Abstract
The Rocche Rosse lava flow marks the most recent rhyolitic extrusion on Lipari island (Italy), and preserves evidence for a multi-stage emplacement history. Due to the viscous nature of the advancing lava (108 to 1010 Pa s), indicators of complex emplacement processes are preserved in the final flow. This study focuses on structural mapping of the flow to highlight the interplay of cooling, crust formation and underlying slope in the development of rhyolitic lavas. The flow is made up of two prominent lobes, small (< 0.2 m) to large (> 0.2 m) scale folding and a channelled geometry. Foliations dip at 2–4° over the flatter topography close to the vent, and up to 30–50° over steeper mid-flow topography. Brittle faults, tension gashes and conjugate fractures are also evident across flow. Heterogeneous deformation is evident through increasing fold asymmetry from the vent due to downflow cooling and stagnation. A steeper underlying topography mid-flow led to development of a channelled morphology, and compression at topographic breaks resulted in fold superimposition in the channel. We propose an emplacement history that involved the evolution through five stages, each associated with the following flow regimes: (1) initial extrusion, crustal development and small scale folding; (2) extensional strain, stretching lineations and channel development over steeper topography; (3) compression at topographic break, autobrecciation, lobe development and medium scale folding; (4) progressive deformation with stagnation, large-scale folding and re-folding; and (5) brittle deformation following flow termination. The complex array of structural elements observed within the Rocche Rosse lava flow facilitates comparisons to be made with actively deforming rhyolitic lava flows at the Chilean volcanoes of Chaitén and Cordón Caulle, offering a fluid dynamic and structural framework within which to evaluate our data.
Highlights
This study aims to focus on Rocche Rosse flow morphology, satellite observations and structural measurements, using detailed qualitative and quantitative structural measurements to formulate new interpretations of the flow dynamics associated with emplacement of the Rocche Rosse flow
We propose that the Rocche Rosse, with the surface characterised by blocky lava, folding, ramp structures and an overridden breccia, was dominated by a surface crust
Due to the high viscosity of the advancing lava, indicators of emplacement processes and flow-related strain are recorded in the preserved structures of the final solidified flow
Summary
Fink 1983; de Silva et al 1994; Fujii and Nakada 1999; Uia et al 1999; Castro et al 2002; Harris et al 2002; Cioni and Funedda 2005; Tuffen et al 2013; Magnall et al 2016, 2017; Latutrie et al 2017). This is due in part to a lack of observations of active flows. As a result of this, our understanding of the mechanics of basaltic lava flow emplacement is confirmed by real-time observations, while our knowledge of rhyolitic lava
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