at frequencies up to 6 Hz. The reversal of velocity acts as a low-pass frequency filter on the horizontal components reducing the amplification effect of the sediment filled valley.  相似文献   

The Aterno valley strong-motion array: seismic characterization and determination of subsoil model   总被引：1，自引：1，他引：0  

G. Lanzo  M. Tallini  G. Milana  G. Di Capua  F. Del Monaco  A. Pagliaroli  S. Peppoloni 《Bulletin of Earthquake Engineering》2011,9(6):1855-1875

The paper focuses on the strong motion array deployed in the upper Aterno River Valley, in the immediate outskirts north-west of the town of L’Aquila, which is part of the Italian Strong Motion Network operated by the Department of Civil Protection. The array is composed of six accelerometric stations located along a cross section of the valley. The importance of this array relies on the fact that a large amount of high-quality records were obtained during the 2009 L’Aquila seismic sequence, from both the mainshock and several aftershocks. These data are especially important to investigate site effects in sediment-filled valleys during moderate earthquakes in epicentral area because well-documented observational studies are very limited in the literature. However, the main drawback for the study of site effects in the Aterno valley is the lack of a detailed knowledge of the geometry of the valley, soil layering and dynamic properties of materials. The main motivation for this study stems from the need to provide a reliable subsoil model of the valley coupled with high-quality strong motion data. Based on the above, in the framework of S4 project, a major effort was undertaken to get a trustworthy cross section of the valley by an ad hoc investigation, comprising geological and geotechnical surveys as well as an extensive geophysical campaign, characterized by both active and passive measurements. These results were complemented by additional geological and geotechnical data available in the literature. By merging all the information acquired, a 2D subsoil model of the transversal section of the upper Aterno valley has been produced. The valley is characterised by an asymmetric shape with a shallower rock basement at the western edge of the valley that deepens at the valley centre. Moreover, based on the results of geophysical tests, representative V_s values were assigned to the different lithologic units forming the alluvial deposits filling the valley. Shear wave velocity is a fundamental parameter for ground response studies and it is also effective in classifying the accelerometric station from a seismic point of view. The 2D model may be therefore, considered a benchmark model for future studies of site effects. It will offer the possibility to examine site effects with a complex underlying geology and to validate the results of numerical simulations of site response analyses with the numerous observations from earthquake recordings, both for weak and strong ground motion conditions.  相似文献   

Contrasting tourmaline types from peraluminous granites: a case study from Moslava?ka Gora (Croatia)     

Dra?en Balen  Zorica Petrinec 《Mineralogy and Petrology》2011,102(1-4):117-134

Two texturally and chemically distinct types of tourmaline are found inside peraluminous granites of the Moslava?ka Gora, Croatia: nodular tourmaline in the two-mica granite and disseminated tourmaline in the cross-cutting leucogranite dykes. Both tourmaline types belong to alkali tourmaline group, nodular tourmaline being dravite to schorl and disseminated tourmaline corresponding to schorl. Comparison of characteristic parameters of nodular (Nt) and disseminated tourmaline (Dt) shows significant differences in #Fe (0.40?C0.65 for Nt vs. 0.74?C0.85 in Dt) along with variations in the calculated X-site vacancy (0.22?C0.37 pfu in Nt and 0.33?C0.44 in Dt) and ??/(??+Na) ratio (0.23?C0.40 in Nt and 0.34?C0.45 in Dt). Disseminated tourmaline from the MG leucogranites is regarded as an early crystallized magmatic phase, while the interstitial tourmaline from the cores of tourmaline nodules originated from more complex mineralogical and chemical interactions inside the two-mica granite melt. Major element gain (Mg) and loss (Fe, Ca, Na, K) for the ??idealized nodule?? (34 vol. % core + 66 vol. % halo) when compared to the host granite shows that the nodule??s volume is not a completely independent and closed system. Based on the observed characteristics, nodule??s halo can be considered as a ??transitional zone?? between the tourmaline-bearing core and the host granite, texturally and mineralogically related to the host two-mica granite, chemically being an integral part of the nodule??s volume at the same time.  相似文献   

1D velocity structure of the Po River plain (Northern Italy) assessed by combining strong motion and ambient noise data     

Giuliano Milana  Paola Bordoni  Fabrizio Cara  Giuseppe Di Giulio  Salomon Hailemikael  Antonio Rovelli 《Bulletin of Earthquake Engineering》2014,12(5):2195-2209

Strong ground motions recorded on the sedimentary deposits of the Po River alluvial plain during the Emilia (Northern Italy) Mw 5.7 earthquake of May 29, 2012 are used to assess the vertical profile of shear-wave velocity above the limestone basement. Data were collected by a linear array installed for site effect studies after the Mw 5.9 mainshock of May 20, 2012. The array stations, equipped with both strong and weak motion sensors, are aligned in the South–North direction, at distances ranging from 1 to 26 km from the epicenter. The vertical components of ground motion show very distinctive, large-amplitude, low-frequency dispersive wave trains. Wavelet analysis yields group-velocity dispersion curve in the 0.2–0.7 Hz frequency band. The availability of a long ambient noise record allows estimates of the site resonance frequency along with its stability among stations. The joint inversion of dispersion of surface waves and ellipticity curves derived from ambient noise H/V allows extending investigations down to the sediment-limestone interface, at a depth of about 5,000 m. Our results add new information about the velocity structure at a scale that is intermediate between the local scale already investigated by other authors with small-aperture arrays using ambient noise and the regional scale inferred from modeling of seismogram waveforms recorded at hundreds of kilometers from the source.  相似文献   

Radio-continuum study of the Nearby sculptor group galaxies. Part 1: NGC 300 at λ=20 cm     

Timothy J. Galvin  Miroslav D. Filipović  Evan J. Crawford  Graeme Wong  Jeff L. Payne  Ain De Horta  Graeme L. White  Nick Tothill  Danica Drašković  Thomas G. Pannuti  Caleb K. Grimes  Benjamin J. Cahall  William C. Millar  Seppo Laine 《Astrophysics and Space Science》2012,340(1):133-142

A series of new radio-continuum (λ=20 cm) mosaic images focused on the NGC?300 galactic system were produced using archived observational data from the VLA and/or ATCA. These new images are both very sensitive (rms?=60 μJy) and feature high angular resolution (<10?″). The most prominent new feature is the galaxy’s extended radio-continuum emission, which does not match its optical appearance. Using these newly created images a number of previously unidentified discrete sources have been discovered. Furthermore, we demonstrate that a joint deconvolution approach to imaging this complete data-set is inferior when compared to an immerge approach.  相似文献   

Petrology and geochemistry of orthoamphibolites from the Variscan metamorphic sequences of the South Tisia in Croatia – an overview with geodynamic implications     

Jakob Pamić  Dražen Balen  Darko Tibljaš 《International Journal of Earth Sciences》2002,91(5):787-798

In the southern Pannonian Basin, the Variscan Barrovian- and overprinted Abukuma-type progressive metamorphic sequences of the South Tisia in Slavonian Mts. (SM) and Mt. Moslava)ka Gora (MG) are interlayered with orthoamphibolites. These sequences represent part of a disrupted Variscan belt that extends southeastwards of the Bohemian Massif through the Carpathians to the Caucasus. Orthoamphibolites contain hornblende (Mg-hornblende, tschermakite, pargasite, and edenite), plagioclase An_48-98 (MG) and An_26-35 (SM), biotite, grossular (MG) and almandine (SM) enriched garnet, diopside (MG), with accessory ilmenite, titanite, and clinozoisite. Based on major and trace element analyses and CIPW norms, these orthoamphibolites, which originally were olivine tholeiites to slightly alkalic basalts, can be correlated with tholeiites of consuming plate margins. '¹⁸O of orthoamphibolites varies from 5.8 to 7.1‰, the measured ⁸⁷Sr/⁸⁶Sr ratio from 0.70435 to 0.70665, which indicates slight continental crust contamination, and the calculated ratio from 0.70262 to 0.70535, indicating an upper mantle origin of the original basaltic melts. For associated penecontemporaneous I-type granitoids, the calculated initial ⁸⁷Sr/⁸⁶Sr ratio also have upper mantle values ranging between 0.70293 and 0.70368. Geochemical data for orthoamphibolites and the associated penecontemporaneous I-type granites, and the occurrence of alpine-type ultramafic bodies within the Barrovian sequence, indicate that they have many features in common with orogenic associations related to recent subduction-related settings. Some characteristic element ratios suggest back-arc basin environments and the Ce/K vs. Ce diagram suggests a pargasite-lherzolite source. Its partial melting gave primitive basaltic melts of olivine tholeiite to slight alkalic affinities that produced at first differentiated mafic rocks by olivine fractionation (future orthoamphibolites) and, afterwards, a strongly differentiated suite of I-type granitoids by amphibole fractionation. Magma emplacement and subsequent AFC processes took place in subduction environments preceding the main Variscan deformational metamorphic event during which orthoamphibolites were generated. This interpretation is compatible with geodynamic modeling of this part of the Paleotethys.  相似文献   

The objective determination of the instantaneous predominant frequency of seismic signals and inferences onQ of coda waves     

Antonio Rovelli  Sandro Marcucci  Giuliano Milana 《Pure and Applied Geophysics》1988,128(1-2):281-293

A technique to detect spectrum variations versus time along seismic signals is applied to coda waves of local earthquakes (Friuli, Northern Italy). The technique consists of an autoregressive modeling and utilizes nonlinear spectral analysis where the spectrum of stochastic processes is estimated as the transfer function of the filter that whitens the process under analysis. This approach appears to be particularly well suited to those investigations where automatic measurements of the instantaneous frequency have to be carried out on digital data. The detection of variations of the instantaneous frequency along the coda allows computation of seismic-Q in the lithosphere and its frequency dependence: the result obtained is $$Q = 100f^{0.4} $$ which appears to be strongly consistent with that, based on the estimate of the coda amplitude decay in the band including the most significant frequencies of the signals under analysis.  相似文献   

Site response using coda-wave techniques: Applications to short period data from central and southern Italy     

Edoardo Del Pezzo  Marcello Martini  Giuliano Milana 《Pure and Applied Geophysics》1991,136(1):127-141

The method of coda waves was applied to two different sets of data for the evaluation of the relative site response.The first set of data consists of low magnitude earthquakes with closely spaced locations, recorded at a small aperture array of velocimeters located in the Abruzzo region, central Italy. The second set of data is composed of events with epicentral distance ranging from 20 to 300 km, recorded at a seismological network with an aperture of about 100 km located in the Puglia region, southern Italy.Results show that the coda wave method furnishes stable estimates of the site effect. An amplification, relative to an arbitrary site, of a factor of about 2 occurs in the 1.7–6 Hz frequency band for two stations of the Abruzzo network, while an amplification factor of about 0.5 occurs in the whole frequency band (1–24 Hz) for one of the stations of the Puglia network. This station is located in an area which is correlated with a low macroseismic intensity anomaly.  相似文献