The Mt. Massico ridge (central southern Apennines, Italy) is characterized by a ~150‐m‐thick tectonic mélange located at the base of a Tortonian‐lower Messinian heterogeneous clastic succession consisting of layered sandstones, limestones, marls, and claystones with intercalated mass wasting deposits and isolated olistoliths, which deposited above Meso‐Cenozoic limestones. Geological mapping and structural analyses, integrated with illite‐smectite paleothermal indicators and U‐Pb dating of syntectonic calcite veins and slickenfibers, allowed us to unravel (1) the tectonic evolution of the Mt. Massico ridge and (2) the development of the intrawedge tectonic mélange in the framework of the Apennine accretionary wedge evolution. Results show that after thrusting and folding of Meso‐Cenozoic limestones during late Tortonian times (7.0 ± 1.6 Ma), late Messinian‐early Pliocene out‐of‐sequence thrusting (5.1 ± 3.7 Ma) juxtaposed ~3,300‐m‐thick, imbricate thrust sheets above the Tortonian‐lower Messinian clastic succession. During out‐of‐sequence thrusting, the base of the weak clastic deposits acted as a décollement horizon due to the rheological contrast and mechanical buttress with the underlying competent Mesozoic‐Cenozoic limestones. Heterogeneous deformation along the base of the clastic succession was accommodated by ductile pressure solution of claystones and marls, by brittle stratal disruption and fracturing/veining of competent olistoliths and primary foliation (i.e., sandstones and limestones strata), thus leading to the development of a tectonic mélange. The compressional phase was followed by extensional tectonics after the late Pliocene (minimum age 2.9 ± 0.5 Ma). We conclude that out‐of‐sequence thrusting, buttressing, and intraformational rheological contrast can be fundamental factors for the development of intrawedge tectonic mélange.

No abstract

One of the main challenges in volcanology and petrology is to define and quantify the interdependence and timescales of processes acting during magma ascent through the crust as well as during eruption and em-

An increasing number of studies are being presented demonstrating that volcanic glasses can be heterogeneous at the nanoscale. These nano-heterogeneities can develop both during viscosity measurements in the laboratory and during magma eruptions. Our multifaceted study identifies here total transition metal oxide content as a crucial compositional factor governing the tendency of basalt melts and glasses towards nanolitization: at both anhydrous and hydrous conditions, an undercooled trachybasalt melt from Mt. Etna readily develops nanocrystals whose formation also hampers viscosity measurements, while a similar but FeO- and TiO2-poorer basalt melt from Stromboli proves far more stable at similar conditions. We therefore outline a procedure to reliably derive pure liquid viscosity without the effect of nanocrystals, additionally discussing how subtle compositional differences may contribute to the different eruptive styles of Mt. Etna and Stromboli.

The 2021 Tajogaite eruption of Cumbre Vieja (La Palma, Spain) was typified by the emission of low viscosity lavas that flowed at high velocities and inundated a large area. We experimentally investigated the rheological evolution of melt feeding the eruption through concentric cylinder viscometry to understand the exceptional flowing ability of these lavas and constrain its emplacement dynamics. We conducted a set of cooling deformation experiments at different cooling rates (from 0.1 to 10 °C/min), and isothermal deformation experiments at subliquidus dwell temperatures between 1225 and 1175°C. All experiments were conducted at a shear rate of 10 s−1. Results show that disequilibrium crystallization and its timescale fundamentally control the rheological evolution of the melt, resulting in different rheological response to deformation of the crystal‐bearing magmatic suspension. Integrating rheological data with field observations allows us to shed light on the mechanisms that govern the high flowability of these lavas.