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Maurizio de'Gennaro Piergiulio Cappelletti Alessio Langella Annamaria Perrotta Claudio Scarpati 《Contributions to Mineralogy and Petrology》2000,139(1):17-35
The study proposes a model by which a thick succession of volcanic tuffs can be zeolitized by alteration of pyroclastic material
in the presence of sufficient eruptive water and at temperatures close to water vapour condensation. In the case of phreatomagmatic
products, the model simplifies interpretation of problematic deposits that exhibit pronounced vertical and lateral variation
in lithification grade. A major feature of the model is that thick zeolitized tuffs can be formed during emplacement of pyroclastic
products, in marked contrast to later alteration in an open hydrologic system. Geological, volcanological and mineralogical
data for the Neapolitan Yellow Tuff, a widespread trachytic pyroclastic deposit outcropping around Campi Flegrei (Southern
Italy), have been used to infer the physico-chemical conditions that determined mineral genesis. This tuff shows a reduction
in lithification grade towards the base, top and with distance from the vent and very variable zeolitization within the lithified
portion. We suggest that during initial emplacement the erupted products chilled against the ground, inhibiting zeolite crystallization.
During rapid deposition of the thick, wet succession thermal insulation allowed the persistence of elevated temperatures for
a time sufficient for enhancement of hydration-dissolution processes in the volcanic glass. The highly reactive alkali-trachytic
glass quickly buffered the acid pH of the system, favouring phillipsite crystallization followed by chabazite nucleation.
The variable zeolite content reflects fluctuating emplacement conditions (e.g. changes in water content and temperature).
Cooling of the upper and relatively thin distal deposits inhibited the zeolitization process, thereby preserving the primary
unlithified deposit.
Received: 25 May 1999 / Accepted: 28 October 1999 相似文献
2.
L. Fedele F. D'A. Tramparulo S. Vitale P. Cappelletti E. P. Prinzi S. Mazzoli 《Journal of Metamorphic Geology》2018,36(6):691-714
The Neotethyan oceanic Diamante‐Terranova unit (DIATU; southern Apennines–Calabria–Peloritani Terrane system) includes basic rocks that during the Cenozoic were subducted and metamorphosed to lawsonite‐blueschist facies conditions. Petrological and structural observations (both at the meso‐ and micro‐scale) show that lawsonite growth was continuous during three distinctive ductile deformation stages (D1–D3). These likely occurred close to the metamorphic peak, estimated at 350–390°C and 0.9–1.1 GPa, producing an equilibrium assemblage made of blue Na‐amphibole, lawsonite, chlorite and pumpellyite. Locally, pods dominated by quartz and epidote (plus chlorite, calcite and green Ca‐amphibole) developed at similar conditions (350–370°C, 0.8–0.9 GPa). Post‐peak evolution during the final exhumation of the DIATU along the subduction channel, also consisted of three deformation stages, defined by folding (D4) and normal faulting (D5) and finally by strike‐slip faulting (D6), affecting both the blueschist unit and the unconformably overlying Tortonian conglomerates. Vorticity analysis on syn‐tectonic lawsonite crystals indicates that severe flattening occurred during the D2 stage, with a significant secondary non‐coaxial strain component along the W–E plane. This is associated with an eastward tectonic vergence, consistent with the subsequent D3 and D4 folding stages characterized by a dominant ENE tectonic transport. It is suggested that exhumation started from the D2 stage and continued during D3 at similar HP/LT metamorphic conditions. The widespread occurrence of unreacted lawsonite crystals suggests that exhumation was very fast and supports the idea that concurrent ductile deformation might play a role in its preservation. 相似文献
3.
Zeolitization of Oligo-Miocene volcaniclastic rocks from Logudoro (northern Sardinia, Italy) 总被引:1,自引:0,他引:1
Guido Cerri Piergiulio Cappelletti Alessio Langella Maurizio de'Gennaro 《Contributions to Mineralogy and Petrology》2001,140(4):404-421
The present study reports the results of research on volcaniclastic products from Logudoro (northern Sardinia), a reconstructed
stratigraphic succession some hundreds of meters thick, comprising two different ignimbritic units separated by an epiclastic
layer (generally ˜10 m thick). Clinoptilolite is the most widely distributed authigenic phase in epiclastite and unwelded
units, always associated with opal-CT and sometimes with smectite. An adularia-like feldspar, cristobalite and epigenetic
quartz are typical phases of welded units. Within the zeolitized units (unwelded ignimbrite and epiclastic units) clinoptilolite
and opal-CT constitute the cement deriving from the transformation of the precursor rhyolitic glass, in agreement with a single
zeolitization process that developed after the deposition of the entire succession. Silica increases in zeolitized rocks with
respect to the precursor material, leading to hypothesize that the secondary mineralization process was favored by mineralized
hydrothermal fluids preferentially circulating through the fault system of the area. Quartz veins in welded subunit and K-feldspar
(adularia-like) preferentially located near the faults are in agreement with this hypothesis. The interaction of these fluids
with the glassy fraction favored its dissolution and the consequent crystallization of clinoptilolite. Furthermore, the pH
increase and the silica supersaturation enhanced the contemporary or subsequent precipitation of opal-CT.
Received: 5 June 2000 / Accepted: 14 August 2000 相似文献
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Alessio Langella Domenico Calcaterra Piergiulio Cappelletti Abner Colella Maria Pia D’Albora Vincenzo Morra Maurizio de Gennaro 《Environmental Earth Sciences》2009,59(1):145-160
Results of a research carried out on the lavas from Campi Flegrei and Somma-Vesuvius volcanic districts are reported here.
The lavas have been widely employed, since Roman age, in several important monumental buildings of the Campania region, mainly
in the town of Naples and in its province. They are classified as trachytes (Campi Flegrei products), tephri-phonolites and
phono-tephrites (Somma-Vesuvius complex) from a petrographical point of view. Sampling was carried out from well-known exploitation
districts. A substantial chemical difference between the products of the two sectors was confirmed, while petrophysical characterization
evidenced similarity among the two different materials, although some differences were recorded even in samples coming from
the same exploitation site. 相似文献
6.
Juan C. Colombo Carlos N. Skorupka Claudio Bilos Leandro Tatone Natalia Cappelletti M. Carolina Migoya 《水文科学杂志》2013,58(6):1155-1163
AbstractWater quality of the Uruguay River was evaluated with multi-parametric (temperature, turbidity, conductivity, pH, dissolved oxygen) and sediment trap data (particle flux, total organic carbon and nitrogen contents) and correlated to precipitation, river discharge and El Niño Southern Oscillation (ENSO) indices for the period 2006–2011. Hydro-meteorological parameters averaged 24–85% variability with coincident precipitation (200–400 mm month-1), discharge (7000–28 000 m3 s-1) and turbidity peaks (50–80 NTU) in the austral spring, and absolute maxima during the El Niño 2009 episode. Spectral analysis of discharge and sea-surface temperature anomaly (SSTA) showed consistent variance maxima at approx. 3 and 1.5 years. Deseasonalized discharge was significantly correlated to SSTA. During river floods, pH decreased (from 7.5 to 6.6) and particle dynamics peaked (turbidity: 15–80 NTU; vertical fluxes: 20–200 g m-2 d-1; total solid load: <1000 to 100 000 t d-1),whereas TOC remained stable (3.2 ± 0.8%) and C/N ratios increased (10–12) due to the higher contribution of terrestrial detritus. 相似文献
7.
G. D. Gatta A. Brundu P. Cappelletti G. Cerri B. de’ Gennaro M. Farina P. Fumagalli L. Guaschino P. Lotti M. Mercurio 《Physics and Chemistry of Minerals》2016,43(9):639-647
A Cs-bearing polyphase aggregate with composition (in wt%): 76(1)CsAlSi5O12 + 7(1)CsAlSi2O6 + 17(1)amorphous, was obtained from a clinoptilolite-rich epiclastic rock after a beneficiation process of the starting material (aimed to increase the fraction of zeolite to 90 wt%), cation exchange and then thermal treatment. CsAlSi5O12 is an open-framework compound with CAS topology; CsAlSi2O6 is a pollucite-like material with ANA topology. The thermal stability of this polyphase material was investigated by in situ high-T X-ray powder diffraction, the combined P–T effects by a series of runs with a single-stage piston cylinder apparatus, and its chemical stability following the “availability test” (“AVA test”) protocol. A series of additional investigations were performed by WDS–electron microprobe analysis in order to describe the P–T-induced modification of the material texture, and to chemically characterize the starting material and the run products. The “AVA tests” of the polyphase aggregate show an extremely modest release of Cs+: 0.05 mg/g. In response to applied temperature and at room P, CsAlSi5O12 experiences an unquenchable and displacive Ama2-to-Amam phase transition at about 770 K, and the Amam polymorph is stable in its crystalline form up to 1600 K; a crystalline-to-amorphous phase transition occurs between 1600 and 1650 K. In response to the applied P = 0.5 GPa, the crystalline-to-amorphous transition of CsAlSi5O12 occurs between 1670 and 1770 K. This leads to a positive Clapeyron slope (i.e., dP/dT > 0) of the crystalline-to-amorphous transition. When the polyphase aggregate is subjected at P = 0.5 GPa and T > 1770 K, CsAlSi5O12 melts and only CsAlSi2O6 (pollucite-like; dominant) and Cs-rich glass (subordinate) are observed in the quenched sample. Based on its thermo-elastic behavior, P–T phase stability fields, and Cs+ retention capacity, CsAlSi5O12 is a possible candidate for use in the immobilization of radioactive isotopes of Cs, or as potential solid hosts for 137Cs γ-radiation source in sterilization applications. More in general, even the CsAlSi5O12-rich aggregate obtained by a clinoptilolite-rich epiclastic rock appears to be suitable for this type of utilizations. 相似文献
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P. Cappelletti G. Cerri A. Colella M. de’Gennaro A. Langella A. Perrotta C. Scarpati 《Mineralogy and Petrology》2003,79(1-2):79-97
Summary ¶This paper deals with the mineralogical features of the most important and widespread pyroclastic formation of Southern Italy: the Campanian Ignimbrite. This formation is characterized by four stratigraphic units, different in colour and mineralogical composition. The lowermost unit (USAF) is constituted by an incoherent, thin (few tens of cm) sequence of glass or feldspar-rich layers. The middle part of the succession is formed by two main units: a lower grey, welded unit (WGI) capped by a yellow and lithified unit (LYT) that differ in both volcanological features and mineralogical composition. Locally these units are found separately. An incoherent unit (max thickness about 2m) mainly represented by fresh glass, forms the upper part of the succession. A detailed analysis has been carried out on six sections representative of the entire succession. The WGI is feldspathized by authigenic mineralization processes, and the feldspar content ranges between 30 and 90%. The LYT has been deeply affected by zeolitization processes and the total zeolite content often reaches 60%. Based on a comparative examination of both volcanological and mineralogical data, it is hypothesized that these two units were involved in different secondary mineralization processes. The portion of the succession characterized by the highest emplacement temperatures suffered welding and feldspathization and the result of these processes gave rise to the WGI unit. In contrast, the overlying lower-temperature and incoherent portion of the deposit was affected by circulation of meteoric water, thus enhancing zeolitization and lithification. The product of this process gave rise to the LYT unit.Received July 4, 2002; revised version accepted April 23, 2003 相似文献