Search results for " petrology"
showing 10 items of 1353 documents
Geodynamic Modeling with Uncertain Initial Geometries
2021
Decompression and Fracturing Caused by Magmatically Induced Thermal Stresses
2023
Studies of host rock deformation around magmatic intrusions usually focus on the development of stresses directly related to the intrusion process. This is done either by considering an inflating region that represents the intruding body, or by considering multiphase deformation. Thermal processes, especially volume changes caused by thermal expansion are typically ignored. We show that thermal stresses around upper crustal magma bodies are likely to be significant and sufficient to create an extensive fracture network around the magma body by brittle yielding. At the same time, cooling induces decompression within the intrusion, which can promote the appearance of a volatile phase. Volatil…
Microtremor Measurements in the City of Palermo, Italy: Analysis of the Correlation between Local Geology and Damage
2008
Abstract This study presents the results of 90 seismic ambient noise measurements in Palermo, the main city of Sicily (Italy). The dataset has been processed using the horizontal-to-vertical spectral ratio (HVNSR) technique and interpreted in terms of local geology, which is characterized by the presence of alluvial sediments of two riverbeds masked by urbanization since the seventeenth century. HVNSRs show significant variations in the study area: when the transition stiff to soft is crossed, a typical spectral peak appears in the HVNSRs, mostly in the frequency band 1–2 Hz, and exceeding a factor of 3 in amplitude. Using available information on subsurface geological structure, we compute…
Geohazard assessment of the north-eastern Sicily continental margin (SW Mediterranean): coastal erosion, sea-level rise and retrogressive canyon head…
2022
Coastal dynamics are the result of several processes controlling the balance between sediment input and output over time. The beach system is not always able to maintain a neutral coastal balance due to natural and anthropogenic causes. We present an integrated marine geology, geomorphological and sea-level rise analysis in the coastal sector between Torre delle Ciavole and Capo Calavà (North-Eastern Sicily, Italy).This sector is characterized by high uplift rates and frequent seismicity (mainly generated by the very active Vulcano-Tindari Fault System), promoting the development of mass-wasting processes in the coastal and offshore sectors. A main erosive feature observed in the area is th…
�ber den ?Hygrophyllit? im Rotliegenden des Saar-Nahe-Gebietes, ein Beitrag zur Diagenese pyroklastischer Gesteine
1971
In certain areas rhyolitic tuffs of the Upper Rotliegend include a greenish, talc-like substance, called “Hygrophyllit”. It has been found too at the base of the Rotliegend in the Saarland. It is shown, that Hygrophyllit corresponds to decomposed pumice, related to the acid permian volcanism. X-ray, DTA and chemical investigations yielded, that Hygrophyllit consists essentially of a mixed layer mica-Ca-montmorillonite with random interstratification and previously about 33 % expandable layers. In consequence there are in the Rotliegend of the Saar-Nahe-Basin three different diagenetic developments of acid pyroclastic rocks: The formation of Kaolinite in the Lower Rotliegend, of devitrificat…
Infrasonic Early Warning System for Explosive Eruptions
2018
Evidences of magma mixing in the "Daly gap" of the alkaline suites: a case study from the enclaves of Pantelleria (Italy)
2006
The island of Pantelleria consists of trachytes, pantellerites and minor mildly alkaline basalts. Rocks of intermediate composition (falling in the so-called ‘Daly Gap’) such as mugearites, benmoreites and mafic trachytes occur only in the form of enclaves in trachytes and pantellerites inside the main caldera of the island (Caldera ‘Cinque Denti’), which collapsed during the ‘Green Tuff ’ ignimbrite eruption at 50 ka. The enclaves include volcanic, subvolcanic and intrusive rock types. The enclaves in host trachyte contain traces of glass; devitrified glass occurs within enclaves in host pantellerites. Minerals in the enclaves show regular compositional variations with whole-rock silica co…
Archaean Intracrustal Differentiation from Partial Melting of Metagabbro--Field and Geochemical Evidence from the Central Region of the Lewisian Comp…
2012
The central region of the mainland Lewisian gneiss complex of NW Scotland is a granulite-facies migmatite terrane. With the exception of ultramafic and rare calc-silicate rocks, all other lithologies partially melted during Neoarchaean, ultrahigh-temperature (Badcallian) metamorphism. The clearest evidence is preserved within large layered mafic^ultramafic bodies that exhibit macroscopic features diagnostic of anatexis. In situ partial melting of metagabbroic rocks produced patches and sheets of coarse-grained plagioclase-rich leucosome containing euhedral peritectic clinopyroxene.These leucosomes connect with larger, laterally continuous tonalite or trondhjemite sheets that record segregat…
Gas Leakage From Shallow Ponding Magma and Trapdoor Faulting at Sierra Negra Volcano (Isabela Island, Galápagos)
2022
We report on new volcanic gas composition results acquired in October 2017 at Minas de Azufre, a persistent fumarolic field topping the resurgent Sierra Negra caldera, in the Galápagos archipelago. Our results indicate that the Minas de Azufre fumaroles are moderately hydrous (52–64 mol.% H2O) and rich in CO2 (35–46 mol.%), with total sulfur (ST) being 21–35 times less abundant than CO2. SO2, the most abundant S species, is released at an average rate of 19 ± 9 tons/day. Using a volatile saturation model that provides the composition of magmatic gases at equilibrium with western Galápagos basaltic melt (48 wt. % SiO2) in the 400–0.1 MPa pressure range, we infer that Minas de Azufre fumaroli…
Bemerkungen über den Einfluss der Verwitterungsschicht auf das Spektrum seismischer Wellen
1958
In Fortfuhung einer fruheren Arbeit der Autoren werden einige weitere theoretische Untersuchungen skizziert, bei denen die elastischen Eigenschaften der Verwitterungschicht geeignet abgeandert sind. Bei Anregung der Schicht durch einen momentanen Impuls (Nadelimpuls) ergibt sich, das die Frequenz der seismischen Welle nicht durch den Gradienten der Geschwindigkeit, sondern durch den Gradienten des Schallwiderstandes bestimmt wird.