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181.
Salvatore Alparone Andrea Cannata Salvatore Gambino Stefano Gresta Vincenzo Milluzzo Placido Montalto 《Bulletin of Volcanology》2010,72(7):803-816
We investigated the relationship between volcano-seismic events, recorded at La Fossa crater of Vulcano (Aeolian Islands,
Italy) during 2004-2006, and the dynamics of the hydrothermal system. During the period of study, three episodes of increasing
numbers of volcano-seismic events took place at the same time as geothermal and geochemical anomalies were observed. These
geothermal and geochemical anomalies have been interpreted as resulting from an increasing deep magmatic component of the
hydrothermal fluids. Three classes of seismic events (long period, high frequency and monochromatic events), characterised
by different spectral content and various similarity of the waveforms, have been recognised. These events, clustered mainly
below La Fossa crater area at depths of 0.5–1.1 km b.s.l., were space-distributed according to the classes. Based on their
features, we can infer that such events at Vulcano are related to two different source mechanisms: (1) fracturing processes
of rocks and (2) resonance of cracks (or conduits) filled with hydrothermal fluid. In the light of these source mechanisms,
the increase in the number of events, at the same time as geochemical and geothermal anomalies were observed, was interpreted
as the result of an increasing magmatic component of the hydrothermal fluids, implying an increase of their flux. Indeed,
such variation caused an increase of both the pore pressure within the rocks of the volcanic system and the amount of ascending
fluids. Increased pore pressures gave rise to fracturing processes, while the increased fluid flux favoured resonance and
vibration processes in cracks and conduits. Finally, a gradual temporal variation of the waveform of the hybrid events (one
of the subclasses of long period events) was observed, likely caused by heating and drying of the hydrothermal system. 相似文献
182.
Abstract— We reviewed here the recent development on the mathematical formulation of closure temperature of a cooling geochronological system, which permits direct retrieval of cooling rate from cooling age when the diffusion parameters, grain size and initial temperature are known. This formulation is used to show how the cooling rate can be retrieved by comparing the core and bulk age of a mineral determined by a single decay system. The cooling rates of seven H chondrites of the metamorphic types H4, H5 and H6 were retrieved from the available data on the Pb‐Pb model ages of the phosphates and the diffusion kinetic data of Pb in apatite. The results are in excellent agreement with the metallographic cooling rates and show an inverse relation with the metamorphic grade of these chondrites. We also addressed the problem of ~90 Ma younger Sm‐Nd mineral isochron age, defined by orthopyroxene, phosphate and plagioclase, of the Morristown mesosiderite compared to the Pb‐Pb age of the Estherville mesosiderite. It is shown that this younger age could have been a consequence of resetting during cooling instead of an “impulsive heating” event, as suggested earlier. 相似文献
183.