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|Authors: ||De Vita, S.*|
Di Vito, M. A.*
|Title: ||THE ROLE OF PRE-EXISTING TECTONIC STRUCTURES ON THE GEOMETRY OF CALDERAS AND RESURGENT BLOCKS: A REVIEW|
|Title of journal: ||Acta Vulcanologica|
|Series/Report no.: ||Special issue 1-2/17(2005)|
|Issue Date: ||2005|
|Keywords: ||Caldera collapse|
|Abstract: ||The role of pre-existing tectonic structures and regional stress regime on the geometry of calderas is widely recognized in the more recent literature on this topic. In fact, although in many cases the shape of calderas is broadly circular at a great scale, a detailed study of the collapse structures, almost always evidences the presence of linear features inherited from the “pre-caldera” regional tectonic setting. These features, commonly visible in the outcropping rocks that form the pre-volcanic basement, also testify the regional stress field in which volcanism took place. A complete range of increasing complexity examples exists in nature, from elliptical calderas, with a variable degree of ellipticity, to fully irregular calderas, with large linear border sectors due to re-activation of pre-existing regional faults.
Elliptical calderas are usually associated with continental rifting, in which regional extension is marked by different horizontal stress components. In these cases the elongation of calderas is parallel to the trend of the regional structures. In some other cases the elongation of the calderas is perpendicular or oblique to the rift structures. This suggests that additional factors may influence the formation of these calderas and the related magma chambers at depth. Examples of such transverse calderas are found along the oceanic ridge of Iceland and along the East African Rift System. Recent studies demonstrated that re-activation of pre-existing structures, orthogonal to the main rift direction, controlled migration and storage of magma bodies at depth, and conditioned activation of volcanism and caldera formation at shallower levels. These so-called transfer structures control the emplacement of surface magma chambers and magma extrusion mainly in that regions in which tectonism and deformational history are very complex, as in the case of the Apennine chain and the peri-Tyrrhenian area. Where multiple extensional systems intersects to each other, transverse depressions are formed, and volcanism is dominated by caldera-forming eruptions. In these cases it is well evident the control exerted by pre-existing regional structures on the geometry of calderas. Some of these calderas have been later affected by resurgence processes, in which the uplifted blocks are bordered by faults whose geometry is inherited by the pre-caldera regional tectonic setting. The Campi Flegrei caldera and the island of Ischia are good examples of complex, resurgent calderas, characterized by a non regular shape, with large linear rim sectors, for which it is possible to demonstrate the control exerted by pre-existing regional tectonic structures|
|Appears in Collections:||04.04.99. General or miscellaneous|
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