The relationship between Late Quaternary deformation and volcanism of Mt. Etna (eastern Sicily): new evidence from the sedimentary substratum in the Catania region

Stratigraphical and structural analyses have been carried out on the Late Quaternary foredeep succession forming the Etnean substratum in the Catania region (eastern Sicily), in order to investigate in detail the chronology of deformation events that have accompanied a significant period of the eruptive activity of Mt. Etna, i.e. from 240 ka to the Present. This episode was characterised, at about 200 ka, by a main change of the petrochemical features of the emitted products from sub-alkaline to alkaline. This can be related to an evolving mantle diapir located beneath the volcano. The new stratigraphical and structural field data, presented in this paper, constrain the development, from 240 to 125 ka, of NW-SE-trending dextral faults associated with minor E-W- to NE-SW-oriented accommodation thrusts and NNW-SSE-trending normal faults that originated in a dominant transpressive regime. Strike-slip tectonics were active during the earlier emissions of sub-alkaline lavas (320-200 ka old) and part of the ancient alkaline products (180-100 ka old), from scattered eruptive systems which developed in local transtensive zones, distributed throughout the whole Etnean region. A major change in the mode of deformation, since 125 ka BP, was related to the propagation of a normal fault belt along the Ionian coast of the Catania region and the eastern sectors of the Etnean edifice. This process was associated with the growth of open folds that deformed the entire foredeep sequence exposed along the southern boundary of the Etnean edifice. During this period, eruptive activity concentrated along the main extensional features where steady and very efficient feeding systems originated. This resulted in a rapid increase in the volume of emitted alkaline products that gave rise to the construction of the modern stratovolcano during the last 80 ka. The collected data emphasise some main aspects of the relationship between tectonic deformation at a regional scale and volcanism in the Etna area. Firstly, the mode of deformation at the onset of Etnean volcanisin seems to be inadequate to explain the emplacement at depth of a mantle diapir related to the occurrence of a hotspot, almost independent from the local crustal dynamics. On the other hand, the Late Quaternary structural assemblages recognised on the surface can be interpreted as direct effects. of the Europe-Africa convergence, rather than as the products of deformation induced by the emplacement of the mantle diapir. In the different stages of Etnean evolution a direct relationship exists between the mode of deformation and the distribution as well as the capacity of the feeding systems. In particular, the amounts of emitted products in the different stages depend on the intensity of crustal stretching associated with deformation, rather than the volume of available molten material at depth. These conclusions represent a new perspective for the interpretion of the early stages and subsequent evolution of the volcanic activity of Mt. Etna. The proposed model also represents an useful tool in deciphering the relationship between the deformation path, seismicity and volcanic activity of Mt. Etna. (C) 2004 Elsevier B.V. All rights reserved.