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Samuele Boschi Birger Schmitz Ellinor Martin Fredrik Terfelt 《Meteoritics & planetary science》2020,55(7):1615-1628
Based on sediment‐dispersed extraterrestrial spinel grains in the Bottaccione limestone section in Italy, we reconstructed the micrometeorite flux to Earth during the early Paleocene. From a total of 843 kg of limestone, 86 extraterrestrial spinel grains (12 grains > 63 μm, and 74 in the 32–63 μm fraction) have been recovered. Our results indicate that the micrometeorite flux was not elevated during the early Paleocene. Ordinary chondrites dominated over achondritic meteorites similar to the recent flux, but H chondrites dominated over L and LL chondrites (69%, 22%, and 9%, respectively). This H‐chondrite dominance is similar to that recorded within an enigmatic 3He anomaly (70, 27, and 3%) in the Turonian, but different from just before this 3He anomaly and in the early Cretaceous, where ratios are similar to the recent flux (~45%, 45%, and 10%). The K‐Ar isotopic ages of recently fallen H chondrites indicate a small impact event on the H‐chondrite parent body ~50 to 100 Ma ago. We tentatively suggest that this event is recorded by the Turonian 3He anomaly, resulting in an H‐chondrite dominance up to the Paleocene. Our sample spanning the 20 cm above the Cretaceous–Paleogene (K–Pg) boundary did not yield any spinel grains related to the K–Pg boundary impactor. 相似文献
23.
M. I. Wilkinson A. Vallenari C. Turon U. Munari D. Katz G. Bono M. Cropper A. Helmi N. Robichon F. Thévenin S. Vidrih T. Zwitter F. Arenou M.-O. Baylac G. Bertelli A. Bijaoui F. Boschi F. Castelli F. Crifo M. David A. Gomboc A. Gómez M. Haywood U. Jauregi P. de Laverny Y. Lebreton P. Marrese T. Marsh S. Mignot D. Morin S. Pasetto M. Perryman A. Pra A. Recio-Blanco F. Royer A. Sellier A. Siviero R. Sordo C. Soubiran L. Tomasella Y. Viala 《Monthly notices of the Royal Astronomical Society》2005,359(4):1306-1335
24.
Large amplification of ground motion at rock sites within a fault zone in Nocera Umbra (central Italy) 总被引:2,自引:1,他引:1
F. Marra R. Azzara F. Bellucci A. Caserta G. Cultrera G. Mele B. Palombo A. Rovelli E. Boschi 《Journal of Seismology》2000,4(4):543-554
During the two mainshocks of September 26, 1997 inthe Umbria-Marche border a strong-motion accelerographrecorded peak ground accelerations as large as 0.6 g,approximately, in the town of Nocera Umbra, atdistances of 10 to 15 km from the epicentres. Thisvalue is significantly larger than expected on thebasis of the usual regressions with magnitude anddistance. A broad-band amplification up to a factor of10 was consistently estimated in previous papers,using both weak and strong motion data recorded at theaccelerograph site during local moderate earthquakes.To study the cause of this amplification we deployedsix seismologic stations across the tectonic contactbetween the Ceno-Mesozoic limestone and the Mesozoicmarly sandstone where the accelerograph is installed.Seismograms of 21 shallow aftershocks in the magnituderange from 2.2 to 4.0 and a subcrustal Mw = 5.3event are analysed. Regardless of epicentre location,waveforms show a large complexity in an approximately200 m wide band adjacent to the tectonic contact. Thisis interpreted as the effect of trapped waves in thehighly fractured, lower velocity materials within thefault zone. 相似文献
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26.
Francesca?ForniEmail author Ben?S.?Ellis Olivier?Bachmann Federico?Lucchi Claudio?A.?Tranne Samuele?Agostini Luigi?Dallai 《Contributions to Mineralogy and Petrology》2015,170(5-6):49
Over the last ~267 ky, the island of Lipari has erupted magmas ranging in compositions from basaltic andesites to rhyolites, with a notable compositional gap in the dacite field. Bulk geochemical and isotopic compositions of the volcanic succession, in conjunction with major and trace elemental compositions of minerals, indicate that the rhyolites were dominantly generated via crystal fractionation processes, with subordinate assimilation. Radiogenic (Sr, Nd, and Pb) and stable (O) isotopes independently suggest ≤30 % of crustal contamination with the majority of it occurring in mafic compositions, likely relatively deep in the system. Within the rhyolites, crystal-rich, K2O-rich enclaves are common. In contrast to previous interpretations, we suggest that these enclaves represent partial melting, remobilization and eruption of cumulate fragments left-over from rhyolite melt extraction. Cumulate melting and remobilization is supported by the presence of (1) resorbed, low-temperature minerals (biotite and sanidine), providing the potassic signature to these clasts, (2) reacted Fo-rich olivine, marking the presence of mafic recharge, (3) An38–21 plagioclase, filling the gap in feldspar composition between the andesites and the rhyolites and (4) strong enrichment in Sr and Ba in plagioclase and sanidine, suggesting crystallization from a locally enriched melt. Based on Sr-melt partitioning, the high-Sr plagioclase would require ~2300 ppm Sr in the melt, a value far in excess of Sr contents in Lipari and Vulcano magmas (50–1532 ppm) but consistent with melting of a feldspar-rich cumulate. Due to the presence of similar crystal-rich enclaves within the rhyolites from Vulcano, we propose that the eruption of remobilized cumulates associated with high-SiO2 rhyolites may be a common process at the Aeolian volcanoes, as already attested for a variety of volcanic systems around the world. 相似文献
27.
Improving basin scale shallow landslide modelling using reliable soil thickness maps 总被引:3,自引:0,他引:3
Soil thickness is a well-known factor controlling shallow landsliding. Notwithstanding, its spatial organisation over large
areas is poorly understood, and in basin scale slope analyses it is often established using simple methods. In this paper,
we apply five different soil thickness models in two test sites, and we use the obtained soil thickness maps to feed a slope
stability model. Validation quantifies how errors in soil thickness influence the resulting factor of safety and points out
which method grants the best results. In particular, in our cases, slope-derived soil thickness patterns produced the worst
slope stability assessment, while the use of reliable soil thickness maps obtained by means of a more complex geomorphologically
indexed model improved shallow landslides modelling. 相似文献
28.
29.
A new dyke intrusion style for the Mount Etna May 2008 eruption modelled through continuous tilt and GPS data 总被引:2,自引:0,他引:2
M. Aloisi A. Bonaccorso F. Cannavò S. Gambino M. Mattia G. Puglisi E. Boschi 《地学学报》2009,21(4):316-321
After a recharge phase that began in 2007, on 13 May 2008, a new eruption started on Mt. Etna volcano. The final intrusion was very fast, accompanied by a violent seismic swarm and marked by ground deformation recorded at permanent tilt and GPS stations. The violence of the eruptive event generated concern that the eruptive fissures might propagate downslope towards populated areas. The ground deformation modelling explains both the mechanism of the intrusion as well as the attempt of the dyke to propagate in the shallower part of the northern sector of the volcano. We show that the 2008 intrusion was characterized by a mechanism, which is new and different to the ones modelled in previous eruptions, following the path of the central conduit in the first part of the intrusion (below 1.6 km) and then breaking off towards the east in the last shallow part. 相似文献
30.
Drying and dying of a subducted slab: Coupled Li and B isotope variations in Western Anatolia Cenozoic Volcanism 总被引:1,自引:0,他引:1
Samuele Agostini Jeffrey G. Ryan Sonia Tonarini Fabrizio Innocenti 《Earth and Planetary Science Letters》2008,272(1-2):139-147
In lavas spanning ~ 10Ma of subduction-related volcanism in Western Anatolia, we observe remarkably similar patterns of δ7Li and δ11B variation. In this setting, magmatism records a transition from calc–alkaline to ultrapotassic character, consistent with overall lower mean extents of melting, and a changing mantle source that reflects a fractionating, higher temperature slab input consistent with the gradual cessation of subduction. Subsequent rift-related intraplate magmatism record δ7Li signatures within the range observed for MORBs and OIBs, indicating an abrupt transition to a mantle source unmodified by subduction. 相似文献