Segmentation and configuration of subducted lithosphere in Italy: An important control on thrust-belt and foredeep-basin evolution

Abstract

The Apennine foredeep-basin system, located on continental crust, consists of four roughly parallel basin segments, each containing a flexural outer rise and an inner trough that deepens continuously toward the thrust belt. Flexural modeling of subsidence data across the basin indicates that this foredeep basin results mainly from deep subsurface loads acting on the subducted slab from within the subduction zone rather than from the topographic load of the Apennine Mountains. The geometry of the four basin segments observed within the Apennine foredeep is thus inferred to reflect subduction of segmented lithosphere, where each lithospheric segment corresponds to a segment of the foredeep basin. Beneath the basin and in the foreland the lithosphere is continuous: segmentation occurs only at depth beneath the thrust belt. This pattern olf segmentation of the subducted lithosphere at depth is reflected in the large-scale geometry of the outer part of the Apennine thrust belt and appears to control it. Similarly, the pattern of segmentation also appears to control the position of the eastern limit of back-arc type extension in western Italy. These relations strongly suggest a genetic relation between subduction-zone processes, foredeep-basin geometry, and thrust-belt evolution, in which the configuration of the subducted lithosphere largely controls the large-scale surface deformation observed in the Apennine system.