The interaction between regional and local tectonics during resurgent doming: the case of the island of Ischia, Italy

The volcanic island of Ischia is located on the Tyrrhenian margin of Centra l Italy, characterized by Plio-Quaternary NW-SE- and NE-SW-trending extensi onal fractures. Ischia displays a resurgent dome uplifted by at least 800 m in the last 33 ka. Remote sensing and field data have been collected to st udy the structural setting of the island, the deformation pattern associate d with resurgence and the superimposition of the regional and the resurgenc e-induced stress fields. NW-SE and NE-SW extensional fracture systems predo minate throughout the island and around the resurgent block, suggesting a r elationship with the regional extensional structures. These systems were fo rmed before resurgence and were partly reactivated during resurgence. The r eactivation of pre-existing regional systems during resurgence confined the extent of the uplifted area. N-S- and E-W-trending systems have been found exclusively at the borders of the dome and are interpreted as being induce d by resurgence. The topmost resurgent block shows an octagonal shape in ma p view and is tilted at an angle of 15 degrees around a NE-SW-trending hori zontal axis; the block is partly bordered by high-angle, inward-dipping reg ional faults. More than 90% in volume of the volcanic products coeval with resurgence on Ischia have been erupted outside the resurgent block area, su ggesting that the resurgence process locally replaced volcanic activity in the last 33 ka. (C) 1999 Elsevier Science B.V. All rights reserved.