Geochemical Alteration of Volcanic Materials

Volcanic materials deposited in diverse environments undergo a suite of geochemical transformations governed by fluid–rock interactions, temperature, pressure and pH conditions. Primary volcanic glass and phenocryst phases react with meteoric, pore and hydrothermal fluids to form a range of secondary minerals, most notably clay minerals (smectite, illite, vermiculite) and zeolites (clinoptilolite, mordenite, analcime). These processes—collectively termed diagenesis and zeolitisation—modulate element mobility, sequester trace metals and rare earth elements (REEs) and record palaeoclimate and palaeoenvironmental signals. Geochemical indices derived from major‐ and trace‐element data in altered tuffs and tephra beds permit reconstruction of redox conditions, fluid chemistry and sedimentary settings. Furthermore, alteration of volcanic materials has practical ramifications: the formation of economically important clay deposits (bentonites, K‐bentonites) and zeolite reserves, the immobilisation or release of environmentally significant elements (e.g. F, Li, REEs), and the preservation of volcanic stratigraphy and chronostratigraphic markers used in basin analysis and hazard assessment. The global distribution of altered volcanic units—from Permian–Triassic boundary successions to Cretaceous basins—underscores their relevance to mineral exploration, carbon sequestration research and the study of fluid‐mediated crustal processes.

Research from Nature Portfolio

Recent studies have advanced our understanding of how sedimentary environment controls diagenetic alteration of volcanic tuffs. Investigations of Permian–Triassic ash beds in both terrestrial and shallow‐marine settings reveal that low‐pH depositional waters foster the development of illite–smectite mixed layers, chlorite and kaolinite without hydrothermal overprint. Differences in mixed‐layer ordering between sections indicate variations in diagenetic grade and chemical weathering intensity. Crucially, the composition and proportion of mixed‐layer clays and their rare‐earth element distribution correlate more strongly with sedimentary environment than with source magma chemistry, demonstrating that geochemical indices of mixed‐layer ratios can serve as robust palaeoenvironmental proxies, independent of volcanic source variations.

Geochemical Alteration of Volcanic Materials publication trend

The graph below shows the total number of articles in geochemical alteration of volcanic materials across all publications each year (not limited to Nature Index journals).

Technical terms

Diagenesis: Low‐temperature chemical and physical changes in sediments and rocks after deposition.

Smectite: A group of 2:1 clay minerals with expandable interlayers, formed by alteration of volcanic glass.

Illite–Smectite (I/S): A mixed‐layer clay mineral exhibiting transitional ordering between smectite and illite within the same crystal structure.

Zeolitisation: Transformation of volcanic glass to zeolite minerals through reaction with alkaline fluids.

Rare Earth Elements (REEs): A set of 17 chemically similar elements key to tracing fluid–rock interactions and valuable in strategic mineral deposits.

References

1. Influences of Sedimentary Environments and Volcanic Sources on Diagenetic Alteration of Volcanic Tuffs in South China. Scientific Reports (2018).
2. Assessing trace-element mobility during alteration of rhyolite tephra from the Dinaride Lake System using glass-phase and clay-separate laser ablation inductively coupled plasma mass spectrometry. Clay Minerals (2022).
3. Distribution, Sedimentology and Origin of Mineralogical Assemblages from a Continental Na-bentonite Deposit in the Cretaceous Neuquén Basin (Argentina). Minerals (2022).
4. Fluorine speciation and origin of Early-Middle Triassic bentonite deposits in Sichuan Basin, South China. Frontiers in Earth Science (2023).