The vast majority of extrusive carbonatites are calcitic rocks which may be confused with sedimentary limestones, thus requiring a disambiguation criterion. Extrusive carbonatites are classified based on quantitative criteria that tend to avoid genetic mechanisms. Carbonatite nomenclature is in progress but regulated by the International Union of Geological Sciences norm for igneous rocks. Carbonate sedimentary rock nomenclature is mainly regulated by the Dunham, Embry and Klovan, and Sibley and Gregg classification systems. These limit the description of rock types from various depositional mechanisms and makes comparison with sedimentary rocks difficult. Igneous and sedimentary carbonate rocks display no apparent differences in the field and at meso–micro-scale. They may be layered, massive crystalline or show discrete clasts in a matrix, which make both rock types resemble one another. The study analyses the situations in which classification inconsistencies are most common. Adopting these guidelines may increase confidence, reliability and value in the petrographic classification of igneous and sedimentary lithologies. This study poses a challenging target. Can igneous carbonate rocks be classified using the same approach that is used for sedimentary carbonate rocks and vice versa? So far, the scheme chosen has been arbitrary or limited to the aim of the study being undertaken. The authors start an unexperienced dialogue for the first time between volcanologists and sedimentologists by examining a range of sedimentary and volcaniclastic rock textures which may resemble each other.

Very primitive ultramafic igneous rocks occur at Mt. La Queglia (Abruzzo, Italy). They form a strongly deformed sill–dyke system now tilted vertically. These rocks were initially classified as alnöite and, subsequently, have been suggested to be a carbonatitic olivine melilitite. However, further investigation and interpretation of these rocks is needed due to the presence of hand-specimen-scale textural variation suggesting a complex petrogenesis. We study the texture, mineral chemistry, and whole-rock geochemistry to define three main rock-types. (1) A brecciated rock with an ocellar texture composed of calcite pseudomorphs after olivine and melilite, plus fresh diopside in a groundmass of mica, aegirine, garnet, calcite, apatite, perovskite, titanate and chlorite. Zoned ocelli in this rock show an amoeboid shape, agglutination, and menisci typical of a plastic state. (2) A quenched rock showing a spinifex texture containing long feathery phenocrysts of cpx and mica suspended in a groundmass of nepheline, aegirine, apatite, Ti–rich magnetite, plus abundant calcite and some K-feldspar and zeolites. (3) A coarse-grained rock is composed of calcite plus intergranular glauconite, a mixture of spinel mineral group and Ti–rich magnetite, accessory barite, pyrite, and chabazite-K. The igneous rocks at Mt. La Queglia show extreme SiO₂-undersaturation (33.5–37.3 wt% SiO₂), high MgO contents and TiO₂/Al₂O₃ ratios. Rock-type 1 has a lower Mg number Mg# = 100 × [Mg/(Mg + Fe²⁺)], higher Ca number Ca# = 100 × [Ca/(Ca + Mg)], high Cr (up to 720 ppm) Ni (up to 379 ppm), higher rare earth elements (REE) contents as well as La/Lu ratio, compared to rock-type 2. Perovskite and chromite accumulation seems an important agent during rock differentiation. Rock-type 3 shows REE cross-over with rock-type 2 suggesting light (L)REE concentration in a carbothermal residuum. Mt. La Queglia rocks are an end-member compared to other Upper Cretaceous and Paleogene Italian lamprophyres, suggesting a low degree of melting of a HIMU (a colloquialism for “high-μ”; referring to mantle domains with high ²³⁸U/ ²⁰⁴Pb) garnet-bearing mantle source.

This study provides insights into the tectonic evolution of the normal Mt Morrone Fault System (MMFS) in Central Italy and highlights the utility of multidisciplinary approaches in reconstructing the seismic history of dormant fault systems. The MMFS comprises two parallel normal faults that traverse the western slope of Mt. Morrone, and although the system can produce M > 6 earthquakes, it has been aseismic in post Roman times. Here, we combine geochemical analysis of carbonate fault‐scarp samples with new structural fault data and Lidar‐based topographic analysis to provide new constraints on fault geometries and kinematics, the paleo‐earthquake history of MMFS since the Last Glacial Maximum and its slip rates. Structural analysis reveals kinematic similarities between the two parallel strands, reflecting their response to the same stress regime. Rare Earth Elements analyses on 53 limestone samples reveal a minimum of eight concentration fluctuations upscarp, here interpreted as tectonic exhumation of the fault scarp due to post LGM earthquakes. Slip per event ranges from 30 to 110 cm typical of earthquakes with 6.3 ≤ M ≤ 6.8. Lidar analysis reveals triangular slip profiles on both fault strands. We estimate that an earthquake with an average M = 6.5–6.6 would have a recurrence interval of ∼2,125 ± 125 years. Slip rates were calculated to be 0.5–0.65 mm/yr on the lower and 0.65–0.7 mm/yr on the upper fault strand, with the combined system having slip rates of 0.62–0.69 mm/yr. Our findings indicate that both strands of the MMFS are active and accumulate slip interdependently, a finding that is critical for seismic hazard assessment.

Discrete zircons, up to 9 mm in length, occur in alluvial deposits from the Veneto area. They are likely derived from the disaggregation of lamprophyric rocks belonging to a regional, pervasive dyke-swarm. Zircon and REE phases occur in both alkaline lamprophyres and connate calcite-bearing felsic lithics and their debris in lamprophyre breccia. We present 36 new complete U–Pb and trace element analyses of zircons and associated inclusions. We used a statistical approach on a larger dataset using new and literature data to evaluate the confidence figure to give an estimation of age of zircons. Inclusions suggest a genetic link with an S–CO₂–ZrO–BaO–SrO–CaO-rich fluid/melt possibly associated with carbonate-rich alkaline parental magma and a metasomatised mantle source. This paper confirms the importance of calcite–syenite and lamprophyre genetic link and zircon magmatic origin, in contrast with hydrothermal and metamorphic zircons. U–Pb dating by LA-ICP-MS provides time constrains (40.5–48.4 Ma, Lutetian), consistent with the age of the alkaline magmatic event. Trace element data indicate a link to anorogenic magmatism associated with mantle upwelling. Complex zoning is highlighted by cathodoluminescence images. The Veneto zircons are helpful for regional geological information and may have commercial potential as a critical resource for green technologies.

We investigated hellandite-group mineral phases from the Roman Region, alkali syenite ejecta, by multimethod analyses. They show a complex crystallisation history including co-precipitation of hellandite-(Ce) with brockite, resorption, sub-solidus substitution with mottanaite-(Ce), exsolution of perthite-like ferri-mottanaite-(Ce), overgrowth of an oscillatory-zoned euhedral shell of ferri-mottanaite-(Ce) and late, secondary precipitation of pyrochlore in the cribrose hellandite-(Ce) core. LREE/HREE crossover and a negative Eu anomaly in hellandite-group minerals follows fO₂ increase during magma cooling. The distinction among the hellandite-group minerals is based on the element distribution in the M1, M2, M3, M4 and T sites. Additional information on miscibility relationship among the hellandite sensu strictu, tadzhikite, mottanaite, ferri-mottanaite and ciprianiite endmembers derives from molar fraction calculation. We observed that change in composition of hellandite-group minerals mimic the ligands activity in carbothermal-hydrothermal fluids related to carbonatitic magmatism.