Deformation patterns in a high-viscosity lava flow inferred from the crystal preferred orientation and imbrication structures: an example from Salina (Aeolian Islands,southern Tyrrhenian Sea,Italy) |
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| Authors: | G Ventura R De Rosa E Colletta R Mazzuoli |
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| Institution: | (1) Osservatorio Vesuviano, Via Osservatorio, I-80056 Ercolano (NA), Italy;(2) Dipartimento Geomineralogico, Università di Bari, Via Orabona, Campus Universitario, I-70121 Bari, Italy;(3) Dipartimento Scienze della Terra, Università della Calabria, I-87036 Areavacata di Rende (CS), Italy;(4) Dipartimento Scienze della Terra, Università di Pisa, Via S. Maria 53, I-56100 Pisa, Italy |
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| Abstract: | Shape-preferred orientation and imbrication structures of crystals have been measured on samples representative of the base, centre and top of a highly viscous lava flow on Salina (Aeolian Islands, southern Tyrrhenian Sea). The data allow zones with different deformation patterns to be identified. In the base and top of the flow, deformation leads to the development of discrete preferred orientation and imbrication of the elongate crystals. The sense of shear is right-lateral at the base and left-lateral at the top of the flow. Shear strain can be estimated by the analysis of crystal preferred orientation. Deformation increases from the flow centre to the outer, more viscous boundary layers. Random orientation of crystals in the inner zone supports the presence of plug flow in a pseudoplastic lava. The textural features of the studied lava may be related to different mechanisms (i.e. lateral expansion). We conclude that the observed crystal alignments and imbrication structures may be related to a plug flow moving between two non-deforming walls. The walls are represented by the solidified, broken upper and basal crust of the flow. The low shear strain values calculated in the outer margins of the flow are indicative of the last deformation event. Crystal preferred orientation and imbrication structures may be related to the occurrence of velocity gradients existing between the inner zone of the flow and its solidus or near-solidus outer margins. |
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| Keywords: | Lava flow Crystal preferred orientation Deformation Simple shear Bingham/viscoplastic flows |
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