Options
Istituto per lo Studio dei Materiali Nanostrutturati, ISMN-CNR, Montelibretti (RM), Italy
5 results
Now showing 1 - 5 of 5
- PublicationRestrictedCO2 Degassing over Seismic Areas: The Role of Mechanochemical Production at the Study Case of Central Apennines(2008-01)
; ; ; ;Italiano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Martinelli, G.; ARPA Emilia Romagna ;Plescia, P.; CNR-ISMN - Montelibretti; ; Field observations coupled with experimental results show that CO2 can be produced by mechanical energy applied to carbonate rocks becoming an unexpected additional gas source besides that degassed from the mantle or produced by thermometamorphism. The evidence that a large amount of carbon dioxide associated with radiogenic-type helium (R/Ra as low as 0.01–0.08) is released through continental areas, denotes the absence of a contribution from the mantle or from mantle-derived fluids. Data collected during the seismic crisis which struck the Central Apennines in 1997–98 have shown an enhanced CO2 flux not associated with the presence of mantle or thermometamorphic-derived fluids. On the other hand, new experimental results highlight the possibility of producing CO2 by mechanical energy that acts on the calcite crystalline lattice. While the CO2 released over the geothermal areas (e.g., Larderello Geothermal Field) is obviously derived by mantlederived activities, this is not the case of the huge amount of CO2 released over the seismically active areas where the presence mantle-derived products is ruled out. We propose that mechanical energy, e.g., released during seismic events, microseismicity or creeping processes is a possible additional energy source able to produce CO2 and thus could explain the presence of CO2 degassing over tectonic areas where the influence of the mantle is low. 1. Introduction Apart from the water va334 53 - PublicationOpen AccessElectromagnetic Emissions from Quartz Subjected to Shear Stress: Spectral Signatures and Geophysical Implications(2020)
; ; ; ; ; Shear tests on quartz rocks and single quartz crystals have been conducted to understand the possible relationship between the intensity of detectable stress in fault areas and the energy released in the form of electromagnetic waves in the range 30 KHz-1 MHz (LF–MF). For these tests, a new type of piston-cylinder has been developed, instrumented to collect the electromagnetic signals generated by the quartz during shear stress tests and that allows energy measurements on electromagnetic emissions (EMR) to be performed. The data obtained indicate that shear-stressed quartz crystals can generate electromagnetic emissions in the LF–MF range. These emissions represent a tiny fraction of the total energy dissipated in the fracturing process. The spectrum of radio emissions consists of continuous radiation and overlapping peaks. For the first time, a characteristic migration of peak frequencies was observed, proportional to the evolution of the fracturing process. In particular, the continuous recording of the radio emission spectra shows a migration of the peaks toward higher frequencies, as stress continues over time and smaller and larger fractures form. This migration could be used to distinguish possible natural signals emitted by quartz in tectonically active environments from possible signals of other geophysical and possibly anthropogenic origin.57 67 - PublicationOpen AccessFracture Analysis of α-Quartz Crystals Subjected to Shear Stress(2020)
; ; ; ; ; ; ; ; ; This study assesses the correlations between the intensity of stress undergone by crystals and the morphological characteristics of particles and fracturing products. The e ects of the fractures on the microstructure of quartz are also studied. Alpha quartz, subjected to shear stress, is quickly crushed according to a fracturing sequence, with a total fracture length that is correlated to the stress rate. The shear stress generates a sequence of macro and microstructural events, in particular localized melting phenomena, never highlighted before on quartz and the formation of di erent polymorphs, such as cristobalite and tridymite together with amorphous silica.53 102 - PublicationOpen Access“Pre-Earthquake” Micro-Structural Effects Induced by Shear Stress on α-Quartz in Laboratory Experiments(2020)
; ; ; ; ; This paper presents the results of measurements performed on -quartz subjected to shear stress in dry conditions, to understand the relationship between the shear intensity and the resulting physical and chemical e ects. If a shear stress of intensity higher than 100 MPa is applied continuously to alpha quartz crystals, they will tend to lose their crystallinity, progressively reduce their friction coe cient (Cof) and change into a low-order material, apparently amorphous under X-ray di raction, but with a structure di erent from silica glass. Raman and Pair Distribution Function analyses suggested a structure like cristobalite, a silica polymorph well-known for its auxetic behavior, i.e., having a negative Poisson ratio. This elastic parameter pre-eminently controls the friction coe cient of the material and, if it is negative, the Cof lowering. As a result, the increase in low crystallinity cristobalite is su cientto explain the lowering of the quartz friction coe cient up to values able to contribute, in principle, to the triggering processes of active faults. This allows hypothesizing a slip induction mechanism that does not include the need to have the interposition of layers of hydrated silica, as invoked by many authors, to justify the low friction coe cients that are achieved in shear stress tests on rocks abundant in quartz.46 110 - PublicationOpen AccessCarbon dioxide and methane emissions from calcareous-marly rock under stress: experimental tests results(2005)
; ; ;Martinelli, G.; ARPA Agenzia Regionale Prevenzione e Ambiente dell Emilia-Romagna, Sezione Provinciale di Reggio Emilia, Italy ;Plescia, P.; Istituto per lo Studio dei Materiali Nanostrutturati, ISMN-CNR, Montelibretti (RM), Italy; The identified emissions of abiogenic carbon dioxide, carbon monoxide and methane are generally attributed to volcanic activity or to geochemical processes associated with thermometamorphic effects. In this paper we show another possible abiogenic source of emission, induced by mechanical, and not thermal, stresses. We investigated the mechanochemical production of carbon dioxide and methane when friction is applied to marly-type rock and studied the mechanisms determining the strong CO2 and CH4 emissions observed. A ring mill was used to apply friction and oriented pressure upon a synthetic calcite-clay mixture of varying proportions. We found that the CO2 and CH4 release versus the grinding action has a non-linear trend reflecting the behaviour of decreasing crystallinity, which indicates a close link between crystallinity and gas production. For the CO2 emission, we propose a release mechanism connected with the friction-induced fractures and the increase in structural disorders induced by creep in the lattice. The CH4 emission could be explained by a Sabatier reaction in which CO2 and hydrogen are involved to form CH4 and water.244 271