Fracture control on type, morphology and distribution of parasitic volcanic cones: An example from Mt. Etna, Italy

This paper uses a coupled morphometric and stratigraphic analysis of several tens of parasitic pyroclastic cones of the SE flank of Mt. Etna volcano, Italy, to explain the structure of a poorly understood, actively deforming zone of the volcano. Moreover, we present a new general classification of pyroclastic cones based on the parameterisation of coeval eruption points along the same magma-feeding fracture. Each cone has been studied in detail in order to define its stratigraphic position, morphometric characteristics, growth evolution in relation to fracture distribution and orientation, stress field and morphology of the substratum. End members of this classification are at one side a simple, circular or elongated edifice that grew around a single eruption point and can be related to a magma-feeding fracture constrained by a relatively high confining stress in the substratum or a low magma pressure; the other end member is a multiple rifted, strongly elongated cone formed along multiple eruption points of a magma-feeding fracture constrained by a relatively low confining stress or a high magma pressure. Lithostratigraphic and historical analyses demonstrate that the cones in this area developed between 15 ka BP and historical times, the most recent one in 1669 AD, testifying to a high rate of lateral eruption occurrence in the area. These cones show N–S elongated maximum crater axes, N–S-trending axis of the depressed points of the crater rim, and southward and southeastward breaching directions, while coeval cones are N–S aligned. These morphometric characteristics reflect the geometry of N–S magma-feeding fractures. The area can be regarded as a transitional weakness zone between the N–S Rift and the releasing system represented by the transtensional Trecastagni and Mascalucia faults, indicating an E–W-oriented local component of extension possibly related to the interplay between the regional Timpe fault system and the eastward gravitational spreading of the volcano. The azimuth of breaching is controlled by magma-feeding fracture orientation and substrate morphology, especially in the eastern part of the area where it is influenced by the scarps related to the Timpe regional fault system, but it is also sensitive to cone development.