Relationships between deformation and mixing processes in lava flows: a case study from Salina (Aeolian Islands,Tyrrhenian Sea) |
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Authors: | Rosanna De Rosa Roberto Mazzuoli Guido Ventura |
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Institution: | (1) Dipartimento Geomineralogico, Università Campus, Via Orabona 4, I-70124 Bari Italy, IT;(2) Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, I-56126 Pisa, Italy, IT;(3) Osservatorio Vesuviano, Via Osservatorio, I-80056 Ercolano (NA), Italy Fax: +39 81 7390644, IT |
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Abstract: | The massive unit of a lava flow from Porri volcano (Salina, Aeolian Islands) displays many unusual structures related to
the physical interaction between two different magmas. The magma A represents approximately 80% of the exposed lava surface;
it has a crystal content of 51 vol.% and a dacitic glass composition (SiO2=63–64 wt.%). The magma B has a basaltic-andesite glass composition (SiO2=54–55 wt.%) and a crystal content of approximately 18 vol.%. It occurs as pillow-like enclaves, banding, boudin-like and
rolling structures which are hosted in magma A. Structural analysis suggests that banding and boudin-like structures are the
result of the deformation of enclaves at different shear strain. The linear correlation between strain and stratigraphic height
of the measured elements indicates a single mode of deformation. We deduce that the component B deformed according to a simple
shear model. Glass analyses of the A–B boundary indicate that A and B liquids mix together at high shear strain, whereas only
mingling occurs at low shear strain. This suggests that the amount of deformation (i.e. forced convection) plays an important
role in the formation of hybrid magmas. High shear strain may induce stretching, shearing and rolling of fluids which promote
both forced convection and dynamical diffusion processes. These processes allow mixing of magmas with large differences in
their physical properties.
Received: 15 July 1995 / Accepted: 30 May 1996 |
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Keywords: | Strain analysis Mixing/mingling processes Lava flow Calc-alkaline rocks Aeolian Islands |
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