The “Tufo Giallo della Via Tiberina” (Sabatini Volcanic District, Central Italy): a complex system of lithification in a pyroclastic current deposit

Abstract

The Sabatini Volcanic District belongs to the Roman magmatic province of Central Italy, and the Tufo Giallo della Via Tiberina was one of the most voluminous pyroclastic flow-forming eruptions in this district. Post-depositional processes strongly affected this pyroclastic flow deposit leading to the crystallization of different authigenic phases (chabazite, phillipsite, feldspar). A field volcanological survey, along with a careful mineralogical characterization of a large amount of samples of the lithified facies, allowed us to reconstruct a type section primarily based on the amounts of the main authigenic phases. Chabazite always prevailed over phillipsite throughout the entire section, although in the innermost portions of the deposit, where temperatures remained high, chabazite mostly converted into a more stable phase such as an adularia-like phase. In addition to the zeolitization process, the fairly strong mechanical properties of this tuff can be also ascribed to the diffuse occurrence of microcrystalline calcite, which reprecipitated as a secondary phase after the dissolution of carbonaceous clasts.

A case study of zeolitization process: “Tufo Rosso a Scorie Nere” (Vico volcano, Italy): inferences for a general model

“…The analysing crystals were provided by CAMECA (LIF, TAP, and PET). Chemical data of single crystals or clusters of chabazite, phillipsite, and analcime of enriched samples obtained with the method described by Cappelletti et al (2015) were integrated with H 2 O content determined by thermal analyses on single zeolites (thermogravimetry, TG) using a Netzch STA 409 multiple thermoanalyser at the following operating conditions: 0.09 g of material in a Al 2 O 3 crucible sample holder, heating rate 10 • C min −1 , and final temperature 1000 • C (Novembre et al, 2019).…”

“…As far as zeolitic formation is concerned, a large number of authors described alteration processes acting on pyroclastic deposits, observing how these processes led to the lithification by replacement of the glassy fraction by authigenic zeolites (Cappelletti et al, 2015;Langella et al, 2013). Temperature and chemical composition of the glass play an important role in determining the type of authigenic minerals formed.…”

“…In the last 40 years research on Italian quaternary pyroclastic deposits as sources of zeolitic minerals has greatly developed. Most studies focused on the possible mechanisms of zeolite formation, and several genetic hypotheses were proposed (Langella et al, 2013;Cappelletti et al, 2015;Colella et al, 2017). The purpose of this work is the study of zeolitization processes occurring at Vico volcano, with particular attention to the identification of the type of zeolites, genetic mechanisms, and factors that influenced/conveyed the volcanic alteration process.…”

Determination of zeolite-group mineral compositions by electron probe microanalysis

“…The inclusion of natural zeolite minerals which display solid-solution ranges was considered important as these minerals are reported widely in occurrence studies and have considerable value in geochemical discrimination when used in conjunction with paragenesis information (e.g. Heister et al, 2001;Weisenberger and Spürgin, 2009;Weisenberger et al, 2012Weisenberger et al, , 2014Langella et al, 2013;Campbell et al, 2015;Cappelletti et al, 2015). The solid-solution samples additionally have value in monitoring reproducibility (see Test 5).…”

“…The scientific value of zeolites in the Earth sciences is found partly in their sensitivity to different temperatures and geochemical environments (Chipera and Apps, 2001), enabling predictive deductions to be made about formation conditions from mineral assemblages and compositions (e.g. Neuhoff et al, 2000;Bish and Ming, 2001;Giampaolo et al, 2008;Campbell et al, 2012;Langella et al 2013;Weisenberger et al, 2014;Cappelletti et al, 2015). This has particular relevance to hydrothermal, surface and diagenetic systems, where mineral compositions can track changing fluid regimes (Hay and Sheppard, 2001;Langella et al, 2001;Utada, 2001, Campbell et al, 2012Langella et al 2013;Weisenberger et al 2014).…”