Eruption and emplacement dynamics of a thick trachytic lava flow of the Sancy volcano (France)

Abstract

International audienceA 70-m-thick, 2200-m-long (51 × 106 m3) trachyticlava flow unit underlies the Puy de Cliergue (Mt. Dore,France). Excellent exposure along a 400-m-long and 60- to85-m-high section allows the flow interior to be accessed ontwo sides of a glacial valley that cuts through the unit. Wecompleted an integrated morphological, structural, textural,and chemical analysis of the unit to gain insights into eruptionand flow processes during emplacement of this thick siliciclava flow, so as to elucidate the chamber and flow dynamicprocessed that operate during the emplacement of such systems.The unit is characterized by an inverse chemical stratification,where there is primitive lava beneath the evolvedlava. The interior is plug dominated with a thin basal shearzone overlying a thick basal breccia, with ramping affectingthe entire flow thickness. To understand these characteristics,we propose an eruption model that first involves processesoperating in the magma chamber whereby a primitive meltis injected into an evolved magma to create a mixed zone atthe chamber base. The eruption triggered by this event firstemplaced a trachytic dome, into which banded lava from thechamber base was injected. Subsequent endogenous domegrowth led to flow down the shallow slope to the east onwhich the highly viscous (1012 Pa s) coulée was emplaced.The flow likely moved extremely slowly, being emplacedover a period of 4–10 years in a glacial manner, where a thick(>60-m) plug slid over a thin (5-m-thick) basal shear zone. Excellent exposure means that the Puy de Cliergue complexcan be viewed as a case type location for understanding anddefining the eruption and emplacement of thick, high-viscosity,silicic lava flow systems

The Geomorphology, Structure, and Lava Flow Dynamics of Peralkaline Rift Volcanoes From High‐Resolution Digital Elevation Models

“…Ogives/folds form on the surface of a lava flow whose viscosity decreases with depth, as the product of compression within the solidifying crust of a flow as it progresses down slope (Fink, ; Fink & Fletcher, ). Ogives on coulees at Corbetti and Fentale have wavelengths of 20–100 m, similar to those previously noted on lava flow deposits of andesitic, dacitic, trachytic, and rhyolitic composition (e.g., Latutrie et al, ; Pyle & Elliott, ; Warner & Gregg, ). Shorter wavelength folds have been observed on dacite deposits (Lescinsky et al, ); post‐emplacement erosion and weathering may have altered small‐scale morphological features on the Corbetti and Fentale lava coulees.…”

Anatomy of the magmatic plumbing system of Los Humeros Caldera (Mexico): implications for geothermal systems

“…Shallow-depth conditions are also obtained for orthopyroxene crystallization with temperatures of 960-1006 • C (weighted mean of 990 ± 7 • C (±1σ ), MSWD = 0.28, n = 49) and pressures of 0.2-3.6 kbar (weighted mean of 1.6 ± 0.9 kbar (±1σ ), MSWD = 0.101, n = 35). The alkali-feldspar-liquid thermometer provided temperature estimates always < 500 • C, here interpreted as feldspar reequilibration in subsolvus and/or subsolidus post-eruptive conditions (Nekvasil, 1992;Brown and Parsons, 1994;Plümper and Putnis, 2009;Kontonikas-Charos et al, 2017;Latutrie et al, 2017). Interestingly, temperatures obtained through the Pl-Liq model are higher than those obtained with Ol-Liq, Cpx-Liq, or Opx-Liq, suggesting an earlier crystallization of plagioclase with respect to mafic minerals.…”

Effusive crises at Piton de la Fournaise 2014–2015: a review of a multi-national response model

“…Vesicle and crystal contents, as well as their size distributions, are also derived from all pyroclasts and lava samples (see Gurioli et al (2015), Latutrie et al (2017) and Colombier et al (2017) for the detail regarding standard procedures, plus the meaning and application of the measurements). These measurements are performed to check variation in space (down a fissure or vent system) and in time, both within single eruptions and between different eruptions.…”